Hokoed up a PC to the mill

Excellent! You'll have a lot more fun once you have the servo loop closed and can play around with precise positioning, accel/decel, homing, etc. Remember to wire the index signal from your encoders back to the control for eventual use for precise homing.

I will definitely use the index signal. As of now, I do not even know, yet, if my encoders work at all.

Another big chunk of work is wiring all external things like limit switches, buttons etc.

If you get ambitious, think about adding decel switches to allow you to home at rapid rate most of the way.

My mill does approximately 70 IPM right now, I think that it is slow enough for homing, no?

Most likely not, but it depends on how fast your decel rate ends up set at. You will probably want to home at around 10 IPM so you can drop down to 1 IPM when you detect the limit switch and creep up on the index without overshooting it. You'll figure it out once you start testing your homing. You can also either adjust your limit switch position slightly, or your encoder position on the motor shaft so that the index pulse isn't too close behind the limit switch trip point.

The key thing with decel switches is that they allow you to home at rapid speed most of the way through the homing process, which on a machine with long travels and high rapid speeds can make a significant difference in homing time.

Crappy ASCII art for homing sequence:

---------->|---------->|--------->| (home) (rapid) ^ (slow) ^ (creep) ^ D L I e i n c m d e i e l t x

You rapid travel in the home direction until you hit the decel switch about an inch out from the limit switch. When you hit the decel switch you drop from rapid to slow until you hit the limit switch. When you hit the limit switch you drops to creep for ~ 1/2 rev until you reach the index signal at which point you stop and zero/home the axis.

Obviously if the axis happens to be near the home end at the start, the decel setup doesn't make much difference, but if the axis is a few feet from home, being able to rapid most of that distance saves a lot of time.

...

The home procedure with a galil card is different. First it homes off only a home switch and an encoder index pulse on each axis

1. rapid till NC home switch opens.
2. reverse slow till home switch closes
3. creep till index pulse made.

This is occurring on all axis simultaneously. If you shut down anywhere near home it only takes a few seconds.

Karl

That's a similar process really. It's basically using a decel switch as the home switch, and needs to have enough travel after that decel/home switch to avoid crashing into the limit when rapiding in to home. One presumes that this setup also includes a home offset, so that axis zero is just off the limit and not +1" out at the decel/home switch.

The X axis home on lathes is nowhere near a limit. You don't want to go clear to the back of the lathe to home it.

At least on my machines decel switches aren't used. Instead softlimits are used to prevent motion out-of-bounds. They allow for a barrier in the work zone like a lathe chuck. Just more than one way to skin a cat.

Karl

Karl, just curious, do you do CNC retrofits for money? As in, "I will set up your machine with a new control for $XXXXXX.XX"? Or do you buy, retrofit and sell machines?

Yes, it makes no difference where along the axis you home, as long as you know where that point is.

Softlimits don't work when you are not sure of your position, such as when you are homing.

EMC2 has a two-stage or 3-stage homing sequence. It runs at a high speed toward the switch, reverses and then approaches the switch slower, then can search for the index pulse from the encoder. So, as long as the initial search is slow enough that the reversal doesn't overtax the machine or run past the safe limit beyond the switch, you can make the initial search as fast as you like. All 3 speeds can be set in the .ini file.

Jon

I'm too slow an electrician and millwright to refit for money. I consult by the hour for control programming. I also buy used control equipment, test it, and resell. And I get a commission on any software I sell. All of this is just a sideline.

Karl

Sounds like a great sideline. What kind of control programming are you referring to, just curious.

This sounds like a perfect implementation. Thanks. I will try to hook up one encoder to your board tonight.

Camsoft and Galil

Karl

On Mon, 12 Jul 2010 14:15:01 -0500, "Karl Townsend" wrote the following:

Yabbut, your real job is giving away (but not shipping) bushels of apples, isn't it, Karl? ;)

I should add that if your home point is not at the end of an axis travel, your homing routine needs to have the intelligence to reverse and search for home in the other direction if it encounters a limit switch instead of a home switch.

I haven't had a real job since 1991. Right now, we're giving away (but not shipping) garden vegetables out of Julie's high tunnel. We just finished strawberries, and then a break until apples.

Karl