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  • Hydraulic servo valve

    I am upgrading a horizontal pipe bender to run off a modern PLC. Currently it is controlled by an old Allen Bradley 9/series DC servo control system. Everything is slap wore out. It uses a 30 ton hydraulic ram to perform the bending operation. The stop point adjustment is set by a mechanical switch riding on a ball screw that is positioned by a DC servo motor. As I understand it, I should be able to use a servo valve to set the position of the ram anywhere I like. My question is, how accurate and repeatable are these? I have my eye on a 4-20ma driven unit from Moog that should be easily controlled by a PLC. Thank you for your input.


  • #2
    Originally posted by Destroyer73 View Post
    My question is, how accurate and repeatable are these? I have my eye on a 4-20ma driven unit from Moog that should be easily controlled by a PLC.

    the accuracy/repeatability should be in the spec sheet from Moog

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    • #3
      One of our machines uses the D631 series valve from Moog, very good valve, I do recommend that you install a filter upstream of the servo valve.


      We use it to do exact positioning (within 1mm) but you really do need a way to get position feedback of the ram to make this work. We have a linear transducer coupled to the mechanical motion and the PLC uses a PID loop to smooth the motion out.

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      • #4
        Is it feasible to use an ultrasonic sensor to obtain position?

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        • #5
          Are you asking about an analog proximity sensor? Could you provide a link to what you have in mind?
          Bob

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          • #6
            Originally posted by Bob S BN View Post
            Are you asking about an analog proximity sensor? Could you provide a link to what you have in mind?
            http://www.baumer.com/us-en/products...D%26perpage%3D

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            • #7
              That could get you feedback on position into the PLC. I would suggest you get the 0-10volt model, as the 0-10ma is not typical. AD sells analog 0-10 volt input cards, and analog 0-20ma cards. If you use the 0-10ma sensor, half your card resolution will be lost. I can not speak for how well this type of sensor will hold up, or work in an application like this, as I've never used one.
              Bob

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              • #8
                I assume your referring to the accuracy of the positioning of the cylinder.

                Sounds like you need cylinder's with temposonic wands.
                I guess you could use a string pot. But I must say I've never used or been around them for that matter.

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                • #9
                  Tube Bender

                  What material are you bending and what type of accuracy are you looking to hold?
                  Bill Floyd

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                  • #10
                    Originally posted by billf_Clark_Pulley View Post
                    What material are you bending and what type of accuracy are you looking to hold?
                    It's a repurposed pipe bender that my company uses to bend copper buss bar material. Thicknesses range from 1/8" to 3/4" and widths up to 5 inches. Bend angles vary. The photo below is similar to what the machine does.

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                    • #11
                      Ok, helps a little to understand, I've replaced the controls on 20+ Horz. Pines benders that are used to bend outdoor furniture that you see at condo's and hotels up and down the east coast and in the Gulf states. Some of the machines had the actual machine manufacture controls (Pines) with some circuit boards and crap that worked, but when they crapped out the customer would have to dish out $$$$ for parts. The customer also had some machines (8 or so) that had AB Micrologix and Panelview 550's. The issue with them was the control shop went out of business and never gave them the password (OEM password Protected) to the plc's or gave them any drawings. Granted shame on them for paying them without checking, but in the real world some people never think about it.

                      I ended up ripping the AB crap out, I only call it crap because it's over priced right along with the software. I designed a system that uses a DL06DR which has a high speed counter function built in and a EA7 (8" HMI). The customer wanted the ability to program up to 20 bends and enter a creep degree slowing the bender down before reaching its target (10 to 180), spring back timer as well. I connected a 2,500 pulse encoder to the bottom of the machine which turns with the bender. A great simple solution for less then $2,100 in parts.

                      Sounds like your on the right track, but I'm not sure if you need a servo and feedback sensor for something that doesn't need it. No point in over engineering something. Now, if you need it accuracy, I'd go with a hydraulic prop valve (ATOS), DL06 PLC, SSI encoder from Siemens and a Single axis Delta Motion Controller (RMC75 or RMC100). I've used them on 17+ machines that controls 3 axis splitting a 2ga metal disk in to a V-groove pulley and hold any wanted position within 0.002".

                      If you have a PLC (DL06DR) and HMI, drop you can get an encoder from AD for less then $200. It's not much money for a good R&D test on position control. Just a thought.
                      Bill Floyd

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                      • #12
                        Nothing fancy, short little video.


                        https://www.youtube.com/watch?v=kCfh2zDgNX0
                        Bill Floyd

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                        • #13
                          Bill's right

                          I agree wholly with Bill. If you are looking for position feedback look at the benders axis of rotation. If you have an acme thread riding some sort of Encoder than boom goes the dynamite.

                          Now getting the coding to do all this is the trick part. PID loop with highspeed counters would suffice. As Bill said, everything is on the site.

                          Bill, I have worked on Pines benders from a hydraulic standpoint. The last one I did had a bad opto22 board which ran the inputs to the digital readout which was also bad. They paid a pretty penny from the interwebs for that one. Email me at calvin@hcshouston.com, It would be cool to pick your brain on the operations of the bender, to include nomenclature of each component.

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