A method and system for impedance control of a robotic arm

Abstract

The application relates to a kind of mechanical arm admittance control method and system, wherein the method comprises: according to the joint current of mechanical arm, the environmental external force suffered by mechanical arm is calculated;By the screw theory unification mechanical arm end tool position and posture, according to environmental external force, and the preset pose trajectory of end tool, the expected pose screw of end tool is calculated;According to the expected pose screw of end tool, the expected joint angle of mechanical arm is calculated, finally control mechanical arm, execute the action corresponding to expected joint angle.It is calculated that external force based on dynamics model and joint current by the present application, without installing high-cost force sensor to measure external force;Based on the description of screw theory unification position and posture, the dimension of pose space is minimized, the complexity of admittance control algorithm is simplified, compared with the separate description of position and posture, it is more accurate and stable, solve the problem of how to realize the accurate, stable, low-cost admittance control of mechanical arm.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of mechanical arm, in particular to a mechanical arm admittance control method and system. BACKGROUND

[0002] With the development of robot technology, the application of mechanical arm in the field of production and manufacturing becomes gradually widespread, and the demand for safe interaction between mechanical arm and human or environment appears in more and more scenarios. As a kind of robot control algorithm, compliant control is widely applied to robot-environment interaction tasks due to its compliant characteristics. Compliant control is divided into active compliant control and passive compliant control. Passive compliant control mainly changes the hardware structure of the mechanical arm, while active compliant control reduces the impact when the robot contacts the environment through algorithm and improves the compliance of the robot. In a complex environment, active compliant control has higher adaptability and a wider range of applications.

[0003] Active compliant control is further divided into impedance control and admittance control. Admittance control performs better than impedance control in the case of small environmental stiffness, and due to the relatively small stiffness of human, admittance control has great significance in human-robot collaboration.

[0004] Admittance control needs to input the contact force between the mechanical arm and the human or flexible environment, calculate the output, i.e. the expected motion trajectory changing with the contact force, through a mass-spring-damper second-order model, and real-time issue to the robot for motion tracking. Therefore, the simple and accurate acquisition of environmental contact force and the reasonable design of admittance control will directly affect the effect of human-robot collaboration, and have an inseparable relationship with enterprise benefits and production safety.

[0005] At present, most of the admittance control schemes are to add a force / torque sensor at the end of the robot to obtain the external force acting on the mechanical arm body, combine the algorithm of admittance control, equivalent the external force measured by the force sensor as the pose disturbance of the tool coordinate system, and then convert the task space to the joint space through the Jacobian matrix, and finally send the set value of the joint angle to the servo motor. However, such a scheme has several disadvantages: first, it cannot uniformly describe the tool position and attitude. Considering the complexity of attitude description, separate description may lead to different control periods of the tool position and attitude, and the attitude description in related materials is various, but none of them combines with the position information to form a unified description. Second, the force sensor is expensive, which may greatly increase the cost of enterprises, and the force sensor cannot sense the external force acting on the connecting rod. Third, many current schemes still obtain the tool pose based on the joint angle feedback from the encoder and combine it with the off-line forward kinematics calculation. Therefore, even in the case of good joint angle tracking, the tool pose tracking error may still occur due to the deviation of kinematics calibration. Therefore, reducing the cost of enterprises, increasing the range of interaction, and ensuring accurate tracking during interaction are of great significance to improve human-robot collaborative work.

[0006] At present, there is no effective solution to the problem of how to realize precise, stable and low-cost admittance control of the mechanical arm in the related art. SUMMARY

[0007] Embodiments of the present application provide a mechanical arm admittance control method and system to at least solve the problem of how to realize precise, stable and low-cost admittance control of the mechanical arm in the related art.

[0008] In a first aspect, embodiments of the present application provide a mechanical arm admittance control method, which comprises:

[0009] According to the joint current of the mechanical arm, the environmental external force acting on the mechanical arm is calculated;

[0010] The position and attitude of the end tool of the mechanical arm are unified by the screw theory;

[0011] According to the environmental external force and the preset pose trajectory of the end tool, the complete expected pose screw of the end tool after the screw theory is unified is calculated;

[0012] According to the expected pose screw of the end tool, the expected joint angle of the mechanical arm is calculated, and the mechanical arm is controlled to perform the action corresponding to the expected joint angle.

[0013] In some embodiments, calculating the environmental external force applied to the robot arm based on joint current of the robot arm comprises:

[0014] modeling the robot arm using a dynamic parameter identification algorithm to obtain an accurate dynamic model of the robot arm;

[0015] and calculating the environmental external force applied to the robot arm based on joint current, joint angle, angular velocity and angular acceleration of the robot arm through the dynamic model.

[0016] In some embodiments, modeling the robot arm using a dynamic parameter identification algorithm to obtain a dynamic model of the robot arm comprises:

[0017] mathematically modeling the robot arm according to Newton-Euler dynamic modeling method;

[0018] linearizing the dynamic equation in the mathematical modeling according to linear property of dynamic equation parameters to obtain a standard parameter linear dynamic equation;

[0019] taking minimizing matrix condition number as optimization objective and using Fourier series function trajectory as excitation trajectory for parameter identification;

[0020] reorganizing regression matrix W according to the standard parameter linear dynamic equation and the excitation trajectory combined with QR decomposition to obtain a minimum parameter equation;

[0021] calculating regression matrix W based on joint angle and joint current and using least square method to fit a parameter linear dynamic expression, i.e. the dynamic model of the robot arm.

[0022] In some embodiments, unifying the position and attitude of the end tool of the robot arm through screw theory comprises:

[0023] unifying the position and attitude of the end tool through a homogeneous transformation matrix wherein R is a rotation matrix and P is a position vector;

[0024] converting the homogeneous transformation matrix into a pose screw wherein w is an angular velocity vector and q is a position vector pointing to the center of mass.

[0025] In some embodiments, before calculating the complete expected pose screw of the end tool in the unified description of the screw theory based on the environmental external force and the preset pose trajectory of the end tool, the method comprises:

[0026] According to the screw theory, a preset pose trajectory of an end tool of a robot arm is generated in a screw representation.

[0027] In some embodiments, the expected pose screw of the end tool after unification of the screw theory is calculated according to the environmental external force and the preset pose trajectory of the end tool, including:

[0028] According to the environmental external force, a screw-based pose correction term is calculated;

[0029] The pose correction term is added to the preset pose trajectory to obtain the expected pose screw of the end tool.

[0030] In some embodiments, the expected joint angle of the robot arm is calculated according to the expected pose screw of the end tool, including:

[0031] According to the expected pose screw of the end tool, the expected joint angle of the robot arm is calculated through inverse kinematics;

[0032] According to the joint angle of the robot arm, the real pose screw of the end tool is calculated through forward kinematics; and the expected joint angle is adjusted based on the real pose screw to obtain an adjusted expected joint angle.

[0033] In some embodiments, the robot arm is further controlled to perform an action corresponding to the expected joint angle, including:

[0034] If the robot arm has a torque input interface, the expected joint angle is converted into servo control information through the torque input interface and is sent to a joint torque PID controller, and if the robot arm does not have a torque input interface, the expected joint angle is directly sent to a servo motor.

[0035] The robot arm is driven to perform a corresponding action through the joint torque PID controller or the servo motor.

[0036] In some embodiments, the joint angle and joint current of the robot arm are read in real time through a joint encoder of the robot arm.

[0037] In a second aspect, the embodiments of the present application provide a robot arm admittance control system, which is used to implement the method of any one of the above first aspect, and the system includes an external force estimator, a screw-based admittance controller and a robot arm motion controller.

[0038] The external force estimator is configured to calculate an environmental external force acting on the robot arm according to a joint current of the robot arm.

[0039] The screw-based admittance controller is configured to unify the position and the posture of the end tool of the robot arm by screw theory, and calculate an expected posture screw of the end tool after the unification according to the external force of the environment and a preset posture trajectory of the end tool.

[0040] The robot arm motion controller is configured to calculate an expected joint angle of the robot arm according to the expected posture screw of the end tool, and control the robot arm to perform an action corresponding to the expected joint angle.

[0041] Compared with the related art, the robot arm admittance control method and system provided in the embodiments of the present application calculate the external force of the environment according to the joint current of the robot arm, unify the position and the posture of the end tool of the robot arm by screw theory, calculate the expected posture screw of the end tool according to the external force of the environment and a preset posture trajectory of the end tool, calculate the expected joint angle of the robot arm according to the expected posture screw of the end tool, and finally control the robot arm to perform an action corresponding to the expected joint angle, thereby solving the problem of how to realize precise, stable and low-cost admittance control of the robot arm, realizing calculation of the external force based on the dynamics model and the joint current, and eliminating the need to install a high-cost force sensor to measure the external force. The screw theory is used to unify the description of the position and the posture, the dimension of the posture space is minimized, the complexity of the admittance control algorithm is simplified, and the description is more precise and stable compared with the separate description of the position and the posture. BRIEF DESCRIPTION OF DRAWINGS

[0042] The accompanying drawings, which are included to provide a further understanding of the present application, constitute a part of the present application and illustrate the illustrative embodiments of the present application and its description, which serve to explain the present application, and do not constitute improper limitations on the present application. In the drawings:

[0043] Figure 1 is a flowchart of a robot arm admittance control system according to an embodiment of the present application;

[0044] Figure 2 is a flowchart of a robot arm admittance control system according to an embodiment of the present application;

[0045] Figure 3 is a flowchart of a robot arm admittance control method according to an embodiment of the present application;

[0046] Figure 4 is a flowchart of a robot arm dynamics parameter identification method according to an embodiment of the present application;

[0047] Figure 5 is a flowchart of a robot arm motion control method according to an embodiment of the present application;

[0048] Figure 6FIG. 1 is a schematic diagram of an internal structure of an electronic device according to an embodiment of the present application.

[0049] Reference numeral 11 is an external force estimator, 12 is a screw-based admittance controller, and 13 is a robot arm motion controller. DETAILED DESCRIPTION

[0050] In order to make the objects, technical solutions and advantages of the present application clearer, the present application will be described and illustrated in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and should not be used to limit the present application. Based on the embodiments provided in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the scope of the present application.

[0051] Obviously, the drawings described below are only some examples or embodiments of the present application, and for those of ordinary skill in the art, the present application can be applied to other similar scenarios according to these drawings without creative work. In addition, it can be understood that although the efforts made in this development process can be complex and lengthy, for those of ordinary skill in the art related to the content disclosed in the present application, some design, manufacture or production changes based on the technical content disclosed in the present application are only routine technical means and should not be understood as insufficient disclosure of the present application.

[0052] In the present application, "embodiments" means that the specific features, structures or characteristics described in conjunction with the embodiments can be included in at least one embodiment of the present application. The phrase appears at various places in the specification does not necessarily all refer to the same embodiment, nor is it necessarily independent or alternative embodiments to other embodiments. It is explicitly and implicitly understood by those of ordinary skill in the art that the embodiments described in the present application can be combined with other embodiments without conflict.

[0053] Unless otherwise defined, the technical or scientific terms used in this application shall have the ordinary meaning understood by one of ordinary skill in the art to which this application pertains. The terms “a,” “an,” “an,” “the,” and similar words used in this application do not indicate quantity limitation and may indicate singular or plural. The terms “comprising,” “including,” “having,” and any variations thereof used in this application are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or device that includes a series of steps or modules (units) is not limited to the listed steps or units, but may also include steps or units not listed, or may include other steps or units inherent to these processes, methods, products, or devices. The terms “connected,” “linked,” “coupled,” and similar words used in this application are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. “Multiple” used in this application refers to two or more. “And / or” describes the relationship between related objects, indicating that three relationships may exist; for example, “A and / or B” can represent: A alone, A and B simultaneously, and B alone. The character " / " generally indicates that the preceding and following objects are in an "or" relationship. The terms "first," "second," and "third" used in this application are merely to distinguish similar objects and do not represent a specific ordering of the objects.

[0054] This application provides a robotic arm admittance control system. Figure 1 This is a flowchart of the robotic arm admittance control system according to an embodiment of this application, such as... Figure 1 As shown, the system includes an external force estimator 11, a spinor-based admittance controller 12, and a robotic arm motion controller 13;

[0055] Figure 2 This is a flowchart illustrating the robotic arm admittance control system according to an embodiment of this application, as shown below. Figure 2 As shown, the external force estimator 11 is used to model the robotic arm using a dynamic parameter identification algorithm to obtain an accurate dynamic model of the robotic arm; then, based on the joint current, joint angle, angular velocity, and angular acceleration of the robotic arm, it calculates the environmental external forces acting on the robotic arm through the dynamic model. The screw-based admittance controller 12 is used to unify the position and attitude of the robotic arm's end-effector using screw theory, and calculates the desired pose screw of the end-effector based on the environmental external forces and the preset pose trajectory of the end-effector. The robotic arm motion controller 13 is used to calculate the desired joint angle of the robotic arm based on the desired pose screw of the end-effector, and then control the robotic arm to execute the action corresponding to the desired joint angle.

[0056] It should be noted that this embodiment adopts a decoupling approach between admittance control and internal position control, such as... Figure 2As shown, the admittance controller only needs the feedback of the desired pose Xd, and the motion controller module only needs the feedback of the real pose X, without feeding the real pose information X back to the admittance control. On the basis of accurate control of the internal attitude loop, the way of designing the external force to only change the tool pose set value is adopted, so as to avoid the failure of the calculation logic of the admittance controller caused by the interference and noise of the real signal.

[0057] It should be noted that each of the above devices can be a functional device or a program device, which can be implemented by software or hardware. For the device implemented by hardware, each of the above devices can be located in the same processor; or each of the above devices can also be located in different processors in any combination.

[0058] The embodiment of the present application provides a mechanical arm admittance control method, which can be implemented by the external force estimator 11, the screw-based admittance controller 12 and the mechanical arm motion controller 13 in the above embodiment, Figure 3 is a step flow chart of the mechanical arm admittance control method according to the embodiment of the present application, as shown in the figure, the method comprises the following steps: Figure 3

[0059] Step S302, the environmental external force received by the mechanical arm is calculated according to the joint current of the mechanical arm;

[0060] Specifically, a dynamics parameter identification algorithm is used to model the mechanical arm, so as to obtain an accurate dynamics model of the mechanical arm; and then the environmental external force received by the mechanical arm is calculated through the dynamics model according to the joint current of the mechanical arm.

[0061] Preferably, Figure 4 is a flow chart of the dynamics parameter identification of the mechanical arm according to the embodiment of the present application, as shown in the figure, step S302 further comprises the following preferred steps: Figure 4

[0062] Step (4.1), the mechanical arm is mathematically modeled according to the Newton-Euler dynamics modeling method. When the kinematics equation is accurate, the dynamics state (velocity, force) of the adjacent two connecting rods can be transmitted through the Newton-Euler method iteration, that is, the dynamics state of the connecting rod close to the base is expressed in the mass center coordinate system of the far connecting rod, and then the external force received by each connecting rod of the whole mechanical arm itself in the mass center coordinate system of the connecting rod and the velocity and acceleration description in the system are obtained.

[0063] Step (4.2), the mechanical arm is a serial mechanical arm, and the dynamics equation is linearized according to the linear property of the dynamics equation parameters of the serial mechanical arm, so as to achieve the purpose of decoupling the parameters and the joint state. Taking a six-link serial mechanical arm as an example, after parameter linearization, it can be uniformly expressed in the following matrix form:​​

[0064]

[0065] where each variable is defined as follows:

[0066]

[0067]

[0068]

[0069] Further,

[0070]

[0071]

[0072]

[0073] where, i p i+1 is the rotation matrix and position vector of the center of mass coordinate system of link i+1 in the coordinate system of link i.m i , and i I i are the mass, center of mass position, and inertia of link i, respectively. Each link is described by ten parameters, including six independent inertia matrix elements, three-dimensional spatial coordinates of the center of mass, and mass. Considering the single degree of freedom factor of the revolute joint, only the row corresponding to the torque of the revolute axis direction is taken out and expressed as follows:

[0074] [τ] (6N×1) = [K] (6N×60) [P] (60×1) ;

[0075] Considering the effect of joint friction, the dynamics equation is extended as follows:

[0076]

[0077] where f cv and F cof are the joint angular velocity vector and the Coulomb friction and viscous friction coefficient vector, respectively.

[0078] Therefore, the final parameter linear dynamics equation (standard parameter linear dynamics equation) is expressed as:

[0079]

[0080] When there are multiple sets of data, the above equation can be expanded in the column direction according to the time sequence, i.e.:

[0081]

[0082] Step (4.3), the Fourier series function trajectory is used as the excitation trajectory of parameter identification, and the optimization objective is to minimize the condition number of the matrix. The function design of the excitation trajectory is as follows:

[0083]

[0084] The optimization problem of minimizing the condition number of the matrix with joint space constraints is constructed as follows:

[0085]

[0086] s.t.

[0087] min(q i )≤q i ≤max(q i );

[0088]

[0089]

[0090] Step (4.4), based on the standard parameter linear dynamics equation and the excitation trajectory, combined with QR decomposition, the minimum parameter is obtained. For the standard parameter linear dynamics equation, the regression matrix W is generally column rank deficient, so through QR decomposition, W is reorganized, and the minimum parameter set is obtained, and the minimum parameter equation is expressed as follows:

[0091]

[0092] Step (4.5), the joint angle and joint current signals are collected, the measured joint current is converted into torque, the regression matrix W is calculated, and the optimal parameter set is obtained by applying the least square form fitting: the expression of the least square method is as follows:

[0093]

[0094] Finally, the parameter linear dynamics expression (i.e. the dynamics model of the robot arm) is obtained. It is worth noting that in the expression of the dynamics equation of step (4.4), the meaning of is the torque τ model calculated according to the model. Therefore, the resultant torque from the motion of the robot arm and the joint friction can also be directly predicted by using the equation in step (4.4).

[0095] Further, according to the joint current of the robot arm, the external force and external torque acting on the robot arm are estimated through a dynamic model, specifically as follows:

[0096]

[0097]

[0098] wherein τ measure is a torque value measured at the motor, M, C and G correspond to an inertia mass matrix, a Coriolis force coefficient matrix and a gravity matrix respectively, F ext is a real value of the external force acting on the robot arm, is an estimated value of the environmental external force acting on the robot arm, I measure is a measured value of the joint current, the motor at the joint is composed of a part based on Lagrange dynamics equation τ model which is a function of the joint space state , F f is a friction resistance at the joint.

[0099] The actual torque at the joint can be obtained through the current at the joint and the motor constant K I , thus, the gear reduction ratio corresponding to the robot arm model and the motor model can be obtained to obtain the constant value. The torque at the joint is composed of τ model which provides the joint space inertia force and the torque generated to resist the external force, that is, the estimated value of the external force can be theoretically obtained by using the model information and the joint angle, angular velocity and other information, wherein the Jacobian matrix J is also only related to the joint angle. When an accurate model is available, this method is feasible. At the same time, the joint angle and the joint current are collected in real time through the joint encoder of the robot arm to ensure the timeliness of the estimated external force.

[0100] In step S304, the position and attitude of the end tool of the robot arm are unified through the screw theory;

[0101] Preferably, the general expression of the admittance control is: wherein x is the pose of the end effector (end tool). When an external force acts on the tool end of the robot arm, a desired response characteristic of a quadratic system will be generated. Different from the current most tool position and attitude description, the screw theory is applied to the unified description of the pose, and the specific form of the screw for describing the attitude is as follows:

[0102] For the most common unified description form of the pose, the homogeneous transformation matrix T can completely represent the position and attitude.

[0103] Its matrix dimension is a 4x4 square matrix, described by a 3x3 rotation matrix R and a position vector p. Due to the orthogonality and redundancy of the rotation matrix, the elements actually representing the pose are not 9, but in principle only three elements can completely represent the pose. Therefore, the representation by screw is as follows:

[0104] Where w is the angular velocity vector, and q is the position vector of the rotation axis pointing to the center of mass. According to the meaning of screw, the general motion of a rigid body in space can always be described as a simple rotation around an axis and a translational velocity in the tangent direction of the rotation track. It completely represents the pose space with the minimum number. In summary, the screw is used as the description of the pose in the present application.

[0105] Step S306, according to the environmental external force and the preset pose trajectory of the end tool, the expected pose screw of the end tool after unified by the screw theory is calculated;

[0106] Specifically, according to the screw theory, the preset pose trajectory of the end tool of the robot arm is generated in the form of screw; the pose correction term based on screw is calculated according to the environmental external force; the pose correction term and the preset pose trajectory are added to obtain the expected pose screw of the end tool.

[0107] Preferably, considering the particularity of screw operation, the kinematic control is extended to correct the error between the external force and a pose on the original trajectory, that is, Therefore, the pose correction term based on screw can be calculated, and the final expected pose is obtained by adding the preset trajectory.

[0108] It should be noted that x e is the error of the expected pose x d and the preset pose trajectory x0, not the error between the preset pose trajectory and the real trajectory. The external force only changes the expected value of the pose screw, not the real trajectory as the input of the kinematic controller, which ensures that the kinematic controller does not fail due to noise or error of the real trajectory signal.

[0109] Step S308, according to the expected pose screw of the end tool, the expected joint angle of the robot arm is calculated, and the robot arm is controlled to perform the action corresponding to the expected joint angle.

[0110] Specifically, according to the expected pose screw of the end tool, the expected joint angle of the robot arm is calculated through inverse kinematics; then according to the joint angle of the robot arm, the real pose screw of the end tool is calculated through forward kinematics; based on the real pose screw, the expected joint angle is adjusted to obtain the adjusted expected joint angle;

[0111] It is judged whether the mechanical arm has a torque input interface. If the torque input interface exists, the expected joint angle is converted into servo control information through the torque input interface and is sent to a joint torque PID controller. If the torque input interface does not exist, the expected joint angle is directly sent to a servo motor. The joint torque PID controller or the servo motor drives the mechanical arm to perform a corresponding action.

[0112] Preferably, Figure 5 A flowchart of the mechanical arm motion control according to the embodiment of the present application is shown in FIG. 3. Figure 5 As shown in FIG. 3, after the expected pose screw is obtained through the above steps S302 to S308, the expected pose screw and the real pose screw are controlled in a feedback loop to ensure accurate tracking of the end tool pose.

[0113]

[0114] The joint angle initial value is set as the joint angle calculated by the inverse kinematics of the preset pose. The real pose screw is calculated according to the real angle information, and the error Δυ of the pose screw is obtained. The Jacobian matrix is calculated according to the current joint angle data, and the corresponding angle correction amount Δθ is obtained. The joint angle of the previous period is integrated to realize the effect of accurately tracking the pose by adjusting the joint angle setting value.

[0115] According to the input interface of the mechanical arm, it is determined whether further conversion to the servo control information at the bottom layer is needed. Different models of mechanical arms provide different servo control interfaces. For example, the UR5 collaborative mechanical arm only provides joint angle (ServoJ) or angular velocity (SpeedJ) input forms. Therefore, the expected joint angle can be directly sent. If the mechanical arm operated provides an interface for sending joint motor torque, a joint angle feedback loop (joint torque PID controller) can be added according to the requirement to ensure accurate tracking in the joint space. Finally, the joint torque PID controller or the servo motor drives the mechanical arm to perform a corresponding action.

[0116] It should be noted that the steps shown in the above flowchart or the flowchart of the accompanying drawings can be executed in a computer system such as a set of computer executable instructions, and although a logical order is shown in the flowchart, in some cases, the steps shown or described can be executed in an order different from that shown here.

[0117] The method provided in the embodiment of the present application is different from the current admittance control which is completely based on the measurement of external force and external torque of the force sensor. The external force can be estimated according to the identified dynamic model combined with the current signal of the joint motor.

[0118] Different from the separate description of tool position and pose, the screw theory unifies the description of position and pose, minimizes the dimension of pose space, and simplifies the computational complexity of the algorithm. For the pose, the traditional representation methods include rotation matrix, Euler angle and quaternion. Since the mathematical definition of these pose descriptions is different from the description of the position vector in the orthogonal space, the position and pose information cannot be calculated uniformly, for example, the rotation matrix cannot be added, the Euler angle is related to the action sequence, and the quaternion does not have the commutative law. These properties hinder the unified description of position and pose. The screw theory simplifies the translation of the center of mass of the rigid body and the rotation around the center of mass of the rigid body into a simple rotation around an axis through the essence of rigid body motion, so it integrates the position and pose information and perfectly describes the pose. On the other hand, the description of the space state vector needs at least 6 degrees of freedom, and the expression of the screw is exactly 6, so it minimizes the description dimension of the pose space and simplifies the computational amount of the entire algorithm process framework.

[0119] The embodiment also provides an electronic device including a memory and a processor, the memory storing a computer program, and the processor being configured to execute the computer program to perform the steps in any of the method embodiments.

[0120] Optionally, the electronic device can further include a transmission device and an input and output device, wherein the transmission device is connected with the processor, and the input and output device is connected with the processor.

[0121] It should be noted that the specific examples in the embodiment can refer to the examples described in the above embodiments and optional implementation manners, and the embodiment will not be described here.

[0122] In addition, in combination with the mechanical arm admittance control method in the above embodiments, the embodiment of the application can provide a storage medium for implementation. The storage medium stores a computer program; when the computer program is executed by a processor, any one of the mechanical arm admittance control methods in the above embodiments is implemented.

[0123] In one embodiment, a computer device is provided, which can be a terminal. The computer device comprises a processor, a memory, a network interface, a display screen and an input device connected through a system bus. The processor of the computer device is configured to provide computing and control capabilities. The memory of the computer device comprises a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system and a computer program. The internal memory provides an environment for running the operating system and the computer program in the non-volatile storage medium. The network interface of the computer device is configured to communicate with an external terminal through a network connection. The computer program is executed by the processor to implement a robot admittance control method. The display screen of the computer device can be a liquid crystal display screen or an electronic ink display screen. The input device of the computer device can be a touch layer overlaid on the display screen, or a key, trackball or touchpad arranged on the housing of the computer device, or an external keyboard, touchpad or mouse, etc.

[0124] In one embodiment, Figure 6 is a schematic diagram of the internal structure of an electronic device according to an embodiment of the present application, as Figure 6 shown, an electronic device is provided, which can be a server, and the internal structure diagram thereof can be as Figure 6 shown. The electronic device comprises a processor, a network interface, an internal memory and a non-volatile memory connected through an internal bus, wherein the non-volatile memory stores an operating system, a computer program and a database. The processor is configured to provide computing and control capabilities, the network interface is configured to communicate with an external terminal through a network connection, the internal memory is configured to provide an environment for running the operating system and the computer program, the computer program is executed by the processor to implement a robot admittance control method, and the database is configured to store data.

[0125] Those skilled in the art can understand that Figure 6 the structure shown in the above embodiment is only a block diagram of part of the structure related to the scheme of the present application, and does not constitute a limitation on the electronic device to which the scheme of the present application is applied. Specifically, the electronic device can comprise more or fewer components than those shown in the diagram, or combine certain components, or have a different arrangement of components.

[0126] Those skilled in the art can understand that all or part of the processes in the above-mentioned embodiment methods can be completed by instructing the relevant hardware through a computer program, and the computer program can be stored in a non-volatile computer readable storage medium. When the computer program is executed, it can include the processes of the above-mentioned embodiment methods. Any reference to memory, storage, database or other medium used in the embodiments provided in the present application can include non-volatile and / or volatile memory. Non-volatile memory can include read-only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM) or flash memory. Volatile memory can include random access memory (RAM) or external cache memory. As an illustration but not limitation, RAM is available in various forms, such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), double data rate SDRAM (DDR SDRAM), enhanced SDRAM (ESDRAM), synchronous link (Synchlink) DRAM (SLDRAM), memory bus (Rambus) direct RAM (RDRAM), direct memory bus dynamic RAM (DRDRAM), and memory bus dynamic RAM (RDRAM), etc.

[0127] Those skilled in the art should understand that each technical feature of the above-mentioned embodiments can be combined arbitrarily, and in order to make the description simple, not all possible combinations of each technical feature in the above-mentioned embodiments are described, however, as long as the combination of these technical features does not exist contradictory, it should be considered as the scope of the present application.

[0128] The above-mentioned embodiments only express several implementation manners of the present application, and the description is more specific and detailed, but it should not be understood as a limitation on the scope of the patent. It should be pointed out that for ordinary skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are all within the scope of the present application. Therefore, the scope of protection of the patent of the present application should be subject to the appended claims.

Claims

1. A method of impedance control of a robot arm, characterized by, The method comprises: According to the joint current of the mechanical arm, the environmental external force acting on the mechanical arm is calculated; The position and attitude of the end tool of the mechanical arm are unified by the screw theory; According to the environmental external force and the preset attitude trajectory of the end tool, the expected attitude screw of the end tool after the screw theory is unified is calculated; According to the expected attitude screw of the end tool, the expected joint angle of the mechanical arm is calculated, and the mechanical arm is controlled to perform an action corresponding to the expected joint angle.

2. The method of claim 1, wherein, According to the joint current of the mechanical arm, the environmental external force acting on the mechanical arm is calculated, comprising: A dynamics parameter identification algorithm is used to model the mechanical arm to obtain an accurate dynamics model of the mechanical arm; Then, according to the joint current, joint angle, angular velocity and angular acceleration of the mechanical arm, the environmental external force acting on the mechanical arm is calculated through the dynamics model.

3. The method of claim 2, wherein, The dynamics parameter identification algorithm is used to model the mechanical arm to obtain a dynamics model of the mechanical arm, comprising: According to the Newton-Euler dynamics modeling method, the mechanical arm is mathematically modeled; Then, according to the linear property of the dynamics equation parameters of the mechanical arm, the dynamics equation in the mathematical modeling is parameterized to obtain a standard parameter linear dynamics equation; Taking the minimization of the condition number of the matrix as the optimization objective, a Fourier series function trajectory is used as the excitation trajectory for parameter identification; According to the standard parameter linear dynamics equation and the excitation trajectory, the regression matrix W is reorganized by QR decomposition to obtain a minimum parameter equation; Then, according to the joint angle and joint current, the regression matrix W is calculated, and the least square method is used to fit the parameter linear dynamics expression, i.e. the dynamics model of the mechanical arm.

4. The method of claim 1, wherein, The position and attitude of the end tool of the mechanical arm are unified by the screw theory, comprising: by a homogeneous transformation matrix a unified description of the position and pose of the end tool, where R is a rotation matrix and P is a position vector; Based on the orthogonality and redundancy of the rotation matrix, the homogeneous transformation matrix is converted into a pose screw where w is the angular velocity vector and q is the position vector of the rotation axis pointing to the center of mass.

5. The method of claim 1, wherein, Before calculating the expected attitude screw of the end tool after the screw theory is unified according to the environmental external force and the preset attitude trajectory of the end tool, the method comprises: According to the screw theory, a preset attitude trajectory of the end tool of the mechanical arm is generated in the form of a screw.

6. The method of claim 1, wherein, According to the environmental external force and the preset attitude trajectory of the end tool, the expected attitude screw of the end tool after the screw theory is unified is calculated, comprising: According to the environmental external force, a screw-based attitude correction term is calculated; The expected attitude screw of the end tool is obtained by adding the attitude correction term to the preset attitude trajectory.

7. The method of claim 1, wherein, According to the expected attitude screw of the end tool, the expected joint angle of the mechanical arm is calculated, comprising: According to the expected attitude screw of the end tool, the expected joint angle of the mechanical arm is calculated through inverse kinematics; Then, according to the joint angle of the mechanical arm, the real attitude screw of the end tool is calculated through forward kinematics; based on the real attitude screw, the expected joint angle is adjusted to obtain an adjusted expected joint angle.

8. The method of claim 1, wherein, The mechanical arm is controlled to perform an action corresponding to the expected joint angle, comprising: determining whether the mechanical arm has a torque input interface, if yes, converting the desired joint angle into servo control information through the torque input interface, and issuing the servo control information to a joint torque PID controller, if not, issuing the desired joint angle directly to a servo motor; driving the mechanical arm to perform corresponding actions through the joint torque PID controller or the servo motor.

9. The method of claim 1 or 6, wherein, reading the joint angle and joint current of the mechanical arm in real time through the joint encoder of the mechanical arm.

10. A manipulator admittance control system, characterized by, The system is used to implement the method of any one of claims 1 to 9, and the system comprises an external force estimator, a screw-based admittance controller, and a mechanical arm motion controller; The external force estimator is configured to calculate the environmental external force acting on the mechanical arm according to the joint current of the mechanical arm. The screw-based admittance controller is configured to unify the position and attitude of the end tool of the mechanical arm through screw theory, calculate the complete desired pose screw of the end tool after the unified description of the screw theory according to the environmental external force and a preset pose trajectory of the end tool, and output the complete desired pose screw to the mechanical arm motion controller. The mechanical arm motion controller is configured to calculate the desired joint angle of the mechanical arm according to the desired pose screw of the end tool, and control the mechanical arm to perform actions corresponding to the desired joint angle.

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