Optical Measurement of Angular Deformation and Torque Inside a Working Drillstring

This paper describes apparatus capable of angular rotation measurements needed to calculate torque applied to a horizontal directional drilling (HDD) drillbit. Measurements are made using a solid-state imager (camera), a single lens, and a special optical target having precision circular apertures. This apparatus is unusual in that it is mounted inside the drillstring housing being measured, for HDD applications are not compatible with conventional externally mounted measurement devices. The measurement approach uses signal centroid calculations associated with image features rather than pattern matching or other standard image analysis techniques.