CN113043272B

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

Info

Publication number: CN113043272B
Application number: CN202110286979.3A
Authority: CN
Inventors: 孙光辉; 卢彦岐; 姚蔚然; 吴立刚; 刘健行
Original assignee: Harbin Institute of Technology
Current assignee: Harbin Institute of Technology
Priority date: 2021-03-17
Filing date: 2021-03-17
Publication date: 2021-09-28
Anticipated expiration: 2041-03-17
Also published as: CN113043272A

Abstract

A control system applied to a space multi-degree-of-freedom rope-driven parallel robot relates to the technical field of rope-driven parallel robot control. The invention aims to solve the problems of low precision, low efficiency and inconvenience in large-space deployment of the existing rope-driven robot control method. The upper computer is used for receiving the expected position coordinates, the main controller is used for carrying out position and tension conversion on the expected position coordinates sent by the upper computer to obtain tension values of ropes of four winding devices of the rope-driven parallel robot, the four sub-controllers are respectively in one-to-one correspondence with the four winding devices of the rope-driven parallel robot, the sub-controllers are used for calculating tension control instructions and rope length control instructions according to the tension values of the ropes of the corresponding winding devices and respectively sending the tension control instructions and the rope length control instructions to the corresponding winding devices, the tension control instructions are expected tension of the ropes at each moment in motion time, and the rope length control instructions are expected rope length of the ropes at each moment in motion time.

Description

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

Technical Field

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

Background

The biggest characteristics and the advantage of rope drive parallel robot are rope drive, compare on the one hand its weight significantly reduce in the rigid connecting rod of equal length, increase its flexibility, compare simultaneously in the rigid connecting rod, the rope can deploy in bigger space, greatly increased its working space. Therefore, the rope-driven parallel robot has the advantages that the traditional industrial mechanical arm and the rope-driven serial robot cannot compare with each other, and plays a great role in aircraft simulation and large radio telescopes at present.

Although the rope-driven parallel robot has the advantages that the serial robot cannot have, the flexibility of the rope and the design of a control system scheme are difficult. Most of rope-driven robots in the current market adopt independent position control, independent force control and switching type force and position hybrid control methods, the control methods are low in precision, and meanwhile, controllers are difficult to design and are difficult to implement. On the whole control system, the current control system is mainly a centralized control system, and the control system scheme has low control efficiency, is inconvenient to deploy in large space and is difficult to control.

Disclosure of Invention

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

Control system for space multi freedom rope drives parallel robot includes: host computer, main control unit and four are followed the controller, the host computer is used for receiving the expected position coordinate, the main control unit is used for carrying out position and tension conversion to the expected position coordinate that the host computer sent, obtain the tension value that four winding device ropes of the parallel robot were driven to the rope, four are driven four winding device one-to-one that the parallel robot was driven to the rope respectively from the controller, follow the controller and be used for calculating tension control command and rope length control command according to the tension value that corresponds the winding device rope to send tension control command and rope length control command to corresponding winding device respectively, tension control command is the rope and expects the tension at each moment in the motion time, rope length control command is the rope and expects the rope length at each moment in the motion time.

Further, the main controller includes: an outer ring PID control module and a position and tension conversion module, wherein the outer ring PID control module is used for converting the position error E_posConverted into outer ring position control quantity U_posSaid position error E_posThe position and tension conversion module is used for utilizing the outer ring position control quantity U as the difference between the expected position coordinate and the current position coordinate of the rope-driven parallel robot_posAnd respectively calculating the tension value of the rope of each winding device.

Further, the outer loop PID control module calculates the position error E by the following equation_posConverted into outer ring position control quantity U_pos：

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

Further, the position and tension conversion module comprises the following units:

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

wherein,

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。

Further, the slave controller includes: an inner ring PID control module, a pulse drive module, a tension sensing module, an encoder and an angle rope length conversion module, wherein the inner ring PID control module is used for converting a 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 is 1,2,3 and 4, and the pulse drive module is used for controlling the quantity U according to the tension of the inner ring_force__iObtaining the voltage and the 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 instruction, and acquiring the current tension value F of the rope of the ith winding device by using a tension sensing module_iThe encoder is used for determining the current tension value F_iObtaining the rotation angle theta of the motor shaft in the ith winding device_iThe 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。

Further, in the above-mentioned case,the tension error E is determined according to the following formula_{force_i}Converted into inner ring tension control quantity U_{force_i}：

Further, the rotation angle θ of the motor shaft in the i-th winding device is determined according to the following equation_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.

Further, the voltage U of the motor of the i-th winding device 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%.

The invention has the following beneficial effects:

(1) master-slave distributed control scheme: the Jeston Nano is adopted as a main controller, the exclusive control board card is adopted as a slave controller, and distributed deployment is adopted, so that control over each set of winding device is more personalized, and more efficient and rapid control can be realized. Distributed deployment can greatly increase product workspace and flexibility in its installation and movement. The master controller and the slave controller can realize accurate task allocation, the upper layer calculates complex control and planning algorithms in a centralized mode, and the lower layer only needs to execute corresponding commands, so that the whole set of control system is better in stability during working, higher in efficiency and more flexible in control.

(2) The exclusive control board card: the control board card of the slave controller can combine all the functional modules together, and all the modules contained in the control board card can enable tasks such as information transmission, control instruction issue and the like to run more stably and efficiently.

(3) Double-loop force position hybrid control: compared with single position control and tension control, the double-loop control system combines the position and the tension together in a double-loop mode, is applied to the spatial multi-degree-of-freedom rope-driven robot, can greatly increase the control of the double-loop control system on the tension of the rope, ensures that the rope is always kept in a tight state in motion, and further improves the control precision on the position of the tail end working platform.

Drawings

Fig. 1 is a block diagram of a control system applied to a spatial multi-degree-of-freedom rope-driven parallel robot;

FIG. 2 is a control schematic of the control system according to one embodiment;

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

FIG. 4 is a schematic diagram of the control flow from the controller.

Detailed Description

The first embodiment is as follows: the present embodiment is described in detail with reference to fig. 1 to 4, and the control system applied to the spatial multiple degrees of freedom rope-driven parallel robot according to the present embodiment includes: host computer, main control unit and four are followed the controller.

An operator serves as an upper computer through a mobile phone or a tablet personal computer, and expected position coordinates are input on the upper computer. And wirelessly transmitting the data to a main controller Jeston Nano board card through a TCP/IP network protocol. 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 master controller sends the tension value to the 4 slave controllers through the CAN bus. The four slave controllers respectively correspond to the four winding devices of the rope-driven parallel robot one by one, and the slave controllers receive instructions to control the winding devices to move, so that the rope is controlled to stretch and retract to complete control of the tail end position. The slave controller is 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 device. The tension control command is the expected tension of the rope at each moment in the movement time, and the rope length control command is the expected rope length of the rope at each moment in the movement time.

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

The outer loop 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_ITo integrate the time constant, T_DIs the differential time constant. The position error E_posIs 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_posAnd respectively calculating the tension value of the rope of each winding device. Specifically, 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,

A_ifor the rope outlet of the ith winding deviceP is the desired position coordinate,

As shown in fig. 3, the position and tension conversion module can ensure that the control effect of the dual-loop full-closed loop control can meet the task requirement. And meanwhile, the conversion from the control quantity output by the outer ring PID control module to the tension value of 4 ropes is completed, and a method for optimizing the tension is added into the module so as to ensure that the expected tension value input into the inner loop is greater than zero, meet the rope tension requirement of the rope-driven robot and enable the inner loop to really play a role in 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, the conversion from the control quantity obtained by the position error of the outer loop to the tension control expected value of the inner loop can be completed, the effective connection of the inner loop and the outer loop is realized, and the completion degree of a control task is improved.

After the conversion from the control quantity obtained by the position error of the outer loop to the expected value of the tension control of the inner loop is completed, the particularity of the rope traction parallel robot is considered, because the used rope is a flexible object, the stress condition of the rope is that only tension can be received, and pressure cannot be borne, once the tension is zero or less than zero and is converted into pressure, the rope is in a loose state at the moment, the motion control of the rope is completely inaccurate, and the task which cannot be realized when the position of the end effector is accurately tracked at the moment. Therefore, the problem of rope tension optimization is considered at the end of the construction of the double-loop control process so as to ensure that the task can be realized. An internal force parameter M is therefore introduced to ensure that the tension is always greater than zero to satisfy the rope tightening condition.

The slave controller utilizes the STM32F407ZGT6 chip as a control chip. The slave controller includes: the device comprises an inner ring PID control module, a pulse driving module, a tension sensing module, an encoder, an angle rope length conversion module, a CAN bus module and a power supply module.

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

The inner ring PID control module is used for controlling the tension error E according to the following formula_{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 between them.

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 module adopts an AM26C32 chip to convert the differential coding signal returned by the encoder into a single-path coding signal, the chip has high conversion speed and stable conversion, and the timeliness of returning the encoder information can be greatly increased.

The angle rope length conversion module is used for converting the rotation angle theta of the motor shaft in the ith winding device according to the following formula_iConverted into rope length control instruction L_i：

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, and sending the pulse signal to a motor driver, specifically, calculating the voltage U of the motor of the ith winding device according to the following formula_pwm：

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

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

Therefore, PWM pulses are generated, and the voltage value of the generated PWM pulses after passing through the low-pass filter is transmitted to a motor driver, so that the motor generates corresponding torque. The pulse driving module provides pulses with certain frequency and duty ratio for a driver of the motor to control the motor to move, so that the rope and the tail end working platform are driven to move. This module adopts ADuM1310 magnetic coupling chip to keep apart and the drawing of level is high, and this chip isolation nature is good, draws high level accuracy, can increase the degree of accuracy of pulse level value, reduces because the level does not reach the minimum and leads to the problem that the pulse is not discerned, further improves control accuracy.

The power module is used for providing power guarantee for the slave controller, and an LM2596 chip is adopted to complete the task of converting from 24V to 5V, and AMS1117 completes the task of converting from 5V to 3.3V. The module can ensure that level conversion is more stable, the output level cannot jump, and the control board card can work normally.

The CAN bus module is used for accessing a slave controller into a CAN bus network to complete the tasks of sending and receiving information, adopts a TJA1050 chip as a CAN level conversion chip, and CAN be isolated by adding an optical coupler or a magnetic coupler, thereby increasing the stability of transmission. The CAN bus is connected to the physical bus via 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 fig. 4, the double-loop inner loop consists of 4 independent inner loops (each independent inner loop represents an inner loop of a rope), and 4 inner loops as a whole. The inner loop mainly comprises an inner loop PID control module, a motor model and a force feedback loop. The working principle is that the outer loop is subjected to variable calculation and conversion to obtain a proper tension value of each rope when the end effector is at a certain point of a working space, the proper tension value of each rope is respectively sent to the input end of the inner loop of each rope, the control quantity output by the inner loop PID control module through calculation is sent to the constructed motor model, meanwhile, the motor model feeds back an actual tension value, finally, the inner loop PID control module is used for completing inner loop closed loop and realizing inner loop tension control, and therefore the tension output by the motor is the proper tension value of the rope calculated through outer loop conversion at the moment. And simultaneously sending the lengths of the ropes to a positive kinematics solving module in the outer ring to solve the point coordinates of the end effector in the working space.

According to the embodiment, the rope-driven robot can be controlled at high precision and operated flexibly, so that the rope-driven robot is more convenient and efficient to apply to the intelligent manufacturing industry. The control of rope tension can be realized by the embodiment, so that the control precision of the tail end working platform is increased, and high-precision position control can be realized.

Claims

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:

wherein, T_i＝U_pos/u_i，

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}：

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：

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, 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.