As a compact linear actuator, linear stepper motors are often used to realize linear motion or linear reciprocating motion. The main principle is through the screws and nuts meshing, adopting some method to prevent screws and nuts relative rotation, to achieve the linear movement of the mechanism. The purpose of this paper is to introduce three basic structures of linear stepper motors.
Non-Captive Linear Stepper Motors
The nuts of the non-captive linear stepper motors are integrated with the rotor. The lead screw can go through the motor or be completely separated from the motor as a part. It has no reasonable stroke limits but the shaft must be attached to an assembly that will not rotate. This will then allow the lead screw to extend and retract without rotating, travel freely in and out of the motor body. In certain setups the motor body may serve as the drive or the nut in the assembly. The anti-rotation is by the attachments point and is commonly a cut or machine thread on the end of the screw. The non-captive is potentially the shortest overall length assembly.
External Linear Stepper Motors
The lead screws of the external linear stepper motors are integrated with the motor rotor as a part. It has an external drive nut that can be mounted to a carriage assembly. Linear motion is created by the nut traversing back and forth on the lead screw as it turns. The common end feature of the screw is a bearing journal. External linear stepper motors are most akin to motorized rails where the nut is replaced by a driven carriage assembly.
Captive Linear Stepper Motors
Captive linear stepper motors have a threaded drive screw held mostly inside the motor connected to a spline. It has built in anti-rotation through the use of a spline shaft that allows it to extend and retract as a unit with no additional requirements for anti-rotation. The captive actuator is designed for short strokes of up to about three inches. The basic design is least tolerant of system misalignment and is the motor protected actuator style because it’s self-contained. The captive has the longest basic body style.