A method for axial force control in a high-stiffness environment based on the combination of active and passive compliance

Abstract

The present invention discloses a method for controlling axial force in a high-stiffness environment based on a combination of active and passive compliance. First, a passive compliance device is set between the end of the robot arm and the end effector, and a physical model of the passive compliance device is constructed and the model parameters are determined. Then, based on the expected trajectory of the active compliance control model and the displacement compensation determined by the passive compliance device, the axial force control of the robot arm in a high-stiffness environment based on active and passive compliance is realized. The method of the present invention solves the problem that traditional admittance control is prone to instability in high-stiffness environments by introducing passive compliance components, and achieves the unification of operational compliance and accuracy of the robot arm in a high-stiffness environment. It fundamentally solves the limitation that admittance control is only applicable to low-stiffness environments. Combined with the environmental parameter estimation method, it can solve the problem of precise force control in unknown time-varying environments, and has good application prospects and value.

Description

Technical Field

[0001] The present invention belongs to the field of compliance control of a robotic arm, and in particular to an axial force control method in a large stiffness environment based on a combination of active and passive compliance. Background Art

[0002] Traditional control strategies for industrial robotic arms primarily rely on position control. These are mostly used in structured work scenarios, such as structured workshops, and tasks that do not require contact with the workpiece, such as painting. However, with the increasing use of robotic arms, the proportion of contact-related tasks has also increased, such as workpiece grinding and shaft-hole assembly. Traditional position control is no longer able to meet these requirements. Consequently, many researchers have proposed compliant control solutions, which can be specifically categorized as passive and active. Passive compliance involves adding an elastic mechanical structure to the end of the robotic arm to absorb excess energy. When the robotic arm contacts the environment, this structure exhibits a certain degree of compliance, allowing the end effector to adapt to the working environment. However, this approach suffers from the inability to precisely control the magnitude of the contact force and still carries the potential for damage to the workpiece and the robotic arm. Consequently, active compliant control strategies have been proposed since the 1970s, primarily categorized as admittance control and impedance control. Given that traditional industrial robotic arms generally feature precise position servo control and are relatively affordable, and that admittance control does not require knowledge of the precise dynamic model of the robotic arm, admittance control is more commonly used and has greater potential for widespread adoption.

[0003] The admittance control strategy is to add a force control outer loop on the basis of the position servo inner loop, but this requires that the bandwidth of the position control inner loop is much larger than the bandwidth of the force control outer loop. However, the bandwidth of the actual robot arm position servo inner loop is limited. When the environmental stiffness reaches a certain value, the bandwidth of the force outer loop will be larger than the bandwidth of the robot arm position servo inner loop, that is, the force outer loop responds faster than the position inner loop, which will destroy the stability of the entire system and cause the actual system to oscillate. At the same time, the extrusion caused by tiny position servo errors may cause huge force mutations, thereby damaging the work object and the robot arm, and even injuring surrounding personnel. This is why traditional admittance control is only applicable to small stiffness working environments. In order to solve this problem, some researchers have combined active compliance with passive compliance. Passive compliance is used to cushion the impact process, and active compliance is used to absorb the residual energy of the impact process. This method is simple and practical when dealing with problems such as the smooth landing of a foot-type robot arm that do not require precise force control. However, it still cannot solve problems that require precise force control accuracy, because the introduction of passive compliance components brings uncertainty to the position of the end of the robot arm tool, and the essence of admittance control is to achieve precise force control accuracy by adjusting the reasonable reference trajectory of the end position. In other words, under this idea, compliance and accuracy are incompatible.

[0004] Based on the above situation, there is an urgent need for a new compliant control method that can enable traditional position servo manipulators to achieve precise force control in high-stiffness environments. However, there is no relevant description in the prior art. Summary of the Invention

[0005] Based on the problems mentioned above, the purpose of the present invention is to provide an axial force control method in a high stiffness environment based on the combination of active and passive compliance, which realizes the unity of operational compliance and accuracy of the robotic arm in a high stiffness environment, and fundamentally solves the limitation that traditional admittance control is only applicable to a low stiffness environment, thereby enabling the traditional position servo type robotic arm to achieve precise force control in a high stiffness environment.

[0006] The technical solutions for achieving the purpose of the present invention are:

[0007] A method for controlling axial force in a high-stiffness environment based on a combination of active and passive compliance includes the following steps:

[0008] Step 1: Set up a passive compliance device between the end of the robot arm and the end effector;

[0009] Step 2: Construct a physical model of the passive compliance device and determine the model parameters;

[0010] Step 3: Determine the desired trajectory of the end effector of the manipulator, that is, the active compliance control model of the end effector of the manipulator;

[0011] Step 4: Based on the active compliance control model in step 3 and the physical model in step 2, displacement compensation is performed on the command position of the manipulator to achieve axial force control of the manipulator in a large stiffness environment based on active and passive compliance.

[0012] Compared with the prior art, the present invention has the following significant advantages:

[0013] (1) The technical solution of the present invention adopts an active compliance method combined with passive compliance. The introduction of passive compliance components is equivalent to "softening" the environment, reducing the bandwidth of the outer force loop, and avoiding the problem that the bandwidth of the outer force loop is larger than the bandwidth of the position servo inner loop, that is, the response of the outer force loop is faster than that of the inner position loop, thereby ensuring the stability of the traditional position control type manipulator in the face of a large stiffness environment under admittance control;

[0014] (2) The technical solution of the present invention achieves the unity of operational compliance and precision of the manipulator in a high-stiffness environment by constructing an accurate physical model of the passive compliance device and using the obtained model to perform displacement compensation on the command position of the manipulator. This fundamentally solves the limitations of admittance control and enables the traditional position servo manipulator to achieve precise force control in a high-stiffness environment.

[0015] (3) The precise physical model parameter identification experiment of the passive compliance device constructed by the technical solution of the present invention is simple and easy to operate. It only needs to give the predetermined command trajectory of the robotic arm and collect the sensor data during the process to obtain the corresponding model parameters, which has high promotion value.

[0016] The present invention is described in further detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a flow chart of the steps of the axial force control method in a large stiffness environment based on the combination of active and passive compliance of the present invention.

[0018] Figure 2 This is a schematic diagram of the Solidwork assembly of the passive compliance device used in the present invention.

[0019] Figure 3 Schematic diagram of force analysis of the passive compliance device of the present invention.

[0020] Figure 4 Schematic diagram of physical model parameter identification of the passive compliance device of the present invention.

[0021] Figure 5 The inertia parameter identification of the physical model of the passive compliance device of the present invention is a schematic diagram of the specified trajectory of the robotic arm.

[0022] Figure 6Axial displacement compensation block diagram defined for the passive compliance device of the present invention.

[0023] Figure 7 This is a block diagram of the axial force control in a high stiffness environment based on the combination of active and passive compliance of the present invention.

[0024] Figure 8 This is a schematic diagram of a passive compliance device used in an embodiment of the present invention.

[0025] Figure 9 Schematic diagram comparing the force control effects of traditional impedance control and the method of the present invention under a low stiffness environment in an embodiment of the present invention.

[0026] Figure 10 Schematic diagram comparing the force control effects of traditional impedance control and the method of the present invention under a high stiffness environment in an embodiment of the present invention. DETAILED DESCRIPTION

[0027] Combine Figure 1 , a method for controlling axial force in a large stiffness environment based on active and passive compliance, comprising the following steps:

[0028] Step 1: Set up a passive compliance device between the end of the robot arm and the end effector, specifically:

[0029] The passive compliant components involved can essentially be simplified into a spring-damper-mass system. The corresponding physical model can be quickly established through dynamics theory, and the model parameters can be determined through experiments.

[0030] The passive compliance device is as follows Figure 2 As shown, it includes: a passive flexible component connected to the six-dimensional force sensor and the end effector at the end of the robotic arm respectively, and an elastic component and a damping component are arranged between the two side components.

[0031] Step 2: Construct a physical model of the passive compliance device and determine the model parameters, specifically:

[0032] Step 2-1: Since the influence of the tool's own weight can be eliminated by zeroing the force sensor, the gravity of the end tool is not considered. The specific force analysis is as follows: Figure 3 As shown;

[0033] Construct a physical model of the passive compliance device, specifically:

[0034] Based on the holistic approach, we conduct an acceptance analysis of the terminal system and obtain the following:

[0035]

[0036] Using isolation method, Analysis yields:

[0037]

[0038] right Analysis yields:

[0039]

[0040] in, is the axial data of the force sensor at the end of the robotic arm, is the axial contact force between the end effector and the high-stiffness environment, is the actual position of the end of the robotic arm, L is the original length of the passive compliance device and the end effector before contacting the high-stiffness environment, X is the actual position of the end effector, is the compression of the passive compliance device after contacting the high-stiffness environment, is the elastic parameter of the elastic component in the passive compliance device, is the damping parameter of the passive compliant device, It represents the mass of the passive compliant component on the side connected to the end of the robot arm. is the total mass of the passive compliant component connected to one side of the end effector and the end effector.

[0041] Any two of the above three formulas can be used to construct the physical model of the passive compliant device.

[0042] Step 2-2, Combination Figure 4 , the specific parameters of the physical model are determined according to the identification experiment, specifically:

[0043] Step 2-2-1. Place the end effector against a high-rigidity environment without squeezing it, and record the position of the end of the robotic arm at this time. ;

[0044] Step 2-2-2: The end of the robotic arm slowly squeezes the passive compliant component After the six-axis force sensor readings are stable, measure the force sensor data along the axial direction at this time, and take the average value of multiple measurements. ;

[0045] Step 2-2-3: The end of the robotic arm compresses the passive compliant component at a unit speed Measure the data of the six-dimensional force sensor along the axial direction at this time, and take the average value of multiple measurements ;

[0046] Step 2-2-4, Combination Figure 5 , make the end of the robot move according to the following trajectory equation, and measure the quantity The data of the six-dimensional force sensor along the axial direction at the moment is measured multiple times and the average value is taken :

[0047]

[0048] in, Indicates the environmental location, Indicates the vibration amplitude, usually selected .

[0049] Step 2-2-5: Determine the elastic parameters, damping parameters and inertia parameters of the physical model:

[0050]

[0051]

[0052]

[0053] in, Indicates unit speed;

[0054] Step 3: Determine the desired trajectory of the end effector of the manipulator, that is, the active compliance control model of the end effector of the manipulator, specifically:

[0055]

[0056] in, is the reference position, is the environmental location, is the reference contact force, is the environmental stiffness.

[0057] Step 4: Based on the active compliance control model in step 3 and the physical model in step 2, the displacement compensation of the manipulator command position is performed to realize the manipulator axial force control in a large stiffness environment based on active and passive compliance. Specifically:

[0058] Step 4-1, Combination Figure 6 , based on the real-time position of the end of the robotic arm And the force sensor axial data , using the physical model of step 2, the axial compression of the passive compliance device is obtained , thus determining the compensation amount:

[0059] Compensation amount =

[0060] in, is the total original length of the passive compliance device and the end effector before contacting the high-stiffness environment;

[0061] Step 4-2: Get the expected trajectory based on the expected trajectory equation in step 3, and subtract the compensation amount from the expected trajectory. , get the real-time command trajectory of the end of the manipulator, and complete the axial force control of the manipulator in a large stiffness environment based on active and passive compliance. The specific axial force control block diagram is as follows Figure 7 shown.

[0062] An axial force control system based on a combination of active and passive compliance in a high-stiffness environment includes the following modules:

[0063] Passive compliance device setting module: used to set a passive compliance device between the end of the robot arm and the end effector;

[0064] Passive compliance model building module: used to build the physical model of the passive compliance device and determine the model parameters;

[0065] Active compliance model building module: used to determine the desired trajectory of the end effector of the manipulator, that is, the active compliance control model of the end effector of the manipulator;

[0066] Active and passive compliance control module: used to perform displacement compensation on the command position of the manipulator based on the active compliance control model and the physical model in the passive compliance model construction module, and realize the axial force control of the manipulator in a high stiffness environment based on active and passive compliance.

[0067] A computer device comprises a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein when the processor executes the computer program, the following steps are implemented:

[0068] Step 1: Set up a passive compliance device between the end of the robot arm and the end effector;

[0069] Step 2: Construct a physical model of the passive compliance device and determine the model parameters;

[0070] Step 3: Determine the desired trajectory of the end effector of the manipulator, that is, the active compliance control model of the end effector of the manipulator;

[0071] Step 4: Based on the active compliance control model in step 3 and the physical model in step 2, displacement compensation is performed on the command position of the manipulator to achieve axial force control of the manipulator in a large stiffness environment based on active and passive compliance.

[0072] A computer storable medium having a computer program stored thereon, wherein when the computer program is executed by a processor, the computer program implements the following steps:

[0073] Step 1: Set up a passive compliance device between the end of the robot arm and the end effector;

[0074] Step 2: Construct a physical model of the passive compliance device and determine the model parameters;

[0075] Step 3: Determine the desired trajectory of the end effector of the manipulator, that is, the active compliance control model of the end effector of the manipulator;

[0076] Step 4: Based on the active compliance control model in step 3 and the physical model in step 2, displacement compensation is performed on the command position of the manipulator to achieve axial force control of the manipulator in a large stiffness environment based on active and passive compliance.

[0077] The present invention will be further described below with reference to the embodiments.

[0078] Example

[0079] Considering the actual high-stiffness environment that the robotic arm needs to face, this embodiment selects the traditional admittance control method and the compliant control method of the present invention to conduct a comparative experiment on the force tracking effect when the environmental stiffness is 50N / mm and 500N / mm. The experiment is carried out on the MATLAB and Simulink simulation platforms.

[0080] A method for controlling axial force in a high-stiffness environment based on a combination of active and passive compliance includes the following steps:

[0081] Step 1: Set up a passive compliance device between the end of the robot arm and the end effector, specifically:

[0082] The passive compliant components involved can essentially be simplified into a spring-damper-mass system. The corresponding physical model can be quickly established through dynamics theory, and the model parameters can be determined through experiments.

[0083] The passive compliance components involved include: passive compliance components connected to the six-dimensional force sensor and the end effector at the end of the robotic arm, respectively, and an elastic component is arranged between the two side components;

[0084] The passive compliance device used in this embodiment is as follows Figure 8 shown.

[0085] Step 2: Construct a physical model of the passive compliance device and determine the model parameters, specifically:

[0086] Step 2-1: Since the influence of the tool's own weight can be eliminated by zeroing the force sensor, the gravity of the end tool is not considered;

[0087] Construct a physical model of the passive compliance device, specifically:

[0088] Based on the holistic approach, we conduct an acceptance analysis of the terminal system and obtain the following:

[0089]

[0090] Using isolation method, Analysis yields:

[0091]

[0092] right Analysis yields:

[0093]

[0094] in, is the axial data of the force sensor at the end of the robotic arm, is the axial contact force between the end effector and the high-stiffness environment, is the actual position of the end of the robotic arm, is the original length of the passive compliance device and the end effector before contacting the high-stiffness environment, is the actual position of the end effector, is the compression of the passive compliance device after contacting the high-stiffness environment, is the elastic parameter of the elastic component in the passive compliance device, is the damping parameter of the passive compliant device, It represents the mass of the passive compliant component on the side connected to the end of the robot arm. is the total mass of the passive compliant component connected to one side of the end effector and the end effector.

[0095] Any two of the above three formulas can be used to construct the physical model of the passive compliant device.

[0096] Step 2-2: Determine the specific parameters of the physical model based on the identification experiment, specifically:

[0097] Step 2-2-1. Place the end effector against a high-rigidity environment without squeezing it, and record the position of the end of the robotic arm at this time. ;

[0098] Step 2-2-2: The end of the robotic arm slowly squeezes the passive compliant component After the six-axis force sensor readings are stable, measure the force sensor data along the axial direction at this time, and take the average value of multiple measurements. ;

[0099] Step 2-2-3: The end of the robotic arm compresses the passive compliant component at a unit speed Measure the data of the six-dimensional force sensor along the axial direction at this time, and take the average value of multiple measurements ;

[0100] Step 2-2-4: Move the end of the robotic arm according to the following trajectory equation and measure the amount The data of the six-dimensional force sensor along the axial direction at the moment is measured multiple times and the average value is taken :

[0101]

[0102] in, Indicates the environmental location, Indicates the vibration amplitude, usually selected ;

[0103] Step 2-2-5: Determine the elastic parameters, damping parameters and inertia parameters of the physical model:

[0104]

[0105]

[0106]

[0107] in, Indicates unit speed;

[0108] The elastic parameters finally obtained in this embodiment are: , Damping parameters: , inertia parameters: .

[0109] Step 3: Determine the desired trajectory of the end effector of the manipulator, that is, the active compliance control model of the end effector of the manipulator, specifically:

[0110]

[0111] in, is the reference position, is the environmental location, is the reference contact force, is the environmental stiffness.

[0112] Step 4: Based on the active compliance control model in step 3 and the physical model in step 2, the displacement compensation of the manipulator command position is performed to realize the manipulator axial force control in a large stiffness environment based on active and passive compliance. Specifically:

[0113] Step 4-1: Based on the real-time position of the end of the robotic arm And the force sensor axial data , using the physical model of step 2, the axial compression of the passive compliance device is obtained , thus determining the compensation amount:

[0114] Compensation amount =

[0115] in, is the total original length of the passive compliance device and the end effector before contacting the high-stiffness environment;

[0116] Step 4-2: Get the expected trajectory based on the expected trajectory equation in step 3, and subtract the compensation amount from the expected trajectory. , obtain the real-time command trajectory of the end of the robot arm, and complete the axial force control of the robot arm in a large stiffness environment based on active and passive compliance.

[0117] The comparison diagrams of the force control effects of the conventional impedance control and the active and passive compliance combination of the present invention are shown in FIG. Figure 9 and Figure 10 As shown, it can be seen that the active and passive compliance combined force control method of the present invention has better stability and higher force control accuracy when operating in a high-rigidity environment, realizing the unity of compliance and accuracy of the robot arm in a high-rigidity environment, and fundamentally solving the limitation that admittance control is only applicable to a low-rigidity environment. Combined with the environmental parameter estimation method, it can solve the problem of precise force control in an unknown time-varying environment, and has good application prospects and value.

[0118] The above embodiments illustrate and describe the basic principles and main features of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention, and such changes and modifications fall within the scope of the invention as claimed.

Claims

1. A method for controlling axial force in a high-stiffness environment based on a combination of active and passive compliance, characterized in that: The following steps are involved: Step 1: A passive compliance device is provided between the end of the robotic arm and the end effector, wherein the passive compliance device comprises: a passive compliance component connected to the six-dimensional force sensor at the end of the robotic arm and the end effector, respectively, and an elastic component and a damping component are provided between the two passive compliance components; Step 2: Construct a physical model of the passive compliance device and determine the model parameters: Step 2-1: Construct a physical model of the passive compliance device: ； ； ； in, is the axial data of the force sensor at the end of the robotic arm, is the axial contact force between the end effector and the high-stiffness environment, is the actual position of the end of the robotic arm, is the original length of the passive compliance device and the end effector before contacting the high-stiffness environment, is the actual position of the end effector, is the axial compression of the passive compliance device after contacting the high-stiffness environment, is the elastic parameter of the elastic component in the passive compliance device, is the damping parameter of the passive compliant device, It represents the mass of the passive compliant component on the side connected to the end of the robot arm. is the total mass of the passive compliant component connected to one side of the end effector and the end effector; Step 2-2: Determine the specific parameters of the physical model based on the identification experiment: Step 2-2-1. Place the end effector against a high-rigidity environment without squeezing it, and record the position of the end of the robotic arm at this time. ; Step 2-2-2: The end of the robotic arm slowly squeezes the passive compliant component until the passive compliant component is compressed. After the six-axis force sensor readings are stable, measure the force sensor data along the axial direction at this time, and take the average value of multiple measurements. ; Step 2-2-3: The end of the robotic arm compresses the passive compliant component at a unit speed and measures the compression amount. The six-axis force sensor data along the axial direction is measured multiple times and the average value is taken. ; Step 2-2-4: Move the end of the robotic arm according to the following trajectory equation and measure The data of the six-dimensional force sensor along the axial direction at the moment is measured multiple times and the average value is taken : ； in, Indicates the environmental location, Indicates the vibration amplitude; Step 2-2-5: Determine the elastic parameters, damping parameters and inertia parameters of the physical model: ； ； ； in, Indicates unit speed; Step 3: Determine the desired trajectory of the end effector of the manipulator, that is, the active compliance control model of the end effector of the manipulator: ； in, is the reference position, is the environmental location, is the reference contact force, is the environmental stiffness; Step 4: Based on the active compliance control model in step 3 and the physical model in step 2, the displacement compensation of the manipulator command position is performed to achieve the manipulator axial force control in a high stiffness environment based on the combination of active and passive compliance: Step 4-1: According to the actual position of the end of the robotic arm And the force sensor axial data , using the physical model of step 2, the axial compression of the passive compliance device is obtained , thus determining the compensation amount: Compensation amount = ; Step 4-2: Get the desired trajectory based on step 3 and subtract the compensation amount from the desired trajectory , obtain the real-time command trajectory of the end of the robot arm, and complete the axial force control of the robot arm in a large stiffness environment based on the combination of active and passive compliance.

2. An axial force control system based on active and passive compliance in a large stiffness environment, characterized in that: Includes the following modules: Passive compliance device setting module: used to set a passive compliance device between the end of the robot arm and the end effector, the passive compliance device includes: a passive compliance component connected to the six-dimensional force sensor at the end of the robot arm and the end effector respectively, and an elastic component and a damping component are set between the two passive compliance components; Passive compliance model building module: used to build the physical model of the passive compliance device and determine the model parameters: Includes: Building a physical model of a passive compliance device: ； ； ； in, is the axial data of the force sensor at the end of the robotic arm, is the axial contact force between the end effector and the high-stiffness environment, is the actual position of the end of the robotic arm, is the original length of the passive compliance device and the end effector before contacting the high-stiffness environment, is the actual position of the end effector, is the axial compression of the passive compliance device after contacting the high-stiffness environment, is the elastic parameter of the elastic component in the passive compliance device, is the damping parameter of the passive compliant device, It represents the mass of the passive compliant component on the side connected to the end of the robot arm. is the total mass of the passive compliant component connected to one side of the end effector and the end effector; Determine the specific parameters of the physical model based on the identification experiment: Place the end effector against a high-rigidity environment without squeezing it, and record the position of the end of the robotic arm at this time. ; The end of the robotic arm slowly squeezes the passive compliant component until the passive compliant component is compressed After the six-axis force sensor readings are stable, measure the force sensor data along the axial direction at this time, and take the average value of multiple measurements. ; The end of the robotic arm compresses the passive compliant component at a unit speed and measures the compression The six-axis force sensor data along the axial direction is measured multiple times and the average value is taken. ; Make the end of the robot arm move according to the following trajectory equation and measure The data of the six-dimensional force sensor along the axial direction at the moment is measured multiple times and the average value is taken : ； in, Indicates the environmental location, Indicates the vibration amplitude; Step 2-2-5: Determine the elastic parameters, damping parameters and inertia parameters of the physical model: ； ； ； in, Indicates unit speed; Active compliance model building module: used to determine the desired trajectory of the end effector of the manipulator, that is, the active compliance control model of the end effector of the manipulator: ； in, is the reference position, is the environmental location, is the reference contact force, is the environmental stiffness; Active and passive compliance control module: It is used to perform displacement compensation on the command position of the manipulator based on the active compliance control model and the physical model in the passive compliance model construction module, and realize the axial force control of the manipulator in a high-stiffness environment based on the combination of active and passive compliance. According to the real-time position of the end of the robotic arm And the force sensor axial data , using the physical model, the axial compression of the passive compliance device is obtained , thus determining the compensation amount: Compensation amount = ; Subtract the compensation amount from the desired trajectory , obtain the real-time command trajectory of the end of the robot arm, and complete the axial force control of the robot arm in a large stiffness environment based on the combination of active and passive compliance.

3. A computer device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein: When the processor executes the computer program, the steps of the method according to claim 1 are implemented.

4. 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 claim 1 are implemented.

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