Design of stepping motor tracking servo system

by:V&T Technologies     2019-11-10
Stepping Motor is a pure digital control motor. It converts the electric pulse signal into an angle displacement, that is, a pulse signal is given, and the stepping motor rotates one step. In the rated power range, the speed of the motor only depends on the frequency of the pulse and the number of pulses, and is not affected by the load change, so it is very suitable for digital control, especially when used with digital equipment, it embodies greater superiority. Modern single chip microcomputer has sufficient I/O ports, multiple PWM channels and rich external interfaces, making it especially suitable for motor control. In this paper, an ARM-based stepping motor servo system is designed with ARM single chip microcomputer as the control core and stepping motor as the driving element. The servo system is used in the near-range UAV measurement and control system. The servo system drives the directional antenna to rotate, completes the real-time tracking of the antenna to the target UAV, and ensures the smooth establishment of the measurement and control link. 1 stepping motor and its driving control technology stepping motor is designed according to the theory of combined electromagnet. The design of the motor is based on accurate positioning, with large blocking torque and high positioning accuracy. Stepping motors can be divided into reactive type, permanent magnet type and hybrid type. Hybrid stepping motors combine the advantages of reactive type and permanent magnet type and are therefore widely used. The working principle of stepping motor makes it very suitable for the control of single chip microcomputer. Although stepping motor is a digital control element, it is easy to interface with digital circuits. However, the signal energy of the general digital circuit is not enough to drive the stepping motor. Therefore, there must be a matching drive circuit to drive the stepping motor. The driving circuit of stepping motor has the following requirements :(1) Can provide fast rising and falling current so that the current waveform is as close as possible to the rectangle; (2) It has a loop for releasing current during the end period to reduce the reverse potential at both ends of the phase winding and accelerate current attenuation; (3)Low power consumption and high efficiency. Commonly used stepping motor drive circuits include single voltage drive, double voltage drive, high and low voltage drive, ripple constant current drive and subdivision drive. The above Drive circuits have their own advantages and disadvantages, and their performance comparison is shown in Table 1. In addition, in order to make the stepping motor work normally, each phase winding must be powered on or powered off in sequence according to the state and sequence specified in the excitation State conversion table of the motor. The driving circuit of the stepping motor works according to the control signal. In the single-chip control of the stepping motor, the control signal is generated by the single-chip microcomputer, and its basic control function is as follows :(1)Control the phase change sequence. The sequence of power-on and phase-changing of stepping motors is strictly in accordance with the working mode of stepping motors. (2)Control the steering of the stepping motor. If the phase is changed according to the given working mode, the stepping motor will turn forward; If the phase is switched on in reverse order, the motor is reversed. (3)Control the speed of the stepping motor. If a control pulse is sent to the stepping motor, it will take one step and then send another pulse, and it will take another step. The shorter the interval between the two pulses, the faster the stepping motor rotates. Therefore, the frequency of the pulse determines the speed of the stepping motor. Adjusting the frequency of the pulse emitted by the single chip microcomputer can adjust the speed of the stepping motor. 2 servo system design scheme 2. 1 overall structure. The servo system adopts azimuth pitch structure, takes azimuth turntable as base, and is equipped with pitch transmission mechanism to control antenna rotation, complete the antenna tracking of the target drone. The azimuth can run between 540 degrees and the pitch can be-30 ~ Rotate between 90 °. Azimuth and pitch respectively use stepping motor as driving element and photoelectric encoder as feedback element to complete closed-loop control of servo system. In addition, in order to meet the requirements of azimuth 540 rotation range, a cable winding device is specially designed to solve the cable winding problem during azimuth rotation. The overall structure of the antenna servo system is shown in Figure 1.
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