DEVELOPMENT OF AN UNDERWATER PLATFORM FOR MEASUREMENTS IN ALL COORDINATE AXES FOR BIOMECHANICAL APPLICATIONS

Abstract

INTRODUCTION:The main objective of this work was the development of a new force platform for the measurement of forces and force moments related to the three orthogonal axis, for the using in biomechanics. This development was focused for applications related to hydrogymnastics, and because of that is a double platform and waterproof. METHODS AND PROCEDURE:Through the analysis of several types of platforms it was chosen the Lywood’(1987) model, a platform built for the three components of small forces. According to this, it was developed a couple of platforms of dimensions 500mm X 500mm, with a sensibility if 2N. Electrical strain gages were bounded to a bar structure whose strain is provided by flexion. These strain gages are connected as „four-arm wheatstone bridge“, for each component of force or force moment. To determinate the best position of the strain gages for higher sensibility and the less interference it was used the Finite Element Method. Each output signal was independent of the others, disregarding any mathematical operations to separate signals. The electrical signals were sent to a signal conditioner linked to an A/D converter, witch was connected to a PC microcomputer for data acquisition and processing. RESULTS AND DISCUSSION: It was reported that the static calibration of the platforms and the linearity deviation were less than 1% and the cross-talk was less than 2%. The dynamic tests showed that the fundamental frequency of the platform is 25Hz. Some physical exercises were done by an athlete inside and outside the pool and the signal analysis at the frequency domain shows that the system is reliable for applications inside water. CONCLUSIONS: The results of the calibrations (including frequency domain analysis) and the tests realized with an athlete at the pool proved to be reliable and the platform can be used for such purposes. REFERENCES: Lywood, D. W., Vaneyken, A., Macpherson, J. M. Small. (1987). Triaxial Force Plate. Med. & Biol. Eng. & Comput. 25, 698-701. Roesler, H. (1997). Desenvolvimento de plataforma subaquática para medições de forças e momentos nos três eixos coordenados para utilização em biomecânica. PROMEC, UFRGS, tese de doutorado.