To assist endodontic therapy, in this paper, a force sensor is designed and fabricated for measuring the axial force and the bending moment simultaneously. By detecting the bending moment, we can know the severity of bending. Axial force detection is also desired, as excessive axial forces may result in instrument buckling or even root canal perforation. This paper installs three sensing cells in each of two planes to detect the bending direction. Each sensing cell consists of a pressure-sensitive electric conductive rubber and an electrode. The size of the force sensor is 1.4-mm wide and 6-mm high for matching the size of endodontic instruments and making it feasible in the endodontic treatment. Experimental results on accuracy, repeatability, and nonlinearity are presented to validate the proposed sensor.

To display information, flexible displays are a promising device. We present energy methods in conjunction with the calculus of variation to obtain deflections of flexible substrates subject to torque. In addition to analytical derivation, in experiments an electric motor under computer control exerts torque to generate display torsion, whose twist angles are obtained by using both optical encoder measurement and theoretical calculation. Comparisons are made between experimental and theoretical results for PET (polyethylene terephthalate) and PEN (polyethylene naphthalate) polymer substrates. Both experimental and theoretical results show that the required torque due to unit twist angle increases with the twist angle. A larger PET substrate is not as easy to be twisted as smaller one. In addition, a square PET substrate is not as easy to be twisted as rectangular one with the same width.