Computer graphics processing and selective visual display system – Display peripheral interface input device – Touch panel
Reexamination Certificate
1998-08-21
2001-08-21
Shalwala, Bipin (Department: 2778)
Computer graphics processing and selective visual display system
Display peripheral interface input device
Touch panel
C345S174000, C345S204000, C178S018010, C178S020010
Reexamination Certificate
active
06278444
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to touch sensitive screens and, more particularly, to a system and method that allows a five-wire screen to be directly used with a four-wire operating system.
BACKGROUND OF THE INVENTION
Touch-screens 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 computer system. When placed over a display, the touch-screen allows a user to select a displayed icon or element by touching the screen in a location that corresponds to the desired icon or element.
A variety of touch-screen types have been developed. One type of touch screen utilizes transparent layers of resistive material separated by a pattern of insulative material. When a user presses on the touch screen, the layers of resistive material come into contact with one another and complete a circuit. By utilizing a voltage gradient in the circuit, the magnitude of the voltage at the point of screen compression can be used to determine the compression location along one axis of the screen. The use of this technique along two orthogonal axes provides the actual location at which the screen was pressed.
There are two types of resistive touch-screens dominating the market today: four-wire systems and five-wire systems. Four-wire systems have had more commercial success than five-wire systems, primarily due to their low power consumption and the simplicity of the required external circuitry. However, five-wire touch-screens are preferable from a reliability standpoint as these touch-screens are typically rated to survive at least an order of magnitude more touches than four-wire systems. The difference in reliability is due to the basic differences in screen design. In a four-wire system the top resistive layer is used to measure directional current along one axis. Therefore the conductivity of the top resistive layer must remain uniform. However, as the top surface undergoes repeated compressions, the uniformity of the resistive layer gradually degrades, leading to inaccurate readings and eventual screen failure. In contrast, all directional measurement in a five-wire system is provided by the lower resistive layer. The upper surface must merely retain its conductivity. Therefore changes in the uniformity of the resistive layer of the top surface does not degrade the performance of the five-wire system until this layer undergoes complete failure (i.e., all conductive pathways are lost).
There is an increasing trend to incorporate touch technology into a wide variety of system applications, and a new generation of microprocessor components and system software designed to serve this new market is becoming commercially available. The initial market for which these components and software were designed employed a four-wire touch screen and consequently, it is this four-wire interface that predominates. Further, there is a large customer base in the process control and medical segments of the touch-screen market that employs custom electronics and software designed to interface with four wire systems, which, by reason of their shorter life cycle, must be replaced on a regular basis. Therefore, if an end-user wishes to incorporate a five wire touch-screen into his design, or to replace a four wire touch-screen with the more reliable five wire unit, new interface electronics and software are necessary, the design of which constitutes an economic barrier to accessing these growing market segments.
From the foregoing it is apparent that a converter that would allow a five-wire touch-screen to be plugged into a four-wire controller without modifying the controller hardware and software is desirable.
SUMMARY OF THE INVENTION
The present invention provides a method and apparatus for making a five-wire touch-screen compatible with a four-wire interface. The invention utilizes a non-microprocessor-based converter that is configured into a module that can be readily integrated into a five-wire touch-screen, e.g., as a 5-pin to 4-pin adapter, for four-wire applications without modification of the five-wire touch-screen design.
In one aspect of the invention, an analog logic and switching element in the converter routes the reference voltage from the four-wire controller to a current injection control device. The current injection control device applies a constant current to the outermost screen member of the touch-screen. When the outermost screen member and the innermost screen member of the touch screen come into contact at a localized region due to a touch, the current from the outermost member is injected into the resistive coating of the innermost member at the point of contact. The injected current is distributed to the four contact electrodes of the innermost member in direct proportion to the coordinates of the point of contact. Each of the four currents is converted to a voltage and routed to a logic amplifier. The logic amplifier outputs a voltage proportional to the x-coordinate of the compression point and a voltage proportional to the y-coordinate of the compression point as expected by the four-wire controller.
In another aspect of the invention, the logic amplifier outputs a voltage that is the sum of the voltages from the four current converters. This voltage sum is routed to a comparator that compares the voltage sum with the reference voltage. If a voltage difference is detected, the current injected into the outermost screen member is adjusted accordingly. This feedback circuit ensures that the voltages proportional to the x- and y-coordinates continuously track the reference voltage, resulting in a stable and reliable coordinate measurement system.
In a further aspect of the invention, the analog logic and switching element senses when the four-wire controller enters its quiescent state, and returns a ‘wake-up’ signal to the controller when the touch-screen is compressed.
A further understanding of the nature and advantages of the present invention may be realized by reference to the remaining portions of the specification and the drawings.
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Babb Joe H.
Wilson Geoffrey D.
Kovalick Vincent E.
Shalwala Bipin
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