What are the options for integrated motor and screw designs?

Integrated motor and screw assemblies are available in a variety of configurations and designs.The motor can be a servo or stepper type and the screw can be a ball screw or a lead screw,although the most common configuration is to pair a lead screw with a stepper motor or a ball screw with a servo motor.

●External motor-screw integration

One of the most popular integrated designs uses a motor with a hollow shaft and integrates the lead screw directly into the motor.The screw is machined so that one end fits into the hollow bore of the motor,and the machined end is permanently attached to the motor bore by welding or adhesive,or secured with fasteners.Attaching the screw shaft to the motor bore by fasteners allows for disassembly of the assembly for maintenance and replacement of either assembly(rather than replacing the entire assembly),but this method also results in loss of alignment and stiffness over time.

In the external design,the shaft of the ball screw or lead screw is integrated into a hollow bore motor,and the nut is external to the motor.

●Non-captive motor-screw integration

In the non-captive integration method,the ballnut or screw nut is integrated into the motor(or mounted on the motor surface)and does not move along the screw.Instead,the screw is prevented from rotating(usually by an additional load)and moves linearly "back and forth" through the motor-nut combination as the motor and nut rotate.In this configuration,the non-additional design provides a better travel to total length ratio,provided the design allows the screw to extend into space beyond the back of the motor.

The non-captive integration method allows either the screw or the nut to be driven.

Alternatively,if the screws are fixed so that they do not move,the assembly essentially becomes a driven nut design in which the rotation of the motor causes the motor nut assembly to move back and forth along the set screws.As with conventional driven nut assemblies,this configuration allows for higher travel speeds because the screw whip is almost completely eliminated.It also allows multiple motor-nut combinations to be mounted to the same screw shaft and driven independently.

Non-captive designs can be mounted with the screw fixed,so the motor-nut assembly travels along the screw,or with the motor fixed,so the screw travels back-and-forth through the motor-nut housing.

●Captive motor-screw integration

Captive designs use a spline shaft to prevent the screw from rotating.

The variant of the motor-screw combination described above is the captive design.As with the non-fixed design,the nut is integrated directly into the motor,but the splined shaft is attached to the screw,preventing the screw from rotating and creating linear motion as the motor turns.In this design,the screw extends and retracts from one end of the assembly and is unsupported.The captive design is essentially a more compact version of the thrust rod actuator,making it best suited for push or press applications where the load is guided and there is no radial force on the screw.

Captive motor-screw integration is similar in function to a thrust rod style actuator.

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