Surface Acoustic Wave(SAW). This technology is more recent than the others and has not received wide Water content of users finger e as yet. It is based on the transmission through the glass of SAWs generated by transducers mounted on Transmitter the glass overlay. These waves are detected by receivers also mounted on the glass, and the time of arrival of the waves at the receivers is known because the wave velocity known. The placing of a finger on the glass weakens the signal and the location of the finger can be deter- mined by the difference in its effect on the SAW. There are two types of SAW systems in use, namely those using reflective techniques and those using atten uation as the source of position information. The reflec tive systems are similar to sonar where the time from the source to the pointing finger and then from the finger to the receiver is measured to arrive at finger location The attenuation technology is illustrated in Fig. 89.17 and consists of two transducers two receivers, and four reflector strips, all mounted on a glass substrate. One FIGURE 89.17 Attenuation SAW technology.(Source: transducer-receiver pair is used for X and the other for A. B. Carrell and J. Carstedt, "Touch input technology ," location. Figure 89.17 shows the X axis pair, and the SID Sem. Lecture Notes, p 15.35, 1987. With permission. transducer transmits a burst of acoustic energy in a hor- Courtesy Society for Information Display. izontal wave. The wave is partially reflected by the top reflector strips and travels down to the bottom strip where the reflectors are at an angle such that it is reflected to the lower left corner receiver. The wave now has a long rectangular shape, and each point in time corresponds a specific vertical path across the substrate. The Y axis is scan the same fashion after the x wave dies out. Then, when the finger touches the substrate, its water content absorbs some of the energy in the wave, and the wave is attenuated. The dip in the wave amplitude corresponds to the amount of absorbed energy, and the time of the lowest point can be determined, allowing the location of the finger to be calculated. Finally, in addition to the Xand Y coordinates, a Z coordinate can be determined, depending on how hard the user presses. This depends on surface contact, which affects the amount of attenuation. The advantages of this system are high resolution, speed of transmission, and the availability of a Z axis component. Its main disadvantages are the variation in moisture content in fingers and sensitivity to local moisture on the substrate. However, it is being used in developmental units and should be considered as another input device technology Scanners Scanners are a means for inputting text and/or images directly into the computer system, thus avoiding the leed for retyping and redrawing information contained in other sources. It is a relatively convenient way to avoid repetition if the data to be entered already exist in readable form. This is done by special image-recognition e that accompanies the scanning hardware, and can transfer an entire image containing both text and illustrations, but without the capability to modify the image. However, the addition of optical character recognition(OCR) software allows the entered text to be modified as if it were entered by typewriter. This can greatly simplify entering and editing text from some preexistent source and has resulted in a proliferation of devices that can perform this function. These devices come in two main forms, hand-held and page scanners, with or without OCR software in addition to the standard image-recognition software. A typical hand-held scanner is shown in Fig. 89.18 and consists of a light source, a light-sensitive device such as a charge-coupled device(CCD) array, and the electronics to actuate the elements of the array sequentially under software control. The scanner window is placed over the page, and is moved down or across the page so that the window covers as much of the page as falls within the capability of the software. The light source is reflected from the page to the CCD and the charge in the CCd is modified by the reflectivity of the printed material. e 2000 by CRC Press LLC
© 2000 by CRC Press LLC Surface Acoustic Wave (SAW). This technology is more recent than the others and has not received wide acceptance as yet.It is based on the transmission through the glass of SAWs generated by transducers mounted on the glass overlay. These waves are detected by receivers also mounted on the glass, and the time of arrival of the waves at the receivers is known because the wave velocity is known. The placing of a finger on the glass weakens the signal and the location of the finger can be determined by the difference in its effect on the SAW. There are two types of SAW systems in use, namely those using reflective techniques and those using attenuation as the source of position information. The reflective systems are similar to sonar where the time from the source to the pointing finger and then from the finger to the receiver is measured to arrive at finger location. The attenuation technology is illustrated in Fig. 89.17 and consists of two transducers, two receivers, and four reflector strips, all mounted on a glass substrate. One transducer-receiver pair is used for X and the other for Y location. Figure 89.17 shows the X axis pair, and the transducer transmits a burst of acoustic energy in a horizontal wave. The wave is partially reflected by the top reflector strips and travels down to the bottom strip where the reflectors are at an angle such that it is reflected to the lower left corner receiver. The wave now has a long rectangular shape, and each point in time corresponds to a specific vertical path across the substrate. The Y axis is scanned in the same fashion after the X wave dies out. Then, when the finger touches the substrate, its water content absorbs some of the energy in the wave, and the wave is attenuated. The dip in the wave amplitude corresponds to the amount of absorbed energy, and the time of the lowest point can be determined, allowing the location of the finger to be calculated. Finally, in addition to the X and Y coordinates, a Z coordinate can be determined, depending on how hard the user presses. This depends on surface contact, which affects the amount of attenuation. The advantages of this system are high resolution, speed of transmission, and the availability of a Z axis component. Its main disadvantages are the variation in moisture content in fingers and sensitivity to local moisture on the substrate. However, it is being used in developmental units and should be considered as another input device technology. Scanners Scanners are a means for inputting text and/or images directly into the computer system, thus avoiding the need for retyping and redrawing information contained in other sources. It is a relatively convenient way to avoid repetition if the data to be entered already exist in readable form. This is done by special image-recognition software that accompanies the scanning hardware, and can transfer an entire image containing both text and illustrations, but without the capability to modify the image. However, the addition of optical character recognition (OCR) software allows the entered text to be modified as if it were entered by typewriter. This can greatly simplify entering and editing text from some preexistent source and has resulted in a proliferation of devices that can perform this function. These devices come in two main forms, hand-held and page scanners, with or without OCR software in addition to the standard image-recognition software. A typical hand-held scanner is shown in Fig. 89.18 and it consists of a light source, a light-sensitive device such as a charge-coupled device (CCD) array, and the electronics to actuate the elements of the array sequentially under software control. The scanner window is placed over the page, and is moved down or across the page so that the window covers as much of the page as falls within the capability of the software. The light source is reflected from the page to the CCD and the charge in the CCD is modified by the reflectivity of the printed material. FIGURE 89.17 Attenuation SAW technology. (Source: A. B. Carrell and J. Carstedt, “Touch input technology,” SID Sem. Lecture Notes, p. 15.35, 1987. With permission. Courtesy Society for Information Display.)
NA FIGURE 89. 18 Hand-held scanner.( Courtesy of Logitech, Freemont, Calif The window area ranges from 4 to 5 in. in width by 0.5 in. in height and may be moved through 14 to 20 in, so that a fairly large area may be covered in a single manual scan. Images wider than the maximum window may be scanned in two passes, and the OCR software can stitch he two scans together into a single image, although this procedure requires considerable care in scanning so that the scans line up properly. Therefore, when images wider than the window of the hand-held scan- ner are to be scanned, it is advisable to use a flatbed scanner of the type shown in Fig. 89.19 which can handle a full 8.5 in. by l1 in. page,or some of the larger scanners than can accept large drawings and input them into the computer system. Resolutions of 400 dpi and higher, with up to 250 levels of gray and 24 bits of color resolution are available. Thus, scanners offer a wide variety of choice and performance capabil ities, and are powerful input devices when prepared data in visual form is to be entered into the computer syste oice Voice input is an intriguing approach to data input, with particular FIGURE 89. 19 Page scanner (Cour- attractiveness to managers who want a simple and direct means for tesy of Chinon, Torrance, Calif. inputting data and commands. For many years, this technology tended to promise more than it could achieve, but recent developments have brought it to the point where it can be considered as a viable input means. This has been due to new developments in software that make it possible to minimize the amount of training required and increase the success rate to close to 100% One basic approach to speech recognition is represented by the block diagram shown in Fig. 89.20. This is a system that is built around a special chip developed by Texas Instruments. This system uses templates and special algorithms for recognizing the input speech patterns. The system is speaker dependent, with the pability of storing up to 32 word templates and user-defined phrases. The output portion may be sup when the system is used only for inputting data and commands, but can be a useful adjunct to response. Other techniques such as speaker-independent and phoneme-recognition systems are also Vocabularies range from 50 to 5000 active words, and both isolated and connected words can be recognized, although the larger numbers tend to be associated with isolated word systems. In general, it seems feasible that a combination of speech input and pen-based computing may find a viable marke e 2000 by CRC Press LLC
© 2000 by CRC Press LLC The window area ranges from 4 to 5 in. in width by 0.5 in. in height and may be moved through 14 to 20 in., so that a fairly large area may be covered in a single manual scan. Images wider than the maximum window may be scanned in two passes, and the OCR software can stitch the two scans together into a single image, although this procedure requires considerable care in scanning so that the scans line up properly. Therefore, when images wider than the window of the hand-held scanner are to be scanned, it is advisable to use a flatbed scanner of the type shown in Fig. 89.19 which can handle a full 8.5 in. by 11 in. page, or some of the larger scanners than can accept large drawings and input them into the computer system. Resolutions of 400 dpi and higher,with up to 250 levels of gray and 24 bits of color resolution are available. Thus, scanners offer a wide variety of choice and performance capabilities, and are powerful input devices when prepared data in visual form is to be entered into the computer system. Voice Voice input is an intriguing approach to data input, with particular attractiveness to managers who want a simple and direct means for inputting data and commands. For many years, this technology tended to promise more than it could achieve, but recent developments have brought it to the point where it can be considered as a viable input means. This has been due to new developments in software that make it possible to minimize the amount of training required and increase the success rate to close to 100%. One basic approach to speech recognition is represented by the block diagram shown in Fig. 89.20. This is a system that is built around a special chip developed by Texas Instruments. This system uses templates and special algorithms for recognizing the input speech patterns. The system is speaker dependent, with the capability of storing up to 32 word templates and user-defined phrases. The output portion may be superfluous when the system is used only for inputting data and commands, but can be a useful adjunct to the visual response. Other techniques such as speaker-independent and phoneme-recognition systems are also available. Vocabularies range from 50 to 5000 active words, and both isolated and connected words can be recognized, although the larger numbers tend to be associated with isolated word systems. In general, it seems feasible that a combination of speech input and pen-based computing may find a viable market. FIGURE 89.18 Hand-held scanner. (Courtesy of Logitech, Freemont, Calif.) FIGURE 89.19 Page scanner. (Courtesy of Chinon, Torrance, Calif.)