Computer graphics processing and selective visual display system – Display peripheral interface input device – Touch panel
Reexamination Certificate
2000-07-06
2003-10-14
Saras, Steven (Department: 2675)
Computer graphics processing and selective visual display system
Display peripheral interface input device
Touch panel
C345S174000
Reexamination Certificate
active
06633279
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a touch panel that detects the coordinates of an input point from a change in resistance due to a pressing force applied to the input point, and a liquid crystal display device including such a touch panel.
Liquid crystal-display devices used as display means for personal computers and monitors of other apparatuses produce a display in the following manner. An image generated on a liquid crystal panel is illuminated by light, and the light carrying the image is transmitted or reflected toward the display plane so as to be visible to a viewer.
More specifically, this type of liquid crystal display device uses a liquid crystal panel including a pair of substrates, each having pixel selection electrodes and the like mounted thereon. The substrates are bonded together with a liquid crystal layer sandwiched therebetween. An image is generated by changing the orientation state of the liquid crystal molecules in a selected pixel region. The generated image is not intrinsically visible. Therefore, the liquid crystal panel is illuminated by an external light so that the transmitted or reflected tight carrying the image is observed by a viewer.
In recent years, information terminals having touch panels have been broadly used, where the above type of liquid crystal display device is used as a display means and a touch panel is formed on the display screen for allowing various types of information to be input via the display screen.
Touch panels come in various types depending on the principle of operation thereof Among them the most popular is a type that detects the coordinates of an input point from changes in the amount of resistance, called an analog resistor type.
The analog resistor type touch panel includes an input-side substrate made of a transparent soft film and a substrate made of a transparent hard plate, preferably a glass plate. Resistor films are formed on the opposing surfaces of the two transparent substrates. The two resistor films come into contact with each other by application of an external pressing force to a point on the input-side substrate. Two-dimensional coordinate values are detected from resistance values between the resistor films and output terminals.
FIG. 10
is a schematic illustration of the construction of a touch panel equipped liquid crystal display device, where a touch panel
4
is formed on a liquid crystal panel
1
. In the illustrated liquid crystal display device, a light guide plate
2
constituting an auxiliary light source device
3
is provided between the liquid crystal panel
1
and the touch panel
4
. A construction excluding the auxiliary light source device
3
has also been commercialized. The auxiliary light source device
3
includes a lamp
3
A and a lamp reflection sheet
3
B.
FIG. 11
is an exploded perspective view illustrating the construction of a conventional analog resistor type touch panel. The touch panel includes two transparent substrates. An upper substrate
4
A is a soft film preferably made of polyethylene terephthatate (PET). A resistor film
11
preferably made of indium tin oxide (ITO) is formed on the entire inner surface of the upper substrate
4
A. A lower substrate
4
B is a hard plate preferably made of glass. A resistor film
22
preferably made of ITO is formed on the entire inner surface of the tower substrate
4
B.
Interconnections
35
are formed on two opposing sides of the resistor film
11
of the upper substrate
4
A along the edges thereof, and are electrically connected with the resistor film
11
. The interconnections
35
have respective terminals at an interface
36
for communication with an external circuit. Connectors
33
and
34
for connection with the lower substrate are formed on the other two opposing sides of the resistor film
11
along the edges thereof, and are electrically isolated from the resistor film
11
. The connectors
33
and
34
have respective terminals at the interface
36
.
Connectors
43
and
44
for connection with the upper substrate are formed at positions of the resistor film
22
of the lower substrate
4
B corresponding to the connectors
33
and
34
. Once the upper and lower substrates
4
A and
4
B are bonded together, connection points T
1
and T
3
of the connectors
33
and
34
are electrically connected with connection points T
2
and T
4
of the connectors
43
and
44
, respectively, via a conductive material, preferably silver paste. The connectors
33
,
34
,
43
, and
44
are preferably made of the same material as the resistor films in consideration of the ease of the fabrication process. It is needless to mention that the connectors may be made of a material different from that of the resistor films. Thus, the resistor films
11
and
22
formed on the upper and lower substrates constitute a two-dimensional coordinate system, and the coordinates (x, y) (x: x-coordinate value, y: y-coordinate value) of a pressing point (input point) are detected with an external circuit.
The above conventional touch panel has the following problems. Since the resistor films
11
and
22
are solidly formed on the entire surfaces of the upper and lower substrates, the resistance values for detecting the position of the information input point are two-dimensional parameters for the solid resistor films extending between the connectors
33
and
34
and the connectors
43
and
44
. Such parameters vary depending on the position of the input point on the resistor films, thereby lowering the linearity.
As a result, the level of detection of the input point becomes degraded, which may cause an input detection error or a deviation (calibration error) between the input point and the display position on a liquid crystal panel mounted on the back of the touch panel. An external circuit (CPU) performs the function of correcting the position. Nevertheless, a detection failure (input failure) is likely to arise, putting this error beyond the ability of function to correct. This causes a lowering in reliability.
Another problem is as follows. The connectors with the opposing substrate are formed on the periphery of one of the substrates (upper substrate in the construction of FIG.
11
). This reduces the area of the effective input region and thus makes it difficult to realize so-called narrow framing. In addition, moisture may enter the inside between the substrates from the bonded edges, causing deterioration in the electrical characteristics of the resistor films and the connectors and thereby causing a variation in resistance value. This makes resistance management difficult.
An object of the present invention is to provide a highly reliable touch panel which is free from the occurrence of an input error and input failure, and a liquid crystal display device including such a touch panel.
SUMMARY OF THE INVENTION
The touch panel of the present invention is constructed as follows. At least one of the resistor films of the upper and lower substrates has a comb shape composed of a plurality of resistive lines and a common connector. The coordinate values of the input point are detected from a one-dimensional resistance value.
Using such a touch panel, the liquid crystal display device of the present invention permits highly reliable detection of a screen input.
Typical constructions according to the present invention are summarized as follows.
(1) A touch panel of the present invention includes an upper substrate in the form of a soft film having an upper resistor film and a lower substrate in the form of a hard plate having a lower resistor film, the upper substrate and the lower substrate being bonded together so as to face each other, the touch panel providing a detection output representing a contact position between the upper resistor film and the lower resistor film as two-dimensional coordinate values,
wherein both the upper resistor film and the lower resistor film are of a comb shape having a plurality of resistive lines with a common connector at one end, and the resistive lines of the upper resistor fil
Chiba Shinsaku
Kono Masao
Antonelli Terry Stout & Kraus LLP
Hitachi , Ltd.
Saras Steven
Spencer William C.
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