Hydraulic Motion Control

I am working on designing a machine that will have 4 axis of hydraulic motion control. All 4 axes are identical, but totally independent of each other. Stroke is 48" with SSI feedback. Cylinder is 4" bore, 2" rod. Maximum speed is 5 inches per second. I need to maintain a final position of within +/- 0.020”. I do not need to follow a precise motion profile; just maintain final position. I am using a CompactLogix L32E for my machine control.

Does this motion control sound possible to do in the PLC or should I look at a dedicated controller. In the past, I have used Rexroth's HACD for other motion control applications.

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If you have done hydraulic motion control before, you know there are aspects of it that are not covered in the standard control loops in PLC's. Some (much/all) of the money you save on HACD's could be eaten up in the extra time required to massage a generic control into a hydraulic application. Also, I find the motion data trace invaluable in startup and debug of these types of systems.

You could actually get away with only 2 HACD cards if you go to analog feedback AND do not need to do pressure override. The next version will have multiple SSI feedbacks and Ethernet/IP but I don't know when that will be available. If you are adventerous you may want to call your distributor and see if you can Beta test them.

What valves are you using?

<disclaimer: I work for a Bosch Rexroth distributor>

Using 2 HACDs instead of 4 would certainly lower the cost, but I'm not sure the math the supports using analog feedback. My 0.020" specification corresponds to only 4.1 millivolts.

I forgot to mention that I am building 4 of these machines, so at $1500 per HACD (including a cardholder) that is nearly $24k worth of controllers. I figure that to get SSI inputs and analog outputs on my PLC, the cost is only $400 per axis in PLC hardware. My potential savings on hardware is nearly $18k if I can do it in the PLC. Even if it takes me a week of development, it would be worth it from a cost standpoint.

If I buy devicenet HACDs, can I send position feedback from the SSI modules in my PLC to them over devicenet? That would reduce my total HACD card requirement from 16 to 8.

The valves will be some sort of proportional valve. In the past we have used Rexroth, but it could be a Parker. We have not yet specified a part number. We are still getting power unit quotes.

Thanks for the tip on the Ethernet I/P card with multiple SSI inputs. I'll check with the distributor.[FONT=&quot][/FONT]

agarb said:

Does this motion control sound possible to do in the PLC or should I look at a dedicated controller.

Click to expand...

0.020 inches is easy.
This is possible in a PLC however it would cost you more time/money to develope the code than if you bought a dedicated controller.
We have a 2,4,6, or 8 axis hydraulic motion controller that has an Ethernet/IP certified interface. The hydraulic motion controller shows up in RSLinx as a SLC5/05 so it plays well with other Rockwell products.
http://www.deltamotion.com/products/motion/rmc100/index.php
follow the links to the RMC150. We have example code on our website.
http://www.deltamotion.com/files/rmc150E_ctrllgx.zip
If you are using RSView or PanelView the following link isn't required but if your are using a VB HMI the RMClink allows easy access to the hydraulic motion controller data.
http://www.deltamotion.com/files/rmclinkinstall.exe

The best benefit is that I am always here and I/we know hydraulic motion control.

Peter Nachtwey
President
Delta Computer Systems

Peter,

I've been playing around on your site this evening. I must say your online quote request is very slick; I never would've thought I'd get a quote after 5pm. Now I just need to call my distributor to see if they discount that list price.

Purchasing multiple 2 axis controllers like the[FONT=Verdana, Arial, Helvetica, sans-serif][SIZE=-2][FONT=Monaco, Courier New, Monospace] RMC75E-MA2 [/FONT][/SIZE][/FONT]would work nice from a physical layout standpoint because I could drop it in a junction box near my valves and SSI feedback and eliminate some long wire runs. It also appears that two [FONT=Verdana, Arial, Helvetica, sans-serif][SIZE=-2][FONT=Monaco, Courier New, Monospace]RMC75E-MA2 would cost about the same as a single RMC150E-S2.[/FONT][/SIZE][/FONT]

You referenced the RMC150 in your post, should I look at that instead of the RMC75?

agarb said:

Using 2 HACDs instead of 4 would certainly lower the cost, but I'm not sure the math the supports using analog feedback. My 0.020" specification corresponds to only 4.1 millivolts.

Click to expand...

Right on that one. Not the way to go. Resolution on 48" stroke will only be around 0.012" without taking into account any temperature drive or non-linearity.

agarb said:

If I buy devicenet HACDs, can I send position feedback from the SSI modules in my PLC to them over devicenet? That would reduce my total HACD card requirement from 16 to 8.

Click to expand...

Should be theoretically possible but leading more to the non-intuitive realm. This will also add some lag in the feedback coming across Devicenet. I would not do this as a first choice.

agarb said:

The valves will be some sort of proportional valve. In the past we have used Rexroth, but it could be a Parker. We have not yet specified a part number. We are still getting power unit quotes.

Click to expand...

I asked because valves with linear flow characteristic and no overlap will be easier to handle in the PLC than overlap and/or non-linear or "progressive" characteristic valves. I'm guessing a 4WREEV6 might be a good 1st choice. I don't know what your load is and so don't now pressure drop and that will determine the spool size.

Are the cylinders horizontal or vertical or some of each?

Cylinders are all vertical; rod up. Load is approx. 700-1000 lbs. I think we used a 4WREE last time we had an HACD application, but I can't remember which spool.

I shouldn't post before Peter, but I use and love the product. The 150 is the same as the 75 but up to 8 axes (it has a better physical look also). The support is super, even on the chat line. I love it cause you can post charts and they can tell you most everything, and they keep on top of it. I have never had a such truthful response. Lately I have had some low flow problems and with the RMC tools I finally convinced them (my people) that we do not have enough GPM. They (my people) want to solve with acculinators ... we will see. I after being taught know we need a prop system and a bang-bang system.
Sorry, anyway 4WRE... has always been good to me.
Except once about 12 years ago I had an extreme low flow app and I couldn't get 2 valves to move together

Follow-up to the original post... Peter will be happy to know that I am starting up my system today. I ended up purchasing qty. 8 of the RMC75E-MA2.

And, in 2 weeks I have a guy coming from Rexroth to "assist" me in setting up one of the new HACDs with Ethernet that ndzied1 referred to. They volunteered to come since it is a relatively new product and the documentation is a little rough. Plus they know they lost the previous order to Delta.

You'll be very happy with the RMC.

I am watching

Let us know how it goes.