Detection Of The Finger Force Signal And Its Variability Analysis

Finger force and motion could reflect finger synergetic motion, and be used as parameters to evaluate hand movement function. Some researcher tentatively suggest that the degree of finger force variability has been not only considered a reflection of the degree of noise in the involved sensori-motor system, but also maybe originates at an upper level of the control hierarchy. The purpose of this paper was to study the variation of finger kinematic by analyzing each finger's force variability at different tasks. The result of this research could not only help to further understanding on the mechanisms of motor control system, but also has both academic and applied significance in the field of neurophysiology and kinesiology.First we designed a FSR-based finger force detection apparatus. A custom-made polycarbonate substrate was used to transfer finger force to the deformation of FSR cell mechanically, and a constant-current source circuit was adopted to transducer the resistance changes of FSR into voltage signal. USB6008 interface card and LabVIEW were combined to acquire and display the digitized finger force signal in real-time. The apparatus was tested and characterized in static and dynamic conditions. Finger force signal were recorded from three experiments. Excepting the first experiments, a range of force levels was used computed as percentages of the maximal voluntary contraction force for each involved finger combination. Root mean square error(RMSE)values, standard deviation(SD) values, coefficient of variation(CV), detrended fluctuation analysis(DFA) index values and approximate entorpy (ApEn) values were calculated, in order to observe the difference between the index finger and middle finger at different tasks. And to find out how synergy influences the variability.By analyzing the finger force signal in the three experiments, The results showed that : (1) In all three experiments , an increase in the target force level was accompanied by an increase in the values of RMSE,SD and ApEn both in index and middle finger . (2) In all three experiments , there were no significant difference in the values of CV both in index and middle finger. (3) In all three experiments , there were no significant difference inαboth in index and middle finger. The value ofαchanged around 1.5, which meaned the finger force signal was corresponding to Brownian noise (4) In all three experiment, index finger showed lower values both in the RMSE and SD as compared to middle finger in the force target level, and showed larger values both in the DFA index and ApEn.(5) At the same relative force level of 30% MVC, multi-finger showed lower values both in the RMSE and as compared to single finger, and showed larger values in the ApEn.In summary, compared to middle finger, the index finger has the lower force variability, which make it to finish the task more accuracy, and synergies may ensure low variability of performance variables in order to offer the precision force.