Load weight determination during dynamic working procedures using the pedar foot pressure distribution measuring systems

Abstract

INTRODUCTION:: In 1994 a new BIA research project was launched, which deals with the development of a portable measuring system for recording of external stress parameters (e.g. body postures and handled load weights) at different places of employment. The investigations are carried out against the background of a newly recognized occupational disease (since 1993), which is that of damage of the spine following long-term repetitive lifting and carrying of heavy loads as well as working in an extreme trunk bending posture. As a part of the study it should be clarified if the worker's handled load weight can be determined by using a foot pressure distribution measuring system. METHODS:: In the case of a static working posture the handled load weight can simply be calculated by taking the difference of the measured weight and the known body rest weight of the worker. In dynamic situations the measured total foot reaction force consists of a static and a dynamic component, which is caused by the body movement and which is normally bigger than the load gravitational force. For load weight determination it is important to separate the dynamic forces from the measured total force to get an idea about its gravitational rest part. Therefore the body dynamics are measured synchronously to the foot pressure by using angle and angular velocity sensors. The herewith received data are used as input values for a developed biomechanical link segment model, with which it is possible to predict the foot reaction force. So even in dynamic situations an estimation of the handled load weight can be made by comparison of the predicted with the measured foot reaction force. RESULTS AND DISCUSSION:: In laboratory tests the load weight could be determinated reliably for different working processes over a total measuring time of 40 seconds. During the measurements the Pedar insoles were placed directly under the foot so that the accuracy of the static force measurement was reasonably high (with a maximal deviation of 5% to the real force). When the insoles were put in shoes, additional forces resulting from the bent shoe leather complicate the load weight determination. This effect still has to be analysed to compensate for it in future measurements. CONCLUSION:: The laboratory results encourage us for future measurements at places of employment. Currently our work focuses on an increase of the total measuring time and on a modification of the measuring system to a portable system without any connection to a computer. A field study is in preparation.