A robot impedance force control method suitable for a variable stiffness environment

Abstract

The application discloses a robot impedance force control method suitable for a variable stiffness environment. First, an impedance filter is determined according to environment parameters, inertia parameters and stiffness parameters of the impedance filter are determined, and a damping parameter is adjusted according to environment stiffness. Then, a reference trajectory of an end effector of a mechanical arm is calculated according to the environment parameters and expected force information, contact force is detected in real time, and a contact force error is calculated, so that the contact force error is converted into a position deviation through a constant impedance filter or a variable impedance filter, the position deviation is superimposed with the reference trajectory to obtain a command position of the end effector of the mechanical arm, and finally, the end effector operates according to the command position to realize accurate force control. The scheme of the application applies different impedance filters according to the known or unknown environment stiffness, can be applied to a work scene with variable environment stiffness, and compared with a traditional impedance force control method, can realize stable operation and accurate force control of the mechanical arm in the variable stiffness environment, and is conveniently applied to various application scenes.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of robot force control, and particularly relates to a robot impedance force control method suitable for a variable stiffness environment. BACKGROUND

[0002] Traditional industrial robots mostly adopt position control, which is sufficient for a structured low stiffness working environment or a non-contact type working task which only needs to strictly perform trajectory tracking. However, with the increasingly wide application of robots, position control is not enough for the actual application of the mechanical arm, for example, the increasingly demanding high-precision assembly, high-precision force control polishing task, and various working tasks involving human-robot interaction. Due to the unstructured characteristics and uncertainty of the working object, position control is likely to cause personnel injury, therefore, for the above-mentioned situations, high-precision force control is the development trend of existing collaborative robots.

[0003] In order to enable the robot to have high-precision force control capability and have certain compliance capability in contact tasks, an impedance force control method is designed, which is effective when the environmental stiffness is fixed. However, when the environmental stiffness is variable, the above-mentioned impedance force control method cannot guarantee that the force tracking error is still convergent. At the same time, in recent years, the expansion of robot application scenarios makes the operation task in the variable stiffness environment more and more common. Such tasks can be divided into two categories: the first category requires the robot end effector to have point contact with the environment and track the expected force, wherein the environmental stiffness of the contact point changes over time, for example, using a robot to massage a human; the second category requires the robot end effector to move along the surface of the environment and track the expected force in the normal direction of the surface of the environment, wherein the environmental stiffness of the contact point changes with the surface position, for example, using a robot to polish a workpiece surface with uneven stiffness. If the traditional impedance force control method is continued to be used in the above-mentioned variable stiffness environment, it may cause the failure of the force control task or even serious work accidents.

[0004] Based on the above-mentioned situation, it is urgent to develop an impedance force control method suitable for a variable stiffness environment, to improve the safety and applicability of robot operation, and to meet the expanding application requirements of robots. However, there is no related description in the prior art. SUMMARY

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

[0006] The specific technical scheme for realizing the purpose of the present application is as follows:

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

[0008] Step 1, determining the impedance filter according to the environment parameters;

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

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

[0011] Step 4, calculating the reference trajectory of the robot end effector according to the environment parameters and the expected force information;

[0012] Step 5, detecting the contact force in real time and calculating the contact force error, so that the position deviation is generated through the constant impedance filter or the variable impedance filter, and the instruction position of the robot end effector is obtained by superimposing the reference trajectory;

[0013] Step 6, the end effector operates according to the instruction position to realize precise force control.

[0014] Compared with the prior art, the beneficial effects of the present application are:

[0015] (1) The technical scheme of the present application is suitable for the operation scene with variable environment stiffness. Compared with the traditional impedance force control method which can only realize precise force control in a fixed stiffness environment, the present application realizes stable operation and precise force control of the robot in a variable stiffness environment;

[0016] (2) When the environment parameters are accurately known, the two impedance parameter configuration rules proposed in the present application do not involve the rate of change of the environment stiffness, and do not require the environment stiffness to have smoothness and continuity, so they can be easily applied to various application scenarios;

[0017] (3) When the environment parameters are unknown, the derivative of the coupling stiffness and the ratio of the coupling stiffness in the damping parameter adjustment constraint rule are not directly calculated, but 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, which is used as the derivative of the coupling stiffness and the ratio of the coupling stiffness. This can effectively suppress the noise caused by directly calculating the derivative of the coupling stiffness;

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

[0019] The application will be further described below in conjunction with the specific embodiments. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 Flow chart of the robot impedance force control method suitable for variable stiffness environment of the application.

[0021] Figure 2 Schematic diagram of the robot impedance force control suitable for variable stiffness environment of the application.

[0022] Figure 3 Curve diagram of the non-continuous environmental stiffness changing with time in embodiment 1 of the application.

[0023] Figure 4 Contact force curve and contact force error curve diagram in embodiment 1 of the application.

[0024] Figure 5 Schematic diagram of the real value curve and the estimated value curve of the ratio of the derivative of the coupling stiffness to the coupling stiffness in embodiment 2 of the application.

[0025] Figure 6 Schematic diagram of the variable damping parameter changing with time in embodiment 2 of the application.

[0026] Figure 7 Contact force curve and contact force error curve diagram in embodiment 2 of the application. DETAILED DESCRIPTION

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

[0028] Step 1, determining the impedance filter according to the environmental parameters:

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

[0030]

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

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

[0033]

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

[0035] Step 2, determine the inertia parameter and the stiffness parameter of the impedance filter;

[0036] Step 3, adjust the damping parameter of the impedance filter according to the environment stiffness:

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

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

[0039]

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

[0041]

[0042] wherein, 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 normal number.

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

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

[0045]

[0046] Θ2 is the solution set of the following inequality:

[0047]

[0048] wherein, k(t):=k d+k e (t) is the stiffness parameter of the environment, and h is a normal number. e (t) is the stiffness parameter of the environment, and h is a normal number.

[0049] The above two constant impedance parameter configuration rules do not require the environment stiffness to have smoothness and continuity, and do not need to know the rate of change of the environment stiffness, which makes the configuration rule convenient to use.

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

[0051] The measured value of the environment stiffness is calculated according to the detected force sensation information and the environment position information when the environment is not deformed under force:

[0052]

[0053] wherein, is the measured value of the stiffness parameter of the environment, is the measured value of the force sensation information, is the measured value of the environment position when the environment is not deformed under force, and the estimated value of the robot-environment coupling stiffness is

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

[0055]

[0056] Step 4, the reference trajectory of the mechanical arm end effector is calculated according to the environment parameters and the expected force information:

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

[0058]

[0059] wherein, f d is the expected contact force, x e (t), k e (t) respectively represent the environment position and the environment stiffness when under force;

[0060] When the environment parameters are known, x e (t), k e (t) are obtained according to known data, and when the environment parameters are unknown, the design of the reference trajectory x r needs to replace the above variables x e (t), k e (t) with the corresponding measured values / estimated values and .

[0061] Step 5, detecting the contact force in real time and calculating the contact force error, making it pass through the constant impedance filter or the variable impedance filter to generate the position deviation, superimposing the reference trajectory to obtain the command position of the end of the robot arm;

[0062] Step 6, the end effector runs according to the command position to realize accurate force control.

[0063] The application also provides a robot impedance force control system suitable for a variable stiffness environment, comprising the following modules:

[0064] The impedance filter selection module is used for determining the selected impedance filter according to the environment parameters;

[0065] The parameter determination module is used for determining the inertia parameter and the stiffness parameter of the impedance filter, and adjusting the damping parameter of the impedance filter according to the environment stiffness;

[0066] The robot control module is used for calculating the reference trajectory of the end effector of the robot arm according to the environment parameters and the expected force information, detecting the contact force in real time and calculating the contact force error, making it pass through the constant impedance filter or the variable impedance filter to generate the position deviation, superimposing the reference trajectory to obtain the command position of the end of the robot arm;

[0067] The execution module is used for controlling the end effector to run according to the command position to realize accurate force control.

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

[0069] Step 1, determining the impedance filter according to the environment parameters;

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

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

[0072] Step 4, calculating the reference trajectory of the end effector of the robot arm according to the environment parameters and the expected force information;

[0073] Step 5, detecting the contact force in real time and calculating the contact force error, making it pass through the constant impedance filter or the variable impedance filter to generate the position deviation, superimposing the reference trajectory to obtain the command position of the end of the robot arm;

[0074] Step 6, the end effector runs according to the command position to realize accurate force control.

[0075] The application further provides a computer storage medium, which stores a computer program, and the computer program is executed by a processor to implement the following steps:

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

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

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

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

[0080] Step 5, detecting the contact force in real time and calculating the contact force error, so that the position deviation is generated through the constant impedance filter or the variable impedance filter, and the instruction position of the end of the robot arm is obtained by superimposing the reference trajectory;

[0081] Step 6, the end effector operates according to the instruction position to realize the precise force control.

[0082] The technical solutions in the embodiments of the application will be described clearly and completely below with reference to the drawings in the embodiments of the application. The described embodiments are only some of the embodiments of the application, rather than all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative work under the premise that the application falls within the scope of protection.

[0083] As shown in the application and claims, unless the context clearly indicates otherwise, the words “one”, “a”, “an” and / or “the” do not refer to the singular, but also include the plural. Generally, the terms “comprise” and “include” only indicate that the steps and elements explicitly identified are included, and these steps and elements do not constitute an exclusive list, and the method or device can also include other steps or elements.

[0084] The application is not limited by the relative positioning of parts and steps, the numerical expressions, and values set forth in the examples unless otherwise specifically stated. It will be appreciated that the dimensions of the various parts illustrated in the drawings are chosen for convenience only and unless otherwise specifically stated, are not intended to limit the application. Techniques, methods, and apparatus known to those of ordinary skill in the relevant art can not be discussed in detail but can be assumed by those of ordinary skill in the art to be within the scope of the present application. In all examples shown and discussed herein, any specific values should be interpreted as merely exemplary and not as a limitation on the application. Thus, other examples of the exemplary embodiments can have different values. It is to be noted that like numbers and letters refer to like elements throughout the several views of the drawings and, as such, no further discussion with regard thereto is deemed necessary.

[0085] Example 1

[0086] The working environment in which the robot arm is facing in this example has the following parameter settings, the environment position when not under force is:

[0087]

[0088] The environment stiffness is set as:

[0089]

[0090] Wherein, the environment parameters are all accurately known, and the image of the environment stiffness changing over time is as shown in Figure 3 It can be seen that the change of the environment stiffness is not smooth, even not continuous. The desired contact force is set as:

[0091]

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

[0093] Step 1, since the environment parameters are accurately known, the controller uses the following constant impedance filter:

[0094]

[0095] Wherein e x is defined as the difference between the actual position x of the robot end effector and the reference position x r , e f is defined as the difference between the desired contact force f d and the actual contact force f e , and m d , bd k d are the inertia parameter, the damping parameter and the stiffness parameter of the constant impedance filter respectively;

[0096] Step 2, the inertia parameter m d = 600 N·s 2 / m of the constant impedance filter is given d = 300 N / m.

[0097] Step 3, according to the known environmental stiffness information, k(t) ∈ [600, 1800], at this time, the range of environmental stiffness does not have obvious high and low characteristics, two different constant impedance parameter configuration rules are adopted:

[0098] (1) Configuration rule 1 is adopted, the damping parameter configured should make the following inequality always hold,

[0099]

[0100] The damping parameter should satisfy

[0101] (2) Configuration rule 2 is adopted, the damping parameter configured should make the following inequality always hold,

[0102]

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

[0104]

[0105] Taking h = 1200, 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 = 650 N·s / m for simulation.

[0106] Step 4, when the environmental parameters are known, the reference trajectory of the manipulator end effector is calculated according to the environmental parameters and the desired force information, and the calculation formula is:

[0107]

[0108] Step 5, the contact force is detected in real time and the contact force error is calculated, so that it passes through the constant impedance filter to generate a position deviation, and the reference trajectory is superimposed to obtain the command position of the manipulator end effector;

[0109] Step 6, the end effector operates according to the instruction position to realize precise force control.

[0110] The contact force curve and the contact force error curve in this embodiment are shown in FIG. 6 and FIG. 7, respectively. Figure 4 It can be seen that the robot impedance force control method applicable to the variable stiffness environment according to the present application can realize precise force control even if the environmental stiffness is not smooth or even discontinuous when facing a variable stiffness environment with precisely known environmental parameters.

[0111] Embodiment 2:

[0112] It is assumed that the working environment faced by the robot has the following parameter settings, and the environmental position when not subjected to force is:

[0113]

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

[0115]

[0116] This embodiment uses the robot impedance force control method applicable to the variable stiffness environment described above to perform force tracking control. The experiment is performed on the 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, the corresponding inertia parameter m d = 600 N·s 2 / m and the stiffness parameter k d = 300 N / m of the impedance filter are given.

[0121] Step 3, the damping parameter is adjusted in real time according to the real-time detected environmental stiffness, and the specific steps are as follows:

[0122] Step 3-1, the measured value of the environmental stiffness is calculated using the detectable force sensation information and the environmental position information when not subjected to deformation, and the calculation formula is:

[0123]

[0124] wherein, is the measured value of the environmental stiffness parameter, is the measured value of the force information, is the measured value of the environmental position when not deformed by force. The estimated value of the coupling stiffness of the robot-environment 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,

[0126]

[0127] Step 3-3, the differential of is obtained by using a tracking differentiator, which is required in step 3-2. wherein the true value of and the estimated value curve are shown in , and then the variable damping parameter is designed as: Figure 5

[0128]

[0129] wherein the designed variable damping parameter b d (t) changes over time as shown in Figure 6 .

[0130] Step 4, when the environmental parameter is known, the reference trajectory of the end effector of the robot arm is calculated according to the environmental parameter and the expected force information, and the calculation formula is:

[0131]

[0132] Step 5, the contact force is detected in real time and the contact force error is calculated, so that it passes through the variable impedance filter to generate a position deviation, and is superimposed with the reference trajectory to obtain the command position of the end effector of the robot arm;

[0133] Step 6, the end effector operates 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 shown in Figure 7 , and it can be seen that the robot impedance force control method of the present application applicable to the variable stiffness environment can also achieve precise force control when facing the variable stiffness environment with unknown environmental parameters.

[0135] ​The above-described embodiments are merely illustrative of several embodiments of the present application, which are described in more detail and in a specific and detailed manner, but should not be construed as limiting the scope of the patent. It should be noted that for those skilled in the art, several modifications 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 should be subject to the appended claims.

Claims

1. A robot impedance force control method suitable for use in a variable stiffness environment, characterized by, The method comprises the following steps: Step 1, determining the impedance filter according to the environmental parameters: When the environmental stiffness information is known, a constant impedance filter is used to realize the impedance force control of the robot: ； wherein, actual position of the robot end effector from the reference position , a difference, desired contact force from the actual contact force , a difference, are, respectively, an inertia parameter, a damping parameter, and a stiffness parameter of the constant impedance filter; When the environmental stiffness information is unknown, a variable impedance filter is used to realize the impedance force control of the robot: ； wherein, wherein is a variable damping parameter of the variable impedance filter; Step 2, determining the inertia parameter and the stiffness parameter of the impedance filter; Step 3, adjusting the damping parameter of the impedance filter according to the environmental stiffness: 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: If the environmental stiffness information is less than a set threshold, the damping parameter range of the constant impedance filter is wherein is the solution set of the following inequality: ； If the environmental stiffness information is greater than a set threshold, the damping parameter range of the constant impedance filter is wherein is the solution set of the following inequality: ； wherein, is the robot-environment coupled stiffness, is a stiffness parameter of the environment, and is a positive constant; 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: The measured value of the environmental stiffness is calculated according to the force sensation information and the environmental position information when the deformation is not subjected to force: ； wherein, is a measured value of the environmental stiffness parameter, is a measured value of the force sense information, is a measured value of the environmental position when not deformed by the force, then the estimate of the coupled stiffness of the robot-environment is ; The adjustment range of the variable damping parameter of the variable impedance filter is: ； Step 4, calculating the reference trajectory of the end effector of the robot arm according to the environmental parameters and the expected force information; Step 5, detecting the contact force in real time and calculating the contact force error, so that it passes through the constant impedance filter or the variable impedance filter to generate the position deviation, and the reference trajectory is superimposed to obtain the command position of the end of the robot arm; Step 6, the end effector operates according to the command position to realize accurate force control.

2. The robot impedance force control method suitable for a variable stiffness environment according to claim 1, characterized by, When the environmental stiffness information is known, the damping parameter range of the constant impedance filter is .

3. The robot impedance force control method suitable for a variable stiffness environment according to claim 1 or 2, characterized by, The reference trajectory of the end effector of the robot arm is: ； wherein, is the desired contact force, respectively represent the environmental position and the environmental stiffness when not under force; When the environmental parameters are known, According to the known data acquisition, when the environmental parameters are unknown, the reference trajectory The design requires replacing the above variables With the corresponding measured / estimated values And ​ 4. A robotic impedance force control system suitable for use in a variable stiffness environment for performing the method of claim 1, characterized by, The method comprises the following modules: An impedance filter selection module is used to determine the selected impedance filter according to the environmental parameters; A parameter determination module is used to determine the inertia parameter and the stiffness parameter of the impedance filter, and to adjust the damping parameter of the impedance filter according to the environmental stiffness; A robot control module is used to calculate the reference trajectory of the end effector of the robot arm according to the environmental parameters and the expected force information, and to detect the contact force in real time and calculate the contact force error, so that it passes through the constant impedance filter or the variable impedance filter to generate the position deviation, and the reference trajectory is superimposed to obtain the command position of the end of the robot arm; An execution module is used to control the end effector to operate according to the command position to realize accurate force control.

5. A computer device comprising a memory, a processor, and a computer program stored on the memory and executable on the processor, characterized in that, The processor executes the computer program to realize the steps of the method in any one of claims 1-3.

6. A computer storable medium having stored thereon a computer program, characterized in that The computer program is executed by the processor to realize the steps of the method in any one of claims 1-3.

Images