Linear servo motor sensorless homing tutorial

A new video tutorial for setting up linear servo axis homing a.k.a. referencing without end switches is online! Drive uses hard-stop homing method to detect end of travel and set soft travel limits. Watch it below:

10 thoughts on “Linear servo motor sensorless homing tutorial

    • Yes! On software side, it’s been developed with Ion and finally the outcome should be transferable to Argon (not 1:1 but helps a lot to have it in Ion). We’re also thinking to produce low cost & high resolution linear encoders as there seems to be absence of them. Or do anyone know where to find new linear encoders around €100?

      • Hi Tero,

        U.S. Digital have low cost linear encoders. Currently their range has a maximum resolution of 500 lines per inch, but they are developing a higher resolution encoder. No idea what the price on it will be, but their other products are pretty reasonably priced.



        • Good to know! 500 LPI is quite low but I hope they start making higher res too.

          Yesterday I received components for the first linear encoder prototype. It has less than 1 µm resolution.

          • That’s exciting! How would Argon/Ion work with very high res incremental encoders, like 1,380,000 counts per pole pair in a linear motor? Is max input and hose rate still 4Mhz?



          • 4 MHz is a default limit but on TODO list is a plan to make it adaptive based on frequency actual demand. Hardware supports up to 30 MHz count rate. Also due to higher resolution encoders becoming better available, also resolution support needs to be increased in standard FW. So someday that should be no problem, but until then, such high rez encoders need customized FW.

  1. Do you need one for testing purposes? (if so, what resolution and length would be most useful). Also, I found this comment on the internet and I wanted to know if this statement is true:

    “It is necessary for the motor encoder to have a greater effective resolution then the load encoder to make sure that the controller will see commanded movements of the motor well before the backlash is taken up on the load. Otherwise, the controller could get into a mode where it is building up too much error before it sees any response from the mechanics(load). This can lead to a slight oscillation around the reference position, or even cause the system to become unstable if the backlash is large enough.”

    Do you agree with that?

    • At the moment we should have everything we need for dual-loop development. But thanks for helping hand! I appreciate that!

      The statement makes sense. At least having motor FB higher resolution than linear FB is preferred than the other way around. I don’t think system would become easily unstable but it might “hunt” more for final position.

    • That’s what I’ve heard,however, here’s a story:
      Many years ago, we built a large (~500mm) system with air bearings over ground granite, with a precision Swiss ball screw with flexures to drive it, and dual encoder feedback. We bought a couple of the subsystems from other suppliers, including the Galil-based motion control system from Vendor I.

      Vendor I said that same thing, however, in the system they actually delivered, the linear load encoder had significantly higher resolution than the motor’s rotary encoder. We might have had some issues with the system, but motor instability wasn’t one of them. Of course, our system didn’t have any significant backlash….

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