In brief
A servo motor is a closed-loop controlled electric motor that uses a feedback system and servo drive to set position, speed and torque precisely.
Contents
What is Servo motor?
A servo motor always operates in a closed control loop. An encoder in the motor reports position and speed to the servo drive, which adjusts the current so that the setpoints from the controller are maintained precisely. Servo drives thus achieve high dynamics, good positioning accuracy and high short-term overload capacity. In industry, permanent magnet synchronous servo motors are the most widespread; there are also asynchronous servo motors for higher power ratings.
Important parameters are standstill torque, rated and maximum speed, peak torque, moment of inertia, voltage level, encoder type and resolution, and degree of protection. Features include a holding brake, shaft design with or without key, flange size, cooling and connector version. Motor, encoder and servo drive are matched to one another; the drive must be able to evaluate the encoder type and must know the motor data.
Servo motors drive axes in machine tools, robots and packaging, printing and assembly equipment. Failures frequently involve the encoder, bearings, holding brake and cables. Connectors and cables in drag chains are under particular stress. Cooling and contamination also play a role. A repair is often available faster than a new motor, especially for discontinued product ranges.
In practice: maintenance and procurement
For a replacement, the complete type designation from the nameplate and the servo drive used should be stated, as an electrically different motor may require new commissioning or parameterisation. It is also worth asking about a repair, such as replacing bearings, brake or encoder.
Synonyms and abbreviations: servomotor · servo drive motor · synchronous servo motor · AC servo motor · servo
Frequently asked questions
What is the difference between a servo motor and a stepper motor?
A servo motor always works in a closed control loop with an encoder and actively corrects deviations. A stepper motor moves in fixed angular steps and is usually controlled without feedback. Servo drives are more dynamic, maintain torque even at high speeds and can handle overloads, while stepper motors are simpler and less expensive for smaller positioning tasks.
What information is needed to replace a servo motor?
Most important is the complete type designation, which encodes options such as encoder type, brake, shaft design and degree of protection. In addition, standstill torque, rated speed, voltage and the servo drive used are needed. A photo of the nameplate and the connectors prevents confusion between similarly named variants.
Can a servo motor be repaired?
Often, yes. Bearings, shaft seal, holding brake and connectors can be replaced, and defective encoders are also exchanged. After an encoder replacement, the commutation, that is, the assignment of encoder position to rotor position, usually has to be set again. In the case of damage to the winding or magnets, a new motor is often the better option.
What does standstill torque mean for a servo motor?
Standstill torque indicates the torque the motor can deliver continuously at zero speed without overheating. It is an important reference value for selection. For short periods, servo motors can deliver a considerably higher peak torque, for example for acceleration. Both values are given in the data sheet.