Unlike motor designations such as DC-motor or induction motor, the term servo motor or servomotor does not describe an actual physical operating principle. Thus, the difference to other motors is not in the motor itself but instead solely in its actuation, which takes place in a closed control loop.
Only servo motors with integrated servo amplifier can independently regulate torque, speed or position without external components after a supply voltage is applied in servo operation. This occurs according to specifications via a bus connection or via digital or analog inputs. Nevertheless, motors that require an external servo amplifier are commonly referred to as servo motors. As in the past, these make up the majority of servo motors.
The combination of motor and amplifier is generally called a servo drive. The modeling servo, which consists of only a servo and which is likewise operated in a closed control loop, is, however, excluded from the term servo motor in this case. Thus, the term small servo motor does not describe one certain type of motor construction but can rather refer to servo motors of a wide variety of design types.
Permanently excited synchronous motors, asynchronous motors and brushed DC-motors are common types of miniature servo motors. AC servo motors are generally motors that are operated on servo amplifiers supplied directly by an alternating voltage (single phase or three phase). These are usually power supplies from approx. 230 V to over 600 V. Standing in contrast to these are servo motors that can be operated directly on a DC voltage of up to approx. 48 V; these are known as DC servo motors. According to this definition, permanently excited synchronous motors are used both as AC and as DC synchronous motors. Asynchronous motors and reluctance motors are used primarily as AC servo motors; permanently or separately excited brushed DC-motors, on the other hand, are used as DC servo motors.
Small servo motors in combination with a servo controller (motion controller) matched to the motor can be accelerated to their rated speed in just a few milliseconds. In the same time, they can be braked and their direction of rotation reversed. They are used as highly dynamic, acceleration-optimized drive units for controlling angles, positions and paths.
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