Note: Descriptions are shown in the official language in which they were submitted.
1~8~)3Z5 ~:
The present in~ention relates~ to a device for determining
positlon coordlnates on a flat surface.
Known devices for determining the coordinates of a point
are constructed with a tablet and a stylus pen and the like. One group
of such devices includes a tablet which has a plurality of conductive
lines located at equal intervals, and a stylus with electromagnetic
induction windings to which signals are applied, the conducti~e line
ad~acent the stylus pen picks up the signal induced from the stylus pen,
whereby the coordinates of the locatlon of the stylus may be determined.
Another type of device iB based on the principle of
electromagnetic induction. The position coordlnate is determined by
comparing the phase difference of an induced signal on a loop-shaped
sensing Iine on the tablet with phase of a slgnal applied to the
excitation coil o~ a cursor, whether it is placed within or outside of
the line.
In the electromagnetic induction type devices, the circuit
for detecting posltion coordlnate~ can be made comparatlvely slmple,
because the interval between scanning lines is equal to the resolution
; of the position coordinate. But on the other hand, the devices are
sensitive to external noise because these devices use a high impedance
sensor.
Another disadvantage of these devices i8 that the scanning
circuit is complicated by the large number of lines involved in a large
tablet having high resolution. Further, manufacturing technique limits
the interval between line8 by which a high resolution can be established.
Devices which determine the coordlnate by continuously
detecting the phase di~ference between an excitation signal and an
inducéd 9ignal, also have the disadvantage that the absolute coordinate
po~ltion csn not be obtalned on the tablet. Because the~e values are
determined in such a way as repetitive 180 phase shift. Once the cursor
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is moved away from the tablet, the established coordinate system is lost.
This can be avoided if the position coordinate is manually stored when
the cursor is removed, or when the sensing lines for detecting the
absolute coordinate position are newly installed. Such operations
require rather difficult procedures or the tablet is made complicated
in structure.
In these existing coordinate determining devices, the
signal of the sensor and the applied signal should be synchronized.
Also it is required that a cable be connected from the signal processor
to the stylus pen or cursor.
In accordance with the invention an automatic coordinate
determining device comprises a coordinate tablet having a plurality of
parallel conductive lines thereon. A scanning circuit generates
scanning signals in response to counting signals, each of tbe output
terminals of the scanning circuit being connected to one of the con-
ductlve lines for applying the scanning signals successively. A probe
for pointing a coordinate positlon has inductive windings and ls used
on the coordinate tablet, the windings belng inductively coupled with
the conductive lines. An oscillatory signal generator generates
signals which are applied to one of the windings or conducti~e lines in
mutual inductive relation, or inducing an oscillatory signal in the
other. A maximum-signal detecting device detects the maxlmum signal
ln the induced signal train which is successively induced in the other
of those ln the mutual inductive relatlon according to the scanning
on the conductive lines. The maximum-signal detecting device detects
the maximum signal in a manner in which at least two success1ve signals
respectively induced in two ad~acent conductive lines are compared
and the forward signal greater than or equal to the latter is regarded
as the maximum signal and is used to generate a detection signal in
response to the maximum-signal detection, the detection signal being
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fed to a gate for passing the counting slgnal corresponding to the maximum
- induced signal.
Figure 1 is a schematic perspective view showing a tablet
and probe of this invention,
Figure 2 is a schematic plan view showing the formation
of one set conductive lines, the pitch interval between lines, and the
probe,
Figures 3a, 3b, and 3c are graphical representations show-
~ ing the waveform of the scanning signal produced on the conductive line
as shown in Tigure 2 and the lnduced signal which superposes on the
scanning signal,
Tigure 4 is a graph showing the relationship of the position
of the excitation coil placed on the conducti~e lines and the induced
voltage developed in the conductive lines,
Figure 5 is a graph showing induced wave form in the
conductive lines in detail,
Figure 6 is a block diagram showing the circuit ~n a probe
of thls invention,
Figure 7 is a block diagram showing clrcuits in a probe
of another embodiment according to this invention,
Figure 8 is a schematic diagram showing the automatic
; coordinate determinlng device of the invention,
Figure 9 is a graphlcal representation of wave forms of
different portions of the circuit sXown in Tigure 8,
Figure 10 is a block diagram showing the maximum signal
detecting circuit ln Tigure 8,
Tigure 11 is a block diagram showing the A,G,C in Figure
8,
Tigure 12 is a graphical representation of output of the
dividing circuit in ~igure 8,
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Fi~u~e 13 ~s ~ g~aph showin~ a co~rection cur~e availed
ln the nonvolatile ~emory circult in ~igure 8,
Figure 14 ls a block diagram showing another automatlc
coordinate determining devlce according to the inventlon,
Pigure 15 is a block diagram showing further an automatic
coordinate determining device of this invention, and ls on the same
sheet as Figure 5.
Flgure 16 is a block diagram showing another embodlment
of the invention,
Figure 17 is a schematic plan vlew showing a tablet
according to the embodiment in Figure 16,
and
Figure 18 is a block diagram showing another embodiment
according to this invention.
Figure 1 is an exploded perspective of a tablet according
to this invention. In Figure 1, numerals 1 and 2 represent 1at plates
made of insulating material which are installed closely contacted to
each other to form ~ulti-layer structure. The flat plates 1 and 2 are
provided with a plurality of conductive lines Xl, X2,...,Xn and Yl,
Y2,... ,Ym each of which i8 respectively ~ormed in a U~shaped having a
pair of parallel lines. The U-shaped conductive lines Xl, X2,...,Xn
are spaced parallel to each other and with little gaps g between ad~acent
lines as shown in Figure 2, or without any gap. This layout provides
efective inductive coupling together with superior sensitivity and
accuracy and eliminating portions of the tablet where coordinate
determination is not po~sible. The U-shaped conductive lines Y~
~Y2,...Ym on plate 2 have same layout and are arranged perpendicular to
the conductive lines Xl, X2,...Xn on plate 1.
One end of each of the conductlve lines is respectively
connected to the outpot terminal of scanning circuits, such as ring-
counters, 3 and 4, the other end of each lines is connected to a rectifler
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Dl, D2~...Dn~m respectively. These recti~iexs have a co~on output
llne 1 which ls connected to a power source through register R and to
a maximum-signal detecting device M.
The conductive lines Yl, Y2,...Y may be installed on
the opposite surface of tablet 1 to the conductive line surface of
Xl~ X2,...Xn.
Numeral 5 designates a probe for indicating a coordinate
position, which generates alternating magnetic field. The probe 5 is
provided with excitation windings 5a having concentric circular and
alternative current signal generator 6.
Figure 2 shows schematically the probe 5 located wlth
respect to the conductive lines Xl, X2,...Xn. As shown in Figure 2,
the conducti~e lines Xl, X2,...Xn are spaced with a pitch r. Pitch r
is set to the basic length, i.e. 2n inch or mm (n = 0, 1, 2,...). Each
of the conductive lines is connected with a ring counter 3 at one end
and the other end is connected to the rectifiers Dl,...Dn. The winding
5a on the probe 5 which is excited by alternating current from the
signal generator 6 preferably has an inner diameter larger than 2r.
The gaps g between a pair of parallel lines, a line to ring counter 3
and the line to maximum signal detecting device M of the next U-shaped
line, i8 made small, preferably to zero, for eliminating dead areas
on the tablet.
Figure 3a shows a time-~oltage chart of the output wave-
_~ form applied to the conductive lines from the ring counter 3. The ring
counter 3 applies one rectangular wave signal after another to the lines
' Xl~ X2,.. Xn. , . ~ . ' .
When the scanning signal Sl is applied to conductive line
Xl, the signal Sl passes through the rectifier Dl to the common output
line. On the output line when the signals Sl, S2,...Sn are gi~en to the
conductive lines Xl, X2,... Xn respectively, the signal has a random
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stepped waVe~orm to the tlme pass~ge as shown in Figure 3b, because of
deviations of the forward drop voltage at the rectifiers.
When an alternating current signal is applled ~o the
winding 5a, the electromagnetlc induction occurs and consequently an
induced voltage is developed in the conductive lines on the tablets
1 and 2.
The maximum magnitude of the induced voltage is obtained
at the lines nearest to windings 5a; some lower voltages are also
induced in ad~acent lines. But the induced voltages do not appear at
the output line unless the scanning signal is applied, since the magni-
tude of the induced voltage is very low in comparison with the forward
voltage drop (approx. 0.6V - 0.7V) of the rectifiers Dl, D2,...Dn.
The rectifiers are uni-directional. So, when the scanning
signal, for example Sl, S2,...Sn as shown in Figure 3a are applied,
the scanning current never flows into other scanning lines because the
cathode terminals of the rectifiers operate for reverse condition.
The scanning signal is a positive going waveform in
Flgure 3a. However, a negative going waveform msy also be u6ed, ln
which case, the anode terminal of the rectifiers are commonly connected,
and the reverse voltage is fed to the output line. Thus as before, the
lnduced voltage does not appear at the output line unless a scanning
signal is applied. That is, the signals which can appear at the output
line are restricted to the scanning signal and the induced signals
carried on the scanning signal.
Therefore, when the probe 5 is placed on an arbitrary
position of the tablets (i.e. near conductive line Xl), the induced
voltages, in which maximum magnitude is obtained on the conductive line
Xl and appear at the output line superposed to the scanning signal, as
~h~wh ln ~igure 3c.
Figure 4 shows the relationshlp between the location of
probe 5 in relation to the conductive lines and magnitude of the induced
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voltages at the conductive llne~, in Which curves Vl, V2 and ~3 respec-
tively represent the lnduced voltages in conductive lines ~ , X2 and X3.
When probe 5 is located at point P, ~c~ ~a and Vb respectively represent
the induced voltages in lines Xl, X2 and X3 Probe 5 being located at
the center Pl, P2 or P3 of U-shaped line Xl, X2 or X3, magnitude maximum
of voltage is induced in line Xl, X2 or X3.
Generally, induced voltage has the maximum magnitude
when probe 5 is just at the center of the U-shaped line and gradually
decreases in proportion to the deviation of the probe to either side.
The voltage again rises a little, as i8 shown in Pigure 5, after further
deviation of the p~obe, making symmetric minor peaks on either side of
the maximum peak. A trough between the maximum and a minor peak appears
when the probe 5 i8 located at a position where inner flux of windings
5a penetrating through the U-shaped area of the conductive line is
equal to outer flux penetrating through the U-shaped area of the same
line. This position of the probe is where the center of the winding 5a
is approximately half the dlstance of the winding inner diameter from
the center of the U-shape. Therefore, if the winding diameter is made
8reater than twice the conductive line pltch r, the induced voltage curve
from the center of the U-shaped conductive line to the next U-shaped
conductive line continuously decreases. This selection of the windlng
lnner diameter with reference to the conductive line pitch is valuable
for determining of accurate intermediate coordinate positions, as will
be described later.
~igure 6 is a block diagram showing the construction of
the probe 5 connected to a signal generator 6. A multi-dividing circuit -
7 receives a signal of high frequency from the signal generator 6 and
,
divides it into several kinds of lower-frequency signals fO fl,... and
fk, which are fed to a switching circuit 8 to be selected for exclting
windings 5a. Numeral 9 designates a hybrid circuit for combining a
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plurality of fre~uency signals ~ed ~o~ the switching circuit 8, ~or
winding 5a. These plural signals which are applied to winding 5a induce
signals of their corresponding fre~uencies in the conductive lines for
determining the coordlnates o~ the probe and further for other command
functions, such as point reading or time-mode reading.
When two or more probes are desired on a wide tablet for
simultaneous use by diferent operators, a combination of a signal
generator 6, a divider 7, a switching circuit 8 and a plurality of
windings 5a, Sb,... and 5k, as shown in Figure 7 is preferred.
Figure 8 is a block diagram of a position coordinate
detecting apparatus according to this invention.
In Figure 8, maximum signal detecting device ~ receives
the induced signals, as shown at a in Figure 9, from output line o
tablets 1 and 2. Device M includes a band-pass filter 10 to pass the
signal of frequency fO shown at b in Figure 5, an automatic gain
controller 11 to control the level of the signal fed from band-pass
filter 10, a rectiier 12 to rectify the signal b in ~igure 9 into the
full-wave slgnal e in the,same Pigure, and a low-pa,ss filter 13 to
smooth the full-wave signal as h in ~igure 9. In the curve of h in
Figure 9, Va d`esignates the maximum signal, Vb the second and Vc the
thlrd respectively induced in ad~ac`ent conductive lines and successively
transferred in the maximum detecting device M.
The maximum detecting device M further includes an analog
to digital converter 14 to convert the smoothed analogue signal into
digital signal, and a maximum detecting circuit 15 to compare the
succe~sive digital signals from the A-D conVerter 14.
The detail of maximum detecting circuit 15 will now be
described hereinater reerring to Figure 10, in which numerals 16 to 18
designate a shift-register to receive the digital signals from A-D
conVerter, numerals 19 and 20 are comparing circuits, comparing circuit 19
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compa~ing the output o~ reglster 16 with that of register 17 and comparing
clrcuit 20 comparing the output o~ reglster 16 with that of register 18.
Numeral 21 designates a selecting circuit to select a signal between the
output of register 16 and that of register 18 with the control signal
from comparing circuit 20.
A signal traln such as h shown in Figure 9 is received
by register 16. Register 16 contains the most recent signal, register
17 the next most recent signal, and registér 18 the next most recent
signal. When the maximum signal Va reaches register 17, the second
largest signal Vb is in register 16 and the signal Vc is in register 18.
At this time, register 17 has a larger signal than that stored in
register 16, while, before this step register 17 had a smaller signal.
Accordingly, comparator 19 detects this change and generates a detection
signal Mx. Comparator 20 generates a control signal for selecting
clrcult 21 to select the output of register 18 with a minus signal when
the signal at register 18 is larger than that at register 16, whlle
otherwise selecting circuit 21 selects the output of register 16 with
a plus ~ignal.
~umeral 22 designates a divlding circuit to make the
20 - second ~rge signal selected by selecting circuit 21 divide the maxi~um
~ignal from register 17. Dividing circuit 22 receives both the outputs
of comparing circuit 20 and selecting circuit 21 using the detection
signal Mx as a cue signal.
As a result of this dividing operation of dividing circuit
22, spurious signals, such as a deviation of the induced voltage in
conductive line~, which is caused by uneveness of the media placed on
the tablet, the variation of the impedances of conductive lines, the
deviation of alternative magnetic field, and the variation of thickness
of the tablet, are all eliminated. Conductive lines in a small area
suffer these deviations approximately in the same extent.
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.
De~ining the dev~ation pa~ameter in a small area as ~ ,
the following equations are represented;
V~ =~ Vs~.,,,,,,.,.--(1) ~ ,
in equation (1), Vs; theoretical lnduced voltage, V~ ; actual induced
voltage.
~ccordingly, in the case of Va and ~b in Figure 9;
Va = c~ Vsa...... .... .(2)
Vb C~ VSb---~ -(3)
In equations (2) and (3), V8a and V b; theoretical induced voltages of ~`
the maximum signal and the second large signal.
The output of dividing circuit 22 ls, therefore;
VR = Va = c~Vsa = Vsa .................. (4)
~b c~ Vsb Vsb
There is no influence of ~ in the output ~R. The output
VR is used for determining the intermediate coordinate between a pair
of ad~oining çonductive lines, as will be descrlbed later.
Figure 11 is a block diagram showing automatic gain
controller 11 in detail, in which numeral 23 designates an amplifier
the gain of which i6 controlled by the maxi~um signal from register 17
through a register 24, a digital to analog converter 25 and a differential
amplifier 26. Register 24 receives the maximum signal at a cue signal
of the detection signal M from comparing circuit 19 and stores it.
By the output of differential amplifier 26, the gain of amplifier 23
is controlled so that the deviation of induced voltages is suppressed. ~ ;
As clarified in the above~description, the induced voltages
show unidirectional increasing or decreasing characteristics which gives
the maximum magnitude in the nearest conductive line to the winding 5a
of probe 5. Accordingly, the divided voltages VR in the equation (4) ~ -
represent a curve shown in Figure 12 including "11' as the minimum.
Now referring to Figure 12, the voltage ~R has a non-
linear relationship to distance ~(, which means that the distance or
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coordinate between a palr of conductiye lines can not i~mediately be
given from the divided voltage ~R
~ or getting the distance, outputs from dividlng circuit
22 shown in Figure 8 are given to a non-volatile memory circuit 27 such
as Read Only Memory. Memory circult 27 stores data to indicate a curve
shown in Figure 13 corresponding to Flgure 12.
That is, the outputs of di~idlng circuit 22 are converted
into true coordinates through memory clrcuit 27 which stores the data
to compensate for nonlinearlity along the curve in Figure 13. Actually,
when, for example, one tenth of the pitch r of the conducting lines
should be determined, distance "a" is divided into six areas as shown
in Figure 13, both side areas being one-half of other areas. Memory
circuit 27 stores "5" in memories corresponding to addresses of VO to Vl,
"4" in memories corresponding to addres6es of V1 to V2,.... ~ "O" in
memories corresponding addresses of V5 to V6 so that coordinate number
ln 1l length unit is obtained according to the probe position. If far
finer division of distance "a" is required, it is preferable for saving
memories to provide memorie~ the number of which is e~ual to that of
the dlvlslon and to only apply some middle blts of the divlded signal
VR to the address of the memory, cutting off lower bits which have no
effect on determinlng coordlnate and hlgher blts which represent zeros.
The number of the lower bits to be cut off increases according as the
slgnal VR reaches to 1.
Numeral 51 (Figure 8) designates a clock-pulse generator
; to generate clock pulses which are fed to a counter 52. The counting
number of said counter 52 is fed to the scanning circuits 3 and 4. ~i
The scannlng clrcuit 3 for X-axis decodes the counting numbers into
scannlng 6lgnals which are applied to the conductive lines Xl, X2,...Xn
successively, and the scanning clrcuit 4 for Y-axis decodes the counting
number6 lnto scanning signal6 which are applied to the conductive lines
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Yl, Y2,...Y suçcesslvely after the X~axis scanning. After the last
scanning signal has been applied to conductive line Xn or Y , counter
52 is reset and again starts to count the clock pulses. Numeral 53
designates a signal detector to alternately detect n or m sending a
changing signal with the detection to the clock terminal of a flip-flop
54. An output terminal Q of the flip-flop 54 is connected to scanning
ci~cuit 4 and the other output terminal Q is connected to scanning
circuit 3, so that the scanning circuits 3 and 4 are alternately enabled
to operate as described above.
The counting number of said counter 52 represents a
conductive line coordinate in X or Y axis, and it is applied for
determining length-unit coordinate, which will be described later.
But the conducti~e lines have respectively positional errors in a strict
sense, and it is required to correct these errors for accurate coordinate
determination. Therefore, converting means 55 and 56, such as read-only
memories, are provided to receive the counting number of said counter
52 for converting it into a corrected conductive line signal. Said
converting means 55 and 56 are alternately operated for X- or Y-axis
under the control of the outputs Q and Q of said flip-flop 5~. Numeral
57 designates a latch register connected between counter 52 and the
palr of converting means 55 and 56 to pass the counting number under
the detection signal M of said maximum detecting circuit 15.
Conductive lines of at least one spaced on both the sides
of the tablet are not suitable for determining coordinate because of
the distortion of inductive effect. Therefore, a signal selector 61 to
invalidate the signals corresponding to both-side conductive lines is
inserted before said latch register, the end signals to be invalidated
being alternately selected according to the outputs Q and Q of flip-flop
54.
The output of said converting means 55 or 56, i.e. the con~
verted length-unlt coordinate signal, and the output of said non~volatile
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memory or another converting means 27, i.e. the true intermediate co-
ordinate signal are ~ed into an operation circuit 58, in which these ~ -
signals are added or subtracted in response to the plus or minus signal
generated by said maximum detecting circult 15.
The output of said operation circuit 58 is fed to registers
59 and 60, which are alternately enabled to receive the output of opera-
tion circuit 58 under the control of the outputs e and ~ of said flip-
flop 54.
Thus, the coardinates of the probe 5 are obtained, the
X-coordinate from register 59 and the Y-coordinate from register 60.
Signals fl, f2, ...and fk ~Figure 7) are also induced in
the conductive lines when wlndings 5a are excited by the corresponding
frequency signals of probe 5. These signals are respectively dis-
criminated through further band-pass fllters, one of which is shown in
Figure 8 with numeral 62. Band-pass filter 62 blocks induced signal f
~or making a point-reading signal. A mono-multi-vibrator 63 receiyes
induced signal fl through a level discriminator 64 such as a Schmidt
trigger circuit to e:liminate low level noises, and the output of mono-
multl-vibrator 63 is used as the point-reading signal with which one
point coordinate of probe 5 as it is located is ~ed to exterlor devices !~''" '' ~'
such as a computer or to a display panel. Signal f2, f3, ....or fk
may be used to instruct the computer or display panel. Further, these
signals may be used for simultaneously determining other probe co-
ordinates uslng a plurality of probes as shown in Figure 7 and further
separate maximum signal detectors. This combination of multi-frequency
inducing and a plura~ity of band-pass filters is useful for providing
a coordinate determining device with wireless probes.
It is to be noted that, in the above-described embodiment,
rectifiers D on conductive l~nes may be replaced with switching elements,
in which case the scanning signals successively turn on-and-off the
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switching elements fo~ allowing induced signals to be transmitted to the
maximum signal detecting device.
It is further to be noted that, with the above replace-
ment, a conversion of the mutual inductive relation of the windings and
the conductive lines may be achieved, in which the conductive lines on
the tablet successively receive exciting signals from the alternating
current signal generator and induced signals induced in the windlngs
of the probe are fed to the maxlmum signal detecting device.
Further, if so accurate determining of the coordinate is
I0 not necessary or very flat media is used, the dividing circuit 22 may be
omitted, the maximum signal being directly converted into true co-
ordinate signal. This embodiment is shown in Figure 14, in which the
same reference numerals are used as in ~igure 8. In Figure 14, the
output of an operation circuit 65 which includes maximum signal detecting
circuit 15 and nonvolatile memory clrcuit 27 to convert the maximum
signal from =aximum signal detecting circuit 15 into the true inter-
mediate coordinate, is fed to operatlon circuit 58. Numeral 66
designstes a command generator as described above, which receives various
signals respectively generated by induced signal6 f1, f2, ...and fk
through band-pass filters 62, 62',.;.62k, level discriminators 64, 64',
...64k, and moDo-multivibrators 63, 63',....63k, and generates, in
response to the induced signals, command signals to a register 67.
Register 67 receives the coordinate value in register 59 and sends it to
the exterior device such as a computer in response to the commands.
In Figure 15, a curve generator 68 is connected between
recti1er 12 and analog to digital converter 14, for converting induced
signals into true intermediate coordinates in analogue. Numeral 69
designates a shift register which operates similar to shift registors
16 to 18 in Figure 10, and numeral 70 designates a comparator including
C Ow~ q
1 cor~or~t1ng circuits to act as same as those 19 and 20 in Figure 10.
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~n the aboye automatic coo~dln~te dete~:minlng device by
the scanning method, a repeated scanning interval is increased when an
area of tablet is increased, and conse~uently sampling frequencies at any
point is decreased. But the drawback can be completely solved by the
embodiment shown in Figure 16. In this embodiment, a limited number of
scanning lines near the probe 5 are scanned and further the scanning
range is ~aried following to the removal of the probe 5.
. Figure 16 shows a detailed circult diagram for the counter
52 shown in Figure 8. On the diagram, circuits 15 and 52 are respectively
corresponding to the maximum magnitude detecting clrcuit 15 and the
counter 52 shown in Figure 8.
In Figure 16, counter 52 renews sequentially scanning
address signals on clock signals from a clock generator 71. Now placing
the probe on the desired position on the tablets, signals are induced ::
on the conductive lines, and the maximum detection signal M ls generated
x
in the maximum magnitude detecting cireuit 15. At the time, the scanning
address signal is stored in a register 72 with trigger of the detection
signal Mx.
The circuit 73 is a subtracter consisting of Exclusive-
OR gate and Full Adder to subtract a value from a setting circuit i4
for designated values from a content of register 72. The subtracted
value i~ transfered through a gate 75 to counter 52 to be stored. ::
Maximum-signal detecting circuit 15 gives the detection
signal Mx to register 72 to move the content of the register 72 to sub-
tractor 73, and further to a controlling circuit 77. Numeral 78
designatés a gate which receives clock signals from clock generator 71
and passes them, on receipt of a control signal from controlling circuit
77, to an M-notation counter 79. A carry signa1 is generated from
M-notation counter 79 and this carry signal is fed to controlling circuit .. ~
.
77 and to an OR-gate 80 the circuit of which is fed to J-terminal of
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108~)3Z5
counter 52. A ~eset s~gnal o~ a ~ nal ~o~ counte~ 52 is also to be
generated in controlling ci~cuit 77.
Controlling circuit 77 operates as follows, if a detection
signal M is generated in maximum signal detectlng circult 15 in one
scan of the conductive lines, controlllng circuit 77 sendsout an opening
signal to gate 78 and further a 3-signal to counter 52 through OR-gate
80 after a desired time delay, so that the output of subtractor 73 is
moved to counter 52, whereby presetting the counter 52. The output of
subtractor 73 has a value of i-i because, at the time of the detection
~ignal Mx generation, the content i (corresponding to the maximum signal)
of register, which is equal to that of counter 52, is moved to subtractor
73 and is sub~racted by the preset value ~ in setting circuit 74. If i
is smaller than ;, a carry signal is generated from subtractor 73 so
- that gate 75 prohibits the output of subtractor 73 from passing, setting
preset value oP counter 52 to zero.
Accordingly, the scanning starts at conductive line Xi ;
immediately after the detection signal Mx generation.
During M pulse counting~ if a detection signal Mx is fed
to controlling circuit 77 and to register 72, a J-signal is again applied
to counter 52, presetting counter 52 to a subtracted value generated at
~ubtractor 73 in the same manner as described above, and a new scanning
begin~ from there. Otherwise, after M pulse counting, i.e. M line
scanning, M-notation counter 79 sends out a carry signal to controlling
circuit 77 and counter 52. Accordingly, counter 52 is preset to a new
subtracted value smaller than the last value of counter 52, and a new
scanning begins fro~ there.
If probe 5 is spaced apart from the tablet or at a position
on an earlier conductive llne than the initial scanning area, the scanning
area reaches at the end line. In this case, neither detection signal Mx
nor carry signal of M-notation counter 79 is applied to controlling
circuit 77 in longer time than an M-clock passage, and, as a result,
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controlling cl~cuit 77 sends out a reset slgnal to c~untex 52, whereby
a scanning begins from conductive line Xl.
Reerring now to ~igure 17, which is a plan view showing
the tablet, on whlch the probe 1s located at XA at first, a scanning
operation of aforementioned method wlll be described in particular.
Setting number in setting circuit 74 is four, M of M-notation counter
79 being eight. Counter 52 starts at first to count from one, scanning
signal from X1. At line X6 which is the nearest to the probe, i.e.
when the content of counter 52 is six, a detection signal Mx is detected
and subtracted number from subtractor 73 becomes "6 - 4 = 2". Accor-
dingly, counter 52 is preset to two and the next scanning begins from
line X2.
If the probe moves rom XA to XB, the next detection
signal Mx is detected when the content of counter 52 is eight, and
accordingly, the subtracted number becomes "8 - 4 - 4" and counter 52
is preset to four, the scanning area being shifted as shown in Figure 3.
For both X and Y axes partial scanning, a modi~ication
as shown Figure 18 i~ available.
In Figure 18, the samé reference numerals as those in
20 Figure 16 are used for designation with or without suffix X or Y.
Q and Q are respectively connected to those of 1ip-flop 54 in Figure 8.
Numerals 81x, 81y, 82x and 82y designate gates to be opened by signal
Q or Q. Numerals 83x and 83y designate gates to be opened by signal
from OR-gate 80y or 80x. Other construction and function are similar
to those in Figure 16.
With this circuit in ~igure 18, an X-axis partial scanning
and a Y-axis partial scanning are alternatively performed.
,'~ ' ' ' .
.
- 17 -
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