Work with probe

More
17 Jul 2015 18:52 - 17 Jul 2015 18:59 #60683 by ruffle
Replied by ruffle on topic Work with probe
Having engaged what's left of my brain... You're right and I'm an idiot :( [1]

If I change xminus.ngc and friends so they do:
G91
G43 H99
.....
G49
G90
and setup tool 99 that should do the trick.

Still might be nice if this was built into probe_screen.py though. I'm sure I'm not the only cheapskate that'll baulk at the cost of a Renishaw and buy a cheapy probe.



[1] - I should know better than to give a moments credence to the silly thought that AtP gave bum advise on something mechanical :laugh:
Last edit: 17 Jul 2015 18:59 by ruffle.

Please Log in or Create an account to join the conversation.

More
25 Jul 2015 21:13 #60906 by lerman
Replied by lerman on topic Work with probe

ruffle wrote: Can I suggest a modest but potentially very useful mod for this?

A probe tip offset/compensation method.

I've bought a probe (admittedly not a Renishaw!) and getting the tip centered to any reasonable accuracy is turning out to be a right pain.

Given that the probe would always be mounted in the same orientation (not unreasonable as the cable kind of dictates a natural place and I'd mark the front of the probe body and always use that facing the front of the machine), I know that probing in -X it measures 0.12 less than +X, +Y some 0.08 more than +X and -Y 0.04 less than +X.

It's easy to measure the offsets by turning the probe through 90 degrees and probing a known face in +X so if I could enter those differences into the probe routines (it doesn't even need to be in the GUI, editing the .pref file or setting a value in the machine's .ini file would be fine) and the calculations took account of the offsets I wouldn't need to worry that the probe tip is not 100% on centre.

Any chance of getting this added? or is it already there? I see references to 'tool_offset[]' in probe_screen.py but that array doesn't seem to be set to anything (warning my Python skills are less than my levitation skills :) so I could be missing the blindingly obvious!).


Ruffle: You have it half right. -- no insult intended. :) In the sense that 90 is half of 180.

I've implemented some probe calibration code. I've added "wings" to my probe to let it be rotated 180 degrees against a stop. I call the two positions A and B. I use a round hole for calibration. I took a drill bushing and glued magnets to the bottom so that I could stick it to my table or vise. The diameter of the calibration hole doesn't matter.
Then:
1 -- Rotate the probe to the A position.
2 -- Find the center of the hole (I use a subroutine I call calibrateA)
3 -- Rotate the probe to the B position.
4 -- Find the center of the hole (I use a subroutine I call calibrateB)
The true center of the hole will be *exactly* the average of the two values -- exactly to the extent that the probe was rotated exactly 180 degrees.

You can then compute the offset necessary. My calibration routines do that and display the new computed offset and any previous computed offset. I use the A position for my measurements, so that's the offset I compute. My probing routines automatically add the offset. (It should be noted that the calibration routine also corrects for errors in the collet that is used to hold the probe.)

Some results (on an old Bridgeport Clone I converted with ball screws). The probe cost me $79 (new on ebay).
1 -- When I probe a center, it regularly repeats to 0.0002 inches on both axes.
2 -- I calibrated the probe, used it, and then removed the probe and calibration fixture from the machine. I later put the probe back on the machine (its not necessary to recalibrate it.) I forgot that it had already been calibrated and calibrated it again. The difference between the old and new offsets was zero (to four decimals) on the X axis and 0.0001 on the Y axis.

Since the probe had been driven into the table by bugs in the software :( the offset was around .018 in one axis (I don't remember the other offset).

I'd like to be able to provide copies of my routines, but they probably aren't ready for prime time.
1 -- There is no documentation
2 -- They are integrated with the software I use for my MPG. That let's me do things like:
A -- Using the MPG move in some direction.
B -- Push the probe edge button. The probe will move in the same direction as the last move to find an edge.
C -- Push the set zero button. The last axis that was be probed will have the last probed position set to zero in the current coordinate system.
D -- Move somewhere else
E -- Push the probe edge button. The probe will find the new edge
F -- Push the half button. The current axis value will have zero as the half value of the new probed position. In other words, the axis was zeroed to the midpoint (line) between the two probed points on the axis.

Ken

Please Log in or Create an account to join the conversation.

More
27 Jul 2015 08:30 #60944 by thor44
Replied by thor44 on topic Work with probe
I love the screen but I am having a hard time getting the probe screen to display the buttons. At this point I am confused as to were these files are and how to get them. Can someone please help?

The following files from the archive are placed in:

your-folder-configuration/python

probe_screen.py

your-folder-configuration/your_subroutine_path

all from folder "macros"

your-folder-configuration/probe_icons

all from folder "probe_icons"

~/

.axisrc

Please Log in or Create an account to join the conversation.

More
27 Jul 2015 13:47 #60948 by verser
Replied by verser on topic Work with probe

thor44 wrote: Can someone please help?

Hopefully, you do not perceive this folder name as literal (your-folder-configuration/your_subroutine_path).
These names should be replaced by the name of your configuration folders.

Please Log in or Create an account to join the conversation.

More
27 Jul 2015 14:04 #60949 by verser
Replied by verser on topic Work with probe

lerman wrote: I've implemented some probe calibration code.

This is a very useful feature, it is very interesting to look at the source code.

Please Log in or Create an account to join the conversation.

More
27 Jul 2015 18:46 #60954 by thor44
Replied by thor44 on topic Work with probe
I have two configs one is axis and the other is gmoccapy I followed the instructions and everything works in axis except the screen it's cut off at the bottom but only the tab screen shows up in gmoccapy no icons.

Please Log in or Create an account to join the conversation.

More
29 Jul 2015 02:58 #61002 by lerman
Replied by lerman on topic Work with probe

verser wrote:

lerman wrote: I've implemented some probe calibration code.

This is a very useful feature, it is very interesting to look at the source code.


Verser -- you asked for it, you got it.
See:
www.se-ltd.com/~lerman/files/safe_probe_init_for_verser.ngc

Notes:
1 -- Some of the code relies on the MPG software that I'm using -- so don't expect it to work without more information
2 -- Some of the code has never been debugged -- so don't expect it to work
3 -- Some of the comments are out of date -- so don't expect the code to work as described

I'm rather proud of the o<safe_probe_xyz> subroutine.
It is a single subroutine that:
1 -- can probe in any direction
2 -- is safe in that all moves STOP if the probe hits something
3 -- adjusts for the diameter of the ball (with the assumption that the ball touched in the direction of motion)
4 -- adds a calibration offset to the returned value
Please note that its probe algorithm is:
1 -- advance at search speed until a probe hit (a maximum of -- as configured -- one inch)
2 -- back off at low speed until the probe releases

The "edge" routine looks at the last direction the MPG moved the probe and probes for an edge in that direction. I use the "probe-z" button on the MPG for that purpose.

Use this code at your own risk. Feel free to use any ideas in it. It would be nice if you give credit for anything of great value, but that's up to you.

Please let me know what bugs you find and any suggestions you might have.

Regards,

Ken
The following user(s) said Thank You: verser, nonante9

Please Log in or Create an account to join the conversation.

More
29 Jul 2015 03:44 #61004 by thor44
Replied by thor44 on topic Work with probe
Wow that's alot of code. Do I put it in the macros folder as one file? Sorry I'm still new to all of this.

Please Log in or Create an account to join the conversation.

More
29 Jul 2015 13:27 #61010 by verser
Replied by verser on topic Work with probe

lerman wrote: Verser -- you asked for it, you got it.
See:
www.se-ltd.com/~lerman/files/safe_probe_init_for_verser.ngc

Enormously grateful.

lerman wrote: I've added "wings" to my probe to let it be rotated 180 degrees against a stop.

I apologize for the excessive curiosity, сould you show this "wings"?

Please Log in or Create an account to join the conversation.

More
29 Jul 2015 22:41 #61017 by lerman
Replied by lerman on topic Work with probe

verser wrote:

lerman wrote: Verser -- you asked for it, you got it.
See:
www.se-ltd.com/~lerman/files/safe_probe_init_for_verser.ngc

Enormously grateful.

lerman wrote: I've added "wings" to my probe to let it be rotated 180 degrees against a stop.

I apologize for the excessive curiosity, сould you show this "wings"?


No need to apologize.

See: www.se-ltd.com/~lerman/files/wings.jpg and www.se-ltd.com/~lerman/files/wings2.jpg

In use, a 5/16 inch diameter rod is mounted on the head of the milling machine oriented vertically so the part of the wing most aligned with the axis of the probe is against the rod. That's for the "A" position. Then the probe is rotated 180 degrees so the face of the opposite wing is against the rod. That's the "B" position.

The wings have been cut so that the line they define is 5/32 (half of 5/16) offset from the center of rotation of the probe. That makes the two positions exactly 180 degrees apart.

Unfortunately, the mounting I have for the rod is no precisely vertical (parallel to the spindle). I'm working on making an alternative mount. When that is done, I will inset magnets into the edges of the wings to hold the probe in contact with the rod.

I've looked, but have been unable to find any reference to the technique of rotating the probe 180 degrees to provide automatic offset calibration. It is certainly easy to do and accurate.

Regards,

Ken
The following user(s) said Thank You: verser

Please Log in or Create an account to join the conversation.

Time to create page: 0.158 seconds
Powered by Kunena Forum