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Selection of Steeper Motor or Servo Motor.

Stepper Motors, DC brush Servos and brush less servos each have their respective benefits and drawbacks. No single motor technology is ideal in every application, despite what some manufacturers may claim. 

This section reviews the relative merits of each technology and lists the application types most appropriate to each.

The following section gives some idea of the applications that are particularly appropriate for each motor type, together with certain applications which are best avoided. It should be stressed that there is a wide range of applications which can be equally well met by more than one motor type, and the choice will often be dictated by customer preference, previous experience or compatibility with existing equipment. With the increased requirement for intelligent drives, the real cost differential between brush and brush less servo systems are diminishing. In the majority of new applications the choice is therefore between stepper and brush less servo. 

Cost conscious applications are always worth attempting with a stepper, as it will generally be hard to beat on cost. This is particularly true when the dynamic requirements are not severe, such as “setting” type applications like periodic adjustments on printing machines.

High Torque, low speed, continuous duty applications are appropriate for direct drive servos and frequently also for stepper motors. At low speeds the stepper is very efficient in terms of torque output relative to both size and input power. A typical example would be a metering pump for accurate flow control.

High torque, high speed, continuous duty applications suit a servo motor, and in fact, a stepper should be avoided in such applications because the high speed losses can lead to excessive motor heating. A DC motor can deliver greater continuous shaft power at high speeds than a stepper of the same frame size. 

Short, rapid repetitive moves may demand the use of a servo if there are high dynamic requirements. However the stepper will offer a more economic solution when the requirements are more modest.

Positioning applications where the load is primarily inertia rather than friction are efficiently handled by a servo. The ability to overdrive a servo motor in intermittent duty allows a smaller motor to be used where the main torque demand only occurs during acceleration an aeceleration.

Very arduous applications with a high dynamic duty cycle or requiring very high speeds will normally require a brushless servo.

Source: Parker Automation
Additional Information can be found at www.compumotor.com

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