Hello Guest it is May 15, 2021, 05:24:01 PM

Author Topic: Accurate Homing and the Boards that can do that, What is everyone else doing?  (Read 3498 times)

0 Members and 1 Guest are viewing this topic.

So I've read the other threads about homing and such. I don't think for my application limit switches will work, unless the built in ones are exceptional.

I'm retrofitting a Mori Seiki SL1 CNC Lathe. What is everyone else doing to home their machines accurately? I used to, on my old Mach 3 lathe, take cuts and measure and go from there, but I'm retrofitting a real cnc lathe and want to use the new hardware to make it work as it should. Which to me means index pulse homing.

At first I was going to use the Pokeys 57E, but after all my research I found out it can't do index pulse homing. I'm probably going to go with DMM 1.8Kw servos and they might be able to do that internally. I've a got an email into them asking that.

As far as boards that can do index pulse homing I'm not sure which direction to go if the DMM can't do it internally.

Here's a list I've compiled of motion controllers that seem to be full functioning.

Galil
Mesa
Rogers Machine Sound Logic Encoder Interface
Dynamotion (kflop)
Smoothstepper, I think.
Vital Systems
CS Lab
I think you have to have a limit switch anyway (usually mechanical) to tell the control when to be looking for the next index pulse.
Milton from Tennessee ya'll.

Offline Davek0974

*
  •  2,606 2,606
    • View Profile
    • DD Metal Products Ltd
I used a cs-labs box on my mill, with a limit switch and index homing, it homes very accurately.
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives.
Plasma table, Mach3 V062, Step motors, C&CNC THC.
Cool. Good to know. I'll take a look at the cs-labs stuff.

I received a response from DMM, very easy to let the servo driver do an index pulse for homing.

Here's what they said:

The servo drive has full encoder output, including the index Z pulse which outputs once per revolution.  But for precise homing, you can use the drive's ABS_H input, which will move the motor to zero absolute position within 1 revolution.

So our usual homing procedure is as follows:

- install a proximity switch near your home position for rough homing
- starting from anywhere one the travel, move the axis back towards the prox switch
- when the prox switch is triggered, turn ON the ABS_H, the motor will move to absolute zero position each time to complete precise homing

I think all motion controllers can support this functionality.  You just need to program the homing procedure into the g-code to read the proximity switch input, then output the ABS_H output to the drive.


So my question is, How do i implement this in mach, obviously I don't want to do this in G-Code. I just want to do it when I start the machine up for the day.

Also if I'm using the homing index within the servo drive then I guess I can use any motion controller I want or BOB??
Hi,
I think most eternal motion controllers support index homing.

I use steppers which don't have index pulses and yet with solidly mounted good quality roller plunger micro switches I can home to
0.05 mm any day any time. Any thing more critical than that I touch off and would still probably do so even if I had index assisted
homing. I think that is the key, indexing assists, without a good reference your indexing could miss.

Craig
My wife left with my best friend...
     and I miss him!
I second the CS Labs CSMIO-IP/A. In conjunction with a limit switch (I use gold contact microswitches). Simply turn index homing on for the CS Labs plugin and the homing function occurs without the need for any code. Homing is more precise than I can measure, certainly better than 5 microns. With this or any similar scheme you need to set your limit switch to operate some distance (ideally half a motor revolution) from the index pulse.

Allan
I use steppers which don't have index pulses and yet with solidly mounted good quality roller plunger micro switches I can home to
0.05 mm any day any time.
Hi Craig, you can get even closer by putting an opto sensor reading a slotted disc on the stepper shaft & wire your microswitch between the opto signal output & the input on your BOB.  It works a treat for me & my steppers.:)
Milton from Tennessee ya'll.

Offline RICH

*
  • *
  •  7,419 7,419
    • View Profile
Quote
What is everyone else doing to home their machines accurately?

Quote
I just want to do it when I start the machine up for the day
.

I don't use any homing switches on my stepper driven lathe nor do I have any fancy drives or break out board and use a quick change tool holder. :o

I just run a probing routine which probes a tool setter mounted in the chuck and the routine automaticaly set's the master tool from the lathes center line and at a defined  point in the Z. I then define home wherever I want it to be. Most of the time there is never a need to be more than half way down the bed from the chuck.

Fast, cheap, very accurate ( +-0.0002" repeatability).

RICH
All good ideas. Thanks.
Hi DICKEYBIRD,
believe it or not the steppers I bought off Ebay actually had encoders on them and I took them off, after reading your suggestion I'm thinking WTF did
I do that for?

The steppers have low backlash 10:1 planetaries so one rev of the motor corresponds to 0.5mm movement with 5mm pitch ballscrews. I did not at the time
think that microswitches, even good ones would get me close enough for index homing to be effective. They do as it turns out. Additionally was using M3 and PP
at the time and the coding required seemed daunting. Have since migrated to M4 and ESS for which index homing is an easy upgrade.
Having said that; the encoders always seem to get in the way in my setup and washed with coolant commonly, its dubious that they would have worked
reliably. Nonetheless some simpler and robust alternative might be possible. Damn! you've given me yet another idea to pursue!

Craig
My wife left with my best friend...
     and I miss him!