Postional referencing
Close
Login to Your Account
Results 1 to 8 of 8
  1. #1
    Join Date
    May 2019
    Country
    UNITED STATES
    State/Province
    California
    Posts
    26
    Post Thanks / Like
    Likes (Given)
    15
    Likes (Received)
    8

    Default Postional referencing

    Could someone give me a quick explanation about the differences in 'dog-type', dogless, stopper, and non-stopper reference configurations. From the parameters my machine is 'non-stopper dogless' and I'm not sure what this means. (Doing a search online for 'dog-type' or 'dog servo' brings up everything that has NOTHING to do with machining.)

    Which is better?

    Thx.

  2. #2
    Join Date
    Nov 2014
    Country
    UNITED STATES
    State/Province
    Colorado
    Posts
    2,703
    Post Thanks / Like
    Likes (Given)
    3216
    Likes (Received)
    711

    Default

    Quote Originally Posted by Bones288 View Post
    Could someone give me a quick explanation about the differences in 'dog-type', dogless, stopper, and non-stopper reference configurations. From the parameters my machine is 'non-stopper dogless' and I'm not sure what this means. (Doing a search online for 'dog-type' or 'dog servo' brings up everything that has NOTHING to do with machining.)

    Which is better?

    Thx.
    What exactly causes a 090 P/S alarm?!

    ^^^ This might help (a bit).[From Pm forum.].

    I'm guessing a "Dog" in this case is an inverted specially profiled mini ramp (that can be bolted or adjusted to a particular position (at the factory when they build the machine)) that triggers a fixed micro switch. As used for homing.

    from post #5 in cited thread …

    "The Feeler is setup with 2 dogs and 2 switches per axis. One dog activates the limit and causes an E-stop. The other switch causes the machine to slow down after hitting the first ramp on the other dog, then when it eases off the back ramp the machine looks for the index encoder pulse. "

    Then a discussion about absolute encoders ensues etc.

    Proximity switch dog | WordReference Forums

    ^^^ This one in Spanish was kinda funny too...

    I agree this is a difficult one to google lol...

    "what to do about dog acceleration and deceleration " (agility training for dogs.).

  3. #3
    Join Date
    Jan 2014
    Country
    UNITED STATES
    State/Province
    Washington
    Posts
    4,384
    Post Thanks / Like
    Likes (Given)
    803
    Likes (Received)
    2362

    Default

    Assuming you are talking about a Fanuc or Mitsubishi control......

    Quote Originally Posted by Bones288 View Post
    Could someone give me a quick explanation about the differences in 'dog-type', dogless, stopper, and non-stopper reference configurations.
    Dog type can be used with incremental or absolute encoders, but typically is only found on machines with incremental encoders. There is a reference position deceleration limit switch and a ramped block (the dog) that actuates the switch. A simplified explanation...The machine travels until the switch is opened and then closed again and the index mark on the encoder is read.


    Dogless is only used with absolute encoders and does away with the reference position limit switch and a ramped block (the dog). The reference point can be set by parameters or by positioning the axis close to the reference position and then moving the axis until the index mark is read while a reference setting parameter is enabled. The encoder positions are retained by backup battery power while the machine is off. Axis movement while the power is off is tracked and the control's position counters are updated when power is applied.

    I've never seen a stopper type reference used with a Fanuc or Mitsu control, but they do offer that ability. It would be used with incremental encoders primarily, but could be applied to absolute encoders. A stopper reference drives the axis at low speed in a torque limited mode against a hard stop. The axis then reverses direction until the encoder index mark is read.


    Quote Originally Posted by Bones288 View Post
    From the parameters my machine is 'non-stopper dogless' and I'm not sure what this means.
    It means it has absolute encoders and no reference limit switches. There usually will be some method determined by the machine builder to establish the machine reference point. Keep the backup batteries in good shape. Lots of folks ignore that then spend some amount of time diddling around trying to properly re-establish the reference point after the batteries die and the position is lost.




    Quote Originally Posted by Bones288 View Post
    Which is better?
    Would not really want to say one method is better than another, they are just different ways to use different hardware and machine builder preference.

  4. Likes Bones288, barbter, Tonytn36, aj, cameraman liked this post
  5. #4
    Join Date
    May 2019
    Country
    UNITED STATES
    State/Province
    California
    Posts
    26
    Post Thanks / Like
    Likes (Given)
    15
    Likes (Received)
    8

    Default

    Mits controller, you're correct. I'm attempting to revive a CV500a and have everything verified EXCEPT turning on the spindle and tool changes.
    (Just a minor thing, right?)

    I'm having some issues with the ATC's '2nd Zero' position and the spindle over traveling past machine zero (0,0,0) and rams into the mechanical stops on the Z+.

    I'm sure it's something on the user end (or some jinxed parameter).

    Also, I took your advice ahead of time and bought a stack of batteries for the servos. Now I just need a few for the actual memory.

    Thanks again.

  6. #5
    Join Date
    Dec 2007
    Location
    Southeastern US
    Posts
    6,401
    Post Thanks / Like
    Likes (Given)
    845
    Likes (Received)
    2803

    Default

    One of the top 3 crashes I've been witness to was due to stopper type referencing, avoid if at all possible.

  7. Likes Vancbiker liked this post
  8. #6
    Join Date
    Feb 2007
    Location
    Aberdeen, UK
    Posts
    3,475
    Post Thanks / Like
    Likes (Given)
    1213
    Likes (Received)
    1296

    Default

    Quote Originally Posted by Tonytn36 View Post
    One of the top 3 crashes I've been witness to was due to stopper type referencing, avoid if at all possible.
    Yeah, it doesn't take a lot of imagination to see how that could go badly wrong..

  9. #7
    Join Date
    Dec 2007
    Location
    Southeastern US
    Posts
    6,401
    Post Thanks / Like
    Likes (Given)
    845
    Likes (Received)
    2803

    Default

    Quote Originally Posted by gregormarwick View Post
    Yeah, it doesn't take a lot of imagination to see how that could go badly wrong..
    It was on an engine block decking / facing machine. 36" diameter cutters, probably 400+hp spindles (big motors on that joker) and 3" twin ball screws. The cutters and block came out in chunks, the ball screws were snapped in two, the machine frame was bent beyond repair. They swapped out the whole section of the block line - under warranty - ouch!. I remember the tech screaming at his design guys "trying to save pennies!" They didn't want the expense of running wire and reference switches or (at the time) much more expensive absolute encoders. It was a loud boom!

  10. #8
    Join Date
    Jan 2014
    Country
    UNITED STATES
    State/Province
    Washington
    Posts
    4,384
    Post Thanks / Like
    Likes (Given)
    803
    Likes (Received)
    2362

    Default

    I was really surprised to find that lots of robotics and positioners used in the semiconductor manufacturing process used stopper type referencing. Lots of times the robot or positioner would be jogged up to a reference fixture until the axes torqued out. The software then set the position to zero and things were off to run. No backing up to an encoder index mark or anything.

    The machine tool industry while usually better is not always good. When I went to Fadal for new dealer tech training session, I was amazed to see their reference method (1960s tech) and the lack of limit switches. Despite that they were telling us techs that they were "on the leading edge of machine tool technology". Half of us in the class nearly choked try to withhold the outright laughter we wanted to let out.

    @OP,

    Is your machine equipped with the MSC802M? If so I have a fair amount of experience with those.


Tags for this Thread

Bookmarks

Posting Permissions

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