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  • Question for 3 phase light bulb

    In one of the postings I saw that you had a Prototrak SMX controller on your Bridgeport mill.
    I have an earlier AGE controller on a Prototrak K3 mill that has worked great since I bought it new.
    Now, the CRT is starting to go bad. I can buy an LCD direct replacement from a third party for about 1.1K
    or, upgrade all together with their new KMX offering for 5.5K. The KMX is very similar to your SMX
    controller.
    The one thing I was surprised to find out was that the new controller does not use any feedback from the table via scales, glass, magnetic or otherwise.
    They only read off the drive motors. My system now reads table position.
    I know the "open loop/closed loop" issue has been ongoing since day one of CNC.

    My long winded question is: Do you have any issues with your system? I'm looking for people that have real experience with them.
    Naturally, my inquires to Prototrak, assures me that the open loop arrangement works just as well as what have now.
    There are some definite advantages to upgrading, besides this possible issue.

    What say you, or anyone else that has any actual experience?

    Thanks, Sid

  • #2
    the motors almost certainly have encoders in them. its up to you to ensure the ballscrews have no backlash.

    anyhow, are you sure you can't buy an industrial lcd or a converter box to use a regular lcd for a lot less than 1.1K?

    Comment


    • #3
      I agree, if the motors are servo's rather than steppers, there has to be something to close the PID loop, there are motors out there that have a internal controller and the encoder also is internal to the motor housing itself, but these are a bit of an exception.
      Max.

      Comment


      • #4
        Like the other guys say, the motors almost certainly have encoders on them. Relying on just scales makes a machine with very low performance because you have to deal with whatever lost motion there is in the ballscrew and bearings.

        What is the part number of the monitor that is going south? It is probably repairable too, chances are it is just capacitors getting old. If not you can get display adapters that will drive new monitors from a variety of odd ball scan freqs. I used one of these XVGA Boxes to make a LCD work with a Fanuc control with a monitor with a dead red gun:

        https://www.aliexpress.com/cheap/che...a-adapter.html

        Amazon has them too, little bit more but probably faster shipping: https://www.amazon.com/s/ref=nb_sb_s...d=67754Y5R0PBR

        Comment


        • #5
          Originally posted by sid pileski View Post
          My long winded question is: Do you have any issues with your system? I'm looking for people that have real experience with them.
          Naturally, my inquires to Prototrak, assures me that the open loop arrangement works just as well as what have now.
          There are some definite advantages to upgrading, besides this possible issue.

          What say you, or anyone else that has any actual experience?

          Thanks, Sid
          I don't have any accuracy issues at all with my 3-Axis ProtoTrak SMX. Everything has calibration constants/coefs applied for all 3 axis. When I use the electronic hand-wheels for manual operation, it feels like the table weighs nothing and there is zero backlash, and you never need to lock the table as it's always rigid while milling. The ball screws and E-wheel controls are amazing. It's a perfect milling machine for both manual and CNC. The only issue is tramming the head is a PITA because you need to remove some of the Z-axis hardware which cover up some of the head bolts -- but I've only had to tram the head once. As far as programming goes, it's extremely easy and very fast as you can switch to different views (2d, 3d, tool path, cut path,etc.) while entering each mill, drill, arc, pocket, etc operation. I also have the DXF option so I can import DXF drawings but haven't needed to use it yet.

          EDIT: I forgot to mention the ProtoTrak SMX (A Retrofit kit like mine) uses Accu-rite glass scales for X, Y, Z feedback/DRO.

          Adrian
          Last edited by 3 Phase Lightbulb; 09-15-2017, 11:31 AM.

          Comment


          • #6
            My 2 axis EZTrak has encoders on the servos. I haven't had any accuracy issues either.

            Comment


            • #7
              Originally posted by 3 Phase Lightbulb View Post
              I don't have any accuracy issues at all with my 3-Axis ProtoTrak SMX. Everything has calibration constants/coefs applied for all 3 axis. When I use the electronic hand-wheels for manual operation, it feels like the table weighs nothing and there is zero backlash, and you never need to lock the table as it's always rigid while milling. The ball screws and E-wheel controls are amazing. It's a perfect milling machine for both manual and CNC. The only issue is tramming the head is a PITA because you need to remove some of the Z-axis hardware which cover up some of the head bolts -- but I've only had to tram the head once. As far as programming goes, it's extremely easy and very fast as you can switch to different views (2d, 3d, tool path, cut path,etc.) while entering each mill, drill, arc, pocket, etc operation. I also have the DXF option so I can import DXF drawings but haven't needed to use it yet.

              EDIT: I forgot to mention the ProtoTrak SMX (A Retrofit kit like mine) uses Accu-rite glass scales for X, Y, Z feedback/DRO.

              Adrian
              I agree. I love my Prototrak for the type of prototype/real short production work I do. It serves all that I ask of it, it's just that the CRT is getting dim. The upgrade does offer some more functionality than I have now. One of the biggest being that I would get a USB port rather than the 3.5 floppy drive!
              My guess is that they would not come out with something (they stopped using separate table scales before this model offering) that did not work as well.
              Yes, the motors use some sort of encoder internally, and all of their systems use ball screws, including mine now.
              I guess my apprehension is stuck on the possibility of play in the system and open loop.

              Sid

              Comment


              • #8
                The ProtoTrak SMX units use high power servo drives. I'm not sure if they have encoders in the drives or not. There are several calibration coefficients that get setup when you run the automatic Servo/Travel/Position calibration. The SMX documentation also mention that the have very sensitive current sense amps for the servo drives so I assume they can easily use proportional/integral current control for very accurate and efficient table movement.

                Comment


                • #9
                  On the subject of floppy drives, if its a standard unit, there are alternatives that go in place of them which take a usb stick and look like a standard floppy drive to the original hardware, which are *very* reasonably priced now.
                  I run my old 90's retro computers with usb stick drives emulating floppies, because floppy corruption is a pain. In fact the only thing I have left with floppies still is my sodick wire edm which sadly has very non standard drives in it's oddball japanese market only computer (nec PC98, the oscillator to keep timing between computer and drive is on the drive and they spin at a different speed) and conversion of such to the same still eludes me.

                  Comment


                  • #10
                    IIRC the PC floppy interface only has ~16 control/data signals. The ~32 or 34 pin ribbon cable is mostly ground lines. I think a Raspberry Pi 3 has enough GPIO available that one could probably bit-bang the Floppy control/data signals. So one could wire up a Raspberry Pi 3 to the floppy interface and with a little bit of software, bit-bang the floppy controller and using the built in WiFi on the Pi3 and mount an NFS or Samba share on someones workstation. No need to walk around with a silly USB stick

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                    • #11
                      If you are using modern brushless servos they have encoder outputs. They will give you motor motion, and not indicate any backlash. If you use glass scales instead of the motor encoder outputs you will see only any backlash there might be in the glass scales, (very little...) and, if the glass scales are of sufficient resolution they will give you more accuracy than will the motor encoders.

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