Patent Publication Number: US-2011069034-A1

Title: Position detection apparatus, sensor, and position detection method

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims the benefit under 35 U.S.C. §119(a) of Japanese Patent Application No. 2009-217752, filed, Sep. 18, 2009, the entire content of which is incorporated by reference herein. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a technique suitably applied to a position detection apparatus, a sensor, and a position detection method. More particularly, the present invention relates to a technique of a position detection apparatus and a position detection method of the capacitance type which can detect two fingers. 
     2. Description of the Related Art 
     Variable position inputting apparatus are available which can be used with a personal computer (hereinafter referred to simply as a computer). For example, in addition to a mouse and a trackball, a touch pad is used widely which detects, when a user&#39;s finger directly touches a sensor substantially in the form of a flat plate, the touched position or the movement of the finger. Then, a cursor of the computer is moved or various operations are carried out in response to the detected position or movement. 
     Among such touch pads, a touch pad which utilizes capacitance is prevalent. In position inputting apparatus of the capacitance type represented by a touch pad, usually a user carries out operation with an single finger. 
     In recent years, a computer incorporates an inputting apparatus which can detect two fingers at the same time and execute various operations in response to the position or movement of the two fingers like, for example, iPod (registered trademark) Touch or iPhone (registered trademark) by Apple Computer, Inc. 
     For such detection of two fingers, for example, a lattice-like sensor is used wherein a plurality of conductors are formed in a juxtaposed relationship and substantially in parallel to each other on two opposite faces of an insulating sheet formed substantially as a flat plate. For detection of two fingers in this instance, two types are available including a type that detects, from among those cross points of a plurality of conductors which form such a sensor as described above, which cross points are touched by the fingers, and another type that only detects which conductors are touched by the fingers. The former type is hereinafter referred to as the cross point detection type, and the latter type is hereinafter referred to as the electrode line detection type. 
     A related technique has been proposed by the assignee of the present application and is disclosed in Japanese Patent Laid-Open No. Hei 10-020992. 
     SUMMARY OF THE INVENTION 
     In the cross point detection, an ac signal is applied to an arbitrary one of the conductors of one conductor group, which forms the lattice-like sensor, while a signal is received from the conductors of the other conductor group to detect a cross point, which exists at the place where a finger touches. If this cross point detection is used, then regardless of the number of fingers that may exist, it is possible to physically detect all of the fingers. However, since this cross point detection detects presence or absence of a finger with regard to all cross points, signal supply and signal detection are carried out repetitively for each of the conductors (detection place number=number of longitudinal conductors×number of transverse conductors). Therefore, the cross point detection is disadvantageous in that much time is required before the detection of the entire sensor is completed, that the circuit configuration is complicated, that a high cost is required for the detection circuit and that power saving is difficult. 
     On the other hand, according to the electrode line detection, for example, a signal is sequentially supplied to all of the conductors which form the lattice-type sensor and a variation of an output signal of a conductor, to which the signal is supplied, is detected for each of the conductors to detect a conductor or line which exists at a place where a finger touches. Therefore, detection of a finger can be carried out in a shorter period of time in comparison with the cross point detection (detection place number=number of longitudinal conductors+number of transverse conductors). As a result, a position detection apparatus of the electrode line detection can be configured at a lower cost and power saving can be readily achieved. Therefore, the position detection apparatus of the electrode line detection is suitable for a portable electronic apparatus. 
     However, the electrode line detection has a problem in that, for example, where two fingers exist on the sensor, four coordinates are detected and coordinates at which the user actually touches cannot be detected. 
       FIG. 19  illustrates a situation which may occur when two fingers are detected by a position detection apparatus based on the electrode line detection. 
     It is assumed now that, as a result of detection of addresses of those conductors juxtaposed in an X-axis direction and a Y-axis direction, to which fingers are near, based on detection of a variation of the capacitance of the conductors, addresses Xa and Xb in the X-axis direction and addresses Ya and Yb in the Y-axis direction are obtained. There are two possible cases of the manner in which the operator is touching the position detection surface, which can be determined from the obtained addresses. In one of the cases, the position of (Xa, Ya) is touched by a finger of the left hand and the position of (Xb, Yb) is touched by a finger of the right hand. In the other case, the position of (Xa, Yb) is touched by a finger of the left hand and the position of (Xb, Ya) is touched with a finger of the right hand. In both cases, the addresses Xa and Xb are obtained in the X-axis direction and the addresses Ya and Yb are obtained in the Y-axis direction. 
     In particular, the electrode line detection wherein the presence of a finger is detected by a “line” has a fundamental defect that, if it is tried to detect the positions of a plurality of different fingers, then accurate positions of the fingers cannot be definitively determined. 
     According to one aspect of the present invention, a position inputting apparatus is provided, which can detect two fingers with a simple circuit configuration. 
     In this connection, according to an aspect of the present invention, there is provided a position detection apparatus including a sensor including a plurality of first conductors juxtaposed in parallel to each other in a first direction, a plurality of second conductors juxtaposed in parallel to each other in a second direction and a plurality of third conductors juxtaposed in parallel to each other in a third direction. The first to third conductors are disposed such that a plane defined by the first conductors, another plane defined by the second conductors, and a further plane defined by the third conductors are placed in a superposed (or overlapping/meshed) relationship with each other. The position detection apparatus further includes a signal processing circuit configured to supply a signal to the sensor and detect a position pointed to by a pointer on the sensor based on a signal obtained from the sensor in response to the signal supplied thereto. The signal processing circuit identifies a position actually pointed to by the pointer based on a signal detected through the third conductors juxtaposed in parallel to each other in the third direction when a plurality of signals originating from pointing by the pointer are detected through the first conductors juxtaposed in parallel to each other in the first direction and the second conductors juxtaposed in parallel to each other in the second direction. 
     According to another aspect of the present invention, there is provided a method of detecting a position pointed to by a pointer using a sensor for detecting a position pointed to by the pointer. The sensor includes a plurality of first conductors juxtaposed in parallel to each other in a first direction, a plurality of second conductors juxtaposed in parallel to each other in a second direction, and a plurality of third conductors juxtaposed in parallel to each other in a third direction. The first to third conductors are disposed in different directions from each other, and a plane defined by the first conductors, another plane defined by the second conductors, and a further plane defined by the third conductors are placed in a superposed relationship with each other. The pointed position detection method includes the steps of: supplying a predetermined signal to the first to third conductors, determining whether or not a plurality of signals corresponding to pointing by the pointer are detected from the first conductors juxtaposed in parallel to each other in the first direction and the second conductors juxtaposed in parallel to each other in the second direction in response to the supplied signal, and identifying a position actually pointed to by the pointer based on a signal from the third conductors juxtaposed in parallel to each other in the third direction when a plurality of signals are detected in response to the pointing by the pointer. 
     The position detection of the electrode line detection type wherein longitudinal electrodes or first conductors and lateral electrodes or second conductors are used can only detect presence of one finger. Therefore, according to the present invention, in order to detect presence of two fingers, the electrodes or third conductors are newly provided such that they are juxtaposed in the third direction different from the first and second directions of the first and second conductors so that the positions of two fingers can be definitively determined. 
     Consequently, the present invention can provide a position detection apparatus, a sensor, and a position detection method which can detect two fingers. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view showing an appearance of an information processing apparatus according to an embodiment of the present invention; 
         FIG. 2  is a schematic view showing a general configuration of a position detection apparatus shown in  FIG. 1 ; 
         FIG. 3  is a top plan view of a sensor substrate of a sensor shown in  FIG. 2 ; 
         FIG. 4  is a partial enlarged view of first conductors shown in  FIG. 3 ; 
         FIG. 5  is a partial enlarged view of second conductors shown in  FIG. 3 ; 
         FIG. 6  is a partial enlarged view of the sensor substrate of  FIG. 3  as viewed from above; 
         FIG. 7  is a partial enlarged view of third conductors shown in  FIG. 6 ; 
         FIG. 8  is a schematic sectional view of the sensor substrate of  FIG. 3 ; 
         FIG. 9  is a block diagram of the position detection apparatus of  FIG. 2 ; 
         FIG. 10  is a block diagram showing an internal configuration of a capacitance detection section shown in  FIG. 9 ; 
         FIG. 11  is a waveform diagram illustrating an output voltage of a low-pass filter shown in  FIG. 10 ; 
         FIG. 12  is a diagrammatic view illustrating position detection plane data outputted from a control section of the position detection apparatus of  FIG. 2  as represented on a time axis; 
         FIG. 13  is a block diagram showing functional blocks of a position calculation section shown in  FIG. 1 ; 
         FIG. 14  is a flow chart illustrating a flow of an entire process of the position calculation section of  FIG. 13 ; 
         FIG. 15  is a flow chart of a finger candidate decision process executed by a coordinate calculation section shown in  FIG. 13 ; 
         FIG. 16  is a diagrammatic view illustrating a relationship of a point at which a finger exists to the angle of an oblique electrode and the distance between oblique electrodes; 
         FIGS. 17 and 18  are schematic views illustrating relationships between the positions of a plurality of fingers and the detection values of oblique electrodes; and 
         FIG. 19  is a schematic view illustrating possible situations which may occur when two fingers are detected by a position detection apparatus based on an electrode line detection method. 
     
    
    
     DETAILED DESCRIPTION 
     One embodiment of the present invention will now be described in referring to  FIGS. 1 to 18 . 
     Referring first to  FIG. 1 , there is shown an appearance of an information processing apparatus according to one embodiment of the present invention. 
     The information processing apparatus  101  shown includes a position detection apparatus  102  which transmits data representative of a state of a sensor  106  to a personal computer  103 . When a finger  105  of a person is positioned in the proximity of the sensor  106 , the position detection apparatus  102  exhibits a variation in data which corresponds to the position to which the finger  105  is near. 
     The personal computer  103  analyzes position detection plane data transmitted thereto to detect presence or absence of the finger  105  and calculate the position of the finger  105 . Then, the personal computer  103  utilizes the obtained information of the presence or absence and the position of the finger  105  in various pieces of application software, that is, in various programs such as rendering software. 
     A position calculation section  109  is provided as a device driver, which operates on an OS (Operating System), in the personal computer  103 . The position calculation section  109  is a program for providing a function of detecting the presence or absence of a finger  105  and calculating the position of the finger  105  from the position detection plane data. 
     The information processing apparatus  101  includes the position detection apparatus  102  and the personal computer  103 . 
     The position detection apparatus  102  is connected to the personal computer  103 , which includes, for example, a display unit, by a cable  104  and is used as an inputting apparatus of the personal computer  103 . 
     The position detection apparatus  102  includes the sensor  106  for detecting a finger  105 , a housing  107  of a hollow substantially parallelepiped form having the sensor  106 , and so forth. The housing  107  includes an upper case  108  having an opening  108   a  for exposing an inputting face of the sensor  106  therethrough, and a lower case not shown on which the upper case  108  is placed. The sensor  106  is fitted in the opening  108   a  of the upper case  108 . Thus, a character, a figure, or the like is inputted by pointing to a position of the upper surface of the sensor  106  of the position detection apparatus  102  using a finger  105 , which serves as a pointer. 
     Now, a general configuration of the position detection apparatus to which the present invention is applied is described with reference to  FIG. 2 . The position detection apparatus  102  shown includes the sensor  106 , on which a protective sheet  106   a  formed, for example, from a PET (polyester) film is provided on an upper surface thereof for protecting third conductors  304  hereinafter described so as not to be touched directly by the human body such as a finger of a hand, and a signal processing circuit  202 . The sensor  106  is for measuring a variation of the capacitance of a conductor hereinafter described and is connected to the signal processing circuit  202 . The signal processing circuit  202  outputs a variation of an electric characteristic, which is caused by a finger  105  positioned in the proximity of the sensor  106 , as data. The signal processing circuit  202  is connected to the personal computer  103  by the cable  104  and outputs position detection plane data which is a result of mathematical operation to a central processing unit (MPU) or the like of the personal computer  103 . 
     Now, a general structure of the sensor  106  of the position detection apparatus  102  is described with reference to  FIG. 3 . The sensor  106  shown includes a base substrate  106   b  of a substantially rectangular shape formed, for example, from a PET sheet, and a detection region  301  of a substantially rectangular shape provided at a substantially central portion of one of the opposite faces of the base substrate  106   b,  that is, a face (hereinafter referred to as surface)  106   c.  The detection region  301  detects the human body such as a finger of a hand or the like positioned in the proximity thereof or contacting therewith and detects the coordinate of the point at which the human body is positioned or contacts. 
     Now, details of the detection region  301  are described with reference to  FIGS. 3 to 7 . 
     The detection region  301  includes a plurality of first and second conductors  302  and  303 , and a plurality of third conductors  304  hereinafter described. The first conductors  302  and the second conductors  303 , which form the detection region  301 , have detection portions  302   a  and  303   a  of a substantially quadrangular shape as shown in  FIGS. 4 and 5 , respectively. 
     Referring particularly to  FIG. 4 , each of the first conductors  302  is formed from a column of a plurality of detection portions  302   a  provided in a predetermined spaced relationship from each other in a lateral direction (hereinafter referred to as Y-axis direction) of the base substrate  106   b.  Each two adjacent ones of the detection portions  302   a  of each first conductor  302  in the Y-axis direction are electrically connected to each other at coupling apexes thereof opposing to each other by a connecting portion  302   b.  A plurality of such first conductors  302  are juxtaposed in a predetermined spaced relationship from each other in the longitudinal direction (hereinafter referred to as X-axis direction) perpendicular to the Y-axis direction of the base substrate  106   b.    
     Similarly, each of the second conductors  303  is formed from a row of a plurality of detecting portions  303   a  provided in a predetermined spaced relationship from each other in the X-axis direction of the base substrate  106   b  as seen in  FIG. 5 . Referring to  FIG. 5 , each two adjacent ones of the detecting portions  303   a  of each second conductor  303  in the X-axis direction are electrically connected to each other at coupling apexes thereof opposing to each other by a connecting portion  303   b.  Further, a plurality of such second conductors  303  are juxtaposed in a predetermined spaced relationship from each other in the Y-axis direction of the base substrate  106   b.    
     The first and second conductors  302  and  303  are disposed such that a gap of a predetermined distance L is provided between the detection portions  302   a  and  303   a  of the first and second conductors  302  and  303  as seen in  FIG. 6 . 
     Referring to  FIGS. 6 and 7 , a plurality of third conductors  304  each having a substantially linear shape are juxtaposed in a direction, that is, in a third direction, inclined by 45 degrees with respect to the X-axis direction and the Y-axis direction. In particular, the third conductors  304  are disposed in a substantially overlapping relationship with the gaps having predetermined distances L provided between the detection portions  302   a  and  303   a  of the first and second conductors  302  and  303  such that each of them traverses cross points of the connecting portions  302   b  and  303   b.    
     The individual detection portions  302   a  and  303   a  which form the detection region  301  preferably have such a size that, for example, when the human body, that is, a finger of a hand, is positioned in the proximity of or touches the sensor  106 , at least two detection portions  302   a  and  303   a  of the first and second conductors  302  and  303  will oppose to the human body or a finger. This arises from the following reason. In particular, where the detection portions  302   a  and  303   a  are designed in such a size as just described, if the human body or a finger of a hand is positioned in the proximity of or touches the sensor  106 , then at least two detection portions  302   a  and  303   a  will oppose to the human body or a finger of a hand. Therefore, the position of the human body or a finger of a hand positioned in the proximity of or contacting the sensor  106  can be detected with a higher degree of accuracy based on a difference in capacitance of the two detection portions  302   a  and  303   a  opposing to the human body or a finger of a hand. It is to be noted that the detection portions  302   a  and  303   a  are configured such that, for example, the length of a diagonal line from an apex to an opposing apex is set to be 3.8 mm and the width of the predetermined distances L is set to be approximately 0.5 mm. 
     It is to be noted that, while, in the embodiment described above, the detection portions  302   a  and  303   a  are formed in a substantially quadrangular shape, the shape of the detection portions  302   a  and  303   a  is not limited to this configuration. For example, the shape of the detection portions  302   a  and  303   a  may otherwise be a hexagonal shape or a circular shape. Where the detection sections are formed in a hexagonal shape, preferably they are disposed in a honeycomb pattern. 
     Now, the structure of the sensor  106  is described with reference to  FIG. 8 . The sensor  106  is formed by laminating the first to third conductors  302 ,  303  and  304  and an insulating coating material layer on one of two faces of a base substrate  106   b.    
     The second conductors  303  are provided on an upper face  301   a  of the base substrate  106   b,  for example, by vapor deposition of silver paste. Further, insulating coating  305  is applied to the upper face  301   a  of the base substrate  106   b  on which the second conductors  303  are provided. The insulating coating  305  is applied in such a manner as to cover gaps between the second conductors  303  and also the upper faces of the second conductors  303 . On an upper face  305   a  of the insulating coating  305 , the first conductors  302  are provided, for example, by vapor deposition of silver paste. Furthermore, insulating coating  306  is applied to the upper face  305   a  of the insulating coating  305  on which the first conductors  302  are provided. The insulating coating  306  is applied in such a manner as to cover gaps between the first conductors  302  and also the upper faces of the first conductors  302  similarly to the insulating coating  305 . 
     On an upper face  306   a  of the insulating coating  306 , the third conductors  304  are provided, for example, by vapor deposition of silver paste. Further, insulating coating  307  is applied to the upper face  306   a  of the insulating coating  306  on which the third conductors  304  are vapor deposited. Also the insulating coating  307  is applied in such a manner as to cover gaps between the third conductors  304  and also the upper faces of the third conductors  304 . The protective sheet  106   a  formed from a PET sheet is pasted to the upper face  307   a  of the insulating coating  307  which covers the third conductors  304 . 
     A user can touch the protective sheet  106   a  with a finger to carry out various operations such as, for example, to move a cursor icon or click on a displayed icon while observing the display unit of the personal computer  103 . 
     Now, a general configuration of the signal processing circuit  202  is described with reference to  FIG. 9 . The signal processing circuit  202  shown includes a switch circuit  902  formed, for example, from an analog multiplexer, a capacitance detection section  903 , and a control section  904  for controlling the switch circuit  902  and the capacitance detection section  903 . 
     The first conductors  302 , second conductors  303  and third conductors  304  are connected to the input side of the switch circuit  902  formed from an analog multiplexer. The first conductors  302 , second conductors  303 , and third conductors  304  form capacitors through the switch circuit  902 . 
     The switch circuit  902  is connected on the output side thereof to the capacitance detection section  903 . The capacitance detection section  903  is connected at an output thereof to the control section  904  which is formed, for example, from a microcomputer. 
     The control section  904  outputs position detection plane data based on an output signal from the capacitance detection section  903  and controls the capacitance detection section  903  and the switch circuit  902 . 
     Now, a configuration of the capacitance detection section  903  is described in detail with reference to  FIG. 10 . The capacitance detection section  903  shown includes a variable capacitor Cv, which equivalently represents the first conductors  302 , the second conductors  303 , the third conductors  304 , and the analog multiplexer. It is to be noted that, in the following description, one of terminals of the variable capacitor Cv which is grounded is referred to as a cold side terminal, and the other terminal is referred to as a hot side terminal. A first switch  1002  is connected between the hot side terminal and the cold side terminal, and a second switch  1003  is connected at one terminal thereof to the first switch  1002 . 
     The first switch  1002  is controlled to an on or off state by a first switching controlling signal supplied thereto from the control section  904 . Similarly, the second switch  1003  is controlled to an on or off state by a second switching controlling signal supplied thereto from the control section  904 . A third switch  1004  is controlled to an on or off state by a third switching signal supplied thereto from the control section  904 . 
     The second switch  1003  is connected at the other terminal thereof to a constant current circuit  1005  through the third switch  1004 . Meanwhile, this other terminal of the second switch  1003  and one of the terminals of the third switch  1004  are connected to one of terminals of a reference capacitor C 1006 . The reference capacitor C 1006  is grounded at the other terminal thereof. 
     One of the terminals of the reference capacitor C 1006 , the other terminal of the second switch  1003 , and the one terminal of the third switch  1004  are connected to an input terminal of a low-pass filter  1007 . The low-pass filter  1007  is connected at an output terminal thereof to one input terminal of a comparator  1008 . The comparator  1008  is connected at the other input terminal thereof to resistors R 1009  and R 1010  such that a power supply voltage is divided by the resistors R 1009  and R 1010  to produce a reference voltage which is applied to the other input terminal of the comparator  1008 . The comparator  1008  is connected at an output terminal thereof to the control section  904  such that an output signal of the comparator  1008  is supplied to the control section  904 . 
     Now, a principle of operation of the capacitance detection section  903  is described with reference to  FIGS. 9 and 10 . 
     The switch circuit  902  shown in  FIG. 9  selects one each of the first conductors  302 , second conductors  303 , and third conductors  304  and connects the selected conductor to the hot side terminal of the variable capacitor Cv and connects those conductors which are positioned on both sides of the conductor connected to the hot side terminal to the cold side terminal of the variable capacitor Cv. Consequently, a capacitor is formed from a combination of the conductor connected to the hot side terminal and the conductors positioned on both sides of the conductor and connected to the cold side terminal. 
     Then, if a finger  105  is positioned in the proximity of the capacitor, then the capacitance of the capacitor varies. Since the finger  105  is substantially equivalent to a conductor, as the finger  105  approaches, the capacitance of the capacitor increases. The capacitance detection section  903  detects the variation of the capacitance of the capacitor due to the approach of the finger  105 . 
     Now, a principle operation of the control section  904  is described with reference to  FIGS. 9 to 11 . It is to be noted that, in  FIG. 11 , a solid line curve is a graph indicative of the variation of the capacitance value of the variable capacitor Cv where the finger  105  exists on the sensor  106  while a broken line curve is a graph indicative of the variation of the capacitance value of the variable capacitor Cv where the finger  105  does not exist on the sensor  106 . 
     The control section  904  supplies first to third switching controlling signals for controlling the first to third switches  1002 ,  1003  and  1004  (refer to  FIG. 10 ) between on and off states, respectively, to the first to third switches  1002 ,  1003  and  1004 . The first and second switching controlling signals are outputted at equal time intervals, and the third switching controlling signal is outputted at predetermined time intervals different from the time intervals at which the first and second switching controlling signals are outputted. 
     The control section  904  first outputs the first switching controlling signal to the first switch  1002  to control the first switch  1002  to an off state and then outputs the second and third switching controlling signals to the second switch  1003  and the third switch  1004  to control the second and third switches  1003  and  1004  to an on state, to charge up the variable capacitor Cv and the reference capacitor C 1006  thereby to raise the terminal-to-terminal voltage to the reference voltage Vref (prior to time t 0  of  FIG. 11 ). 
     Then at time t 0 , the control section  904  outputs the third switching controlling signal to the third switch  1004  to control the third switch  1004  to an off state and outputs the first and second switching controlling signals to the first and second switches  1002  and  1003 , respectively. The first and second switching controlling signals operate the first switch  1002  and the second switch  1003  alternately to on and off states. By the on and off operations of the first switch  1002 , the variable capacitor Cv repeats charging and discharging. Therefore, the variable capacitor Cv operates as a switched capacitor. In other words, the first switch  1002 , second switch  100 , 3  and variable capacitor Cv can be regarded equivalently as a resistor. 
     On the other hand, when the control section  904  outputs the third switching controlling signal to the third switch  1004  at time t 0  to control the third switch  1004  to an off state, the charge accumulated in the reference capacitor C 1006  is discharged through the equivalent resistor formed from the variable capacitor Cv. The equivalent resistor formed from the variable capacitor Cv varies depending upon the capacitance of the variable capacitor Cv. It is to be noted that, as the capacitance of the variable capacitor Cv increases, the resistance value of the equivalent resistor decreases, and therefore, the drop of the voltage across the reference capacitor C 1006  by the discharge becomes steeper. 
     Then, after lapse of a predetermined interval of time, that is, at time t 1 , the control section  904  outputs the third switching controlling signal to the third switch  1004  to control the third switch  1004  to an on state. Thereupon, since the control section  904  continuously outputs the first and second switching controlling signals to the first switch  1002  and the second switch  1003 , respectively, the first switch  1002  and the second switch  1003  operate alternately to on and off states so that the variable capacitor Cv functions as a switched capacitor while the constant current circuit  1005  is connected to the reference capacitor C 1006  to charge the reference capacitor C 1006 . When the constant current circuit  1005  is connected, the voltage across the reference capacitor C 1006  rises until it reaches the reference voltage Vref applied to the comparator  1008  (refer to times t 2  and t 3  of  FIG. 11 ). Consequently, the output of the comparator  1008  changes from a high potential to a low potential. 
     The control section  904  receives the output of the comparator  1008  and controls the switch circuit  902  to carry out changeover to a next conductor, and then repeats the operations described above to carry out measurement of the capacitance of the conductor. 
     Incidentally, the gradient of the voltage drop from time t 0  to time t 1  illustrated in  FIG. 11  and the gradient of the voltage rise after time t 1  vary depending upon the equivalent resistor formed by the switched capacitor. In other words, when a finger  105  is not positioned in the proximity of any conductor and the capacitance of the variable capacitor Cv does not exhibit an increase, the resistance value of the variable capacitor Cv is higher than that when a finger  105  is positioned in the proximity of the conductor. Accordingly, discharge of the reference capacitor C 1006  becomes moderate within the period from time t 0  to time t 1  in  FIG. 11 , and the charging becomes steep within the period from time t 1  to time t 2 . As a result, the period before the voltage across the reference capacitor C 1006  becomes equal to the reference voltage Vref again becomes shorter, as seen from the graph indicated by a broken line in  FIG. 11 . 
     In contrast, when a finger  105  is positioned in the proximity of the conductor and the capacitance of the variable capacitor Cv indicates an increase, the equivalent resistor of the variable capacitor Cv indicates a decreased resistance value. Accordingly, the discharge of the reference capacitor C 1006  is steep within the period from time t 0  to time t 1  and the charging is moderate within the period of time from t 1  to t 3 . As a result, the period of time in which the voltage across the reference capacitor C 1006  becomes equal to the reference voltage Vref again becomes longer as seen from the solid line graph in  FIG. 11 . 
     If the period of time from time t 0  to time t 1  is controlled to be a fixed value T, then the drop of the voltage across the reference capacitor C 1006 , that is, the charge amount of the reference capacitor C 1006 , can be varied by the variation of the equivalent resistor of the variable capacitor Cv. Thereafter, by measuring the period of time before the reference voltage Vref is reached, that is, the period of time from time t 1  to time t 2  or t 3 , the variation of the resistance of the equivalent resistor of the variable capacitor Cv, that is, the variation of the capacitance of the variable capacitor Cv, can be detected. 
     Then, the control section  904  uses a predetermined clock and defines the time period T by means of a counter and then measures the period of time from time t 1  to time t 2  or t 3  using the counter. If this measurement is executed for all of the first conductors  302 , second conductors  303 , and third conductors  304 , then measurement values of the conductors are obtained. Since the measurement values vary in response to the capacitance of the variable capacitor Cv, the measurement value with regard to a conductor to which the finger  105  is proximate is high, while the measurement value with regard to a conductor to which the finger  105  is not proximate is low. 
     Now, the position detection plane data outputted from the control section  904  of the position detection apparatus  102  is described with reference to  FIG. 12 . 
     The control section  904  of the position detection apparatus  102  sends the measurement values of the first conductors  302 , second conductors  303 , and third conductors  304  with header information added thereto. In particular, the position detection plane data outputted from the control section  904  include a longitudinal electrode header  1202  which is header information for the first conductors  302 , a lateral electrode header  1203  which is header information for the second conductors  303 , an oblique electrode header  1204  which is header information for the third conductors  304 , and the measurement values of the first to third conductors  302 ,  303  and  304 , and are outputted in order of the first conductors  302 , second conductors  303 , and third conductors  304 . More particularly, if it is assumed that m first conductors  302 , n second conductors  303 , and p third conductors  304  are provided, then the control section  904  first sends the lateral electrode header  1202  and then sends the first measurement value, second measurement value, . . . and mth measurement value which are measurement values of the first conductors  302 . Subsequently to the mth measurement value, the control section  904  sends the lateral electrode header  1203 , and then sends the first measurement value, second measurement value, . . . and nth measurement value which are measurement values of the second conductors  303 . Similarly, the control section  904  sends the oblique electrode header  1204  subsequently to the nth measurement value, and then sends the first measurement value, second measurement value, . . . and pth measurement value which are measurement values of the third conductors  304 . 
     Now, a configuration of the position calculation section  109  is described with reference to  FIG. 13 . It is to be noted that the position calculation section  109  is a function implemented, for example, by a device driver on the personal computer  103  side. 
     The position calculation section  109  includes a storage section  1302 , a center of gravity calculation section  1303 , and a coordinate calculation section  1304 . The position detection plane data outputted from the control section  904  of the position detection apparatus  102  are stored once into the storage section  1302 , which may be formed from a RAM (Random Access Memory). 
     When data of the first conductors  302  from within the position detection plane data are received and when data of the second conductors  303  from within the position detection plane data are received, the center of gravity calculation section  1303  carries out center of gravity calculation for the data of the first and second conductors  302  and  303  and then calculates position data of at most two points each of the first conductors  302  and the second conductors  303 . Then, the center of gravity calculation section  1303  outputs a result of the calculation to the coordinate calculation section  1304  at the succeeding stage. 
     The coordinate calculation section  1304  receives the result of the calculation obtained from the center of gravity calculation section  1303 , that is, position data of at most two points each of the first conductors  302  and the second conductors  303 , and calculates the position of a finger or fingers  105 . Thereupon, if two fingers  105  exist, then the coordinate calculation section  1304  uses the data of the third conductors  304  from among the position detection plane data stored in the storage section  1302  to definitively determine the true position of the finger or fingers  105 . 
     Now, an operation process of the position calculation section  109  is described with reference to a flow chart of  FIG. 14 . 
     If the position calculation section  109  starts processing at step S 1401 , then the center of gravity calculation section  1303  checks an accumulation state of data in the storage section  1302  to confirm whether or not all data of the first conductors  302  are received at step S 1402 . This process is repeated until all data of the first conductors  302  become complete. 
     If all data of the first conductors  302  become complete (YES at step S 1402 ), then the center of gravity calculation section  1303  carries out center of gravity calculation for the first conductors  302  at step S 1403 . 
     Then, the center of gravity calculation section  1303  checks the accumulation state of data in the storage section  1302  to confirm whether or not all data of the second conductors  303  are received at step S 1404 . This process is repeated until all data of the second conductors  303  become complete. If all data of the second conductors  303  become complete (YES at step S 1404 ), then the center of gravity calculation section  1303  carries out center of gravity calculation for the second conductors  303  at step S 1405 . 
     If the center of gravity calculation of the first conductors  302  and the center of gravity calculation of the second conductors  303  are completed, then the coordinate calculation section  1304  first determines whether or not a finger  105  exists on the sensor  106  at step S 1406 . If a finger  105  exists on the sensor  106  (YES at step S 1406 ), then the coordinate calculation section  1304  determines at step S 1407  whether or not the center of gravity of a first conductor  302  or the center of gravity of a second conductors  303  exists at two places, that is, whether or not two fingers  105  exist. If two fingers  105  exist (YES at step S 1407 ), then the coordinate calculation section  1304  executes a finger candidate final determination process for definitively determining the positions at which the fingers  105  exist at step S 1408 . Then, the series of processes is ended at step S 1409 , and the processing returns to step S 1401  to repeat the series of processes described above. 
     On the other hand, if a finger  105  does not exist (NO at step S 1406 ), then the coordinate calculation section  1304  outputs data representing that no finger  105  exists at step S 1410 , and the processing is ended at step S 1409 . Thereafter, the processing returns to step S 1401  to repeat the series of processes described above. 
     Now, the finger candidate final determination process at step S 1408  executed by the coordinate calculation section  1304  in the flow chart of  FIG. 14  is described with reference to  FIGS. 15 to 18 .  FIG. 15  illustrates the finger candidate final determination process executed by the coordinate calculation section  1304 , and  FIG. 16  illustrates a relationship of the point at which a finger exists to the angle of an oblique electrode and the distance between oblique electrodes.  FIG. 17  schematically illustrates a relationship between a result of the center of gravity calculation based on measurement values obtained from the first and second conductors where fingers exist at coordinates A and B, and measurement values obtained from the third conductors at the coordinates A and B at which fingers actually exist. Further,  FIG. 18  schematically illustrates a relationship between a result of the center of gravity calculation based on measurement values obtained from the first and second conductors where fingers exist at coordinates A and B, and measurement values obtained from the third conductors at the coordinates A′ and B′ to which a finger is not proximately positioned. It is to be noted that as shown in  FIGS. 17 and 18 , the following description proceeds under the assumption that a finger  105  is positioned in the proximity of each of the coordinate A (X 1 , Y 1 ) and the coordinate B (X 2 , Y 2 ), for convenience. 
     Where a finger  105  exists at each of the coordinates A and B shown in  FIGS. 17 and 18 , if the longitudinal electrode center of gravity calculation S 1403  and the lateral electrode center of gravity calculation S 1405  are carried out, then the values X 1 , X 2  and Y 1 , Y 2  are obtained. Based on the results of the calculation obtained in this manner, the coordinate calculation section  1304  carries out calculation for specifying the coordinates of the two points from among the coordinate A (X 1 , Y 1 ), coordinate B (X 2 , Y 2 ), coordinate A′ (X 1 , Y 2 ), and coordinate B′ (X 2 , Y 1 ) at which a finger  105  may possibly exist actually. 
     In particular, referring to  FIG. 15 , after the coordinate calculation section  1304  starts processing at step S 1501 , it calculates a candidate number of a third conductor  304  with regard to each of the four coordinates A, A′, B and B′ at step S 1502 . In particular, the following calculation is carried out for the coordinates A, A′, B and B′. 
         Z =( x  sin θ+ y  cos θ)÷ d 
 
     x: calculation result obtained by longitudinal center of gravity calculation
     y: calculation result obtained by lateral center of gravity calculation   θ: angle of third conductor  304  with respect to x axis   d: distance between third conductors  304     Z: (index) number of third conductor  304     

     The expression given above is clear in view of  FIG. 16  which illustrates a relationship of the point at which a finger  105  exists to the angle of third conductors  304  and the distance between the third conductors. 
     Then, the coordinate calculation section  1304  executes the following calculation based on the expression given above: 
         Za =( X 1 sin θ+ Y 1 cos θ)÷ d 
 
         Zb =( X 2 sin θ+ Y 2 cos θ)÷ d 
 
         Za ′=( X 1 sin θ+ Y 2 cos θ)÷ d 
 
         Zb ′=( X 2 sin θ+ Y 1 cos θ)÷ d 
 
     Za, Zb, Za′, Zb′: (index) numbers of third conductors  304   
     The combination of Za and Zb in the expression is determined as a first candidate and the combination of Za′ and Zb′ is determined as a second candidate. 
     Then, the coordinate calculation section  1304  checks the accumulation state of data in the storage section  1302  to confirm whether or not all data of the third conductors  304  become available at step S 1503 . This process is repeated until all data of the third conductors  304  become complete. 
     If all data of the third conductor  304  become complete (YES at step S 1503 ), then the coordinate calculation section  1304  executes calculation based on the measurement values of the third conductors  304  based on the first candidate, and calculation based on the measurement values of the third conductors  304  based on the second candidate at step S 1504 . In particular, the coordinate calculation section  1304  carries out the following calculation: 
     In particular, the coordinate calculation section  1304  carries out for the first candidate 
         Vt=V ( Za )+β V ( Za+ 1)+β V ( Za− 1)+ V ( Zb )+β V ( Zb+ 1)+β V ( Zb− 1)
 
     and for the second candidate 
         Vt′=V ( Za ′)+β V ( Za′+ 1)+β V ( Za′− 1)+ V ( Zb ′)+β V ( Zb′+ 1)+β V ( Zb′− 1)
 
     V(Za): measurement value of Za−th third conductor  304 
     V(Za+1): measurement value of Za+1th third conductor  304     V(Za−1): measurement value of Za−1th third conductor  304     V(Zb): measurement value of Zb−th third conductor  304     V(Zb+1): measurement value of Zb+1th third conductor  304     V(Zb−1): measurement value of Zb−1th third conductor  304     V(Za′): measurement value of Za′th third conductor  304     V(Za′+1): measurement value of Za′+1th third conductor  304     V(Za′−1): measurement value of Za′−1th third conductor  304     V(Zb′): measurement value of Zb′th third conductor  304     V(Zb′+1): measurement value of Zb′+1th third conductor  304     V(Zb′−1): measurement value of Zb′−1th third conductor  304     Vt: calculation value of first candidate   Vt′: calculation value of second candidate   

     Then, the coordinate calculation section  1304  compares the calculation value Vt of the first candidate and the calculation value Vt′ of the second candidate determined by the calculation described above with each other at step S 1505 . If a result of the comparison reveals that the calculation value Vt of the first candidate is greater than the calculation value Vt′ of the second candidate (YES at step S 105 ), then the coordinate calculation section  1304  outputs the coordinate data of the two points corresponding to the first candidate, that is, the data (X 1 , Y 1 ) and (X 2 , Y 2 ) at step S 1506 . 
     On the other hand, if the calculation value Vt′ of the second candidate is greater than the calculation value Vt of the first candidate (NO at step S 1505 ), then the coordinate calculation section  1304  outputs the coordinate data of the two points corresponding to the second candidate, that is, the data (X 1 , Y 2 ) and (X 2 , Y 1 ) at step S 1507 . Then, the series of processes is ended at step S 1508 . 
     In the present embodiment described hereinabove with reference to  FIGS. 3 to 7 , the angle θ of the third conductors  304  with respect to the x axis is 45°. Accordingly, the calculation at step S 1502  is carried out in accordance with the following expression: 
         Z =( x/√ 2+ y/√ 2)÷ d 
 
     It is to be noted that, since, according to the present invention, it is only necessary to compare the calculation value Vt of the first candidate and the calculation value Vt′ of the second candidate with each other in magnitude to determine which one of them is greater, the calculation may be carried out in accordance with the following expression in place of the calculation expression given hereinabove: 
         Z ′=( x+y )÷ d 
 
     The present embodiment may be applied to the following applications: 
     (1) Where a candidate number of a third conductor  304  is calculated at step S 1502  of  FIG. 15 , the conductor numbers Za and Zb of the first candidate may be the same or the conductor numbers Za′ and Zb′ of the second candidate may be the same. This is a case wherein two fingers are positioned at the same third conductor  304 . In this instance, since the number of measurement values of the third conductor  304  increases, upon calculation at step S 1504 , a calculation process which does not use a sum value can be used instead. In particular, the following mathematical expressions may be used. Where the values Za and Zb of the first candidate are equal to each other: 
         Vt=V ( Za )+β V ( Za+ 1)+β V ( Za− 1)
 
     Where the values Za′ and Zb′ of the second candidate are equal to each other: 
         Vt′=V ( Za ′)+β V ( Za′+ 1)+β V ( Za′− 1)
 
     V(Za): measurement value of the Za−th third conductor  304 
     V(Za+1): measurement value of the Za+1th third conductor  304     V(Za−1): measurement value of the Za−1th third conductor  304     V(Za′): measurement value of the Za′th third conductor  304     V(Za′+1): measurement value of the Za′+1th third conductor  304     V(Za′−1): measurement value of the Za′−1th third conductor  304     Vt: calculation value of the first candidate   Vt′: calculation value of the second candidate   

     (2) The angle of the third conductors  304  is not limited to 45° as disclosed in  FIGS. 3 to 7 . It is only necessary for the third conductors  304  to be juxtaposed at an angle different from those of the first conductors  302  and the second conductors  303 . 
     While, in the present embodiment, the present invention is applied to an information processing apparatus formed from a position detection apparatus and a personal computer connected to the position detection apparatus, the present invention is not limited to this configuration. For example, the position calculation section may be built in the personal computer according to the present embodiment. 
     As described above, according to the present invention, the positions of two fingers which cannot be specified based on the conventional electrode line detection method can be definitively determined due to addition of the oblique conductors. As a result, a (multi-touch) position detection apparatus can be provided, which has a less expensive configuration but can detect a plurality of fingers. 
     While a preferred embodiment of the present invention has been described using specific terms, such description is for illustrative purpose only, and it is to be understood that changes and variations may be made without departing from the spirit or scope of the following claims.