In double-sided lapping and polishing processes, the friction coefficients between the workpiece and platens or pads are important parameters for understanding or improving the lapping and polishing processes. However, the friction coefficients have not been investigated in detail owing to insufficient measurement methods for the torques acting on the upper and lower platens, which are necessary to evaluate the friction coefficients. Thus, a novel measurement method for the torque acting on the upper platen in a three-way double-sided machine was proposed in this study. In the method, the torque is measured based on the forces acting on the holders supporting the upper platen rotation. The torques were measured with the method in double-sided lapping experiments, and they were confirmed to agree with the theoretical torque variation. Furthermore, the friction coefficient between the workpiece and upper pad identified with the proposed method was also verified by comparing with the friction coefficient measured in the single-sided lapping experiment. In addition, the estimation method of the lower platen torque based on the motor torque was investigated by utilizing the proposed method, and we found the lower platen torque was estimated accurately by taking a sufficient warm-up time or by modeling the torque loss in transmission path. Therefore, accurate measurement of the torques acting on the upper and lower platens, which is an effective tool for understanding or improving the process, was realized.
