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  1. #41
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    Using 4000 series logic chips a 4069 inverting buffer will give you the NOT and a 4081 will give you the AND. You could also get it done with only three transistors. Or you could search for a sigle or dual package as these chips have 6 NOT gates and 4 AND gates, respectively. So they are a bit overkill. I don't have time to elaborate now, maybe this afternoon.

    Matt



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    Community Moderator Al_The_Man's Avatar
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    Why use hardware logic when EMC has a PLC type Ladder for I/O processing, this is boolean in software form, at least it shows one on their web site.
    If you use the DC coils, it will also prevent burn outs caused by sticking spools, or someone 'inadvertently' pushing the spool over when the other side is picked up.
    Al.

    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
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  3. #43
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    Al

    While I agree that it would be easier to accomplish in software, it seems that has failed once already. I agree with supahonkey that EMC should not be able to energize both M3 and M4 at the same time, but something caused the failure. The problem might be mechanical (sticking valve) as you said, which would fry the solenoid no matter the circuitry.

    It seems it would be worth while to switch to DC coils to eliminate this costly failure. You already have a valve with DC solenoids so you might as well use it. Or you could replace the burnt AC coils with DC coils and avoid redoing any plumbing.

    On another note, I think it would be possible to achieve servo valve motion from a standard valve by using a servo motor to actuate the valve and controlling the servo motor from within software. This would add some complexity but might make for a nicer bender.

    servo motor and encoder $150
    surplus manual control valve $50
    power supply for servo motor $60

    Then you just need to devise some way of connecting the two so the motor could control the manual valve. It may not be worth doing but if you have more time than money, it would be a nice addition.

    Matt

    Last edited by keebler303; 12-02-2008 at 06:01 PM.


  4. #44
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    Quote Originally Posted by keebler303 View Post
    Al

    While I agree that it would be easier to accomplish in hardware,
    Matt
    I think you meant to say software??

    There was a company some time ago that came up with a servo valve the spool was stepper motor actuated, this reduced the servo valve cost drastically, I kept tabs on them for a while and I believe they have been taken over, if they still exist, I will see if I can dig up the info.
    They developed this long before Mach was even thought of, had they brought it out now, it would probabally have taken off.
    Unfortunately it look like they folded in 2007.
    http://www.victorycontrols.com/
    Al..

    Last edited by Al_The_Man; 12-02-2008 at 05:46 PM. Reason: Added Stepper Valve info
    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.


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    Yep I meant software.

    I'm trying to visualize how you could hook that up in EMC. I am not sure if you could control it in EMC or not.

    The number of steps the valve took would be proportional to the command signalfrom the control loop? Then it would have to step back toward zero as the cylinder reached the correct position. I think this could be done in Mach with a macro, if you could acquire the encoder signal. I don't know if you can do your own code development in EMC, I've never used it.

    Matt



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    I assume you are talking of the present set up now? with the valve on/off and an encoder feedback through the parallel port, if possible.
    I also have not used EMC or familiar with the ladder logic feature, but I would look into the EMC ability to input a differential input through the parallel port, which it apparently has, at least for PWG control.
    If a M code to start the valve A coil (fwd) was used.
    When a pre-programmed position was reached with the encoder, a coincidence bit would be set and programmed into the logic rung, this would turn off the A coil and energize the B coil to return the cyclinder to zero position.
    This is all conjecture as to whether this route is possible, but it is just one avenue to explore.
    Al.

    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.


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    I am talking about the stepper servo control. It would not be like a conventional "move x steps to go y distance" control. You would have to take x steps, then take x steps backwards as the angle approached the setpoint. I am curious as to whether or not this can be done in EMC, or Mach for that matter. The number of steps forward or backward would have to be proportional to the output of your control loop which looked at what the angle is now and where you want to be.

    Now that I think about it, maybe a 2 valve approach would work pretty well too. Have a large valve to make the majority of the bend quickly, then close that valve and open a valve with a restriction when you are say, 5 degrees shy of your target. Then you will decrease the speed at the last bit and will be much easier to hit your target each time. Sound plausible?

    Matt



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    Quote Originally Posted by keebler303 View Post
    Now that I think about it, maybe a 2 valve approach would work pretty well too. Have a large valve to make the majority of the bend quickly, then close that valve and open a valve with a restriction when you are say, 5 degrees shy of your target. Then you will decrease the speed at the last bit and will be much easier to hit your target each time. Sound plausible?

    Matt
    That approach could work also, a flow control valve would meant another output.
    But In this application, I would think that a single acting main valve (one coil) would work to decrease the output # burden.
    IOW, the pressure would always normally be on for the piston retract.
    The single coil activation would place the cyclinder in the Forward stroke, and the subsequent flow control valve, until the position is reached.
    The only reason that you really need the double acting closed centre position, is if you want to stop the cylinder anywhere in its stroke and lock it there.
    Al.

    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.


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    Quote Originally Posted by Al_The_Man View Post
    decrease the output # burden.
    Its not as if you are hurting for outputs, you've got 10 free even after a double acting valve.

    Matt



  10. #50
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    I'm just thinking a double acting valve may not be necessary.
    Al.

    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.


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    I've never used a bender before but I think some designs might require removing the tube or at least loosening the follower die prior to retracting the ram. I think it would be nice to be able to stop it for whatever reason (check angle, adjust something, etc.). I guess you could always turn off the pump though if you really wanted it to stop mid stroke.

    Matt



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    Yes, if you needed to incorporate some kind of manual jog, fwd/rev, then the double acting would be needed here also.
    Al.

    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.


  13. #53
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    Quote Originally Posted by Al_The_Man View Post
    Yes, if you needed to incorporate some kind of manual jog, fwd/rev, then the double acting would be needed here also.
    Al.
    I must have the ability to stop at any time to check an angle. Most of the work I do won't need repeatability (i.e. building a roll cage for my Jeep). I also am retaining manual control by means of a foot switch. The valve must be of a tandem configuration. Because the valve is spring centered, fluid from the pump automatically dumps to tank. Ports A and B are locked in "neutral".

    Per your discussions, I still don't know if I will be able use Mach or EMC to actually do custom programming. I like Mach because it is easy to change the interface. I have been considering going back to Mach. I know it can't reliably handle encoders, but I am hoping that rule applies when an encoder must rotate quickly. My encoder rotates 95 degrees in 15 seconds. It will never exceed that amount of rotation.

    I will consider a servo valve down the road. I must get my project complete so I can turn it in.



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    For your grade, worst case, you can use limit switches to stop the ram. You might look into a solution using something like this:

    http://www.usdigital.com/products/in...rial-bus/ad4b/

    You could probably interface the serial port to mach using a macro if nothing else. It seems a bit pricey but might get the job done if you really need it.

    Matt



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    Default The problem with using Mach3

    Just reading on your post and it is very interesting.

    Thought I would chime in here on Mach3, it will read encoders, that shouldn't be a problem. The problem is what it will do with that information.

    All Mach3 will do with encoder inputs is display the inputs, it will not do closed loop control with them. So if you wanted Mach to look at the encoder input and stop when you reach a certain setpoint, its not going to happen.

    What Mach can do is output a pulse train that corresponds to a desired movement. It has no feedback loop control.

    I am not familiar with EMC so I can't comment on it.

    One poster here mentioned something about using a stepper motor to manuver a limitswitch to a desired point and using that as the controlling
    element for the control valve, that should work ok.

    I have 3 machines I can use mach3 on.

    Arnie



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    Quote Originally Posted by aminear View Post

    Thought I would chime in here on Mach3, ...

    Arnie
    You are right that it will not do closed loop control. However you can use it for an MPG. That being said, I am pretty confident that the variable associated with an encoder input would be available to a user defined macro. It won't do it out of the box, but with a little work with VB, I think it could be done.

    Matt



  18. #58
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    I also have a JD2 bender. I've been talking about adding hydraulics for a while, but for the little bit of bending that I do, that in it's self is overkill.

    But my friend asked why not CNC it with Mach3 using a servo to actually power the hydraulic pump and the servo's encoder on the pivot pin?

    My answer was I'm not sure if that would work. I would probably need a 1hp servo and a servo drive which could accept a step/direction input, but I'm not so sure the servo/encoder would work properly seems how it may take 2000 steps to get the pump up to enough pressure to move the cylinder and start bending, then maybe 50 steps per encoder line to bend 1 degree, or something of the sort...

    What do you guys think? I doubt the servo/encoder would work properly seems how it would be erratic vs. having a servo mechanically connected to the encoder let alone the servo mechanically connected to a ballscrew or what not in a normal application.

    But it did make me wonder...?



  19. #59
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    As per the early posts on this, the traditional way is to use a hydraulic servo valve to precisely position the cylinder not the pump, the servo valve drive is virtually the same as a motorized servo, the hydraulic pump pressure would always be at system max.
    The encoder is the feedback source and would be the angular detection device.
    Unless you get one surplus, hydraulic servo's are expensive.
    Al.

    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.


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    Sorry for the lack of updates. My tube bender was placed on hold for the past two weeks while I studied for finals. The semester is finally over! Unfortunately, I am taking a 3 credit hour “super accelerated” course over the Christmas break. The break won’t be much of a break for me. Take a 3 credit hour semester-long course and condense it into 4 days!

    I am back on track with the tube bender. I purchased a diff. rotary encoder from AutomationDirect.com. I bought a 360 PPR quad encoder with a hollow shaft.

    I have decided to change direction again in terms of software. I reverted back to Windows XP so I can run Visual Basic. I am going to buy the Quad Encoder to RS-232 adapter from US Digital. A thanks goes out to Keelber for the suggestion! The US Digital Adapter comes with a sample VB program. I can use this program as a template to create my own program. My job has recently demanded the use of VB. I am being forced to re-learn VB from my freshman year. I am glad I have chosen this route. I wanted to make my own program from the start. I will now be able to implement a simple interface with a desired angle text box and a current angle field. It will contain extend and retract buttons and nothing else.

    I will post pics of recent progress later.



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