The use of a capacitive sensor matrix to determine the grip forces applied to the olive hand held harvesters

The hand held olive harvesters increase the work productivity but they submit the operator's hand arm system to high vibration level values and to relevant efforts to drive them through the tree branches. Many scientific works demonstrate that a correlation exists among the intensity of vibration, their direction and the grip force applied by the operators' hands. It is not easy to measure these parameters, unless instruments which permit the measurement in an objective way are available. Aim of the work is to present the results of the application of a measurement instrument that allows to detach the operator's hands grip force applied to drive the olive harvesting shaker. This device is done using a capacitive sensor matrix that can be wrapped around the machine handlebars. The matrix is thin (approximately 0.9 millimetres of thickness): for this reason its presence does not modify the operator's behaviour and allows to obtain measures of the pressure dynamic contact distribution and its time history. In this way we have the grip forces applied by the operator's hand over the machine handlebars. This matrix has been fixed over olive harvesting machine handlebars and the grip forces time histories have been recorded. The tests have been carried out in a laboratory simulating the olive harvesting operations by means of the arms movements towards to targets positioned at different heights. Obtained results permit to appreciate both the grip force time history and the spatial force application: with the spatial and temporal applied force values, more ergonomic solutions and implementations are possible for olive hand held harvesters.