Servomotor Part 3-5
As mentioned earlier, due to the advantages of closed loop operation, armature controlled d.c. servomotors is more preferred than field controlled d.c. servomotor. Let us see one or two applications in detail.
1.1 Servostabilizer
The supply voltage in practice may vary due to number of reasons. But such variations in the supply voltage are undesirable for many practical applications. The supply voltage for various appliance is required to be kept constant.
The stabilizer is a device which keeps the output voltage constant, accepting a variable voltage. In a servostabilizer there is a transformer whose secondary can be smoothly tapped using a servomotor drive. The servomotor drives the shaft and controls the position of tap on the secondary as per the control signal, to keep output constant.
The armature controlled d.c. servomotor is used for such servostabilizer. Any change in the secondary voltage is fed back to the error detector. The error signal is generated, comparing it with a reference input. This is given to the controller which decides proper controlling action. The signal from the controller is not enough to drive the servomotor. Hence the signal obtained from the controller is amplified and then given to the armature of the servomotor, which inturn adjusts the tapping on the secondary to keep voltage constant.
The entire scheme is shown in the Fig. 5.
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| Fig. 5 Application of d.c. servomotor : Servostabilizer |
1.2 Position Control System
In such application, it is required to keep the position of the load constant. Such a system where output position is kept constant is called as position control system. The output position is sensed and fedback to the potentiometer used as an error detector. For any change in the output position θL, the potentiometer generates an error signal proportional to the difference θr and θL. The θr is the reference position corresponding to the ideal output position. The error signal is given to the amplifier and the output of the amplifier is given to the armature of a d.c. motor. The d.c. motor maintains the output shaft position constant. The entire scheme is called d.c. position control system which is shown in the Fig. 6.
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| Fig. 6 Application of d.c. servomotor : D.C. position control system |
The other applications of d.c. servomotors are,
1. Air craft control systems
2. Electromechanical actuators
3. Process controllers
4. Robotics
5. Machine Tools