Handling light disturbances in a Micro Motion Sensing System and investigation of the system performance

The authors had previously developed a system to assess accuracy of micromanipulation tasks. The system includes an optical Micro Motion Sensing System (M
²
S
²
). The M
²
S
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, consisting of a pair of orthogonally placed position sensitive detectors (PSD) and an infra-red (IR) diode, tracks 3D displacement of the tip of a microsurgical instrument in real-time. The IR diode is used to illuminate the workspace. A ball is attached to the tip of an intraocular shaft to reflect IR rays onto the PSDs. Instrument tip position is then calculated from the centroid position of the light falling on the PSDs. The system did not account for the effect of different ambient and environment light conditions. The system required that ambient light and environment light had to be maintained the same as those existing during calibration of the system. In some situations, they cannot be maintained the same and hence system accuracy is affected. This paper presents a method to make the system accuracy invariant to different ambient light and environment light conditions. The accuracies of the system at different orientations of the instrument are also reported.