Patent Publication Number: US-2015062075-A1

Title: Capacitive input device

Description:
CLAIM OF PRIORITY 
     This application claims benefit of priority to Japanese Patent Application No. 2013-181813 filed on Sep. 3, 2013, which is hereby incorporated by reference in its entirety. 
     BACKGROUND 
     1. Field of the Disclosure 
     The present disclosure relates to a capacitive input device that includes a plurality of electrodes and detects the approach of an operating body, such as a finger or the palm of a hand. 
     2. Description of the Related Art 
     Japanese Unexamined Patent Application Publication No. 2013-134698 discloses a capacitive input device. 
     A plurality of first detection electrodes, which are continuous in an X direction, and a plurality of second detection electrodes, which are continuous in a Y direction, are provided in this input device so as to be insulated from each other, and the first and second detection electrodes are capacitively-coupled to each other. The capacitance of the plurality of first detection electrodes and the capacitance of the plurality of second detection electrodes are sequentially measured at the time of driving. It is possible to detect the touch point of a finger by comparing capacitance between the detection electrodes, which is obtained when the finger touches the detection electrodes, with capacitance between the detection electrodes that is obtained when the finger does not touch the detection electrodes. 
     The capacitive input device disclosed in Japanese Unexamined Patent Application Publication No. 2013-134698 is a touch panel, and is to detect the position of a finger that comes into contact with the surface of the panel. 
     Meanwhile, an input device, which can detect the coordinates of the position where a finger or the palm of a hand approaches, that is, a so-called space gesture when the finger or the palm of the hand approaches a position apart from the surface of an input device to some extent, has been required in recent years. In the detection of this space gesture, it is necessary to detect a change in capacitance between the respective electrodes with high resolution. 
     However, since the plurality of detection electrodes are continuous and extend in the X direction and the Y direction in the input device in the related art disclosed in Japanese Unexamined Patent Application Publication No. 2013-134698 or the like, an electric field, which is generated around the detection electrodes when drive power is applied to the detection electrodes, extends long and thin in the continuous direction of the detection electrodes. For this reason, it is difficult to detect the position in a space gesture where a finger or the palm of a hand approaches with high resolution. In particular, it is difficult to individually and accurately detect the approach of a plurality of fingers. 
     SUMMARY 
     A capacitive input device comprises a plurality of electrodes provided on a substrate, and drive power is applied to a selected electrode, and a detection output is obtained from any electrode. All the electrodes are independent electrodes that are insulated from each other and are capacitively-coupled to each other. The capacitive input device includes a drive controller configured to apply drive power to a drive electrode selected from the independent electrodes and obtains detection outputs from the plurality of electrodes adjacent to the drive electrode. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a plan view showing the disposition of electrodes of a capacitive input device according to an embodiment of the invention; 
         FIG. 2  is an enlarged view of the cross-section of the input device shown in  FIG. 1  taken along line II; 
         FIG. 3  is a view illustrating an electric field generated from a drive electrode; 
         FIG. 4  is a partial plan view showing the disposition of the drive electrode and detection electrodes; 
         FIG. 5  is a partial plan view showing the disposition of the drive electrode and detection electrodes when a selected drive electrode is moved; 
         FIG. 6  is a partial plan view showing the disposition of the drive electrode and detection electrodes when a selected drive electrode is moved; 
         FIG. 7  is a view illustrating a method of obtaining the center position of a finger, which has approached, by a quadratic interpolation method; 
         FIG. 8  is a view illustrating an image pattern that detects the approach of two fingers; 
         FIG. 9  is a view illustrating a method of obtaining interpolation-detection outputs of other electrodes on the basis of detection outputs that are obtained from a limited number of electrodes; 
         FIG. 10  is a view illustrating a method of obtaining interpolation-detection outputs of other electrodes on the basis of detection outputs that are obtained from a limited number of electrodes; 
         FIG. 11  is a view illustrating a method of obtaining interpolation-detection outputs of other electrodes on the basis of detection outputs that are obtained from a limited number of electrodes; and 
         FIG. 12  is an enlarged plan view showing a modification of the shape of electrodes. 
     
    
    
     DESCRIPTION OF THE EXEMPLARY EMBODIMENTS 
     A capacitive input device  1  according to an embodiment of the invention shown in  FIG. 1  includes a detection panel  10  and a drive controller  20 . 
     The detection panel  10  includes a substrate  11 . A plurality of electrodes  12  are provided on a surface  11   a  of the substrate  11 . As shown in  FIG. 1 , the electrodes  12 , which are present in a detection area, are independent electrodes that are electrically insulated from each other. The electrodes  12  are regularly disposed at a constant pitch in an X direction that is a first direction and are regularly disposed at a constant pitch in a Y direction that is a second direction. 
     As shown in  FIG. 1 , each electrode  12  has a quadrangular shape, more specifically, a square shape. The widths W1 and W2 of each electrode  12  are about 10 mm, and an interval S between the adjacent electrodes  12  is about 2 mm. 
     As shown in a cross-sectional view of  FIG. 2 , the substrate  11  is a multilayer substrate. A plurality of wiring layers  13  are embedded in a lower layer of the substrate  11 . As shown in  FIG. 1 , tip end portions  13   a  of the respective wiring layers  13  are individually connected to the respective electrodes  12  through connection layers  14  that are formed in the substrate  11 . The connection layers  14 , which are connected to the electrodes  12 , pass through a portion of the substrate  11  below the plurality of other electrodes  12 , and base end portions  13   b  of the wiring layers  13  are connected to connectors  15  that are positioned at a lower edge portion of the substrate  11  as shown in  FIG. 1 . 
     As shown in  FIG. 2 , a shield layer  16  is embedded in an upper layer of the substrate  11 . Holes  16   a  are formed at a plurality of positions of the shield layer  16 , and the connection layers  14  pass through the holes  16   a . Since the shield layer  16  is positioned between the electrodes  12  and the wiring layers  13  and is set to a ground potential, capacitance is not substantially formed between a finger, the palm of a hand of a human, or the like that approaches the surface  11   a  of the substrate  11  and the wiring layers  13 . Accordingly, the wiring layers  13  do not cause noise to be generated in a detection output. 
     The detection panel  10  is disposed on operation panels of various electronic devices, and the surfaces of the electrodes  12  are covered with a non-conductive cover layer when the detection panel  10  is used. Further, when a display panel such as a color liquid crystal panel is disposed on the back of the detection panel  10 , the entire detection panel  10  is made of a translucent material so that a user can visually check contents displayed on the display panel through the detection panel  10 . 
     The drive controller  20  shown in  FIG. 1  is mounted on a circuit board included in the detection panel  10 , and includes a CPU, a memory, and the like. In  FIG. 1 , a plurality of functional circuits and functional units, which are provided in the drive controller  20 , are denoted by reference numerals for each block, but these functional units are executed on the basis of software, which is stored in the memory, by the CPU. 
     A switching circuit  21  is provided in the drive controller  20 . All the wiring layers  13  of the detection panel  10 , which are individually connected to the respective electrodes  12 , are connected to the switching circuit  21  through the connectors  15 . 
     A drive circuit  22  and a detection circuit  23  are provided in the drive controller  20 . The drive circuit  22  is connected to the respective independent electrodes  12  in order by being switched by the switching circuit  21 . 
     In  FIGS. 4 to 6 , rows of the electrodes  12  that are lined up at a constant pitch in the first direction (X direction) are denoted by X1, X2, X3, . . . and columns of the electrodes  12  that are lined up at a constant pitch in the second direction (Y direction) are denoted by Y1, Y2, Y3, . . . . In  FIG. 4 , the electrode  12 , which is positioned at an intersection between the column Y2 and the row X2, is selected, is connected to the drive circuit  22 , and functions as a drive electrode D. In  FIG. 5 , the electrode  12 , which is positioned at an intersection between the column Y3 and the row X2, is selected and is switched to the drive electrode D. In  FIG. 6 , the electrode  12 , which is positioned at an intersection between the column Y4 and the row X2, is selected and is switched to the drive electrode D. 
     The detection circuit  23 , which is provided in the drive controller  20 , is connected to the electrodes  12 , which are independent electrodes, in order by the switching circuit  21 . As shown in  FIGS. 4 to 6 , two electrodes  12 , which are disposed on both sides of the drive electrode D in the X direction (first direction) so as to be adjacent to the drive electrode D, are connected to the detection circuit  23  by the switching circuit  21  and function as detection electrodes S0 and S1 and two electrodes  12 , which are disposed on both sides of the drive electrode D in the Y direction (second direction) so as to be adjacent to the drive electrode D, are connected to the detection circuit  23  by the switching circuit  21  and function as detection electrodes S2 and S3. Further, four electrodes, which are positioned between the X direction and the Y direction and are adjacent to the drive electrode D, are connected to the detection circuit  23  and function as detection electrodes S4, S5, S6, and S7. 
     These detection electrodes S0, S1, S2, S3, S4, S5, S6, and S7 are capacitively-coupled to the drive electrode D. 
     The detection circuit  23  includes a detection unit having eight channels, and the eight detection electrodes S0, S1, S2, S3, S4, S5, S6, and S7 surrounding the drive electrode D are simultaneously connected to the detection unit of the detection circuit  23 . Alternatively, when the detection circuit  23  includes a detection unit having one channel, the eight detection electrodes S0, S1, S2, S3, S4, S5, S6, and S7 surrounding the drive electrode D may be switched in a short time by the switching circuit  21  so as to be connected to the detection circuit  23 , which has one channel, in order. 
     As shown in  FIGS. 4 to 6 , a rectangular wave, which has a short width, of a predetermined voltage is repeated at a short interval, so that drive power  28  supplied to the drive electrode D from the drive circuit  22  is applied. 
     All the electrodes  12  are independent electrodes that are electrically insulated from each other. Accordingly, when the drive power  28  is applied to the drive electrode D, an electric field E generated by the drive electrode D is distributed from the drive electrode D, which serves as a generation spot, with substantially uniform strength in all directions in the X-Y plane as shown in  FIG. 3  and the same strength plane where the same electric field strength can be observed is formed on the drive electrode D in a substantially spherical shape. Since it is possible to improve the resolution of a detection output of each electrode with respect to an operating body by this electric field distribution, it is possible to also accurately detect a so-called space gesture and it is also easy to detect a plurality of fingers. 
     Since the drive electrode D is capacitively-coupled to the detection electrodes S0, S1, S2, S3, S4, S5, S6, and S7 surrounding the drive electrode D, a current flows in the detection electrodes S0, S1, S2, S3, S4, S5, S6, and S7 at the timing of the rise and fall of the rectangular wave when the drive power  28  having a rectangular wave is applied to the drive electrode D. A current value at this time, that is, a detection output depends on the capacitance between the drive electrode and the detection electrodes. Since a difference in capacitance between adjacent electrodes is detected using a capacitive coupling method, detection is hardly affected by surrounding changes. Accordingly, resolution is improved. 
       FIG. 3  shows a state in which a finger  31 , which is a conductive operating body substantially having a ground potential, has approached the surface  11   a  of the substrate  11  between the drive electrode D and the detection electrode S1. When the finger  31  substantially having a ground potential approaches the surface  11   a  of the substrate  11 , the capacitance between the drive electrode D and the detection electrode S1 is substantially changed and the amount of current of a detection output flowing in the detection electrode S1 at the timing of the rise and fall of the rectangular wave of the drive power  28  is reduced. Since the capacitance between the drive electrode D and each of the other detection electrodes S0, S2, S3, S4, S5, S6, and S7 is also substantially changed according to a distance between the finger  31  and the surface  11   a , the amount of current of a detection output is changed. 
     As shown in  FIG. 1 , an operation determining unit  24  is provided in the drive controller  20 . A detection output, which is obtained from the detection circuit  23  connected to the respective detection electrodes S0, S1, S2, S3, S4, S5, S6, and S7, is sent to the operation determining unit  24 . In the operation determining unit  24 , the determination of the shape of the operating body approaching the surface  11   a  of the substrate  11 , the calculation of the coordinates of the center of the operating body, and the like are performed from detection outputs that are obtained from the plurality of electrodes  12 . 
     The electrode is selected in order so that the position of the electrode  12  used as the drive electrode D is moved to the next column one by one. After all the electrodes  12  present in the detection area are selected as the drive electrode D, detection outputs obtained from all the electrodes present in the detection area are individually and temporarily stored in a storage unit in the operation determining unit  24 . The detection area mentioned here may be an area that includes all the electrodes  12  arranged on the surface  11   a  of the substrate  11  shown in  FIG. 1 , and may be a limited area that includes a part of the electrodes  12  arranged on the surface  11   a.    
     When the electrode is selected in order so that the position of the electrode  12  used as the drive electrode D is moved to the next column one by one as shown in  FIGS. 4 to 6 , the same electrode  12  is selected as the detection electrode several times. For example, the electrode  12 , which is positioned at an intersection between the column Y3 and the row X1, is selected as the detection electrode S5 in  FIG. 4 , is selected as the detection electrode S3 in  FIG. 5 , and is selected as the detection electrode S4 in  FIG. 6 . Time required for selecting all the electrodes  12 , which are present in a predetermined detection area, as the drive electrode D is very short, and the position of the finger  31  or the like is not almost changed during the time. Further, when the same electrode  12  is sequentially selected as the detection electrodes S5, S3, and S4, an average of the respective detection outputs detected by the detection electrodes S5, S3, and S4 is used as a normal detection output and the determination of the operating body is performed using this normal detection output in the operation determining unit  24 . 
     When the same electrode  12  is selected as the detection electrode several times, it is possible to accurately obtain the detection output of the electrode  12  by obtaining an average of the detection outputs at the time of the respective selections. 
     Meanwhile, the adjacent electrode  12  may not be selected as the drive electrode D in order and every other electrode  12  or every two electrodes  12  may be selected as the drive electrode D so that the number of times of the selection of the same electrode  12  as the detection electrode is reduced and, for example, the same electrode  12  is selected as the detection electrode only one time. 
     Further, when any one of the electrodes  12  is selected as the detection electrode, differences in a detection output between the plurality of detection electrodes selected at that time are obtained and output of these differences may be used as detection outputs. Furthermore, a detection output is estimated while the drive electrode D is assumed as a detection electrode, and a difference between the estimated detection output of the drive electrode and a detection output, which is actually obtained from the detection electrode, may be used as a detection output obtained from the detection electrode. 
     For example, in  FIG. 4 , the average of the detection outputs, which are obtained from the eight detection electrodes S0, S1, S2, S3, S4, S5, S6, and S7, is estimated as a detection output that is obtained when the drive electrode D is assumed as a detection electrode. Further, a difference between an actual detection output of the detection electrode S1 and the estimated detection output is used as a detection output that is obtained from the detection electrode S1. Likewise, a difference between a detection output of each of the other detection electrodes S0, S2, S3, S4, S5, S6, and S7 and the estimated detection output is used as a detection output that is obtained from each of the detection electrodes. 
     It is possible to cancel noise or temperature drift components and the like by obtaining a difference between the detection outputs as described above. 
       FIG. 7  illustrates a determining method when the finger  31  as an operating body approaches the surface  11   a  of the substrate  11 . 
     Immediately after all the electrodes  12 , which are present in the detection area, are selected as the drive electrode D, the detection outputs (normal detection outputs) obtained from all the electrodes  12 , which are present in the detection area, are stored in the storage unit only for a short time. In  FIG. 7 , detection outputs (normal detection outputs) obtained from electrodes  12   a ,  12   b ,  12   c ,  12   d , and  12   e  are denoted by Ea, Eb, Ec, Ed, and Ee. In the operation determining unit  24 , a quadratic function f(x), which includes the detection outputs Ea, Eb, Ec, Ed, and Ee or in which distances from the detection outputs Ea, Eb, Ec, Ed, and Ee are shortest, is calculated by a quadratic interpolation method. An X-coordinate xp where an extreme value Ep of the quadratic function f(x) is obtained is calculated as an X-coordinate position of the center (centroid) of the finger  31 . 
     Even in the Y direction, a coordinate of the extreme value is calculated by a quadratic interpolation method in the same manner as shown in  FIG. 7 . As a result, it is possible to obtain the coordinates of the center of the finger  31  that is approaching. 
     Further, it is possible to generate image data  41  and  42  of the operating body based on the detection output as shown in  FIG. 8  by interpolating a difference in detection output between the adjacent electrodes  12  by a quadratic function or a linear function to give an output difference gradient and developing the difference in all directions in the X-Y plane. It is possible to determine whether or not the finger approaches or the palm of a hand approaches by the image data. 
     Furthermore, it is possible to calculate the centers  41   a  and  42   a  of the image data  41  and  42  by obtaining the centroids of the respective image data  41  and  42  or obtaining the coordinates of an extreme value by a quadratic interpolation method. 
     In the example shown in  FIGS. 4 to 6 , all the eight electrodes  12 , which surround the electrode  12  selected as the drive electrode D, are connected to the detection circuit  23  and are selected as the detection electrodes S0, S1, S2, S3, S4, S5, S6, and S7. Accordingly, eight detection outputs are obtained. In contrast,  FIGS. 9 to 11  show an example in which the detection circuit  23  includes only a detection unit having four channels, only four electrodes  12  between which the drive electrode D is interposed are selected as the detection electrodes, and only four detection outputs are obtained per drive electrode D. 
     In  FIG. 9 , the electrode  12 , which is positioned at an intersection between the column Y3 and the row X3, is selected as the drive electrode D. Further, detection outputs are obtained from two detection electrodes S0 and S1 that are adjacent to the drive electrode D in the X direction and two detection electrodes S2 and S3 that are adjacent to the drive electrode D in the Y direction, that is, a total of four detection electrodes. 
     As shown in  FIG. 1 , an interpolation calculation unit  25  is provided in the drive controller  20 . In the interpolation calculation unit  25 , interpolation-detection outputs are calculated from four electrodes S4′, S5′, S6′, and S7′, which are adjacent to the drive electrode D, except for the four detection electrodes S0, S1, S2, and S3 as shown in  FIG. 9 . Interpolation calculation using a linear interpolation method is performed in the interpolation calculation unit  25 . 
     In a method of the interpolation calculation, an assumed detection output Sd, which is obtained when the drive electrode D is assumed as a detection electrode, is obtained as an average that is obtained from the four detection electrodes S0, S1, S2, and S3. 
         Sd=ΣSn/ 4 ( n= 0,1,2,3) 
     An added output difference, which is obtained by adding an output difference between the assumed detection output Sd and the detection output of the detection electrode S3 to an output difference between the assumed detection output Sd and the detection output of the detection electrode S0, is obtained on the basis of the assumed detection output Sd. A value, which is obtained by adding the added output difference to the assumed detection output Sd, is set as an interpolation-detection output of the electrode S4′ that is positioned between the first direction (X direction) and the second direction (Y direction) and is adjacent to the drive electrode. The interpolation-detection outputs of the electrodes S4′, S5′, S6′, and S7′ are calculated by the following expressions. 
         S 4′= Sd +( S 0− Sd+S 3− Sd )
 
         S 5′= Sd +( S 1− Sd+S 3− Sd )
 
         S 6′= Sd +( S 1− Sd+S 2− Sd )
 
         S 7′= Sd +( S 0− Sd+S 2− Sd )
 
       FIG. 10  illustrates interpolation calculation when the electrode  12  positioned on the column Y1 is selected as the drive electrode D. 
     In this case, the assumed detection output Sd, which is obtained when the drive electrode D is assumed as a detection electrode, is obtained by “Sd=ΣSn/3 (n=0, 1, 2)”. Interpolation-detection outputs of electrodes S3′ and S4′, which are positioned between the first direction (X direction) and the second direction (Y direction) and are adjacent to the drive electrode, are obtained as follows. 
         S 3′= Sd +( S 0− Sd+S 1− Sd )
 
         S 4′= Sd +( S 1− Sd+S 2− Sd )
 
       FIG. 11  is a view illustrating interpolation calculation when the drive electrode D is set to an electrode, which is positioned at a corner, among the electrodes  12  disposed in the detection area. 
     Here, three electrodes, which surround the drive electrode D, are set to detection electrodes S0, S1, and S2, and three detection outputs are obtained from the three detection electrodes. In this case, a detection output Sd of the electrode  12 , which is positioned at an intersection between the column Y1 and the row X5 and is selected as the drive electrode D, is assumed as follows. 
       avg=( S 0+ S 2)/2 
         Sd =avg−( S 1−avg)
 
       FIG. 12  shows a modification of electrodes provided in the input device  1 . 
     Electrodes  112  shown in  FIG. 12  are formed in a rhombic shape based on X-Y directions that are vertical and horizontal directions of the substrate  11 . In this case, a first direction of the drive electrode D is a α direction, and a second direction thereof is a β direction. It is possible to obtain detection outputs in the same manner as the embodiment by replacing the X direction with the α direction and replacing the Y direction with the β direction in the embodiment. 
     It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and alterations may occur depending on design requirements and other factors insofar as they are within the scope of the appended claims of the equivalents thereof.