Development of a haptically explorable sensor-actuator system for virtual reality

Project description

In most conventional virtual reality systems a large amount of reliance is placed on auditory and visual data with tactile information being largely ignored. However, haptic information is also important in the real world of man-machine communication interfaces. In fact there are many potential applications for tactile displays in medical technology, automation and modern communications systems.

The necessary data for the development of such a system is already available. Medical ultra-sound elastography can provide information concerning the hardness of tissue and organs. Such tactile information can then be reproduced using electrorheological fluids allowing medical doctors to haptically explore regions of the body normally only accesible during invasive surgery.

This particular "SMART" material has several distinct advantages over other technologies (such as pneumatic, hydraulic, electromagnetic etc.) previously used for tactile displays:

• Horizontal resolutions of within 3mm are possible
• Being passive elements with controlled damping, vertical strokes of several centimeters are possible.
• The power requirement is in the region of 20 mW per element making large arrays viable without excessive heat dissipation.
• The necessary switching elements are no larger than the tactile elements themselves.

A number of 4 by 4 element arrays have now been produced (as seen at CeBIT 2003) and the next step is to build 16 by 16 and eventually 32 by 32 element arrays.

The high voltage switching (ca. 2000 Volts at around 20 microamps) is carried out by light driven bulk Gallium-Arsenide switches. This new (and patented) technology is just one spin-off from this project. Further devices have been built which are capable of switching over 10,000 volts! (as demonstrated at the recent Mechatronics Conference in Regensburg). Being an optically driven system galvanic isolation between the computer and the high voltage switching is inherent. The ultrasound image to be haptically explored may simply be optically scanned or beamed onto the GaAs element array.

• Conversion of data from the sensor in a format that is adequate for the actor-elements
• Switching of high Voltage (about 2000 V) with low curent (microamps)
• galvanic isolation between the control unit and the high voltage unit
• Testing of the electromagnetic compatibility (EMC)

The picture above shows the second prototype of the haptic display using electrorheological fluid. Despite the high driving voltage, each haptic element requires only a very low electric current (in the µA range). Consequently, relatively high switch-resistances (in MOhm-range) can be tolerated as long as the dark resistance remains very high (GOhm range).
Because of the lack of such physically small high-voltage switching elements on the market, we were forced to develop a new component ourselves. Since it was necessary to create galvanic isolation between the low-voltage control unit and high-voltage switching components, we decided to use an optically controlled device. Many direct band gap semiconductor (group III and IV) materials are light sensitive without the necessity for doping and the creation of voltage sensitive PN-junctions. Gallium Arsenide (GaAs) is particularly robust in this respect, often even capable of recovery after electrical breakdown. The concatenation of several elements to form arrays is simple.

	Fraunhofer Institute for Silicate Research, Würzburg URL: www.isc.fhg.de/analytik/a3.html This e-mail address is being protected from spam bots, you need JavaScript enabled to view it This e-mail address is being protected from spam bots, you need JavaScript enabled to view it
	Institute for Micromachine Technology, Mainz URL: www.imm-mainz.de This e-mail address is being protected from spam bots, you need JavaScript enabled to view it This e-mail address is being protected from spam bots, you need JavaScript enabled to view it This e-mail address is being protected from spam bots, you need JavaScript enabled to view it This e-mail address is being protected from spam bots, you need JavaScript enabled to view it
	Fachhochschule Regensburg URL: www.fh-regensburg.de This e-mail address is being protected from spam bots, you need JavaScript enabled to view it This e-mail address is being protected from spam bots, you need JavaScript enabled to view it This e-mail address is being protected from spam bots, you need JavaScript enabled to view it This e-mail address is being protected from spam bots, you need JavaScript enabled to view it
	Ruhr-University Bochum URL: www.hf.uni-bochum.de This e-mail address is being protected from spam bots, you need JavaScript enabled to view it This e-mail address is being protected from spam bots, you need JavaScript enabled to view it This e-mail address is being protected from spam bots, you need JavaScript enabled to view it This e-mail address is being protected from spam bots, you need JavaScript enabled to view it