Computer graphics processing and selective visual display system – Display peripheral interface input device – Touch panel
Reexamination Certificate
2001-05-22
2002-08-27
Brier, Jeffery (Department: 2672)
Computer graphics processing and selective visual display system
Display peripheral interface input device
Touch panel
C345S173000, C345S176000, C178S018040
Reexamination Certificate
active
06441809
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an acoustic touch position sensor and more particularly to a touch panel of the type wherein an acoustic wave is generated within a substrate, the acoustic wave propagating in the substrate having a range of characteristic time delays from a transmitted signal, representing the differing path lengths associated with each axial displacement along an axis of the substrate. A touch on the substrate results in a perturbation of the wave, which is sensed to determine the axial displacement of the touch on the substrate. Touch panels of this type are used as computer input devices in connection with computer image displays.
BACKGROUND OF THE INVENTION
Conventional touch panels are utilized as input-output devices, applicable in various fields, in combination with a display device or unit such as a cathode ray tube (CRT), a liquid crystal display (LCD) or a plasma display panel (PDP). Resistive, capacitive, and acoustic touch panels are presently the dominant types of touch panels in the market-place. Acoustic touch panels provide a more robust touch surface and greater image clarity than resistive and capacitive touch panels.
Resistive and capacitive touch panels include a resistance layer formed on a substrate. Due to its strength, optical clarity, and low cost, soda-lime glass is generally the preferred substrate material. The resistance layer is essential for the detection of touch position information. In addition, a conventional resistive touch panel includes an overlaying plastic cover sheet. For many applications, such added components to the glass substrate may be susceptible to accidental or malicious damage. Furthermore, these added components degrade the visibility of data and images in a display device as a result of decreased light transmission and increased reflection of ambient light.
In contrast, conventional acoustic touch panels can be advantageously employed in order to insure a robust touch surface and an enhanced display image quality. Because ultrasonic acoustic waves are used to detect coordinate data on input positions, a resistance layer need not be formed on the glass soda-lime substrate and no plastic cover sheet is required. Soda-lime glass is quite transparent and supports propagation of acoustic waves at ultrasonic frequencies. Soda-lime glass is the substrate material of conventional acoustic touch panels. For the end user, such an acoustic touch panel is optically and mechanically little more than a piece of windowpane glass.
Typically, 4% of incident light is reflected off each glass surface resulting in a maximum light transmission of about 92%. Reflection of ambient light reduces image contrast. These reflections are caused by the index-of-refraction mismatch between air and the glass substrate. Decreased light transmission reduces image brightness. These can be important effects when a touch panel is placed in front of a display device having a relatively low luminance (brightness) such as a liquid crystal display. Known methods for reducing reflections and increasing transmission are optical bonding or anti-reflective coatings. These methods address the index-of-refraction mismatch between air and glass. These methods do not improve the inherent transparency of the substrate material itself.
Soda-lime glass is not completely transparent. This is mainly due to color centers caused by iron ion impurities.
These iron impurities decrease light transmission and distort the colors of displayed images. These are minor effects relative to, for example, the optical differences between acoustic and resistive touch panels. Nevertheless, improved transmission relative to common soda-lime glass would provide a useful enhancement of the optical advantages of acoustic touch panels.
Display technology is evolving rapidly. This evolution includes introduction and market acceptance of large sized display products. This in turn creates demand for larger touch panels. However, all touch panel technologies encounter problems when scaled to larger sizes. For resistive and capacitive touch panels, it becomes more difficult to maintain sufficient uniformity in resistance layers as panel sizes increase. For acoustic touch panels, the challenge for larger sizes is to assure sufficient signal amplitudes.
For acoustic touch panels, acoustic signals decrease as panel dimensions increase. This signal loss occurs because of the attenuation or damping of the ultrasonic waves as they propagate through the substrate. Thus, large-sized acoustic touch panels may fail to provide sufficient signal-to-noise ratio to reliably determine input positions. Hence there is a need for means to enhance the signal-to-noise ratio for acoustic touch panels. This is all the more true because there are other market pressures for product enhancements that reduce signal amplitudes: lower-cost controller electronics; reduced area reflective arrays; signal-absorbing seals; etc.
Due to the relatively long acoustic path lengths of commercially successful acoustic touch panel designs, acoustic attenuation properties of the glass substrate are particularly important. To understand the need for long acoustic path lengths, consider this first and simplest concept for acoustic touch panels.
Conceptually, the simplest acoustic touch position sensor is of the type described in U.S. Pat. No. 3,673,327. Such touch panels includes a plate having an array of transmitters positioned along one edge of a substrate for generating parallel beams of acoustic waves. A corresponding array of receivers is positioned along the opposite edge of the substrate. Touching the panel at a point causes attenuation in one of the beams of acoustic waves. Identification of the corresponding transmitter/receiver pair determines a coordinate of the touch. The acoustic touch panel disclosed in U.S. Pat. No. 3,673,327 uses a type of acoustic wave known as a “Rayleigh” wave. These Rayleigh waves need only propagate from one edge of the touch panel to the other. However, note that this type of acoustic touch panel requires many transducers, and hence associated cable conductors and electronics channels. This type of acoustic sensor has never been commercialized due to the expense of providing a large numbers of transducers.
Now consider acoustic touch panels that have been commercially successful. Representative of a set of pioneering patents in this field is Adler, U.S. Pat. No. Re. 33,151. An acoustic transducer generates a burst of waves that are coupled into a sheet-like substrate. These acoustic waves are deflected 90° into an active region of the system by an array of wave redirecting gratings. The redirecting gratings are oriented at 45° to the axis of propagation of waves from the transducer. These gratings are analogous to partially silvered mirrors in optics. Acoustic waves after traversing the active region are, in turn, redirected by another array of gratings towards an output transducer. A coordinate of the location of a touch is determined by analyzing a selective attenuation of the received signal in the time domain, each characteristic delay corresponding to a coordinate value of the touch on the surface. Use of the arrays of gratings greatly reduces the required number of transducers, thus making possible acoustic touch panels at commercially competitive prices. On the negative side, this clever use of grating arrays considerably increases the maximum distance acoustic waves must propagate through the substrate.
Signal amplitudes in acoustic touch panels are further decreased by inefficiencies in the scattering process at the grating arrays. Such inefficiencies can be minimized through proper array design. Efficient coherent scattering from the arrays is achieved by orienting the grating elements at a 45° angle and spacing them at integral multiples of the acoustic wavelength. Most efficient use of acoustic energy is provided when the acoustic power “illuminating” the active area is equalized. Known techniques compensate for the tendency for signal amplitudes
Kent Joel
Tsumura Masahiro
Blackman Anthony J.
Brier Jeffery
Elo Touchsystems, Inc.
Milde & Hoffberg LLP
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