Servo Amplifier

A servo amplifier is a part of the closed loop servo control drive system is designed to primarily control the performance of a mechanism. Basically they are four-quadrant, power amplifiers with regenerative features and equipped to supply power according to the control voltage to the overall motor. These servo amplifiers can supply energy to the load, as well as absorb energy from the load. They are also designed to convert the kinetic energy of the combined motor load into electrical energy while the load is decelerating.

The output of a servo amplifier is an analogue circuit. The circuit enables the current and voltage of the motor to be adjusted to control position, torque and velocity. The feedback and comparator stages though can have a mixture of analog and digital devices.

Few ideal characteristics that are desired in a servo amplifier are as follows:

• Constant Velocity – ability to maintain the commanded velocity. Tachometers are used to record the aberrations between the commanded and actual motor speed.

·         Infinite Acceleration – an ideal amplifier must be able to provide infinite acceleration which can be observed by abruptly starting and stopping the motor.

·         Linear response – the amplifier need to respond proportionally to the changes in the velocity input command.

·         Hold Position – the amplifier should drive the motor in such a way that the latter holds its position irrespective of any external force or disturbance.

·         Overload protection – a low resistance circuit should be there to protect the amplifier from excessive current.

There are a host of servo amplifiers in the market but one should be careful while choosing an amplifier. The compatibility of the servo amplifier with its servo is to be ensured. Some notable types of servo amplifiers are as follows:

• Push Pull amplifiers – one of the earliest designs of amplifiers designed primarily for two transistors to get switched on/off to share the current load for the motor.
• Chopper amplifier – another primitive DC-motor based amplifier that finds limited usage today.
• L Type (Linear Motion) Servo Amplifier – it is fitted with linear positioning function you can basically construct a linear positioning system using such amplifiers as a ball screw or rack & pinion.
• Digital Amplifier – it is usually used for higher machine performance as it promises improved reliability and repeatability through digital technology.
• R Type (Rotation) Servo Amplifier – it provides an additional rotation angle indexing function. Rotation angle index system can be constructed using this amplifier.
• DC servo amplifier – both brush and brushless amplifiers can be found in simple DC motors