Precision Acme thread movement with help of encoder.

Results 1 to 4 of 4

Thread: Precision Acme thread movement with help of encoder.

  1. #1
    Activation process cncstudies's Avatar
    Join Date
    Dec 2018
    Posts
    11
    Downloads
    0
    Uploads
    0

    Default Precision Acme thread movement with help of encoder.

    Hello All
    I have built a large Z axis with using 40mm x 5mm pitch precision Acme thread rod (0.01mm tolerance). The rod is turned via a planetary 100:1 gearbox fixed to a 1.5kw Servo motor. The idea is that the Acme nut(which is fixed to a plate )must allow this plate to move move in 50 micron step. The problem I face is that being a large Z Axis, the gearbox movement may not respond to such a minute movement of 50 microns, despite the servo "reaching its 50micron" motion through its built in encoder. I would like to put an encoder on the acme nut but how do i control the servo with this encoder? All help will be appreciated



  2. #2
    Member awerby's Avatar
    Join Date
    Apr 2004
    Posts
    5770
    Downloads
    0
    Uploads
    0

    Default Re: Precision Acme thread movement with help of encoder.

    I don't think the controller cares where the encoder is mounted. It's usually on the back of the motor for convenience, but with all the backlash from the gear train, I can see why you'd want to monitor the screw instead. You should be able to remove and re-mount it, but if that doesn't work, use a different but similar one on the screw. Just realize that the encoder won't be able to tell if the spindle moves 50 microns; it will only tell you what the screw does, but its backlash will likely take up most or all of that on a change of direction.

    [FONT=Verdana]Andrew Werby[/FONT]
    [URL="http://www.computersculpture.com/"]Website[/URL]


  3. #3
    Member
    Join Date
    Nov 2013
    Posts
    4674
    Downloads
    0
    Uploads
    0

    Default Re: Precision Acme thread movement with help of encoder.

    Hi,
    what is your Z axis servo?.

    An AC servo using FOC (Field Oriented Control) requires an encoder which is intimately linked to the servo. Any lash or other non-linearity will almost certainly screw the servo operation ie
    the encoder has to be mounted on the servo shaft.

    There are other servos, somewhat specialist, that can have two encoders. The first encoder and the main one is the servo mounted rotary encoder, and that has to be there in order for FOC to work,
    but has an auxiliary encoder that can close the position loop. The auxiliary encoder could be a linear scale, another rotary encoder linked direct to the ACME or a LDVT or even an interferometer
    as might be use in ultra precision semiconductor machines. This is called 'load sensing'. The load is the actual position of the Z axis.

    As an example the Delta A2 series of servos have this auxiliary encoder or load sensing input. The normal B2 series servos (that don't have this load sensing feature) are $438USD (750W kit) while
    the A2 series is $634USD (750W kit)....so you pay for the feature. I mention Delta because I use Delta B2's in my machine and am familiar with them, but most of the top tier servo manufacturers
    have models that have this load sensing feature. Somewhat specialised and more expensive.

    Craig



  4. #4
    Member
    Join Date
    Jan 2008
    Location
    Australia
    Posts
    1551
    Downloads
    2
    Uploads
    0

    Default Re: Precision Acme thread movement with help of encoder.

    What CNC controller?



Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  


About CNCzone.com

    We are the largest and most active discussion forum for manufacturing industry. The site is 100% free to join and use, so join today!

Follow us on


Our Brands

Precision Acme thread movement with help of encoder.

Precision Acme thread movement with help of encoder.