Controlling hydraulic pressure feedback for chuck etc

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18 May 2022 23:43 #243306 by smc.collins
did some google foo here in the forum and elsewhere, I didn't find anything, so here is the question, can linux CNC control a pid to control hydraulic pressures ? IE, I might need to add or subtract clamping force from my lathe chuck, and I would like to be able to set that as either a Mcode " specify the pressure of the chuck, tailstock etc"  or ladder control just generally on a per program basis to prevent operator crushing small delicate aluminum parts and housing bores. Generally it would also be nice to be able to keep pressures to a bare minimum to reduce motor loads and conserve electricity also. this unit has a single 7.5hp constant speed AC induction motor " I think I am going to control this with a VFD in the future" , so it will only consumer the current needed to maintain pressure and flow AFAICT

My machine has 3 main circuits and all of them are adjustable for pressure. would be nice to automate this, and if I did, I am thinking steppers and pressure transducers would obviously be optimal.

Thougths and feedback ? 

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19 May 2022 01:04 #243307 by andypugh
If you have a pressure sensor and a controllable regulator then yes, a PID should do the job.

No need for anything clever like Ladder, just use M68 to drive the PID command pin directly.

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19 May 2022 04:27 - 19 May 2022 05:24 #243314 by smc.collins
I'd have to either swap out the regulator for a pwm regulator or put a motor on it to control it by turning the regulator adjustment knob

It's a down the road thing, bit I'd like to be able to do it
Last edit: 19 May 2022 05:24 by smc.collins.

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19 May 2022 09:09 #243325 by andypugh

I'd have to either swap out the regulator for a pwm regulator or put a motor on it to control it by turning the regulator adjustment knob

Yes, to control it electronically it needs to be electronically controllable :-)
 

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19 May 2022 11:46 #243334 by smc.collins
I kinda think turning the knob,while being slower offers redundancy and simplicity in the pressure loop. Needs to be a lazy numb pid too.

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19 May 2022 12:12 #243336 by andypugh
You need feedback of the actual pressure too. (Or, possibly a homing switch on the knob)

There is probably a Modbus / EtherCAT / serial regulator out there.

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20 May 2022 00:39 #243376 by smc.collins
Yeah, I was looking into analog 0-70 bar sensor, 0-4.5v, Not sure how I would implement a home switch on the knob though, I will have to measure the turns gain ratio and report back.

If you see any of the other options, please share links !

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20 May 2022 19:55 #243423 by andypugh
Actually, with a velocity-mode stepper or a DC motor you don't need to know where the knob is, as long a the motor is strong enough to turn the knob but not to break it.

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21 May 2022 04:45 - 21 May 2022 04:46 #243459 by smc.collins
I would lean heavily towards a steep0er, maybe take a tq wrench once under power and measure turning tq and calculate servo/stepper demand. I don't need it to be super fast, just good enough
Last edit: 21 May 2022 04:46 by smc.collins.

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