CAN MACH CONTROL HYDRAULIC CYLINDER?

[beezerlm]

Hi,
I have an old heald ID grinder which is in great shape other than the hydraulic system. There is a clog some where in the core and the table does not function properly. Had 3 different "experts" come in and work on it to no avail. My original thought was to put a ballscrew on the table and run it with mach 3. Here is my question: Can I put a glass scale on the table for feedback, and then control the existing hydraulic cylnder with mach3? It wouldn't need to be super accurate it would just need to repeat good if I was grinding up to a shoulder. Any thoughts???

[Al_The_Man]

You probably could work something out, it would not be as accurate as a hydraulic servo valve.
The problem is the Mach uses step/dir pulses and the scale would go back to the drive, not the PC.
This would entail figuring a drive that would give you a permanent output for the period of positioning.
If this is a simple point to point positioning, I would look at one of the Legacy Galil cards on ebay such as the 1500 stand alone single axis controller.
A 2 or 3 line keypad and readout can be hooked up for control.
Al.

[beezerlm]

Thanks AL

Well I neglected to mention that I wanted to mount a servo on the infeed and build a custom macro that would allow you to set a stroke length, total grind amount, and increment feed amount per stroke. So it would be a hybrid. I didn't know if there was some way of converting step and direction pulses to work for a hydraulic control unit/drive. I don't have much experience in hydraulics and I don't know what is available.

-Brandon

[Al_The_Man]

There was a Hydraulic cylinder Co, that made a cyclinder and valve where the spool was positioned by a stepper motor, this turned out much cheaper than the normal hydraulic servo valves. And was a simple control of servo hydraulics.
I don't know whether they are still in business.
If I find the literature I will post a link.
Al.

[beezerlm]

Thanks Al. I'm open to any other idea's too. I just trying to find the the easiest way to get control of the table and infeed with the least amount of time and money. I thought using the existing cylinder would save me from trying to adapt a ball screw to the machine which could be a big job.

[Al_The_Man]

There was also a previous post here about 12mths ago from a member that built a hyd bender using Mach and an encoder, I believe he got fairly good results.
Found it:
http://www.cnczone.com/forums/bendin...der_build.html
Al.

[PoppaBear10]

Parker hydraulics sells a servo valve/drive that can run off of step/dir, but
Parker = not cheap

scott

[beezerlm]

hmmm From what I have been reading it looks like most hydraulic servo valves operate on 24vdc and the control voltage is +-10vdc. In that case, could I build a macro in mach 3 that would adjust the control voltage based on how far the machine is from its destination? For example, if the machine is moving 5 inches in the positive direction, the control voltage would be +10vdc until it got within say 1/2" then it would gradually reduce the voltage to zero as it came to its final destination. I know the parallel port only puts out 5vdc so I would need to beef up the voltage somehow.

Could I connect a glass scale to the input of my BOB and have the macro count each encoder pulse for positioning purposes?

[PoppaBear10]

yes you could do that, easily with the macropump and VB.......

also, It would be FAR, FAR cheaper to buy a CHEAP 250 count encoder put a gear on it, and have that gear/encoder travel along a Plastic "rack" style gear. You can buy little plastic gear racks that come in 6" or 12" lengths and put them end to end. Or if you want to spend a little more get a Metal Rack/Pinion and put the encoder on the pinion. The encoder is NO LOAD so the Rack/pinion doesnt have to be heavy duty.

In Mach3 you can bring in "encoder counts" (encoders 1-4), depending on the gear size on your encoder you will need to figure out, how many counts you get back per unit of measure i.e. counts/inch.

So, at your rest position you would have 0 counts in your encoder dro, in the VB macro you would count as it moved till you got a little greater than your slow down distance. At that point since you know what your MAX count is for the full travel,
I would then do, an equation that would take the number of counts that your slow down point is, subtract it from your actual counts, so at your slow down point this would make your number "0", I wold subtract the slow down point counts also from the MAX as well, so in that last part of travel, you would have some value from 0 - xxxx counts. make that remaining as a percentange.

Then, you have two options I think depending on which way you want to go.
1). Natively, you could use Machs Spindle Speed out as a PWM spindle, or step/dir
spindle, and buy an after market pulse to analog converter, from i.e. CNC4PC, Peter Holman, etc.
2). If you using modbus, or PoKeys or a PLC, what ever, you can send your value to
that device.
I.e. Lets say your using a PLC, in your function above, you know that the PLC is a 12
bit analog register. So your factor will be 4095. In mach3 you have a Spindle Percent DRO, so you can take DRO99 and multiply it by your factor 4095 so if your "pully range"
for range 1, is 0-100, then at 50 rpm your SS% would be 0.5 * 4095. drop that value into the register that is what controls the Analog output of your module.
so in your function you would to "Reverse" the math, so that when you reach your slow down point, your SS% would be 1.00 *4095. For control as my distance to go would grow less over the final range, I would multipl the distance to go (used as a percent), then feed that back into the SS% dro. So as your traveling across that last distance, your reducing Machs ss%, and as it reduces, your Speed (or poor mans feed in this case), reduces. Until you reach "0". At that pont I would obviously reverse the system.

scott

[beezerlm]

Poor mans feed! Haha! Thanks Scott. Would the rack and pinion repeat well? my concern is that if I am grinding a part up to a shoulder I don't want to crash into the shoulder at the end of my stroke.

[Al_The_Man]

The rack idea would work you can go with a very fine mesh rack for finer resolution.
But If just switching the hydraulic valve off when in position a simple PLC with fast encoder input type could be used with a Maple systems 2 line keyboard/display for data stroke input and a 3 posn valve with centre blocked off configuration, there would be no need to involve Mach or a PC at all.
Al.

[beezerlm]

Al,
I have never used a PLC before but I have set up mach 3 on a few machines. Could a Plc control a servo or stepper in unison with the stroke so the machine operator would be able to set variables such as:


Stroke length:
Stroke feedrate:
Total Grind amount:
Infeed per stroke amount:
Spark out passes:
Retract position after grind cycle:

Would this system work?

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