Tactile display for presenting stiffness distribution using magnetorheological fluid

Abstract

This paper describes a tactile display for reproducing stiffness distributions based on magnetorheological (MR) fluid. This display can represent stiffness distribution by controlling the applied magnetic field locally. Computed tomography (CT) and endoscopy are currently used to diagnosis intravital conditions. However, CT cannot detect tumors smaller than 5 mm, and endoscopy can only diagnosis the tissue surface. Since tumors are stiffer than normal tissue, endoscopic palpation may be effective for detecting tumors smaller than 5 mm located beneath the tissue surface. To perform such palpation, a tactile display that can reproduce the spatial stiffness distribution of tissue is strongly required. For intravital tissue, the display must be capable of creating stiffness values ranging from about 200 to about 600 kPa with a spatial resolution of less than 5 mm. In the present study, a tactile display is proposed that exploits the ability of a MR fluid to change its stiffness in a magnetic field. In the proposed device, the MR fluid is encapsulated in an acrylic chamber covered by a thin flexible membrane. We first characterized the mechanical properties of the device and then, conducted sensory experiments with five subjects to verify that the device could display stiffness distribution. The magnetic field was produced by a cylindrical permanent magnet with a diameter of 5 mm, and the applied field strength was controlled by varying the separation between the magnet and the display. The experimental results indicated that the proposed display could successfully recreate the stiffness distribution including stiffness of tumor tissue under a local magnetic field of 200 mT. The device was then evaluated using five subjects, who were asked to touch the device with their index fingers and estimate the size of the stiff spot. Although the results varied among subjects, all were capable of perceiving spots smaller than 5mm.