Some Human Engineering Investigations on the Seat and Controls of Tractors. (II)

On Controls and Instrumentation

Abstract

Operating conveniences of steering wheels, hand and foot controls and meters installed on 34 tractors were investigated, in relation to the standard physique of Japanese adult male.
(1) Steering wheel: Both diameters and inclinations are generally too large, especially in imported tractors. The large part of gripping points are longitudinally so distant and vertically so low, that few operators can keep their adequate carriages (angle of upper arm 0-25°, angle of elbow 90°, when sitting on seat) (Fig. 1).
(2) Control levers: Reasonable correlations cannot be found between frequency of use and arrangement of levers. Because of inadequacy of positions of grips, operation of some controls often cause contact of operators' bodies with other controls and unnatural carriages (Fig. 2, 3). Especially, the Pto lever needs severe foreward inclination and bending of the upper body (Tab. 1). The starter lever and the main switch are almost too distant longitudinally, but low frequency of use may permit the existing circumstances. The size, shape and operating direction of grips should be standardized from the view-point of convenience, comfort and safety of work.
(3) Control pedals: In general, positions of pedals are longitudinally so near from the tuber points of hackle bones of operators that operation, especially of differential locks, causes exessive bending of knees and stress of back muscles, and horizontally so distant that operation, especially of imported tractors, brings twisting of bodies (Fig. 4). In several domestic tractors, size of the pedal is too short horizontally to be under a half of standard width of foot (Tab. 2). Shortage of surface inclination often brings too large front angle of ankles and exessive tension of legs. The operating angle of pedals of domestic tractors is generally beyond adequate range (about 20°), except differential lock pedals.
(4) Meter installation (Tab. 3): Considerations for human engineering are seemed to be insufficient in regard to arrangement, size and colour conditioning of meters.