Integrating a BCL-AMP capacitive sensor to LinuxCNC

Ah, that's very interesting! I'll try to keep track of customizations that would make sense as we continue to integrate our machine. I've been pretty pleased at how workable QtPlasmaC is "out of the box" for our simple fiber laser with very little additional customization.

On thing I've wondered is if there an existing thread or any discussion/thoughts on the possibility of adding additional properties to a material (e.g. laser focus height)? If not I'll start a separate thread. I expect that would take some doing.

Thanks!

Scott

shasse wrote:

Ah, that's very interesting! I'll try to keep track of customizations that would make sense as we continue to integrate our machine.

We could possibly add a fibre laser mode into QtPlasmaC and integrate any required changes into the base code.

One thing I've wondered is if there an existing thread or any discussion/thoughts on the possibility of adding additional properties to a material (e.g. laser focus height)?

Not that I am aware of.

I expect that would take some doing.

Yes, it probably would. I will look into it.
If we did have a fibre laser mode we could do it there.

I added a 74HC74 flip flop IC and divided the frequency signal by 1/2, which now works perfectly with a muxed A encoder. I couldn't get periodm to read the signal cleanly, it only updated the frequency if I touched the nozzle, but that's probably user error.

The good news about the 74HC74 chip is that by reducing the frequency sent to the encoder, it is a cleaner signal and the detection distance from the sensor increased from 0.1" to approximately 0.75". I am able to detect way further now with great response which should help immensely.

I'll have to grab some data to see how linear the response is now. One weird thing though, when the surface approaches the nozzle, the frequency increases until contact, and then it goes back to 0 (approximately) Hz. It has the opposite effect as before.

Glad that the flip-flop worked. A bit surprising that a frequency
output sensor didn't output a square wave to begin with.

On the periodM, did you set the input filter fast enough to catch
the narrow input pulse? (say 0.1 usec or shorter)

Setting the input filter to 0.1 usec did the trick. The sensor does output a square wave, but it's not very clean or stable. For some reason, I can't get the periodm frequency value to show any change in sensor output no matter how close or far I am from the sensor. With the sensor at a static range, there is a considerable amount of noise causing the sensor to range from 2.38 MHz to 2.42 MHz, with some blips above and below that even. For now I'm going to revert back to the flip/flop as that was working, although the sensor still has oddities at the extremes. Perhaps I need to buy a new BCL-Amp.

I am powering the sensor from the +5v from the encoder rail on the 7i76e. Is this power clean enough? Or should I add decoupling caps/use an external power supply?

 

Edit: I've added the current frequency response I get from the sensor once it's gone through a 74HC14 Schmitt Trigger and then a 74HC74 Flip Flop. The Z move is 0.500", and the peak BCL-Amp-freq is at about 0.060" above material. Perhaps I don't need the first Schmitt Trigger because the 74HC74 has a Schmitt Trigger as well. I'm having issues figuring out how to deal with the response after ~0.100" Z, it causes my "voltage" to go back up. I only care about the first 0.050" or so for THC purposes, but if the metal buckles or there is a drastic change in height, it will cause issues with the THC.

Note that I wasn't seeing this inversion when I plugged the signal straight into a non-muxed encoder without the flip flop. The signal started high and decreased to zero, my current frequency reading is starting low and increasing and then decreasing the further it gets away.

That frequency response is odd and not like anything I've gotten. It has certainly not been a linear response (far from it), but the frequency has always increased with lower capacitance. One thought: is your workpiece well grounded? I added a wire off the star ground in my machine that has a clamp on the end, and I clamped that to the metal standoffs that the workpiece sits directly on.