Abstract:
A transcription system, for determining a position of a stylus relative to a writing surface by receiving supersonic wave transmitted from the stylus when the stylus is positioned adjacent the writing surface, has a pair of supersonic wave detectors provided on a whiteboard. The supersonic wave detector has a detector cover for covering at least a front portion of a supersonic wave receiver of the supersonic wave detector with reference to the supersonic wave transmitted from the stylus. The detector cover has a hole, which is defined right in front of the receiver, having a diameter smaller than a diameter of the receiver. The detector cover further has a conical reflection board provided adjacent the hole of the detector cover.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority of Japanese Patent Application No. 2001-108173 filed on Apr. 6, 2001, the contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a system and its kit for recording writing performed on a writing surface, and more particularly to a system and its kit wherein sound waves generated on the writing surface are detected using a sound waves detector. 
     2. Description of Related Art 
     Existing technologies for capturing and storing handwritten notes include digitized writing surfaces such as electronic whiteboards. These electronic whiteboards employ a stylus for generating infrared light and supersonic wave. A pair of detectors, provided on both sides of a writing surface, detects the infrared light and supersonic wave to send a position signal transmitted from the stylus on the writing surface to a personal computer. 
     If the detectors detect not only supersonic wave directly transmitted from the stylus but also the one reflected on the writing surface after transmitted from the stylus, stable signal transmission may be prevented because the reflected supersonic wave may interfere with the directly transmitted supersonic wave. Such interference may cause a decrease in amplitude of supersonic wave to be detected and may result in incorrect detection. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide a transcription system and its kit capable of achieving stable signal transmission. 
     According to a first aspect of the present invention, a transcription system, for determining a position of a stylus relative to a writing surface by receiving supersonic wave transmitted from the stylus when the stylus is positioned adjacent the writing surface, has a pair of supersonic wave detectors provided on a whiteboard. The supersonic wave detector has a detector cover for covering at least a front portion of a supersonic wave receiver of the supersonic wave detector with reference to the supersonic wave transmitted from the stylus. The detector cover has a hole, which is defined right in front of the receiver, having a diameter smaller than a diameter of the receiver. The detector cover further has a conical reflection board provided adjacent the hole of the detector cover. 
     According to another aspect of the present invention, the holes of the detector covers are aligned with the writing surface instead of providing the conical reflection board. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other features and advantages of the present invention will be appreciated, as well as methods of operation and the function of the related parts, from a study of the following detailed description, the appended claims, and the drawings, all of which form a part of this application. In the drawings: 
     FIG. 1 is a schematic illustration of a transcription system according to a first embodiment of the present invention; 
     FIG. 2 is a schematic diagram showing output signals of an infrared light detector and a supersonic wave detector according to the first embodiment of the present invention; 
     FIG. 3 is a schematic diagram showing a correction for damping of supersonic wave according to the first embodiment of the present invention; 
     FIG. 4 is a perspective illustration of a sensor portion according to the first embodiment of the present invention; 
     FIG. 5 is a schematic cross sectional illustration showing the operational principle of the supersonic wave detector according to the first embodiment of the present invention; 
     FIG. 6 is a directivity diagram showing directivity characteristics of the supersonic wave detector according to the first embodiment of the present invention; 
     FIG. 7 is an illustration showing the operational principle of the supersonic wave detector according to the first embodiment of the present invention; and 
     FIG. 8 is an illustration showing a second embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     (First Embodiment) 
     FIG. 1 illustrates a first embodiment of a transcription system according to the present invention. As illustrated, the system includes an electronic stylus  110  which transmits infrared light and supersonic wave to a pair of sensor portions  120  provided on top corners of a whiteboard  100 . Each of the sensor portion  120  has an infrared light detector  121  and a supersonic wave detector  122  to output detection signals to a controller  130 . 
     The controller  130  determines respective distances from the electronic stylus  110  to the sensor portions  120  according to detection time differences between the infrared light and supersonic wave, and transfers distance data to a personal computer  140 . The personal computer  140  processes distance data using trigonometry to determine the location of the electronic stylus  110  on the whiteboard  100 , and then shows location information of the electronic stylus  110  on a display of the personal computer  140 . 
     Referring to FIGS. 2 and 3, processes carried out by the controller  130  will now be described. In FIG. 2, OUT(I) represents an output signal of the infrared light detector  121  and OUT(S) represents an output signal of the supersonic wave detector  122 . A point ‘A’ on the OUT(I) shows a timing when the infrared light detector  121  receives infrared light transmitted from the electronic stylus  110 . 
     FIG. 3 shows a correction for damping of supersonic wave according to the first embodiment of the present invention. Supersonic wave is generally damped as its transmission distance (time) increases as shown by damping amount R in FIG.  3 . Therefore, the controller  130  makes the correction for the OUT(S) by taking the damping of supersonic wave into consideration. The OUT(S) is corrected by amplified amount I in FIG. 3 to cancel the damping. 
     The controller  130  also recognizes signal waves of the corrected output signal OUT(S) which are greater than a predetermined value B shown in FIG. 2, and then, it determines an arrival time T from the point A to point D if a next signal wave which is greater than a predetermined value C greater than the value B is recognized as shown in FIG.  2 . Accordingly, distance is determined by the arrival time T and the speed of sound. In the first embodiment of the present invention, the controller  130  determines distance at the end of the third wave (point D) when the second wave is greater than the value B and the third wave is greater than the value C. The values B and C are, but not limited to, 2.5 Volts and 3.5 Volts respectively. 
     Referring to FIG. 4, more details of the sensor portion  120  will now be described. The infrared light detector  121  and the supersonic wave detector  122  are mounted on an electronic circuit board  40 . The infrared light detector  121  detects infrared light transmitted from the electronic stylus  110  and converts it into electrical signals to transmit it to the controller  130  via a cable  50 . 
     The supersonic wave detector  122  detects supersonic wave transmitted from the electronic stylus  110  and converts it into electrical signals to transmit it to the controller  130  via a cable  50 . 
     The controller  130  determines distance from the electronic stylus  110  to the supersonic wave detectors  122  according to the arrival time T, that is the time until the supersonic wave detector  122  detects supersonic wave after the infrared light detector  121  detects infrared light. A position coordinate of the electronic stylus  110  on the whiteboard  100  is determined by distance obtained from the sensor portions  120  by using the triangulation or trigonometry. 
     A detector cover  30  is provided in front of the supersonic wave detector  122 . The detector cover  30  is fixed to the electronic circuit board  40  by a screw  41 . Supersonic wave transmitted from the electronic stylus  110  goes through a hole  31  of the detector cover  30  to be detected by the supersonic wave detector  122 . The hole  31  has a circular shape having a diameter of 3 millimeters. Accordingly, it is capable of obtaining stable outputs having wide directivity characteristics from the supersonic wave detector  122  by providing the hole  31 . 
     Alternatively, a longitudinal hole  32  having a width of 3 millimeters may be employed instead of the hole  31 . In that case, wide directivity characteristics on a horizontal surface of the whiteboard  100  and strong directivity characteristics in a vertical direction with reference to the surface of the whiteboard  100  can be obtained. Accordingly, stable detection of the necessary supersonic wave to be detected on the whiteboard  100  can be achieved. 
     The detector cover  30  has a conical reflection board  33  which reflects a part of supersonic wave transmitted from the electronic stylus  110 . The supersonic wave detector  122  generally detects both of supersonic wave directly transmitted from the electronic stylus  110  and the one once reflected on the surface of the whiteboard  100 . Occasionally, such direct transmission and the reflected transmission of the wave cancel each other when one of the directly transmitted wave and the reflected wave is delayed by half wavelength from the other. 
     The reflection board  33  has a inclination of about 200 and a length of 25 millimeters for generating cancellation wave which cancels the reflected wave. Accordingly, stable outputs are obtained for any location of the electronic stylus  110 . Since the reflection board  33  has the inclined conical surface as shown in FIG. 4, the cancellation wave can be obtained in all directions on the whiteboard  100 . 
     Mechanism of the wave cancellation by the reflection board  33  will now be described in detail referring to FIGS. 5-8. FIG. 5 is a schematic cross sectional illustration of the supersonic wave detector  122  viewed from the top. 
     Assuming supersonic waves A 1 , A 2  and A 3  transmitted from the electronic stylus  110  on the whiteboard  100  exist as shown in FIG.  5 . The supersonic wave detector  122  has a receiver  21 . If the detector cover  30  does not exist, a phase difference between supersonic waves A 1  and A 2  may cause the cancellation of these waves A 1  and A 2  when the phase difference is integral times as large as the half wavelength of the supersonic wave. In that case, the directivity of the supersonic wave detector  122  becomes intense as shown by “F” in FIG. 6. A supersonic wave detector generally has an intensive directivity as shown by “F” in FIG.  6 . Accordingly, sensitivity for supersonic wave comes from front of the supersonic wave detector is greater than the one for supersonic wave comes from both sides of the supersonic wave detector. This sensitivity difference may prevent a stable detection of supersonic wave since the sensitivity changes depending on the location of the electronic stylus  110 . Therefore, the supersonic wave detector is required to have a wide directivity to obtain the same output signals for supersonic waves transmitted from the electronic stylus  110  on any place on the white board  100 . 
     According to the first embodiment of the present invention, however, the hole  31  or  32  formed on the detector cover  30  leads supersonic wave to the receiver  21  within the range between A 1  and A 3 . Accordingly, the directivity of the supersonic wave detector  122  is widened as shown by “E” in FIG.  6 . 
     Furthermore, the conical reflection board  33  is provided adjacent to the supersonic wave detector  122  to cancel the reflected supersonic wave reflected by the whiteboard  100 . Accordingly, the influence of the reflected supersonic wave reflected by the whiteboard  100  is reduced. 
     Referring to FIG. 7, B 1  represents supersonic wave directly transmitted to the receiver  21  and B 2  represents supersonic wave reflected on the surface  101  of the whiteboard  100  and received by the receiver  21 . Assuming supersonic waves B 1 , B 2  and B 3  transmitted from the electronic stylus  110  on a surface  101  of the whiteboard  100  exist as shown in FIG. 7, B 1  and B 2  interfere and cancel each other when the phase difference between B 1  and B 2  is integral times as large as the half wavelength of the supersonic wave. In that case, the amplitude of the supersonic wave B 1  is reduced as shown by B 4 . When the amplitude of OUT(S) of the supersonic detector  122  is too small or too large, the arrival time T is incorrectly determined since next wave or prior wave may be recognized for determining the arrival time T. 
     According to the first embodiment of the present invention, however, supersonic wave B 3  reflected by the reflection board  33  is also received by the receiver  21  in addition to B 1  and B 2 . Supersonic wave B 3  has very little phase difference with supersonic wave B 1  because supersonic wave B 3  reflects at the reflection board  33  provided very close to the receiver  21  and the distance between supersonic wave B 3  and supersonic wave B 1  is very small. Accordingly, supersonic wave B 3  makes up the amplitude reduction caused by supersonic wave B 2  as shown by B 5 . 
     Since the reflection board  33  has the conical shape, supersonic wave B 3  for compensating for the amplitude reduction can be collected in all directions on the writing surface  101  of the whiteboard  100 . Thus, uniform and stable supersonic wave is received by the supersonic wave detector  122  in a wide range of the surface  101  of the whiteboard  100 . Accordingly, drawing information is correctly sent to the personal computer  140 . 
     (Second Embodiment) 
     Referring to FIG. 8, a second embodiment of the present invention will now be described. In the second embodiment, components which are substantially the same as those in the first embodiment are assigned the same reference numerals. 
     According to the second embodiment, a supersonic wave detector  222  does not have the reflection board  33  employed in the first embodiment. Instead of employing the reflection board  33 , the hole  31  of the detector cover  30  of the supersonic wave detector  222  is aligned with the writing surface  101  of the whiteboard  100  so that the supersonic wave detector  222  does not detect supersonic wave B 2  reflected on the surface  101  of the whiteboard  100 . In other words, the holes  31  of the detector covers  30  of the supersonic wave detectors  222  are located on the same plane of the writing surface  101  as shown in FIG.  8 . Accordingly, the detection by the supersonic wave detector  222  of the supersonic wave reflected on the writing surface  101  is prevented. 
     Although the present invention has been described in connection with the preferred embodiments thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications will be apparent to those skilled in the art. Such changes and modifications are to be understood as being included within the scope of the present invention as defines in the appended claims.