Proportional hydraulic valves - digger

Discussion in 'The Projects Forum' started by GerryR, May 21, 2014.

  1. GerryR

    Thread Starter New Member

    May 21, 2014
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    Hi,
    I have a mitsibushi 4 ton digger and the electronic valve controller was stolen from it which renders all the joystick functions useless. Apparently this was an imported machine and the part is not even available in Japan, where it originated from. Caterpillar parts are not compatible either.

    I have managed to get schematics and info on the system and I would like to bypass this missing part. The potentiometer joysticks operate on a 5v circuit putting out a range from 0.35v to 4.65v. The bank of 4 proportional valves however are activated by 10 – 12 volts. Can anyone suggest a circuit or a system to replace the missing part. I am a computer technician so I should be able to do some limited technical work on it.

    I would be most grateful if you can help,


    Thank you

    Gerry
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
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    These proportional valves are usually operated with ±10vdc analogue controllers.
    In your case is sounds like ±5vdc for the input.
    Is the original system a closed loop type, IOW is there a feedback from the cylinders etc.
    Or does the joystick move the cylinders in a speed proportional to the joystick and when the stick is released the cylinder is locked, hydraulically?
    A little H bridge PWM controller with a 555 PWM generator may be the answer.
    Max.
     
    Last edited: May 21, 2014
  3. GerryR

    Thread Starter New Member

    May 21, 2014
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    Thanks for your prompt reply.
    The valves move in proportion to the joysticks and return to zero position when released. Each valve has 4 cables. When the joystick is pulled rearward, for example, the power is applied to the valve using two of the cables in proportion to gradual movement of the joystick and operates a two way hydraulic ram in one direction. When the joystick is pushed forward, a different signal is produced which utilises the other two cables, moving the valve in a different direction to operate the ram in the opposite direction. There are two joysticks with six cables each (Power, GND and 4 signal, I presume). Can you advise on how to make this as I have little previous knowledge.


    Many Thanks
    Gerry
     
    Last edited: May 22, 2014
  4. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Do you have a part No for the valve?
    By 'Return to zero position' I assume when the J.S. is released the actuator stop dead at that point?
    Also if any electronics appears to be attached to the valve or does it just terminate with a couple of connections?
    It would help to post or make available any copy of the schematic if possible.
    I am used to working with prop valves with feedback, but I guess with power equipment, operator eye sight is the feedback for necessary control. :)
    Max.
     
  5. GerryR

    Thread Starter New Member

    May 21, 2014
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    When the JS is released the actuator moves to close the valve and the hydraulic ram stops (ie if the electronics were present that's what is supposed to happen) There are only cables left hanging as the electronics box was stolen. There are four hydraulic proportional valves in the one unit and I am unable to identify it at the moment. What power do prop valves normally require to operate and is it continuous or pulsed and does each valve require its own electronic device or can all controls be incorporated as a unit?

    Thanks
    Gerry
     
  6. MaxHeadRoom

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    Jul 18, 2013
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    As in post #2, the valve itself is controlled a ±10vdc voltage that operates a pilot spool either side of zero, the ±10vdc move the spool proportionately in either direction by an amount equal to the DC applied.
    A return to centre (zero) stops the cylinder motion.
    So the power to the coil itself is usually a analogue (proportional) signal.
    But a PWM type should work equally well presumably.
    It would be best if you can obtain a make/part # for the valve.
    Max.
     
  7. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
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    Check with MOOG corporation for proportional valves....they aren't cheap..but precision hydraulic stuff seldom is. They probably have a suitable substitute.
    Eric
     
  8. MaxHeadRoom

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    I take it he still has the valves, it is the controller that is missing as I read it?
    Max.
     
  9. John P

    AAC Fanatic!

    Oct 14, 2008
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    So how much current do these valves take? I assume since they're solenoids, it's significant, more than an op amp can produce. But still, boosting 5V up to +/- 10V with 250mA capacity is pretty easy stuff. But is it really a single-ended input and bipolar output, and what is the neutral (i.e. valve is closed) level coming from the pot?

    I can imagine that if you have to test a control circuit for a powerful machine that can do serious damage, you'd need to be feeling adventurous!
     
  10. MaxHeadRoom

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    Jul 18, 2013
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    In most servo valves the solenoids are operated by a pilot spool so the current is less significant that a large direct solenoid.
    Traditionally it has simply been done with a op amp operating a small push-pull transistor drive, but in mobile equipment the luxury of having +12v/-12v supplies is not available.
    In this case it sounds like just the on board 12v supply.
    The valve controller on the original sounds like single ended with 0-5v input but I am wondering if they split the 12v to provide +/-6v with a 0v reference, and on mobile equipment, the centre has to be servo off or equivalent so that the main cylinder is locked hydraulically.
    Details on the actual servo valve would help greatly. part No etc.
    Also confirmation of exactly how the J.S. are set up at present, if simply just one POT with centre off or? and if a off position detection switch is included, which it sounds like it has by the edits.?
    If the OP can include the original schematic here is would help greatly.

    I re-read the posts and see a couple of edits so some has been cleared up.
    Max.
     
    Last edited: May 23, 2014
  11. Alec_t

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    Sep 17, 2013
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    I like the 'can-do' attitude, but a 4-ton digger is a mean beast. Before getting too far along the DIY path, is public liability insurance involved here? If so, would the insurer accept a DIY fix?
     
  12. GerryR

    Thread Starter New Member

    May 21, 2014
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    Regarding insurance, this is my own digger operated(hopefully) by myself on my own farm, so I guess insurance is not an issue.
    I fed a 12 v supply to the joysticks which produced around 6v in neutral, 1v when moved fully in one direction and 11.4v when moved fully in the other. This was only for testing purposes so I hope I have not done any damage as the output cables were not attached to any electronics (other than my meter) I will try the same test using a 5v supply which I believe is supposed to be used.
    I'm not sure if the solenoids depend on ±10v as there are 4 cables to each valve. Two of which, when fed battery power, operate the valve in one direction and the other two cables operate the valve in the opposite direction. So perhaps it is simply +12v supplied to both cables alternatively.
    I'll try and ascertain the valve make/model shortly.
    I have attached some schematics for the original configuration which include other safety controls such as controlling levels and grading slopes which I don't require.
     
  13. MaxHeadRoom

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    In the mean time I will peruse the PDF's.
    Max.
     
  14. Alec_t

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  15. MaxHeadRoom

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    After looking over the prints, it is as I suspected, that each J.S. has 0-5v across it with the centre position at 2.5v, moving the stick off centre engages a momentary N.O. switch used to indicate the direction of travel.
    And the prop valves have two coils, one for each direction.
    The J.S. would have gone into some form of analogue/op-amp/processor input that fed the indicated device and direction signal to a 0-10v amplifier that would have enabled/operated the coil indicated by the J.S. dir switch.
    The hydraulic cylinder would move in the dir and rate indicated by the J.S. and associated sw.
    When neither switch is made, the power would be removed from the coils and the spool would return to the centre, effectively locking the Hyd cylinders
    The system appears to have had some form of central processor together with means of operation safety.
    Also it may be required to interlock some functions, IOW not allow A Cyl to operate if B Cyl is in progress.
    In light of the above, although it could possibly be made to operate in a simple fashion, to implement anything like the original set up, it would really require have hands on when implementing any new design process, IMHO.
    Max.
     
    Last edited: May 24, 2014
  16. John P

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    Oct 14, 2008
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    My experience with electronic circuits operating machinery is that the safety requirements are two independent control or sensing systems, and they have to agree in order for the machine to be allowed to run. The idea is that no single point of failure can create a dangerous condition. So with a medical positioning system I worked on, there was an encoder on the back of the motor, and another one on the axis being controlled, and they had to agree within a certain amount (to allow for backlash in the drive) or the machine wasn't allowed to move.

    With this earth-moving machine, you might run the solenoids from an op amp circuit with the potentiometer as input, but then you could back-calculate the voltage that should be coming from the pot, based on the voltage being sent to the solenoid. Then there would be a couple of comparators verifying that the actual pot's output falls in a narrow range close to the calculated value, and if they don't match, a relay drops and the drive to the solenoid gets cut off. Note "a relay drops"--the relay should need power in order to run the machine, not to stop it.

    If you're going to trust your life to this system, you'd better be 100% sure that it'll never get out of control. Think what the newspaper would say: "He was operating a piece of hydraulic equipment for which he'd built his own control circuit, when suddenly the machine..."
     
  17. crutschow

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    Mar 14, 2008
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    From the safety point-of-view it would be good to have a large "kill switch" button close to the operator if all else fails. [​IMG]
     
  18. GerryR

    Thread Starter New Member

    May 21, 2014
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    All of these potential hazards are based on the assumption that I will get the machine going again. I'm willing to take my chances, besides I already have the kill switch within inches of my right hand.

    I took some joystick measurements using 5v input which yielded signals from 0.02 on one side to 2.4 in neutral and 2.55 on the other side.

    I wish I had you guys here to tell me what to do next. I have accounts with RS Components and CPC Farnell in the UK, if they can provide the necessary items. Alternatively I'm open to suggestions from any interested parties who think they can construct something that'll work. The "simple" option appeals to me right now Max.

    I'm still willing to learn.
    Many thanks for your interest,
    Gerry
     
  19. Alec_t

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    Is that 2.55 figure correct? I would have expected at least 4.5.
     
  20. MaxHeadRoom

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    Looking at the prints it I believe it should be

    Also is it Hydrostatic drive? It appears to be a controller for it also.
    Max.
     
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