Advances in Force and Moments Measurements by an Innovative Six-axis Load Cell

In this paper the design, the accuracy assessment and the calibration procedure of an innovative six axis load cell are presented. The load cell is able to measure the three forces and three moments and has been designed at the Politecnico di Milano (Technical University of Milan) as a result of 10 years of research in this field. The sensing structural element of the six-axis load cell is a three spoke structure constrained to the frame of the load cell by means of special joints conceived to avoid friction. Strain gauges are conveniently located on highly stressed areas. Mathematical models, both analytical and numerical, are implemented and presented in order to describe the behaviour of the load cell, to optimize its parameters and to theoretically assess its accuracy. A special device has been designed and constructed in order to accurately and quickly calibrate the load cell. Particular attention has been devoted to the processing of the strain gauges signals. An electronic DSP board, located inside the load cell, has been realized able to compute the six components of the generalized force from the strain gauge signals and return six voltage signals proportional to the measured forces. Software selectable filters and gains are implemented on the DSP board.