WO2009007952A2

WO2009007952A2 - Thermoelectric tactile display

Info

Publication number: WO2009007952A2
Application number: PCT/IL2008/000928
Authority: WO
Inventors: Tal Oron-Gilad; Yael Salzer
Original assignee: Ben Gurion University Of The Negev Research And Development Authority
Priority date: 2007-07-10
Filing date: 2008-07-07
Publication date: 2009-01-15
Also published as: WO2009007952A3

Abstract

Provided is a thermal tactile display for haptic communication with a human subject, employing the thermal grill illusion. The display is formed by arrays of thermal units which are placed on the skin, the units being preferably based on thermoelectric pumps. The communication via the display may substitute or enrich visual or acoustic sensations in security applications or in gaming.

Description

THERMOELECTRIC TACTILE DISPLAY

Field of the Invention

The present invention relates to an information display of the tactile modality based on thermal sensation, particularity using the thermal-grill illusion. The thermo-tactile display is implemented by using a set of thermoelectric coolers creating hot and cold stimuli sensed by the human skin.

Background of the Invention

The most common modalities for man-machine communication are vision and sound, less common is the modality of touch. The use of the modality of touch is found contributory when either of the mentioned common modalities are damaged at some level, such as in case of deafness or blindness, or when either or both modalities are over-occupied, as appears at workplaces that are noisy or require high visual and auditory attention (e.g. battlefield, production plants).

Tactile displays are means of communication through touch, intended to transfer an input signal as a haptic signal for the human skin. The signal to the skin may be modulated in several sub-modalities, comprising pressure, vibration or temperature changes. Information is transferred to the user by change of the input signal to the skin, in space and time. Most of the existing tactile displays are based on modulated information transfer onto the skin through changes in pressure and vibration. Thermal stimuli have been used in haptic displays to assist in supporting the mechanical modalities of object identification; thermal sensation has not been used to create an independent display vocabulary, or as a channel of specific, independent information, as the skin thermal discrimination capabilities are low. The limitations in using a temperature-based tactile language include the low prominence or thermal sensations below pain threshold, and the adaptability of the thermal receptors [Green B.G.: J. Neurobiol. 61 (2004) 13-29]. It is therefore an object of the present invention to provide a haptic display using thermal effects for transmitting specific information. Thermal displays have been described, such as a display comprising thermoelectric elements and liquid crystals [US 3,936,817]. A practical haptic thermal display should transmit information within a health-safe range of stimuli, below pain threshold, and with a sufficient signal resolution and channel capacity.

It was observed, as early as 1896, that applying warm and cold stimuli simultaneously near to each other on the skin caused a sensation of burn or sting. This phenomenon, called thermal grill illusion (TGI), can, thus, lead to a strong sensation signal even if applying relatively moderate thermal stimuli which are out of an injury range and below pain threshold. US 7,321,309 employs the TGI in a deterring system that delivers pain without damage, together with a visual or acoustic signal, warning a human or animal subject against touching certain object. It is another object of the invention to utilize the sensation of heat associated with thermal grill illusion to transmit information, and to manipulate tactile data transfer.

It is a further object of the invention to provide a thermal two-dimensional means for information transfer to the human skin.

It is still a further object of the present invention to produce a thermal display, comprising creating hot and cold thermal stimuli onto the skin.

It is still another object of the present invention to provide a communication system comprising thermal sensation of the communicating subjects, particularly employing TGI.

Other objects and advantages of present invention will appear as description proceeds. Summary of the Invention

This invention provides a haptic display for communicating with a human subject comprising the thermal grill illusion (TGI). The display creates hot and cold thermal stimuli to convey tactile information to the subject's skin. In a preferred embodiment of the invention, the thermal stimuli are conveyed to the skin by means of independently managed heat units, preferably comprising thermoelectric cooler (TEC) units. The TGI is created by an array of at least two TEC units, of which at least one conveys a cold stimulus, and at least one conveys a hot stimulus. In a preferred embodiment, said array comprises two TEC units conveying simultaneously or nearly simultaneously a cold stimulus and a hot stimulus on two different sites of the subject's skin, wherein the distance between the sites is preferably less than 8 cm; said distance between said two TEC units in said array on said two sites on the subject's skin is preferably greater than 0.3 cm. In the display according to the invention, the presence of said thermal grill effect created by said array of two heat units (providing a relatively colder stimulus and a relatively hotter stimulus) represents a unit signal, and the presence or the absence of said TGI created by said array represents a unit information which is communicated by said display to said subject. The display according to the invention comprises, in a preferred embodiment, a plurality of TEC units arranged into arrays of at least two TEC units, wherein each array causes TGI independently on the other TEC units, creating a plurality of signals in time and space, wherein the space is a two- dimensional space essentially defined by the skin surface of said subject. Said hot stimuli usually comprise a temperature higher than the normal skin's temperature, (commonly at about 33°C) and said cold stimuli usually comprise a temperature lower than said normal skin's temperature. A display according to the invention is advantageously used by subjects whose vision or audition is impaired or overloaded. The display according to the invention may be integrated into a computer game, enriching the computer/human communication by tactile sensation beside audio and visual sensations. Said games may involve arcade games, or said games may be a part of home gaming interaction devices. A display according to the invention may comprise means for attaching to the skin, selected from straps, belts, gloves, socks, and shirts. The heat units forming the display may be connected to form a set with fixed distances, which set may then be attached to the skin. Alternatively, the units may be attached separately to the skin according to the need.

The invention relates to a method of communicating with a subject, comprising contacting the skin of said subject with a plurality of TEC units conveying cold and hot stimuli, wherein at least two of said TEC create the TGI. The method comprising conveying information to said subject, independently on visual or acoustic signals. The communication will advantageously be unnoticed by other subjects. Conveyed to the subject may be alert or warning. However, a more complex information may be transmitted via the skin to the subject. Preferably, at least two thermal units creating heat stimuli at two different sites on the skin of a subject are employed, wherein the distance is preferably between the sites 0.2 and 10 cm, more preferably between 0.3 and 8 cm, and wherein the temperature difference between the two stimuli may be at least 4⁰C, preferably at least 8⁰C. In the communication according to the invention, at least two heat stimuli create the TGI. In a preferred embodiment of the invention, the communication system comprises a plurality of TEC units in contact with the skin of said subject, the TEC units creating heat stimuli of different temperatures, whereas both the predetermined temperatures of the stimuli, and real temperatures near the skin are processed by a computer interface. Each TEC has in fact two sides, one side being attached to a thermally conducting material which contacts the skin (face side), the other side being attached to heat sink (back side), forming a basic thermal unit. In a preferred embodiment, the communication system according to the invention further comprises an AfD component and control unit mounted on a PC managing a plurality of basic thermal units, the control unit managing the an AfD component, the isolator component changing the electric current flow through the TEC of the thermal unit, thus controlling the thermal signals. Said an AfD component and control unit mounted on a PC manage each thermal unit separately, ensuring that each thermal signal has a duration and a temperature sized independently of the parameters of other thermal units. Preferably, each thermal unit comprises a thermal-sensor measuring the temperature near to the face side of the thermal unit and providing a feedback to a PC. Said sensor may be located within said face side, in a tunnel drilled inside the thermal conductive material.

Brief Description of the Drawings

The above and other characteristics and advantages of the invention will be more readily apparent through the following examples, and with reference to the appended drawings, wherein:

Fig. 1. is a schematic overall description of the entire system in one embodiment of the invention; Fig. 2. is a schematic description of a thermal unit array in one embodiment, for use in the system of the invention; Fig. 3. is a schematic cross section of the thermal unit array in one embodiment, for use in the system of the invention; Fig. 4. is a graph of suggested theoretical idealized thermal signal behavior in one embodiment of the invention;

Fig. 5. schematically shows a system for tactile information transfer in one embodiment of the invention, comprising an array of thermoelectric coolers, Analog-to-Digital (AfD) interface, and computer; Fig. 6. illustrates sensing altering simultaneous hot and cold stimuli by an individual, such stimuli producing a sensation that may be stinging, burning-cold, or itching; Fig. 7. is a block diagram of a thermoelectric tactile display in one embodiment of the invention; and 8

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Fig. 8. is a photo of the thermal actuating unit (TAU) in one embodiment of the invention, as used in Example 1.

Detailed Description of the Invention It has now been found that thermal sensation can serve in an efficient communication system, when employing thermal grill illusion (TGI) for transmitting information via a haptic display. Such display is essentially a two-dimensional display consisting of an array of thermal units.

The sensory receptors of the skin are involved in differentiating various sensations, comprising at least pain, mechanical forces, heat and cold. Said forces may comprise pressure and vibration. The total haptic impression, or the sense of touch, is affected by mixed energy signals including mechanical forces on - and heat flow to - the body surface and volume. In the context of the invention, particularly considered are effects onto the skin. Further, the terms haptic and tactile are used interchangeably, relating mainly to the sense of touch. The term haptic display relates to an essentially two- dimensional array of elements capable to convey tactile sensation onto the skin.

Normally, pain caused by hot and cold sensations is also derived from separated cutaneous nociceptive thermo-receptors, sensed once the temperature of stimuli increases above approximately 45⁰C or decreases below approximately 10⁰C. Normally, warm and cold sensations, derived from separate warm and cold cutaneous thermo-receptors, would be sensed once the temperature of stimuli increases above or decreases below the skin's base temperature (commonly at about 33°C). But when suitably "mixing" warm and cold stimuli, an unexpectedly strong sensation may appear even though the threshold of neither hot nor cold nociceptors is exceeded, the sensation on the skin, thus, being enhanced when utilizing the phenomenon of TGI. In a display according to the invention, the thermal signals may be conveyed to the skin by any known methods. In a preferred embodiment, said method comprises thermoelectric cooling units using the Peltier effect, creating a heat flux between the junction of opposing doped semiconductors. In a thermoelectric heat pump, the heat may be transferred against the temperature gradient with consumption of electrical energy, enabling both cooling and heating while utilizing the same phenomenon. Although the device may be used for conveying both cool and hot signals to the skin, depending on the electrical current direction, or on the device orientation on the skin, the device is abbreviated here as TEC (thermoelectric cooler).

In accordance with the invention, there is provided a basic thermal unit creating the unitary thermal signal. The unit, abbreviated here as TAU (thermal actuating unit), may be an assembly of a thermoelectric cooler (TEC), for example a TEC unit obtained commercially (e.g. Melcor®), attached to a thermally conducting material, such as aluminum, placed next to the skin. On its opposite side the TEC is attached to a heat sink for heat dissipation. In accordance with the invention, there is therefore provided an voltage isolator component to prevent current, and control unit mounted on a PC. The control unit manages the isolator component. The isolator component changes the current flow through the TEC of the TAU, thus controlling the thermal signals. Each TAU is controlled unitarily by the control unit. Thus, the duration and the temperature amplitude of each thermal stimulus would vary independently of the other parameters of the adjacent TAUs. In accordance with the invention, there is therefore provided a feedback reading of the temperature generated by the TEC measured on the face adjacent to the skin of the body organ. The temperature is read by a thermal-sensor situated in a tunnel drilled inside the thermal conductive material (e.g. aluminum slab). The temperature read by the thermal sensor is transmitted to the control unit. The proposed designs have the flexibility to change physical dimensions of the two-dimensional array. The distance between adjacent warm and cold contact elements, such as for example cloth strips as shown in Fig. 5 or bars in Fig. 6, defines the grid width of the thermal grill created for the thermal grill illusion. In one embodiment of the invention, the design of the TAU provides an area of contact with the body of about 15mm x 15mm, for sufficient recognition of thermal stimulus by the organ's thermal sensors. The dimensions of the TAU contact area is preferably more than about 100 mm², for example up to 1600 mm². The perceptive sensation of the signal is a function of this distance.

With specific reference to the figures, it is stressed that the particulars shown are presented by way of example and for purposes of illustrative discussion of the preferred embodiments of the present invention only, and they are presented in what is believed to be a useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention, the description taken with the drawings, making apparent to those skilled in the art how the several forms of the invention may be embodied in practice.

Referring now to Fig 1, shown is a thermal-units array (10) attached with a connecting strap (8) to a location on the body (6) (e.g. arm, leg, trunk). The thermal units array is controlled through electronic connection by the A/D component (4) responsible for the change of current drive to the thermal units within the array (10). The isolator component (4) receives commands from a control program running on a PC (2).

Figure 2 illustrates a proposal to the setting of the TAUs within the TAU array. An embodiment shown in Fig. 2 comprises two-dimensional array of TAUs (14), (16), (18), (20), (22), and (24), arranged in rows spaced by displacement (28) and in columns spaced by displacement (30), according to the user's skin characteristics. The array can vary in size and in number of TAUs included. The suggested array of TAUs could be activated in a variety of warm and cold combinations, creating a variety of TGI signals.

Figure 3 shows by cross section the placement of the array of thermal units on the surface of the skin of the body (42). A thermal actuating unit (TAU) is composed of three components, aluminum (38), TEC (32), and a heat sink (34). AU TAUs are held together with a connecting strap (36), creating an array. The aluminum (38) is drilled to provide cavities (40) for holding thermal sensors.

Fig 4 illustrates the intended signal stimuli created by a single TAU. The temperature of the TAU contacting the skin varies (axis Y) in pulses over time (axis X). -

Fig. 5 shows a system for tactile information transfer in one embodiment of the invention, comprising an array of TAUs, A/D interface, and computer unit. Three TAU doublets are shown, but other number of doublets or triplets may be employed. The TAUs are strapped with elastic fabric to the anterior forearm, adapted to suit the circumference of the forearm.

Fig. 6 illustrates creating the TGI, by conveying altering simultaneous hot and cold stimuli to the skin; the figure is adapted from Craig et al. [Craig A. D. et al.: Nature(372) (1994) 770-2].

Fig. 7 shows a possible arrangement of functional units in a tactile system (display), according to the invention. Fig.8 shows a possible representation of a single TAU. The thermal grill illusion or synthetic heat was described by Thunberg in 1896. Alternating 20°C and 4O⁰C stimuli produced burning and stinging equivalents in intensity to that produced by 10°C stimuli. Normally, warm and cold sensations, derived from separate warm and cold cutaneous thermo- receptors, should be sensed once temperature of stimuli has exceeded or decreased below skin's base temperature (commonly at 33°C). Thermal pain is derived from nociceptive thermal sensors activated at more extreme temperatures, commonly above 45⁰C and below 1O⁰C. Thus, when alternating warm and cold stimuli, a sensation appears even though the threshold of neither hot nor cold pain related receptors has been exceeded. Recent work suggests that the TGI may not necessarily depend on the activity of the nociceptive pathway. Furthermore, it has been demonstrated that TGI (burning cold, stinging, currents) occurs even with mild temperature differences, i.e., when cold stimuli varied at range of 27°C to 33°C, and hot stimuli at about 36⁰C [Green B.G.: Somatosensory & Motor Res. 19 (2002) 130-8]. One of the aims of the invention is to utilize the sensation of heat and the like to manipulate tactile data transfer. Tactile sensation is a channel of communication ordinarily not overloaded. Tactile displays can utilize the tactile modality to supplant the more commonly used modalities of communication, vision and audition, particularly when either one or both of these modalities are overloaded or impaired, or when providing additional information is beneficial.

In one aspect of the invention, the haptic display comprising the TGI is to be employed in security associated applications, for example for performing a communication unnoticed by other subjects, for conveying covert alerts and warnings. In other aspect of the invention, the haptic display comprising the

TGI should add another sense to the computer gaming, enriching the computer/human communication by another dimension. The haptic display may comprise various contact means creating the required sensation on the skin of a receiving subject, either means attached to the subject's body (such T/IL2008/000928

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as in Fig. 5), or separate means to be reached for and touched (such as in Fig. 6). Said mans may comprise, for example, wearable items (gloves, socks, shirts, etc.) or attachable items (belt, strap). Thus, beside contributing to the security/safety field, the invention enables to broaden the virtual environments gaming; by including the subject's temperature receptors and the object's physical properties such as temperature and conductance, a new dimension of reality is added in the virtual reality. The display may be used in gaming, such as in arcade games, in home gaming interaction devices (such as Wii of Nintendo®).

The invention enables modulating heat-based signals, and distinguishing various features, such as spatial organization of components, etc. Transmitting information through TGI-signals, eventually together with simulating/mimicking real tactile data to virtual tactile data and with creating a meaningful tactile language, adds touch to traditional communication through vision and audition. The usage of tactile sensation for communicating according to the invention may be applied in two modes - as a simple alert or as a more complex language. The TGI sensation can be modulated to create a set of tactile vocabulary. Communication may comprise various devices and remote control thereof.

Thus, provided is a two-dimensional thermal display, creating hot and cold thermal stimuli to the skin, which display produces the sensation of thermal grill illusion, created by alternating hot and cold temperature stimuli, to be utilized for tactile communication. A basic thermal unit — an element of the thermal display — creates a unitary thermal signal, said thermal unit being preferably represented by a TEC units attached to a thermal conducting material, such as aluminum, on one side (called face side), and heat sink on the other (called back side). A plurality of the basic units are assembled in a an array defining said display, the face sides of those units essentially defining a two-dimensional space of said display. An isolator component and control unit mounted on a PC are a part of the communication system, managing the thermal units array. The control unit manages the isolator component; the isolator component changes the current flow through the TEC of the thermal unit, thus controlling the thermal signals. An isolator component and control unit mounted on a PC, manage each thermal unit separately. Thus, each thermal signal's duration and temperature amplitude vary independently of the other thermal units' parameters. A thermal sensor, measuring a feedback temperature, is placed inside the thermal unit adjacent to the skin of the body organ. The thermal-sensor is preferably situated in a tunnel drilled inside the thermal conductive material (e.g. aluminum). The provided temperature is processed in the control unit. The thermal units form arrays with an adjustable size. The arrays may be, for example, attached on a strap; the distance between adjacent cloth straps defines the grid width of the thermal-grill created for the thermal-grill illusion. So, in one embodiment, a thermoelectric tactile display is provided composed of an array of thermal units placed next to the bare skin of a human body, the array being controlled by a control unit which manages each of the thermal units separately, changing their temperature amplitude and signal duration to form the sensation of thermal grill illusion utilized to create thermal based tactile signaling.

It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing described and illustrated embodiments and that the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes, which come within the meaning and range of equivalency of the claims, are therefore intended to be embraced therein. The invention will be further described and illustrated by the following examples.

Examples Experiments 1 and 2 explored the configuration of the thermal signal; i.e. the effects of the change in spatial order between the simultaneous hot and cold stimuli which produce the compound elements of the TGI signal. Any configuration of hot (H) and cold (C) stimuli (i.e.: H-C, C-H-C or H-C-C, etc.) is referred to as TGI-type signal. The sensation created by the TGI-type signal was examined, as well as the resolution among different signals. Experiment 1 confirmed the ability to create and sense TGI sensations by generating signals created by two actuating units (one hot and one cold). Experiment 2 investigated more complex sensations by using three actuating units (e.g., one hot and two cold in various orders). Experiment 3 examined the effect of the distance between the thermal actuators on the perceived TGI sensation. Throughout all three experiments, the participants' attention was fully directed toward the temperature stimuli.

Experimental arrangement

To generate Thermal Grill Illusion (TGI) signals, a Thermoelectric Tactile Display (TTD) prototype was self-developed. The TTD is based on Thermoelectric Coolers (TEC), a technology commonly used for cooling electronic devices. The TTD system comprises the Thermal Actuator Unit (TAU), NI 9211 (National Instruments©) component, Voltage Control Unit (VCU), PC Controller, and Thermo-Couple (TC) sensors (see Fig. 7). The software supporting this effort ran on a 1.73GHz HP Compaq nxβllO with the Windows XP Home operating system. The software was programmed in Lab View (National Instruments©). The TAUs were mounted on the glabrous skin of the forearm. As the arm of the participant lays relaxed on a cushion, the TAUs are strapped with elastic fabric to the anterior forearm, adapted to suit the circumference of the forearm as shown in Fig. 5). TAUs are a structure made of a thermoelectric cooler (TEC, SH0.1-23-06L, Melcor ©), heat-sink (Fisher Elektronik©) and a drilled aluminum plate (see Fig. 8). The TEC is made of rows of semiconductors, alternating N- and P- doping inserted between two layers of ceramic plates. The semiconductors are electronically linked serially but in parallel thermally. Whether heat is absorbed or generated is determined by the direction of the running current through a single junction of two different conductors, which is also known as Peltier effect.

The heat sink mounted on top of the TEC, dissipates the heat from by the TEC. The drilled aluminum plate transfers the heat between the skin and the TEC in a relatively uniform manner with little thermal resistance. A TC inserted into the drilled aluminum of the TAUs senses the temperature of the TAU-Skin contact (illustrated in Fig. 8). The 15 by 15 mm dimension of the TAUs provides a surface that is big enough to cover thermal receptors of the skin, assuming existence of warmth insensitive fields (WIF) [Green B. G.& Zharachuk R.: Somatosensory and Motor Res. 18 (2001) 181-90]. As a consequence of the structure of the mounting grip the minimal proximity possible between adjacent TAUs is 0.8cm. The PC controller controls the VCU and receives data from the VCU and the NI9211. The VCU supplies voltage to each TAU separately. Direct and separate computer control for each TAU allows defining the temperature and the signal duration of each one of the TAUs separately, permitting alternating hot and cold stimuli, separated in time and space. Data from TC is collected by the NI9211 transmitted to the PC controller. For each trial the temperature of each TC is collected and recorded for up to three seconds before the initiation of the pulse till 10 seconds after the last pulse ends. The TTD controls each TAU separately. Each TAU has a separate activation command, executed at its own programmed timing, generating either hot or cold sensation for a specified pulse length. The control over the TAUs permits a range of possible signals, finite in the dimension of mode-configuration, yet infinite in time domain. Since each TAU can be configured to either of the modes, hot or cold. When a pair of TAUs is activated a set of four configurations is available: proximal hot - distal cold (H-C), proximal and distal hot (H-H), proximal cold - distal hot (C-H), proximal and distal cold (C-C). The duration of the pulse length of each TAU and the delay between two adjacent TAUs can be configured. When all three TAUs are activated a set of six TGI-type signal configurations are available: proximal cold, center cold and distal hot (C-C- H), proximal cold, center hot and distal hot (C-H-H), proximal hot, center hot and distal cold (H-H-C), proximal hot, center cold and distal cold (H-C-C), proximal cold, center hot and distal cold (C-H-C) and proximal hot, center cold and distal hot (H-C-H). An emergency stop switch provides a physical shut down of the system. This switch was accessible to both the participant and researcher. Participants were always instructed to use the switch with no hesitation in any case of uncomfortable sensation. For all trials the participant sat comfortably on a padded office chair, as the arm lay on a cushion at the height of a desk. The participant had no view of the PC controller screen. Because of the posture of the apparatus, the forearm on trial was the right hand for two of the participants and left hand for the third participant, regardless of their tendency. Once all conditions within the experiment were presented the TAUs were dismounted to provide the participant with a respite.

Example 1

The purpose of this Example, Experiment 1, was to establish a TGI sensation by two actuating units at two spatial configurations; proximal hot and distal cold stimulus, or vice versa.

Participants

Three undergraduate students participated in this experiment, two females (D, and E) and one male (O), all age 27. The participants will be referred to by their initial: D, E and O. Procedure

The experiment employed a design of non-repeating actuators' configurations; proximal cold and distal hot (C-H), proximal hot and distal cold (H-C), proximal and distal cold (C-C) and proximal and distal hot (H-H), (similarly as in Fig. 5, but with two TAUs only). Before the apparatus was mounted on the participant's arm, the room temperature was read from the three TCs. At the beginning of the session, the participant was made aware of the emergency-stop switch and was instructed to use it if a wrong or uncomfortable sensation was felt. Furthermore, he was told that if necessary, the TAUs could be dismounted from the forearm to provide a respite to the participant.

Due to unique physical characteristics of each participant before the experimental trial began, a calibration process was conducted. The aim of the calibration was to verify for each individual participant that he or she were capable of sensing hot-warm and cold-cool sensations with the TTD, and to verify that the stimuli did not exceed a non-painful temperature range. The participant's thermal response was observed for each TAU separately. All three TAUs were placed on the forearm of the participant close to each other as much as the elastic straps and wiring permits (0.8 cm between two TAUs). The straps were adapted to comfortably fit the participant's forearm. Within few minutes, the temperature read from the TC-s stabilized to indicate the temperature of the outermost layer of the skin. TAUs were activated one at a time at random order. Each TAU was activated twice in hot mode and twice in cold mode. Pulse length of all stimuli was fixed at 15 seconds. This duration was chosen to assure the temperature does not exceed the non- painful thermal range of below 5⁰C and above 45⁰C. The participant was asked to report when thermal sensation was first sensed, and its quality (cold, cool, hot, warm, burning, painful, stinging, currents or other). Two measures were taken; time of the report and temperature read at time of report, both were logged manually. Another signal was activated only when a) the temperature read by the TC of the activated TAU has stabilized, and when b) the participant reported that he or she no longer felt a thermal sensation.

The most distal TAU was dismounted leaving only two TAUs on the forearm. Activation of two TAUs permits 16 combinations of pairs of signals. Each participant was presented with 16 trials, at a randomly generated order. If the calibration verified that the thermal sensation was felt within few seconds, pulse length of all stimuli was set to 10 seconds. The time delay between two spatial adjacent TAUs within a signal was set to zero. In order to have the participant's attention directed toward the TTD stimuli, the experimenter informed the participant, that the first signal will be expected within few seconds. Then again, the experimenter informed the participant of the coming of the second signal few seconds before its activation. The participant was instructed to report the sensation she felt by each signal during the signal. Each trial ended when the participant reported whether the two signals felt the same or different. The verbal reports of the perceived sensations for each signal and the signals' resemblance, were logged manually by the experimenter, the temperature of the signal, was automatically logged by the software. When the description of the sensation that was reported verbally by the participant changed over the duration of the signal occurrence (i.e., the participant initially reported a certain sensation and then reported a change to a different sensation), the sensations were logged as "initial sensation" and "final sensation" by the order of their report. When the verbal description did not change over time, the initial sensation was registered as equivalent to the final sensation. The reported sensations were classified into seven categories. Three categories described simple thermal sensations: hot (or warm), cold (or cool), burning-hot. Four categories describe TGI sensations: sting, burn cold, currents and other (other included itch, prick, and combination of few sensations or simultaneous sensation of hot/warm and cool/cold). If both sting and cold or hot were sensed they were logged as sting. At the case where hot was followed by burn, the burn was logged as burning-hot. If a participant reported simultaneous but specific sensation of cold or hot at separate loci the experimenter registered that both hot and cold sensations were felt at the same time, but were spatially differentiated (i.e., the physical distance between the TAUs was too large and no TGI was generated). Once the experiment was complete, the ratio of the most frequent final-sensation was calculated per signal per participant. If a certain reported sensation was associated with a signal for more than 50% of its occurrence (50%-criterion), this sensation was defined as the relevant sensation for the identification of the signal. Otherwise, if the 50% criterion was not met, the sensation produced by the signals was not sufficiently robust (or distinguishable) and would not be further analyzed.

Results

As for the calibration, all three participants sensed the simple (hot or cold) thermal sensations within less than 10 seconds. TGI sensations were successfully created by TGI-type signals. When a C-H stimulus was applied, the participants reported sensations of either stinging or burning. All participants reported, for the most, that C-H differed from H-C. When H-H, C-C and C-H were compared to identical signals, all three participants recognized immediately that the signals were the same. H-C and C-H stimuli were sensed and judged as different from H-H or C-C stimuli, verifying the ability to create a distinguishable sensation with the combination of simultaneous hot and cold cues. The data confirmed that the invention may employ different sensations and their variations, associated with different loci of generated stimuli compounds of TGI-type signals. For example, the most frequent sensation described for H-C was different than the most frequent sensations described for C-H. The results confirmed the possibility to generate TGI sensations, and further to vary the sensations by varying the spatial configurations of its compounds. Example 2

Example 1 showed the generation of the TGI sensations with two TAUs. It showed that H-C and C-H were sensed differently, thus suggesting that more complex TGI stimuli may also vary as a function of the spatial order of their hot and cold components. Experiment 2, this Example 2, further investigated the possible sensations created by using three TAUs and the extent to which these signals were distinguishable, when activating three TAUs simultaneously. Similar design was used as in example 1, comprising nonrepeating actuators' configurations (C-C-H, C-H-H, H-H-C, H-C-C, C-H-C, H- C-H) (illustrated in Fig. 5). The same participants were employed as in Example 1, as well as the same experimental system. The six possible configurations of TGI-type signals permit 15 pairs in two sequential orders and 6 pairs of repeating identical signal, hence 36 trials were conducted. The participants were offered to take a short break every 10 to 15 trials (i.e., twice or three times during the experiment). As in Experiment 1, the order of trials was randomly generated and unique for each participant. The intention was to examine the degree to which the TGI-type signals are robust and distinguished. The participants somewhat differed in their ability to distinguish all the combinations, but TGI sensation, was consistently present. Generally, robustness of the sensation and the ability of the subjects to distinguish between signals, as found during the experiments, provided the basis for determining which of the TGI signals could be used to form a tactile language.

Example 3

Within Experiments 1 and 2, it was found that the sensation felt with TGI- type signal was dependent on the spatial order of the hot and cold compounds of the signal. The distance between the compounds in Experiments 1 and 2 was kept constant, at 0.8 cm. Experiment 3, this Example 3, further investigated the impact of spatial distance on the sensation of TGI-type signals. Experiment 3 was designed to establish if and to what extent 'phantom' and/or salutatory sensation existed when TGI-type signals of two TAUs were applied at various distances between the hot and cold stimuli component. As such, this experiment consisted of four blocks of trials, that differed by the distance between the hot and cold stimuli (1, 3, 5, and 7 or 9 cm, respectively). Two repetitions for each of the configurations (H-C and C- H), summing to total of four trials were presented at random order for each one of the blocks. Blocks were administered at a fixed order from the adjacent (1 cm) to the farther apart (9 cm) distance. The same participants as in the previous Examples were employed, each participant performing all of the experiments on the same day. A short break was offered between the experiments. The same experimental system was used as in Example 1. Two TAUs were used. The TAUs were initially placed 1 cm apart on the subject's forearm. At the end of each block the fabric straps attaching the TAUs to the participant's skin were re-adjusted to the required distance. Each trial was constructed of a single signal. The participants were instructed to report at the time of the signal whether the signal felt as having one or two origins of stimulation. Once a block was completed, the elastic strap of the distal TAU was released and relocated at the required distance of the proceeding block. There were differences in the participants' perception of the TGI-type signals as function of the distance between the TAUs. Some of the participants were able to distinguish between the two origins of the signal as the distance between them increased. The results suggested that different spatial arrangements of hot and cold stimuli produced a varying set of sensations, somewhat differing among the participants, suggesting that the design of signals and the pattern of their perception may require individual attitude in some aspects of the display construction in transmitting more complex signals. In any case, the invention enables practical approach for the design of thermal display system modulated by thermal grill illusion sensation, based on TEC technology. While the invention has been described using some specific examples, many modifications and variations are possible. It is therefore understood that the invention is not intended to be limited in any way, other than by the scope of the appended claims.

Claims

1. A haptic display for communicating with a human subject comprising the thermal grill illusion (TGI).

2. A display according to claim 1, creating hot and cold thermal stimuli to convey tactile information to the subject's skin.

3. A display according to claim 2, comprising thermoelectric cooler (TEC) units.

4. A display according to claim 3, wherein the TGI is created by an array of at least two TEC units, of which at least one conveys a cold stimulus, and at least one conveys a hot stimulus.

5. A display according to claim 4, wherein said array comprises two TEC units conveying simultaneously a cold stimulus and a hot stimulus on two different sites of the subject's skin, wherein the distance between the sites is less than 8 cm.

6. A display according to claim 5, wherein said distance between said two TEC units in said array on said two sites on the subject's skin is greater than 0.3 cm.

7. A display according to claim 6, wherein the presence of the TGI created by said array represents a unit signal, and wherein the presence or the absence of the TGI created by said array represents a unit information communicated by said display to said subject.

8. A display according to claim 3, comprising a plurality of TEC units arranged into arrays of at least two TEC units, wherein each array causes TGI independently on the other TEC units, creating a plurality of signals in time and space, wherein the space is a two-dimensional space essentially defined by the skin surface of said subject.

9. A display according to claim 2, wherein said hot stimuli comprise a temperature higher than 33⁰C and said cold stimuli comprise a temperature lower than 33⁰C.

10. A display according to claim 1, wherein vision or audition of said human subject is impaired.

11. A display according to claim 1, wherein vision or audition of said human subject is overloaded.

12. A display according to claim 1, integrated into a computer game, enriching the computer/human communication by tactile sensation beside audio and visual sensations.

13. A display according to claim 12, comprising arcade games or home gaming interaction devices.

14. A display according to claim 1, comprising means for attaching to the skin, selected from straps, belts, gloves, socks, and shirts.

15. A method of communicating with a subject, comprising contacting the skin of said subject with a plurality of TEC units conveying cold and hot stimuli, wherein at least two of said TEC create the TGI.

16. A method according to claim 15, comprising conveying information to said subject while unnoticed by other subjects.

17. A method according to claim 15, comprising conveying to said subject alert or warning.

18. A communication system comprising at least two thermal units creating heat stimuli at two different sites on the skin of a subject, wherein the distance between the sites is less than 8 cm and greater than 0.3 cm, and wherein the temperature difference between the two stimuli is at least 8⁰C.

19. A communication system according to claim 18, wherein at least two heat stimuli create the TGI.

20. A communication system according to claim 18, comprising a plurality of TEC units in contact with the skin of said subject, and a computer interface.

21. A communication system according to claim 18, wherein each TEC has two sides, one side being attached to a thermally conducting material which contacts the skin (face side), the other side being attached to heat sink (back side), forming a basic thermal unit.

22. A communication system according to claim 18, further comprising an A/D component and control unit mounted on a PC managing a plurality of basic thermal units, the control unit managing the isolator component, the A/D component changing the electric current flow through the TEC of the thermal unit, thus controlling the thermal signals.

23. A communication system according to claim 22, wherein said A/D component and control unit mounted on a PC manage each thermal unit separately ensuring that each thermal signal has a duration and a temperature sized independently of the parameters of other thermal units.

24. A communication system according to claim 18, wherein each thermal unit comprises a thermal-sensor measuring the temperature near to the face side of the thermal unit and providing a feedback to a PC.

25. A communication system according to claim 24, wherein said sensor is located within said face side, in a tunnel drilled inside the thermal conductive material.