I've seen this linear actuator end effector on a few industrial SCARA 'bots but I am having trouble visualizing how it works internally:

Linear Actuator

It looks like a type of lead screw, but the nut must spin instead of the rod to cause motion. If this is the case would the end part of the effector not also spin with the rod? Does this end effector design have a specific name ? If you can explain how the mechanics of this joint works It would be very helpful.

All help appreciated.

Edit: Sorry for the low res picture, more detail about the type of joint im looking at can be found at:

Models that have this type of joint include the Epson T3

Epson T3 Video

Fanuc SR-3iA

  • $\begingroup$ Welcome to Robotics, kp122. You've posted a low-resolution image and it's hard for me to see the actuator in detail. You stated you found a few robots with this style of end effector; could you please post some model numbers and/or links to datasheets? $\endgroup$
    – Chuck
    Dec 13, 2019 at 19:12
  • $\begingroup$ Thanks @Chuck , I have edited the post to include more info about the type of machines I'm asking about. $\endgroup$
    – kp122
    Dec 13, 2019 at 21:02
  • $\begingroup$ i remember answering this exact question a year or so ago ... looking for it $\endgroup$
    – jsotola
    Dec 14, 2019 at 1:31

1 Answer 1


The actuator has two raceways cut into it.

One is a screw thread, and engages with a rotary screw nut that is turned by a motor. Turning the nut moves the actuator linearly.

The other is a spline groove and is cut parallel to the actuator axis, and engages with a rotary spine nut that is turned by another motor. Turning the nut spins the actuator on its axis



enter image description here

  • $\begingroup$ Perfect, thank you so much @jsotola. Is this type of shaft preferred to a regular CNC lead screw because of torque and/or precision ? Though CNC machines have the same precision and higher torque needs generally. Any idea why this type of shaft is so widely used ? $\endgroup$
    – kp122
    Dec 14, 2019 at 8:27
  • $\begingroup$ it is not a lead screw ... it is a robotic arm ... a manipulator would be mounted on the end of the shaft $\endgroup$
    – jsotola
    Dec 14, 2019 at 9:10
  • $\begingroup$ Thanks very much, really appreciate it @jsotola $\endgroup$
    – kp122
    Dec 14, 2019 at 9:18
  • $\begingroup$ this is supperior in most performance characteristics when compared to a lead screw. Just for completeness sake, high-en CNCs use ball screws not lead screws! $\endgroup$
    – 50k4
    Dec 16, 2019 at 11:47

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