On Sun, 9/22/13, 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. I will install a linear scale for position feedback. The actuator/end effector ratio is at least 5:1 so the scale would not need to be super high resolution. Has anyone done this? What are the problems? thanks Stuart If there's a fixed relationship between rotations of the pump and extension/retraction of the cylinder, you could put a rotary encoder on the pump or motor and simple limit switches on the cylinder. That'd only work in a constant volume system without any leakdown while running.
If it leaks down while at rest, to the point where the cylinder fully retracts or extends so that the limit switch is triggered, the control system would know where things are when started. Otherwise it'd need to home the cylinder to the switch before commencing regular operation if the cylinder doesn't stay exactly in place with the control system off. If the cylinder isn't used in an environment where the linear scale could be damaged, then any 'slippage' in the hydraulics wouldn't matter. Just run the pump as needed to get the linear encoder to the desired position. Another possibility is putting the encoder on whatever load it is the hydraulic cylinder is moving. If it's tilting a hinged plate the encoder could be mounted between the plate and its non-moving base or put a rotary one right at the hinge. If you just need the cylinder to shift between two points without any need for position control in between, it wouldn't need an encoder, just a couple of limit switches that communicate it has reached one or the other. As a failsafe use a time out so that if it doesn't cycle in the expected time the system will shut down. I like the concept of directly measuring the movement instead of measuring the input and expecting the rest of the mechanism from there to the other end to always be accurate and functioning. ------------------------------------------------------------------------------ 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
