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(pseudo)NC Hydraulic Surface Grinder

PLC control, hydraulics, self-measurement

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Jelly04/10/2016 00:41:25
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474 forum posts
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I'm just starting to look at a project to convert a manually operated "Surface Grinder" into a hydraulic one with a numerical control system, and would value the experience and ideas of others as I'm not 100% how to accomplish some of the details.

Basically the machine is a small Pallas/Trident horizontal mill, on which the bearings and spindle were improved by a previous owner to allow it to run at speeds sufficient for grinding, along with fitting a high speed motor. The current feed is via a rack for the X axis and Acme Screw for Y&Z axes, which is suboptimal for my needs, but suited the man who re-manufactured it very well.

My basic plan is to start by replacing the t-slotted table designed for milling, with a purpose built carriage consisting of a cast iron dovetailed slideway to which a welded metal drip tray and an assembly to allow quick-change between mounting of both an 18"*6" magnetic chuck and a dedicated machine vice. This would not be driven by the rack, but by a hydraulic ram attached to the saddle, rather than using limit switches to reverse the valves during operation, I was planning to have a linear scale output to a PLC (likely a 32-IO Mitsubishi unit I have sitting about) allowing control of where the machine begins and ends it's stroke to minimise wasted time during the cycle.

This leaves me with enough IO's left over to also automatically actuate the other two axes (y&z), using the same linear scale self measurement system with either more hydraulics, or via servos acting on a leadscrew.

I have a couple of stumbling blocks, firstly actuating the knee by leadscrew gives a issue as to both replacement of the crude acme with a much higher tolerance ball screw in order to realise the kind of accuracy a surface grinder should deliver, and then the issue of developing sufficient torque to move it... But equally, using a ram as an actuator, opens up scope for it to move slightly during operation if the system isn't perfectly sealed in order to resist any downward force, that's after accurately quantifying the behaviour of the cylinder and valves to allow very precise movement initially

The second is how to set and display the parameters of the machine, a shared numeric keypad, parameters selection switch and LCD for each is logical, but would take up quite a lot of IO's; the alternative approach is to have a separate logic controller to deal with the input of settings, which then simply outputs the setting for each to the PLC.

The Y-axis would need to remain on a leadscrew due to space constraints, and is likely to be sufficiently precise retaining the existing acme, torque is also less of an issue, compared to raising the knee.

In an ideal world, I'm aiming to finish up building a system where I can chuck a part; set the final dimension to grind to, Y-axis & z-axis step distance, x-axis limit postions and feed-speed; touch it off using a jog-function; press run and leave it to cycle.
Michael Gilligan04/10/2016 08:22:21
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23121 forum posts
1360 photos

Wow !! ... That's one heck of an opening post, Joshua.

Way out of my league; but I wish you well.

MichaelG.

Chris Evans 604/10/2016 09:24:08
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2156 forum posts

I have recently passed on the purchase of a Jones & Shipman 540 at £600. It was not a "P" (powered rise and fall) which I am looking for but a better starting point to do what you want ? I can see though that the challenge of making your ideas work has some merit. I wish you luck with sorting all the issues, keep us posted and welcome to the forum.

Jelly04/10/2016 12:08:49
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474 forum posts
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You're entirely correct, an existing hydraulic grinder would be a lot easier to start from and I had an opportunity to get a Norton grinder, which simply needed the hydraulic cylinder reconditioned, and some new piping...

The issue that stopped me is twofold, this ision loan in a communal workshop by agreement with the other users, so to take it back to a mill and bring in a purpose built for see would need quite a lot of non-engineering effort to build consensus (and I don't quite have it in me to do all that right now). Secondly we're tight on both space and floor load (with a Bridgeport Mill, Myford Super 7, Warco Engine Lathe, jig borer, Another small lather, Denford Novaturn, CNC mill, donkey saw, Vertical and horizontal bandsaws, plus three welders and a Layout table, all on a concrete slab support ed by RSJ's over a basement we're really wary of additional floor loading), so the aim is to make the Pallas conversion both smaller and lighter than a conventional grinder would be,accepting that it involves possibly sacrificing some accuracy when using the full 18" of the chuck.
Clive Foster04/10/2016 13:37:26
3630 forum posts
128 photos

Joshua

In your position I'd take a serious look at whether LabView Home edition would be a simpler to get going platform for your control system than working directly with the PLC you have. Unlike the full fat version its not impossibly expensive, probably around £30 but I don't know where to get it in the UK, and the interface does make programming and sorting out things much easier than going direct to a PLC. Back in wage slave days I used older versions of LabView to make mechanical drive control and data capture systems and found it far easier than working direct. Especially when sorting the difference between "sort of does what its supposed to" and "actually does it right"!

Supposed to be projects to develope code compilers onto Ardino and Raspberry Pi too. Apparently its easy to go from LabView code to the PLC once you have everything debugged. Well thats what the guys on the LabView stands at shows always told me. But then they would, wouldn't they! I guess as a ahldway house the LabView thing could be tweaked to make it a data logger to monitor what teh PLC is doing.

The MakerSpace folks seem to be interested in using it too. That has to mean a good deal of motion control stuff doesn't it. maybe something close enough to your needs to just borrow and modify.

Clive.

Jelly04/10/2016 16:14:08
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474 forum posts
103 photos
LabVIEW looks and sounds ideal, but looking at their I/O hardware, made my wallet make some funny hissing noises and snap shut...

I think need to fully document the intended process flow and then start building up specifics until I really understand where the big challenges are, and probably end up buying LabVIEW because the savings in time are enough to justify the cost of getting an interface board.

Unless of course I've misunderstood and I can use the software to directly access the PLC's I/O via serial.
Clive Foster04/10/2016 17:25:57
3630 forum posts
128 photos

Its getting on for 20 years since I last used LabView so not only am I well out of date I've also fogotten most of the details. However as I recall things I didn't use much of the fearfully expensive dedicated hardware so I'm pretty sure there are inexpensive ways of doing simple things like scale reading and basic motion control. One early project involved a stepper motor, analogue distance transducer and lock-in amplifier output all hung off the back of a Mac SE which I'm pretty sure used only the standard LabView interface gubbins with no extra cards.

If the "maker" folk are getting involved there have got to be inexpensive solutions for the sort of stuff they use.

Clive

Carl Wilson 406/10/2016 15:55:39
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670 forum posts
53 photos
Hello,

I can heartily recommend you get Labview home edition. You can download a toolkit for it called Linx. This makes it possible to write a program in Labview for an Arduino, beaglebone black or rasp pi.

You have the Labview front end running on a pc or laptop and the Arduino doing the input/ output stuff. On the beaglebone and rasp pi you can do that or you can run the Labview program on the device stand alone.

It speeds up development by several orders of magnitude. I got mine direct from Diligent that is a Labview company.
You won't look back.
Carl Wilson 406/10/2016 16:08:57
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670 forum posts
53 photos
It's Digilent.And it's ?35 ish. Linx toolkit is free.

Edited By Carl Wilson 4 on 06/10/2016 16:12:25

Carl Wilson 406/10/2016 16:09:11
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670 forum posts
53 photos
It's Digilent.And it's ?35 ish. Linx toolkit is free.
Jelly07/10/2016 14:04:40
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474 forum posts
103 photos
Thanks Carl that's quite useful to know, it's looking like to be affordable I'll need to use an arduino based controller to handle inputting the settings and displayi g them via seven-segment displays... The price per I/O for PLC's being too high to run the I/O heavy displays and 16 key input.

(I don't really want to dispense with the PLC altogether as native support for gray-code, 24v outputs, analogue outputs and relays for 240vac are very useful features that wouldn't be available nearly so easily from an arduino).

Carl Wilson 407/10/2016 22:47:54
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670 forum posts
53 photos
If you get Labview you won"t need 7segment displays etc. You will have a fully featured Labview front end for your Arduino. Labview has support built in for reading encoders etc. The power is phenomenal.

So is the support. If you go to Labview maker hub forum or Labview ni website there is lots of help and tutorials.

Also Labview comes packaged with hundreds of examples to get you familiar.

Carl.

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