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Research Papers

Comparison of Simulation and Experimental Results of a Tractor Seat With Nonlinear Stiffness and Dead-Band Damping

[+] Author and Article Information
Mike Duke1

School of Engineering, Faculty of Science and Engineering,  University of Waikato, Private Bag 3105, Hamilton, New Zealanddukemd@waikato.ac.nz

Alista Fow

School of Engineering, Faculty of Science and Engineering,  University of Waikato, Private Bag 3105, Hamilton, New Zealand

1

Corresponding author.

J. Vib. Acoust 134(5), 051006 (Jun 05, 2012) (6 pages) doi:10.1115/1.4006411 History: Received February 09, 2011; Revised January 18, 2012; Published June 04, 2012; Online June 05, 2012

A low friction tractor seat with nonlinear stiffness and dead-band damping was investigated both by simulation and experimentation. The objective was to determine if a practical, “soft” suspension system could be developed that offered improved vibration performance compared to a typical mechanical commercial tractor seat suspension. A “hard” damper was used to prevent end stop impacts that were more likely with the soft suspension. In addition the damper had a dead-band centered at the seat’s static equilibrium position. The dead-band damping was achieved with a switchable damper using relative seat displacement as the control signal. The objective of the dead-band was to allow a soft undamped operating region that gave good vibration attenuation. If the relative seat displacement passed the dead-band limits due to sudden harsh inputs, the hard damping would take over and prevent end stop impacts. An experimental rig with nonlinear seat and switchable damping was built and tested with the same parameters and inputs as those used in the simulations. The simulation and experimental results compared well. Both the simulation and experimental results showed that a combination of nonlinear stiffness and dead-band damping used on a tractor seat gives reduced rms acceleration compared to a linear, conventionally damped seat.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 12

Experiment and simulation results of the scissor seat: Simulated scissor seat with different damping constants from 0 to 1000 N s/m (◊); experimental scissor seat with different damping levels (▴); and experimental scissor seat with ± 10 mm dead-band damping (○)

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Figure 11

Simulation results of: Scissor seat with different damping constants from 0 to 1000 N s/m (◊); scissor seat with dead-band damping ranging from 300 to 600 N s/m when the damper is on (○); and linear seat with a spring rate of 5500 N/m and different damping constants from 0 to 1000 N s/m (▴)

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Figure 10

Measured tractor body acceleration power spectral density (PSD)

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Figure 9

Measured tractor body acceleration at the attachment point of the seat

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Figure 8

Experimental (dashed line) versus simulated response (solid line) of the scissor seat with damper switched on when subjected to a 50 mm ramp input for 0.2 s at constant 250 mm/s

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Figure 7

Experimental (dashed line) versus simulated response (solid line) of the scissor seat with damper switched off when subjected to a 50 mm ramp input for 0.2 s at constant 250 mm/s

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Figure 6

Experimental set up of scissor seat mounted on a hydraulic shaker, where (1) cushioned seat with 68 kg rigid mass, (2) scissor mechanism, (3) bearings for reduced friction, (4) horizontally mounted steel extension spring, (5) on-off computer controlled hydraulic damper, (6) rubber end stops, and (7) sensors—acceleration, relative velocity, relative displacement

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Figure 5

Forces on scissor seat showing the spring and damper forces as a tan function of scissor angle α

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Figure 4

Geometry of scissor mechanism showing relationship between z and y-x with changing scissor angle α

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Figure 3

Scissor seat—effective stiffness change as load is increased

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Figure 2

Scissor seat—static deflection change as static load increases

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Figure 1

Schematic of scissor seat showing position of the spring, damper, and mass

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