Variable speed control of weight stacks in 3 kN force standard machine

In calibrations of force measuring instruments using dead-weight type force standard machines, increasing the moving speed of dead-weights in linkage-weight stacks generally improves working efficiency but makes the calibration uncertainty worse due to oscillation of the weights. This conflict can be solved by introducing variable speed control of the linkage-weight stacks to drive the weights quickly in most loading/unloading processes and reduce the speed only when the moving weight comes close to a neighboring weight. Thus, variable speed control reduces the calibration time and prevents weight oscillation. The 3 kN dead-weight type force standard machine of NMIJ has already been equipped with AC servo motors for weight actuation, and variable speed control can be realized by modifying the existing control software. This report describes the design and results of the modification.