Patent Publication Number: US-2015084919-A1

Title: Information Input Device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to Japanese Patent Application No. 2013-197504 filed on Sep. 24, 2013, the disclosure of which is herein incorporated by reference in its entirety. 
     BACKGROUND 
     The present disclosure relates to an information input device that is capable of acquiring information that has been input using a writing tool on a recording medium, such as paper, as digitized information. 
     In known art, an information input device is known that can digitize written content, using a digitizer, when characters or graphics etc. are written on a paper medium (a booklet-like recording medium that is formed of a plurality of sheets that are bound together, for example) using a writing tool. More specifically, for example, this type of device is configured so that a movement trajectory of the writing tool on the paper medium that is placed on a pad is read by a digitizer provided in the pad. For example, in this type of known device, an electromagnetic induction type tablet is provided as the digitizer. The electromagnetic induction type digitizer can detect a position at which the writing tool comes into contact with or comes close to a detection surface of the digitizer, convert the detected position to coordinate data, taking the detection surface as an XY plane, and output the coordinate data to the information input device. By sampling the coordinate data output by the digitizer, the information input device can acquire trajectory information, which is an aggregate of the coordinate data that can reproduce the movement trajectory of the writing tool. 
     SUMMARY 
     However, the electromagnetic induction type digitizer can detect not only the position at which the writing tool comes into contact with the detection surface, but also the position at which the writing tool comes close to the detection surface. As a result, when the digitizer detects the position of the writing tool in a state in which the writing tool is positioned outside the detection surface, there is a possibility that when the trajectory is reproduced based on trajectory information, noise-like points and lines are drawn on an outermost peripheral portion of the XY plane. 
     Various exemplary embodiments of the general principles described herein provide an information input device that can acquire accurate trajectory information, by not including acquired position information in the trajectory information when a writing tool is positioned outside a predetermined area, which is an area that is obtained by excluding, from a detection area, an area of a predetermined width along an outer edge of the detection area. 
     Exemplary embodiments herein provide an information input device having a sensor portion and a processor. The sensor portion is configured to generate an output corresponding to a position of a writing tool inside a predetermined detection area, in the course of writing that is performed on a recording medium using the writing tool, the recording medium being set on the information input device such that the recording medium corresponds to the detection area. The processor is configured to acquire position information based on the output of the sensor portion, the position information being information corresponding to the position of the writing tool. The processor is also configured to store trajectory information in a storage medium. The trajectory information is formed of a series of the position information as a result of chronologically storing the acquired position information in the storage medium. Specifically, the trajectory information is information corresponding to a trajectory of writing performed using the writing tool. The processor is also configured to determine whether the position of the writing tool corresponding to the acquired position information is included in a second area, which is an area obtained by excluding a first area from the detection area. The first area is an area of a predetermined width along an outer edge of the detection area. The processor is also configured to prohibit processing that adds the acquired position information to the trajectory information and stores the updated trajectory information, when it is determined that the position of the writing tool corresponding to the acquired position information is not included in the second area. The processor is also configured to perform processing that adds the acquired position information to the trajectory information and stores the updated trajectory information, when it is determined that the position of the writing tool corresponding to the acquired position information is included in the second area. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments will be described below in detail with reference to the accompanying drawings in which: 
         FIG. 1  is a perspective view of an information input device  1 ; 
         FIG. 2  is a partial plan view of the information input device  1 ; 
         FIG. 3  is a block diagram showing an electrical configuration of the information input device  1 ; 
         FIG. 4  is a flowchart of main processing; and 
         FIG. 5  is a diagram illustrating relationships between an effective area P and stroke data M 1 , M 2  and M 3 . 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, an embodiment will be explained with reference to the drawings. The drawings referred to are used to illustrate technological features that can be adopted by the present disclosure. Device configurations and flowcharts of various processing etc. shown in the drawings are merely explanatory examples and are not intended to limit the present disclosure to only those examples. An overview of an information input device  1  according to a present embodiment will be explained with reference to  FIG. 1  and  FIG. 2 . In the following explanation, the upper left side, the lower right side, the upper side, the lower side, the lower left side and the upper right side of  FIG. 1  respectively define a left side, a right side, an upper side, a lower side, a front side and a rear side of the information input device  1 . 
     The information input device  1  is a thin, lightweight handwriting input device. The information input device  1  is configured to detect and digitize positions of an electronic pen  3  over time when a user uses the electronic pen  3  to write information on a paper medium  100  that is mounted on the information input device  1 . The information input device  1  is provided with housings  8 L and  8 R. The housings  8 L and  8 R are made of synthetic resin, and each is formed as a thin rectangular plate. The information input device  1  is configured so that the housings  8 L and  8 R can be changed between a folded over state that is not shown in the drawings, and a state in which they are open in a two-page spread in the left-right direction, as shown in  FIG. 1 . 
     In the state in which the housings  8 L and  8 R shown in  FIG. 1  are in the open two-page spread state in the left-right direction, the paper medium  100  is fixed to upper surfaces (which can also be referred to as front surfaces as they are the surfaces on the side facing the user) of the housings  8 L and  8 R. 
     In the present embodiment, the paper medium  100  is a booklet shaped medium that can be opened out to a two-page spread in the left-right direction. The paper medium  100  is formed of a pair of cover sheets (a front cover sheet  110 L and a back cover sheet  110 R) and a plurality of paper sheets  120  that are bound together at their respective edge portions. As an example, the paper medium  100  is an A5 size notebook. In a specific example corresponding to  FIG. 1 , the paper medium  100  is mounted on the information input device  1  such that the front cover sheet  110 L is placed on the upper surface of the housing  8 L and the back cover sheet  11 OR is placed on the upper surface of the housing  8 R. When the paper medium  100  is mounted on the information input device  1 , the user can use the electronic pen  3  to write information on the paper sheet  120 . The information input device  1  is configured to detect position information of the electronic pen  3  that is being used to write the information on the paper sheet  120 , using a sensor board  71  or a sensor board  72  (the sensor boards  71  and  72  will be explained in more detail later) that is housed inside the housing  8 L or  8 R that corresponds to the paper sheet  120  on which the electronic pen  3  is being used to write the information. 
     As shown in  FIG. 2 , position determining portions  81 L and  81 R are respectively formed on the upper surfaces (the front surfaces) of the housings  8 L and  8 R. The position determining portions  81 L and  81 R are recessed portions that are formed in order to provide a positioning function when the front cover sheet  110 L and the back cover sheet  11 OR of the paper medium  100  are respectively fixed to the housings  8 L and  8 R. The housing  8 R houses the sensor board  71 , a sensor control board  28  and a main board  20  (refer to  FIG. 3 ). The housing  8 L houses the sensor board  72  and a sensor control board  29  (refer to  FIG. 3 ). As will be explained in more detail later, each of the sensor boards  71  and  72  is formed in a substantially rectangular flat plate shape in a plan view. The sensor boards  71  and  72  are sensors that detect, by an electromagnetic induction method, a position of the electronic pen  3  that comes into contact with or comes close to detection areas  71 A and  72 A that are provided on upper surfaces of the sensor boards  71  and  72 . The housings  8 L and  8 R are configured to house the sensor boards  71  and  72  in a state in which the position determining portions  81 L and  81 R are respectively arranged in alignment with the detection areas  71 A and  72 A of the sensor boards  71  and  72 . 
     As shown in  FIG. 1 , the electronic pen  3  is a known electromagnetic induction-type electronic pen and is provided with a core body  31 , a coil  32 , a variable capacity condenser  33 , a board  34 , a condenser  35  and an ink storage portion  36 . The core body  31  is provided on the leading end portion of the electronic pen  3 . The core body  31  is arranged so as to be urged toward the leading end of the electronic pen  3  by an elastic member that is not shown in the drawings. The core body  31  is also arranged so as to project its tip to the outside of a cylindrical body  30 . The rear end of the core body  31  is connected to the ink storage portion  36  in which ink is stored. The ink storage portion  36  is provided to supply the ink to the core body  31 . Thus, when the user writes using the electronic pen  3 , the written characters (letters, numerals and graphics etc.) are formed on the paper sheet  120  by the ink. 
     In a state in which the coil  32  is wound around the periphery of the ink storage portion  36 , the coil  32  is held between the core body  31  and the variable capacity condenser  33 . The variable capacity condenser  33  is fixed to the inside of the electronic pen  3  by the board  34 . The condenser  35  is mounted on the board  34 . The condenser  35  and the variable capacity condenser  33  are connected in parallel to the coil  32  so as to form a known resonance (tuning) circuit. 
     An electrical configuration of the information input device  1  will be explained with reference to  FIG. 3 . The information input device  1  is mainly provided with the main board  20 , the sensor boards  71  and  72  and the sensor control boards  28  and  29 . As described above, the main board  20 , the sensor board  71  and the sensor control board  28  are housed in the housing  8 R. The sensor board  72  and the sensor control board  29  are housed in the housing  8 L. 
     The main board  20  is provided with a CPU  21 , a RAM  22 , a flash ROM  23  and a wireless communication portion  24 . The RAM  22 , the flash ROM  23  and the wireless communication portion  24  are electrically connected to the CPU  21 . The CPU  21  is provided so as to control the entire operation of the information input device  1 . The RAM  22  is provided so as to temporarily store various data, such as arithmetic calculation data and the like. The flash ROM  23  is provided so as to store various programs executed by the CPU  21  to perform the control of the information input device  1 . Further, the flash ROM  23  is provided so as to store stroke data representing a trajectory of the electronic pen  3  that is used to write information on the paper medium  100 . The stroke data is formed by adding header information (a stroke header) to data in which a plurality of pieces of position information (coordinate data, for example) of the electronic pen  3  detected chronologically by the sensor board  71  and the sensor board  72  are arranged in an order of detection. The stroke header includes, for example, data number information representing a number of pieces of coordinate data included in one set of the stroke data and time information representing a time at which the stroke data is generated. In other words, the stroke data is data that can reproduce the information (characters, numerals and graphics etc) written by the user on the paper sheet  120 , by connecting the individual pieces of coordinate data along a time series. The wireless communication portion  24  is a controller that is used to perform near-field wireless communication with an external electronic device. Although not shown in the drawings, the information input device  1  can transmit the generated stroke data from a personal computer (PC) or the like that is used by the user, via the wireless communication portion  24 . 
     As described above, the sensor boards  71  and  72  are electromagnetic induction-type sensors, and are configured to detect the position of the electronic pen  3  that comes into contact with or comes close to the detection areas  71 A and  72 A (refer to  FIG. 2 ). In the sensor boards  71  and  72 , a plurality of rectangular loop coils that are arrayed at a predetermined interval in an X axis direction (left-right direction) and a Y axis direction (up-down direction) are arranged inside the detection areas  71 A and  72 A. The sensor board  71  is electrically connected to an application-specific integrated circuit (ASIC)  28 A that is mounted on the sensor control board  28 . An antenna resonance circuit (not shown in the drawings) is built into the sensor control board  28 . The ASIC  28 A controls the sensor board  71  in order to realize an operation to detect the position of the electronic pen  3 . The ASIC  28 A generates coordinate data, taking the detection area  71 A as the XY plane, based on the position of the electronic pen  3  detected by the sensor board  71  when the writing operation using the electronic pen  3  is performed on the housing  8 R that houses the sensor board  71 . 
     Similarly, the sensor board  72  is electrically connected to an ASIC  29 A that is mounted on the sensor control board  29 . An antenna resonance circuit is built into the sensor control board  29 . The ASIC  29 A controls the sensor board  72  in order to realize an operation to detect the position of the electronic pen  3 . The ASIC  29 A generates coordinate data, taking the detection area  72 A as the XY plane, based on the position of the electronic pen  3  detected by the sensor board  72  when the writing operation using the electronic pen  3  is performed on the housing  8 L that houses the sensor board  72 . Of the ASIC  28 A and the ASIC  29 A, the ASIC  28 A that is on the master side is directly connected to the CPU  21  and outputs the coordinate data to the CPU  21 . The ASIC  29 A that is on the slave side is connected to the CPU  21  via the ASIC  28 A and outputs the coordinate data to the CPU  21 . 
     Next, the principle of an operation by which the sensor boards  71  and  72  detect the position of the electronic pen  3  (this operation will hereinafter simply be referred to as “scanning”) will be briefly explained. Based on a command of the CPU  21 , the ASIC  28 A and the ASIC  29 A respectively control the sensor control boards  28  and  29 . The sensor control boards  28  and  29  generate a magnetic field by causing an electric current of a specific frequency to flow through the plurality of loop coils of the sensor boards  71  and  72 . When the electronic pen  3  comes close to the sensor boards  71  and  72  in this state, a resonance circuit of the electronic pen  3  resonates as a result of electromagnetic induction of the loop coils and an induction field is generated. 
     The sensor control boards  28  and  29  stop the flow of the electric current to the loop coils and scan the loop coils one by one. An electric current generated by the induction field caused by the resonance circuit of the electronic pen  3  flows through the loop coils. The electric current flowing through the loop coil closest to the electronic pen  3  is large, and the electric current flowing through the loop coil that is adjacent to the “loop coil closest to the electronic pen  3 ” is comparatively small. The sensor control boards  28  and  29  use a differential amplifier circuit (not shown in the drawings) to perform voltage conversion on the electric current flowing through the loop coils of each of the sensor boards  71  and  72 , and input the converted voltage to the ASIC  28 A and the ASIC  29 A. The ASIC  28 A and the ASIC  29 A calculate the position of the electronic pen  3  based on the input voltage values, convert the position to coordinate data and output the coordinate data to the CPU  21 . 
     When the user is using the electronic pen  3  to write information on the paper medium  100 , a writing pressure is applied to the core body  31  of the electronic pen  3 . The inductance of the coil  32  varies depending on the writing pressure applied to the core body  31 , and thus the resonance frequency of the resonance circuit of the electronic pen  3  changes. The ASIC  28 A and the ASIC  29 A determine whether or not information is being written on the paper medium  100  by detecting changes in the resonance frequency, namely, phase changes. When the ASIC  28 A and the ASIC  29 A determine, based on the changes in the resonance frequency, that the user is writing information on the paper medium  100  (when the writing pressure is applied to the electronic pen  3 ), the ASIC  28 A and the ASIC  29 A output a pen down signal (a high signal) to the CPU  21 . Further, when the ASIC  28 A and the ASIC  29 A determine, based on the changes in the resonance frequency, that the user is not writing information on the paper medium  100  (the writing pressure on the electronic pen  3  is released), the ASIC  28 A and the ASIC  29 A output a pen up signal (a low signal) to the CPU  21 . When the CPU  21  receives the pen down signal, the CPU  21  generates stroke data by acquiring the coordinate data output by the ASIC  28 A and the ASIC  29 A and stores the stroke data in the flash ROM  23 . 
     As described above, the position of the electronic pen  3  that comes into contact with or comes close to the detection areas  71 A and  72 A of the sensor boards  71  and  72  is detected by the electromagnetic induction method. As a result, even when the position of the electronic pen  3  is a position that is outside the detection areas  71 A and  72 A, there are cases in which the position of the electronic pen  3  is detected. In this case, it is possible that the ASIC  28 A and the ASIC  29 A may output, as the coordinate data based on a result of scanning the sensor boards  71  and  72 , coordinate data representing a position along the side on which the electronic pen  3  moved outside the detection areas  71 A and  72 A, of the four sides of the detection areas  71 A and  72 A. In the information input device  1  of the present embodiment, as shown in  FIG. 2 , an ineffective area D is set around the outer edges of each of the detection areas  71 A and  72 A. Each of the ineffective areas D has a predetermined width ( 100  dots, for example, when the coordinate data is expressed as a dot number). At the same time, an area of each of the detection areas  71 A and  72 A that excludes the ineffective area D is set as an effective area P. By performing main processing that will be explained below, the information input device  1  treats coordinate data that is outside the effective areas P as invalid and generates stroke data represented by an aggregate of coordinate data that is inside the effective areas P. 
     The main processing of the information input device  1  will be explained with reference to  FIG. 4  and  FIG. 5 . When the power source of the information input device  1  is switched on, the CPU  21  supplies power to the sensor boards  71  and  72  from the ASIC  28 A and the ASIC  29 A, by outputting a command to the ASIC  28 A and the ASIC  29 A. Specifically, the ASIC  28 A and the ASIC  29 A start scanning by the sensor boards  71  and  72 . The CPU  21  reads the program that is stored in the flash ROM  23  into the RAM  22  and performs the main processing (refer to  FIG. 4 ). At that time, the CPU  21  stores data that is acquired in the course of the processing in the RAM  22 , as appropriate. 
     As shown in  FIG. 4 , in the main processing, the CPU  21  first performs initialization processing. More specifically, the CPU  21  secures a storage area for the stroke data in the flash ROM  23 . Further, the CPU  21  secures a storage area for a variable [NowPoint] and a storage area for a flag [Flg] in the RAM  22 , and sets [Flg] to zero (False), as an initial value (step S 11 ). After this initialization processing, the CPU  21  determines whether or not the pen down signal has been received from the ASIC  28 A and/or the ASIC  29 A (step S 13 ). If the pen down signal has not been received (no at step S 13 ), [Flg] is still False (no at step S 15 ) and thus the processing returns to step S 11 . The CPU  21  repeats the processing at step S 11  to step S 15  until the pen down signal is received, and thus waits for the writing of information on the paper medium  100  by the user using the electronic pen  3 . When the pen down signal has been received (yes at step S 13 ), the CPU  21  acquires the coordinate data output by the ASIC  28 A and/or the ASIC  29 A (step S 17 ). Next, the CPU  21  stores the acquired coordinate data in [NowPoint] (step S 19 ). 
     The CPU  21  determines whether or not the coordinate data stored in [NowPoint] is inside the effective area P (step S 21 ). If the coordinate data of the position at which the user pressed the pen down is inside the effective area P (yes at step S 21 ), the CPU  21  determines whether or not [Flg] is True (step S 23 ). When [Flg] is False (no at step S 23 ), the CPU  21  sets an area to which a stroke header is added in the storage area for the stroke data secured in the flash ROM  23  (step S 25 ). The CPU  21  acquires time information from a clock that is not shown in the drawings, and stores the acquired time information in the stroke header. The CPU  21  adds the coordinate data stored in [NowPoint] to the end of the stroke data and stores the updated stroke data (step S 27 ). The CPU  21  sets  1  (True) for [Flg] (step S 29 ) and returns the processing to step S 13 . Note that, although not shown in the drawings, when the CPU  21  returns the processing to step S 13  after the processing at step S 29 , the CPU  21  waits for a predetermined period of time to elapse, so that the acquisition of the coordinate data at step S 17  is performed periodically. 
     After this, the user continues to write information in the same manner, and if the coordinate data of the electronic pen  3  is not outside the effective area P (yes at step S 21 ), the CPU  21  continues the processing to add the coordinate data of the electronic pen  3  to the end of the stroke data (step S 27 ). In this case, in the processing at step S 23 , as [Flg] is set to True by the above-described processing at step S 29 , the CPU  21  advances the processing to step S 27 . 
     When the ASIC  28 A and the ASIC  29 A have received the pen up signal (no at step S 13 ) while the processing to generate the stroke data is being performed, as [Flg] is True (yes at step S 15 ), the CPU  21  performs processing to determine the stroke header (step S 33 ). The CPU  21  counts up the number of the pieces of coordinate data added to the stroke data, and stores a counted result in the stroke header as the data number information. The CPU  21  ends the generation of the stroke data by confirming the stroke header, and returns the processing to step S 11 . 
     The following looks at stroke data M 1  shown in  FIG. 5  that is generated based on a character “1” written by the user on the paper medium  100  using the electronic pen  3 . The user presses the pen down at a point H 1  and starts to write the character “1.” The CPU  21  acquires coordinate data of the point H 1  (step S 17 ) based on the pen down signal (yes at step S 13 ). The point H 1  is inside the effective area P (yes at step S 21 ) and thus the CPU  21  generates a stroke header (step S 25 ), and adds the coordinate data to the stroke data (step S 27 ). The user starts writing the character “1” from the point H 1  and reaches a point F 1  without going outside the effective area P on the way. As a result, the CPU  21  repeatedly performs the processing at step S 13  and step S 17  to step S 29 , and adds the coordinate data that is based on the trajectory of the electronic pen  3  to the stroke data. The user lifts the pen up at the point Fl and ends the writing of the character “1.” The CPU  21  determines the stroke header (step S 33 ) based on the pen up signal (no at step S 13 ) and completes the stroke data M 1 . In the stroke data M 1 , both the point H 1  and the point F 1  are inside the effective area P. Further, in the stroke data M 1 , between the point H 1  and the point F 1  there is no section that goes outside the effective area P. As a result, using the stroke data M 1 , a line segment connecting the point H 1  and the point F 1  is formed. 
     As shown in  FIG. 4 , while the user continues to write information and the CPU  21  continues the processing to add the coordinate data of the electronic pen  3  to the end of the stroke data (step S 13 , step S 17  to step S 29 ), there is a case in which the coordinate data of the electronic pen  3  is outside the effective area P. In this case (no at step S 21 ), the CPU  21  advances the processing to step S 31 . In a similar manner to the above description, because [Flg] is True as a result of the processing at step S 29  (yes at step S 31 ), the CPU  21  advances the processing to step S 33  and determines the stroke header (step S 33 ). The CPU  21  ends the generation of the stroke data and returns the processing to step S 11 . Specifically, at a point in time at which the coordinate data of the electronic pen  3  goes outside the effective area P while the user is writing the information, the CPU  21  generates a single independent set of stroke data based on the information written by the user up to that point. 
     Even when the user further continues writing the information in a state in which the coordinate data of the electronic pen  3  is outside the effective area P, the ASIC  28 A and the ASIC  29 A continue to output the pen down signal (yes at step S 13 ). As a result, the CPU  21  acquires the coordinate data and stores the coordinate data in [NowPoint] (step S 17 , step S  19 ). As the coordinate data of [NowPoint] is outside the effective area P (no at step S 21 ), the CPU  21  determines whether or not [Flg] is True (step S 31 ). As the CPU  21  set [Flg] to zero (no at step S 31 ) in the processing at step S 11  performed when the coordinate data of the electronic pen  3  moved outside of the effective area P, the CPU  21  returns the processing to step S 13 . The CPU  21  repeats the processing at step S 13 , step S 17  to step S 21  and step S 31  and stands by until the user finishes writing the information and the pen up signal is received from the ASIC  28 A and/or the ASIC  29 A (step S 13 ) or until the coordinate data of [NowPoint] enters inside the effective area P (step S 21 ). Then, if the coordinate data of the electronic pen  3  once more enters inside the effective area P (yes at step S 21 ), the CPU  21  generates the stroke header (step S 25 ) and, in the same manner as described above, starts the processing that adds the coordinate data of the electronic pen  3  to the end of the stroke data. More specifically, in the writing of a series of information, when the coordinate data of the electronic pen  3  temporarily moves from inside the effective area P to outside the effective area P, and once more returns inside the effective area P, the CPU  21  treats the coordinate data that is outside the effective area P as invalid, and generates two independent sets of stroke data from the coordinate data inside the effective area P. 
     Further, as shown in  FIG. 4 , when the CPU  21  receives the pen down signal (yes at step S 13 ) while the CPU  21  is repeating the processing from step S 11  to step S 15  and standing by, when the CPU  21  has acquired the coordinate data (step S 17 ) and the coordinate data is outside the effective area P (no at step S 21 ), the CPU  21  repeats the processing at step S 13 , step S 17  to step S 21  and step S 31  and stands by, in the same manner as described above. Then, if the coordinate data of the electronic pen  3  enters inside the effective area P (yes at step S 21 ), the CPU  21  generates the stroke header (step S 25 ), and starts the processing that adds the coordinate data of the electronic pen  3  to the end of the stroke data. In other words, even if the user starts writing the information, using the electronic pen  3 , from outside the effective area P, the CPU  21  waits until the coordinate data of the electronic pen  3  enters inside the effective area P. Then, the CPU  21  generates the stroke header when the coordinate data of the electronic pen  3  enters inside the effective area P, and starts the processing that adds the coordinate data of the electronic pen  3  to the end of the stroke data. 
     The following looks at stroke data M 2  and M 3  shown in  FIG. 5  that is generated by the CPU  21  based on a character “S” written by the user on the paper medium  100  using the electronic pen  3 . The user presses the pen down at a point H 2  and starts to write the character “S.” The CPU  21  acquires coordinate data of the point H 2  (step S 17 ) based on the pen down signal (yes at step S 13 ). As the point H 2  is not inside the effective area P (no at step S 21 ), the CPU  21  treats the acquired coordinate data as invalid and does not generate the stroke data. Thus, the CPU  21  returns the processing to step S 13  and repeats the processing at step S 13 , step S 17  to step S 21  and step S 31 . The character “S” that the user starts writing from the point H 2  enters into the effective area P at a point B 1  (yes at step S 21 ). At that time, the CPU  21  generates the stroke header (step S 25 ), and adds the coordinate data to the stroke data (step S 27 ). After that, the CPU  21  repeatedly performs the processing at step S 13  and step S 17  to step S 29 , and adds the coordinate data based on the trajectory of the electronic pen  3  to the stroke data. The character “S” that is written by the user temporarily moves outside the effective area P at a point B 2  (no at step S 21 ). The CPU  21  determines the stroke header (step S 33 ) based on [Flg] set at step S 29  (yes at step S 31 ). The CPU  21  completes the stroke data M 2  in this manner and returns the processing to step S 11 . [Flg] is set to False (step S 11 ). 
     The user continues to write the character “S” without lifting the pen up while remaining outside the effective area P (yes at step S 13 , no at step S 21 ). The CPU  21  repeats the processing at step S 13 , step S 17  to step S 21  and step S 31 , treats the acquired coordinate data as invalid and does not generate the stroke data. The character “S” written by the user once more enters the effective area P at a point B 3  (yes at step S 21 ). At that time, the CPU  21  generates the stroke header (step S 25 ) and adds the coordinate data based on the trajectory of the electronic pen  3  to the stroke data, by repeating the processing at step S 13  and step S 17  to step S 29  in a similar manner. The user lifts the pen up at a point F 2  of the written character “S.” The CPU  21  determines the stroke header (step S 33 ) based on the pen up signal (no at step S 13 ), and completes the stroke data M 3 . In this manner, the CPU  21  generates the two sets of stroke data M 2  and M 3  as a result of the fact that the character “S” written by the user moves outside the effective area P during the writing. The stroke data M 2  and M 3  are each formed by the coordinate data inside the effective area P. 
     As explained above, the CPU  21  of the information input device  1  of the present embodiment does not add the coordinate data to the stroke data when the coordinate data of [NowPoint] is outside the effective area P. Specifically, even if the CPU  21  acquires, from the ASIC  28 A and the ASIC  29 A, the coordinate data based on a result of a position detected by the sensor boards  71  and  72  that is inside the ineffective area D or is further to the outside of the ineffective area D (outside the detection areas  71 A and  72 A), the CPU  21  does not include that coordinate data in the stroke data. When the electronic pen  3  is positioned outside the detection areas  71 A and  72 A, depending on a sensitivity of the sensor boards  71  and  72 , the CPU  21  may acquire coordinate data representing a trajectory that is not intentional by the user. However, with the configuration of the present embodiment, this type of coordinate data is not included in the stroke data and thus it is possible to generate the accurate stroke data. Further, by including the coordinate data inside the ineffective area D in data to be excluded from the stroke data information, it is possible to further improve the accuracy of the stroke data. 
     In addition, when the writing using the electronic pen  3  is initially performed inside the effective area P, temporarily moves outside the effective area P and is then once more performed inside the effective area P, there is a case in which, in the stroke data, the coordinate data immediately before moving outside the effective area P from inside the effective area P, and the coordinate data immediately after moving inside the effective area P from outside the effective area P are treated as continuous data. In this case, depending on an application using the stroke data, it is possible that the coordinate data immediately before moving outside the effective area P from inside the effective area P and the coordinate data immediately after moving inside the effective area P from outside the effective area P may be connected by a line segment, or the like, that connects the two sets of coordinate data in a straight line. Thus, by independently forming the stroke data for each set of a series of coordinate data based on the writing performed inside the effective area P, it is possible to more accurately reproduce the trajectory of the electronic pen  3  that is reproduced by the stroke data. 
     In addition, by adding the stroke header to the stroke data, the information input device  1  can generate the stroke data as the single independent information and not simply as the aggregate of the coordinate data. 
     Further, the CPU  21  acquires the coordinate data output by the ASIC  28 A and the ASIC  29 A during the period from when the CPU  21  receives the pen down signal to when the CPU  21  receives the pen up signal. In addition, the CPU  21  stores the acquired coordinate data based on the result of the determination as to whether the coordinate data is included in the effective area P. As a result, the CPU  21  obtains the stroke data from which the unnecessary coordinate data is excluded. In this manner, the accuracy of the stroke data can be even further improved. 
     It should be noted that the present disclosure is not limited to the above-described embodiment, and various modifications are possible. For example, in the above-described embodiment, the CPU  21  generates the stroke header when the coordinate data based on the trajectory of the electronic pen  3  enters into the effective area P from outside the effective area P. However, the present disclosure is not limited to this mode. For example, the CPU  21  may constantly prepare to generate the stroke data by generating the stroke header in the processing at step S 11 . In this case, it is possible to omit the determination processing at step S 23 , and it is thus possible to reduce the load on the CPU  21  in the execution of the main processing. 
     Further, in the above-described embodiment, the information input device  1  uses the known electromagnetic induction method to detect the position at which the electronic pen  3  approaches. However, the information input device  1  may use a resistive membrane method (a so-called pressure-sensitive method), an electrostatic capacitance method or another method to detect the approach or the contact of the electronic pen  3  on the housings  8 L and  8 R that house the sensor boards  71  and  72 . Further, the structure, the size, the format and the material etc. of the paper medium  100  are not limited to the above-described embodiment. 
     In addition, the ASIC  28 A and the ASIC  29 A generate the coordinate data based on the position of the electronic pen  3  detected by the sensor boards  71  and  72  and output the coordinate data to the CPU  21  of the main board  20 . However, the present disclosure is not limited to this mode. For example, the ASIC  28 A and the ASIC  29 A may perform voltage conversion on the electric current flowing through the loop coils of each of the sensor boards  71  and  72 , perform A/D conversion on an obtained voltage value and output the converted voltage value to the CPU  21 . The CPU  21  may generate the coordinate data based on the voltage value obtained from each of the ASIC  28 A and the ASIC  29 A. 
     A “processor” of the present disclosure is not limited to the CPU  21 . That is, it goes without saying that an ASIC or a field programmable gate array (an FPGA) can be favorably used as the “processor” of the present disclosure, in place of the CPU  21 . Alternatively, it goes without saying that a computer that is connected to the information input device  1  can be favorably used as the “processor.” 
     The apparatus and methods described above with reference to the various embodiments are merely examples. It goes without saying that they are not confined to the depicted embodiments. While various features have been described in conjunction with the examples outlined above, various alternatives, modifications, variations, and/or improvements of those features and/or examples may be possible. Accordingly, the examples, as set forth above, are intended to be illustrative. Various changes may be made without departing from the broad spirit and scope of the underlying principles.