Friction compensation method, computer equipment, storage device and dragging teaching method

Abstract

The invention discloses a friction compensation method of a collaborative robot, computer equipment, a storage device and a dragging teaching method, and relates to the technical field of robots. A speed reducer and a motor are arranged at the joint of the collaborative robot, the output end of the motor is connected with the input end of the speed reducer, and the friction compensation method comprises the steps that a static friction model is established; obtaining the value of each parameter in the static friction model through a friction model parameter identification experiment; monitoring the output end rotating speed of the speed reducer; when the rotating speed of the output end of the speed reducer is smaller than the dynamic friction compensation minimum speed, a static friction model is selected to calculate the internal friction torque of the speed reducer; and obtaining compensated friction torque according to the internal friction torque of the speed reducer so as to compensate the internal friction torque of the speed reducer. According to the invention, the jamming phenomenon in the static friction stage can be relieved.

Description

Technical Field

[0001] The present application relates to the technical field of robots, and in particular, to a friction compensation method for a collaborative robot, a computer device, a storage device, and a teaching-by-dragging method. Background Technology

[0002] The collaborative robot was invented in 1996 by professors J. Edward Colgate and Michael Peshkin of Northwestern University in Illinois. A 1997 US patent describes a collaborative robot as "a device and method for direct physical interaction between humans and a general-purpose robot controlled by a computer."

[0003] Teaching-by-dragging is one of the essential functions of a collaborative robot. During the teaching-by-dragging process, it is necessary to compensate for the frictional torque at the joints to facilitate dragging the robotic arm of the collaborative robot. There are many teaching-by-dragging schemes, and one of the teaching-by-dragging schemes is to estimate the external force based on the current for teaching-by-dragging.

[0004] During the teaching-by-dragging process of estimating the external force based on the current, when starting to drag the robotic arm, it is necessary to transition the servo motor at the robot joint from a stationary state to a moving state. During this process, it is impossible to compensate for the frictional torque at the joint, resulting in a serious jamming phenomenon. Summary of the Invention

[0005] In view of this, to solve the above technical problems, the present application provides a friction compensation method for a collaborative robot, a computer device, a storage device, and a teaching-by-dragging method.

[0006] To achieve the above object, the present application provides a friction compensation method for a collaborative robot. A speed reducer and a motor are provided at the joint of the collaborative robot, and the output end of the motor is connected to the input end of the speed reducer. The friction compensation method includes:

[0007] Establish a static friction model;

[0008] Obtain the values of the parameters in the static friction model through a friction model parameter identification experiment;

[0009] Monitor the output speed of the speed reducer;

[0010] In response to the output speed of the speed reducer being less than the minimum dynamic friction compensation speed, select the static friction model to calculate the frictional torque in the speed reducer;

[0011] Obtain the compensated frictional torque based on the frictional torque in the speed reducer to compensate for the frictional torque in the speed reducer.

[0012] To solve the above technical problems, another technical solution adopted by this application is to provide a computer device, which includes a memory and a processor. Among them, the memory stores program data; the program data can be executed by the processor to implement the method of any one of the above.

[0013] To solve the above technical problems, another technical solution adopted by this application is to provide a storage device, which stores program data that can be executed by a processor to implement the method of any one of the above.

[0014] To solve the above technical problems, another technical solution adopted by this application is to provide a drag teaching method, which includes:

[0015] Collect the output torque of the motor;

[0016] Compensate the frictional torque in the reducer according to the above friction compensation method;

[0017] According to the output torque of the motor and the frictional torque in the reducer, calculate the external torque through inverse dynamics;

[0018] According to the external torque, obtain the additional displacement through the admittance control model;

[0019] The collaborative robot executes the additional displacement at the current position to obtain a new displacement.

[0020] Beneficial effects: Different from the prior art, in this application, when the rotational speed of the output end of the reducer is less than the minimum dynamic friction compensation speed, a static friction model is selected to calculate the frictional torque in the reducer; the compensated frictional torque is obtained according to the frictional torque in the reducer to compensate the frictional torque in the reducer, so that the frictional torque can be compensated specifically in the static friction stage, thereby being able to alleviate the jamming phenomenon in the static friction stage. Description of the Drawings

[0021] Figure 1 It is a schematic structural diagram of a collaborative robot according to an embodiment of this application;

[0022] Figure 2 It is a schematic diagram of the joint structure of a collaborative robot according to an embodiment of this application;

[0023] Figure 3 It is a schematic diagram of the output flange structure of a collaborative robot according to an embodiment of this application;

[0024] Figure 4 It is a schematic flowchart of the first embodiment of the friction compensation method of the collaborative robot of this application;

[0025] Figure 5It is a schematic flowchart of the second embodiment of the friction compensation method for the collaborative robot of the present application;

[0026] Figure 6 It is a schematic diagram of the stribeck friction model of the present application;

[0027] Figure 7 It is a schematic structural diagram of the computer device embodiment of the present application;

[0028] Figure 8 It is a schematic structural diagram of the storage device embodiment of the present application;

[0029] Figure 9 It is a schematic flowchart of the teaching by dragging method embodiment of the present application. Detailed implementation manners

[0030] To enable those skilled in the art to better understand the technical solutions of the present application, the present application will be further described in detail below with reference to the accompanying drawings and specific implementation manners. Obviously, the described implementation manners are only a part of the implementation manners of the present application, rather than all of the implementation manners. All other implementation manners obtained by those of ordinary skill in the art based on the implementation manners in the present application without making creative efforts shall fall within the scope of protection of the present application.

[0031] To facilitate the understanding of the present invention, the structure of the collaborative robot in this embodiment will be briefly described below.

[0032] Please refer to Figure 1 , Figure 1 It is a schematic structural diagram of the collaborative robot of an embodiment of the present application.

[0033] As Figure 1 shown, the collaborative robot 10 may include a plurality of joints 12 and joint connectors 11. The plurality of joints 12 may be connected through the joint connectors 11 to form a linear arrangement, thereby forming the collaborative robot 10 of the robotic arm type.

[0034] Please refer to Figures 2 - 3 , Figure 2 It is a schematic diagram of the joint structure of the collaborative robot of an embodiment of the present application; Figure 3 It is a schematic diagram of the output flange structure of the collaborative robot of an embodiment of the present application.

[0035] The joint 12 of the above-mentioned collaborative robot 10 may adopt the joint 100 as Figure 2 shown. The joint 100 may include a joint housing 110, a motor 120, a reducer 130, an input end encoder 140, an output end encoder 150, a driving device 160, an output flange 170, and a mounting bracket 180.

[0036] The joint housing 110 can be designed with a closed top and an open bottom, and the output flange 170 can be arranged corresponding to the open bottom of the joint housing 110. The output flange 170 can include a bottom disk 171 and a transmission shaft 172 arranged on one side of the upper end face of the bottom disk 171. The bottom disk 171 can be arranged at the open bottom of the joint housing 110. The first end of the transmission shaft 172 can be fixedly connected to the bottom disk 171, so that during the rotation of the bottom disk 171, the transmission shaft 172 can rotate synchronously with the bottom disk 171, and the second end of the transmission shaft 172 can be inserted into the joint housing 110.

[0037] A speed reducer 130, a motor 120, and an output end encoder 150 can be sequentially sleeved between the first end and the second end of the transmission shaft 172. The motor 120 can include a hollow stator 121 and a hollow rotor 122. Among them, the hollow stator 121 can be sleeved on the transmission shaft 172 and is relatively fixed to the joint housing 110, and the hollow rotor 122 can be sleeved on the transmission shaft 172 and is located inside the hollow stator 121. The hollow rotor 122 is connected to the input end of the speed reducer 130, and the output end of the speed reducer 130 can be connected to the bottom disk 170. Thus, when the hollow rotor 122 rotates relative to the hollow stator 121, the bottom disk 171 and the transmission shaft 172 can be indirectly driven to rotate through the speed reducer 130.

[0038] The driving device 160 can be sleeved on the transmission shaft 172 and connected to the joint housing 110, so that when the transmission shaft 172 rotates, the driving device 160 can be relatively stationary with respect to the joint housing 110. The driving device 160 can be arranged corresponding to the motor 120 and electrically connected to the motor 120 to drive the motor 120 to act.

[0039] The input end encoder 140 can include an input end encoder disk 141 and an input end encoder reading head 142. The input end encoder disk 141 can be sleeved on the hollow rotor 122 and connected to the hollow rotor 122, so as to be able to rotate synchronously with the hollow rotor 122. The input end encoder reading head 142 can be arranged corresponding to the input end encoder disk 141 and form a relatively fixed connection with the joint housing 110. For example, the driving device 160 can be arranged corresponding to the input end encoder disk 141, and the input end encoder reading head 142 can be fixedly arranged on the driving device 160.

[0040] In this embodiment, when the hollow rotor 122 is driven by the driving device 160 to rotate, it drives the input end encoder disk 141 to rotate synchronously, and the input end encoder reading head 142 is stationary relative to the joint housing 110. Thus, the rotation angle of the input end of the speed reducer 130 can be read by reading the rotation angle of the input end encoder disk 141 to complete the measurement of the rotation angle of the input end of the speed reducer 130.

[0041] The output encoder 150 may include an output encoder code disk 151 and an output encoder reading head 152. The output encoder code disk 151 may be mounted on and in transmission connection with the transmission shaft 172. The output encoder reading head 152 may be positioned corresponding to the output encoder code disk 151 and secured to the joint housing 110 via a fixing bracket 180. For example, the output encoder reading head 152 may be positioned above the output encoder code disk 151 and secured to the top of the joint housing 110 via a fixing bracket 180.

[0042] In this embodiment, when the transmission shaft 172 rotates, the output end encoder code disk 151 rotates synchronously, and the output end encoder reading head 152 is stationary relative to the joint housing 110, so that the angle of rotation of the output end encoder code disk 151 can be read to read the angle of rotation of the output end of the reducer 130, thereby completing the measurement of the rotation angle of the output end of the reducer 130.

[0043] To facilitate braking, the joint 100 may further include a brake device 190 disposed within the joint housing 110. The brake device 190 may be disposed corresponding to a transmission structure such as the transmission shaft 172, the bottom disc 171, or the hollow rotor 122. For example, the brake device 190 may be mounted on a transmission structure such as the transmission shaft 172 or the hollow rotor 122.

[0044] A collaborative robot is generally provided with a joint controller (not shown), which is coupled to at least the output encoder 150, the motor 120, and the input encoder 140. The joint controller is used to receive measurement data from the output encoder 150 and the input encoder 140 and control the movement of the motor 120.

[0045] During the dragging teaching, the collaborative robot 10 needs to overcome the internal friction torque. To facilitate the dragging of the collaborative robot 10, the friction torque inside the joint 12 needs to be compensated during the dragging teaching process. The friction torque includes the friction torque inside the reducer 130.

[0046] The inventors of this application have discovered through extensive research that when cobot 10 is first being towed, it must overcome the maximum static friction torque within reducer 130 to generate work, driving joint 12 to move. Only then can the joint controller identify the direction of the friction torque and compensate for it. Consequently, joint 12 may experience significant stalling during the initial towing of cobot 10.

[0047] The inventors of the present application further studied and found that when initially dragging the collaborative robot 10, although the input end of the speed reducer 130 cannot rotate due to the existence of static friction inside the speed reducer 130, due to the certain flexibility of the speed reducer 130, the output end of the speed reducer 130 will produce slow sliding under the action of an external force. During this process, the output end of the speed reducer 130 will rotate. For the convenience of description, the following will refer to this process as the static friction stage. Thereafter, the operator continues to increase the external force. When the external force can overcome the maximum static friction inside the speed reducer 130 and cause both the input end and the output end of the speed reducer 130 to rotate, for the convenience of description, this stage is referred to as the dynamic friction stage. The rotational speed of the output end of the speed reducer 130 in the dynamic friction stage is faster than that in the static friction stage. There is a rotational speed of the output end of the speed reducer 130 at the boundary between the static friction stage and the dynamic friction stage. When it is less than the rotational speed of the output end of the speed reducer 130, it is in the static friction stage, and when it is greater than the rotational speed of the output end of the speed reducer 130, it is in the dynamic friction stage. In the present application, the rotational speed of the output end of the speed reducer 130 at the boundary between the static friction stage and the dynamic friction stage is referred to as the minimum dynamic friction compensation speed. Therefore, the inventors of the present application believe that the rotational speed of the output end of the speed reducer 130 can be monitored, and when the rotational speed of the output end of the speed reducer 130 is less than the minimum dynamic friction compensation speed, the static friction compensation method is used to compensate the frictional torque, so as to alleviate the jamming phenomenon when initially dragging the collaborative robot 10. For this purpose, the present application proposes at least the following embodiments.

[0048] Refer to Figure 4 , Figure 4 is a schematic flowchart of the first embodiment of the friction compensation method for the collaborative robot of the present application.

[0049] As Figure 4 shown, the friction compensation method for the collaborative robot at least includes the following steps:

[0050] Step S110: Establish a static friction model.

[0051] The friction model, in mathematical form, is a function of frictional torque with respect to variables such as speed, displacement, temperature, etc. The friction model can be divided into a static friction model and a dynamic friction model. In the static friction model, the frictional torque is a unary function of speed, and the function analytical formula can be a constant value (Coulomb model), a linear function (Coulomb-viscous model), a non-linear function, etc. Once the function form is determined, the function parameters are constant values. In this embodiment, the static friction model can be a static friction model.

[0052] When establishing the friction model, generally, the function analytical formula of the friction model is established, and there can be undetermined parameters in the function analytical formula. The function analytical formula of the static friction model in this step can be as shown in the following equation (1):

[0053] τf = τ c k ·············· (1)

[0054] where τ f is the frictional torque in the reducer, τ c is the Coulomb frictional torque in the reducer, and k is the static friction compensation parameter.

[0055] Step S120: Obtain the values of the parameters in the static friction model through a friction model parameter identification experiment.

[0056] In this step, it is necessary to obtain the values of the parameters in the static friction model through a friction model parameter identification experiment. For example, when establishing the static friction model using equation (1), it is necessary to obtain the values of parameters such as the static friction compensation parameter through a friction model parameter identification experiment.

[0057] Step S130: Monitor the rotational speed of the output end of the reducer.

[0058] During the drag teaching process, when the rotational speed of the output end of the reducer is less than the minimum dynamic friction compensation speed, static friction occurs inside the reducer, and when the rotational speed of the output end of the reducer is greater than the minimum dynamic friction compensation speed, dynamic friction occurs inside the reducer. Therefore, it is necessary to monitor the rotational speed of the output end of the reducer to facilitate static friction compensation when the rotational speed of the output end of the reducer is less than the minimum dynamic friction compensation speed in subsequent steps.

[0059] Take Figures 1 - 2 as an example for illustration. The rotational speed of the output end of the reducer 130 can be obtained by taking the derivative with respect to time of the relative rotational angle between the rotational angle measured by the output end encoder 150 and the rotational angle measured by the input end encoder 140, or by taking the derivative with respect to time of the rotational angle measured by the output end encoder 150.

[0060] Step S140: In response to the rotational speed of the output end of the reducer being less than the minimum dynamic friction compensation speed, select the static friction model to calculate the frictional torque in the reducer.

[0061] In order to achieve a better compensation effect for the frictional torque in the reducer, it is necessary to reasonably set the minimum dynamic friction compensation speed. Through long-term research by the inventors of this application, it is found that when the minimum dynamic friction compensation speed is 0.1° / s, it has a better effect of distinguishing the static friction stage and the dynamic friction stage.

[0062] When selecting the static friction model to calculate the frictional torque in the reducer, taking the above equation (1) as an example for illustration, it means that the frictional torque in the reducer can be calculated using equation (1) after obtaining the static friction compensation parameter.

[0063] When selecting the static friction model to calculate the frictional torque in the reducer, the direction of the compensated frictional torque can be determined based on the velocity direction obtained by taking the derivative of the relative rotation angle with respect to time between the rotation angle of the output end of the reducer and the rotation angle of the input end of the reducer. That is, the direction of the compensated frictional torque can be opposite to the velocity direction obtained by taking the derivative of the relative rotation angle with respect to time between the rotation angle of the output end of the reducer and the rotation angle of the input end of the reducer. Compared with determining the direction of the compensated frictional torque based on the velocity direction obtained by taking the derivative of the rotation angle of the output end of the reducer with respect to time, determining the direction of the compensated frictional torque using the velocity direction obtained by taking the derivative of the relative rotation angle with respect to time between the rotation angle of the output end of the reducer and the rotation angle of the input end of the reducer in this step has a smaller calculation delay and can improve the timeliness of compensating the frictional torque in the reducer.

[0064] Further, when the rotational speed of the output end of the reducer is obtained by taking the derivative of the rotation angle of the output end of the reducer with respect to time, before step S140, steps S141 and S142 are further included.

[0065] Step S141: Monitor the variance of multiple measurement values of the rotation angle of the output end of the reducer within a preset time interval.

[0066] In this step, taking Figures 1 - 2 as an example for illustration, the rotation angle of the output end of the reducer 130 can be measured by the output end encoder 150. In this step, since when an external torque is received at the output end of the reducer 130, the output end can rotate due to the flexibility of the reducer 130, and the output end encoder 150 will measure the rotation angle of the output end of the reducer 130 multiple times within each preset time interval, and the joint controller can calculate the variance of the measurement values within the preset time interval.

[0067] Step S142: If the variance is greater than the threshold, jump to the step of selecting the static friction model to calculate the frictional torque in the reducer in response to the rotational speed of the output end of the reducer being less than the minimum dynamic friction compensation speed.

[0068] In this embodiment, only when the variance of the rotation angle of the output end of the reducer is greater than the threshold will step S142 be performed, which can effectively eliminate the interference caused by individual data jitters during the measurement of the rotation angle of the output end of the reducer. The accuracy of the judgment result of step S142 is increased.

[0069] Step S150: Obtain the compensated frictional torque based on the frictional torque in the reducer to compensate for the frictional torque in the reducer.

[0070] In the step, the direction opposite to the direction of the frictional torque in the speed reducer can be taken as the direction of the compensated frictional torque, and the magnitude of the compensated frictional torque can be equal to the magnitude of the frictional torque in the speed reducer, so as to compensate for the frictional torque in the speed reducer by using the compensated frictional torque.

[0071] In this embodiment, by responding that the rotational speed of the output end of the speed reducer is less than the minimum dynamic friction compensation speed, a static friction model is selected to calculate the frictional torque in the speed reducer; a compensated frictional torque is obtained according to the frictional torque in the speed reducer to compensate for the frictional torque in the speed reducer, so that the frictional torque can be compensated specifically in the static friction stage, thereby being able to alleviate the jamming phenomenon in the static friction stage.

[0072] Further referring to Figure 5 , Figure 5 is a schematic flowchart of the second embodiment of the friction compensation method for the collaborative robot of the present application. The friction compensation method for the collaborative robot in this embodiment is based on the Figure 4 embodiment, and before step S130, it further includes step S210 and step S220, and after step S130, it further includes step S230 and step S240.

[0073] Steps S110 to S150 can refer to the description of steps S110 to S150 in Figure 4 , and will not be elaborated here.

[0074] Step S210: Establish a Stribeck friction model.

[0075] The friction model, in mathematical form, is a function of the frictional torque with respect to variables such as speed, displacement, and temperature. The friction model can be divided into a static friction model and a dynamic friction model. In the dynamic friction model, the frictional torque is a multivariate function of speed, displacement, temperature, etc., and the function analytical form is generally a non-linear function. The Stribeck friction model established in this embodiment can be a dynamic friction model.

[0076] Referring to Figure 6 , Figure 6 is a schematic diagram of the Stribeck friction model of the present application.

[0077] As Figure 6 shown, the Stribeck friction model shows that under the lubrication state, when the two mutually contacting surfaces in the system change from static to sliding, the change of the frictional force experiences four stages, namely the static friction stage A, the boundary lubrication stage B, the partial lubrication stage C, and the full lubrication stage D.

[0078] First is the static friction stage A. In this stage, no relative sliding occurs, and the frictional force is generated by the elastic deformation of the contact surface, which is also called "pre-sliding displacement". For general engineering materials, the pre-sliding displacement is only 2 - 5 micrometers. Then comes the boundary lubrication stage B. In this stage, due to the very low speed, a liquid film cannot be established between the contact surfaces, and at this time, the frictional force is caused by the shear action between the contact surfaces. The third stage is the partial lubrication stage C. In this stage, as the speed increases, a liquid film is formed between the contact surfaces. However, the normal pressure squeezes out some of the lubricating liquid from the contact surface, so there are still some areas of solid contact. As the relative movement speed increases, the thickness of the liquid film increases, and the area of solid contact decreases, thus causing the frictional force to show a downward trend. The frictional force in this stage shows a negative slope characteristic, which is also called the Stribeck effect and is the main factor causing the crawling phenomenon. The fourth stage is the full lubrication stage D. In this stage, the liquid film between the contact surfaces is completely formed, eliminating the solid contact area. At this time, the frictional force is generated by the viscous action of the liquid film. As the relative movement speed increases, the viscous action increases, and the frictional force becomes larger.

[0079] When establishing a friction model, generally, a functional analytical formula of the friction model is established, and undetermined parameters can exist in the functional analytical formula. Through research by the inventors of this application, it is found that the functional analytical formula of the Stribeck friction model in this step can be shown as the following equation (2):

[0080] τ f (qd, T) = c0(T) + c1(T)qd + c2(T)qd 2 + c3(T)qd 3 + c4(T)qd 4 + c5(T)qd 5

[0081] ····························(2)

[0082] Among them, τ f (qd, T) is the frictional torque in the reducer, qd is the output speed of the reducer, T is the temperature of the reducer, c0(T), c1(T), c2(T), c3(T), c4(T), and c5(T) are the first parameters, and the relationship between the first parameters and the temperature of the reducer can be shown as the following equation (3):

[0083] c j (T) = b j0 + b j1 T + b j2 T 2 ··············(3)

[0084] where j is equal to 0, 1, 2, 3, 4, or 5, and c j (T) is the first parameter, T is the temperature of the speed reducer, and b j0 、b j1 and b j2 are the second parameters.

[0085] In the Stribeck friction model established according to Equation (2) and Equation (3), the independent variables are the temperature of the speed reducer and the output speed of the speed reducer, and the dependent variable is the internal friction torque of the speed reducer. In this embodiment, the independent variables of the Stribeck friction model include both the temperature of the speed reducer and the output speed of the speed reducer. The friction torque calculated using this Stribeck friction model is more accurate than the friction torque calculated using a friction model whose independent variable only includes the output speed of the speed reducer.

[0086] Step S220: Obtain the values of the parameters in the Stribeck friction model through a friction model parameter identification experiment to determine the mathematical relationship between the output speed of the speed reducer and the internal friction torque of the speed reducer.

[0087] In this step, it is necessary to obtain the values of the parameters in the Stribeck friction model through a friction model parameter identification experiment. For example, when establishing the Stribeck friction model using Equation (2) and Equation (3), in this step, the internal friction torque - output speed curve of the speed reducer at different temperatures can be measured respectively, and Equation (2) can be used to fit the internal friction - output speed curve of the speed reducer at different temperatures to obtain the values of the first parameter in the Stribeck friction model at different temperatures, and further Equation (3) can be used to fit the relationship between the first parameter and the temperature of the speed reducer to obtain the value of the second parameter. Thus, the mathematical relationship between the internal friction torque of the speed reducer, the output speed of the speed reducer, and the temperature of the speed reducer is determined. In the above fitting process, the least squares method can be used for fitting.

[0088] In the above description, the analytical formula of the Stribeck friction model is expressed in the form of a polynomial. In this way, the calculation difficulty of obtaining the parameters in the Stribeck friction model can be simplified during the fitting process. Through research by the inventors of this application, it is found that in the Stribeck friction model, when the degree of the polynomial is five, that is, when the highest exponent of the output speed qd of the speed reducer is 5, the established friction model has a good fitting effect during the fitting process. When fitting the relationship between the first parameter and the temperature of the speed reducer, when the degree of the polynomial is 2 or less, that is, when the highest exponent of the temperature T of the speed reducer in the equation of the relationship between the first parameter and the temperature of the speed reducer is 2 or less, it has a good fitting effect during the fitting process.

[0089] Step S230: Determine whether the rotational speed of the output end of the reducer is less than the minimum speed for dynamic friction compensation.

[0090] In this step, if it is determined that the rotational speed of the output end of the reducer is less than the minimum speed for dynamic friction compensation, then jump to step S140, which is equivalent to responding to the rotational speed of the output end of the reducer being less than the minimum speed for dynamic friction compensation; if it is determined that the rotational speed of the output end of the reducer is greater than or equal to the minimum speed for dynamic friction compensation, then jump to step S240, which is equivalent to responding to the rotational speed of the output end of the reducer being greater than or equal to the minimum speed for dynamic friction compensation.

[0091] Step S240: Select the Stribeck friction model to calculate the internal friction torque of the reducer according to the mathematical relationship between the rotational speed of the output end of the reducer and the internal friction torque of the reducer.

[0092] In this step, taking the function analytic formula of the Stribeck friction model as the above equation (3) as an example for illustration, first, the first parameter at the current temperature of the reducer can be calculated using the above equation (2), and then substituting the first parameter into equation (2), and then the internal friction torque of the reducer can be calculated using the rotational speed of the output end of the reducer.

[0093] When selecting the Stribeck friction model to calculate the internal friction torque of the reducer according to the mathematical relationship between the rotational speed of the output end of the reducer and the internal friction torque of the reducer, the direction of the compensated friction torque can be determined according to the direction of the speed obtained by differentiating the rotational angle of the output end of the reducer with respect to time, that is, the direction of the compensated friction torque can be opposite to the direction of the speed obtained by differentiating the rotational angle of the output end of the reducer with respect to time.

[0094] Refer to Figure 7 , Figure 7 which is a schematic structural diagram of an embodiment of the computer device of the present application.

[0095] As Figure 7 shown, the computer device 2 may include a memory 210 and a processor 220. The processor 220 is electrically coupled to the memory 210. The memory 210 is used to store program data. The program data can be loaded and executed by the processor 220, so as to implement the friction compensation method of the above embodiments of the present application.

[0096] Refer to Figure 8 , Figure 8 which is a schematic structural diagram of an embodiment of the storage device of the present application.

[0097] As Figure 8 shown, the storage device 3 may include at least one storage block 31, and the program data is stored in at least one storage block 31 respectively, or stored in some of the storage blocks 31. The program data can be executed by the processor to implement the friction compensation method of the above embodiments.

[0098] The storage device 3 in this embodiment may be, for example, Figure 7 the memory 210 of the computer device 2 in

[0099] Refer to Figure 9 , Figure 9 which is a schematic flowchart of an embodiment of the drag teaching method of this application.

[0100] As Figure 9 shown, the drag teaching method of this application at least includes the following steps:

[0101] Step S310: Collect the motor output torque.

[0102] The motor output torque can be obtained according to the motor current. For example, the motor output torque can be obtained by referring to the following formula (4):

[0103] τ m = k0i ············ (4)

[0104] where τ m is the motor output torque, k0 is the current torque coefficient, and i is the motor current. The current torque coefficient is a constant. Therefore, the motor current can be substituted into formula (4) for calculation to obtain the motor output torque.

[0105] Step S320: Compensate the frictional torque in the reducer according to the Figure 4 or Figure 5 friction compensation method shown.

[0106] This step can refer to the relevant descriptions of the above Figure 4 or Figure 5 shown embodiments, and will not be elaborated here.

[0107] Step S330: Calculate the external force torque through inverse dynamics according to the motor output torque and the frictional torque in the reducer.

[0108] After obtaining the motor output torque and the frictional torque in the reducer, the external force torque can be calculated through the inverse dynamics equation. The inverse dynamics equation can be as shown in the following equation (5):

[0109]

[0110] where n is the reduction ratio of the reducer, τ f is the frictional torque in the reducer, τ ext is the external force torque, is the inertia matrix, is the rotation angle of the output end of the reducer, a is the acceleration of the speed of the output end of the reducer, is the matrix containing Coriolis force and centrifugal force, qd is the output speed of the reducer, is the gravity matrix.

[0111] Step S340: obtaining additional displacement through the admittance control model according to the external force torque.

[0112] Admittance control models can employ compliant control, also known as force-aware control. Over the years, many researchers have proposed a variety of effective control methods, including stiffness control, impedance control, force / position hybrid control, and implicit force control. Impedance control and force / position hybrid control are the most widely studied control methods in practical research. Hogan's impedance control plays a crucial role in force-aware control algorithms, successfully integrating trajectory and force control into a single dynamic framework. This avoids the need for separate control strategies for position and force, which increases the control workload, and provides strong stability to environmental changes and disturbances. However, this basic impedance control algorithm only indirectly controls force characteristics, making force control accuracy difficult to guarantee. Adjusting the trajectory indirectly alters the force between the vehicle and the environment, and control accuracy depends on the accuracy of the environment modeling, which is practically impossible to guarantee. To address this issue, an improved impedance control algorithm combines position and force control into a single system with compensatory properties. This unified control system allows for convenient simultaneous control of both position and force. Therefore, position and force control are transformed into impedance equations, which incorporate position, velocity, and force. This makes it much easier to control both force and position, which are difficult to control simultaneously, through the impedance relationship. The ideal values for the inertia coefficient, damping coefficient, and stiffness coefficient in the impedance equation directly affect the system's dynamic performance.

[0113] Impedance Control: The impedance control algorithm first emerged in the mid-1980s. Over the years, a large number of scientific researchers and scholars in the field of force control have continuously deepened their research, making this algorithm one of the basic methods of force control. This control algorithm regards the physical system as interacting, aiming to include inertia in the external environment. Then, the relationship between the robot and the environment is studied in a unified system. To implement the algorithm, the forces generated by the manipulator and the external environment can be regarded as reaching a certain equilibrium point, and the dynamic system in this case is converted into a unified formula. In free space, the actual position of the system is compared with the desired position, and position tracking can be achieved by reducing the difference from the desired value through the algorithm. However, in most cases, the force between the manipulator and the external environment (assumed to be a purely rigid environment) exists dynamically. In this case, the force is neither zero nor can it be ignored by the system. In the actual process, the robot is mostly in such a state when it comes into contact with the external environment. At this time, the manipulator is not in the same mode as in free space, and the algorithm must have the ability to control the form to resist interference, adjust and control the force feedback of the manipulator. This is "impedance control".

[0114] Specifically, in simple terms, it is to describe the relationship between force and displacement. The force passes through a filter and is fed into the admittance control model, and the additional displacement is added to the current position to generate a new displacement. Its transfer function is shown in the following formula (6):

[0115]

[0116] Among them, X(s) is the frequency-domain representation of displacement, τ ext (s) is the frequency-domain representation of the external force torque, M is the inertia coefficient, B is the damping coefficient, and K is the stiffness coefficient.

[0117] Step S350: The collaborative robot executes the additional displacement at the current position to obtain a new displacement.

[0118] In this embodiment, by judging whether the rotational speed of the output end of the reducer is less than the minimum speed of dynamic friction compensation, if so, the static friction model is selected to calculate the frictional torque in the reducer; the compensated frictional torque is obtained according to the frictional torque in the reducer to compensate the frictional torque in the reducer, so that the frictional torque can be compensated specifically in the static friction stage, thereby being able to alleviate the jamming phenomenon in the static friction stage.

[0119] The above is only the implementation mode of this application, and does not limit the patent scope of this application. Any equivalent structure or equivalent process transformation made by using the content of the specification and drawings of this application, or directly or indirectly applied in other related technical fields, shall be included in the patent protection scope of this application by the same token.

Claims

1. A friction compensation method for a collaborative robot, characterized in that: A reducer and a motor are provided at the joint of the collaborative robot. The output end of the motor is connected to the input end of the reducer. The friction compensation method includes: Establish a static friction model; Obtain the values of the parameters in the static friction model through a friction model parameter identification experiment; Monitor the rotational speed of the output end of the reducer; In response to the rotational speed of the output end of the reducer being less than the minimum dynamic friction compensation speed, select the static friction model to calculate the frictional torque in the reducer; Obtain the compensated frictional torque based on the frictional torque in the reducer to compensate the frictional torque in the reducer.

2. The friction compensation method according to claim 1, wherein Before the step of monitoring the rotational speed of the output end of the reducer, it includes: Establish a Stribeck friction model; Obtain the values of the parameters in the Stribeck friction model through a friction model parameter identification experiment to determine the mathematical relationship between the rotational speed of the output end of the reducer and the frictional torque in the reducer; After the step of monitoring the rotational speed of the output end of the reducer, the friction compensation method further includes: Judge whether the rotational speed of the output end of the reducer is less than the minimum dynamic friction compensation speed; In response to the rotational speed of the output end of the reducer being greater than or equal to the minimum dynamic friction compensation speed, before the step of obtaining the compensated frictional torque based on the frictional torque in the reducer to compensate the frictional torque in the reducer, it further includes: Select the Stribeck friction model to calculate the frictional torque in the reducer according to the mathematical relationship between the rotational speed of the output end of the reducer and the frictional torque in the reducer.

3. The friction compensation method according to claim 2, characterized in that: The joint of the collaborative robot further includes an input end encoder and an output end encoder. The input end encoder is connected to the input end of the reducer, and the output end encoder is connected to the output end of the reducer; The rotational speed of the output end of the reducer is obtained by taking the derivative of the relative rotational angle between the rotational angle of the output end of the reducer and the rotational angle of the input end of the reducer with respect to time, or by taking the derivative of the rotational angle of the output end of the reducer with respect to time; When the rotational speed of the output end of the reducer is obtained by taking the derivative of the rotational angle of the output end of the reducer with respect to time, before the step of judging whether the rotational speed of the output end of the reducer is less than the minimum dynamic friction compensation speed, it further includes: Monitor the variance of multiple measurement values of the rotational angle of the output end of the reducer within a preset time interval; If the variance is greater than the threshold, jump to the step of judging whether the rotational speed of the output end of the reducer is less than the minimum dynamic friction compensation speed.

4. The friction compensation method according to claim 3, wherein When selecting the static friction model to calculate the frictional torque in the reducer, judge the direction of the compensated frictional torque according to the direction of the speed obtained by taking the derivative of the relative rotational angle between the rotational angle of the output end of the reducer and the rotational angle of the input end of the reducer with respect to time; When calculating the frictional torque in the reducer according to the mathematical relationship between the output speed of the reducer and the frictional torque in the reducer by using the Stribeck friction model, the direction of the compensated frictional torque is determined according to the direction of the speed obtained by differentiating the rotation angle of the output end of the reducer with respect to time.

5. The friction compensation method according to claim 4, wherein the analytical formula of the Stribeck friction model is as follows: τ f (qd,T) = c0(T) + c1(T)qd + c2(T)qd 2 + c3(T)qd 3 + c4(T)qd 4 + c5(T)qd 5 where τ f (qd,T) is the internal friction torque of the reducer, qd is the rotational speed of the output end of the reducer, T is the temperature of the reducer, c0(T), c1(T), c2(T), c3(T), c4(T) and c5(T) are first parameters, and the relationship between the first parameters and the temperature of the reducer is shown in the following equation: c j (T) = b j0 +b j1 T + b j2 T 2 where j is equal to 0, 1, 2, 3, 4 or 5, and c j (T) is the first parameter, T is the temperature of the reducer, and b j0 , b j1 and b j2 are the second parameters.

6. The friction compensation method according to claim 5, wherein obtaining the values of the parameters in the Stribeck friction model through the friction model parameter identification experiment includes: measuring the curve of the frictional torque in the reducer - the output speed of the reducer at different temperatures respectively; using the Stribeck friction model to fit the curve of the frictional force in the reducer - the output speed of the reducer at different temperatures to obtain the values of the first parameter at different temperatures; fitting the relationship between the first parameter and the temperature of the reducer to obtain the value of the second parameter.

7. The friction compensation method according to claim 1, wherein the function analytical formula of the static friction model is as follows: τ f (qd) = τ c k Among them, the τ f (qd) is the internal frictional torque of the reducer, and τ c is the Coulomb frictional torque in the reducer, and k is the static friction compensation parameter.

8. A computer device, characterized in that, The computer device includes: a memory storing program data; and a processor, and the program data can be executed by the processor to implement the friction compensation method according to any one of claims 1 - 7.

9. A storage device, characterized in that, The storage device stores program data, and the program data can be executed by the processor to implement the friction compensation method according to any one of claims 1 - 7.

10. A drag teaching method, characterized in that, The dragging teaching method includes: collecting the output torque of the motor; compensating the frictional torque in the reducer according to the method according to claim 1; calculating the external torque through inverse dynamics according to the output torque of the motor and the frictional torque in the reducer; obtaining an additional displacement through the admittance control model according to the external torque; The collaborative robot executes the additional displacement at the current position to obtain a new displacement.

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