7i77 + glass scales on the table + Leadshine EasyServo Step and dir drives

Hi guys,

I have a friend who is using LinuxCNC encoded motors and glass scales on his mill table to get great accuracy and remove any movement in his drive chain (ie backlash and the like)

Leadshine Drives
I would like to do this too but I have Leadshine EasyServo drives and motors which are basically 3 phase steppers with an encoder and a driver that knows what to do with them. They are considered servos but are step and direction driven not the usual PWM voltage variable servos.

You can find them here.
www.leadshine.com/series.aspx?type=produ...-drives&series=ES-DH

My issue
Now the issues I have is if send steps and direct to those drives and would like closed loop feedback from the glass scales on the table what Meas card do I use. Oh yeah, I am also going to be hacking pathpilot to do this as well. If you're going to be going into the ocean you might as well go in over your head. I have it working on a PC its talking to both the 5i25 and the 7i77 card and just needs to be configured. Like saying I just have to figure out how to be rich and I should be sorted.

I will sort out the HAL and INI issues, thats not my question... yet

Which Card the 7i77 or 7i76 or something else
What I would like to know is can this be done with the 7i77 BOB from Mesa which I bought (yes I have the 5i25 in the PC) because if I use the 7i76 which this set up is more suited to then I can't use the glass encoders because there are no encoder pins other than for the spindle on that card? Or is that not an issue because I can send that signal through a GPIO pin and its no issue?

or is it possible to use the 7i77 as a step and direction card?

Any thoughts on this situation? Appreciate any experience you have had with this?

Gus

If you already have a 7I76 and 7I77, you can certainly run both and use the encoder inputs on
the 7I77 for linear encoder feedback, though the 7I77 is wasted and expensive if you dont use its
analog outputs

If you are starting from scratch I would probably recommend a 7I85S ( 4 step/dir + 4 encoder BOB )
and add a 7I84 connected to the 7I85S expansion connector for misc I/O
If 4 axis total is not enough you could run 2X 7I85S giving 8 encoders and 8 step/dir pairs

You can also use a 7I76 + a 7I85S to gain 4 more encoders if you already have a 7I76

Thank you and I do get that the 7i85S was what I should have started with but sometimes when you start a project with an idea, that idea ends up changing or the assumptions were just flat out wrong.

I have the 7i77. Can I use the 7i77 as a step and direction card. Just sending digital signals through those pins? Is that even possible?

No, the 7I77 is designed for analog servo interfacing and has no high speed digital outputs that are required for step/dir drives.

You could add a low cost generic parallel port breakout on one 5I25 connector for step/dir outputs while retaining the 7I77 for encoder inputs and field I/O

I don't know that you can easily use any of the 7i77's outputs easily as step/dir outputs. But you could fairly easily use the extra parallel port header on the 5i25 port bare or with a parallel port breakout board to run your step/dir signals. (Remember the optos on the breakout board will likely be your speed limit.)

If you haven't used the 7i77 yet, perhaps you could exchange it for a 7i85S+7i84, or sell the 7i77 or just save it for another project.

OK so I have a few different machines and I realise that I actually have a 7i76 that I put away from a previous project where I changed the boards out. I would like to use the 7i76 only. I would like to not use two boards because of space issues inside my controller box. Is it possible to input linear scale signals into the 7i76?

I have very little knowledge of the type of signal they would out put.

So I looked into this a little more. Nope that ain't going to work.

It looks like I am going to have to use a combination of BOBs... damn it.

Thank you for your help guys.

A 7i85S + 7i84 is only about the same total size as a 7i76 (It is pretty much a 7i76 cut in half). Obviously two bards will still take a little more space than one, but is an inch or two really going to be a deal breaker for you?