Servomechanism (Tracking Mechanism)

A servomechanism is an automatic control system designed to operate in accordance with input control parameters. The mechanism continuously compares the input signal to the feedback signal to adjust the operating conditions for error correction. Commercially available servo systems vary according to their methods for error detection, amplification, communication, and output.

Hydraulic servo systems have been widely applied in general industrial areas, as well as in the airline, maritime, and military industries. Servo systems, capable of automatic position, speed, and force (load) control with high accuracy and quick response, are used for high-speed injection molding, die-casting, rolling mill, press machines, industrial robots, simulators, testing machinery, and table feeders.

A hydraulic servo system consists of an actuator (hydraulic motor/cylinder), servo valves, sensors, and a servo amplifier, as shown in Fig. 9.1. Figure 9.2 shows a servo system applied to a high-speed vibration test machine.

Servo System Configuration

There are two types of electro-hydraulic servo valves: the pilot operated type, which drives a torque motor to amplify the hydraulic power with a nozzle flapper mechanism, and the direct type, which directly drives a spool with a linear motor and electrically provides feedbacks about the spool position. Mechanical servo valves are also available that have a stylus at one side of the spool to control the flow direction by the mechanical motion of the stylus.

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