Current-based robot end flexibility control method, device, storage medium and equipment

Abstract

The present application relates to the field of automation, in particular to a robot end flexible control method based on current, by introducing the joint flexibility of the robot, introducing a certain impulse when the robot contacts with the plane to be assembled, so that the robot end can automatically compensate the horizontal problem of the posture, without using six-dimensional moment sensor, effectively reducing the cost, and can improve the assembly adjustment efficiency.

Description

Technical Field

[0001] This invention relates to the field of automation technology, and in particular to a method, apparatus, storage medium, and device for flexible control of the end effector of a robot based on electric current. Background Technology

[0002] Automated tooling assembly using robots is a common mechanical design. The specific structure is as follows: the robot has a long connecting rod at its end, and at the end of the connecting rod is a tool to be assembled. The robot end needs to be moved to a flexible worktable, aligned with the hole, and then force control is executed to assemble the tool to be assembled at the end of the long connecting rod with the required tool.

[0003] Because the machine tool may shake during use, and the worktable is flexible and cannot be guaranteed to remain perfectly horizontal, the robot's position during teaching cannot be maintained at the same state as at the time of teaching; it may tilt slightly. In this case, continuing to press down using force control to move the robot along the z-axis will cause the connecting rod to be non-perpendicular to the worktable, resulting in poor assembly. Therefore, force control needs to provide feedback not only in the z-axis but also in the rx and ry rotational directions.

[0004] The biggest problem with end-effector assembly based on current is the inaccuracy of the estimated external force. In the application scenario described above, the requirement is that the robot's end effector should be horizontal to the plane of the object to be assembled during assembly. However, in actual use, due to vibration and platform flexibility, the plane of the object to be assembled cannot be guaranteed to be horizontal to the teaching point. Therefore, during assembly, not only does the robot need to maintain a certain set force in the z-direction, but the torque of the assembly contact also needs to be zero in the attitude direction. However, due to the limited accuracy of the external force estimated by the robot's current, the current-based robot dynamics model cannot achieve control where the expected observed external force torque direction is always zero. This results in a large error in the robot's rotational attitude, preventing the robot from actively adjusting itself.

[0005] To address the aforementioned issues, existing technologies, such as patent document CN201710558197.4, disclose a method and system for assembling shafts and holes using an industrial robot. This method uses joint torque sensors to measure the output torque of each joint and calculates the contact force vector between the assembly shaft and the assembly hole. It then controls the robot's movement, ensuring that the assembly shaft and hole contact according to a pre-set contact force vector even under unknown environmental changes and assembly shaft / hole errors, thus completing the shaft / hole assembly task. This method introduces a six-dimensional torque sensor at the robot's end effector to determine its posture, ensuring the robot remains horizontal to the plane of the object being assembled during assembly. However, six-dimensional torque sensors are expensive, require operating current, and necessitate real-time verification of readings to determine the robot's state and adjust its posture accordingly, resulting in low efficiency and high cost. Summary of the Invention

[0006] This invention addresses the problems of existing technologies by providing a current-based robot end-effector flexibility control method. It can introduce the robot's joint flexibility and a certain impulse when the robot contacts the assembly plane into the current-based robot dynamics model, so that the robot end can automatically compensate for the horizontal posture problem. It is low-cost and highly efficient.

[0007] To address the aforementioned technical problems, this invention discloses a current-based flexible control method for the end effector of a robot, comprising the following steps:

[0008] S1. Obtain the robot's current posture, and based on the robot's posture, obtain the robot's desired assembly motion direction and the desired joint flexibility direction;

[0009] S2. Based on the robot's desired assembly motion direction and the desired joint flexibility direction, and based on the Jacobian matrix of the robot's current posture, calculate the required flexibility of each joint of the robot.

[0010] S3. After adjusting the flexibility of the corresponding joints of the robot according to the calculated required flexibility, the current of the joints is collected, and a dynamic model of the robot joints is established based on the current. The estimated value of the current external force of the robot is obtained based on the dynamic model of the joints. ;

[0011] S4. Valuation based on external forces Establish an impedance control model for the robot's external forces, based on the robot's end effector's speed, acceleration, and estimated external forces. The desired external force on the robot's end effector is controlled by impedance, so that the assembly of the robot's end effector is stable.

[0012] Preferably, in step S2, the desired direction of robot motion and the desired direction of flexibility are determined by the Jacobian matrix of the robot's current posture.

[0013] Preferably, the required flexibility of each joint of the computational robot is calculated using the following formula:

[0014] ;

[0015] in, Let be the torque vector of each joint of the robot. Let F represent the Jacobian matrix of the robot in its current pose, and let F represent the expected external force vector at the robot's end effector.

[0016] Preferably, in the method for adjusting the flexibility of the corresponding joints of the robot, the joint flexibility is adjusted by PID control of the robot's motion.

[0017] Furthermore, the robot's joint flexibility is adjusted by proportionally scaling down the parameters of the PID control for robot motion.

[0018] Preferably, the established impedance control model is as follows:

[0019] ;

[0020] Where M and B are the inertia and damping coefficients that need to be adjusted in the impedance control model, respectively, and x is the pose in the Cartesian direction. The speed of the robot's end effector. For the acceleration of the robot's end effector, The external force required for the desired assembly. These are the external force values ​​observed using a current-based dynamic model.

[0021] Preferably, the inertia M and damping coefficient B are adjusted, and the fusion coefficient a, fusion coefficient b and external force error e are set.

[0022] Let the required inertia for the robot to achieve stable contact with the assembly station be... The damping coefficient is ;

[0023] Assume the required inertia of the robot during rapid compression. The damping coefficient is ;

[0024] Inertia used in impedance models Damping coefficient ;

[0025] The relationship between the fusion coefficient a, the fusion coefficient b, and the external force error e is as follows:

[0026] .

[0027] A second aspect of this invention discloses a current-based flexible end-effector assembly device for robots, comprising:

[0028] A robot, the end effector of which is used to install the tooling to be assembled and to move the tooling to be assembled.

[0029] The central control module is used to acquire the robot's posture, determine the desired assembly motion direction and joint flexibility direction based on the robot's posture before assembly, and then calculate the flexibility of each joint by combining the judgment result with the Jacobian matrix of the robot's current posture. After adjusting the robot's joint flexibility according to the calculation result, the module collects the robot's joint current and establishes a joint dynamics model of the robot based on the current. The module obtains the robot's current external force estimate through the dynamics model, establishes an impedance control model of the robot's external force based on the external force estimate, and regulates the assembly stability of the robot's end effector by controlling the impedance control model.

[0030] The third aspect of the present invention discloses a computer-readable storage medium, characterized in that: the computer-readable storage medium stores a computer program, which, when executed by a processor, implements the steps of the above-described robot protection control method based on dynamic current detection.

[0031] A fourth aspect of the present invention discloses an electronic device, wherein the electronic device comprises:

[0032] Processor; and,

[0033] A memory is configured to store computer-executable instructions, which, when executed, cause the processor to perform the steps of the current-based robot end-effector flexible control method.

[0034] The beneficial effects of this invention are:

[0035] This invention provides a current-based robot end-effector flexibility control method. By introducing the robot's joint flexibility and introducing a certain impulse when the robot contacts the assembly plane, the robot end-effector can automatically compensate for the horizontal posture problem. It does not require the use of a six-dimensional torque sensor, effectively reducing costs and improving assembly adjustment efficiency. Attached Figure Description

[0036] Figure 1 This is a flowchart of the method of the present invention;

[0037] Figure 2 This is a model diagram of the external force control model of the present invention. Detailed Implementation

[0038] To facilitate understanding by those skilled in the art, the present invention will be further described below with reference to embodiments and accompanying drawings. The content mentioned in the embodiments is not intended to limit the present invention. The present invention will be described in detail below with reference to the accompanying drawings.

[0039] Example 1:

[0040] This embodiment provides a current-based flexible control method for the end effector of a robot, which can be applied to the central control module of a robot, such as... Figure 1 This includes the following steps:

[0041] Optionally, the robot can be moved to the assembly position first; or the robot can be moved above the assembly position under external control and wait for the next control command.

[0042] S1. Obtain the robot's current posture, and based on the robot's posture, obtain the robot's desired assembly motion direction and the desired joint flexibility direction; where the robot's desired assembly motion direction is the direction of the force required by the robot. For example, in an ideal state, the desired assembly motion direction is a straight descent in the z-direction, or a combined movement in the x, y, and z directions. The desired joint flexibility direction is the passive flexibility direction of the joint, such as rotation; optionally, the required motion direction and flexibility direction can be determined and calculated using the Jacobian matrix of the robot's current posture. For example, based on the current Jacobian matrix and the robot's standard descent posture, the current required assembly motion direction and joint flexibility direction of the robot can be determined.

[0043] S2. Based on the robot's desired assembly motion direction and the desired joint flexibility direction, and combined with the Jacobian matrix of the robot's current posture, calculate the flexibility required for each joint of the robot; for example, among the robot's six torques, two joints need to be flexible, that is, to rotate and adjust their orientation, while the other joints remain stationary.

[0044] S3. After adjusting the flexibility of the corresponding joints of the robot according to the calculated required flexibility, the current of the joints is collected, and a dynamic model of the robot joints is established based on the current. The estimated value of the current external force of the robot is obtained based on the dynamic model of the joints. The establishment of the joint dynamic model and the estimation of the robot's external force based on current are existing technologies, and the specific process will not be described in detail in this embodiment.

[0045] S4. Valuation based on external forces Establish an impedance control model for the robot's external forces, based on the robot's end effector's speed, acceleration, and estimated external forces. The desired external force of the robot's end effector is controlled by impedance to ensure stable assembly of the end effector. The desired external force of the robot's end effector is related to the robot's desired assembly motion direction, and this desired external force is used to control the robot to move in that direction.

[0046] Specifically, existing technologies using current-based external force estimation are far from accurate enough for robot control because this method only estimates the robot's torque in the z-direction, failing to proactively adjust for situations like swaying during descent, resulting in poor assembly performance. While alternative control methods using six-dimensional torque sensors avoid current-based estimation, they are costly and inefficient. Therefore, this embodiment addresses this by introducing flexible joint adjustments and impulse control when the robot contacts the assembly platform, based on current-based external force estimation. Joint flexibility compensates for the inaccuracy of current-based external force estimation, and an impedance control model, combined with the estimated current force value, controls the robot's external force. This allows for torque adjustment in other directions while the robot moves up and down in the z-direction, enabling the robot to proactively adapt to its position on the assembly platform and ensuring assembly quality.

[0047] The specific method is as follows: After the robot moves to the assembly position, the direction of motion required for assembly and whether the robot's joints need flexibility are determined. Based on these determinations, the flexibility of the robot's joints is adjusted. After adjusting the joint flexibility, the joint current, such as the current of the joint motor (this is existing technology), is acquired. A dynamic model of the joint is established under this current, and the estimated external force on the robot can be obtained based on the dynamic model of the joint after flexibility adjustment and compensation. According to the valuation of this external force An external force impedance control model is established for the robot, enabling it to move in the desired direction. This model tracks and regulates the assembly forces acting on the robot. The impedance control model can be adjusted based on the speed and acceleration of the robot's end effector, as well as the desired external force on the end effector. Furthermore, by adjusting the inertia and damping of the impedance control model, a unified state can be achieved between rapid descent and smooth assembly, maintaining stable assembly at a given speed. This embodiment compensates for the accuracy of current-based force estimation by adjusting the flexibility of the joints before assembly, and regulates the robot during assembly using the impedance control model, allowing it to maintain a smooth and stable assembly at a certain speed. This achieves improved assembly quality and reduced costs without compromising assembly efficiency.

[0048] Furthermore, after determining the required direction of robot movement and the direction of flexibility, it is necessary to calculate whether each joint of the robot requires flexibility. The calculation method is as follows:

[0049] ;

[0050] in, The torque vectors of each joint of the robot , Let F represent the Jacobian matrix of the robot in its current pose, and let F represent the expected external force vector at the robot's end effector. .

[0051] Specifically, during robot assembly, it is necessary to first determine, under the current assembly pose, the direction of the Cartesian desired force and the direction of desired introduced flexibility, and the amount of motion (i.e., torque vector) that each joint will bring. For example, in this embodiment, the robot's end effector moves downward into the tool slot, so the required force control direction is the control direction Z=40N. Simultaneously, it is desired that the end effector is perpendicular to the tool slot during assembly, so torques of rx and ry in the tool direction are undesirable. Therefore, we can set... (The six parameters represent the six joints respectively), and a set of parameters can be calculated. ;make This allows us to obtain the joint torque that contributes to the rotation of the end force. Therefore, in this pose, we need to maintain rigid control for joints 1, 2, 3, and 6, and activate flexible control for joints 4 and 5.

[0052] One way to adjust joint flexibility is to proportionally reduce the PID parameters of the robot's joint modules, thus minimizing the impact of integral effects. For example, if it's determined through debugging that the overall PID parameters need to be adjusted to 20%, then at the start of flexibility adjustment, all joint PID parameters can be changed to 20% of their normal movement value. The specific amount of PID parameter adjustment needed can be determined based on the actual situation. In the application scenario of this embodiment, the desired motion direction for assembly is translation, and the desired flexibility direction is rotation. This combination usually achieves good assembly results.

[0053] Furthermore, in this embodiment, the external force control model may be an impedance control model.

[0054] like Figure 2 The established impedance control model is as follows:

[0055] ;

[0056] Where M and B are the inertia and damping coefficients that need to be adjusted in the impedance control model, respectively, and x is the pose in the Cartesian direction. The speed of the robot's end effector. For the acceleration of the robot's end effector, The external force required for the desired assembly. These are the external force values ​​observed using a current-based dynamic model.

[0057] Specifically, besides the expected force in the z-direction (i.e., the applied external force), the observed forces in other directions may not be zero due to model errors. Therefore, the external force errors in other directions are forcibly set to zero, ensuring the robot moves strictly in the z-direction. This prevents unexpected movements in other directions caused by model errors. Based on the above calculations of robot joint flexibility, uneven postures require passive compensation through the flexibility of joints 4 and 5. This necessitates a large impulse at the moment of contact (the robot's end effector contacts the assembly platform) to trigger the passive adjustment of the flexible joints and level the overall assembly posture. This requires a large contact velocity, and according to the impedance model, a small inertia M and damping coefficient B are needed.

[0058] Adjust the inertia M and damping coefficient B, and let the fusion coefficients a, b, and external force error e be defined; where a and b are two linear fusion coefficients in [0,1].

[0059] Let the required inertia for the robot to achieve stable contact with the assembly station be... for

[0060] Assume the required inertia of the robot during rapid compression. for

[0061] Inertia used in impedance models Damping coefficient ;

[0062] The relationship between the fusion coefficient a, the fusion coefficient b, and the external force error e is as follows:

[0063] .

[0064] In this embodiment, there are two states: a stable contact state between the robot and the assembly station, and a state where the robot rapidly presses down. The inertia M and damping coefficient B are mainly adjusted by harmonizing these two states. One is a basic impedance model parameter, i.e. One is the impedance model parameters after the two states are merged. The fusion rule is to perform linear fusion based on the magnitude of the external force error e.

[0065] The required inertia for the robot to maintain stable contact with the assembly station can be obtained from the tests. Damping coefficient Inertia required during rapid downward pressure Damping coefficient ;

[0066] The difference lies in the different effects of the two impedance model parameters. One set of parameters, used when the robot presses down rapidly, is beneficial for stimulating passive compliance of the joints but affects stability. The other set of parameters is more stable but less likely to stimulate passive flexibility of the joints. Therefore, during the movement, the two sets of parameters are linearly fused based on the external force error value e. The external force error e varies in the range of [0, 10N], resulting in fusion. For example, if the force error is 5N, then according to the rules, a is 0.5 and b is 0.5. The current impedance parameters can then be calculated, resulting in a stable impedance model control parameter that can maintain a certain speed.

[0067] Therefore, by adjusting the fusion coefficients a and b, the inertia M and damping coefficient B can be adjusted to meet the requirements of the impedance control model in this embodiment. This ensures the robot maintains stability when in contact with the assembly platform and during assembly, guaranteeing assembly quality and efficiency. It also achieves the goal of autonomously adjusting the robot's pose even with an external force estimation method based on current. Compared to existing impedance control models, the impedance control model in this embodiment is based on the external force value estimated by the robot's joint flexibility compensation current. This allows for compliant and flexible adjustment of the entire control, preventing forced return to the designed zero position and enabling better external force control of the robot.

[0068] Example 2:

[0069] This embodiment provides a current-based flexible assembly device for a robot end effector, specifically including a robot and a central control module. The robot end effector is used to install the tooling to be assembled and to move the tooling to be assembled. The central control module is used to acquire the robot's posture, determine the desired assembly motion direction and desired joint flexibility direction of the robot based on the robot's posture before assembly, and then calculate the flexibility of each joint of the robot by combining the judgment result with the Jacobian matrix of the robot's current posture. After adjusting the joint flexibility of the robot according to the calculation result, the robot's joint current is collected and a joint dynamics model of the robot is established based on the current. The current external force estimate of the robot is obtained through the dynamics model, and an impedance control model of the robot's external force is established based on the external force estimate. The assembly stability of the robot end effector is regulated by controlling the impedance control model.

[0070] The central control module includes:

[0071] The acquisition unit is used to acquire data that needs to be collected and obtained, such as the robot's posture, the direction of the robot's movement, the required joint flexibility direction, the current of the joint after adjusting the joint flexibility, and the robot's external force estimate based on the current.

[0072] The adjustment unit is used to calculate the required flexibility of each joint of the robot according to the direction of movement and the direction of flexibility required by the robot, and to adjust the flexibility of each joint.

[0073] The control unit is used to control the external forces on the robot during assembly work through an impedance control model, so as to keep the robot's assembly action stable.

[0074] The central control module can be a robot control center system, etc. The acquisition unit can be a unit that acquires data from various sensors by the control center system. The adjustment unit and control unit can be different or the same actuators in the control system, such as a PLC control center. Specifically, the robot's end effector mounting fixture is existing technology and will not be elaborated here. In this embodiment, the acquisition module mainly acquires the robot's posture on the assembly platform, such as the angles and heights of each joint of the robot, to determine the direction of movement and the required flexibility of the robot during assembly. Movements include translation and lifting, while flexibility includes rotation. Based on the required flexibility and direction of movement, the adjustment module calculates the required flexibility of each joint of the robot, such as the required rotation angle of each joint, and automatically controls the robot to adjust its posture based on the calculation results. This includes joint flexibility adjustment. Then, the robot is controlled to move along the direction to be assembled, such as descending along the z-direction. This process requires an external force to be applied to the robot (such as an external force estimated based on current). The control module establishes an external force control model for this external force, which can be an impedance control model. By adjusting the inertia M and damping coefficient B of the impedance control model, and combining the robot's rapid descent and smooth assembly states, the robot can maintain stability when in contact with the platform to be assembled and during assembly, ensuring assembly quality and efficiency. This achieves the goal of autonomously adjusting the robot's posture even with an external force estimation method based on current.

[0075] Example 3:

[0076] This embodiment discloses a computer-readable storage medium storing a computer program for electronic data interchange, wherein the computer program causes a computer to perform the steps of the current-based robot end-effector flexible control method described in Embodiment 1.

[0077] Example 4:

[0078] This embodiment discloses a computer program product, which includes a non-transitory computer-readable storage medium storing a computer program, and the computer program is operable to cause a computer to perform some or all of the steps in the current-based robot end-effector flexible control method described in Embodiment 1.

[0079] Example 5:

[0080] This embodiment discloses an electronic device, wherein the electronic device includes:

[0081] The processor; and a memory arranged to store computer-executable instructions (program code), which may be an electronic memory such as flash memory, EEPROM (Electrically Erasable Programmable Read-Only Memory), EPROM, hard disk, or ROM. The memory has storage space for storing program code for performing any method steps in the embodiments. For example, the storage space for program code may include various program codes for implementing the various steps in the methods described above. This program code can be read from or written to one or more computer program products. These computer program products include program code carriers such as hard disks, compact discs (CDs), memory cards, or floppy disks. Such computer program products are typically the computer-readable storage medium of Embodiment 4. This computer-readable storage medium may have storage units such as storage segments, storage spaces, etc., arranged similarly to the memory in the electronic device of this embodiment. The program code may be compressed, for example, in a suitable form. Typically, the storage units store program code for performing the method steps according to the invention, i.e., program code that can be read by a processor such as a processor, which, when run by the electronic device, causes the electronic device to perform the various steps in the methods described above.

[0082] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some changes or modifications to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and modifications made to the above embodiments based on the present invention without departing from the scope of the present invention are within the scope of the present invention.

Claims

1. A current-based flexible control method for robot end effectors, characterized in that, Includes the following steps: S1. Obtain the robot's current posture, and based on the robot's posture, obtain the robot's desired assembly motion direction and the desired joint flexibility direction; S2. Based on the robot's desired assembly motion direction and the desired joint flexibility direction, and based on the Jacobian matrix of the robot's current posture, calculate the required flexibility of each joint of the robot. S3. After adjusting the flexibility of the corresponding joints of the robot according to the calculated required flexibility, the current of the joints is collected, and a dynamic model of the robot joints is established based on the current. The estimated value of the current external force of the robot is obtained based on the dynamic model of the joints. ; S4. Valuation based on external forces Establish an impedance control model for the robot's external forces, based on the robot's end effector's speed, acceleration, and estimated external forces. The desired external force on the robot's end effector is controlled by impedance, so that the assembly of the robot's end effector is stable.

2. The current-based flexible control method for robot end effectors according to claim 1, characterized in that, In step S1, the desired direction of the robot's motion and the desired direction of its flexibility are determined by the Jacobian matrix of the robot's current posture.

3. The current-based flexible end-effector control method for robots according to claim 1, characterized in that, The formula for calculating the required flexibility of each joint of the computational robot is as follows: ； in, Let be the torque vector of each joint of the robot. Let F represent the Jacobian matrix of the robot in its current pose, and let F represent the expected external force vector at the robot's end effector.

4. The current-based flexible control method for a robot end effector according to claim 1 or 3, characterized in that, In the method for adjusting the flexibility of the corresponding joints of the robot, the joint flexibility is adjusted by PID control of the robot's motion.

5. The current-based flexible end-effector control method for robots according to claim 4, characterized in that: The robot's joint flexibility is adjusted by proportionally scaling down the parameters of the PID control for robot motion.

6. The current-based flexible end-effector control method for robots according to claim 1, characterized in that, The established impedance control model is as follows: ； Where M and B are the inertia and damping coefficients that need to be adjusted in the impedance control model, respectively, and x is the pose in the Cartesian direction. The speed of the robot's end effector. For the acceleration of the robot's end effector, The external force required for the desired assembly. These are the external force values ​​observed using a current-based dynamic model.

7. The current-based flexible end-effector control method for robots according to claim 6, characterized in that, Adjust the inertia M and damping coefficient B, and set the fusion coefficient a, fusion coefficient b and external force error e; Let the required inertia for the robot to achieve stable contact with the assembly station be... The damping coefficient is ; Assume the required inertia of the robot during rapid compression. The damping coefficient is ; Inertia used in impedance models Damping coefficient ; The relationship between the fusion coefficient a, the fusion coefficient b, and the external force error e is as follows: 。 8. An assembly apparatus based on the current-based flexible control method for robot end effectors according to any one of claims 1-7, characterized in that: include A robot, the end effector of which is used to install the tooling to be assembled and to move the tooling to be assembled. The central control module is used to acquire the robot's posture, determine the desired assembly motion direction and joint flexibility direction based on the robot's posture before assembly, and then calculate the flexibility of each joint by combining the judgment result with the Jacobian matrix of the robot's current posture. After adjusting the robot's joint flexibility according to the calculation result, the module collects the robot's joint current and establishes a joint dynamics model of the robot based on the current. The module obtains the robot's current external force estimate through the dynamics model, establishes an impedance control model of the robot's external force based on the external force estimate, and regulates the assembly stability of the robot's end effector by controlling the impedance control model.

9. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores a computer program that, when executed by a processor, implements the current-based robot end-effector flexible control method according to any one of claims 1-7.

10. An electronic device, wherein, The electronic device includes: Processor; and, A memory configured to store computer-executable instructions, which, when executed, cause the processor to perform the current-based robot end-effector flexible control method as described in any one of claims 1-7.

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