What Is a Servo Drive?
The term "servo drive" is rather ambiguous, as it has acquired a number of different possible meanings. "Servo drive" can be synonymous with "servo-mechanism" -- an electromechanical system that includes a motor, drive shaft, sensors, electronic amplification and feedback stages, and frequently a computer control system. It can also be used to refer to various elements of a servo-mechanism system.
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Servo-Mechanism Systems
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The term "servo-drive" is sometimes used to describe or refer to an entire servo-mechanism system. The basic elements of a servo-mechanism system are the servo motor itself; the motor's drive shaft or output shaft; sensors, which provide information about the state of the motor; a circuit to handle feedback from the motor; and a power electronics amplification stage. Typically a computer control stage sends instructions to the motor, although in very simple systems, this may not be necessary. The computer control stage sends signals to the system via the amplification stage, telling the servo motor what to do. The feedback circuit relays information from the sensors back to the computer control system, which amends the instructions it sends to the motor.
The Motor
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"Servo-drive" can refer specifically to the motor in a servo-mechanism system. This can include the drive shaft or output shaft -- the connector that attaches the motor to the system it drives. It can also include elements such as a ball-screw feed, an element that converts rotational motion from the motor to linear motion.
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The Power Electronics Amplification Stage
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The power electronics amplification stage itself is sometimes termed the servo-drive, as it drives the motor. The electrical signals from the computer control system have a very low voltage, far too low to power the motor by itself. The power electronics amplification stage can handle higher voltages and supplies the necessary power to the motor.
The Computer Control Stage
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The computer control system dictates the speed, angle and other settings for the motor based on the signals sent from the sensors and feedback processing circuits. In the case of older or very simple servo-mechanisms, the computer control stage is absent, with control provided by a variable resistor. The computer control and power electronics amplification stages, taken together, are sometimes termed the servo-drive.
Servo-Drive Applications
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Servo-drives are used in applications where a motor's speed, angle and direction need to be controlled. A simple servo-drive without a computer control stage might be used to power a radio-controlled airplane, for example. Robotic systems need to use servo-drive systems, often very sensitive ones with precise feedback and sophisticated computer control.
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