A Novel Technique to Design and Optimize Performances of Custom Load Cells for Sport Gesture Analysis

Background: The assessment of the force exerted during a gesture in human motion analysis can provide direct and indirect information regarding the expended energy, especially during the execution of a sport gesture. In this field, assessment and improvement of the performance can be supported by instrumented devices able to measure and process mechanical quantities. In cycling, strain gauges-based instrumented pedals represent one of the last innovations in the sector, because they can provide data about the power exerted (produced)during training and the pedal efficiency. Optimization of the strain-gauges positioning is thus required to improve accuracy in the exerted force estimation. Methods: A new technique to give a support for evaluating the best compromise between maximum sensitivity and ease of assembly was developed in the present work, based on a Finite Element Model (FEM)and a parametric analysis of the strain field at different sensor placements. Optimal positions were identified as those combining high sensitivity and low dependence from positioning inaccuracies. Results: Parametric strain-load trends obtained from the developed model show a linear behavior of strain gauges pairs and confirm that there is a good sensitivity of the adopted sensors if they are mounted in handy positions of the developed load cell. Discussion: The conducted analysis enables to calculate the sensitivity of the load cell to the exerted forces, and evaluates its dependence to the positioning of strain gauges, and makes it possible to appropriately choose strain gauges positioning in areas where border effects are minimized. The strain distributions obtained by the FEM analysis in the presented load cells gives useful indications for all the situations where small strain gauges are requested to be mounted on a reduced offered area.