Active Suspension of Truck Seat.

The driver's seat of a heavy-duty truck is usually supported by a spring-damper assembly on the cab floor. This passive suspension isolates the driver from vibration of the cab floor effectively except for a 2 to 3 Hz vibration, which still leads to an uncomfortable ride for drivers ; thus it is desirable to achieve isolation from this low-frequency vibration. To improve riding comfort of the driver's seat, we propose a newly designed active suspension system, where an actuator is installed in parallel with the spring-damper assembly. The actuator is constructed using a DC servo-motor and ball-screw mechanism. A dynamic model of the seat is represented by a two-degree-of-freedom system including a cushion, but influences between foot and floor, arm and steering wheel etc. are neglected. The control system is designed using optimal control theory to minimize rms acceleration of a driver's hip point (seat cushion surface). In this system, accelerations of the hip point, the seat frame and the cab floor are measured and integrated to obtain the state variables to be fed back and fed forward. An experimental study was carried out on a shaker realizing vibration of the cab floor of the truck, and the active seat suspension system achieved satisfactory performance for the human body.