3D Digitizing Probe

[luke]

I broke my Starrett 827B edge finder and am wondering if there is a way to use the digitizing probe as an edge finder?

Would the accuracy be comparable?

[Brady Watson]

Yes. There are 2D digitizing routines built into the CopyMachine.

As far as accuracy goes, I don't know what your Starrett does now. What resolution are you looking to get out of the probe?

-B

[luke]

Hi Brady. Thanks for the quick response. Before my Starrett became a high velocity projectile, I was getting about +- .0002 on a CNC milling machine. On the shopbot I suspect +-.0005.

With the probe I would be very happy with +-.010

I would like to use the probe to bump the edge something like a proximaty switch and mark zero.
Also, I don’t want to muddy the thread but I would also like to be able to compare or find the upper most height of something like say a dome.

[Brady Watson]

You can use the SB probe for this. I'm not sure if it has been corrected/compensated for in the latest version of the software or not, but in some cases, you have to account for 1/2 of the probe stylus' diameter. E.G. - If probing a 10" circle with a .125" tip, the scan may come out to be 10.0625" in CAD. You'll want to check this to be sure.

-B

[luke]

I did the same with the edge finder.
I've searched all available documentation and am unable to locate any specific instructions for using the probe to find the edge.

[Brady Watson]

When you get into SB3, Type in the 'TC' command, and then go thru the Probe 'wizard' :


4872
4873
4874

[luke]

I understand outline a pattern function. How does this serve to touch off a point on a edge to set x=0 and the same for y=0.

For instance with an edge finder I move the machine in until I bump the piece and move off until the wobble stops. Perfect Zero every time. I thought there might a efficiant way to treat the probe much like a proximaty switch and accomplish the same thing.

[bill.young]

Luke,

Look in the c:\SBParts folder for a file named "S_Center_inHole.sbp". It uses a metal rod to find the center of a hole and you may be able to pull bits and pieces from it to do what you want. There are a handful of issues I see though...

1) That file's written for a "normally open" system and the probe is normally closed, so you would have to change all the INPUT tests from "ON INPUT (1,1)" to "ON INPUT (1,0)". You would also need to change the "IF %(51)= 1" tests to "IF %(51)= 0"

2) I don't believe there's a way to be able to use the keypad to steer it around and have it stop when it makes contact, if you're using one of the regular input switch(1,2,5,6,7, or 8), though I must admit I've never tried. If you could rig up the probe somehow (maybe with a relay?) so that it was normally open then you could connect it to input 3 and use it like a limit switch, so that it stopped moving when it made contact..that could work. You would have to be very careful that you didn't mess up your regular limit switches, though...you're on your own with this one!

3) one other limitation is that the probe stylus moves a little before it triggers when it makes side contact so that the center might not be directly above the stylus tip when it triggers. Not sure that would matter but it's worth thinking about.


Bill

[luke]

Thank you Bill for opening my eyes to a whole new world of possibilities. I’ve spent the last couple of days trying to figure out a new edge finding solution and I think the following routine accomplishes just that. I would greatly appreciate if my fellow Botters would critique this X-Axis Edge Finding routine for me. Please keep in mind a few points;

I am not a programmer. This is my first attempt and I could only locate a very limited amount of documentation. I took Bill’s advice and borrowed from what is already working. Does anyone have a command list on how to use, ON INP and conditional statements? Is there a Shopbot Routine Programmers guide?

I work in Inches so I made no accommodations for metric.
I chose to keep separate X and Y Edge finding routines because I may want to locate a different or an irregular area of a part.
I am not automatically setting X to zero because if there is a problem I do want to have to reprobe the edge after rezeroing using the proximity switches.
If I just reinvented the wheel please clue me in to the better way. Thanks.

'**************Verify Move/Cut mode
&modenow = %(22)
IF &modenow = 1 THEN GOSUB CHANGEMODE

'**************Initialize
SR, 'Relative Mode
SF,0 'Turn off limit checking

&xbot = 1
&xback = -.5
&big_move = 2 'value X move
&start_Xmove_Speed = %(71) 'Current X speed values to reset later
&new_Xmove_Speed = .25

'Make First Move

' *** Hit ENTER if Probe is within Two Inches of X-Axis ***
PAUSE
ON INP (1,0) GOTO CONTACT1
VS, (&new_Xmove_Speed * 2 )
MX, &big_move
VS, &start_Xmove_Speed

[luke]

Corrected Routine.

'Find X Edge
'**************Verify Move/Cut mode
&modenow = %(22)
IF &modenow = 1 THEN GOSUB CHANGEMODE

'**************Initialize
SR, 'Relative Mode
SF,0 'Turn off limit checking

&xbot = 1
&xback = -.5
&big_move = 2 'value X move
&start_Xmove_Speed = %(71) 'Current X speed values to reset later
&new_Xmove_Speed = .25

'Make First Move

' *** Hit ENTER if Probe is within Two Inches of X-Axis ***
PAUSE
ON INP (1,0) GOTO CONTACT1
VS, (&new_Xmove_Speed * 2 )
MX, &big_move
VS, &start_Xmove_Speed

[bill.young]

Hi Luke,

With many thanks to Ralph for all his help (and motivation
), the Programming manual is getting an update. The current version is installed with the beta software and downloadable in the Documentation section of the ShopBot web site at http://www.shopbottools.com/documentation.htm

One quick note to all: There's a new MSGBOX command that will only work in version 3.5 or later of the Control Software...the beta software at the moment. Don't use it in files that will be run in older versions...

Bill

[luke]

Wow, that's a lot of well written documantation. Bill and Brady, thank you for all your direction. I always look forward to reading your opinions and advice.