Drive mechanism

Abstract

The present invention provides a transmission mechanism capable of good bidirectional torque transmission, and a robot equipped with the transmission mechanism. [Solution] A transmission mechanism 10 interposed between a drive device 6 capable of outputting torque in both directions and a driven member 4 driven by the torque output by the drive device, the transmission mechanism 10 having a flexible shaft 21 having an input end to which torque is input and an output end to which torque is output, and the shaft has torsional rigidity characteristics that are point-symmetric with respect to the torque input to the input end and the twist angle of the shaft.

Description

Technical Field

[0001] The present invention relates to a transmission mechanism for transmitting torque and a robot provided with the transmission mechanism.

Background Art

[0002] Conventionally, a robot hand provided with a rotationally driving actuator has been known (for example, Patent Document 1). The robot hand of Patent Document 1 includes a palm portion and finger portions rotatably connected to the palm portion. One end of a flexible cable is connected to the finger portions. The finger portions are displaced between an extended position (hereinafter, the extended position) and a bent position (hereinafter, the bent position) with respect to the palm portion by linearly moving the other end of the flexible cable.

[0003] The rotational actuator is connected to a lead screw assembly via a flexible shaft. The torque of the actuator is transmitted to the lead screw assembly via the flexible shaft. The lead screw assembly converts the transmitted torque into linear motion of one end of the flexible cable. Thereby, by driving the rotational actuator, one end of the finger portion moves, and the finger portion is displaced between the extended position and the bent position.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Flexible shafts are primarily used to transmit torque in a predetermined unidirectional direction. Therefore, the inventors of this invention have found that if such a flexible shaft is used to transmit torque in both directions, the torsional rigidity of the flexible shaft will depend on the magnitude and direction of the torque, which can lead to problems, for example, in the drive control of a driven member.

[0006] In view of the above background, the object of the present invention is to provide a transmission mechanism that can transmit torque in both directions effectively, and a robot equipped with the transmission mechanism. [Means for solving the problem]

[0007] To solve the above problems, one aspect of the present invention provides a transmission mechanism (10) interposed between a drive device (6) capable of outputting torque in both directions and a driven member (4) driven by the torque output by the drive device, the transmission mechanism having a flexible shaft (21) having an input end to which torque is input and an output end to which torque is output, wherein the shaft has torsional rigidity characteristics that are point-symmetric with respect to the torque input to the input end and the twist angle of the shaft.

[0008] According to this embodiment, the shaft has torsional rigidity characteristics that are point-symmetrical between torque and torsional angle. As a result, the torsional rigidity of the flexible shaft becomes less dependent on the magnitude and direction of torque, providing a transmission mechanism that can transmit torque well in both directions.

[0009] In the above embodiment, preferably, the shaft has torsional stiffness characteristics such that the magnitude of the rate of change of torque with respect to the torsional angle is minimized when the torsional angle is zero.

[0010] According to this embodiment, the change in the torsion angle with respect to torque is maximized when the torsion angle is zero. Therefore, when a torque input is applied to the shaft when the torsion angle is near zero, the torsional deformation of the shaft can be promoted, thereby enabling good shock absorption.

[0011] In the above embodiment, preferably, the torsional rigidity characteristics of the shaft include a low-rigidity region (D1) in which the torsional angle is zero and the rate of change of torque with respect to the torsional angle is less than or equal to a predetermined threshold, and a high-rigidity region (D2) in which the rate of change of torque with respect to the torsional angle is greater than the threshold.

[0012] In this embodiment, the change in the twist angle with respect to torque is larger in the low-rigidity region compared to the high-rigidity region. Therefore, when the twist angle is near zero and the shaft is in the low-rigidity region, if a torque input is applied to the shaft, the torsional deformation of the shaft is promoted, enabling good shock absorption.

[0013] In the above embodiment, preferably, the casing (22) has a through hole into which the shaft is inserted, and at least a portion of the wall defining the through hole is made of fluororesin.

[0014] According to this embodiment, the shaft can be protected by the casing. Furthermore, since at least a portion of the wall defining the through-hole of the casing is made of a highly sliding fluororesin, the frictional force that may occur between the casing and the shaft can be suppressed.

[0015] In the above embodiment, preferably, grease (35) is filled between the outer circumferential surface of the shaft and the inner circumferential surface of the casing defining the through hole.

[0016] According to this embodiment, the durability and torque transmission efficiency of the transmission mechanism can be improved.

[0017] In the above aspect, preferably, the grease contains the fluororesin made of the same material as at least a part of the wall body that defines the through hole.

[0018] According to this aspect, the durability of the transmission mechanism and the torque transmission efficiency can be improved.

[0019] In order to solve the above problems, another aspect of the present invention is a robot (1) including the driving device, the driven member, the driving device, the driven member, and the transmission mechanism according to any of the above aspects, including a base body (2) that supports the driving device, a link (3) interposed between the base body and the driven member and displaceable with respect to each of the base body and the driven member, and a displacement mechanism (13) supported by the link and displacing the driven member with respect to the link by torque input through the transmission mechanism.

[0020] According to this aspect, a robot provided with a transmission mechanism capable of performing bidirectional torque transmission satisfactorily can be provided.

[0021] According to the above aspects, a transmission mechanism capable of performing bidirectional torque transmission satisfactorily, and a robot provided with the transmission mechanism can be provided.

Brief Description of the Drawings

[0022] [Figure 1] Configuration example of a robot including a transmission mechanism according to an embodiment [Figure 2] Explanatory drawing for explaining the state of the robot when the nut has moved to the right compared to FIG. 1 [Figure 3] Block diagram of a control device according to an embodiment [Figure 4] Side view showing (A) the first embodiment, (B) the second embodiment, and (C) the third embodiment of a flexible shaft [Figure 5] Side view showing the fourth embodiment of a flexible shaft [Figure 6] Graph showing the torsional rigidity characteristics of the flexible shaft according to the present invention [Figure 7] Graphs showing the torsional stiffness characteristics of flexible shafts in examples 1 to 3. [Figure 8] (A) A graph showing the dependence of torque T on the torsion angle θ for the flexible shaft in the third example; (B) A graph showing the derivative dT / dθ of graph (A) with respect to the torsion angle θ; and (C) A graph showing the second derivative of graph (A) with respect to the torsion angle θ. [Modes for carrying out the invention]

[0023] Hereinafter, embodiments of the flexible shaft according to the present invention and a robot equipped with the flexible shaft will be described in detail with reference to the drawings.

[0024] The robot 1 according to the present invention is a so-called articulated robot and is equipped with multiple joints. Figure 1 shows an example of the configuration of the robot 1 according to an embodiment. However, the configuration shown in Figure 1 is merely an example, and the present invention is not limited to this configuration.

[0025] As shown in Figure 1, the robot 1 comprises a base body 2, an intervening link 3 displaceably connected to the base body 2, and a driven member 4 displaceably connected to the intervening link 3.

[0026] The base unit 2 is equipped with a first drive unit 6, a second drive unit (not shown), and a control device 7 that independently controls the first drive unit 6 and the second drive unit, respectively.

[0027] The first drive unit 6 is configured to output torque in both directions. The first drive unit 6 may be various types of motors comprising a main body 6A fixed to a base 2 and an output shaft 6B supported by the main body 6A and capable of rotating in both directions.

[0028] The second drive unit is also configured to output torque in both directions. The second drive unit may be various motors comprising a main body fixed to the base 2 and an output shaft supported by the main body that rotates in both directions.

[0029] As shown in Figure 3, the control device 7 is composed of a so-called microcomputer comprising a processor 7A consisting of a central processing unit (CPU), a storage device 7B such as an HDD or SSD, and a memory 7C consisting of RAM or ROM. The control device 7 is configured such that the processor 7A reads necessary data and software from the storage device 7B and executes predetermined arithmetic processing according to the software. The first drive unit 6, the second drive unit, and the control device 7 may each be supported on the base 2 via multiple members, or they may be provided on members other than the base 2.

[0030] As shown in Figure 1, the intervening link 3 is a rod-shaped member and is rotatably connected to the base 2 at one end. In this embodiment, the intervening link 3 is pivotally supported on the base 2 and rotatably supported relative to the base 2. A gearbox may be provided between the intervening link 3 and the output shaft of the second drive unit to convert the rotation of the output shaft into rotation of the intervening link 3 relative to the base 2. However, the connection method between the intervening link 3 and the base 2 is not limited to this embodiment; for example, the intervening link 3 may be rotatably supported on the base 2 via the second drive unit by being directly coupled to the output shaft of the second drive unit.

[0031] The driven member 4 (also called the driven member) is connected to the first drive unit 6 via a transmission mechanism 10. The transmission mechanism 10 is interposed between the driven member 4 and the first drive unit 6 and plays the role of transmitting the rotation and torque output from the first drive unit 6 to the driven member 4. The driven member 4 is driven by the rotation and torque output by the first drive unit 6, which are transmitted by the transmission mechanism 10.

[0032] In this embodiment, the driven member 4 is connected to the intervening link 3 so as to be rotatable in both directions around axis Y. The transmission mechanism 10 transmits bidirectional torque output from the first drive unit 6 to the driven member 4, and the driven member 4 is rotated bidirectionally relative to the intervening link 3.

[0033] Figure 1 shows an example in which the rotation axis X of the intervening link 3 relative to the base 2 and the rotation axis Y of the driven member 4 relative to the intervening link 3 are configured to be perpendicular to the plane of the paper and parallel to each other. However, the direction of the rotation axis X of the intervening link 3 relative to the base 2 is not limited to this embodiment; for example, the rotation axis X of the intervening link 3 relative to the base 2 may be configured to be parallel to the plane of the paper (for example, in the vertical direction of the paper).

[0034] The transmission mechanism 10 includes a single-axis actuator 11 supported by an intervening link 3 that converts torque output from the first drive unit 6 into axial force, a flexible shaft 12 interposed between the first drive unit 6 and the single-axis actuator 11, and a displacement mechanism 13 that converts the axial force of the single-axis actuator 11 into the displacement of the driven member 4.

[0035] The single-axis actuator 11 is composed of a so-called ball screw, comprising a screw shaft 15, a nut 16, and a ball (not shown). When one of the screw shaft 15 or nut 16 is rotated, the other moves linearly along the axis of the screw shaft 15. In this embodiment, the screw shaft 15 is supported by an intervening link 3 so as to be rotatable but immovable in the axial direction, and the nut 16 is supported by the intervening link 3 so as to be movable in the axial direction of the screw shaft 15 but immovable. In other words, the single-axis actuator 11 is a conversion mechanism that converts the rotational motion (torque) of the screw shaft 15 into linear motion (axial force) of the nut 16 and outputs it. Figure 2 shows the state of robot 1 when the nut 16 moves due to the rotation of the screw shaft 15, as shown in Figure 1.

[0036] The flexible shaft 12 transmits the torque output from the first drive unit 6 to the single-axis actuator 11. As shown in Figure 4, the flexible shaft 12 comprises an inner shaft 21 (also called a shaft or core) and an outer tube 22 (also called an outer case or casing).

[0037] As shown in Figures 4(A) to 4(C) and Figure 5, the inner shaft 21 is linear in shape and extends along the axis. The inner shaft 21 is flexible and configured to be bendable. The inner shaft 21 may be composed of multiple wires twisted together in a helical shape, for example. As shown in Figure 4(A), the inner shaft 21 may be made by winding one or more layers of wire 26 around a single bendable core wire 25.

[0038] As shown in Figures 4(B) and 4(C), the inner shaft 21 may be constructed by arranging several strands 27 made of steel wire or the like in a strip and winding them in a direction that is a predetermined pitch angle with respect to the axis to form the first winding layer 28, and then repeating the process of arranging strands 27 in a strip in the opposite direction on top of that to form the second and third winding layers 28.

[0039] In this embodiment, as shown in Figure 4(C), the inner shaft 21 comprises a first layer made of a circular cross-section wire 27 wound in one direction over its entire length, a second layer made of a circular cross-section wire 27 wound in the opposite direction to the first layer over its entire length, and a third layer made of a circular cross-section wire 27 wound in the opposite direction to the second layer over its entire length.

[0040] The inner shaft 21 may also be constructed by connecting two shafts that are mirror-symmetrical at their ends. For example, the inner shaft 21 may comprise a drive-side shaft provided on the drive side and a driven-side shaft provided on the driven side and having the same length as the drive-side shaft, configured such that the winding direction of the wires 27 constituting the drive-side shaft and the winding direction of the wires 27 constituting the driven-side shaft are opposite, and the end of the driven-side shaft and the end of the drive-side shaft are connected.

[0041] In addition, the inner shaft 21 may have a core wire and a cylindrical small-diameter pipe with a through hole through which the core wire is inserted, and the small-diameter pipe may be configured to be bendable by providing the through hole at a desired position.

[0042] In addition, the inner shaft 21 may be composed of a plurality of link members 29 arranged in a line along the axial direction and linearly connected to each other by universal joints, as shown in Figure 5. It is desirable that the inner shaft 21 be inversely symmetric (mirror symmetry) with respect to the plane passing through the axis. When the inner shaft 21 is composed of a small-diameter pipe with a through hole, it is desirable that the through hole be formed to be rotationally symmetric with respect to the axis and mirror symmetric with respect to the plane containing the axis.

[0043] As shown in Figures 4(A) to (C) and Figure 5, the outer tube 22 is cylindrical and has an inner hole 30 (through hole) through which the inner shaft 21 is inserted. The outer tube 22, like the inner shaft 21, is configured to bend and deform. The inner shaft 21 is slidably inserted into the inner hole 30 of the outer tube 22. In this way, the outer tube 22 protects the inner shaft 21 from dust and moisture.

[0044] Furthermore, because the outer tube 22 is provided, the flexible shaft 12 does not directly contact surrounding objects such as the base 2, intervening link 3, or driven member 4 during high-speed rotation of the inner shaft 21. Therefore, damage to surrounding objects is prevented, and surrounding objects can be protected. Even when power is transmitted with multiple flexible shafts 12 bundled together, adjacent inner shafts 21 do not directly contact each other, so it is possible to prevent the inner shafts 21 from contacting other adjacent inner shafts 21 due to high-speed rotation of the inner shafts 21 and damaging at least one of them.

[0045] When torque is applied to one end of the inner shaft 21 (for example, the end on the drive unit side), the inner shaft 21 rotates relative to the outer tube 22. This transmits torque to the other end of the inner shaft 21. In other words, the inner shaft 21 functions as a transmission member that transmits rotation or torque input to one end to the other end.

[0046] The outer tube 22 can be any shape with an inner bore 30, such as a cylinder, a square tube, or a bellows, as long as it is flexible and can be bent and deformed. In this embodiment, the outer tube 22 is cylindrical. Since the inner shaft 21 and the outer tube 22 are configured to be flexible, the flexible shaft 12 is configured to be flexible and can be bent and deformed.

[0047] The outer tube 22 is made of fluororesin (polytetrafluoroethylene, PTFE). However, the entire outer tube 22 does not necessarily have to be made of fluororesin; at least a portion of the wall defining the inner pore 30 may be made of fluororesin.

[0048] As shown in Figure 4(C), it is preferable that grease 35 is filled between the outer circumferential surface of the inner shaft 21 and the inner circumferential surface of the outer tube 22 that defines the inner bore 30. However, the embodiment is not limited to this, and the grease 35 may be applied to either the outer circumferential surface of the inner shaft 21 or the inner circumferential surface of the outer tube 22 that defines the inner bore 30. It is preferable that the grease 35 has a higher viscosity than general-purpose lubricants.

[0049] The grease 35 may contain a fluororesin. In this embodiment, the grease 35 contains a fluororesin made of the same material as the wall that defines the through-hole of the outer tube 22.

[0050] It is preferable that a recess 37 for storing grease 35 is provided on either the outer surface of the inner shaft 21 or the wall surface (inner circumferential surface) defining the through hole of the outer tube 22. In this embodiment, since the outer surface of the inner shaft 21 is composed of strands 27 with a circular cross-section arranged parallel to each other, a recess 37 is formed between the strands 27 of the winding layer 28 that constitutes the outer circumferential surface, as shown in Figure 4(C). Grease 35 is stored in the recess 37. However, the recess 37 is not limited to this embodiment, and for example, a recess 37 (groove) extending in the circumferential direction may be formed on the inner circumferential surface defining the through hole of the outer tube 22.

[0051] Figure 6 shows the torsional stiffness characteristics (characteristic diagram) of the flexible shaft 12 according to this embodiment, which represents the relationship between the torsion angle θ of the inner shaft 21 and the torque T acting on one end of the inner shaft 21. As shown in Figure 6, the flexible shaft 12 according to this embodiment has torsional stiffness characteristics such that the graph showing the relationship between the torsion angle θ and the torque T is symmetrical with respect to the origin.

[0052] The smaller the slope dT / dθ of the graph in Figure 6, the easier it is for the inner shaft 21 to twist (i.e., it is more flexible) in response to the input torque T. The larger the slope, the more difficult it is for the inner shaft 21 to twist (i.e., it is more rigid) in response to the input torque T.

[0053] As shown in Figure 6, the flexible shaft 12 according to the present invention exhibits a nonlinear characteristic in which it is soft when the torsional angle θ is small and becomes stiff when the torsional angle θ is large. Hereinafter, the region in which the slope dT / dθ of the graph, which includes the point where the torsional angle θ is zero, is less than or equal to a predetermined threshold Th will be described as the first rigidity region D1, and the region in which the slope dT / dθ of the graph is greater than the predetermined threshold Th will be described as the second rigidity region D2. As shown in Figure 6, the second rigidity region D2 corresponds to the region outside the first rigidity region D1 in which the absolute value of the torsional angle θ is larger than that of the first rigidity region D1.

[0054] Since the slope dT / dθ of the graph in the second stiffness region D2 is greater than the slope dT / dθ of the graph in the first stiffness region D1, the second stiffness region D2 is also called the high-stiffness region, and the first stiffness region D1 is also called the low-stiffness region.

[0055] The torsional stiffness characteristics of such an inner shaft 21 have been discussed, for example, in Asano et al.'s "Measurement of Bidirectional Torsional Characteristics of Flexible Shafts" (Japan Society of Mechanical Engineers, 2011 Annual Meeting, S111053) and Aida et al.'s "On Torsional Characteristics of Flexible Shafts" ("Materials" Vol. 15, No. 153, pp. 410-417, 1996). According to Asano et al., in the first stiffness region D1, the contact between the wires 27 is insufficient, and the wires 27 deform almost freely, so the slope of the graph dT / dθ is thought to be small. On the other hand, in the second stiffness region D2, the wires 27 tighten and come into contact with the wires 27 that constitute the inner layer, and a contact load is generated due to the contact between the wires 27 and the inner layer. Therefore, in the second stiffness region D2, the torsional stiffness is increased by this contact load, and the slope of the graph dT / dθ is thought to be large.

[0056] The torsional rigidity characteristics of the flexible shaft 12, which is composed of strands 27 (wires) wound in alternating directions in each layer, depend on the spacing of the strands 27 in each layer, the number of strands 27 constituting each layer, and the thickness of the strands 27. By adjusting at least one of these parameters, a flexible shaft 12 can be realized in which the graph showing the relationship between torque T and torsional angle θ is approximately symmetrical with respect to the origin.

[0057] When realizing a flexible shaft 12 in which the graph showing the relationship between torque T and torsional angle θ is approximately symmetrical with respect to the origin, for example, one can select at least one (preferably two or more) of the parameters of the number of strands 27 constituting each layer and the thickness of the strands 27, prepare multiple flexible shafts 12 with modified parameters, measure their torsional stiffness characteristics, and select the flexible shaft 12 in which the graph showing the relationship between torque T and torsional angle θ is most symmetrical with respect to the origin.

[0058] In this context, the graph being symmetrical with respect to the origin means that, within the range Θ of the torsional angle θ until plastic deformation occurs in the inner shaft 21, the point (θ, T(θ)) on the graph showing the relationship between torque T and the torsional angle θ satisfies the following equation (1).

[0059]

number

[0060] In equation (1), δ may preferably be set to 0, except when T(θ)=0.

[0061] As shown in Figure 1, one end of the flexible shaft 12, more precisely one end of the inner shaft 21 (the input end), is connected to the output shaft 6B of the first drive unit 6. The other end of the inner shaft 21 (the output end) is connected to the screw shaft 15 of the single-axis actuator 11. When the output shaft 6B of the first drive unit 6 rotates, the inner shaft 21 rotates, causing the screw shaft 15 of the single-axis actuator 11 to rotate. As a result, the nut 16 moves linearly along the axis of the screw shaft 15. In other words, when torque output from the first drive unit 6 is input to the input end of the flexible shaft 12, it is output to the output end and transmitted to the single-axis actuator 11. The rotation transmitted to the single-axis actuator 11 is converted into linear motion by the single-axis actuator 11.

[0062] The displacement mechanism 13 includes a conversion link 40 provided between the driven member 4 and the uniaxial actuator 11. The conversion link 40 is rotatably connected to the driven member 4 at one end via a rotation axis Z1, and rotatably connected to a nut 16 at the other end via a rotation axis Z2. The rotation axis Z1 of the driven member 4 with respect to the conversion link 40 is located at a different position from the rotation axis Y of the driven member 4 with respect to the intervening link 3. As shown in Figure 1, in this embodiment, the extending direction of the rotation axis Z2 of the conversion link 40 with respect to the nut 16 is set to be perpendicular to the extending direction of the screw shaft 15.

[0063] As shown in Figures 1 and 2, when the output shaft 6B of the first drive unit 6 rotates, causing the nut 16 to move, the driven member 4 rotates relative to the intervening link 3 in accordance with the movement of the nut 16. In the examples shown in Figures 1 and 2, the driven member 4 is described as being composed of a single member, but the present invention is not limited to this embodiment. The driven member 4 may be composed of, for example, a plurality of members that are connected to each other in a rotatable or slidable manner.

[0064] The first drive unit 6 can output torque in both directions, and the output shaft 6B also rotates in both directions. In addition, the inner shaft 21 can rotate in both directions relative to the outer tube 22. Therefore, when the direction of action of the torque output by the first drive unit 6 is reversed, the direction of movement of the nut 16 is also reversed, and the direction of rotation of the driven member 4 is also reversed. In the example shown in Figure 2, when the nut 16 moves to the right side of the paper, the driven member 4 rotates clockwise. When the direction of the torque output by the first drive unit 6 is reversed, and the nut 16 moves to the left side of the paper, the driven member 4 rotates counterclockwise.

[0065] Next, we will explain the effects of the flexible shaft 12 configured in this way and the robot 1 equipped with the flexible shaft 12.

[0066] The inventors of this invention constructed the robot shown in Figure 1 using various flexible shafts with different torsional rigidity characteristics (see, for example, Figures 7(A) to (C)). As a result, they found that the torque output to the driven member 4 sometimes depends on the direction and magnitude of the torque of the first drive unit 6. In such cases, since the torque output to the driven member 4 depends on the direction and magnitude of the torque of the first drive unit 6, it is necessary to take measures such as changing the rotation angle of the output shaft 6B depending on the direction and magnitude of the torque.

[0067] Therefore, the inventors of the present invention diligently investigated the reason why the torque output to the driven member 4 depends on the direction and magnitude of the torque of the first drive device 6. As a result, they concluded that this is because the torsional rigidity characteristics of the flexible shaft depend on the direction and magnitude of the torque. Therefore, the inventors of the present invention evaluated the torsional rigidity characteristics of various flexible shafts.

[0068] Figures 7(A) to 7(C) show three examples (hereinafter referred to as the first to third examples) of the torsional stiffness characteristics of flexible shafts obtained through evaluation. Figures 7(A) and 7(B) show the torsional stiffness characteristics of the first and second examples of conventional flexible shafts, respectively. Figure 7(C) shows the torsional stiffness of the third example flexible shaft 12 according to the present invention.

[0069] As shown in Figures 7(A) to (C), in the first to third examples of flexible shafts, when torque T is zero and the torsional angle θ is zero (origin), applying torque in a predetermined direction (hereinafter, positive direction) causes the torsional angle θ to gradually increase. When the torsional angle θ reaches a predetermined angular threshold (hereinafter, positive angular threshold θu), the torsional rigidity increases sharply, and the torsional angle θ becomes less likely to increase with increasing torque T.

[0070] Subsequently, when the torque is reduced to zero, as shown in Figure 7(A), the torsional angle θ in the first example of the flexible shaft does not return to zero, but remains at a value significantly deviating from zero. Therefore, the flexible shaft in the first example has torsional stiffness characteristics in which the graph showing the relationship between the torsional angle θ and torque T is asymmetrical with respect to the origin.

[0071] On the other hand, as shown in Figures 7(B) and 7(C), in the second and third examples of flexible shafts, when the torque is reduced to zero after the torsional angle θ exceeds the positive angle threshold θu, the torsional angle θ becomes almost zero. Furthermore, when torque is applied in the opposite direction to the positive direction (hereinafter referred to as the negative direction), the torsional angle θ gradually decreases. When the torsional angle θ reaches a predetermined angle threshold (hereinafter referred to as the negative angle threshold θd), the torsional rigidity increases, and the torsional angle θ becomes less likely to decrease. Subsequently, when the torque is increased to zero, the torsional angle θ becomes almost zero.

[0072] As shown in Figure 7(B), in the second example of the flexible shaft, the absolute value of the positive angle threshold θu is different from the absolute value of the negative angle threshold θd. Therefore, the second example of the flexible shaft has torsional stiffness characteristics in which the graph showing the relationship between the torsional angle θ and the torque T is asymmetrical with respect to the origin.

[0073] As shown in Figure 7(C), the flexible shaft 12 of the third example has torsional stiffness characteristics such that the graph showing the relationship between the torsional angle θ and the torque T is symmetrical with respect to the origin, and the absolute value of the positive angle threshold θu is approximately equal to the absolute value of the negative angle threshold θd.

[0074] Thus, the conventional flexible shafts (Examples 1 and 2) have torsional stiffness characteristics in which the graph showing the relationship between the torsional angle θ and torque T is asymmetrical with respect to the origin. In the flexible shaft of Example 1, as shown in Figure 7(A), the graph showing the torsional stiffness characteristics does not pass through the origin and exhibits large hysteresis, which can cause problems in controlling the position of the driven member 4.

[0075] In the second example of the flexible shaft, as shown in Figure 7(B), the graph showing the torsional stiffness characteristics passes through the origin, and the hysteresis is also small.

[0076] However, in the second example of the flexible shaft, the absolute value of the positive angle threshold θu and the absolute value of the negative angle threshold θd are different. Therefore, when controlling the driven member 4, the control device 7 needs to change the rotation angle of the output shaft 6B and the magnitude of the torque output depending on the rotation direction of the output shaft 6B of the first drive device 6, that is, the direction of torque action and the magnitude of torque.

[0077] On the other hand, in the third example of the flexible shaft 12, as shown in Figure 7(C), the graph showing the relationship between the torsional angle θ and the torque T has torsional rigidity characteristics that are symmetrical with respect to the origin. Therefore, the flexible shaft 12 according to the third example (an embodiment of the present invention) can transmit torque in both directions well, regardless of the direction of torque application. When controlling the driven member 4, the control device 7 can effectively control the drive of the driven member 4 without significantly changing the rotation angle of the output shaft 6B or the magnitude of the torque output, depending on the rotation direction of the output shaft 6B of the first drive device 6, i.e., the direction of torque application and the magnitude of the torque.

[0078] Figure 8(A) shows the torsional rigidity characteristics of the flexible shaft 12 according to the third example (embodiment), and Figure 8(B) shows a graph of the derivative dT / dθ of the corresponding torque T with respect to the torsional angle θ. As can be seen from Figure 8(B), in the flexible shaft 12 according to the third example (embodiment), the slope dT / dθ of the graph (i.e., the rate of change) is smaller than the threshold Th in the region between the positive angle threshold θu and the negative angle threshold θd, and larger in the other ranges.

[0079] Figure 8(C) shows the second derivative d of the torque T with respect to the torsional angle θ. 2 T / dθ 2 This is shown. At the positive angle threshold θu, d 2 T / dθ 2 When it reaches a maximum, at the negative angle threshold θd, d 2 T / dθ 2 Since this becomes a minimum, the positive angle threshold θu and the negative angle threshold θd can also be considered as the torsional angles θ corresponding to the extrema, respectively.

[0080] As shown in Figures 8(A) and 8(B), the region between the positive angle threshold θu and the negative angle threshold θd corresponds to the first stiffness region D1, and the remaining region corresponds to the second stiffness region D2. As shown in Figure 6, the first stiffness region D1 includes a point where the torsional angle θ is zero. In the first stiffness region D1, the torsional stiffness is lower than in the second stiffness region D2, and the inner shaft 21 is more prone to twisting. On the other hand, in the second stiffness region D2, the torsional stiffness is higher than in the first stiffness region D1, and the inner shaft 21 is less prone to twisting.

[0081] When an external load is applied to the free end of the driven member 4, torque is transmitted to the flexible shaft 12. When the robot 1 is mainly operated in the first rigidity region D1, the torsional rigidity is low, making the inner shaft 21 prone to deformation, and making it difficult for impact forces to be transmitted to the single-axis actuator 11. Therefore, by operating the robot 1 in the first rigidity region D1, it is possible to prevent impact forces from being transmitted to the single-axis actuator 11, thereby effectively protecting the single-axis actuator 11.

[0082] Furthermore, when the robot 1 is mainly operated in the first rigidity region D1 where the torsional angle θ is small, the flexible shaft 12 deforms in response to external loads, and the driven member 4 follows flexibly. In other words, the driven member 4 can be given appropriate springiness without the need for the first drive unit 6 to control the driven member 4.

[0083] The outer tube 22 is made of a highly sliding fluororesin. Therefore, friction that may occur between the wall surface defining the through hole and the inner shaft 21 can be reduced.

[0084] Furthermore, as shown in Figure 4, grease 35 is filled between the outer surface of the inner shaft 21 and the inner surface of the inner bore 30 of the outer tube 22. Therefore, friction that may occur between the inner shaft 21 and the outer tube 22 can be further reduced.

[0085] Furthermore, by using grease 35, which has a higher viscosity than lubricating oil, leakage of lubricant from both ends of the outer tube 22 can be suppressed. This reduces the frequency of maintenance such as replacing the flexible shaft 12 or replenishing lubricant between the inner shaft 21 and the outer tube 22.

[0086] In this embodiment, the grease 35 further contains a fluororesin made of the same material as the fluororesin wall defining the inner bore 30. Therefore, friction that may occur between the inner shaft 21 and the outer tube 22 can be further reduced. This reduces the frequency of replacing the flexible shaft 12 and replenishing the lubricant, thereby improving the durability of the flexible shaft 12.

[0087] Furthermore, recesses 37 are formed on the outer surface of the inner shaft 21 to store grease 35 between the strands 27. As a result, the rotation of the inner shaft 21 agitates and circulates the grease 35. This agitation and circulation helps to maintain the condition of the grease 35 in good condition. Moreover, when the driven member 4 repeatedly performs reciprocating motion, as in the robot 1, the grease 35 between the outer surface of the inner shaft 21 and the inner circumferential surface of the inner bore 30 of the outer tube 22 is not pushed out in one direction very often. As a result, the grease 35 can be well retained between them, preventing lubrication depletion.

[0088] This concludes the description of specific embodiments. However, the present invention is not limited to the above embodiments or modifications and can be broadly modified and implemented. Furthermore, the specific configuration, arrangement, and quantity of each member or part can be changed as appropriate, as long as it does not depart from the spirit of the present invention. In addition, some or all of the configurations of the above embodiments may be combined with each other. On the other hand, not all of the components shown in the above embodiments are necessarily essential and can be selected as appropriate.

[0089] In the above embodiment, the case was described in which the inner shaft 21 has torsional rigidity characteristics that are symmetrical with respect to the input torque and the twist angle. However, the present invention is not limited to the torsional rigidity characteristics being symmetrical with respect to the origin. That is, the inner shaft 21 only needs to have torsional rigidity characteristics that are point-symmetrical with respect to the input torque and the twist angle.

[0090] In the above embodiment, it was explained that the graph showing the relationship between torque T and torsional angle θ being symmetrical with respect to the origin means that equation (1) is satisfied within the range Θ of torsional angle θ until plastic deformation occurs in the inner shaft 21. However, the embodiment is not limited to this, and for example, the graph showing the relationship between torque T and torsional angle θ being symmetrical with respect to the origin may be defined as satisfying equation (1) within the range Θ of torsional angle θ that can be generated by the driving of the first drive unit 6. In other words, the control device 7 may limit the torque output by the first drive unit 6 to be within the range of torsional angle θ that satisfies equation (1). [Explanation of symbols]

[0091] 1: Robot 4: Driven member 6: First drive unit (drive unit) 10: Transmission mechanism 12: Flexible shaft 13: Displacement Mechanism 21: Inner shaft (shaft) 22: Outer tube (casing) 30: Inner hole (through hole) 35: Grease D1: 1st stiffness region (low stiffness region) D2: 2nd rigidity area (high rigidity area)

Claims

1. A transmission mechanism interposed between a drive device capable of outputting torque in both directions and a driven member driven by the torque output by the drive device, for transmitting torque, It has a flexible shaft with an input end to which torque is input and an output end to which torque is output, A transmission mechanism having torsional rigidity characteristics that are point-symmetrical between the torque applied to the input end of the shaft and the twist angle of the shaft.

2. The transmission mechanism according to claim 1, wherein the shaft has torsional rigidity characteristics such that the magnitude of the rate of change of torque with respect to the torsional angle is minimized when the torsional angle is zero.

3. The transmission mechanism according to claim 1, wherein the torsional rigidity characteristics of the shaft include a low-rigidity region in which the rate of change of torque with respect to the torsional angle is less than or equal to a predetermined threshold, and a high-rigidity region in which the rate of change of torque with respect to the torsional angle is greater than the threshold.

4. The casing has a through hole into which the shaft is inserted, The transmission mechanism according to any one of claims 1 to 3, wherein at least a portion of the wall defining the through hole is made of fluororesin.

5. The transmission mechanism according to claim 4, wherein grease is filled between the outer circumferential surface of the shaft and the inner circumferential surface of the casing defining the through hole.

6. The transmission mechanism according to claim 5, wherein the grease comprises the fluororesin made of the same material as at least a portion of the wall defining the through hole.

7. A robot comprising the drive device, the driven member, and the transmission mechanism according to any one of claims 1 to 3, A base supporting the aforementioned drive device, A link interposed between the base and the driven member, which is displaceable relative to the base and the driven member, A robot having a displacement mechanism supported by the link and which displaces the driven member relative to the link by torque input via the transmission mechanism.

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