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Researchers from the Keio University (Yokohama, Japan) designed a MEMS tactile display to create virtual surface textures. The small prototype unit features large-displacement MEMS actuators underneath a titanium faceplate with 0.48mm diameter holes in it. Each large-displacement MEMS consists of a piezoelectric actuator pushing a plastic piston through a cavity filled with an incompressible polymer fluid that pushes its way through a deformable latex membrane. Keio University’s MEMS actuators for bulging taxels. Upon actuation, the hydraulic amplification mechanism squashes the fluid and makes the small latex membrane bulge through the faceplate hole. For a good discrimination through a finger’s tactile receptors, the tactile pixels were spaced a few millimetres apart, with the bulges protruding over 100μm at several Hz, and several μm at high frequencies up to 200Hz. By controlling the displacement, the vibration frequency, and the actuator driving patterns, the researchers reported various tactile feelings, mimicking various surface textures such as wood, urethane foam, and sandpapers. Researchers from the University of Michigan detailed a tactile display prototype using pneumatics to actuate a 7x8 array of pins, 1.2mm in diameter and spaced 2.5mm apart, with a clear orientation to hapticallyencode information to visually impaired users (such as Braille and tactile graphics). You may call it the steampunk of haptic displays, with pressurized air routed via small pipes to move the sliding pins up (with a 0.75mm vertical course). Pushed upwards, the pins deflect a thin elastic membrane and protrude from the faceplate. The system has a fairly slow refresh rate just under 2Hz, which really makes it applicable to Braille reading but would fall short of simulating textures and “click” feels. At the CEA’s Sensorial and Ambient Interfaces Laboratory, researchers came up with an interesting piston-variant of the bulging haptic display. In a paper titled “Morphing Tactile Display for Haptic Interaction in Vehicles”, co-authored by research engineers from car maker Renault, the CEA LIST lab described a tactile display based on an array of 32 electromagnetic actuators (individual coils with composite iron/ aluminium cores) overlaid by a capacitive touch deformable layer for finger position detection. A matrix of thin copper wires moulded into an elastic silicone layer makes the deformable touch screen with taxels that can move out of plane up to 1.9mm. A two-stage locking mechanism makes them bi-stable so as to reduce power consumption. In its current implementation, the device which is to be integrated in the centre console of vehicles has a reported refresh rate of 2Hz. At a reasonable deformation of about 0.25mm, a force of about 1.25N can be applied to the device, which would provide enough haptic feedback to give a “clicking impression” to the user. The researchers hope to redesign their system with a higher actuator density, packing 289 taxels spaced about 3mm apart to enable a non-pixelated surface shape. Slightly different but qualifying as a bulging screen, Tactus Technology’s Tactile Layer panel, showcased two years ago at SID 2012, relies on a transparent layer of microfluidics to raise liquid-filled bumps over ordinary touch-LCDs, creating dynamic physical buttons that users can see and feel. With a refresh rate about 1Hz, this interface is clearly aimed at keyboard-on-screen implementations. Tactus’ Tactile Layer panel with raised buttons Tactus Technology claims it could create almost any type of button configuration or layout on a panel (set in the manufacturing process). The company has yet to find a tablet or smartphone partner to integrate the pumped-up keyboard to their offering. Close encounter of the haptic type An interesting branch of haptics deals with so-called encountered-type interfaces, whereby the user can not only touch but grasp the interface (often a joystick, a pen, a plate or a ball) mounted on a retro-active feedback mechanism. The retro-active force allows the system to “resist” the user’s input based on what the user ought to feel when interacting with the objects shown on a screen. The force feedback can be calculated based on simulated material properties (for example when interacting with virtual objects), or it can be derived from real sensor data, for example when the user is operating a robot remotely. Two industrial sponsors of this year’s EuroHaptics, Force Dimension and Haption are well established players in this market, offering joystick-like interfaces with resistive forces and torques felt across multiple degrees of freedom. The perception you get is bluffing as you manipulate virtual objects in 3D, with hard and Pneumatic actuators for Braille reading. CEA LIST’s morphing tactile display. Force Dimension’s offering. www.electronics-eetimes.com Electronic Engineering Times Europe July/August 2014 11


EETE JULAUG 2014
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