Tractor controls actuating force limits for Indian operators

In four-wheel tractors, proper design of controls is important for comfortable and safe operation of the tractor. The design involves location and dimensions of controls as well as strength limits for operating these controls. The present study was aimed to quantify human strength for operation of tractor controls and to recommend the maximum control actuating forces for normal operation of tractors based on strength capability of 3,423 Indian male agricultural workers. The 5th percentile values of strength parameters i.e. leg strength sitting (left and right), foot strength sitting (right), torque strength (both hands) sitting, push strength (left hand and right hand) sitting and pull strength (left hand and right hand) sitting of agricultural workers collected using a strength measurement set-up were taken into consideration for the study. It was recommended that the maximum actuating forces for normal operation of frequently operated brake and clutch pedals of tractors should not exceed 260 N and 125 N based on 5th percentile values of right and left leg strength of male agricultural workers, respectively. The maximum actuating force required in steering wheel operation should not exceed 51 N based on 5th percentile value of torque strength (both hands) sitting of workers. The maximum actuating forces required for operating frequently operated levers viz. gear selection, speed selection, hydraulic control and hand throttle of Indian tractors should not exceed 46 N, 46 N, 25 N and 25 N, respectively. It may be concluded that the maximum actuating force limits as given in Bureau of Indian Standards IS 10703 are very high as compared to the findings of the study based on strength data of Indian male operators, which highlight the need to revise the standard.