Motion control with analog feedback

Is it possible to use analog feedback for motion commands (motion planner)? I only see digital feedback. I was hoping to use a 4-20mA LVDT for the feed back and a hydraulic proportional valve to move the cylinder. This is with a 1756-L62 processor. I need to travel at 13in/sec and hold a tolerance of .200".

Can this be done with motion commands and be closed loop positioning? Can I use a simple analog input and output card or do I need a HYD02 card?

Suggestions?

There is no analog motion card that AB makes that will take 4-20ma as input. Your choices are SSI (m02AS), AQB encoder(m02AE) and Tempo II (HYD).
These cards give you a lot of nice features, but you should be able (depending on the rest of your hydraulics) to write something in the application code.
The approach that I have successfully implemented several times is to use a virtual axis to calculate motion profiles, and have a PI (logix builtin command) loop follow the VirtualAxis.CommandPosition. That means you can do an MAM on your virtual axis, logix will calculate the motion profile and you "just" try to keep your cylinder where the virtual axis tells you.
It takes a bit of programming to sync them up and stuff, but it's not impossible.
Oh... and this is by no means high performance. The best loop update time you can hope for is nowhere near that of a dedicated hardware card/device.

If you're stuck with 4-20mA input, you can look at other vendors (Rexroth, Delta) that have the option.

Tom

The answer is yes.

This motion controller will interface to analog feedback. It supports voltage or current feedback and interfaces easily with Rockwell PLCs.
This motion controller will communicate with your PLC using Ethernet/IP and it shows up on RSLinx looking like a SLC500.

http://www.deltamotion.com/products/motion/rmc70/

I recently posted a link to the controller in action interfacing with a MTS rod
http://www.mtssensors.com/news/index.html
but it used SSI feedback but we support analog feedback too.
Analog is OK in a pinch but SSI or quadrature encoder is much better.

Originally posted by Peter Nachtwey:

...and it shows up on RSLinx looking like a SLC500.

Click to expand...

I never really took notice of this statement before. Does the RMC communicate to the plc using implicit or explicit messages? As far as I know the SLC500 doesn't support implicit messaging. But I would assume you would use implicit messaging to the RMC.

Keith

Peter Nachtwey said:

This motion controller will interface to analog feedback. It supports voltage or current feedback and interfaces easily with Rockwell PLCs.
This motion controller will communicate with your PLC using Ethernet/IP and it shows up on RSLinx looking like a SLC500.

http://www.deltamotion.com/products/motion/rmc70/

I recently posted a link to the controller in action interfacing with a MTS rod
http://www.mtssensors.com/news/index.html
but it used SSI feedback but we support analog feedback too.
Analog is OK in a pinch but SSI or quadrature encoder is much better.

Click to expand...

Thanks for the replies. I have some questions.

I already have a 1756-HYD02 card and am only using 1 axis. I believe I would just need a MTS LDT and a Bosch servo valve ?with O.B.E.

Do you have any suggestions for a servo valve or proportional that is cost effective for my application? What options do I have that will work with the 1756-HYD02 and the tolerance above?

Heh, nice demonstration with the balloon!

I never really took notice of this statement before. Does the RMC communicate to the plc using implicit or explicit messages?

Click to expand...

Both, usually status information and commands use implicit mode ( Ethernet/IP IO ). Parameters, splines/camtable and graphs use explicit messaging ( MSG Blocks )

As far as I know the SLC500 doesn't support implicit messaging. But I would assume you would use implicit messaging to the RMC.

Click to expand...

A SLC must use MSG blocks.

rocksalt said:

I believe I would just need a MTS LDT and a Bosch servo valve ?with O.B.E.

Click to expand...

Yes but the MTS sensor must use start/stop or PWM digital pulses to work with the HYD02.

Do you have any suggestions for a servo valve or proportional that is cost effective for my application? What options do I have that will work with the 1756-HYD02 and the tolerance above?

Click to expand...

Bosch valve has good but expensive valves but make sure you get servos valves with linear spools!!
The HYD02 can hold that tolerance easily. It should be able to hold 0.001" and is limited by the feedback and the hydraulic components. Linear valves will make achieving fine positioning easy. Over lapped or non-linear spools may still work but you won't be happy.

rocksalt said:

T
Do you have any suggestions for a servo valve or proportional that is cost effective for my application? What options do I have that will work with the 1756-HYD02 and the tolerance above?

Click to expand...

You have not given enough information to recommend a valve. You gave a speed but not what size the cylinder is to even guess at the size of the valve. Also, there are many application issues which need to be taken into consideration.

ndzied1 said:

You have not given enough information to recommend a valve. You gave a speed but not what size the cylinder is to even guess at the size of the valve. Also, there are many application issues which need to be taken into consideration.

Click to expand...

I realize that and should have specified I was looking for a brand/model rather than the specific valve part number. The Bosch 0811 404 612 is in the realm of what I am looking for.

That is a nice valve but you have to do the work of determining your pressure drop and flow requirements to see if it is the right size.

Then you need to calculate your acceleration and natural frequency and see if the dynamic response of the vale will work.

Most importantly, you have to have a mechanical system capable of meeting your motion requirements or no valve will work.

To use the VCCM equation one needs the area of both sides of the piston. The rate flow of the valve, the supply pressure and the force needed to move the load at the desired speed and acceleration.

ndzied1 said:

That is a nice valve but you have to do the work of determining your pressure drop and flow requirements to see if it is the right size.

Then you need to calculate your acceleration and natural frequency and see if the dynamic response of the vale will work.

Most importantly, you have to have a mechanical system capable of meeting your motion requirements or no valve will work.

Click to expand...

Peter Nachtwey said:

To use the VCCM equation one needs the area of both sides of the piston. The rate flow of the valve, the supply pressure and the force needed to move the load at the desired speed and acceleration.

Click to expand...

HELP!!

I found the Maxima program and the difeq.wxm file. I have never used it. Can I enter the variables in it to solve my dilema?

I have done some searching on VCCM but am busy trying to do to many things at one time. I don't have the data now post the force needed or the pressure drop.

Can you point me in the right direction?

Edit: I found this website: http://www.pipeflowcalculations.com/controlvalve/