Abstract:
Disclosed is a touch panel comprising a display panel (for example, a liquid crystal panel) ( 1 ); a plurality of mirrors ( 2 ) provided on an edge of a display surface side of the display panel ( 1 ); a light source ( 3 ); a plurality of light sensors ( 4 ) embedded in the display panel ( 1 ), positioned immediately under the mirrors ( 2 ), and for which light emitted from the light source ( 3 ) is guided by the mirrors ( 2 ); and a data interpolation processing unit that, if an output signal from a certain light sensor included in the plurality of light sensors ( 4 ) is at most at a threshold, calculates interpolation data from output signals that are stronger than the threshold from light sensors about a periphery of the certain light sensor.

Description:
TECHNICAL FIELD 
     The present invention is related to a touch panel, and in particular, to an optical-sensor touch panel which uses an optical sensor to detect an input position on which an input operation is performed by using a pen point or a fingertip. 
     BACKGROUND ART 
     An example of a configuration of an LM (Light Matrix) type optical-sensor touch panel is schematically shown in  FIGS. 1 and 2 .  FIG. 1  is a front view showing an LM-type optical-sensor touch panel, and  FIG. 2  is a cross sectional view of the LM-type optical-sensor touch panel shown in  FIG. 1 , taken along line A-A of  FIG. 1 . 
     As shown in  FIG. 1 , mirrors  2  are arranged at upper, left, and right edges of a display surface of a liquid crystal panel  1 . A plurality of mirrors  2  need to be arranged at each of the upper, left, and right edges for lower implementation cost. In addition, as shown in  FIG. 1 , a plurality of LEDs are arranged at a lower edge of the display surface of the liquid crystal panel  1  as an LED (Light Emitting Diode)  3 . 
     The liquid crystal panel  1  has optical sensors  4  embedded therein at positions immediately under the mirrors  2  (see  FIG. 2 ), such that a plurality of optical sensors  4  are arranged at each of the upper, left, and right edges. 
     Light emitted from the LED  3  spreads out to cover a surface of the liquid crystal panel  1  (see  FIG. 1 ). The light that has spread over the surface of the liquid crystal panel  1  is directed by the mirrors  2  to the optical sensors  4  (see  FIG. 2 ). The LM-type optical-sensor touch panel shown in  FIGS. 1 and 2  includes a data processing section (not shown), and input positions on which input operations are performed by using, for example, a pen point or a fingertip is detected through processing of outputs from the optical sensors  4  performed by the data processing section. 
     CITATION LIST 
     Patent Literature 
     
         
         Patent Literature 1: JP-A-2005-236770 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     However, light is not reflected in a desirable manner at overlapping positions of the mirrors  2 , and thus, optical sensors located immediately under, or in the vicinity of, the overlapping positions of the mirrors  2  suffer a phenomenon that their output values are remarkably lower than those of the other optical sensors (hereinafter, an optical sensor that suffers this phenomenon will be referred to as a missing sensor). As a result, whether the data processing section processes calibration data or processes sensor read-out data, a defect occurs in an image (sensor image) obtained from outputs of the optical sensors  4  at a portion of the image corresponding to an output of a missing sensor (see  FIG. 3 ). 
     Patent Literature 1 discloses an image scanner and a signal processing method which are capable of appropriately interpolate a missing pixel (a portion of a contact image sensor where intervals between adjacent imaging elements are not uniform) and further can perform the interpolation with high accuracy even when sensitivity characteristics of the imaging elements of the contact image sensor are not uniform. However, the image scanner disclosed in Patent Literature 1 performs interpolation of a missing pixel by using linear interpolation or a high-order function, and thus, unevenness of, for example, sensitivity characteristics of the imaging elements constituting the contact image sensor may prevent correct interpolation, resulting in disadvantageously degraded image scanning quality. In particular, interpolation results in a considerable error in a case where an image of high periodicity is scanned, causing remarkable degradation of the scanned image quality. In addition, image scanner disclosed in Patent Literature 1 is not intended to alleviate the inconvenience of periodic remarkable output reduction of a sensor caused by arranging a plurality of mirrors in an LM-type optical-sensor touch panel. 
     The present invention has been made in view of the foregoing, and an object of the present invention is to provide a touch panel capable of alleviating the problem of periodical occurrence of remarkable output reduction of an optical sensor caused by arranging a plurality of mirrors. 
     Solution to Problem 
     To achieve the above object, according to the present invention, a touch panel includes a display panel, a plurality of mirrors arranged at an edge of a display surface of the display panel, a light source, a plurality of optical sensors which are embedded in the display panel to be positioned immediately under the mirrors such that light emitted from the light source is directed to the plurality of optical sensors by the mirrors, and a data interpolation processing section which, in a case where an output signal from an optical sensor included in the plurality of optical sensors is not greater than a threshold value, calculates interpolation data by using output signals from optical sensors around the optical sensor which are greater than the threshold value. 
     According to the present invention, the touch panel may be configured as follows: the data interpolation processing section includes a holding section, a comparison section, a calculation section, and an interpolation section; the holding section holds output signals from a predetermined number of optical sensors included in output signals from the plurality of optical sensors; the comparison section compares each of the output signals from the predetermined number of optical sensors included in the output signals from the plurality of optical sensors with the threshold value such that, in a case where an output signal from an optical sensor is not greater than the threshold value, the comparison section notifies the calculation section that the output signal from the optical sensor is insufficient, and, in a case where an output signal from an optical sensor is greater than the threshold value, the comparison section notifies the interpolation section that the output signal from the optical sensor is sufficient; the calculation section calculates interpolation data for an output signal from an optical sensor which is notified to the calculation section by the comparison section as outputting an insufficient output signal; and the interpolation section outputs an output from the holding section as output data with respect to an output signal from an optical sensor which is notified to the interpolation section by the comparison section as outputting a sufficient output signal, and the interpolation section outputs an output from the calculation section as output data with respect to an output signal from an optical sensor which is not notified to the interpolation section by the comparison section as outputting a sufficient output signal. 
     According to the present invention, in the touch panel, the calculation section may calculate the interpolation data by using a linear least-squares method. 
     Advantageous Effects of Invention 
     According to a touch panel of the present invention, an output signal of a missing sensor is automatically detected, and an output signal from the missing sensor is interpolated by using output signals from optical sensors around the missing sensor. With this feature, it is possible to alleviate the problem of periodical occurrence of considerable reduction of outputs from optical sensors caused by arranging a plurality of mirrors. 
     Furthermore, according to the touch panel of the present invention, since an output signal from a missing sensor is automatically detected, it is not necessary for the data interpolation processing section to acquire information of overlapping positions of the mirrors in advance. Thus, the same data interpolation processing section can be commonly used in different cases in which mirrors are arranged in different fashions, and this widens the application range of the data interpolation processing section of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       [ FIG. 1 ] A front view schematically showing an example of a configuration of an LM-type optical-sensor touch panel; 
       [ FIG. 2 ] A sectional view schematically showing an example of a configuration of an LM-type optical-sensor touch panel; 
       [ FIG. 3 ] A diagram showing a relationship between mirrors and a sensor image; 
       [ FIG. 4 ] A block diagram schematically showing an example of a configuration of data interpolation processing section which is a characteristic section of a touch panel embodying the present invention; 
       [ FIG. 5A ] A diagram showing an example of a part of input data of the data interpolation processing section shown in  FIG. 4 ; 
       [ FIG. 5B ] A diagram showing an example of a part of output data corresponding to the part of the input data shown as an example in  FIG. 5A ; 
       [ FIG. 6 ] A diagram showing an example of a configuration of the data interpolation processing section shown in  FIG. 4 ; 
       [ FIG. 7 ] A diagram showing parameters generated by a parameter generation section provided in the data interpolation processing section shown in  FIG. 4 ; and 
       [ FIG. 8 ] A diagram showing an example of a configuration of an interpolator provided in the data interpolation processing section. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, a description will be given of an embodiment of the present invention with reference to the accompanying drawings. A touch panel embodying the present invention is configured such that a data interpolation processing section is newly added between an optical sensor and a data processing section of a typically-configured LM-type optical-sensor touch panel. 
     An example of a configuration of the data interpolation processing section, which is a characteristic section of the touch panel embodying the present invention, is schematically shown in  FIG. 4 . The data interpolation processing section shown in  FIG. 4  includes a holding section  5 , a comparison section  6 , a calculation section  7 , and an interpolation section  8 . 
     Input data is a group of output signals from optical sensors  4 , and in the input data, the output signals are arranged in an order according to locations of the corresponding optical sensors  4 , that is, for example, in the order from a lower end to an upper end of a left edge of a liquid crystal panel  1  as seen from the display surface side thereof, then from a left end to a right end of an upper edge of the liquid crystal panel  1 , then from an upper end to a lower end of a right edge of the liquid crystal panel  1 . 
     The holding section  5  holds output signals of a predetermined number of optical sensors  4  included in the input data. The comparison section  6  compares each of the output signals of the predetermined number of optical sensors  4  included in the input data with a threshold value which is set in advance; if an output signal from an optical sensor  4  is not greater than the threshold value, the comparison section  6  notifies the calculation section  7  that the output signal from the optical sensor  4  is insufficient, and, if an output signal from an optical sensor  4  is greater than the threshold value, the comparison section  6  notifies the interpolation section  8  that the output signal from the optical sensor  4  is sufficient. The calculation section  7  calculates interpolation data for the output signal of the optical sensor  4  which has been notified to the calculation section  7  by the comparison section  6  as being insufficient. With respect to the output signal of the optical sensor  4  that has been notified to the interpolation section  8  by the comparison section  6  as being sufficient, the interpolation section  8  outputs a corresponding output from the holding section  5  as output data. With respect to the output signal of the optical sensor  4  that has not been notified to the interpolation section  8  by the comparison section  6  as being sufficient, the interpolation section  8  outputs a corresponding output from the calculation section  7  as output data. 
     With the data interpolation processing section shown in  FIG. 4 , for example, a part of output data corresponding to the part of input data shown in  FIG. 5A  is as shown in  FIG. 5B . In this example, an output signal D 4  from an optical sensor  4  is judged to be insufficient by the comparison section  6 , and output signals D 1 -D 3 , D 5 , and D 6  from other optical sensors  4  are judged to be sufficient by the comparison section  6 . 
     Next, an example of a configuration of the data interpolation processing section shown in  FIG. 4  is shown in  FIG. 6 . Flip-flops FF 1 -FF 5  correspond to the holding section  5 . Comparators COM 1 -COM 5  and flip-flops FF 1 ′-FF 5 ′ correspond to the comparison section  6 . The parameter generation section  9 , a first selector  10 , and an interpolator  11  correspond to the calculation section  7 . A second selector  12  and a flip-flop FF 6  correspond to the interpolation section  8 . This configuration makes it possible to judge up to three optical sensors in series to be missing sensors. 
     A system clock signal SCLK, a reset signal FINIT, and a threshold value TH are supplied from a control section which controls the entire touch panel embodying the present invention. The threshold value TH is stored in a nonvolatile memory incorporated in the control section. 
     The flip-flops FF 1 -FF 5  hold five data components of sequentially inputted input data DATA_IN. Likewise, the flip-flops FF 1 ′-FF 5 ′ also hold the five data components of the sequentially inputted input data DATA_IN. A comparator COMk compares an output signal from an optical sensor  4  held by a corresponding flip-flop FFk′ with the threshold value TH which is set in advance; if the output signal from the optical sensor  4  held by the flip-flop FFk′ is not greater than the threshold value TH, the comparator COMk feeds the parameter generation section  9  with a comparison result signal (high level signal) indicating that the output signal from the specific optical sensor  4  is insufficient, in other words, that the specific optical sensor  4  is a missing sensor, and if the output signal from the optical sensor  4  held by the flip-flop FFk′ is greater than the threshold value TH, the comparator COMk feeds the parameter generation section  9  with a comparison result signal (a low level signal) indicating that the output signal from the specific optical sensor  4  is sufficient, in other words, that the specific optical sensor  4  is not a missing sensor (here, “k” is a natural number that is 1 or larger and 5 or smaller). 
     The parameter generation section  9  generates parameters which are necessary for calculating the interpolation data based on output signals of the comparators COM 1 -COM 5 . There are a total of 32 (=2 5 ) combinations of output signals of comparators COM 1 -COM 5 . Also, as described above, with the configuration shown in  FIG. 6 , it is possible to judge up to three optical sensors in series to be a missing sensor. Here, the calculation section  7  would need to have a large circuit scale to perform interpolation processing with respect to all of the 32 combinations of comparison results, and thus, in the configuration shown in  FIG. 6 , the calculation section  7 , by using the optical-sensor output signal held by the flip-flop FF 5  as a reference signal, judges how many optical sensors following the optical sensor of the reference signal output insufficient output signals. Seven comparison results shown in  FIG. 7  cover all the patterns possible in a case where interpolation is performed. Each of the comparison results shown in  FIG. 7  indicates an output signal of the comparator COM 5 , an output signal of the comparator COM 4 , an output signal of the comparator COM 3 , an output signal of the comparator COM 2 , and an output signal of the comparator COM 1 , in this order from left to right. 
     In cases of comparison results of combinations other than the seven combinations of comparison results shown in  FIG. 7 , interpolation does not need to be performed, and thus, the parameter generation section  9  does not set first to third parameters. 
     In a case in which the comparison result is any one of LHLLL, LHLLH, LHLHL, and LHLHH, the parameter generation section  9  sets the first parameter to a value indicating the flip-flop FF 5 , sets the second parameter to a value indicating the flip-flop FF 3 , and sets the third parameter to an inclination factor “2” (see  FIG. 7 ). 
     In a case in which the comparison result is either LHHLL or LHHLH, the parameter generation section  9  sets the first parameter to a value indicating the flip-flop FF 5 , sets the second parameter to a value indicating the flip-flop FF 2 , and sets the third parameter to an inclination factor “3” (see  FIG. 7 ). 
     In a case in which the comparison result is LHHHL, the parameter generation section  9  sets the first parameter to a value indicating FF 5 , sets the second parameter to a value indicating the flip-flop FF 1 , and sets the third parameter to an inclination factor “4” (see  FIG. 7 ). 
     The first selector  10  outputs an output value of the flip-flop that is set as the first parameter to the interpolator  11  as PAM 1 , outputs an output value of the flip-flop that is set as the second parameter to the interpolator  11  as PAM 2 , and outputs the inclination factor set as the third parameter to the interpolator  11  as PAM 3 . 
     Next, an example of a configuration of the interpolator  11  is shown in  FIG. 8 . In the configuration shown in  FIG. 8 , the interpolator  11  includes a first latch  13 , a second latch  14 , a third latch  15 , a processing counter  16 , a subtractor  17 , a calculator  18 , a comparator  19 , and a selection instructing signal generation section  20 . 
     While the number of pieces of data to be interpolated (“1” if the comparison result is LHLLL, LHLLH, LHLHL, or LHLHH; “2” if the comparison result is LHHLL or LHHLH; and “3” if the comparison result is LHHHL) is processed by the calculator  18 , the first latch  13  holds the output value PAM 1  of the flip-flop set as the first parameter, the second latch  14  holds the output value PAM 2  of the flip-flop set as the second parameter, and the third latch  15  holds the inclination factor PAM 3  set as the third parameter. 
     The processing counter  16  counts a clock number of a system clock SCLK. While a selection instructing signal IPENABLE from the selection instructing signal generation section  20  remains “L”, a count value is held at “1”, and at the same time that the selection instructing signal IPENABLE from the selection instructing signal generation section  20  is changed to “H”, the processing counter  16  starts counting up from “1”. 
     The subtractor  17  outputs a value S 1 , which is obtained by subtracting a count number of the processing counter  16  from an output L 3  of the third latch  15 , to the calculator  18  and the comparator  19 . 
     The calculator  18  calculates an interpolation value IPDATA by a linear least-squares method, by using an output L 1  of the first latch  13 , an output L 2  of the second latch  14 , an output L 3  of the third latch  15 , and the output S 1  of the subtractor  17 . The formula used here is as follows:
 
IPDATA= S 1×( L 1 −L 2)/ L 3 +L 2
 
     As shown in the formula, the calculator  18  performs division in the calculation, inviting a delay in the calculation processing. To cope with this, the selection instructing signal IPENABLE is inputted to the first latch  13 , the second latch  14 , the third latch, and the selection instructing signal generation section  20 , such that the selection instructing signal IPENABLE is latched and the selection instructing signal IPENABLE is held during a data number delayed by the interpolation processing. 
     The comparator  19  compares the output S 1  of the subtractor  17  with a comparison set value “1”, to thereby judge whether or not the output S 1  of the subtractor  17  is “1”. In a case in which an output signal of the comparator  19  is a signal indicating that the output S 1  of the subtractor  17  is “1”, the selection instructing signal generation section  20  makes the selection instructing signal IPENABLE “L”. In contrast, in a case in which an output signal of the comparator  19  is not a signal indicating that the output S 1  of the subtractor  17  is “1”, the selection instructing signal generation section  20  makes the selection instructing signal IPENABLE “H”. 
     Here, with reference back to  FIG. 6 , a description will be given of the second selector  12  and the flip-flop FF 6  which correspond to the interpolation section  8  in  FIG. 4 . The second selector  13  selects the interpolation value IPDATA outputted from the interpolator  11  and supplies it to the flip-flop FF 6  only when the selection instructing signal IPENABLE from the interpolator  11  is “H”, while, when the selection instructing signal IPENABLE from the interpolator  11  is “L”, the second selector  13  selects the output of the flip-flop FF 5  and supplies it to the flip-flop FF 6 . An output of the flip-flop FF 6  is output data DATA_OUT of the data interpolation processing section. 
     With the above-configured touch panel embodying the present invention, which automatically detects an output signal of a missing sensor and interpolates the output signal of the missing sensor by using output signals of optical sensors around the missing sensor, it is possible to alleviate the problem of periodical occurrence of remarkable output reduction of an optical sensor caused by arranging a plurality of mirrors. 
     Furthermore, with the above-configured touch panel embodying the present invention, which automatically detects an output signal of a missing sensor, the data interpolation processing section does not need to acquire information of overlapping positions of the mirrors. Thus, the data interpolation processing section can be commonly used for cases of different mirror arrangements, and this makes the data interpolation processing section highly versatile. 
     It should be understood that the embodiments specifically described above are not meant to limit the present invention, and that many variations and modifications can be made within the spirit of the present invention. 
     INDUSTRIAL APPLICABILITY 
     The present invention is useful for optical-sensor touch panels which use optical sensors to detect positions on which input operations are performed by using a pen point, a fingertip, or the like. 
     LIST OF REFERENCE SYMBOLS 
     
         
         
           
               1  liquid crystal panel 
               2  mirror 
               3  LED 
               4  optical sensor 
               5  holding section 
               6  comparison section 
               7  calculation section 
               8  interpolation section 
               9  parameter generation section 
               10  first selector 
               11  interpolator 
               12  second selector 
               13  first latch 
               14  second latch 
               15  third latch 
               16  processing counter 
               17  subtractor 
               18  calculator 
               19  comparator 
               20  selection instructing signal generation section 
             FF 1 -FF 6 , FF 1 ′-FF 6 ′ flip-flop 
             COM 1 -COM 5  comparator