Differential gear, differential unit, and differential system

Abstract

To provide a differential gear which can achieve downsizing and reduction of the thickness with a simple structure, and to provide a differential unit and a differential system.SOLUTION: A differential gear includes: a case; an eccentric shaft including a main shaft pivotally supported by one end side of the case and a cam pin which is eccentric relative to the main shaft; and a side shaft pivotally supported by the other end side of the case. The differential gear includes: a first inscribed gear mechanism disposed at one end side in the case and including a first gear fixed to the case, and a second gear pivotally supported by the cam pin rotatably and configured to engage with the first gear; and a second inscribed gear mechanism disposed at the other end side in the case and including a third gear fixed to the second gear, and a fourth gear fixed to one end of the side shaft and configured to engage with the third gear. In the differential gear, with respect to one of the case, the eccentric shaft, and the side shaft, differential motion occurs between the other two.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a differential gear that generates differential motion between at least two members based on an externally input driving force, a differential unit that combines a plurality of differential gears, and a differential system equipped with any of these. [Background technology]

[0002] Conventionally, automobiles have used differential gears that absorb the speed difference between the inside and outside wheels that occurs when turning a corner and distribute power between the inside and outside wheels. Differential gears are also used in drive mechanisms in the field of robots (see, for example, Patent Document 1). The robot hand in Patent Document 1 is configured to move multiple finger members by combining one motor with multiple differential gears and to grasp objects to be grasped, including objects with different diameters. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2001-277175 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the conventional differential gear as disclosed in Patent Document 1, bevel gears are used for the pinion gear and the side gear, so that the diameter of the approximately cylindrical differential case with the rotation axis of the side gear as the central axis becomes large, and it is not possible to reduce the size. In addition, the bevel gear used in the conventional differential gear has a structure in which the pinion gear is disposed between a pair of side gears. Therefore, a certain amount of gap is required between the side gears to interpose the pinion gear, so that it is not possible to reduce the thickness in the axial direction. In addition, in the bevel gear, the pinion gear is disposed on the outer diameter side of the side gear, so that it is not possible to reduce the size in the radial direction.

[0005] The present invention has been made to solve the above-mentioned problems, and has an object to provide a differential device, a differential unit, and a differential system that realizes miniaturization and thinness with a simple structure. [Means for solving the problem]

[0006] A differential gear according to one embodiment of the present invention has a case, a main shaft journaled on one end of the case, an eccentric shaft including a cam pin eccentric to the main shaft, a side shaft journaled on the other end of the case, a first internal gear mechanism including a first gear arranged on one end inside the case and fixed to the case, and a second gear supported rotatably by the cam pin and engaging with the first gear, and a second internal gear mechanism arranged on the other end inside the case and fixed to the second gear, and a fourth gear fixed to one end of the side shaft and engaging with the third gear, and differential motion is generated between the remaining two of the case, the eccentric shaft, and the side shaft, with any one of them as a reference.

[0007] A differential unit (multi-shaft differential) according to one embodiment of the present invention is composed of a plurality of differential devices, including at least one of the above-mentioned differential devices that satisfy the relationship "N×O×Q=(N+1)×P×R" when the number of teeth of the first gear is O, the number of teeth of the second gear is P, the number of teeth of the third gear is Q, the number of teeth of the fourth gear is R, and the rotation speed ratio of the eccentric shaft to the side shaft is N, and the above-mentioned differential devices that satisfy the relationship "(M+1)×O×Q=P×R" when the rotation speed ratio of the case to the side shaft is M.

[0008] More specifically, the differential unit according to the first aspect has a first differential gear corresponding to the former and having a rotation speed ratio N of 0.5, and a second differential gear corresponding to the latter and having a rotation speed ratio M of 1, in which the main shaft of the first differential gear and the side shaft of the second differential gear are fixed so that their rotation axes are coaxial, and the driving force input to the case of the first differential gear is distributed and transmitted to the side shaft of the first differential gear, the case of the second differential gear, and the main shaft of the second differential gear.

[0009] The differential unit according to the second embodiment has a first differential gear corresponding to the former and having a rotation speed ratio N of 2, and a second differential gear corresponding to the latter and having a rotation speed ratio M of 1, in which the side shafts of the first differential gear and the side shafts of the second differential gear are fixed so that their rotation axes are coaxial, and the driving force input to the case of the first differential gear is distributed and transmitted to the main shaft of the first differential gear, the case of the second differential gear, and the main shaft of the second differential gear.

[0010] A differential unit according to a third aspect has a first differential gear corresponding to the latter and having a rotation speed ratio M of 2, and a second differential gear corresponding to the latter and having a rotation speed ratio M of 1, in which the main shaft of the first differential gear and the side shaft of the second differential gear are fixed so that their rotation axes are coaxial, and the driving force input to the side shaft of the first differential gear is distributed and transmitted to the case of the first differential gear, the case of the second differential gear, and the main shaft of the second differential gear.

[0011] A differential unit according to a fourth aspect has a first differential gear corresponding to the latter and having a rotation speed ratio M of 3, a second differential gear corresponding to the latter and having a rotation speed ratio M of 2, and a third differential gear corresponding to the latter and having a rotation speed ratio of 1, wherein the main shaft of the first differential gear and the side shaft of the second differential gear are fixed so that their rotating axes are coaxial, and the main shaft of the second differential gear and the side shaft of the third differential gear are fixed so that their rotating axes are coaxial, and the driving force input to the side shaft of the first differential gear is distributed and transmitted to a case of the first differential gear, a case of the second differential gear, a case of the third differential gear, and the main shaft of the third differential gear.

[0012] A differential system according to one aspect of the present invention includes the above-described differential device and an actuator that is a drive source for the differential device. Moreover, a differential system according to one embodiment of the present invention includes a differential unit formed by connecting two or three of the above-mentioned differential devices to each other, and an actuator that is a drive source for the differential unit. Effect of the Invention

[0013] According to the present invention, two internal gear mechanisms are integrally arranged inside the case, and a mechanism for meshing gears is realized in two stages. This makes it possible to suppress size increase in the direction perpendicular to the rotation axis (radial direction) and in the direction along the rotation axis (axial direction), thereby enabling a compact and thin design to be achieved with a simple structure. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is a schematic diagram illustrating a basic structure of each differential gear in a first to sixth embodiments of the present invention. [Diagram 2] FIG. 11 is an explanatory diagram illustrating the positional relationship between the meshing points of the first internal gear mechanism, the meshing points of the second internal gear mechanism, the case rotation axis, and the cam pin rotation axis in each differential gear in the first to sixth embodiments of the present invention. [Diagram 3]1 is a perspective view illustrating an example of the appearance of a differential system including a differential gear according to a first embodiment of the present invention. [Figure 4] FIG. 4 is a plan view illustrating the differential system of FIG. 3. [Diagram 5] 4 is an exploded perspective view illustrating each component member of the differential gear of FIG. 3 from a fourth gear side. FIG. [Figure 6] 4 is an exploded perspective view illustrating each component of the differential gear of FIG. 3 from a first gear side. FIG. [Figure 7] 4 is an explanatory diagram showing the operating principle of the first internal gear mechanism, the second internal gear mechanism, the case, the eccentric shaft, and the side shaft in the differential device of FIG. 3. FIG. [Figure 8] 8 is an explanatory diagram showing a state in which the eccentric shaft has rotated 90 degrees counterclockwise relative to the case and the side shaft has rotated 90 degrees clockwise relative to the case in the differential gear shown in FIG. 3 from the state shown in FIG. 7. [Figure 9] 8 is an explanatory diagram showing a state in which the eccentric shaft has rotated 180 degrees counterclockwise relative to the case and the side shaft has rotated 180 degrees clockwise relative to the case in the differential gear shown in FIG. 3 from the state shown in FIG. 7. [Figure 10] 8 is an explanatory diagram showing an example of a state in which the eccentric shaft has rotated 270 degrees counterclockwise relative to the case and the side shaft has rotated 270 degrees clockwise relative to the case in the differential gear shown in FIG. 3 from the state shown in FIG. 7. [Figure 11] 8 is an explanatory diagram showing a state in which the eccentric shaft has rotated 360 degrees counterclockwise relative to the case and the side shaft has rotated 360 degrees clockwise relative to the case in the differential gear shown in FIG. 3 from the state shown in FIG. 7. [Figure 12] FIG. 11 is a perspective view illustrating an example of the appearance of a differential system including a differential gear according to a second embodiment of the present invention. [Figure 13] FIG. 13 is a plan view illustrating the differential system of FIG. 12. [Figure 14] 13 is an exploded perspective view illustrating each component member of the differential gear in FIG. 12 from the fourth gear side. FIG. [Figure 15] 13 is an exploded perspective view illustrating each component member of the differential gear of FIG. 12 from the first gear side. FIG. [Figure 16] 13 is an explanatory diagram showing the operating principle of the first internal gear mechanism, the second internal gear mechanism, the case, the eccentric shaft, and the side shaft in the differential device of FIG. 12. FIG. [Figure 17] 17 is an explanatory diagram showing an example of a state in which the eccentric shaft has rotated 90 degrees counterclockwise relative to the side shafts and the case has rotated 90 degrees clockwise relative to the side shafts from the state shown in FIG. 16 in the differential gear of FIG. [Figure 18] 17 is an explanatory diagram showing an example of a state in which the eccentric shaft has rotated 180 degrees counterclockwise relative to the side shafts and the case has rotated 180 degrees clockwise relative to the side shafts from the state shown in FIG. 16 in the differential gear of FIG. [Figure 19] 17 is an explanatory diagram showing an example of a state in which the eccentric shaft has rotated 270 degrees counterclockwise relative to the side shafts and the case has rotated 270 degrees clockwise relative to the side shafts from the state shown in FIG. 16 in the differential gear of FIG. [Figure 20] 17 is an explanatory diagram showing an example of a state in which the eccentric shaft has rotated 360 degrees counterclockwise relative to the side shafts and the case has rotated 360 degrees clockwise relative to the side shafts from the state shown in FIG. 16 in the differential gear of FIG. 12 . FIG. [Figure 21] FIG. 11 is a perspective view illustrating an example of the appearance of a differential system including a differential unit according to a third embodiment of the present invention. [Figure 22] FIG. 22 is a plan view illustrating the differential system of FIG. 21. [Diagram 23] 22 is an exploded perspective view illustrating each component member of the differential device on the driving force input side in FIG. 21, viewed from the fourth gear side. FIG. [Figure 24] 22 is an exploded perspective view illustrating each component member of the differential device on the driving force input side of FIG. 21, viewed from the first gear side. FIG. [Diagram 25] 22 is an explanatory diagram showing the operating principle of the first internal gear mechanism, the second internal gear mechanism, the case, the eccentric shaft, and the side shaft in the differential device on the driving force input side of FIG. 21. FIG. [Figure 26]FIG. 27 is an explanatory diagram showing an example of a state in which the eccentric shaft has rotated 45 degrees counterclockwise relative to the case and the side shaft has rotated 90 degrees clockwise relative to the case from the state shown in FIG. 25 for the differential gear on the driving force input side of FIG. 21 . [Figure 27] FIG. 27 is an explanatory diagram showing an example of a state in which the eccentric shaft has rotated 90 degrees counterclockwise relative to the case and the side shaft has rotated 180 degrees clockwise relative to the case from the state shown in FIG. 25 for the differential gear on the driving force input side of FIG. 21 . [Figure 28] FIG. 27 is an explanatory diagram showing an example of a state in which the eccentric shaft has rotated 135 degrees counterclockwise relative to the case and the side shaft has rotated 270 degrees clockwise relative to the case from the state shown in FIG. 25 for the differential gear on the driving force input side of FIG. 21 . [Figure 29] FIG. 27 is an explanatory diagram showing an example of a state in which the eccentric shaft has rotated 180 degrees counterclockwise relative to the case and the side shaft has rotated 360 degrees clockwise relative to the case from the state shown in FIG. 25 for the differential gear on the driving force input side of FIG. 21 . [Diagram 30] FIG. 11 is a perspective view illustrating an example of the appearance of a differential system including a differential unit according to a fourth embodiment of the present invention. [Diagram 31] FIG. 31 is a plan view illustrating the differential system of FIG. 30. [Diagram 32] 31 is an exploded perspective view illustrating each component member of the differential device on the driving force input side in FIG. 30, viewed from the fourth gear side. FIG. [Diagram 33] 31 is an exploded perspective view illustrating each component member of the differential device on the driving force input side of FIG. 30, viewed from the first gear side. FIG. [Diagram 34] FIG. 31 is an explanatory diagram showing the operating principle of the first internal gear mechanism, the second internal gear mechanism, the case, the eccentric shaft, and the side shaft in the differential device on the driving force input side in FIG. 30. [Diagram 35] FIG. 35 is an explanatory diagram showing an example of a state in which the eccentric shaft has rotated 90 degrees counterclockwise relative to the case and the side shaft has rotated 45 degrees clockwise relative to the case from the state shown in FIG. 34 for the differential gear on the driving force input side of FIG. 30 . [Diagram 36]FIG. 35 is an explanatory diagram showing an example of a state in which the eccentric shaft has rotated 180 degrees counterclockwise relative to the case and the side shaft has rotated 90 degrees clockwise relative to the case from the state shown in FIG. 34 for the differential gear on the driving force input side of FIG. 30 . [Figure 37] FIG. 35 is an explanatory diagram showing an example of a state in which the eccentric shaft has rotated 270 degrees counterclockwise relative to the case and the side shaft has rotated 135 degrees clockwise relative to the case from the state shown in FIG. 34 for the differential gear on the driving force input side of FIG. 30 . [Figure 38] FIG. 35 is an explanatory diagram showing an example of a state in which the eccentric shaft has rotated 360 degrees counterclockwise relative to the case and the side shaft has rotated 180 degrees clockwise relative to the case from the state shown in FIG. 34 for the differential gear on the driving force input side of FIG. 30 . [Figure 39] FIG. 11 is a perspective view illustrating an example of the appearance of a differential system including a differential unit according to a fifth embodiment of the present invention. [Diagram 40] FIG. 40 is a plan view illustrating the differential system of FIG. 39. [Diagram 41] FIG. 40 is an exploded perspective view illustrating each component member of the differential device on the driving force input side of FIG. 39, viewed from the fourth gear side. [Diagram 42] 40 is an exploded perspective view illustrating each component member of the differential device on the driving force input side of FIG. 39 from the first gear side. FIG. [Diagram 43] FIG. 40 is an explanatory diagram showing the operating principle of the first internal gear mechanism, the second internal gear mechanism, the case, the eccentric shaft, and the side shaft in the differential device on the driving force input side of FIG. 39. [Diagram 44] FIG. 45 is an explanatory diagram showing an example of a state in which, for the differential device on the driving force input side of FIG. 39, the eccentric shaft has rotated 45 degrees counterclockwise relative to the side shaft and the case has rotated 90 degrees clockwise relative to the side shaft from the state shown in FIG. 43. [Diagram 45] FIG. 44 is an explanatory diagram showing an example of a state in which, for the differential device on the driving force input side of FIG. 39, the eccentric shaft has rotated 90 degrees counterclockwise relative to the side shaft and the case has rotated 180 degrees clockwise relative to the side shaft from the state shown in FIG. 43. [Figure 46]FIG. 44 is an explanatory diagram showing an example of a state in which, for the differential device on the driving force input side of FIG. 39, the eccentric shaft has rotated 135 degrees counterclockwise relative to the side shaft and the case has rotated 270 degrees clockwise relative to the side shaft from the state shown in FIG. 43. [Figure 47] FIG. 44 is an explanatory diagram showing an example of a state in which, for the differential device on the driving force input side of FIG. 39, the eccentric shaft has rotated 180 degrees counterclockwise relative to the side shaft and the case has rotated 360 degrees clockwise relative to the side shaft from the state shown in FIG. 43. [Figure 48] FIG. 13 is a perspective view illustrating an example of the appearance of a differential system including a differential unit according to a sixth embodiment of the present invention. [Figure 49] FIG. 49 is a plan view illustrating the differential system of FIG. 48. [Figure 50] FIG. 49 is an exploded perspective view illustrating each component member of the differential device on the driving force input side of FIG. 48, viewed from the fourth gear side. [Figure 51] FIG. 49 is an exploded perspective view illustrating each component member of the differential device on the driving force input side of FIG. 48, viewed from the first gear side. [Figure 52] FIG. 49 is an explanatory diagram showing the operating principle of the first internal gear mechanism, the second internal gear mechanism, the case, the eccentric shaft, and the side shaft in the differential device on the driving force input side of FIG. 48. [Figure 53] FIG. 53 is an explanatory diagram showing an example of a state in which, for the differential device on the driving force input side of FIG. 48, the eccentric shaft has rotated 30 degrees counterclockwise relative to the side shaft and the case has rotated 90 degrees clockwise relative to the side shaft from the state shown in FIG. 52. [Figure 54] FIG. 53 is an explanatory diagram showing an example of a state in which, for the differential device on the driving force input side of FIG. 48, the eccentric shaft has rotated 60 degrees counterclockwise relative to the side shaft and the case has rotated 180 degrees clockwise relative to the side shaft from the state shown in FIG. 52. [Figure 55] FIG. 53 is an explanatory diagram showing an example of a state in which, for the differential device on the driving force input side of FIG. 48, the eccentric shaft has rotated 90 degrees counterclockwise relative to the side shaft and the case has rotated 270 degrees clockwise relative to the side shaft from the state shown in FIG. 52. [Figure 56]FIG. 53 is an explanatory diagram showing an example of a state in which, for the differential device on the driving force input side of FIG. 48, the eccentric shaft has rotated 120 degrees counterclockwise relative to the side shaft and the case has rotated 360 degrees clockwise relative to the side shaft from the state shown in FIG. 52. [Figure 57] FIG. 49 is an explanatory diagram that illustrates a schematic example of a robot hand including the differential system of FIG. 48. [Figure 58] 1 is an explanatory diagram illustrating the rotational relationship between an eccentric shaft, a case, and a side shaft in each state in each differential gear according to the first to sixth embodiments of the present invention. FIG. [Figure 59] FIG. 1 is a schematic diagram illustrating a configuration of a conventional planetary gear mechanism. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Embodiment First, the basic structure and operating principle of the differential gear according to the embodiment of the present invention (including Examples 1 to 6) will be described with reference to Fig. 1 and Fig. 2. Fig. 1 is a schematic side view illustrating the basic structure of the differential gear according to Examples 1 to 6 of the present disclosure. Fig. 2 is a conceptual diagram illustrating the positional relationship of components related to each internal gear mechanism of the differential gear according to Examples 1 to 6 of the present disclosure. Hereinafter, the differential gears (131 to 136) of Examples 1 to 6 will be collectively referred to by the symbol "130."

[0016] The differential gear 130 has a case 161, an eccentric shaft 171, and a side shaft 181. The case 161 illustrated in FIG. 1 has a first case 161L having a cylindrical shape with a bottom and a second case 161R having a cylindrical shape with a bottom. The first case 161L is composed of a first side portion 13a and a first bottom portion 16a. The second case 161R is composed of a second side portion 13b and a second bottom portion 16b. That is, the case 161 has a side portion 13s having a cylindrical shape with the first side portion 13a and the second side portion 13b, and the first bottom portion 16a is provided to close one opening, and the second bottom portion 16b is provided to close the other opening. The cylindrical shape includes a cylindrical shape that is circular or oval (such as an elliptical shape) in cross section, or a square cylindrical shape that is polygonal in cross section. The first bottom portion 16a and the second bottom portion 16b each have a shaft support hole 13h formed in the center.

[0017] The eccentric shaft 171 includes a main shaft 171S journaled on one end of the case 161 and a cam pin 171P eccentric to the main shaft 171S. That is, in the eccentric shaft 171, the axis of the main shaft 171S and the axis of the cam pin 171P are misaligned, and the axis of the cam pin 171P is offset from the axis of the main shaft 171S. The main shaft 171S is disposed so as to pass through a journal hole 13h formed in the first bottom 16a of the case 161. That is, the main shaft 171S is disposed from the outside to the inside of the case 161. The side shaft 181 is journaled on the other end of the case 161. The side shaft 181 is disposed so as to pass through a journal hole 13h formed in the second bottom 13b of the case 161.

[0018] The differential 130 also has a first internal gear mechanism 141 and a second internal gear mechanism 151. The first internal gear mechanism 141 is disposed at one end inside the case 161 and has a first gear 142 fixed to the case 161, and a second gear 143 rotatably supported by a cam pin 171P and engaged with the first gear 142. The second internal gear mechanism 151 is disposed at the other end inside the case 161 and has a third gear 152 fixed to the second gear 143, and a fourth gear 153 fixed to one end of the side shaft 181 and engaged with the third gear 152.

[0019] Here, the rotation axis of the case 161 is referred to as a case rotation axis 162. With regard to the eccentric shaft 171, the rotation axis of the main shaft 171S is referred to as a main rotation axis 172, and the rotation axis of the cam pin 171P is referred to as a cam pin rotation axis 173. The eccentric shaft 171 is configured so that the main rotation axis 172 and the cam pin rotation axis 173 are parallel to each other. In addition, the rotation axis of the side shaft 181 is referred to as a side rotation axis 182. As shown in FIG. 1, the case rotation axis 162, the main rotation axis 172, and the side rotation axis 182 are coaxial.

[0020] The main shaft 171S is journaled to the case 161 so that the main rotation shaft 172 is coaxial with the rotation shaft of the first gear 142. That is, the first gear 142 rotates coaxially with the main rotation shaft 172. The side shaft 181 is journaled to the case 161 so that the side rotation shaft 182 is coaxial with the rotation shaft of the fourth gear 153. That is, the fourth gear 153 rotates coaxially with the side rotation shaft 182. The second gear 143 and the third gear 152 rotate coaxially with the cam pin rotation shaft 173. Since the second gear 143 is journaled by the cam pin 171P of the eccentric shaft 171, it revolves around the main rotation shaft 172 and freely rotates around the cam pin rotation shaft 173. The third gear 152 fixed to the second gear 143 also revolves around the main rotation shaft 172 in the same manner as the second gear 143 , and also freely rotates around the cam pin rotation shaft 173 .

[0021] FIG. 2 is an explanatory diagram illustrating the positional relationship between the meshing points of the first internal gear mechanism 141 (the meshing points of the first gear 142 and the second gear 143), the meshing points of the second internal gear mechanism 151 (the meshing points of the third gear 152 and the fourth gear 153), the case rotation shaft 162, and the cam pin rotation shaft 173 in the differential gears according to the first to sixth embodiments of the present disclosure. In FIG. 2, the shapes of the first gear 142, the second gear 143, the third gear 152, and the fourth gear 153 are depicted by a pitch circle that is approximated by a cylinder. As illustrated in FIG. 2, the differential gear 130 is configured such that the case rotation shaft 162 is disposed between the meshing points of the first internal gear mechanism 141 and the meshing points of the second internal gear mechanism 151.

[0022] With the above-mentioned configuration, in the differential gear 130, a differential motion is generated between the case 161, the eccentric shaft 171, and the side shaft 181, with one of them being a reference. Note that FIG. 1 shows a configuration example in which the cam pin 171P extends to the center of the third gear 152 and the third gear 152 is journaled by the cam pin 171P, but the cam pin 171P may be configured to journal only the second gear 143. Hereinafter, the direction in which the case rotation shaft 162, the main rotation shaft 172, the cam pin rotation shaft 173, and the side rotation shaft 182 extend will be referred to as the "axial direction" (see the white arrows in FIG. 1). Also, the direction perpendicular to the axial direction will be referred to as the "radial direction".

[0023] Example 1. A configuration example of a differential gear 131 and a differential system 201 according to a first embodiment of the present invention will be described with reference to Figs. 3 to 11. The same reference numerals are used for components equivalent to those shown in Figs. 1 and 2, and descriptions thereof will be omitted or simplified. In the differential gear 131 of this embodiment, the first gear 142 and the third gear 152 are configured as internal gears (internal gears), and the second gear 143 and the fourth gear 153 are configured as external gears (external gears). In each drawing, some of the reference numerals may be omitted with the intention of avoiding complication of the drawings.

[0024] As shown in FIG. 3 and FIG. 4, the differential system 201 includes an actuator 110, an encoder 110E, a transmission device 110T, a transmission shaft 121, a transmission gear 121G, and a differential device 131. The actuator 110 is a drive source of the differential device 131, and is configured by an electric motor or the like. The actuator 110 is connected to an encoder 110E at one end and to a transmission device 110T at the other end. The encoder 110E detects the number of rotations of the motor as the actuator 110. The transmission device 110T incorporates a reducer such as a planetary gear and has a function of decelerating the actuator 110. The transmission device 110T is connected to a transmission shaft 121 on the opposite side to the actuator 110, and a transmission gear 121G is fixed to the tip of the transmission shaft 121. The transmission shaft 121 and the transmission gear 121G rotate integrally on the same axis.

[0025] That is, the actuator 110 rotates the transmission shaft 121 via the transmission device 110T, thereby outputting a driving force to the differential device 131 via a transmission gear 121G at the tip of the transmission shaft 121. The actuator 110 is fixed to a base frame (not shown), such as the body of an automobile, the body of a robot, or the palm of a robot hand. The differential device 131 is journaled to such a base frame via a bearing (not shown). The differential device 131 is immobile in the axial direction relative to the base frame, and the case 161, the eccentric shaft 171, and the side shaft 181 are each capable of rotating freely.

[0026] As shown in FIG. 5 and FIG. 6, the differential gear 131 has a case 161, a first internal gear mechanism 141, a second internal gear mechanism 151, an eccentric shaft 171, and a side shaft 181. The case 161 has a cover 161F, a first case 161L, a second case 161R, and a case gear 161G. Furthermore, the differential gear 131 has an eccentric shaft gear 171G and a side shaft gear 181G. The differential gear 131 may have bearings B1, B2, and B3, which are so-called bearings, as shown in each figure. Furthermore, the differential gear 131 may have a retaining ring 11 and a retaining ring 12 that serve to prevent parts from coming off, as shown in each figure.

[0027] The eccentric shaft gear 171G is fixed to an end of the eccentric shaft 171S opposite to the cam pin 171P of the eccentric shaft 171. The eccentric shaft gear 171G is disposed so that its rotation axis is coaxial with the main rotation axis 172. The side shaft gear 181G is fixed to an end of the side shaft 181 opposite to the fixed side of the fourth gear 153. The rotation axis of the side shaft gear 181G is coaxial with the side rotation axis 182. In the differential device 131, the eccentric shaft 171, the side shaft 181, and the case 161 are combined so that the main rotation axis 172 and the side rotation axis 182 are coaxial with the case rotation axis 162.

[0028] The first internal gear mechanism 141 includes a first gear 142 made of an internal gear, and a second gear 143 made of an external gear and inscribed in the first gear 142. An involute curve is used for the curved shape of the teeth of the first gear 142 and the second gear 143. Therefore, the first gear 142 and the second gear 143 engage with each other with the second gear 143 inscribed in the first gear 142, and they rotate smoothly relative to each other.

[0029] The second internal gear mechanism 151 includes a third gear 152 formed of an internal gear and a fourth gear 153 formed of an external gear and internally engaging with the third gear 152. An involute curve is used for the curve shape of the teeth of the third gear 152 and the fourth gear 153. Therefore, the third gear 152 and the fourth gear 153 engage with each other in a state where the fourth gear 153 internally engages with the third gear 152 and rotate smoothly with each other.

[0030] The first gear 142 is fixed to the case 161 in a non-rotatable manner relative to the case such that its rotation axis is coaxial with the case rotation axis 162. Therefore, the rotation axis of the first gear 142 is also coaxial with the main rotation axis 172. The first gear 142 may be configured separately from the first case 161L or may be integrally formed with the first case 161L.

[0031] The lid 161F is for fixing the bearing B1 to the first case 161L and is fixed to the first case 161L by screws 1n. The bearing B1 is attached to a portion of the main shaft 171S of the eccentric shaft 171 on the side of the cam pin 171P. The retaining ring 11 is attached to the main shaft 171S so as to abut against the end face of the bearing B1 opposite to the cam pin 171P, and suppresses the bearing B1 from coming off the main shaft 171S. The first case 161L and the second case 161R are fixed by screws 4n.

[0032] The second gear 143 is rotatably supported by the cam pin 171P such that its rotation axis is coaxial with the cam pin rotation axis 173. More specifically, the second gear 143 is connected to the cam pin 171P by screws 3n via a bearing B2. Therefore, the second gear 143 is immovable in the axial direction with respect to the eccentric shaft 171 and can rotate about the cam pin rotation axis 173. That is, when the eccentric shaft 171 rotates when considering the second gear 143 with respect to the case 161 and the first gear 142 as a reference, the second gear 143 revolves around the main rotation axis 172 (while performing an eccentric motion) and rotates about the cam pin rotation axis 173.

[0033] The third gear 152 is arranged so that its rotation axis is coaxial with the cam pin rotation axis 173, that is, so that it is coaxial with the rotation axis of the second gear 143. FIGS. 5 and 6 show a configuration example in which the second gear 143 and the third gear 152 are fixed by a screw 2n. The third gear 152 may be configured separately from the second gear 143 as shown in each figure, or may be integrally formed with the second gear 143. That is, the third gear 152 is immovable in the axial direction with respect to the eccentric shaft 171, but can rotate about the cam pin rotation axis 173. Therefore, when the case 161 and the first gear 142 are considered as references, the third gear 152 rotates about the cam pin rotation axis 173 while revolving around the main rotation axis 172 (while performing eccentric motion) when the eccentric shaft 171 rotates. The method for fixing the second gear 143 and the third gear 152 is not limited to the examples shown in the figures, and various methods can be used.

[0034] The fourth gear 153 is fixed to one end of the side shaft 181 and cannot rotate relative to it. The fourth gear 153 may be a separate component from the side shaft 181, or may be molded integrally with the side shaft 181. The bearing B3 is attached to a location on the side shaft 181 on the fourth gear 153 side. The retaining ring 12 is attached to the side shaft 181 so as to abut against an end face of the bearing B3 on the side opposite to the fourth gear 153, and prevents the bearing B3 from coming off the side shaft 181.

[0035] The case gear 161G is fixed to the case 161 by, for example, a screw 5n so that its rotation axis is coaxial with the case rotation axis 162. That is, the case gear 161G is fixed to the case 161 so as not to rotate relative to the case 161. With this configuration, in the differential system 201, the output of the actuator 110 is transmitted to the case 161 via the transmission shaft 121, the transmission gear 121G, and the case gear 161G. That is, in the differential system 201, the driving force of the actuator 110 is transmitted to the case 161 by meshing the case gear 161G with the transmission gear 121G.

[0036] The differential device 131 is configured so that the amount of eccentricity of the first internal gear mechanism 141 is the same as the amount of eccentricity of the second internal gear mechanism 151. Here, the amount of eccentricity of the first internal gear mechanism 141 refers to the amount of misalignment between the rotation axis of the first gear 142 and the rotation axis of the second gear 143. The amount of eccentricity of the second internal gear mechanism 151 refers to the amount of misalignment between the rotation axis of the third gear 152 and the rotation axis of the fourth gear 153. With this configuration, the eccentric motion of the eccentric gear of the first internal gear mechanism 141 (the second gear 143 in the first embodiment) and the eccentric motion of the eccentric gear of the second internal gear mechanism 151 (the third gear 152 in the first embodiment) can be realized only by the eccentric shaft 171 without using separate eccentric shafts, and the main rotation shaft 172 and the side rotation shaft 182 can be arranged coaxially. Therefore, in the differential gear 131, a differential motion is generated between the eccentric shaft 171 and the side shaft 181 with respect to the case 161.

[0037] Next, the principle of differential motion of the differential gear 131 will be described with reference to FIGS. 7 to 11. All of these figures show the operation of each part as viewed from the case 161 that is rotationally driven by the actuator 110. In FIGS. 7 to 11, (a) is a side view of the differential gear 131, (b) is a schematic cross-sectional view taken along line AA in (a), and (c) is a schematic cross-sectional view taken along line BB in (a). In each figure, (b) and (c) correspond to the same state of the differential gear 131 and have the same viewing direction, so they are referred to as "cross-sectional views" when referring to them without distinction. FIGS. 8 to 11 respectively show a state in which the eccentric shaft 171 has rotated a predetermined angle in the counterclockwise direction relative to the case 161 and the side shaft 181 has rotated a predetermined angle in the clockwise direction relative to the case 161 from the state shown in FIG. 7.

[0038] The differential system 201 of the first embodiment is configured such that the output of the actuator 110 is transmitted to the case 161 by a transmission mechanism using a transmission gear 121G and a case gear 161G, and the case 161, the eccentric shaft 171, and the side shaft 181 rotate integrally (without any relative rotation difference between the case 161, the eccentric shaft 171, and the side shaft 181). On the other hand, in the differential device 131, a motion difference (difference in rotation speed) occurs between the eccentric shaft 171 and the side shaft 181 depending on the driving conditions of both shafts.

[0039] For example, when a radio-controlled model automobile in which the eccentric shaft 171 of the differential gear 131 is fixed to the right driving wheel and the side shaft 181 of the differential gear 131 is fixed to the left driving wheel corners, a difference in motion (difference in rotational speed) occurs between the left and right wheels. In other words, in the differential gear 131, a difference in motion (difference in rotational speed) occurs between the case 161 (case gear 161G) and the eccentric shaft 171 (eccentric shaft gear 171G), and similarly, a difference in motion (difference in rotational speed) also occurs between the case 161 (case gear 161G) and the side shaft 181 (side shaft gear 181G).

[0040] Here, it is assumed that a motion difference (difference in rotational speed) occurs between the case 161 (case gear 161G) and the eccentric shaft 171 (eccentric shaft gear 171G). Specifically, in the state of FIG. 7, when the eccentric shaft 171 (main shaft 171S) rotates counterclockwise, this rotation causes the cam pin 171P to revolve counterclockwise around the main rotation shaft 172 and the case rotation shaft 162. At the same time, in the state of FIG. 7, the second gear 143 revolves counterclockwise around the main rotation shaft 172 and the case rotation shaft 162 while inscribed in the first gear 142 and meshing with each other, and rotates clockwise around the cam pin rotation shaft 173.

[0041] The third gear 152 is disposed so that its rotation axis is coaxial with the rotation axis of the second gear 143, and is fixed to the second gear 143 so as to be non-rotatable relative to the second gear 143. Therefore, in the state shown in FIG. 7, the third gear 152 revolves counterclockwise around the main rotation axis 172 and the case rotation axis 162, and rotates clockwise around the cam pin rotation axis 173. The second gear 143 and the third gear 152 may be integrally molded, and in this case as well, the third gear 152 is non-rotatable relative to the second gear 143.

[0042] The differential device 131 is configured so that the amount of eccentricity of the first internal gear mechanism 141 and the amount of eccentricity of the second internal gear mechanism 151 are the same, and the main rotation shaft 172 and the side rotation shaft 182 are arranged coaxially. Therefore, the fourth gear 153 rotates clockwise around the side rotation shaft 182 and the case rotation shaft 162 while inscribed in the third gear 152 and meshing with each other due to the motion (revolution and rotation) of the third gear 152. Thus, in the differential device 131, the eccentric shaft 171 rotates counterclockwise and the side shaft 181 rotates clockwise relative to the case 161. In other words, the differential device 131 is configured so that a differential motion is generated between the eccentric shaft 171 and the side shaft 181.

[0043] 7, when the eccentric shaft 171 (main shaft 171S) rotates clockwise, the revolution direction and rotation direction of the second gear 143 and the third gear 152, the rotation direction of the fourth gear 153, and the rotation direction of the side shaft 181 are opposite to those when the eccentric shaft 171 (main shaft 171S) rotates counterclockwise. That is, in this case, the eccentric shaft 171 rotates clockwise and the side shaft 181 rotates counterclockwise relative to the case 161. Then, in the differential gear 131, a differential motion is generated between the eccentric shaft 171 and the side shaft 181.

[0044] Next, consider the case where the side shaft 181 rotates clockwise in the state shown in FIG. 7. When the side shaft 181 rotates clockwise, the fourth gear 153 rotates clockwise. The third gear 152 is disposed so that its rotation axis is coaxial with the rotation axis of the second gear 143, and is not capable of relative rotation with respect to the second gear 143. Therefore, in the state shown in FIG. 7, the third gear 152 revolves counterclockwise around the side rotation axis 181 and the case rotation axis 162 while meshing with the inscribed fourth gear 153, and rotates clockwise around the cam pin rotation axis 173.

[0045] The second gear 143 is disposed so that its rotation axis is coaxial with the rotation axis of the third gear 152, and is not rotatable relative to the third gear 152. Therefore, in the state of FIG. 7, the second gear 143 revolves counterclockwise around the main rotation axis 172 and the case rotation axis 162, and rotates clockwise around the cam pin rotation axis 173. At that time, the differential device 131 is disposed so that the amount of eccentricity of the first internally-scribed gear mechanism 141 and the amount of eccentricity of the second internally-scribed gear mechanism 151 are the same, and the main rotation axis 172 and the side rotation axis 182 are coaxial, so that the second gear 143 revolves around the main rotation axis 172 and rotates around the cam pin rotation axis 173 while inscribed in the first gear 142 and meshes with each other.

[0046] The revolution motion of the second gear 143 is transmitted to the main shaft 171S through the cam pin 171P of the eccentric shaft 171, generating a rotational motion of the main shaft 171S. In this manner, in the differential gear 131, the eccentric shaft 171 rotates counterclockwise relative to the case 161, and the side shaft 181 rotates clockwise, generating a differential motion between the eccentric shaft 171 and the side shaft 181.

[0047] In the state of FIG. 7, when the side shaft 181 rotates counterclockwise, the revolution direction and rotation direction of the second gear 143 and the third gear 152, the rotation direction of the fourth gear 153, and the rotation direction of the eccentric shaft 171 (main shaft 171S) are opposite to those when the side shaft 181 rotates clockwise. That is, in this case, the eccentric shaft 171 rotates clockwise and the side shaft 181 rotates counterclockwise relative to the case 161. Then, in the differential gear 131, a differential motion is generated between the eccentric shaft 171 and the side shaft 181. The principle of the differential motion generated between the eccentric shaft 171 and the side shaft 181 in the differential gear 131 with respect to the case 161 is as described above.

[0048] Next, the operation of each component due to the differential motion of the differential gear 131, that is, the change in the position and rotation angle of each component, will be specifically described with reference to Figs. 7 to 11. Figs. 7 to 11 show, in the order of the numbers in the drawings, the change over time of each component when the eccentric shaft 171 (main shaft 171S) rotates counterclockwise and the side shaft 181 rotates clockwise relative to the case 161. In Figs. 7 to 11, a mark S7 is attached to each cross-sectional view to indicate the movement of the eccentric shaft gear 171G. In (b) of each drawing, a mark Sa is attached to indicate the movement of the first case 161L, a mark S1 is attached to indicate the movement of the first gear 142, a mark S2 is attached to indicate the movement of the second gear 143, and a mark Sh is attached to indicate the movement of the eccentric shaft 171. In (c) of each figure, a mark Sb is provided to indicate the movement of the second case 161R, a mark S3 is provided to indicate the movement of the third gear 152, and a mark S4 is provided to indicate the movement of the fourth gear 153. In each figure, the positions of the marks Sa and Sb are not changed because the relative changes of the eccentric shaft 171 and the side shaft 181 with respect to the case 161 are shown. In addition, the first gear 142 is fixed to the case 161 so that its rotation axis is coaxial with the case rotation axis 162 and is not allowed to rotate relatively, so the position of the mark S1 is also not changed. The meshing positions of the gears will be described based on the orientation on the paper.

[0049] 7 shows a state in which the marks Sa, S1, S2, S7, and Sh are aligned on the same line, and the marks Sb, S3, S4, and S7 are aligned on the same line. In the state shown in FIG. 7, as shown in (b), the second gear 143 meshes with the upper side of the inner part of the first gear 142, and as shown in (c), the fourth gear 153 meshes with the lower side of the inner part of the third gear 152.

[0050] 8 shows a state in which the eccentric shaft 171 has rotated 90 degrees counterclockwise relative to the case 161 (see marks S7 and Sh), the side shaft 181 and the fourth gear 153 have rotated 90 degrees clockwise relative to the case 161 (see marks S4), the second gear 143 and the third gear 152 have revolved 90 degrees counterclockwise relative to the case 161 (see marks S2 and S3), and have rotated 30 degrees clockwise around the cam pin rotation shaft 173 (see marks S2 and S3). In the state shown in FIG. 8, as shown in (b), the second gear 143 is engaged with the left side of the inner side of the first gear 142, and as shown in (c), the fourth gear 153 is engaged with the right side of the inner side of the third gear 152.

[0051] 9 shows a state in which the eccentric shaft 171 rotates 180 degrees counterclockwise relative to the case 161 (see marks S7 and Sh), the side shaft 181 and the fourth gear rotate 180 degrees clockwise relative to the case 161 (see marks S4), the second gear 143 and the third gear 152 revolve 180 degrees counterclockwise relative to the case 161 (see marks S2 and S3), and rotate 60 degrees clockwise around the cam pin rotation shaft 173 (see marks S2 and S3). In the state shown in FIG. 9, as shown in (b), the second gear 143 meshes with the lower side of the inner part of the first gear 142, and as shown in (c), the fourth gear 153 meshes with the upper side of the inner part of the third gear 152.

[0052] 10 shows a state in which the eccentric shaft 171 rotates 270 degrees counterclockwise relative to the case 161 (see marks S7 and Sh), the side shaft 181 and the fourth gear rotate 270 degrees clockwise relative to the case 161 (see marks S4), the second gear 143 and the third gear 152 revolve 270 degrees counterclockwise relative to the case 161 (see marks S2 and S3), and rotate 90 degrees clockwise around the cam pin rotation shaft 173 (see marks S2 and S3). In the state shown in FIG. 10, as shown in (b), the second gear 143 meshes with the right side of the inner side of the first gear 142, and as shown in (c), the fourth gear 153 meshes with the left side of the inner side of the third gear 152.

[0053] 11 shows a state in which the eccentric shaft 171 rotates 360 degrees counterclockwise relative to the case 161 (see marks S7 and Sh), the side shaft 181 and the fourth gear rotate 360 ​​degrees clockwise relative to the case 161 (see marks S4), the second gear 143 and the third gear 152 revolve 360 ​​degrees counterclockwise relative to the case 161 (see marks S2 and S3), and rotate 120 degrees clockwise around the cam pin rotation shaft 173 (see marks S2 and S3) from the state shown in FIG. 5. In the state shown in FIG. 11, the second gear 143 meshes with the upper side of the inner part of the first gear 142 as shown in (b), and the fourth gear 153 meshes with the lower side of the inner part of the third gear 152 as shown in (c).

[0054] That is, when the eccentric shaft 171 (main shaft 171S) rotates counterclockwise and the side shaft 181 rotates clockwise relative to the case 161, the state of the differential gear 131 changes in the order of Figures 7, 8, 9, 10, and 11. On the other hand, when the eccentric shaft 171 (main shaft 171S) rotates clockwise and the side shaft 181 rotates counterclockwise relative to the case 161, the state of the differential gear 131 changes over time in the order of Figures 11, 10, 9, 8, and 7.

[0055] Next, regarding the differential device 131, the relationship between the number of teeth of each gear and the rotation speed ratio (N) between the eccentric shaft 171 and the side shaft 181 will be specifically analyzed. Here, when the eccentric shaft 171 rotates N times in the clockwise (counterclockwise) direction, and the side shaft 181 rotates once in the counterclockwise (clockwise) direction, the rotation speed ratio between the eccentric shaft 171 and the side shaft 181 is defined as N (= N / 1). That is, when the ratio of the absolute values of the rotation speeds between the eccentric shaft 171 and the side shaft 181 is N:1 (when the ratio of their rotation speeds is N:-1), the rotation speed ratio between the eccentric shaft 171 and the side shaft 181 corresponds to the said N. Hereinafter, let the number of teeth of the first gear 142 be O, the number of teeth of the second gear 143 be P, the number of teeth of the third gear 152 be Q, and the number of teeth of the fourth gear 153 be R (P, Q, R, S are natural numbers). Here, the case where the eccentric shaft 171 (main shaft 171S) rotates once counterclockwise with respect to the case 161 will be considered. In the examples of each figure, the number of teeth O of the first gear 142 is 16, the number of teeth P of the second gear 143 is 12, the number of teeth Q of the third gear 152 is 12, and the number of teeth R of the fourth gear 153 is 8.

[0056] When the eccentric shaft 171 rotates once counterclockwise, the second gear 143 also makes one revolution in the counterclockwise direction. At that time, the second gear 143 rotates while its plurality of external teeth are sequentially engaged with the plurality of internal teeth of the first gear 142. And the number of engaged teeth between the teeth of the first gear 142 and the teeth of the second gear 143 that are internally engaged is O teeth. The number of engaged teeth is, in the second gear 143, the total number of crest teeth contributing to its one revolution of revolution, that is, the total number of crest teeth of the second gear 143 that fit into the trough teeth of the first gear 142. Hereinafter, it is also referred to as the "first number of engaged teeth" in the sense of the number of engaged teeth between the two gears in the first internal gear mechanism 141. Therefore, the second gear 143 rotates around the cam pin rotation shaft 173 in the same direction as the rotation direction of the eccentric shaft 171 by the number of teeth difference "P - O", which is the difference between its own number of teeth and the first number of engaged teeth. Specifically, when P > O, the second gear 143 rotates counterclockwise by the number of teeth difference "P - O". Conversely, when P < O, the second gear 143 rotates clockwise by the absolute value of the number of teeth difference "P - O".

[0057] Hereinafter, the rotation of the second gear 143 is considered to be counterclockwise when the sign is positive and clockwise when the sign is negative. In other words, when the eccentric shaft 171 rotates once, the second gear 143 rotates on its axis of "(PO) / P" rotations in the same direction. In the example of each figure, when the eccentric shaft 171 rotates once, the second gear 143 rotates on its axis of "-1 / 3" rotations in the same direction (calculation formula: (12-16) / 12=-1 / 3), that is, rotates on its axis of "+1 / 3" rotations in the opposite direction to the eccentric shaft 171. For example, when the eccentric shaft 171 rotates once counterclockwise, the second gear 143 rotates on its axis of "+1 / 3" rotations in the clockwise direction.

[0058] The third gear 152 is disposed so that its rotation axis is coaxial with the rotation axis of the second gear 143, and is integrally formed or fixed to the second gear 143 so as not to rotate relative to it. Therefore, when the eccentric shaft 171 rotates once, the third gear 152 also rotates on its axis by "-1 / 3" rotation in the same direction, that is, by "+1 / 3" rotation in the opposite direction to the eccentric shaft 171. For example, when the eccentric shaft 171 rotates once counterclockwise, the third gear 152 rotates on its axis by "+1 / 3" rotation in the clockwise direction.

[0059] As described above, when the eccentric shaft 171 rotates once counterclockwise, the number of meshings (first meshing number) between the teeth of the first gear 142 and the teeth of the second gear 143 that mesh with each other inwardly is O teeth. In addition, in the second gear 143, the ratio of the first meshing number to the number of teeth P of the second gear 143 is "O / P". Here, since the third gear 152 is fixed to the second gear 143 so as not to rotate relatively, the number of meshings between the teeth of the third gear 152 and the teeth of the fourth gear 153 that mesh with each other inwardly is the first meshing number (O) multiplied by the ratio of the number of teeth (Q) of the third gear 152 to the number of teeth (P) of the second gear 143, that is, "O×Q / P (teeth)". Here, "×" represents a multiplication operator, and will be used in the same manner hereinafter. The number of meshings is the total number of lobe teeth in the third gear 152 that contribute to one revolution of itself, in other words, the total number of lobe teeth of the third gear 152 that fit into the valley teeth of the fourth gear 153, and is hereinafter also referred to as the "second number of meshings" to mean the number of meshings in the second internal gear mechanism 151.

[0060] That is, when the eccentric shaft 171 rotates once counterclockwise, the number of meshing teeth (second meshing number) of the third gear 152 and the fourth gear 153 that mesh inwardly with each other is "O×Q / P (teeth)". Therefore, the fourth gear 153 rotates (spins) around the side rotation shaft 182 in the same direction as the rotation direction of the eccentric shaft 171 by the tooth number difference "R-(O×Q / P)" which is the difference between the number of teeth of the fourth gear 153 and the second meshing number. That is, when the eccentric shaft 171 rotates once, the fourth gear 153 rotates on its own axis by "(P×RO×Q) / (P×R)" rotations in the same direction as the eccentric shaft 171.

[0061] In the example of each figure, when the eccentric shaft 171 rotates once, the fourth gear 153 rotates "-1" rotation in the same direction (calculation formula: (12×8-16×12) / (12×8)=-1), that is, rotates once in the opposite direction to the eccentric shaft 171. For example, when the eccentric shaft 171 rotates once counterclockwise, the fourth gear 153 (side shaft 181) rotates once clockwise. In this way, in the differential gear 131 illustrated in each figure, a differential operation occurs between the eccentric shaft 171 and the side shaft 181, with the case 161 as the reference, in which the ratio of the absolute values ​​of the rotation speeds of each is 1:1 (the ratio of the rotation speeds is 1:-1).

[0062] As described above, when the eccentric shaft 171 rotates once, the side shaft 181 rotates in the same direction by "(P×RO×Q) / (P×R)". In other words, for the differential gear 131, in order to generate a differential motion between the eccentric shaft 171 and the side shaft 181 with respect to the case 161 as a reference, the relationship of "(P×RO×Q) / (P×R)<0 (zero)" must be established between the number of teeth O of the first gear 142, the number of teeth P of the second gear 143, the number of teeth Q of the third gear 152, and the number of teeth R of the fourth gear 153. Hereinafter, the differential motion between the eccentric shaft 171 and the side shaft 181 with respect to the case 161 as a reference is also simply referred to as "differential motion". By summarizing this relationship, the conditional expression for the generation of the differential motion in the differential gear 131 is expressed as the following expression (1).

[0063] (Number 1) P × R < O × Q (1)

[0064] When an internal gear is selected for the first gear 142 (number of teeth O) and an external gear is selected for the second gear 143 (number of teeth P), "O>P" is satisfied, and when an internal gear is selected for the third gear 152 (number of teeth Q) and an external gear is selected for the fourth gear 153 (number of teeth P), "Q>R" is satisfied. The differential device 131 satisfies formula (1) because the first gear 142 and the third gear 152 are internal gears (internal gears) and the second gear 143 and the fourth gear 153 are external gears (external gears). That is, in the differential device 131, a differential motion is generated between the eccentric shaft 171 and the side shaft 181 with the case 161 as a reference.

[0065] Here, the relational expressions of the rotation speed ratio N, the number of teeth O, the number of teeth P, the number of teeth Q, and the number of teeth R between the eccentric shaft 171 and the side shaft 181 are found. As described above, when the eccentric shaft 171 rotates once, the side shaft 181 rotates in the same direction by "(P×RO×Q) / (P×R)" rotations. Therefore, the conditional expression for generating differential motion with a rotation speed ratio of N between the eccentric shaft 171 and the side shaft 181, that is, the conditional expression for "(rotation speed of the eccentric shaft 171):(rotation speed of the side shaft 181)=N:-1" is given by the following expression (2). Then, by rearranging the expression (2), the following expression (3) is obtained.

[0066] (Number 2) (P×RO×Q) / (P×R)=-1 / N (2)

[0067] (Number 3) N × O × Q = (N+1)× P × R (3)

[0068] The differential gear 131 is a differential gear in which the rotation speed ratio N between the eccentric shaft 171 and the side shaft 181 is 1 (the ratio of the rotation speeds between them is 1:-1). In the differential gear 131, the conditional expressions for the number of teeth O, the number of teeth P, the number of teeth Q, and the number of teeth R that satisfy N=1 are derived as shown in Expression (4) by substituting N=1 into Expression (2). Note that the relationships in Expressions (3) and (4) both satisfy Expression (1).

[0069] (Number 4) O × Q = 2 × P × R (4)

[0070] In addition, in the differential gear 131, as described above, the number of teeth O of the first gear 142 is 16, the number of teeth P of the second gear 143 is 12, the number of teeth Q of the third gear 152 is 12, and the number of teeth R of the fourth gear 153 is 8, satisfying formula (4).

[0071] Furthermore, when no differential motion is occurring between the eccentric shaft 171 and the side shaft 181, in the differential device 131, the driving force input to the case 161 (case gear 161G) is equally distributed (1:1) to the eccentric shaft 171 (eccentric shaft gear 171G) and the side shaft 181 (side shaft gear 181G). Therefore, for example, by arranging finger driving mechanisms corresponding to each of the two fingers of the robot hand in correspondence with the eccentric shaft gear 171G and the side shaft gear 181G, respectively, the differential device 131 can operate the two fingers with equal driving forces.

[0072] In addition, when a robot hand equipped with the differential gear 131 is made to grasp an object, if one of the two fingers of the robot hand touches an uneven object before the other finger, a differential motion occurs between the eccentric shaft gear 171G and the side shaft gear 181G, the motion of the finger that touched the object stops, and the other finger continues to move until it touches the object. In other words, by using the differential gear 131, the two fingers of the robot hand can be made to adapt to the object while grasping the object.

[0073] As described above, the differential 131 of the first embodiment includes the case 161, the main shaft 171S journaled on one end of the case 161, the eccentric shaft 171 including the cam pin 171P eccentric with respect to the main shaft 171S, the side shaft 181 journaled on the other end of the case 161, the first internal gear mechanism 141, and the second internal gear mechanism 151. The first internal gear mechanism 141 is disposed on one end inside the case 161, and includes the first gear 142 fixed to the case 161, and the second gear 143 journaled rotatably by the cam pin 171P and engaged with the first gear 142. The second internal gear mechanism 151 is disposed at the other end side inside the case 161, and has a third gear 152 fixed to the second gear 143, and a fourth gear 153 fixed to one end of the side shaft 181 and engaged with the third gear 152. The differential device 131 is configured so that a differential motion occurs between the remaining two of the case 161, the eccentric shaft 171, and the side shaft 181, with one of them being a reference. In this manner, the first internal gear mechanism 141 and the second internal gear mechanism 151 are disposed inside the case 161 with the third gear 152 fixed to the second gear 143. That is, the differential device 131 can suppress a radial size increase because two internal gear mechanisms are integrally disposed. Also, the differential device 131 can suppress a size increase in the axial direction because a mechanism in which gears mesh with each other is realized in two stages and these are integrally configured. Therefore, a small and thin device can be achieved with a simple structure.

[0074] More specifically, in the differential device 131, the first gear 142 and the third gear 152 are internal gears, and the second gear 143 and the fourth gear 153 are external gears. The differential device 131 is configured to satisfy the above formula (3) using the number of teeth O of the first gear 142, the number of teeth P of the second gear 143, the number of teeth Q of the third gear 152, the number of teeth R of the fourth gear 153, and the rotation speed ratio N. The differential device 131 illustrated in each drawing is configured so that the rotation speed ratio N is 1. Furthermore, in the differential device 131, the second gear 143 and the third gear 152 are integrally connected, which also contributes to a thinner axial direction.

[0075] The differential device 131 is configured so that the amount of eccentricity of the first internal gear mechanism 141 and the amount of eccentricity of the second internal gear mechanism 151 are the same. With this configuration, the eccentric motion of the eccentric gears of the first internal gear mechanism 141 and the second internal gear mechanism 151 is achieved by only the eccentric shaft 171 without using separate eccentric shafts, and the main rotating shaft 172 and the side rotating shaft 182 are coaxially arranged. In the differential device 131, the eccentric shaft 171 and the side shaft 181 are differentially rotated with respect to the case 161.

[0076] For example, when the right and left driving wheels of a radio-controlled model automobile are fixed to the eccentric shaft 171 and side shaft 181 of the differential gear 131, respectively, the driving force of the actuator 110 is distributed to the eccentric shaft 171 and side shaft 181. The differential gear 131 absorbs the rotation difference between the left and right driving wheels even when the radio-controlled model automobile turns, thereby achieving smooth cornering.

[0077] In the conventional planetary gear mechanism, the sun gear (external teeth type) and the internal gear (internal teeth type) are arranged coaxially with the rotation axis of the case, and the planetary gear (external teeth type) is arranged between the sun gear and the internal gear so as to mesh with them. Therefore, in the planetary gear mechanism, as shown in Figure 59, the meshing point (part 2) between the planetary gear and the sun gear exists between the meshing point (part 1) between the sun gear and the planetary gear and the rotation axis of the case. In other words, the planetary gear mechanism has meshing point (part 1) and meshing point (part 2) lined up radially outward from the rotation axis of the case, and a total of four meshing points lined up in a straight line, making it difficult to reduce the size in the radial direction.

[0078] 2, the differential device 131 has a configuration in which the case rotation shaft 162 is disposed between the meshing point of the first internal gear mechanism 141 (the meshing point of the first gear 142 and the second gear 143) and the meshing point of the second internal gear mechanism 151 (the meshing point of the third gear 152 and the fourth gear 153), and the first gear 142, the second gear 143, the third gear 152, and the fourth gear 153 are disposed so as to overlap in a plan view perpendicular to the axial direction. This makes it possible to achieve a reduction in size in the radial direction.

[0079] In particular, in a robot hand, multiple finger joints are required to move independently, so multiple differential gears must be installed in a limited space, and it is desirable to simultaneously solve the conflicting issues of miniaturization and robustness. In this regard, the differential gear 131 can distribute the driving force input to an input element to two or more output element parts, so that by applying it to driving the finger joints of a robot hand, a small and lightweight robot hand can be provided.

[0080] 3 and 4, a transmission mechanism using the transmission gear 121G and the case gear 161G is illustrated as an example of a mechanism for transmitting the output of the actuator 110 to the case 161, but the present invention is not limited thereto. Various transmission mechanisms other than those described above can be adopted for the differential system 201. For example, a transmission mechanism using a driving pulley and a driven pulley may be adopted for the differential system 201. That is, a driving pulley may be fixed to the tip of the transmission shaft 121 so as to rotate coaxially therewith, and a driven pulley may be fixed to the case 161 so as to be coaxial with the main rotating shaft 172 and the side rotating shaft 182 and not to rotate relative thereto. Then, a transmission belt may be wound around the driving pulley and the driven pulley so that they are interlocked with each other, thereby transmitting the output of the actuator 110 to the case 161.

[0081] Example 2. A configuration example of a differential gear 132 and a differential system 202 according to a second embodiment of the present invention will be described with reference to Figs. 12 to 20. The same reference numerals are used for each component shown in Figs. 1 and 2, and each component that functions similarly or is arranged similarly to that of the first embodiment, and the description is omitted or simplified as appropriate. In the differential gear 132 of the second embodiment, the first gear 142 and the third gear 152 are configured as external gears, and the second gear 143 and the fourth gear 153 are configured as internal gears. In each drawing, some of the reference numerals may be omitted with the intention of avoiding complication of the drawings, etc.

[0082] 12 and 13, similar to the differential system 201 of the first embodiment, the differential system 202 of the second embodiment is configured to transmit the output of the actuator 110 to the transmission shaft 121 via the transmission device 110T to rotate the transmission gear 121G, thereby driving the differential device 132. The actuator 110 of the second embodiment is a drive source of the differential device 132, and is configured by an electric motor or the like. The actuator 110 is fixed to a base frame (not shown), such as the body of an automobile, the body of a robot, or the palm of a robot hand.

[0083] However, the differential system 202 differs from the differential system 201 in that a side shaft gear 181G meshes with the transmission gear 121G, and the side shaft gear 181G is fixed to one end of the side shaft 181 so as to rotate coaxially together. That is, in the differential system 202, the driving force of the actuator 110 is transmitted to the side shaft 181. That is, in the differential gear 131 of the first embodiment, the driving force of the actuator 110 is input to the case 161, whereas in the differential gear 132 of the second embodiment, the driving force of the actuator 110 is input to the side shaft 181.

[0084] 12 and 13, the side shaft gear 181G and the side shaft 181 are fixed to each other so as not to rotate relative to each other, and each rotation axis is coaxial with the side rotation shaft 182. With this configuration, in the differential system 202, the output of the actuator 110 is transmitted to the side shaft 181 via the transmission shaft 121, the transmission gear 121G, and the side shaft gear 181G. Other configurations of the differential system 202 are similar to those of the differential system 201.

[0085] 14 and 15, the differential gear 132 has a case 161, a first internal gear mechanism 141, a second internal gear mechanism 151, an eccentric shaft 171, and a side shaft 181. The differential gear 132 is journaled to a base frame (not shown), such as the body of an automobile, the body of a robot, or the palm of a robot hand, via a bearing (not shown). The differential gear 132 is immobile in the axial direction with respect to the base frame, and the case 161, the eccentric shaft 171, and the side shaft 181 are each capable of rotating freely.

[0086] The first internal gear mechanism 141 includes a first gear 142 made of an external gear and a second gear 143 made of an internal gear. In the first internal gear mechanism 141, the first gear 142 is disposed so as to be inscribed in the second gear 143. An involute curve is used for the curved shape of the teeth of the first gear 142 and the second gear 143. Therefore, the first gear 142 and the second gear 143 are engaged with each other in a state in which the first gear 142 is inscribed in the second gear 143, and they rotate smoothly relative to each other.

[0087] The second internal gear mechanism 151 includes a third gear 152 made of an external gear and a fourth gear 153 made of an internal gear. In the second internal gear mechanism 151, the third gear 152 is disposed so as to be inscribed in the fourth gear 153. An involute curve is used for the curved shape of the teeth of the third gear 152 and the fourth gear 153. Therefore, the third gear 152 and the fourth gear 153 are engaged with each other in a state in which the third gear 152 is inscribed in the fourth gear 153, and they rotate smoothly relative to each other.

[0088] The first gear 142 is fixed to the case 161 so as to be non-rotatable relative to the case 161, so that its rotation axis is coaxial with the case rotation axis 162. Therefore, the rotation axis of the first gear 142 is also coaxial with the main rotation axis 172. The first gear 142 may be configured separately from the first case 161L, or may be molded integrally with the first case 161L. The second gear 143 is rotatably supported by the cam pin 171P so that its rotation axis is coaxial with the cam pin rotation axis 173. More specifically, the second gear 143 is connected to the cam pin 171P by a screw 3n via a bearing B2. Therefore, the second gear 143 is immovable in the axial direction with respect to the eccentric shaft 171, and is rotatable around the cam pin rotation axis 173. In other words, when the eccentric shaft 171 rotates, if the case 161 and the first gear 142 are considered as reference points, the second gear 143 rotates around the cam pin rotation axis 173 while revolving (performing eccentric motion) around the main rotation axis 172.

[0089] The third gear 152 is arranged so that its rotation axis is coaxial with the cam pin rotation axis 173, that is, so that it is coaxial with the rotation axis of the second gear 143. FIG. 14 and FIG. 15 show a configuration example in which the second gear 143 and the third gear 152 are fixed by a screw 2n. The second gear 143 and the third gear 152 may be configured as separate bodies as shown in each figure, or may be integrally molded. That is, the third gear 152 is immovable in the axial direction with respect to the eccentric shaft 171, but can rotate about the cam pin rotation axis 173. Therefore, when the case 161 and the first gear 142 are considered as references, the third gear 152 rotates about the cam pin rotation axis 173 while revolving around the main rotation axis 172 (while performing eccentric motion) when the eccentric shaft 171 rotates. The fourth gear 153 is fixed to the side shaft 181 so as not to rotate relative to it. The fourth gear 153 may be a separate component from the side shaft 181, or may be molded integrally with the side shaft 181. Note that the method for fixing the second gear 143 and the third gear 152 is not limited to the examples shown in the figures, and various methods can be used.

[0090] The differential device 132 is configured so that the amount of eccentricity of the first internal gear mechanism 141 and the amount of eccentricity of the second internal gear mechanism 151 are the same. With this configuration, the eccentric motion of the eccentric gear of the first internal gear mechanism 141 (the second gear 143 in the second embodiment) and the eccentric motion of the eccentric gear of the second internal gear mechanism 151 (the third gear 152 in the second embodiment) are realized by the same eccentric shaft 171 only, without using separate eccentric shafts, and the main rotating shaft 172 and the side rotating shaft 182 are coaxially arranged. In the differential device 132, the eccentric shaft 171 and the side shaft 181 are differentially rotated with respect to the case 161.

[0091] Next, the principle of the differential motion of the differential gear 132 will be described with reference to Figs. 16 to 20. All of these figures show the operation of each part as viewed from the side shaft 181 that is rotationally driven by the actuator 110. In Figs. 16 to 20, (a) is a side view of the differential gear 132, (b) is a schematic cross-sectional view taken along line AA in (a), and (c) is a schematic cross-sectional view taken along line BB in (a). In each figure, (b) and (c) correspond to the same state of the differential gear 132 and have the same viewing direction, so they are referred to as "cross-sectional views" when referring to them without distinction. Figs. 17 to 20 respectively show a state in which the eccentric shaft 171 has rotated a predetermined angle counterclockwise relative to the side shaft 181 and the case 161 has rotated a predetermined angle clockwise relative to the side shaft 181 from the state shown in Fig. 16.

[0092] In the differential system 202 of the second embodiment, the output of the actuator 110 is transmitted to the side shaft 181 by a transmission mechanism using a transmission gear 121G and a side shaft gear 181G, and the case 161, the eccentric shaft 171, and the side shaft 181 rotate integrally (without any relative rotation difference between the case 161, the eccentric shaft 171, and the side shaft 181). On the other hand, in the differential device 132, a motion difference (difference in rotation speed) occurs between the case 161 and the eccentric shaft 171 depending on the driving conditions of both members.

[0093] For example, when a radio-controlled model automobile in which the case 161 of the differential gear 132 is fixed to the right driving wheel and the eccentric shaft 171 of the differential gear 132 is fixed to the left driving wheel corners, a motion difference (rotational speed difference) occurs between the left and right wheels. In other words, in the differential gear 132, a motion difference (rotational speed difference) occurs between the side shaft 181 (side shaft gear 181G) and the case 161 (case gear 161G), and similarly, a motion difference (rotational speed difference) occurs between the side shaft 181 (side shaft gear 181G) and the eccentric shaft 171 (eccentric shaft gear 171G).

[0094] Here, it is assumed that a motion difference (difference in rotational speed) occurs between the side shaft 181 (side shaft gear 181G) and the eccentric shaft 171 (eccentric shaft gear 171G). Specifically, when the eccentric shaft 171 (main shaft 171S) rotates counterclockwise in the state of FIG. 16, this rotation causes the cam pin 171P to revolve counterclockwise around the main rotation shaft 172 and the case rotation shaft 162. At the same time, in the state of FIG. 16, the second gear 143 revolves counterclockwise around the main rotation shaft 172 and the case rotation shaft 162 while meshing with the inscribed first gear 142, and rotates clockwise around the cam pin rotation shaft 173.

[0095] The third gear 152 is disposed so that its rotation axis is coaxial with the rotation axis of the second gear 143, and is integrally formed or fixed to the second gear 143 so as to be non-rotatable relative to the second gear 143. Therefore, in the state shown in FIG. 16, the third gear 152 revolves counterclockwise around the main rotation axis 172 and the case rotation axis 162, and rotates clockwise around the cam pin rotation axis 173. The second gear 143 and the third gear 152 may be integrally formed, and in this case as well, the third gear 152 is non-rotatable relative to the second gear 143.

[0096] The differential device 132 is configured such that the eccentricity of the first internal gear mechanism 141 is the same as the eccentricity of the second internal gear mechanism 151, and is arranged such that the main rotation shaft 172 and the side rotation shaft 182 are coaxial. Therefore, the third gear 152 is internally engaged with the fourth gear 153 and moves (revolves and rotates) while meshing with each other. The first gear 142 rotates clockwise around the case rotation shaft 162 (main rotation shaft 172, side rotation shaft 182) while meshing with each other with the second gear 143 in an internally engaged state due to the movement (revolution and rotation) of the second gear 143 and the third gear 152. That is, the case L161L (case gear 161G) rotates clockwise around the case rotation shaft 162 (main rotation shaft 172, side rotation shaft 182). Thus, in the differential device 132, with respect to the side shaft 181, the eccentric shaft 171 rotates counterclockwise, the case 161 rotates clockwise, and a differential motion occurs between the eccentric shaft 171 and the case 161.

[0097] In addition, in the state of FIG. 16, when the eccentric shaft 171 (main shaft 171S) rotates clockwise, the rotation direction of the first gear 142, the revolution direction and the rotation direction of the second gear 142 and the third gear 152, and the rotation direction of the case 161 are all opposite to the case when the eccentric shaft 171 (main shaft 171S) rotates counterclockwise. That is, in this case, with respect to the side shaft 181, the eccentric shaft 171 rotates clockwise, the case 161 rotates counterclockwise, and a differential motion occurs between the eccentric shaft 171 and the case 161.

[0098] Next, consider the case where the case 161 rotates clockwise in the state of FIG. 16. When the case 161 rotates clockwise, the first gear 142 rotates clockwise.

[0099] The third gear 152 is disposed so that its rotation axis is coaxial with the rotation axis of the second gear 143, and is integrally formed or fixed to the second gear 143 so as not to rotate relative to the second gear 143. Therefore, in the state shown in FIG. 16, the third gear 152 revolves counterclockwise around the side rotation shaft 181 and the case rotation shaft 162 while inscribed in the fourth gear 153 and meshing with each other, and rotates clockwise around the cam pin rotation shaft 173.

[0100] The second gear 143 is disposed so that its rotation axis is coaxial with the rotation axis of the third gear 152, and is integrally formed or fixed to the third gear 152 so as not to rotate relative to it. Therefore, in the state of FIG. 16, the second gear 143 revolves counterclockwise around the main rotation axis 172 and the case rotation axis 162, and rotates clockwise around the cam pin rotation axis 173. At that time, the differential device 132 is configured so that the eccentricity amount of the first internal gear mechanism 141 and the eccentricity amount of the second internal gear mechanism 151 are the same, and the main rotation axis 172 and the side rotation axis 182 are disposed so as to be coaxial, so that the second gear 143 revolves and rotates while inscribed in the first gear 142 and meshes with each other. The revolution motion of the second gear 143 is generated as the rotation motion of the eccentric shaft 171 (main shaft 171S). Thus, in the differential gear 132, the eccentric shaft 171 rotates counterclockwise relative to the side shaft 181, and the case 161 rotates clockwise, generating a differential motion between the eccentric shaft 171 and the case 161.

[0101] 16, when the case 161 rotates counterclockwise, the rotation direction of the first gear 142, the revolution direction and rotation direction of the second gear 143 and the third gear 152, and the rotation direction of the eccentric shaft 171 (main shaft 171S) are all opposite to the direction when the case 161 rotates clockwise. That is, in this case, the eccentric shaft 171 rotates clockwise and the case 161 rotates counterclockwise relative to the side shaft 181, and a differential motion is generated between the eccentric shaft 171 and the case 161. The principle of the differential motion generated between the eccentric shaft 171 and the case 161 with respect to the side shaft 181 in the differential gear 132 is as described above.

[0102] Next, the operation of each component due to the differential motion of the differential gear 132, that is, the change in the position and rotation angle of each component will be specifically described with reference to Figs. 16 to 20. Figs. 16 to 20 illustrate the change in state of each component over time in the order of the numbers in the drawings when the eccentric shaft 171 (main shaft 171S) rotates counterclockwise and the case 161 rotates clockwise relative to the side shaft 181. Each figure is marked with marks Sa, Sb, Sh, S1, S2, S3, S4, and S7, as in Figs. 7 to 11. Since each figure shows the relative change of the eccentric shaft 171 and the case 161 relative to the side shaft 181, the position of the mark S4 marked on the fourth gear 153 does not change. The meshing positions of each gear will be described based on the orientation on the paper.

[0103] Fig. 16 shows a state in which the marks Sa, S1, S2, S7, and Sh are aligned on the same line, and the marks Sb, S3, S4, and S7 are aligned on the same line. In the state shown in Fig. 16, the first gear 142 meshes with the lower side of the inner part of the second gear 143 as shown in (b), and the third gear 152 meshes with the upper side of the inner part of the fourth gear 153 as shown in (c).

[0104] 17 shows a state in which the eccentric shaft 171 rotates 90 degrees counterclockwise relative to the side shaft 181 (see marks S7 and Sh), the case 161 and the first gear 142 rotate 90 degrees clockwise relative to the side shaft 181 (see marks Sa, Sb, and S1), the second gear 143 and the third gear 152 revolve 90 degrees counterclockwise relative to the side shaft 181 (see the movement of the cam pin rotation shaft 173 which is the (rotation) rotation shaft of the second gear 143 and the third gear 152), and rotate 45 degrees clockwise around the cam pin rotation shaft 173 (see marks S2 and S3). In the state shown in FIG. 17, as shown in (b), the first gear 142 meshes with the right side of the inner part of the second gear 143, and as shown in (c), the third gear 152 meshes with the left side of the inner part of the fourth gear 153.

[0105] 18 shows a state in which the eccentric shaft 171 rotates 180 degrees counterclockwise relative to the side shaft 181 (see marks S7 and Sh), the case 161 and the first gear 142 rotate 180 degrees clockwise relative to the side shaft 181 (see marks Sa, Sb, and S1), the second gear 143 and the third gear 152 revolve 180 degrees counterclockwise relative to the side shaft 181 (see the movement of the cam pin rotation shaft 173 which is the (rotation) rotation shaft of the second gear 143 and the third gear 152), and rotate 90 degrees clockwise around the cam pin rotation shaft 173 (see marks S2 and S3). In the state shown in FIG. 18, as shown in (b), the first gear 142 meshes with the upper side of the inner part of the second gear 143, and as shown in (c), the third gear 152 meshes with the lower side of the inner part of the fourth gear 153.

[0106] 19 shows a state in which the eccentric shaft 171 rotates 270 degrees counterclockwise relative to the side shaft 181 (see marks S7 and Sh), the case 161 and the first gear rotate 270 degrees clockwise relative to the side shaft 181 (see marks Sa, Sb, and S1), the second gear 143 and the third gear 152 revolve 270 degrees counterclockwise relative to the side shaft 181 (see the movement of the cam pin rotation shaft 173 which is the (rotation) rotation shaft of the second gear 143 and the third gear 152), and rotate 135 degrees clockwise around the cam pin rotation shaft 173 (see marks S2 and S3). In the state shown in FIG. 19, as shown in (b), the first gear 142 meshes with the left side of the inner part of the second gear 143, and as shown in (c), the third gear 152 meshes with the right side of the inner part of the fourth gear 153.

[0107] 20 shows a state in which the eccentric shaft 171 rotates 360 degrees counterclockwise relative to the side shaft 181 (see marks S7 and Sh), the case 161 and the first gear rotate 360 ​​degrees clockwise relative to the side shaft 181 (see marks Sa, Sb, and S1), the second gear 143 and the third gear 152 revolve 360 ​​degrees counterclockwise relative to the side shaft 181 (see the movement of the cam pin rotation shaft 173 which is the (rotation) rotation shaft of the second gear 143 and the third gear 152), and rotate 180 degrees clockwise around the cam pin rotation shaft 173 (see marks S2 and S3). In the state shown in FIG. 20, as shown in (b), the first gear 142 meshes with the lower side of the inner part of the second gear 143, and as shown in (c), the third gear 152 meshes with the upper side of the inner part of the fourth gear 153.

[0108] That is, when the eccentric shaft 171 (main shaft 171S) rotates counterclockwise and the case 161 rotates clockwise relative to the side shaft 181, the state of the differential gear 132 changes in the order of Figures 16, 17, 18, 19, and 20. On the other hand, when the eccentric shaft 171 (main shaft 171S) rotates clockwise and the case 161 rotates counterclockwise relative to the side shaft 181, the state of the differential gear 132 changes over time in the order of Figures 20, 19, 18, 17, and 16.

[0109] Next, for the differential device 132, the relationship between the number of teeth of each gear and the rotation speed ratio (M) between the case 161 and the eccentric shaft 171 is specifically analyzed by appropriately using the analysis method in the first embodiment. The number of teeth of each gear is defined similarly to the first embodiment. Here, when the case 161 rotates M times in the clockwise direction (counterclockwise direction) and the eccentric shaft 171 rotates once in the counterclockwise direction (clockwise direction), the rotation speed ratio between the case 161 and the eccentric shaft 171 is defined as M (=M / 1). That is, when the ratio of the absolute values ​​of the rotation speeds between the case 161 and the eccentric shaft 171 is M:1 (when the ratio of the rotation speeds between them is M:-1), the rotation speed ratio between the case 161 and the eccentric shaft 171 corresponds to the M.

[0110] In the example of each figure, the number of teeth O of the first gear 142 is 9, the number of teeth P of the second gear 143 is 12, the number of teeth Q of the third gear 152 is 8, and the number of teeth R of the fourth gear 153 is 12. The difference in the number of teeth between the first gear 142 and the second gear 143 (3=12-9) is different from the difference in the number of teeth between the third gear 152 and the fourth gear 153 (4=12-8). Even in this configuration, a positively shifted gear (a gear with a positive shift applied) is used for the second gear 143 so that the amount of eccentricity of the first internally-spoken gear mechanism 141 and the amount of eccentricity of the second internally-spoken gear mechanism 151 are the same. Standard gears are used for the first gear 142, the third gear 152, and the fourth gear 153. Here, a "profile shifted gear" refers to a gear whose diameter (such as pitch circle diameter or tip circle diameter) has been increased or decreased without changing the number of teeth by changing the tooth profile. The operation of increasing the diameter without changing the number of teeth is called "positive profile shift," and the operation of decreasing the diameter without changing the number of teeth is called "negative profile shift." Gears that have not been subjected to positive or negative profile shifting are called "standard gears."

[0111] If the amount of eccentricity of the first internal gear mechanism 141 and the amount of eccentricity of the second internal gear mechanism 151 are configured to be the same, then shifted gears may be used for all four gears, the first gear 142, the second gear 143, the third gear 152, and the fourth gear 153, or shifted gears may be used for three of the four gears, or even for only two of the four gears.

[0112] That is, even in a situation where the difference in the number of teeth between the first gear 142 and the second gear 143 is different from the difference in the number of teeth between the third gear 152 and the fourth gear 153, if the difference in the number of teeth is about 1 (tooth), the amount of eccentricity of the first internal gear mechanism 141 and the amount of eccentricity of the second internal gear mechanism 151 can be made the same by using profile shifted gears. This allows for more leeway in selecting the number of teeth of the gears that satisfy the tooth number condition equation (such as the above-mentioned equation (3) or the below-mentioned equation (7)) for achieving the desired differential operation, making it possible to avoid selecting gears with large diameters, and as a result, the diameter of the differential device 132 can be made smaller.

[0113] As described above, the differential gear 131 of the first embodiment and the differential gear 132 of the second embodiment are different in the portion to which the driving force of the actuator 110 is transmitted, and the types of gears used for the first gear 142, the second gear 143, the third gear 152, and the fourth gear 153 are different, but the basic configuration of the differential gear 132 is the same as the configuration shown in FIG. 1. Therefore, the same analysis method as that for the differential gear 131 can be used for the differential gear 132. That is, in the first embodiment, it was shown that when the eccentric shaft 171 is rotated once with the case 161 as the reference, the side shaft 181 performs a rotational motion of "(P×RO×Q) / (P×R)" rotations in the same direction. Hereinafter, the state in which such a relative motion is performed is referred to as "state A" (see (A) of FIG. 58). Hereinafter, the analysis method of the second embodiment will be described using the analysis result shown in FIG. 58.

[0114] In the differential gear 132 of the second embodiment, a differential motion occurs between the eccentric shaft 171 and the case 161 with respect to the side shaft 181. Therefore, in order to stop the rotation of the side shaft 181 in the analysis state of the first embodiment (the state in which the side shaft 181 rotates by "(P×RO×Q) / (P×R)"), i.e., in state B, a state will be considered in which the entire differential gear 132 is rotated by "(P×RO×Q) / (P×R)" in the opposite direction.

[0115] Here, the state in which the entire differential gear 132 is rotated in the opposite direction by "(P×RO×Q) / (P×R)" is hereinafter referred to as "state B" (see FIG. 58 (B)). Also, the state in which the entire differential gear 132 in state A is rotated in the opposite direction by "(P×RO×Q) / (P×R)" is referred to as "state C" (see FIG. 58 (C)). That is, the side shaft 181 is rotated in the opposite direction by "(P×RO×Q) / (P×R)" from the state in which it was rotating by "(P×RO×Q) / (P×R)" in state A, and therefore in state C it is in a state of "0 (zero)" rotation. Considering this, the rotation of the side shaft 181 is stopped, so the differential motion between the eccentric shaft 171 and the case 161 can be analyzed based on the side shaft 181.

[0116] Since the eccentric shaft 171 has rotated "(P×RO×Q) / (P×R)" in the opposite direction from the state where it rotated "1" in state A, it is rotated "1-(P×RO×Q) / (P×R)" in state C. By rearranging this, it can be seen that the eccentric shaft 171 is rotated "(O×Q) / (P×R)" in state C.

[0117] It can be seen that the case 161 has been rotated by "(P×RO×Q) / (P×R)" in the opposite direction from the non-rotating state in state A, and therefore is in a state of rotating by "(O×QP×R) / (P×R)" in state C. In other words, it can be seen that the first gear 142, which is integrally formed or fixed to the case 161 so as not to rotate relative to it, is also in a state of rotating by "(O×QP×R) / (P×R)" in state C.

[0118] The revolution of the second gear 143 and the third gear 152 is the same as the rotation of the eccentric shaft 171, and since the second gear 143 and the third gear 152 have been rotated in the opposite direction by "(P×RO×Q) / (P×R)" from the state in which they rotated "1" in state A, the revolution of the second gear 143 and the third gear 152 is in a state of "(O×Q) / (P×R)" revolutions in state C. Also, the second gear 143 and the third gear 152 have been rotated in the opposite direction by "(P×RO×Q) / (P×R)" from the state in which they rotated "(PO) / P" in state A, and the rotation of the second gear 143 and the third gear 152 is in a state of "(PO) / P-(P×RO×Q) / (P×R)" revolutions in state C. To summarize, the rotation of the second gear 143 and the third gear 152 in state C can be said to be (O×QO×R) / (P×R).

[0119] Here, based on the results of the analysis of State C above, we will consider the case where the eccentric shaft 171 rotates once relative to the side shaft 181. Specifically, we will consider a state where the results of the analysis of State C above are multiplied by "(P×R) / (O×Q)". Hereinafter, this state will be referred to as "State D" (see (D) in Figure 58).

[0120] Since the side shaft 181 was in a state of "0 (zero)" rotation in state C, multiplying this result by "(P×R) / (O×Q)" means that the side shaft 181 is in a state of "0 (zero)" rotation in state D. In other words, even if the result of the above state analysis is multiplied by "(P×R) / (O×Q)", it is still possible to analyze the rotation of the case 161 and the rotation of the eccentric shaft 171 based on the side shaft 181.

[0121] Since the eccentric shaft 171 has rotated "(O×Q) / (P×R)" in state C, multiplying this result by "(P×R) / (O×Q)" results in the eccentric shaft 171 having rotated "1" in state D. In other words, by multiplying the result of the above state analysis by "(P×R) / (O×Q)", it is possible to proceed with the analysis of the case where the eccentric shaft 171 has rotated once.

[0122] In case 161, in state C, the rotation was "(O×QP×R) / (P×R)", so if this result is multiplied by "(P×R) / (O×Q)", in state D, case 161 becomes a state in which the rotation is "(O×QP×R) / (O×Q)".

[0123] The second gear 143 and the third gear 152 rotate the same as the eccentric shaft 171, and in state C, they are revolving at "(O×Q) / (P×R)" revolutions. Therefore, multiplying this result by "(P×R) / (O×Q)" results in the second gear 143 and the third gear 152 revolving at "1" revolution in state D. Also, the second gear 143 and the third gear 152 rotate on their own axes at "(O×QO×R) / (P×R)" revolutions in state C. Therefore, multiplying this result by "(P×R) / (O×Q)" results in the second gear 143 and the third gear 152 rotating on their own axes at "(O×QO×R) / (O×Q)" revolutions, i.e., rotating at "(QR) / Q)" revolutions in state D.

[0124] FIG. 58 shows the rotational relationship between the eccentric shaft 171, the case 161, and the side shaft 181, sorted by state A, state B, state C, and state D, based on the analysis results described above.

[0125] 16 to 20, when the eccentric shaft 171 rotates once, the second gear 143 and the third gear 152 rotate in the same direction by "-1 / 2 (calculation formula: (8-12) / 8=-1 / 2)" rotations. In other words, since the sign is negative, when the eccentric shaft 171 rotates once in the counterclockwise direction, the second gear 143 and the third gear 152 rotate in the clockwise direction by "+1 / 2" rotations.

[0126] When the eccentric shaft 171 rotates once, the case 161 (first gear 142) rotates "(O×QP×R) / (O×Q)" in the same direction with respect to the side shaft 181. In the example of each figure, when the eccentric shaft 171 rotates once, the case 161 (first gear 142) rotates "-1" (calculation formula: (9×8-12×12) / (9×8)=-1)" in the same direction. In other words, since the sign is negative, when the eccentric shaft 171 rotates once in the counterclockwise direction, the case 161 (case gear 161G) rotates "+1" in the clockwise direction.

[0127] In this way, in the differential gear 132 illustrated in each figure, differential operation occurs between the case 161 and the eccentric shaft 171, with the side shaft 181 as the reference, in which the ratio of the absolute values ​​of their rotational speeds is 1:1 (the ratio of rotational speeds is 1:-1).

[0128] Furthermore, when no differential motion is occurring between the eccentric shaft 171 and the case 161, the differential device 132 distributes the driving force input to the side shaft 181 (side shaft gear 181G) equally (1:1) to the case 161 (case gear 161G) and the eccentric shaft 171 (eccentric shaft gear 171G). Therefore, for example, by arranging finger driving mechanisms corresponding to each of the two fingers of the robot hand in correspondence with the case gear 161G and the eccentric shaft gear 171G, respectively, the differential device 132 can operate the two fingers with equal driving forces.

[0129] In addition, when gripping an object with a robot hand equipped with a differential device 132, if one of the two fingers of the robot hand contacts an uneven object earlier than the other finger, differential motion occurs between the case gear 161G and the eccentric shaft gear 171G, the movement of the finger that has contacted the object stops, and the other finger operates until it contacts the object. That is, by using the differential device 132, the object can be gripped while adapting the two fingers of the robot hand to the object.

[0130] As shown in the analysis result in state two, when the eccentric shaft 171 rotated "1" time, the case 161 rotated "(O×Q - P×R) / (O×Q)" times in the same direction as the rotation direction of the eccentric shaft 171. Therefore, based on the side shaft 181, the condition for generating differential motion between the eccentric shaft 171 and the case 161 is "(O×Q - P×R) / (O×Q) < 0", and this conditional expression can be arranged as the following formula (5).

[0131] (Equation 5) P×R > O×Q ···· (5)

[0132] In the second embodiment, since the first gear 142 (tooth number O) is an external gear and the second gear 143 (tooth number P) is an internal gear, "O < P", and since the third gear 152 (tooth number Q) is an external gear and the fourth gear 153 (tooth number P) is an internal gear, "Q < R", it can be seen that the differential device 132 satisfies formula (5). That is, in the differential device 132, since the first gear 142 and the third gear 152 are constituted by external gears and the second gear 143 and the fourth gear 153 are constituted by internal gears, differential motion can be generated between the eccentric shaft 171 and the case 161 based on the side shaft 181.

[0133] Here, the relational expressions of the rotation speed ratio M between the case 161 and the eccentric shaft 171, the number of teeth O, the number of teeth P, the number of teeth Q, and the number of teeth R are found. As in the above-mentioned state 2, when the eccentric shaft 171 rotates once, the case 161 rotates in the same direction by "(O×QP×R) / (O×Q)". Therefore, the conditional expression for which a differential motion with a rotation speed ratio of M occurs between the case 161 and the eccentric shaft 171, that is, the conditional expression for "(rotation speed of the case 161):(rotation speed of the eccentric shaft)=M:-1" is given by the following expression (6). Then, by rearranging this expression (6), the following expression (7) is obtained.

[0134] (Number 6) (O×QP×R) / (O×Q)=-M ···· (6)

[0135] (Number 7) (M+1) × O × Q = P × R (7)

[0136] As described above, in the differential device 132 of the second embodiment, the first internal gear mechanism 141 and the second internal gear mechanism 151 are disposed inside the case 161 with the third gear 152 fixed to the second gear 143. That is, the differential device 132 has two internal gear mechanisms disposed integrally, so that an increase in size in the radial direction can be suppressed. Also, the differential device 132 has a mechanism in which the gears mesh with each other in two stages, and these are configured integrally, so that an increase in size in the axial direction can be suppressed. Therefore, a simple structure can be used to achieve a reduction in size and thickness.

[0137] More specifically, in the differential device 132, the first gear 142 and the third gear 152 are external gears, and the second gear 143 and the fourth gear 153 are internal gears. The differential device 132 is configured to satisfy the above formula (5) using the number of teeth O of the first gear 142, the number of teeth P of the second gear 143, the number of teeth Q of the third gear 152, the number of teeth R of the fourth gear 153, and the rotation speed ratio M. The differential device 132 illustrated in each drawing is configured so that the rotation speed ratio M is 1. Furthermore, in the differential device 132, the second gear 143 and the third gear 152 are integrally connected, which also contributes to a thinner axial direction.

[0138] 2, the differential gear 132 has a configuration in which a case rotation shaft 162 is disposed between a meshing point of the first internal gear mechanism 141 (a meshing point between the first gear 142 and the second gear 143) and a meshing point of the second internal gear mechanism 151 (a meshing point between the third gear 152 and the fourth gear 153), and the first gear 142, the second gear 143, the third gear 152, and the fourth gear 153 are disposed so as to overlap each other in a plan view perpendicular to the axial direction. This makes it possible to achieve a reduction in size in the radial direction.

[0139] For example, when the right and left driving wheels of a radio-controlled model car are fixed to the case 161 and eccentric shaft 171 of the differential gear 132, respectively, the driving force of the actuator 110 is distributed to the case 161 (case gear 161G) and the eccentric shaft 171 (eccentric shaft gear 171G). The differential gear 132 absorbs the rotation difference between the left and right driving wheels even when the radio-controlled model car turns, so smooth cornering is realized. In addition, since a robot hand requires independent movement of multiple finger joints, multiple differential gears must be mounted in a limited space, and it is desired to simultaneously solve the conflicting problems of miniaturization and robustness. In this regard, the differential gear 132 can distribute the driving force input to an input element part to two or more output element parts, so that a small and lightweight robot hand can be provided by applying it to driving the finger joints of the robot hand.

[0140] 12 and 13, a transmission mechanism using the transmission gear 121G and the side shaft gear 181G is illustrated as an example of a mechanism for transmitting the output of the actuator 110 to the side shaft 181, but the present invention is not limited thereto. Various transmission mechanisms other than those described above can be adopted for the differential system 202. For example, a transmission mechanism using a driving pulley and a driven pulley may be adopted for the differential system 202. That is, a driving pulley may be fixed to the end of the transmission shaft 121 so as to rotate coaxially therewith, and a driven pulley may be fixed to the side shaft 181 so as to be coaxial with the case rotation shaft 162 and the main rotation shaft 172 and not to rotate relative thereto. Then, a transmission belt may be wound around the driving pulley and the driven pulley so that they are interlocked with each other, thereby transmitting the output of the actuator 110 to the side shaft 181. Other effects and the like obtained by the differential system 202 are similar to those of the differential system 201 of the first embodiment.

[0141] Example 3. A configuration example of a differential unit 30 and a differential system 203 according to a third embodiment of the present invention will be described with reference to Figs. 21 to 29. The same reference numerals are used for components shown in Figs. 1 and 2 and components equivalent to those described in the first and second embodiments, and descriptions thereof will be omitted or simplified. In each figure, some of the reference numerals may be omitted in order to avoid complication of the drawings.

[0142] 21 and 22, the differential system 203 of the third embodiment includes an actuator 110, an encoder 110E, a transmission device 110T, a transmission shaft 121, a transmission gear 121G, and a differential unit (multi-shaft differential device) 30. The differential system 203 is configured to transmit the output of the actuator 110 to the transmission shaft 121 via the transmission device 110T and rotate the transmission gear 121G to drive the differential unit 30. The actuator 110 of the third embodiment functions as a drive source for the differential unit 30.

[0143] The differential unit 30 is composed of a differential gear 132 and a differential gear 133. However, the differential gear 132 of the third embodiment does not have a side shaft gear 181G. Note that the differential principle of the differential gear 132 has been explained in the second embodiment, and therefore the explanation thereof will be omitted.

[0144] The differential gear 133 has a basic configuration similar to that of the differential gear 131 of the first embodiment, but the number of teeth of each gear is different from that of the differential gear 131. That is, the differential gear 133 is different from the differential gear 131 in the number of teeth O of the first gear 142, the number of teeth P of the second gear 143, the number of teeth Q of the third gear 152, and the number of teeth R of the fourth gear 153. The differential gear 133 illustrated in FIGS. 21 to 24 has a coupler 191 for coupling with the differential gear 132, instead of the eccentric shaft gear 171G.

[0145] Hereinafter, the components of the differential gear 132 will be distinguished by adding "a" to the reference numerals, and the components of the differential gear 133 will be distinguished by adding "b" to the reference numerals (see Figs. 21 and 22). However, Figs. 23 to 29 show the differential gear 133 arranged on the driving force input side, and since there is no need to distinguish them from the components of the differential gear 132, the suffixes will be omitted along with their descriptions.

[0146] 21 and 22, in the differential unit 30, the side shaft 181a of the differential gear 132 and the main shaft 171Sb of the differential gear 133 are fixed via a coupler 191 and cannot rotate relative to each other. In the differential unit 30, the side shaft 181a and the main shaft 171Sb may be integrally formed so as to be unable to rotate relative to each other.

[0147] Fig. 23 is an exploded perspective view illustrating each component of the differential gear 133 from the side shaft gear 181G side, and Fig. 24 is an exploded perspective view illustrating each component of the differential gear 133 from the coupler 191 side. As shown in these drawings, the differential gear 133 is configured by connecting multiple members with screws or the like, similar to the differential gear 131.

[0148] 25 to 29, similar to FIGS. 7 to 11, illustrate, in the order of the numbers in the drawings, the change over time of each component member when the eccentric shaft 171 rotates counterclockwise and the side shaft 181 rotates clockwise relative to the case 161. In FIGS. 25 to 29, (a) is a side view of the differential gear 133, (b) is a schematic cross-sectional view taken along line AA in (a), and (c) is a schematic cross-sectional view taken along line BB in (a). In each figure, (b) and (c) correspond to the same state of the differential gear 133. FIGS. 26 to 29 respectively show a state in which the eccentric shaft 171 has rotated a predetermined angle counterclockwise relative to the case 161 and the side shaft 181 has rotated a predetermined angle clockwise relative to the case 161 from the state shown in FIG. 25.

[0149] In (b) of each figure, a mark Sa is attached to indicate the movement of the first case 161L, a mark S1 is attached to indicate the movement of the first gear 142, a mark S2 is attached to indicate the movement of the second gear 143, and a mark Sh is attached to indicate the movement of the eccentric shaft 171. In (c) of each figure, a mark Sb is attached to indicate the movement of the second case 161R, a mark S3 is attached to indicate the movement of the third gear 152, and a mark S4 is attached to indicate the movement of the fourth gear 153. From the state of change of the marks S2 and S3, it can be seen that the second gear 143 and the third gear 152 revolve counterclockwise by 45 degrees and rotate clockwise by 22.5 degrees in the transition between each figure from FIG. 25 to FIG. 29. Also, from the state of change of the mark S4, it can be seen that the fourth gear 153 rotates clockwise by 90 degrees in the transition between each figure from FIG. 25 to FIG. 29. In addition, from the change in the mark Sh, it can be seen that the eccentric shaft 171 rotates counterclockwise by 45 degrees in each transition between Figures 25 to 29. Note that, since the case 161 is used as the reference in Figures 25 to 29, the marks Sa, Sb, and S1 do not move.

[0150] Since the differential gear 133 has the same configuration as the differential gear 131 of the first embodiment, its differential operation can be analyzed in the same way as the differential gear 131. That is, the analysis result of state A in FIG. 58 can be used. Below, the behavior (operation) of the differential gear 133 will be explained taking into consideration the number of teeth of each gear. Note that, in the differential gear 133 illustrated in the examples of each figure, the number of teeth O of the first gear 142 is 18, the number of teeth P of the second gear 143 is 12, the number of teeth Q of the third gear 152 is 12, and the number of teeth R of the fourth gear 153 is 6.

[0151] According to the analysis results of the first embodiment described above, in the differential gear 133, when the eccentric shaft 171 rotates once, the side shaft 181 (fourth gear 153) rotates "(P×RO×Q) / (P×R)" in the same direction.

[0152] Calculation using the specific number of teeth in the differential gear 133 of the third embodiment is as follows. Here, in order to indicate the flow of the driving force transmitted from the differential gear 133 to the differential gear 132, as described above, each of these components is distinguished by adding "b" and "a". That is, when the eccentric shaft 171b rotates once, the side shaft 181b rotates "-2" in the same direction (calculation formula: (12×6-18×12) / (12×6)=-2). Because the sign of the rotation number of the side shaft 181b is negative, in the differential gear 133, it can be seen that when the eccentric shaft 171b rotates once in the counterclockwise direction, the side shaft 181b (fourth gear 153) rotates "+2" in the clockwise direction.

[0153] From this, it can be seen that in the differential gear 133 illustrated in each drawing, a differential operation occurs between the eccentric shaft 171b and the side shaft 181b, with the case 161b as the reference, in which the ratio of the absolute values ​​of the rotation speeds between them is 0.5:1 (the rotation speed ratio is 0.5:-1). As in the first embodiment, if the rotation speed ratio of the eccentric shaft 171b to the side shaft 181b is N, then in the differential gear 133 illustrated in each drawing, the "rotation speed ratio N=0.5".

[0154] When no differential motion is occurring between the eccentric shaft 171b and the side shaft 181b, the differential gear 133 distributes the driving force input to the case 161b (case gear 161Gb) unequally (2:1) to the eccentric shaft 171b (side shaft 181a of the differential gear 132) and the side shaft 181b (side shaft gear 181Gb).

[0155] When no differential motion is occurring between the eccentric shaft 171a and the case 161a, the differential device 132 distributes the driving force of the actuator 110, which is transmitted to the side shaft 181a via the differential device 133, equally (1:1) to the eccentric shaft 171a (eccentric shaft gear 171Ga) and the case 161a (case gear 161Ga).

[0156] That is, when no differential motion is generated between the eccentric shaft 171a (eccentric shaft gear 171Ga), the case 161a (case gear 161Ga), and the side shaft 181b (side shaft gear 181Gb), the differential unit 30 of the third embodiment distributes the driving force input to the case 161b (case gear 161Gb) equally (1:1:1) to the eccentric shaft 171a (eccentric shaft gear 171Ga), the case 161a (case gear 161Ga), and the side shaft 181b (side shaft gear 181Gb). Therefore, for example, by arranging finger driving mechanisms corresponding to each of the three fingers of the robot hand in correspondence with the eccentric shaft gear 171Ga, the case gear 161Ga, and the side shaft gear 181Gb, the differential unit 30 can operate the three fingers with equal driving forces.

[0157] In addition, when a robot hand equipped with the differential system 203 grasps an object, if one of the three fingers of the robot hand contacts an uneven object before the other two fingers, a differential motion occurs between the eccentric shaft 171a (eccentric shaft gear 171Ga), the case 161a (case gear 161Ga), and the side shaft 181b (side shaft gear 181Gb). Specifically, the rotation of the component (eccentric shaft 171a (eccentric shaft gear 171Ga), the case 161a (case gear 161Ga), or the side shaft 181b (side shaft gear 181Gb)) that was driving the finger that contacted the uneven object stops, and the movement of the finger associated with it stops. Then, the remaining two fingers continue to move, but if one of the two fingers contacts the object before the other finger, the movement of the finger that contacted the object stops, and the other finger continues to move until it contacts the object. In this way, the robot hand including the differential system 203 can grasp an object while adapting the three fingers to the object. Other configurations and alternative configurations of the differential system 203 are similar to those of the differential system 201 of the first embodiment and the differential system 202 of the second embodiment.

[0158] As described above, the differential unit 30 of the third embodiment is configured by combining the differential 133 (first differential) having the same basic structure as the differential 131 of the first embodiment and the differential 132 (second differential) of the second embodiment. In the differential 132, the first gear 142 and the third gear 152 are external gears, and the second gear 143 and the fourth gear 153 are internal gears. On the other hand, in the differential 133, the first gear 142 and the third gear 152 are internal gears, and the second gear 143 and the fourth gear 153 are external gears. In the differential unit 30, when no differential motion is generated between the eccentric shaft 171a, the case 161a, and the side shaft 181b, the driving force input to the case gear 161Gb is equally distributed to the eccentric shaft gear 171Ga, the case gear 161Ga, and the side shaft gear 181Gb, and a differential motion is generated between each gear according to the force applied to each gear. Therefore, for example, when incorporated in a robot hand, the differential unit 30 can grip an object with a well-balanced grip by three fingers even if the object has an irregular shape. Other effects and the like obtained by the differential system 203 are similar to those of the differential systems of the first and second embodiments.

[0159] Example 4. A configuration example of a differential unit 40 and a differential system 204 according to a fourth embodiment of the present invention will be described with reference to Figs. 30 to 38. The same reference numerals are used for components equivalent to those shown in Figs. 1 and 2 and those described in the first to third embodiments, and descriptions thereof will be omitted or simplified. In each figure, some of the reference numerals may be omitted in order to avoid cluttering the drawings.

[0160] 30 and 31, the differential system 204 of the fourth embodiment includes an actuator 110, an encoder 110E, a transmission device 110T, a transmission shaft 121, a transmission gear 121G, and a differential unit (multi-shaft differential device) 40. The differential system 204 is configured to transmit the output of the actuator 110 to the transmission shaft 121 via the transmission device 110T and rotate the transmission gear 121G to drive the differential unit 40. The actuator 110 of the fourth embodiment functions as a drive source for the differential unit 40.

[0161] The differential unit 40 is composed of a differential gear 132 and a differential gear 134. However, the differential gear 132 of the fourth embodiment does not have a side shaft gear 181G. Note that the differential principle of the differential gear 132 has been described in the second embodiment, and therefore the description thereof will be omitted.

[0162] The differential 134 has a basic configuration similar to that of the differential 131 of the first embodiment, but the tooth shape and number of teeth of each gear are different from those of the differential 131. That is, the number of teeth O of the first gear 142, the number of teeth P of the second gear 143, the number of teeth Q of the third gear 152, and the number of teeth R of the fourth gear 153 of the differential 134 are different from those of the differential 131. In addition, the teeth of the first gear 142 and the second gear 143 of the differential 134 adopt a tooth shape designed using a trocholoid curve. Note that the teeth of the first gear 142 and the second gear 143 may adopt a tooth shape designed using a cycloid curve instead of a trocholoid curve. In the differential 134, the first gear 142 and the second gear 143 form a first internal gear mechanism 141 in which they are inscribed with a certain amount of eccentricity, which is the same as the differential 131 of the first embodiment. The teeth of the third gear 152 and the fourth gear 153 of the differential gear 134 also adopt a tooth shape designed using a trocholoid curve. Note that the teeth of the third gear 152 and the fourth gear 153 may adopt a tooth shape designed using a cycloid curve instead of a trocholoid curve. The differential gear 134 is the same as the differential gear 131 of the first embodiment in that the third gear 152 and the fourth gear 153 constitute a second internal gear mechanism 151 inscribed with a certain amount of eccentricity. Note that the differential gear 134 illustrated in FIGS. 30 to 33 has a coupler 191 for coupling with the differential gear 132 instead of the side shaft gear 181G.

[0163] Hereinafter, the components of the differential device 132 will be distinguished by adding "a" to the reference numerals, and the components of the differential device 134 will be distinguished by adding "b" to the reference numerals (see Figs. 30 and 31). However, Figs. 32 to 38 show the differential device 134 disposed on the driving force input side, and since there is no need to distinguish them from the components of the differential device 132, the suffixes will be omitted along with their descriptions.

[0164] 30 and 31, in the differential unit 40, the side shaft 181a of the differential gear 132 and the side shaft 181b of the differential gear 134 are fixed via a coupler 191 and cannot rotate relative to each other. In the differential unit 40, the side shaft 181a and the side shaft 181b may be integrally formed so as to be unable to rotate relative to each other.

[0165] Fig. 32 is an exploded perspective view illustrating each component of the differential gear 134 from the coupler 191 side, and Fig. 33 is an exploded perspective view illustrating each component of the differential gear 134 from the eccentric shaft gear 171Ga side. As shown in these drawings, the differential gear 134 is configured by connecting multiple members with screws or the like, similar to the differential gear 131.

[0166] 34 to 38, similar to FIGS. 7 to 11, illustrate, in the order of the numbers in the drawings, the change over time of each component member when the eccentric shaft 171 rotates counterclockwise and the side shaft 181 rotates clockwise with respect to the case 161. In FIGS. 34 to 38, (a) is a side view of the differential gear 134, (b) is a schematic cross-sectional view taken along line AA in (a), and (c) is a schematic cross-sectional view taken along line BB in (a). In each figure, (b) and (c) correspond to the same state of the differential gear 134. FIGS. 35 to 38 respectively show a state in which the eccentric shaft 171 has rotated a predetermined angle counterclockwise with respect to the case 161 and the side shaft 181 has rotated a predetermined angle clockwise with respect to the case 161 from the state shown in FIG. 34.

[0167] In Fig. 34 to Fig. 38, a mark S7 is attached to each cross-sectional view to indicate the movement of the eccentric shaft gear 171G. In (b) of each figure, a mark Sa is attached to indicate the movement of the first case 161L, a mark S2 is attached to indicate the movement of the second gear 143, and a mark Sh is attached to indicate the movement of the eccentric shaft 171. In (c) of each figure, a mark Sb is attached to indicate the movement of the second case 161R, a mark S3 is attached to indicate the movement of the third gear 152, and a mark S4 is attached to indicate the movement of the fourth gear 153. From the change in the marks S2 and S3, it can be seen that the second gear 143 and the third gear 152 revolve counterclockwise by 90 degrees and rotate clockwise by 18 degrees in the transition between each figure from Fig. 34 to Fig. 38. Also, from the change in the mark S4, it can be seen that the fourth gear 153 rotates clockwise by 45 degrees in the transition between each figure from Fig. 34 to Fig. 38. In addition, from the changes in the marks S7 and Sh, it can be seen that the eccentric shaft 171 rotates counterclockwise by 90 degrees in each transition between Figures 34 to 38. Note that, since the case 161 is used as the reference in Figures 34 to 38, the marks Sa, Sb, and S1 do not move.

[0168] Since the differential gear 134 has the same configuration as the differential gear 131 of the first embodiment, its differential operation can be analyzed in the same way as the differential gear 131. That is, the analysis result of state A in FIG. 58 can be used. Below, the behavior (operation) of the differential gear 134 will be described taking into consideration the number of teeth of each gear. Note that, in the differential gear 134 illustrated in the examples of each figure, the number of teeth O of the first gear 142 is 6, the number of teeth P of the second gear 143 is 5, the number of teeth Q of the third gear 152 is 5, and the number of teeth R of the fourth gear 153 is 4.

[0169] According to the analysis results of the first embodiment described above, in the differential gear 134, when the eccentric shaft 171 rotates once, the side shaft 181 (fourth gear 153) rotates "(P×RO×Q) / (P×R)" in the same direction.

[0170] Calculation using the specific number of teeth in the differential gear 134 of the fourth embodiment is as follows. Here, in order to indicate the flow of the driving force transmitted from the differential gear 134 to the differential gear 132, as described above, each of these components is distinguished by adding "b" and "a". That is, when the eccentric shaft 171b rotates once, the side shaft 181b rotates "-1 / 2" in the same direction (calculation formula: (5×4-6×5) / (5×4)=-1 / 2). Since the sign of the rotation speed of the side shaft 181b is negative, in the differential gear 134, it can be seen that when the eccentric shaft 171b rotates once counterclockwise, the side shaft 181b (fourth gear 153) rotates "+1 / 2" in the clockwise direction.

[0171] From this, it can be seen that in the differential gear 134 illustrated in each drawing, a differential operation occurs between the eccentric shaft 171b and the side shaft 181b, with the case 161b as the reference, in which the ratio of the absolute values ​​of the rotation speeds between them is 2:1 (the rotation speed ratio is 2:-1). As in the first embodiment, if the rotation speed ratio of the eccentric shaft 171b to the side shaft 181b is N, then in the differential gear 134 illustrated in each drawing, the "rotation speed ratio N=2".

[0172] When no differential motion is occurring between the eccentric shaft 171b and the side shaft 181b, the differential gear 134 distributes the driving force input to the case 161b (case gear 161Gb) unequally (1:2) to the eccentric shaft 171b and the side shaft 181b (side shaft 181a of the differential gear 132).

[0173] When no differential motion occurs between the eccentric shaft 171a and the case 161a, the differential device 132 distributes the driving force of the actuator 110, which is transmitted to the side shaft 181a via the differential device 134, equally (1:1) to the eccentric shaft 171a (eccentric shaft gear 171Ga) and the case 161a (case gear 161Ga).

[0174] That is, when no differential motion is generated between the eccentric shaft 171a (eccentric shaft gear 171Ga), the case 161a (case gear 161Ga), and the eccentric shaft 171b (eccentric shaft gear 171Gb), the differential unit 40 of the fourth embodiment distributes the driving force input to the case 161b (case gear 161Gb) equally (1:1:1) to the eccentric shaft 171a (eccentric shaft gear 171Ga), the case 161a (case gear 161Ga), and the eccentric shaft 171b (eccentric shaft gear 171Gb). Therefore, for example, by arranging finger driving mechanisms corresponding to each of the three fingers of the robot hand in correspondence with the eccentric shaft gear 171Ga, the case gear 161Ga, and the eccentric shaft gear 171Gb, the differential unit 40 can operate the three fingers with equal driving forces.

[0175] In addition, when a robot hand equipped with the differential system 204 grasps an object, if one of the three fingers of the robot hand contacts an uneven object before the other two fingers, a differential motion occurs between the eccentric shaft 171a (eccentric shaft gear 171Ga), the case 161a (case gear 161Ga), and the eccentric shaft 171b (eccentric shaft gear 171Gb). Specifically, the rotation of the component (eccentric shaft 171a (eccentric shaft gear 171Ga), the case 161a (case gear 161Ga), or the eccentric shaft 171b (eccentric shaft gear 171Gb)) that was driving the finger that contacted the uneven object stops, and the movement of the finger associated with it stops. Then, the remaining two fingers continue to move, but if one of the two fingers contacts the object before the other finger, the movement of the finger that contacted the object stops, and the other finger continues to move until it contacts the object. In this way, the robot hand including the differential system 204 can grasp an object while adapting the three fingers to the object. Other configurations and alternative configurations of the differential system 204 are similar to those of the differential systems 201 to 203 of the first to third embodiments.

[0176] As described above, the differential unit 40 of the fourth embodiment is configured by combining the differential 134 (first differential) having the same basic structure as the differential 131 of the first embodiment and the differential 132 (second differential) of the second embodiment. In the differential 132, the first gear 142 and the third gear 152 are external gears, and the second gear 143 and the fourth gear 153 are internal gears. On the other hand, in the differential 134, the first gear 142 and the third gear 152 are internal gears, and the second gear 143 and the fourth gear 153 are external gears. In the differential unit 40, when no differential motion is generated between the eccentric shaft 171a, the case 161a, and the eccentric shaft 171b, the driving force input to the case gear 161Gb is equally distributed to the eccentric shaft gear 171Ga, the case gear 161Ga, and the eccentric shaft gear 171Gb, and a differential motion is generated between each gear according to the force applied to each gear. Therefore, for example, when incorporated in a robot hand, the differential unit 40 can grip an object with a well-balanced grip by three fingers even if the object has an irregular shape. Other effects and the like obtained by the differential system 204 are similar to those of the differential systems of the first to third embodiments.

[0177] Moreover, in the differential 134, gears having tooth shapes designed using a trochoroid curve are used for the first internal gear mechanism 141 and the second internal gear mechanism 151. Therefore, the number of meshing portions between the first gear 142 and the second gear 143 and the number of meshing portions between the third gear 152 and the fourth gear 153 are increased, which increases the rigidity of the gear mechanism and makes it possible to transmit a large driving force (high torque).

[0178] In the first internal gear mechanism 141 of the fourth embodiment, the number of meshing portions between the first gear 142 and the second gear 143 is large, but the meshing points considered in terms of the pitch circle are the same as the "meshing points of the first internal gear mechanism" illustrated in Fig. 2. In the second internal gear mechanism 151 of the fourth embodiment, the number of meshing portions between the third gear 152 and the fourth gear 153 is large, but the meshing points considered in terms of the pitch circle are the same as the "meshing points of the second internal gear mechanism" illustrated in Fig. 2. Therefore, the differential device 134 also has a configuration in which the case rotation shaft 162 is disposed between the meshing point of the first internal gear mechanism 141 (the meshing point of the first gear 142 and the second gear 143) and the meshing point of the second internal gear mechanism 151 (the meshing point of the third gear 152 and the fourth gear 153), and the first gear 142, the second gear 143, the third gear 152, and the fourth gear 153 are disposed so as to overlap in a plan view perpendicular to the axial direction. This makes it possible to achieve a reduction in size in the radial direction.

[0179] Although each drawing illustrates the differential 134 in which both the first internal gear mechanism 141 and the second internal gear mechanism 151 use gears with teeth profiles using a trocholoid curve, the present invention is not limited to this. The differential 134 may be configured such that one of the first internal gear mechanism 141 and the second internal gear mechanism 151 is configured with gears with teeth profiles using a trocholoid curve, and the other is configured with gears with teeth profiles using an involute curve. Also, one may be configured with gears with teeth profiles using a cycloid curve, and the other is configured with gears with teeth profiles using an involute curve.

[0180] In addition, in each drawing, an example is shown in which the differential gear 134 has a first internal gear mechanism 141 in which a first gear 142 made of an internal gear with a tooth shape using a trocholoid curve and a second gear 143b made of an external gear with a tooth shape using a trocholoid curve are combined, but the present invention is not limited to this. The differential gear 134 may have a first internal gear mechanism 141 in which a first gear 142 made of an external gear with a tooth shape using a trocholoid curve and a second gear 143b made of an internal gear with a tooth shape using a trocholoid curve are combined. However, since the relationship between the internal gear and the external gear is interchanged, the operation principle of the differential gear 134 in this configuration is the same as the operation principle of the differential gear 132 in the second embodiment. Similarly, in each drawing, an example is shown in which the differential gear 134 has a second internal gear mechanism 151 in which a third gear 152 made of an internal gear with a tooth shape using a trocholoid curve and a fourth gear 153 made of an external gear with a tooth shape using a trocholoid curve are combined, but the present invention is not limited to this. The differential gear 134 may have a second internal gear mechanism 151 that combines a third gear 152 made of an external gear with teeth formed using a trochoroid curve and a fourth gear 153 made of an internal gear with teeth formed using a trochoroid curve. However, since the relationship between the internal gear and the external gear is reversed, the operating principle of the differential gear 134 configured in this manner is the same as the operating principle of the differential gear 132 of the second embodiment. Other effects and the like obtained by the differential system 204 are similar to those of the differential systems of the first to third embodiments.

[0181] Example 5. A configuration example of a differential unit 50 and a differential system 205 according to a fifth embodiment of the present invention will be described with reference to Figs. 39 to 47. The same reference numerals are used for components shown in Figs. 1 and 2 and components equivalent to those described in the first to fourth embodiments, and descriptions thereof will be omitted or simplified. In each figure, some of the reference numerals may be omitted in order to avoid complication of the drawings.

[0182] 39 and 40, the differential system 205 of the fifth embodiment includes an actuator 110, an encoder 110E, a transmission device 110T, a transmission shaft 121, a transmission gear 121G, and a differential unit (multi-shaft differential device) 50. The differential system 205 is configured to transmit the output of the actuator 110 to the transmission shaft 121 via the transmission device 110T and rotate the transmission gear 121G to drive the differential unit 50. The actuator 110 of the fifth embodiment functions as a drive source for the differential unit 50.

[0183] The differential unit 50 is composed of a differential gear 132 and a differential gear 135. However, the differential gear 132 of the fifth embodiment does not have a side shaft gear 181G. Note that the differential principle of the differential gear 132 has been described in the second embodiment, and therefore the description thereof will be omitted.

[0184] The differential 135 has a basic configuration similar to that of the differential 132 of the second embodiment, but the tooth profile and number of teeth of each gear are different from those of the differential 132. That is, the number of teeth O of the first gear 142, the number of teeth P of the second gear 143, the number of teeth Q of the third gear 152, and the number of teeth R of the fourth gear 153 are different from those of the differential 132. Also, while a profile shifted gear is used for the second gear 143 of the differential 132, a standard gear is used for the second gear 143 of the differential 135. The differential 135 illustrated in FIGS. 39 to 42 has a coupler 191 for coupling with the differential 132 instead of the eccentric shaft gear 171G.

[0185] Hereinafter, the components of the differential gear 132 will be distinguished by adding "a" to the reference numerals, and the components of the differential gear 135 will be distinguished by adding "b" to the reference numerals (see Figs. 39 and 40). However, Figs. 41 to 47 show the differential gear 135 arranged on the driving force input side, and since there is no need to distinguish them from the components of the differential gear 132, the suffixes will be omitted along with their descriptions.

[0186] As shown in FIGS. 39 and 40, in the differential unit 50, the side shaft 181a of the differential device 132 and the eccentric shaft 171b of the differential device 135 are fixed via the coupler 191 and are non-rotatable relative to each other. The differential unit 50 may be integrally formed such that the side shaft 181a and the eccentric shaft 171b are non-rotatable relative to each other.

[0187] FIG. 41 is an exploded perspective view illustrating each component of the differential device 135 from the side shaft 181 side, and FIG. 42 is an exploded perspective view illustrating each component of the differential device 135 from the coupler 191 side. As shown in these figures, the differential device 135, like the differential device 132, is configured by connecting a plurality of members with screws or the like.

[0188] FIGS. 43 to 47 illustrate, in the order of the drawing numbers, the temporal state changes of each component when the eccentric shaft 171 rotates counterclockwise and the case 161 rotates clockwise with respect to the side shaft 181, similar to FIGS. 16 to 20. In FIGS. 43 to 47, (a) is a side view of the differential device 135, (b) is a schematic cross-sectional view taken along line A-A in (a), and (c) is a schematic cross-sectional view taken along line B-B in (a). In each figure, (b) and (c) correspond to the same state of the differential device 135. FIGS. 44 to 47 each show a state in which the eccentric shaft 171 has rotated counterclockwise by a predetermined angle with respect to the side shaft 181 and the case 161 has rotated clockwise by a predetermined angle with respect to the side shaft 181 from the state shown in FIG. 43.

[0189] In (b) of each figure, a mark Sa is attached to indicate the movement of the first case 161L, a mark S1 is attached to indicate the movement of the first gear 142, a mark S2 is attached to indicate the movement of the second gear 143, and a mark Sh is attached to indicate the movement of the eccentric shaft 171. In (c) of each figure, a mark Sb is attached to indicate the movement of the second case 161R, a mark S3 is attached to indicate the movement of the third gear 152, and a mark S4 is attached to indicate the movement of the fourth gear 153. From the state of change of the marks Sa, Sb, and S1, it can be seen that the first case 161L, the second case 161R, and the first gear 142 rotate 90 degrees in the clockwise direction in the transition between each figure from FIG. 43 to FIG. 47. From the state of change of the marks S2 and S3, it can be seen that the second gear 143 and the third gear 152 revolve 45 degrees in the counterclockwise direction and rotate 45 degrees in the clockwise direction in the transition between each figure from FIG. 43 to FIG. 47. In addition, from the change in the mark Sh, it can be seen that the eccentric shaft 171 rotates counterclockwise by 45 degrees in each transition from Figure 43 to Figure 47. Note that, since the side shaft 181 is used as the reference in Figures 43 to 47, the mark S4 given to the fourth gear 153 does not move.

[0190] Since the differential gear 135 has the same configuration as the differential gear 132 of the second embodiment, the differential operation thereof can be analyzed in the same manner as the differential gear 132. The behavior (operation) of the differential gear 135 will be described below, taking into consideration the number of teeth of each gear. In the differential gear 135 illustrated in the examples of each figure, the number of teeth O of the first gear 142 is 12, the number of teeth P of the second gear 143 is 18, the number of teeth Q of the third gear 152 is 6, and the number of teeth R of the fourth gear 153 is 12.

[0191] According to the analysis results of the second embodiment described above, in the differential device 135, when the eccentric shaft 171 rotates once, the case 161 (case gear 161G) rotates "(O×QP×R) / (O×Q)" in the same direction.

[0192] Calculation using the specific number of teeth in the differential gear 135 of the fifth embodiment is as follows. Here, to indicate the flow of the driving force transmitted from the differential gear 135 to the differential gear 132, as above, each of these components is distinguished by adding "b" or "a". That is, when the eccentric shaft 171b rotates once, the case 161b rotates "-2" in the same direction (calculation formula: (12×6-18×12) / (12×6)=-2). Because the sign of the number of rotations of the case 161b is negative, when the eccentric shaft 171b rotates once counterclockwise, the case 161b (case gear 161Gb) rotates "+2" in the clockwise direction.

[0193] From this, it can be seen that in the differential gear 135 illustrated in each drawing, a differential operation occurs between the case 161b and the eccentric shaft 171b, with the side shaft 181b as the reference, in which the ratio of the absolute values ​​of the rotation speeds between them is 2:1 (the rotation speed ratio is 2:-1). As in the second embodiment, if the rotation speed ratio of the case 161b to the eccentric shaft 171b is M, then in the differential gear 135 illustrated in each drawing, the "rotation speed ratio M=2".

[0194] When no differential motion occurs between the eccentric shaft 171b and the case 161b, the differential gear 135 distributes the driving force input to the side shaft 181b (side shaft gear 181Gb) unequally (1:2) to the case 161b (case gear 161Gb) and the eccentric shaft 171b (eccentric shaft gear 171Gb).

[0195] When no differential motion occurs between the eccentric shaft 171a and the case 161a, the differential gear 132 distributes the driving force of the actuator 110, which is transmitted to the side shaft 181a via the differential gear 135, equally (1:1) to the case 161a (case gear 161Ga) and the eccentric shaft 171a (eccentric shaft gear 171Ga).

[0196] That is, when no differential motion is generated between the eccentric shaft 171a (eccentric shaft gear 171Ga), the case 161a (case gear 161Ga), and the case 161b (case gear 161Gb), the differential unit 50 of the fifth embodiment distributes the driving force input to the side shaft 181b (side shaft gear 181Gb) equally (1:1:1) to the eccentric shaft 171a (eccentric shaft gear 171Ga), the case 161a (case gear 161Ga), and the case 161b (case gear 161Gb). Therefore, for example, by arranging finger driving mechanisms corresponding to each of the three fingers of the robot hand in correspondence with the eccentric shaft gear 171Ga, the case gear 161Ga, and the case gear 161Gb, respectively, the differential unit 50 can operate the three fingers with equal driving forces.

[0197] In addition, when the robot hand equipped with the differential system 205 is made to grasp an object, if one of the three fingers of the robot hand contacts the uneven object before the other two fingers, a differential motion occurs between the eccentric shaft 171a (eccentric shaft gear 171Ga), the case 161a (case gear 161Ga), and the case 161b (case gear 161Gb). Specifically, the rotation of the component (eccentric shaft 171a (eccentric shaft gear 171Ga), the case 161a (case gear 161Ga), or the case 161b (case gear 161Gb)) that was driving the finger that contacted the uneven object stops, and the movement of the finger associated with it stops. Then, the remaining two fingers continue to move, but if one of the two fingers contacts the uneven object before the other finger, the movement of the finger that contacted the object stops, and the other finger continues to move until it contacts the object. In this way, the robot hand including the differential system 205 can grasp an object while adapting the three fingers to the object. Other configurations and alternative configurations of the differential system 205 are similar to those of the differential systems 201 to 204 of the first to fourth embodiments.

[0198] As described above, the differential unit 50 of the fifth embodiment is configured by combining the differential 135 (first differential) having the same basic structure as the differential 132 of the second embodiment and the differential 132 (second differential) of the second embodiment. Therefore, in both the differential 132 and the differential 135, the first gear 142 and the third gear 152 are external gears, and the second gear 143 and the fourth gear 153 are internal gears. In the differential unit 50, when no differential motion is generated between the eccentric shaft 171a and the case 161a and the case 161b, the driving force input to the side shaft gear 181Gb is equally distributed to the eccentric shaft gear 171Ga, the case gear 161Ga, and the case gear 161Gb, and a differential motion is generated between each gear according to the force applied to each gear. Therefore, for example, when the differential unit 50 is incorporated into a robot hand, even an object having a deformed shape can be held in a well-balanced manner by three fingers.

[0199] Moreover, the differential unit 50 is provided with a side shaft gear 181Gb, which is an input element of the driving force, at its end. The differential system 205 is arranged so that the driving mechanism such as the actuator 110 and the differential unit 50 face each other in a state where the transmission gear 121G, which outputs the driving force of the actuator 110, and the side shaft gear 181Gb of the differential unit 50 are engaged with each other. That is, the differential system 205 is arranged so that the actuator 110 and the differential unit 50 are arranged in the same direction with respect to the transmission side of the driving force. Therefore, since the axial length of the differential system 205 is relatively short, it can be suitably mounted in a space with limited installation space, such as the back of a robot hand. More specifically, if the eccentric shaft gear 171Ga, the case gear 161Ga, and the case gear 161Gb are associated with different fingers, the differential system 205 can drive three fingers of the robot hand with one actuator 110. If the technology disclosed in, for example, JP 2019-063886 A is applied to drive the fingers of the differential system 205, a single actuator 110 can be used to cause the three fingers of the robot hand to adapt to the object to be grasped and grasp it.

[0200] However, the configuration of the differential system 205 is not limited to the examples of FIG. 39 and FIG. 40. For example, the differential system 205 may not have the transmission gear 121G and the side shaft gear 181Gb, and the transmission shaft 121 and the side shaft 181b may be fixed so as not to rotate relative to each other. In this case, the transmission shaft 121 and the side shaft 181b may be fixed using the coupler 191, or the transmission shaft 121 and the side shaft 181b may be integrally formed. If the differential system 205 does not have the transmission device 110T, the output shaft of the actuator 110 and the side shaft 181b may be fixed so as not to rotate relative to each other. The differential system 205 having such a configuration is a driving mechanism that is thin (small diameter) in the radial direction, and therefore is suitable for a case where a smaller diameter in the radial direction is prioritized over a shorter axial length. Other effects and the like obtained by the differential system 205 are the same as those of the differential systems of the first to fourth embodiments.

[0201] Example 6. A configuration example of a differential unit 60 and a differential system 206 according to a sixth embodiment of the present invention will be described with reference to Figs. 48 to 57. The same reference numerals are used for components equivalent to those shown in Figs. 1 and 2 and those described in the first to fifth embodiments, and descriptions thereof will be omitted or simplified. In each figure, some of the reference numerals may be omitted in order to avoid cluttering the drawings.

[0202] 48 and 49, the differential system 206 of the sixth embodiment includes an actuator 110, an encoder 110E, a transmission device 110T, a transmission shaft 121, a transmission gear 121G, and a differential unit (multi-shaft differential device) 60. The differential system 206 is configured to transmit the output of the actuator 110 to the transmission shaft 121 via the transmission device 110T and rotate the transmission gear 121G to drive the differential unit 60. The actuator 110 of the sixth embodiment functions as a drive source for the differential unit 60.

[0203] The differential unit 60 is composed of a differential gear 132, a differential gear 135, and a differential gear 136. However, the differential gear 132 of the sixth embodiment does not have a side shaft gear 181G. Moreover, the differential gear 135 of the sixth embodiment does not have a side shaft gear 181G. The differential principle of the differential gear 132 has been described in the second embodiment, and the differential principle of the differential gear 135 has been described in the fifth embodiment, so that the description thereof will be omitted.

[0204] The differential 136 has a basic configuration similar to that of the differential 132 of the second embodiment, but the tooth profile and number of teeth of each gear are different from those of the differential 132. That is, the number of teeth O of the first gear 142, the number of teeth P of the second gear 143, the number of teeth Q of the third gear 152, and the number of teeth R of the fourth gear 153 are different from those of the differential 132. Also, while a profile shifted gear is used for the second gear 143 of the differential 132, a standard gear is used for the second gear 143 of the differential 136. The differential 136 illustrated in FIGS. 48 to 51 has a coupler 191 for coupling with the differential 135 instead of the eccentric shaft gear 171G.

[0205] Hereinafter, the components of the differential gear 132 will be distinguished by adding "a" to the reference numeral, the components of the differential gear 135 will be distinguished by adding "b" to the reference numeral, and the components of the differential gear 136 will be distinguished by adding "c" to the reference numeral (see Figs. 48 and 49). However, Figs. 50 to 56 show the differential gear 136 arranged on the driving force input side, and since there is no need to distinguish the components from the differential gears 132 and 135, the suffixes will be omitted together with their descriptions.

[0206] As shown in FIGS. 48 and 49, in the differential unit 60, the side shaft 181a of the differential gear 132 and the main shaft 171Sb of the differential gear 135 are fixed via a coupler 191 and cannot rotate relative to each other. In the differential unit 60, the side shaft 181a and the main shaft 171Sb may be integrally formed so as to be unable to rotate relative to each other. In the differential unit 60, the side shaft 181b of the differential gear 135 and the main shaft 171Sc of the differential gear 136 are also fixed via a coupler 191. In the differential unit 60, the side shaft 181b and the main shaft 171Sc may be integrally formed so as to be unable to rotate relative to each other.

[0207] Fig. 50 is an exploded perspective view illustrating each component of the differential gear 136 from the side shaft gear 181G side, and Fig. 51 is an exploded perspective view illustrating each component of the differential gear 136 from the coupler 191 side. As shown in these drawings, the differential gear 136 is configured by connecting multiple members with screws or the like, similar to the differential gear 132.

[0208] 52 to 56, similar to FIGS. 16 to 20, illustrate, in the order of the numbers in the drawings, the change in state of each component over time when the eccentric shaft 171 rotates counterclockwise relative to the side shaft 181 and the case 161 rotates clockwise. In FIGS. 52 to 56, (a) is a side view of the differential gear 136, (b) is a schematic cross-sectional view taken along line AA in (a), and (c) is a schematic cross-sectional view taken along line BB in (a). In each figure, (b) and (c) correspond to the same state of the differential gear 136. FIGS. 53 to 56 each show a state in which the eccentric shaft 171 has rotated a predetermined angle counterclockwise relative to the side shaft 181 and the case 161 has rotated a predetermined angle clockwise relative to the side shaft 181 from the state shown in FIG. 52.

[0209] In (b) of each figure, a mark Sa is attached to indicate the movement of the first case 161L, a mark S1 is attached to indicate the movement of the first gear 142, a mark S2 is attached to indicate the movement of the second gear 143, and a mark Sh is attached to indicate the movement of the eccentric shaft 171. In (c) of each figure, a mark Sb is attached to indicate the movement of the second case 161R, a mark S3 is attached to indicate the movement of the third gear 152, and a mark S4 is attached to indicate the movement of the fourth gear 153. From the state of change of the marks Sa, Sb, and S1, it can be seen that the first case 161L, the second case 161R, and the first gear 142 rotate 90 degrees in the clockwise direction in the transition between each figure from FIG. 52 to FIG. 56. From the state of change of the marks S2 and S3, it can be seen that the second gear 143 and the third gear 152 revolve counterclockwise by 30 degrees and rotate clockwise by 30 degrees in the transition between each figure from FIG. 52 to FIG. 56. In addition, from the change in the mark Sh, it can be seen that the eccentric shaft 171 rotates counterclockwise by 30 degrees in each transition from Figure 52 to Figure 56. Note that, since the side shaft 181 is used as the reference in Figures 52 to 56, the mark S4 given to the fourth gear 153 does not move.

[0210] Since the differential gear 136 has the same configuration as the differential gear 132 of the second embodiment, the differential operation thereof can be analyzed in the same manner as the differential gear 132. The behavior (operation) of the differential gear 136 will be described below, taking into consideration the number of teeth of each gear. Note that, in the differential gear 136 illustrated in the examples of each figure, the number of teeth O of the first gear 142 is 9, the number of teeth P of the second gear 143 is 18, the number of teeth Q of the third gear 152 is 9, and the number of teeth R of the fourth gear 153 is 18.

[0211] According to the analysis results of the second embodiment of the present invention, in the differential device 136, when the eccentric shaft 171 rotates once, the case 161 (case gear 161G) rotates "(O×QP×R) / (O×Q)" in the same direction.

[0212] Calculation using the specific number of teeth in the differential gear 136 of the sixth embodiment is as follows. Here, in order to show the flow in which the driving force is transmitted from the differential gear 136 to the differential gear 135 and then from the differential gear 135 to the differential gear 132, as described above, each of these components is distinguished by adding "c", "b", and "a". That is, when the eccentric shaft 171c rotates once, the case 161c rotates "-3" in the same direction (calculation formula: (9×9-18×18) / (9×9)=-3). Because the sign of the number of rotations of the case 161c is negative, when the eccentric shaft 171c rotates once counterclockwise, the case 161c (case gear 161Gc) rotates "+3" in the clockwise direction.

[0213] From this, it can be seen that in the differential gear 136 illustrated in each drawing, a differential operation occurs between the case 161c and the eccentric shaft 171c, with the side shaft 181c as the reference, in which the ratio of the absolute values ​​of the rotation speeds between them is 3:1 (the rotation speed ratio is 3:-1). As in the second embodiment, if the rotation speed ratio of the case 161c to the eccentric shaft 171c is M, then in the differential gear 136 illustrated in each drawing, the "rotation speed ratio M=3".

[0214] When no differential motion occurs between the eccentric shaft 171c and the case 161c, the differential gear 136 distributes the driving force input to the side shaft 181c (side shaft gear 181Gc) unequally (1:3) to the case 161c (case gear 161Gc) and the eccentric shaft 171c (eccentric shaft gear 171Gc).

[0215] When no differential motion occurs between the eccentric shaft 171b and the case 161b, the differential gear 135 distributes the driving force of the actuator 110, which is transmitted to the side shaft 181b via the differential gear 135, unequally (1:2) to the case 161b (case gear 161Ga) and the eccentric shaft 171b (eccentric shaft gear 171Gb).

[0216] When no differential motion is occurring between the eccentric shaft 171a and the case 161a, the differential gear 132 distributes the driving force of the actuator 110, which is transmitted to the side shaft 181a via the differential gear 136 and the differential gear 135, equally (1:1) to the case 161a (case gear 161Ga) and the eccentric shaft 171a (eccentric shaft gear 171Ga).

[0217] That is, when no differential motion is occurring between the eccentric shaft 171a (eccentric shaft gear 171Ga), case 161a (case gear 161Ga), case 161b (case gear 161Gb), and case 161c (case gear 161Gc), the differential unit 60 of the sixth embodiment distributes the driving force input to the side shaft 181c (side shaft gear 181Gc) equally (1:1:1:1) to the eccentric shaft 171a (eccentric shaft gear 171Ga), case 161a (case gear 161Ga), case 161b (case gear 161Gb), and case 161c (case gear 161Gc). Therefore, for example, by arranging finger drive mechanisms corresponding to each of the four fingers of the robot hand in correspondence with the eccentric shaft gear 171Ga, case gear 161Ga, case gear 161Gb, and case gear 161Gc, respectively, the differential unit 60 can operate the four fingers with equal driving force.

[0218] In addition, when a robot hand equipped with the differential system 206 is made to grasp an object, if any one of the four fingers of the robot hand touches an uneven object before the other three fingers, a differential motion occurs between the eccentric shaft 171a (eccentric shaft gear 171Ga), the case 161a (case gear 161Ga), the case 161b (case gear 161Gb), and the case 161c (case gear 161Gc). Specifically, the rotation of the component (eccentric shaft 171a (eccentric shaft gear 171Ga), the case 161a (case gear 161Ga), the case 161b (case gear 161Gb), or the case 161c (case gear 161Gc)) that was driving the finger that touched the uneven object stops, and the movement of the finger associated with it stops. The remaining three fingers continue to move, but when any one of the three fingers touches an uneven object before the other two fingers, the movement of that finger stops, and the other two fingers continue to move. When any one of the two fingers that continued to move touches an uneven object before the other finger, the movement of the finger that touched the object stops, and the other finger moves until it touches the object. In this way, the robot hand including the differential system 206 can grasp the object while making the four fingers familiar with the object. Other configurations and alternative configurations of the differential system 206 are the same as those of the differential systems 201 to 205 of the first to fifth embodiments.

[0219] 57 is a schematic diagram of a robot hand 301 equipped with the differential system 206 of this embodiment 6. The robot hand 301 has the differential system 206, and also has a finger drive mechanism 302a arranged in correspondence with the eccentric shaft gear 171Ga of the differential device 132, a finger drive mechanism 302b arranged in correspondence with the case gear 161Ga of the differential device 132, a finger drive mechanism 302c arranged in correspondence with the case gear 161Gb of the differential device 135, and a finger drive mechanism 302d arranged in correspondence with the case gear 161Gc of the differential device 136.

[0220] In the example of Fig. 57, the finger drive mechanism 302a drives the first finger corresponding to a person's little finger, the finger drive mechanism 302b drives the second finger corresponding to a person's ring finger, the finger drive mechanism 302c drives the third finger corresponding to a person's middle finger, and the finger drive mechanism 302d drives the fourth finger corresponding to a person's index finger. The differential system 206 drives the four fingers of the robot hand 301 by transmitting the driving force from the eccentric shaft 171a (eccentric shaft gear 171Ga) to the finger drive mechanism 302a, transmitting the driving force from the case 161a (case gear 161Ga) to the finger drive mechanism 302b, transmitting the driving force from the case 161b (case gear 161Gb) to the finger drive mechanism 302c, and transmitting the driving force from the case 161c (case gear 161Gc) to the finger drive mechanism 302d. For example, if the technology disclosed in JP 2019-063886 A is applied to drive the fingers of the differential system 206, the four fingers of the robot hand can grasp an object to be grasped while adapting them to the object by a single actuator 110. Other configurations and alternative configurations of the differential system 206 are similar to those of the differential systems 201 to 205 of the first to fifth embodiments.

[0221] As described above, the differential unit 60 of the sixth embodiment is configured by combining the differential 136 (first differential) and the differential 135 (second differential) having the same basic structure as the differential 132 of the second embodiment with the differential 132 (third differential) of the second embodiment. Therefore, in the differential 132, the differential 135, and the differential 136, the first gear 142 and the third gear 152 are external gears, and the second gear 143 and the fourth gear 153 are internal gears. In the differential unit 60, when no differential motion is generated between the eccentric shaft 171a and the case 161a, the case 161b, and the case 161c, the driving force input to the side shaft 181c is equally distributed to the eccentric shaft gear 171Ga, the case gear 161Ga, the case gear 161Gb, and the case gear 161Gc, and a differential motion is generated between each gear according to the force applied to each gear. Therefore, for example, when incorporated into a robot hand, the differential unit 60 can grip an object with good balance using the four fingers, even if the object has an irregular shape.

[0222] Further, the differential unit 60 is provided at its end with a side shaft gear 181Gc, which is an input element of the driving force. The differential system 206 is arranged such that the driving mechanism such as the actuator 110 and the differential unit 60 face each other in a state in which the transmission gear 121G, which outputs the driving force of the actuator 110, and the side shaft gear 181Gc of the differential unit 60 are engaged with each other. In other words, the differential system 206 is arranged such that the actuator 110 and the differential unit 60 are arranged in the same direction with respect to the transmission side of the driving force. In this way, the differential system 206 is configured to have the shortest axial length, and therefore can be suitably mounted in a space with limited installation space, such as the back of a robot hand.

[0223] However, the configuration of the differential system 206 is not limited to the examples of FIGS. 48 and 49. For example, the differential system 206 may not have the transmission gear 121G and the side shaft gear 181Gc, and the transmission shaft 121 and the side shaft 181c may be fixed so as to be non-rotatable relative to each other. In this case, the transmission shaft 121 and the side shaft 181c may be fixed using the coupler 191, or the transmission shaft 121 and the side shaft 181c may be integrally formed. If the differential system 206 does not have the transmission device 110T, the output shaft of the actuator 110 and the side shaft 181c may be fixed so as to be non-rotatable relative to each other. The differential system 206 having such a configuration is a driving mechanism that is thin (small diameter) in the radial direction, and therefore is suitable for a case where a smaller diameter in the radial direction is prioritized over a shorter axial length.

[0224] Here, the above-mentioned first to sixth embodiments are examples of the differential device, the differential unit, and the differential system, and the technical scope of the present invention is not limited to these embodiments. For example, the first to sixth embodiments have been described as an example of the first internal gear mechanism 141 in which one second gear 143 is inscribed with one first gear 142 and the teeth mesh with each other, but the present invention is not limited to this. The first internal gear mechanism 141 may have a plurality of second gears 143 and may employ an eccentric shaft 171 having cam pins 171P configured so that the plurality of second gears 143 are evenly arranged (equally spaced) around the main rotation shaft 172 (case rotation shaft 162). The first internal gear mechanism 141 having such a configuration can suppress vibration during rotation and realize smoother rotation. Similarly, the first to sixth embodiments have been described as an example of the second internal gear mechanism 151 in which one fourth gear 153 is inscribed with one third gear 152 and the teeth mesh with each other, but the present invention is not limited to this. The second internal gear mechanism 151 may have a plurality of third gears 152 and may employ an eccentric shaft 171 having cam pins 171P configured so that the plurality of third gears 152 are evenly spaced (distributed) around the side rotation shaft 182 (case rotation shaft 162). The second internal gear mechanism 151 having such a configuration can suppress vibration during rotation and achieve smoother rotation.

[0225] The shape and structure of the case 161 illustrated in each drawing are merely examples. Here, if the part of the case 161 that is composed of the first case 161L and the second case 161R is defined as the case main body, the case main body can have various shapes and structures as long as it can accommodate the first internal gear mechanism 141 and the second internal gear mechanism 151 inside. For example, the case main body may be composed of two parts that are divided by a plane parallel to the axial direction, instead of two parts (the first case 161L and the second case 161R) that are divided by a plane perpendicular to the axial direction. Alternatively, the case main body may have a three-part structure of the first bottom 16a, the side part 13s, and the second bottom 16b. However, at least one of the lid 161F and the case gear 161G may not be a component of the case 161, that is, it may be an external configuration of the case 161. The differential devices 131-136 may not have the bearings B1, B2, and B3, and may be configured to have one or two of the bearings B1, B2, and B3. If speed reduction or the like is not required, the differential systems 201-206 may have the transmission gear 121G fixed directly to the tip of the output shaft of the actuator 110 without the transmission device 110T, so that the transmission gear 121G rotates coaxially and integrally with the output shaft of the actuator 110. [Explanation of symbols]

[0226] 1n~5n screws, 11, 12 retaining ring, 13a first side portion, 13b second side portion, 13s side portion, 13h shaft support hole, 16a first bottom portion, 16b second bottom portion, 30, 40, 50, 60 differential unit (multi-shaft differential device), 110 actuator, 110E encoder, 110T transmission device, 121 transmission shaft, 121G transmission gear, 130, 131~136 differential device, 141 first internal gear mechanism, 142 first gear, 143 second gear, 151 second internal gear mechanism, 152 third gear, 153 fourth gear, 161, 161a~161c case, 161F, 161Fa~161Fc cover, 161G, 161Ga~161Gc Case gear, 161L, 161La~161Lc First case, 161R, 161Ra~161Rc Second case, 162, 162a~162c Case rotating shaft, 171, 171a~171c Eccentric shaft, 171G, 171Ga~171Gc Eccentric shaft gear, 171P Cam pin, 171S, 171Sa~171Sc Main shaft, 172, 172a~172c Main rotating shaft, 173 Cam pin rotating shaft, 181, 181a~181c Side shaft, 181G, 181Ga~181Gc Side shaft gear, 182, 182a~182c Side rotating shaft, 191 Coupler, 201~206 Differential system, 301 Robot hand, 302a~302d Finger drive mechanism.

Claims

1. Case and an eccentric shaft including a main shaft journaled on one end side of the case and a cam pin eccentric to the main shaft; A side shaft journaled on the other end of the case; a first internal gear mechanism including a first gear disposed on the one end side inside the case and fixed to the case, and a second gear rotatably supported by the cam pin and engaged with the first gear; a second internal gear mechanism including a third gear disposed on the other end side of the case and fixed to the second gear, and a fourth gear fixed to one end of the side shaft and engaged with the third gear, A differential device in which differential motion occurs between the remaining two of the case, the eccentric shaft, and the side shaft, with one of them as a reference.

2. one of the first gear and the second gear is an internal gear and the other is an external gear, 2. The differential device according to claim 1, wherein one of the third gear and the fourth gear is an internal gear and the other is an external gear.

3. the first gear and the third gear are internal gears, 2. The differential according to claim 1, wherein the second gear and the fourth gear are external gears.

4. When the number of teeth of the first gear is O, the number of teeth of the second gear is P, the number of teeth of the third gear is Q, the number of teeth of the fourth gear is R, and a rotation speed ratio of the eccentric shaft to the side shaft is N, N × O × Q = (N+1) × P × R The differential device according to claim 1 ,

5. 5. The differential device according to claim 4, wherein said rotational speed ratio N is 1.

6. 5. The differential device according to claim 4, wherein said rotational speed ratio N is 0.

5.

7. 5. The differential device according to claim 4, wherein said rotational speed ratio N is 2.

8. the first gear and the third gear are external gears, 2. The differential of claim 1, wherein the second gear and the fourth gear are internal gears.

9. When the number of teeth of the first gear is O, the number of teeth of the second gear is P, the number of teeth of the third gear is Q, the number of teeth of the fourth gear is R, and a rotation speed ratio of the case to the side shaft is M, (M+1)×O×Q=P×R The differential device according to claim 1 ,

10. 10. The differential device according to claim 9, wherein the rotational speed ratio M is 1.

11. 10. The differential device according to claim 9, wherein the rotational speed ratio M is 2.

12. 10. The differential device according to claim 9, wherein the rotational speed ratio M is 3.

13. A first differential device which is the differential device according to claim 6 and a second differential device which is the differential device according to claim 10, the main shaft of the first differential gear and the side shaft of the second differential gear are fixed to each other so that their rotation axes are coaxial, A differential unit that distributes and transmits driving force input to the case of the first differential gear to the side shafts of the first differential gear, the case of the second differential gear, and the main shaft of the second differential gear.

14. A first differential device which is the differential device according to claim 7, and a second differential device which is the differential device according to claim 10, the side shaft of the first differential gear and the side shaft of the second differential gear are fixed to each other so that their rotation axes are coaxial, A differential unit that distributes and transmits driving force input to the case of the first differential gear to the main shaft of the first differential gear, the case of the second differential gear, and the main shaft of the second differential gear.

15. A differential device comprising: a first differential device which is the differential device according to claim 11; and a second differential device which is the differential device according to claim 10, the main shaft of the first differential gear and the side shaft of the second differential gear are fixed to each other so that their rotation axes are coaxial, A differential unit that distributes and transmits driving force input to the side shafts of the first differential device to the case of the first differential device, the case of the second differential device, and the main shaft of the second differential device.

16. a first differential gear as recited in claim 12, a second differential gear as recited in claim 11, and a third differential gear as recited in claim 10, the main shaft of the first differential gear and the side shaft of the second differential gear are fixed to each other so that their rotation axes are coaxial, the main shaft of the second differential gear and the side shaft of the third differential gear are arranged so that their rotation axes are coaxial with each other, A differential unit that distributes and transmits driving force input to the side shafts of the first differential gear to the case of the first differential gear, the case of the second differential gear, the case of the third differential gear, and the main shaft of the third differential gear.

17. A differential device according to claim 5 or 10; and an actuator that is a drive source for the differential device.

18. A differential unit formed by connecting two or three differential devices according to claim 1 to each other; and an actuator that is a drive source for the differential unit.

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