Proposal of a Low Profile Piezoelectric Based Insole to Measure the Perpendicular Force Applied by a Cyclist

Abstract

This paper presents the development of a one-dimensional force platform for the pedaling analysis in a bicycle using piezoelectric films. A 3D-printed insole was designed to accommodate an array of Polyvinylidene Fluoride films without changing the pedaling characteristic. The sensor’s positioning sought to cover the point of contact between the shoe and the pedal. An instrumentation amplifier, a charge amplifier and an anti-aliasing filter with a cutoff frequency of 20Hz composed the conditioning circuit. The system dynamic calibration was executed with the application of mechanical impulses to the sensors’ surface using an impact hammer of model 8206 by Brüel and Kjær, and a chassis model NI SCXI-1600 acquired the output signal. Hence, the experimental transfer functions were defined for each one of the 20 channels of the system. The maximum linearity error was 5.98% for the channel #4 of the right insole and 5.81% for the channel #7 of the left insole. A NI USB-6289 board acquired the data coming from the trials with a bicycle. In the collected data analysis, it was possible to define the pedaling phases by observing the sum of all channels for each insole. The average value for the maximum force applied on the right insole was 235.8 N, and the average value for the maximum force applied on the left insole was 223.2 N. It was possible to map the zones of greater and minor activation during the movement via a single channel analysis for each insole, being the regions of greatest activation located at the top of the medial forefoot region (right foot), and at the bottom of the lateral forefoot region (left side). The regions with the least activation are at the bottom of the medial forefoot region (at the end of the medial longitudinal arch) on both sides.