Differential control circuit and method for robot torque control

Abstract

Disclosed are a differential control circuit and method for robot torque control. The circuit comprises a PI controller, a current differential loop, and a controlled motor. The PI controller uses a current difference between a desired current value and an actual current value as input, and performs proportional-integral control on the current difference, and then outputs a reference current value. The current differential loop uses the reference current value as input and performs differential feedback, and then outputs a differential current value. The controlled motor uses the differential current value as input, drives a motor operation to form an actual current value, and outputs the actual current value. The present invention incorporates a current differential loop under the current loop of the PI controller, so that dynamic characteristics of the current loop can be detected via the current differential loop, preventing currents from changing too quickly or too slowly, and ensuring the accuracy of actual output currents while improving system stability. The present invention is compatible with multiple motors performing collaborative torque control, and provides a current differential loop for each motor, enabling each motor to better implement torque distribution.

Description

A differential control circuit and control method for robot torque control Technical Field

[0001] The present invention relates to the technical field of torque control, and in particular to a differential control circuit and a control method for robot torque control. Background Art

[0002] When robots perform tasks that interact with environmental forces, such as grinding and assembly, using position control alone can cause excessive forces due to position errors, potentially damaging the parts or the robot. To prevent this type of damage, when operating in such confined environments, in addition to position control, torque control is also required.

[0003] Conventional robot torque control is mainly achieved through PID controllers. The differential term of the PID controller is set to 0, and only the proportional parameter and the integral parameter are used for control. However, simple PI control can easily cause the current to change too fast or too slowly, and the control accuracy is also not up to expectations. Therefore, it is impossible to achieve coordinated torque control of multiple motors.

[0004] Summary of the Invention

[0005] In view of this, an embodiment of the present invention provides a differential control circuit and a control method for robot torque control.

[0006] A first aspect of the present invention provides a differential control circuit for robot torque control, characterized in that it includes a PI controller, a current differential loop, and a controlled motor; the PI controller, the current differential loop, and the controlled motor form a current loop for torque control; the current loop takes a desired current value as input and an actual current value as output;

[0007] The PI controller takes the current difference between the desired current value and the actual current value at the previous moment as input, performs proportional-integral control on the current difference, and then outputs a reference current value;

[0008] The current differential loop takes the reference current value as input, performs differential feedback and outputs a differential current value;

[0009] The controlled motor takes the differential current value as input, drives the motor to operate, forms an actual current value and outputs it.

[0010] Furthermore, the current differential loop includes a differential unit and a differentiator connected in sequence; the differential unit takes the current differential difference between the reference current value and the differential current value at the previous moment as input, adds a differential bias and inputs it into the differentiator for differential operation to obtain a differential current value output.

[0011] Furthermore, the expected current value represents the most ideal current value for torque control of the robot; the actual current value represents the current value actually output by the motor at the last moment; the current difference between the expected current value and the actual current value is expressed in the following form: i (t)=I0(t)-I(t)

[0012] Where I0(t) is the expected current value, I(t) is the actual current value, and t represents time.

[0013] Furthermore, the PI controller is expressed in the following form:

[0014] where K p is the proportional parameter of the PI controller, K i is the integral parameter of the PI controller, K d is the differential parameter of the PI controller, t represents time;

[0015] When taking K d =0, the reference current value obtained after the PI controller performs proportional-integral control on the current difference is expressed as follows:

[0016] Where μ(t) represents the reference current value.

[0017] Furthermore, the reference current value represents the current compensation value output by the PI controller, and the current differential difference between the reference current value and the differential current value at the previous moment is expressed in the following form: u (t)=μ(t)-μ ‘ (t)

[0018] The differential current value output obtained by the differential operation of the differentiator is expressed in the following form:

[0019] Where μ'(t) represents the differential current value, K' d Represents the differential parameter value of the differentiator.

[0020] Furthermore, after the controlled motor outputs the actual current value, the actual current value is multiplied by the preset torque coefficient to obtain the target torque for controlling the robot: F = K c ×I(t)

[0021] Where F is the target torque, K c is the motor torque coefficient, and I(t) is the actual current value.

[0022] A second aspect of the present invention provides a differential control method for robot torque control, which is applied to the aforementioned differential control circuit for robot torque control and comprises the following steps:

[0023] Setting a torque distribution strategy, and determining a desired current value of each differential control circuit according to the torque distribution strategy;

[0024] Inputting the expected current value into a differential control circuit to obtain an actual current value;

[0025] The actual current value is converted into a torque and acts on the robot.

[0026] Furthermore, converting the actual current value into a torque and applying it to the robot specifically includes the following steps:

[0027] Multiply the actual current value by the preset torque coefficient to obtain the target torque used to control the robot: F = K c ×I(t)

[0028] Where F is the target torque, K c is the motor torque coefficient, I(t) is the actual current value;

[0029] The robot is controlled using the target torque.

[0030] Furthermore, the torque distribution strategy includes average distribution, linear distribution and nonlinear distribution; when the torque distribution strategy is average distribution, the expected current value of each differential control circuit is set to the same value; when the torque distribution strategy is linear distribution, the expected current value of the differential control circuit is in a linear increasing relationship; when the torque distribution strategy is nonlinear distribution, the expected current value of the differential control circuit is determined according to a preset nonlinear relationship function.

[0031] The present invention also discloses a computer program product or computer program, which includes computer instructions stored in a computer-readable storage medium. A processor of a computer device can read the computer instructions from the computer-readable storage medium and execute the computer instructions, causing the computer device to perform the above method.

[0032] The embodiments of the present invention have the following beneficial effects: The present invention adds a current differential loop below the current loop of the PI controller. This current differential loop detects the dynamic characteristics of the current loop, preventing current changes from being too fast or too slow, improving system stability while also ensuring the accuracy of the actual output current. The present invention is compatible with the coordinated torque control of multiple motors, and by providing a current differential loop for each motor, each motor can achieve better torque distribution.

[0033] Additional aspects and advantages of the present invention will be set forth in part in the description which follows and, in part, will be obvious from the description which follows, or may be learned by practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0035] FIG1 is a block diagram of a current loop control circuit and a control method for a differential control of a robot torque under a motor condition according to the present invention;

[0036] FIG2 is a block diagram of differential current distribution of multiple motors in a differential control circuit and control method for robot torque control according to the present invention. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical solutions and advantages of this application more clearly understood, the present application is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0038] The parameters of the PID controller are proportional K p , integral K i and differential K d , the following describes these two parameters in detail.

[0039] Ratio K p :It is a static parameter. When the expected value of the closed loop and the measured value have an error, K p It will immediately act on the circuit and adjust the system accuracy. p The larger the K, the faster the system responds, but p If it is too large, the system will oscillate. p If it is too small, the system accuracy will be reduced, the adjustment time will be prolonged, and the system error will be increased. Therefore, in actual experiments, it is necessary to repeatedly adjust the Kp value to obtain the most appropriate value.

[0040] Point K i : It is a dynamic parameter of the process to prevent oscillation. The integral link is mainly used to eliminate the static error of the system, that is, the steady-state error. K i The larger the value, the faster the integration speed. i If the value is too large, the system actuator will be saturated, causing excessive overshoot, which will be difficult to recover within a certain period of time, and the dynamic performance of the system will also deteriorate. iIf the value is too small, it will be difficult to eliminate the system's error problems, and the transition process will be prolonged, causing the system to fail to meet performance indicators for a long time. From a phase perspective, an integral link will have a 90-degree phase delay, which may undermine system stability.

[0041] Generally, PID controllers do not use differential K d , that is, it is only used as a PI controller. Differential K d The main function of K is to suppress the error from changing in any direction during the system response process and respond to the error change in advance. Differentiation only affects the trend of the system error. d An overly large system will cause the response process to be braked prematurely. The failure to respond will cause the system to take time to adjust and reduce the system's anti-interference performance.

[0042] The embodiment of the present invention adds a current differential loop after the PI controller, which not only detects the rate of change of the control current but also improves the anti-interference performance and control accuracy of the control system.

[0043] As shown in FIG1 , an embodiment of the present invention provides a differential control circuit for robot torque control, including a PI controller, a current differential loop, and a controlled motor. The PI controller, the current differential loop, and the controlled motor form a current loop for torque control. The current loop uses a desired current value as input and an actual current value as output.

[0044] The PI controller takes the current difference between the desired current value and the actual current value at the previous moment as input, performs proportional-integral control on the current difference, and then outputs a reference current value.

[0045] The current differential loop takes the reference current value as input and outputs the differential current value after differential feedback;

[0046] The controlled motor takes the differential current value as input, drives the motor to operate to form the actual current value and output it.

[0047] In the embodiment of the present invention, the current loop input is a reference current value, and the output is the actual current value. The difference between the two is a current difference, which is the input to the PI controller. This article also adds a new current differential loop, a loop between the PI controller and the model (the dashed box in Figure 1). The current difference passing through the PI controller serves as the reference input of the differential loop. The difference between the reference input and the actual output serves as the differentiator input. The actual output of the differential loop serves as the reference input of the physical model, and the actual output of the model is the actual current value. The model here refers to the controlled motor.

[0048] In this embodiment, the current differential loop includes a differential unit and a differentiator connected in series. The differential unit takes the current differential difference between the reference current value and the previous differential current value as input, adds a differential bias, and then inputs the current differential into the differentiator for differential calculation, resulting in a differential current output. The desired value input to the differential loop is the current differential, i.e., the rate of change of the current. The output of the differential loop is the actual current differential. By feeding back the current differential error, the current differential rate of change is controlled to the desired differential value, i.e., the rate of change of the current, thereby achieving current stability.

[0049] Specifically, in this embodiment, the expected current value represents the most ideal current value for torque control of the robot; the actual current value represents the current value actually output by the motor at the previous moment; the current difference between the expected current value and the actual current value is expressed in the following form: i (t)=I0(t)-I(t)

[0050] Where I0(t) is the expected current value, I(t) is the actual current value, and t represents time.

[0051] In this embodiment, the PI controller is expressed as follows:

[0052] where K p is the proportional parameter of the PI controller, K i is the integral parameter of the PI controller, K d is the differential parameter of the PI controller, and t represents time;

[0053] When taking K d =0, the reference current value obtained by the PI controller after proportional-integral control of the current difference is expressed as follows:

[0054] Where μ(t) represents the reference current value.

[0055] In this embodiment, the reference current value represents the current compensation value output by the PI controller. The current differential difference between the reference current value and the differential current value at the previous moment is expressed in the following form: u (t)=μ(t)-μ ‘ (t)

[0056] The differential current value output obtained by the differentiator is expressed as follows:

[0057] Where μ'(t) represents the differential current value, K' d Represents the differential parameter value of the differentiator.

[0058] In this embodiment, after the controlled motor outputs the actual current value, the actual current value is multiplied by the preset torque coefficient to obtain the target torque for controlling the robot: F = K c ×I(t)

[0059] Where F is the target torque, K c is the motor torque coefficient, and I(t) is the actual current value. As can be seen, since the torque is proportional to the current, controlling the stability of the current loop can play a role in torque control of the robot.

[0060] An embodiment of the present invention further provides a differential control method for robot torque control, which is applied to a differential control circuit for robot torque control and includes the following steps:

[0061] Setting a torque distribution strategy, and determining an expected current value of each differential control circuit according to the torque distribution strategy;

[0062] Input the expected current value into the differential control circuit to obtain the actual current value;

[0063] The actual current value is converted into torque and acts on the robot.

[0064] Figure 2 illustrates the control of multiple motors with current differential loops. Each motor and its drive system has a current loop, and each model represents a motor. The controller sets the current distribution, allocating the desired current from 1 to N in real time. The desired current values ​​are processed by their respective current loops to obtain the actual current values. The process of adding a differential loop to each current loop is shown in Figure 1. The difference from the single-motor control is the addition of a distribution strategy for the desired current input, which determines how each motor works together. The motors control flexible materials, generating varying deformations and output torques.

[0065] In this embodiment, the actual current value is converted into a torque and applied to the robot, specifically including the following steps:

[0066] Multiply the actual current value by the preset torque coefficient to obtain the target torque used to control the robot: F = K c ×I(t)

[0067] Where F is the target torque, K c is the motor torque coefficient, I(t) is the actual current value;

[0068] The target torque is used to control the robot.

[0069] In this embodiment, the torque distribution strategy includes average distribution, linear distribution and nonlinear distribution; when the torque distribution strategy is average distribution, the expected current value of each differential control circuit is set to the same value; when the torque distribution strategy is linear distribution, the expected current value of the differential control circuit is in a linear increasing relationship; when the torque distribution strategy is nonlinear distribution, the expected current value of the differential control circuit is determined according to a preset nonlinear relationship function.

[0070] (1) Equal distribution

[0071] This distribution method can be used in situations where uniform output torque, uniform force, or symmetrical deformation is required. For example, the distribution is as follows: each motor is set to the same current, and the desired total current is set to I, where I is a constant greater than 0 and the upper limit of this value is the maximum input current supported by the controller. The desired input currents of the four current loops are then: i1 = i2 = i3 = i4 = I / 4, and each motor will produce the same torque and output current.

[0072] (2) Linear distribution

[0073] This distribution method can be used in situations requiring varying torque outputs, linear deformation, and more. For example, if the desired total current is 10I, the desired inputs for each current loop are: i1 = 1, i2 = 2I, i3 = 3I, and i4 = 4I. Each motor will generate proportional torque and output current, and the resulting torque will act together on the controlled object.

[0074] (3) Nonlinear distribution

[0075] This method can be used in situations where different torque outputs or nonlinear deformations are required. For example, the distribution is a nonlinear function related to the expected current input and the actual t: Each motor will generate torque and output current according to a nonlinear functional relationship, and the generated torque will act together on the controlled object.

[0076] The present invention establishes a current differential loop below the current loop, which increases the stability of the current loop, detects the dynamic characteristics of the current loop, prevents the current from changing too fast or too slow, and increases the control accuracy of the current loop. The advantages of the current loop here are equivalent to the advantages of force control, namely, it improves the stability of force control, detects changes in force, and improves the accuracy of force control. The present invention realizes the coordinated torque control of multiple motors. Each motor is provided with a current differential loop to detect the dynamic output of each motor, so that each motor can better distribute the torque.

[0077] Embodiments of the present invention further disclose a computer program product or computer program, which includes computer instructions stored in a computer-readable storage medium. A processor of a computer device can read the computer instructions from the computer-readable storage medium and execute the computer instructions, causing the computer device to perform the method shown in FIG1 .

[0078] In some optional embodiments, the function / operation mentioned in the block diagram may not occur in the order mentioned in the operation diagram. For example, depending on the function / operation involved, the two boxes shown in succession can actually be executed substantially simultaneously or the boxes can sometimes be executed in reverse order. In addition, the embodiment presented and described in the flow chart of the present invention is provided in an exemplary manner for the purpose of providing a more comprehensive understanding of the technology. The disclosed method is not limited to the operation and logic flow presented herein. Optional embodiments are contemplated in which the order of the various operations is changed and the sub-operations described as a part of a larger operation are performed independently.

[0079] Furthermore, although the present invention is described in the context of functional modules, it should be understood that, unless otherwise indicated, one or more of the functions and / or features described may be integrated into a single physical device and / or software module, or one or more functions and / or features may be implemented in separate physical devices or software modules. It will also be understood that a detailed discussion of the actual implementation of each module is not necessary for understanding the present invention. More specifically, given the properties, functions, and internal relationships of the various functional modules in the devices disclosed herein, the actual implementation of the module will be understood within the ordinary skill of an engineer. Therefore, a person skilled in the art using ordinary skill will be able to implement the present invention set forth in the claims without undue experimentation. It will also be understood that the specific concepts disclosed are merely illustrative and are not intended to limit the scope of the present invention, which is determined by the full scope of the appended claims and their equivalents.

[0080] The logic and / or steps represented in the flowcharts or otherwise described herein, for example, can be considered as an ordered list of executable instructions for implementing the logical functions, and can be embodied in any computer-readable medium for use by, or in conjunction with, an instruction execution system, apparatus, or device (e.g., a computer-based system, a system including a processor, or other system that can fetch and execute instructions from an instruction execution system, apparatus, or device). For purposes of this specification, a "computer-readable medium" can be any device that can contain, store, communicate, propagate, or transport a program for use by, or in conjunction with, an instruction execution system, apparatus, or device.

[0081] It should be understood that various parts of the present invention can be implemented using hardware, software, firmware, or a combination thereof. In the above-described embodiments, multiple steps or methods can be implemented using software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented using hardware, as in another embodiment, any one of the following technologies known in the art or a combination thereof can be used: a discrete logic circuit having a logic gate circuit for implementing a logic function on a data signal, an application-specific integrated circuit having a suitable combination of logic gate circuits, a programmable gate array (PGA), a field programmable gate array (FPGA), etc.

[0082] Throughout this specification, reference to terms such as "one embodiment," "some embodiments," "examples," "specific examples," or "some examples" means that a specific feature, structure, material, or characteristic described in conjunction with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, schematic representations of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0083] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to the embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the claims and their equivalents.

[0084] The above is a specific description of the preferred implementation of the present invention, but the present invention is not limited to the embodiments. Those skilled in the art can make various equivalent modifications or substitutions without violating the spirit of the present invention. These equivalent modifications or substitutions are all included in the scope defined by the claims of this application.

Claims

1. A differential control circuit for robot torque control, characterized in that: It includes a PI controller, a current differential loop and a controlled motor; the PI controller, the current differential loop and the controlled motor form a current loop for torque control; the current loop takes the expected current value as input and the actual current value as output; The PI controller takes the current difference between the expected current value and the actual current value at the previous moment as input, performs proportional-integral control on the current difference, and then outputs a reference current value; The current differential loop takes the reference current value as input, performs differential feedback and outputs a differential current value; The controlled motor takes the differential current value as input, drives the motor to operate, forms an actual current value and outputs it.

2. A differential control circuit for robot torque control according to claim 1, characterized in that: The current differential loop includes a differential unit and a differentiator connected in sequence; the differential unit takes the current differential difference between the reference current value and the differential current value at the previous moment as input, adds a differential bias and inputs it into the differentiator for differential operation to obtain a differential current value output.

3. A differential control circuit for robot torque control according to claim 2, characterized in that: The expected current value represents the most ideal current value for torque control of the robot; the actual current value represents the current value actually output by the motor at the last moment; the current difference between the expected current value and the actual current value is expressed in the following form: i (t)=I0(t)-I(t) Where I0(t) is the expected current value, I(t) is the actual current value, and t represents time.

4. A differential control circuit for robot torque control according to claim 3, characterized in that: The PI controller is expressed in the following form: Where K p is the proportional parameter of the PI controller, K i is the integral parameter of the PI controller, K d is the differential parameter of the PI controller, and t represents time; When taking K d =0, the reference current value obtained after the PI controller performs proportional-integral control on the current difference is expressed in the following form: Where μ(t) represents the reference current value.

5. A differential control circuit for robot torque control according to claim 4, characterized in that: The reference current value represents the current compensation value output by the PI controller, and the current differential difference between the reference current value and the differential current value at the previous moment is expressed in the following form: u (t) = μ(t) - μ'(t) The differential current value output obtained by the differential operation of the differentiator is expressed in the following form: Where μ'(t) represents the differential current value, K' d Represents the differential parameter value of the differentiator.

6. A differential control circuit for robot torque control according to claim 1, characterized in that: After the controlled motor outputs the actual current value, the actual current value is multiplied by the preset torque coefficient to obtain the target torque for controlling the robot: F = K c ×I(t) Where F is the target torque, K c is the motor torque coefficient, and I(t) is the actual current value.

7. A differential control method for robot torque control, applied to at least one differential control circuit for robot torque control as claimed in any one of claims 1 to 5, characterized in that: The following steps are involved: Setting a torque distribution strategy, and determining a desired current value of each differential control circuit according to the torque distribution strategy; Inputting the expected current value into a differential control circuit to obtain an actual current value; The actual current value is converted into a torque and acts on the robot.

8. The differential control method for robot torque control according to claim 7, characterized in that: The actual current value is converted into a torque and acts on the robot. The following steps are involved: Multiply the actual current value by the preset torque coefficient to obtain the target torque used to control the robot: F=K c ×I(t) Where F is the target torque, K c is the motor torque coefficient, I(t) is the actual current value; The robot is controlled using the target torque.

9. The differential control method for robot torque control according to claim 7, characterized in that: The torque distribution strategy includes average distribution, linear distribution and nonlinear distribution; when the torque distribution strategy is average distribution, the expected current value of each differential control circuit is set to the same value; when the torque distribution strategy is linear distribution, the expected current value of the differential control circuit is in a linear increasing relationship; when the torque distribution strategy is nonlinear distribution, the expected current value of the differential control circuit is determined according to a preset nonlinear relationship function.

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