Position signals

  1. Hood

    Hood If it walks like a duck....

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    Not sure if this is the place to post this or even if such an enquiry should even be asked on a welding forum :D I know there are a lot of people here with all sorts of knowledge and experiences from different disiplines so...

    What I am wanting to do is make up a compact sensor (for the want of a better word) to inform a CNC control of the position of a lathes tool change turret.

    The turret has 8 positions so I was going to use 4 signals/sensors/switches and use binary to define the positions, table below shows what I mean.

    ScreenHunter_2197 Dec. 28 11.04.jpg

    I have a few options for doing this which are easily within my capabilities but they are not as compact as I would like.
    1 option would be to use prox switches and make up a disc with either holes or triggers (depending on prox type) on the periphery such as in the pics below.
    I could also use micro switches with similar trigger drum, just have to make the transitions more of a cam shape.

    ScreenHunter_2198 Dec. 28 11.07.jpg ScreenHunter_2199 Dec. 28 11.08.jpg

    The micro switches would probably be the more compact as they would allow me to have a slightly narrower cam/trigger wheel as switches are about 6.5mm wide where the prox's I have are 8mm thread so 10mm per prox would be required.Also the length of the prox's are much more than the height of the micro switches. Prox however would probably be more resillient in the long term and certainly easier to adjust if that were required.

    I was however thinking of making up a slotted disc, sort of like an encoder disc and using optical switches but so far I have not really found anything suitable and that is the reason I am posting here.

    Using 4 slotted optical switches would likely not make things any more compact as the size of the disc would have to be quite large to accomodate them so I was wondering if anyone knew of a single bodied switch with 4 optos built in. I have done a Google search but my terminology is obviously wrong as I keep getting hits for network switches :D

    I really need the optos to be able to handle 24v from the sourcing Input of the CNC and I am not really great with electronics so I am not sure if such a thing even exists. I could probably however use an optocoupler such as the PC817 I have used in the past to convert 5v encoder signals to 24v for sinking inputs on a CNC control.
     
  2. rtbcomp

    rtbcomp Moderator Staff Member

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  3. pressbrake1

    pressbrake1 Forum Supporter

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    essex england
    I’d use a single proxy for counting and one for orientation ie one disc with eight lobes with the extra sensor allowing orientation using a and gate configuration to be able to recognise no1 tool

    Or
    Multi disc arrangement like you have drawn with proximity switches on each tool position with one for orientation but like those euchner boxes found on old nc
     
  4. What movement does it have, rotational or linear? How far does it move between positions?

    How about a photo of the turret etc?

    What signal is the CNC controller expecting from the turret?
     
  5. Assuming it is rotational, it would be a simple matter to couple it to a potentiometer. Read the value with an Arduino and job's done. Software for that would be trivial "READ,IF, THEN,RELAY ON"
     
  6. Maker

    Maker nEw mEmBeR

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    I believe it rotates further than a pot but an optical encoder would do it, just slightly more complicated control circuitry than Hoods idea.
     
  7. So gear the pot down to give 270 degrees for a full rotation. It perhaps could be done with a rubber idler wheel in contact with the turret.
     
  8. Seadog

    Seadog Forum Supporter

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    You're assuming that the rotation isn't a continuous 360°
     
  9. Hood

    Hood If it walks like a duck....

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    The turret is made by myself, pic and video below. It uses an Indexing servo drive to position it so the feedback is only to let the control know the correct position for safety purposes.
    The turret clamps/unclamps via hydraulics but the part I would be putting the switch/sensors on will only have rotational movement as I have a splined coupling in the drivetrain to allow the turret plate to move out/in without affecting the drive.

    ScreenHunter_2200 Dec. 28 12.31.jpg ScreenHunter_2201 Dec. 28 12.32.jpg



    The signals the control is looking for can probably be anything if you are clever enough with macro programming and understanding Chinglish but basically the inputs are as below.

    ScreenHunter_2202 Dec. 28 12.36.jpg
     
  10. Hood

    Hood If it walks like a duck....

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    Yes rotaion needs to be full rotation in either direction as will be seen in the video.
     
  11. Hood

    Hood If it walks like a duck....

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    11,323
    Location:
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  12. It matters not. Wherever the turret happens to be, there will be a corresponding analogue Voltage. That fed into the Arduino's AD converter will report the exact position. Feed the Arduino into simple relays to provide the isolated inteface to the controller. If you like optical isolators, use those instead, but I like a physical switch personally.
     
  13. awemawson Forum Supporter

    My 12 position turret on my Beaver TC-20 uses a 'hedgehog drum' with rectangular pegs sticking outwards sensed by extremely expensive Balluff proximity sensors in a special adjustable housing.

    :sheep::sheep::sheep:


    BES 516-B4 T0B-08-650-#4.jpg
     
  14. Hood

    Hood If it walks like a duck....

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    What I mean by full rotation is there can not be any stops in the switch as it needs to have full rotation as it can, for example be on tool 1 and I call tool 2 and it will move clockwise (looking from front) If I then call tool 8 it will go anti clockwise past tool 1 and on to tool 8 .
     
  15. Seadog

    Seadog Forum Supporter

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    It does if it rotates 400°, or 720°, or 5000° or whatever. How is a standard pot going to cope with that?
     
  16. So to sum up, a 2:1 reduction idler wheel in contact with the mechanism that runs 360 degrees. Medium value potentiometer fed from the Arduino's stabilsed supply and wiper fed to AD converter. Outputs from Arduino fed to a relay board (cheaper than building the relays with drive transistors yourself) and connected to the CNC controller.
     
  17. Hood

    Hood If it walks like a duck....

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    Location:
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    Yes that is what I was kind of going to do with the prox switches but I am trying to make it as small and compact as possible as I don't really want to have to alter the covers too much. With Mach I didn't bother too much about feedback as the servo drive provided the feedback and if anything failed the chances are it wouldn't clamp properly and thus throw an error as the clamped signal wouldn't be seen. The Chinese controller I am considering fitting however seems to prefer that I have proper position feedback although I think possibly it may not really be required.
     
  18. I was under impression that the turret rotates 360 degrees and back, but just to be clear, are you saying that it can do many complete revolutions?

    Edit:

    I see that it does go past 360 degrees, so will rethink it!
     
  19. No stops on a potentiometer, which is why I suggested it. You can sense the position to the nearest degree if you needed to.
     
  20. Hood

    Hood If it walks like a duck....

    Messages:
    11,323
    Location:
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    Yes it needs to be capable of continuos rotation. It will never keep rotating as the most it will ever move between a tool change is 4 positions as it takes the shortest route but there is never a position in the rotation that it will not go past hence it needs to be capable of continuous rotation.

    Clear as mud :D
     
    eLuSiVeMiTe likes this.
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