Wednesday, 11 December 2013

My Rep-Rap Prusa

This weekend I finally finished the new housing for my 3d printer.

I made it out of 12mm MDF and 3mm Acrylic glass. The nasty smell of plastic during operation is now completly gone and it is now considerably less loud. I used a gasket which is actually used for doors and windows to seal the gap between the glass and the MDF what makes it pretty air tight.
Also the new mounting of the filament spool works great, cause before I had the spool mounted underneath the table what caused some problems from time to time when the filament got stuck.

Proof of Concept 2: The cheap DIY optical potentiometer

Today I found some time to do some further tests regarding the idea of a printable optical potentiometer.
I tried to print gradients on some overhead sheets I had laying around and the result was this:
The vertical axis is the voltagae, the horizontal axis are the centimeters of the test-strip.
As you can see the average error is 13mm on a distance of 23 cm. That´s absolutely too much and if you calculate how much error it would be for an angular sensor then you get an average error of 21 degree.

To explain how I made the measurements: I wrote a Qt program which produced the gradient together with a millimeter raster. then I printed it out with my HP Officejet 5605z All-in-One with the maximum possible resolution and finally I used the millimeter raster to do a measurement every centimeter. The schematic of the measurement circuit

and the sensor.

As it seems the nonlinear curve that I got when I did the tests with the paper was caused by the paper, cause this time I got relatively linear values without changing the gradient.
I think if I would have access to a better printer I could improve the results but the precision is so bad that I don´t think that you could get acceptable results with this kind of sensor without using any special materials/printers. So for the use in robots it will be better to simply use the approved quadrature sensors.