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I am new to robotics and mechanical engineering. I am trying to understand how the Z-axis (and effector) of a SCARA robot can be driven by a stepper motor with it's shaft coaxially aligned along the same Z axis. In the photo below, one can clearly see the Z-axis lead screw and effector on the SCARA arm. I am familiar with lead screws in X-Y stages, where a block is pushed along the length of the screw by rotation. In this case, the lead screw itself is being translated.

(1) What mechanism can be used to cause the lead screw itself to translate along the Z-axis?

(2) How can the effector (say a robotic claw) be prevented from rotating while it is in motion?

enter image description here

I have seen so-called "through type" stepper motors (see below) in which the lead screw moves right through the motor. Since this type of motor seems less prevalent on markets such as Amazon, and more expensive, I would like to use a standard stepper motor and actuate the lead screw mechanism using a belt. This stepper motor will have it's shaft oriented along the Z axis (and will be "coaxial" with the effector arm).

enter image description here

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i found out that it is called an RZ tool ... google scara RZ tool

  1. there is a captive rotating "nut" on the threaded shaft that causes the shaft to move linearly

  2. there is a spline (raceway) in the screw shaft to prevent turning

the picture that you posted probably uses a ball screw/spine like this one ... https://tech.thk.com/upload/catalog_claim/pdf/327E_BNS_NS.pdf

here is another closeup

https://patentimages.storage.googleapis.com/38/43/1e/12ef07c54bdf2f/US20050087034A1.pdf

enter image description here

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