Power transmission device

Abstract

The gear motor (1) is provided with a motor (60) and a speed reducer (70). The gear motor (1) is provided with a motor shell (64), a speed reducer shell (75) and a fastening bolt (91) used for connecting the motor shell (64) and the speed reducer shell (75). The linear expansion coefficient of the fastening bolt (91) is smaller than the linear expansion coefficient of the motor shell (64) and larger than the linear expansion coefficient of the speed reducer shell (75).

Description

Technical Field

[0001] The present invention relates to a power transmission device. Background Art

[0002] Conventionally, a power transmission device including a motor and a speed reducer has been known (for example, refer to Patent Document 1). In such a power transmission device, generally, for weight reduction and the like, an aluminum alloy is used for the motor housing, a steel material (carbon steel for mechanical structures or alloy steel for mechanical structures, cast iron) is used for the speed reducer housing, and carbon steel for mechanical structures or alloy steel for mechanical structures is used for the fastening bolts for fastening the motor housing and the speed reducer housing.

[0003] Prior Art Documents

[0004] Patent Documents

[0005] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2021-73842 Summary of the Invention

[0006] Technical Problem to be Solved by the Invention

[0007] In a power transmission device, during operation, the temperature rises due to heat generation, and each component expands. At this time, since the linear expansion coefficients between the housing components (motor housing, speed reducer housing) and the fastening bolts are different, the amount of expansion of the housing components is larger than that of the fastening bolts. As a result, the motor housing may be pressed against the support surface of the fastening bolt, causing deformation of the housing components.

[0008] The present invention has been made in view of the above circumstances, and an object thereof is to appropriately fasten the motor housing and the speed reducer housing together.

[0009] Means for Solving the Technical Problem

[0010] The present invention is a power transmission device including a motor and a speed reducer, wherein

[0011] the power transmission device includes a motor housing, a speed reducer housing, and a connecting member for connecting the motor housing and the speed reducer housing,

[0012] the linear expansion coefficient of the connecting member is smaller than the linear expansion coefficient of the motor housing and larger than the linear expansion coefficient of the speed reducer housing.

[0013] Advantageous Effects of the Invention

[0014] According to the present invention, the motor housing and the speed reducer housing can be appropriately fastened together. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a cross-sectional view showing a gear motor according to the first embodiment.

[0016] Figure 2 It is a cross-sectional view showing the gear motor according to the second embodiment. Specific Embodiment

[0017] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0018] <1. First Embodiment>

[0019] Figure 1 It is a cross-sectional view showing the gear motor 1 according to the first embodiment of the present invention.

[0020] The gear motor 1 according to the present embodiment is an example of the power transmission device according to the present invention, and its use is not particularly limited. For example, it can be used as a joint gear motor of a collaborative robot that collaborates with a person to perform work.

[0021] [1-1. Structure of Gear Motor]

[0022] Specifically, the gear motor 1 includes a motor 60, a speed reducer 70, a brake 80, and a rotation detection unit 85.

[0023] In addition, in the description of the first embodiment, the direction along the central axis Ax1 of the gear motor 1 is referred to as the "axial direction", and the radial direction and the circumferential direction of the circle centered on the central axis Ax1 are referred to as the "radial direction" and the "circumferential direction", respectively. And in the axial direction, the side connected to the external driven component E1 ( Figure 1 the left side) is referred to as the "load side", and the side opposite to the load side ( Figure 1 the right side) is referred to as the "opposite load side".

[0024] The motor 60 includes a rotor shaft 61 that rotates about the central axis Ax1, a motor rotor 62, a motor stator 63, and a motor housing 64.

[0025] In the present embodiment, the rotor shaft 61 penetrates from the motor 60 to the speed reducer 70.

[0026] The motor rotor 62 is externally fitted to the rotor shaft 61 and rotates together with the rotor shaft 61. The motor rotor 62 has a permanent magnet such as a neodymium magnet, for example.

[0027] The motor stator 63 is formed by winding a coil around a stator core made of laminated steel plates. The motor stator 63 is concentrically arranged on the outer diameter side (outer side in the radial direction) of the motor rotor 62.

[0028] The motor housing 64 covers the outer diameter sides of the motor rotor 62 and the motor stator 63. The motor stator 63 is embedded in the inner peripheral surface of the motor housing 64.

[0029] In this embodiment, the speed reducer 70 is a cylindrical flexure engagement type gear device, which includes: a vibration generating body shaft (input shaft) 71 having a vibration generating body 71a, an external gear 72 disposed on the outer diameter side of the vibration generating body 71a and flexurally deformed by the vibration generating body 71a, and two internal gears 73, 74 meshing with the external gear 72. Further, the speed reducer 70 includes a speed reducer housing 75 covering the outer peripheral portion of the speed reducer 70, and an output member 78 that outputs the decelerated rotation.

[0030] The vibration generating body shaft 71 is externally fitted to the rotor shaft 61. A part of the vibration generating body shaft 71 constitutes the vibration generating body 71a, and the outer shape of the cross section of the vibration generating body 71a orthogonal to the central axis Ax1 is non-circular (for example, elliptical). The outer shape of the cross section of the portion of the vibration generating body shaft 71 other than the vibration generating body 71a orthogonal to the central axis Ax1 is circular.

[0031] The vibration generating body shaft 71 is supported by input bearings 76a, 76b (for example, ball bearings) on both sides in the axial direction of the vibration generating body 71a. One of the input bearings 76a is internally fitted to the first speed reducer housing 75a described later and rotatably supports the vibration generating body shaft 71, and the other input bearing 76b is internally fitted to the output member 78 and rotatably supports the vibration generating body shaft 71.

[0032] The external gear 72 is supported to be relatively rotatable with respect to the vibration generating body 71a via a vibration generating body bearing 77 (for example, a roller bearing) disposed between the external gear 72 and the vibration generating body 71a. The external gear 72 is fitted to the outer diameter side of the vibration generating body 71a along the outer peripheral surface of the vibration generating body 71a via the vibration generating body bearing 77. The external gear 72 has flexibility, and when the vibration generating body shaft 71 rotates, it flexurally deforms into an elliptical shape matching the vibration generating body 71a.

[0033] The two internal gears 73, 74 are arranged side by side in the axial direction. One of the internal gears 73 is disposed on the side opposite to the load, and the other internal gear 74 is disposed on the load side. The number of teeth of the two internal gears 73, 74 is different from each other. For example, the number of teeth of one of the internal gears 73 is more than the number of teeth of the external gear 72, and the number of teeth of the other internal gear 74 is equal to the number of teeth of the external gear 72.

[0034] The speed reducer housing 75 includes a first speed reducer housing 75a, a second speed reducer housing 75b, and a third speed reducer housing 75c arranged side by side in the axial direction.

[0035] The first speed reducer housing 75a is disposed at the position closest to the side opposite to the load.

[0036] The second speed reducer housing 75b is disposed between the first speed reducer housing 75a and the third speed reducer housing 75c, and also serves as one of the internal gears 73.

[0037] The third speed reducer housing 75c is arranged at the position closest to the load side and on the outer diameter side of the internal gear 74, and can rotatably support the internal gear 74 via a main bearing 79 (for example, a crossed roller bearing). The third speed reducer housing 75c integrally has an outer ring portion (rolling surface on the outer ring side) of the main bearing 79.

[0038] As will be described later, these first speed reducer housings 75a, second speed reducer housings 75b, and third speed reducer housings 75c are connected axially together by fastening bolts 91.

[0039] The output member 78 is fixed to the internal gear 74 and the driven member E1, and outputs the rotational force transmitted from the internal gear 74 to the driven member E1.

[0040] A hollow shaft 65 is fitted into the inner peripheral portion of the output member 78. The hollow shaft 65 is arranged at a position closer to the inner diameter side (radial direction inside) than the rotor shaft 61, and penetrates from the motor 60 to the speed reducer 70. The end of the hollow shaft 65 on the side opposite to the load is supported to be rotatable by a bearing 66 arranged between the hollow shaft 65 and the rotor shaft 61, and the end on the load side is supported to be rotatable by the main bearing 79 via the output member 78 and the internal gear 74.

[0041] The brake 80 is arranged between the motor 60 and the speed reducer 70 in the axial direction. The brake 80 includes a brake rotor 81 mounted on the rotor shaft 61 and a braking mechanism 83 for braking the brake rotor 81. The braking mechanism 83 is constituted by, for example, a coil and a spring, and applies a braking force to the rotor shaft 61 by sandwiching the brake rotor 81 between a plurality of friction members by their action.

[0042] The rotation detection unit 85 is arranged on the side opposite to the load of the motor 60. The rotation detection unit 85 includes a first rotation part 86a that rotates integrally with the rotor shaft 61, a second rotation part 86b that rotates integrally with the hollow shaft 65, sensors 87 that respectively detect the rotation amounts of the first rotation part 86a and the second rotation part 86b, and an encoder substrate 88 on which the sensors 87 are mounted. The rotation detection unit 85 of the present embodiment is a rotary encoder that outputs the displacement of the rotation part as a digital signal, but it can also be a resolver that outputs the displacement as an analog signal, or other rotation detectors. The rotary encoder can have a structure with an optical detection part or a structure with a magnetic detection part.

[0043] [1-2. Connection Structure and Material of the Housing]

[0044] In the gear motor 1, the motor housing 64 and the three speed reducer housings 75 (75a to 75c) are connected to each other by a plurality of fastening bolts 91 arranged circumferentially. Each fastening bolt 91 is inserted axially from the side opposite to the load to fasten the motor housing 64 and the three speed reducer housings 75 together.

[0045] An example of the materials (raw materials) of the motor housing 64, the speed reducer housing 75, and the fastening bolts 91 and their linear expansion coefficients (representative values) is shown in Table I below.

[0046] [Table 1]

[0047] Table I

[0048]

[0049] However, among the materials of the speed reducer housings shown in Table I, "alloy steel for mechanical structures" is mainly used when the speed reducer housing 75 is integrated with the (internal gear) gear. In the present embodiment, it is the material of the second speed reducer housing 75b that also serves as the internal gear 73. And among the materials of the speed reducer housing 75, "high-carbon chromium bearing steel (so-called bearing steel)" is mainly used when the speed reducer housing 75 is integrated with the bearing. In the present embodiment, it is the material of the third speed reducer housing 75c that integrally has the outer ring portion (rolling surface on the outer ring side) of the main bearing 79. And "aluminum-based" widely includes aluminum and aluminum alloys, and "magnesium-based" widely includes magnesium and magnesium alloys.

[0050] In addition, the materials and linear expansion coefficients of the housing, etc. of the gear motor 1 are not limited to the materials and linear expansion coefficients shown in Table I, as long as the linear expansion coefficient of the fastening bolt 91 is less than the linear expansion coefficient of the motor housing 64 and greater than the linear expansion coefficient of the speed reducer housing 75 (at least one of the three). Thus, as will be described later, the motor housing 64 and the speed reducer housing 75 can be properly fastened together. And the linear expansion coefficient of the fastening bolt 91 can be approximately equal to the linear expansion coefficient of the motor housing 64.

[0051] [1-3. Materials of the speed reduction mechanism]

[0052] An example of the materials (raw materials) of the speed reducer 70 (speed reduction mechanism) and their linear expansion coefficients (representative values) is shown in Table II below.

[0053] [Table 2]

[0054] Table II

[0055]

[0056] However, the "oscillator bearing" in Table II refers to at least one of the rolling elements and the cage (including the inner and outer rings if present) in the oscillator bearing 77. Also, "titanium-based" broadly includes titanium and titanium alloys.

[0057] In addition, the material and the linear expansion coefficient of the speed reduction mechanism are not limited to those shown in Table II, as long as the linear expansion coefficient of the oscillator 71a is smaller than that of the external gear 72. Thus, as will be described later, it is possible to suppress a decrease in the radial clearance between the external gear 72 and the internal gears 73, 74 during operation. Further, the linear expansion coefficient of the oscillator 71a is preferably smaller than that of the oscillator bearing 77, and more preferably smaller than the linear expansion coefficients of both of the internal gears 73, 74.

[0058] [1-4. Operation of the Gear Motor]

[0059] In the gear motor 1 of the present embodiment, when the motor 60 is driven and the rotor shaft 61 rotates, the rotational output is input to the oscillator shaft 71 of the speed reducer 70 integrated with the rotor shaft 61.

[0060] In the speed reducer 70, when the oscillator shaft 71 rotates, the motion of the oscillator 71a is transmitted to the external gear 72. At this time, the shape of the external gear 72 is restricted to the shape along the outer peripheral surface of the oscillator 71a and is deflected into an elliptical shape when viewed axially. Further, since the external gear 72 meshes with one of the fixed internal gears 73 at its major axis portion, it does not rotate at the same speed as the oscillator 71a, but rather the oscillator 71a rotates relatively inside the external gear 72. Moreover, along with this relative rotation, the external gear 72 is deflected and deformed in such a manner that its major axis position and minor axis position move circumferentially. This deformation period is proportional to the rotation period of the oscillator shaft 71.

[0061] When the external gear 72 is deflected and deformed, its major axis position moves, so that the meshing position between the external gear 72 and one of the internal gears 73 changes in the rotational direction, causing the external gear 72 to rotate itself. On the other hand, since the external gear 72 also meshes with the other internal gear 74, the meshing position between the external gear 72 and the other internal gear 74 also changes in the rotational direction as the oscillator shaft 71 rotates. Here, if the number of teeth of the other internal gear 74 is the same as that of the external gear 72, the external gear 72 and the other internal gear 74 do not rotate relative to each other, and the rotational motion of the external gear 72 is transmitted to the other internal gear 74 at a reduction ratio of 1:1. Thus, the rotational motion of the oscillator shaft 71 is decelerated and transmitted to the internal gear 74 and the output member 78, and this rotational motion is output to the driven member E1.

[0062] Here, in the present embodiment, the linear expansion coefficient of the fastening bolt 91 is smaller than that of the motor housing 64 and larger than that of the speed reducer housing 75. Thus, the motor housing 64 and the speed reducer housing 75 can be properly fastened together.

[0063] That is, conventionally, the material of the fastening bolt is, for example, alloy steel for mechanical structures or carbon steel for mechanical structures, and its linear expansion coefficient is the same as that of the speed reducer housing (for example, 12 [×10 -6 / °C]). Therefore, when the temperature rises due to the heat generated by the motor and the speed reducer during operation, since the linear expansion coefficients of the housing components (motor housing (for example, made of aluminum alloy), speed reducer housing) and the fastening bolt (for example, alloy steel for mechanical structures) are different from each other, the housing components expand more in the axial direction. As a result, the motor housing is pressed against the support surface of the fastening bolt, and thus dent deformation may occur.

[0064] In contrast, in the present embodiment, as described above, the linear expansion coefficient of the fastening bolt 91 is smaller than that of the motor housing 64 and larger than that of the speed reducer housing 75. That is, compared with the conventional case where the linear expansion coefficient of the fastening bolt and the speed reducer housing is the same, the difference in the thermal expansion amount between the housing components (motor housing 64, speed reducer housing 75) and the fastening bolt 91 is small. Thus, when each component expands due to heat, the force pressing the motor housing 64 against the support surface of the fastening bolt 91 can be suppressed. Therefore, the possibility of the motor housing 64 being pressed against the fastening bolt 91 and causing dent deformation can be reduced.

[0065] Moreover, in the present embodiment, the linear expansion coefficient of the vibration generating body 71a is smaller than that of the external gear 72. Thus, the reduction in the radial clearance between the external gear 72 and the internal gears 73 and 74 during operation can be suppressed.

[0066] That is, conventionally, the material of the vibration generating body is, for example, alloy steel for mechanical structures or carbon steel for mechanical structures, and its linear expansion coefficient is the same as that of the external gear (for example, 12×10 -6 / °C). And in the speed reducer, the temperature rise during operation is greater the closer to the inner diameter side. Therefore, the thermal expansion amount of the vibration generating body on the inner diameter side is larger than that of the external gear on the outer diameter side. As a result, the radial clearance between the external gear and the internal gears may decrease during operation. The decrease in this radial clearance leads to an increase in sliding friction, which may further cause deterioration of the transmission efficiency or a further rise in temperature.

[0067] Therefore, in the present embodiment, as described above, the linear expansion coefficient of the oscillation body 71a on the inner diameter side is smaller than that of the external gear 72 on the outer diameter side. As a result, compared with the conventional case where the linear expansion coefficients of the oscillation body and the external gear are the same, the difference in the amount of thermal expansion between the oscillation body 71a and the external gear 72 can be reduced. Therefore, it is possible to suppress the reduction of the radial clearance between the external gear 72 and the internal gears 73 and 74 during operation.

[0068] [1-5. Technical effects of the first embodiment]

[0069] As described above, according to the first embodiment, the linear expansion coefficient of the fastening bolt 91 that connects the motor housing 64 and the speed reducer housing 75 is smaller than that of the motor housing 64 and larger than that of the speed reducer housing 75.

[0070] Therefore, compared with the conventional case where the linear expansion coefficients of the fastening bolt and the speed reducer housing are the same, the difference in the amount of thermal expansion between the housing components (motor housing 64, speed reducer housing 75) and the fastening bolt 91 is small. As a result, when each component expands due to heat generation, the force pressing the motor housing 64 against the support surface of the fastening bolt 91 can be suppressed. Therefore, it is possible to reduce the possibility of the motor housing 64 being deformed by being pressed against the fastening bolt 91. Furthermore, it is possible to properly fasten the motor housing 64 and the speed reducer housing 75 together.

[0071] Moreover, according to the first embodiment, the linear expansion coefficient of the oscillation body 71a is smaller than that of the external gear 72 disposed on the outer diameter side of the oscillation body 71a.

[0072] As a result, compared with the conventional case where the linear expansion coefficients of the oscillation body and the external gear are the same, the difference in the amount of thermal expansion between the oscillation body 71a and the external gear 72 can be reduced. Therefore, it is possible to suppress the reduction of the radial clearance between the external gear 72 and the internal gears 73 and 74 during operation.

[0073] Moreover, according to the first embodiment, the linear expansion coefficient of the oscillation body 71a is smaller than that of the oscillation body bearing 77 disposed between the oscillation body 71a and the external gear 72.

[0074] As a result, compared with the conventional case where the linear expansion coefficients of the oscillation body and the oscillation body bearing are the same, the difference in the amount of thermal expansion between the oscillation body 71a and the oscillation body bearing 77 can be reduced. Therefore, it is possible to suppress the reduction of the radial clearance between the oscillation body bearing 77 and the external gear 72 during operation, and it is also possible to further suppress the reduction of the radial clearance between the external gear 72 and the internal gears 73 and 74.

[0075] <2. Second embodiment>

[0076] Next, a second embodiment of the present invention will be described.

[0077] [2-1. Structure of the gear motor]

[0078] Figure 2 It is a cross-sectional view showing the gear motor 2 according to the second embodiment of the present invention.

[0079] The gear motor 2 according to the present embodiment is an example of the power transmission device according to the present invention. The main difference from the gear motor 1 according to the first embodiment described above is that the speed reducer is an eccentric swing type gear device instead of a flexure engagement type gear device.

[0080] Specifically, as Figure 2 shown, the gear motor 2 includes a motor 20, a speed reducer 30, a brake 40, and a rotation detection unit 50. These speed reducer 30, motor 20, brake 40, and rotation detection unit 50 are arranged in sequence along the central axis Ax2 of the gear motor 2.

[0081] In addition, in the description of the second embodiment, the direction along the central axis Ax2 of the gear motor 2 is referred to as the "axial direction", and the radial direction and the circumferential direction of the circle centered on the central axis Ax2 are referred to as the "radial direction" and the "circumferential direction", respectively. And, in the axial direction, the side connected to the external driven component E2 ( Figure 2 the left side) is referred to as the "load side", and the side opposite to the load side ( Figure 2 the right side) is referred to as the "opposite side of the load".

[0082] The motor 20 includes a rotor shaft 21 that rotates around the central axis Ax2, a motor rotor 22, a motor stator 23, and a motor housing 24.

[0083] In the present embodiment, the rotor shaft 21 penetrates from the speed reducer 30 to the brake 40. As will be described later, the rotor shaft 21 is rotatably supported by a first bearing 36 provided on the speed reducer 30 and a second bearing 48 provided on the brake 40.

[0084] The motor rotor 22 is externally fitted to the rotor shaft 21 and rotates together with the rotor shaft 21. The motor rotor 22 has a rotor yoke 22a and rotor magnets 22b. The rotor yoke 22a is made of a non-magnetic material and is fitted and fixed to the outer peripheral surface of the rotor shaft 21. The rotor magnets 22b are permanent magnets such as neodymium magnets, for example, and a plurality of magnets corresponding to a predetermined number of poles are pasted on the outer peripheral surface of the rotor yoke 22a.

[0085] The motor stator 23 is formed by winding a coil 23b around a stator core 23a made of laminated steel plates. The motor stator 23 is concentrically arranged on the outer diameter side of the motor rotor 22.

[0086] The motor housing 24 covers the outer diameter sides of the motor rotor 22 and the motor stator 23, and holds the motor stator 23 in a state where the stator core 23a of the motor stator 23 is embedded.

[0087] Moreover, the motor housing 24 is not particularly limited, but for the purpose of weight reduction and improvement of cooling performance, the motor housing 24 is made of an aluminum-based material.

[0088] In addition, the type of the motor 20 is not particularly limited. For example, it may be an induction motor instead of a permanent magnet type motor.

[0089] In the present embodiment, the speed reducer 30 is a center crank type eccentric swing type speed reducer and is disposed on the load side of the motor 20. Specifically, the speed reducer 30 includes an eccentric shaft 31, outer gears 32A, 32B, an output shaft 33, and a speed reducer housing 34.

[0090] The eccentric shaft 31 is an input shaft of the speed reducer 30 having a hollow structure (hollow construction). In the present embodiment, the eccentric shaft 31 and the rotor shaft 21 of the motor 20 are integrally formed of a single material. However, the eccentric shaft 31 and the rotor shaft 21 may be separate, and in this case, as long as they are connected by, for example, a spline or a key structure to transmit rotation.

[0091] A plurality (two) of eccentric bodies 311a, 311b are provided on the eccentric shaft 31.

[0092] The outer gears 32A, 32B have a plurality of inner pin holes circumferentially spaced at positions offset from the center and a central through hole through which the eccentric shaft 31 is inserted.

[0093] The outer gear 32A is supported by an eccentric bearing 35a disposed between the outer gear 32A and the eccentric body 311a so as to be rotatable relative to the eccentric body 311a and swing as the eccentric body 311a rotates; the outer gear 32B is supported by an eccentric bearing 35b disposed between the outer gear 32B and the eccentric body 311b so as to be rotatable relative to the eccentric body 311b and swing as the eccentric body 311b rotates.

[0094] The output shaft 33 is disposed on the outer diameter side of the eccentric shaft 31 and on the load side of the outer gears 32A, 32B, and is fixed to the driven member E2. The output shaft 33 has a plurality of inner pins 33a formed so as to protrude in a pin shape toward the side opposite to the load. The inner pins 33a are inserted into the inner pin holes of the outer gears 32A, 32B. A plate body 331 fixed to the speed reducer housing 34 is disposed on the side opposite to the load of the inner pins 33a.

[0095] The output shaft 33 rotatably supports the eccentric shaft 31 via a first bearing 36 disposed between the eccentric shaft 31 and the output shaft 33. The first bearing 36 is, for example, a crossed roller bearing.

[0096] Moreover, the output shaft 33 is made of a metallic material such as a steel material, for example.

[0097] The speed reducer housing 34 is disposed on the outer diameter sides of the external gears 32A and 32B and the output shaft 33. The speed reducer housing 34 is fixed to the motor housing 24 of the motor 20.

[0098] An internal gear 34g is provided on the inner peripheral portion of the speed reducer housing 34. The internal gear 34g has a plurality of external teeth as internal teeth, which are internally engaged with the external gears 32A and 32B.

[0099] The speed reducer housing 34 rotatably supports the output shaft 33 via a main bearing 37 disposed between the speed reducer housing 34 and the output shaft 33. The main bearing 37 is a crossed roller bearing. In the present embodiment, the inner ring (rolling surface) is integrally provided on the outer peripheral portion of the output shaft 33, and the outer ring (rolling surface) is integrally provided on the inner peripheral portion of the speed reducer housing 34.

[0100] Moreover, like the output shaft 33, the speed reducer housing 34 is made of a metallic material such as a steel material, for example.

[0101] The brake 40 brakes the rotation of the rotor shaft 21 (eccentric shaft 31) and is disposed on the side opposite to the load of the motor 20.

[0102] The brake 40 includes: a hub member 41 fixed to the rotor shaft 21 in a manner to restrict relative rotation; a disk-shaped rotor 42 spline-fitted into the hub member 41; an armature 43 displaceable in the direction of the rotor 42; an electromagnetic coil 44 for driving the armature 43; a spring member 45 for returning the armature 43 to its original position; a plate body 46 opposed to the rotor 42 on the side opposite to the armature 43; and a frame 47 for holding the electromagnetic coil 44 and the plate body 46, etc. Friction linings (wear materials) are respectively fastened to the two surfaces of the rotor 42 opposed to the plate body 46 and the armature 43.

[0103] The frame 47 is fixed to the motor housing 24 of the motor 20. In the present embodiment, the speed reducer housing 34 of the speed reducer 30, the motor housing 24 of the motor 20, and the frame 47 are fastened together by fastening bolts 92.

[0104] The frame 47 supports the rotor shaft 21 so as to be rotatable through a second bearing 48 disposed between the frame 47 and the rotor shaft 21. The second bearing 48 is disposed between the motor rotor 22 and the rotation detector 51. More specifically, the second bearing 48 is disposed between the hub member 41 of the brake 40 and the rotation detector 51. In the present embodiment, the second bearing 48 is a ball bearing. However, the type of the second bearing 48 is not particularly limited, and for example, it may be a roller bearing such as a crossed roller bearing. Also, from the aspect of improving the detection accuracy of the rotation detection unit 50, it is more preferable to dispose the second bearing 48 near the rotation unit 51a of the rotation detection unit 50 described later.

[0105] Also, the frame 47 is not particularly limited, but for the purpose of weight reduction, the frame 47 is made of aluminum alloy or resin.

[0106] In the brake 40, by the action of the electromagnetic coil 44 or the action of the spring material 45, the rotor 42 is clamped between the armature 43 and the plate body 46 by a lining, thereby applying a braking force to the rotor shaft 21 (eccentric body shaft 31). Also, by the action of the spring material 45 or the action of the electromagnetic coil 44, the force between the armature 43 and the plate body 46 that clamps the rotor 42 is released, thereby releasing the braking force on the rotor shaft 21 (eccentric body shaft 31).

[0107] The rotation detection unit 50 is disposed on the side opposite to the load of the brake 40. The rotation detection unit 50 includes a rotation detector 51 that detects the rotation of the rotor shaft 21 (eccentric body shaft 31) and an encoder substrate 52 on which its detection circuit is mounted.

[0108] The rotation detector 51 has a rotation unit 51a that rotates integrally with the rotor shaft 21 and a sensor 51b that is disposed on the side opposite to the load of the rotation unit 51a and detects the rotation amount of the rotation unit 51a. The rotation detector 51 is, for example, a rotary encoder that outputs the rotational displacement of the rotation unit as a digital signal, but may also be a resolver that outputs the displacement as an analog signal, or may be other rotation detectors. The rotary encoder may have a structure with an optical detection unit or a structure with a magnetic detection unit.

[0109] The encoder substrate 52 mounts the sensor 51b, and the sensor 51b detects the rotation of the rotor shaft 21 (eccentric body shaft 31) and outputs it to the circuit unit having the drive circuit of the motor 20.

[0110] [2-2. Connection Structure and Material of the Housing]

[0111] In the gear motor 2, the motor housing 24, the speed reducer housing 34, and the frame 47 are connected to each other by a plurality of fastening bolts 92 arranged circumferentially. Each fastening bolt 92 is axially inserted through from the side opposite to the load, fastening the frame 47, the motor housing 24, and the speed reducer housing 34 together.

[0112] In addition, the fastening bolt 92 only needs to connect at least the motor housing 24 and the speed reducer housing 34. At this time, the frame 47 can be connected to the motor housing 24 by a connecting member different from the fastening bolt 92.

[0113] The materials (raw materials) of the motor housing 24, the speed reducer housing 34, and the fastening bolt 92 and their linear expansion coefficients are the same as those of the motor housing 64, the speed reducer housing 75, and the fastening bolt 91 in the above first embodiment.

[0114] That is, the linear expansion coefficient of the fastening bolt 92 can be smaller than the linear expansion coefficient of the motor housing 24 and larger than the linear expansion coefficient of the speed reducer housing 34. Thus, as will be described later, the motor housing 24 and the speed reducer housing 34 can be properly fastened together.

[0115] [2-3. Operation of the Gear Motor]

[0116] In the gear motor 2 of the present embodiment, when the motor 20 is driven and the rotor shaft 21 rotates, the rotational output is input to the eccentric shaft 31 of the speed reducer 30 integrated with the rotor shaft 21.

[0117] In the speed reducer 30, as the eccentric shaft 31 rotates, the eccentric bodies 311a, 311b rotate inside the external gears 32A, 32B, and thereby the external gears 32A, 32B swing with different phases from each other. By the swinging, the outer teeth of the external gears 32A, 32B farthest from the central axis Ax2 mesh with the internal gear 34g, and the meshing position changes circumferentially as the swinging occurs. Specifically, every time the eccentric shaft 31 rotates once, the meshing position between the internal gear 34g and the external gears 32A, 32B rotates one week circumferentially. There is a difference in the number of teeth between the external gears 32A, 32B and the internal gear 34g. Every time the meshing position with the internal gear 34g rotates one week, the external gears 32A, 32B rotate by an amount equivalent to the above-mentioned difference in the number of teeth. This rotation is transmitted to the output shaft 33 via the inner pin 33a. Thus, the rotational movement of the eccentric shaft 31 is decelerated and output from the driven member E2 connected to the output shaft 33.

[0118] Here, in the present embodiment, the linear expansion coefficient of the fastening bolt 92 is smaller than the linear expansion coefficient of the motor housing 24 and larger than the linear expansion coefficient of the speed reducer housing 34. Thus, the motor housing 24 and the speed reducer housing 34 can be properly fastened together.

[0119] That is, conventionally, the material of the fastening bolt is, for example, alloy steel for mechanical structures or carbon steel for mechanical structures, and its coefficient of linear expansion is equal to that of the speed reducer housing (for example, 12 [×10 -6 / °C]). Therefore, when the temperature rises due to the heat generated by the motor and the speed reducer during operation, due to the difference in the coefficients of linear expansion between the housing components (motor housing (for example, made of aluminum alloy), speed reducer housing) and the fastening bolt (for example, alloy steel for mechanical structures), the housing components expand more in the axial direction. As a result, the motor housing is pressed against the support surface of the fastening bolt, and thus dent deformation may occur.

[0120] In contrast, in the present embodiment, as described above, the coefficient of linear expansion of the fastening bolt 92 is smaller than that of the motor housing 24 and larger than that of the speed reducer housing 34. That is, compared with the conventional case where the coefficient of linear expansion of the fastening bolt and the speed reducer housing is equal, the difference in the amount of thermal expansion between the housing components (motor housing 24, speed reducer housing 34) and the fastening bolt 92 becomes smaller.

[0121] [2-4. Technical effects of the second embodiment]

[0122] As described above, according to the second embodiment, the same effects as those of the first embodiment can be achieved.

[0123] That is, the coefficient of linear expansion of the fastening bolt 92 that connects the motor housing 24 and the speed reducer housing 34 is smaller than that of the motor housing 24 and larger than that of the speed reducer housing 34.

[0124] Therefore, compared with the conventional case where the coefficient of linear expansion of the fastening bolt and the speed reducer housing is equal, the difference in the amount of thermal expansion between the housing components (motor housing 24, speed reducer housing 34) and the fastening bolt 92 becomes smaller. Therefore, the motor housing 24 and the speed reducer housing 34 can be properly fastened together.

[0125] <3. Others>

[0126] The embodiments of the present invention have been described above, but the present invention is not limited to the above embodiments.

[0127] For example, in the above embodiment, as the connecting member for connecting the motor housing and the speed reducer housing, a fastening bolt is exemplified. However, the connecting member is not limited to a bolt, and for example, it may also be a pin or a rivet.

[0128] Further, in the above-described embodiments, as an example of the speed reducer according to the present invention, a cylindrical flexure engagement type gear device and a center crank type eccentric swing type gear device are exemplified. However, the speed reducer according to the present invention is not particularly limited as long as it can transmit power. For example, it may be a cup type or a top hat side flexure engagement type gear device, a distribution type eccentric swing type gear device or a simple planetary type gear device, etc., or it may be a gear device such as a parallel shaft speed reducer or an orthogonal speed reducer, or it may be a traction drive.

[0129] In addition, within the scope not departing from the gist of the invention, the details shown in the above-described embodiments can be appropriately changed.

[0130] Industrial Applicability

[0131] As described above, the present invention helps to appropriately fasten the motor housing and the speed reducer housing together.

[0132] Symbol Explanation

[0133] 1, 2 - Gear motor (power transmission device), 20 - Motor, 21 - Rotor shaft, 24 - Motor housing, 30 - Speed reducer, 34 - Speed reducer housing, 37 - Main bearing (bearing), 40 - Brake, 50 - Rotation detection unit, 60 - Motor, 61 - Rotor shaft, 64 - Motor housing, 70 - Speed reducer, 71 - Oscillator shaft, 71a - Oscillator, 72 - External gear, 73 - Internal gear, 74 - Internal gear, 75 - Speed reducer housing, 75a - First speed reducer housing, 75b - Second speed reducer housing, 75c - Third speed reducer housing, 77 - Oscillator bearing, 78 - Output member, 79 - Main bearing (bearing), 80 - Brake, 85 - Rotation detection unit, 91, 92 - Fastening bolt (connecting member), Ax1, Ax2 - Central axis, E1, E2 - Driven member.

Claims

1. A power transmission device having a motor and a speed reducer, wherein, The power transmission device includes a motor housing, a speed reducer housing, and a connecting member for connecting the motor housing and the speed reducer housing. The linear expansion coefficient of the connecting member is less than that of the motor housing and greater than that of the speed reducer housing.

2. The power transmission device according to claim 1, wherein, The motor housing is made of an aluminum-based material. The speed reducer housing is made of alloy steel for mechanical structures, carbon steel for mechanical structures, high-carbon chromium bearing steel, or cast iron. The connecting member is made of austenitic stainless steel.

3. The power transmission device according to claim 1, wherein, The speed reducer housing integrally has a rolling surface of a bearing.

4. The power transmission device according to claim 1, wherein, The speed reducer is a flexure engagement type gear device, and the flexure engagement type gear device has a vibration generating body, an outer gear disposed on the outer side in the radial direction of the vibration generating body and flexurally deformed by the vibration generating body, and an inner gear meshing with the outer gear. The linear expansion coefficient of the vibration generating body is less than that of the outer gear.

5. The power transmission device according to claim 4, wherein, The vibration generating body is made of a titanium-based material. The outer gear is made of alloy steel for mechanical structures, carbon steel for mechanical structures, high-carbon chromium bearing steel, or cast iron.

6. The power transmission device according to claim 4, having a vibration exciter bearing disposed between the vibration exciter and the external gear, The linear expansion coefficient of the vibration exciter is less than that of the vibration exciter bearing.

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