Computer graphics processing and selective visual display system – Display peripheral interface input device – Touch panel
Reexamination Certificate
2000-08-28
2003-02-11
Mengistu, Amare (Department: 2673)
Computer graphics processing and selective visual display system
Display peripheral interface input device
Touch panel
Reexamination Certificate
active
06518959
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a device which optically detects the coordinates of a specified position, thereby it can be used to draw images, write text on electronic boards or the like. More particularly, this invention relates to a device in which a probe beam is emitted towards a reflecting member, probe beam reflected from the reflecting member are received, and the coordinates of the specified position is detected based on the intensity of the received light.
BACKGROUND OF THE INVENTION
As a conventional device which optically detects the coordinates of a specified position and inputs the detected coordinates to some other device (hereafter referred to as coordinate-position input device), there is one comprising a light emitter that emits a probe beam (irradiation light), a reflector that reflects the probe beam emitted by the light emitter, and a light receiver that receives and converges the probe beam reflected by the reflector. The radiated light is a flux of collimated light beam which is parallel but at a certain height from a coordinate input surface (a whiteboard or a blackboard).
FIG. 9
schematically shows the conventional coordinate-position input device
200
.
FIG. 10
schematically shows the light receiver when viewed from the vertical direction with respect to the coordinate input surface
202
. A light reception/emission section
203
is provided in this coordinate-position input device
200
. This light reception/emission section
203
comprises a light emitter that emits irradiation light (probe beam) along the coordinate input surface
202
, and a light receiver
220
that receives the reflected light. The light emitter is not specifically shown in these figures. A recursive reflector
204
is provided on the three sides of the coordinate input surface
202
. This recursive reflector
204
comprises a reflection plate that reflects an incoming probe beam recursively to the direction from which light came in. The light emitter comprises a light-emitting element that emits irradiation light, and a cylindrical lens that converges or diffuses the irradiation light emitted by the light-emitting element in a prescribed direction of its travel. The functions of this light emitter will be explained in detail later. The light receiver
220
comprises a light receiving lens
221
that receives and converges the reflection light, and a photoreceptor
222
that detects the intensity of the received light converged by the light receiving lens
221
. When a position on the coordinate input surface
202
is specified by pointing that position with a pointing tool, the coordinate-position input device
200
detects the specified position in terms of its coordinates. The specified position is detected base on detection of the direction &thgr; in which the light is blocked due to the invasion of the pointing tool in the light flux. By the way, the pointing tool may be a pen, finger or the like.
Structure of the light emitter will now be explained in detail here.
FIG. 11A
shows the conventional light emitter when viewed from the direction parallel to the coordinate input surface
202
and also from the direction perpendicular to the direction of travel of the irradiation light. In this light emitter, a positional relation between the light-emitting element
211
and the cylindrical lens
212
is so adjusted that the irradiation light travels parallel to the coordinate input surface
202
. Precisely, the light-emitting element
211
is disposed at one focal point of the cylindrical lens
212
. In other words, the light-emitting element
211
is so positioned that the light coming out of the cylindrical lens
212
is parallel to the optical axis of the light emitted from the light-emitting element
211
. The reason why the light-emitting element
211
is positioned in this manner is as follows. That is, by positioning the light-emitting element
211
in this manner, if the collimated light beam is blocked by the pointing tool at some place, then the shadow of the pointing tool proceeds as it is without changing its shape because of the property of the collimated light beam. In other words, a sharp shadow of the pointing took fall on the photoreceptor. Conventionally, as shown in
FIG. 11B
, it was considered that, because the shadow of the pointing tool is sharp it appears as a dark spot on the photoreceptor, whereby the position of the pointing tool can be detected with highest precision.
On the other hand, in another conventional method, the cylindrical lens
212
and the light-emitting element
211
are so adjusted that the light coming out of the cylindrical lens
212
is not parallel but becomes narrower (that, is the light converges) as it reaches the recursive reflector
204
as shown in FIG.
12
A. This method will be called as the method of converging the light to differentiate it from the above-explained method of parallel light. When the light is converging, since the irradiation light is not collimated light, due to diffraction or the like, the shadow of the pointing tool is not sharp. Accordingly, as shown in
FIG. 12B
, the negative peak of the intensity of the, corresponding to the position of the pointing tool is not very distinct, furthermore, the peak is not sharp. Because of these facts the precision in detection of the position of the pointing tool degrades.
An experiment was conducted as follows.
FIG. 13A
to
FIG. 13B
show detection characteristics of the coordinate-position input device observed in this experiment. The distance between the pointing tool and the coordinate input surface is plotted along the horizontal axis. The degree of detection precision (sensitivity of the photoreceptor) is plotted along the vertical axis. The lower the value of this degree of detection precision, the higher is the precision. The method of converging light explained with respect to
FIG. 12A
was employed in this experiment. Further, two pointing tools, one with a diameter of 5 mm and the other with a diameter of 20 mm were used to specify a position.
FIG. 13A
shows the detection characteristics when the direction
0
of the pointing tool is zero degree.
FIG. 13B
shows the detection characteristics when the direction &thgr; of the pointing tool is 20 degrees. Finally,
FIG. 13C
shows the detection characteristics when the direction &thgr; of the pointing tool is 40 degrees. Each line in these plots shows the detection characteristics corresponding to the distance between the pointing tool and the light receiving lens
221
.
FIG. 14A
to
FIG. 14C
correspond to
FIG. 13A
to
FIG. 13C
with the difference that the method of parallel light explained with respect to
FIG. 11A
was employed.
When the method of parallel light is employed, it is clear from
FIG. 14A
to
FIG. 14C
that, the precision of detection of the specified position increases as the distance between the pointing tool and the coordinate input surface decreases. Further, it is apparent that, the distance between the pointing tool and the light receiving lens
221
, the direction &thgr;, or the size of the pointing tool does not make any difference. In other words, if the method of parallel light is employed in the coordinate-position input device, then the specified position can be detected at a high precision. Furthermore, the detection characteristics depend only on the distance between the pointing tool and the coordinate input surface and does not depend on any other parameter.
On the contrary, when the method of converging light is employed, it is clear from
FIG. 13A
to
FIG. 13C
that, the detection precision is not uniform because it is affected by the distance between the pointing tool and the light receiving lens
221
, the direction &thgr;, or the size of the pointing tool. Particularly, the detection precision is low even if the pointing tool is brought very close (of the order of 1.0 mm) to the coordinate input surface.
As can be seen from the results of the experiments, the detection precision in the conventional coordinate-position input device
Ito Takahiro
Saka Yasuhiko
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