Strain gauge foil for the measurement of elastic deformations in orthopedic milling tools

Miniaturized platinum strain gauges on a polyimide foil have been developed for the measurement of the elastic bending deformation in two directions. They were integrated into orthopedic milling tools used for bone cement removal in hip surgery. The integration of strain gauges into surgical instruments is of great interest because the accuracy of surgeries can highly be improved. For measurement of strain in two directions four strain gauges were used in two Wheatstone half-bridge configurations. To improve the alignment they were fabricated on a single polyimide foil, which then was mounted onto the tool. The sensitivity of the system at a supply voltage of 2 V was found to be about s ap 1.22 V/m with a cross sensitivity of about s_c ap -0.03 V/m for the perpendicular direction. From these values the bending deformation of the milling tool was calculated using a set of two linear equations.