When the parking robot completes the parking task of the intelligent garage, it mainly includes: omnidirectional motion control, visual line inspection navigation, two-dimensional code positioning, and self-inspection operation before the robot starts. The motion control algorithm has a decisive impact on the performance of the parking robot. The control algorithm is designed according to the mechanical structure characteristics of the parking robot and the specific application scenarios of the indoor parking lot.
Overview of PID algorithm
During the omnidirectional movement of the parking robot, the deflection angle of the driving wheel set is used as the basic motion control index. The angle sensor detects the current wheel set angle information in real time and compares it with the expected angle of the wheel set to obtain the wheel set angle deviation. The deviation angle is calculated by the PID angle controller. Correction; in the process of visual inspection and navigation, the visual sensor is driven to capture the image information of the signal line for image processing to obtain the pose information of the robot relative to the signal line. After comparing with the expected angle and lateral movement distance, the angle PID controller is used for correction and adjustment. The parking robot moves straight along the signal line steadily. The difference between the input value r(t) of the control system and the actual output value y(t) at the previous moment collected by the feedback link sensor is used as the system deviation at the current time, and the deviation is corrected by the PID angle controller and acts on the controlled object To achieve system adjustment, the basic principle of the PID closed-loop control system is shown in Figure 4: The
PID controller is composed of proportional, differential, and integral units. By adjusting the PID parameters, the control system can respond stably, quickly, and accurately. The proportional link adjusts the deviation generated by the system. The larger the proportional coefficient, the stronger the system adjustment effect. Due to the existence of the system steady-state error, the system oscillation phenomenon will occur; the integral link eliminates the static error of the system by accumulating the error, which will cause The system response speed decreases and the overshoot increases; the differential link is controlled according to the variation trend of the deviation, so that the system overshoot decreases and the oscillation phenomenon disappears, and the system adjustment process is shortened to make the system tend to be stable. The general control of the PID control system law:
Omni-directional motion control strategy for parking robot
The omnidirectional movement of the parking robot includes: straight travel, lateral movement, adjustment of the driving wheel set, recovery of the driving wheel set, and rotation in situ, etc. The omnidirectional motion control of the parking robot can be realized through the orderly combination of individual actions. Stability and running accuracy have an important influence on the motion control of the parking robot vehicle. The coordinated control of multi-channel brushless DC motors is the key during the straight driving process of the parking robot. The driver board writes the brushless DC motor torque to the broadcast address through the function code 0X06 (write a single register) of the MODBUS communication protocol, and the eight motor drivers simultaneously Receive the motion control command and execute the host task request to realize the straight-line operation of the robot. The host sends the information frame through the broadcast address, and the slave device can receive the information at the same time, thus solving the control problem caused by the asynchronous start of multiple motors and meeting the real-time requirements of the system. The lateral movement control process of the parking robot is shown in the figure:
parking The lateral movement of the car robot is firstly composed of the drive wheel set rotating 90°, and then the angle sensor determines that the rotation has passed a fixed position and then starts to move straight. According to the original rotation radius of the drive wheel set, the arc length corresponding to a quarter of the rotation is calculated as the drive. For the amount of rotation of the wheel set, the position control mode is used to operate and drive the wheel set to rotate in situ. When the angle of the driving wheel set is 0 to 80°, the rotation speed is faster, and the rotation speed is slower at 80 to 90°. After rotating to the set amount of rotation, the angle sensor detects the current angle information of the wheel set to determine whether the drive wheel set has reached the target angle position. When the rotation angle of the wheel set exceeds or falls short of the set angle caused by the phenomenon of slipping and idling of the driving wheel set, the angle of the wheel set is corrected through the PID angle controller, and then the robot moves straight ahead to realize the lateral movement of the parking robot.
Navigation strategy of visual line inspection for parking robot
The parking robot combines the visual line inspection and navigation algorithm to cooperatively control the driving wheel group to realize the elimination of the robot body deflection angle and lateral movement distance. Vehicle motion control is equivalent to two-degree-of-freedom control. The deflection angle of the driving wheel set relative to the robot body is the basis of motion control. The angle adjustment needs to be prioritized. The angle PID controller is used to output PWM to realize the angle correction of the driving wheel set. The deflection angle of the parking robot relative to the signal line is another degree of freedom. The angle correction control of the robot body is carried out by using the forward drive wheel set to correct the angle and the rear drive wheel set to drive the robot body. The deflection angle of the robot body is related to the lateral It is closely related to the moving distance, and the angle correction will also eliminate the lateral moving distance. Therefore, an appropriate lateral moving distance threshold is set through the test to prevent the parking robot from derailing. Finally, eliminate the lateral movement distance of the parking robot body. During the movement of the robot, the accumulation of lateral deviation distance will occur. At this time, after the robot corrects the deflection angle of the vehicle body, the deflection angle of the robot body is within the threshold range but there is still a lateral deviation. By adjusting the omnidirectional drive wheel set to rotate at a fixed small angle and then move a certain distance to quickly eliminate the robot's accumulated lateral movement distance deviation.