Computer graphics processing and selective visual display system – Display peripheral interface input device – Touch panel
Reexamination Certificate
1999-09-29
2002-05-28
Saras, Steven (Department: 2675)
Computer graphics processing and selective visual display system
Display peripheral interface input device
Touch panel
C345S173000, C345S176000
Reexamination Certificate
active
06396484
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates generally to touchscreens and, more particularly, to a method and apparatus for adapting the frequency of a touchscreen controller in order to match the controller to the particular operating characteristics of a specific touchscreen.
BACKGROUND OF THE INVENTION
Touchscreens are used in conjunction with a variety of display types, including cathode ray tubes (i.e., CRTs) and liquid crystal display screens (i.e., LCD screens), as a means of inputting information into a data processing system. When placed over a display or integrated into a display, the touchscreen allows a user to select a displayed icon or element by touching the screen in a location corresponding to the desired icon or element. Touchscreens have become common place in a variety of different applications including, for example, point-of-sale systems, information kiosks, automated teller machines (i.e., ATMs), data entry systems, etc.
In one specific type of touchscreen, an acoustic touchscreen, acoustic or ultrasonic waves are generated and directionally propagated across the touchscreen surface utilizing the phenomena of surface acoustic waves, e.g., Rayleigh waves, Love waves, or other waves. Typically each axis of the touch panel includes a single transmitter transducer, a single receiver transducer, and a pair of reflective arrays. The transmitting transducers and the receiving transducers are coupled to a controller, the controller generating the drive signals that are applied to the transmitting transducers and amplifying, conditioning and responding to the signals from the receiving transducers. The acoustic wave produced by each transmitter transducer is reflected by the reflective array located near the touchscreen edge. The array reflects the acoustic wave, typically at a right angle along the entire length of the array, producing a surface acoustic wave pattern that propagates across the active area of the touchscreen. The propagated surface acoustic wave has a substantially linear wavefront with a uniform amplitude. The opposing reflective array reflects the surface propagated acoustic wave to a receiving transducer. By monitoring the arrival time and the amplitude of the propagated wave along each axis of the touchscreen, the location of any wave attenuation point on the touchscreen surface can be determined. Attenuation can be caused by touching the screen with a finger or stylus or other media.
Typically a manufacturer of touchscreen systems produces or purchases controllers with a predetermined oscillation frequency that is within a well defined frequency range, the reference frequency being provided by a crystal oscillator. Then during the manufacturing process the characteristic frequency of each touchscreen is determined and adjusted, as necessary, to ensure that there is sufficient match between the touchscreen and the oscillation frequency of the controller.
Let us more carefully define the characteristic frequency of a touchscreen. Acoustic touchscreens of the types of interest here have the property of being a narrow band pass filter. The center frequency of the narrow band is determined by the spacing of the reflectors and by the velocity of the acoustic waves. As a consequence, a brief burst applied to a transmitter transducer appears, after a time delay corresponding to an acoustic wave traveling the shortest possible path to a receiving transducer, in the form of a long drawn-out wave train. While the frequency spectrum of the input burst is typically quite wide due to the short duration of the burst, the spectrum of the output wave train is ideally very narrow and sharply peaked at a specific frequency. This specific frequency is referred to as the touchscreen's characteristic frequency. It is desired that the touch system's operating frequency match the touchscreen's characteristic frequency.
In principle, an ideal touchscreen has a single characteristic frequency. In practice, manufacturing variations can result in a plurality or range of characteristic frequencies. Current practice involves making a sufficient investment in the touchscreen manufacturing process so that there is effectively only a single characteristic frequency of the touchscreen and that this characteristic frequency matches that determined by the controller's reference oscillator. In order to achieve the desired control over the touchscreen manufacturing process, precise coordination of array design, careful monitoring of the supply chains of incoming materials, and prompt electronic testing of reflective arrays are required. In addition, when an unanticipated change or variation is discovered, rapid corrective action is necessary. For example, the array may need to be redesigned and a new printing mask fabricated. The degree of coordination, monitoring, and testing required to maintain control of the touchscreen characteristic frequency adds cost to the process and limits production to facilities with a workforce well trained in the intricacies of acoustic touchscreen manufacture. This is an important limitation of present acoustic touchscreen technology.
In general, frequency mismatch can be categorized as being either global or localized in nature. In cases in which the frequency mismatch is global, the source of mismatch affects the entire touchscreen. For example, if the reference oscillator of a controller drifts, or alternatively, if the glass substrate has an unexpected acoustic velocity (e.g., due to the glass substrate being fabricated by a different glass supplier), the frequency match between the touchscreen and the controller is compromised regardless of the location of interest on the touchscreen. In contrast, in cases in which the frequency mismatch is localized, only a specific region of the touchscreen may exhibit mismatch with the controller.
Both global and localized frequency mismatch can be caused by a variety of sources. Although some sources of mismatch can be overcome through sufficient quality control, often the cost of such control can be quite high. For example, variations in the touchscreen glass substrate can vary the acoustic wave velocity thereby causing global frequency mismatch, controlling the glass supply chain and manufacturing process sufficiently to ensure that the acoustic wave velocity of all substrates fall within a narrow range may be economically unfeasible. Controlling the glass supply chain and manufacturing process is even more problematic in those instances in which acoustic reflective arrays are printed directly onto the faceplate of a cathode ray tube (i.e., CRT). Specific glass characteristics that are difficult to control to the degree necessary to avoid global frequency mismatch include the chemical composition and the thermal history (e.g., annealing time and temperature, etc.).
Another source of frequency mismatch is due to undesired variations within the reflective array printed on the touchscreen substrate. These variations may, for example, result from the array mask being distorted during the screen printing process. Print mask distortion is especially problematic if the array is to be printed directly onto a CRT faceplate. Other array printing techniques such as pad printing are also subject to the registration errors introduced during the printing process that can lead to further frequency mismatch. Another source of frequency mismatch can arise from improperly correcting for the spherical geometric effects of a non-planar substrate surface.
What is needed in the art is a method and apparatus for adapting the oscillation frequency of a controller to the operating frequency requirements of specific touchscreens. The present invention provides such a method and apparatus.
SUMMARY OF THE INVENTION
The present invention provides a method and apparatus for adapting the frequency of a controller to the operating frequency requirements of a specific touchscreen substrate, wherein the touchscreen substrate includes reflective arrays. More specifically, the controller is adapted
Adler Robert
Ravid Arie
Wilson Geoffrey D.
Anyaso Uchendu O.
Elo Touchsystems, Inc.
Saras Steven
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