Dr. Weihua Li Profile

Dr. Weihua Li

Research Fellow at Nanyang Technological Univ

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Proceedings Article | 14 November 2002 Paper

Haptic interfacing system using magnetorheological fluids

Weihua Li, Hejun Du, Lit Ding, N. Q. Guo

Proceedings Volume 4935, (2002) https://doi.org/10.1117/12.469066

KEYWORDS: Actuators, Haptic technology, Feedback control, Magnetism, Control systems, Computing systems, Human-machine interfaces, Visualization, Prototyping, Transistors

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This paper presents design and development of a haptic interfacing system working with magnetorheological fluids. This system consists of three interchangeable parts: a MR actuator, an interfacing circuitry, and a computer program. The MR actuator is optimally analyzed and designed with finite element simulation, by considering the effects of both magnetic field formation and MR effect formation mechanism. The computer screen is portioned in various segments and the controllable software monitors the attributed values of the voltage to the screen. The computer program, via the parallel port-interfacing circuitry, monitors the current through the electromagnet. Simultaneously, a sensor detects the knob position; the corresponding motion can be observed through a cursor on a computer display. An interactive program is written to demonstrate the working of the haptic interface system. It displays a series of colour bands across the screen, each representing an assigned resistive torque value. As the cursor enters these zones, the corresponding feedback signal is sent to the haptic device.

Proceedings Article | 2 July 2001 Paper

Viscoelastic properties of MR fluids under oscillatory shear

Weihua Li, Hejun Du, G. Chen, Song Yeo

Proceedings Volume 4331, (2001) https://doi.org/10.1117/12.432732

KEYWORDS: Fluid dynamics, Magnetism, Particles, Microfluidics, Chromium, Temperature metrology, Optical character recognition, Lithium, Solids, Phase measurement

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In this paper, viscoelastic properties of MR fluids under oscillatory shear were experimentally studied using a rheometer with parallel-plate geometry. The experiments were conducted with amplitude sweep mode and frequency sweep mode. For the amplitude sweep mode, the driving frequency is fixed at a given value of (omega) rad/s and the strain amplitude, (gamma) ₀, is swept from 0.01% to 100$; For the frequency sweep mode, the strain amplitude is fixed at a certain strain, (gamma) ₀, and driving frequency is swept from 1 to 11 Hz. Consequently, the effects of strain amplitude, frequency, magnetic field strength, and temperature on the viscoelastic properties of MR fluids were investigated. MR fluid behaves as a linear viscoelastic body for sufficiently small strain amplitude ((gamma) ₀<EQ(gamma) _lin), while nonlinear viscoelastic behavior is observed for high strain ranges ((gamma) ₀>(gamma) _lin). At small strain amplitudes, the storage modulus and the loss modulus are independent of strain amplitude. At high strain amplitudes, the storage modulus is independent of the frequency and approaches plateau values at low frequencies. With increasing frequency, the storage modulus shows a decreasing trend before increasing again. The loss modulus varies slightly with frequency. MR fluid shows elastic-dominated properties in a magnetic field. Both the storage modulus and the loss modulus increase significantly with increasing field of strength. The temperature dependence of viscoelastic properties is also discussed. For the experimental temperature range of 20 degree(s)C to 60 degree(s)C, the storage modulus shows a slightly decreasing trend with temperature.

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