The servomotors applied in present industry are worked in a closed-loop servo system. To know better how the servomotor is functioning in the system, it is necessary to review the whole system. Figure 1. indicates a block diagram of a typical servo motor system.
Figure 1. Typical servo system block diagram
A reference input typically called a velocity input is transmitted to the servo amplifier controlling the speed of the servo motor. Directly the piece mounted to the machine is a feedback device or called an encoder or resolver playing a key role in servo motor operation principle. This device makes mechanical motion turn into electrical signals and is used as a feedback loop. Then this feedback loop is passed to the error detector, which contrasts the actual operation with that of the reference input. If there is an error, that error is delivered directly to the amplifier, which can correct errors .
In lots of servo motor systems, both velocity usually used to measure speed control as well as position is supervised. Velocity indicates a rate of change of position towards time. It also implies a rate of motion in a specific direction, with regard to time.The velocity loop control may take its controls from the velocity loop feedback device--a resolver or tachometer installed directly to the servo motor. The position loop control may take its controls from the position feedback device--an encoder. Relaying on the system, both devices may be fixed to the actual machine or controlled device.
The stability of the entire servo system is reliable upon the tuning of the parts in the system and how well those parts are coordinated with each other. Making the system keeping turning gets in involved in working with a PID (proportional integral derivative) control. This type of closed loop control is very standard and perfect on all high-accuracy systems. And it is significant to servo motor operation principle. The gain, integration time, and derivative time of the loop are the main factors in this closed loop system.
The amplifier gain must be set satisfactorily. The gain must be set how amplifier will respond during changes in error signal. A high gain will make the servo motor overshoot the intended speed target. A too low gain may indicate that the target is reached late in the cycle. The integration time permits the amplifier to get responsive to changes in the error signal, mostly at speed of zero. The error signal of zero speed is zoomed in by the gain setting, results in increased servo motor responsiveness and accuracy. It is hardest to accurately adjust the derivative function, which controls the dampening or vibration of the system. This function basically determines the amount of correction given per unit of error. The error signal can be corrected immediately or throughout seconds.
The derivative setup is a difficult part to the tuning task. The gain and integration time can react to each other. Proper setup of the derivative function get involved in multiplying the position error by the position error rate . If the system components are not coordinated with each other, there would be unstable operation of overshoot, oscillations, or undershoot of velocity. Servo motors are a kind of special electromechanical devices as for the operation principle, which operate in precise degrees of rotation. This kind of motor quickly gets responsive to positive or negative signals from a servo amplifier. Torque, fast and accurate speed and direction control are the remarkable characteristics of a servo motor.