Beam deflection sensor built and tested

posted Apr 27, 2013, 11:54 PM by Sensorica Group   [ updated Apr 27, 2013, 11:56 PM by Tiberius Brastaviceanu ]
On 26th of April we finished the assembly of the first beam deflection optical sensor. Tibi worked on the photonics and the optomechanical assembly. Jonathan supplied the electronics. Ivan and Daniel also helped with the understanding of how it actually works. 

The night before the demo, Tibi, Ivan and Daniel tested the prototype.

YouTube Video

This prototype uses the Optical Design - Tape sensor one in (glass) 3 out (PMMA).

Optical Design - Tape sensor one in ‎(glass)‎ 3 out ‎(PMMA)‎

As you can see in the video above, we used an aluminum tube as the main structure of the beam. The fibers were placed into a grove made on a wooden rod, which was about the same diameter as the inner diameter of the aluminum tube. Glue was pored into the grove to keep the fibers in place. For lever we used an 2mm OD, 10cm long acrylic rod, which we coated with silver on a tip. The tip was polished with 1 micron paper before coating. For joint we used a transparent polymer tube. The gap was set at around 150 microns. The tip of the smaller glass fiber was rounded using a modified fiber splicer, in order to reduce the exit cone of the light from the fiber. A high power red LED was used to power the device. The wood rod with the fiber assembly was introduced within the aluminum tube.
Open main document for optomechanical assembly and electronics.

The fiber assembly was first tested using a gimbal, see video below.

YouTube Video

We assumed that once assembled into a aluminum beam, the sensor will behave very similarly to the bench test using the gimbal, in which the mirror rotates around a point on its surface, facing the laser emitting fiber. In reality, the prototype was assembled with the fibers off axis, i.e. not in the center of the beam. They were placed into a grove made on the surface of the wooden rod. When the beam is bent, the fibers are stretched or compressed, if they find themselves within the bending plane. When stretched, the mirror get's away from the fibers. When compressed, the mirror get's closer to the fibers. This induces an intensity variation that is greater than what is produced by the small tilt of the mirror. The signal is dominated by this compression/stretching mode. We were not able to extract 2D spatial information from the device, but we can easily detect bending in the plane containing the optical fibers.

Photo album

Tape sensor prototype and demo