A robot joint with a mechanical elastic body and a low reduction ratio reducer and a torque control method

Abstract

The present invention belongs to the field of robot technology, and discloses a robot joint and torque control method with a mechanical elastic body and a low reduction ratio reducer, comprising a hollow motor, a reducer and a joint output shaft, wherein the hollow motor comprises a motor rotor and a motor stator, the reducer is located at the center of the hollow motor, the reducer comprises a reducer input end and a reducer output end, the reducer input end is fixedly connected to the motor rotor of the hollow motor, and comprises an elastic body, the elastic body comprises an elastic body input end and an elastic body output end, the elastic body input end is connected to the reducer output end, and the elastic body output end is connected to the joint output shaft. The present invention sets an elastic body at the output end of the reducer, connects to the joint output shaft through the elastic body, and obtains the torque acting on the joint output shaft in real time by measuring the angular position of the elastic body input end and the output end, and the joint control system can quickly respond to the change of torque, thereby improving the response frequency to mechanical shock and protecting the reducer.

Description

Technical Field

[0001] The present invention belongs to the technical field of robots, and in particular relates to a robot joint with a mechanical elastic body and a low reduction ratio reducer and a torque control method. Background Art

[0002] With the development of information technology, electronic technology and the application of artificial intelligence, robots are entering many new application fields, such as medical, service and human-computer interaction environments. Compared with traditional robotic arm applications, these new fields have high requirements for the contact safety of robotic arms. Such systems have extremely high requirements for safety, which is the highest among all robot applications, that is, the robotic arm is required to ensure the safety of both parties when contact and collision occur. This requires the robotic arm to be able to "sense" contact and have tactile functions. In addition, the system rigidity of the robotic arm must be reduced. When a collision occurs, the robotic arm will change its shape and posture to reduce the impact force on the contact point and the robotic arm joint to avoid damage caused by the impact. Therefore, this type of robotic arm is called a tactile robotic arm, or a non-rigid robotic arm. The "rigidity" here refers to the rigidity of the robot joint, which is affected by the joint structure and control, rather than the rigidity of the mechanical components. The mechanical parts of the robotic arm still have good rigidity to ensure its positioning accuracy. Because such equipment is often used in human-machine collaborative environments, it is also often called a collaborative robot, or a flexible robot. Such robots have the following application examples: polishing collaborative robotic arms, artificial exoskeletons, quadruped robots and tactile devices (robotic arms). The driving joint with corresponding functions is one of the core components that determine the overall performance of the robot, and it determines the dynamic performance of the entire robot. The contact safety of the driving joint is guaranteed by the corresponding mechanical structure design on the one hand, and the force and torque control on the other hand, to avoid damage to the driving joint in the event of a violent collision.

[0003] In recent years, elastic joints represented by serial elastic actuators have attracted the attention of many researchers and have been applied in many experimental robot platforms. Serial elastic actuators are usually equipped with high transmission ratio reducers to achieve large torque output. Moreover, this type of actuator has good control performance and can achieve precise torque and position control. However, due to its own mechanical characteristics, the control of serial elastic actuators is relatively complex and difficult, and due to design requirements, serial elastic actuators are usually expensive. These have affected the widespread use of serial elastic actuators to a certain extent.

[0004] In addition, a drive structure using a reducer with a low transmission ratio (usually less than 8) has also attracted attention. Compared with a direct drive (i.e., a drive system that does not include a reducer), this low transmission ratio drive structure has a larger output torque. However, compared with a series elastic drive, this low transmission ratio drive structure has a smaller output torque but a smaller loss. The output torque can be obtained by the motor model and is called a proprioceptive actuator or quasi-direct drive. This makes the price of this drive much lower than that of a series elastic drive. However, the control accuracy of this proprioceptive actuator is low, and contact control cannot be fully guaranteed. In order to improve the safety of contact and mechanical impact, some drives use a clutch, but the clutch's response frequency and speed to impact cannot meet the requirements of eliminating dynamic impact, and the clutch will increase the size and weight of the drive, and bring common disadvantages of mechanical clutches such as heat generation and maintenance. Summary of the invention

[0005] The object of the present invention is to provide a robot joint and a torque control method having a mechanical elastic body and a low reduction ratio reducer to solve the above-mentioned technical problems.

[0006] In order to solve the above technical problems, the specific technical solutions of a robot joint and torque control method with a mechanical elastic body and a low reduction ratio reducer of the present invention are as follows:

[0007] A robot joint with a mechanical elastic body and a low reduction ratio reducer, comprising a hollow motor, a reducer and a joint output shaft, wherein the hollow motor comprises a motor rotor and a motor stator, the reducer is located at the center of the hollow motor, the reducer comprises a reducer input end and a reducer output end, the reducer input end is fixedly connected to the motor rotor of the hollow motor, and comprises an elastic body, the elastic body comprises an elastic body input end and an elastic body output end, the elastic body input end is connected to the reducer output end, and the elastic body output end is fixedly connected to the joint output shaft.

[0008] Furthermore, the hollow motor has a casing on the outside, and the reducer is a first-stage precision planetary gear reducer, which includes a reducer pinion, planetary gears, a planetary gear carrier, a ring gear and a reducer output shaft; the reducer pinion is located at the center of the reducer, the reducer pinion is coaxially fixedly connected to the motor shaft, the reducer pinion rotates synchronously with the motor rotor, the three planetary gears are fixed on the planetary gear carrier, and are meshed with the reducer pinion at the same time, the planetary gear has a ring gear on the outside, the ring gear is fixedly connected to the casing of the hollow motor, the three planetary gears are meshed with the ring gear, the planetary gear carrier is fixedly connected to the reducer output shaft, the reducer pinion is the input end of the reducer, and the planetary gear carrier is the output end of the reducer.

[0009] Furthermore, the elastomer is a spatial torque spring, the elastomer is a spiral disc structure, the inner side of the center of the elastomer is the elastomer input end, the outer ring is the elastomer output end, the reducer output shaft is fixedly connected to the elastomer input end, the elastomer output end is fixedly connected to the joint output shaft, and the joint output shaft is fixedly connected to the load.

[0010] Furthermore, it includes a motor encoder, which includes a motor encoder stator and a motor encoder rotor. The motor encoder stator is fixedly connected to the housing, and the motor encoder rotor is fixedly connected to the motor rotor. The motor encoder is used to measure the position of the motor rotor.

[0011] Furthermore, the joint output encoder includes a joint output encoder stator and a joint output encoder rotor, the joint output encoder stator is fixedly connected to the casing, the joint output encoder rotor is fixedly connected to the elastomer output end, and rotates with the elastomer output end and the joint output shaft, and the joint output encoder is used to measure the position of the joint output shaft.

[0012] Furthermore, the motor encoder has a resolution of no less than 12 bits.

[0013] Furthermore, the resolution of the joint output encoder is not less than 16 bits.

[0014] Furthermore, the diameter of the robot joint is between 60 mm and 130 mm, and the length is between 80 mm and 150 mm.

[0015] The present invention also discloses a torque control method for a robot joint, comprising the following steps:

[0016] Step 1: The joint output encoder measures the deformation of the elastic body in real time, and then measures the contact torque of the robot joint in real time:

[0017] T j =k e ∙(θ o -θ i ) (1)

[0018] in,

[0019] T j represents the torque acting on the output end of the robot joint;

[0020] k e It represents the elastic modulus of an elastic body;

[0021] θ o represents the angular position of the output end of the elastic body;

[0022] θ i represents the angular position of the input end of the elastic body;

[0023] The elastic coefficient is the design parameter of the elastic body and is known; the angular positions of the input end and the output end of the elastic body are both measured values ​​and are known;

[0024] Step 2: Based on the torque obtained in step 1, the robot joint control system is used to control the torque in real time to achieve closed-loop torque control.

[0025] Furthermore, the maximum torque of the elastic body is 80 Nm, and the maximum angular displacement is 0.5 rad.

[0026] A robot joint and torque control method with a mechanical elastomer and a low reduction ratio reducer of the present invention has the following advantages: the present invention sets an elastomer at the output end of the reducer, connects it to the joint output shaft through the elastomer, and obtains the torque acting on the joint output shaft in real time by measuring the angular position of the input and output ends of the elastomer. The joint control system can quickly respond to changes in torque, thereby improving the response frequency to mechanical shocks and protecting the reducer. Real-time torque measurement supports closed-loop torque control and can achieve smoother contact control. Real-time joint output shaft position measurement provides accurate load position and improves position control accuracy. The present invention has a simple structure and small size, which effectively reduces the cost of systems with equivalent accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a front cross-sectional view of the robot joint structure of the present invention;

[0028] Figure 2 For the present invention Figure 1 FF cross-sectional view;

[0029] Figure 3 It is a front cross-sectional view of the robot joint structure of the present invention;

[0030] Figure 4 For the present invention Figure 3 EE cross-sectional view;

[0031] Figure 5 It is a schematic diagram of the encoder structure of the present invention.

[0032] Explanation of the marks in the figure: 1. Hollow motor; 11. Casing; 12. Motor shaft; 13. Motor rotor; 14. Motor stator; 2. Reducer; 21. Reducer pinion; 22. Planetary gear; 23. Planetary gear carrier; 24. Ring gear; 25. Reducer output shaft; 3. Elastomer; 31. Elastomer input end; 32. Elastomer output end; 4. Joint output shaft; 5. Encoder; 51. Motor encoder; 511. Motor encoder stator; 512. Motor encoder rotor; 52. Joint output encoder; 521. Joint output encoder stator; 522. Joint output encoder rotor. DETAILED DESCRIPTION

[0033] In order to better understand the purpose, structure and function of the present invention, the following is a further detailed description of a robot joint and a torque control method with a mechanical elastic body and a low reduction ratio reducer in conjunction with the accompanying drawings.

[0034] like Figure 1 , Figure 2 As shown, the robot joint with a mechanical elastic body and a low reduction ratio reducer of the present invention comprises a hollow motor 1, a reducer 2 and an elastic body 3. The hollow motor 1 has a housing 11 on the outside, and the housing 11 has a motor shaft 12 and a motor rotor 13 fixedly connected to the motor shaft 12. The inner ring of the motor rotor 13 is a motor stator 14. The reducer 2 is a first-level precision planetary gear reducer. The reducer 2 is located at the center of the hollow motor 1 and fits tightly with the hollow motor 1. The reducer 2 comprises a reducer pinion 21, a planetary gear 22, a planetary gear carrier 23, a gear ring 24 and a reducer output shaft 25. The reducer pinion 21 is located at the center of the reducer 2. The reducer pinion 21 is coaxially fixedly connected with the motor shaft 12. The reducer pinion 21 rotates synchronously with the motor rotor 13. The three planetary gears 22 are fixed on the planetary gear frame 23 and mesh with the reducer pinion 21 at the same time. The planetary gear 22 has a ring gear 24 outside. The ring gear 24 is fixedly connected with the housing 11 of the hollow motor 11, and the three planetary gears 22 mesh with the ring gear 24. The planetary gear frame 23 is fixedly connected with the reducer output shaft 25. The reducer pinion 21 is the input end of the reducer, and the planetary gear frame 23 is the output end of the reducer.

[0035] like Figure 3 , Figure 4 As shown, the elastomer 3 adopts a spatial torque spring, and the material is preferably spring steel or stainless steel. The elastomer 3 is a spiral disc structure, the inner side of the center is the elastomer input end 31, and the outer ring is the elastomer output end 32. The reducer output shaft 25 is fixedly connected to the elastomer input end 31, and the elastomer output end 32 is fixedly connected to the joint output shaft 4. The joint output shaft 4 is fixedly connected to the load for driving the load.

[0036] like Figure 4 , Figure 5As shown, the robot joint of the present invention also includes an encoder 5, which includes a motor encoder 51 and a joint output encoder 52. The motor encoder 51 includes a motor encoder stator 511 and a motor encoder rotor 512. The motor encoder stator 511 is fixedly connected to the housing 11, and the motor encoder rotor 512 is fixedly connected to the motor rotor 13. The motor encoder 51 is used to measure the position of the motor rotor 13. The joint output encoder 52 includes a joint output encoder stator 521 and a joint output encoder rotor 522. The joint output encoder stator 521 is fixedly connected to the housing 11, and the joint output encoder rotor 522 is fixedly connected to the elastomer output end 32, and rotates with the elastomer output end 32 and the joint output shaft 4. The joint output encoder 52 is used to measure the position of the joint output shaft 4. Preferably, the motor encoder resolution is not less than 12 bits. The joint output encoder resolution is not less than 16 bits.

[0037] During operation, the motor shaft 12 rotates to drive the reducer pinion 21 of the reducer 2 to rotate, and the reducer pinion 21 drives the planetary gear frame 23 to rotate, thereby driving the reducer output shaft 25 to rotate, and the reducer output shaft 25 drives the joint output shaft 4 to rotate through the elastic member 3, and the angular position of the motor rotor 13 and the elastic body output end 32 is still measured by the encoder 5. When the robot arm encounters an obstacle, the robot is reversely driven, and the above-mentioned input and output relationship is reversed. The joint output shaft 4 drives the elastic body 3 and then drives the reducer output shaft 25 to rotate, and then drives the planetary gear frame 23 and the planetary gear 22, and finally drives the motor rotor 13 to rotate through the reducer pinion 21. At this time, the hollow motor 1 works in the generator mode and can achieve energy regeneration. The angular position of the motor rotor 13 and the elastic body output end 32 in this process is still measured by the encoder 5. The torque acting on the joint output shaft 4 is also obtained according to the angle difference between the elastic body input end 31 and the elastic body input end 32, but the torque direction is opposite to that in the forward drive.

[0038] Because the transmission ratio of the reducer is known, the position of the reducer output end, that is, the position of the elastic body input end 31, can be calculated according to the position of the motor rotor 13, thereby obtaining the angle difference between the elastic body input end 31 and the elastic body output end 32. The torque of the joint output end can be obtained by referring to the elastic coefficient of the elastic body 3.

[0039] Specifically, the torque control method of the robot joint with a mechanical elastic body and a low reduction ratio reducer of the present invention comprises the following steps:

[0040] Step 1: The joint output encoder 52 measures the deformation of the elastic body in real time, and further, the contact torque of the robot joint can be measured in real time.

[0041] T j =ke ∙(θ o -θ i ) (1)

[0042] Formula (1) is the calculation formula for joint contact force.

[0043] T j represents the torque acting on the output end of the robot joint;

[0044] k e It represents the elastic modulus of an elastic body;

[0045] θ o represents the angular position of the output end of the elastic body;

[0046] θ i represents the angular position of the input end of the elastic body;

[0047] The elastic coefficient is the design parameter of the elastic body, which is known; the angular positions of the elastic body input end and the elastic body output end are both measured values, which are known. Therefore, the torque acting on the output end of the robot joint, that is, the output end of the elastic body, can be directly calculated.

[0048] Step 2: Based on the torque obtained in step 1, the robot joint control system is used to control the torque in real time to achieve closed-loop torque control.

[0049] Preferably, the maximum torque of the elastic body 3 of the present invention is 80 Nm, the maximum angular displacement is 0.5 rad, and the size of the entire robot joint is: the diameter is between 60 mm and 130 mm, and the length is between 80 mm and 150 mm.

[0050] The present invention sets an elastic body at the output end of the reducer, connects the elastic body to the joint output shaft, measures the angular position of the input and output ends of the elastic body, and obtains the torque acting on the joint output shaft in real time. The joint control system can quickly respond to the change of torque, thereby improving the response frequency to mechanical shock and protecting the reducer. Real-time torque measurement supports closed-loop torque control and can achieve smoother contact control. Real-time joint output shaft position measurement provides accurate load position and improves position control accuracy.

[0051] The real-time control system of the robot joint has an adjustable sampling frequency in the range of tens to several kilohertz. The output torque of the drive motor can be controlled in real time to provide precise torque control. Compared with the self-sensing joint, the present invention can adopt a more flexible control strategy, the peak torque of the mechanical impact can be more effectively controlled, and the reducer gear is protected from damage. Compared with the self-sensing joint with a clutch, the present invention has a faster response time and does not use a clutch, avoiding unfavorable factors such as mechanical heating, and because there is no mechanical clutch, no special maintenance is required. Compared with the series elastic drive, although the output torque of the present invention is lower, it uses a single-pole precision planetary gear reducer, which is more efficient and has better reverse drive performance. The reducer with a smaller transmission ratio of the present invention can be designed to be more compact, smaller in size, and higher in torque density. At the same time, an elastomer is used, the backlash is smaller, and only the angular displacement of the output end of the elastomer needs to be measured. It has better feedback drive performance and can achieve energy regeneration during deceleration.

[0052] It is to be understood that the present invention is described by some embodiments, and it is known to those skilled in the art that various changes or equivalent substitutions may be made to these features and embodiments without departing from the spirit and scope of the present invention. In addition, under the teachings of the present invention, these features and embodiments may be modified to adapt to specific circumstances and materials without departing from the spirit and scope of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are within the scope of protection of the present invention.

Claims

1. A method for controlling torque of a robot joint having a mechanical elastic body and a low reduction ratio reducer, the robot joint comprising a hollow motor (1), a reducer (2) and a joint output shaft (4), the hollow motor (1) comprising a motor rotor (13) and a motor stator (14), the reducer (2) being located at the center of the hollow motor (1), the reducer (2) comprising a reducer input end and a reducer output end, the reducer input end being fixedly connected to the motor rotor (13) of the hollow motor (1), characterized in that: The hollow motor (1) comprises an elastic body (3), wherein the elastic body (3) comprises an elastic body input end (31) and an elastic body output end (32), wherein the elastic body input end (31) is connected to the reducer output end, and the elastic body output end (32) is fixedly connected to the joint output shaft (4); the hollow motor (1) has a housing (11) on the outside, and the reducer (2) is a first-stage precision planetary gear reducer, wherein the reducer (2) comprises a reducer pinion (21), a planetary gear (22), a planetary gear carrier (23), a gear ring (24), and a reducer output shaft (25); the reducer pinion (21) is located at the center of the reducer (2), and the reducer pinion (21) is aligned with the motor shaft. (12) are coaxially fixedly connected, the reducer pinion (21) rotates synchronously with the motor rotor (13), the three planetary gears (22) are fixed on the planetary gear frame (23), and mesh with the reducer pinion (21) at the same time, the planetary gear (22) has a gear ring (24) outside, the gear ring (24) is fixedly connected to the housing (11) of the hollow motor (1), the three planetary gears (22) mesh with the gear ring (24), the planetary gear frame (23) is fixedly connected to the reducer output shaft (25), the reducer pinion (21) is the reducer input end, and the planetary gear frame (23) is the reducer output end; the elastic body (3) is a space torque The spring is a spiral disc structure, the inner side of the center of the elastic body (3) is the elastic body input end (31), the outer ring is the elastic body output end (32), the reducer output shaft (25) is fixedly connected to the elastic body input end (31), the elastic body output end (32) is fixedly connected to the joint output shaft (4), and the joint output shaft (4) is fixedly connected to the load; the robot joint also includes an encoder (5), the encoder (5) includes a motor encoder (51) and a joint output encoder (52), the motor encoder (51) includes a motor encoder stator (511) and a motor encoder rotor (512), the motor encoder stator (511) and the motor encoder rotor (512) are connected to the joint output shaft (4), and the joint output shaft (4) is fixedly connected to the load; the robot joint also includes an encoder (5), the encoder (5) includes a motor encoder (511) and a joint output encoder (52), the motor encoder (51) includes a motor encoder stator (511) and a motor encoder rotor (512), and the motor encoder stator (511) and the motor encoder rotor (512) are connected to the joint output shaft (4). 11) is fixedly connected to the housing (11), the motor encoder rotor (512) is fixedly connected to the motor rotor (13), and the motor encoder (51) is used to measure the position of the motor rotor (13); the joint output encoder (52) comprises a joint output encoder stator (521) and a joint output encoder rotor (522), the joint output encoder stator (521) is fixedly connected to the housing (11), the joint output encoder rotor (522) is fixedly connected to the elastic body output end (32), and rotates with the elastic body output end (32) and the joint output shaft (4), and the joint output encoder (52) is used to measure the position of the joint output shaft (4); Characterized in that the torque control method comprises the following steps: Step 1: The joint output encoder (52) measures the deformation of the elastic body (3) in real time, and then measures the contact torque of the robot joint in real time: T j =k e ∙(θ o -θ i ) (1) in, T j represents the torque acting on the output end of the robot joint; k e It represents the elastic modulus of an elastic body; θ o represents the angular position of the output end of the elastic body; θ i represents the angular position of the input end of the elastic body; The elastic coefficient is the design parameter of the elastic body and is known; the angular positions of the input end and the output end of the elastic body are both measured values ​​and are known; the maximum torque of the elastic body (3) is 80 Nm, and the maximum angular displacement is 0.5 rad; Step 2: Based on the torque obtained in step 1, the robot joint control system is used to control the torque in real time to achieve closed-loop torque control.

2. The torque control method according to claim 1, characterized in that: The motor encoder (51) has a resolution of no less than 12 bits.

3. The torque control method according to claim 1, characterized in that: The resolution of the joint output encoder (52) is not less than 16 bits.

4. The torque control method according to claim 1, characterized in that: The robot joint has a diameter between 60 mm and 130 mm and a length between 80 mm and 150 mm.

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