Hydraulic 6-axis Robotic Arm EMC Configuration

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26 Aug 2011 01:22 #12742 by emcYK
andypugh wrote:

www.hydraulicspecialties.com.au/products...ucts?keyword=pv72-20
Looks like AU$700


Do you have specifications on these proportional valves? I gather that the price is too expensive; I think that stepper-controlled needle valves must be given a solid consideration, given the price difference (for which if it was lower and the specifications right, I would have gone straight to the proportional valves). The stepper-operated needle valves are right now around 100 apiece (mainly because it's not ordered as a product, we're ordering the raw materials to build a custom design).

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26 Aug 2011 09:48 #12746 by andypugh
emcYK wrote:

I think I am seeing proportional valves of the right sort of flow rate for £200 or thereabouts.
uk.rs-online.com/web/p/valves/7040389/


The link is to a solenoid valve, which does not grant infinitely variable flow control; this 3-position type of valve is designed for full forward, full reverse, and either open or closed neutral. A solenoid valve has been already selected for use in the industrial robot as to provide directional control.


The pdf linked from that page does describe proportional valves which look identical to that one, though the part numbers don't match.
With PID-contrlled PWM you can position the spool in intermediate positions to give variable flow, but the coils might not be well-suited to it in the general case. I suspect that the dedicated variable valves probably have softer cut-off geometry in the spool too.
I am working on the control system for a hydraulic valve at the moment, it is an automotive application so I suspect that the part costs about $10. It only has a max flow of 30 litres per hour, though (you were looking at 17 litres per minute, I think?)

The stepper-controlled valve is an interesting idea, I think it is certainly worth trying it with one axis to demonstrate feasibility.

Note that your design is probably going to need hard stops on the stepper motor motion, or something a little cleverer, to home the motors. I don't think that it will be easy to add the steppers themselves to the homing sequence.

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