Servo motor is a conventional motor. It is the implementation of automatic device components. The biggest characteristic of the servo motor control. In a control signal, the servo motor to rotate, and the speed is proportional to the size of the control voltage. Remove the control voltage, the servo motor to stop turning. Wide application of servo motor, almost all automatic control systems have to be used. In home appliances, such as VCRs, CD player, etc. are all important and indispensable component.
  1. The working principle of a simple servo motor

Figure shows the most simple servo motor applications. RV1 potentiometer driven by a servo motor. Optional motor current does not exceed 700mA, 12 ~ 24V voltage of any of the servo motor. RV1 and RV2 figure is connected as Wheatstone (Wheatstone) bridge. IC LM378 is a dual 4 watt power amplifier, but also constitute a way to bridge motor drive differential amplifier.
When RV2 any changes would undermine the balance of the bridge, so RV1-RV2 a difference between the voltage to be amplified and sent to the motor. Motor will rotate, drag to the new RV1 potentiometer position, the bridge again to reach a new equilibrium. So, RV1 RV2 to track the movement.

Figure is a block diagram form, draw a speed sensor servo motor system, can be used as precision turntable speed control schematic. Institutions using traditional belt motor drive turntable. Dial edge graphics with the provisions of spaced reflective structure. With a photoelectric tachometer monitoring and testing. Photoelectric tachometer output signal is proportional to the speed dial. The photoelectric tachometer output signal phase and frequency, and oscillator phase and frequency standard comparison, with its error signal to control the motor drive circuit. Therefore, the speed dial to precisely maintain the rated speed. Rated speed of the shift, by operation of switch control. The control circuit, has made a dedicated integrated circuit manufacturers.
  2. Digital Proportional Servo Motor

One of the best types of servo motors, is to use digital proportional remote control system. In fact these devices are composed of three parts: integrated circuit, servo motor, reduction gear boxes potentiometer body. Figure is a block diagram of such a system. Circuit of the drive input, is a period of 15ms and pulse width of 1 ~ 2ms pulse signal drive. Input pulse width, the position control servo mechanical output. For example: 1ms pulse width, location in the far left; 1.5ms in a position, 2ms in the right position.
  Three columns for each input pulse simultaneous transmission. 1.5ms pulse width all the way to a fixed trigger pulse generator. An input trigger pulse generator, the third road into the pulse width comparison circuit. Gear box output to the RV1, the control variable width pulse generator. The three pulse width comparator to post the same time, all the way to determine the direction of the motor drive circuit. Another way to give pulse width extender to control the servo motor speed, making the location of RV1 quickly driven machinery output follows the input pulse width of any changes.
  The servo motor type commonly used in multi-channel remote control system. Figure shows the four digital proportional control system waveforms.

It can be seen from the figure is the serial data input, through the separation of each group decoder control signal. Each frame contains synchronization pulses 4ms, immediately behind the four variable width (1 ~ 2ms) Order of the "road" pulse. Decoder will be transformed into parallel form of four pulses, can be used to control the servo motor.
  3. Digital servo motor circuit
  Digital servo motor control unit, you can buy ready-made integrated circuits. For example ZN409CE or NE544N-type servo motor amplifier integrated circuits. Figure and Figure shows a typical application of the two integrated circuits.

Figure in component values for the input pulse width of 1 ~ 2ms, 18ms frame pulse width is about the situation.
  Figure is a servo motor for the type of universal test circuit. Servo Power Battery typically 5V. Input pulse by a standard servo outlet to the servo circuit. Pulse width of the frame 13-28ms; with RV1 conditioning control. RV2 conditioning control pulse width between the 1-2ms. Fine-tuning with the RV4 median 1.5ms. Output level adjusted by the RV3

Two integrated circuit CMOS7555 too basic type, supply voltage can be as low as 3V still work. IC1 is no stable multivibrator to generate the frame time pulse, its output trigger IC2. The IC2 is a one-shot circuit to generate the output test pulse.