JP2002333950A - Coordinate inputting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the coordinate calculating precision by excluding or reducing the influence of ultrasonic reflected wave by an ultrasonic coordinate input device. SOLUTION: An envelope signal 13 corresponding to an envelope 121 is extracted from a vibration detection signal 12 of a vibration sensor which detects ultrasonic vibration from an input pen for instructing an input point on a coordinate input face, and a signal 14 obtained by first order differentiation and a signal 16 obtained by forth order differentiation are generated. A vibration detecting timing signal 17 based on the envelope 121 is generated by comparing the signals 14 and 16 while the voltage of the signal 13 is not less than a reference level signal 131. On the other hand, a phase signal 19 indicating a phase 122 is generated from the vibration detection signal 12, and a vibration detecting timing signal 20 based on the phase 122 is generated by comparing the phase signal 19 with a gate signal 171 obtained by inverting the signal 17. Then, the coordinates of the input point are calculated based on the vibration detecting timing indicated by the vibration detecting timing signal 20 and the signal 17.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coordinate input device having a coordinate input surface and detecting the coordinates of an input point arbitrarily designated on the coordinate input surface, and more particularly to a coordinate input device utilizing ultrasonic waves. The present invention relates to an ultrasonic coordinate input device for detecting an ultrasonic wave.

[0002]

2. Description of the Related Art At present, a display device for displaying various information outputted by a computer and an input pen (pen-shaped coordinate input point indicating means) are arbitrarily specified on the display screen using the display screen as a coordinate input surface. There is an information input / output device including a coordinate input device that detects coordinates of an input point and outputs coordinate data to a computer.

[0003] Display devices constituting this information input / output device include a CRT, an LCD, a PDP, and a projector.
In recent years, flat panels such as LCDs and PDPs have increased their market share in the display device market from the viewpoint of improving display performance and installation space.

On the other hand, a coordinate input device is called a touch panel or a tablet. When an input point is used to specify an arbitrary input point in an inputtable area of a coordinate input surface, the coordinates of the input point are detected and connected. This device outputs coordinate data to a computer so that the computer can display input points on a display device.

[0005] As a method for detecting the coordinates of an input point, a resistive film method, an electromagnetic induction method, and an ultrasonic method are particularly known, and the method has been diversified so that a user can select according to the price and application. . In particular, since the ultrasonic method has a feature of being resistant to electromagnetic noise and being inexpensive in cost, active development is being promoted.

The ultrasonic system includes a vibration transmission plate system and an aerial ultrasonic system. In the vibration transmission plate method, an ultrasonic vibration input from an input point designated by an input pen equipped with a vibrator for generating ultrasonic waves is applied to a vibration transmission plate constituting a coordinate input surface around the vibration transmission plate. Detected by a plurality of vibration sensors provided in the unit, and the coordinates of the input point are calculated based on the detection timing.

In the aerial ultrasonic system, vibrations of ultrasonic waves radiated into the air from an input pen for designating an input point on a coordinate input surface are detected by a plurality of vibration sensors provided around the coordinate input surface. The coordinates of the input point are calculated based on the detection timing.

[0008]

In the above-mentioned coordinate input device of the aerial ultrasonic system, ultrasonic waves emitted into the air are greatly attenuated, and the attenuation is proportional to the square of the ultrasonic frequency. For this purpose, an ultrasonic wave in a low frequency band is used. However, the signal detected by the vibration sensor is still weak and is not suitable for performing the signal processing as it is. Therefore, the signal is generally amplified using a preamplifier.

[0009] In this coordinate input device, the detection signal level of the ultrasonic vibration changes very greatly. The factors include the transmission distance of the ultrasonic wave, the angle of the input pen, and the variation of each component. Usually, the threshold value for judging that the detection signal is valid is determined in consideration of the fluctuation range of the level due to the above factors, the level of the unnecessary reflected wave, the electromagnetic noise level, and the power supply voltage.

As for the unnecessary reflected wave, the reflected wave from the coordinate input surface of the coordinate input device as shown in FIG. 2 is mainly used. In such a case, there are reflected waves from an unspecified number of objects such as desks located very close to the input pen.

[0011] Such a reflected wave is a difference in the distance between the direct wave and the reflected wave transmission path (hereinafter referred to as the position of the input pen that emits the ultrasonic wave, ie, the transmission path of the ultrasonic wave from the coordinate input point to the vibration sensor. , Transmission path difference) is large, it does not affect the processing after the detection of the ultrasonic wave. For example, when the operating frequency is 40 kHz, the transmission path difference is several tens mm (several wavelengths).
If so, the reflected wave and the direct wave can be separated without affecting the above processing.

However, if the transmission path difference cannot be sufficiently obtained, an ultrasonic wave in which the reflected wave and the direct wave are superimposed is detected and the detection signal is processed, resulting in erroneous detection, and the accuracy of coordinate calculation is reduced. Will deteriorate.

On the other hand, if a transmission path difference of several tens of millimeters is to be ensured, there is a problem that the degree of freedom in the design of the apparatus is lost in the position of the vibrator of the input pen, the configuration of the vibration sensor, and the like. The problem due to the influence of the reflected wave is common to the vibration transmission plate type device.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems, and in an ultrasonic coordinate input device, a difference in transmission path between a direct ultrasonic wave and a reflected wave from a coordinate input point to a vibration sensor. It is an object of the present invention to provide a configuration which can eliminate or reduce the influence of the reflected wave even if it is not possible to secure a large value, and is not affected by the level fluctuation of the ultrasonic vibration detection signal, and can obtain a stable coordinate calculation accuracy. .

[0015]

According to the present invention, when an input point on a coordinate input surface is designated by a coordinate input point designating means provided with an ultrasonic wave generating means, the present invention has been made to solve the above problem. A coordinate input for detecting the vibration of the ultrasonic wave emitted from the ultrasonic wave generating means by a plurality of vibration detecting means provided on the periphery of the coordinate input surface and calculating the coordinates of the input point based on the vibration detection timing. In the device, an envelope detection circuit for extracting an envelope signal corresponding to an envelope of the vibration detection signal output from the vibration detection means, a first differentiation circuit for differentiating the envelope signal, and the first differentiation circuit A second differential signal for further differentiating the first differential signal to be output and outputting a second differential signal
And a first timing signal indicating a vibration detection timing by the envelope of the vibration detection signal by comparing the first and second differential signals while the voltage of the envelope signal is equal to or higher than a predetermined reference level. A first comparator for generating a phase signal indicating a phase of the vibration detection signal from the vibration detection signal;
A second comparator for comparing a gate signal generated by inverting the timing signal with the phase signal to generate a second timing signal indicating a vibration detection timing based on a phase of the vibration detection signal, A configuration is employed in which the coordinates of the input point are calculated based on each of the vibration detection timings indicated by the first and second timing signals.

The second differentiating circuit outputs, for example, a differentiated signal obtained by differentiating the envelope signal by four or more orders.

Further, for example, the first rising point of the pulse of the first timing signal is set as the vibration detection point by the envelope of the vibration detection signal.

Further, for example, a rising time or a falling time of a pulse in a predetermined order in the second timing signal is set as a vibration detection time based on the phase of the vibration detection signal.

[0019]

Embodiments of the present invention will be described below with reference to the drawings.

[Explanation of Overall Configuration (FIG. 1)] First, the overall configuration of a coordinate input device of the aerial ultrasonic system according to an embodiment of the present invention will be described with reference to FIG.

In FIG. 1, reference numeral 1 denotes an arithmetic control circuit,
It controls the entire coordinate input device, calculates the coordinates of the input point on the coordinate input surface, and outputs it to a host device 4 such as a computer via a serial cable or the like.

An optical transmission / reception circuit 2 detects an optical signal emitted from the input pen 21, which will be described later, and transmits an input pen control signal as an optical signal for controlling the operation of the input pen 21. .

Reference numeral 3 denotes a signal processing circuit, and an optical transmitting / receiving circuit 2
And outputs the data to the arithmetic and control circuit 1, converts the input pen control signal output from the arithmetic and control circuit 1 into a pulse train, and outputs to the optical transmitting and receiving circuit 2.

An image projection device 5 such as a projector projects an image based on various types of image information output from the host device 4 onto a screen 8 made of acrylic, vinyl chloride, or the like. The surface of the screen 8 is a coordinate input surface of the coordinate input device.

Numeral 21 denotes an input pen as a pen-type coordinate input point indicating means for the user of the apparatus to specify a desired input point on the coordinate input surface and to input coordinates. The coordinate input by the input pen 21 is performed by designating a desired input point in the effective area indicated by reference numeral 7 with the pen tip of the input pen 21 on the surface of the screen 8 as a coordinate input surface.

The effective area 7 on the surface of the screen 8
Vibration sensors 6a to 6d for converting mechanical vibrations made of a piezoelectric element or the like into electric signals are fixed to the four corners on the outer peripheral side of.

Reference numeral 9 denotes a vibration detection signal processing circuit which processes the vibration detection signals output from the respective vibration sensors 6a to 6d by detecting and outputting ultrasonic vibrations, and detects the ultrasonic vibration detection timing of each of the sensors 6a to 6d. A signal indicating (the arrival timing of the ultrasonic vibration to each sensor) is generated, and each signal is output to the arithmetic and control circuit 1.

The arithmetic and control circuit 1 calculates the
The coordinates of the input point on the coordinate input surface specified by the input pen 21 are calculated as described below, and output to the host device 4.

The host device 4 outputs the input coordinate information as image information to the image projection device 5, whereby the image projection device 5 projects an image on the screen 8, and a dot or the like is provided at the position of the input point on the screen 8. Is displayed.

[Description of Input Pen 21 and Vibration Sensors 6a to 6d (FIG. 2)] Next, the input pen 21 and the vibration sensor 6a
6d will be described with reference to FIG.

In FIG. 2, a vibrator 25 as ultrasonic wave generating means built in the input pen 21 is a vibrator driving circuit 2.
4. The electric drive signal from the circuit 24 is converted into mechanical ultrasonic vibration by a vibrator 25, and the ultrasonic wave is reflected by a conical reflector 27 made of metal such as aluminum, and passes through the ultrasonic wave. Radiated from the window 28 into the air.

The vibrator 25 has a structure in which an acoustic matching layer 26 is provided on the front surface of a piezoelectric vibrator that vibrates in the thickness direction. The acoustic matching layer 26 is made of a thin layer of silicon rubber or the like, matches acoustic impedance with air, enables high sensitivity and broadband characteristics, and enables transmission of ultrasonic signals with good pulse response. And

Ultrasonic waves radiated into the air from the ultrasonic wave passing window 28 are reflected by a conical reflector 211 made of metal provided on the vibration sensors 6a to 6d (only 6a is shown in FIG. 2).
And the ultrasonic vibrations are detected by the vibration sensors 6a to 6d, and the coordinates of the input point are calculated based on the vibration detection timing (the vibration arrival timing) as described later.

The vibrator drive circuit 24 pulse-drives the vibrator 25 at a predetermined frequency of its resonance frequency and simultaneously modulates the light at a predetermined frequency to a light emitting element 22 such as an infrared LED provided on the input pen 21. A light emission timing signal is transmitted.

The vibrator drive circuit 24 operates using the battery 23 as a power supply. Battery 23 is one of alkaline batteries or the like.
Secondary batteries or secondary batteries such as nickel-metal hydride batteries,
It is exchangeable. The vibrator drive circuit 24 includes the battery 2
3 operates as the power supply voltage, and the pulse drive voltage of the vibrator 25 is also driven at the same voltage value as the power supply voltage.
When it is desired to increase the output level, it is possible to drive the vibrator 25 at a voltage higher than the power supply voltage via a step-up transformer or the like. However, current consumption increases, which is disadvantageous in terms of battery life.

[Explanation of Overall Operation] Next, the operation of the entire coordinate input device will be described. As described above, the input pen 2
The vibrator driving circuit 24 in 1 outputs a light emission timing signal modulated at a predetermined frequency to the light emitting element 22 at the same time as driving the vibrator 25, and emits an optical signal corresponding to the light emission timing signal. After the optical signal is detected by the optical transmitting / receiving circuit 2 and demodulated by the signal processing circuit 3, the arithmetic control circuit 1
It is input as a start timing signal for starting time measurement of the vibration transmission time of the ultrasonic vibration transmitted to the vibration sensors 6a to 6d.

The arithmetic and control circuit 1 starts measuring the vibration transmission time by an internal timer (constituted by a counter) in response to a start timing signal from the signal processing circuit 3. The ultrasonic wave generated from the transducer 25 of the input pen 21 is a distance from the input point (strictly speaking, the position of the transducer 25) designated by the input pen 21 on the coordinate input surface to the vibration sensors 6a to 6d. Arrives at each of the vibration sensors with a delay of the vibration transmission time according to, and its ultrasonic vibration is detected,
The detection signal is input to the vibration detection signal processing circuit 9 from each vibration sensor.

The vibration detection signal processing circuit 9 includes the vibration sensors 6
Signal processing described later is performed on the detection signals from a to 6d, and a vibration detection timing signal indicating the vibration detection timing of each vibration sensor is generated and input to the arithmetic and control circuit 1.

The arithmetic and control circuit 1 measures the time measured by the internal timer at the time when the signal is input to each vibration sensor 6.
Based on the ultrasonic vibration transmission times from a to 6d, the coordinates of the input point pointed by the input pen 21 are calculated based on the transmission times. Then, the arithmetic control circuit 1 inputs the calculated coordinate information of the input point to the host device 4, and the host device 4 controls the display of an image by the image projection device 5 based on the input coordinate information.

[Description of Operation Control Circuit 1 (FIG. 3)]
The configuration and operation of the arithmetic and control circuit 1 will be described with reference to the block diagram of FIG. In the figure, reference numeral 31 denotes a microcomputer for controlling the arithmetic control circuit 1 and the whole coordinate input device, which is a CPU 311 serving as a main body for performing control processing, a ROM 312 storing the control program, a RAM 313 used as a working area for calculations and the like, and It is composed of a non-volatile memory (not shown) for storing constants and the like.

Reference numerals 32a to 32d denote counters constituting timers for counting a reference clock (not shown) and counting the time. The counters 32a to 32d correspond to the respective vibration sensors 6a to 6d and measure the respective vibration transmission times. Counter 32a ~
32d, the light signal emitted from the light emitting element 22 is detected by the light detection circuit 2 at the same time as the driving of the vibrator 25 in the input pen 21, and the start timing signal is input to the arithmetic and control circuit 1 via the signal processing circuit 3. Then, it is started and starts counting time. As a result, the start of timekeeping is synchronized with the generation of the ultrasonic vibration from the vibrator 25, and the ultrasonic vibration transmission time from the input point until the ultrasonic vibration is detected by the vibration sensors 6a to 6d is measured. You can do it.

When the vibration sensors 6a to 6d detect the ultrasonic vibration, the detection signal is input to the vibration detection signal processing circuit 9, and the vibration detection timing signal of each of the vibration sensors 6a to 6d is generated. Are input to the counters 32a to 32d. And the counter 32a
Within 32d, the data of the time count value at the time of input of the vibration detection timing signal is latched by the latch circuit (not shown) as the data of the vibration transmission time.

When the determination circuit 33 determines that all the vibration detection timing signals of the vibration sensors 6a to 6d have been received, a signal to that effect is output to the microcomputer 31. In accordance with the signal, the microcomputer 31 reads time measurement data of the vibration transmission time from the latch circuits of the counters 32a to 32d to the respective vibration sensors 6a to 6d. Then, the coordinates of the input point of the input pen 21 on the screen 8 are calculated by performing an operation described later based on the time measurement data.

The vibration detection timing signal includes a timing signal generated by envelope processing of vibration detection signals of the vibration sensors 6a to 6d and a timing signal generated by phase processing, as described later. There are signals, and the two types of vibration transmission time are measured based on the signals, and the coordinates of the input point are calculated based on each.

The microcomputer 31 outputs information on the coordinates thus calculated to the host device 4 via the I / O port 35. The host device 4 can output image information to the image projection device 5 according to the input coordinate information, and can display a dot or the like at a position of an input point by the input pen 21 on the screen 8. Or I / O port 35
And output the coordinate information to another external device via the interface circuit for the other external device.

[Description of Vibration Detection Signal Processing Circuit 9 and Signal Processing (FIGS. 4 and 5)] Next, the configuration of the vibration detection signal processing circuit 9 and the processing of the vibration detection signals of the vibration sensors 6b to 6d thereby. This will be described with reference to the block diagram of FIG. 4 and the timing chart of FIG. In the following, the vibration sensor 6
The configuration and signal processing of the vibration detection signal processing circuit 9 for “a” will be described. Of course, the same configuration is provided for the other vibration sensors 6b to 6d, and the same signal processing is performed. .

As described above, the time for transmitting the ultrasonic vibration from the input point of the input pen 21 to the vibration sensor 6a is measured by the counter 32a by the output of the start timing signal from the signal processing circuit 3 to the arithmetic and control circuit 1. Be started. At this time, the vibrator driving circuit 24 in the input pen 21
The drive signal 11 is applied to the vibrator 25 from. As shown in FIG. 5, the drive signal 11 is a short (for example, one) rectangular pulse. The reason why the drive signal 11 is a short pulse is as follows.
This is to prevent erroneous detection due to interference (superposition) between the unnecessary reflection component and the vibration to be detected, and to reduce the size of the entire apparatus.

The driving signal 11 causes the input pen 21
Is driven, and ultrasonic waves are emitted into the air.
The ultrasonic vibration is detected by the vibration sensor 6a after traveling in the air with a vibration transmission time corresponding to the distance from the input point of the input pen 21 (strictly speaking, the position of the vibrator 25) to the vibration sensor 6a. .

At this time, the vibration detection signal of the vibration sensor 6a that has detected the ultrasonic vibration is indicated by reference numeral 12 in FIG. This vibration detection signal 12 is input to the configuration for the vibration sensor 6a of the vibration detection signal processing circuit 9 shown in FIG. 4, and is first amplified by the preamplifier 401, and then the waveform of the vibration detection signal 12 shown in FIG. Envelope detection circuit 402 for each of envelope (envelope) 121 and phase 122
The signals are separately processed by the following signal processing system and the signal processing system below the bandpass filter 408.

First, with respect to the envelope 121, an envelope signal 13 corresponding to the envelope 121 having the waveform is extracted from the vibration detection signal 12 by the envelope detection (detection) circuit 402 by detection. The extracted envelope signal 13 is supplied to a gate signal generation circuit 406.
Is input to The gate signal generation circuit 406 compares the envelope signal 13 with a reference level signal 131 having a predetermined voltage, and outputs a gate signal 132 having a pulse width corresponding to the width and height of the waveform of the envelope signal 13.

The envelope signal 13 is input to an envelope first-order differentiating circuit 403, where it is first-order differentiated to generate a first-order differentiated signal 14. In FIG. 5, the negative part of the second half of the first-order differential signal 14 is cut away in order to briefly show the waveforms of signals 15 and 16 described later.

Further, the first-order differential signal 14 is input to an envelope fourth-order differential circuit 404. The envelope fourth-order differentiation circuit 404 performs third-order differentiation on the input first-order differentiation signal 14 to generate a fourth-order differentiation signal 16.

The first-order differential signal 14, the fourth-order differential signal 16, and the gate signal 132 are converted into a differential signal comparator 405.
Is input to The comparator 405 operates while the gate signal 132 is open, that is, the envelope signal 13
Is higher than the reference level signal 131 and the gate signal 132 is low level,
A vibration detection timing signal indicating a vibration detection timing in which the fourth and fourth order differential signals 16 are compared, and a pulse signal that becomes high while the voltage of the first order differential signal 14 exceeds the fourth order differential signal 16 is detected from the envelope 121. 1
7 is output.

The vibration detection timing signal 17 is input to the arithmetic and control circuit 1. In this signal 17, the first rising time point corresponding to the time point when the first-order differential signal 14 and the fourth-order differential signal 16 first cross while the gate signal 132 is open is defined as the vibration detection time by the envelope 121. The data of the count value of the counter 32a is latched, and the time based on the count value, that is, the time tg from the rising point of the drive signal 11 of the vibrator 25 of the input pen 21 to the first rising point of the detection timing signal 17 is the envelope 121. Is the vibration transmission time up to the vibration sensor 6a.

On the other hand, the vibration detection signal 12 of the vibration sensor 6a
In the process for the phase 122, the vibration detection signal 1
2 is converted into a signal 18 of a frequency component having a predetermined width by a narrow-band bandpass filter 408,
By 09, the waveform is sliced (waveform level compression) to a predetermined amplitude level or less. And the slice circuit 4
The output signal 09 is input to the phase signal comparator 410 as the phase signal 19 indicating the phase of the vibration detection signal 12.

Further, the vibration detection timing signal 17 output from the differential signal comparator 405 is input to the gate signal generation circuit 407 and inverted, and the gate signal 171 is generated. This gate signal 171 is also input to the phase signal comparator 410.

The comparator 410 compares the phase signal 19 and the gate signal 171, extracts a portion of the phase signal 19 while the gate signal 171 is open (during low level), and detects the portion of the phase signal 19 from the phase 122. It is output as a vibration detection timing signal 20 indicating the detection timing.

The vibration detection timing signal 20 is input to the arithmetic and control circuit 1. Among the pulses of the signal 20, a pulse in a predetermined order, for example, the rising point of the second pulse here is set as the vibration detection point by the phase 122,
At this time, the data of the count value of the counter 32a is latched, and the time based on the count value, that is, from the rising point of the drive signal 11 of the vibrator 25 of the input pen 21 to the second rising point of the vibration detection timing signal 20 is obtained. Time tp is the vibration sensor 6a for the phase 122
The vibration transmission time up to

[Explanation of Calculation of Distance between Input Point and Vibration Sensor] Next, the vibration transmission time t measured as described above is calculated.
The calculation of the distance between the input point of the input pen 21 and the vibration sensors 6a to 6d performed by the arithmetic and control circuit 1 based on g and tp will be described. Hereinafter, the position of the input point indicated by the pen tip of the input pen 21 on the coordinate input surface and the position of the vibrator 25 will be described as being substantially the same.

Since the ultrasonic wave used in the apparatus of this embodiment travels in the air, the relationship between the envelope 121 and the phase 122 of the waveform of the vibration detection signal 12 of the vibration sensors 6a to 6d is determined during the transmission of the vibration. It is constant regardless of the distance. Here, the traveling speed of the envelope 121, that is, the group velocity is Vg, and the traveling speed of the phase 122, that is, the phase velocity is Vp. The distance between the input point of the input pen 21 and the vibration sensor 6a can be detected from the group velocity Vg and the phase velocity Vp.

First, focusing only on the envelope 121, the speed is Vg, and the detection point of the specific point on the waveform of the envelope 121 (the gate signal 13 in this embodiment).
2 while the first differential signal 14 and the fourth differential signal 1 are open
The distance d between the input point of the input pen 21 and the vibration sensor 6a is given by d = Vg · tg (1), where tg is the vibration transmission time up to the first crossing point of 6). Although this equation relates only to the vibration sensor 6a, the other equations are the same for the other three vibration sensors 6b to 6b.
The distance between 6d and the input point can be similarly expressed.

Further, in order to determine coordinates with higher accuracy, processing is performed based on the vibration transmission time tp based on the vibration detection timing detected from the phase 122 of the vibration detection signal 12 as described above. The vibration transmission time tp and the phase velocity V
From p, the distance d between the vibration sensor 6a and the input point is as follows: d = n · λp + Vp · tp (2) Here, λp is the wavelength of the ultrasonic wave, and n is an integer.
From the formulas (1) and (2), the above integer n is the following (3), (4)
It can be obtained by an equation.

N = int [(Vg · tg−Vp · tp) / λp + ／] (3) From V = Vg = Vp n = int [V · (tg−tp) / λp + ／] (4) Here Therefore, it cannot be said that the linearity of the envelope with the distance of the vibration transmission time tg is good, and the reason why the integer conversion is performed in the equation (4) is as follows. The necessary and sufficient conditions for finding the exact integer n are the equations derived from the following equation (5)
(6), n * = V * (tg−tp) / λp (5) ΔN = n * −n ≦ 0.5 (6) That is, if the error amount generated is within ±± wavelength. If
This indicates that the integer n can be accurately determined even if the linearity of the vibration transmission time tg by the envelope is not good. The distance d between the input point of the input pen 21 and the vibration sensor 6a can be accurately calculated by substituting n obtained as described above into the equation (2). The distance between each of the other vibration sensors 6b to 6d and the input point can be accurately calculated in the same manner.

[Explanation of Coordinate Calculation (FIG. 6)] Next, the calculation of the coordinates of the input point based on the distance between the input point calculated as described above and the vibration sensors 6a to 6d will be described with reference to FIG.

When the four vibration sensors 6a to 6d are provided at the four corners Sa to Sd on the surface of the screen 8 shown in FIG. 6, that is, on the coordinate input surface, the vibration transmission time based on the vibration detection timing described above is used. In the arithmetic and control circuit 1, the linear distances da to from the input point P of the input pen 21 to the positions Sa to Sd of the respective vibration sensors 6a to 6d.
dd can be calculated.

Further, in the arithmetic and control circuit 1, the linear distance d
Based on a to dd, the coordinates (x, y) of the input point P can be obtained from the following equations (7) and (8) from the square theorem.

X = (da + dd) · (da−dd) / 2X (7) y = (da + db) · (da−db) / 2Y (8) where X and Y are distances between the vibration sensors 6a and 6d, respectively. And the distance between the vibration sensors 6a and 6b. As described above, the coordinates of the input point of the input pen 21 can be calculated in real time.

Although the above calculation can be performed using the distance information between the input point P and the three vibration sensors, in the present embodiment, since four vibration sensors are provided, the remaining one is used.
The distance information between the vibration sensors and the input point P may be used to verify the certainty of the coordinates calculated by the above calculation.

Further, for example, the distance information of the vibration sensor having the largest distance L from the input point P is not used (the distance L becomes large, the level of the vibration detection signal decreases, and the probability of being affected by noise increases). Alternatively, the coordinates may be calculated based on the distance information of the remaining three vibration sensors.

Although four vibration sensors are arranged in this embodiment, it goes without saying that the number of sensors is set according to the product specifications.

According to the present embodiment as described above, as shown in FIG. 5, the first rise time of the vibration detection timing signal 17 which is the vibration detection time of the vibration detection signal 12 by the envelope 121, and the vibration by the phase 122 The rising point of the second pulse of the vibration detection timing signal 20, which is the detection point, is before the peak of the envelope signal 13. In other words, in the portion of the vibration detection signal 12 before the peak of the envelope 121, the component of the reflected wave of the ultrasonic wave is not superimposed or is small even if it is superimposed. Since the timing can be obtained, the influence of the reflected wave can be eliminated or reduced, and the vibration can be detected with high accuracy. Therefore, the vibration transmission time tg,
The measurement of tp can be performed with high accuracy, and the calculation of the distance between the input point and the vibration sensor and the calculation of coordinates based on the tp can be performed with high accuracy.

The result of confirming the performance of the apparatus of this embodiment by experiments will be described with reference to FIG. FIG. 7 shows the configuration of each of the apparatus of the present embodiment and the conventional example, which detects (calculates) the distance L between the input point of the input pen and the vibration sensor based on the detection of vibration by the envelope and the measurement of the vibration transmission time tg.
The result shows the relationship between the distance L and the measurement error ΔL.

In the conventional example, in the configuration of the vibration detection signal processing circuit of FIG.
And an inflection point detection circuit (a second-order differentiation circuit) for detecting an inflection point of the envelope 121 in place of the envelope fourth-order differentiation circuit 404, and the output signal (indicated by reference numeral 15 in FIG. 5) is used. The time point of the first zero-cross point while the gate signal 132 is open is defined as the vibration detection time point.

As can be seen from FIG. 7, in the present embodiment,
As compared with the conventional example, the measurement error Δ
L is extremely small, and good linearity is obtained. This good linearity indicates that the margin of ΔN in the above equation (6) becomes large. Therefore, according to the present embodiment, the coordinates of the input point can be calculated with high accuracy.

In the measurement results of the present embodiment shown in FIG. 7, a portion where the distance L is smaller than 100 mm, that is, a non-linear portion is recognized when the input point is close to the vibration sensor. This is caused by the waveform of the vibration detection signal of the vibration sensor being deformed when approaching the vibration sensor. In response to this phenomenon, when the input point is close to one of the four vibration sensors 6a to 6d, the coordinates are determined based on the vibration detection signals of the other sensors without using that sensor. This can be dealt with by calculating.

In the embodiment described above, for example, in the vibration detection timing signal 20 as a part of the phase signal 19 while the gate signal 171 in FIG. However, the falling point of the same pulse, or the rising or falling point of the pulse in another order may be set as the vibration detecting point. Which time point is the vibration detection time point is determined according to the specifications of the apparatus such as the sampling rate of coordinate detection.

The first-order differential signal 14 of the envelope is third-order differentiated by the fourth-order envelope differential circuit 404 to generate the fourth-order differential signal 16 of the envelope.
Differentiation of the envelope may be performed to generate differential signals of the fifth or higher order. However, if the floor number is increased, the noise margin of the circuit is reduced, and at the same time the signal delay in the circuit becomes a problem.

Further, the envelope first-order differentiating circuit 403 may be replaced with a second-order differentiating circuit that performs a second-order differentiation, and the envelope fourth-order differentiating circuit 404 may be replaced with a differentiating circuit that performs a differentiation of a smaller order than the third order. Good.

In the above, the embodiment of the coordinate input device of the aerial ultrasonic system has been described. However, it is needless to say that the configuration according to the present invention can be applied to a device of a vibration transmission plate type which is another ultrasonic system.

[0080]

As is apparent from the above description, according to the present invention, in the coordinate input device of the ultrasonic system, the vibration is detected by the processing before the peak of the envelope of the vibration detection signal output by the vibration detecting means. Since the detection timing can be obtained, even if it is not possible to secure a large transmission path difference between the direct wave of the ultrasonic wave and the reflected wave from the coordinate input point to the vibration detecting means, the influence of the reflected wave can be eliminated or reduced, and the ultrasonic vibration can be eliminated. , Which is not affected by the fluctuation of the level of the detection signal, a stable coordinate calculation accuracy can be obtained, and the degree of freedom in design can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an overall configuration of a coordinate input device according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a configuration of an input pen and a vibration sensor of the apparatus, a state of transmission of ultrasonic waves, and the like.

FIG. 3 is a block diagram showing a configuration of an arithmetic control circuit of the device.

FIG. 4 is a block diagram illustrating a configuration of a vibration detection signal processing circuit of the device.

FIG. 5 is a timing chart showing waveforms and timings of signals related to signal processing of a vibration detection signal processing circuit.

FIG. 6 is an explanatory diagram for explaining a method of calculating coordinates of an input point.

FIG. 7 is a graph showing a relationship between a distance between an input point and a vibration sensor and a measurement error as a result of an experiment performed with the configuration of the embodiment and a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Arithmetic control circuit 2 Optical transmission / reception circuit 3 Signal processing circuit 4 Host device 5 Image projection device 6a-6d Vibration sensor 9 Vibration detection signal processing circuit 11 Vibrator drive signal 12 Vibration detection signal 13 Envelope signal 14 First order differential signal 16 4 First derivative signal 17 Vibration detection timing signal by envelope 19 Phase signal 20 Vibration detection timing signal by phase 21 Input pen 25 Vibrator 31 Microcomputer 32a to 32d Counter 131 Reference level signal 132,171 Gate signal 402 Envelope detection circuit 403 Envelope first floor Differentiating circuit 404 Envelope fourth-order differentiating circuit 405 Differentiated signal comparator 406, 407 Gate signal generating circuit 408 Bandpass filter 409 Slicing circuit 410 Phase signal comparator

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yuichiro Yoshimura 3-30-2 Shimomaruko, Ota-ku, Tokyo F-term in Canon Inc. (reference) 5B068 AA04 BB21 BC03 BD02 BD09 BD11 BE06 CC11 5B087 AA10 BC03 BC26 BC31 CC01 CC05 CC26 CC47 DD11

Claims (4)

[Claims] 1. A vibration of an ultrasonic wave emitted from an ultrasonic wave generating means when an input point on a coordinate input surface is specified by a coordinate input point specifying means having an ultrasonic wave generating means. In a coordinate input device for detecting by a plurality of vibration detecting means provided in a peripheral portion and calculating coordinates of the input point based on the vibration detection timing, an envelope of the signal is obtained from a vibration detection signal output by the vibration detecting means. An envelope detection circuit for extracting an envelope signal corresponding to the following; a first differentiation circuit for differentiating the envelope signal; a first differentiation signal output from the first differentiation circuit, and a second differentiation signal A second differentiating circuit that outputs the first and second differential signals while the voltage of the envelope signal is equal to or higher than a predetermined reference level; A first comparator that generates a first timing signal indicating a vibration detection timing by an envelope, a phase signal generation circuit that generates a phase signal indicating a phase of the signal from the vibration detection signal, A second comparator that compares a gate signal generated by inversion with the phase signal and generates a second timing signal indicating a vibration detection timing based on a phase of the vibration detection signal; 2. A coordinate input device for calculating coordinates of the input point based on each of the vibration detection timings indicated by the timing signal of No. 2. 2. The coordinate input device according to claim 1, wherein the second differentiating circuit outputs a differentiated signal obtained by differentiating the envelope signal by four or more orders. 3. The coordinate input device according to claim 1, wherein a first rising point of the pulse of the first timing signal is set as a vibration detection time by an envelope of the vibration detection signal. 4. A vibration detecting time according to a phase of the vibration detecting signal, wherein a rising time or a falling time of a pulse in a predetermined order in the second timing signal is set as a vibration detecting time. 2. The coordinate input device according to claim 1.