Optimization of tractor seat position parameters based on biomechanical characteristics

Abstract: High-driving comfort seat has been one of the core components in various vehicles for market competitiveness. Among them, the driving comfort of tractors has also received much more attention in agricultural production. The seat is the main contact part between the tractor and the driver. However, the current ergonomics design of the tractor seat can easily trigger driver back fatigue, even waist occupational disease. It is a high demand to optimize the parameter of the seat for better human-machine matching of the tractor. In this study, a three-dimensional model of the driving environment was established under the layout of the tractor, according to the relevant standards of cab design. A "Hill muscle model" was adopted to propose a musculoskeletal model suitable for the human body size of Chinese adults, according to the Chinese human body size standard GB 10000-1988 "Human Size of Chinese Adults". An operator-operation environment coupled biomechanical model was also established using the biomechanical software AnyBody, where the contact constraints were set to balance the degree of freedom. The short, medium, and tall drivers were selected as the research objects. The target parameters were taken as the tractor seat backrest inclination, the horizontal distance between the SWC point and the SIP point, as well as the vertical height between the SIP point and the floor. The indicators were the activity of the lumbar muscle group erector spinae, multifidus, rectus abdominis, and external oblique. The contribution rate of each muscle group was determined by the coefficient of variation, in order to measure the overall comfort of the waist. A systematic analysis was then made to clarify the effect of the seat parameters on the biomechanical characteristics of the driver's lumbar muscle. As such, the optimal seat parameters were determined using inverse dynamics. A multi-degree-of-freedom driving platform was developed to test the different seat positions under the condition of various parameters. The muscle activity of the four main muscle groups in the lumbar region was also calculated for the different percentages of drivers. The results show that a better consistence between the test and simulation was achieved to effectively adjust the seat parameters for the better comfort of the driver's lumbar. In the short and medium percentile drivers, the seat backrest inclination was a dominant effect on lumbar comfort. By contrast, the seat horizontal distance and vertical height were dominated by the lumbar comfort of the tall driver. An optimal combination of parameters was also obtained for the lowest total activity of the four muscle groups and the highest comfort of the driver's lumbar. For the tall, the optimal combination was: the seat backrest inclination was 9.7°, the horizontal distance was 472.1 mm, and the vertical height was 465.3 mm. For the tall driver, the optimal seat backrest inclination was 13.9°, the horizontal distance was 495.6 mm, and the vertical height was 485.3 mm. For the tall driver, the optimal seat backrest inclination was 14.8°, the horizontal distance was 526.4 mm, and the vertical height was 520.7 mm. The dynamic and static driving comfort of the seat can be expected to further quantify in the combination with the actual driving operations when turning the steering wheel or stepping on the pedal. The finding can provide a new idea to optimize the seat position parameters of agricultural equipment.