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Evaluation and improvement of suspension seat vibration isolation performance


A study was designed to determine the rate of growth of discomfort, the absolute level of discomfort, and the principal locations of discomfort arising from exposure to roll, lateral, pitch and fore-and-aft oscillation of subjects seated on a flat rigid seat and on a rigid seat with a backrest. The study also tested whether exposure to rotational and translational stimuli in the same plane, with matched accelerations in the plane of the seat, results in similar rates of growth of discomfort and similar absolute discomfort. The results showed that the presence of a backrest reduced the discomfort experienced by subjects at frequencies between 0.25 and 0.4 Hz. The results showed that the discomfort arising from rotational and translational motions has a broadly similar character below 0.5 Hz, while above 0.5 Hz subjects were more sensitive to rotational than to translational oscillation.
The extensive experience of the VIBSEAT partners in the development and use of standards and the knowledge of leading European suspension seat manufacturers have facilitated the development of a laboratory test protocol for assessing the performance of seats equipped with suspensions for the attenuation of shocks and vibrations in horizontal axes. The development of the protocol has led to significant progress in the understanding of methods of testing the performance of seats in horizontal directions. The test protocol includes sections on each of the following:Test rig, seats, persons and posture / Excitation signals / Measurements / Test progress / Criteria / Report content / Incertainty estimation in measurements / Seat behaviour analysis guide. The proposed test protocol has been evaluated by the partners in laboratory tests to ensure that the test method is viable. Discussions of field and laboratory studies undertaken for the project have led to the provision of a relevant protocol, leading the way to appropriate future studies on Criteria / Shock excitations / Rotational vibrations / Multi-axis excitations and analysis / Continuous solicitations ergonomics criteria / Test persons and posture / Range of signal.
Marine craft field motion measurements for the VIBSEAT project took place during April 2003 on a prototype FSB2 lifeboat intended for use with the RNLI. Situations that caused discomfort or resulted in difficulty in operating the controls were identified from discussion with boat crews. Measurements of the motion of the deck and the seat were obtained during these conditions. These data were required by the VIBSEAT project to provide test motions for use in laboratory testing, mathematical modelling and for development of the test method.
Field studies have been conducted to measure the characteristics of representative motions of current production seat from Isringhausen and the vibration characteristics of one typical articulated on-road truck. These data have been used in subsequent work packages for reproduction in the laboratory, as inputs to the mathematical models, and to define the range of test conditions applicable to the development of a testing method. The data have also been used during dynamic simulation for development of a completely new vertical and horizontal suspension technology. Follow up field studies have been performed to evaluate the differences between the old and modified seat.
While driving off-road vehicles, drivers are exposed to whole-body vibration in all directions. Seat manufacturers supply products equipped with fore-and-aft suspension but only a few studies report their performance. The work done proposes a numerical method applicable to design fore-and-aft suspensions for off-road vehicle seats. 5 steps were required to achieve this goal: a) Measurements of realistic vibration and shock signals on the cab floor in a wheel loader during working operations. b) Measurements in laboratory of the dynamic response of a seated subject exposed to fore-and-aft random vibrations c) Development of a numerical model describing the dynamical response of the seat/man system d) Definition of criteria to assess the vibration performance of a fore-and-aft suspension and realisation of simulations to optimise suspension properties e) Verification in laboratory of the increased performance with a suspension prototype