Can stack linear stepper motor actuators are based on can stack stepper motors, which are a form of permanent magnet steppers that consist of two stators (and therefore two coils) stacked on top of each other. The poles of each stator are “claw tooth” design and are offset from each other by one-half of the pole pitch. The rotor consists of a permanent magnet, and it has the same number of pole pairs that each coil has.
The stacked design of the two stators, or cans, means there are four discrete positions that can be induced for each pole pitch. A common design for can stack actuators has 24 poles in each coil, or phase. With 24 poles around a 360 degree cylinder, the pitch between poles on a single stator is 15 degrees.
In order to make a linear actuator out of a can stack stepper motor, the rotor is threaded, and a screw (typically a lead screw) is integrated into the rotor, so that it extends and retracts as the motor turns. There are three common designs for can stack linear actuators.
Like other stepper motors, can stack linear actuators are commonly operated in open-loop mode. Although stepper motors do have step error (± 0.5 degrees, for example), the error doesn’t accumulate over multiple steps, which allows good positioning accuracy. And many designs can be operated in full-, half-, or micro-stepping modes. Can stack linear actuators also take advantage of the detent torque of the stepper motor to hold position, even when there’s no power supplied to the motor.
Industrial applications for can stack linear actuators (external linear actuator, non captive linear actuator )include medical diagnostic equipment and pumps. But suitable applications for these small, precise linear actuators range from consumer devices such as printers and copiers to military applications for radar and antenna positioning.
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