Improvement of accuracy in a high-capacity, six degree-of-freedom load cell: Application to robotic testing of musculoskeletal joints

This study investigated a previously unaccounted for source of error in a h igh-capacity, six degree-of-freedom load cell used in multi-degree-of-freed om robotic testing of musculoskeletal joints, an application requiring a lo ad cell with high accuracy in addition to high load capacity. A method of c alibration is presented for reducing the error caused by changes in univers al force-moment sensor (UFS) orientation within a gravitational field. Unco rrected, this error can exceed a magnitude of 1% of the full-scale load cap acity-the manufacturer-stated accuracy of the UFS. Implementation of the ca libration protocol reduced this error by approximately 75% for a variety of loading conditions. This improvement in load cell accuracy (while maintain ing full load capacity) should improve both the measurement and control of specimen kinetics by robotic/UFS and other biomechanical testing systems. ( C) 1999 Biomedical Engineering Society. [S0090-6964(99)00606-2].