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Machine Tool Repair

Discussion in 'Troubleshooting and Repair' started by Machine Doctor 13, Jul 13, 2019.

  1. Machine Doctor 13

    Machine Doctor 13

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    Jul 13, 2019
    I want to replace an antiquated stepper relay with something more modern. The stepper relay is being used on an older Mazak turret lathe to give feedback to the CNC control and tell it what tool station is currently active.

    The CNC control sends a 2 second +24 VDC signal to the coil of the stepper relay each time the program calls for a different tool to be used and their are 8 tools. I'm thinking their might be an 8 channel multiplexer circuit I can used such that every time a new tool is commanded a signal advances to another output from 1 to 8 depending on the tool desired.

    Any ideas will be greatly appreciated.
     
  2. Minder

    Minder

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    Apr 24, 2015
    The best idea is to use the logic in the ladder, but unfortunately, Mazak which uses their own version of Mitsubishi control, makes it hard for any on-site changes to ladder.
    You may have to make use of the 2sec signal into a separate outboard PLC controller.
    Modern T.C. generally put tool away at the nearest empty pocket, and keep track of all tool positions, rather than travel around the carosel etc.
    If familiar with PLC programming that may be the cleanest way.
    M.
     
  3. Machine Doctor 13

    Machine Doctor 13

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    0
    Jul 13, 2019
    I'm looking at a 4017 Decade Counter. This just might work.
     
  4. 73's de Edd

    73's de Edd

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    Aug 21, 2015
    Sir Machine Doctor . . . . . . (C'mon . . . . .show me YOUR confirmational sheepskin )

    I was just reading as you wanting to replace an electromechanical. . . . old school . . . stepping relay. . . . Click (step). . . .Click (step) . . . Click . . . .(step) . . . .Click (step) . . . . . . . . . .CLUNK (reset) . . . with a silent all electronics solution.
    BUT . . . how many poles does it have with those 8 positions, and is it being uni (resets and counts up )or bi directional ( reversible direction, to take the shortest route) drive on the tool selection?

    73's de Edd

    Want to REALLY stymy someone . . . . .Send them a text message of . . . ." Ignore previous message. "
    Then you ignore all of their callbacks.
     
    Last edited: Jul 15, 2019
  5. Machine Doctor 13

    Machine Doctor 13

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    Jul 13, 2019
    Kind of a witch doctor. And looking for other ideas so not a genius either.
    It is unidirectional. Only counts up so right now I'm looking into using a 4017 Decade Counter which was suggested by two people.
     
  6. Machine Doctor 13

    Machine Doctor 13

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    Jul 13, 2019
    I constructed the attached circuit on a breadboard and it works. The clock pulse to the 4022 is + 15 VDC and the outputs from the 4022 are also + 15 V. The outputs from the 2981A are + 15 V too but I need to convert them to + 24 V for the CNC control board inputs.
    Any ideas would be greatly appreciated.
     

    Attached Files:

  7. Tha fios agaibh

    Tha fios agaibh

    1,918
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    Aug 11, 2014
    I haven't looked at the specs but a uln2003 driver may work for you.

    edit : With, but not in place of the 2981a
     
    Last edited: Jul 26, 2019
  8. Martaine2005

    Martaine2005

    2,405
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    May 12, 2015
    It appears this thread has a twin sister..and answered...

    Martin
     
  9. 73's de Edd

    73's de Edd

    2,726
    1,114
    Aug 21, 2015
    Sir Machine Doctor 13 . . . . .

    You say . . . . .
    The outputs from the 2981A are + 15 V too but I need to convert them to + 24 V for the CNC control board inputs.

    I don't know if you already have found a 2981A . . . . from old stock, but that chip will accept +24VDC (on upwards, to just under +50VDC) as its supply . . . .vice your now provided +15.
    What you REALLY need to do is delve into the machine and evaluate its existing stepping relay and its rotor that sequentially swings into 8 contacts.
    You need to go to . . . .say . . . . .tool position #1 and put a small insulative shim of plastic to open the stepping relays contact then being made.
    THEN you shunt an ammeter across the now opened contacts in order to see WHAT level of current is being involved / consumed with that +24 VDC supply.
    ( Or it might even happeen to be AC on that entirely separate circuitry .)
    The sections of the 2981A can handle up to 500 MA at that 24 VDC, if you find more that that level being consumed, more power buffering will be needed in addition to the 2891A's output capability.

    I have see stepping relays used in telephone centrals of the past, pin ball machines,.juke boxes for coin counting of plays left, but those were all way back in the 1930's on up thru about the 60- 70's ? ? ? ?, as the latest.
    The last ones I ever have seen recently were akin to this 12 pole one, and note its selenium rectifier for AC--DC conversion of its coil driver power :

    What does your units look like ?

    References . . . . .
    ULN2981A Da Da Sheet

    https://www.jameco.com/Jameco/Products/ProdDS/1762681.pdf

    60-70'ish vintage Stepping Relay . . . . .
    upload_2019-7-27_7-53-32.png




    73's de Edd . . . . .

    HEY . . . . . I just found out that this post is being duplicated between 2 places ?



    Beware of people who are ignorant without having come by their ignorance the hard way.




     
  10. Machine Doctor 13

    Machine Doctor 13

    7
    0
    Jul 13, 2019
    I installed the attached circuit on the old Mazak turret lathe and it works 80% of the time. Here is the sequence:

    1. The machine has a relay shown on page 1 bottom left labeled INDF which sends a +24 V signal to a voltage divider to produce a 12V clock pulse every time a tool change is called for. There are 8 tools on a turret.

    2. Every time there is a clock pulse the 4022 outputs sequentially go high to + 5V from 0 to 7 for the tool being selected.

    3. The corresponding outputs from the 2981 go high to + 24V and turn on the relay for that particular tool.

    4. The output from the relay that is energized goes to the machine CNC control and is displayed on the operator monitor as the tool number that is currently active. That is the sole purpose of this circuit. To provide feedback to the operator as to what tool is currently

    The circuit works fine 80% of the time, but occasionally when the clock signal goes from + 24V to 0V it acts like another clock pulse. So if you are using tool 2 and wish to go to tool 3 instead the relay for tool 4 turns on and the operator display shows tool 4 is active even though on the machine tool 3 is active. The ascending slope of the clock pulse is working good but sometimes the descending pulse is triggering the 4022 again.

    To verify that this is what is occurring I installed a push button to simulate a clock pulse (shown lower right pg. 1). If I hold the push button in for 10 seconds or so the next relay led turns on as expected, but occasionally when I release the push button the next relay led lights up. So I know it is activated by the descending slope of the clock pulse.

    What I am wondering about is the fact that the 4022 is using a + 5VDC power supply with VSS (pin 8) connected to the negative terminal of the power supply, not ground, whereas the 2981 is connected to ground for pin 10.Is this a possible problem? If not any ideas on eliminating this occasional extra clock pulse?
     

    Attached Files:

  11. 73's de Edd

    73's de Edd

    2,726
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    Aug 21, 2015
    Le Machine Docteur . . . .

    HOLY . . .GUACAMOLE ! . . . . . . aren't you "Whacking that mole " (4022) quite HARD in the respect of hitting it with a full 24V logic level, into it.
    Also, I don't see any good logic housekeeping, in the respect of sweeping its different I.C.'s Vcc power supply buss clean, with a CLOSE to the pins mounted, Low Freq bypassing with a 10 ufd E-cap and a like Hi Freq shunt 0.1 ufd ceramic placed across it .

    I see that you dropped the clock input level in, to HALF level , with that pair of 100K voltage divider resistors.

    Now, look at the input specs on that 4022 and you will see that its input likes to see a HI level of 3.5 thru 11, with 7 being in the middle of the spec and LOW level of 1.5 thrru 4 with 3 being in the middle of that spec.
    Experiment with a like resistive voltage divider, to see if you might get down to that logic level spec , and see what that does for your phantom situation .
    If that doesn't clear all up for you, lastly you might feed your reduced machine logic input, into a CMOS logic one shot or CMOS 555 in a one shot configuration, to thereby totally clean up that input pulse.

    REFERENCE . . . .

    upload_2019-8-1_0-56-50.png




    Thaaaaaaassssssit . . . . .


    73's de Edd . . . . .



    Physically fit . . . . . PHYSICALLY FIT ! . . . . . Me, I'm just physically . . . . . pffffffft !



     
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