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Measuring Length with Stepper

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  • Measuring Length with Stepper

    I am wanting to measure the length of a cylindrical part after it has been trimmed. Parts are cylindrical in shape, and wall thickness is approx. .010" (think cartridge cases). Thoughts were originally to use laser, ultrasonic, or prox. sensor, but end-on I don't know if the exposed material will be enough to get an accurate measurement (+/- .001" is desirable). Other idea is to do like CNC machines with tool-length scanners, and use an AD Fork Sensor mounted to a liner slide with stepper, sense when the sensor beam is broken, then retract until the beam "reappears", then read counts from stepper to determine position (length). From this I can output a sorting function based in "in-spec", "long", short".

    Any ideas or suggestions on ladder?


  • #2
    If it was me, I think I'd do this with vision.

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    • #3
      I'm presuming you mean like my second idea using the fork-sensor?

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      • #4
        I believe that CG is speaking of a vision system like Datalogic, Cognex etc makes. They uses an actual camera to look at your part, and then uses software to calculate dimensions etc based on the images it acquires.
        Circumstances don't determine who we are, they only reveal it.
        Jason Wolthuis

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        • #5
          Vision System sounds overly complicated for what I need to measure. Right now we are hand-measuring with calipers as a QC check which works perfectly fine. I envision the PLC doing the QC check as parts are completed, then sorting them. I was thinking something simple like a tool-length setter on a VMC (Vertical Machining Center). HAAS uses the Renishaw Probe, other companies use simple continuity as the "limit switch" when the tool touches a "pad". I did review the video on AD's website about "homing" stepper motors, and this is exactly what I am looking for (option 4), just need to be able to write the "home" to a tag that I can then manipulate.

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          • #6
            All the other mechanics sounds more complicated to me, honestly. Vision is actually fairly easy (though the hardware can be expensive). Are you trying to do 100% inspection real-time with a manufacturing operation (in which case it would need to be fast)? Or just sample a single part out of every every 100 or so to make sure the process is on track? Or measure all parts but in offline batches, where throughput isn't as critical?

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