A linear series elastic actuator with cooling

Abstract

The present invention belongs to the field of robots, specifically, a linear series elastic actuator with cooling, one end of the motor shaft is installed in the motor housing, the other end is inserted in the cooling device, the motor rotor is connected to the other end of the motor shaft, the motor stator is located outside the motor rotor and fixed in the cooling device; the lead screw nut of the ball screw is connected to the inside of one end of the motor shaft, one end of the ball screw passes through the motor shaft and the cooling device, and the other end is installed in the motor housing through the lead screw support; one end of the motor housing is connected to the cooling device, and the other end is connected to the rear connecting piece through the guide shaft, the actuator bracket is slidably installed on the guide shaft, and compression springs are provided between the motor housing and the rear connecting piece, a linear potentiometer is installed between the motor housing and the rear connecting piece, and the actuator bracket is connected to the linear potentiometer through the potentiometer connecting rod. The present invention has a compact structure, lightweight and miniaturized, and can output high power sustainably.

Description

Technical Field

[0001] The invention belongs to the field of robots, in particular to a linear series elastic actuator with cooling. Background Art

[0002] As a new type of actuator, linear series elastic actuator has attracted much attention from the robotics academic community and enterprises, and is used in various robotic mechanisms that require elasticity, such as bipedal walking robots, upper limb mechanisms, quadruped bionic robot leg mechanisms or exoskeletons.

[0003] Existing actuators can be based on four criteria: power source (electric or hydraulic), transmission system flexibility (rigid or elastic), transmission system type (direct, harmonic actuation, ball screw, etc.) and cooling type (air or liquid). Among them, one of the most powerful solutions is to combine hydraulics, liquid cooling, rigidity and direct drive. This can achieve high power-to-weight and torque-to-weight ratios, joint position controllability and shock tolerance. However, hydraulics are less energy efficient, mainly because they require more energy conversion. Typically, a gasoline engine or electric motor rotates a pump, which compresses hydraulic oil, which is regulated by a hydraulic servo valve, and finally causes the hydraulic piston to apply force. Each stage in this process will produce some efficiency loss, and the total loss can be very significant.

[0004] Although serial elastic actuators have been widely used in robotic systems, linear serial elastic actuators still face deficiencies in terms of precise force perception and parameter selection. In addition, compared with rigid drive devices, serial elastic actuators have higher volume, weight and cost due to the addition of flexible devices and position sensors. Therefore, it is an issue to be explored to promote the miniaturization and lightweight of serial elastic actuators and reduce the design cost while increasing the continuous output power of the actuator. Summary of the invention

[0005] In view of the above-mentioned defects or improvement needs of the existing linear series elastic actuator, the purpose of the present invention is to provide a linear series elastic actuator with cooling. The elastic actuator improves the continuous output power of the actuator through liquid cooling, and makes the structure compact and small in size through the reasonable arrangement of the mechanism; at the same time, by measuring the deformation of the elastic body, the force condition of the actuator can be obtained to achieve precise force control.

[0006] The objective of the present invention is achieved through the following technical solutions:

[0007] The present invention comprises a motor housing, a motor assembly, a screw assembly, a cooling device, a compression spring assembly and a linear potentiometer, wherein the motor assembly comprises a motor shaft, a motor stator and a motor rotor, the screw assembly comprises a ball screw and a screw support, one end of the motor shaft is rotatably mounted in the motor housing, and the other end is inserted in the cooling device, the motor stator and the motor rotor are both accommodated in the cooling device, the motor rotor is connected to the outer surface of the other end of the motor shaft, the motor stator is located outside the motor rotor and is fixed to the cooling device; the screw nut of the ball screw is connected to the inside of one end of the motor shaft, and one end of the ball screw is supported by the motor The motor housing is connected to the cooling device at one end, and the other end is connected to the rear connecting piece at the other end through the guide shaft. The actuator bracket is slidably mounted on the guide shaft. Compression springs are arranged between the actuator bracket and the motor housing and the rear connecting piece. A linear potentiometer for measuring the relative displacement between the actuator bracket and the motor housing is arranged between the motor housing and the rear connecting piece. The linear potentiometer is installed on the motor housing, and the actuator bracket is connected to the linear potentiometer through a potentiometer connecting rod.

[0008] Wherein: the cooling device includes a cooling jacket and a motor cooling shell, the cooling jacket is sealed and connected to one end of the motor shell, the motor cooling shell is nested in the cooling jacket, the motor stator and the motor rotor are both accommodated in the motor cooling shell, a spiral water groove is axially provided on the outer surface of the motor cooling shell, a water inlet and a water outlet are respectively provided on the cooling jacket, and the water inlet and the water outlet are respectively connected to the spiral water groove.

[0009] A sealing groove A and a sealing groove B are respectively provided on the outer surface of the motor cooling shell, and the spiral water groove, water inlet and water outlet are all located between the sealing groove A and the sealing groove B. O-rings for forming a seal with the cooling sleeve are respectively installed in the sealing groove A and the sealing groove B.

[0010] An encoder is provided at the other end of the motor shaft, and the encoder includes an encoder stator disk and an encoder movable disk. The encoder stator disk is fixedly connected to the inside of the cooling device, and the encoder movable disk is located on the inner side of the encoder stator disk and is fixedly connected to the other end of the motor shaft. An encoder end cover connected to the cooling device is provided on the outer side of the encoder stator disk.

[0011] The encoder is a magnetic encoder, and an iron sheet installed in a cooling device is provided between the motor assembly and the encoder.

[0012] One end of the motor shaft is rotatably mounted inside the motor housing via a ball bearing, the outer ring of the ball bearing is axially limited by a positioning sleeve sleeved on the motor shaft, the inner ring of the ball bearing is locked and limited by a locking positioning sleeve mounted on the motor shaft, and there is a clearance fit between the ball bearing and the inner wall of the motor housing to limit the radial movement of the ball screw.

[0013] There are multiple guide shafts between the other end of the motor housing and the rear connecting piece, and they are respectively passed through the actuator bracket. A bushing is provided between each guide shaft and the actuator bracket, and the guide shaft and the actuator bracket are guided by the bushing; the bushing is axially limited by a bushing shoulder on one side of the actuator bracket, and the bushing shoulder is installed on the actuator bracket.

[0014] A compression spring A is provided between the actuator bracket and the rear connecting piece, and the two ends of the compression spring A are respectively abutted against the rear connecting piece and the actuator bracket; a compression spring B is provided between the actuator bracket and the motor housing, and the two ends of the compression spring B are respectively abutted against the motor housing and the actuator bracket.

[0015] One end of the potentiometer connecting rod passes through a threaded hole opened on the actuator bracket and is locked and fixed by a nut. The other end of the potentiometer connecting rod is connected to a slider of the linear potentiometer, and the slider is slidably installed in a slide groove opened on the linear potentiometer.

[0016] The length direction of the slide groove is the same as the axial direction of the ball screw, and the slide groove is parallel to the ball screw; the potentiometer connecting rod is parallel to the ball screw.

[0017] The advantages and positive effects of the present invention are:

[0018] 1. The series elastic actuator proposed in the present invention is provided with a cooling device, which can effectively improve the continuous output power of the actuator.

[0019] 2. The present invention utilizes the advantages of the torque motor to achieve the advantages of compact structure and miniaturized design of the actuator; the shell is made of aluminum alloy, the whole is easy to install, and the mass and volume are small.

[0020] 3. In addition to the actuator bracket being fixedly connected to the ground bracket, the entire joint is moved by a guide shaft, thereby compressing the mold spring and making the entire joint flexible.

[0021] 4. The actuator of the present invention can measure the external force and realize precise force control. It is cheaper than the traditional method of using a torque sensor to measure the torque at the output end of the motor, and is safer and has a good buffering effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic diagram of the overall structure of the present invention;

[0023] Figure 2 It is a cross-sectional view of the internal structure of the present invention;

[0024] Figure 3 This is a schematic diagram of the structure of the present invention after the compression springs on both sides of the actuator bracket are removed;

[0025] Figure 4 It is a schematic diagram of the internal structure of the actuator bracket of the present invention;

[0026] Figure 5A It is a schematic diagram of the external structure of the cooling device of the present invention;

[0027] Figure 5B It is a schematic diagram of the internal structure of the cooling device of the present invention;

[0028] Figure 6 It is a structural schematic diagram of the encoder of the present invention;

[0029] Figure 7 It is a schematic diagram of the end surface structure of the actuator bracket facing the motor housing of the present invention;

[0030] Figure 8 It is a partial enlarged view of the linear potentiometer of the present invention;

[0031] Among them: 1 is a ball screw, 2 is an encoder end cover, 3 is a water inlet, 4 is a water outlet, 5 is a motor housing, 6 is a rear connector, 7 is a compression spring A, 8 is an actuator bracket, 9 is a compression spring B, 10 is a cooling jacket, 11 is a motor shaft, 12 is a screw support, 13 is a screw nut, 14 is a linear potentiometer, 15 is a potentiometer connecting rod, 16 is a guide shaft, 17 is a motor cooling housing, 18 is a motor stator, 19 is a motor rotor, 20 is an encoder static disk, 21 is an encoder dynamic disk, 22 is a ball bearing, 23 is a locking and positioning sleeve, 24 is a potentiometer clamping piece, 25 is a potentiometer connecting piece, 26 is a bushing, 27 is a sealing groove A, 28 is a sealing groove B, 29 is a rectangular spiral water trough, 30 is an iron sheet, 31 is a slider, 32 is a slide groove, 33 is a nut, 34 is a bushing shoulder, and 35 is a positioning sleeve. DETAILED DESCRIPTION

[0032] The present invention will be further described below in conjunction with the accompanying drawings.

[0033] like Figures 1 to 8 As shown, the present invention includes a motor housing 5, a motor assembly, a screw assembly, a cooling device, a compression spring assembly and a linear potentiometer 14.

[0034] The motor assembly of this embodiment includes a motor shaft 11, a motor stator 18, a motor rotor 19, an encoder and an iron sheet 30. One end of the motor shaft 11 is rotatably mounted in the motor housing 5, and the other end is inserted in the cooling device. The motor stator 18 and the motor rotor 19 are both contained in the cooling device. The motor rotor 19 is bonded to the outer surface of the other end of the motor shaft 11. The motor stator 18 is located outside the motor rotor 19 and bonded to the cooling device. An encoder is provided at the other end of the motor shaft 11. The encoder includes an encoder static disk 20 and an encoder dynamic disk 21. The encoder static disk 20 is fixedly connected to the inside of the cooling device. The encoder dynamic disk 21 is located on the inner side of the encoder static disk 20 and is fixedly connected to the other end of the motor shaft 11. The outer side of the encoder static disk 20 is provided with an encoder end cover 2 connected to the cooling device. The encoder of this embodiment is a commercially available product, a magnetic encoder purchased from Guangdong Yingdong High-Tech Automation Co., Ltd., model CAPRO-S060020. Since a magnetic encoder is used and the motor rotor 19 has a strong magnet, an iron sheet 30 installed in a cooling device is provided between the motor assembly and the encoder to change the motor magnetic field distribution and protect the magnetic encoder.

[0035] The screw assembly of this embodiment includes a ball screw 1 and a screw support 12. The screw nut 13 of the ball screw 1 is threadedly connected to the inside of one end of the motor shaft 11 and is linked to the motor shaft 11. The inside of the screw nut 13 is connected to the ball screw 1 through a ball installed in the spiral path. One end (front end) of the ball screw 1 passes through the motor shaft 11 and the cooling device and is connected to the end of the shank connecting rod. The other end (rear end) of the ball screw 1 is fixed with a retaining spring to the screw support 12, and is installed in the motor housing 5 through the screw support 12, so that the ball screw 1 can be extended and retracted in the motor housing 5. One end of the motor shaft 11 of this embodiment is rotatably installed in the motor housing 5 through a ball bearing 22. The outer ring of the ball bearing 22 is axially limited by a positioning sleeve 35 sleeved on the motor shaft 11. The inner ring of the ball bearing 22 is locked and limited by a locking positioning sleeve 23 installed on the motor shaft 11. There is a clearance fit between the ball bearing 22 and the inner wall of the motor housing 5 to limit the radial movement of the ball screw 1. The lead screw nut 13 is driven by the motor assembly and rotated by the motor shaft 11 ; the lead screw nut 13 is installed in the motor housing 5 through the ball bearing 22 on the motor shaft 11 , so that the lead screw nut 13 is axially fixed.

[0036] The compression spring assembly of this embodiment includes a compression spring A7, an actuator bracket 8, a compression spring B9 and a guide shaft 16. One end of the motor housing 5 is connected to the cooling device, and the other end is connected to the rear connecting member 6 through the guide shaft 16. The compression assembly is located between the motor housing 5 and the rear connecting member 6. The actuator bracket 8 is fixedly connected to the ground bracket and slidably installed on the guide shaft 16. Compression springs are provided between the actuator bracket 8 and the motor housing 5 and the rear connecting member 6. A compression spring A7 is provided between the actuator bracket 8 and the rear connecting member 6. The two ends of the compression spring A7 abut against the rear connecting member 6 and the actuator bracket 8 respectively. A compression spring B9 is provided between the actuator bracket 8 and the motor housing 5. The two ends of the compression spring B9 abut against the motor housing 5 and the actuator bracket 8 respectively. The compression spring A7 and the compression spring B9 are both in a pre-compression state when installed and have a pre-compression amount. A linear potentiometer 14 installed on the motor housing 5 is provided between the motor housing 5 and the rear connecting member 6. The relative displacement between the actuator bracket 8 and the motor housing 5 is measured by the linear potentiometer 14. There are multiple guide shafts 16 (four in this embodiment) between the other end of the motor housing 5 and the rear connecting member 6, and they are respectively passed through the actuator bracket 8. The relative displacement between the actuator bracket 8 and the motor housing 5 is achieved by relative sliding of each guide shaft 16. A bushing 26 is provided between each guide shaft 16 and the actuator bracket 8, and the guide shaft 16 and the actuator bracket 8 are guided by the bushing 26; the bushing 26 is axially limited by the bushing shoulder 34 on one side of the actuator bracket 8, and the bushing shoulder 34 is installed on the actuator bracket 8.

[0037] The actuator bracket 8 is connected to the linear potentiometer 14 through the potentiometer connecting rod 15. One end of the linear potentiometer 14 is fixedly mounted on the motor housing 5 through the potentiometer connecting piece 25, and the other end is pressed on the motor housing 5 through the potentiometer clamping piece 24. The linear potentiometer 14 of this embodiment is a commercially available product purchased from Tianjin Novotek Automation Technology Co., Ltd., model PTP-0050-111-002-001. A slide groove 32 is provided on the linear potentiometer 14, and the length direction of the slide groove 32 is the same as the axial direction of the ball screw 1, and the slide groove 32 is parallel to the ball screw 1. A slider 31 is slidably installed in the slide groove 32, one end of the potentiometer connecting rod 15 passes through the threaded hole provided on the actuator bracket 8, and is locked and fixed by a nut 33, and the other end of the potentiometer connecting rod 15 is connected to the slider 31 of the linear potentiometer 14. The potentiometer connecting rod 15 is pressed into the sliding groove 32 in a direction parallel to the sliding groove 32 , and the potentiometer connecting rod 15 is parallel to the ball screw 1 .

[0038] The cooling device of this embodiment includes a cooling jacket 10 and a motor cooling shell 17. The cooling jacket 10 is sealed and connected to one end of the motor housing 5. The motor cooling shell 17 is concentrically pressed into the cooling jacket 10 and is firmly glued with a sealant to prevent water leakage. The motor stator 18 and the motor rotor 19 are both accommodated in the motor cooling shell 17. The motor stator 18 and the motor cooling shell 17 are glued together. The other end of the motor shaft 11 extends into the motor cooling shell 17. The encoder end cover 2 is connected to the outer end of the motor cooling shell 17. The encoder stator 20 is fixed to the motor cooling shell 17, and the iron sheet 30 is fixed in the positioning hole of the motor cooling shell 17. In order to improve the continuous output power of the linear series elastic actuator, a spiral water groove is provided in the axial direction on the outer surface of the motor cooling shell 17. The spiral water groove in this embodiment is a rectangular spiral water groove 29. The cooling jacket 10 is provided with a water inlet 3 and a water outlet 4. One end of the water inlet 3 and the water outlet 4 are respectively connected to the rectangular spiral water groove 29, the other end of the water inlet 3 is connected to one end of the water inlet pipe, and the other end of the water outlet 4 is connected to one end of the water outlet pipe. The other end of the water inlet pipe and the other end of the water outlet pipe are respectively connected to a water pump. A sealing groove A27 and a sealing groove B28 are also provided on the outer surface of the motor cooling shell 17. The rectangular spiral water groove 29, the water inlet 3 and the water outlet 4 are all located between the sealing groove A27 and the sealing groove B28. O-type sealing rings for forming a seal with the cooling jacket 10 are respectively installed in the sealing groove A27 and the sealing groove B28. The water from the water pump enters the water inlet 3 of the cooling jacket 10, passes through the rectangular spiral water groove 29 of the motor cooling shell 17, and finally exits through the water outlet 4 of the cooling jacket 10, thus realizing the cooling system circulation.

[0039] The working principle of the present invention is:

[0040] When the linear series elastic actuator of the present invention is working, the motor rotor 19 rotates according to the control signal input by the control system (the control system of the present invention is the prior art), provides a torque, drives the motor shaft 11 to rotate, and outputs to the screw nut 13, drives the screw nut 13 to rotate; the ball bearing 22 on the motor shaft 11 is installed in the motor housing 5, so that the screw nut 13 is axially fixed; at the same time, the inner ring of the ball bearing 22 is locked with a locking sleeve 23, and there is a clearance fit between the ball bearing 22 and the inner wall of the motor housing 5, which limits the radial movement of the screw nut 13. As the screw nut 13 rotates, the ball screw 1 is driven to extend and retract in the motor housing 5 to make linear motion. The actuator bracket 8 is fixedly connected to the ground bracket. Since the entire series elastic actuator moves through the guide shaft 16 except the actuator bracket 8, and the compression spring A7 and the compression spring B9 are both in a pre-compressed state when installed, and have a pre-compression amount, the stiffness of the overall series elastic actuator is twice that of a compression spring. When one end of the ball screw 1 is subjected to a force to the left (i.e., under the action of an external load), the motor housing 5 and the actuator bracket 8 form a relative displacement, and the compression spring B9 on the right is compressed again; the axial force is transmitted from the screw nut 13 to the motor housing 5 and to the compression spring B9 on the right; at the same time, the linear potentiometer 14 measures the deformation of the compression spring B9, and the force control of the series elastic actuator can be achieved based on the deformation value and the measured spring stiffness curve. At the same time, the cooling device circulates the cooling of the motor, which increases the continuous output power of the series elastic actuator.

[0041] The motor of the present invention is a torque motor, which is used to provide rotation speed and torque. The encoder can measure the rotation of the torque motor, thereby facilitating the control of the torque motor by the control system.

[0042] The present invention realizes the advantages of compact structure and miniaturized design of the series elastic actuator, and effectively improves the continuous output power of the series elastic actuator.

Claims

1. A linear series elastic actuator with cooling, characterized in that: The invention comprises a motor housing (5), a motor assembly, a screw assembly, a cooling device, a compression spring assembly and a linear potentiometer (14), wherein the motor assembly comprises a motor shaft (11), a motor stator (18) and a motor rotor (19), the screw assembly comprises a ball screw (1) and a screw support (12), one end of the motor shaft (11) is rotatably mounted in the motor housing (5), and the other end is inserted in the cooling device, the motor stator (18) and the motor rotor (19) are both accommodated in the cooling device, the motor rotor (19) is connected to the outer surface of the other end of the motor shaft (11), the motor stator (18) is located outside the motor rotor (19) and is fixed to the cooling device; the screw nut (13) of the ball screw (1) is connected to the inside of one end of the motor shaft (11), and one end of the ball screw (1) is connected to the inside of the motor shaft (11), and the motor stator (18) and the cooling device are fixed to the cooling device; The cooling device is passed through the motor housing (5), and the other end of the ball screw (1) is installed in the motor housing (5) through the screw support (12); the compression spring assembly includes a compression spring, an actuator bracket (8) and a guide shaft (16); one end of the motor housing (5) is connected to the cooling device, and the other end is connected to the rear connecting member (6) through the guide shaft (16); the actuator bracket (8) is slidably installed on the guide shaft (16); compression springs are provided between the actuator bracket (8) and the motor housing (5) and the rear connecting member (6); a linear potentiometer (14) for measuring the relative displacement between the actuator bracket (8) and the motor housing (5) is provided between the motor housing (5) and the rear connecting member (6); the linear potentiometer (14) is installed on the motor housing (5); and the actuator bracket (8) is connected to the linear potentiometer (14) through a potentiometer connecting rod (15); The cooling device comprises a cooling jacket (10) and a motor cooling shell (17); the cooling jacket (10) is sealedly connected to one end of a motor shell (5); the motor cooling shell (17) is nested in the cooling jacket (10); the motor stator (18) and the motor rotor (19) are both accommodated in the motor cooling shell (17); a spiral water groove is axially provided on the outer surface of the motor cooling shell (17); a water inlet (3) and a water outlet (4) are respectively provided on the cooling jacket (10); the water inlet (3) and the water outlet (4) are respectively connected to the spiral water groove.

2. The linear series elastic actuator with cooling according to claim 1, characterized in that: A sealing groove A (27) and a sealing groove B (28) are respectively formed on the outer surface of the motor cooling housing (17); the spiral water groove, the water inlet (3) and the water outlet (4) are all located between the sealing groove A (27) and the sealing groove B (28); and O-rings for forming a seal with the cooling jacket (10) are respectively installed in the sealing groove A (27) and the sealing groove B (28).

3. The linear series elastic actuator with cooling according to claim 1, characterized in that: An encoder is provided at the other end of the motor shaft (11), and the encoder comprises an encoder stator (20) and an encoder movable disk (21). The encoder stator (20) is fixedly connected to the interior of the cooling device, and the encoder movable disk (21) is located on the inner side of the encoder stator (20) and is fixedly connected to the other end of the motor shaft (11). An encoder end cover (2) connected to the cooling device is provided on the outer side of the encoder stator (20).

4. The linear series elastic actuator with cooling according to claim 3, characterized in that: The encoder is a magnetic encoder, and an iron sheet (30) installed in a cooling device is provided between the motor assembly and the encoder.

5. The linear series elastic actuator with cooling according to claim 1, characterized in that: One end of the motor shaft (11) is rotatably mounted inside the motor housing (5) via a ball bearing (22); the outer ring of the ball bearing (22) is axially limited by a positioning sleeve (35) sleeved on the motor shaft (11); the inner ring of the ball bearing (22) is locked and limited by a locking positioning sleeve (23) mounted on the motor shaft (11); and there is a clearance fit between the ball bearing (22) and the inner wall of the motor housing (5), thereby limiting the radial movement of the ball screw (1).

6. The linear series elastic actuator with cooling according to claim 1, characterized in that: There are a plurality of guide shafts (16) between the other end of the motor housing (5) and the rear connecting member (6), and the guide shafts (16) are respectively passed through the actuator bracket (8). A bushing (26) is provided between each guide shaft (16) and the actuator bracket (8), and the guide shaft (16) and the actuator bracket (8) are guided by the bushing (26); the bushing (26) is axially limited by a bushing shoulder (34) on one side of the actuator bracket (8), and the bushing shoulder (34) is mounted on the actuator bracket (8).

7. The linear series elastic actuator with cooling according to claim 1, characterized in that: A compression spring A (7) is provided between the actuator bracket (8) and the rear connecting member (6), and two ends of the compression spring A (7) are respectively in contact with the rear connecting member (6) and the actuator bracket (8); a compression spring B (9) is provided between the actuator bracket (8) and the motor housing (5), and two ends of the compression spring B (9) are respectively in contact with the motor housing (5) and the actuator bracket (8).

8. The linear series elastic actuator with cooling according to claim 1, characterized in that: One end of the potentiometer connecting rod (15) passes through a threaded hole formed on the actuator bracket (8) and is locked and fixed by a nut (33); the other end of the potentiometer connecting rod (15) is connected to a slider (31) of the linear potentiometer (14); and the slider (31) is slidably mounted in a slide groove (32) formed on the linear potentiometer (14).

9. The linear series elastic actuator with cooling according to claim 8, characterized in that: The length direction of the slide groove (32) is the same as the axial direction of the ball screw (1), and the slide groove (32) is parallel to the ball screw (1); the potentiometer connecting rod (15) is parallel to the ball screw (1).

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