Collision Detection and compensated bed leveling

Hi,
I'm new to the reprap scene. I've begun sourcing parts and am hoping to put together my first machine.

Would it be possible to put a small force sensor like:
[www.sparkfun.com]
between the extruder and the hot end to detect when the hot end contacts the bed?


I've attached a crude paint drawing for everyone's pleasure.

At the least, the firmware can detect a collision when the nominal resistance value spikes and avoid damage.

If this is taken further we could implement software compensated levelling of the bed. The tilt is first calculated using the following pseudo code:

home x and y
drop z until contact occurs
set origin point
raise z slightly
//Get x rise over run
travel x 1000 steps
drop z until contact
get z difference
set new z rise over x run
//Repeat for y axis from home

So we now have the tilt of the bed. If, for example, the tilt is -1 z step per +100 x steps the firmware can now compensate
by keeping a counter for each axis.

counter_x = 0
When the firmware receives move x +125 steps, it also moves the z down one step and sets counter_x = 25

To keep things building square in the z axis the same counter is applied. every 100 steps its told to move in the z direction, it also moves +1 step in the x direction.

Has this been tried before? What are everyone's thoughts on the feasibility?

nophead has been THERE and done THAT.

---

Bob Morrison
Wörth am Rhein, Germany
"Luke, use the source!"
BLOG - PHOTOS - Thingiverse

Awesome thanks, I hadn't though about running a script on the g-code. I will look into what nophead and James have done. So I guess the question now is whether the sensor will actually work in that position.

Edited 1 time(s). Last edit at 04/17/2012 12:43PM by tonyt.

I don't think you normally want any movement between the extruder and hot end, they will be tightly bolted together. In which case, a force sensor will read that as a high load. You then want to sense a small additional force when the extruder hits the bed, which makes for a difficult combination of range and sensitivity.

This particular sensor has a low temperature range, I don't think it would work well next to the hotend.

The problem with using the hot end as a probe is that it soon gets covered in burnt on crud and usually has plastic oozing from it. When you are trying to measure distances accurate to around 0.01mm these get in the way.

---

[www.hydraraptor.blogspot.com]