Abstract:
An electronic device used to identify loci containing more than one stroke. This electronic device utilizes a ball rotation sensor to detect the position and movement while it is in contact with a surface and an acceleration sensor when the device is not in contact with the surface. Further, this device is able to correct for inaccuracies in the acceleration sensor utilizing data received from the ball rotation sensor. This correction is based on a calculated detection error determined while the ball rotation sensor is active. The correction occurs when the device is again no longer in contact with the surface and again utilizing the acceleration sensor to determine position.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an electronic pen device and a character recognition method employing the same, and more particularly, it relates to an electronic pen device allowing pen-based character entry and a character recognition method employing the same. 
     2. Description of the Prior Art 
     In general, a method of detecting the coordinates of a character handwritten on a tablet with a pen and recognizing the character on the basis of a detection result is widely known as a method of pen-based character entry. However, this method has only limited uses due to the requirement for a large-sized member, i.e., the tablet. 
     In this regard, various devices for inputting coordinates without employing tablets are recently proposed. For example, a pen-type input device inputting coordinates on the basis of a detection result in a ball rotation sensor provided on a pen point is proposed. For example, Japanese Patent Laying-Open No. 7-281827 (1995) discloses such an input device employing a ball rotation sensor. 
     FIG. 10 is a perspective view showing the appearance of the conventional input device  140  employing a ball rotation sensor disclosed in Japanese Patent Laying-Open No. 7-281827, and FIG. 11 is a sectional view showing the internal structure of the conventional input device  140  employing a ball rotation sensor shown in FIG.  10 . FIG. 12 is a perspective view showing the structure of a rotation detection part of the conventional input device  140  employing a ball rotation sensor shown in FIG. 10, and FIG. 13 is a perspective view for illustrating a busy condition of the conventional input device  140  employing a ball rotation sensor shown in FIG.  10 . 
     Referring to FIGS. 10 and 11, the conventional input device  140  employing a ball rotation sensor includes a substantially pen-shaped body part  110 , a spherical rotator  112 , an annular ring  136 , a rotation detection part  114 , an electric circuit part  132 , a manual switch  134  and a cable  142 . The body part  110  is in the form of a cylinder having an open lower end. The rotation detection part  114  and the electric circuit part  132  are arranged in the body part  110 . The rotation detection part  114  rotatably holds the spherical rotator  112  and detects the direction and the amount of rotation of the spherical rotator  112 . The annular ring  136  has a function of fixing the electric circuit part  132  and the rotation detection part  114  to the body part  110 . The electric circuit part  132  amplifies outputs detected by the rotation detection part  114  and transmits the amplified outputs to a computer. The manual switch  134  is provided on the side surface of the body part  110 , and employed for defining input coordinates. 
     With reference to FIG. 12, the detailed structure of the rotation detection part  114  is now described. The rotation detection part  114  is provided with a cylindrical case  116 . A small ball  118  is set in the case  116  to rotate in correspondence to rotation of the spherical rotator  112 . The small ball  118  is in contact with rollers  120  and  122  having rotation axes intersecting each other at an angle of 90°. Slit disks  124  and  126  having a number of radially extending slits formed at regular intervals are fixed to the rollers  120  and  122  respectively. An optical sensor  128  detects the direction and the amount of rotation of the slit disk  124 , and an optical sensor  130  detects the direction and the amount of rotation of the slit disk  126 . 
     Each of the optical sensors  128  and  130  includes two photodetectors arranged with a phase difference of 90° with respect to the interval between the slits and a light emitting device opposed to the two photodetectors through the slits. 
     In operation, the two photodetectors provided on each of the optical sensors  128  and  130  detect light passing through the slits respectively for determining the directions of rotation of the rollers  120  and  122  from the phase difference between the detected signals. The amounts of rotation of the slit disks  124  and  126  are obtained by accumulating the numbers of output pulses from the photodetectors. Further, composition of vectors of the amounts of rotation obtained by the two optical sensors  128  and  130  is performed thereby obtaining the directions and the amounts of rotation of the small ball  118  and the spherical rotator  112 . 
     The conventional input device  140  employing a ball rotation sensor having the aforementioned structure is connected to a computer mainframe  144  through the cable  142  as shown in FIG.  13 . The computer mainframe  114  includes a display part  146  and a keyboard  148 . When the input device  140  is in use, the display part  146  displays a cursor (pointer)  150 . This cursor  150  moves following rotation of the spherical rotator  112  of the input device  140 . More specifically, the cursor  150  moves in the same direction as the direction of rotation of the spherical rotator  112  by a distance proportionate to the amount of rotation of the spherical rotator  112 . 
     In order to input a character with the input device  140 , the spherical rotator  112  provided on the pen point of the input device  140  is brought into an entry plane (plane for writing characters or the like) for writing a prescribed character with the input device  140 , and the switch  134  is pressed so that the written character is input in the computer mainframe  144 . 
     In the aforementioned conventional input device  140  employing a ball rotation sensor, however, the spherical rotator  112 , which rotates when the pen point is in contact with the entry plane (contact state), does not rotate when the pen point separates from the entry plane (noncontact state). Therefore, a locus in the noncontact state cannot be detected. More specifically, when a character “+” is written as shown in FIG. 14, the locus from end coordinates  161  of the transverse line to start coordinates  162  of the vertical line cannot be detected and hence it is difficult to recognize to which one of those shown in FIGS. 15 to  17  this character belongs. In other words, it is difficult for the conventional input device  140  employing a ball rotation sensor to recognize a character, which cannot be written with one stroke, formed by a locus in a contact state and a locus in a noncontact state, although the input device  140  can detect a character, which can be written with one stroke, formed by only a locus in a contact state. 
     In order to cope with this problem, there has generally been proposed a method of writing a character, which cannot be written with one stroke by a general writing method, with one stroke by a specific writing method without separating a pen point from an entry plane and performing character recognition on the character written with one stroke. Such a method is disclosed in Pilot Handbook (1996 by U.S. Robotics, Inc.), Chapter 2 (Working with Pilot), pp. 22 to 31, for example. In this proposed method, however, a specific way of writing is necessary for writing a character with one stroke, and hence the writer must abandon a familiar way of writing. Consequently, this method imposes a burden on the writer, and readily leads to miswriting. Thus, it is difficult to employ this method. 
     As another exemplary device for recognizing a character without employing a tablet, a pen-type input device recognizing a character with an acceleration sensor is generally proposed. For example, Japanese Patent Laying-Open No. 6-67799 (1994) discloses such an input device employing an acceleration sensor. The conventional input device employing an acceleration sensor detects both of a locus in a contact state and that in a noncontact state with the acceleration sensor. 
     FIG. 18 is a perspective view showing the structure of a conventional input device  201  employing acceleration sensors, and FIG. 19 is a block diagram showing the electrical structure of a signal processing circuit of the conventional input device  201  employing acceleration sensors shown in FIG.  18 . FIG. 20 is a schematic diagram for illustrating a busy condition of the conventional input device  201  employing acceleration sensors shown in FIG.  18 . 
     Referring to FIG. 18, the conventional input device  201  employing acceleration sensors includes a pen body  216 , an X-directional acceleration sensor  206  detecting acceleration in a direction X, a Y-directional acceleration sensor  207  detecting acceleration in a direction Y, a signal processing circuit  220  and a writing part  208 . The Y-directional acceleration sensor  207  is arranged to be orthogonal to the X-directional acceleration sensor  206 . The signal processing circuit  220  calculates coordinate values on the basis of the acceleration detected by the X-directional acceleration sensor  206  and that detected by the Y-directional acceleration sensor  207 . 
     As shown in FIG. 19, the signal processing circuit  220  includes an acceleration detection part  209 , an integration circuit  210 , a voltage-to-frequency conversion circuit  211 , a direction discrimination circuit  212  and an output circuit  213 . The acceleration detection part  209  detects acceleration signals output from the X-directional acceleration sensor  206  and the Y-directional acceleration sensor  207 , and the integration circuit  210  integrates the acceleration signals and converts the same to speed signals. The voltage-to-frequency conversion circuit  211  has a function of converting voltage values as the speed signals obtained in the integration circuit  210  to frequencies of pulses. In this case, the numbers of the pulses indicate the amounts of movement, and the frequencies of the pulses correspond to the velocities of movement. 
     The direction discrimination circuit  212  detects the directions of movement of the input device  201  on the basis of the acceleration signals detected by the acceleration detection part  209 . The output circuit  213  outputs the directions and the amounts of movement input from the direction discrimination circuit  212  and the voltage-to-frequency conversion circuit  211  respectively. Output signals from the output circuit  213  are input in a personal computer  215  through an interface  214 . 
     With reference to FIG. 20, operations of the conventional input device  201  employing acceleration sensors are now described. When a character or the like is written on a recording paper  203  with the input device  201 , a display of a computer  202  displays the character or the like. More specifically, the conventional input device  201  employing acceleration sensors detects both of acceleration in a state (contact state) where a pen point is in contact with the recording paper  203  and that in another state (noncontact state) where the pen point is not in contact with the recording paper  203  when writing a character on the recording paper  203 . On the basis of the values of the detected acceleration, the input device  201  calculates the amounts and the directions of movement in the contact state and the noncontact state. The input device  201  recognizes the character on the basis of the calculated directions and amounts of movement, and the display of the computer  202  displays the recognized character. 
     In the conventional input device  201  employing acceleration sensors, however, the acceleration sensors  206  and  207  are inferior in accuracy, particularly in detection accuracy for a fine loop and for refraction or bending, to the aforementioned ball rotation sensor in measurement of acceleration when the pen point is in contact with an entry plane. In the conventional input device  201  employing acceleration sensors, therefore, it is difficult to discriminate “y” from “g” or “U” from “V”, for example. 
     More specifically, FIG. 22 shows a coordinate detection result obtained by the conventional input device  201  employing acceleration sensors when detecting a character “V” shown in FIG.  21 . With the coordinate detection result shown in FIG. 22, it is difficult to identify whether a bottom portion  250  of the character is refracted or bent. When writing the character “V” shown in FIG.  21  and detecting this character with the input device  201 , therefore, it is difficult to identify whether this character is “U” or “V”. 
     Further, FIG. 23 shows a detection result on the locus of a circle, written with one stroke with a ruler, for example, detected by the conventional input device  201  employing acceleration sensors. Referring to FIG. 23, the start point and the end point of the circle are not connected with each other. Thus, it is understood difficult to detect a fine stroke in a contact state with the acceleration sensors  206  and  207 . This example is disclosed in Transactions of the Institute of Electronics, Information and Communication Engineers (IEICE), D-I, Vol. J76-D-I, No. 10, October 1993, pp. 541 to 543, for example. 
     As hereinabove described, it is difficult for the conventional input device  140  employing a ball rotation sensor to detect the loci of a character, which cannot be written with one stroke, formed by a locus in a contact state and that in a noncontact state, although the input device  140  can detect the locus of a character, which can be written with one stroke, formed only by a locus in a contact state. In the conventional input device  201  employing acceleration sensors detecting both of a locus in a contact state and that in a noncontact state with the acceleration sensors  206  and  207 , on the other hand, it is difficult to recognize a fine stroke in a contact state since the acceleration sensors  206  and  207  are inferior in accuracy to the ball rotation sensor. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide an electronic pen device capable of accurately obtaining a locus drawn on an entry plane with a pen point even if the locus cannot be written with one stroke. 
     Another object of the present invention is to provide a character recognition method employing an electronic pen device capable of accurately recognizing a character written on an entry plane with a pen point even if the character cannot be written with one stroke. 
     An electronic pen device according to a first aspect of the present invention comprises a first measuring part, a contact state determination part, a second measuring part and a movement locus operation part. The first measuring part measures movement loci of a pen point in directions X and Y on the basis of a detection result in a ball rotation sensor detecting rotation of a ball provided on the pen point. The contact state determination part determines whether the pen point is in a contact state or in a noncontact state with an entry plane. The second measuring part measures movement loci of the pen point in the directions X and Y on the basis of acceleration detected by an acceleration sensor. The movement locus operation part obtains a contact movement locus of the pen point on the basis of a measurement result in the first measuring part when the contact state determination part determines that the pen point is in the contact state with the entry plane, while obtaining a noncontact movement locus of the pen point on the basis of a measurement result in the second measuring part when the contact state determination part determines that the pen point is in the noncontact state with the entry plane. 
     Due to the aforementioned structure, the electronic pen device according to the aforementioned aspect obtains the contact movement locus of the pen point on the basis of the detection result in the ball rotation sensor having relatively high accuracy in the contact state of the pen point and the entry plane requiring detection of a fine stroke, while obtaining the noncontact movement locus of the pen point on the basis of the detection result in the acceleration sensor in the noncontact state where the pen point separates from the entry plane. Thus, the electronic pen device can accurately obtain movement loci, which cannot be written with one stroke, having a contact movement locus and a noncontact movement locus. 
     In the electronic pen device according to the aforementioned aspect, the movement locus operation part may employ end coordinates of a noncontact movement locus obtained on the basis of a measurement result in the second measuring part in the immediately preceding noncontact state as start coordinates of each contact movement locus and employ end coordinates of a contact movement locus obtained on the basis of a measurement result in the first measuring part in the immediately preceding contact state as start coordinates of each noncontact movement locus. Thus, continuity of the coordinates in the contact state and those in the noncontact state is ensured, whereby the movement loci can be readily obtained. 
     The electronic pen device according to the aforementioned aspect may further comprise a correction part correcting the measurement result in the second measuring part in the noncontact state on the basis of a measurement result in the first measuring part in a first period in the contact state of the pen point and the entry plane and a measurement result in the second measuring part in the first period in the contact state. Due to this structure, the correction part improves the measurement accuracy of the acceleration sensor in the noncontact state, and the movement loci of the pen point can consequently be more accurately obtained. 
     In the electronic pen device according to the aforementioned aspect, the contact state determination part may determine whether the pen point is in the contact state or in the noncontact state with the entry plane on the basis of a result of detection of pressing force applied from the pen point. Further, the contact state determination part may determine whether the pen point is in the contact state or in the noncontact state with the entry plane on the basis of presence/absence of rotation of a ball detected by a ball rotation sensor and presence/absence of acceleration detected by the acceleration sensor. 
     The electronic pen device according to the aforementioned aspect may further comprise a character recognition part recognizing a character drawn with the pen point on the entry plane on the basis of a contact movement locus for a single character obtained by the movement locus operation part. In this case, the electronic pen device may further comprise a telephone circuit for making communication with the destination of transmission/receiving, a microphone for inputting a transmission tone, a speaker for outputting a receiving tone, and a call control part obtaining a telephone number of the destination of transmission on the basis of a character string recognized by the character recognition part and outputting the obtained telephone number to the telephone circuit for allowing the telephone circuit to make a call. Due to this structure, the electronic pen device can be readily used as a portable telephone set, while the character is recognized on the basis of the accurately obtained locus and hence it is possible to effectively prevent transmission to a wrong destination. 
     A telephone set employing an electronic pen device according to another aspect of the present invention comprises a first measuring part, a contact state determination part, a second measuring part, a movement locus operation part, a character recognition part, a telephone circuit, a microphone, a speaker and a call control part. The first measuring part measures movement loci of a pen point in directions X and Y on the basis of a detection result in a ball rotation sensor detecting rotation of a ball provided on the pen point. The contact state determination part determines whether the pen point is in a contact state or in a noncontact state with an entry plane. The second measuring part measures movement loci of the pen point in the directions X and Y on the basis of acceleration detected by an acceleration sensor. The movement locus operation part obtains a contact movement locus of the pen point on the basis of a measurement result in the first measuring part when the contact state determination part determines that the pen point is in the contact state with the entry plane, while obtaining a noncontact movement locus of the pen point on the basis of a measurement result in the second measuring part when the contact state determination part determines that the pen point is in the noncontact state with the entry plane. The character recognition part recognizes a character drawn with the pen point on the entry plane on the basis of a contact movement locus for a single character obtained by the movement locus operation part. The telephone circuit is employed for making communication with the destination of transmission/receiving, the microphone is employed for inputting a transmission tone, and the speaker is employed for outputting a receiving tone. The call control part obtains a telephone number of the destination of transmission on the basis of a character string recognized by the character recognition part and outputs the obtained telephone number to the telephone circuit for allowing the telephone circuit to make a call. 
     Due to this structure, the contact movement locus of the pen point is obtained on the basis of a detection result in the ball rotation sensor having relatively high accuracy in the contact state of the pen point and the entry plane requiring detection of a fine stroke while the noncontact movement locus of the pen point is obtained on the basis of a detection result in the acceleration sensor in the noncontact state where the pen point and the entry plane separate from each other, whereby the movement loci can be accurately obtained also in the case of a character, having a contact movement locus and a noncontact movement locus, which cannot be written with one stroke. Thus, it is possible to provide a telephone set employing an electronic pen device which can effectively prevent transmission to a wrong destination by recognizing the character on the basis of the accurately obtained movement loci. 
     In the structure of the aforementioned telephone set employing an electronic pen device, the movement locus operation part may employ end coordinates of a noncontact movement locus obtained on the basis of a measurement result in the second measuring part in the immediately preceding noncontact state as start coordinates of each contact movement locus and employ end coordinates of a contact movement locus obtained on the basis of a measurement result in the first measuring part in the immediately preceding contact state as start coordinates of each noncontact movement locus. Thus, continuity of the coordinates in the contact state and those in the noncontact state is ensured, whereby the movement loci can be readily obtained. 
     In the aforementioned structure, the telephone set employing an electronic pen device may further comprise a correction part correcting the measurement result in the second measuring part in the noncontact state on the basis of a measurement result in the first measuring part in a first period in the contact state of the pen point and the entry plane and a measurement result of the second measuring part in the first period in the contact state. Due to this structure, the correction part improves the measurement accuracy of the acceleration sensor in the noncontact state, and the movement loci of the pen point can consequently be more accurately obtained. Thus, the accuracy of character recognition can be further improved, and it is consequently possible to provide a telephone set employing an electronic pen device which can further effectively prevent transmission to a wrong destination. 
     A character recognition method employing an electronic pen device according to still another aspect of the present invention comprises steps of detecting a movement locus of a pen point with a ball rotation sensor detecting rotation of a ball provided on the pen point, detecting a movement locus of the pen point with an acceleration sensor, and performing character recognition on the basis of detection results in the ball rotation sensor and the acceleration sensor. Due to this structure, it is possible to accurately obtain movement loci of a character, which cannot be written with one stroke, having a contact movement locus and a noncontact movement locus by obtaining a contact movement locus of the pen point on the basis of a detection result in the ball rotation sensor having relatively high accuracy in a contact state of the pen point and an entry plane requiring detection of a fine stroke and obtaining a noncontact movement locus of the pen point on the basis of a detection result in the acceleration sensor in a noncontact state where the pen point and the entry plane separate from each other. The character is recognized on the basis of the accurately obtained loci, whereby the accuracy of character recognition can be improved. 
     In the aforementioned character recognition method employing an electronic pen device, the step of detecting the movement locus of the pen point with the ball rotation sensor may include steps of detecting that the pen point is in the contact state with the entry plane and detecting the contact movement locus of the pen point with the ball rotation sensor in the contact state, and the step of detecting the movement locus of the pen point with the acceleration sensor may include steps of detecting that the pen point is in the noncontact state with the entry plane and detecting the noncontact movement locus of the pen point with the acceleration sensor in the noncontact state. In this structure, further, the step of detecting the contact movement locus may include a step of employing end coordinates of a noncontact movement locus obtained on the basis of a detection result in the acceleration sensor in the immediately preceding noncontact state as start coordinates of each contact movement locus, and the step of detecting the noncontact movement locus may include a step of employing end coordinates of a contact movement locus obtained on the basis of a detection result in the ball rotation sensor in the immediately preceding contact state as start coordinates of each noncontact movement locus. Thus, continuity of the coordinates in the contact state and those in the noncontact state is ensured, whereby the movement loci can be readily obtained. In the aforementioned structure, further, the character recognition method may further comprise a step of correcting the detection result in the acceleration sensor in the noncontact state on the basis of a detection result in the ball rotation sensor in a first period in the contact state of the pen point and the entry plane and a detection result in the acceleration sensor in the first period in the contact state. In this case, the detection accuracy of the acceleration sensor in the noncontact state is improved, whereby the movement loci of the pen point can consequently be more accurately obtained. Thus, the accuracy for character recognition can be further improved. 
    
    
     The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic diagram showing the structure of an electronic pen device (pen-type telephone set) according to a first embodiment of the present invention; 
     FIG. 2 is a flow chart for illustrating operations of the electronic pen device according to the first embodiment shown in FIG. 1; 
     FIG. 3 is a model diagram for illustrating a method of obtaining an error in acceleration detected by an acceleration sensor of the electronic pen device according to the first embodiment; 
     FIG. 4 is a graph showing an acceleration error function of the electronic pen device according to the first embodiment; 
     FIG. 5 is a flow chart for illustrating a method of obtaining (X, Y) coordinates from corrected acceleration α 2  in the electronic pen device according to the first embodiment; 
     FIG. 6 is a schematic diagram showing an exemplary character accurately identifiable with the electronic pen device according to the first embodiment; 
     FIG. 7 is a schematic diagram showing another exemplary character accurately identifiable with the electronic pen device according to the first embodiment; 
     FIG. 8 is a schematic diagram showing the structure of an electronic pen device (pen-type telephone set) according to a second embodiment of the present invention; 
     FIG. 9 is a flow chart for illustrating a contact state determination method in the electronic pen device according to the second embodiment shown in FIG. 8; 
     FIG. 10 is a perspective view showing the appearance of a conventional input device employing a ball rotation sensor; 
     FIG. 11 is a sectional view showing the internal structure of the conventional input device employing a ball rotation sensor shown in FIG. 10; 
     FIG. 12 is a perspective view showing the structure of a rotation detection part of the conventional input device employing a ball rotation sensor shown in FIG. 10; 
     FIG. 13 is a perspective view for illustrating a busy condition of the conventional input device employing a ball rotation sensor; 
     FIG. 14 is a schematic diagram showing a character hardly identifiable with the conventional input device employing a ball rotation sensor; 
     FIGS. 15 to  17  are schematic diagrams for illustrating a problem in the case of identifying the hardly identifiable character shown in FIG. 14 with the conventional input device employing a ball rotation sensor; 
     FIG. 18 is a perspective view showing the structure of a conventional input device employing acceleration sensors; 
     FIG. 19 is a block diagram showing the electrical structure of a signal processing circuit of the conventional input device employing acceleration sensors shown in FIG. 18; 
     FIG. 20 is a schematic diagram showing a busy condition of the conventional input device employing acceleration sensors; 
     FIG. 21 is a schematic diagram showing a character hardly identifiable with the conventional input device employing acceleration sensors; 
     FIG. 22 is a schematic diagram for illustrating a problem in the case of identifying the hardly identifiable character shown in FIG. 21 with the conventional input device employing acceleration sensors; and 
     FIG. 23 is a schematic diagram showing a coordinate detection result obtained by detecting the locus of a circle drawn with one stroke with a ruler by the conventional input device employing acceleration sensors. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments of the present invention are now described with reference to drawings. 
     First Embodiment 
     With reference to FIG. 1, the structure of an electronic pen device (pen-type telephone set)  1  according to a first embodiment of the present invention is described. The electronic pen device  1  according to the first embodiment includes a ball  22   a  rotatably provided on a pen point, a ball rotation sensor  22 , a contact state determination part  25 , an acceleration sensor  23 , a CPU  30 , a memory  32  and another memory  35 . The ball rotation sensor  22  detects rotation of the ball  22   a . This ball rotation sensor  22  has a structure similar to that of the ball rotation sensor part of the conventional input device shown in FIG.  12 . The acceleration sensor  23  includes an X-directional acceleration sensor  23   a  detecting acceleration in a direction X and a Y-directional acceleration sensor  23   b  detecting acceleration in a direction Y. 
     The contact state determination part  25  detects pressing force applied to the ball  22   a , thereby determining whether the pen point is in a contact state or in a noncontact state with an entry plane. The memory  32  stores a main control program, a character recognition program etc. of the CPU  30 . The memory  35  stores coordinates, an acceleration correction table, a result of character recognition, a correspondence table of names and telephone numbers and the like. 
     The electronic pen device  1  according to the first embodiment further comprises a telephone circuit  50  for making communication with the destination of transmission/receiving, a microphone  52  for inputting a transmission tone, a speaker  53  for outputting a receiving tone, and an antenna  35 . 
     With reference to FIG. 1, schematic operations of the electronic pen device  1  according to the first embodiment are now described. In the electronic pen device  1  according to the first embodiment, the ball rotation sensor  22  first detects rotation of the ball  22   a  provided on the pen point. The X-directional acceleration sensor  23   a  and the Y-directional acceleration sensor  23   b  detect acceleration of the pen point. The contact state determination part  25  detects pressing force applied to the ball  22   a , thereby determining whether the pen point is in a contact state or in a noncontact state with the entry plane. The detection results in the ball rotation sensor  22  and the acceleration sensor  23  and the result of determination by the contact state determination part  25  are input in the CPU  30 . 
     On the basis of the detection results in the contact state determination part  25  and the ball rotation sensor  22 , the CPU  30  measures movement loci (contact movement loci) of the pen point in the directions X and Y in the contact state of the pen point and the entry plane. On the basis of the detection results in the contact state determination part  25  and the acceleration sensor  23 , the CPU  30  measures movement loci (noncontact movement loci) of the pen point in the directions X and Y in the noncontact state of the pen point and the entry plane. 
     Further, the CPU  30  calculates acceleration in the contact state from the contact movement locus obtained with the ball rotation sensor  22  and compares this acceleration with that detected by the acceleration sensor  23  in the same contact state, thereby calculating a detection error of the acceleration sensor  23 . On the basis of the detection error of the acceleration sensor  23 , the CPU  30  corrects the detection result in the acceleration sensor  23  in the noncontact state for obtaining a noncontact movement locus. On the basis of the obtained noncontact locus and the contact movement locus measured on the basis the detection result in the ball rotation sensor  22 , the CPU  30  obtains a contact movement locus of the pen point for a single character while recognizing the character drawn with the pen point on the basis of the obtained contact movement locus for the single character. Further, the CPU  30  obtains a telephone number on the basis of a recognized character string and outputs the obtained telephone number to the telephone circuit  50  for allowing the telephone circuit  50  to call the destination of transmission. 
     As hereinabove described, the electronic pen device  1  according to the first embodiment obtains the contact movement locus of the pen point on the basis of the detection result in the ball rotation sensor  22  having relatively high accuracy in the contact state of the pen point and the entry plane requiring detection of a fine stroke while obtaining the noncontact movement locus of the pen point on the basis of the detection result in the acceleration sensor  23  in the noncontact state where the pen point and the entry plane separate from each other. Thus, it is possible to accurately obtain movement loci of a character, which cannot be written with one stroke, having a contact movement locus and a noncontact movement locus. 
     According to the first embodiment, further, it is possible to further improve the measurement accuracy for the noncontact movement locus by comparing the acceleration in the contact state obtained from the detection result in the ball rotation sensor  22  with the acceleration in the acceleration sensor  23  in the same contact state thereby correcting the detection result of acceleration in the noncontact state detected by the acceleration sensor  23  and measuring the noncontact movement locus. Consequently, the movement loci can be more accurately obtained. 
     As hereinabove described, the electronic pen device  1  according to the first embodiment comprises the telephone circuit  50 , the microphone  52 , the speaker  53  and the antenna  55 . Thus, the electronic pen device  1  can be readily used as a portable telephone set, while the character is recognized on the basis of accurately obtained loci and hence it is possible to effectively prevent transmission to a wrong destination. 
     The details of operations of the electronic pen device (pen-type telephone set)  1  according to the first embodiment are now described with reference to FIGS. 2 to  5 . Referring to a flow chart shown in FIG. 2, a timer is cleared at a step S 1 . This timer is employed for regarding that a single character is completely written when the pen point separates from the entry plane in excess of a constant time. Thereafter whether or not the timer makes a time-out is determined at a step S 2 . If the timer is determined as making no time-out at the step S 2 , whether the pen point is in contact with the entry plane (pen-down state) or not in contact with the entry plane (pen-up state) is determined at a step S 3 . If the pen point is determined as in the pen-down state at the step S 3 , processing of steps S 4  to S 8  is performed. 
     The processing of the steps S 4  to S 8  is performed in a period (contact state) when the contact state determination part  25  determines that the pen point is in contact with the entry plane. In this period, the ball rotation sensor  22  detects rotation of the ball  22   a  provided on the pen point, thereby obtaining movement loci (contact movement loci) in the directions X and Y, which are a set of (X, Y) coordinates, at a step S 4 . At a step S 5 , the information on the pen-down state (contact state) and the aforementioned (X, Y) coordinates are stored in a coordinate memory in a prescribed area of the memory  35 . The contact movement loci are measured from when the pen point comes into contact with the entry plane until when the pen point separates from the entry plane. The movement loci may be obtained with the ball rotation sensor  22  in a method similar to that in the conventional input device employing a ball rotation sensor shown in FIGS. 10 to  13 . 
     In the state (pen-down state) where the pen point is in contact with the entry plane, a timer for measuring a time in which the pen point separates from the entry plane is cleared at a step S 6 . Thereafter acceleration is calculated on the basis of the detection result in the ball rotation sensor  22  in the contact state at a step S 7 . In order to calculate acceleration α 1  on the basis of the detection result in the ball rotation sensor  22 , a velocity V 1  is obtained from a movement distance XL 1  in a prescribed time Δt, and a velocity V 2  is obtained from a movement distance XL 2  in a next prescribed time Δt, as shown in FIG.  3 . Then, the acceleration α 1  is obtained through the following equation (1): 
     
       
         α 1 =( V   2 − V   1 )/Δ t   (1) 
       
     
     Thereafter at a step S 8  of the flow chart shown in FIG. 8, a detection error Δβ 1  of the acceleration sensor  23  is calculated on the basis of the acceleration al obtained from the detection result in the ball rotation sensor  22  in the contact state and acceleration β 1  detected by the acceleration sensor  23  in the same contact state through the following equation (2): 
     
       
         Δβ 1 =β 1 −α 1   (2) 
       
     
     The calculated detection error Δβ 1  of the acceleration sensor  23  is stored in an error table formed in the memory  35 . The detection error Δβ 1  of the acceleration sensor  23  thus obtained per small time is accumulated in the error table, which consequently accumulates an acceleration error function “Δβ=F(β)” shown in FIG.  4 . In other words, the error table accumulates data univocally deciding the error Δβ from the detection result β in the acceleration sensor  23 . On the basis of the data in the error table, the detection result in the acceleration sensor in a next noncontact state is corrected. More specifically, corrected acceleration α 2  is calculated from the acceleration β detected by the acceleration sensor  23  in the noncontact state through the following equation (3): 
     
       
         α 2 =β− F (β)  (3) 
       
     
     The correction based on the data of the error table may be performed per locus as in the first embodiment, or per character or per start of use. 
     If the pen point is determined as in the pen-up state (noncontact state) at the step S 3  of the flow chart shown in FIG. 2, processing of steps S 9  to S 12  is performed. 
     The processing of the steps S 9  to S 12  is performed in a period (noncontact state) when the contact state determination part  25  determines that the pen point separates from the entry plane. In this period, the acceleration sensor  23  detects acceleration at the step S 9 . At the step S 10 , the detection result β of the acceleration is corrected through the above equation (3) with reference to the aforementioned error table, thereby calculating corrected acceleration α 2 . Then, at the step S 11 , movement loci (noncontact movement loci) in the directions X and Y, which are a set of (X, Y) coordinates, are obtained on the basis of the corrected acceleration α 2 . Thereafter the obtained noncontact movement loci and the information of the pen-up state are stored in the coordinate memory in the prescribed area of the memory  35  at the step S 12 . 
     A principle of obtaining the (X, Y) coordinates from the corrected acceleration α 2  at the step S 11  is now described in more detail with reference to FIG.  5 . At a step S 31  of a flow chart shown in FIG. 5, whether the state immediately preceding the pen-up state (noncontact state) is a pen-up state (noncontact state) or a pen-down state (contact state) is determined. If the state immediately preceding the pen-up state is determined as the pen-down state at the step S 31 , processing of steps S 32  and S 33  is performed. This processing is performed when the pen point changes from the pen-down state (contact state) to the pen-up state (noncontact state), for ensuring continuity between start coordinates of the non-contact state and end coordinates of the contact state immediately preceding the noncontact state. In other words, this processing is performed for employing the end coordinates of the immediately preceding contact state as the start coordinates of the successive noncontact state. 
     In this case, the coordinates immediately preceding the pen-up state are regarded as the coordinates (X 0 , Y 0 ) for starting the pen-up state at the step S 32 . Then, the initial velocity (V 0 x, V 0 y) for starting the pen-up state is calculated at the step S 33 . More specifically, the velocity in termination of the pen-down state is obtained on the basis of the difference between the coordinates immediately preceding the pen-up state and coordinates preceding these coordinates, for regarding the obtained velocity as the initial velocity (V 0 x, V 0 y) for starting the pen-up state. 
     Also when making transition from a pen-up state (noncontact state) to a pen-down state (contact state), processing similar to that of the steps S 32  and S 33  must be performed in order to ensure continuity between end coordinates in the noncontact state and start coordinates of the successive contact state. 
     If the state immediately preceding the pen-up state (noncontact state) is determined as a pen-up state (noncontact state) at the step S 31 , processing of a step S 34  is performed. This processing is performed when the pen-up state (noncontact state) is continuous. In this case, coordinates (Xn, Yn) are calculated at the step S 34  on the basis of preceding coordinates (Xn−1, Yn−1), the initial velocity (V 0 x, V 0 y), corrected acceleration (α 2 x, α 2 y) and a detection time interval At through the following equations (4) and (5): 
     
       
           Xn=Xn −1 +V   0   x·Δt +α 2   x ( t )·Δ t   2   (4) 
       
     
     
       
           Yn=Yn −1 +V   0   y·Δt +α 2   y ( t )·Δ t   2   (5) 
       
     
     The movement loci (noncontact movement loci) in the directions X and Y, which are a set of (X, Y) coordinates obtained in the aforementioned manner, and the information of the pen-up state are stored in the coordinate memory in the prescribed area of the memory  35  at the step S 12  of the flow chart shown in FIG.  2 . 
     If the time starting counting every termination of the contact state is determined as making a time-out at the step S 2  of the flow chart shown in FIG. 2, it is regarded that a single character is completely written and processing of steps S 13  to S 21  is performed. In this case, whether or not a character (at least one pen-down state) is present at the step S 13 . If it is determined that a character is present, a movement locus (contact movement locus) in the contact state of the pen point for the single character is obtained on the basis of the data of contact movement loci and noncontact movement loci stored in the coordinate memory at the step S 14 , for performing character recognition on the basis of the obtained contact movement locus. The CPU  30  performs this character recognition. 
     In order to recognize the character from the contact movement locus, the coordinate points of the written character, the direction of the stroke on each coordinate point and the rotational direction characteristic on each coordinate point are detected. The direction of the stroke is detected with reference to four directions including “horizontal”, “vertical”, “right-downward oblique” and “left-downward oblique”. As to the rotational direction characteristic, on which position the writing direction is bent clockwise or anticlockwise is detected. Character recognition is performed by comparing the detection results of the coordinate points, the direction of the stroke and the rotational direction characteristic with dictionary data. 
     Thus, also as to characters such as “g”, “y” and “9” having generally similar forms and local differences, collation of the local differences can be reinforced with rotational direction characteristics by performing character recognition in consideration of not only directions of strokes but also rotational direction characteristics of writing. Also when manually writing such similar characters, therefore, the accuracy of character recognition can be improved. Further, the rotational direction characteristic is detected by simply separately arranging two characteristic spaces of “clockwise” and “anticlockwise”, and hence the operation processing is not much complicated. 
     When employing the movement locus measuring method and the character recognition method of the electronic pen device according to the first embodiment, a character shown in FIG. 6, which cannot be written with one stroke, having both of a contact movement locus and a noncontact movement locus can be accurately recognized. Referring to FIG. 6, solid lines show coordinate detection parts (contact movement loci) with the ball rotation sensor  22 , and a dotted line shows a coordinate detection part (noncontact movement locus) with the acceleration sensor  23 . In order to write the character “+” shown in FIG. 6, the pen point is first brought into contact with the entry plane (contact state) to draw the horizontal line (A). Then, the pen point is separated from the entry plane (noncontact state) and moved to the start point for the vertical line (B). Finally, the pen point is brought into contact with the entry plane (contact state) to draw the vertical line (C). When applying the movement locus measuring method and the character recognition method according to the first embodiment to the loci (A, C) in the contact state and the locus (B) in the noncontact state, the character “+” shown in FIG. 6 can be accurately recognized. 
     Also as to a character “V” shown in FIG. 7, which can be written with one stroke, formed by only a contact movement locus, the ball rotation sensor  22  having relatively high accuracy can accurately measure the contact movement locus thereby consequently improving the accuracy of character recognition. 
     When character recognition is terminated at the step S 14  of the flow chart shown in FIG. 2, the data of the movement loci subjected to character recognition are deleted from the area for storing coordinate data in the memory  35  at the step S 15 . The timer is cleared at the step S 16 . Thereafter whether or not the recognized character is a character (⊚) prompting a telephone call is determined at the step S 17 . If the recognized character is not the character (⊚) prompting a telephone call, the recognized character is stored in a character storage memory in a prescribed area of the memory  35  at the step S 18 . 
     If the recognized character is determined as the character (⊚) prompting a telephone call at the step S 17 , the name of a person or a company forming a character string stored previously to the currently recognized character (⊚) is converted to a telephone number at the step S 19 . At the step S 20 , a command for calling the telephone number is issued to the telephone circuit  50 . Thus, the electronic pen device (pen-type telephone set)  1  according to the first embodiment makes a call to the destination, similarly to an ordinary telephone set. 
     Second Embodiment 
     Referring to FIG. 8, an electronic pen device (pen-type telephone set)  10  according to a second embodiment of the present invention is basically similar in structure to the first embodiment shown in FIG.  1 . In the second embodiment, however, the contact state determination part  25  in the structure of the first embodiment is omitted. When the contact state determination part  25  is thus omitted, a CPU  30  determines whether a ball  22   a  is in a contact state (pen-down state) or in a noncontact state (pen-up state) with an entry plane. In other words, the CPU  30  forms contact state determination means (contact state determination part) according to the present invention in the second embodiment. 
     More specifically, an acceleration sensor  23  first detects acceleration at a step S 40  of a flow chart shown in FIG.  9 . At a step S 41 , whether or not acceleration is present is determined. If absence of acceleration is determined, the pen-down state (contact state) is determined at a step S 45 . If presence of acceleration is determined, on the other hand, rotation of the ball  22   a  is further detected at a step S 42 . Further, whether or not the ball  22   a  is rotating is determined at a step S 43 . If the ball  22   a  is determined as rotating, the pen-down state (contact state) is determined at the step S 45 . If the ball  22   a  is determined as not rotating, on the other hand, the pen-up state (noncontact state) is determined at a step S 44 . 
     Thus, in the electronic pen device  10  according to the second embodiment, the CPU  30  determines whether the ball  22   a  is in the contact state (pen-down state) or in the noncontact state (pen-up state) with the entry plane. 
     Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of the present invention being limited only by the terms of the appended claims.