Computer graphics processing and selective visual display system – Display peripheral interface input device – Touch panel
Reexamination Certificate
2000-07-28
2004-08-31
Nguyen, Jimmy H. (Department: 2673)
Computer graphics processing and selective visual display system
Display peripheral interface input device
Touch panel
C345S173000, C178S018020, C178S018010, C178S018070
Reexamination Certificate
active
06784876
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a coordinate reading device.
2. Description of Related Art
Various types of coordinate reading device have been proposed. Representative examples of the conventional coordinate reading device are disclosed in Japanese Patent Application Publication (Kokai) Nos. HEI-5-165560, HEI-2-190199, HEI-8-202491, and HEI-5-143224 and in Japanese Patent Application Publication (Kokoku) No. SHO-58-16507.
Japanese Patent Application Publication (Kokoku) No. SHO-58-16507 describes one type of the coordinate reading device. As shown in
FIG. 1
, the coordinate reading device of this type has a tablet provided with a sense loop (conductive wire)
391
. The sense loop
391
is mounted on the tablet so as to extend following a rectangular-wave shape. The coordinate reading device detects the position of a pen or position indication unit that is mounted with a magnetic coil
390
. A correction sense loop
392
is additionally provided around the sense loop
391
. The sense loop
391
generates an induction signal due to magnetic coupling with a magnetic field generated at the magnetic coil
390
. The induction signal, however, may receive influence from the peripheral portion of the sense loop
391
. According to this coordinate reading device, such a portion of the induction signal that receives the influence is canceled out by the induction signal generated by the correction loop
392
so that an error in the positional coordinates of the pen at the periphery portion can be corrected.
Japanese Patent Application Publication (Kokai) No. HEI-2-190199 discloses a coordinate detecting device that calculates positional coordinates of a pen or position indication unit by obtaining the number of pulses obtained from the outputs of a conductive wire. When the indication device is positioned at an edge portion of the coordinate detecting device, the positional coordinates are corrected by adding or subtracting a predetermined pulse number from the obtained pulse numbers.
However, the coordinate reading device disclosed in Japanese Patent Application Publication (Kokai) No. SHO-58-16507 has a problem in that efficiency of manufacturing the tablet is low because extra operations are required to mount the correction loop
392
around the sense loop
391
. Also, because the correction loop
392
has to be provided around the sense loop
391
, the surface area of the coordinate input sheet where the correction loop
392
is provided cannot be used for detection, but is wasted in vain.
The coordinate retrieval device described in Japanese Patent Application Publication (Kokai) No. HEI-2-190919 has a problem in that circuitry for counting the number of pulses and for adding or subtracting pulse number has to be provided.
SUMMARY OF THE INVENTION
FIG.
2
(
a
) is a configuration of a conceivable coordinate reading device. The conceivable coordinate reading device includes: a tablet
91
, a scanning circuit
92
, and a detection circuit
90
. The tablet
91
is provided with a plurality of X sense coils (conductive wires) X
1
to Xm and Y sense coils (conductive wires) Y
1
to Yn. The X sense coils X
1
to Xm are for detecting X coordinates of a pen
400
, the Y sense coils Y
1
to Yn are for detecting Y coordinates of the pen
400
. The scan circuit
92
is for serially scanning the sense coils X
1
-Xm and Y
1
-Yn on the tablet
91
. The detection circuit
90
is for calculating the x and y coordinates of the pen by detecting induction signals generated at the sense coils X
1
-Xm and Y
1
-Yn.
The pen or position indication unit
400
includes a coil
401
that generates an alternating magnetic field. When the pen
400
contacts the tablet
91
, some sense coils that are located near to the pen
400
generate induction signals
97
due to magnetic coupling with the alternating magnetic field from the coil
401
. The induction signals
97
are inputted into the detection circuit
90
. The induction signals
97
are amplified at an amplifier
93
and then its amplitude is detected at an amplitude detection circuit
94
. Next, an A/D conversion circuit
95
converts the measured amplitude into digital values, and outputs the digital values to a CPU
96
. The CPU
96
calculates the positional coordinate of the pen
400
based on the inputted digital values from the A/D conversion circuit
95
. For example, the CPU
96
may refer to a table that stores a relationship between a plurality of digital values and coordinate positions. The CPU
96
selects a positional coordinate that corresponds to the digital values presently inputted from the A/D conversion circuit
95
.
FIG.
2
(
b
) is a graph showing the relationship how the voltage generated at the sense coil Y
1
changes when the position of the electric pen
400
, defined as the distance D from the edge Y
1
d
of the sense coil Y
1
, changes. As shown in FIG.
2
(
b
), when the pen
400
is located at a position P
1
in the sense coil Y
1
, the sense coil Y
1
generates voltage value V
1
. However, the closer the pen
100
is to the lengthwise end (short side Y
1
d
) of the sense coil Y
1
, the generated voltage value V is effected by the induction signal from the short side Y
1
d
. The voltage V rises, and the voltage value increases from V
1
to V
2
when the pen
400
is at position P
2
. The closer the pen
400
is to the short side Y
1
d
from the position P
2
, however, the voltage value V drops.
As can be seen, in this conceivable technology, the voltage detected by the detection circuit
90
changes as the pen goes near to the edges of the tablet
91
. It is impossible to accurately detect the position of the pen when the pen is located near to the edges of the tablet
91
. The range of the tablet that can be used for accurate detection is narrower than it is desired.
Japanese Patent-Application Publication No. HEI-8-202491 discloses decreasing the width of the sense coils at their edge portions. Japanese Patent-Application Publication No. HEI-5-143224 discloses using a sub loop. However, with both of these methods, the configuration at the edge portions becomes quite complicated, or the number of coils need to be increased, which also complicates the configuration.
Additionally, in the conceivable technology of FIG.
2
(
a
), the voltage detected by the detection circuit
90
increases as the pen goes near to the edges of the tablet
91
. When the pen
400
is located near to some edge of the tablet
91
, therefore, the digital amplitude value outputted from the A/D conversion circuit
95
will increase. Therefore, the burden on the CPU
96
increases. Also, the dynamic range of the amplifier
93
has to be broadened to match the voltage values at the edge portions of the tablet
91
.
In view of the above-described drawbacks, it is an objective of the present invention to provide an improved coordinate reading device that has a simple configuration but that is capable of accurately reading coordinates of a target (alternating magnetic field generating unit), even when the target is located at some edge portion of the coordinate reading device.
In order to attain the above and other objects, the present invention provides a coordinate reading device reading a coordinate of a position of a target which generates an alternating magnetic field, the coordinate reading device comprising: a base member; a plurality of loop wires provided on the base member, each loop wire being capable of producing an electric signal in response to an alternating magnetic field generated from a target, each loop wire having at least one edge portion; a detection unit that detects levels of the signals generated from the plurality of loop wires, thereby determining a coordinate of the position of the target; and a correction unit correcting the coordinate of the position of the target when the target is located in each of the at least one edge portion of some loop wire.
The correction unit may correct each loop wire to produce a corrected signal when the target is located in each of the at le
Nagai Takuya
Ohashi Tsuyoshi
Brother Kogyo Kabushiki Kaisha
Nguyen Jimmy H.
Oliff & Berridg,e PLC
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