A robot grasping control system and its DC motor compliant control method

Abstract

This invention discloses a robot gripping control system and its DC motor compliant control method, comprising a communication port, a controller, a drive circuit, an H-bridge circuit, a DC motor, and a robot gripper connected in sequence. The H-bridge circuit is powered by a DC power supply. The DC motor is equipped with an incremental encoder to detect its operating speed and achieve closed-loop speed control. The communication port is used by the controller to receive instructions from a host computer. The controller controls the DC motor and outputs a pulse-width modulation signal to the drive circuit. The drive circuit drives the H-bridge circuit. The H-bridge circuit controls the DC motor. The robot gripper is a two-finger gripper. This invention, without installing force sensors or motor current sensors, achieves steady-state current control of the motor by controlling the motor voltage during compliant control when gripping an object and thus controlling the gripping force of the gripper.

Description

Technical Field

[0001] This invention belongs to the field of automatic control technology, specifically, it relates to a robot grasping control system and a DC motor compliant control method. Background Technology

[0002] In a robot gripping control system, in order to grip different objects, it is necessary to control the gripping force of the robot's gripper to avoid damage to the gripped object due to excessive gripping force.

[0003] In existing technologies, force sensors are typically installed in gripper systems to detect the actual gripping force and thus control it. For example, application number CN201910942571.X discloses an adaptive gripping method and system for a compliant gripper, which achieves precise control of the gripping force by placing a gripping force sensor on the compliant gripper and connecting it to a microprocessor signal. However, installing force sensors not only increases costs but also adds complexity to the system structure design and control system. Furthermore, robot grippers are usually mounted on the robot's end effector, increasing the weight of the robot's end effector gripper device. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention provides a robot gripping control system and its DC motor compliant control method, which eliminates the need for force sensors, simplifying the structural design of the robot gripping control system and the weight of the gripper.

[0005] To achieve the above technical objectives, the technical solution adopted by this invention is as follows: a robot grasping control system, comprising a communication port, a controller, a drive circuit, an H-bridge circuit, a DC motor, and a robot gripper connected in sequence. The H-bridge circuit is powered by a DC power supply. The DC motor is equipped with an incremental encoder for detecting the operating speed of the DC motor and realizing closed-loop speed control of the DC motor. The communication port is used by the controller to receive instructions from a host computer. The controller is used to control the DC motor and output pulse width modulation signals to the drive circuit. The drive circuit is used to drive the H-bridge circuit. The H-bridge circuit is used to control the DC motor. The robot gripper is a two-finger gripper, which is driven by the DC motor through a worm gear to perform gripping or releasing actions.

[0006] Furthermore, the controller includes a speed controller, a compliant controller, a pulse width modulator, and a speed calculator. The speed calculator is used to calculate the actual speed of the DC motor. The speed controller is used to receive the speed deviation between the set speed and the actual speed of the DC motor to realize closed-loop speed control of the DC motor. The compliant controller receives the output of the speed control and transmits the output of the compliant controller to the pulse width modulator. The pulse width modulator signal is transmitted to the drive circuit. The pulse width modulator, the drive circuit, and the H-bridge circuit together form a DC motor voltage amplification module.

[0007] Furthermore, before the robot gripper picks up the object, the compliant controller does not process the received speed control output and directly transmits it to the pulse width modulator to achieve closed-loop control of the DC motor speed; when the robot gripper picks up the object, the compliant controller outputs a fixed voltage related to the clamping force required to pick up the object to control the DC motor.

[0008] Furthermore, the present invention also provides a compliant control method for a DC motor based on a robot grasping control system, specifically including the following steps:

[0009] Step S1: Set the speed of the DC motor driving the robot gripper to the set speed, and use speed closed-loop control to control the running speed of the DC motor;

[0010] Step S2: By comparing the rated speed of the DC motor with the actual speed of the DC motor, until the deviation between the actual speed of the DC motor and the set speed is less than the first threshold, theoretically the actual speed of the DC motor reaches the set speed.

[0011] Step S3: Continue to compare the rated speed of the DC motor with the actual speed of the DC motor. When the deviation between the actual speed and the set speed is greater than the second threshold, it is determined that the robot gripper has contacted the object to be grasped, and the DC motor begins to decelerate.

[0012] Step S4: After the robot gripper has made contact with the object to be gripped, the gripping force of the robot gripper is maintained by the output voltage of the compliant controller, the DC motor is stalled, and the robot gripper clamps the object.

[0013] Furthermore, the first threshold is set to 2% of the set speed.

[0014] Furthermore, the second threshold is set to 5% of the set speed.

[0015] Furthermore, the output voltage of the compliant controller in step S3 is a fixed voltage U2, and the calculation process of U2 is as follows:

[0016]

[0017] Where I is the DC motor current corresponding to the gripping force required to grasp the object, R is the internal resistance of the DC motor, and K... a This represents the voltage and power amplification factor of the H-bridge circuit.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] (1) The present invention is based on a robot gripping control system and a DC motor compliant control method, which eliminates the need for force sensors, thus simplifying the structural design of the robot gripper system and the weight of the gripper.

[0020] (2) By utilizing the definite relationship between the clamping force of the robot gripper and the output torque of the DC motor, and the linear relationship between the output torque of the DC motor and the current, the clamping force of the gripper can be controlled by controlling the current of the DC motor, thus simplifying the control of the robot gripper.

[0021] (3) When the robot gripper clamps an object, the DC motor is in a stall state. At this time, the motor current is approximately only related to the motor impedance. The motor current is linearly related to the voltage across the motor armature. By adding a compliant controller between the speed control and pulse width modulator in the conventional DC motor control structure, there is no need to install a motor current sensor or design a motor current control circuit. The motor voltage is controlled when the object is clamped, thereby controlling the motor torque and realizing the control of the clamping force, which simplifies the control system and control method. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the robot grasping control system of the present invention;

[0023] Figure 2 This is a control diagram of the controller in this invention;

[0024] Figure 3 This is a flowchart of the DC motor compliant control method based on a robot grasping control system according to the present invention.

[0025] Figure 4 A simulation diagram showing the current required to grip an object using the method of this invention (0.45A).

[0026] Figure 5 A simulation diagram showing the current required to clamp an object using the method of this invention, which is 0.35A. Detailed Implementation

[0027] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings.

[0028] like Figure 1The robot gripping control system of this invention includes a communication port, a controller, a drive circuit, an H-bridge circuit, a DC motor, and a robot gripper connected in sequence. A DC power supply provides power to the H-bridge circuit. An incremental encoder is installed on the DC motor to detect the running speed of the DC motor and realize closed-loop speed control of the DC motor. The communication port is used by the controller to receive instructions from the host computer. The controller is used to control the DC motor and outputs a pulse width modulation signal to the drive circuit. The drive circuit is used to drive the H-bridge circuit. The H-bridge circuit is used to control the DC motor. The robot gripper is a two-finger gripper, which is driven by the DC motor through a worm gear to perform gripping or releasing actions.

[0029] like Figure 2 The controller in this invention includes a speed controller, a compliant controller, a pulse width modulator, and a speed calculator. The speed calculator calculates the actual speed of the DC motor. The speed controller receives the speed setpoint and the actual speed of the DC motor calculated by the speed calculator, calculates the speed deviation between them, and performs proportional correction control to achieve closed-loop speed control of the DC motor. The compliant controller receives the output of the speed control and transmits the output of the compliant controller to the pulse width modulator. The pulse width modulator signal is transmitted to the drive circuit, which drives the H-bridge circuit. The pulse width modulator, drive circuit, and H-bridge circuit together form a DC motor voltage amplification module. Based on the DC motor control principle, the output value of the compliant controller, after passing through the pulse width modulator, drive circuit, and H-bridge circuit, has a linear relationship with the voltage across the motor armature. That is, the output value of the compliant controller has a linear relationship with the voltage across the motor armature.

[0030] In this invention, before the robot gripper picks up an object, the compliant controller receives the speed control output without any processing and directly transmits it to the pulse width modulator. At this time, the DC motor uses conventional methods for closed-loop speed control. When the robot gripper picks up the object, it outputs a fixed voltage related to the clamping force required to pick up the object. At this time, the DC motor voltage is independent of the speed control, and the speed control no longer plays a role. The compliant controller directly outputs a fixed voltage to control the DC motor.

[0031] like Figure 3 The present invention also provides a compliant control method for a DC motor based on a robot grasping control system, which specifically includes the following steps:

[0032] Step S1: Set the speed of the DC motor driving the robot gripper to the set speed of the motor, and use speed closed-loop control of the DC motor to control the running speed. At this time, the compliant controller will not process the speed control output voltage and directly transmit it to the pulse width modulator. That is, the output voltage of the compliant controller is equal to the output voltage of the speed controller. At this time, the control of the DC motor is the conventional speed closed-loop control method.

[0033] Step S2: Since the distance between the robot gripper and the object to be gripped is large enough, the robot gripper cannot reach the object before the actual speed of the DC motor reaches a steady state. By comparing the rated speed of the DC motor with the actual speed of the DC motor, until the deviation between the actual speed of the DC motor and the set speed is less than the first threshold, theoretically the actual speed of the DC motor has reached the set speed. Since the speed fluctuation is usually less than 2% when the DC motor speed closed-loop control reaches a steady state, when the speed deviation is less than 2%, it is considered that the DC motor has reached a steady state speed. Therefore, the first threshold in this invention is set to 2% of the set speed.

[0034] Step S3: Continue to compare the rated speed of the DC motor with the actual speed of the DC motor. When the deviation between the actual speed and the set speed is greater than the second threshold (in this invention, the second threshold is 5% of the set speed), the gripper has contacted the object to be grasped, and the DC motor begins to decelerate. Since the fluctuation of the actual speed of the DC motor in steady state is less than 2%, when the speed deviation is greater than the second threshold, it can be confirmed that the robot gripper has started to contact the object and decelerate. When the deviation between the actual speed and the steady-state speed is greater than the second threshold, the output of the compliant controller is independent of the speed control output, and the compliant control output is a fixed voltage U2. The calculation process of U2 is as follows:

[0035] Based on the dimensions and structure of the robot gripper's clamping mechanism, as well as the clamping force required for the object to be gripped, the required motor torque of the DC motor when the robot gripper clamps the object is calculated. Since the motor torque and motor current are linearly related, the motor current relationship corresponding to the motor torque when the gripper clamps the object is determined based on the parameters of the DC motor.

[0036] U m =U2×K s (1)

[0037] U m =I×R+n×C e (2)

[0038]

[0039] Among them, U m U1 is the output voltage of the H-bridge, U2 is the output voltage of the compliant controller, and K is the output voltage of the H-bridge. s Here, I is the voltage amplification factor of the H-bridge circuit, R is the DC motor current, n is the internal resistance of the DC motor, and C is the operating speed of the DC motor. e This is the back electromotive force of the DC motor.

[0040] When the robot gripper has made contact with the object to be grasped, the DC motor stalls, i.e., n=0, resulting in a fixed compliant control output voltage U2.

[0041]

[0042] Step S4: After the robot gripper has contacted the object to be gripped, when the DC motor stops rotating, the gripping force of the robot gripper is maintained by the output voltage of the compliant controller based on the linear relationship between the DC motor current and the output torque. The DC motor stalls, and the robot gripper clamps the object.

[0043] Figure 4 , Figure 5 The simulation results of the current experiment when gripping two objects according to the present invention are shown. The vertical axis represents the current value in amperes, and the horizontal axis represents the number of data points recorded. The time for each data point is 10 milliseconds. In the first stage, the DC motor overcomes the frictional force of the gripper transmission, and the operating current is approximately 0.2A. Figure 4 The experimental results show that 0.45A of current is required to grip the object. Figure 5 The experimental result shows that a current of 0.35A is required to grip the object. Figure 4 and 5 As can be seen, after the DC motor clamps the object, the motor current is basically stable at a set value, which can realize the clamping force control of different objects.

[0044] The above are merely preferred embodiments of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should be considered within the scope of protection of the present invention.

Claims

1. A robot-based grasping control system, characterized by, The robot gripping control system comprises a communication port, a controller, a driving circuit, an H-bridge circuit, a direct current motor and a robot gripper connected in sequence, the H-bridge circuit is powered by a direct current power supply, an incremental encoder is arranged on the direct current motor to detect the running speed of the direct current motor and realize speed closed-loop control of the direct current motor, the communication port is used for the controller to receive instructions from an upper computer, the controller is used for controlling the direct current motor and outputting a pulse width modulation signal to the driving circuit, the driving circuit is used for driving the H-bridge circuit, the H-bridge circuit is used for realizing control of the direct current motor, and the robot gripper is a two-finger gripper driven by the direct current motor through a worm gear to clamp or release an object. The soft control method of the direct current motor based on the robot gripping control system specifically comprises the following steps. In step S1, the speed of the direct current motor driving the robot gripper is set as a set speed, and the speed closed-loop control is adopted to control the running speed of the direct current motor. In step S2, the set speed of the direct current motor is compared with the actual speed of the direct current motor until the deviation between the actual speed and the set speed is less than a first threshold value, at which time the actual speed of the direct current motor theoretically reaches the set speed. In step S3, the set speed of the direct current motor is continuously compared with the actual speed of the direct current motor, and when the deviation between the actual speed and the set speed is greater than a second threshold value, it is determined that the robot gripper has contacted the object to be gripped, and the direct current motor starts to slow down. In step S4, after the robot gripper has contacted the object to be gripped, the output voltage of the soft controller is used to maintain the clamping force of the robot gripper, the direct current motor is blocked, and the robot gripper clamps the object. The output voltage of the compliance controller outputs a fixed voltage , The calculation process is as follows: Wherein, I is the clamping force required for the object to be grabbed corresponding to the DC motor current, R is the internal resistance of the DC motor, Is the H-bridge circuit voltage power amplification multiple.

2. The robot-based grasping control system of claim 1, wherein, The controller comprises a speed controller, a soft controller, a pulse width modulator and a rotation speed calculator, the rotation speed calculator is used to calculate the actual speed of the direct current motor, the speed controller is used to receive the speed deviation between the set speed and the actual speed of the direct current motor to realize the speed closed-loop control of the direct current motor, the soft controller receives the output of the speed control and transmits the output of the soft controller to the pulse width modulator, the pulse width modulation signal is transmitted to the driving circuit, and the pulse width modulator, the driving circuit and the H-bridge circuit jointly constitute a direct current motor voltage amplification module.

3. A robot-based grasping control system according to claim 2, wherein, The soft controller does not process the received speed control output before the robot gripper clamps the object, directly transmits the output to the pulse width modulator to realize the closed-loop control of the direct current motor speed, and outputs a fixed voltage related to the clamping force required by the object to be clamped to control the direct current motor when the robot gripper clamps the object.

4. The robot-based grasping control system of claim 1, wherein, The first threshold value is 2% of the set speed.

5. The robot-based grasping control system of claim 1, wherein, The second threshold value is 5% of the set speed.

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