Voltage servo motor and control circuit

Voltage servo motor and control circuit

The above two speed stabilizing devices are used in the motor circuits of most recorders. Among the tape recorder motors, there are
two more special motors: voltage servo motor and frequency servo motor. The speed stabilization method they adopt is also quite special.
    ④ In the voltage servo motor,
    a magnetic ring that rotates together with the rotor is installed in the DC motor, and a speed measuring head is installed on the stator. The magnetic ring is magnetized with multiple
magnetic poles, so when the magnetic ring rotates together with the motor, the magnetic head will output a sinusoidal signal. The faster the rotation speed, the higher the frequency of the output signal. Therefore
, the tachometer head is called a frequency signal generator (FG), and this motor is called a servo motor. The voltage servo motor and control circuit
are shown in Figure 8-22.
    The speed of motor M is controlled by transistor VI2, and the current of VT2 is the current of the motor. VT2 is
controlled by the collector voltage of VT1. The higher the voltage, the higher the current. The circuit is designed so that VT1 is directly controlled by the FG signal. When the motor speed increases, the voltage of FG
increases, causing the base voltage of VT1 to increase. As a result, the collector voltage of VT1 decreases, causing the collector current of VT2 to decrease, automatically causing the motor speed
to decrease. When the speed drops below the standard value, the voltage output by FG ​​also decreases, causing the base voltage of VT1 to decrease and the collector voltage to increase, which automatically
increases the collector current of VI2 and increases the motor speed automatically. In this way, the speed of the motor is automatically maintained at a certain value, thereby achieving
the purpose of stable speed. VR1 fine-tunes the speed of the motor.
    ② Frequency servo motor
    Frequency servo motor can detect the speed of the electric machine based on the frequency value. And the detected frequency is added to the servo circuit to
keep the motor speed constant. This type of motor can use a brushless motor, which reduces the generation of sparks.
    In brushless motors, Hall elements are often used as speed measuring elements to output a frequency signal proportional to the rotational speed. The Hall element is a
magnetic induction element that can be used to detect magnetic fields. Used as a speed measuring head in electric motors . Its function is to convert changes in the magnetic field into changes in voltage
, that is, to convert changes in the magnetic field into electrical signal output.