ESR Pollmeier GmbH
Servo Drive Technology


Frequently Asked Questions – and answers

What is a servo drive system?

A servo drive system consists of a servo drive and a servo motor. The main task of a servo drive (also called "servo amplifier", "servo inverter", "servo controller", or just "controller") is the control of the motor current. In addition, ESR servo drives offer a broad spectrum of functionality (see Applications).

While most of the electrical drive systems are operated at constant speed, a servo drive has a rather "hectic" life. Often it has to accelerate to the rated speed within a few milliseconds only to decelerate a short time later just as quick. And of course the target position is to be reached exactly with an error of a few hundredths of a millimeter.

Compared to other controlled drives servo drive systems have the advantage of high dynamics and accuracy, full stall torque, and compact motors with high power density.

Where are servo drive systems used?

Servo drive systems are used where high dynamics (i. e. fast acceleration and deceleration) and good accuracy at reaching target positions are important. The good control behavior allows the optimal adaptation to the application (e. g. positioning without overshoot). But also the smooth run (due to sinusoidal commutation) and the possibility of exact synchronization of two or more drives open a wide field. Because of their wide speed range servo drives can be used in a huge number of applications.

Servo drives run in large, highly automated installations with several dozens of axes as well as in machines with only a few axes which perhaps operate independently. Further information on servo drive systems and their usage can be found at Applications.

What is a servo motor?

Servo motors are electric motors that are designed specially for high dynamics. Servo motors by ESR distinguish themselves by a compact design with high power density and a high degree of protection (up to IP 65). They come as AC servo motors (brushless) or DC servo motors (with brushes for the commutation). The high power density is achieved by permanent magnets made of neodymium-iron-boron (NdFeB), samarium-cobalt (SmCo), or ferrite material. The servo motor is equipped with a position sensor which provides the controller with position and speed information.

What kind of motor position sensor can be used?

As a standard, the AC servo motors are equipped with resolvers. In combination with the digital servo drives sincos encoders (absolute encoder, single-turn or multi-turn) and high-resolution incremental encoders may be used as well, in case higher accuracy or dynamics is required.

The DC servo motors can be equipped with tachogenerators and/or incremental encoders.

How to choose the appropriate servo motor?

For dimensioning the motor the following data are important: the mass of the parts to be moved, the cycle time of the application, and the friction torque. With these data the rated and peak torque (maximum acceleration or deceleration) and the rated speed can be calculated. If required, gears are used to match the moment of inertia of the motor to the moment of inertia of the application.

You can find technical specifications on ESR's servo motors at Products/Servo motors.

As a specialist for servo drive technology we offer a comprehensive support at choosing the right servo drive system, from drive system configuration in cooperation with users to solutions for special applications (see Support).

What is a servo drive?

The servo drive (also called "servo amplifier", "servo inverter", "servo controller", or just "controller") controls the current of the motor phases in order to supply the servo motor with exactly the current required for the desired torque and the desired speed. The essential parts of a servo drive are the power section and the control loops.

The power section consists of a mains rectifier, a DC-bus, and a power circuit which supplies the individual motor phases with current.

The control loops (analog or digital) drive the power circuit and by constantly comparing setpoint with actual values ensure that the motor keeps exactly to the desired motions even under varying load.

In addition, ESR servo drives offer a broad spectrum of functionality (see Applications).

How to choose the appropriate servo drive?

The servo drive has to supply the motor with the required current (rated current at continuous operation, peak current) and match the terminal voltage of the motor (125 V, 320 V, or 560 V). Also the intended purpose is important for the choice of the right drive:

Is the servo drive going to be used in velocity mode in a multi-axis application with a higher-level controller (e. g. CNC)? Then an analog servo drive may be sufficient.

Or should the drive be equipped with more functionality (e. g. for positioning control or axis synchronization) or a fieldbus (e. g. Interbus, CANopen, or Profibus-DP) for communication with the higher-level controller? In this case a digital servo drive has to be used.

Further information on ESR's servo drives and their functionality can be found at Applications. For technical specifications please take a look at Products/Servo drives.

We help you choose the right servo drive system matching your application and offer our support regarding drive system configuration (see Support).

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