FORCE SENSOR AND FORCE DETECTION SYSTEM PRESSING FORCE SENSOR

A force sensor includes a plurality of detection electrodes disposed in respective individual detection regions, a sensor layer facing the detection electrodes, a common electrode through which current flows to the detection electrodes via the sensor layer at inputting of force, a plurality of signal lines that are coupled to the detection electrodes and through which the current having flowed to the detection electrodes is output to outside, a plurality of switch elements configured to open and close the coupling of the signal lines and the detection electrodes, a plurality of gate lines for controlling opening and closing of the switch elements, a plurality of correction circuits disposed in the respective individual detection regions, and correction gate lines for driving the correction circuits.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of priority from Japanese Patent Application No. 2023-020249 filed on Feb. 13, 2023, the entire contents of which are incorporated herein by reference.

BACKGROUND

1. Technical Field

The present disclosure relates to a force sensor and a force detection system.

2. Description of the Related Art

A force detection system includes a force sensor to which force is input and a control device configured to calculate a force value based on an output value that is output from the force sensor. A force sensor of Japanese Patent Application Laid-open Publication No. 2018-146489 includes an array substrate provided with a plurality of detection electrodes, a common electrode facing the detection electrodes, and a sensor layer sandwiched between the detection electrodes and the common electrode. When force is input to the force sensor, the common electrode and the sensor layer deform toward the array substrate. Then, when the sensor layer contacts the detection electrode, current flows from the common electrode to the detection electrodes through the sensor layer. The sensor layer contains conductive particles dispersed inside insulating resin. As the resin deforms, the conductive particles contact one another and the resistance value of the sensor layer decreases. As the amount of deformation of the resin increases, the number of conductive particles contacting one another increases and the decrease amount of the resistance value of the sensor layer increases. Thus, the value of current flowing to the detection electrodes increases as force input to the force sensor increases. In this manner, the force sensor can detect force at each detection electrode. In other words, the force sensor has a detection region divided into a plurality of individual detection regions.

Characteristics of each switch element such as a thin film transistor (TFT) is different for each individual detection region in some cases. Furthermore, characteristics vary for each path through which a detection signal (current) detected by a detection electrode is transferred to the control device, in other words, for the path of each analog front end (hereinafter referred to as AFE) in some cases. For such a reason, different output values are received by the control device in some cases even when force of the same magnitude is input to a plurality of individual detection regions. Thus, the control device corrects the output value of each individual detection region.

To acquire correction data for the individual detection regions, it is needed to apply uniform force to each individual detection region and acquire the output value of the individual detection region. In an exemplary method of applying uniform force to each individual detection region, a jig that can contact the entire detection region is prepared and pressed against the detection region. However, in a case where a detection surface included in the detection region has minute irregularity and distortion, uniform force is not applied to each individual detection region when the jig is pressed. Thus, it is desired to acquire correction data by a simple method other than the method of applying uniform force to the detection surface.

The present disclosure is intended to provide a force sensor and a force detection system that are capable of acquiring correction data by a simple method.

SUMMARY

A force sensor according to a first embodiment of the present disclosure includes a plurality of detection electrodes disposed in respective individual detection regions, a sensor layer facing the detection electrodes, a common electrode through which current flows to the detection electrodes via the sensor layer at inputting of force, a plurality of signal lines that are coupled to the detection electrodes and through which the current having flowed to the detection electrodes is output to outside, a plurality of switch elements configured to open and close the coupling of the signal lines and the detection electrodes, a plurality of gate lines for controlling opening and closing of the switch elements, a plurality of correction circuits disposed in the respective individual detection regions, and correction gate lines for driving the correction circuits. A value of the current output through the signal lines is proportional to the magnitude of force input to the individual detection regions, each correction circuit includes a first wire and a second wire each having one end coupled to the common electrode and the other end coupled to the signal lines, the first wire and the second wire being coupled in parallel to the detection electrodes and the switch elements, the first wire includes a first resistance component having a first resistance value, and a first wire switch element configured to open and close the first wire, the second wire includes a second resistance component having a second resistance value larger than the first resistance value, and a second wire switch element configured to open and close the second wire, and the correction gate lines include a first correction gate line for controlling the first wire switch element, and a second correction gate line for controlling the second wire switch element.

A force sensor according to a second embodiment of the present disclosure includes a plurality of detection electrodes disposed in respective individual detection regions, a sensor layer facing the detection electrodes, a common electrode through which current flows to the detection electrodes via the sensor layer at inputting of force, a plurality of signal lines that are coupled to the detection electrodes and through which current having flowed to the detection electrodes is received, a plurality of switch elements configured to open and close the coupling of the signal lines and the detection electrodes, a plurality of gate lines for controlling opening and closing of the switch elements, a plurality of correction circuits disposed in a detection target region outside the individual detection regions, correction gate lines for driving the correction circuits, and a correction signal line for outputting signals from the correction circuits. A value of the current output through the signal lines is proportional to the magnitude of force input to the individual detection regions, the detection electrodes are arrayed in a first direction in which the signal lines extend and a second direction intersecting the first direction, the correction circuits are provided for the respective detection electrodes arrayed in the second direction, each correction circuit includes a first wire and a second wire each having one end coupled with the common electrode common to the detection electrodes arrayed in the second direction and the other end coupled with the correction signal line, the first wire includes a first resistance component having a first resistance value, and a first wire switch element configured to open and close the first wire, the second wire includes a second resistance component having a second resistance value larger than the first resistance value, and a second wire switch element configured to open and close the second wire, the correction gate lines include a first correction gate line for controlling the first wire switch element, and a second correction gate line for controlling the second wire switch element.

A force sensor according to a third embodiment of the present disclosure includes a plurality of detection electrodes disposed in respective individual detection regions, a sensor layer facing the detection electrodes, a common electrode through which current flows to the detection electrodes via the sensor layer at inputting of force, a plurality of signal lines that are coupled to the detection electrodes and through which current having flowed to the detection electrodes is received, a plurality of switch elements configured to open and close the coupling of the signal lines and the detection electrodes, a plurality of gate lines for controlling opening and closing of the switch elements, a plurality of correction circuits disposed in a detection target region outside the individual detection regions, and a correction gate lines for driving the correction circuits. A value of the current output through the signal lines is proportional to the magnitude of force input to the individual detection regions, the detection electrodes are arrayed in a first direction in which the signal lines extend and a second direction intersecting the first direction, the correction circuits are provided for the plurality of respective detection electrodes arrayed in the first direction, each correction circuit includes a first wire and a second wire each having one end coupled to the common electrode and the other end coupled to a signal line common to the detection electrodes arrayed in the first direction, each correction circuit includes a first wire and a second wire each having the other end coupled to the signal line, the first wire includes a first resistance component having a first resistance value, and a first wire switch element configured to open and close the first wire, the second wire includes a second resistance component having a second resistance value larger than the first resistance value, and a second wire switch element configured to open and close the second wire, and the correction gate lines include a first correction gate line for controlling the first wire switch element, and a second correction gate line for controlling the second wire switch element.

A force detection system according to an embodiment of the present disclosure includes the force sensor, and a control device configured to calculate a force value based on results of outputting from the signal lines of the force sensor. The control device calculates an output value characteristic line for each individual detection region based on a first output value when the first wire switch element is closed and a second output value when the second wire switch element is closed, calculates a correction coefficient with which the output value characteristic line matches a correction target line representing a desired output value, and corrects an output value by using the correction coefficient.

DETAILED DESCRIPTION

Aspects (embodiments) of a force sensor of the present disclosure will be described below in detail with reference to the accompanying drawings. Contents described below in the embodiments do not limit the invention of the present disclosure. Constituent components described below include those that could be easily thought of by the skilled person in the art and those identical in effect. Constituent components described below may be combined as appropriate. What is disclosed herein is merely exemplary, and any modification that could be easily thought of by the skilled person in the art as appropriate without departing from the gist of the invention is contained in the scope of the present disclosure. For clearer description, the drawings are schematically illustrated for the width, thickness, shape, and the like of each component as compared to an actual aspect in some cases, but the drawings are merely exemplary and do not limit interpretation of the present disclosure. In the present specification and the drawings, any constituent component same as that already described with reference to an already described drawing is denoted by the same reference sign, and detailed description thereof is omitted as appropriate in some cases.

In the present specification and the claims, an expression with “on” in description of an aspect in which one structural body is disposed on another structural body includes both a case in which the one structural body is directly disposed on the other structural body in contact and a case in which the one structural body is disposed above the other structural body with still another structural body interposed therebetween, unless otherwise stated in particular.

First Embodiment

FIG.1is a perspective view schematically illustrating a force detection system according to a first embodiment. As illustrated inFIG.1, a force detection system100includes a force sensor1and a control device101. The force sensor1is formed in a flat plate shape and includes a detection surface1ato detect force. The force sensor1is formed in a rectangular shape when viewed in the normal direction of the detection surface1a. The detection surface1aof the force sensor1is divided into a detection region2in which force can be detected and a peripheral region3surrounding the outside of the detection region2. The detection region2is divided into a plurality of individual detection regions4. InFIG.1, a virtual line L is illustrated to facilitate recognition of the boundary between the detection region2and the peripheral region3.

The individual detection regions4are arrayed in a first direction Dx and a second direction Dy. The first direction Dx is parallel to the detection surface1a. The second direction Dy is parallel to the detection surface1aand intersects the first direction Dx. In the present embodiment, the first direction Dx is parallel to a long side of the force sensor1. The second direction Dy is parallel to a short side of the force sensor1. Accordingly, the first direction Dx and the second direction Dy are orthogonal to each other. The normal direction of the detection surface1ais orthogonal to the first direction Dx and the second direction Dy and referred to as a third direction Dz in some cases.

FIG.2is a sectional view taken along line II-II inFIG.1when viewed in the direction of arrows. As illustrated inFIG.2, the force sensor1includes a substrate5, a circuit formation layer10, a detection electrode20, a common electrode30, a sensor layer60, and a protective layer70.

The substrate5is an insulating plate material. The substrate5is, for example, a glass substrate, a resin substrate, or a resin film. The substrate5is integrates with the circuit formation layer10to form an array substrate6. In the following description, an upper side is one side in the third direction Dz and means a side on which the circuit formation layer10is disposed when viewed from the substrate5.

A plurality of drive transistors (switch elements)13are provided in a region in which the circuit formation layer10overlaps the detection region2. The drive transistors13correspond to the array of the individual detection regions4and are arrayed in the first direction Dx and the second direction Dy. Accordingly, one drive transistor13is provided in each individual detection region4. In addition, a plurality of correction circuits40and correction gate lines50(refer toFIG.3) are provided in the circuit formation layer10. The correction circuits40and the correction gate lines50will be described later.

The circuit formation layer10includes various components for driving the drive transistors13. Specifically, as illustrated inFIG.1, the circuit formation layer10includes a coupling part7, gate line drive circuits8, a signal line selection circuit9, gate lines11(refer toFIG.3), and signal lines12(refer toFIG.3).

The coupling part7, the gate line drive circuits8, and the signal line selection circuit9are disposed in the peripheral region3. The coupling part7is used to couple with a drive integrated circuit (IC) disposed outside the force sensor1. In the present embodiment, the control device101has functions of the drive IC, and the coupling part7is coupled to the control device101. In the present disclosure, the drive IC may be mounted as a chip-on film (COF) on a flexible printed board or a rigid substrate coupled with the coupling part7. Alternatively, the drive IC may be mounted as a chip-on glass (COG) in the peripheral region3.

The gate line drive circuits8are circuits configured to drive the gate lines11(refer toFIG.3) based on various kinds of control signals from the control device101. The gate line drive circuits8sequentially or simultaneously select the gate lines11and supply a gate drive signal to the selected gate lines11. The signal line selection circuit9is a switch circuit configured to sequentially or simultaneously select the signal lines12(refer toFIG.3). The signal line selection circuit9is, for example, a multiplexer. The signal line selection circuit9couples the selected signal lines12to the control device101based on a selection signal supplied from the control device101.

FIG.3is a circuit diagram illustrating a circuit configuration of the force sensor of the first embodiment. As illustrated inFIG.3, the gate lines11extend in the second direction Dy. The gate lines11are arrayed in the first direction Dx. The signal lines12extend in the first direction Dx. The signal lines12are arrayed in the second direction Dy. In addition, although not particularly illustrated, the circuit formation layer10includes a common wire extending along the peripheral region3. The common wire is a wire for supplying current to the common electrode30. The common wire is coupled to the control device101through the coupling part7and supplied with a constant amount of current from the control device101.

As illustrated inFIG.2, each drive transistor13includes a semiconductor layer13a, a gate insulating film13b, a gate electrode13c, a drain electrode13d, and a source electrode13e. The source electrode13eis coupled to the detection electrode20. The gate electrode13cis coupled to a gate line11. The drain electrode13dis coupled to a signal line12. Accordingly, when the gate line11is scanned, the detection electrode20is closed. As a result, an electric signal (current value) input to the detection electrode20is output to the signal line12.

In the array substrate6, a first surface6afacing the sensor layer60is flattened by an insulating layer14covering the drive transistors13and the like.

The detection electrode20and the common electrode30are provided on the first surface6aof the array substrate6. The detection electrode20and the common electrode30are made of a metallic material such as indium tin oxide (ITO). In the present disclosure, the detection electrode20and the common electrode30may be made of metallic materials different from each other and are not particularly limited.

The common electrode30is coupled to the common wire (not illustrated) through a non-illustrated wire buried in the insulating layer14of the circuit formation layer10. Accordingly, the common electrode30is supplied with a constant amount of current from the control device101. The common electrode30is separated from the detection electrode20.

The sensor layer60is a made of a material containing conductive fine particles inside a highly insulating resin layer. The fine particles are separated from one another inside the resin layer. Accordingly, the resistance value of the sensor layer60is large when the resin layer is not deformed. When the resin layer is deformed, the fine particles contact or approach one another and the resistance value of the sensor layer60decreases. As the deformation amount of the resin layer increases, the number of contacting fine particles increases and the resistance value of the sensor layer60largely decreases. The sensor layer60is also called a pressure-sensitive layer.

As illustrated inFIG.2, the sensor layer60is disposed on the upper side of the array substrate6. Accordingly, the sensor layer60faces the detection electrode20and the common electrode30. The sensor layer60is supported by a spacer (not illustrated) provided on the array substrate6. Accordingly, a space S is provided on the lower side of the sensor layer60, and the sensor layer60is separated from each of the detection electrode20and the common electrode30. The spacer (not illustrated) may be provided in the peripheral region3on the first surface6aof the array substrate6or provided between the individual detection regions4and is not particularly limited in the present disclosure.

The protective layer70is an insulating layer disposed on the upper side of the sensor layer60and extending along the sensor layer60. The protective layer70is integrated with the sensor layer60by a non-illustrated bonding layer. The upper surface of the protective layer70is the detection surface1a.

FIG.4is a diagram illustrating a state in which force is input to the detection surface of the force sensor of the first embodiment.FIG.5is a diagram (graph) illustrating the relation between the value of force applied to the force sensor (individual detection regions) and an output value (current value) that is output from a signal line.FIG.6is a diagram (graph) illustrating the relation between the decrease amount of the resistance value of the sensor layer and the output value (current value) that is output from a signal line. As illustrated inFIG.4, part of the protective layer70and the sensor layer60is recessed toward the array substrate6when force F is input to the detection surface1a. Accordingly, the sensor layer60contacts the detection electrode20and the common electrode30. The resistance value of the sensor layer60decreases through deformation by pressing. Accordingly, the detection electrode20and the common electrode30are electrically coupled to each other through the sensor layer60. Thus, current (refer to arrow I) flows from the common electrode30to the detection electrode20. Then, the current having flowed to the detection electrode20is output to the outside (control device101) of the force sensor1through the signal line12. With this configuration, whether force is applied to the detection surface1acan be detected based on existence of a signal output from the signal line12.

As the force F increases, the deformation amount of the sensor layer60increases and the resistance value of the sensor layer60decreases. In addition, as the force increases, the area of a contact region in which the sensor layer60contacts the detection electrode20and the common electrode30increases and the amount of current flowing to the detection electrode20increases. Accordingly, as force applied to the detection surface1aincreases, the output value (current value) that is output from the signal line12increases. Thus, the magnitude of force applied to the detection surface1acan be detected by measuring the magnitude of the value of current input to the detection electrode20.

As illustrated inFIG.5, the magnitude of the value of force input to the force sensor1and the magnitude of the output value that is output from the signal line12have a proportional relation in the present embodiment.

In the present embodiment, the resistance value of the sensor layer60is 1000Ω in a no-load state. The resistance value of the sensor layer60is 0Ω when largest possible force is input. Thus, the proportional relation is such that the decrease amount of the resistance value of the sensor layer60is larger as input force is larger. Accordingly, in the present embodiment, the proportional relation between the force value and the output value, which is illustrated inFIG.5can be replaced with the relation between (proportional relation) the decrease amount of the resistance value of the sensor layer60and the output value from the signal line12as illustrated inFIG.6.

In the force sensor1described above, a plurality of the detection electrodes20arrayed in the first direction Dx are coupled to signal lines12at mutually different positions in the first direction Dx. Accordingly, their path lengths to the control device101are mutually different. Furthermore, a plurality of the signal lines12disposed in the second direction Dy have mutually different characteristics. Thus, different output values are received by the control device101in some cases even when force input to the individual detection regions4has the same magnitude. The following describes correction circuits40and correction gate lines50for determining such a characteristic (that is, unevenness) of the output value of each individual detection region4.

As illustrated inFIG.3, one correction circuit40is provided in each individual detection region4. Each correction circuit40includes a first wire41and a second wire42. The first wire41and the second wire42each have one end coupled to the common electrode30and the other end coupled to the signal line12. Accordingly, the first wire41and the second wire42couple the detection electrode20and the drive transistor13in parallel.

The first wire41is provided with a first resistance component43having a first resistance value and a first wire switch element44configured to open and close the first wire41. The second wire42is provided with a second resistance component45having a second resistance value larger than the first resistance value and a second wire switch element46configured to open and close the second wire42.

The first resistance value of the first resistance component43is 200Ω. The first resistance value is relatively small in the range (0Ω to 1000Ω) of resistance value change assumed for the sensor layer60. The second resistance component45is a value larger than the first resistance value and 800Ω. The second resistance value is relatively large in the range (0Ω to 1000Ω) of resistance value change assumed for the sensor layer60.

As illustrated inFIG.2, the first wire switch element44and the second wire switch element46are transistors. The first wire switch element44and the second wire switch element46include semiconductor layers44aand46a, gate insulating films44band46b, gate electrodes44cand46c, drain electrodes44dand46d, and source electrodes44eand46e, respectively. The drain electrodes44dand46dare coupled to the signal line12(refer toFIG.3). The source electrodes44eand46eare coupled to the first resistance component43and the second resistance component45, respectively.

As illustrated inFIG.3, the correction gate lines50include a first correction gate line51for controlling the first wire switch element44and a second correction gate line52for controlling the second wire switch element46. The first correction gate line51and the second correction gate line52extend in the second direction Dy. The first correction gate line51is coupled to the gate electrode44cof the first wire switch element44. The second correction gate line52is coupled to the gate electrode46cof the second wire switch element46. A plurality of the first correction gate lines51and a plurality of the second correction gate lines52are disposed in the first direction Dx. The first correction gate lines51and the second correction gate lines52are coupled to the gate line drive circuits8.

The following describes the control device101. The control device101is what is called a computer and includes a central processing unit (CPU), a random access memory (RAM), a read only memory (ROM), and a storage unit102such as a hard disk drive (HDD). The CPU reads and executes a computer program stored in the RAM (performs calculation) and outputs a result of the calculation to a storage device. The RAM is a main memory in and from which computer programs and data can be recorded and read. The ROM stores a computer program such as a basic input/output system (BIOS).

FIG.7is a diagram illustrating the process of correction data calculation processing in the first embodiment. The control device101executes correction data calculation processing for correcting an output value received from the force sensor1. As illustrated inFIG.7, correction data calculation processing S1includes a first process S11of acquiring the output value of the individual detection region4, a second process S12of calculating an output value characteristic line representing characteristics of the output value of the individual detection region4, a third process S13of determining whether the output value characteristic line of every individual detection region4is calculated, and a fourth process S14of calculating correction coefficients (correction data) based on the output value characteristic line.

In the following description, the total number of the individual detection regions4of the present embodiment is N. An identification number i (i=1, 2, 3, . . . , N) is allocated to each individual detection region4to identify the individual detection region4. At the first process S11and the second process S12, one of the individual detection regions4is identified, and the first process S11and the second process S12are continuously performed for the identified individual detection region4. One of the individual detection regions4is identified in ascending order of the identification number i.

FIG.8is a diagram (graph) illustrating the relation between the output value obtained through the first process of the correction data calculation processing and the decrease amount of a resistance value. The first process S11acquires a first output value in a case where the first wire switch element44is closed and a second output value in a case where the second wire switch element46is closed.

Specifically, at the first process S11, for example, the first correction gate line51of the individual detection region4corresponding to the identification number i is scanned and the first wire switch element44is closed. Accordingly, current flows from the common electrode30to the first wire41. The current is transferred from the signal line12to the control device101through the first resistance component43and the first wire switch element44. An output value received by the control device101in this case is the first output value. Accordingly, characteristics (refer to points L1, L2, L3, . . . ) of the output value in a case where the resistance value of the sensor layer60is 200Ω, in other words, in a case where the decrease amount of the resistance value of the sensor layer60is 800Ω as illustrated inFIG.8are obtained.

Subsequently, the second correction gate line52of the individual detection region4corresponding to the identification number i is scanned and the second wire switch element46is closed. Accordingly, current flows from the common electrode30to the second wire42. The current is transferred from the signal line12to the control device101through the second resistance component45and the second wire switch element46. An output value received by the control device101in this case is the second output value. Accordingly, characteristics (refer to points M1, M2, M3, . . . ) of the output value in a case where the resistance value of the sensor layer60is 800Ω, in other words, in a case where the decrease amount of the resistance value of the sensor layer60is 200Ω as illustrated inFIG.8are obtained.

Through the first process described above, two of the first output value through the first resistance component43(in a case where the decrease amount of the resistance value is 800Ω) and the second output value through the second resistance component45(in a case where the decrease amount of the resistance value is 200Ω) are obtained in the individual detection region4of the identification number i as illustrated inFIG.8.

The second process S12calculates the output value characteristic line of the individual detection region4corresponding to the identification number i. The output value characteristic line is a straight line connecting the first output value (refer to points L1, L2, L3, . . . ) and the second output value (refer to points M1, M2, M3, . . . ) as illustrated inFIG.8. The output value characteristic line can be expressed in Expression (1) below.

In Expression (1), Oraw_Nrepresents the output value of the individual detection region4with the identification number of N. The number r represents the decrease amount of the resistance value of the sensor layer60(Ω). The numbers aNand bNare coefficients, and specifically, aNis the gradient of a straight line inFIG.8and bNis the intercept of the straight line. As illustrated inFIGS.5and6, the output value and the value of force input to the force sensor1(the decrease amount of the resistance value of the sensor layer60) have a proportional relation. Accordingly, a linear function of the resistance value r can be obtained as in Expression (1).

Then, at the second process S12, in order to calculate the coefficients aNand bNof the output value characteristic line, the first output value obtained when the first wire switch element44is closed is substituted into Oraw_N, and 800Ω as the decrease amount of the resistance value of the sensor layer60is substituted into r, thereby forming a first equation. Similarly, the second output value obtained when the second wire switch element46is closed is substituted into Oraw_N, and 200Ω as the decrease amount of the resistance value of the sensor layer60is substituted into r, thereby forming a second equation. Then, the coefficients aNand bNare calculated from the first equation and the second equation. Accordingly, Expression (1) representing the output value characteristic line of the individual detection region4is calculated.

Subsequently, at the third process S13, it is determined whether the output value characteristic line of every individual detection region4is calculated. In the present embodiment, the first process S11and the second process S12are performed in ascending order of the identification number i of the individual detection region4. Accordingly, at the third process S13, it is determined whether the identification number i of the individual detection region4for which the second process S12has ended is “N”. In a case where the identification number i is “N”, the individual detection region4is the last one, and thus it is determined that the output value characteristic line of every individual detection region4is calculated and the processing proceeds to the fourth process S14. In a case where it is determined that the identification number i is not “N”, the processing returns to the first process S11and the first and second output values of the individual detection region4to which the identification number “i+1” is allocated are obtained. In the present disclosure, the first process S11and the second process S12may be performed in descending order of the identification number i and the order does not matter.

The fourth process S14calculates a correction formula for each individual detection region4. The correction formula is a formula for obtaining an appropriate output value by correcting an output value received from the signal line12. Specifically, the control device101stores Expression (2) below as the correction formula.

In the expression, Onrepresents an appropriate (corrected) output value and A and B are correction coefficients (correction data). In addition, Oraw_Nrepresents an output value actually received from the signal line12and is expressed in Expression (1). The control device101stores the correction formula (2) for each individual detection region4. The following describes a process of calculating the correction coefficients A and B based on the output value characteristic line.

The control device101stores a correction target line of Expression (3) below.

FIG.9is a diagram (graph) illustrating the relation between the decrease amount of the resistance value of the sensor layer and the output value (current value) output from a signal line, and is a schematic diagram for description of matching of the output value characteristic line with the correction target line. As illustrated inFIG.9, a correction target line T (refer to a straight line denoted by reference sign T inFIG.9) is a linear expression for a predetermined output value when a predetermined amount of force is input. Characteristics of the output value characteristic line (refer to dashed lines P1and P2inFIG.9) obtained at the second process S12should normally match among all individual detection regions4but are different among the individual detection regions4due to difference in the path lengths of the signal lines12and the like. Accordingly, the output value characteristic line is calculated so as to overlap the correction target line T so that the output value characteristic line (refer to dashed lines P1and P2inFIG.9) matches among all individual detection regions4(refer to arrows inFIG.9). The calculation multiplies Expression (1) of the output value characteristic line by a coefficient that changes the gradient and adds a coefficient that changes the intercept to the expression. Specifically, Expression (4) below is obtained.

In Expression (4), “atarget/aN” is a coefficient that corrects the gradient of Expression (1) and corresponds to the correction coefficient A of Expression (2). In addition, “btarget−((atarget×bn)/aN)” is a coefficient that corrects the intercept of Expression (1) and corresponds to the correction coefficient B of Expression (2). Accordingly, the correction coefficients A and B of Expression (2) are calculated from the output value characteristic line.

FIG.10is a diagram illustrating the correction coefficients A and B stored in the storage unit of the control device. When having calculated the correction coefficients A and B of the individual detection regions4, the control device101stores the correction coefficients A (A1, A1, . . . , An) and B (B1, B1, . . . , Bn) of the individual detection regions4in the storage unit102as illustrated inFIG.10and ends the correction data (the correction coefficients A and B) calculation processing S1(END).

Through the above-described processing, the correction data (correction coefficients A and B) can be acquired. Moreover, it is possible to eliminate work of preparing a jig that can contact the entire detection region2and pressing the jig against the detection region2. Thus, according to the present embodiment, the correction data (correction coefficients A and B) can be easily acquired. The following describes force value calculation processing S2of the control device101.

FIG.11is a diagram illustrating the process of force value calculation processing of the first embodiment. As illustrated inFIG.11, the force value calculation processing S2includes a process S21of acquiring the output value of each individual detection region4, a process S22of calculating a corrected output value based on the output value, and a process S23of calculating a force value based on the corrected output value.

At the process S21of acquiring the output value of each individual detection region4, the control device101sends a drive signal to the gate line drive circuits8and the signal line selection circuit9. Then, the control device101acquires the output value from each individual detection region4through the signal line12.

At the process S22of correcting the output value, the received output value is substituted into Expression (2). In addition, the correction coefficients A and B of the individual detection region4corresponding to the output value are read from the storage unit102and substituted into Expression (2) described above. Accordingly, a corrected output value Onis obtained. Through this process, characteristics (what is called unevenness) of the output value of each individual detection regions4are eliminated. Thus, the corrected output value has the same value when the same force is applied.

The process S23of calculating a force value calculates a force value corresponding to the corrected output value On. The control device101calculates the force value corresponding to the corrected output value Onbased on the correction target line T and ends the calculation processing S2(END).

Although the first embodiment is described above, the present disclosure is not limited to the above-described example. For example, the control device101of the first embodiment stores the calculated correction coefficients A and B in the storage unit102, but according to the present disclosure, the correction coefficients A and B may be temporarily held in the RAM. Alternatively, the correction coefficients A and B do not necessarily need to be temporarily held as described in the following second embodiment. The second embodiment will be described below.

Second Embodiment

FIG.12is a diagram illustrating the process of calculation processing according to the second embodiment. As illustrated inFIG.12, calculation processing S3by the control device101includes a process S1A of calculating correction data (correction coefficients A and B), a process S2of calculating a force value, and a process S31of determining whether the force value of every individual detection region4is calculated. The process S2of calculating a force value performs the same processing as the force value calculation processing S2described in the first embodiment (refer toFIG.11). The process S31of determining whether the force value of every individual detection region4is calculated performs the same processing as the third process S13included in the correction data calculation processing S1of the first embodiment. Thus, description of the process S2and the process S31is omitted.

The process S1A of calculating correction data is the same as the correction data calculation processing S1of the first embodiment in that the process S1A includes the first process S11, the second process S12, and the fourth process S14(refer toFIG.7). However, the process S1A of calculating correction data is different from the first embodiment in that the process S1A does not include the third process S13. Moreover, the process S1A of calculating correction data is different from the first embodiment in that the process S1A proceeds to the process S2of calculating a force value without storing the correction coefficients A and B after calculating the correction coefficients A and B at the fourth process S14. Thus, in the second embodiment, a force value is continuously calculated without interruption after the process S1A of calculating correction data ends. In other words, in the present embodiment, the correction coefficients are calculated in the units of frames (for each frame) where one frame is a duration in which force detection is completed in all individual detection regions4. Accordingly, detection accuracy improves.

In the first embodiment, the correction circuits40are provided in the respective individual detection regions4, but the present disclosure is not limited thereto. The following describes a third embodiment and a fourth embodiment in which the correction circuits40are not disposed for the respective individual detection regions4.

Third Embodiment

FIG.13is a circuit diagram illustrating a circuit configuration of a force sensor of the third embodiment. Correction circuits40B of a force sensor1B of the third embodiment are different from those of the first embodiment in that each correction circuit40B is provided for a plurality of the detection electrodes20arrayed in the second direction Dy (in that each correction circuit40B is provided for a row of the detection electrodes20). Moreover, the force sensor1B of the third embodiment is different from that of the first embodiment in that the force sensor1B includes two correction signal lines47and48extending in the first direction Dx.

A first wire41B and a second wire42B of each correction circuit40B are disposed in the peripheral region3. Similarly, the correction signal lines47and48are disposed in the peripheral region3. The correction signal lines47and48are coupled to the signal line selection circuit9. The first wire41B and the second wire42B each have one end coupled to the common electrode30common to the detection electrodes20arrayed in the second direction Dy. The other ends of the first wire41B and the second wire42B are coupled to the correction signal lines47and48.

According to the third embodiment, the correction coefficients A and B obtained by each correction circuit40B are used to correct output values detected in the individual detection regions4arrayed in the second direction Dy for the correction circuit40B. Specifically, the output values detected in the individual detection regions4arrayed in the second direction Dy are corrected by the common correction coefficients A and B. Thus, according to the third embodiment, the number of correction coefficients A and B to be calculated decreases. Moreover, characteristics (what is called unevenness) of the output values of the individual detection regions4arrayed in the second direction Dy are eliminated.

Fourth Embodiment

FIG.14is a circuit diagram illustrating a circuit configuration of a force sensor of the fourth embodiment. Correction circuits40C of a force sensor1C of the fourth embodiment are different from those of the first embodiment in that each correction circuit40C is provided for the detection electrodes20arrayed in the first direction Dx. A first wire41C and a second wire42C of each correction circuit40C are disposed in the peripheral region3. In addition, correction gate lines50C (a first correction gate line51C and a second correction gate line52C) and the common electrode30are disposed in the peripheral region3. The first wire41C and the second wire42C each have one end coupled to the common electrode30. The other ends of the first wire41C and the second wire42C are coupled to the signal line12common to the detection electrodes20arrayed in the first direction Dx.

According to the fourth embodiment, the correction coefficients A and B obtained by each correction circuit40C are used to correct output values detected in the individual detection regions4arrayed in the first direction Dx for the correction circuit40C. Specifically, the output values detected in the individual detection regions4arrayed in the first direction Dx are corrected by the common correction coefficients A and B. Thus, according to the third embodiment, the number of correction coefficients A and B to be calculated decreases. Moreover, characteristics (what is called unevenness) of the output values of the individual detection regions4arrayed in the first direction Dx are eliminated.

Although the embodiments are described above, the present disclosure only needs to have a proportional relation between force input to each individual detection region4and the output value from the signal line12, and the sensor layer60is not limited to that described above. For example, a configuration obtained by adding any one or both of the third embodiment and the fourth embodiment to the above-described configuration of the first embodiment is employable. The following describes modifications of the sensor layer60.

First Modification

FIG.15is a sectional view illustrating a section of a force sensor of a first modification. A sensor layer60D of a force sensor1D of the first modification is provided between the first surface6aof the array substrate6and the protective layer70and no space S (refer toFIG.2) is provided. The sensor layer60D contacts the detection electrode20and the common electrode30even when no deformation occurs. The sensor layer60D contains conductive fine particles inside insulating resin as described above in the first embodiment. The sensor layer60provides insulation when no force is applied, in other words, when no deformation is present. When force is applied and deformation occurs, the resistance value decreases and the common electrode30and the detection electrode20are electrically coupled to each other. As the force increases, the deformation amount of the sensor layer60D increases and the amount of current flowing to the detection electrode20increases. However, the area of a contact region in which the sensor layer60D contacts the common electrode30and the detection electrode20does not change as the force increases. In other words, the sensor layer60D does not have such a function that the amount of current flowing to the detection electrode20changes as the contact area changes, which is a difference from the sensor layer60of the first embodiment.

Second Modification

FIG.16is a sectional view illustrating a section of a force sensor of a second modification.FIG.17is a sectional view of the force sensor of the second modification when force is input. A sensor layer60E of a force sensor1E of a fourth modification includes two convex portions61protruding toward the detection electrode20and the common electrode30. A distal end part of each convex portion61contacts the detection electrode20or the common electrode30. The sensor layer60E is made of ITO or a semiconductor material and made of a highly insulating material. In such a state, the distal end part of each convex portion61has a small area of contact with the detection electrode20and the common electrode30. Accordingly, the detection electrode20and the common electrode30are not electrically coupled to each other.

However, when the detection surface1ais pressed as illustrated inFIG.17, the sensor layer60E deforms in the third direction Dz and the area of contact between each convex portion61and the detection electrode20or the common electrode30increases. Accordingly, the sensor layer60E electrically couples the detection electrode20and the common electrode30and current flows to the detection electrode20. As force applied to the sensor layer60E increases, the area of contact between each convex portion61and the detection electrode20or the common electrode30increases, and accordingly, the amount of current flowing through the sensor layer60E increases. Specifically, the amount of current input to the detection electrode20increases in proportion to increase in the area of contact of the sensor layer60E. Thus, the magnitude of force input to the detection surface1acan be detected.

The sensor layer60E of the second modification is described above as an exemplary sensor layer having a resistance value that changes as the area of contact changes, but the force sensor of the present disclosure may include a sensor layer shaped and disposed differently from the sensor layer60E and is not limited to a particular sensor layer.

The common electrode30is disposed on the first surface6aof the array substrate6in the embodiments but may be a solid film provided between the sensor layer60and the protective layer70and is not particularly limited.