Computer graphics processing and selective visual display system – Display peripheral interface input device – Touch panel
Reexamination Certificate
2000-11-03
2003-07-15
Shalwala, Bipin (Department: 2673)
Computer graphics processing and selective visual display system
Display peripheral interface input device
Touch panel
C345S174000, C345S176000, C345S177000, C345S178000
Reexamination Certificate
active
06593916
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to devices for determining the coordinates (i.e., X and Y coordinates) of a location in a two-dimensional system such as touch sensitive screens for producing output signals related to a touched position. The present invention more particularly provides a 5-wire (or 9-wire) resistive touch sensor having improved linearity near the periphery of the touch sensitive area.
2. Description of the Prior Art
A touchscreen is a transparent input device that can sense the two-dimensional position of the touch of a finger or other electronically passive stylus. Touchscreens are placed over display devices such as cathode-ray-tube monitors and liquid crystal displays to provide inputs for restaurant order entry systems, industrial process control applications, interactive museum exhibits, public information kiosks, lap-top computers, etc.
Presently, the dominant touch technologies are 4-wire resistive, 5-wire resistive, capacitive, ultrasonic, and infrared. These are technologies that have delivered high standards of performance at cost-competitive prices. An important aspect of touchscreen performance is a close correspondence between true and measured touch positions at all locations within the touch sensitive area.
5-wire resistive touchscreens, e.g. the AccuTouch™ product line of Elo TouchSystems, Inc. of Fremont, Calif., have been widely accepted for many touchscreen applications. In these touchscreens, mechanical pressure from a finger or stylus causes a plastic membrane coversheet to flex and make physical contact with an underlying glass substrate. The glass substrate is coated with a resistive layer upon which voltage gradients are excited. Via electrical connections to the four corners of the coated glass substrate, associated electronics can sequentially excite gradients in both the X and Y directions, as described in U.S. Pat. No. 3,591,718. The underside of the coversheet has a conductive coating that provides an electrical connection between the touch location and voltage sensing electronics. Since both X and Y voltage gradients are generated on the substrate's resistive coating, the coversheet coating need only provide electrical continuity. Further details regarding 5-wire resistive touchscreens are found U.S. Pat. No. 4,220,815 to Gibson; U.S. Pat. Nos. 4,661,655 and 4,731,508 to Gibson et al.; U.S. Pat. No. 4,822,957 to Talmadge et al.; U.S. Pat. No. 5,045,644 to Dunthorn; and U.S. Pat. No. 5,220,136 to Kent.
Electronics can obtain touch information from a 5-wire resistive touchscreen via current injection as well as the voltage excitation described above. For current injection read out, a current source injects current though the coversheet and the currents arriving at each of the four corner connection points are then measured during a touch. From the sums and ratios of these corner currents, touch positions are reconstructed. The choice between current injection and voltage excitation is an electronics design choice and is largely independent of touchscreen design. Peripheral electrode pattern designs for touch systems with voltage-excitation electronics are equally applicable to touch systems with current-injection electronics.
Capacitive touchscreens often require peripheral electrode patterns that serve the same basic function as in 5-wire resistive touchscreens. MicroTouch Systems, Inc. offers both capacitive touchscreens (ClearTek™) and 5-wire resistive touchscreens (TouchTek™) with peripheral electrode patterns similar to FIG. 1
b
of U.S. Pat. No. 4,371,746 of Pepper. In a capacitive touchscreen, the coversheet is replaced by a thin transparent dielectric coating that then forms the exterior surface of the ITO or ATO coated substrate. An oscillating voltage is applied to the four corner connection points. A finger touch provides an AC shunt to ground and hence serves as an AC current source (sink) at the location of the touch. The division of this AC current between the four corner connection points is measured and used to determine touch coordinates. An AC variant of current-injection electronics is used.
It is sometimes advantageous to have both a drive and a sense line connection between the electronics and each of the four corner connection points. With appropriate feedback loops in the electronics, the combination of drive and sense lines gives the electronics better control over the excitation voltages applied to the corner connection points. This leads to a variant of “5-wire” touchscreens with 9 wire connections between the electronics and the touchscreen. The design of the peripheral electrode pattern is largely unaffected by the choice between 5-wire and 9-wire connection schemes.
A 5-wire resistive touchscreen typically includes a glass substrate 1 to 3 mm thick on which a transparent resistive coating has been applied. A peripheral electrode pattern is formed on the substrate as a geometric pattern of printed conductive ink on the resistive coating, and insulating regions formed in the resistive coating. ITO (indium tin oxide) and ATO (antimony tin oxide) are examples of degenerate semi-conductors which have the important property of being both conductive and transparent, and may serve as resistive coatings. The regions between the conductive electrodes form resistors, with the insulating regions defining conductive paths therebetween. Details of the electrode pattern and its manufacture are found in U.S. application Ser. No. 08/989,928 (allowed), which is incorporated herein by reference. This information is also found in published PCT application No. WO99/30272.
U.S. Pat. Nos. 3,591,718 (Asane & Baxter), 4,198,539 (Pepper), and 4,797,514 (Talmadge & Gibson) disclose peripheral electrode patterns that include a continuous resistive electrode between corner connection points. The performance of such electrode patterns is sensitive to the stability and uniformity of the resistivity of the electrodes. Non-uniformity of the electrical properties of a continuous electrode along its length will distort the linearity of the sensor. Humidity and temperature variations in the application environment may have different effects on the electrical properties of continuous resistive electrodes, e.g. fabricated from a printed composite polymer ink, and the resistive coating in the touch area, e.g. ITO. If so, the linearity of the touchscreen may be compromised.
This sensitivity is in contrast to peripheral electrode patterns using discrete overlap resistors such as those found in Elo TouchSystems' AccuTouch™ products and disclosed in U.S. Pat. No. 5,045,644 to Dunthorn, which is incorporated herein by reference. Provided that good electrical contact is made between the electrode and the resistive coating, the resistance of discrete overlap resistors is dominated by the resistance of the resistive coating in the gap between the electrodes. The resistance of the electrodes printed with conductive inks is small in comparison, and hence there is little effect if the electrical properties of the conductive inks vary. Furthermore, as the gap resistance is formed of the same coating as used in the touch area, it will track variations of active region resistivity as a function of temperature and humidity. This provides the touchscreen with stable linearity even if the ohms/square of the resistive coating changes with environmental conditions.
Use of discrete overlap resistors leads to a discrete set of parallel connections between the peripheral electrode pattern and the touch sensitive region. This produces a ripple non-linearity in the touch area near the peripheral electrode pattern. An example of ripple can be seen in FIG. 4B of U.S. Pat. No. 5,045,644. Equipotential lines for both X and Y excitations are shown. Consider the set of equipotential lines used for X coordinate measurements. In the lower left corner, towards the center of the touch area and far from the peripheral electrode pattern, the X equipotential lines appear as uniformly spaced vertical lines. However, on
Dharia Prabodh M.
Shalwala Bipin
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