How the sensors work, and what you can and cannot do

[DocWheeler]

Attached is an explanation of the "measurement" sensor and what is needed for the firmware to measure correctly.
This text was part of an earlier project that fell into the cracks somewhere.

Please note that there are current sensors on the smaller motors to tell the machine things, and there is the brass roller that senses board movement. This text is not about those sensors, it is about how the firmware uses the sensor that is mounted under the "Y" truck that detects the edges of the board.

Imagine that the figure is a small block of wood mounted between two rails with tape across the ends of the rails.
The letters and numbers are points along the sensor paths as described in the text.

53519
53553

[dcalvin4]

Wow Doc now i know why you were absent from this forum all those months.....................PROOF READING........
this is an excellent xplanation
i never would have ben able to splane that..........GOOD JOB
denny

[DocWheeler]

Thank you Denny, it has had a few revisions!

[Digitalwoodshop]

Ken,

Can you save it or post it as a PDF? I can't open a .doc file. My Word is too old... Like ME working on a Sunday... The Tags of my Life... LOL...

Thanks,

Word Challanged... AL

[DocWheeler]

Al,

I wasn't thinking, sorry. I attached a pdf to the original post.

[Digitalwoodshop]

Thanks Buddy... It was ME..... "Word Challanged...." I should update my WORD and EXCEL.... Heck, it's a Business Tax Deduction....

Great PDF... Great Info...

Thanks,

AL

I can quit now after wondering what the .doc said..... Thanks !!! Midnight... I am out of here...

[brdad]

Regarding the "The sensor stays "off" until somewhere after point 5..." statement...

I have always assumed the sensor turns "on" i.e. near point 5 once the board leaves the brass roller. I make this assumption based on the fact once the board leaves the brass roller, the board travel slows down a lot as it prepares to find point 6. But I could be wrong - I often am! But it might be worth checking for yourself.

[DocWheeler]

Al, I was in such a hurry to see the size of the file, that I clipped from a pending T-N-T, that I wasn't thinking of anything else. Just trying to get the data out there since there seemed to be some confusion. Glad to hear that it was helpful.

brdad, I'm assuming that you are talking about the right roller rather than the brass roller; I agree that it seems to start looking when it is more than an inch from the end, but LHR told me it was 1/2". When the firmware decides to start using data from the sensor would not necessarily be associated with any mechanical actions that you would notice.

[bergerud]

Brdad: A sled under a board may extend past the ends of the board. (try it.) The brass roller can remain in rolling contact during the whole process. It seems that the cues for the board sensor to sense the board ends come only from the roller switches.

[brdad]

Brdad: A sled under a board may extend past the ends of the board. (try it.) The brass roller can remain in rolling contact during the whole process. It seems that the cues for the board sensor to sense the board ends come only from the roller switches.

Ah, thanks - that's probably why I never noticed otherwise as I have not used a sled designed like that.

[bergerud]

Actually, I think the computer ignores the brass roller data while the front roller is dropped. This may have some accuracy consequences. While the front roller is dropped, the X measurement must be handled only by the X encoder data. There is a backlash problem in the X drive system because of all the gears, bearings, and belts. The normal comparing and updating with the brass roller data cannot be done and hence, determining the location of the front of the board may not be so accurate. I think this is why LG always places his projects from the end. The place on center involves this uncertain front edge position.

In cases where the position of a carving or milling on the board is important, one might follow LG and use place on end (or corner).

[cestout]

Thanks, now I understand a lot that I wondered about. From my experience a sled can extend past the end of the board if that part of the sled is not under the eye. Right now I am carving with skids on both edges longer than the board, but I have tried thin stuff extending past the board and under the eye and confused the machine. But taping skids to hot glued end extensions works well. Right now my sled developed a little bow, so I taped on skids to compensate.
Clint