Development and preliminary characterization of a novel system for the force platforms dynamic calibration

In this work a transportable calibration system for dynamic performance testing of medical force platforms (FP) is proposed. Although in literature many devices have been proposed for the calibration of force platforms, most of them are static and among those proposed to simulate a dynamic phenomenon it is difficult to satisfy ergonomic needs (i.e. transportability) with performance characteristics as the capability to control the frequency and the amplitude of the calibration force with continuity in the useful range of the human gait analysis and posturography. In particular the system proposed is equipped with a calibrated load cell (LC) to provide force measurement feedback and can apply a calibration force in every point of the FP under testing, with amplitude range 0-1500N, frequency range 1-12 Hz and a preload range 300-1000N with an inclination to the FP of 0-15°. With the aim to do a first validation of the system some test and a first application to a novel Force Platform are described. Tests at different preloads (30-100 daN), frequencies (1-12Hz) and amplitudes (7.5-25 daN) are carried out to study the dynamic behavior of the device: some difference on the peak to peak measurements are shown, nevertheless the ratio of the mean force ratio platform/calibrator is very close to 1 in quite all cases, although a little distortion (<4%) is revealed at 2 Hz. Moreover the evaluation of the total harmonic distortion (THD) is carried out and results show some difference in the readings between the FP and the system LC. In future works it seems interesting to investigate how the frequency influences the dynamic behavior of FP and propose a calibration procedure where the calibration parameters are frequency dependent and the control software is optimized to improve the system performance and the force signal characteristics.