I agree with Andy. I do quite a few industrial control jobs using hydraulic servos. The normal setup is a swash plate pump that is self pressure regulated feeding an accumulator (for pump efficiency and fast response) and that feeds a 4 way servo valve or servo grade proportional valve. That drives the cylinder. A feedback device, usually a temposonics type device or a linear pot, provide position feedback. If the cylinder is not going to move very fast and you have a big enough pump (servo valves don't like pressure variations since it destabilizes the PID loops) then you can oftentimes get away from the accumulator. But accumulators make the system a lot more efficient in that you can use a smaller pump and still move the cylinder quickly without a big pressure drop. If you want to move fast, the valve needs to be mounted very close to the cylinder.
I'd keep an eye on Ebay for servo valves. Most people don't know what to do with them. About two years ago I did a railroad service vehicle control job that drills concrete railroad ties and I used two PCs running LinuxCNC that controlled 4 proportional valves to control position and pressure on 4 drill cylinders. Each drill cylinder moved 2 drills up and down. I wasn't doing precise closed loop position control but I used 4 temposonics tranducers with analog outputs to close the position loop on the cylinders. The proportional valves I used were ok, as in they allowed the machine to drill automatically but in hindsight I should have used better valves since the positioning aspects of the valves could have been better. Parker and Moog make some really nice valves which I have used on some PLC related jobs. I used Mesa components to do all of the Analog I/O for the positioning loops and stepper motor control as there was also 12 stepper motors used to position the 8 drills. It was a very complicated machine. Everything was powered off a Kubota diesel engine as the entire machine can drive the railroad tracks under its own power. It was a fun job, but a lot of work - too much in too short of time. :-) Dave On 9/23/2013 7:01 AM, andy pugh wrote: > On 23 September 2013 03:50, Stuart Stevenson <stus...@gmail.com> wrote: >> Gentlemen, >> I want to control a hydraulic cylinder (extension and retraction) with >> LinuxCNC. >> I want to use an axial piston swash plate pump. >> I want to control the swash plate with a servo motor. > This ought to work, but it isn't the usual way to do it. The > servo-hydraulic machines I used to work with (and that are used > extensively on the vehicle test rigs) use a "Moog valve" to divert > pressure to one side or the other of the cylinder. The pump runs under > closed-loop pressure control (I think). > > http://www.moog.com/literature/ICD/RCE18N11_Moog-LOW.pdf > > Looks like a reasonable description, albeit from a motorsport rather > than industrial perspective. > ------------------------------------------------------------------------------ LIMITED TIME SALE - Full Year of Microsoft Training For Just $49.99! 1,500+ hours of tutorials including VisualStudio 2012, Windows 8, SharePoint 2013, SQL 2012, MVC 4, more. BEST VALUE: New Multi-Library Power Pack includes Mobile, Cloud, Java, and UX Design. Lowest price ever! Ends 9/20/13. http://pubads.g.doubleclick.net/gampad/clk?id=58041151&iu=/4140/ostg.clktrk _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
