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Servo System

A servo drive essentially comprises an intelligent servo amplifier and a servo motor that operates with a PLC or CNC to perform complex, specialized moves in one or more directions, or axes. These complex and specialized moves, which are needed in the automation of industrial tasks, are collectively known as motion control.

Servo drives are applied in many different field for automation - in the motor industry, the petrol industry, the textile industry, in packaging systems, warehousing systems and so on.


Servo drives are used for applications with requirement to high dynamic and high control quality. The table below compares typical data of Induction Machines, DC motors and Servo motors. The highlighted data show the advantage of servomotors.


Power conversion

The graphic shows the principle of power conversion in a servo amplifier.

mains, rectifier, capacitors, DC-link bus with switched brake resistor capacitors, power stage, motor

Closed Loop Servo Systems

In a servo drive, feedback information - motor position and motor velocity is sent from the feedback unit of the motor back to the servo amplifier. The servo amplifier analyzes the feedback, makes adjustments as needed, and generates new currents to bring the motor to the commanded velocity. This cycle constantly repeats itself in a closed loop. A closed loop that controls the position of the shaft or load is called a position loop. A closed loop that keeps the velocity of the motor on the commanded value is called a velocity loop.


Servo Drive Components

Servo Amplifier The servo amplifier comprise a three-phase, power supply, and high-performance control unit all housed in a single enclosure. The several control loops are realize totally digital in the micro controller.
Communication Servo Amplifiers, controls and sensors which are available in the system can communicate over bus systems. With the Kollmorgen servo amplifiers several bus systems are supported by the MultiFieldbus concept like e.g. SERCOS, CANopen, PROFIBUS, SYNQNET, ETHERCAT and many different.
Motor A motor moves machinery in a single axis of motion. Electrical motors are driven by magnetic fields. Every motor has at least two magnetic motor poles, normally four or six. The servo amplifier generates the current in the stator so that a controllable torque is available at the shaft. The servo amplifier operates with standard synchronous servo motors, induction machines, and with direct drive motors (rotary or linear).
Feedback Device Every closed-loop servo system needs at least one device to return feedback information from each motor (or load) to servo amplifiers. Depending on the feedback device, feedback is transmitted back to the servo drive in the form of digital signals or analog signals. The Kollmorgen servo amplifiers support a lot of different feedback devices due to the MultiFeedback interface.
Load The load is the machinery and equipment that each motor drives. It is everything connected to the output shaft of a motor, including the shaft itself. A motor must be appropriately sized to its load to ensure the motor is powerful enough to carry out your automation tasks. A servo system delivers and converts motion to a load via one or more of the following mechanical techniques:
Direct Drive - motor is connected directly to the load, e.g. to a rotating table
Gearhead Drive - motor is connected to the load via a gearhead
Screw drive - motor connected to a lead screw carrying a slide (moving table)
Rack and pinion - motor connected to a cogwheel that moves a rack
Belt and pulleys - motor connected to rollers that move conveyor belts or chains and sprockets.