Self-calibrating torque measuring system

In combination with a power plant having an output shaft, a universal torque measuring system for hollow drive shafts which automatically compensates variations in wall thickness exhibited by different drive shafts having the same nominal dimensions comprising:

• a hollow drive shaft coupled to said output shaft and having a longitudinal axis and a plurality of first indicia thereon at spaced peripheral locations;
• an elongated reference shaft coaxial with said drive shaft and having a plurality of second indicia thereon at spaced peripheral locations and proximately disposed relative to said first indicia, said reference shaft being fixed to said drive shaft at a location distant from said first and second indicia such that relative angular displacement of said first and second indicia about said longitudinal axis without regard to the wall thickness of said drive shaft when said drive shaft is subjected to a first predetermined torque produces an initial phase shift, said initial phase shift and said first predetermined torque defining a first operating condition, a second phase shift and said second predetermined torque defining a second operating condition of said drive shaft, said first and second operating conditions defining a characteristic relationship between torque and phase shift for said drive shaft;
• sensor means for detecting deviations from said initial phase shift as said drive shaft is rotated under load and operable to generate a signal proportional to each such deviation;
• and
• signal processing means responsive to said signals from said sensor means for automatically deriving an operating value of torque different from said first predetermined torque being experienced by said drive shaft as a function of each such deviation according to said characteristic relationship.

A universal method of measuring torque sustained by hollow drive shafts which automatically compensates for variations in wall thickness exhibited by different drive shafts having the same nominal dimensions comprising the steps of:

• providing first indicia on a hollow drive shaft at spaced peripheral locations;
• providing second indicia on a reference shaft coaxial with the drive shaft and fixed to the drive shaft distant from an end thereof, the second indicia being proximately disposed relative to the first indicia;
• imparting a first predetermined torque to the drive shaft;
• simultaneous with the preceding step, angularly displacing about the longitudinal axis of the drive shaft the first indicia relative to the second indicia to cause an initial phase shift therebetween;
• simultaneous with the preceding two steps, angularly positioning and affixing the first indicia to the drive shaft such that the initial phase shift and the first predetermined torque define a first operating condition;
• imparting to the drive shaft a second predetermined torque less than the first predetermined torque thereby causing a second phase shift between the first and second indicia, the second phase shift and the second predetermined torque defining a second operating condition;
• rotating the drive shaft;
• sensing deviations from the initial phase shift as the drive shaft is rotated;
• generating a signal proportional to each such deviation;
• and
• processing the signals to automatically derive a value of torque being experienced by the drive shaft as a function of each such deviation according to a characteristic relationship for the drive shaft as defined by the first and second operating conditions.