Patent ID: 6268601
Filing Date: 2001-07-31
Classification: G01D

Abstract:
An apparatus for determining the position of a shaft rotatably displaceable along a longitudinal axis, comprising:a source of light energy positioned on said apparatus in a first position adiacent to said shaft;detecting means positioned on said apparatus in a first position adjacent said shaft, said detecting means arranged to produce first and second output signals responsive to the detection of said light energy from said source of light energy;light energy directing means interposed between said source of light energy and said detecting means, said light energy directing means arranged to be rotated in association with said shaft to expose variable amounts of light energy to said detecting means, said detecting means producing said first output signal based on the magnitude of light energy detected and representative of the rotational displacement of said shaft;determining means arranged to receive said first and said second output signals, whereby in response to the magnitude of said first output signal said determining means determines the position of said shaft along said longitudinal axisdisplacement means mechanically mounted to said source of light energy and said light energy detecting means and under control of said determining means said displacement means periodically moves said source of light energy and said light energy detecting means into a second position distant from said shaft, whereby said light energy detecting means produces said second output signal and said directing means receives and uses said second output signal to determine and compensate for drift in said apparatus.