Live demos of the Tape sensor

posted Feb 6, 2013, 12:16 PM by Sensorica Group   [ updated Mar 19, 2013, 12:01 PM by Tiberius Brastaviceanu ]
Today we made some progress on the Tape sensor. We made and tested two prototypes: the 4 fibers all 1mm PMMA fiber, and the 4 fiber one glass 125/62.5 MM delivery and 3 PMMA 1mm collectors 


Test of the 4 fibers all PMMA - 0.1 degrees resolution

First, we built and tested the all 1mm PMMA transducer: one fiber in and 3 fibers out. The resolution test was done  at around 800 microns gap. The device was feed by a red LED. We measured signal steps induced by 0.1 angle degree variations. The acquisition rate was slow in this experiment, only 1kHz. Moreover, 100 points are digitally averaged to reduce noise. The video below shows the results. The signal plotted was intensity of one fiber minus intensity of another fiber. The test was performed on a single axis.


a stereo microscope was used for visualization and optical alignment
experimental setup using mirror on gimbal

The operation of the transducer was simulated using a flat mirror on a gimbal, which is positioned on a XY manual stage.

fiber assembly in front of the mirror
experimental setup using mirror on gimbal
 

Test of the 4 fibers, one glass 3 PMMA - 0.02 degrees resolution

Two versions were made, one with the glass fiber having a flat tip, like in the first picture below, and the other one using a glass fiber with round tip, made by melting, see second picture below.

first version, flat tip glass fiber version


second version, round tip

In both cases a green laser was used. The picture below shows, from left to right,  the laser, a lens, and the fiber.

one 62.5 glass fiber in and three 1mm PMMA fibers out - laser and optics for coupling

In both cases, a flat mirror on a gimbal was used to simulate the operation of the device. The gimbal was placed on a XY stage.

one 62.5 glass fiber in and three 1mm PMMA fibers out and the gimbal

The the case of the flat tip version the results obtained were only sightly better than in the case of the 4 fibers all PMMA prototype. We also noticed that the light coming out of the glass fiber was not very gaussian, almost resembles a flat top, with a lot of speckles.
We moves right a way to the second version, with the round tip, since the results were not encouraging.

The advantage of the round tip is that it makes the exit cone of the glass fiber smaller, and increases the sensitivity of the device. This was confirmed by observing the light out of the round tip of the fiber using a white piece of paper. We used a fiber splicer modified by Jonathan to process the tip of the fiber.

on the computer screen, the 125 micron diameter glass fiber
between the two electrodes, waiting to get zapped
zapped fiber on the sceen

fiber getting zapped on the same screen, you can see the plasma
between the two electrodes. this plasma melts the glass
fiber being zapped on the screen

the kind of shapes we can get, a much smaller sphere was created
in the case of the fiber used in the tested device, see picture above
125 micron D 62.5 MM glass fiber with ball formed on tip


The video below shows the results obtained. Angle steps of 0.02 degrees were made while the signal was recorded. The signal plotted was intensity of one fiber minus intensity of another fiber. The test was performed on a single axis.  We can clearly see that we have a resolution of at least 0.02 degrees. This can be greatly improved by doing some signal conditioning on the electronic board.

YouTube Video




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