JPH05224813A - Handwriting input device - Google Patents

Abstract

PURPOSE:To improve the detection precision of input coordinates on a tablet by interposing a grounded conductive shield member between a liquid crystal display plate and the tablet. CONSTITUTION:A pressure-sensitive tablet 7 is provided above a liquid crystal display plate 6 and a conductive shield plate (conductive shield member) 14 is provided between the liquid crystal display plate 6 and pressure-sensitive tablet 7. A capacitor C1 is composed of an LCD transparent electrode 2a of the liquid crystal plate 6 and the conductive shield plate 14 and a capacitor C2 is composed of the conductive shield plate 14 and the resistance shield 9h of the pressure-sensitive tablet 7. Therefore, when an LCDCOM signal A as an AC rectangular wave is applied to a LCD transparent electrode 2b, a noise which is generated on the resistance sheet 9h of the pressure-sensitive tablet 7 before flows to the GND through the conductive shield plate 14, so the conventional noise is not generated on the pressure-sensitive tablet 7.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a handwriting input device for displaying an image input by handwriting on a liquid crystal display device, and more particularly to a handwriting input device in which a pressure sensitive tablet and a liquid crystal display plate are arranged to face each other. It is about.

[0002]

2. Description of the Related Art Liquid crystal display devices (LCD) for handwritten characters
As shown in FIG. 4, there is a handwriting input device which is configured to display a transparent pressure-sensitive tablet 57 above a liquid crystal display board 56.

The liquid crystal display board 56 is basically a pair of transparent glass substrates 5 arranged opposite to each other with the liquid crystal layer 53 interposed therebetween.
LCD transparent electrodes 52a, 5 are provided on the respective facing surfaces of 1a, 51b.
2b is provided, and transparent glass substrates 51a and 51a are provided.
Of the polarization filters 54a, 54a
b is provided, and the reflection plate 55 is provided on the surface of the polarization filter 54b.
Is provided.

Electrode drivers 62a and 62b are connected to the LCD transparent electrodes 52a and 52b, respectively, and an AC square wave LCD / COM signal as shown in FIG. 5A is output from the electrode drivers 62a and 62b. Thus, the liquid crystal of the liquid crystal layer 53 is driven.

The pressure sensitive tablet 57 has a transparent resistance film 59 formed on the upper surface of a transparent glass substrate 58. The transparent resistance film 59 is, for example, two resistance sheets 59a and 59b bonded to face each other with a transparent dot spacer or a transparent pressure-sensitive conductive rubber interposed therebetween. A constant voltage is applied to the electrode 60a of one resistance sheet 59a from a power source 65, and the electrode 60b of the other resistance sheet 59b is connected to a control unit 61 including a microprocessor or the like.

When the transparent resistance film 59 is pressed by the pen 63 or the fingertip, the resistance sheets 59a and 59b above and below the pressed coordinates are electrically connected to each other.
The voltage applied to the resistance sheet 59a is resistance-divided according to the coordinates, and the resistance sheet 59b outputs a voltage according to the coordinates to the control unit 60 as a coordinate detection signal.
The control unit 60 discriminates the coordinates based on the coordinate detection signal and controls the electrode drivers 62a and 62b of the liquid crystal display board 56 in accordance with the coordinates to display the input image of the pressure sensitive tablet 57 on the liquid crystal display board 56. Is displayed.

[0007]

In the above conventional handwriting input device, the LCD transparent electrode 52a of the liquid crystal display plate 56 and the resistance sheet 59b of the transparent resistance film 59 are used for the transparent glass substrate 51a of the liquid crystal display plate 56 and the touch panel. Pressure tablet 5
The structure is such that the No. 7 transparent glass substrate 58 is sandwiched. That is, the LCD transparent electrode 52a and the transparent resistance film 5
The two conductive plates of the resistance sheet 59b of No. 9 form a capacitor C ₅₁ as shown in FIG.

Since the pull-down resistor R ₅₁ is connected to the output line of the coordinate detection signal connected to the resistor sheet 59b, a differentiation circuit is constructed by the capacitor C ₅₁ and the pull-down resistor R _51. It will be.

For this reason, the LCD transparent electrode 52a has a structure shown in FIG.
When an AC square wave LCD / COM signal as shown in (a) is input, differential wave-shaped noise as shown in (b) of the figure appears in the coordinate detection signal.

Since the capacitance of the capacitor is proportional to the facing area, it does not cause much problem in the case of a small handwriting input device, but in the case of a large handwriting input device having a large input screen, the parasitic capacitance of the capacitor C ₅₁ will be described. Therefore, the noise appearing in the coordinate detection signal increases, and the control unit 61 cannot accurately detect the input coordinates of the pressure-sensitive tablet 57.

The present invention has been made in view of the above, and an object thereof is to eliminate the noise appearing in the coordinate detection signal due to the influence of the liquid crystal display plate and to improve the detection accuracy of the coordinates input by the tablet. It is to provide a handwriting input device capable of performing.

[0012]

In order to solve the above problems, a handwriting input device according to a first aspect of the present invention includes a liquid crystal display plate having a liquid crystal display electrode to which a liquid crystal drive voltage is applied, and a coordinate detection signal. The following means are taken in the handwriting input device in which the tablet having the resistive film for outputting is arranged oppositely.

That is, a grounded conductive shield member is interposed between the liquid crystal display plate and the tablet.

Further, in order to solve the above problems, the handwriting input device according to the invention of claim 2 is the handwriting input device according to claim 1, wherein the conductive shield member is
It is characterized in that it is a transparent electrode formed on at least one surface of the opposed surfaces of the liquid crystal display plate and the tablet.

[0015]

According to the structure of claim 1, since the conductive shield member is interposed between the liquid crystal display plate and the tablet, the capacitor is formed by the conductive shield member and the liquid crystal display electrode of the liquid crystal display plate. Along with being formed, a capacitor is formed by the conductive shield member and the resistance film of the tablet.

When an alternating liquid crystal drive voltage is applied to the liquid crystal display electrodes, noise that would have been generated in the resistance film of the tablet in the conventional case is transferred to the conductive shield member.
Since the conductive shield member is grounded, the above noise flows to GND via the conductive shield member,
The coordinate detection signal output from the resistive film of the tablet does not include noise as in the conventional case.

According to the second aspect of the invention, since the transparent electrode serving as the conductive shield member is integrally formed with the liquid crystal display panel or the tablet, the number of parts does not increase and the handwriting input device can be assembled easily. Can be converted.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The following will describe one embodiment of the present invention with reference to FIGS. 1 and 2.

In the handwriting input device of this embodiment, as shown in FIG. 1, a pressure sensitive tablet 7 is provided above the liquid crystal display plate 6, and a conductive material is provided between the liquid crystal display plate 6 and the pressure sensitive tablet 7. The shield plate (conductive shield member) 14 is provided.

The liquid crystal display panel 6 is a pressure sensitive tablet 7.
It is a dot matrix type that corresponds to the resolution of
Basically, LCD transparent electrodes (liquid crystal display electrodes) 2a and 2b in which an electrode pattern is formed by an ITO film or the like on each of the opposing surfaces of a pair of transparent glass substrates 1a and 1b that are opposed to each other with the liquid crystal layer 3 sandwiched therebetween. And the polarizing filter 4 is provided on the surface of the transparent glass substrates 1a and 1b opposite to the facing surface.
a. 4b are provided, and the reflection plate 5 is provided on the surface of the polarization filter 4b.

Electrode patterns are formed on the LCD transparent electrode 2a and the LCD transparent electrode 2b in directions orthogonal to each other, and electrode drivers 12a and 12b are connected to the ends of these electrodes, respectively.

The electrode drivers 12a and 12b receive a control voltage signal C supplied from a control unit 11 which will be described later, and the LCD transparent electrodes 2a and 2b have an AC square wave LCD.C.
An OM signal (liquid crystal drive voltage) A is supplied to drive the liquid crystal of the liquid crystal layer 3.

The pressure-sensitive tablet 7 comprises a transparent glass substrate 8 and a transparent resistive film (resistive film) 9 formed on the upper surface thereof. This transparent resistance film 9 has two resistance sheets 9a and 9b in which a transparent resistance film is uniformly printed on a transparent plastic film such as polyethylene, and a resistance element is formed by interposing transparent dot spacers or transparent pressure-sensitive conductive rubber. They are laminated so as to face each other. Electrodes 10a and 10b are formed on the edges of the resistance sheets 9a and 9b, respectively, and a constant voltage power supply 15 is connected to the electrodes 10a of the resistance sheet 9a. On the other hand, the electrode 10b of the resistance sheet 9b is connected to the controller 11 and grounded via the pull-down resistor R ₁ .

When the pressure-sensitive tablet 7 is pressed by the pen 13, the upper and lower resistance sheets 9a and 9b are electrically connected to each other at the pressed position (coordinates), so that the resistance sheet 9a is impressed. The applied voltage is resistance-divided according to the coordinates, and the resistance sheet 9b outputs a voltage according to the coordinates to the control unit 11 as a coordinate detection signal B.

The control unit 11 is a microprocessor,
The coordinate detection signal B is composed of a memory device, an interface circuit, etc., and is input from the resistance sheet 9b.
The input coordinates are determined on the basis of the coordinates, and the liquid crystal drive voltage signal C corresponding to the coordinates is output to the electrode drivers 12a and 12b to display the input image of the pressure sensitive tablet 7 on the liquid crystal display plate 6. ..

As shown in FIG. 2, the conductive shield plate 14 has electrodes 14 on the edges of a transparent conductive film 14a.
b is adhered, and this electrode 14b is connected to GND.

In the above configuration, when the upper surface of the pressure-sensitive tablet 7 is pressed by the pen 13, the resistance sheet 9b outputs the coordinate detection signal B corresponding to the coordinates to the control section 11.
The control unit 11 outputs the liquid crystal drive voltage signal C to the electrode drivers 12a and 12b based on the coordinate detection signal B.
The electrode driver 12 that receives the liquid crystal drive voltage signal C
a ・ 12b is LCD ・ C on the LCD transparent electrodes 2a ・ 2b.
The OM signal A is output.

By the way, in the above structure, the liquid crystal display panel 6 is used.
1. The LCD transparent electrode 2a and the conductive shield plate 14 form a capacitor C ₁ as shown in FIG. 1, and the conductive shield plate 14 and the resistance sheet 9b of the pressure-sensitive tablet 7 form a capacitor C _2. It will be done.

Therefore, when an AC square wave LCD / COM signal A is applied to the LCD transparent electrode 2b, the noise that would have been generated in the resistance sheet 9b of the pressure-sensitive tablet 7 in the conventional case is the conductive shield. Glue on the plate 14,
Since the noise flows to GND, no noise is generated in the pressure-sensitive tablet 7 as in the conventional case.

This improves the detection accuracy of the input coordinates of the pressure-sensitive tablet 7 in the control unit 11.

In the handwriting input device of this embodiment, the conductive shield plate 14 independent of the liquid crystal display plate 6 and the pressure sensitive tablet 7 is interposed between the liquid crystal display plate 6 and the pressure sensitive tablet 7. In the configuration, a transparent electrode as a conductive shield member is formed on at least one of the facing surfaces of the pressure-sensitive tablet 7 and the liquid crystal display plate 6 which are vertically opposed to each other, and the transparent electrode is connected to the ground wire by the GND connection. Even with the above configuration, the same noise removal effect as described above can be obtained.

FIG. 3 shows an example in which the transparent electrode 16 is formed on the liquid crystal display plate 6 side. The transparent electrode is formed on the lower surface of the transparent glass substrate 8 of the pressure-sensitive tablet 7, and this transparent electrode is GN.
It may be connected to D. Of course, the liquid crystal display board 6
Transparent electrodes may be formed on both surfaces of the pressure-sensitive tablet 7 and the opposite surface.

In the case of the figure, a capacitor C ₃ is formed by the LCD transparent electrode 2a of the liquid crystal display plate 6 and the transparent electrode 16, and the transparent electrode 16 and the resistance sheet 9 of the pressure sensitive tablet 7 are formed.
With b, the capacitor C ₄ is formed,
A noise component when an AC square wave LCD / COM signal A is applied to the LCD transparent electrode 2b flows to the GND via the transparent electrode 16.

In this way, when the transparent electrode 16 serving as a conductive shield member is integrally formed with the liquid crystal display plate 6 or the pressure sensitive tablet 7, the number of parts does not increase, and the assembly of the device is simplified.

[0035]

As described above, the handwriting input device according to the first aspect of the present invention is configured such that the grounded conductive shield member is interposed between the liquid crystal display panel and the tablet.

Therefore, a capacitor is formed by the conductive shield member and the liquid crystal display electrode of the liquid crystal display plate, and a capacitor is formed by the conductive shield member and the resistance film of the tablet. When an alternating liquid crystal drive voltage is applied, noise that would have been generated in the resistive film of the tablet in the past flows to GND through the conductive shield member, and the coordinate detection signal is different from the conventional one. Since noise is not included, it is possible to improve the detection accuracy of the input coordinates of the tablet.

A handwriting input device according to the invention of claim 2 is
As described above, in the handwriting input device according to the first aspect, the conductive shield member is a transparent electrode formed on at least one of the facing surfaces of the liquid crystal display plate and the tablet.

Therefore, in addition to the effect of the structure described in claim 1, since the transparent electrode serving as the conductive shield member is formed integrally with the liquid crystal display panel or the tablet, the number of parts is increased. Therefore, it is possible to simplify the assembly of the handwriting input device.

[Brief description of drawings]

FIG. 1 shows an embodiment of the present invention and is a cross-sectional configuration diagram showing a main part of a handwriting input device.

FIG. 2 is a schematic perspective view showing a conductive shield plate used in the handwriting input device.

FIG. 3 shows another embodiment of the present invention and is a cross-sectional configuration diagram showing a main part of a handwriting input device.

FIG. 4 illustrates a conventional example and is a cross-sectional configuration diagram illustrating a main part of a handwriting input device.

FIG. 5 is a waveform diagram showing an LCD / COM signal applied to an LCD transparent electrode and noise generated in a coordinate detection signal.

[Explanation of symbols]

2a / 2b LCD transparent electrode (liquid crystal display electrode) 6 Liquid crystal display plate 7 Pressure sensitive tablet (tablet) 9 Transparent resistance film (resistive film) 9a / 9b Resistance sheet 11 Control part 14 Conductive shield plate (conductive shield member) 16 Transparent electrode A LCD / COM signal (liquid crystal drive voltage) B Coordinate detection signal

Claims (2)

[Claims] 1. A handwriting input device in which a liquid crystal display plate having a liquid crystal display electrode to which a liquid crystal drive voltage is applied and a tablet having a resistance film for outputting a coordinate detection signal are arranged to face each other. A handwriting input device, wherein a grounded conductive shield member is interposed between the tablet and the tablet. 2. The handwriting input device according to claim 1, wherein the conductive shield member is a transparent electrode formed on at least one surface of the liquid crystal display plate and the tablet which face each other.