Seat belt and headrest adjustment: Increasing truck driver comfortability

Sammanfattning: Truck drivers spend long, consecutive periods of time seated down, and the truck cab becomes their immediate work environment. Therefore, it is important to make sure that this space is properly adapted to fit the driver’s needs well. The driver seat is something the driver are very much in contact with. The seat can be adjusted in many ways to accommodate for drivers of different heights and body types. However, two of the components which are fixed today are the upper seat belt anchorage position and the headrest. In this thesis project, the aim has been to investigate the adjustment possibilities of these components in terms of desired adjustment range and mechanical solutions. The first part of the project was spent on ergonomic evaluations of the seat, and finding what properties are the most important when designing a truck seat. Both literature reviews as well as interviews and observations helped build the knowledge foundation to base adjustment concepts on. For example, it was found that to minimise the negative effects of sedentary work, the single most important action is to frequently change the sitting position. Therefore, it is of high importance that adjustment procedures are as simple as possible. It was also found that many truck drivers do not use their seat belt at all, and that having a headrest which is adjustable in height is important for the driver’s visual area. Several ideas and concepts were generated and evaluated. The initial ideas included both solutions applicable on the current seat belt design, while some would use other means of securing the driver in a collision. The ideas were compared and evaluated, and three were chosen to develop further; one being easy to implement, and two being mechanical solutions both making use of the current seat belt design. These three concepts were investigated more deeply, and were subsequently also compared using different methods for evaluation. Eventually, a final concept was chosen; a mechanical solution in which the seat belt and headrest can be adjusted separately in one and two directions respectively. This concept was further developed in terms of both mechanical as well as visual design. In the final concept, Hoop, the seat belt is adjusted sideways, as this was proven to give the largest comfortability improvement for the driver. The headrest is adjustable in both height and depth. The mechanisms are locked using ratchets, however, both can be adjusted in what is believed to be the most critical direction without the need to unlock first. The buttons for unlocking the mechanisms are placed directly on the adjustment mechanisms in order to keep the procedure as intuitive and easy to use as possible. The adjustment ranges were determined based on Scania’s anthropometric dataset in order to make sure that the adjustment features will be useful for an as large part of the driver population as possible.