Coordinates input apparatus

It is an object to provide a portable coordinates input apparatus which can be manufactured at low costs. An input pen applies a voltage to a desired position in a coordinate input area on a vibration propagating plate having a piezoelectric performance and having a first surface including the coordinate input area and a second area that faces the first surface. A vibration generated by the voltage is detected as an electric signal by a vibration detecting electrode arranged out of the coordinate input area.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to a coordinates input apparatus for inputting 
coordinates by an input pen. 
2. Related Background Art 
Hitherto, in a coordinates input apparatus disclosed in, for example, 
Japanese Patent Publication No. 5-60615, as shown in FIG. 11, a vibration 
such as a supersonic wave or the like which is generated by driving a 
vibrator 4 built in an input pen 3 by a drive signal which is inputted 
from a vibrator driver 2 is used, thereby calculating a distance L between 
a position instructed by a contact 5 of the input pen 3 and a 
piezoelectric sensor provided at an edge point of a vibration propagating 
plate 8. Specifically speaking, the vibration is inputted from the 
coordinate input pen 3 to the vibration propagating plate 8 serving as a 
coordinate input surface. The vibration is detected by a plurality of 
piezoelectric sensors attached to the vibration propagating plate 8. A 
time which is required until the vibration arrives at each sensor is 
measured by a signal waveform detector 9. On the basis of measured 
results, a coordinate position where the vibration was inputted is 
calculated by a controller 1. The coordinates of the position instructed 
by the input pen 3, for example, a character or a figure which was 
inputted can be outputted to an information processing apparatus such as a 
personal computer or the like. 
However, the above conventional coordinates input apparatus has the 
following problems. 
Since the conventional apparatus has a construction such that the vibration 
which is inputted from the input pen to the vibration propagating plate 
and propagates through the vibration propagating plate is detected by the 
plurality of piezoelectric sensors (vibration detecting devices) attached 
to the vibration propagating plate, there is a problem such that the 
apparatus itself is thick by an amount corresponding to a thickness of 
piezoelectric sensor and, for example, a portability when the apparatus is 
used as a portable type apparatus is low. 
As a calculating principle of the position of the coordinates, the distance 
between the input point instructed by the input pen and each piezoelectric 
sensor is obtained and the position instructed by the input pen is 
outputted on the basis of the distance information. Therefore, in order to 
accurately calculate the coordinates, it is necessary to precisely 
position the absolute position of each piezoelectric sensor and to fix the 
piezoelectric sensors. For this purpose, it is necessary to strictly 
manage the positions of the piezoelectric sensors. There is a problem such 
that a productivity when producing a large number of apparatuses 
deteriorates and the apparatus cannot be manufactured at low costs due to 
such a low mass productivity. 
The invention is made in consideration of the above problems and it is an 
object of the invention to provide a coordinates input apparatus having an 
excellent portability which can be manufactured at low costs. 
SUMMARY OF THE INVENTION 
According to an embodiment of the invention, there is provided a 
coordinates input apparatus for inputting coordinates by an input pen, 
comprising: a vibration propagating plate having a piezoelectric 
performance and having a first surface including a coordinate input area 
and a second surface that faces the first surface; applying means for 
applying a voltage to the vibration propagating plate by making the input 
pen come into contact with a desired position of the coordinate input 
area; and detecting means for detecting a vibration which is generated by 
the voltage as an electric signal at a position of an electrode which is 
arranged out of the coordinate input area.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
A preferred embodiment of the invention will now be described in detail 
hereinbelow with reference to the drawings. 
A construction of a whole coordinates input apparatus in the embodiment 
will be first explained with reference to FIG. 1. 
FIG. 1 is a block diagram showing a construction of the coordinates input 
apparatus of the embodiment. 
Reference numeral 1 denotes the controller for controlling the whole 
coordinates input apparatus and for calculating coordinates; 2A a driver 
to form a drive signal for allowing the vibration propagating plate 8 to 
generate a vibration; and 3 the input pen whose tip is constructed by the 
conductive contact 5. By making the input pen 3 come into contact with the 
vibration propagating plate 8, which will be explained hereinlater, a 
voltage is applied to the direction of a thickness of vibration 
propagating plate 8, so that a vibration is generated from the vibration 
propagating plate 8 having a piezoelectric performance. Coordinates are 
inputted by designating the inside of an area A (hereinafter, referred to 
as an "effective area") surrounded by a broken line in the diagram by the 
input pen 3. 
Reference numeral 8 denotes the vibration propagating plate. In the 
embodiment, the plate 8 is made of, for example, piezoelectric ceramics 
made of PZT (titanium lead zirconium). The vibration propagating plate 8 
has a predetermined thickness and electrodes 6a to 6d for detection of a 
vibration each for converting a mechanical vibration into an electric 
signal are arranged at four corners of the top surface (coordinate input 
surface) of the plate 8. A specific structure will be described 
hereinlater with reference to FIGS. 2A to 5B. A damping material 7 to 
prevent (reduce) that the reflected vibration is returned to the center 
portion is provided around the outer periphery of the vibration 
propagating plate 8. 
Processes which are executed by the coordinates input apparatus of the 
embodiment will now be described with reference to FIG. 1. 
The mechanical vibrations which are detected by the electrodes 6a to 6d for 
detection of the vibration are converted into the electric signals and are, 
further, amplified by an amplifier (not shown). After that, the signals are 
inputted to the signal waveform detector 9. The electric signals inputted 
to the signal waveform detector 9 are subjected to waveform signal 
processes, which will be explained hereinlater, and signals indicative of 
timings when the vibration reaches the electrodes 6a to 6d are outputted 
to the controller 1. On the basis of the inputted signals, the controller 
1 detects the vibration arrival times to the electrodes 6a to 6d, 
calculates distances between the input pen 3 and the electrodes 6a to 6d, 
and calculates coordinates by a method, which will be explained 
hereinlater. The detailed processing operations of the signal detector 9 
and controller 1 will be separately described hereinlater. 
The controller 1 can also output the calculated coordinate values to an 
external device (not shown) by a serial/parallel communication or the 
like. 
On the other hand, the drive signal to vibrate the vibration propagating 
plate 8 is first supplied as a pulse signal (for example, every 5 msec.) 
at a low level from the controller 1 and starts the time counting 
operation by an internal timer (constructed by a counter). After the drive 
signal was amplified by the driver 2A at a predetermined gain, it is 
applied to the contact 5. When the contact 5 comes into contact with the 
inside of the effective area A of the vibration propagating plate 8, the 
electric drive signal is converted into a mechanical supersonic vibration. 
The vibration generated by the contact of the input pen 3 is delayed in 
accordance with the distance to each of the vibration detecting electrodes 
6a to 6d and arrives. 
A frequency of drive pulse which is formed by the driver 2A is selected so 
that the vibration generated by the vibration propagating plate 8 becomes 
a Lamb wave and propagates on the vibration propagating plate 8. Further, 
the elastic wave which propagates on the vibration propagating plate 8 is 
a Lamb wave and has an advantage such that it is difficult to be subjected 
to an influence by a scratch, an obstacle, or the like of the surface of 
the vibration propagating plate as compared with a surface wave or the 
like. It will be obviously understood that the vibration is not limited to 
such a wave but another vibrating mode can be also used in accordance with 
an object or an application. 
A plurality of constructions of the vibration detecting electrodes 6a to 6d 
which are fixed onto the top surface of the vibration propagating plate 8 
in the embodiment will now be described with reference to FIGS. 2A to 5B. 
FIG. 2A is an external perspective view showing a first construction of a 
part of the vibration propagating plate 8. FIG. 2B is a perspective view 
when it is seen from the direction of an arrow A1 in FIG. 2A. 
In the effective area A in which the coordinates can be inputted in FIG. 
2A, electrodes are uniformly arranged on the bottom surface of the 
vibration propagating plate 8 and are connected to the ground. On the 
other hand, mesh-like electrodes are formed on the top surface (coordinate 
input surface) as a surface opposite to the bottom surface. When the 
contact 5 of the input pen 3 comes into contact with one of the top 
electrodes, a voltage as a drive signal to drive the vibration propagating 
plate 8 in the thickness direction of the vibration propagating plate 8 is 
supplied from the driver 2A. The vibration propagating plate 8 starts to 
vibrate at the contact position. The generated vibration propagates on the 
vibration propagating plate 8 like a wave pattern which is generated when a 
stone is dropped onto a water surface. 
The vibration propagated on the vibration propagating plate 8 soon reaches 
the four corners of the plate 8. As for the vibration detecting electrodes 
6a to 6d provided at the four corners of the vibration propagating plate 8, 
the electrodes which are connected to the ground are fixed to the opposite 
surfaces. 
The electrodes which are arranged on the vibration propagating plate 8 are 
formed by a method such that electrodes (electrodes which are formed 
uniformly on the top and bottom surfaces of the vibration propagating 
plate 8) formed to polarize a piezoelectric material in the thickness 
direction are previously formed in a shape as shown in the diagram by an 
etching or the like or a method such that after the electrodes were formed 
in a shape as shown in the diagram by a printing or the like, the 
piezoelectric material is polarized by using those electrodes as 
electrodes for polarization, and the vibration propagating plate 8 is 
formed. The structure of the electrode is not limited to that shown in 
FIGS. 2A and 2B. For example, it is also possible to uniformly form the 
electrode on the bottom surface and to form only the electrodes on the top 
surface (coordinate input surface) by an etching or the like as shown in 
FIGS. 3A and 3B. 
FIG. 3A is an external perspective view showing a second construction of a 
part of the vibration propagating plate 8. FIG. 3B is a perspective view 
when it is seen from the direction of an arrow B in FIG. 3A. 
As shown in FIGS. 3A and 3B, by using the whole bottom surface as an 
electrode, the influence can be eliminated against the electric noises. As 
compared with the construction of FIGS. 2A and 2B, a process for 
positioning the electrodes on the top and bottom surfaces and the like are 
unnecessary and the apparatus can be also relatively cheaply manufactured. 
Further, the positions of the vibration propagating electrodes 6 are not 
limited to the corners of the vibration detecting plate 8 but can be also 
properly set every vibration propagating plate 8. The number of vibration 
detecting electrodes is also not limited to 4 but it is also possible to 
use a structure such that at least two or more vibration detecting 
electrodes are fixed. Further, it is also possible to use an electrode 
arrangement as shown in, for example, FIGS. 4A and 4B. 
FIG. 4A is an external perspective view showing a third construction of a 
part of the vibration propagating plate 8. FIG. 4B is a perspective view 
when it is seen from the direction of an arrow C in FIG. 4A. 
As shown in FIGS. 4A and 4B, even if no electrode is formed on the contact 
surface in the effective area A, so long as an enough voltage can be 
applied by making the input pen 3 come into contact with the plate 8, a 
vibration is generated in the plate thickness direction, so that 
coordinates can be detected. Although the vibration propagating plate 8 
has been constructed by PZT in the embodiment, the invention is not 
limited to such a material but can also use another material having a 
piezoelectric performance such as ZnO, PLZT, PVDF, or the like. Although 
FIGS. 2A to 4B show the constructions in which the bottom surface (side 
opposite to the coordinate input surface) of the vibration propagating 
plate 8 is connected to the ground and the voltage is applied from the 
input pen 3, the invention is not limited to such constructions. For 
example, it is also possible to use an electrode arrangement as shown in 
FIGS. 5A and 5B. 
FIG. 5A is an external perspective view showing a fourth construction of a 
part of the vibration propagating plate 8. FIG. 5B is a perspective view 
when it is seen from the direction of an arrow D in FIG. 5A. 
FIGS. 5A and 5B show the construction such that the drive signal for 
driving the vibration propagating plate 8 from the bottom surface side is 
supplied from the driver 2A. When the input pen 3 comes into contact with 
the vibration propagating plate 8, a voltage is applied to the vibration 
propagating plate 8 and a vibration is generated. In this instance, 
although the electrode on the bottom surface side which faces the 
vibration detecting electrode 6a on the top surface is connected to the 
ground, the invention is not limited to such a structure. For example, it 
will be obviously understood that it is also possible to use a 
construction such that the vibration detecting electrode 6a is fixed to 
the bottom surface side. When the vibration detecting electrode is fixed 
to the bottom surface side, a state such that the electrodes in the 
effective area A and the vibration detecting electrodes are not 
electrically connected as shown in FIGS. 5A and 5B are preferable. This is 
because if the vibration detecting electrode is included in the electrodes 
to be arranged uniformly on the bottom surface side, the drive signal that 
is supplied from the driver 2A also causes a vibration even at the position 
of the vibration detecting electrode and the coordinates cannot be 
correctly detected. 
&lt;Explanation of the controller&gt; 
FIG. 6 is a block diagram showing a detailed construction of the controller 
1 of the embodiment. 
In the diagram, reference numeral 31 denotes a microcomputer for 
controlling the controller 1 and the whole coordinates input apparatus. 
The microcomputer 31 is constructed by: an internal counter (not shown); 
an ROM (not shown) in which operating procedures have been stored; an RAM 
(not shown) which is used as a data work area or a temporary shunt area 
when coordinates are calculated; a non-volatile memory (not shown) for 
storing constants (for example, constants such as frequency f, phase 
velocity Vp, group velocity Vg, and the like, which will be explained 
hereinlater, regarding a sound velocity of the wave) which are necessary 
to calculate the distance; and the like. 
Reference numerals 33a and 33b denote counters for counting reference 
clocks. When a start signal for generating a drive pulse to the contact 5 
is inputted to the driver 2A, for example, the counter 33a to count a 
phase delay time tp which is calculated on the basis of a detection 
waveform that is detected by the vibration detecting electrode 6a and the 
counter 33b to count a group delay time tg start the time counting 
operations. Thus, the timing to start the time counting operation and the 
timing to generate the vibration of the input pen 3 are synchronized. A 
delay time until the vibration is detected by the electrode can be 
measured. In FIG. 6, although only one set of the counters 33a and 33b for 
the vibration detecting electrode 6a has been shown, when the vibration 
detecting electrodes 6a to 6d are arranged at four positions as shown in 
the embodiment, four counters corresponding to the four vibration 
detecting electrodes 6a to 6d exist. It is also possible to construct in a 
manner such that the detection signals from the electrodes 6a to 6d are 
time-sequentially divided by the signal waveform detector 9, which will be 
explained hereinlater, and to detect the times necessary for calculation of 
the coordinates. Namely, the apparatus is constructed so as to process the 
signal from another vibration detecting electrode every vibration that is 
generated from the position which is instructed by the input pen 3. For 
example, when two signals from the vibration detecting electrodes are 
necessary to calculate the coordinates, the coordinates can be calculated 
only when the vibration is generated twice from the position instructed by 
the input pen 3. 
As for a vibration arrival timing signal from the vibration detecting 
electrode 6a which is outputted from the signal waveform detector 9, an 
arrival timing signal of the phase delay time tp regarding the phase 
velocity Vp of the Lamb wave and an arrival timing signal of the group 
delay time tg regarding the group velocity Vg are inputted to the counters 
33a and 33b through a detected signal input unit 35, respectively. When the 
timing signals are received from the vibration detecting electrode 6a, the 
counters 33a and 33b are stopped and count values at that time are 
latched. A determinator 36 decides that those timing signals were 
generated. When receiving a determination signal from the determinator 36, 
the microcomputer 31 reads out the vibration propagation times from the 
counters 33a and 33b and executes a predetermined calculation. On the 
basis of the calculation result, the distance between the input pen 3 of 
the vibration propagating plate 8 and the vibration detecting electrode 6a 
and the coordinates of the position of the input point are calculated. From 
the calculation results, the microcomputer outputs the coordinate 
information to an external information device or the like through an I/O 
port 37. When coordinates are newly inputted, the microcomputer 31 outputs 
reset signals to the counters 33a and 33b and clears the contents in the 
counters 33a and 33b to zero. 
&lt;Explanation of detection of vibration propagation times (FIGS. 7 and 8)&gt; 
Explanation will now be made with respect to a principle such that the 
vibration propagation times on the vibration propagating plate 8, namely, 
the times which are required until the vibration sensors 6a to 6d detect 
the vibration which is generated by making the input pen 3 come into 
contact with the coordinate input surface. 
FIG. 7 is a diagram for explaining detected waveforms which are inputted to 
the signal waveform detector 9 and a process for measuring the vibration 
propagation times based on the detected waveforms in the embodiment. 
Among the vibration detecting electrodes 6a to 6d, the electrode 6a will 
now be described as an example. Explanation about the remaining electrodes 
6b to 6d are omitted because it is similar to the explanation about the 
electrode 6a. 
The measurement of the vibration propagation time to the vibration 
detecting electrode 6a is started simultaneously with the output of the 
start signal to the vibrator driver 2A. In this instance, a drive signal 
41 is applied from the driver 2A to the contact 5. When the contact 5 
comes into contact with the vibration propagating plate 8, the signal 41 
allows the vibration propagating plate 8 to generate a vibration. The 
vibration propagates with a time corresponding to the distance to the 
vibration propagating electrode 6a. After that, the vibration is detected 
by the vibration detecting electrode 6a. A signal 42 in the diagram shows 
a signal waveform detected by the vibration detecting electrode 6a. 
Since the vibration which is used in the embodiment is the Lamb wave as 
mentioned above, a velocity (group velocity Vg) at which an envelope 421 
of the detected waveform propagates and a velocity (phase velocity Vp) at 
which a phase 422 propagates are different. Therefore, for the propagation 
distance in the vibration propagating plate 8, the relation between the 
envelope 421 of the detected waveform and phase 422 changes in accordance 
with the propagation distance during the propagation of the vibration. In 
the embodiment, the distance between the input pen 3 and vibration 
detecting electrode 6a is detected from the group delay time tg based on 
the group velocity Vg and the phase delay time tp based on the phase 
velocity Vp. 
FIG. 8 is a block diagram showing a detailed construction of the signal 
waveform detector 9 in the embodiment. 
In the diagram, although the signal waveform detector 9 for the vibration 
detecting electrode 6a is shown, four signal waveform detectors actually 
exist in correspondence to the vibration detecting electrodes 6a to 6d. 
A method of detecting the group delay time tg and phase delay time tp will 
now be explained also with reference to FIG. 7. 
The output signal 42 of the vibration detecting electrode 6a is amplified 
up to a predetermined level by a pre-amplifier 51. The amplified signal is 
supplied to a band pass filter 511 and surplus frequency components in the 
detection signal are eliminated by the BPF 511, thereby obtaining a signal 
44. When paying attention to an envelope of the signal 44, a sound velocity 
at which the waveform propagates is the group velocity Vg. When a point on 
a certain specific waveform, for example, a peak of the envelope or an 
inflection point of the envelope is detected, the delay time tg regarding 
the group velocity Vg is derived. 
The signal 44 is inputted to an envelope detector 52 constructed by, for 
example, an absolute value circuit, a low pass filter, and the like and 
only an envelope signal 45 in the detection signal is extracted. A gate 
signal generator 56 constructed by a multivibrator or the like forms a 
gate signal 46 which gives a predetermined period after the level exceeded 
a predetermined threshold level 441 for the extracted envelope signal 45. 
To detect the group delay time tg regarding the group velocity Vg, it is 
sufficient to detect the peak, inflection point, or the like of the 
envelope as mentioned above. In case of the embodiment, however, the first 
inflection point (trailing zero-cross point of the signal 43, which will be 
explained hereinlater) of the envelope is detected. The envelope signal 45 
outputted by the envelope detector 52 is inputted to the envelope 
inflection point detector 53, so that a double differentiated waveform 
signal 43 of the envelope is obtained. The double differentiated waveform 
signal 43 is masked by the gate signal 46 by a tg detector 54 constructed 
by a multivibrator or the like and a tg signal 49 as an envelope delay 
time detection signal of a predetermined waveform is formed and supplied 
to the controller 1. A time from the trailing edge of the signal 41 to the 
leading edge of the tg signal 49 is set to tg. 
As for the phase delay time tp regarding the phase velocity Vp, a 
zero-cross point (first point when the phase changes from negative to 
positive) of the first leading edge of the phase signal 44 is detected by 
a tp detector 57 constructed by a zero-cross comparator, a multivibrator, 
or the like for detecting the phase delay time tp. Further, the phase 
signal 44 is masked by the gate signal 46 and a tp signal 47 as a phase 
delay time detection signal is formed and supplied to the controller 1. A 
time from the trailing edge of the signal 41 to the leading edge of the tp 
signal 47 is set to tp. 
&lt;Explanation of calculation of distance between the input pen and the 
electrode (FIG. 9)&gt; 
A method of respectively calculating the distance between the input pen and 
each electrode from the group delay time tg and phase delay time tp 
obtained as mentioned above will now be described. 
FIG. 9 schematically shows the relations among the group delay time tg and 
phase delay time tp and the distance L between the input pen and the 
vibration detecting electrode in the embodiment. 
Although the relation between the group delay time tg and distance L is 
continuous, it doesn't have an excellent linearity. On the other hand, it 
is not continuous. Such a discontinuity occurs due to a nature of the Lamb 
wave in which the group velocity Vg and phase velocity Vp differ. 
The sound velocity of wave (group velocity Vg, phase velocity Vp) is 
obtained by those relations and is defined as follows. The group velocity 
Vg is defined as a velocity in which its inclination is obtained by a 
method of least squares of the first degree due to the relation between 
the group delay time tp and distance L. The phase velocity Vp is defined 
as a velocity in which inclinations of individual straight lines are 
obtained by a method of least squares of the first degree and values of a 
plurality of inclinations obtained in a measured distance range are 
averaged and a mean value is set to such a velocity. Further, as for the 
frequency f of the Lamb wave, a segment of each straight line of the phase 
delay time tp is obtained by a method of least squares of the first degree 
by using the phase velocity Vp defined before and an interval between the 
straight lines is obtained. A mean value obtained by averaging the values 
of a plurality of intervals obtained in the measured distance range is 
defined as a wavelength .lambda.. The frequency f is defined as (phase 
velocity Vp/wavelength .lambda.). It will be understood that a highest 
distance measurement precision is derived by calculating the distance by a 
method, which will be explained hereinlater, by using the phase velocity 
Vp, group velocity Vg, and frequency f which were defined as mentioned 
above. 
A distance calculating algorithm will now be specifically explained. In the 
embodiment, the Lamb wave is used as a detected wave and the linearity of 
the relation between the group delay time tg and distance L which are 
outputted is not so good. Therefore, when the distance L between the input 
pen 3 and vibration detecting electrode 6 is obtained as a product of the 
group delay time tg and group velocity Vg as shown by the following 
equation (1), the distance L cannot be accurately obtained. 
EQU L=Vg.multidot.tg (1) 
Therefore, in order to determine the coordinates at a high precision, an 
arithmetic operating process is executed by the following equation (2) on 
the basis of the phase delay time tp with an excellent linearity. 
EQU L=Vp.multidot.tp+N.multidot..lambda.p (2) 
where, .lambda.p is a wavelength of an elastic wave and N is an integer. 
That is, the first term of the right side of the equation (2) shows a 
distance L0 in FIG. 9. As will be obviously understood from the diagram, a 
difference between the distance L to be obtained and distance L0 is integer 
times as large as the wavelength a width T* on a time base is equal to one 
period of the signal waveform 44, so that T*=1/frequency (f); if the width 
is expressed by a distance, it is equal to the wavelength .lambda.p!. 
Consequently, by obtaining the integer N, the distance L between the input 
pen and the vibration detecting electrode can be accurately obtained. 
Therefore, the integer N can be obtained by the following equation (3) 
from the above equations (1) and (2). 
EQU N=INT(Vg.multidot.tg-Vp.multidot.tp)/.lambda.p+0.5! (3) 
The equation (3) shows that even if the linearity of the relation between 
the group delay time tg and the distance is improved, so long as an error 
which occurs due to it lies within a range of .+-.1/2 wavelength, N can be 
accurately determined. By substituting the value of N obtained as mentioned 
above into the equation (2), the distance L between the input pen 3 and 
vibration detecting electrode 6 can be accurately set. 
The vibration propagation time which is outputted by the signal waveform 
detector 9 includes a phase circuit delay time etp and a group circuit 
delay time etg. The same amount is certainly included in each of the 
errors which occur due to those delay times in the series of operations 
which are executed in a range from the input pen 3 to the vibration 
propagating plate 8, vibration detecting electrode 6a, and signal process. 
Therefore, for example, in FIG. 10, assuming that vibration propagation 
times which are actually measured by a well-known distance (hereinafter, 
such a well-known distance is defined as Ra and an origin is defined as 0 
hereinafter) from the vibration detecting electrode 6a are set to tg0* and 
tp0* and propagation times which are required until the wave actually 
propagates on the propagating plate from the origin 0 to the electrode are 
set to tg0 and tp0, there are the following relations. 
EQU tg0*=tg0+etg (4) 
EQU tp0*=tp0+etp (5) 
On the other hand, actual measured values tg* and tp* at an arbitrary input 
point P are similarly 
EQU tg*=tg+etg (6) 
EQU tp*=tp+etp (7) 
When obtaining a difference between the equations (4) and (6) and a 
difference between the equations (5) and (7), respectively, 
EQU tg*-tg0*=(tg+etg)-(tg0+etg)=tg-tg0 (8) 
EQU tp*-tp0*=(tp+etp)-(tp0+etp)=tp-tp0 (9) 
The phase circuit delay time etp and group circuit delay time etg included 
in the propagation times are eliminated and the true propagation time 
delays when the wave propagates on the vibration propagating plate can be 
obtained, respectively. Therefore, by setting 
EQU tg=tg*-tg0* (10) 
EQU tp=tp*-tp0 (11) 
calculating the distance by using the equations (1), (2), and (3), and 
lastly adding the distance Ra between the vibration detecting electrode 6a 
and origin 0 to the value of the calculated distance, the distance between 
the input pen 3 and vibration detecting electrode 6a can be accurately 
obtained. Namely, it will be understood that if the distance between the 
vibration detecting electrode 6a and origin 0 and the vibration 
propagation times tg0* and tp0* which are measured at that time point are 
previously stored into a non-volatile memory or the like, the distance 
between the input pen 3 and vibration detecting electrode 6 can be 
accurately determined. 
Although the embodiment has been described with respect to the Lamb wave, 
it will be obviously understood that when selecting another vibrating 
mode, namely, when selecting a vibrating mode such that the relation 
between the group delay time tg and distance L has an excellent linearity, 
the distance can be also obtained by the product of the group delay time tg 
and group velocity Vg as shown in the equation (1). 
&lt;Explanation of calculation of the coordinate position (FIG. 10)&gt; 
A principle for actually detecting the coordinate position on the vibration 
propagating plate 8 by the input pen 3 will now be described. 
FIG. 10 is a diagram for explaining a method of calculating the coordinate 
position by the coordinates input apparatus according to the embodiment. 
As shown in FIG. 10, when the effective area A on the vibration propagating 
plate 8 is set to XY coordinates in which the origin 0 is set to the center 
and the four vibration detecting electrodes 6a to 6d are fixed to 
coordinates S1 to S4 at four corners of the effective area A, straight 
line distances da to dd from the position P of the input pen 3 to the 
positions of the vibration detecting electrodes 6a to 6d can be obtained 
on the basis of the above-described principle, respectively. Further, 
coordinates (x, y) of the position P of the input pen 3 can be obtained by 
the controller 1 from a theorem of three squares on the basis of the 
straight line distances da to dd as shown in the following equations (12) 
and (13). 
The distance between the vibration detecting electrodes 6a and 6b is set to 
X and the distance between the vibration detecting electrodes 6a and 6c is 
set to Y. 
EQU x=(da+db).multidot.(da-db)/2X (12) 
EQU y=(da+dc).multidot.(da-dc)/2Y (13) 
As mentioned above, the coordinates of the position instructed by the input 
pen 3 can be detected in a real-time manner. 
The coordinates have been calculated by using the distance information 
between the position instructed by the input pen 3 and the three vibration 
detecting electrodes 6a to 6c in the above example. In the embodiment, 
however, since the electrodes are arranged at four positions, a precision 
of the output coordinates is verified by using the distance information of 
the remaining one electrode. As a verifying method, for instance, the 
coordinates are calculated by using another combination of the vibration 
detecting electrodes 6b to 6d, the calculation results are compared, and 
the precision of the coordinate positions can be confirmed. 
Further, in accordance with an application, for example, it is also 
possible to construct in a manner such that the distance information of 
the vibration detecting electrode in which the distance L between the 
input pen and the vibration detecting electrode is largest (when the 
distance L increases, the detected signal level decreases and a 
probability at which the information is influenced by the noises 
increases) is not used but the coordinates are calculated by using the 
distance information of the remaining three or two electrodes (although 
calculating equations are not shown, a construction using the two 
electrodes is possible in principle). In this case, the effective area 
where the coordinates can be inputted can be also enlarged. With respect 
to the number of vibration detecting electrodes, the coordinates can be 
geometrically calculated by using the vibration detecting electrodes 
arranged at two or more positions. It will be obviously understood that 
the installing positions of the vibration detecting electrodes are set in 
accordance with the specifications of products. 
According to the embodiment as described above, the material having the 
piezoelectric performance is used as a vibration propagating plate and the 
voltage is applied from the input pen, thereby vibrating the vibration 
propagating plate, and the vibration can be detected as an electric signal 
at the electrode position. Therefore, a thickness of apparatus can be made 
thin as compared with the construction using the piezoelectric devices 
such as vibration sensors or the like according to the conventional 
method. Since there is no need to vibrate the input pen itself, a 
structure of input pen can be simplified and a mass productivity is 
improved. Further, in the coordinates input apparatus for calculating the 
coordinates by calculating the distances between the vibration input 
source and the vibration detecting points by using the vibration, since a 
positioning precision of the detecting device for detecting the vibration 
directly exerts an adverse influence on the coordinate calculating 
precision, it is necessary to strictly manage the position accuracies of 
the fixing position of the detecting device. According to the invention, 
however, since the accurate positioning process is unnecessary, the 
management of the position accuracy is easier than the conventional one. 
Thus, the coordinates input apparatus having an excellent mass 
productivity and a high performance can be constructed at low costs. 
The invention can be applied to a system constructed by a plurality of 
equipment such as host computer, interface, printer, and the like or can 
be also applied to an apparatus comprising one equipment. It will be 
obviously understood that the invention can be also applied to the case 
where the invention is embodied by supplying a program to a system or an 
apparatus. In this case, a memory medium in which programs regarding the 
invention have been stored constructs the invention. By reading out the 
programs from the memory medium and supplying to a system or an apparatus, 
the system or apparatus operates by a predetermined method. 
As will be obviously understood from the above description, according to 
the invention, the portable coordinates input apparatus which can be 
manufactured at low costs can be provided.