Robot impedance force control method suitable for variable stiffness environment

Abstract

The invention discloses a robot impedance force control method applicable to a variable stiffness environment, which comprises the following steps: firstly, determining an impedance filter according to environmental parameters, determining inertial parameters and stiffness parameters of the impedance filter, and adjusting damping parameters according to environmental stiffness; then, according to the environment parameters and expected force information, a reference track of a mechanical arm tail end actuator is obtained through calculation, contact force is detected in real time, contact force errors are calculated, position deviation is generated through a fixed impedance filter or a variable impedance filter, and the position deviation and the reference track are overlapped to obtain the instruction position of the mechanical arm tail end; and finally, the end effector operates according to the instruction position so as to realize accurate force control. According to the scheme, different impedance filters are applied according to the known or unknown condition of the environment rigidity, the method can be suitable for the working scene with the environment rigidity changing, compared with a traditional impedance force control method, stable operation and accurate force control of the mechanical arm in the variable rigidity environment can be achieved, and the mechanical arm control method is suitable for large-scale popularization and application. And the method can be conveniently applied to various application scenes.

Description

Technical Field

[0001] The invention belongs to the field of robot force control, and in particular relates to a robot impedance force control method suitable for a variable stiffness environment. Background Art

[0002] Traditional industrial robots mostly use position control, which is sufficient for structured low-rigidity working environments or non-contact work tasks that only require strict trajectory tracking. However, with the increasing application of robots, position control is no longer sufficient for the actual application of robotic arms. For example, the growing demand for high-precision assembly, high-precision force-controlled grinding tasks, and various work tasks involving human-machine interaction, due to the unstructured characteristics and uncertainty of the work object, the use of position control is very likely to cause personal injury. Therefore, in view of the above situation, high-precision force control is the development trend of existing collaborative robots.

[0003] In order to make the robot have high-precision force control capability and a certain degree of compliance in contact tasks, an impedance force control method was designed, which is effective when the environment stiffness is fixed. However, when the environment stiffness is changing, the above impedance force control method cannot guarantee that the force tracking error is still converged. At the same time, the expansion of robot application scenarios in recent years has made operation tasks in variable stiffness environments more and more common. Such tasks can be divided into two categories: the first category requires the robot end effector to make fixed-point contact with the environment and track the desired force, where the environmental stiffness of the contact point changes with time, such as using a robot to massage humans; the second category requires the robot end effector to move along the surface of the environment and track the desired force in the normal direction of the surface of the environment, where the environmental stiffness of the contact point changes with the surface position, such as using a robot to perform grinding operations on the surface of a workpiece with uneven stiffness. If the traditional impedance force control method continues to be used in the above variable stiffness environment, it may lead to the failure of the force control task or even serious operation accidents.

[0004] Based on the above situation, there is an urgent need to develop an impedance control method suitable for variable stiffness environments to improve the safety and applicability of robot operations and meet the ever-expanding needs of robot applications. However, there is no relevant description in the prior art. Summary of the invention

[0005] In view of the above problems, the purpose of the present invention is to provide a robot impedance force control method suitable for a variable stiffness environment, aiming to ensure the stability and force control effect of the robot performing force control operations in a variable stiffness environment.

[0006] The specific technical solution for achieving the purpose of the present invention is:

[0007] A robot impedance force control method suitable for a variable stiffness environment comprises the following steps:

[0008] Step 1, determine the impedance filter according to environmental parameters;

[0009] Step 2, determining the inertia parameters and stiffness parameters of the impedance filter;

[0010] Step 3, adjusting the damping parameters of the impedance filter according to the environmental stiffness;

[0011] Step 4: Calculate the reference trajectory of the end effector of the robot arm according to the environmental parameters and the expected force information;

[0012] Step 5: Detect the contact force in real time and calculate the contact force error, so that it can generate a position deviation through a fixed impedance filter or a variable impedance filter, and superimpose it with the reference trajectory to obtain the command position of the end of the robot arm;

[0013] Step 6: The end effector moves according to the command position to achieve precise force control.

[0014] Compared with the prior art, the present invention has the following beneficial effects:

[0015] (1) The technical solution of the present invention is applicable to working scenarios where the environment stiffness changes. Compared with the traditional impedance force control method which can only realize accurate force control in a fixed stiffness environment, the technical solution of the present invention realizes the stable operation and accurate force control of the robot arm in a variable stiffness environment;

[0016] (2) When the environmental parameters are precisely known, the two impedance parameter configuration rules proposed in the technical solution of the present invention do not involve the rate of change of the environmental stiffness, nor do they require the environmental stiffness to be smooth and continuous, so it can be conveniently applied to a variety of application scenarios;

[0017] (3) In the technical solution of the present invention, when the environmental parameters are unknown, the ratio of the derivative of the coupling stiffness to the coupling stiffness in the proposed damping parameter adjustment constraint rule is not directly calculated. Instead, the logarithm of the coupling stiffness is first calculated, and then the derivative of the logarithm of the coupling stiffness is obtained using a tracking differentiator. This is used as the ratio of the derivative of the coupling stiffness to the coupling stiffness, which can effectively suppress the noise caused by directly calculating the derivative of the coupling stiffness.

[0018] (4) Compared with the robot impedance control in a fixed stiffness environment, when the environmental parameters are precisely known, this scheme only needs to reasonably configure the impedance parameters according to the environmental stiffness information before the task starts; when the environmental parameters are unknown, this scheme only needs to adjust the damping parameters in real time according to the measured environmental stiffness information during the task. The other steps of the scheme are the same as those of the robot impedance control in a fixed stiffness environment, so this scheme has a high promotion value and application prospects.

[0019] The present invention is further described below in conjunction with specific implementation modes. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The figure is a flow chart of the robot impedance force control method applicable to a variable stiffness environment according to the present invention.

[0021] Figure 2 It is a schematic diagram of the robot impedance force control applicable to a variable stiffness environment according to the present invention.

[0022] Figure 3 This is a graph showing the variation of the discontinuous environment stiffness with time in Example 1 of the present invention.

[0023] Figure 4 Graphs showing the contact force curve and the contact force error curve in Example 1 of the present invention.

[0024] Figure 5 Schematic diagram of a true value curve and an estimated value curve of the ratio of the derivative of the coupling stiffness to the coupling stiffness in Example 2 of the present invention.

[0025] Figure 6 Schematic diagram of a curve showing a change in the variable damping parameter over time in Example 2 of the present invention.

[0026] Figure 7 Graphs showing the contact force curve and the contact force error curve in Example 2 of the present invention. DETAILED DESCRIPTION

[0027] Combination Figure 1 and Figure 2 , a robot impedance force control method suitable for a variable stiffness environment, comprising the following steps:

[0028] Step 1: Determine the impedance filter based on environmental parameters:

[0029] When the environment stiffness information is known, a constant impedance filter is used to realize the robot impedance force control:

[0030]

[0031] Among them, e x is the actual position x of the robot end effector and the reference position x r The difference, e f is the expected contact force f d The actual contact force f e The difference, m d ,b d ,k d They are respectively the inertia parameter, damping parameter, and stiffness parameter of the constant impedance filter;

[0032] When the environment stiffness information is unknown, a variable impedance filter is used to realize the robot impedance force control:

[0033]

[0034] Among them, b d (t) is the variable damping parameter of the variable impedance filter.

[0035] Step 2, determining the inertia parameters and stiffness parameters of the impedance filter;

[0036] Step 3: Adjust the damping parameters of the impedance filter according to the environmental stiffness:

[0037] When the environmental stiffness information is known, the damping parameter range of the constant impedance filter is determined according to the value of the environmental stiffness, including two cases:

[0038] (1) When the environmental stiffness information is known, if the environmental stiffness information is less than the set threshold, the damping parameter range of the constant impedance filter is b d ∈Θ1, where Θ1 is the solution set of the following inequality:

[0039]

[0040] If the environmental stiffness information is greater than the set threshold and the stiffness variation range is small, the damping parameter range of the constant impedance filter is b d ∈Θ2, where Θ2 is the solution set of the following inequality:

[0041]

[0042] Where, k(t): = k d +k e (t) is the robot-environment coupling stiffness, k e (t) is the stiffness parameter of the environment, and h is a positive constant.

[0043] (2) In addition, when the range of environmental stiffness does not have obvious high and low characteristics, it can also be determined according to the following formula. The damping parameter range of the constant impedance filter is b d ∈Θ1∪Θ2:

[0044] where Θ1 is the solution set of the following inequality:

[0045]

[0046] Θ2 is the set of solutions to the following inequality:

[0047]

[0048] Where, k(t): = k d+k e (t) is the robot-environment coupling stiffness, k e (t) is the stiffness parameter of the environment, and h is a positive constant.

[0049] The above two constant impedance parameter configuration rules do not require the environmental stiffness to be smooth and continuous, nor do they need to know the rate of change of the environmental stiffness, which makes the configuration rules convenient to use.

[0050] When the environmental stiffness information is unknown, the variable damping parameter range of the variable impedance filter is determined based on the real-time detection data:

[0051] The measured value of the environmental stiffness is calculated based on the force information obtained by the detection and the environmental position information when there is no force deformation:

[0052]

[0053] in, is the measured value of the environmental stiffness parameter, is the measured value of force information, is the measured value of the environment position when there is no force deformation, then the estimated value of the robot-environment coupling stiffness is

[0054] Then the adjustment range of the variable damping parameter of the variable impedance filter is:

[0055]

[0056] Step 4: Calculate the reference trajectory of the end effector of the robot arm based on the environmental parameters and the expected force information:

[0057] The reference trajectory of the end effector of the robot arm is:

[0058]

[0059] Among them, f d is the desired contact force, x e (t),k e (t) respectively represent the environmental position and environmental stiffness when subjected to force;

[0060] When the environmental parameters are known, x e (t),k e (t) is obtained based on known data. When the environmental parameters are unknown, the reference trajectory x r The design requires the above variables x e (t),k e (t) Use the corresponding measured / estimated values as well as Replace.

[0061] Step 5: Detect the contact force in real time and calculate the contact force error, so that it can generate a position deviation through a fixed impedance filter or a variable impedance filter, and superimpose it with the reference trajectory to obtain the command position of the end of the robot arm;

[0062] Step 6: The end effector moves according to the command position to achieve precise force control.

[0063] The present invention also provides a robot impedance control system suitable for use in a variable stiffness environment, comprising the following modules:

[0064] Impedance filter selection module: used to determine the selected impedance filter according to environmental parameters;

[0065] Parameter determination module: used to determine the inertia parameters and stiffness parameters of the impedance filter, and adjust the damping parameters of the impedance filter according to the environmental stiffness;

[0066] Robot control module: used to calculate the reference trajectory of the end effector of the robot arm according to the environmental parameters and the expected force information, detect the contact force in real time and calculate the contact force error, so that it can generate the position deviation through the fixed impedance filter or the variable impedance filter, and superimpose it with the reference trajectory to obtain the command position of the end of the robot arm;

[0067] Execution module: used to control the end effector to run according to the command position to achieve precise force control.

[0068] The present invention also provides a computer device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the following steps when executing the computer program:

[0069] Step 1, determine the impedance filter according to environmental parameters;

[0070] Step 2, determining the inertia parameters and stiffness parameters of the impedance filter;

[0071] Step 3, adjusting the damping parameters of the impedance filter according to the environmental stiffness;

[0072] Step 4: Calculate the reference trajectory of the end effector of the robot arm according to the environmental parameters and the expected force information;

[0073] Step 5: Detect the contact force in real time and calculate the contact force error, so that it can generate a position deviation through a fixed impedance filter or a variable impedance filter, and superimpose it with the reference trajectory to obtain the command position of the end of the robot arm;

[0074] Step 6: The end effector moves according to the command position to achieve precise force control.

[0075] The present invention also provides a computer storable medium having a computer program stored thereon, wherein when the computer program is executed by a processor, the following steps are implemented:

[0076] Step 1, determine the impedance filter according to environmental parameters;

[0077] Step 2, determining the inertia parameters and stiffness parameters of the impedance filter;

[0078] Step 3, adjusting the damping parameters of the impedance filter according to the environmental stiffness;

[0079] Step 4: Calculate the reference trajectory of the end effector of the robot arm according to the environmental parameters and the expected force information;

[0080] Step 5: Detect the contact force in real time and calculate the contact force error, so that it can generate a position deviation through a fixed impedance filter or a variable impedance filter, and superimpose it with the reference trajectory to obtain the command position of the end of the robot arm;

[0081] Step 6: The end effector moves according to the command position to achieve precise force control.

[0082] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the accompanying drawings in the embodiments of the present invention. The described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0083] As shown in this application and claims, unless the context clearly indicates an exception, the words "a", "an", "an kind" and / or "the" do not refer to the singular and may also include the plural. Generally speaking, the terms "include" and "comprise" only indicate the inclusion of the steps and elements that have been clearly identified, and these steps and elements do not constitute an exclusive list. The method or device may also include other steps or elements.

[0084] Unless otherwise specifically stated, the relative arrangement, numerical expressions and numerical values ​​of the parts and steps set forth in these embodiments do not limit the scope of the present application. At the same time, it should be understood that, for ease of description, the sizes of the various parts shown in the accompanying drawings are not drawn according to the actual proportional relationship. The technology, method and equipment known to those of ordinary skill in the relevant field may not be discussed in detail, but in appropriate cases, the technology, method and equipment should be considered as a part of the authorization specification. In all examples shown and discussed here, any specific value should be interpreted as being merely exemplary, rather than as a limitation. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters represent similar items in the following drawings, so that once a certain item is defined in an accompanying drawing, it does not need to be further discussed in subsequent drawings.

[0085] Example 1

[0086] In this embodiment, the working environment faced by the robot arm has the following parameter settings, and the environmental position when no force is applied is:

[0087]

[0088] The environment stiffness is set to:

[0089]

[0090] Among them, the environmental parameters are all known accurately, and the image of the environmental stiffness changing with time is as follows Figure 3 As shown, we can see that the change in the environment stiffness is not smooth or even continuous. Set the desired contact force to:

[0091]

[0092] This embodiment adopts the above-mentioned robot impedance force control method applicable to variable stiffness environment to perform force tracking control. The experiment is carried out on MATLAB and simulink simulation platform, including the following steps:

[0093] Step 1: Since the environmental parameters are precisely known, the controller uses the following fixed impedance filter:

[0094]

[0095] where e x Defined as the actual position x of the robot end effector and the reference position x r The difference, e f Defined as the desired contact force f d The actual contact force f e The difference, and m d ,bd ,k d They are the inertia parameter, damping parameter, and stiffness parameter of the constant impedance filter;

[0096] Step 2: Give the corresponding inertia parameter m of the impedance filter d =600N·s 2 / m, and stiffness parameter k d =300N / m.

[0097] Step 3: According to the known environmental stiffness information, k(t)∈[600, 1800] is obtained. At this time, the range of environmental stiffness does not have obvious high and low characteristics. Two different fixed impedance parameter configuration rules are used:

[0098] (1) Using configuration rule 1, the configured damping parameters should make the following inequality always hold true:

[0099]

[0100] The damping parameters should satisfy

[0101] (2) Using configuration rule 2, the configured damping parameters should make the following inequality always hold true:

[0102]

[0103] That is, the following inequality should always hold true,

[0104]

[0105] Taking h = 1200, we can solve that the damping parameter should satisfy Where k(t): = k d +k e (t) is defined as the robot-environment coupling stiffness, k e (t) is the stiffness parameter of the environment. Finally, the damping parameter is set to b d =650N·s / m for simulation.

[0106] Step 4: When the environmental parameters are known, the reference trajectory of the end effector of the robot arm is calculated according to the environmental parameters and the expected force information. The calculation formula is:

[0107]

[0108] Step 5: Detect the contact force in real time and calculate the contact force error, so that it can generate a position deviation through a constant impedance filter, and superimpose it with the reference trajectory to obtain the command position of the end of the robot arm;

[0109] Step 6: The end effector moves according to the command position to achieve precise force control.

[0110] The contact force curve and the contact force error curve in this embodiment are as follows: Figure 4 As shown, it can be seen that the robot impedance force control method applicable to variable stiffness environments of the present invention can still achieve precise force control when facing a variable stiffness environment with precisely known environmental parameters, even if the environmental stiffness is not smooth or even continuous.

[0111] Embodiment 2:

[0112] Considering that the working environment faced by the robot arm has the following parameter settings, the environmental position when no force is applied is:

[0113]

[0114] The environment stiffness is set to k e (t) = 900 + 600 sin (3 t) N / m, where the environmental parameters are not known. Set the desired contact force to:

[0115]

[0116] This embodiment adopts the above-mentioned robot impedance force control method applicable to variable stiffness environment to perform force tracking control. The experiment is carried out on MATLAB and simulink simulation platform, including the following steps:

[0117] Step 1: Since the environmental parameters are not precisely known, the controller uses the following variable impedance filter:

[0118]

[0119] where b d (t) is the variable damping parameter of the variable impedance filter;

[0120] Step 2: Give the corresponding inertia parameter m of the impedance filter d =600N·s 2 / m, and stiffness parameter k d =300N / m.

[0121] Step 3: adjust the damping parameters in real time according to the environmental stiffness obtained by real-time detection. The specific steps are as follows:

[0122] Step 3-1: Calculate the measured value of the environmental stiffness using the detectable force information and the environmental position information when there is no force deformation. The calculation formula is:

[0123]

[0124] in, is the measured value of the environmental stiffness parameter, is the measured value of force information, is the measured value of the environment position when no force is applied. The estimated value of the robot-environment coupling stiffness is

[0125] Step 3-2: The adjustment rule of the variable damping parameter in the variable impedance filter should make the following inequality always hold true:

[0126]

[0127] Step 3-3: Obtain by using the tracking differentiator The differential of in The true value and estimated value curves are as follows Figure 5 As shown, the variable damping parameters are then designed as:

[0128]

[0129] The designed variable damping parameter b d (t) The image changes over time. Figure 6 shown.

[0130] Step 4: When the environmental parameters are known, the reference trajectory of the end effector of the robot arm is calculated according to the environmental parameters and the expected force information. The calculation formula is:

[0131]

[0132] Step 5: Detect the contact force in real time and calculate the contact force error, so that it can generate a position deviation through a variable impedance filter, and superimpose it with the reference trajectory to obtain the command position of the end of the robot arm;

[0133] Step 6: The end effector moves according to the command position to achieve precise force control.

[0134] The contact force curve and the contact force error curve in this embodiment are as follows: Figure 7 As shown, it can be seen that the robot impedance force control method applicable to variable stiffness environments of the present invention can also achieve precise force control when facing a variable stiffness environment with unknown environmental parameters.

[0135] The above-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the attached claims.

Claims

1. A robot impedance control method suitable for a variable stiffness environment, characterized in that: The following steps are involved: Step 1, determine the impedance filter according to environmental parameters; Step 2, determining the inertia parameters and stiffness parameters of the impedance filter; Step 3, adjusting the damping parameters of the impedance filter according to the environmental stiffness; Step 4: Calculate the reference trajectory of the end effector of the robot arm according to the environmental parameters and the expected force information; Step 5: Detect the contact force in real time and calculate the contact force error, so that it can generate a position deviation through a fixed impedance filter or a variable impedance filter, and superimpose it with the reference trajectory to obtain the command position of the end of the robot arm; Step 6: The end effector moves according to the command position to achieve precise force control.

2. The robot impedance control method suitable for variable stiffness environment according to claim 1, characterized in that: Determining the impedance filter according to the environmental parameters in step 1 is specifically as follows: When the environment stiffness information is known, a constant impedance filter is used to realize the robot impedance force control: Among them, e x is the actual position x of the robot end effector and the reference position x r The difference, e f is the expected contact force f d The actual contact force f e The difference, m d ,b d ,k d They are respectively the inertia parameter, damping parameter, and stiffness parameter of the constant impedance filter; When the environment stiffness information is unknown, a variable impedance filter is used to realize the robot impedance force control: Among them, b d (t) is the variable damping parameter of the variable impedance filter.

3. The robot impedance control method suitable for variable stiffness environment according to claim 2, characterized in that: The damping parameters in step 3 are adjusted according to the environmental stiffness, specifically: When the environmental stiffness information is known, the damping parameter range of the constant impedance filter is determined according to the value of the environmental stiffness; When the environmental stiffness information is unknown, the variable damping parameter range of the variable impedance filter is determined according to the real-time detection data.

4. The robot impedance control method suitable for variable stiffness environment according to claim 3, characterized in that: When the environmental stiffness information is known, if the environmental stiffness information is less than the set threshold, the damping parameter range of the constant impedance filter is b d ∈Θ1, where Θ1 is the solution set of the following inequality: If the environmental stiffness information is greater than the set threshold, the damping parameter range of the constant impedance filter is b d ∈Θ2, where Θ2 is the solution set of the following inequality: Where, k(t): = k d +k e (t) is the robot-environment coupling stiffness, k e (t) is the stiffness parameter of the environment, and h is a positive constant.

5. The robot impedance control method suitable for variable stiffness environment according to claim 3, characterized in that: When the environmental stiffness information is known, the damping parameter range of the constant impedance filter is b d ∈Θ1∪Θ2: where Θ1 is the solution set of the following inequality: Θ2 is the set of solutions to the following inequality: Where, k(t): = k d +k e (t) is the robot-environment coupling stiffness, k e (t) is the stiffness parameter of the environment, and h is a positive constant.

6. The robot impedance control method suitable for variable stiffness environment according to claim 3, characterized in that: When the environment stiffness information is unknown, the measured value of the environment stiffness is calculated based on the force information obtained by detection and the environment position information when there is no force deformation: in, is the measured value of the environmental stiffness parameter, is the measured value of force information, is the measured value of the environment position when there is no force deformation, then the estimated value of the robot-environment coupling stiffness is Then the adjustment range of the variable damping parameter of the variable impedance filter is:

7. The robot impedance control method suitable for variable stiffness environment according to claim 2, characterized in that: The reference trajectory of the end effector of the robot arm is: Among them, f d is the desired contact force, x e (t),k e (t) represent the ambient position and ambient stiffness when no force is applied, respectively.

8. A robot impedance control system suitable for use in a variable stiffness environment, characterized in that: Includes the following modules: Impedance filter selection module: used to determine the selected impedance filter according to environmental parameters; Parameter determination module: used to determine the inertia parameters and stiffness parameters of the impedance filter, and adjust the damping parameters of the impedance filter according to the environmental stiffness; Robot control module: used to calculate the reference trajectory of the end effector of the robot arm according to the environmental parameters and the expected force information, detect the contact force in real time and calculate the contact force error, so that it can generate the position deviation through the fixed impedance filter or the variable impedance filter, and superimpose it with the reference trajectory to obtain the command position of the end of the robot arm; Execution module: used to control the end effector to run according to the command position to achieve precise force control.

9. A computer device comprising a memory, a processor and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the computer program, the steps of the method according to any one of claims 1 to 7 are implemented.

10. A computer storable medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the method according to any one of claims 1 to 7 are implemented.

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