Laser Sensor Apparatus and Method for Detecting Transmission Shaft Torque

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 with respect to 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.

An apparatus for measurement of transmitted torque in a transmission shaft, comprising:

• an elongated shaft for transmitting torque having a cavity in at least a portion of said shaft, said shaft having at least one light entrance aperture and at least one light exit aperture, said first and second apertures spaced apart along an axis of rotation of said shaft, said apertures extending from an exterior surface of said shaft into said cavity;
• a light source for emitting light along a first light path, said light source secured proximate to and separate from said shaft;
• a first polarizing filter positioned to intercept said first light path and having a first axis of polarization, said first polarizing filter positioned between said light source and said shaft;
• a beam splitter positioned in said first light path, said beam splitter splitting said first light path into a first measurement light path and a reference light path, said first measurement light path positioned and directed towards said shaft to be alignable with said at least one of said entrance apertures by rotation of said shaft, wherein said first measurement light path enters said cavity through said at least one entrance aperture, wherein polarization of light in said reference light path is determined by polarization of light in said first measurement light path;
• a first reflectance element secured to said shaft within said cavity and having a first reflective surface, said first reflective surface configured to reflect said measurement light path to a second measurement light path, said second measurement light path directed along a length of said cavity parallel to said axis of rotation of said shaft;
• a second reflectance element secured to said shaft within said cavity in said second portion of said shaft and having a second reflective surface, said second reflective surface configured to reflect said second measurement light path to a third measurement light path, said third measurement light path directed to exit said cavity through at least one of said at least one exit apertures;
• a second polarizing filter having a second axis of polarization, said second polarizing filter positioned to intercept and polarize light in said second measurement light path, said second polarizing filter secured in said second portion of said cavity proximate to said second reflectance element between said first reflectance element and said second reflectance element, wherein said second polarizing filter is secured to said shaft to rotate in unison with said second portion of said shaft;
• a measurement device positioned to receive light from said reference light path and from said third measurement light path, said measurement device configured and adapted to detect a difference in polarization angle between said third measurement light path and said reference light path;
• wherein torque transmitted by said shaft produces angular twisting in said shaft between said first portion and said second portion of said shaft, said angular twisting altering said polarization angle of light in said third measurement path relative to said reference light path;
• wherein said detected difference in polarization angle is indicative of torque in said shaft by which said shaft torque may be determined.

A method of measuring torque transmitted by a shaft, comprising:

• providing a light source emitting a polarized light beam;
• directing said polarized light beam along a length of said shaft;
• changing angular polarization of said light beam along said length of said shaft according to torsional twisting of said shaft;
• measuring said angular change in polarization;
• determining said torque from said measured change in polarization.