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tactile rendering (density, temporal bandwidth, force, etc.). The actuator is made up
of a permanent magnet and a solenoid coil. The results of the characterisation of the
actuator show that the outlet force is linearly proportional to the input current in the
intervals of [0-0.5]A and [0-8]mN.
The researchers, in the department of technology and engineering of the Karl-
sruhe research centre, have developed a tactile rendering system that can be used with
flexible endoscope forceps. These studies have helped to make a tactile interface com-
posed of 3
24 needle actuator heads, thus providing a total of 72 actuators. The
various needles are electromagnetically actuated and vibrate at a maximum frequency
of 600Hz.
Moy and Fearing have demonstrated that optimal spacing between two tactile
actuators must have a spatial distribution density of 1 actuator/mm 2 , generate a force of
2N per actuator or provide a 2mm skin indentation, 3bits resolution and a bandwidth
of at least 50Hz (Fearing et al., 1997). Wagner et al. (2002) offer a tactile actuator
based on an RC servomotor technology. These servomotors provide a large bandwidth,
high spatial distribution density of the actuators, high vertical displacement and a firm
static response for a relatively low cost and simple construction. The final interface
vertically generates a displacement of 2mmwith a resolution of 4bits, on a distribution
of 6
×
6 mechanical pins spaced out by 2mm each. The rise time from 10% to 90% is
41msec.
The Exeter interface has been designed to simulate the interaction of the finger
with different objects. By using the density of the contact receptors in the skin as
the base, which is 1mm 2 on the fingertip, the interface has been designed with 100
contactor terminals, arranged on a surface of 1 cm 2 , required to cover the fingertip.
Each contactor is run by a piezoelectric actuator - the 100 actuators can be individually
addressed by software.
A stimulator with 400 tactile elements was made by a collaboration between the
Indiana University and Johns Hopkins University. The purpose of these works is to
study the properties of the neurons, located in the areas of the cortex responsible for
somatesthesia, the part of the brain that receives and processes somatic senses (contact,
temperature and pain). The researchers used the most precise specifications that were
closest to the physiological characteristics of man: 0.5mm spacing of the actuators, a
frequency band that reaches 300Hz, and an indentation amplitude that reaches 2mm
(Pawluk et al., 1998).
In 1995, researchers (Akamatsu et al., 1995) worked on the comparison between
tactile, auditory and visual rendering in a pointing test using a desktop mouse interface.
They modified a standard mouse, so that it could generate a tactile rendering at
the fingertip. The tactile information is provided using an aluminium pin (1
×
2mm)
projected from a hole located on the left button of the mouse. The pin is controlled by
a solenoid with a lever-type traction mechanism. Since then, a company by the name
of VirTouch has manufactured and marketed computer mice incorporating two Braille
modules of 4
×
4 mobile elements with 1mm strokes.
The TiNi company developed a tactile interface of 5
×
6 actuators. The spacing of
the pins is 1.5mm, the diameter of each pin is 1mm and a force of 6 g is developed by
each AMF wire. The response time is 100msec. A.D. Johnson of TiNi Alloy Company,
Inc. proposed another 5
×
6 matrix architecture tactile interface. At the base, an SMA
wire with a diameter of 0.076mm and a length of 15.24mm, with a 0.2A current
×
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