Touch input device that detects a touch position and a pressing input

A touch input device includes a touch panel, a press detection signal generating unit and a touch detection signal generating unit. The touch panel is formed by laminating a piezoelectric sensor and a capacitive sensor. The piezoelectric sensor is connected to the press detection signal generating unit, and the capacitive sensor is connected to the touch detection signal generating unit. The piezoelectric sensor includes a piezoelectric film, and first and second press detecting conductors disposed with the piezoelectric film sandwiched therebetween. The piezoelectric film is disposed such that a polarity of electric charges produced by a press in the piezoelectric film, and a polarity of excited electric charges produced in the piezoelectric film when the capacitive sensor detects a touch become reverse polarities.

TECHNICAL FIELD

The present invention relates to a touch input device that detects a touch position and a pressing input on an operation surface.

BACKGROUND

Conventionally, various touch input devices which each detect a touch position and a press on an operation surface have been devised. For example, Patent Literature 1 discloses a resistive touch panel. The touch panel in Patent Literature 1 includes a first conductive film and a second conductive film including principal surfaces parallel to an operation surface, and the first conductive film and the second conductive film are disposed at an interval in a direction orthogonal to the principal surfaces. When the operation surface is pushed, the first conductive film and the second conductive film contact with each other at a pushed position. The touch input device in Patent Literature 1 detects a touch position based on a partial pressure at this touched position, and detects a press based on the partial pressure and a resistance.

Such a configuration and an operation need a switch circuit which switches a touch position detection circuit and a press detection circuit to the first conductive film and the second conductive film to connect. Further, according to the configuration of Patent Literature 1, if a first electrode film and a second electrode film do not contact, i.e., if the operation surface is not pushed to some degree, it is not possible to detect a position.

Meanwhile, conventionally, a touch input device whose position detection sensor and press detection sensor are formed by using different base members, and which employs a configuration obtained by overlaying the position detection sensor and the press detection sensor has also been devised. According to this configuration, the position detection sensor is connected to a touch position detection circuit, and the press detection sensor is connected to a press detection circuit, and therefore a switch circuit is not necessary. Further, according to this configuration, it is possible to detect a position even when an operation surface is softly touched.

In this regard, by using a capacitive position detection sensor as the position detection sensor, it is possible to detect a touch position based on a change in a capacitance. Even when the operation surface is softly touched, i.e., even when the operation surface is not strongly pushed, it is possible to detect a touch position.

Further, while such a position detection sensor is used, a piezoelectric sensor for which a piezoelectric film is used is used as the press detection sensor in some cases.PTL 1: Japanese Patent Application Laid-Open No. 2000-283869.

However, a combination of the capacitive position detection sensor and the press detection sensor formed by the piezoelectric sensor causes a following problem.

Electric charges are regularly injected to the position detection sensor to enable the capacitive position detection sensor to measure a capacitance. This injection amount changes according to the capacitance, and therefore changes between the case when a dielectric such as a finger touches the operation surface and the case when the dielectric does not touch the operation surface.

When the position detection sensor and the press detection sensor are disposed close to each other, the press detection sensor and the position detection sensor are capacitively coupled. In this case, electric charges are produced in the press detection sensor due to an influence of part of the electric charges injected to the position detection sensor.

The press detection sensor formed by the piezoelectric sensor detects whether or not there is a press or a pressing force based on electric charges produced when a piezoelectric film is deformed by a press on the operation surface.

Hence, when electric charges produced by the influence of the electric charges of the position detection sensor are produced in the press detection sensor, the press detection sensor erroneously detects these electric charges as electric charges produced by the piezoelectric sensor in response to a press. Therefore, it is not possible to accurately detect a pressing amount in some cases.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a touch input device that can accurately detect a press even for a touch sensor having a capacitive position detection sensor and a press detection sensor formed by a piezoelectric sensor disposed close to each other.

A touch input device according to the present invention includes a position detection sensor, a press detection sensor, a press detection signal generating unit and a touch detection signal generating unit. The position detection sensor is a capacitive sensor, and includes a first position detecting conductor and a second position detecting conductor. The press detection sensor is a so-called piezoelectric sensor, and includes a piezoelectric film, and a first press detecting conductor and a second press detecting conductor disposed with the piezoelectric film sandwiched therebetween. The press detection signal generating unit generates a press detection voltage signal by using an electric charge outputted from the press detection sensor. The touch detection signal generating unit generates a touch detection voltage signal by applying a voltage to the position detection sensor and obtaining the electric charge of the position detection sensor.

The position detection sensor and the press detection sensor are disposed close to each other. The press detection sensor is disposed such that the electric charge produced in the press detection sensor by the voltage applied to the position detection sensor, and the electric charge produced in the press detection sensor in response to a press become reverse polarities.

According to this configuration, electric charges excited in the press detection sensor by the voltage applied to the position detection sensor when there is no press (push), and electric charges produced in the press detection sensor by the press have opposite influences which are given on a voltage value of the press detection voltage signal. When, for example, the electric charges excited by the voltage applied to the position detection sensor cause the press detection voltage signal to function to increase the voltage, the electric charges produced by a press function to decrease the voltage of the press detection voltage signal. Consequently, it is possible to distinguish between a change in a voltage value of the press detection voltage signal caused by the electric charges excited by a touch, and a change in a voltage of the press detection voltage signal caused by the electric charges in response to a press.

Further, preferably, in the touch input device according to the present invention, the first position detecting conductor and the first press detecting conductor are formed on a same plane.

According to this configuration, it is possible to make thin a combined body (touch sensor) on which the position detection sensor and the press detection sensor are laminated.

Further, preferably, in the touch input device according to the present invention, the piezoelectric film is made of a chiral polymer. Furthermore, preferably, in the touch input device according to the present invention, the piezoelectric film is made of polylactic acid stretched in at least a uniaxial direction.

These configurations are a preferable example of the piezoelectric film.

According to the present invention, it is possible to accurately detect a press while using a touch sensor in which a capacitive position detection sensor and a press detection sensor formed by a piezoelectric sensor are disposed close to each other.

DETAILED DESCRIPTION

A touch input device according to an embodiment of the present invention will be described with reference to the drawings.FIG. 1is a block diagram of the touch input device according to the embodiment of the present invention.

FIG. 2is a side sectional view illustrating main components of a touch panel according to the embodiment of the present invention.

A touch input device1includes a touch panel10, a press detection signal generating unit200and a touch detection signal generating unit300. The touch panel10includes a piezoelectric sensor10P and a capacitive sensor10D. The piezoelectric sensor10P corresponds to a “press detection sensor” according to the present disclosure, and the capacitive sensor10D corresponds to a “capacitive position detection sensor” according to the present disclosure.

The touch panel10has a flat shape, and includes an operation surface which is at least one principal surface (flat surface) of the flat surface, and receives an operator's operation. The piezoelectric sensor10P and the capacitive sensor10D also have flat shapes, and are laminated such that the principal surfaces of the flat shapes are parallel with each other. The capacitive sensor10D and the piezoelectric sensor10P are laminated in order from an operation surface side on the touch panel10according to the present embodiment.

The piezoelectric sensor10P includes a piezoelectric film110, first press detecting conductors111and second press detecting conductors112. The piezoelectric film110is made of a material including polylactic acid (PLA) and, more specifically, poly-L-lactic acid (PLLA). In addition, the piezoelectric film110needs to be a film having piezoelectricity, and is preferably made of a material including chiral polymers and is more preferably made of a material including PLA and PLLA. In addition, when the piezoelectric film110is formed by using PLLA, the piezoelectric film110is uniaxially stretched. A piezoelectric constant of the uniaxially stretched PLLA belongs to a group of high piezoelectricities among polymers.

In addition, the stretching ratio is preferably about three to eight times. Applying heat processing after the stretching encourages crystallization of extended chain crystal of polylactic acid, and increase the piezoelectric constant. In addition, when a film is biaxially stretched, it is possible to provide the same effect as that of the uniaxial stretching by varying stretching ratios of respective axes. When, for example, a film is stretched eight times in a given direction serving as an X axis, and the film is stretched two times in a Y axis direction orthogonal to the X axis, it is possible to provide for a piezoelectric constant the substantially same effect obtained when the film is uniaxially stretched four times in the X axis direction. Simply uniaxially stretching a film is likely to break along a stretching axis direction, and therefore it is possible to increase a stretch by biaxially stretching the film as described above. Thus, even when a film is biaxially stretched, if the film is in a state which is substantially equal to a state obtained by uniaxially stretching the film, the film corresponds to polylactic acid stretched in at least the uniaxial direction of the present invention.

Further, PLLA produces piezoelectricity by orientation processing of molecules such as stretching, and does not need to be subjected to polling processing unlike other polymers such as PVDF or piezoelectric ceramics. That is, the piezoelectricity of the PLLA which does not belong to ferroelectrics does not appear due to the ion polarization unlike ferroelectrics such as PVDF and PZT, and derives from a spiral structure which is a characteristics structure of molecules. Hence, the PLLA does not have pyroelectricity included in piezoelectric bodies of the other ferroelectrics, and therefore electric charges are not produced by the pyroelectricity. Further, the PVDF or the like shows a temporal fluctuation of a piezoelectric constant, and the piezoelectric constant remarkably lowers depending on cases. However, the piezoelectric constant of the PLLA is temporarily very stable.

Furthermore, a relative permittivity of the PLLA is about 2.5 and very low, and therefore when d is a piezoelectric constant and ∈Tis a permittivity, a piezoelectric output constant (=piezoelectric g constant where g=d/∈Tholds) takes a high value.

In this regard, permittivity ∈33T=13×∈0, the piezoelectric g constant of the PVDF having a piezoelectric constant d31=25 pC/N is g31=0.2172 Vm/N according to the above equation. Meanwhile, when the piezoelectric g constant of the PLLA having a piezoelectric constant d14=10 pC/N is converted into g31and calculated, d14=2×d31holds, and therefore d31=5 pC/N holds and the piezoelectric g constant takes g31=0.2258 Vm/N. Consequently, it is possible to provide the same sufficient pressing force (push amount) detection sensitivity as that of the PVDF by using the PLLA having the piezoelectric constant d14=10 pC/N. Further, the inventors of the present invention have experimentally obtained the PLLA having d14=15 to 20 pC/N. By using this PLLA, it is possible to detect a pressing force with a very high sensitivity.

Further, the PLLA has high translucency. Consequently, by forming the piezoelectric film110by using the PLLA, and making the first and second press detecting conductors111and112described below by using a material having high translucency, it is possible to realize the piezoelectric sensor10P having translucency.

On a first principal surface of the piezoelectric film, the first press detecting conductors111are formed. Further, on a second principal surface of the piezoelectric film110, the second press detecting electrodes112are formed.

By using, for a plurality of these first and second press detecting conductors111and112, any one of an organic electrode whose main component is polythiophene and polyaniline, and inorganic electrodes such as ITO, ZnO, silver nanowires, carbon nanotubes and graphene, it is possible to form a conductor pattern having high translucency. In addition, when translucency is not necessary, an electrode formed by using a silver paste or a metal electrode formed by deposition, sputtering or plating can also be used.

The first and second press detecting conductors111and112are connected to the press detection signal generating unit200via a wiring conductor113.

The capacitive sensor10D includes a dielectric substrate120, first position detecting conductors121and second position detecting conductors122. The dielectric substrate120is made of a dielectric material having translucency, and is made of glass, for example.

On a first principal surface of the dielectric substrate120, in other words, on a surface of the dielectric substrate120at a side of the piezoelectric sensor10P, a plurality of first position detecting conductors121is formed. A plurality of first position detecting conductors121is each formed in an elongated shape, and each has a shape stretched in a first direction of the first principal surface of the dielectric substrate120. A plurality of first position detecting conductors121is formed respectively by being aligned at intervals in a second direction (a direction orthogonal to the first direction) of the first principal surface.

In addition, the first press detecting electrodes111of the above piezoelectric sensor10P, and the first position detecting conductors121of the capacitive sensor10D are disposed between the piezoelectric film110and the dielectric substrate120, and are disposed at the same positions of the touch sensor10in a lamination direction. The first press detecting electrodes111and the first position detecting conductors121are disposed without touching each other.

On a second principal surface of the dielectric substrate120, in other words, on a surface of the dielectric substrate120at a side of the operation surface, a plurality of second position detecting conductors122is formed. A plurality of second position detecting conductors122is each formed in an elongated shape, and each has a shape stretched in a second direction of the second principal surface of the dielectric substrate120. A plurality of second position detecting conductors122is formed respectively by being aligned at intervals in the first direction (the direction orthogonal to the second direction) of the second principal surface.

The first and second position detecting conductors121and122are formed by using transparent electrodes such as ITO. The first and second position detecting conductors121and122are connected to the touch detection signal generating unit300via a wiring conductor pattern123.

An insulation film114is attached to an outer surface of the piezoelectric sensor10pat the side of the second press detecting electrode112, and an insulation film124is attached to an outer surface (operation surface) of the capacitive sensor10D at the side of the second position detecting conductors122.

When a dielectric such as a finger (referred to simply as a finger below) approaches or touches the operation surface of the touch sensor10employing this configuration, a capacitance of the capacitive sensor10D at a touched position changes. This change in the capacitance is detected as a touch detection voltage by the touch detection signal generating unit300, and the touch detection signal generating unit300generates and outputs a touch detection signal taking this voltage value.

The capacitance produced by the capacitive sensor10D changes according to a distance between the finger and the operation surface or between a touch area of the finger and the operation surface. Therefore, when the touch area does not change, the capacitance is the same irrespectively of whether a pressing force is high or low. That is, depending on whether or not the finger touches the operation surface, the voltage value of the touch detection signal changes. Further, by observing the voltage value of this touch detection signal, it is possible to determine whether or not the operation surface is touched. Furthermore, the first position detecting conductors121and the second position detecting conductors122are disposed as described above, so that overlapping portions of the first position detecting conductors121and the second position detecting conductors122are projected on the operation surface as a matrix pattern.

Still further, the capacitance changes the most at the touch position. Consequently, by obtaining a touch detection signal per pair of the first and second position detecting conductors121and122, the capacitive sensor10D can detect the touch position.

Further, when the finger pushes the operation surface of the touch sensor10, the piezoelectric film110of the piezoelectric sensor10pdeflects according to the pressing force (push amount). The piezoelectric film110produces electric charges corresponding to the amount of this deflection. A potential difference is produced between the first and second press detecting conductors111and112by electric charges as a result of this piezoelectric effect. The press detection signal generating unit200generates a press detection signal taking a voltage value including this potential difference.

The touch detection signal generating unit300is connected to the capacitive sensor10D as described above, and includes circuitry to generate a touch detection signal corresponding to a touch detection voltage. In particular, the touch detection signal generating unit300can be a circuit that includes comparators and similar circuitry as would be understood to one skilled in the art to compare the output from capacitive sensor10D with predetermined touch detection threshold. Moreover, the unit can include an electronic storage unit that stores programs for the control process and the threshold value. The unit reads the programs and threshold value and executes the controls and processes. Thus, the electronic storage unit can be used as a computation memory at executing the controls and processes. Moreover, the touch detection signal is a signal binarized into High or Low. Specifically, the touch detection signal generating unit300sets a touch detection threshold to the touch detection voltage, and outputs a touch detection signal of a High state in a period in which a touch detection voltage is equal to or more than the touch detection threshold. The touch detection signal generating unit300outputs a touch detection signal of a Low state in a period in which the touch detection voltage is not equal to or more (i.e., is less) than the touch detection threshold.

The touch detection signal generating unit300outputs a touch detection signal to the press detection signal generating unit200and a first output terminal Pout1. In this case, the touch detection signal generating unit300needs to output only the touch detection signal to the press detection signal generating unit200, and outputs the touch detection signal together with information related to a touch position to the first output terminal Pout1.

As shown inFIG. 2, the press detection signal generating unit200includes an operational amplifier U1, a resistor R1, a capacitor C1, a discharge resistor R0and a switch element S0. An inverting input terminal of the operational amplifier U1is connected to the piezoelectric sensor10P via the resistor R1.

Hence, a signal having a potential difference produced by the piezoelectric sensor10P is inputted to the inverting input terminal of the operational amplifier U1via the resistor R1. A reference potential V1is applied to a non-inverting input terminal of the operational amplifier U1.

An output terminal of the operational amplifier U1is connected to a second output terminal Pout2of the touch input device1. The capacitor C1is connected between the inverting input terminal and the output terminal of the operational amplifier U1. The discharge resistor R0and the switch element S0are connected in series, and this serial circuit is connected in parallel to the capacitor C1.

On and off of the switch element S0is controlled according to High or Low of the touch detection signal. For example, the switch element S0enters an ON state when the touch detection signal is in a Low state, and enters an OFF state when the touch detection signal is in a High state. More specifically, the switch element S0is realized by a normally-on FET, for example.

Thus, control to turn on the switch element S0is performed in a period in which the touch detection signal of the Low state is inputted, and control to turn off the switch element S0is performed in a period in which the touch detection signal of the High state is inputted. That is, control to turn on the switch element S0is performed in a period in which the touch is not detected, and control to turn off the switch element S0is performed in a period in which the touch is detected.

In addition, when a normally-on element is used for the switch element S0, a touch detection signal taking the above binary value needs to be used. However, when a normally-off element is used for the switch element S0, a binary state of the touch detection signal needs to be inverted. That is, a touch detection signal which enters the Low state in a period in which a touch is detected and which enters a High state in a period in which a touch is not detected needs to be used.

By employing such a circuit configuration, in a period in which the switch element S0is in an OFF state, an integration circuit formed by the operational amplifier U1, the resistor R1and the capacitor C1is formed in the press detection signal generating unit200. Hence, the press detection signal generating unit200integrates a difference between potentials produced by the piezoelectric sensor10P, and the reference potential, and outputs a press detection signal which is an integration result, to the second output terminal Pout2.

That is, in a period in which a touch is detected, the press detection signal generating unit200integrates differences between potentials produced by the piezoelectric sensor10P, and the reference potential. Further, the press detection signal generating unit200outputs the press detection signal which is this integration result, to the second output terminal Pout2.

Meanwhile, when the switch element S0is in the ON state, a circuit configuration with the capacitor C1and the discharge resistor R0connected in parallel is employed. Thus, the press detection signal generating unit200stops functioning as the integration circuit. Hence, the press detection signal generating unit200outputs a signal based on a potential produced by the piezoelectric sensor10P as is, to the second output terminal Pout2. Further, a closed-loop circuit formed by the capacitor C1and the discharge resistor R0is configured, so that electric charges stored in the capacitor C1are discharged and consumed by the discharge resistor R0. Hence, the potential of the output terminal Pout2is reset to the reference potential.

That is, in a period in which a touch is detected, the press detection signal generating unit200resets the potential of the second output terminal Pout2to the reference potential.

In the touch input device10employing such a configuration, the first position detecting conductors121of the capacitive sensor10D and the first press detecting electrodes111of the piezoelectric sensor10P are close to each other. Therefore, as the problem is described above, electric charges produced by the capacitive sensor10D excite electric charges in the piezoelectric sensor10P. That is, electric charges excited in response to detection of a touch are produced.

However, even in case where the excited electric charges are produced, by employing the following configuration, it is possible to accurately detect electric charges produced when the piezoelectric film110deflects.FIGS. 3(A) and 3(B)are views for explaining a principal for detecting electric charges produced by a press on the touch input device according to the embodiment of the present invention.

The piezoelectric film110of the piezoelectric sensor10P produces electric charges corresponding to a deflection amount when deflection occurs as described above. In this regard, the electric charge amount is determined based on a relationship between a deflection direction and a uniaxial stretching direction, and a deflection amount. Further, the polarity at which electric charges are produced is determined based on a relationship between the deflection direction and the uniaxial stretching direction.

Hence, the polarity of electric charges produced by the piezoelectric film110in response to a press, and the polarity of excited electric charges produced in the piezoelectric film110are made to have reverse polarities.

In, for example, a case illustrated inFIGS. 3(A) and 3(B), when the finger touches (or approaches) the operation surface, the first position detecting conductors121and the second position detecting conductors122are connected to the touch detection signal generating unit300and are applied voltages by the touch detection signal generating unit300via the wiring conducting pattern123, such that the first position detecting conductor121side of the dielectric substrate120are charged with negative electric charges and the second position detecting conductor122side of the dielectric substrate120are charged with positive electric charges.

In this case, as illustrated inFIG. 3(A), the first press detecting conductor111side of the piezoelectric film110is charged with positive electric charges, and the second press detecting conductor112side of the piezoelectric film110is charged with negative electric charges.

Hence, as illustrated inFIG. 3(B), a uniaxial stretching direction is set to the piezoelectric film110such that the first press detecting conductor111side is charged with negative electric charges, and the second press detecting conductor112side is charged with positive electric charges in response to a press on the operation surface.

By using such a configuration, a touch detection voltage and a press detection voltage (a voltage value of the press detection signal) have waveforms illustrated inFIG. 4.FIG. 4is a waveform diagram of a touch detection voltage and a press detection voltage detected by the touch input device according to the embodiment of the present invention.

When the above configuration is employed and the finger touches the operation surface, the touch detection voltage rises. Consequently, it is possible to detect a touch of the finger on the operation surface. Simultaneously, the press detection voltage also rises from a reference voltage. However, as described above, when a press is applied, the piezoelectric sensor10P is configured to produce a negative voltage. Consequently, even when the press detection voltage rises from the reference voltage, it is possible to determine that the rise is not caused by the press.

Next, when the operation surface is pushed by a finger (the press is applied), the press detection voltage lowers from a second reference voltage obtained by adding a voltage of excited electric charges to the reference voltage according to a pressing force. Consequently, by detecting a decrease in this press detection voltage, it is possible to detect that the operation surface has been pushed (pressed). Further, by detecting a voltage decrease amount, it is possible to detect the pressing force. In addition, the press detection voltage rises in such a way that the press detection voltage gradually returns to the second reference voltage according to a constant of the integration circuit included in the press detection signal generating unit200.

Next, when the push of the finger on the operation surface is released (the press is released), the press detection voltage rises from the second reference voltage. Consequently, by detecting a decrease in this press detection voltage, it is possible to detect that the push on the operation surface has been released.

In addition, the press detection voltage lowers in such a way that the press detection voltage gradually returns to the second reference voltage according to a constant of the integration circuit included in the press detection signal generating unit200.

Next, when the finger is moved away from the operation surface, the touch detection voltage lowers. Consequently, it is possible to detect a touch of the finger on the operation surface. Simultaneously, the press detection voltage also lowers to the reference voltage, and can return to a press detection standby state.

As described above, by employing the configuration according to the present embodiment, even a touch sensor in which a capacitive position detection sensor and a press detection sensor formed by a piezoelectric sensor are disposed close to each other can accurately detect a press.

In addition, in the above embodiment, the first position detecting conductors121of the capacitive position detection sensor and the first press detecting conductors111of the press detection sensor are disposed on the same plane, i.e., on the piezoelectric film110. However, the present embodiment is not limited to this. For example, even in case of a touch sensor including an adhesive layer between the first position detecting conductors121of the capacitive position detection sensor and the first press detecting conductors111of the press detection sensor, the capacitive position detection sensor and the press detection sensor formed by the piezoelectric sensor are disposed close to each other. Accordingly, a technical idea of the present invention is effective. However, to make the touch sensor thinner, it is preferably to dispose the first position detecting conductors121and the first press detecting conductors111on the same plane.

Further, by adopting a structure in which the first position detecting conductors121and the first press detecting conductors111are disposed on one surface of the piezoelectric film110and disposing the second position detecting conductors122and the second press detecting conductors112on the other surface of the piezoelectric film110without using the dielectric substrate120, it is possible to form a thinner touch sensor.

DESCRIPTION OF REFERENCE SYMBOLS

1: TOUCH INPUT DEVICE10: TOUCH SENSOR10D: CAPACITIVE SENSOR10P: PIEZOELECTRIC SENSOR110: PIEZOELECTRIC FILM111: FIRST PRESS DETECTING CONDUCTOR112: SECOND PRESS DETECTING CONDUCTOR113: WIRING CONDUCTOR PATTERN114: INSULATION FILM120: DIELECTRIC SUBSTRATE121: FIRST POSITION DETECTING CONDUCTOR122: SECOND POSITION DETECTING CONDUCTOR123: WIRING CONDUCTOR PATTERN124: INSULATION FILM200: PRESS DETECTION SIGNAL GENERATING UNIT300: TOUCH DETECTION SIGNAL GENERATING UNIT