Suspension motion control design based on 32-bit DSP and motor driver chip

　　With the popularity of 32-bit DSP, 32-bit processors have become the mainstream products in the control field. Compared with traditional microprocessors, they are faster, more powerful, and more resource-rich, and more in line with the pace of development. TMS320F28027 is a 32-bit DSP with the advantages of fast computing speed and high stability. This article uses TMS320F28027 to control two stepper motors, so that objects can move in a plane and draw specified curves and circles in the plane.

　　1. Design of the overall system solution

　　Figure 2 is a control block diagram of the suspension system. TMS320F28027 is used as the control chip, and L298N is used to drive two stepper motors. The stepper motor uses 42HS4813A4, with a rated current of 1.3A and a step angle of 1.8°. LCD-12864 is used to display the real-time coordinates of the controlled object. The two stepper motors are controlled to rotate forward and reverse to achieve the effect of arbitrary movement of the object in the plane.

　　Figure 1 Model of the suspension system

　　Figure 2 Suspension system control block diagram

　　2 Hardware Circuit Design

　　2.1 L298N

　　L298N is a high voltage, high current motor driver chip produced by ST. Figure 3 is the circuit schematic of the L298N module. The main features of this chip are: high operating voltage, the highest operating voltage can reach 46V; large output current, instantaneous peak current can reach 3A, continuous working current is 2A; contains two H-bridge high voltage and high current full bridge drivers. Use two L298N to control two stepper motors respectively. The rated current of the stepper motor is 1.3A. When two phases are connected at the same time, the current is 2.6A. L298N can meet the current requirements of 42HS4813A4 stepper motors.

　　Figure 3 L298N module circuit schematic

　　2.2 Absolute encoder

　　The accuracy of the absolute encoder must be higher than that of the stepper motor, so a 10-bit absolute encoder is used here. The model selected is Mini1024J, which has an accuracy of 10 bits. The advantage is that it uses non-contact Hall detection technology, and the sensor operation is not affected by dust or other debris, which overcomes the shortcomings of optical detection principles.

　　3 System Software Design

　　3.1 Geometric Relationship 1: Algorithm for Moving from Any Point to Any Point

　　The coordinate diagram is shown in Figure 4, with the following relationship between side length and angle:

　　Figure 4 Coordinate diagram

　　3.2 Geometric Relationship 2: Current Position Coordinate Display Algorithm

　　As shown in Figure 5, the following angle and side length relationships exist:

　　The control code is as follows:

　　Figure 5 Coordinate diagram

　　3.3 Motor position closed-loop control method

　　The closed-loop control block diagram of the stepper motor is shown in Figure 6. TMS320F28027 uses two timers to control the two motors respectively, and uses an absolute encoder to monitor the position and perform step-out compensation to ensure the correct position and make the curve smooth.

　　Figure 6 Stepper motor closed-loop control block diagram

　　The model of the stepper motor is 42HS4813A4. In order to prevent step loss, the minimum interval of each step of the stepper motor is 4ms, and the stepper motor is subdivided into sixteen parts by software, that is, the spacing of each step is 0.45°. The program flow chart of the motor control part is shown in Figure 7.

　　Figure 7 Flowchart of the program for controlling the motor

　　The control code is as follows:

　　3.4 Drawing Algorithm

　　By using the algorithm of geometric relationship from any point to any point, a series of position coordinates are given to the processor to control the motion trajectory of the object, as shown in Figure 8.

　　Figure 8 Schematic diagram of drawing a circle and selecting points

　　Take N points at the same interval and input them into the processor to control the coordinates of the object. When passing the points to TMS320F28027, 200 points are taken on the circle to make the circle smooth enough and eliminate jaggedness. The control code is as follows:

　　4 System Testing

　　After the system was completed, two tests were conducted, namely, drawing a circle and moving to a specified point.

　　The circle drawing test is to compare the actual diameter of the circle drawn with the theoretical diameter after inputting the coordinates of the center of the circle and the radius, and record the time taken to draw the circle. In this test, the coordinates of the center of the circle are (40.0cm, 40.0cm), and the input radius value is 30.0cm. The test results are listed in Table 1.

　　Table 1 Drawing motion test results

　　Among them, the test of moving to a designated point takes the origin of the coordinates as the starting point. After inputting the designated coordinates, the theoretical value and actual value of the distance from the origin to the designated point are compared, and the error distance of returning to the origin after the movement is completed is recorded, that is, whether it can accurately return to the origin. In this test, the coordinates of the origin of the movement are (0cm, 0cm), and the target coordinates are (49.0cm, 50.0cm), that is, the distance from the origin is 70.0cm. In the actual test, the movement is to (49.1cm, 49.2cm), that is, 69.5cm from the origin. The test results are listed in Table 2.

　　Table 2 Movement to a designated point test

　　It can be seen from the test results that the system has the advantages of high efficiency, stability and accuracy, which meets the experimental expectations.