plcs and proportional hydralic valves

Has anyone ever used a plc to control a proportional hydraulic valve. The valve I have is an old Parker (model # d31fse01b4nxp020),this valve uses a transducer to communicate how much the spool has traveled,via a dc voltage.
This old valve had a control card with pots to determine the max spool travel and the speed. This card played out on us and the replacement is costly very costly. I would like to see if it can be done cheaper with a plc.

I do it all the time. With great success I might add. However, you do need an amplifier. The PLC analog output does not have the power to drive the valve, and most valves require that a dither frequency be applied over the coil driver current to overcome static friction. I bring the spool position feedback to the PLC as well as the actuator feedback and use a cascaded PID loop (two loops, one inner loop controls the valve spool position, the outer loop controlling the process variable)

What is the process variable being controlled, pressure, position, or velocity?

I will try to explain the process. This valve control the movement of a unistacker (wich stacks bags of feed on plastic mini pallets). There is a set of forks that raise and lower with a mini pallet on them this valve runs the elevator up and then lower the forks as the bags are stacked on them at a designated number of bags it then loawers the forks to the take away conveyer wich moves the stack and replaces the mini pallet and starts over again. The vavle controls the speed of the upstroke and the speed of the stack stokes and the speed of the final down stroke.

I had outstanding success using some GE Fanuc 9030's for proportional control on some tire curing presses ten years ago. I do not remember having any external amps on them. That doesn't mean that there wasn't any, I just don't remember. I do not recall the brand of the valves, they were quite large, but may have had some internal amps.

Programming wasn't too bad, I was just learning GE, and was ablw to find everything I needed in the manuals.

At the time, AB could not do the same proportional control that Goodyear required, but I believe that they have since remidied this situation.

I do remember that at THAT time, for the cost of three AB plcs, I could get about 24 GE's.

regards.....casey

Your best bet is to change to a valve with "On Board Electronics" or (OBE). Many of these are set up to take a direct voltage or current analog signal from a PLC and close the spool position loop directly on the valve. Besides these signals you will need to bring the valve 24V to power the on board electronics and some require a digital signal to enable it.

Basically, the amplifier others are talking about is put directly on the valve.

Here is an example of such a valve:
http://www.boschrexroth.com/Rexroth-IHD/Home.cfm?Page=RDSearch&Filter=29064

Other manufacturer's also carry similar product.

<Disclaimer, I work for a Bosch Rexroth distributor>

CaseyK said:

I do not remember having any external amps on them. That doesn't mean that there wasn't any, I just don't remember. I do not recall the brand of the valves, they were quite large, but may have had some internal amps.

Click to expand...

Many valves do have internal amps, and in fact that is the sort of valve that I prefer.

I use Bosch/Rexroth valves, Moog valves, and Parker valves the most often (Bosch being my favorite). I know Parker does offer a model with an internal amp because I have three of them here.

I find that the Moog valves have better durability than the parker valves I've worked with. The problems I had with the Parker line was that they tended to leak into the amplifier circuitry with 5 pounds of back pressure even though they were rates at a much higher level. Also the quality assurance and tech support was beeter with Moog. However thats just from some of the experiences here which does not include a large number of models.

We use proportionair units, and cartiridge valves from sun.

arthur said:

Has anyone ever used a plc to control a proportional hydraulic valve.

Click to expand...

Yes, it is done all the time. High speed or accuracy applications usually require a hydraulic motion controller. There are hydraulic motion controllers that fit in the rack or communicate using a field bus or Ethernet. The PLC was not specified.

I agree with ndzied1, bringing your valve up to date shouldn't be too costly and it can be controlled with an analog signal from the plc with position feedback from a transducer in the cylinder. I use AB 1771-QB modules in the plc's to get this done. I also use Bosch or Moog proportional valves, they do the same job. GE should have plc modules to compare to the AB also, I'm not sure, I use GE or Automation Direct PLC's for less intensive applications and AB for everything else.

One of my customers recently replaced 4 old parkers with a seperate amp card with the new valves using on board amps. The cost of the old ones was 3500 each and it was 7k for the 4 new ones. I directly drive them with the analog out from a CS1.