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New Design for a 6 DOF vibration simulator with improved reliability and performance

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  Pp. 279-287 in Automation Technology for Off-Road Equipment, Proceedings of the July 26-27, 2002 Conference (Chicago, Illinois, USA)  701P0502.(doi:10.13031/2013.10017)
Authors:   Ivo Hostens, J. De Baerdemaeker, Herman Ramon
Keywords:   Vibration Simulation, Stewart platform, 6 degrees of freedom

Simulators are an indispensable tool to study present-day machinery dynamics in a repeatable way and under controlled laboratory conditions. In this paper an already designed and constructed 6 degrees of freedom (DOF) electro-hydraulic vibration platform is virtually redesigned. The present structure has fundamental faults, which prohibit an optimised performance. An important weakness lies in the use of Hook’s-joints, which are to weak for the exerted forces and have an eigenfrequency that lies in the excitation band of the simulator. They were chosen because of their larger angle, which is necessary in the actual unsymmetrical design. A new design is chosen with a Stewart configuration. For optimisation the characteristics of the hydraulic power unit and hydraulic cylinders need to be taken into account. The aim is to find the optimal angle between ground and cylinder that 1) provides a minimum of movement of the Hook’s-joints, to improve stability; 2) provides (pure kinematics) a total stroke in all three translational Degrees of Freedom of 0.30 m and 3) makes it possible to have an amplitude of 0.1 m at a frequency of 1 Hz and an amplitude of 0.001 m at a frequency of 10 Hz, without modifying the existing hydraulics. The found angle was 56 degrees. With a finite element analysis is checked whether the chosen new Hook’s-joints eigenfrequency is in the frequency excitation band of interest. With a dynamic analysis, using the maximum power in the cylinders and the maximum allowable weight of 750 kg on the platform is checked whether the Hook’sjoints are suitable for the maximum found torque. All criteria are met. The conclusion is that this new design will increase 1) the stability of the system, by reducing the forces on and the movement of the Hook’s joints, and 2) the performance of the platform.

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