Load controlled pneumatic ram

Is this to be a proportional valve ?

Is the load dynamic. What sort of loop response time do you need.

It would be much easier to help you if you explained the overall function of the system.

MK

Yes the valve is to proportional. The system is needed for cycle testing aircraft seats. A ram will act upon a armrest of a seat and the load cell will sense what load is being applied and once a certain load, a response is sent to the pi to retract the ram and repeat the process over a number of cycles.

You don't need a proportional valve for that and you may not need the load cell except for calibration.

The last time I did this kind of test it was on a scale so it could check the load itself !

Just use an on/off type of valve and flow restrictors to control the rate of operation and a pressure regulator to control the ultimate force.

Use your load cell to check the force actually applied.

You could close the loop by measuring fairly quickly and cutting off the air when the force limit is reached.

I wouldn't use a Pi for this but a full blown PC with a maybe a development board (I would use an ST Nucleo but an Arduino would do as the interface.). There are better interface things around if you want simple of the shelf - Moxa make nice industrial IO modules.

The hardest part will be the load cell to computer (whatever you use) interface - if you already have one obviously you'll use that but if not it won't be cheap.

(The reason I would use a full PC is: you need a screen, keyboard, hard drive to store results etc - a suitable PC is cheap, will support any programming languages you like, has loads of storage capacity, can be easily networked etc. A PC does all this when you switch it on, with a Pi you have to mess about.)

Picture shows my scale testing rig, nothing fancy but worked OK (for >2M cycles). You can just about see the valve and flow restrictor on the right.

The rig was tuned by the addition of weights and careful setting of the flow to get the correct rate of increase of the force on the DUT.

MK

Thanks for reply.

https://www.youtube.com/watch?v=qiGkJaPnqFI . If you skip to 1:50 in the attached video , you will see what I am trying to create. I only thought about using a pi due to their simplicity and I'm open to using a PC and I am fairly familiar with using a PI The video shows what I am trying to create and looking to find what way to do this. I have a multitude of load cells available so no problem there.

I'd stick with simple pressure and flow control with the load cell as a monitor. If I really felt I had to close the loop I would use an electrically controlled pressure regulator - to set the max cylinder pressure. You can buy these and all the pneumatic parts from loads of different places including Farnell and RS. You can buy the slotted aluminum stuff from similar places.

On this sort of stuff, where the load cell and pneumatic parts will cost getting on for 2k I'd choose a real PC - it's easier to work with but you could do it with a Pi.

Here's a link to Moxa's nice little daisy chain-able Ethernet boxes for IO

https://www.iiotzone.com/iologik-e1200-series

Is the video from your company or are you using it as a source of inspiration.

MK