HEALD ID GRINDER EMC2 PROJECT

[beezerlm]

I have an old heald ID grinder model 271, I believe from 1951. The machine is in good shape other than the hydraulics. I have decided to attempt to take over control of the main table cylinder by means of a moog servovalve operated by EMC2. I have never used EMC, but I have done a lot of Mach 3 retrofits in the past. Also, my knowledge of hydraulics is limited, so I hope to learn a lot from this.
Here are pics of the machine. I tore it all apart and painted it a few years back the same color as my chevalier surface and OD grinder. It needs cleaned up a bit cause its been sitting for a few years.

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[beezerlm]

Here is a picture of the Moog valve, a Mesa 7i43, and a precision level that was build into the machine table. The back of the level says "June 51" on it. I also have a dell optiplex 620 with EMC2 installed I plan to use.

Here are the specs on the servovalve:


-772-280 has model code HXXFOFM4VAL
H high response (standard)
XX 4 GPM
F 3000 psi max pressure
O 4-way, axis cut spool
F standard, low flow pilot
M midposition spool (no bias offset)
4 internal pilot supply pressure
V Viton seals
A 4 pin connector, orientation over "A" port
L +/-40mA command signal

[beezerlm]

Here the diagram of the hydraulic system from the manual. I plan on keeping just the area circled.

[beezerlm]

Here is a sketch of a manifold block I plan on making to mount to the moog servovalve.

[svenakela]

Cool! Did you post this to the mailing list?

[beezerlm]

Cool! Did you post this to the mailing list?

I did not know there was a mailing list. Is this the URL? Gmane -- Mail To News And Back Again

[Al_The_Man]

How do you intend controlling the valve? or are you going to use a simple ±10vdc analogue to 40ma conversion?
Al.

[svenakela]

I did not know there was a mailing list. Is this the URL? Gmane -- Mail To News And Back Again

The mailing list is the info channel number on when it comes to EMC2.

LinuxCNC.org - Community

[beezerlm]

How do you intend controlling the valve? or are you going to use a simple ±10vdc analogue to 40ma conversion?
Al.

Yes, I was hoping to accomplish exactly that. Is that possible with the mesa 7i43?

[beezerlm]

The mailing list is the info channel number on when it comes to EMC2.

LinuxCNC.org - Community

I subscribed to the list. Should I post a link to this thread on the mailing list? I am not familiar with the mailing lists and what to expect.

[svenakela]

I subscribed to the list. Should I post a link to this thread on the mailing list? I am not familiar with the mailing lists and what to expect.

Write a hello and describe what you're doing, that would be fine.
I think you'll get some good response, all the sharp edged guys are there.

[beezerlm]

Today I made a trip to a friends shop who's sole focus is hydraulics. I had him make up a couple new lines for the machine and and talked to him a bit about what I am doing.
He said he would run a few calculations on what I can expect for a feedrate in in/min with 4gpm rating on the servovalve and a 3" cylinder bore ( 3" is a guess ).
I also posted a message on the emc2 mailing list regarding this project. ( I don't see it there yet? )

[Al_The_Man]

Yes, I was hoping to accomplish exactly that. Is that possible with the ?

From what I see of the 7i43 card, it is a plain I/O card?
What you need is a 0-40ma or 2x 0-20ma drivers, these could be driven by a +-10v analogue card with 10v to 40ma or 2x20ma drivers.
Do you intend to have any feedback of any kind, this is usual with a servo valve such as you are using.
Al.

[beezerlm]

From what I see of the 7i43 card, it is a plain I/O card?
What you need is a 0-40ma or 2x 0-20ma drivers, these could be driven by a +-10v analogue card with 10v to 40ma or 2x20ma drivers.
Do you intend to have any feedback of any kind, this is usual with a servo valve such as you are using.
Al.

Al,

I think I could get the +-10v by adding a 7i33 daugter card to the 7i43. But I am not sure how to convert that to current control?
My servovalve says the coil is 40 ohms, could I dial in the resistance of the circuit to 250 ohms so that 10vdc would produce 40ma? For some reason That sounds like it would be too easy

[beezerlm]

As for feedback, I was thinking about a rack/pinion setup with a rotary encoder on the pinion. But if I can find a good deal on a glass scale, I may go that route.

[svenakela]

I didn't find the mail on the list. Did you subscribe? Must do that.

[beezerlm]

I didn't find the mail on the list. Did you subscribe? Must do that.

Yes I did subscribe. I think it may not have gotten posted because I included a link to this thread?

[Al_The_Man]

Al,

I think I could get the +-10v by adding a 7i33 daugter card to the 7i43. But I am not sure how to convert that to current control?
My servovalve says the coil is 40 ohms, could I dial in the resistance of the circuit to 250 ohms so that 10vdc would produce 40ma? For some reason That sounds like it would be too easy

You need to get or make a ±10vdc to 0-40ma convertor, I read on a another site a while ago someone had paralleled a couple of the more common ±10vdc to 0-20ma controls.
40ma will give you full tilt on the servo, you need to regulate it from 0 to ±40ma for variable servo control.
I built one for a similar valve using a National Semi LM759, they have a very simple circuit in their app notes for the IC, In your case using it with a simple series resistor to limit to 40ma max. may work.
http://www.national.com/ds/LM/LM759.pdf
Page 10 DC servo.
Input standard ±10vdc analogue.
Al .

[Al_The_Man]

Apparently the LM759 is obsolete now, there is a close equivalent TI OPA547, DigiKey has for around $8.00.
Al.

[beezerlm]

Apparently the LM759 is obsolete now, there is a close equivalent TI OPA547, DigiKey has for around $8.00.
Al.

Thanks Al, I found the data sheet www.ti.com/lit/ds/sbos056f/sbos056f.pdf

I see it has a current limit feature, but I cant find a diagram that shows a relationship between Vin and Iout?

I see a motor control circuit in the datasheet, but could there be a more basic circuit since I won't have the regenerative force of a motor to deal with?

I also found an Operational Transconductance amplifier IC OP861 that looks like it may work. Data sheet here: http://www.ti.com/lit/ds/sbos338f/sbos338f.pdf What do you think?