Patent ID: 7586083

Claim:
An apparatus for measurement of transmitted torque, comprising: a shaft for transmitting torque having a portion of said shaft extending between a first portion of said shaft and a second portion of said shaft; a light source emitting polarized light along a measurement light path from said first portion to said second portion; a polarizing filter secured at least partially within said second portion of said shaft, said polarizing filter operable to change an angle of polarization of light in a portion of said measurement light path; a measurement device adapted to measure said change in polarization angle; wherein torque transmitted by said shaft produces twisting of said shaft, said twisting producing an angular rotation in said polarizing filter resulting in said change in polarization angle; and wherein said measurement device is configured to determine said transmitted torque from said measured change in polarization angle; a beam splitter configured to provide a reference light path split from a portion of said polarized light emitted by said light source, said reference light path having an angular polarization determined by angular polarization of light from said light source; wherein said measurement device measures said change in polarization angle as a difference in angular polarization between said reference light path and angular polarization of said light in said measurement light path after said polarizing filter; wherein said shaft has a cavity; wherein said light source is a laser light source positioned external to said shaft; wherein said measurement light path after leaving said beam splitter is directed to enter said cavity through an entrance aperture in said first portion of said shaft; a first reflectance element secured within a first portion of said cavity and configured to redirect said measurement light path from said entrance aperture in a direction to intercept said polarizing filter in a second portion of said cavity; and a second reflectance element secured within said cavity and configured to redirect polarized light leaving said polarizing filter to exit said shaft through an exit aperture in said shaft; wherein said entrance aperture and said exit aperture are aligned to permit light from said light source to redirect through said cavity and reach said measurement device when said shaft is in at least one angular position of rotation.