Actuator

Abstract

An object of the present invention is to provide an actuator capable of improving comprehensive reverse driving capability including a motor. The actuator (100) is provided with a motor (40) and a speed reducer (10) for reducing the rotation of the motor (40), the efficiency of the speed reducer (10) is 60% or more, and the motor (40) is a low-cogging-torque motor in which the reduction ratio of the cogging torque multiplied by the speed increase starting torque of the speed reducer (10) is equal to or less than the speed increase starting torque of the speed reducer (10).

Description

[0001] This application claims priority based on Japanese Patent Application No. 2023-146730 filed on September 11, 2023. The entire contents of the Japanese Patent Application are incorporated herein by reference. Technical Field

[0002] The present invention relates to an actuator. Background Art

[0003] An actuator that is a combination of a motor and a reducer is known. The inventor of the present application disclosed a joint of a robot in which an actuator having a motor and a reducer is assembled through Patent Document 1. In this document, based on the knowledge related to the influence of the reduction ratio of the reducer on the transmission efficiency of the reducer, an actuator that can cope with external force without relying on an external force sensor is disclosed.

[0004] Patent Document 1: Japanese Patent Application Publication No. 2021-030344

[0005] If the joints of the robot receive external forces from the arms through direct teaching or the like, the actuators of the joints are reversely driven (backdrive). In order to control the actuators with high precision, it is important to reduce the friction accompanying power transmission and improve the reverse drive capability (backdriveability).

[0006] From this point of view, the technology described in Patent Document 1 still has room for improvement in terms of enhancing the reverse driving capability of the entire actuator including the motor. Summary of the invention

[0007] The present invention has been made in view of such a problem, and an object of the present invention is to provide an actuator capable of improving the comprehensive reverse driving capability including a motor.

[0008] In order to solve the above problems, an actuator according to one embodiment of the present invention comprises a motor and a reducer for reducing the rotation of the motor. The efficiency of the reducer is 60% or more, and the motor is a low cogging torque motor whose reduction ratio of the cogging torque is less than the speed-increasing starting torque of the reducer.

[0009] In addition, any combination of the above-mentioned constituent elements or any form of substitution of constituent elements or expressions of the present invention in methods, systems, etc. may also be practiced as additional embodiments of the present invention.

[0010] According to the present invention, there is provided an actuator capable of improving the overall reverse driving capability including a motor. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 This is a diagram schematically showing an actuator according to an embodiment.

[0012] Figure 2 yes Figure 1 Side cross-sectional view of the reducer.

[0013] Figure 3 yes Figure 1 The front cross-sectional view of the reducer.

[0014] Figure 4 This is an illustration of the contact point trajectory.

[0015] Figure 5 It is a front cross-sectional view showing the first example of the motor.

[0016] Figure 6 This is a diagram showing the combination of the number of magnetic poles of the rotor and the number of slots of the stator core.

[0017] Figure 7 This is a diagram showing the combinations of the number of magnetic poles and the number of slots.

[0018] Figure 8 This is a front cross-sectional view showing a motor having a split-core type stator core.

[0019] Fig. 9 It is a front cross-sectional view showing a motor having an integral core type stator core.

[0020] Fig.10 It is a diagram showing the machined surface of the split-core type stator core.

[0021] Fig.11 This is an enlarged view showing the magnet arrangement surface of the rotor core.

[0022] Fig.12 This is a block diagram showing an example of a control structure of an actuator.

[0023] Fig.13 It is a graph showing the reverse driving resistance of the actuator.

[0024] Fig.14 is another diagram showing the reverse driving resistance of the actuator.

[0025] In the figure: 10-reducer, 40-motor, 42-output shaft, 50-stator, 51-stator core, 53-slot, 57-inner circumference, 58-outer circumference, 60-rotor, 61-rotor core, 62-magnet configuration surface, 65-magnet, 70-detection component, 80-control component, 90-output shaft, 100-actuator. DETAILED DESCRIPTION

[0026] The description begins with the background of the actuator of the present embodiment. As described above, the actuator is configured to be reversely driven (back-driven) if an external force is applied to the output shaft. In order to control the actuator with high precision, it is important to reduce the resistance (back-drive resistance) relative to the back-drive to improve the back-drive capability (back drivability). The back-drive capability of the actuator can also be said to be the degree of transmission difficulty of the output shaft being movable when an external force is applied to the output shaft of the actuator and the external force being transmitted to the input side of the actuator.

[0027] Therefore, the inventors of the present application studied the reverse driving resistance of an actuator including a motor and a speed reducer, and obtained the following findings.

[0028] Fig.13 This is a graph showing the reverse drive resistance Ra of a conventional actuator (hereinafter referred to as "actuator A"). The graph shows the reverse drive resistance Ra of actuator A relative to the rotation angle (horizontal axis) of the output shaft. The research results show that the reverse drive resistance of actuator A can be divided into the reverse drive resistance of the reducer part and the reverse drive resistance of the motor part. Fig.13 In the example, the reverse drive resistance of the speed reducer accounts for the majority. This is because the friction on the transmission path of the speed reducer is large and the efficiency is low.

[0029] Therefore, the inventor of the present application invented a speed reducer which reduces the friction of the transmission path and improves the efficiency. Fig.14 , the reverse drive resistance Rb relative to the rotation angle (horizontal axis) of an actuator (hereinafter referred to as "actuator B") in which a high-efficiency speed reducer is assembled on the motor of a conventional actuator. Fig.13 The vertical axis shows the magnified Fig.14 The vertical axis of Fig.14 As shown in the figure, in the actuator B with a highly efficient speed reducer, the reverse drive resistance of the speed reducer part is reduced, and the reverse drive resistance of the motor part is relatively strongly affected, and the balance of the comprehensive reverse drive capability is deteriorated. In other words, in the actuator B, there is still room for improvement in improving the comprehensive reverse drive capability including the motor.

[0030] The inventors of the present application have discovered that in actuator B, the influence of the cogging torque of the motor causes an imbalance in the comprehensive reverse drive capability. That is, the reverse drive resistance of the motor based on the cogging torque will be amplified to the reduction ratio of the reducer (= input speed / output speed, for example 50) times and affect the output shaft. In the previous actuator A, the reverse drive resistance of the reducer part was large, so the influence of the reverse drive resistance of the motor was ignored. In contrast, the inventors of the present application came up with the insight that the influence of the reverse drive resistance of the motor becomes greater in actuator B that adopts a high-efficiency reducer, and aimed to reduce this influence.

[0031] In view of these circumstances, the inventors of the present application have thought of assembling a motor with reduced cogging torque on a high-efficiency reducer in order to improve the comprehensive reverse driving ability including the motor. In particular, the inventors of the present application have found that if a motor whose cogging torque is suppressed by the control of a control member is assembled on a reducer with an efficiency of more than 60%, the comprehensive reverse driving ability including the motor will be significantly improved. Moreover, it is known that if a low cogging torque motor whose reduction ratio times the cogging torque (the result obtained by multiplying the cogging torque by the reduction ratio) is less than the speed-increasing starting torque of the reducer is used in order to reduce the cogging torque non-controllably, the comprehensive reverse driving ability including the motor can be further improved. The following is a specific description with reference to the embodiment.

[0032] Hereinafter, the preferred embodiments of the present invention will be described with reference to the accompanying drawings. In the following embodiments and modified examples, the same or equivalent components and parts are marked with the same symbols, and repeated descriptions are appropriately omitted. In addition, in order to facilitate understanding, the size of the components is appropriately enlarged or reduced in each figure. In addition, in each figure, a part of the components that are not important for the description of the embodiment is omitted.

[0033] Furthermore, terms including numbers such as 1 and 2 are used to describe various constituent elements, but these terms are only used to distinguish one constituent element from other constituent elements, and the constituent elements are not limited by these terms.

[0034] The terms used in this specification are defined.

[0035] (1) The efficiency of a speed reducer refers to the ratio of the output torque to the input torque and can be calculated using Equation 1.

[0036] Speed ​​reducer efficiency (%) = (output torque) / (input torque × speed reducer reduction ratio) × 100% ... (Formula 1)

[0037] (2) The operating rate of the actuator represents the ratio of the operating time TJ of the actuator to the operating time TR of the main machine (for example, a collaborative robot or a service robot) in which the actuator is assembled, and can be expressed as (TJ / TR)×100%[ED]. In addition, the operating time TR of the main machine itself can be defined as the power-on time of the main machine, or, in the case of a robot, it can be defined as the power-on time of the driving source (servo motor) that drives each joint. Therefore, the standby time of the main machine waiting for the setting of the next workpiece after working on a certain workpiece is also included in the operating time TR of the main machine itself. In addition, the operating time TJ of the actuator (reducer) can be defined as the time when the reducer, which is the object of the calculation of the operating rate, is driven, or the time when the driving source (servo motor) that drives the reducer rotates (is controlled by rotation).

[0038] (3) The speed-up starting torque of a speed reducer refers to the torque required to start the speed reducer from the output side under no-load conditions. In other words, when a torque greater than the speed-up starting torque acts on the speed reducer output shaft, the speed reducer input shaft will rotate at a higher speed if the speed reducer input shaft is set to no-load conditions.

[0039] (4) The reduction ratio of a speed reducer is the value obtained by dividing the input speed by the output speed. In other words, the speed reducer reduces the input speed to "1 / reduction ratio" and then outputs the speed. For example, when the input speed is reduced to "1 / 3", the reduction ratio is "3".

[0040] (5) The cogging torque of a motor refers to the resistance that can be felt even when no current is flowing (due to the action of the motor's components, namely the core and permanent magnets). The cogging torque is measured by the following method: the output shaft of the motor is driven externally to rotate at a low speed (for example, 0.5 to 5 r / min) while measuring the torque, and the torque variation is plotted as a graph to obtain the width from 0 to the peak value or the width from peak to peak value. For this measurement, for example, the "TS-8700Torque Station Pro" manufactured by ONO SOKKI CO., LTD. can be used. In addition, when the output shaft of an actuator (not a motor unit) is driven externally to rotate at a low speed while measuring the torque, as in Fig.14 As shown, the torque variation of the motor with the reducer part supplemented occurs, so after excluding the reducer part (moving it toward 0), the width from peak to peak is obtained or 1 / 2 of the width from peak to peak (equivalent to the width from 0 to the peak) is obtained.

[0041] In this embodiment, the reduction ratio of the cogging torque obtained based on the width from 0 to the peak is less than the speed-up starting torque of the reducer. More preferably, the reduction ratio of the cogging torque obtained based on the width from peak to peak is less than the speed-up starting torque of the reducer.

[0043] refer to Figure 1 , the overall structure of the actuator 100 involved in the embodiment is described. Figure 1 1 is a diagram schematically showing an actuator 100. The actuator 100 has a motor 40 and a reducer 10 that reduces the rotation of the motor 40. The output shaft 42 of the motor 40 is connected to the input shaft 12 of the reducer 10, so that the rotation of the motor 40 is input. The output member 16 of the reducer 10 functions as the output shaft 90 of the actuator 100. The reducer 10 of the embodiment is a high-efficiency reducer with an efficiency of more than 60%. The motor 40 of the embodiment is a low cogging torque motor with a reduction ratio of the cogging torque times less than the speed-increasing starting torque of the reducer. The actuator 100 of the embodiment has a detection component 70 and a control component 80. The control component 80 performs control to suppress the cogging torque of the motor 40.

[0044] Hereinafter, the configurations of the speed reducer 10 and the motor 40 will be described first, and the detection means 70 and the control means 80 will be described later.

[0045] refer to Figure 2 and Figure 3 , the reducer 10 is described. The inventor of the present application has obtained the knowledge that the efficiency of the reducer can be improved by reducing the friction loss of the gears, and the reducer 10 is an example of a reducer with improved efficiency based on this knowledge. The reducer 10 is an eccentric oscillating gear device having an external gear 22 and an internal gear 24 that mesh with each other. The external gear 22 and the internal gear 24 constitute a gear mechanism 14. The reducer 10 includes an input shaft 12 that receives input rotation from a motor 40, a gear mechanism 14 that transmits the rotation of the input shaft 12, an output member 16 that outputs the output rotation transmitted from the gear mechanism 14 to a driven device, a housing 18 that accommodates the gear mechanism 14, and wheel carriers 20A and 20B arranged on the side of the axial direction of the external gear 22.

[0046] The speed reducer 10 of the embodiment is an eccentric oscillating speed reducer including an external gear 22 and an internal gear 24 as a gear mechanism 14. The speed reducer 10 can transmit output rotation to the output member 16 by oscillating the external gear 22 using the eccentric body 30 of the crankshaft 26.

[0047] The input shaft 12 of the embodiment is a crankshaft 26. The crankshaft 26 includes a shaft body 28 and at least one (here, two) eccentric bodies 30 that can rotate integrally with the shaft body 28. The eccentric body 30 is eccentric with respect to the rotation center C26 of the crankshaft 26. The shaft body 28 and the eccentric body 30 may be configured as separate bodies or may be provided as part of the same component.

[0048] The external gear 22 is supported by the input shaft 12 via the bearing 32 in a relatively rotatable manner. The external gear 22 includes a plurality of external teeth 22a provided on the outer peripheral portion of the external gear 22 and a through hole 22b through which the input shaft 12 passes. The internal gear 24 includes an internal gear body 24a integrated with the housing 18 that accommodates the external gear 22 and a plurality of internal teeth 24b provided on the inner peripheral portion of the internal gear body 24a. The internal teeth 24b of the embodiment are directly formed on the inner peripheral surface of the internal gear body 24a.

[0049] The wheel carriers 20A and 20B of the embodiment are respectively arranged on both sides in the axial direction relative to the external gear 22. The wheel carriers 20A and 20B include a first wheel carrier 20A arranged on the opposite side of the input and a second wheel carrier 20B arranged on the input side. In the embodiment, the first wheel carrier 20A is formed by integrating a first wheel carrier component 20a arranged on the input side and a second wheel carrier component 20b arranged on the opposite side of the input. By passing through the inner pin 34 of the external gear 22, the wheel carriers 20A and 20B can be synchronized with the rotation component of the external gear 22 when the external gear 22 swings.

[0050] The bearing 32 supporting the external gear 22 includes a plurality of rolling elements 32a. The bearing 32 of the embodiment does not include a dedicated outer ring, and the inner peripheral surface of the through hole 22b of the external gear 22 also serves as the outer ring, and an outer rolling surface is provided on the inner peripheral surface. The bearing 32 of the embodiment does not include a dedicated inner ring, and the outer peripheral surface of the input shaft 12 (here, the outer peripheral surface of the eccentric body 30) also serves as the inner ring, and an inner rolling surface is provided on the outer peripheral surface. In addition, the bearing 32 may also include a dedicated outer ring and inner ring, and an outer rolling surface and an inner rolling surface are provided on them.

[0051] The operation of the above speed reducer is explained. If the input shaft 12 rotates based on the input rotation input from the motor 40, the eccentric body 30 of the crankshaft 26 causes the external gear 22 to swing. If the external gear 22 swings, the meshing position of the external gear 22 and the internal gear 24 changes in the circumferential direction in sequence. As a result, for each rotation of the crankshaft 26, either the external gear 22 or the internal gear 24 (here, the external gear 22) rotates by the amount of the difference in the number of teeth between the two. This rotation component is transmitted to the output component (here, it is transmitted to the wheel carrier 20A via the inner pin 34) and then output to the driven component as an output rotation.

[0052] refer to Figure 4 , the locus of the contact point between the outer gear 22 and the inner gear 24 (hereinafter referred to as the contact point locus) will be described. Figure 4This is an explanatory diagram of the contact point trajectory. Hereinafter, the radial direction with the center O2 of the internal gear 24 as the center is referred to as the "radial direction". Also, the straight line passing through the center O1 of the external gear 22 and the center O2 of the internal gear 24 when viewed from the axial direction of the internal gear 24 is referred to as the gear center line L1. Also, the rectangular coordinate system fixed relative to the gear center line L1 is referred to as the reference coordinate system. The origin of the reference coordinate system becomes the gear center of a certain gear, and one of its coordinate axes (y-axis) becomes the gear center line L1. In Figure 4 In FIG. 1 , the reference coordinate system becomes a stationary coordinate system that remains stationary even when the external gear 22 and the internal gear 24 are meshing.

[0053] The tooth addendum circle of the external gear 22 is referred to as the external tooth addendum circle C22, and the tooth addendum circle of the internal gear 24 is referred to as the internal tooth addendum circle C24. The external tooth addendum circle C22 refers to a circle formed by connecting the ends of the plurality of external teeth 22a of the external gear 22, and the internal tooth addendum circle C24 refers to a circle formed by connecting the ends of the plurality of internal teeth 24b of the internal gear 24. In the embodiment, the external tooth addendum circle C22 and the internal tooth addendum circle C24 are respectively circular.

[0054] The area surrounded by the external tooth top circle C22 and the internal tooth top circle C24 is called the meshing area R1. The meshing area R1 is formed on the radial inner side of the external tooth top circle C22 and the radial outer side of the internal tooth top circle C24. The meshing of the external gear 22 and the internal gear 24 is performed in the meshing area R1. The contact position of the tooth profile curve of the external gear 22 and the tooth profile curve of the internal gear 24 that mesh with each other is called the contact point C. The contact point C moves in the direction D1 (here, clockwise) in the reference coordinate system as the external gear 22 and the internal gear 24 mesh. The trajectory drawn by the contact point C that moves as the meshing is performed in the reference coordinate system is called the contact point trajectory Lc. The range with the contact point trajectory Lc in the meshing area R1 becomes the actual meshing range.

[0055] The node P of the external gear 22 and the internal gear 24 is the intersection of the common normal line L2 of the two tooth profile curves at the contact point C and the gear center line L1. The node P is the instantaneous center of relative motion between the external teeth of the external gear 22 and the internal teeth of the internal gear 24 that mesh with each other. In the case of an eccentric oscillating speed reducer or a simple planetary speed reducer, the node P is a fixed point that does not move in the reference coordinate system during the meshing process of the external gear 22 and the internal gear 24.

[0056] The intersection point of the normal line L3 (hereinafter referred to as the normal line L3) of the contact point trajectory Lc at the contact point C and the gear center line L1 is set as the intersection point K, and the length from the intersection point K to the node P is set as k. The normal line L3 is a straight line perpendicular to the tangent line of the contact point trajectory Lc at the contact point C. Figure 4As shown, the sign of k is positive when the intersection point K is located on the opposite side of the center O2 of the internal gear 24 from the node P, and is negative when the intersection point K is located on the center O2 side of the internal gear 24 from the node P.

[0057] In the reference coordinate system, the angle formed by the gear center line L1 with the node P as the center is defined as angle θ. Regarding angle θ, the side away from the contact point C in the movement direction D1 from the gear center line L1 is defined as positive.

[0058] The inventors of the present application have found that if the gear mechanism 14 (the external gear 22 and the internal gear 24 ) satisfies the three conditions described below, the friction loss of the gears is reduced.

[0059] (1) First condition: The pitch point P is located radially inward of each of the addendum circles C22 and C24.

[0060] (2) Second condition: The intersection point K is located between the node P and the center O1 of the external gear 22. This second condition needs to be satisfied throughout the entire process of the contact point C moving along the contact point trajectory Lc in the meshing region R1.

[0061] (3) Third condition: The contact point trajectory Lc is located within the angle range where the angle θ is 0 to π / 2 [Rad] in the meshing region R1.

[0062] The third condition can also be expressed as follows: in the meshing region R1, the contact point trajectory Lc does not exceed the angle range where the angle θ is 0 to π / 2 (the angle range where θ is less than 0 and exceeds π / 2). Figure 4 2 shows an example in which the contact point trajectory Lc is within the angular range from the position C0 where the angle θ is 0 to the position C1 where the angle θ is π / 2 (ie, the entire angular range in which the angle θ is 0 to π / 2).

[0063] By making the external gear 22 and the internal gear 24 satisfy the above three conditions, the speed reducer 10 of the embodiment achieves a high efficiency of 60% or more. The efficiency of the speed reducer 10 is more preferably 70% or more, and even more preferably 80% or more. The speed reducer 10 in this example achieves an efficiency of 75% to 85%.

[0064] Next, refer to Figure 5 , a first example of the motor 40 is described. Figure 5It is a front cross-sectional view showing the first example of the motor 40. The specific example of the low cogging torque motor is not particularly limited, for example, it can be a motor with a core or a motor without a core. The first example of the motor 40 is an ironless motor. The ironless motor is also called a gap winding motor (Gap Winding Motor), which includes a so-called slotless structure in which the pole-opposing surfaces of the stator core do not have teeth or slots, and a completely coreless structure without a stator core. The first example of the motor 40 has a slotless structure in which the inner circumference (pole-opposing surface) of the stator core 51 does not have teeth or slots.

[0065] The motor 40 has an annular stator 50 and a rotor 60 surrounded by the stator 50. The rotor 60 is rotatably supported by the stator 50 through a predetermined bearing member (not shown). The stator 50 has a hollow tubular stator core 51 made of a magnetic body and a plurality of (for example, 12) armature windings 56 fixed to the inner circumference of the stator core 51. The armature winding 56 is an air-core coil. The motor 40 is a three-phase motor, and the coil of each phase is composed of four armature windings 56 connected in series.

[0066] The rotor 60 has a rectangular cylindrical rotor core 61 made of a magnetic body and a plurality of (for example, 14) magnets 65 fixed to the outer peripheral surface of the rotor core 61. The surface of the magnet 65 facing the stator core 51 has an excitation magnetic pole, which supplies an excitation magnetic flux to the radial air gap (magnetic gap) between the stator 50 and the rotor 60. On the outer peripheral surface of the rotor core 61, a plurality of magnet arrangement surfaces 62 (for example, 14 surfaces) for arranging the magnets 65 are provided in the circumferential direction, and the cross section of the rotor core 61 is a tetradecagon when viewed from the axial direction. A cylindrical output shaft 42 is fixed to the rotation center of the rotor 60.

[0067] In the motor 40 , when a three-phase drive current is supplied to the armature winding 55 , the armature winding 55 generates a rotating magnetic field, which interacts with the field magnetic flux from the magnet 65 to generate torque on the rotor 60 and the output shaft 42 , thereby driving the input shaft 12 of the speed reducer 10 .

[0068] The motor 40 of the first example is a coreless motor, so the torque density of the motor is low, but even if the rotor 60 rotates, the magnetic resistance hardly changes, and the cogging torque caused by the change in magnetic resistance hardly occurs. Although the output torque of the motor 40 of the first example is small, by combining it with the high-efficiency reducer 10, an actuator 100 with practical performance can be realized. Regarding the actuator 100 having the motor 40 of the first example, since the reverse drive resistance of the motor is small, it is suitable for driving the joints of a collaborative robot that works with humans in the same space as humans. In particular, the actuator 100 equipped with the motor 40 of the first example is suitable for driving the joints of a collaborative robot with a low operating rate (for example, an operating rate of less than 20% ED).

[0069] refer to Figure 6 to Figure 11 , a second example of the motor 40 is described. The motor 40 of the second example is a motor with an iron core. The inventors of the present application have found that, with respect to the motor with an iron core, the reverse driving capability of the actuator can be improved by combining a motor having a structure for suppressing a cogging torque of an order lower than the least common multiple of the number of poles and the number of slots (hereinafter sometimes referred to as a "reduction structure") and a high-efficiency speed reducer.

[0070] As an example of a reduction structure, a multi-pole motor with a fractional slot structure (hereinafter referred to as a "fractional slot motor") can be cited. A fractional slot structure is a structure in which the number obtained by dividing the number of slots by the product of the number of poles and the number of phases (hereinafter referred to as "the number of slots per pole per phase") is a fraction, and can suppress low-order cogging torque compared to a structure in which the number of slots per pole per phase is an integer. The motor 40 of the second example adopts a fractional slot motor as a reduction structure.

[0071] Figure 6 1 is a diagram showing the combination of the number of magnetic poles P of the rotor 60 and the number of slots S of the stator core 51, and shows the winding coefficients for each combination of the number of magnetic poles P and the number of slots S. Figure 6 In the example, the winding coefficient is entered into the combination of the number of poles P and the number of slots S that is useful as a fractional slot motor. Figure 7 In the figure, the evaluation results based on simulation tests for the combinations of the number of poles P and the number of slots S with a winding coefficient exceeding 0.9 are indicated by symbols. The evaluation results show that the ratio of the number of poles P to the number of slots S (number of poles P: number of slots S) is 5:6, 7:6, 7:9, 8:9, 10:9 or 11:9 (in Figure 7 The combination represented by ◎ or ○ can suppress the low-order cogging torque. Among them, the combination represented by ◎ is particularly preferred.

[0072] Specifically, low-order cogging torque can be suppressed in a combination of 10 poles and 12 slots, 14 poles and 12 slots, 14 poles and 18 slots, 16 poles and 18 slots, 20 poles and 18 slots, 20 poles and 24 slots, 22 poles and 18 slots, 24 poles and 27 slots, 28 poles and 24 slots, 30 poles and 27 slots, 30 poles and 36 slots, or 32 poles and 36 slots.

[0073] The structure of the motor 40 of the second example will be described. Figure 8 and Fig. 9 It is a front cross-sectional view showing the structure of a motor 40 according to a second example. Figure 8 An example of a split core type stator core 51 (hereinafter, marked as 51A when necessary) is shown. Fig. 9 The example shown has a stator core 51 of an integral core type (hereinafter, referred to as 51B when necessary). In the following description, unless otherwise specified, it is assumed that the integral core type and the split core type are common.

[0074] In the second example, the motor 40 has an annular stator 50 and a rotor 60 surrounded by the stator 50. The rotor 60 is rotatably supported on the stator 50 by a predetermined bearing member (not shown). The stator 50 has a stator core 51 and a plurality of (for example, 12) armature windings 55. The stator core 51 has a plurality of (for example, 12) teeth 52 arranged at predetermined intervals in the circumferential direction and slots 53 arranged between the teeth 52, and is annular. Each armature winding 55 is installed in each slot 53. The motor 40 is a three-phase motor, and the coil of each phase is composed of four armature windings 55 connected in series.

[0075] The rotor 60 has a rectangular cylindrical rotor core 61 made of a magnetic body and a plurality of (for example, 14) magnets 65 fixed to the outer peripheral surface of the rotor core 61. The surface of the magnet 65 facing the stator core 51 has an excitation magnetic pole, which supplies an excitation magnetic flux to the radial air gap (magnetic gap) between the stator 50 and the rotor 60. On the outer peripheral surface of the rotor core 61, a plurality of magnet arrangement surfaces 62 (for example, 14 surfaces) for arranging the magnets 65 are provided in the circumferential direction, and the cross section of the rotor core 61 is a tetradecagon when viewed from the axial direction. A cylindrical output shaft 42 is fixed to the rotation center of the rotor 60.

[0076] In the motor 40 , when a three-phase drive current is supplied to the armature winding 55 , the armature winding 55 generates a rotating magnetic field, which interacts with the field magnetic flux from the magnet 65 to generate torque on the rotor 60 and the output shaft 42 , thereby driving the input shaft 12 of the speed reducer 10 .

[0077] The motor 40 of the second example is a fractional slot motor, so it can suppress the low-order cogging torque, but in addition to the high-order component of the ideal cogging torque, it also generates abnormal cogging torque of the number of poles or the number of slots. If the motor 40 is assembled to the reducer 10, the abnormal cogging torque generates a speed-up starting torque of the reduction ratio times. The results of the study found that, with respect to the cogging torque of the motor 40, by suppressing the speed-up starting torque of the reducer 10 times of the cogging torque to less than the speed-up starting torque of the reducer 10, the desired level of reverse drive resistance can be achieved.

[0078] Furthermore, the results of the study revealed that the main cause of the magnetic pole number component of the abnormal cogging torque is that the stator core 51 is incompletely deformed relative to the designed shape due to manufacturing errors, etc. In order to reduce this deformation, it is effective to ensure the core accuracy of the stator core 51.

[0079] When the split core type stator core 51A is used, in order to ensure the concentricity accuracy, at least one of the inner peripheral surface 57 and the outer peripheral surface 58 of the stator core 51A of the assembled stator 50 may be additionally processed by machining. Fig.101 is a diagram showing machined surfaces 572 and 582 of the stator core 51A. As shown in the figure, the inner peripheral surface 57 has a machined surface 572 that has been additionally processed, and the outer peripheral surface 58 has a machined surface 582 that has been additionally processed. If the machined surfaces 572 and 582 are provided, the concentricity accuracy of the stator core 51A can be improved. The split core type stator core 51A can be installed with the armature winding 55 in a split state, so the productivity is high and the slot fill rate of the coil can be improved.

[0080] Furthermore, in order to ensure the concentricity accuracy, a one-piece core type stator core 51B may be adopted. Compared with the split core type, the one-piece core type has less deformation, so the concentricity accuracy can be easily ensured.

[0081] Furthermore, the results of the study revealed that the abnormal cogging torque includes multiple components of the number of slots and the number of magnetic poles (hereinafter referred to as "multiple components"), and the main cause of the multiple components is the imbalance of the magnetic poles, which is the deviation of the magnetic force of the magnet 65 and the deviation of the attachment position of the magnet 65. There is already a suggestion to alleviate the deviation of the magnetic force of the magnet 65 by multipolarization. Therefore, the deviation of the attachment position of the magnet 65 is the cause of the slot number component and the multiple component.

[0082] It is generally believed that the magnet 65 is arranged at the center of the magnet arrangement surface 62 in the circumferential direction, but the deviation of the pasting position will become larger due to the dimensional tolerance of the components of the magnet 65 or the pasting accuracy during assembly. That is, a gap greater than the dimensional tolerance of the circumferential width of the magnet 65 will be set on the clamp supporting the magnet 65 during pasting, so the deviation of the pasting position of the magnet 65 will become larger corresponding to the gap amount. Therefore, the inventor of the present application proposed a structure in which the magnet 65 is arranged on one side of the circumferential direction of the magnet arrangement surface 62 in order to reduce the deviation of the pasting position of the magnet 65.

[0083] Fig.11 62 of the rotor core 61. As shown in the figure, in the embodiment, the magnet 65 is arranged on one side of the magnet arrangement surface 62 in the circumferential direction. Fig.11 In the example, the end face 67 of the magnet 65 is located at one end portion 63. The end face 67 may also be separated from the end portion 63. According to this structure, the end face 67 of one side of the magnet 65 can be abutted against the fixture for positioning without being affected by the gap between the fixture, thereby reducing the deviation of the pasting position of the magnet 65.

[0084] In the second example motor 40 configured as above, cogging torque including abnormal cogging torque is suppressed. Also, the actuator 100 including the second example motor 40 has a small reverse drive resistance and is therefore suitable for use in driving joints of a cooperative robot.

[0085] Next, a technique for suppressing the cogging torque of a motor using a control technique is described. The inventor of the present application has proposed a technique for suppressing the reverse drive resistance of an actuator having a motor and a reducer using a control technique. As a control technique, characteristic improvement can be performed based on feedforward or feedback that takes into account torque pulsation or cogging characteristics. As torque pulsation and cogging torque, cogging torque based on the relationship between the number of poles and the number of slots of a motor or cogging torque caused by manufacturing errors, etc. can be cited.

[0086] As the cogging torque caused by manufacturing errors, there are cogging torques generated in the form of multiple components of the number of slots due to deviations in the position of the magnet or the magnetic strength, and cogging torques generated in the form of multiple components of the number of rotor poles due to stator eccentricity or stator deformation. The cogging torques generated by these cogging torques include cogging torques of a lower order than the least common multiple of the number of magnetic poles and the number of slots of the motor. The specific control structure is described below.

[0087] refer to Fig.12 , the control structure of the actuator 100 is described. Fig.12 1 is a block diagram showing an example of a control structure of the actuator 100. The actuator 100 includes a detection member 70 for detecting a force acting on an output shaft 90 of the actuator 100 and a control member 80 for controlling the actuator 100 based on the detection result of the detection member 70. Fig.12 The structure includes control for feeding back the force acting on the output shaft 90 as torque and control for feeding forward cogging information for eliminating cogging torque.

[0088] The detection member 70 is not limited, but in this example, a strain gauge for detecting the moment load of the output shaft 90, an encoder for detecting the rotation angle θx of the output shaft 90, a current sensor for detecting the motor current Id, etc. can be cited. The detection member 70 can be one or two of the strain gauge, the encoder, and the current sensor. In addition, for example, it can be an encoder for detecting the rotation of the output shaft 42 of the motor, or it can detect the current command value of the motor drive unit 82. The detection member 70 of the embodiment includes a strain gauge 71, a torque conversion unit 74, an encoder 72, and a rotation angle conversion unit 75. The strain gauge 71 detects the moment load applied to the output shaft 90. The torque conversion unit 74 converts the detection result of the strain gauge 71 into a detection torque Tx for feedback. The encoder 72 is a rotary encoder for detecting the rotation of the output shaft 90. The rotation angle conversion unit 75 converts the detection result of the encoder 72 into the rotation angle θx of the output shaft 90.

[0089] The control member 80 is not limited, but in this example, the control member 80 includes a motor control unit 81, a motor drive unit 82, and a cogging information storage unit 83. The motor control unit 81 provides a torque command Ts of the motor 40 based on a comparison result of the rotation angle command θs and the rotation angle θx of the output shaft 90. The cogging information storage unit 83 is a storage member that stores cogging information related to the cogging torque of the motor 40. The motor drive unit 82 supplies a drive current Id to the motor 40 based on a result of adding the cogging information Tc to the comparison result of the torque command Ts and the detected torque Tx to drive the motor 40. The motor drive unit 82 can be configured to include an inversion circuit, for example.

[0090] The control means 80 performs control to suppress the cogging torque based on the cogging information stored in the cogging information storage unit 83. The control means 80 can suppress the reverse driving resistance caused by the cogging torque by, for example, feeding the cogging information forward to the motor driving unit 82.

[0091] As an example, the cogging information may be data for eliminating the cogging torque of the motor 40 that appears on the output shaft 90 of the actuator 100. In particular, the cogging information may be data in which the relationship between the cogging torque that appears on the output shaft 90 of the actuator 100 and the rotational position of the output shaft 90 is acquired in advance. The rotational position of the output shaft 90 may be acquired using the encoder 72.

[0092] The tooth groove information may be information common to a group of actuators 100 based on measurement data obtained during design, or may be individual information based on measurement data acquired from each actuator 100 .

[0093] The period of acquiring the cogging information and storing it in the cogging information storage unit 83 is not limited. For example, the cogging information may be stored before the actuator 100 is shipped, or a measurement mode for measuring the cogging torque may be installed in the actuator 100 and the cogging information may be acquired and stored at the client after the actuator 100 is shipped. Furthermore, the cogging information may be updated as needed.

[0094] The actuator 100 thus configured performs feedback control in such a manner that the rotation angle θx of the output shaft 90 approaches the rotation angle command θs, and performs feedforward control on the cogging information in such a manner that the cogging torque is eliminated. In particular, the control member 80 performs control to suppress the cogging torque of a lower order than the least common multiple of the number of magnetic poles P and the number of slots S of the motor 40. According to this structure, the reverse driving resistance of the actuator 100 is suppressed. Fig.12 The elements shown are merely examples, and various modifications are possible.

[0095] The features of the actuator 100 constructed as above are described. The actuator 100 is an actuator having a motor 40 and a reducer 10 for reducing the rotation of the motor 40, the efficiency of the reducer 10 is 60% or more, and the motor 40 is a low cogging torque motor whose reduction ratio of the cogging torque is less than the speed-up starting torque of the reducer 10.

[0096] According to this configuration, by assembling the motor 40 with reduced cogging torque on the high-efficiency speed reducer 10 , it is possible to improve the overall reverse driving capability of the actuator including the motor 40 .

[0097] The above is the description of the implementation mode.

[0098] The present invention has been described above based on the embodiments. These embodiments are examples, and various modifications and changes can be made within the technical scope of the present invention, and such modifications and changes also belong to the technical scope of the present invention, which is understandable to those skilled in the art. Therefore, the description and drawings in this specification should not be regarded as limiting, but should be regarded as illustrative.

[0099] (Variation Example)

[0100] In the following, a modification example is described. In the drawings and description of the modification example, the same reference numerals are given to the same or equivalent components and parts as those in the embodiment. The description repeated with the embodiment is appropriately omitted, and the structure different from the embodiment is described in detail.

[0101] The type of reducer is not particularly limited. For example, the reducer 10 may be a simple planetary reducer or a flexure meshing reducer in addition to an eccentric oscillating reducer. In the case of an eccentric oscillating reducer, its specific type is not particularly limited. Regarding its type, in addition to being a center crank type in which the crankshaft 26 is arranged at the center of the internal gear 24 as in the present embodiment, it may also be a distribution type in which a plurality of crankshafts are arranged at positions radially offset from the axis of the internal gear 24. Furthermore, in the case of an eccentric oscillating reducer, in addition to being able to swing the external gear 22, the internal gear 24 may also be able to swing. In the case of a flexure meshing reducer, its specific type is not particularly limited. Regarding the type of flexure meshing reducer, for example, in addition to being able to be a barrel type with two internal gears 24, it may also be a cup type or a top hat type with one internal gear 24. Furthermore, the reducer may function as any one of a reduction device, a speed increase device, and a power transmission device (power distribution device).

[0102] In the description of the embodiment, the wheel carrier 20A of the speed reducer 10 is shown as the output member 16 and the output shaft 90 of the actuator 100, but the present invention is not limited to this. For example, a structure in which the housing of the speed reducer is used as the output member to transmit the output rotation to the output shaft of the actuator may be adopted.

[0103] In the description of the embodiment, an example is shown in which the rotor 60 has a plurality of segmented magnets 65, but, for example, the rotor may also have an annular integral magnet. Furthermore, the type of motor is not particularly limited, and may be, for example, an outer rotor type or an axial gap type, and is not limited to a magnet motor. Furthermore, the motor does not necessarily have to have a cogging torque reduction ratio times less than the speed-up starting torque of the reducer, but may also be a motor in which the cogging torque reduction ratio times is slightly higher than the speed-up starting torque of the reducer. Even such a motor can improve the comprehensive reverse drive capability as an actuator when combined with a high-efficiency reducer by having various structures for suppressing the cogging torque described in the above embodiment (the structures described in claims 2 to 7, 9, and 11 of the initial application). In the embodiment, two methods are described, namely, a method for suppressing the cogging torque by improving the structure of the motor 40 and a method for suppressing the cogging torque by control. However, it is not necessary to have both at the same time, and it is sufficient to have one of them.

[0104] These modifications also have the same functions and effects as those of the embodiment.

[0105] Any combination of the above-mentioned embodiments and modifications is also effective as an embodiment of the present invention. A new embodiment generated by the combination has the effects of the combined embodiments and modifications.

Claims

1. An actuator comprising a motor and a speed reducer for reducing the rotation of the motor, wherein: The efficiency of the reducer is more than 60%, The motor is a low cogging torque motor whose reduction ratio of cogging torque is less than the speed-increasing starting torque of the reducer.

2. The actuator according to claim 1, characterized in that The motor is an ironless motor.

3. The actuator according to claim 2, characterized in that The actuator is an actuator that drives a joint of a collaborative robot having an operation rate of 20% ED or less.

4. The actuator according to claim 1, characterized in that The motor has a structure for suppressing a cogging torque of an order lower than the least common multiple of the number of magnetic poles and the number of slots of the motor.

5. The actuator according to claim 4, characterized in that The ratio of the number of poles to the number of slots, i.e. the number of poles: the number of slots, is 5:6, 7:6, 7:9, 8:9, 10:9 or 11:

9.

6. The actuator according to claim 5, characterized in that The combination of the number of magnetic poles and the number of slots is 10 poles and 12 slots, 14 poles and 12 slots, 14 poles and 18 slots, 16 poles and 18 slots, 20 poles and 18 slots, 20 poles and 24 slots, 22 poles and 18 slots, 24 poles and 27 slots, 28 poles and 24 slots, 30 poles and 27 slots, 30 poles and 36 slots, or 32 poles and 36 slots.

7. The actuator according to claim 1, characterized in that The motor has an integral core type stator core.

8. An actuator comprising a motor and a speed reducer for reducing the rotation of the motor, wherein: The efficiency of the reducer is more than 60%, The motor has an integral core type stator core.

9. The actuator according to claim 1, characterized in that The motor has a split-core stator core. At least one of the inner peripheral surface and the outer peripheral surface of the stator core has a machined surface.

10. An actuator comprising a motor and a speed reducer for reducing the rotation of the motor, wherein: The efficiency of the reducer is more than 60%, The motor includes a split core type stator core, and at least one of an inner peripheral surface and an outer peripheral surface of the stator core includes a machined surface.

11. The actuator according to claim 1, characterized in that The motor includes a rotor core having a plurality of magnet arrangement surfaces for arranging magnets arranged along a circumferential direction. The magnet is disposed biased toward one side in the circumferential direction of the magnet arrangement surface.

12. The actuator according to claim 1, characterized in that Also features: a detection member, used for detecting a force acting on an output shaft of the actuator; and A control member controls the actuator according to the detection result of the detection member.

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