MoveSpeed vs Acceleration

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  • MoveSpeed vs Acceleration

    Does anyone know if these values need to be matched in some manner? For no reason I always keep them the same and don't know why.
    The set of XYZ accelerations are all the same and I'm wondering, if they should be that way then why are different settings available for each axis? How closely (if it matters at all) should the MoveSpeed be to the Acceleration values?
    "It ain't what you don't know that gets you into trouble. It's what you know for sure that just ain't so." (Samuel Clemens)

  • #2
    Acceleration is how how quickly the machine can ramp up from 0 to it's set move speed, or back to 0. For example, my Global Advantages have a max move speed of 500 millimeters/second (mm/s), but they can accelerate/decelerate to or from that speed at a rate of 2500 millimeters/second/second (mm/s2).

    I documented move speeds and accelerations for a number of different machines here: http://www.pcdmisforum.com/showthrea...l=1#post338567
    (╯°□°)╯︵ ┻━┻

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    • #3
      Good Reading! Must have taken a while to compile all of that.

      Our 20.40.20 had a DefMoveSpeed of 289 and maxAccel of 462 for XYZ at installation. I usually run @ 150 for all since the carriage has a high CG. I'm just curious if these proportions need to be retained if one or the other is changed. If anything I would think they would be inversely proportional. Don't know if it actually matters but if so I was hoping for some guideline. When using long probe extensions or going into narrow slots I will slow everything down and don't know if I'm doing this correctly.
      "It ain't what you don't know that gets you into trouble. It's what you know for sure that just ain't so." (Samuel Clemens)

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      • #4
        They shouldn't have to be kept proportional. If your machine can safely accelerate at a given rate to one move speed, it should (for the most part) be able to do the same to any move speed it's capable of. If you have an acceleration setting where the machine works reliably and does not false trigger, I wouldn't mess with it anymore.
        (╯°□°)╯︵ ┻━┻

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        • #5
          You can leave these values alone and not worry. They both really only affect move speeds and not touch speeds so as long as your acceleration is not causing false triggers then you're fine leaving it as is.
          Systems Integrator
          Hexagon Manufacturing Intelligence

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          • #6
            Originally posted by ewe0006 View Post
            They shouldn't have to be kept proportional.
            Originally posted by Peter Fuller View Post
            You can leave these values alone and not worry.
            Good enough for me. Time to find something else to worry about...
            "It ain't what you don't know that gets you into trouble. It's what you know for sure that just ain't so." (Samuel Clemens)

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            • #7
              Originally posted by GomoFazter View Post
              Good enough for me. Time to find something else to worry about...
              Then try global cooling, er, global warming, er, climate change, er, climate chaos, er, WEATHER
              sigpic
              Originally posted by AndersI
              I've got one from September 2006 (bug ticket) which has finally been fixed in 2013.

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              • #8
                Originally posted by Matthew D. Hoedeman View Post
                Then try global cooling, er, global warming, er, climate change, er, climate chaos, er, WEATHER
                Well, I do have a GLOBAL and am concerned with temperature. I do have an issue where my TEMPCOMP readings don't seem to agree with the CurTemp & PriorTemp values in the registry. Need to look into that a little more.
                "It ain't what you don't know that gets you into trouble. It's what you know for sure that just ain't so." (Samuel Clemens)

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                • #9
                  Originally posted by Matthew D. Hoedeman View Post
                  Then try global cooling, er, global warming, er, climate change, er, climate chaos, er, WEATHER
                  OR try deciding which restroom you might frequent, worse who (or what) may be there already / arrive after you

                  TK
                  sigpicHave a homebrew

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                  • #10
                    Originally posted by GomoFazter View Post
                    Does anyone know if these values need to be matched in some manner? For no reason I always keep them the same and don't know why.
                    The set of XYZ accelerations are all the same and I'm wondering, if they should be that way then why are different settings available for each axis? How closely (if it matters at all) should the MoveSpeed be to the Acceleration values?
                    I have always been told that what ever speed you are calibrating your probes to is the same speed you should be using when checking your parts...I have heard and read that if you don't it could cause reporting errors, giving you bad data .GIGO!!

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                    • #11
                      At one point, we had a 'sensitive' (overheated/errored out at 'normal' speed) drive motor on the X-axis of our CMM, and it was suggested that we lower the acceleration value on that axis. The CMM is ~30 years old and we have another on order, but the replacement was about 6 months out. The errors have gone away and everything seems to be working fine. Just can't wait for my new 'toy'.

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                      • #12
                        What got me wondering was occasionally getting air hits with longer probe builds having lengthy star tips. I reduced the default acceleration a year ago which helped some (the original values were for a 20.40.15). I never liked the idea of running at full throttle even though it's "rated" for it. I just prefer a smoother transition from the braking through the prehit to the touch - too much mass for me stopping on a dime. From what I can gather the acceleration of any one axis can be anything up to the max without consequence. I would have thought the individual max values would be more dependent on the mass of the axis moving. If accelerating/decelerating less than the max rating is nothing more than a hit in execution speed I can live with it. I don't know if it helps the settling before a touch or bearing life but doubt it hurts any.
                        "It ain't what you don't know that gets you into trouble. It's what you know for sure that just ain't so." (Samuel Clemens)

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                        • #13
                          So if my max velocity is 289 mm/s and max acceleration is 462 mm/s² it takes .625 seconds to reach max speed after traveling 90mm. At that rate a 180mm move would start slowing down just as it finished speeding up. Any shorter distance and max speed doesn't occur for me. At first I thought the acceleration was just a small portion of the overall point to point move time. It turns out to be the majority for the parts I get. Lowering the accel values is a bigger hit than I ever imagined.

                          Velocity & Displacement links:
                          http://www.calculatorsoup.com/calcul...locity_a_t.php
                          http://www.calculatorsoup.com/calcul...ment_v_a_t.php
                          Last edited by GomoFazter; 05-30-2016, 06:27 PM. Reason: added links
                          "It ain't what you don't know that gets you into trouble. It's what you know for sure that just ain't so." (Samuel Clemens)

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                          • #14
                            Has anyone ever experimented with increasing acceleration on one of the new 7.10.7 SF machines? These machines are specd at 1000mm/s2 but I suspect that I can accelerate faster; possibly up to 1250 or more. This is the only hard bearing machine that I have in the shop so not exactly sure what I can get away with. All other machines are air bearing machines. Is false triggering the only observable symptom of accel set too high?
                            2013MR1 SP6
                            Global Frames, Tesastar-M Heads, LSP-X1M/H Probes

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                            • #15
                              Originally posted by DaSalo View Post
                              Has anyone ever experimented with increasing acceleration on one of the new 7.10.7 SF machines? These machines are specd at 1000mm/s2 but I suspect that I can accelerate faster; possibly up to 1250 or more. This is the only hard bearing machine that I have in the shop so not exactly sure what I can get away with. All other machines are air bearing machines. Is false triggering the only observable symptom of accel set too high?
                              You can't exceed the controllers maximum value so it won't make much of a difference.
                              Systems Integrator
                              Hexagon Manufacturing Intelligence

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