Abstract:
A surface wave touch screen) comprising a hydrophobic touch panel capable of propagating surface acoustic waves, wherein a touch on the touch panel causes a perturbation of a surface wave propagating through the region of the touch. Surface wave transducer means are coupled to the touch panel for transmitting and receiving surface acoustic waves on the panel and processing means are capable of determining the position of a touch on the panel. Use of a hydrophobic panel is advantageous in that operation of the touch screen is unaffected by moisture and so can be used in external environments.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a surface wave touch screen for a cathode ray tube (CRT) display panel or other touch-controlled device which is capable of recognizing touch positions along a predetermined coordinate axis on a touch surface. More particularly, it relates to a surface wave touch screen for use in an external environment. 
     Systems employing a touch screen as a data input device are widely known. By touching the touch screen at a predetermined position with a finger or other object, data is selected that is indicative of that particular position. Thereupon, the associated data is introduced into the system and processed. A touch screen may be combined with a display for selecting data according to the zones shown on the display, such as virtual buttons. Also, the display may function as a means for providing visual feedback to the user by showing the information pertaining to the data after processing. 
     On the basis of the mechanism for activating the touch screen, several types of touch screens can be distinguished. Touch screens of choice for self service terminals, such as automated teller machines (ATMs), are so-called surface wave touch screens that locate the absorption of surface acoustic waves propagating in a front panel, the absorption occurring as a result of the contact between the panel and a soft tissue such as the user&#39;s finger. These touch screens, which have been on the market since 1980, work exceptionally well, are very stable, have no drift and are very resistant to damage. They are currently the preferred touch screens for heavy use self service terminals in unprotected environments, such as through the wall applications, because they will survive a large amount of abuse and vandalism. They do however have the disadvantage that they are adversely affected by water on the screen. Water is a good absorber of acoustic waves, and hence strongly absorbs the surface waves. Water on the touch screen surface results in a local dead area. Even if the touch screen is inclined or mounted vertically, if exposed to water, droplets can adhere to the screen, rendering it inoperative. Drying the water restores the operation of the screen. For this reason, surface wave touch screens are only suitable for dry or sheltered environments, such as shopping malls, where water on the screen is not a major problem. 
     SUMMARY OF THE INVENTION 
     It is an object to provide a surface wave touch screen which operates even if water is applied to the surface, and which is thus suitable for use in external environments. 
     According to the invention there is provided a surface wave touch screen comprising a touch panel capable of propagating surface acoustic waves wherein a touch on the touch panel causes a perturbation of a surface wave propagating through the region of the touch, transmitter and receiver means coupled to the touch panel for transmitting and receiving surface acoustic waves on the touch panel and control means for determining the position of a touch on the touch panel, characterized in that the touch surface is hydrophobic. 
     By use of a touch surface which is hydrophobic, any water droplets landing on the surface would immediately be shed off the inclined or vertical face of the screen and allow the touch screen to function normally. 
     Preferably, the panel of the touch screen comprises glass coated with Ritec “CLEAR-SHIELD”. 
     By the use of “CLEAR-SHIELD”, the glass touch screen is rendered hydrophobic and anti-static, and its coefficient of friction is reduced. Hence, the touch screen glass becomes a non-stick, easy clean surface, and water and other contaminants are shed more rapidly. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be described with reference to the accompanying drawing in which: 
     FIG. 1 shows an external perspective view of an automated teller machine (ATM) embodying the present invention; 
     FIG. 2 is a block diagram representation of the ATM of FIG. 1; and 
     FIG. 3 is a diagrammatic representation of a surface wave touch screen embodying the present invention. 
    
    
     DETAILED DESCRIPTION 
     Referring to FIG. 1, the ATM  10  shown therein comprises a user interface  12  to allow a user to interact with the terminal during a transaction. The user interface  12  includes a card reader slot  14  for insertion of user identification card  16  bearing encoded user data at the commencement of a transaction, a cash dispenser slot  20  for delivery of currency notes stored within the ATM  10  to a customer in a cash withdrawal transaction, a display screen  22  for displaying information to the customer during a transaction, a deposit slot  24  for receiving deposit envelopes containing cash or cheques during a deposit transaction, and a receipt printer slot  26  for delivery of a receipt to a customer at the end of a transaction. The card reader, cash dispenser, depository and receipt printer modules associated with the respective slots  14 ,  20 ,  24  and  26  in the user interface  12  of the ATM  10  are designated by the same reference numerals in FIG.  2 . 
     With reference to FIG. 2, the ATM  10  further comprises a controller unit  30  which communicates with components of the user interface  12 . The controller unit  30  includes a processor unit  32  and a memory unit  34  connected via a bus line to the processor unit  32 . The processor unit  32  receives signals from display screen  22  and from various mechanisms of the card reader  14  and the depository  24 , and provides output signals to the display  22 , the receipt printer  26 , the cash dispenser module  20  and to various mechanisms of the card reader module  14 . It should be understood that the processor unit  32  controls the amount of cash dispensed by the cash dispenser  20 , the information displayed on the display  22  and the information printed by the receipt printer  26 . The processor unit  32  may include a microcomputer, and the memory unit  34  may be a non-volatile RAM. The structure and operation of such microcomputer and memory are well known and therefore will not be described. 
     The display screen  22  of the ATM  10  will now be described with reference to FIG.  3 . The display screen  22  comprises a surface wave touch screen disposed in front of a flat display, for example of the CRT or LCD type. The surface wave touch screen comprises a transparent panel  46  which is provided with two ultrasonic transmitters  42  and  44  at diametrically opposite comers for transmitting waves to be radiated as surface acoustic waves (SAWs) across the surface thereof and with two series of reflective elements  48  and  50  disposed along two sides of the panel  46  which serve to reflect the SAWs waves across the panel  46 . Panel  46  is further provided with two receivers  52  and  54  that receive the waves after they have been reflected by the series of reflective elements  56  and  58  respectively. 
     The surface wave touch screen  22  operates to cause the waves from transmitters  42  and  44  to be radiated as surface acoustic waves at a high inaudible ultrasonic frequency of around 5.13 MHz. A SAW-pulse transmitted by transmitters  42  or  44  will be received, retarded and broadened by receivers  52  or  54 . In order to avoid mutual interference, transmitters  42  and  44  may transmit alternately. When a soft tissue, such as a human finger makes contact at a position B on the panel  46 , some of the energy of the SAW-pulse will be absorbed by the tissue, resulting in pulse components of decreased amplitude passing through the location of contact B. Receivers  52  and  54  receive the SAWs after reflection by reflective elements  56  and  58  and are designed to distinguish the reduced pulse components resulting from contact with the panel at point B. The processor unit  32  (FIG. 2) compares the time of receipt of these reduced pulse components by receivers  52  and  54  with the time of transmission from transmitters  42  and  44  respectively and determines the momentary position B at which the absorption of the SAWs occurs. 
     As the panel  46  is transparent, the display can be viewed through it, for instance in order to provide visual feedback to the user or in order to select data to be processed on the basis of information shown on the display by touching panel  46  at a predetermined position B associated with the data. By determining the momentary position at which the absorption occurs, the processing unit  32  may identify the data associated with position B and process such data as required. 
     Although panel  46  may be made of other materials which will be known to the skilled person, a particularly suitable material for touch screens is glass (sodium calcium silicate), which has a low coefficient of expansion, while the speed of propagation of acoustic waves remains relatively stable with changes in temperature. This makes the device exceptionally stable with time and temperature. For this reason, glass is the preferred touch screen panel material for ATMs and other self service terminals. However, glass is naturally hydrophilic, so any water droplets landing on its surface are inclined to remain there. This characteristic is particularly disadvantageous for touch screens as they are adversely affected by water, which is a good absorber of acoustic waves. Hence, any water droplets on the surface of the touch screen absorb the surface waves, resulting in local dead areas. Even if the touch screen is inclined or mounted vertically, if exposed to water, droplets tend to adhere to the glass panel, rendering the touch screen inoperative. 
     Furthermore, glass is a complex inorganic structure having several natural characteristics that make it difficult to keep clean. It does not have a completely smooth surface; microscopic irregularities enable many substances, including lime scale, plaster, mortar, sealants, hydrocarbon pollutants, metal oxides and carbonized food deposits, to stick or bond chemically to the surface such that they cannot be removed by normal cleaning methods. 
     It has now been found that these problems may be overcome by making the surface of the panel hydrophobic. Preferably, this is achieved by coating the glass panel  46  with a copolymer sold under the trademark “CLEAR-SHIELD”, which modifies the glass surface rendering it hydrophobic and anti-static. “CLEAR-SHIELD” chemically cross-links with itself and the glass, forming a completely transparent multi-molecular layer which is non-hazardous, thermally stable, chemically inert to most substances as soon as it is cured, and which will not crack, peel or flake. “CLEAR-SHIELD” also reduces the coefficient of friction of the glass to 60-70% that of untreated glass. Modifying the surface of the glass in this way prevents moisture from sitting on the touch screen  40 , so allowing it to function normally in wet conditions. “CLEAR-SHIELD” is commercially available from Ritec International Ltd., 15 Royal London Estate, West Road, London N17 0XL, UK. 
     Although coating the glass panel with “CLEAR-SHIELD” offers distinct advantages as discussed above, it is to be understood that the present invention is not limited to the use of “CLEAR-SHIELD”; any material which renders the surface of a touch screen hydrophobic to prevent moisture from sitting on the inclined or vertical screen may be used. For example, this may be achieved by coating the glass panel with a silicone fluid-based water repellent. 
     When a touch screen modified in this way is used in an ATM or other self-service terminal, any water, including rain drops and cleaning water, which might fall on the screen is immediately repelled from the inclined or vertical surface of the screen leaving it dry and operational. In this way, the touch screen according to the invention enables self service terminals to be installed in unsheltered external environments, unaffected by rain or other ambient moisture. In particular, self-service terminals already installed in such locations may now be fitted with the preferred glass touch screen according to the invention. Furthermore, if the touch screen is provided with a non-stick anti-static surface, it will enable the screen to keep clean for longer, and will also allow it to be easily cleaned with water, whilst leaving the terminal immediately useable after cleaning. 
     It will be understood that the present disclosure is for the purpose of illustration only, and the invention extends to modifications, variations and improvements thereto.