Simple Hydraulic Motion Control using Analog input

Hi,
I’m hopping someone can help.
I am designing a simple automated movement for a performance robot. I would like to move a hydraulic cylinder with position feed back using a 0-10vdc analog input. What Delta control device can do this and what valve?

At the moment I’m using an Enfield S2 pneumatic valve/positioning device. I need the strength and lack of air compression bounce that I believe hydraulics would give me.
My control device can output 0-10 vdc and I need that to translate into a cylinders position. Accuracy is not terribly important, it’s only a performance robot.

Thank You.

Well, For a single axis an RMC75 would fit the bill but you would need to do some more specification before a final version could be speced.

Do you ever need to control/limit force or pressure?

No, I do not need to control/limit force or pressure.
I simply need to control the motion of a 12" stroke cylinder using analog 0-10vdc input. I’m guessing the feed back would be a linear transducer?
I’m moving approximately 2,000 lbs and am trying to achieve 12" in 3 seconds. It will not cycle more than 6 times per minute.
I’m really new to hydraulics and am unsure about the valve and pump as well.
Thanks for your help.

I suggest an RMC75E-MA1-A2. This will give you one +/-10 V output to go to a valve, one feedback input of type SSI or Start/Stop or PWM, and two analog inputs, of which you can use one for the 0-10 V signal.

I recommend the following system components:

  • A linear, high-performance valve. This will make the setup easy and give you great control. What kind of accuracy do you need? This would dictate whether you need a good valve or a very good valve. See [url]Hydraulic Valves]
  • SSI position feedback sensor. If you are purchasing a new hydraulic cylinder, get a cylinder designed for sensor that goes inside the cylinder. For sensor recommendations, see [url]SSI Linear Displacement Transducers]
  • Mount the valve on the cylinder. This will give the best control. If the valve is far from the cylinder, the compression of the oil (and hose, if it has that) will act as a spring, making control more difficult.
  • Use an accumulator. This will help provide constant system pressure, and will allow you to size the hydraulic power unit for the average load, not the peak load, saving you money and energy.
  • On the hydraulic power unit, a variable-flow pump will use the least energy. You should be able to buy a hydraulic power unit from any hydraulics distributor, and they should be able to recommend components.

Have you determined a cylinder diameter yet? If you are simply moving a mass of 2000 lbs, with not much friction, then I think you can use the smallest cylinder that allows an internal sensor, which is a 1.5" bore. The max speed of you motion is probably around 4.5"/sec. This will give you the 3 second total move time, including acceleration and deceleration. Just based on experience and gut feel, a 1.5" bore cylinder with 1500 psi system pressure should be able to handle it just fine.

For calculating pump flow needs, if you do use a 1.5" bore cylinder, then one extend stroke will use a volume of PI*(1.5/2)^2 * 12 = 21 cu. in. The retract will use less, of course, so back and forth would be max 40 cu. in. Therefore, if you do 6 strokes per minute, that would be 6 * 40 = 240 cu. in., which is about 4 liters. Therefore, the average pump flow should be at least 4 liters/minute.

For valve sizing, assuming a max speed of 4.5 "/sec, the flow would be PI*(1.5/2)^2 * 4.5 = 7.9 cu.in./sec., which is 477 cu.in./min, or about 7.8 L/min. So, get a valve around 10 L/min or so.

If you want a copy of Delta’s hydraulic design guide, go to deltamotion.com and click Free Design Guide.