CN113043272B - Control system applied to space multi-degree-of-freedom rope-driven parallel robot - Google Patents

Abstract

The invention discloses a control system applied to a space multi-degree-of-freedom rope-driven parallel robot, and relates to the technical field of rope-driven parallel robot control. The present invention is to solve the problems of low precision, low efficiency and inconvenience of large-space deployment in the existing rope-driven robot control method. The host computer of the present invention is used to receive the desired position coordinates, the main controller is used to perform position and tension conversion on the desired position coordinates sent by the host computer, and obtain the tension values of the ropes of the four winding devices of the rope-driven parallel robot, and the four slave controllers are respectively One-to-one correspondence with the four winding devices of the rope-driven parallel robot, the slave controller is used to calculate the tension control command and the rope length control command according to the tension value of the rope of the corresponding winding device, and send the tension control command and The rope length control command, the tension control command is the expected tension of the rope at each moment during the movement time, and the rope length control command is the expected rope length of the rope at each moment during the movement time.

Description

A control system applied to a multi-DOF rope-driven parallel robot

technical field

The invention belongs to the technical field of rope-driven parallel robot control.

Background technique

The biggest feature and advantage of the rope-driven parallel robot is the rope drive. On the one hand, compared with the rigid link of the same length, its weight is greatly reduced, which increases its flexibility. At the same time, compared with the rigid link, the rope can be deployed in a larger space. inside, greatly increasing its working space. Therefore, the rope-driven parallel robot has the incomparable advantages of traditional industrial manipulators and rope-driven serial robots. Now it has played a huge role in aircraft simulation and large radio telescopes.

Although rope-driven parallel robots have incomparable advantages over serial robots, the design of rope flexibility and control system solutions is a big problem. At present, most of the rope-driven robots on the market use individual position control, individual force control, and switching force-position hybrid control methods. These control methods have low precision, and at the same time, the controller design is difficult, and the specific implementation is difficult. In the overall control system, the current centralized control system is mainly used. This control system solution has low control efficiency, is not convenient for large-space deployment, and is not easy to control.

SUMMARY OF THE INVENTION

The present invention is to solve the problems of low precision, low efficiency and inconvenience of large-space deployment in the existing rope-driven robot control method, and now provides a control system applied to a space multi-degree-of-freedom rope-driven parallel robot.

A control system applied to a multi-DOF rope-driven parallel robot, including a host computer, a master controller and four slave controllers. The host computer is used to receive the desired position coordinates, and the master controller is used to send the desired position coordinates to the host computer. Perform position and tension conversion to obtain the rope tension values of the four winding devices of the rope-driven parallel robot. The four slave controllers correspond to the four winding devices of the rope-driven parallel robot one-to-one, and the slave controllers are used for winding according to the corresponding The tension value of the device rope calculates the tension control instruction and the rope length control instruction, and sends the tension control instruction and the rope length control instruction to the corresponding winding device respectively, and the tension control instruction is the expected tension of the rope at each moment during the movement time, The rope length control command is the desired rope length of the rope at each moment in the movement time.

Further, the above-mentioned main controller includes: an outer loop PID control module and a position and tension conversion module, and the outer loop PID control module is used to convert the position error E _pos to the outer loop position control quantity U _pos , and the position error E _pos is The difference between the desired position coordinate and the current position coordinate of the rope-driven parallel robot, the position and tension conversion module is used to calculate the tension value of the rope of each winding device separately by using the outer ring position control quantity U _pos .

Further, the above-mentioned outer loop PID control module converts the position error E _pos into the outer loop position control amount U _pos through the following formula:

Among them, _{K p} is the proportional coefficient, _TI is the integral time constant, and TD is the differential time constant.

Further, the above-mentioned position and tension conversion module includes the following units:

The unit of the i-th tension parameter T _i is obtained according to the outer ring position control quantity U _p o _s , i=1, 2, 3, 4,

A_i为第i个绕线装置出绳口的坐标，P为期望位置坐标，in,

A _i is the coordinate of the rope exit of the i-th winding device, P is the desired position coordinate,

When T _i ≥ 0, take T _i as the unit of the tension value of the rope of the i-th winding device,

When T _i <0, make the unit of the i-th winding device rope tension value T _i =T _i +M≥0, where M is an internal force parameter and u _i M=0 is satisfied.

Further, the above-mentioned slave controller includes: an inner loop PID control module, a pulse drive module, a tension sensing module, an encoder and an angle rope length conversion module, and the inner loop PID control module is used to convert the tension error E _{force_i} into the inner loop tension. Control variable U _{force_i} , the tension error is the difference between the tension value T _i of the rope of the i-th winding device and the current tension value F _i of the rope of the i-th winding device, i=1, 2, 3, 4, pulse The drive module is used to obtain the voltage and duty cycle of the _ith winding device motor according to the inner ring tension control quantity U _{force_i} to generate a pulse signal, and send the pulse signal to the motor driver as a tension control command, and the tension sensing module It is used to collect the current tension value F _i of the rope of the i-th winding device, the encoder is used to obtain the rotation angle θ _i of the motor shaft in the i-th winding device according to the current tension value F _i , and the angle rope length conversion module is used to convert the The rotation angle θ _i of the motor shaft in the _i winding devices is converted into the rope length control command Li .

Further, the tension error E _{force_i} is converted into the inner ring tension control amount U _{force_i} according to the following formula:

Among them, _{K p} is the proportional coefficient, _TI is the integral time constant, and TD is the differential time constant.

Further, according to the following formula, the rotation angle θ _i of the motor shaft in the i-th winding device is converted into the rope length control command L _i :

Among them, Q is the reduction ratio of the motor, R is the radius of the motor shaft, and N is the transmission ratio of the transmission device.

Further, the voltage U _pwm of the ith winding device motor is calculated by the following formula:

Among them, F is the maximum value of the motor torque when the duty cycle is 100%, V is the maximum value of the motor analog input voltage when the duty cycle is 100%,

Calculate the duty cycle D of the ith winding device motor by the following formula:

Among them, U _full is the voltage value of the motor when the duty cycle is 100%.

The beneficial effects of the present invention are as follows:

(1) Master-slave distributed control scheme: Jeston Nano is used as the master controller, exclusive control board is used as the slave controller, and distributed deployment can make the control of each winding device more personalized, more efficient and fast. Distributed deployment can greatly increase the flexibility of the product workspace and its installation and movement. The master-slave controller can achieve precise assignment of tasks, the upper layer centrally calculates complex control and planning algorithms, and the lower layer only needs to execute the corresponding commands, making the entire control system more stable, more efficient, and more flexible in operation.

(2) Exclusive control board: The control board of the slave controller can combine various functional modules together, and each module it contains can make tasks such as information transmission and control instruction issuance run more stably and efficiently.

(3) Dual-loop force-position hybrid control: Compared with separate position control and tension control, the present invention combines position and tension in a dual-loop way, and is applied to a multi-degree-of-freedom rope-driven robot in space, which can greatly increase the The control of the rope tension ensures that the rope is always in a tight state during the movement, thereby improving the control accuracy of the position of the end working platform.

Description of drawings

Fig. 1 is a structural block diagram of a control system applied to a space multi-DOF rope-driven parallel robot;

FIG. 2 is a schematic control diagram of the control system according to Embodiment 1;

3 is a schematic diagram of the conversion process of the position and tension conversion module;

Figure 4 is a schematic diagram of the internal control flow of the slave controller.

Detailed ways

Embodiment 1: This embodiment will be described in detail with reference to FIG. 1 to FIG. 4. The control system applied to a spatial multi-degree-of-freedom rope-driven parallel robot described in this embodiment includes: a host computer, a master controller and four slave controllers device.

The operator uses the mobile phone or tablet as the host computer, and inputs the desired position coordinates on the host computer. It is wirelessly transmitted to the main controller Jeston Nano board through the TCP/IP network protocol. The main controller is used to convert the position and tension of the desired position coordinates sent by the host computer, and obtain the tension values of the ropes of the four winding devices of the rope-driven parallel robot.

The master controller sends the tension value to 4 slave controllers via CAN bus. The four slave controllers are in one-to-one correspondence with the four winding devices of the rope-driven parallel robot, and the slave controller receives commands to control the winding devices to move, thereby controlling the extension and retraction of the rope to complete the control of the end position. The slave controller is used to calculate the tension control command and the rope length control command according to the tension value of the rope of the corresponding winding device, and send the tension control command and the rope length control command to the corresponding winding device respectively. The tension control command is the expected tension of the rope at each moment during the movement time, and the wire length control command is the expected wire length of the rope at each moment during the movement time.

Specifically, the above-mentioned main controller includes: an outer loop PID control module and a position and tension conversion module.

The outer loop PID control module converts the position error E _pos to the outer loop position control variable U _pos through the following formula:

Among them, _{K p} is the proportional coefficient, _TI is the integral time constant, and TD is the differential time constant. The position error E _pos is the difference between the desired position coordinates and the current position coordinates of the rope-driven parallel robot.

The position and tension conversion module is used to calculate the tension value of the rope of each winding device separately by using the position control quantity U _pos of the outer ring. Specifically, the position and tension conversion module includes the following units:

The unit of the i-th tension parameter T _i is obtained according to the outer ring position control quantity U _pos , i=1, 2, 3, 4,

A_i为第i个绕线装置出绳口的坐标，P为期望位置坐标，in,

A _i is the coordinate of the rope exit of the i-th winding device, P is the desired position coordinate,

When T _i ≥ 0, take T _i as the unit of the tension value of the rope of the i-th winding device,

When T _i <0, make the unit of the i-th winding device rope tension value T _i =T _i +M≥0, where M is an internal force parameter and u _i M=0 is satisfied.

As shown in Figure 3, the position and tension conversion module can ensure that the control effect of the double-loop full closed-loop control can meet the task requirements. At the same time, the conversion of the control value output by the outer loop PID control module to the tension values of the four ropes is completed, and the method of optimizing the tension is added to this module to ensure that the expected tension values input to the inner loop are all greater than zero, which meets the requirements of the rope-driven robot. Rope tension requirements and make the inner loop really play the role of tension control. The resultant external force solved by the dynamic model directly acts on the control quantity output by the outer loop PID control module, which can complete the conversion from the control quantity obtained from the position error of the outer loop to the expected value of the inner loop tension control, realize the effective connection of the inner and outer loops, and improve the control the completion of the task.

After completing the conversion from the control value obtained from the position error of the outer loop to the expected value of the tension control of the inner loop, consider the particularity of the rope-pulled parallel robot, because the rope used is a flexible object, and its force can only receive tension, not It may be under pressure. Once the tension is zero or less than zero, the rope is in a relaxed state. At this time, the motion control of the rope is completely inaccurate. At this time, the position of the end effector is accurately tracked. is an impossible task. Therefore, at the end of completing the construction of the dual-loop control process, the problem of rope tension optimization should be taken into account to ensure that the task can be achieved. Therefore, the internal force parameter M is introduced to ensure that the tension is always greater than zero to satisfy the condition of the rope tension.

The slave controller uses the STM32F407ZGT6 chip as the control chip. The slave controller includes: inner loop PID control module, pulse drive module, tension sensing module, encoder, angle rope length conversion module, CAN bus module and power supply module.

The tension sensing module is used to collect the current tension value F _i of the rope of the i-th winding device.

The inner loop PID control module is used to convert the tension error E _{force_i} into the inner loop tension control amount U _{force_i} according to the following formula:

The tension error is the difference between the tension value T _i of the rope of the ith winding device and the current tension value F _i of the rope of the ith winding device.

The encoder is used to obtain the rotation angle θ _{i of the motor shaft in the i-th winding device according to the current tension value F i .} The module uses AM26C32 chip to convert the differential encoded signal returned by the encoder into a single-channel encoded signal. The chip has fast conversion speed and stable conversion, which can greatly increase the timeliness of encoder information transmission.

The angle rope length conversion module is used to convert the rotation angle θ _i of the motor shaft in the _i -th winding device into the rope length control command Li according to the following formula:

Among them, Q is the reduction ratio of the motor, R is the radius of the motor shaft, and N is the transmission ratio of the transmission device.

The pulse drive module is used to obtain the voltage and duty cycle of the ith winding device motor according to the inner ring tension control value U _{force_i} to generate a pulse signal, and send the pulse signal to the motor driver. Specifically, calculate the ith winder by the following formula Voltage U _pwm of each winding device motor:

Among them, F is the maximum value of the motor torque when the duty cycle is 100%, and V is the maximum value of the motor analog input voltage when the duty cycle is 100%.

Calculate the duty cycle D of the ith winding device motor by the following formula:

Among them, U _full is the voltage value of the motor when the duty cycle is 100%.

In this way, PWM pulses are generated, and the voltage value of the generated PWM pulses after passing through the low-pass filter is transmitted to the motor driver, so that the motor can generate corresponding torque. The pulse drive module provides the motor driver with pulses of a certain frequency and duty cycle to control the movement of the motor, thereby driving the rope and the end working platform to move. The module uses ADuM1310 magnetic coupling chip for isolation and level pull-up. The chip has good isolation and accurate pull-up level, which can increase the accuracy of the pulse level value and reduce the pulse failure caused by the level not reaching the minimum value. Identify the problems and further improve the control accuracy.

The power module is used to provide power guarantee for the slave controller. The LM2596 chip is used to complete the level conversion from 24V to 5V, and the AMS1117 is used to complete the level conversion task of 5V to 3.3V. This module can ensure that the level conversion is more stable, and the output level will not jump, which better ensures that the control board can work normally.

The CAN bus module is used to connect the controller to the CAN bus network to complete the task of sending and receiving information. The module uses the TJA1050 chip as the CAN level conversion chip. At the same time, optocoupler or magnetic coupling can be added for isolation to increase the stability of transmission. sex. The CAN bus is connected to the physical bus through the two output terminals CANH and CANL of the CAN transceiver interface chip 82C250, and the state of the CANH terminal can only be a high level or a floating state, and the CANL terminal can only be a low level or a floating state.

As shown in Figure 4, it is divided into 4 separate inner loops, (each independent inner loop represents the inner loop of a rope) 4 inner loops as a whole constitute the inner loop in the double loop. The inner loop is mainly composed of the inner loop PID control module, the motor model and the force feedback loop. Its working principle is that the outer loop is converted by variable calculation to obtain the appropriate tension value on each rope when the end effector is at a certain point in the working space, and is sent to the input end of the inner loop of each rope respectively, through the calculation of the inner loop PID control module. The output control quantity is sent to the constructed motor model, and the motor model feeds back the actual tension value. Finally, the inner loop closed loop is completed through the inner loop PID control module and the inner loop tension control is realized to ensure that the output tension of the motor is converted through the outer loop. Calculate the appropriate tension value of the rope at this time. At the same time, the length of each rope is sent to the forward kinematics solving module in the outer ring to solve the point coordinates of the end effector in the workspace now.

This embodiment can realize high-precision control and flexible operation of the rope-driven robot, so that it can be more conveniently and efficiently applied to the intelligent manufacturing industry. This embodiment can realize the control of the rope tension, thereby increasing the control accuracy of the end working platform and realizing high-precision position control.

Claims (12)

1. Control system for space multi freedom rope drives parallel robot, its characterized in that includes: an upper computer, a master controller and four slave controllers,

the upper computer is used for receiving the expected position coordinates,

the main controller is used for converting the position and the tension of the expected position coordinate sent by the upper computer to obtain the tension values of the ropes of the four winding devices of the rope-driven parallel robot,

the four slave controllers are respectively corresponding to the four winding devices of the rope-driven parallel robot one by one, are used for calculating a tension control instruction and a rope length control instruction according to the tension value of the rope of the corresponding winding device and respectively sending the tension control instruction and the rope length control instruction to the corresponding winding devices,

the tension control instruction is the expected tension of the rope at each moment in the movement time, and the rope length control instruction is the expected rope length of the rope at each moment in the movement time;

the main controller includes: an outer ring PID control module and a position and tension conversion module,

the outer loop PID control module is used for converting the position error E_posConverted into outer ring position control quantity U_posSaid position error E_posAs the difference between the desired position coordinates and the current position coordinates of the rope-driven parallel robot,

the position and tension conversion module is used for controlling the quantity U by utilizing the position of the outer ring_posRespectively calculating the tension value of each rope of the winding device;

the position and tension conversion module comprises the following units:

according to the outer ring position control quantity U_posObtaining the ith tension parameter T_iI is 1,2,3,4,

wherein, T_i＝U_pos/u_i，

A_iIs the coordinate of the rope outlet of the ith winding device, P is the coordinate of the expected position,

when T is_iWhen T is more than or equal to 0, adding_iAs a unit of the tension value of the i-th winder rope,

when T is_i<At 0, make the tension value T of the i-th winding device rope_i＝T_iA unit of + M ≧ 0, wherein M is an internal force parameter and satisfies u_iM＝0。

2. The control system applied to the spatial multi-degree-of-freedom rope-driven parallel robot as claimed in claim 1, wherein the outer ring PID control module calculates the position error E by the following formula_posConverted into outer ring position control quantity U_pos：

Wherein, K_pIs a proportionality coefficient, T_IIs integration time constantNumber, T_DIs the differential time constant.

3. The control system applied to the spatial multiple degree of freedom rope-driven parallel robot as claimed in claim 1, wherein the slave controller comprises: an inner ring PID control module, a pulse drive module, a tension sensing module, an encoder and an angle rope length conversion module,

the inner ring PID control module is used for controlling the tension error E_{force_i}Converted into inner ring tension control quantity U_{force_i}The tension error is the tension value T of the ith winding device rope_iCurrent tension value F of the i-th winding device rope_iThe difference, i is 1,2,3,4,

the pulse drive module is used for controlling the quantity U according to the tension of the inner ring_{force_i}Obtaining the voltage and duty ratio of the motor of the ith winding device to generate a pulse signal, sending the pulse signal to a motor driver as a tension control command,

the tension sensing module is used for acquiring the current tension value F of the ith winding device rope_i，

The encoder is used for generating the current tension value F_iObtaining the rotation angle theta of the motor shaft in the ith winding device_i，

The angle rope length conversion module is used for converting the rotation angle theta of the motor shaft in the ith winding device_iConverted into rope length control instruction L_i。

4. The control system applied to the rope-driven parallel robot with multiple degrees of spatial freedom according to claim 3, wherein the tension error E is calculated according to the following formula_{force_i}Converted into inner ring tension control quantity U_{force_i}：

Wherein, K_pIs a proportionality coefficient, T_ITo integrate the time constant, T_DIs the differential time constant.

5. The control system for the spatial multi-degree-of-freedom rope-driven parallel robot as claimed in claim 3, wherein the rotation angle θ of the motor shaft in the ith winding device is determined according to the following formula_iConverted into rope length control instruction L_i：

Wherein Q is the motor reduction ratio, R is the motor rotating shaft radius, and N is the transmission ratio of the transmission device.

6. The control system for the spatial multi-degree-of-freedom rope-driven parallel robot as claimed in claim 3, wherein the voltage U of the i-th winder motor is calculated by the following formula_pwm:

Wherein F is the maximum value of the motor torque when the duty ratio is 100 percent, V is the maximum value of the motor analog input voltage when the duty ratio is 100 percent,

calculating the duty ratio D of the ith winding device motor by the following formula:

wherein, U_fullThe voltage value of the motor when the duty ratio is 100%.

7. The control system applied to the spatial multi-degree-of-freedom rope-driven parallel robot as claimed in claim 1,2,3,4, 5 or 6, wherein data interaction is realized between the upper computer and the main controller in a wireless transmission mode.

8. The control system applied to the spatial multi-degree-of-freedom rope-driven parallel robot as claimed in claim 7, wherein the upper computer and the main controller are wirelessly transmitted through a TCP/IP network protocol.

9. The control system applied to the spatial multi-degree-of-freedom rope-driven parallel robot as claimed in claim 1,2,3,4, 5 or 6, wherein the master controller and the four slave controllers are connected through a CAN bus.

10. The control system applied to the space multi-degree-of-freedom rope-driven parallel robot as claimed in claim 1,2,3,4, 5 or 6, wherein the main controller is a Jeston Nano board card.

11. The control system applied to the spatial multiple degree of freedom rope-driven parallel robot is characterized in that the slave controller utilizes an STM32F407ZGT6 chip as a control chip according to the claim 1,2,3,4, 5 or 6.

12. The control system applied to the spatial multi-degree-of-freedom rope-driven parallel robot as claimed in claim 1,2,3,4, 5 or 6, wherein the upper computer is a mobile phone or a tablet computer.

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