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Author Topic: MPG gear ratio - Is there even a solution? Also limit problem?  (Read 3357 times)

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MPG gear ratio - Is there even a solution? Also limit problem?
« on: December 07, 2014, 05:26:58 PM »
Hi guys,

Thanks as always for all the effort that has gone into Mach and the Galil plugin,

Here is my problem. I'm retrofitting a high precision CNC grinder that has resolvers on it.

I have completed one before with a different PC based control and it was a breeze in comparison to this, but now I'm running a Galil DMC-4080 and Mach3 with the Galil plugin.

I have Vega boards that convert the resolver feedback to quadrature encoder signals, but those resolvers are geared so this machine has high counts per revolution of the leadscrew, and the leadscrew is fine pitch so I think I have something like 200,000 counts per inch. My pendant however is a 100PPR encoder that is sending the Galil 4 counts per detent, or 400 counts per full revolution.

If I want to turn the MPG at .1" per detent, I need a gear ratio of 20,000:4.

The Galil allows for a max GR value of 127. I read in the Galil documentation that you can have an axis slaved (GA command) to a master virtual axis of M or N, but I think that only really is applicable to move commands. I haven't tried making a virtual axis a slave to my master MPG axis (the D axis on my Galil) and then being able to have a gear ratio on that multiplied by the gear ratio from the virtual to the X or Z axis (A and B on the Galil), if I were able to do that I could then have a max ratio of 127 * 127 which would be 16129:1 which would be above the 5000:1 I need. I think from the "Arguments" in the Galil Command list that virtual axis cannot be used as a slave with the GA command. Assuming that is true, is there another way?

Also, my homing routines are functioning well, but when I hit a limit switch with the MPG I can still jog as though nothing has been triggered (Mach3 and Galil show the appropriate limit LED has been activated), if I jog via buttons I can also keep jogging after hitting the limit, but if I stop jogging and then try to start jogging again it will only let me jog off the switch. Still, if I wasn't watching I could easily damage the machine!

This is pretty strange, I would have thought the software would tell motion to cease once a limit has been triggered by default. Have a missed a checkbox somewhere? Auto limit override is off. I'm surprised the Galil unit itself even allows it! The Galil has axis specific with direction specific pins... I would think once the servos and encoders were properly configured the machine simply wouldn't allow such motion! The Galil does know it has hit the switch, this isn't an "active low/high" issue.

Anyway, I have spent so many hours searching to find the right button to click, the right value to change to rectify the smallest of problems, I really need some feedback on these issues. The development of Galil use as an add-on to Mach3 probably is partially to blame for the tricky configuration issues. The other PC based control I installed was an absolute walk in the park in comparison, especially the ladder logic editor compared to brains. Brains do work well though!

Thanks,

Dave