Precessional speed reducing or increasing device

Abstract

To provide a precession type speed reducing or increasing device capable of increasing load capacity.SOLUTION: In a precessional speed reducing or increasing device provided with a first face gear 1 and a second face gear 2 engaged with the first face gear 1 and precessing, either one of a flank 21a part of teeth 21 of the first face gear 1 and a flank 22a part of teeth 22 of the second face gear 2 engaged with each other is formed in a recessed surface, and the other is formed in a projecting surface.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a precession speed reducer or speed increaser. [Background technology]

[0002] A known precession type reduction gear includes a first face gear and a second face gear that meshes with the first face gear and undergoes differential motion (see Patent Document 1). Precession is a motion in which the rotation axis of the second face gear describes a cone with the center of precession as its apex, similar to the oscillating motion of a top.

[0003] As in the precession type reduction gear described in Patent Document 1, for example, if the first face gear is fixed and the input shaft is rotated to cause the second face gear to precess, the second face gear will rotate at a reduced speed by the difference in the number of teeth between the first and second face gears. If the reduced rotation of the second face gear is output to the output shaft, it can be used as a reduction gear. If the output shaft is made the input side and the input shaft is made the output side, it can be used as a speed-up gear.

[0004] In the reduction gear disclosed in Patent Document 1, the tooth tips of the first face gear and the second face gear are formed in the shape of a portion of a cone. The tooth roots of the first face gear are formed on an envelope curve when the tooth tips of the second face gear are precessed. The tooth roots of the second face gear are formed on an envelope curve when the tooth tips of the first face gear are precessed relative to each other. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 6777404 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in conventional reduction gears, the tips of the teeth of the first and second face gears are formed on part of a cone with a small base radius, so contact occurs between an arc with a small radius of curvature and an envelope, which increases the contact stress of the teeth and makes it difficult to increase the load capacity.

[0007] The present invention has been made in view of the above-mentioned problems, and has an object to provide a precession type speed reducer or speed increaser that can increase the load capacity. [Means for solving the problem]

[0008] In order to solve the above-described problems, one aspect of the present invention is a precession type speed reducer or speed accelerating device including a first face gear and a second face gear that meshes with the first face gear and precesses, wherein one of the tooth flanks of the teeth of the first face gear and the tooth flanks of the teeth of the second face gear that mesh with each other is formed as a concave surface, and the other is formed as a convex surface.

[0009] Another aspect of the present invention is a precession type speed reducer or speed increaser including a first face gear and a second face gear that meshes with the first face gear and precesses, wherein the cross-sectional shape of the tooth flanks of the teeth of the first face gear is formed into an involute tooth profile, or a precession tooth profile based on a precession locus obtained by projecting onto a two-dimensional plane a three-dimensional locus of the teeth of the moving cone of the second face gear when the moving cone of the second face gear is precessed relative to the fixed cone of the first face gear, and the cross-sectional shape of the tooth flanks of the teeth of the second face gear is formed into an involute tooth profile, or a precession tooth profile based on a precession locus obtained by projecting onto a two-dimensional plane a three-dimensional locus of the teeth of the fixed cone of the first face gear when the fixed cone of the first face gear is precessed relative to the moving cone of the second face gear.

[0010] In another aspect of the present invention, the tooth flanks of the teeth of both the first face gear and the second face gear may be formed into an involute tooth profile, or the tooth flanks of both the teeth may be formed into a precession tooth profile. Also, the tooth flanks of the teeth of either the first face gear or the second face gear may be formed into an involute tooth profile, and the tooth of the other may be formed into a precession tooth profile. [Effects of the Invention]

[0011] According to one aspect of the present invention, one of the tooth flanks of the teeth of the first face gear and the second face gear that mesh with each other is formed concave and the other is formed convex, which increases the contact area of ​​these tooth flanks and reduces contact stress, thereby increasing the load capacity of the precession type speed reducer or speed increaser.

[0012] According to another aspect of the present invention, the cross-sectional shapes of the tooth flanks of the teeth of the first face gear and the second face gear are formed into an involute tooth profile or a precession tooth profile defined on a two-dimensional plane, so that the tooth flanks of the first face gear and the second face gear can be brought into contact with each other at arcs with large radii of curvature, thereby reducing the contact stress of these tooth flanks and increasing the load capacity of the precession type speed reducer or speed increaser. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a cross-sectional view of a precession type reduction gear device according to an embodiment of the present invention. [Figure 2] FIG. 2 is a perspective view of a first face gear and a second face gear. [Figure 3] FIG. 10 is a side view showing the meshing of the teeth of the first face gear and the teeth of the second face gear. [Figure 4] FIG. 2 is a perspective view of a first face gear. [Figure 5] FIG. 5 is an enlarged view of part V in FIG. 4. [Figure 6] FIG. 2 is a perspective view of a second face gear. [Figure 7] FIG. 7 is an enlarged view of part VII in FIG. [Figure 8] FIG. 10 is a side view showing the meshing of a plurality of teeth of a first face gear and a plurality of teeth of a second face gear. [Figure 9] FIG. 9(a) is a perspective view showing the meshing of the first face gear and the second face gear at the closest point, and FIG. 9(b) is a perspective view showing the taper of the first face gear and the second face gear. [Figure 10] FIG. 1 is a perspective view showing a constant cone of a first face gear and a dynamic cone of a second face gear. [Figure 11] FIG. 10 is a perspective view showing a state in which teeth are formed on a fixed cone and a moving cone. [Figure 12] FIG. 10 is a perspective view showing a state in which teeth are arranged on the pitch circles of a fixed cone and a moving cone. [Figure 13] FIG. 13(a) is a top view of FIG. 12, and FIG. 13(b) is a diagram showing the positional relationship between the teeth of the fixed cone and the teeth of the moving cone projected onto the sketch plane. [Figure 14] FIG. 14(a) is a diagram showing a precession locus and a precession tooth profile on a sketch surface, and FIG. 14(b) is a diagram showing an involute tooth profile that approximates the precession tooth profile. [Figure 15] FIG. 10 is a diagram showing an involute tooth profile on a sketch plane. [Figure 16] FIG. 10 is a diagram showing the state in which a tooth tip and a tooth root are added to an involute tooth profile on a sketch surface. [Figure 17] FIG. 17(a) is a perspective view of the first face gear and the taper, and FIG. 17(b) is a side view. [Figure 18] FIG. 18(a) is a perspective view of the second face gear and the taper, and FIG. 18(b) is a side view. [Figure 19] FIG. 1 is a conceptual diagram of tooth profile modification using a pseudo number of teeth. [Figure 20] FIG. 20(a) is a conventional example showing the meshing length of spur gears, and FIG. 20(b) is an example of the present invention showing the meshing length of this embodiment. [Figure 21] 1 is a cross-sectional view of an actuator to which a precession type reduction gear transmission according to an embodiment of the present invention is applied. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, a reduction gear according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings. However, the reduction gear according to the present invention can be embodied in various forms and is not limited to the embodiments described in this specification. The present embodiment is provided with the intention that those skilled in the art will be able to fully understand the invention by fully disclosing the specification.

[0015] (Configuration of the precession type reduction gear according to the embodiment of the present invention) 1 is a cross-sectional view of a precession type reduction gear 10 according to one embodiment of the present invention. In the following explanation, for convenience of explanation, the configuration of the precession type reduction gear 10 will be explained using the directions when the rotation axis A of the precession type reduction gear 10 is arranged vertically, and the input unit 3 is arranged below and the output unit 4 is arranged above, that is, the up / down and left / right directions in FIG. 1. Of course, the arrangement of the precession type reduction gear 10 is not limited to this.

[0016] 1, the precession type reduction gear 10 includes a first face gear 1 and a second face gear 2 that meshes with the first face gear 1 and precesses. The precession is a motion in which the rotation axis B of the second face gear 2 describes a cone surface with its vertex at point O (precession center O) on the rotation axis A of the precession type reduction gear 10, similar to the oscillating motion of a top.

[0017] Reference numeral 3 denotes an input section, reference numeral 4 an output section, reference numeral 5 a motion conversion section, and reference numeral 6 a spherical spline. When the input section 3 is rotated around the rotation axis A, the inclined cam 12 of the motion conversion section 5 rotates together with the input section 3, causing the second face gear 2 to precess. The first face gear 1 is fixed to a housing 7. Therefore, when the second face gear 2 precesses, the second face gear 2 rotates at a reduced speed by the difference in the number of teeth between the first face gear 1 and the second face gear 2. The reduced rotation of the second face gear 2 is taken out to the output section 4 via the spherical spline 6.

[0018] Here, if the number of teeth of the first face gear 1 is Z1 and the number of teeth of the second face gear 2 is Z2, the rotation ratio 1 / U between the input portion 3 and the output portion 4 is expressed as 1 / U = (Z1 - Z2) / Z2.

[0019] The motion converting unit 5 includes an inclined cam 12, a plurality of first rolling elements 11 interposed between the inclined cam 12 and the second face gear 2, and a plurality of second rolling elements 13 interposed between the inclined cam 12 and the housing 7. The motion converting unit 5 presses the second face gear 2 against the first face gear 1. The inclined cam 12 is connected to the input unit 3. When the input unit 3 is rotated, the motion converting unit 5 presses the second face gear 2 against the first face gear 1, causing it to precess.

[0020] The spherical spline 6 includes an inner ring 14, an outer ring (output portion 4), and a plurality of balls 15 between the inner ring 14 and the output portion 4. The reduced rotation of the second face gear 2 is transmitted to the output portion 4 via the spherical spline 6. The second face gear 2 is supported by the spherical spline 6 so as to be capable of precessing.

[0021] An inner ring 14 is formed integrally with the second face gear 2. Spline grooves 14a are formed on the outer surface of the inner ring 14. Spline grooves 4a facing the spline grooves 14a are formed on the inner surface of the output part 4. The output part 4 is rotatably supported by the housing 7 via a bearing 17.

[0022] As shown in Fig. 2, the first face gear 1 is annular. A plurality of teeth 21 are formed on the lower surface of the first face gear 1, i.e., the surface facing the second face gear 2. The outer surface 1a of the first face gear 1 is formed as part of a spherical surface centered on the precession center O.

[0023] The second face gear 2 includes an annular main body 16 and an inner ring 14 formed integrally with the main body 16. A plurality of teeth 22 are formed on the upper surface of the main body 16 of the second face gear 2, i.e., the surface facing the first face gear 1. The number of teeth of the second face gear 2 is different from the number of teeth of the first face gear 1. The outer surface 2a of the main body 16 is formed as part of a spherical surface centered on the precession center O.

[0024] In this embodiment, an example of a precession type reduction gear 10 including a first face gear 1 and a second face gear 2 that meshes with the first face gear 1 and precesses is described, but the precession type reduction gear is not limited to one that includes only a first face gear and a second face gear. For example, a precession type reduction gear may be one that includes a first face gear, a second face gear that meshes with the first face gear and precesses, a third face gear that precesses together with the second face gear, and a fourth face gear that meshes with the third face gear.

[0025] (Tooth surfaces of the first and second face gears) As shown in Fig. 3, the cross-sectional shape of the tooth flanks 21a of the teeth 21 of the first face gear 1 is formed into an involute tooth profile or a precession tooth profile. The cross-sectional shape of the tooth flanks 22a of the teeth 22 of the second face gear 2 is also formed into an involute tooth profile or a precession tooth profile. Involute tooth profiles and precession tooth profiles will be described later.

[0026] As shown in Fig. 3, the tooth flanks 22a of the teeth 22 of the second face gear 2 are formed convexly, i.e., convexly, with an external tooth shape. On the other hand, the tooth flanks 21a of the teeth 21 of the first face gear 1 are formed concavely, i.e., concavely, with an internal tooth shape. In the first face gear 1, the tooth flanks 21a of the internal tooth shape are on the side opposite to the involute tooth profile or precession tooth profile of the external tooth shape. Alternatively, the tooth flanks 21a of the teeth 21 of the first face gear 1 may be formed convexly, and the tooth flanks 22a of the teeth 22 of the second face gear 2 may be formed concavely.

[0027] 4 and 5, the teeth 21 of the first face gear 1 have similar shapes on the inner diameter side and the outer diameter side, and are tapered to become larger from the inner diameter side toward the outer diameter side. The taper converges at the precession center O. A crowning 21d is formed at the radial end of the first face gear 1, for example, at the end on the inner diameter side.

[0028] 6 and 7, the teeth 22 of the second face gear 2 are also similar in shape on the inner diameter side and the outer diameter side, and are tapered to become larger from the inner diameter side to the outer diameter side. The taper converges at the precession center O. A crowning 22d is formed at the radial end of the second face gear 2, for example, at the end on the outer diameter side.

[0029] In the case of the precession type reduction gear 10, the difference in the number of teeth between the first face gear 1 and the second face gear 2 is small. For example, the number of teeth of the first face gear 1 is 101, and the number of teeth of the second face gear 2 is 100. As a result, the teeth 21 of the first face gear 1 and the teeth 22 of the second face gear 2 are close to each other, making interference and edge loads likely to occur. For this reason, as shown in FIG. 3 , reliefs 23 are provided at the tip 21b and the root 21c of each tooth 21 of the first face gear 1 to avoid interference and edge loads. Similarly, reliefs 23 are provided at the tip 22b and the root 22c of each tooth 22 of the second face gear 2. The shape of the reliefs 23 is not particularly limited, and may be, for example, an arc shape.

[0030] 8 and 9, the meshing between the plurality of teeth 21 of the first face gear 1 and the plurality of teeth 22 of the second face gear 2 will be described. As shown in FIG. 9, at the point P1 where the base of the cone of the first face gear 1 and the base of the cone of the second face gear 2 are closest to each other, the teeth 21 of the first face gear 1 and the teeth 22 of the second face gear 2 do not mesh, and a gap exists between them. The base of the cone of the first face gear 1 is a fixed cone 41, which will be described later, and the base of the cone of the second face gear 2 is a dynamic cone 42, which will be described later. In FIGS. 9(a) and 9(b), reference numeral 32 denotes the taper of the valley shape of the tooth 21 of the first face gear 1, and reference numeral 31 denotes the taper of the valley shape of the tooth 22 of the second face gear 2. As shown in FIG. 9(b), a gap g exists between them.

[0031] As shown in Figure 8, the first face gear 1 and the second face gear 2 are meshed at meshing positions 24, with multiple teeth 21 of the first face gear 1 and multiple teeth 22 of the second face gear 2, at positions circumferentially to the right and left of the closest point of approach P1. The meshing positions are symmetrical from the closest point of approach P1. When a clockwise (rightward) torque acts on the second face gear 2, multiple teeth 22 of the second face gear 2 and multiple teeth 21 of the first face gear 1 mesh at positions circumferentially to the right of the closest point of approach P1. The opposite is true when a counterclockwise (leftward) torque acts on the second face gear 2.

[0032] (Involute tooth profile and precession tooth profile) The involute tooth profile and precession tooth profile of the first face gear 1 and the second face gear 2 are formed as follows. For ease of understanding, let us assume that the number of teeth Z1 of the first face gear 1 is 101 and the module is 1, and the number of teeth Z2 of the second face gear 2 is 100 and the module is 1. The number of teeth and module can be set as desired.

[0033] FIG. 10 shows the fixed cone of the first face gear 1 and the dynamic cone of the second face gear 2. Reference numeral 41 denotes the fixed cone of the first face gear 1, and reference numeral 42 denotes the dynamic cone of the second face gear 2. Reference numeral θ denotes the precession angle. As shown in FIG. 11, the fixed cone 41 is equal to the cone on which the tooth trace of the first face gear 1 extends; that is, it has the same apex angle and pitch circle (base circle) as the first face gear 1. The dynamic cone 42 is equal to the cone on which the tooth trace of the second face gear 2 extends; that is, it has the same apex angle and pitch circle (base circle) as the second face gear 2. Note that the shapes of the fixed cone and dynamic cone in FIG. 10 are exaggerated vertically for clarity, but in reality they are flattened as shown in FIG. 9.

[0034] As shown in Fig. 10, first, the fixed cone 41 and the moving cone 42 are arranged so that their generating line 43 is common. That is, the apex of the fixed cone 41 and the apex of the moving cone 42 are positioned at the precession center O, and the base circle 41a of the fixed cone 41 and the base circle 42a of the moving cone 42 are positioned on the surface of a sphere Q whose center is the precession center O. The base circle 42a of the precessing moving cone 42 is always positioned on the surface of the sphere Q. The base circle 41a of the fixed cone 41 is the pitch circle of the first face gear 1, and the base circle 42a of the moving cone 42 is the pitch circle of the second face gear 2.

[0035] The tooth profile of the first face gear 1 can be formed by forming an involute tooth profile I or a precession tooth profile F (see FIG. 14(b)) of a constant cone 41 on a two-dimensional plane R (hereinafter referred to as sketch plane R) perpendicular to the generatrix 43 and converging this involute tooth profile I or precession tooth profile F to the precession center O. Similarly, the tooth profile of the second face gear 2 can be formed by forming an involute tooth profile or a precession tooth profile of a moving cone 42 on sketch plane R and converging this involute tooth profile or precession tooth profile to the precession center O.

[0036] The involute tooth profile I or precession tooth profile F of the fixed cone 41 is defined on the sketch plane R. The precession tooth profile F of the fixed cone 41 is obtained by projecting the three-dimensional trajectory of the teeth of the moving cone 42 when the moving cone 42 precesses relative to the fixed cone 41 onto the sketch plane R, and adding a tooth space width W to the precession trajectory T (see FIG. 14(a)).

[0037] The precession locus T and precession tooth profile F of the fixed cone 41 will now be explained. As shown in Fig. 10, when the number of teeth Z1 of the first face gear 1 is 101 and the module is 1, the fixed cone 41 is set so that the diameter of the pitch circle 41a is 101. When the number of teeth Z2 of the second face gear 2 is 100 and the module is 1, the dynamic cone 42 is set so that the diameter of the pitch circle 42a is 100. In practice, to reduce the heights of the first face gear 1 and the second face gear 2, the pitch circle 41a of the fixed cone 41 is shifted negatively (for example, the diameter of the pitch circle 41a of the fixed cone 41 is set to 100.8), and the pitch circle 42a of the dynamic cone 42 is shifted positively (for example, the diameter of the pitch circle 42a of the dynamic cone 42 is set to 100.2).

[0038] Next, a precession locus T is obtained by projecting onto the sketch plane R the three-dimensional locus of the teeth of the moving cone 42 when the moving cone 42 precesses relative to the fixed cone 41. Here, as shown in FIG. 12, teeth 51a to 51e (points) of the fixed cone 41 are arranged at a predetermined pitch on the pitch circle 41a of the fixed cone 41. The predetermined pitch is, for example, 100.8×π÷101=3.135. Similarly, teeth 52a to 52e (points) of the moving cone 42 are arranged at a predetermined pitch on the pitch circle 42a of the moving cone 42. The predetermined pitch is, for example, 100.2×π÷100=3.148. Tooth 51a of fixed cone 41 and tooth 52a of moving cone 42 overlap on common generatrix 43, but teeth 51b-51e of fixed cone 41 and teeth 52b-52e of moving cone 42 are shifted horizontally by δ1 mainly due to the difference in pitch, and shifted vertically by δ2 mainly due to the precession angle θ. Also, as shown in the top view of Figure 13, teeth 51b-51d of fixed cone 41 and teeth 52b-52d of moving cone 42 are shifted radially by δ3 mainly due to the difference in pitch circle diameter.

[0039] Figure 13(b) shows the positional relationship between the teeth 51a to 51d of the fixed cone 41 and the teeth 52a to 52d of the moving cone 42 projected onto a sketch plane R. Figure 13(b) also shows multiple sketch planes. Symbol R indicates a sketch plane perpendicular to the common generatrix 43, symbol R1 indicates a sketch plane perpendicular to the generatrix passing through the tooth 51b of the fixed cone 41, symbol R2 indicates a sketch plane perpendicular to the generatrix passing through the tooth 51c of the fixed cone 41, and symbol R3 indicates a sketch plane perpendicular to the generatrix passing through the tooth 51d of the fixed cone 41.

[0040] When the moving cone 42 is caused to precess, the teeth 52a to 52d of the moving cone 42 trace a three-dimensional trajectory along the surface of the sphere Q and overlap with the teeth 51a to 51d of the fixed cone 41. Therefore, by consolidating the positional relationships between the teeth 51a to 51d of the fixed cone 41 and the teeth 52a to 52d of the moving cone 42 projected onto multiple sketch planes R, R1 to R3, onto a single sketch plane R, it is possible to trace the precession trajectory T of the teeth 52a to 52d of the moving cone 42.

[0041] This precession locus T becomes the basis of the precession tooth profile F of the fixed cone 41. As shown in FIG. 14, the precession tooth profile F of the fixed cone 41 can be formed by drawing multiple circles C centered on the precession locus T and drawing lines tangent to the circles C. The radius of the circles C is set to have a predetermined tooth space width W on the pitch circle 41a of the fixed cone 41. For example, the predetermined tooth space width W is set to 100.8 × π ÷ 202 so that the tooth thickness and tooth space width are the same. A symmetrical precession tooth profile F can be formed by arranging the precession tooth profiles F symmetrically with respect to a common generatrix 43.

[0042] The precession tooth profile F of the constant cone 41 thus obtained may be used as the tooth profile of the first face gear 1, or as shown in FIG. 14(b), an involute tooth profile I that is similar to the precession tooth profile F may be used as the tooth profile of the first face gear 1. As described above, the tooth flanks 21a of the teeth 21 of the first face gear 1 are formed into a concave surface of the internal tooth shape. In other words, in the first face gear 1, the side opposite to the involute tooth profile I or precession tooth profile F of the external tooth shape becomes the tooth flank 22a.

[0043] As shown in Figure 15, involute tooth profile I is the path traced by the end of a thread 62 when a thread 62 is wound around a base circle 61 and then unwound while being pulled by holding the end of the thread 62. The involute tooth profile I is also defined on the sketch plane R. By setting the base circle 61 on the sketch plane R, the involute tooth profile I can be formed. The base circle 61 can be set from the diameter of the pitch circle 41a and the pressure angle (for example, 20°).

[0044] In this way, the involute tooth profile I or precession tooth profile F of the constant cone 41 can be determined, but the tooth tip and tooth root are not yet determined. For this reason, as shown in Fig. 16, the tooth root J and tooth tip K are added to the involute tooth profile I or precession tooth profile F. As shown in Fig. 8, the tooth 21 of the first face gear 1 and the tooth 22 of the second face gear 2 mesh only near the pitch circle PC (41a), so the tooth root J and tooth tip K can be set arbitrarily, and a relief can be provided.

[0045] As shown in FIG. 17, the teeth 21 of the first face gear 1 can be formed by forming a taper 31 with the involute tooth profile I or precession tooth profile F of a fixed cone 41 drawn on a sketch plane R at the precession center O.

[0046] On the other hand, when forming an involute tooth profile or a precession tooth profile for the second face gear 2, it is sufficient to find a precession locus by projecting onto the sketch plane R the three-dimensional locus of the teeth of the fixed cone 41 of the first face gear 1 when the fixed cone 41 is precessed relative to the dynamic cone 42 of the second face gear 2. Then, by providing a tooth space width to the precession locus of the fixed cone 41, it is possible to form the precession tooth profile F' of the dynamic cone 42, and to form an involute tooth profile I' that approximates the precession tooth profile F'. By adding a tooth bottom and a tooth tip to the involute tooth profile I' or the precession tooth profile F' and forming a taper 32 with the precession tooth profile F' or the involute tooth profile I' drawn on the sketch plane R as shown in FIG. 18, the teeth 22 of the second face gear 2 can be formed.

[0047] (Tooth profile correction using pseudo-number of teeth) Reducing the difference in the number of teeth between the first face gear 1 and the second face gear 2 or shifting the teeth may reduce the precession angle θ to, for example, 1 to 3°. In this case, with a normal involute tooth profile, the teeth 21 of the first face gear 1 and the teeth 22 of the second face gear 2 interfere with each other and do not mesh. For this reason, as shown in FIG. 19, the involute tooth profile of the first face gear 1 is modified using a pseudo number of teeth (e.g., 20) that is smaller than the actual number of teeth (e.g., 101). Reference numeral 64 denotes the involute tooth profile before modification, and reference numeral 65 denotes the involute tooth profile after modification. The involute tooth profile of the second face gear 2 is similarly modified using a pseudo number of teeth (e.g., 20) that is smaller than the actual number of teeth (e.g., 100). By modifying the tooth profile using the pseudo number of teeth, the radius of curvature of the involute tooth profile 65 becomes smaller, so that interference between the teeth 21 of the first face gear 1 and the teeth 22 of the second face gear 2 can be more effectively avoided.

[0048] Tooth profile modification using a pseudo number of teeth will now be explained. As shown in Fig. 19, for example, if the first face gear 1 has 101 teeth and a module of 1, an involute tooth profile 64 is formed on a pitch circle with 101 teeth (a pitch circle with a diameter of 101 mm). Also, an involute tooth profile 65 is formed on a pitch circle with a pseudo number of teeth (a pitch circle with a diameter of 20 mm), for example, which is fewer than the actual number of teeth. If the involute tooth profile 65 formed with the pseudo number of teeth is placed on the pitch circle with 101 teeth, tooth profile modification using the pseudo number of teeth becomes possible.

[0049] However, if the first face gear 1 is profile shifted, even if the involute tooth profile 65 formed on a pitch circle with 20 pseudo teeth is placed directly on a pitch circle with 101 teeth, it will not match the pitch after profile shifting. In this case, the involute tooth profile 65 after tooth profile modification can be divided into right and left halves, and the distance between the right and left halves can be adjusted to match the pitch after profile shifting.

[0050] (Manufacturing method of the first face gear and the second face gear) There are no particular limitations on the manufacturing method for the first face gear 1 and the second face gear 2, but considering mass production, plastic processing by forging is desirable. If a die is machined with an end mill or the like to have a shape complementary to the teeth 21 of the first face gear 1 and the die is pressed against the base material of the first face gear 1, the shape of the die is transferred to the base material of the first face gear 1, and the first face gear 1 can be manufactured. The second face gear 2 can be manufactured in a similar manner.

[0051] (actuator) 21 shows a cross-sectional view of an actuator 80 to which the precession type reduction gear 10 according to this embodiment is applied. Reference numeral 81 denotes a motor, reference numeral 10 denotes a precession type reduction gear, reference numeral 1 denotes a first face gear, reference numeral 2 denotes a second face gear, reference numeral 3 denotes an input section, reference numeral 4 denotes an output section, reference numeral 5 denotes a motion converting section, and reference numeral 6 denotes a spherical spline. A motor shaft 81a of the motor 81 is connected to the input section 3. When the motor 81 rotates the input section 3, the motion converting section 5 causes the second face gear 2 to precess, and the second face gear 2 rotates at a reduced speed by an amount corresponding to the difference in the number of teeth between the first face gear 1 and the second face gear 2. The reduced rotation of the second face gear 2 is output to the output section 4 via the spherical spline 6.

[0052] The above has described the configuration of the precession type reduction gear 10 of this embodiment. The precession type reduction gear 10 of this embodiment has the following advantages.

[0053] Since one of the tooth surfaces 21a of the teeth 21 of the first face gear 1 and the tooth surfaces 22a of the teeth 22 of the second face gear 2, which mesh with each other, is formed concave and the other is formed convex, the contact area between these tooth surfaces 21a, 22a can be increased, reducing contact stress, and therefore the load capacity of the precession type reduction gear device 10 can be increased.

[0054] 10, the tooth flanks 21a of the first face gear 1 and the tooth flanks 22a of the second face gear 2 are formed into an involute tooth profile I or a precession tooth profile F defined on a two-dimensional plane R, so that the tooth flanks 21a of the first face gear 1 and the tooth flanks 22a of the second face gear 2 can be brought into contact with each other on arcs with large radii of curvature. This reduces the contact stress of these tooth flanks 21a, 22a, and increases the load capacity of the precession type reduction gear transmission 10.

[0055] Since the teeth 21, 22 of the first face gear 1 and the second face gear 2 are formed with tapers 31, 32 that converge to the precession center O, the meshing length of the first face gear 1 and the second face gear 2 in the radial direction can be increased.

[0056] Since the involute tooth profile I of the first face gear 1 and / or the second face gear 2 is modified using a pseudo number of teeth that is smaller than the actual number of teeth, interference between the teeth 21 of the first face gear 1 and the teeth 22 of the second face gear 2 can be avoided.

[0057] Relief 23 is provided at the tooth tip 21b and tooth root 21c of the first face gear 1, and at the tooth tip 22b and tooth root 22c of the second face gear 2, thereby preventing interference and edge loading between the tooth 21 of the first face gear 1 and the tooth 22 of the second face gear 2. In addition, the teeth 21, 22 of the first face gear 1 and the second face gear 2 can be made closer to each other, preventing either tooth 21 or 22 from becoming thinner.

[0058] By forming the teeth 21 of the first face gear 1 and the teeth 22 of the second face gear 2 into an involute tooth profile I or a precession tooth profile F, as shown in Fig. 8, a plurality of (e.g., 10) teeth 21 of the first face gear 1 and a plurality of (e.g., 10) teeth 22 of the second face gear 2 mesh only near the pitch circle PC. For this reason, even if the first face gear 1 and the second face gear 2 are provided with a recess 23, this does not adversely affect the number of meshes and uniform velocity between the first face gear 1 and the second face gear 2.

[0059] The number of meshing teeth and uniform velocity will now be explained. As shown in Figure 20(a), conventional spur gears 71 and 72 have only one meshing tooth, and it is necessary to use involute tooth profiles evenly, which results in a long meshing length L. Reference numeral 73 denotes the meshing position. As the spur gears 71 and 72 rotate, the meshing position 73 moves above and below the pitch circles 74 and 75. In the case of conventional spur gears 71 and 72, providing relief at the tooth tips and tooth roots reduces the meshing length L and the number of meshing teeth, resulting in a loss of uniform velocity.

[0060] As shown in Fig. 8, in the precession type reduction gear 10 of this embodiment, the first face gear 1 and the second face gear 2 have multiple meshing teeth, for example, about 10 teeth, and the meshing positions 24 are only in the vicinity of the pitch circle PC. As shown in Fig. 20(b), the meshing length L is also short. For this reason, even if reliefs 23 are provided at the tooth tip and tooth bottom, there is no adverse effect on the number of meshing teeth and uniform velocity.

[0061] At the closest point P1 between the base of the cone of the first face gear 1 and the base of the cone of the second face gear 2, the teeth 21 of the first face gear 1 and the teeth 22 of the second face gear 2 do not mesh with each other and a gap g exists between them, which prevents interference between the teeth 21 of the first face gear 1 and the teeth 22 of the second face gear 2. Furthermore, the multiple teeth 21 of the first face gear 1 and the multiple teeth 22 of the second face gear 2 mesh with each other at a position circumferentially away from the closest point P1, which increases the load capacity.

[0062] The outer surfaces 1a, 2a of the first face gear 1 and the second face gear 2 are formed as part of a spherical surface centered on the precession center O, thereby improving the strength of the first face gear 1 and the second face gear 2. [Explanation of symbols]

[0063] 1...first face gear, 1a...outer surface of first face gear, 2...second face gear, 2a...outer surface of second face gear, 10...precession type reduction gear, 21...first face gear tooth, 21a...tooth flank of first face gear, 21b...tooth tip of first face gear, 21c...tooth root of first face gear, 22...second face gear tooth, 22a...tooth flank of second face gear, 22b...tooth tip of second face gear, 22c...tooth root of second face gear, 23...Relief, 31...Taper of first face gear tooth, 32...Taper of second face gear tooth, 41...Constant cone, 42...Dynamic cone, 51a to 51e...Constant cone teeth, 52a to 52e...Dynamic cone teeth, 65...Involute tooth profile after tooth profile correction using pseudo number of teeth, g...Gap, T...Precession locus, F...Precession tooth profile, I...Involute tooth profile, R...Sketch plane (two-dimensional plane), O...Precession center, P1...Closest point of first and second face gears

Claims

1. a first face gear; a second face gear that meshes with the first face gear and precesses, a precession type speed reducing or increasing device in which either the tooth flanks of the teeth of the first face gear or the tooth flanks of the teeth of the second face gear that mesh with each other are formed as a concave surface, and the other is formed as a convex surface.

2. a first face gear; a second face gear that meshes with the first face gear and precesses, a cross-sectional shape of a tooth surface of the first face gear is formed into an involute tooth profile or a precession tooth profile based on a precession locus obtained by projecting onto a two-dimensional plane a three-dimensional locus of the teeth of a moving cone of the second face gear when the moving cone is caused to precess relative to a fixed cone of the first face gear, a precession type speed reducer or speed increaser in which a cross-sectional shape of the tooth flank of the second face gear is formed into an involute tooth profile, or a precession tooth profile based on a precession locus obtained by projecting onto a two-dimensional plane a three-dimensional locus of the teeth of a fixed cone of the first face gear when the fixed cone of the first face gear is caused to precess relative to a moving cone of the second face gear.

3. 3. The precession type speed reducer or speed increaser according to claim 1, wherein the teeth of the first face gear and the teeth of the second face gear are tapered to converge toward a center of precession.

4. a cross-sectional shape of a tooth surface of the tooth of the first face gear and a cross-sectional shape of a tooth surface of the tooth of the second face gear are formed into an involute tooth profile; 3. The precession type speed reducing or increasing device according to claim 2, wherein the involute tooth profiles of the teeth of the first face gear and the second face gear are modified using a pseudo number of teeth that is smaller than the actual number of teeth.

5. 3. The precession type speed reducing or increasing device according to claim 1, wherein reliefs are provided at the tips and bottoms of the teeth of the first face gear and at the tips and bottoms of the teeth of the second face gear.

6. the teeth of the first face gear and the teeth of the second face gear do not mesh with each other at a location where a base of a cone of the first face gear and a base of a cone of the second face gear are closest to each other, and a gap is present therebetween; 3. The precession type speed reducing or speed increasing device according to claim 1, wherein a plurality of teeth of the first face gear and a plurality of teeth of the second face gear mesh with each other at a position circumferentially spaced from the closest point.

7. 3. The precession type speed reducer or speed increaser according to claim 1, wherein the outer surfaces of the first face gear and the second face gear are formed as parts of a sphere centered on a precession center.

8. The precession type speed reducing or speed increasing device according to claim 1 or 2; a motor that causes the second face gear to precess.

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