Sensitive coordinate input device

Details Sensitive coordinate input device Sensitive coordinate input device

1995-06-28

2001-12-04

Teska, Kevin J. (Department: 2123)

Telegraphy

Systems

Position coordinate determination for writing

C345S173000, C341S033000, C703S002000

Reexamination Certificate

active

06326564

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a sensitive coordinate input device which is capable of changing a coordinate signal based on variation of electrostatic capacitance, and particularly to a sensitive coordinate input device adopting a system in which an operator's finger is regarded as one electrode, and an electrostatic capacitance is varied depending on a change in the distance between the finger and another electrode which is separated therefrom by a dielectric.
2. Description of the Prior Art
Conventional coordinate input devices include a mouse, a track ball, a controller, a cursor key, and the like, and also a sensitive coordinate input device.
Prior art examples of such a sensitive coordinate input device is shown for explanation in
FIGS. 3
,
4
, and
5
.
The sensitive coordinate input device shown in
FIGS. 3 and 4
comprises four electrodes
1
,
2
,
3
, and
4
which are closely arranged at regular angular positions. A dielectric film
5
is disposed so as to cover these electrodes
1
to
4
. The sensitive coordinate input device converts variation of electrostatic capacitance which is caused by pressing the dielectric film
5
with an operator's finger F or by moving the finger F on the dielectric film
5
, into a coordinate signal by a conversion circuit which is not shown.
The sensitive coordinate input device shown in
FIG. 5
is described in Japanese National Patent Publication No. 4-507316 (WO 91/03039). In this sensitive coordinate input device, a plurality of columns of first electrodes
6
convert variation of electrostatic capacitance which is caused by making the operator's finger F contact with the second electrodes
7
, into a coordinate input signal by a conversion circuit which is not shown.
In the sensitive coordinate input device described with reference to
FIGS. 3 and 4
, the electrostatic capacitance is varied in accordance with the increase or decrease of the contact area in which the finger F is in contact with the dielectric films. Therefore, in the case where the electrodes
1
and
2
are assigned to indicate the X axis on the screen of a CRT display apparatus, and the electrodes
3
and
4
are assigned to indicate the Y axis thereon, in order that the movement of the cursor on the screen of the CRT display apparatus always follows the movement of the finger F on the dielectric film
5
, it is necessary to closely dispose the four electrodes
1
to
4
as shown in FIG.
3
.
The sensitive coordinate input device described with reference to
FIG. 5
is considered to adopt a system in which the electric field is disturbed by depressing the second electrodes
7
with the finger F, thereby varying the electrostatic capacitance C. Accordingly, in the case where two of the four overlap portions formed by the columns of first electrodes
6
and the rows of second electrodes
7
are assigned to indicate the X axis on the screen of the CRT display apparatus, and the remaining two overlap portions are assigned to indicate the Y axis thereon, in order that the movement of the cursor on the CRT display apparatus always follows the movement of the finger F on the second electrodes
7
, it is necessary to closely dispose the plural columns of first electrodes
6
and the plural rows of second electrodes
7
, in the same way as in the prior art example shown in
FIGS. 3 and 4
.
However, in a sensitive coordinate input device in which electrodes must be closely disposed as in the above-described two examples, if attempts to improve operability by increasing an area of a sensitive area, i.e., an electrode formation area, the will have to be modified in the following manner. In the example shown in
FIGS. 3 and 4
, the sizes of the electrodes
1
to
4
must be increased, and, in the example shown in
FIG. 5
, the number of columns of first electrodes
6
and the number of rows of second electrodes
7
must be increased. In the example shown in
FIGS. 3 and 4
, the increase of the size of each of the electrodes
1
to
4
inevitably results in an increase in cost for forming electrodes on a substrate. In the example shown in
FIG. 5
, an increase in the number of columns of first electrodes
6
and rows of second electrodes
7
inevitably results in a complicated construction. For these reasons, the sensitive area is conventionally confined to a small rectangular area having a side of about 20 mm, or to a small circular area having a diameter of about 20 mm. Such a small sensitive area, however, hinders improvement in operability.
The contact area with the finger F is varied because of various magnitudes of forces exerted when the finger F touches the dielectric film
5
or the second electrodes
7
, and accordingly the electrostatic capacitance is varied. Thus, there exists a problem in that it is difficult to determine the position of the cursor on the CRT display apparatus.
SUMMARY OF THE INVENTION
The present invention has been conducted in view of the aforementioned circumstances and problems.
The present invention has been accomplished by adopting a system in which an operator's finger is regarded as one electrode, and an electrostatic capacitance is varied by changing the distance between the finger and another electrode which is separated therefrom by a dielectric.
It is an object of the present invention to provide a sensitive coordinate input device in which the sensitive area can easily be increased, and the position of the cursor can readily be determined on the screen of a CRT display apparatus.
The sensitive coordinate input device according to the present invention comprises at least two electrodes which are spaced by an interval, and a sensitive member made of a dielectric, the sensitive member extending across the two electrodes, and the surface of the sensitive member being touched with a finger.
The number of the electrodes is not limited to two, but may be four. In the case of four electrodes, the four electrodes are disposed at regular angular positions, and respective two electrodes which are located at opposite positions among the four electrodes are spaced by an interval. A sensitive member made of a dielectric is laid across the four electrodes. The surface of the sensitive member is to be touched with a finger. It is preferable that the sensitive member is made of a ceramic plate.
In general, an electrostatic capacitance C between conductors is expressed by the following expression:
C=∈
(
s/d
)  (1)
where ∈ denotes a dielectric constant, s denotes a counter area of the conductors, and d denotes a distance between the counter conductors. Accordingly, the electrostatic capacitance C is varied by changing any one of ∈, s, and d.
In the sensitive coordinate input device according to the present invention, the electrostatic capacitance C is varied by changing d in expression (1). Specifically, when the operator moves the finger on the surface of the dielectric sensitive member, the finger comes closer to or further from either of the two or four electrodes, and hence d in expression (1) is changed.
According to the present invention, the electrostatic capacitance is accurately affected by the finger which is in contact with the sensitive member at a position distant from the two or four electrodes, so that operability can easily be improved by increasing the size the sensitive member. Advantageously, the increase of in size of the sensitive member does not involve an increase of cost or a complication of the construction. These advantages are remarkably attained by using a ceramic plate having a high dielectric constant as the sensitive member. Since the present invention adopts a system in which the electrostatic capacitance is varied depending on the change of the distance between the finger and the electrode, the magnitude of the force exerted when the finger touches the sensitive member does not affect the electrostatic capacitance. This is advantageously useful for easily determining the cursor position on the screen of the CR

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