Finding the center of a rotary on the table (probe)

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15 Sep 2018 20:29 #117587 by Marcodi
Hi,

I am coming up with my next issue to tackle.

How are you guys finding the center point of rotation on a rotary attached to the table turning around Y axis.

As for programming purposes in cad and cam the coordinate system is set always in the center of rotation.

I would like to be able to probe the chuck to find the center as I think that would be easiest but than I need to find the center based on probing 3 points. Mathematically that is a little far.

Buy maybe you guys have a better solution cause in the end the tooltip need to be set to 0 on the center of rotation and that isn't a flat surface.

Hope someone can help.

Regards,

Stephane

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16 Sep 2018 21:48 #117618 by andypugh
One complication with this, where does LinuxCNC think that the end of the probe is? For this task you need to set it to be the _centre_ of the sphere. ie touched-off to the ball radius.

It is a lot easier if you can simply measure the diameter of the stock first, then you can jog to just above the 3 / 9 O'Clock position to find horizontal centre, then go to the middle and probe the top to find the vertical centre (knowing the diameter)

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16 Sep 2018 21:56 #117624 by Marcodi
Hi Andy,

I want this to be an automated script to find the center. To touch off the probe shouldn't be the hardest issue I guess.

I was thinking that with 3 points on a circle it should be calculable.

On the other hand what you say is true aswell, knowing the diameter of the chuck holder , I should be able to just center it and substract the radius.

Is there any script around doing exactly that movement. In Y direction. Going left, touch off, going right touch off. Centering it touching off and setting xyz to 0. If than I can touch off the probe as reference height as first tool in a gcode , i could work with my current manual tool change script from the forum that works perfectly.

So did anyone write a script like this already?

Regards,

Stephane

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17 Sep 2018 12:45 #117649 by andypugh
There are several worked examples in the internet, here is one.
www.enotes.com/homework-help/find-centre...gh-points-7-4-345231

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17 Sep 2018 22:15 #117677 by Grotius
@Hi Stephane,

To find the centerpoint of a chuck with a probe sensor :

Input's :
1.Chuck_diameter
2.Probe_correction (if needed)
3.Probe_sequence ( 2 circle or 3 circle arc centre point's calculation )
4.Probe_trigger_x
5.Probe_trigger_y

Output's :
1.Centerpoint_x
2.Centerpoint_y

If you want to write a scrips to find the center point, that is possible. Script's in linuxcnc are usually written in C language, this language include's all the mathimatical possibilities so far i know. This script's / function's are named component's in linuxcnc. You can write your own. This way of programming is almost unlimited. You can even make multiple component's to achieve your goal.

You could imagine, that number 3 input parameters is handy. Then you can select a formula routine with the chuck diameter input.
In C code, you can make a Case 1 or 2 or 3.
After that the C code will trigger your sensor in 2 or 3 step's while your probe function is executing. It will calculate your centre point exactly.

For 2 poin't circles, you could go negative or positive centre point's. That you can solve to do *-1 to get it to the positive quadrant.

So this can be your solution. If i needed it, i would write this solution.

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17 Sep 2018 22:19 #117678 by andypugh
No need for C. G-code has all the required mathematical functions.

(and, in fact, it is very difficult to start a probe move, or any axis move at all from a HAL component).

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17 Sep 2018 22:32 - 17 Sep 2018 22:35 #117679 by Grotius
Hi Andy,

Last there was a academic guy in other topic who could not solve circle crossing point's in linuxcnc.
You solved that in matlab.
But maybe the solution is to add a minus/max implementation in linuxcnc too. Then the restart function at arc's can also be solved.

(and, in fact, it is very difficult to start a probe move, or any axis move at all from a HAL component).

For the most user's i agree.
If you use external offset's, you can imagine your right or left hand is moving in the air. Your hand is moving in all kind of position's.
In the external offset branche the robot will follow your hand exactly. Offset's are not difficult. Probing is easy.

Also adaptive feed. Negative g-code speed. Where is it?
I have it all in one version merged myself.

The linuxcnc boss has work to do.
Last edit: 17 Sep 2018 22:35 by Grotius.

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18 Sep 2018 12:07 #117705 by andypugh

The linuxcnc boss has work to do.


The problem there is that there isn't one.

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