This robot controller adopts "master controller+servo controller". The servo controller is responsible for the closed-loop positioning of a single joint. In robot control, it is required that the motion is stable without overshoot, so the operation task of servo controller is very heavy. The main controller mainly completes all the work except the position closed loop made by the servo controller, including the command receiving of the upper computer, the monitoring and display of the robot state, the spatial trajectory interpolation and the comprehensive processing of the sensor information according to a certain control algorithm. Therefore, the task of the supervisor is also very heavy. The power amplifier of the system is based on LMD 18200. LMD 18200 is an H-bridge module specially designed for DC motor drive, which is introduced by American National Semiconductor Company. Four DMOS tubes are integrated on the same chip to form a standard H drive shaft, and the DC motor can be driven by few external devices. Its instantaneous driving current can reach 6A, normal working current can reach 3A, and there is no "breakdown" current. LMD 18200 provides bipolar driving mode and unipolar driving mode [4]. Because the bipolar current fluctuates greatly and the power loss is large, the system adopts unipolar drive.

The specific interface circuit is shown in Figure 2 (the robot uses three omni-directional orthogonal wheels, and the robot can complete the movement in any direction through the cooperation of the three wheels, and the space diagram is limited to the related circuit of one wheel). LM629 outputs a PWM signal with variable duty ratio but fixed frequency at PWM pin according to PID control algorithm, and applies it to five pins of LMD 18200 through photoelectric isolation. The duty ratio of the PWM signal is passed by LMD 18200. In order to reduce the influence of the power supply on the controller, two signals are connected through the photoelectric isolation device TLP52 1, as shown in Figure 2. Pin 2 and 10 are connected to the armature of DC motor, and the current direction flows from pin 2 to pin10 when rotating forward; The opposite is true. The circuit has high driving power, good stability, convenient implementation, small size, safety and reliability. In order to increase the reliability of the system and reduce the interference of power supply circuit to weak current, the system adopts two groups of ungrounded power supplies. S3C44B0X minimum system photoelectric encoder uses 3.3V power supply and 5V power supply, 1 group, LMD 18200 group uses 24V power supply and 5V power supply. The signal transmission between the two power sources is isolated by the photoelectric isolation device TLP52 1. The encoder signal and clock signal of LM629 are both shaped by Schmidt trigger. In addition, the WDT module of S3C44B0X itself is used.

In order to reduce the power consumption of the system, the following measures are taken (1): The main controller turns off the peripheral modules such as SPI, timer 1 and I2C that are not used. (2): The master controller controls the robot to enter the braking state before reaching the designated position without any new tasks (receiving through the serial port). At this time, pin 4 of LMD 18200 is set to logic high level, pin 5 is set to logic low level, all transistors in the H bridge are turned off, and each output terminal only has a bias current of about 1.5mA; (3): The main controller enters the idle mode after executing step (2), and the value of its register can be saved. When a new interrupt occurs, it will wake up the main controller to enter the normal working state.

In order to increase the reliability of the system, the over-current and overheating protection of the system is designed by using the protection function of LMD 18200. LMD 18200 has a built-in measuring circuit with overcurrent protection. The current sampling signal is output at pin 8 of LMD 18200, with a typical value of 377 & micro； Quarter. Ground the resistor R2, and monitor the output overcurrent by comparing the voltage on the resistor with the given voltage. LMD 18200 provides temperature alarm signal. When the junction temperature of the chip reaches 145℃, pin 9 of LMD 18200 goes low. After photoelectric isolation, these protection signals are transmitted to S3C44B0X to realize the monitoring of overheating and overcurrent.