Actuator

Abstract

This actuator comprises: a motor 12 having a motor shaft 20; and an eccentric oscillation type reduction gear 14 having a crank shaft 40 that is driven by the motor shaft 20, and an external gear 44 that is caused to oscillate by an eccentric portion 42 of the crank shaft 40, wherein the motor 12 is provided by a motor space 82 for accommodating at least a portion of the motor shaft 20, the crank shaft 40 is provided only with an eccentric portion 42 having a single eccentric phase as the eccentric portion 42, and a plurality of balance weights 100A and 100B having different eccentric phases in the motor space 82 are integrally and rotatably provided to a shaft body 74 including the motor shaft 20 and the crank shaft 40.

Description

Actuator

[0001] The present disclosure relates to actuators.

[0002] Patent Document 1 discloses an actuator including a motor and an eccentric oscillating reducer connected to the motor. The eccentric oscillating reducer includes a crankshaft that is rotatable integrally with the motor shaft and an external gear that oscillates due to an eccentric portion of the crankshaft. The actuator in Patent Document 1 has a single balance weight disposed within the motor space of the motor to suppress vibrations caused by oscillation of the external gear in a shaft body consisting of the motor shaft and the crankshaft.

[0003] Japanese Patent Application Publication No. 10-51999

[0004] In the technology disclosed in Patent Document 1, a single balance weight can only offset either the centrifugal force acting on the shaft due to the oscillation of the external gear or the moment around the bearing. The inventors of the present application recognized that there is room for improvement in the technology disclosed in Patent Document 1 in order to advantageously suppress vibration of the shaft due to the oscillation of the external gear while reducing the axial length of the actuator.

[0005] One object of the present disclosure is to provide an actuator that can advantageously suppress vibration of the shaft body while reducing the axial length of the actuator.

[0006] The actuator of the present disclosure is an actuator comprising: a motor having a motor shaft; a crankshaft driven by the motor shaft; and an eccentric oscillating reducer having an external gear that oscillates due to an eccentric portion of the crankshaft; wherein the motor has a motor space that accommodates at least a portion of the motor shaft; the crankshaft has only an eccentric portion with a single eccentric phase as the eccentric portion; and a shaft body including the motor shaft and the crankshaft has multiple balance weights with different eccentric phases mounted within the motor space so as to be rotatable together.

[0007] According to the present disclosure, it is possible to provide an actuator that is advantageous in suppressing vibration of the shaft body while reducing the axial length of the actuator.

[0008] Fig. 2(A) is a side cross-sectional view showing the actuator of the embodiment. Fig. 2(A) is an explanatory diagram showing the centrifugal force and moment acting on the shaft by the oscillator of the embodiment, and Fig. 2(B) is an explanatory diagram showing the centrifugal force and moment acting on the shaft by the oscillator and balance weight of the embodiment. Fig. 3(A) is a schematic explanatory diagram showing the centrifugal force and moment acting on the shaft by the oscillator and balance weight of a modified form, as viewed from the Y direction, and Fig. 3(B) is a schematic explanatory diagram showing the centrifugal force as viewed from the axial direction.

[0009] Hereinafter, an embodiment for implementing the actuator of the present disclosure will be described. The same or equivalent elements will be given the same reference numerals, and duplicate explanations will be omitted. In each drawing, for the sake of convenience, components will be omitted, enlarged, or reduced as appropriate. The drawings should be viewed in accordance with the orientation of the reference numerals.

[0010] Referring to FIG. 1 , the actuator 10 includes a motor 12 and an eccentric oscillating reducer 14 (hereinafter simply referred to as the reducer 14) that reduces the rotational speed output from the motor 12. Additionally, the actuator 10 optionally includes a driver unit 16 that drives the motor 12. The main feature of the actuator 10 is balance weights 100A and 100B, which will be described later, but the peripheral structure will be described first. In this specification, the direction along the rotational centerline of the motor shaft 20 of the motor 12 is simply referred to as the axial direction, and the radial and circumferential directions of a circle centered on the rotational centerline are also simply referred to as the radial and circumferential directions. Furthermore, the side of the reducer 14 relative to the motor 12 in the axial direction is referred to as the load side, and the side opposite the load side in the axial direction is referred to as the anti-load side.

[0011] The actuator 10 includes an actuator casing 18 that is made up of a motor casing 26 (described later) of the motor 12 and a reducer casing 50 (described later) of the reducer 14. When the actuator 10 includes a driver unit 16, the actuator casing 18 also forms a driver casing 88 (described later) of the driver unit 16.

[0012] The motor 12 comprises a motor shaft 20, a rotor 22 that is rotatable integrally with the motor shaft 20, a stator 24 that cooperates with the rotor 22 to generate a rotating magnetic field that rotates the motor shaft 20, and a motor casing 26 that houses the motor shaft 20, rotor 22, stator 24, etc.

[0013] The rotor 22 is disposed in a rotor disposing portion 20a provided on the outer periphery of the motor shaft 20. The rotor 22 is disposed so as to be rotatable integrally with the motor shaft 20, for example, by interference fitting, adhesive bonding, etc. The type of the rotor 22 is not particularly limited, and may be, for example, a permanent magnet rotor, a squirrel-cage rotor, a wound rotor, a coreless rotor, etc.

[0014] The stator 24 is disposed on the inner periphery of the motor casing 26 (a motor frame 32, described later). The stator 24 is fixed to the motor casing 26 by, for example, interference fitting, adhesive bonding, or the like. The stator 24 of this embodiment includes a stator core 28 and a coil 30 incorporated into the stator core 28. The coil 30 includes a load-side coil end portion 30a provided on the load side of the stator core 28, and a counter-load-side coil end portion 30b provided on the counter-load side of the stator core 28. The type of the stator 24 is not particularly limited, and may be a coreless stator in which a stator core is omitted.

[0015] The motor casing 26 of this embodiment includes a cylindrical motor frame 32 and a load-side cover 34 provided on the axial load side of the motor frame 32. In this embodiment, the motor frame 32 and the load-side cover 34 are provided separately from each other and then integrated with bolts or the like, but they may also be provided integrally using the same member. The load-side cover 34 covers the rotor 22 and the stator 24 from the load side. The load-side cover 34 protrudes radially inward from the motor frame 32.

[0016] The reducer 14 includes a crankshaft 40, an external gear 44 that oscillates due to an eccentric portion 42 of the crankshaft 40, an internal gear 46 that meshes with the external gear 44, a carrier 48 that can be synchronized with the rotation component of the external gear 44, and a reducer casing 50 that houses the external gear 44, the carrier 48, etc. The reducer 14 of this embodiment is a center crank type eccentric oscillating reducer in which the crankshaft 40 is located on the oscillation center C44a of the external gear 44.

[0017] The reducer 14 includes a fixed body 52 that is fixed to an external member, and an output body 54 that outputs rotation to an external driven member. Here, an example will be described in which the reducer casing 50 constitutes the fixed body 52 and the carrier 48 constitutes the output body 54. The driven member is driven by the output of the output body 54. Examples of the driven member include (1) robots such as industrial robots and service robots, (2) industrial machinery such as machine tools and construction machinery, (3) transport machinery such as conveyors and film transport devices, and (4) parts of various machines such as vehicles.

[0018] In addition to the eccentric portion 42, the crankshaft 40 also includes shaft portions 56 provided on both axial sides of the eccentric portion 42. In this embodiment, the eccentric portion 42 is integrally formed from the same member as the shaft portion 56, but may also be provided separately from the shaft portion 56 using a different member.

[0019] The crankshaft 40 is driven by the motor shaft 20. In this embodiment, the crankshaft 40 is provided so as to be rotatable integrally with the motor shaft 20. To achieve this, the motor shaft 20 and the crankshaft 40 in this embodiment are formed from separate members and are provided so as to be rotatable integrally by means of an interference fit, screws, splines, keys, or the like. In this embodiment, the motor shaft 20 and the crankshaft 40 are provided so as to be rotatable integrally with each other, with the shaft portion 56 of the crankshaft 40 inserted into the motor shaft 20 through an opening 20b provided on the load side of the motor shaft 20. Alternatively, the motor shaft 20 and the crankshaft 40 may be provided so as to be rotatable integrally by being formed from the same member.

[0020] The center of gravity C42 of the eccentric portion 42 is eccentric with respect to the rotation center line C40 of the crankshaft 40. The eccentric portion 42 can oscillate the external gear 44 by rotating around the rotation center line C40. "Oscillation" here means that the gear center C44b of the external gear 44 rotates around the oscillation center C44a. The eccentric portion 42 has a circular shape centered on the center of gravity C42.

[0021] The crankshaft 40 has only one eccentric portion 42 with a single eccentric phase as the eccentric portion 42. This means that the crankshaft 40 does not have multiple eccentric portions 42 with different eccentric phases. To satisfy this condition, the crankshaft 40 may have only a single eccentric portion 42, or multiple eccentric portions 42 with the same eccentric phase. The "eccentric phase" here refers to the phase around the rotation center line C40 in the eccentric direction D1 from the rotation center line C40 of the crankshaft 40 toward the center of gravity C42 of the eccentric portion 42.

[0022] The external gear 44 is supported by the eccentric portion 42 of the crankshaft 40 via an eccentric bearing 64 so as to be rotatable relative to the eccentric portion 42. The internal gear 46 of this embodiment is integrated with the reducer casing 50.

[0023] The carrier 48 is disposed on the axial load side of the external gear 44. The carrier 48 in this embodiment is formed by combining multiple (here, two) carrier members 66. A pin 68 protrudes axially from the carrier 48 and penetrates the external gear 44. This allows the carrier 48 to synchronize with the rotation component of the external gear 44. Here, "synchronizing with the rotation component" means maintaining the rotation component of the carrier 48 at the same magnitude as the rotation component of the external gear 44, within a numerical range including zero. For example, when the carrier 48 serves as the output body 54, the external gear 44 rotates, and the rotation component is transmitted to the carrier 48 via the pin 68, causing the carrier 48 to rotate. As a result, the carrier 48 synchronizes with the rotation component of the external gear 44. In contrast to this, when the carrier 48 serves as the fixed body 52, the rotation component of the carrier 48 is maintained at zero, and the rotation of the external gear 44 is constrained by the carrier 48 and the pin 68, so that the rotation component of the external gear 44 is also maintained at zero. As a result, the carrier 48 is synchronized with the rotation component of the external gear 44.

[0024] The reducer casing 50 is connected to the motor casing 26 with bolts or the like. The reducer casing 50 in this embodiment is formed by combining a plurality of (here, two) reducer casing members 70. A main bearing 72 is disposed between the reducer casing 50 and the carrier 48.

[0025] The actuator 10 includes a shaft body 74 including a motor shaft 20 and a crankshaft 40. The shaft body 74 in this embodiment is made up of the motor shaft 20 and the crankshaft 40, which are arranged to rotate together. The shaft body 74 in this embodiment includes a hollow portion 74a that passes through the shaft body 74 in the axial direction. A center pipe 76 is disposed within the hollow portion 74a of the shaft body 74. The load side portion of the center pipe 76 is fixed to the carrier 48 by bolts, interference fit, or the like. A counter-load side member 78 is fixed to the counter-load side portion of the center pipe 76.

[0026] The actuator 10 includes bearings 80A and 80B that support the shaft body 74. The bearings 80A and 80B include a load-side bearing 80A arranged on the load side and a counter-load-side bearing 80B arranged on the counter-load side. The load-side bearing 80A in this embodiment is arranged between the shaft portion 56 of the crankshaft 40 of the shaft body 74 and the carrier 48. The counter-load-side bearing 80B in this embodiment is arranged between the shaft portion 56 of the crankshaft 40 of the shaft body 74 and the actuator casing 18. More specifically, the counter-load-side bearing 80B is arranged between the shaft body 74 and an inner periphery of the load-side cover 34 of the motor casing 26. Alternatively, the counter-load-side bearing 80B may be arranged between the shaft body 74 and a counter-load-side cover that is located on the counter-load side of the stator 24 and the rotor 22 and that is part of the motor casing 26. The bearings 80A and 80B are formed of various types of bearings, such as ball bearings and roller bearings.

[0027] The motor 12 includes a motor space 82 that accommodates at least a portion of the motor shaft 20. The motor space 82 accommodates the stator 24 and the rotor 22 in addition to the motor shaft 20. The motor space 82 is provided within the motor casing 26 on the load side of the anti-load side end 26a of the motor casing 26.

[0028] The reducer 14 includes a reducer space 84 that accommodates at least the external gear 44. The reducer space 84 accommodates the carrier 48 and the like in addition to the external gear 44. The reducer space 84 is provided inside the reducer casing 50 on the load side of the motor casing 26.

[0029] At least a portion of the motor space 82 is provided on the anti-load side of the load-side cover 34 of the motor casing 26, and at least a portion of the reducer space 84 is provided on the load side of the load-side cover 34. The load-side cover 34 functions as a partition wall that separates the reducer space 84 and the motor space 82 in the axial direction.

[0030] The reducer 14 includes sealing members 86A and 86B that seal the reducer space 84. In this embodiment, the sealing members 86A and 86B include a counter-load side sealing member 86A disposed between the motor casing 26 and the shaft 74, and a load side sealing member 86B disposed between the reducer casing 50 and the carrier 48. In this embodiment, the counter-load side sealing member 86A is incorporated between the outer ring and inner ring of the counter-load side bearing 80B, which constitutes a sealed bearing. Alternatively, the counter-load side sealing member 86A may be an oil seal or the like disposed between the inner periphery of the load side cover 34 of the motor casing 26 and the shaft 74. The counter-load side sealing member 86A separates the counter-load side motor space 82 from the load side reducer space 84.

[0031] The driver unit 16 is disposed on the opposite side to the load of the motor 12. The driver unit 16 includes a driver casing 88 and at least one circuit board 90A, 90B housed within the driver casing 88.

[0032] The driver casing 88 is fixed to the motor casing 26. The driver casing 88 is formed by combining multiple (three in this example) driver casing members 92. A bearing 98 for supporting the center pipe 76 is disposed between the driver casing 88 and the center pipe 76. In this embodiment, the bearing 98 is disposed in the anti-load side member 78 and supports the center pipe 76 via the anti-load side member 78.

[0033] The circuit boards 90A, 90B in this embodiment include a load side circuit board 90A and an anti-load side circuit board 90B fixed to the driver casing 88. A driver circuit for driving the motor 12 is incorporated into either of the circuit boards 90A, 90B.

[0034] The actuator 10 includes a first rotation detector 94 that detects rotation of the shaft 74 and a second rotation detector 96 that detects relative rotation between the actuator casing 18 and the carrier 48. The first rotation detector 94 includes a first detectable portion 94a fixed to the shaft 74 and a first detecting portion 94b mounted on the load side circuit board 90A. The second rotation detector 96 includes a second detectable portion 96a fixed to the anti-load side member 78 and a second detecting portion 96b mounted on the anti-load side circuit board 90B. For example, the detectable portions 94a, 96a are scales such as optical scales or magnetic scales, and the detecting portions 94b, 96b are sensors such as optical sensors or magnetic sensors.

[0035] The operation of the actuator 10 described above will now be described. When the stator 24 and rotor 22 generate a rotating magnetic field, the motor shaft 20 rotates, and the motor shaft 20 drives the crankshaft 40, causing the crankshaft 40 to rotate. When the crankshaft 40 rotates, the external gear 44 oscillates. When the external gear 44 oscillates, the meshing position between the external gear 44 and the internal gear 46 changes circumferentially. Accordingly, with each rotation of the crankshaft 40, one of the external gear 44 and the internal gear 46 (here, the external gear 44) rotates on its axis, and the rotation component is extracted by the output body 54 and output to the driven member. At this time, rotation slower than the rotation of the crankshaft 40 is output to the driven member.

[0036] Next, we will explain the balance weights 100A and 100B. A plurality of balance weights 100A and 100B with different eccentric phases are mounted on the shaft 74 so as to rotate together within the motor space 82. In this embodiment, the plurality of balance weights 100A and 100B consist of two balance weights: a load-side balance weight 100A (first balance weight) and an anti-load-side balance weight 100B (second balance weight). The anti-load-side balance weight 100B is mounted on the anti-load side of the load-side balance weight 100A. The balance weights 100A and 100B are mounted on the shaft 74 so as to be rotatable around the rotational center line C20 of the motor shaft 20. The directions from the rotational center line C20 of the motor shaft 20 toward the centers of gravity C100A and C100B of the balance weights 100A and 100B are referred to as eccentric directions D2 and D3. The eccentric direction of the load-side balance weight 100A is D2, and the eccentric direction of the anti-load-side balance weight 100B is D3. In this case, the eccentric phases of the balance weights 100A and 100B refer to the phases of the eccentric directions D2 and D3 of the balance weights 100A and 100B around the rotation center line C20.

[0037] To satisfy the condition of "plurality of balance weights with different eccentricity phases," it is sufficient that the eccentricity phases of at least two balance weights 100A, 100B are different. Therefore, to satisfy this condition, if there are three or more balance weights, the eccentricity phases of the third and subsequent balance weights may be the same as those of two balance weights with different eccentricity phases. In this embodiment, the eccentricity phases of the load-side balance weight 100A and the anti-load-side balance weight 100B are different. In other words, to satisfy the condition of "plurality of balance weights with different eccentricity phases," it is sufficient that there are a first balance weight (load-side balance weight 100A) and a second balance weight (anti-load-side balance weight 100B) with different eccentricity phases.

[0038] In this embodiment, the multiple balance weights 100A, 100B are integrally formed from the same member, but they may also be formed separately from different members. When the multiple balance weights 100A, 100B are integrally formed from the same member, multiple locations with different eccentricity phases that become the balance weights 100A, 100B are provided at different axial locations on the same member. In this embodiment, the balance weights 100A, 100B have the same cross-sectional shape in the axial direction. However, the cross-sectional shape may also change in the axial direction so as to change the amount of eccentricity while maintaining the same eccentricity phase. The latter cross-sectional shape is intended, for example, for cases in which the outer shape of the balance weight gradually becomes smaller or larger in the axial direction.

[0039] The centers of gravity C100A and C100B of the balance weights 100A and 100B are located radially eccentric to the rotational center line C20 of the motor shaft 20. The specific shape for achieving this is not particularly limited. For example, the balance weights 100A and 100B may be circular, centered on the centers of gravity C100A and C100B, like the eccentric portion 42, or may have other shapes. In this embodiment, the balance weights 100A and 100B are integrally formed with the motor shaft 20 using the same member as the motor shaft 20, but they may also be formed separately from the motor shaft 20. In this embodiment, the load-side balance weight 100A has an eccentricity phase opposite to that of the eccentric portion 42, i.e., its eccentricity phase is shifted by 180° from that of the eccentric portion 42. This means that the eccentric direction D2 of the load-side balance weight 100A and the eccentric direction D1 of the eccentric portion 42 are opposite to each other. To satisfy the condition "opposite" here, the eccentric phase of the load side balance weight 100A and the eccentric phase of the eccentric portion 42 may be shifted by 180°±several degrees. Also, in this embodiment, the anti-load side balance weight 100B has the same eccentric phase as the eccentric portion 42. This means that the eccentric direction D3 of the anti-load side balance weight 100B and the eccentric direction D1 of the eccentric portion 42 are the same. To satisfy the condition "same" here, the eccentric phase of the anti-load side balance weight 100B and the eccentric phase of the eccentric portion 42 may be shifted by several degrees.

[0040] The multiple balance weights 100A, 100B are provided on both axial sides of the rotor 22. In this embodiment, the load side balance weight 100A is provided on the axial load side of the rotor 22, and the anti-load side balance weight 100B is provided on the axial anti-load side of the rotor 22.

[0041] At least one of the multiple balance weights 100A, 100B is disposed in a position that radially overlaps the stator 24. In this embodiment, both the load side balance weight 100A and the anti-load side balance weight 100B satisfy this condition. Specifically, the load side balance weight 100A is disposed in a position that radially overlaps the load side portion of the stator 24. To achieve this, the load side balance weight 100A in this embodiment is disposed in a position that radially overlaps the load side coil end portion 30a of the stator 24. Furthermore, the anti-load side balance weight 100B is disposed in a position that radially overlaps the anti-load side portion of the stator 24. To achieve this, the anti-load side balance weight 100B in this embodiment is disposed in a position that radially overlaps the anti-load side coil end portion 30b of the stator 24.

[0042] Please refer to Figures 1 and 2. Figure 2 schematically shows an oscillating body 102 including the external gear 44, the shaft 74, bearings 80A and 80B, and balance weights 100A and 100B. The oscillating body 102 here refers to an object that oscillates integrally with the eccentric portion 42 and the external gear 44, and includes the eccentric bearing 64 in addition to the external gear 44 and eccentric portion 42.

[0043] 2A. When the external gear 44 oscillates due to the rotation of the shaft body 74, a centrifugal force F1 acts on the shaft body 74 due to the oscillation of the external gear 44. This centrifugal force F1 acts along the eccentric direction D1 of the eccentric portion 42. This centrifugal force F1 also causes a moment M1 around the bearings 80A and 80B to act on the shaft body 74. In other words, the oscillation of the external gear 44 causes the centrifugal force F1 and moment M1 to act on the shaft body 74. These centrifugal force F1 and moment M1 cause vibrations in the shaft body 74. For ease of explanation, only the moment M1 around the anti-load side bearing 80B is shown here.

[0044] 2(B) , the multiple balance weights 100A, 100B are configured to offset the centrifugal force F1 and the moment M1 around the bearings 80A, 80B that act on the shaft body 74 due to the oscillation of the external gear 44. The multiple balance weights 100A, 100B can also be said to be configured to apply centrifugal forces F2, F3 that offset the centrifugal force F1 to the shaft body 74, and to apply moments M2, M3 that offset the moment M1 to the shaft body 74. The multiple balance weights 100A, 100B can also be said to be configured to suppress vibration of the shaft body 74 caused by the centrifugal force F1 and the moment M1, respectively.

[0045] First, the conditions for canceling out centrifugal force F1 will be described. When shaft 74 rotates, centrifugal forces F2 and F3 act on shaft 74 due to the rotation of each of the balance weights 100A and 100B. Here, the centrifugal force acting due to the rotation of load-side balance weight 100A is designated F2, and the centrifugal force acting due to the rotation of anti-load-side balance weight 100B is designated F3. These centrifugal forces F2 and F3 act along the eccentric directions D2 and D3 of the balance weights 100A and 100B, respectively.

[0046] Centrifugal force F1 is expressed as the product of the eccentricity (mm) of eccentric portion 42 and the total weight (N) of oscillating body 102, as shown in the following formula (1). The eccentricity of eccentric portion 42 refers to the amount of deviation from the rotational center line C40 of crankshaft 40 to the center of gravity C42 of eccentric portion 42. When considering the total weight of oscillating body 102, the weight of the entire portion of crankshaft 40 that overlaps radially with eccentric portion 42 is defined as the weight of eccentric portion 42. Centrifugal force F1 = eccentricity of eccentric portion 42 × total weight of oscillating body 102 (1)

[0047] The centrifugal forces F2 and F3 are expressed as the product of the eccentricity (mm) of the balance weights 100A and 100B and the weights (N) of the balance weights 100A and 100B, as shown in the following equation (2). The eccentricity of the balance weights 100A and 100B refers to the deviation between the rotational center line C20 of the motor shaft 20 and the centers of gravity C100A and C100B of the balance weights 100A and 100B. When considering the weights of the balance weights 100A and 100B, the weight of the entire portion of the shaft 74 that radially overlaps with the balance weights 100A and 100B is defined as the weight of the balance weights 100A and 100B. For example, when considering the weight of the load-side balance weight 100A, the weight of the entire portion of the motor shaft 20 and crankshaft 40 that radially overlaps with the load-side balance weight 100A is defined as the weight of the load-side balance weight 100A. Centrifugal forces F2, F3 = eccentricity of balance weights 100A, 100B × weight of balance weights 100A, 100B (2)

[0048] The direction in which the centrifugal force F1 acts is called the X direction (the vertical direction in FIG. 2), and the direction perpendicular to the axial direction and the X direction is called the Y direction (the depth direction in FIG. 2). The X direction is parallel to the eccentric direction D1 of the eccentric portion 42.

[0049] Consider a case where centrifugal forces F2 and F3 containing only an X-direction component act on the shaft body 74. This refers to a case where only balance weights 100A and 100B are present that have the same or opposite eccentric phase as the eccentric phase of the eccentric portion 42, as in the present embodiment. In this case, the condition of canceling out the centrifugal force F1 is satisfied if the magnitude of the resultant force F(sum) of the centrifugal force F1 and the centrifugal forces F2 and F3 corresponding to each balance weight 100A and 100B is smaller than the magnitude of the centrifugal force F1. In other words, this condition is satisfied if at least a portion of the centrifugal force F1 acting from the external gear 44 is canceled out by the centrifugal forces F2 and F3 acting from each balance weight 100A and 100B.

[0050] Next, the conditions for canceling out moment M1 will be described. When shaft 74 rotates, moments M2 and M3 act on shaft 74 around bearings 80A and 80B due to centrifugal forces F2 and F3 corresponding to balance weights 100A and 100B, respectively. Here, the moment acting due to centrifugal force F2 corresponding to load-side balance weight 100A is referred to as M2, and the moment acting due to centrifugal force F3 corresponding to anti-load-side balance weight 100B is referred to as M3. Furthermore, L1 to L3 are the distances from a fulcrum, which is the center of rotation of the moments and is located axially at a position overlapping anti-load-side bearing 80B, to the force points at which centrifugal forces F1 to F3 are applied. Here, the fulcrum is the axial center of anti-load-side bearing 80B, and the axial center of eccentric portion 42 and balance weights 100A and 100B are referred to as force points at which centrifugal forces F1 to F3 are applied. Each moment M1 to M3 is expressed as the product of the centrifugal force F1 to F3 and the distance L1 to L3. For example, moment M1 is expressed as the product of centrifugal force F1 and distance L1 (= F1 × L1), moment M2 is expressed as the product of centrifugal force F2 and distance L2 (= F2 × L2), and moment M3 is expressed as the product of centrifugal force F3 and distance L3 (= F3 × L3).

[0051] Consider the case where centrifugal forces F2 and F3, each containing only an X-direction component, act on shaft 74, as in this embodiment. In this case, the condition for canceling out moment M1 is satisfied if the sum M (sum) of moment M1 corresponding to oscillator 102 and moments M2 and M3 corresponding to balance weights 100A and 100B is smaller than moment M1 corresponding to oscillator 102. In other words, this condition is satisfied if at least a portion of moment M1 acting on bearings 80A and 80B is canceled out by moments M2 and M3 acting from balance weights 100A and 100B.

[0052] For example, in this embodiment, the resultant force F(sum) of the centrifugal forces F1 to F3 described above is expressed as F1 + F3 - F2. Also, in this embodiment, the sum M(sum) of the moments M1 to M3 is expressed as M1 + M2 - M3. In this embodiment, the resultant force F(sum) of the centrifugal forces F1 to F3 is zero, which satisfies the following equation (3), and the centrifugal force F1 is completely canceled out. Also, in this embodiment, the sum M(sum) of the moments M1 to M3 described above is zero, which satisfies the following equation (4), and the moment M1 is completely canceled out. F1 + F3 - F2 = 0 ... (3) M1 + M2 - M3 = 0 ... (4)

[0053] Since the moments M1 to M3 are expressed as the products of the centrifugal forces F1 to F3 and the distances L1 to L3, the formula (4) can be expressed as the following formula (4)': F1×L1+F2×L2-F3×L3=0 (4)'

[0054] Thus, to cancel out the centrifugal force F1 and moment M1, F2, F3, L2, and L3 need only be set to satisfy equations (3) and (4)'. In this case, since there are two equations and four unknowns, by setting appropriate values ​​for two of the four unknowns, the magnitude of the remaining unknown can be determined from equations (3) and (4)'. For example, if we assume that F1 = F3 and L2 = L1 x 2, then equations (3) and (4)' yield F2 = F1 x 2, and L3 = L1 x 5. In other words, when F3 = F1, F2 = F1 x 2, L2 = L1 x 2, and L3 = L1 x 5, the centrifugal force F1 and moment M1 can be completely canceled out.

[0055] In this way, by providing multiple balance weights 100A, 100B with different eccentric phases, it becomes possible to cancel out the centrifugal force F1 and moment M1 corresponding to the oscillator 102. As described above, this is achieved by adjusting the eccentricity and weight of each balance weight 100A, 100B to change the centrifugal forces F2, F3 corresponding to each balance weight 100A, 100B, and by adjusting the axial position of each balance weight 100A, 100B to change the distances L2, L3 from the bearings 80A, 80B to each balance weight 100A, 100B. The specific examples of F2, F3, L2, and L3 given above are merely examples given for the purpose of explanation, and it goes without saying that they may be set to various sizes. Those skilled in the art can determine not only the conditions for completely canceling out the centrifugal force F1 and moment M1, but also the conditions for the centrifugal forces F2 and F3 and the distances L2 and L3 for at least partially canceling out the centrifugal force F1 and moment M1, without excessive trial and error, by using experiments, simulations, etc.

[0056] The condition of canceling out the centrifugal force F1 and moment M1 corresponding to the oscillator 102 need only be realized by using multiple balance weights 100A, 100B. When focusing on any one of the balance weights 100A, 100B, the centrifugal force and moment corresponding to that balance weight 100A, 100B may amplify the centrifugal force F1 and moment M1 without canceling them out. For example, in the illustrated example, when focusing on the moment M2 corresponding to the load side balance weight 100A, that moment M2 amplifies the moment M1, but it is sufficient that the moments M2 and M3 corresponding to the two balance weights 100A, 100B cancel out the moment M1.

[0057] The effects of the actuator 10 described above will now be described.

[0058] The multiple balance weights 100A, 100B are provided in the motor space 82. When providing the balance weights 100A, 100B on the shaft body 74, it is easier to ensure free space around the shaft body 74 in the motor space 82 than in the reducer space 84. This free space can be ensured, for example, in a position that radially overlaps with the stator 24. Providing the multiple balance weights 100A, 100B in this motor space 82 is advantageous for reducing the axial length of the actuator 10 compared to providing the balance weights 100A, 100B in the reducer space 84.

[0059] If only a single balance weight 100A, 100B were provided in the motor space 82, it would only be possible to offset either the centrifugal force F1 acting on the shaft body 74 due to the oscillation of the external gear 44 or the moment M1 around the bearings 80A, 80B. In contrast, if multiple balance weights 100A, 100B with different eccentric phases are provided, it would be possible to configure the balance weights 100A, 100B with different eccentric phases to offset each of the centrifugal force F1 and moment M1 acting on the shaft body 74 by adjusting their weights, eccentricity amounts, axial positions, eccentric phases, etc. This is more advantageous for suppressing vibrations occurring in the shaft body 74 than when only one of the centrifugal force F1 and moment M1 acting on the shaft body 74 can be canceled out. This advantageous suppression of vibrations occurring in the shaft body 74 also contributes to suppressing noise associated with that vibration.

[0060] If the crankshaft 40 includes eccentric portions 42 with different eccentric phases, the centrifugal forces and moments acting on the shaft body 74 can be balanced by adjusting the eccentric phases of the individual eccentric portions 42. For example, if the crankshaft 40 includes two eccentric portions 42, the balance of the centrifugal forces and moments can be achieved by shifting the eccentric phases of the individual eccentric portions 42 by 180°. In contrast, if the crankshaft 40 includes only eccentric portions 42 with a single eccentric phase, as in the present embodiment, the eccentric phases of the individual eccentric portions 42 cannot be adjusted in this manner. Therefore, in a structure such as the present embodiment, an imbalance in the centrifugal forces and moments acting on the shaft body 74 occurs, which causes the aforementioned vibration problem. According to the present embodiment, even in a structure in which vibration of the shaft body 74 is a problem, the use of multiple balance weights 100A, 100B as described above is particularly effective in effectively suppressing the vibration.

[0061] Thus, to solve the problem of "favorably suppressing vibrations" occurring in the shaft body 74, it is sufficient that multiple balance weights 100A, 100B with different eccentric phases are provided in the motor space 82 so as to be rotatable integrally with the shaft body 74. To solve this problem, it is not essential that the multiple balance weights 100A, 100B be configured to cancel out the centrifugal force F1 and the moment M1, respectively. In other words, to solve the problem of "favorably suppressing vibrations," it is sufficient to reduce the difficulty of achieving the vibration suppression, but achieving this is not essential. To achieve the effect of "favorably suppressing...," it can be said that it is sufficient to reduce the difficulty of achieving the mentioned effect, but achieving this effect is not essential.

[0062] The multiple balance weights 100A, 100B are provided on both axial sides of the rotor 22. Therefore, the individual balance weights 100A, 100B can be provided in the empty spaces on both axial sides of the rotor 22. This allows the empty spaces on both axial sides of the rotor 22 to be effectively utilized, which is further advantageous in reducing the axial length of the actuator 10.

[0063] At least one of the multiple balance weights 100A, 100B is provided at a position that radially overlaps with the stator 24. Therefore, the balance weights 100A, 100B are provided in the empty space at a position that radially overlaps with the stator 24, which is advantageous for reducing the axial length of the actuator 10 compared to when the balance weights 100A, 100B are provided in the reducer space 84.

[0064] The load side balance weight 100A has an eccentric phase opposite to that of the eccentric portion 42, and the anti-load side balance weight 100B has an eccentric phase that is the same as that of the eccentric portion 42. This simplifies the eccentric phases of the eccentric portion 42 and the balance weights 100A and 100B compared to when the eccentric phases of the balance weights 100A and 100B are opposite to or not the same as that of the eccentric portion 42.

[0065] Next, other features of the actuator 10 will be described. In this embodiment, as described above, F2 and F3 are set so as to satisfy the condition of formula (3) in order to cancel out the centrifugal force F1. As can be seen from formula (3), the centrifugal force F2 corresponding to the load-side balance weight 100A is greater than the centrifugal force F3 corresponding to the anti-load-side balance weight 100B. The eccentricities of the load-side balance weight 100A and the anti-load-side balance weight 100B are e2 and e3, respectively. Furthermore, the weights of the load-side balance weight 100A and the anti-load-side balance weight 100B are m2 and m3, respectively. In this case, to make the centrifugal force F2 greater than the centrifugal force F3, as can be seen from formula (2), the eccentricity e2 is made greater than the eccentricity e3, or the weight m2 is made greater than the weight m3.

[0066] To achieve this, in this embodiment, weight m2 is made greater than weight m3. This makes it easier to make centrifugal force F2 greater than centrifugal force F3 without making eccentricity e2 larger than eccentricity e3. This in turn makes it easier to reduce the radial length of load-side balance weight 100A, which is advantageous for reducing the radial length of actuator 10.

[0067] In this embodiment, to make weight m2 greater than weight m3, the axial length L100A of the load-side balance weight 100A is longer than the axial length L100B of the anti-load-side balance weight 100B (see also FIG. 1). Making length L100A longer than length L100B is advantageous for making weight m2 greater than weight m3. This allows weight m2 of the load-side balance weight 100A to be greater than weight m3 of the anti-load-side balance weight 100B with a simple configuration.

[0068] In this embodiment, the load side balance weight 100A and the anti-load side balance weight 100B are made of the same material. This material is, for example, a metal material such as a steel material. Alternatively, to make weight m2 greater than weight m3, the specific gravity of the load side balance weight 100A may be greater than the specific gravity of the anti-load side balance weight 100B. In this case, for example, the axial length L100A of the load side balance weight 100A and the axial length L100B of the anti-load side balance weight 100B do not matter, and they may be the same.

[0069] Next, variations of the components described above will be described.

[0070] Up to this point, the eccentric phases of the balance weights 100A and 100B have been described as being either opposite to or the same as the eccentric phase of the eccentric portion 42. As will be described next, the eccentric phases of the balance weights 100A and 100B are not limited to this.

[0071] Please refer to Figures 3(A) and (B). Figures 3(A) and (B) show an example in which three balance weights 100A, 100B, and 100C are provided on the shaft body 74. Each of the balance weights 100A to 100C is provided in the motor space 82. Other than the number of balance weights 100A to 100C, the same configuration as the actuator 10 of the embodiment may be applied. Figure 3(A) is a diagram showing centrifugal forces F1, F2x to F4x and moments M1, M2x to M4x acting on the shaft body 74 by the oscillator 102 and each of the balance weights 100A to 100C in a modified form, as viewed from the Y direction, and Figure 3(B) is a diagram showing the centrifugal forces F1 to F4 as viewed from the axial direction.

[0072] In this embodiment, the eccentric phases of the balance weights 100A, 100B, and 100C are offset by (180°+θ2), (180°-θ3), and θ4 from the eccentric phase of the eccentric portion 42 (not shown) of the oscillator 102. Centrifugal forces F2 to F4 are applied to the shaft 74 by the balance weights 100A, 100B, and 100C along directions that form angles θ2, θ3, and θ4 with respect to the X direction. In this embodiment, θ2, θ3, and θ4 are angles greater than 0° and less than 90°. The balance weights 100A to 100C apply centrifugal forces F2 to F4 that have a Y-direction component in addition to an X-direction component to the shaft 74. The distances from the fulcrum, which is the center of rotation of the moment and located axially overlapping the anti-load side bearing 80B, to the force points at which the centrifugal forces F2 to F4 are applied are designated L2 to L4. The definitions of the distances L2 to L4 are the same as those described above.

[0073] The X-direction components of each centrifugal force F2, F3, and F4 are designated as F2x, F3x, and F4x, and the Y-direction components are designated as F2y, F3y, and F4y. Furthermore, the moments acting on shaft 74 due to the X-direction components F2x, F3x, and F4x of each centrifugal force are designated as M2x, M3x, and M4x, and the moments acting on shaft 74 due to the Y-direction components F2y, F3y, and F4y of each centrifugal force are designated as M2y, M3y, and M4y. Moments M2x to M4x are moments about the Y-direction axis passing through bearings 80A and 80B, and moments M2y to M4y are moments about the X-direction axis passing through bearings 80A and 80B. Here, only the moment about anti-load side bearing 80B is considered.

[0074] In this case, to satisfy the condition that the centrifugal force X1 is offset by each balance weight 100A-100C, it is sufficient to maintain balance between the Y-direction components F2y-F4y of the centrifugal forces F2-F4 while at least a portion of the centrifugal force F1 is offset by the resultant force of the X-direction components F2x-F4x of the centrifugal forces F2-F4. Here, "maintaining balance between the Y-direction components F2y-F4y of the centrifugal forces F2-F4" means that the resultant force of the Y-direction components F2y-F4y of the centrifugal forces F2-F4 is zero.

[0075] Furthermore, to satisfy the condition that moment M1 is offset by each balance weight 100A-100C, it is sufficient to offset at least a portion of moment M1 with the sum of moments M2x-M4x corresponding to the X-direction components F2x-F4x of centrifugal forces F2-F4, while maintaining balance among moments M2y-M4y corresponding to the Y-direction components F2y-F4y of centrifugal forces F2-F4. Here, "maintaining balance among moments M2y-M4y" means that the sum of moments M2y-M4y corresponding to the Y-direction components is zero.

[0076] It should be noted that the magnitudes of θ2, θ3, θ4, F1 to F4, and L1 to L4 in the drawings are merely shown schematically and do not represent the exact magnitudes required to balance the centrifugal forces F1 to F4 and moments M1 to M4. Furthermore, as mentioned above, setting the resultant force of the Y-direction components F2y to F4y of the centrifugal forces F2 to F4 and the sum of the moments M2y to M4y corresponding to these Y-direction components F2y to F4y to zero includes not only setting them to mathematically strict zero, but also setting them to approximately zero.

[0077] For example, in this embodiment, the balance of the X-direction components of the centrifugal forces F1 to F4 is expressed by the following equation (5), and the balance of the Y-direction components is expressed by the following equation (6): F1+F4×cos θ4=F2×cos θ2+F3×cos θ3 (5) F2×sin θ2=F3×sin θ3+F4×sin θ4 (6)

[0078] In this embodiment, the balance of the moments M1, M2x to M4x about the Y axis is expressed by the following equation (7), and the balance of the moments M2y to My4 about the X axis is expressed by the following equation (8): M1+M2x+M3x=M4x (7) M2y=M3y+M4y (8)

[0079] When the moments M1, M2x to M4x, and M2y to M4y in equations (7) and (8) are expressed as the products of the centrifugal forces F1, F2x to F4x, and F2y to F4y and the distances L1 to L4, they can be expressed as the following equations (7)' and (8)': F1×L1+F2×cos θ2×L2+F3×cos θ3×L3=F4×cos θ4×L4 (7)' F2×sin θ2×L2=F3×sin θ3×L3+F4×sin θ4×L4 (8)'

[0080] To cancel out the centrifugal force F1 and moment M1, F2 to F4 and L2 to L4 need only be set to satisfy equations (5), (6), (7)', and (8)'. In this case, there are four equations and six unknowns (nine unknowns when θ2 to θ4 are added). Therefore, by setting appropriate values ​​for two of the unknowns F2 to F4 and L2 to L4 and then setting appropriate values ​​for θ2 to θ4, the magnitudes of the remaining unknowns can be determined from equations (5), (6), (7)', and (8)'. In this case, the resultant force of the X-direction components F2x to F4x of the centrifugal forces F2 to F4 completely cancels out the centrifugal force F1, while maintaining balance between the Y-direction components F2y to F4y of the centrifugal forces F2 to F4. Furthermore, the moment M1 is completely offset by the sum of the moments M2x to M4x corresponding to the X-direction components F2x to F4x of the centrifugal forces F2 to F4, while the balance of the moments M2y to M4y corresponding to the Y-direction components F2y to F4y of the centrifugal forces F2 to F4 can be maintained.

[0081] The angles of the eccentric phase of each balance weight 100A-100C relative to the eccentric phase of the eccentric portion 42, as well as the aforementioned F2-F4 and L2-L4, are merely examples given for the purpose of explanation and may, of course, be set to various values. Furthermore, the number of balance weights 100A-100C may be four or more. Furthermore, if the centrifugal forces F2-F4 of the balance weights 100A-100C include a Y-direction component, those skilled in the art can determine the conditions for the centrifugal forces F2-F4, distances L2-L4, and angles θ2-θ4 of each balance weight to partially cancel out the centrifugal forces F1 and M1, as well as the conditions for completely canceling out the centrifugal forces F1 and M1, without excessive trial and error, by using experiments, simulations, or the like.

[0082] The multiple balance weights 100A, 100B may be provided on only one axial side of the rotor 22. It is sufficient that at least one of the multiple balance weights 100A, 100B is provided in a position that radially overlaps with the stator 24. For example, either one of the load side balance weight 100A or the anti-load side balance weight 100B may be provided in a position that radially overlaps with the stator 24, and the other may be provided in a position that does not radially overlap with the stator 24.

[0083] The reducer 14 may be an eccentric oscillating reducer of a distribution type in which multiple crankshafts 40 are provided at positions radially offset from the oscillation center C44a of the external gear 44. In this case, the reducer 14 includes a distribution gear that rotates integrally with the motor shaft 20, a crankshaft gear that meshes with the distribution gear and rotates integrally with the crankshaft 40, and multiple crankshafts 40. In this case, the crankshafts 40 are driven by the motor shaft 20 as the rotation of the motor shaft 20 is transmitted via the distribution gear and the crankshaft gear. In this case, the shaft body 74 is considered to be formed by a combination of the motor shaft 20, the distribution gear, the crankshaft gear, and multiple crankshafts 40. In this case, the distribution gear and the crankshaft gear may have the same number of teeth to transmit rotation at a constant speed.

[0084] The above-described embodiments and variations are merely examples. The abstract technical ideas should not be interpreted as being limited to the contents of the embodiments and variations. Many design changes are possible in the contents of the embodiments and variations, such as changing, adding, or deleting components. In the above-described embodiments, the contents that allow such design changes are emphasized by adding the notation "this embodiment" or "embodiment." However, design changes are also permitted even in contents without such notation. Hatching on cross sections in the drawings does not limit the material of the hatched objects.

[0085] The structures and numerical values ​​referred to in the embodiments and variants naturally include those that can be considered to be the same when errors such as manufacturing errors and dimensional errors are taken into consideration. A component constituted by a single member in the embodiments may be constituted by multiple members. Similarly, a component constituted by multiple members in the embodiments may be constituted by a single member.

[0086] The present disclosure relates to actuators.

[0087] 10...actuator, 12...motor, 14...eccentric oscillating reducer, 20...motor shaft, 22...rotor, 24...stator, 40...crankshaft, 42...eccentric portion, 44...externally toothed gear, 74...shaft body, 80A, 80B...bearing, 82...motor space, 100A...load side balance weight, 100B...anti-load side balance weight

Claims

1. An actuator comprising: a motor having a motor shaft; a crankshaft driven by the motor shaft; and an eccentric swing type speed reducer having an external gear that swings by an eccentric portion of the crankshaft, wherein the motor includes a motor space that houses at least a part of the motor shaft, the crankshaft includes only the eccentric portion having a single eccentric phase as the eccentric portion, and a plurality of balance weights having different eccentric phases are provided integrally rotatably in the motor space on a shaft body including the motor shaft and the crankshaft.

2. The actuator according to claim 1, further comprising a bearing that supports the shaft body, wherein the plurality of balance weights are configured to cancel out, respectively, a centrifugal force acting on the shaft body due to the swing of the external gear and a moment around the bearing.

3. The actuator according to claim 1 or 2, wherein the motor includes a rotor provided rotatable integrally with the motor shaft, and the plurality of balance weights are provided on both axial sides with respect to the rotor.

4. The actuator according to any one of claims 1 to 3, wherein the motor includes a stator, and at least one of the plurality of balance weights is provided at a position radially overlapping the stator.

5. The actuator according to any one of claims 1 to 4, wherein the plurality of balance weights include a load-side balance weight and a counter-load-side balance weight, the load-side balance weight has an eccentric phase opposite to that of the eccentric portion, and the counter-load-side balance weight has the same eccentric phase as the eccentric portion.

6. The actuator according to claim 5, wherein a centrifugal force acting on the shaft body due to the rotation of the load-side balance weight is greater than a centrifugal force acting on the shaft body due to the rotation of the counter-load-side balance weight.

7. The actuator according to claim 6, wherein the weight of the load-side balance weight is greater than the weight of the counter-load-side balance weight.

8. The actuator according to claim 6 or 7, wherein an axial length of the load-side balance weight is greater than an axial length of the counter-load-side balance weight.

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