SureServo Drives and Motors Frequently Asked Questions
Question
What are the differences between steppers and servos.
Answer
Stepper motor control is the most cost-effective way to control a motion but it is an open loop. The accuracy is good if motor is properly sized and the price is reasonable. The torque decreases sharply when the speed increases. Also, the maximum speed for rapid moves and cutting moves are not as high as for servo control. The stepper motors need an amplifier to a train of pulses to deliver current to the windings. The controller is typically a PLC that will generate a speed trapezoidal profile to move the shaft angle from one position to other. There are also dedicated controllers called indexers that will do the same type of pulse generation. Or there are still more sophisticated controllers that can do coordinated motion of several axes.Servo control uses feedback from an encoder to constantly monitor the motion exact position. Modern servos have constant torque over the speed range, and some field weakening only at the top speeds. Using the feedback signals, the control system can correct itself to achieve high speeds and perfect accuracy, even under very strenuous conditions. The modern servos have an amplifier with intelligence to allow several motion types, and can deliver torque, speed or position control with its own intelligence. In any case, a PLC is advisable when there is a need to execute some logic not possible to get from the internal algorithms.
FAQ Subcategory: None
This item was last updated on 2009-03-05
Document ID: 1151
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