Computer graphics processing and selective visual display system – Display peripheral interface input device – Touch panel
Reexamination Certificate
2001-09-04
2004-08-17
Wu, Xiao (Department: 2674)
Computer graphics processing and selective visual display system
Display peripheral interface input device
Touch panel
C345S156000, C345S174000, C345S179000, C345S586000, C178S018010, C178S019030, C235S449000
Reexamination Certificate
active
06778167
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The invention relates to a coordinate reading device that reads a coordinate of a position of a coordinate input device, in accordance with a signal generated on a plurality of coils laid in a coordinate input sheet by an alternating magnetic field generated from the coordinate input device.
2. Description of Related Art
FIG. 35
shows a structure of a conventional coordinate reading device. (Japanese Laid-Open Patent Publication No. 5-165560).
The coordinate reading device shown in
FIG. 35
includes a tablet (coordinate input sheet)
91
, a scanning circuit
92
, and a detection circuit
90
. The tablet
91
is provided with a plurality of X-sense coils X
1
to Xm for detecting X-coordinates of a stylus (coordinate input device)
100
and Y-sense coils Y
1
to Yn for detecting Y-coordinates of the stylus
100
. The scanning circuit
92
serially scans the sense coils X
1
to Xm and Y
1
to Yn in the tablet
91
. The detection circuit
90
calculates the X- and Y-coordinates of the stylus
100
by detecting induction signals generated at the sense coils X
1
to Xm and Y
1
to Yn.
The stylus
100
includes a coil
101
that generates an alternating magnetic field. When the stylus
100
contacts the tablet
91
, some sense coils located near the stylus
100
generate induction signals
97
due to magnetic coupling with the alternating magnetic field from the coil
101
. Selection signals
98
, that serially specify the sense coils X
1
to Xm and Y
1
to Yn to detect the respective introduction signals
97
generated at the sense coils X
1
to Xm and Y
1
to Yn, are inputted into the scanning circuit
92
. The induction signals
97
are inputted into the detection circuit
90
. The inputted induction signals
97
are amplified at an amplifier
93
where the 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 a positional coordinate of the stylus
100
based on the inputted digital values from the A/D conversion circuit
95
. For example, the CPU
96
may refer to a coordinate table that stores data indicative of 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
.
When the stylus
100
is tilted against a coordinate input plane of the tablet
91
, a distribution of the alternating magnetic field generated from the coil
101
is changed. Therefore, a voltage generated on the sense coils is changed.
However, the digital values in the coordinate table used in the conventional coordinate reading device are measured in advance, based on the voltage generated at the sense coils due to the magnetic coupling with the alternating magnetic field from the coil
101
when a center axis of the stylus
100
is perpendicular to the coordinate input plane (that is, when the center axis of the stylus
100
is not tilted against the coordinate input plane). Accordingly, when the stylus
100
is tilted against the coordinate input plane of the tablet
91
, an error occurs in the coordinate by selecting the coordinate of the digital value corresponding to the voltage generated at the sense coils.
Further, when the output level of the alternating magnetic value is reduced due to exhaustion of a battery in the stylus
100
, induction signals generated at the sense coils due to the alternating magnetic field having the reduced output level is detected and coordinates corresponding to an amplitude of the induction signals are selected, thereby reducing reading accuracy of the coordinates.
SUMMARY OF THE INVENTION
The invention provides a coordinate reading device that can precisely read coordinates of a coordinate input device even when the coordinate input device is tilted against a coordinate input area or when an output level of an alternating magnetic field generated from the coordinate input device is reduced.
In various embodiments, the coordinate reading device includes a coordinate input sheet that has a coordinate input area for inputting a coordinate by a coordinate input device generating an alternating magnetic field, and a plurality of loop coils laid under the coordinate input area; a coil detecting device that detects a coil that generates a maximum signal level and a coil that generates a first signal level that is a larger signal level generated from one of coils adjacent to the coil generating the maximum signal level, in accordance with a strength of the alternating magnetic field generated from the coordinate input device; a first storage device that stores a first relationship between the maximum signal level and the first signal level and a second relationship between the first relationship and a distance between a predetermined position and the coordinate input device on the coordinate input area; a reading controller that reads a distance, corresponding to the first relationship obtained based on the detected maximum signal level and the first signal level, from the first storage device, and reads a positional coordinate of the coordinate input device on the coordinate input area based on the read distance; a signal level detecting device that detects a second signal level in which two signal levels detected from coils adjacent to each other of the plurality of coils are substantially equal to each other, in accordance with the strength of the alternating magnetic field; a signal level calculating device that calculates a third relationship between a third signal level and a fourth signal level which are generated from at least two coils adjacent to the outside of the adjacent coils generating the second signal level detected by the signal level detecting device; a second storage device that stores relationships between the second signal level and the third relationship and a correction; and a correcting device that corrects the second relationship stored in the first storage device by reading the correction, corresponding to the second signal level detected by the signal level detecting device and the third relationship calculated by the signal level calculating device, from the second storage device.
The signal level detecting device detects a second signal level in which two signal levels detected from coils adjacent to each other of the plurality of coils are substantially equal to each other, in accordance with the strength of the alternating magnetic field.
That is, in the coordinate reading device that detects coordinates of the coordinate input device based on a difference between two signal levels detected from the adjacent coils of the plurality of coils, when the coordinate input device exists in a middle of two coils adjacent to each other, the difference of the two signal levels generated on the two coils is zero, that is, the two signal levels indicate the same value. This relationship is also established when a strength of the alternating magnetic field generated from the coordinate input device becomes weak or when the coordinate input device is tilted with respect to the coordinate input area.
Therefore, if the two signal levels are detected when the relationship is established, the strength of the alternating magnetic field can be obtained.
The signal level calculating device calculates a third relationship between a third signal level and a fourth signal level which are generated from at least two coils adjacent to the outside of the adjacent coils generating the second signal level detected the second signal level detecting device.
That is, when the coordinate input device is perpendicular to the coordinate input area (when the coordinate input device is not tilted against the coordinate input area), a relationship that the third signal level and the fourth signal level, which are generated from at least two coils adjacent to the outside of the adjacent coils generating the seco
Abdulselam Abbas I
Brother Kogyo Kabushiki Kaisha
Oliff & Berridg,e PLC
Wu Xiao
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