JP3959532B2 - Ultrasonic contact position detector - Google Patents

Description

BACKGROUND OF THE INVENTION
The present invention relates to an ultrasonic contact position detecting device for detecting that a human finger or an object has touched a piezoelectric substrate provided with interdigital electrodes for input and output, and detecting the position thereof.
[Prior art]
A conventional touch panel using an ultrasonic method utilizes the fact that a surface acoustic wave is attenuated by exciting a surface acoustic wave on a non-piezoelectric plate and coming into contact with the non-piezoelectric plate. Examples of conventional methods for exciting a surface acoustic wave on a non-piezoelectric plate include a method of indirectly exciting with a wedge-shaped transducer using a bulk wave vibrator, a method of directly exciting with a piezoelectric thin film transducer, and the like. The wedge-shaped transducer is used for non-destructive inspection using ultrasonic waves, but is used only in a relatively low frequency range due to the problem of the working accuracy of the wedge angle. A piezoelectric thin film transducer is a method in which a piezoelectric thin film such as ZnO is vapor-deposited on a substrate and a surface acoustic wave is excited by a comb-like electrode. There are problems in workability and mass productivity as well as in the VHF band. As described above, the conventional ultrasonic touch panel has problems in response time, sensitivity, durability, work accuracy, workability, mass productivity, ease of use, and the like, and the use frequency range is also limited. Therefore, an ultrasonic touch panel that solves these problems has been filed by the present inventor in Japanese Patent Application No. 4-218336. This ultrasonic touch panel is formed by providing at least two ultrasonic devices each composed of a piezoelectric thin plate and a comb-like electrode on one surface of a non-piezoelectric plate. It can be excited on the plate surface of the plate. Therefore, when one ultrasonic device is used for input and the other ultrasonic device is used for output, if the finger or object comes into contact with the propagation path of the surface acoustic wave on one plate surface of the non-piezoelectric plate, Since the surface wave attenuates or disappears, the electric signal output to the interdigital electrode in the output ultrasonic device also attenuates or disappears. However, the conventional touch panel including the ultrasonic touch panel requires further improvement in the fineness of the contact position, and the signal processing method has to be complicated.
[Problems to be solved by the invention]
Conventional ultrasonic touch panels not only have problems in sensitivity, machining accuracy, workability, mass productivity, power consumption, etc., but also have problems in signal processing methods and circuit configurations.
The object of the present invention is excellent in workability, durability and mass productivity, low power consumption drive, short response time, simple signal processing, small circuit scale, and precise detection of contact position. Another object of the present invention is to provide an ultrasonic contact position detecting device excellent in ease of use.
[Means for Solving the Problems]
The ultrasonic contact position detecting device according to claim 1, wherein the interdigital electrodes T and R are provided on one plate surface of the piezoelectric substrate,
The thickness of the piezoelectric substrate has a value more than three times the electrode period length P of the interdigital electrode T;
The direction of the electrode finger of the interdigital electrode T and the direction of the electrode finger of the interdigital electrode R are not parallel to each other, and the direction of the electrode finger of the interdigital electrode R is the direction of the electrode finger of the interdigital electrode T. With a slope of angle α,
The period length P _N of the electrode fingers in the direction perpendicular to the electrode fingers of the interdigital electrode R is equal to the product of the electrode period length P and cos α,
The interdigital electrode T receives an electric signal having a frequency substantially corresponding to the electrode periodic length P, and thereby has a wavelength substantially equal to the electrode periodic length P in the vicinity of the surface of the one plate surface of the piezoelectric substrate. Exciting a surface acoustic wave having
The interdigital electrode R converts the surface acoustic wave excited on the piezoelectric substrate into an electric signal E _j (j = 1, 2,...) Having a phase θ _j (j = 1, 2,..., Χ). …, Χ),
The electrical signal E _j has a frequency substantially corresponding to the electrode period length P,
The phase Totalθ _j generated by combining the phase θ _j is zero, the amplitude of the electric signal TotalE _j generated by combining the electric signal E _j is zero, and the electric signal TotalE _j is the interdigital shape. Is not detected at the electrode R,
The phase θ _j corresponds to a position F _j (j = 1, 2,..., Χ) along the direction of the electrode finger of the interdigital electrode T,
The position F _j corresponds to the ultrasonic wave propagation path Z _j (j = 1, 2,..., Χ) between the interdigital electrodes T and R on the one plate surface of the piezoelectric substrate. ,
When a finger or an object contacts a position F _x corresponding to the ultrasonic wave propagation path Z _x , an output electric signal E having a phase θ is detected at the interdigital electrode R,
The position F _x corresponds to an electrical signal E _x having a phase θ _x ,
The output electrical signal E is equal to components except for the electrical signals E _x from said electrical signal totale _j, the phase theta is equal to components except for the phase theta _x from the phase Totalθ _j,
The position F _x is specified from the value of the phase θ _x .
In the ultrasonic contact position detecting device according to claim 2, the intersection width L _P of the interdigital electrode R in the direction of the electrode finger is equal to the product of the electrode intersection width L of the interdigital electrode T and secα.
In the ultrasonic contact position detecting apparatus according to a third aspect, the piezoelectric substrate is made of piezoelectric ceramic, and the direction of the polarization axis of the piezoelectric ceramic is parallel to the thickness direction of the piezoelectric ceramic.
DETAILED DESCRIPTION OF THE INVENTION
The structure of the ultrasonic contact position detection apparatus of the present invention is formed by providing the interdigital electrodes T and R on one plate surface of a piezoelectric substrate. At this time, the direction of the electrode fingers of the interdigital electrode T and the direction of the electrode fingers of the interdigital electrode R are not parallel to each other, and the direction of the electrode fingers of the interdigital electrode R is in the direction of the electrode fingers of the interdigital electrode T. It has an inclination of angle α. The period length P _N of the electrode fingers in the direction perpendicular to the electrode fingers of the interdigital electrodes R is set to a size equal to the product of the electrode period length P of the interdigital electrodes T and cos α. The intersection width L _P of the interdigital electrode R in the direction of the electrode fingers is set to a size equal to the product of the electrode intersection width L of the interdigital electrode T and secα.
Since the thickness of the piezoelectric substrate has a value more than three times the electrode period length P of the interdigital electrode T, an electric signal having a frequency substantially corresponding to the electrode period length P of the interdigital electrode T is input to the interdigital electrode T. By adopting the structure, a surface acoustic wave having a wavelength substantially equal to the electrode period length P can be excited in the vicinity of the surface of the plate surface of the piezoelectric substrate on which the interdigital electrodes T and R are provided. This surface acoustic wave is converted into an electric signal E _j (j = 1, 2,..., Χ) having a phase θ _j (j = 1, 2,..., Χ) by the interdigital electrode R. The electric signal E _j has a frequency substantially corresponding to the electrode period length P. The phase Totalθ _j generated by synthesizing the phase θ _j becomes zero, and the amplitude of the electric signal TotalE _j generated by synthesizing the electric signal E _j becomes zero. That is, the electric signal TotalE _j is not detected at the interdigital electrode R.
The phase θ _j can be made to correspond to the position F _j (j = 1, 2,..., Χ) along the direction of the electrode fingers of the interdigital electrode T. At this time, the position F _j is an ultrasonic propagation path Z _j (j = 1, 2, between the interdigital electrodes T and R on the plate surface of the piezoelectric substrate on which the interdigital electrodes T and R are provided. ……, χ) respectively. When a finger or an object contacts the position F _x corresponding to the ultrasonic wave propagation path Z _x , the output electric signal E is detected at the interdigital electrode R. At this time, the output electrical signal E is equal to the electrical signal TotalE equal components except electrical signals E _x from _j, the phase theta component excluding the phase theta _x from the phase Totalshita _j of the output electrical signal E. That is, when the piezoelectric substrate is not contacted, the electrical signal TotalE _j converted from the surface acoustic wave at the interdigital electrode R is balanced and zero, but the ultrasonic propagation path Z _x is blocked by the contact. Then, since the surface acoustic wave corresponding to the propagation path Z _x is not converted into the electric signal E _x having the phase θ _x in the interdigital electrode R, the overall balance is lost, and the interdigital electrode An output electrical signal E having a phase θ is detected at R. Therefore, the output electrical signal E is equal to the component excluding the electric signals E _x from the electrical signal totale _j, the phase theta of the output electrical signal E is equal to the ingredients except the phase theta _x from the phase Totalθ _j. In this way, the position F _x can be determined by obtaining the phase θ _x .
In the ultrasonic contact position detection device of the present invention, a piezoelectric ceramic is adopted as the piezoelectric substrate, and the interdigital electrode of the piezoelectric substrate is adopted by adopting a structure in which the direction of the polarization axis of the piezoelectric ceramic is parallel to the thickness direction. It is possible to efficiently excite a surface acoustic wave near the surface of the plate surface on which T and R are provided. In addition, the surface acoustic wave can be efficiently converted into the electric signal Ej in the interdigital electrode R.
【Example】
FIG. 1 is a plan view showing an embodiment of the ultrasonic contact position detecting apparatus of the present invention. This embodiment comprises interdigital electrodes T and R and a piezoelectric substrate 1. The piezoelectric substrate 1 is made of a piezoelectric ceramic having a thickness of 1.5 mm. The interdigital electrodes T and R are made of an aluminum thin film, have 10 pairs of electrode fingers, and are provided on one plate surface of the piezoelectric substrate 1. The interdigital electrode T has a regular structure, the electrode crossing width L is 12 mm, and the electrode period length P is 400 μm. The direction of the electrode finger of the interdigital electrode T and the direction of the electrode finger of the interdigital electrode R are not parallel to each other. In the ultrasonic contact position detection apparatus of the present invention, when the position F _j (j = 1, 2,..., Χ) along the direction of the electrode finger of the interdigital electrode T is contacted with a human finger or an object, The position can be detected.
FIG. 2 is a plan view showing the interdigital electrode R. FIG. The direction of the electrode finger of the interdigital electrode R has an inclination of an angle α with respect to the direction of the electrode finger of the interdigital electrode T. The period length P _N of the electrode finger in the direction orthogonal to the electrode finger of the interdigital electrode R is set to a size equal to the product of the electrode period length P of the interdigital electrode T and cos α. The intersection width L _P of the interdigital electrode R in the direction of the electrode fingers is set to a size equal to the product of the electrode intersection width L of the interdigital electrode T and secα.
FIG. 3 is a diagram showing a drive circuit of the ultrasonic contact position detection apparatus of FIG. Part (1) of the electrical signal from the oscillator 2 is sent to the interdigital electrode T, and the remaining part (2) is sent to the phase comparator 4 via the attenuator 3. When an electric signal is input to the interdigital electrode T, only the electric signal having a frequency in the vicinity of the center frequency indicated by the interdigital electrode T in the frequency of the electric signal is converted into a surface acoustic wave. It propagates near the surface of the plate surface on which the interdigital electrodes T and R are provided. The propagation direction of the surface acoustic wave is the direction indicated by the arrow on the piezoelectric substrate 1. Of the surface acoustic waves propagated to the piezoelectric substrate 1, only the surface acoustic wave having the center frequency indicated by the interdigital electrode R and the frequency in the vicinity thereof has a phase θ _j (j = 1, 2,...) At the interdigital electrode R. , Χ) is converted into an electrical signal E _j (j = 1, 2,..., Χ). Since the phase Totalθ _j generated by synthesizing the phase θ _j becomes zero, the amplitude of the electric signal TotalE _j generated by synthesizing the electric signal E _j becomes zero. Therefore, the electric signal TotalE _j is not output from the interdigital electrode R.
The phase θ _j corresponds to the position F _j and also corresponds to the ultrasonic propagation path Z _j (j = 1, 2,..., Χ) between the interdigital electrodes T and R. If a finger or an object touches the position F _x , an electric signal E having a phase θ is output from the interdigital electrode R. At this time, the position F _x from Be for the electric signals E _x having a phase theta _x, the output electrical signal E is equal to the component excluding the electric signals E _x from the electrical signal totale _j, the phase theta phase It is equal to the component obtained by removing the phase θ _x from Total θ _j . That is, when the piezoelectric substrate 1 is not contacted, the electrical signal TotalE _j converted from the surface acoustic wave in the interdigital electrode R is balanced and zero, but the ultrasonic propagation path Z _x is changed by the contact. When cut off, the surface acoustic wave corresponding to the propagation path Z _x is not converted into the electric signal E _x in the interdigital electrode R, so that the overall balance is lost and the electric signal E is output from the interdigital electrode R. Will be output. Therefore, the output electrical signal E is equal to the component excluding the electric signals E _x from the electrical signal totale _j, the phase theta of the output electrical signal E is equal to the ingredients except the phase theta _x from the phase Totalθ _j. In this way, the position F _x can be determined by obtaining the phase θ _x . Since the phase of the electrical signal sent from the oscillator 2 to the phase comparator 4 via the attenuator 3 is zero, this is equivalent to the phase Totalθ _j . Therefore, it is possible to detect a phase theta _x the difference between the phase Totalshita _j and the phase theta by the phase comparator 4.
FIG. 4 is a characteristic diagram showing the relationship between the contact position F _x on the piezoelectric substrate 1 in FIG. 1 and the phase θ _x detected by the phase comparator 4. However, the distance between the positions F _x and F _x-1 was 0.5 mm. The reason why the position F _x is between zero and 12 mm is that the interelectrode width L of the interdigital electrode T is 12 mm. It can be seen that there is good linearity between the position F _x and the phase θ _x . In this way, it is possible to determine the contact position F _x from the phase θ _x .
【The invention's effect】
The ultrasonic contact position detection apparatus of the present invention has a simple structure in which the interdigital electrodes T and R are provided on one plate surface of a piezoelectric substrate. The directions of the interdigital electrodes T and R are not parallel to each other, and the direction of the interdigital electrodes R has an inclination of an angle α with respect to the direction of the interdigital electrodes T. The period length P _N of the electrode finger in the direction perpendicular to the electrode finger of the interdigital electrode R is set to a size equal to the product of the electrode period length P of the interdigital electrode T and cos α, and the interdigital electrode The crossing width L _{P in} the direction of the R electrode fingers is set to a size equal to the product of the electrode crossing width L of the interdigital electrode T and secα.
In the ultrasonic contact position detection apparatus of the present invention, the thickness of the piezoelectric substrate has a value that is at least three times the electrode period length P of the interdigital electrode T, and therefore the frequency substantially corresponding to the electrode period length P of the interdigital electrode T. Is input to the interdigital electrode T, so that a surface acoustic wave can be excited in the vicinity of the surface of the surface of the piezoelectric substrate on which the interdigital electrodes T and R are provided. This surface acoustic wave is converted into an electric signal E _j (j = 1, 2,..., Χ) having a phase θ _j (j = 1, 2,..., Χ) by the interdigital electrode R. By adopting a piezoelectric ceramic as the piezoelectric substrate and adopting a structure in which the direction of the polarization axis of the piezoelectric ceramic is parallel to the thickness direction, the plate surface of the piezoelectric substrate on which the interdigital electrodes T and R are provided The surface acoustic wave can be efficiently excited in the vicinity of the surface, and the surface acoustic wave can be efficiently converted into the electric signal E _j at the interdigital electrode R. However, the phase Totalθ _j generated by synthesizing the phase θ _j becomes zero, and the amplitude of the electric signal TotalE _j generated by synthesizing the electric signal E _j becomes zero, so that the electric signal TotalE _j becomes the interdigital electrode R. Is not detected.
In the ultrasonic contact position detection device of the present invention, the phase θ _j can be made to correspond to the position F _j (j = 1, 2,..., Χ) along the direction of the electrode finger of the interdigital electrode T. . The position F _j can correspond to the ultrasonic wave propagation path Z _j (j = 1, 2,..., Χ) between the interdigital electrodes T and R, respectively. When a finger or an object contacts the position F _x , an output electric signal E having a phase θ is detected at the interdigital electrode R. When the piezoelectric substrate is not contacted, the electrical signal TotalE _j converted from the surface acoustic wave in the interdigital electrode R is balanced and zero, but the ultrasonic propagation path Z _x is blocked by the contact. Since the surface acoustic wave corresponding to the propagation path Z _x is not converted into the electric signal E _x having the phase θ _x in the interdigital electrode R, the overall balance is lost and the output is output from the interdigital electrode R. The electric signal E is detected. Therefore, the output electrical signal E is equal to the component excluding the electric signals E _x from the electrical signal totale _j, the phase theta of the output electrical signal E is equal to the ingredients except the phase theta _x from the phase Totalθ _j. In this way, the position F _x can be determined from the value of the phase θ _x .
[Brief description of the drawings]
FIG. 1 is a plan view showing an embodiment of an ultrasonic contact position detection apparatus of the present invention.
FIG. 2 is a plan view showing an interdigital electrode R;
FIG. 3 is a diagram showing a drive circuit of the ultrasonic contact position detection device of FIG. 1;
4 is a characteristic diagram showing a relationship between a contact position F _x on the piezoelectric substrate 1 in FIG. 1 and a phase θ _x detected by a phase comparator 4. FIG.
[Explanation of symbols]
1 Piezoelectric substrate 2 Oscillator 3 Attenuator 4 Phase comparator T, R Interdigital electrode

Claims (3)

An ultrasonic contact position detecting device in which interdigital electrodes T and R are provided on one plate surface of a piezoelectric substrate,
The thickness of the piezoelectric substrate has a value more than three times the electrode period length P of the interdigital electrode T;
The direction of the electrode finger of the interdigital electrode T and the direction of the electrode finger of the interdigital electrode R are not parallel to each other, and the direction of the electrode finger of the interdigital electrode R is the direction of the electrode finger of the interdigital electrode T. With a slope of angle α,
The period length P _N of the electrode fingers in the direction perpendicular to the electrode fingers of the interdigital electrode R is equal to the product of the electrode period length P and cos α,
The interdigital electrode T receives an electric signal having a frequency substantially corresponding to the electrode periodic length P, and thereby has a wavelength substantially equal to the electrode periodic length P in the vicinity of the surface of the one plate surface of the piezoelectric substrate. Exciting a surface acoustic wave having
The interdigital electrode R converts the surface acoustic wave excited on the piezoelectric substrate into an electric signal E _j (j = 1, 2,...) Having a phase θ _j (j = 1, 2,..., Χ). …, Χ),
The electrical signal E _j has a frequency substantially corresponding to the electrode period length P,
The phase Totalθ _j generated by combining the phase θ _j is zero, the amplitude of the electric signal TotalE _j generated by combining the electric signal E _j is zero, and the electric signal TotalE _j is the interdigital shape. Is not detected at the electrode R,
The phase θ _j corresponds to a position F _j (j = 1, 2,..., Χ) along the direction of the electrode finger of the interdigital electrode T,
The position F _j corresponds to the ultrasonic wave propagation path Z _j (j = 1, 2,..., Χ) between the interdigital electrodes T and R on the one plate surface of the piezoelectric substrate. ,
When a finger or an object contacts a position F _x corresponding to the ultrasonic wave propagation path Z _x , an output electric signal E having a phase θ is detected at the interdigital electrode R,
The position F _x corresponds to an electrical signal E _x having a phase θ _x ,
The output electrical signal E is equal to components except for the electrical signals E _x from said electrical signal totale _j, the phase theta is equal to components except for the phase theta _x from the phase Totalθ _j,
The ultrasonic contact position detection device in which the position F _x is specified from the value of the phase θ _x . The ultrasonic contact position detecting device according to claim 1, wherein an intersection width L _P of the interdigital electrode R in the direction of the electrode fingers is equal to a product of the electrode intersection width L of the interdigital electrode T and secα. The ultrasonic contact position detecting device according to claim 1, wherein the piezoelectric substrate is made of a piezoelectric ceramic, and a direction of a polarization axis of the piezoelectric ceramic is parallel to a thickness direction of the piezoelectric ceramic.

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