JPS63263517A - Ultrasonic application tablet - Google Patents

Abstract

PURPOSE:To eliminate the measurement error of the propagation time of an ultrasonic wave based on the variance of the intensity of contact between an input pen and a write board and to correctly plot the position by providing an intermediate layer medium and an input layer medium on a propagation layer medium and attaching an ultrasonic receiver on the end face of the propagation layer medium. CONSTITUTION:An intermediate layer medium 3b where the sound speed is >1/6 and <1/3 of the sound speed in a propagation layer medium 3c and the thickness is >1/10 and <2/5 of the thickness of the propagation layer medium 3c is provided on the propagation layer medium 3c whose thickness is set to >1/8 and <1/4 of the longitudinal wave wavelength of the ultrasonic wave propagated in the write board. An input layer medium 3a in which the sound speed is >1/4 and <1/2 of the sound speed in the propagation layer medium 3c and the thickness is >1/2 of the thickness of the propagation layer medium 3c is provided on the intermediate layer medium 3b, and an ultrasonic receiver 4 is attached to the end face of the propagation layer medium 3c. Thus, the input pen is correctly plotted even if the intensity of contact between the input pen and the write board is changed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an ultrasonic tablet for inputting information into a computer or the like by hand, and particularly to a writing device suitable for highly accurate writing.

[Conventional technology]

Ultrasonic application tablets use a glass plate or the like as a writing plate. Ultrasonic waves are incident on the writing plate from the tip of the pen, and the time it takes for the waves to be received by a wave receiver installed around the writing plate is measured. The position of the pen tip on the writing board is determined based on time, sound speed and dimensions of the writing board, and the position of the wave receiver.

As this ultrasonic wave, longitudinal waves, plate waves, surface waves, etc. are used.

In the conventional writing device using surface waves, one using a writing plate having a layered structure was proposed in Japanese Patent Laid-Open No. 50830/1983. This is a contact-type position encoder that uses surface acoustic waves, and has a structure that includes a second sheet made of a material that absorbs volume acoustic waves beneath a first sheet that transmits surface waves. The purpose of this is to avoid attenuating volume waves that propagate faster than surface waves and causing undesired erroneous reactions. However, as proposed in the present invention, no consideration has been given to the structure and material of the writing board necessary to reduce errors in positioning when the input pen is brought into contact with and released from the pen.

[Problem that the invention seeks to solve]

One of the problems with the ultrasonic tablet writing device conventionally used as a handwriting input device is the positional error that occurs when the input pen is brought into contact with the writing board and when it is released.

The reason why the input pen makes a mistake in positioning when it comes into contact with or leaves the writing board will be explained with reference to FIG. Figure 2 shows the waveform detected by the wave receiver when a wave receiver 4 is installed at the end of the writing board 3 and longitudinal ultrasonic waves are inputted by the input pen 1. 1 begins to touch the writing board 3 or just before leaving the writing board 3 and the input pen 1.
This shows the detected waveform of the receiver when the contact with the receiver is weak. Figure 2 (
0) is the detected waveform of the wave receiver when the input pen 1 is in contact with the writing board 3 with sufficient contact strength.

(b) of the same figure shows a detected waveform of the wave receiving element when the contact strength is intermediate between (a) and (c). In FIG. 2, the contact positions of the input pen are all the same. By the way, the time required for the ultrasonic wave that has entered the writing board from the input pen to be detected by the wave receiver is measured when the signal level of the wave detected by the wave receiver is lower than the threshold value vth after the ultrasonic wave has entered the writing board. This can be done by measuring the time it takes for it to grow. However, a problem occurs when the signal level of the wave detected by the wave receiver is such that the first wave is small and the subsequent wave becomes large. For example, in Figure 2 (a
), when the contact between the input pen and the writing board is weak, the signal level of the first few waves of the detection wave is smaller than the threshold value vth, and the sparse waves finally become larger than the threshold value vth, and the As shown in Figure 2 (Q), if the contact is strong enough, the signal level of the first wave will be greater than the threshold value vth, and the signal level of the detected wave will depend on the strength of the contact between the input pen and the writing board. The time it takes for vth to become larger than the threshold value vth differs. This results in measurement errors in the propagation time of the ultrasonic waves, which leads to errors in positioning when the strength of the contact changes, such as when the input pen is brought into contact with and released from the writing board.

SUMMARY OF THE INVENTION An object of the present invention is to provide an ultrasonic tablet that can accurately locate a position even if the strength of contact between an input pen and a writing board changes.

[Means for solving problems]

The above purpose is to create a writing board on which the sound speed is one-sixth of the sound speed of the propagation layer medium on a propagation layer medium whose thickness is one-eighth or more and one-fourth or less of the longitudinal wavelength of the ultrasonic waves propagating through the writing plate. The thickness is 1/10 or more and 2/5 of the propagation layer medium.
The following intermediate layer medium is provided, and the sound velocity is 4/61 or more and 1/2 or less of the sound speed of the propagation layer medium, and the thickness is 2/7 or more of the thickness of the propagation layer medium. By providing a layered medium and having a structure in which an ultrasonic wave receiver is attached to the end face of the propagation layered medium, 1. achieved.

[Effect]

As a result of simulating the sound propagation of a writing board with a multilayer structure made of materials with different sound velocities, it was found that changing the material and thickness of each layer significantly changes the amplitude of the second and subsequent waves of the received wave. Therefore, a condition was determined under which the amplitude of the second and subsequent received waves is smaller than the amplitude of the first wave. As an example, the results obtained for the writing plate having the structure shown in FIG. 3 are shown in FIG. 4. The sound velocity, density, and thickness of the materials used in this case are as shown in Table 1. Figure 4 (
(a) is the received waveform when the thickness of the input layer medium 3a is 0.4 mm, and (b) is the received waveform when the thickness of the input layer medium 3a is 1 mm.
．． This is the received waveform when the distance is 6 m. The waveform of FIG. 4(a) is preferable because the amplitude of the waves after the second wave (after the third peak) is larger than the first wave (first and second peaks), and the situation shown in FIG. 2 occurs. do not have. However, in (b), the amplitude of the first wave is the maximum, and even if the overall amplitude increases or decreases depending on the strength of the contact between the input pen and the writing board, the first wave always reaches the threshold first. It will take a while. In other words, this means that even if the strength of contact between the input pen and the writing board changes, there will be no measurement error in the propagation time of the ultrasonic waves, and the misorientation of the input position caused by the measurement error in the propagation time can be corrected. It can be prevented.

FIG. 5 shows the relationship between the wave peak value obtained by the above simulation and the thickness of the input layer medium. When the thickness of the input layer medium is in the range from 1.4 m to 1.8 m, the amplitude of the first wave (first and second peaks) is the same as or greater than the amplitude of the second and subsequent waves (third and subsequent peaks). It has become. Therefore, in order to achieve the above-mentioned objective, the thickness of the input layer medium should ideally be determined in the range of 1.4 rm to 1.8 m. Also, the amplitude of the second and subsequent waves is the same as that of the first wave.
In this case, the thickness of the input layer medium should be 1.3 m or more, and the thickness of the input layer medium should be 1.3 m or more. If the propagation time measured at the beginning is not used, it can be put to practical use even if the amplitude of the second and subsequent waves is twice as large as the first wave, so in this case, the thickness of the input layer medium should be reduced to 1 It is possible to decide within a range of .0 m or more.

however.

Unnecessarily increasing the thickness increases parallax, which is not preferable.

As a result of various experiments and simulations, we found that the thickness of the propagation layer medium is between one-eighth and one-fourth of the longitudinal wavelength of the ultrasound to be propagated, and the sound velocity of the intermediate layer medium is six times the sound speed of the propagation layer medium. 1/3 or more, 1/3 or less of the thickness of the propagation layer medium
1/0 to 2/5, the sound velocity of the input layer medium is 1/4 to 1/2 of the sound speed of the propagation layer medium, and the thickness is 1/2 or more of the thickness of the propagation layer medium. I found out that it's okay to do this.

【Example〕

An embodiment of the present invention will be described below with reference to FIG. The writing section is composed of an input pen 1 and the aforementioned writing board 3 having a multilayer structure. There is a wave receiver 4a in a part of the corner of the writing board.
, b, c, and d are installed. The input pen 1 has a wave transmitter 1a and a pen tip 1b.

It consists of a grip 1c. A pulse voltage is applied by the pulse excitation circuit 5, and a longitudinal ultrasonic wave is incident on the writing plate 3 from the pen tip 1b of the input pen 1, propagates through the writing plate, and is detected by the wave receivers 4a, b, c, and d. be done. The detected signal passes through the waveform shaping circuit 6 and then is input to the time counting circuit 7, and the ultrasonic waves are detected from the ultrasonic incident point, that is, the contact position between the pen tip 1b of the input pen 1 and the writing plate 3, and each wave receiver. The propagation time of is measured. The measured propagation time is input to the coordinate calculating circuit 8, and after the positional calculation of the ultrasonic wave incident point is performed, the positioning result is displayed on the display device 9.

In this embodiment, polycarbonate is used as the input layer medium of the writing board 3, and ethylene vinyl acetate is used as the intermediate layer medium.
Glass is used as the propagation layer medium, and the wave receiver 4 is also attached to the propagation layer medium with the fastest sound speed, so even if the strength of contact between the input pen 1 and the writing board 3 changes, the position can be determined correctly. It is possible to create an ultrasonic application tablet that can perform

Furthermore, the materials mentioned above are transparent, and if a tablet made of such a transparent material is laminated onto the display surface of a liquid crystal display device, CRT, etc., an ultrasonic application tablet with an integrated input surface and display surface can be created. There are benefits that can be achieved. There are many transparent materials with different sound velocities other than those mentioned above, and various combinations are possible.

Although the case where the structure is made of a transparent material has been described above, the effect of the present invention is of course the same even if an opaque material is used.

Next, another embodiment of the structure of the writing board 3 is shown in FIG. In the structure shown in FIG. 6, the thicknesses of the input layer medium and the intermediate layer medium described above are each divided into two, and the propagation layer medium is sandwiched between the intermediate layer medium and the input layer medium from both sides. By adopting such a structure, even if the coefficient of thermal expansion of the writing plate is different for each medium, a writing plate that is less warped due to temperature changes can be realized.

Table 1 [Effects of the Invention] According to the present invention, an ultrasonic application tablet is used to eliminate measurement errors in ultrasonic propagation time due to changes in the strength of contact between an input pen and a writing board. Therefore, it is possible to realize an ultrasonic application tablet that can accurately determine the position.

[Brief explanation of drawings]

Fig. 1 is a configuration diagram of an ultrasonic application tablet using longitudinal waves according to an embodiment of the present invention, Fig. 2 is a diagram showing the contact strength of an input pen and the state of detected waveforms, and Fig. 3 is a diagram showing writing according to the present invention. A diagram showing the structure of the plate and how to install the wave receiver, Figure 4 is a diagram of the detected waveform obtained by simulation, and Figure 5 is the relationship between the peak value of the wave obtained by simulation and the thickness of the input layer medium. FIG. 6 is a diagram showing another embodiment of the structure of the writing plate and the mounting of the wave receiver according to the present invention. DESCRIPTION OF SYMBOLS 1... Input pen, 3... Writing board, 4... Wave receiver, 5... Pulse excitation circuit, 6... Waveform shaping circuit, 7
...Time counting circuit, 8...Coordinate calculation circuit, 9...
Display device.

Claims (1)

[Claims] 1. An ultrasonic device that propagates ultrasonic waves from a pen tip that emits ultrasonic waves through a writing plate, receives the propagated ultrasonic waves, and locates the coordinate position of the pen tip. In the sonic application tablet, the wavelength of the longitudinal wave of the ultrasonic wave propagating through the writing plate is 8.
On top of a propagation layer medium whose thickness is one-tenth or more and one-fourth or less, the sound velocity is one-third or less of the sound speed of the propagation layer medium and the thickness is one-tenth or more of the propagation layer medium, An input layer medium having a sound velocity of two-fifths or less of the propagation layer medium and a thickness of one-half or more of the propagation layer medium is provided on the intermediate layer medium. An ultrasonic application tablet characterized in that the tablet has a structure in which an ultrasonic wave receiver is attached to an end face of the propagation layer medium. 2. According to claim 1, the thickness of the input layer medium and the intermediate layer medium are each divided into two, and the propagation layer medium is sandwiched from both sides in the order of the intermediate layer medium and the input layer medium. Ultrasonic application tablet.