The DC motor has a simple structure, stable and reliable, easy to achieve servo control. In this paper, the PIC16F1508 microcontroller is used as the controller, and its PWM module and the CWG module are used to generate a complementary PWM waveform of the dead zone, input to the upper and lower bridge arm driven by the H-bridge, effectively solve the DC motor H-bridge drive up and down the backpapers.
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introduction
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The DC motor is the earliest invention, and it is also the earliest speed motor. In most speed control situations, preferred or DC motors, because of its cheap, speed adjustment is more easy, and the speed control is relatively stable. Currently, DC electric motors are still widely used in smart toys and button regulatory automobile seats.
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1 DC motor servo system composition
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The DC motor servo system mainly includes a controller PIC16F1508, a photoelectric isolation circuit, a drive circuit, a speed detecting and a level conversion circuit, as shown in FIG.
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Figure 1 DC motor servo system block diagram
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2 hardware design of servo system
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2.1 PIC16F1508
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The PIC16F1508 is a 8-bit flash microcontroller, which increases some feature function modules, such as complementary waveform generator module (CWG), configurable logic unit module (CLC) and CNC oscillator module ( NCO), etc. The CWG module is mainly used in the DC motor servo system.
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Complementary Waveform Generator Module (CWG) has a function of producing a complementary waveform of the dead zone delay for the selected input source [2]. Briefly, the CWG module can generate a dual output complementary waveform for the selected input source, and there is a deadline delay in a certain period of time. In this servo system, a specific PWM input source is selected by the CWG module, generates a complementary PWM waveform with dead-delay, outputs the upper and lower bridge arms of the H-bridge, effectively avoiding the straight-up problem of the upper and lower, is this A large advantage in the servo system. Further, the PWM waveform with dead zone is produced by the single chip itself, which not only adjusts the system to adjust and stabilize, but also the entire system structure is more compact, but the cost is greatly reduced.
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2.2 Optoelectric Isolation Circuit
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In order to protect the security of the PIC controller and effectively suppress signal interference, the photoelectric isolation chip HCPL4504 is added between the controller and the H bridge. Its 4-way PWM pulse output from the PIC16F1508 is photoelectrically isolated, where the photoelectric isolation circuit output from the PWM signal is shown in Figure 2, and other 3 is similar.
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Figure 2 PWM signal output photocouple isolation circuit
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2.3 Drive Circuit
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The driving of the DC motor reversible system mainly includes bipolar driving and single pole drive. Bipolar driving means that the voltage polarity of the motor armature is positive and negative in a PWM cycle; while the single pole is in a PWM period, the motor electrical electrical electrical electrical electromechanical voltage [3]. This system uses unipolar drives, and the single pole drive has a T type and an H-type division, and there is more applications of H-type, as shown in FIG.
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Figure 3 H-type single polarity reversible PWM drive system
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As can be seen from Fig. 3, the H-type single-polar reversible PWM drive system is mainly composed of four MOSFET tubes. The bridge arm on this system is a PMOS tube. The lower bridge arm is NMOS tube, effectively avoiding the boost or step-down circuitry required to use NMOS or both PMOS, reduce the complexity of the circuit, and Relatively improves the stability of the system.
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Further, both the MOSFET tube is a voltage-type driving element, the G pole driving circuit of the P MOS tube, and the N MOS tube uses a low cost, and the specific circuitry is made, and the specific circuit is shown in FIGS. 4 and 5. The overall H bridge drive circuit is shown in Figure 6.
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Figure 4 PMOS drive circuit
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Figure 5 NMOS drive circuit
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Figure 6 H-bridge drive circuit
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2.4 Speed Detection and Level Conversion Circuit
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The speed detection method of DC electric motors has Hall sensor detection, photoelectric encoder detection and DC speed generator detection. The system is selected to detect the speed of the DC speed generator. The DC speed generator is mounted on the diameter of the rotational motor shaft to rotate with the same speed as the measured motor. The selected DC speed generator model is Zcf221a, and the DC motor speed is detected by the DC speed generator feedback voltage, taking into account the DC generator output -50 ~ 50 V voltage, far exceeding the A / D conversion acquisition input signal. The range is required to level conversion. Read more
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