Design and Research of Stabilized Platform Servo System Based on DSP

In the high-performance stable platform servo system composed of servo motor and servo drive, it is necessary to obtain the servo motor's rotation angle and speed information in real time. High-speed and high-precision sensors and corresponding peripheral circuit designs are indispensable. Due to the limitations of the microcontroller's own resources, it is difficult to meet the current servo system's requirements for high precision, high computing rate and fast real-time performance. In the stable platform servo control system, DSP has gradually replaced the microcontroller and become the mainstream chip. This design uses TI's 32-bit floating-point DSP chip TMS320F28335, which has a working clock frequency of up to 150 MHz and has powerful computing power. It can complete complex control algorithms in real time. The chip integrates a wealth of motor control peripheral components and circuits, simplifies the hardware design of the control circuit, and improves the reliability of the system.

This study uses the new DSP development board ICETEK-F28335-A, and uses the EQEP module and photoelectric encoder in it to design a solution for measuring the servo motor speed. At the same time, the digital-to-analog conversion (D/A) module on the development board is used to complete the control of the servo motor speed through voltage conversion and amplification, realizing a closed-loop system for the stable platform servo motor control. Practice shows that the system has the advantages of low power consumption, low cost and simple structure, and has the characteristics of high precision, high resolution and fast real-time performance, so that the stable platform servo system achieves a good control effect.

1 Servo system structure of stable platform

The main technology applied in the stable platform is servo control technology. This system realizes the speed control of Panasonic servo MINAS A series servo motor. It is mainly composed of Panasonic servo MINAS A series servo driver, servo motor, corresponding photoelectric encoder, TMS320F28335 motion control development board, corresponding ICETEK-5100USB emulator and peripheral circuits necessary for realizing the closed-loop process. The structure of the servo system is shown in Figure 1. The speed closed-loop process of the servo system of the stable platform is as follows: the DSP controller calculates the error value of the motor speed according to the speed command value given by the host computer minus the speed feedback value, and generates the motor speed control signal through the digital filter (regulation algorithm) of the drive unit, that is, the D/A module generates an analog voltage, which is converted to a voltage range that can control the servo motor through level conversion, thereby realizing the speed control of the servo motor. Among them, the feedback value is the orthogonal pulse signal fed back by the incremental photoelectric encoder. After optical coupling isolation and shaping, the feedback signal is provided to the eQEP module of TMS320F28335. The collected pulse signal calculates the motor speed according to the M/T counting method and feeds it back to the host computer to achieve automatic control, so that the stable platform can isolate the carrier motion and establish a stable reference surface [1]. The power module converts the +5 V voltage provided by the switching power supply to +3.3 V to power the system [2].
TMS320F28335 . The software development tool CCS (Code Composer Studio) provided by TI provides a visual window and integrates all code generation tools. All user development processes are carried out in CCS, including project establishment, source program editing, program compilation and debugging. In addition, CCS also provides a real-time operating system DSP/BIOS, which greatly facilitates debugging and development. The DSP program of this system is mainly divided into two modules: the main program and the interrupt service program. The main program module [10] mainly implements the initialization of each functional module, the definition of memory variables and the declaration of interrupt vectors. The interrupt program module mainly implements the setting of related registers, reading and latching the pulse count of the eQEP module, the feedback of the detection circuit and the program of the control algorithm. Its software flow is shown in Figure 6. This paper proposes the design of a stable platform servo system. The eQEP module of the DSP chip TMS320F28335 is used to decode and count the pulse signal of the photoelectric encoder to obtain the angle and speed information of the servo motor, which is then compared with the given value of the host computer. The D/A module is adjusted to generate a voltage signal to control the speed of the servo motor. The study shows that the design has high response speed, stable accuracy and strong anti-load disturbance ability, and fully realizes the high-precision control of the stable platform. At the same time, the system has strong robustness and adaptability, which verifies the effectiveness of the scheme and provides high-performance digital solutions for different control fields.