Servo Control

Technical Literature

Types of Servo Systems

POSITION SERVO SYSTEM

A load positioning servo system is comprised of a Servo, ServoJet® or Direct Drive Valve, actuator, position feedback transducer, position command generator, and a Servoamplifier. A typical linear position servo system using a double-ended piston is shown to the right (a rotary position servo system can be created by substituting the appropriate rotary components). The valve’s two output control ports are connected across the load cylinder. In the Servoamplifier, the command input is compared to the present position output of the position transducer. If a difference between the two exists, it is amplified and fed to the valve as an error signal.The signal shifts the valve spool position, adjusting flow to the actuator until the position output agrees with the command input.

VELOCITY SERVO SYSTEM

A velocity servo system is comprised of a Servo, ServoJet® or Direct Drive Valve, hydraulic motor, tachometer, velocity command generator, and a Servoamplifier whose summing and gain amplifier are configured to also act as an integrating amplifier.A typical rotary servo system is shown to the right (a linear velocity servo system can be created by substituting the appropriate linear components). The valve’s two output control ports are connected across the hydraulic motor. In the Servoamplifier, the command input is compared to the present velocity output of the tachometer. If a difference between the two exists, then it is the integrated over time and subsequently fed to the valve as an error signal. This signal shifts the valve spool position, adjusting flow to the motor until the velocity output agrees with the command input.

FORCE SERVO SYSTEM

A force servo system can be created with a Servo, ServoJet® or Direct Drive Valve, actuator, load cell or pressure transducer, and a Servoamplifier (an Adjustable Metering Orifice may be used to improve system performance). A typical force servo system is shown to the right. The valve’s two output control ports are connected across the cylinder. In the Servoamplifier, the command input is compared to the present force output of the load cell. If a difference between the two exists, it is amplified and fed to the valve as an error signal.The signal shifts the valve spool position, adjusting pressure to the actuator until the force output agrees with the command input.

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