Abstract: Based on the analysis of the characteristics of the PIC16C77 microcontroller, the hardware block diagram of the robot dexterous hand control system is given. Several important modules are introduced in detail, especially the motor drive module and the generation principle of PWM signal. A control algorithm is given, and the reliability of the design is demonstrated by experiments. Keywords: multi-finger dexterous hand; PIC; PWM; microcontroller The field of contemporary robot research has moved from fixed-point operation in structured environments to autonomous operation in unstructured environments. The robot dexterous hand is equivalent to a set of robots installed on the robot arm that can independently realize fine operation. It is a truly anthropomorphic robot hand that can realize flexible operation. It is of great significance for improving the working ability of space robots, and in the future, it can also be used for dangerous operations such as mine detection and clearance on the battlefield and inspection and repair of nuclear industrial equipment [1]. Research on robot dexterous hand control is carried out by only a few research institutions in China, and the cost is high. In this paper, a more suitable microcontroller is sought as the core of the control. Based on the powerful function of the PIC microcontroller, the PIC series microcontroller is adopted. 1. Characteristics of PIC Microcontrollers The PIC series of microcontrollers are 8-bit microprocessors produced by Microchip Technology Inc. in the United States. However, their speed and functionality are much stronger than some ordinary 8-bit 51 microcontrollers because they adopt a RISC architecture, which is different from the general CISC architecture of the past. The RISC architecture uses a Hardward dual-bus structure, separating the address bus and the data bus, so data and address can be transmitted simultaneously, improving the operation speed [2]. PIC microcontrollers are small in size, have low power consumption, and integrate a variety of peripheral circuits, making the design more convenient. There is no need to add some peripheral circuits to the microcontroller design, which is very important in control systems. The PIC16C77 microcontroller used in this paper has 8k of program memory; 368B of RAM; 2 PWM ports; and an integrated 5-channel 8-bit A/D converter with power-down reset function. These features make the hardware design very convenient. In the control of a robot's dexterous hand, the driving of the micro-motor requires PWM signals. Traditional designs utilize transistor circuits, which necessitate timers in ordinary 51-series microcontrollers. However, PIC microcontrollers inherently include two PWM signal outputs, simplifying the design. 2. Overall Hardware Design of the Control System Before grasping and manipulating, the dexterous hand performs complex calculations such as determining the contact point of the grasped object, analyzing and judging the grasping configuration, solving the forward and inverse kinematics of the three-finger hand, and trajectory planning. This process is time-consuming. During grasping and manipulating, motor speed control, joint position detection control, and fingertip force detection are required. Some of these controls must occur simultaneously. Therefore, the dexterous hand designed in this paper adopts a hierarchical control system as shown in Figure 1. The host computer, a PC, primarily performs main control, including grasping trajectory planning and issuing operation commands to the slave computers. The slave computers consist of three control units that communicate with the host computer, receiving commands and performing PID adjustment on the feedback signals to control motor rotation. Each microcontroller controls the movement of one finger. The advantages of this control system are that the overall control scheme is relatively clear, the control is flexible, and it meets the design requirements. 2.1 Lower-level software design: The main role of the microcontroller in this system is to receive instructions from the upper-level computer, control the operation of the motor and the movement of the finger joints, and perform PID adjustment on the feedback signals, sending the results to the upper-level computer, and sending the collected signals to the upper-level computer to prepare for the next instruction reception. The main process is shown in Figure 2. 2.2 Serial communication module: Serial communication mainly adopts asynchronous serial transmission mode, and the data transmission format is RS232 protocol. For the PIC microcontroller, the operation of the serial port mainly involves the operation of the following registers: TXSTA transmit status and control, RCSTA receive status and control register, TXREGUSART transmit register, RCREGUSART receive register, and SPBRG baud rate generation register. 2.3 Motor drive module: The movement of the dexterous hand is mainly controlled by the movement of motors at the joints. Each finger of the three-finger dexterous hand has three degrees of freedom, meaning that the movement of one finger requires three motors to drive it. The drive method uses a rope and pulley transmission. The motor selected is the REmax21 DC servo motor manufactured by Maxon of Switzerland, along with its matching reducer and encoder. The motor is driven by a PWM signal, which is achieved using the PWM signal port built into the PIC microcontroller and a power amplifier. The PWM signal mainly sets the internal Time2 and two registers: one is the PR2 register which stores the PWM cycle, and the other is the CCPRXL register which stores the duty cycle [3]. The schematic diagram of the PWM signal output is shown in Figure 3. When Time2 starts working, the PWM output is high. Then Time2 is compared with the two registers PR2 and CCPRXL. When Time2 equals the set value in CCPRXL, the pin output becomes low. When Time2 counts to be equal to the number in PR2, the pin output becomes high, and Time2 will reset to zero and start counting again. This is the output process of the PWM signal. A power amplifier circuit is connected to the output of the PWM signal. The L298 chip is used to implement unipolar reversible drive. The PWM pulse width modulation signal generated by the microcontroller is directly driven by the L298 dual H-bridge PWM driver. The L298 is a high-voltage, high-current power amplifier chip. The driving voltage can reach 46V, and the total DC current can reach 4A. TTL logic level control is directly used. 2.4 A/D Module For the signal acquisition part, since the PIC microcontroller integrates a 5-channel 8-bit A/D, there is no need to connect an external A/D. It can be used directly. The use of the internal A/D mainly involves setting the three registers ADCON0, ADCON1, and ADRES. 3 Control Algorithm In industrial control, the PID algorithm is a commonly used algorithm. When the general 8-bit microcontroller runs this algorithm, the speed will be affected, and there will be a certain time delay in the control of the system. However, based on the structure and high-speed characteristics of the PIC microcontroller, this can be overcome [4]. The software flowchart of the PID algorithm in this system is shown in Figure 4. 4 Conclusion The three-finger dexterous hand designed with PIC microcontroller successfully completed the grasping experiment. All hardware designs are simpler, the system is more stable, and the operation is simpler than that of ordinary 8-bit microcontrollers. Compared with the system composed of dedicated integrated drive circuits and high-performance digital signal processors, the cost of this scheme is lower and the overall performance is also quite good. References [1] Okada T. An artificial finger equipped with adaptability to an object. Bullelectrotech.lab, 1974, 37 (2): 1078-1090. [2] Wu Feng. Development and application technology of PIC series microcontrollers [M]. Beijing: Beijing University of Aeronautics and Astronautics Press, 2000. [3] He Xinlong, Li Xueyin. Introduction and application examples of PIC16C7X [M]. Beijing: Tsinghua University Press, 2001. [4] Wang Xiaoming. Microcontroller control of electric motors [M]. Beijing: Beijing University of Aeronautics and Astronautics Press, 2002.