Flow (stroke) control of multiple pumps

Our customer has 4 pumps which he wishes a 0-10V signal to stroke 0-100%. Plans are 1 signal to control all 4 pumps; if one is not in use, positioning will fail. BoschRexroth recommends a 15 bit SSI rotary encoder to replace old, obsolete, noisy, potentiometers. They have used the Allen-Bradley 845G-F3GAHS032KU successfully in similar applications (with their proprietary controller)

Initial question relates to the 15 bit absolute SSI encoder; RMCTools only allows 13 bit for rotary; I see nothing wrong with configuring as linear, but ???

I proposed the RMC100-S2-A1-DI/0; this will replace a very old rack of analog servo amps which always control. Are we missing anything?

You are correct in that the RMC100 allows only 13 bits rotary. The RMC150E, however, allows up to 32 bits rotary. Therefore, I would recommend using the RMC150E (which uses RMCTools) instead of the RMC100. The RMC150E is newer and nicer to use, especially if the axis is configured as rotary.

So you don’t have a valve you are just controlling position with the flow of the pump?

If you are using one signal to control all 4 pumps then do you have one position sensor? If so then you only have one axis so you could use a RMC70.

In either event, the scaling will be to 0-100%. There may be some gearing in the old “pot drive”; if not, actual rotation won’t be but about 13 degrees or roughly 1000 counts total. Gearing means backlash, so I’d rather not have it. REAL resolution of flow control of 1% is better than I expect.

I don’t have a problem with learning the RMC150, but wouldn’t the RMC100 handle this fine? More encoder counts from Allen-Bradley might be nice, but we’ll take what they can give us.

Charles, most (all of which I am aware) stroke controlled pumps have a valve operating on some sort of “cylinder” which may or may not be part of the pump. The pump displacement in those with closed loop control (vs force against spring) has a feedback device proportional to (approximately, cosine theta comes into play, but angles are in my experience less than 20 degrees trig errors are is less than other errors).

Each pump will have a valve which strokes it. Each pump will have a feedback device. If a single pump existed that would supply appropriate flow and pressure, it may have been selected. As is, each of these is 500cc, 300 bar, and is driven by a 250HP motor; maximum flow and pressure are not simultaneously needed, else a 450HP motor would be required on each pump. Customers seem to prefer machine manufacturers who divide requirements over multiple sources as reduced capacity is possible with equipment in service; indeed, usually this would have been designed to run 3 of 4 with capability to run at reduced capacity with 2 of 4.

Ok I see what your doing now. (I think)

The RMC100 is a good controller but the new controllers make it look bad. RMC Tools is a great program and allows you to be much more flexible. Unless I was repeating a project that was done with the 100 I would use the 150.

OK, I’m advised to go to modern hardware. The customer would prefer 4 stand-alone systems. What would I need to do this to look just like an analog PID controller? Is it as simple as a RMC75(S or E)-MA1-A2? Quickly going through the software, the SSI 15 bit rotary is fine. I don’t see how to make an analog input the reference (think joystick); on the RMC100, that is more straightforward.

Thanks, George

With the RMC75 MA1 - A2 you will have one SSI input and two analog inputs. You can config them in any way you want.

I have never done joystick control but I know you can do it. It was talked about in one of my classes. My first thought would be setup gearing. Gearing the axis to the joystick input. But this would be limited. You could use the analog input as a speed ref input. I think that would be easy to do. The guy’s at Delta can tell you the best way to do a joystick control.

If you want 4 stand alone systems then the 70 may be the way to go. I would base it on how it wires. If you can put it all in one box and wire the control power (e-stops etc.) without any trouble you could save some money using the 150. The program will be the same in both.

I understand both of those items; separation of loops is great in heavy industry as one failure does not affect the others. The $ for the controller(s) is a small part of the system. BUT monitoring all 4 loops at the same time is nice too … and easier with one controller.

To receive an analog signal and SSI feedback, and output a +/-10V velocity(and direction by polarity) command would need nothing else using analog controllers; do I need any way to “start”, “go” or whatever? With JUST power, position command, feedback, and output, do I need anything else like digital IO?

You can get I/O with the 150 & 70 so you should be good. Are you going to have any kind of PLC or HMI to work with? If not you can have the motion control start running on start up. If you do have a PLC or HMI you can pass data back and forth and may not need the I/O at all.

OK, there are four pumps and the swash plate angle can be controlled by a 0-10 volt signal. What do the pumps control? Is the sole purpose of the RMC150 to control 4 pump swash plates?

Hi, Peter!

As far as I was asking, just controlling pump swash plates. The 4 pump outputs are “summed” and are used to drive an extruder. Pumps are Uchida (Rexroth legal copy from Japan) with obsolete servo valves and noisy cermet pots. An A-B PLC selects which pumps run via 4 analog outputs, those depending on extruded product; occasionally just 1, most often 3, very rarely all 4. I’m supporting the local BoschRexroth distributor (you know them; I’ve been in one of your RMC100 classes in their conference room.) providing commissioning services.

The goal here is to replace servo valves with prop valves (4WREE6V) and the pots with A-B SSI encoders. Presently, each analog PID module stands alone. I recommended the RMC100 using the 15 bit SSI rotary configured as linear; suggestions here were to go more modern and use either the 150 or 4 70’s. The account manager and I have decided to recommend the RMC150 for the ability to monitor all 4 pump performances simultaneously.