Open access publications in the SLU publication database

Abstract

Farm tractor drivers are forced to twist their bodies in order to observe the equipment and the work result behind the tractor. To make it possible to quantify and describe the degree of these inconveniences, to test and present different kinds of improvements and to get unambiguous arguments for these improvements, we have to use some kind of equipment that measures the twisted postures and collects the information. The equipment must be - functional and reliable - useable under field conditions - useable in different kinds of tractors - designed in a way that allows the driver to act normally. We have within the frame of this project, found a number of different solutions. Most of them have been rejected after theoretical or practical tests. A quite new method, based on outspreading and detecting polarized light, satisfies the requirements in a sufficient manner. From a source in the ceiling, light is sent through a polarization film. This polarized light hits a number of photocells attached to some special points on the driver. These photocells, which are able to produce a measurable current (or voltage) when illuminated, are covered with a second polarization film. Thanks to the fact that the light passes two polarization films, of which one is turnable, the produced voltage will vary with the rotation of the driver. Some interacting factors with influence on the reliability, e g the inclination of the driver, the distance between the light source and the photocells, the sunlight etc, have been neutralized. The precision is today about ±5° but can probably be improved. With an optical IR-filter between the secondary film and the photocell, the precision will be about ±10 The rotation of the driver can be measured in the interval of ±180 degrees. Photocells on his head, shoulders and hips will expose how much he rotates his back spine and neck and in which position he sits on the seat. The equipment will also tell us the period of time he spends in different working postures and how many times he has to rotate. The equipment collects the data automatically and continuously. The working posture is determined every one second. The experimental sequences may be as long as desired. A computer analyses the collected data and the results are delivered without almost any kind of manual help. The researcher can focus his attention on the interpreting, the conclusions and the presentation of the results.