JPH0319967B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to a graphic input device, and more particularly to a graphic input device that improves the accuracy and resolution of coordinate reading in a capacitively coupled tablet.

[Prior art and its problems]

Among graphics input devices, tablet input devices are devices that can directly convert information existing in the form of graphics into the form of coordinate values and input it digitally. It is widely used for inputting handwritten characters, figures, etc.

There are various types of graphic input devices such as capacitive coupling type and electromagnetic coupling type. Among these, the capacitive coupling type has multiple electrode wires laid in parallel at equal intervals inside the tablet, and uses the capacitance between the input pen or cursor and the electrode wires to connect the electrode wires. This is a tablet that detects sequentially applied pulse voltages and determines the position coordinates of an input pen, etc. With this method, when attempting to improve resolution by narrowing the spacing between the electrode wires, the electrode wires become thinner and there is a risk of wire breakage, and it is also difficult to maintain sufficient parallelism between the wires. As a practical matter, it is almost impossible to manufacture a tablet with a large input area.

In an attempt to solve this problem, conventional methods have been to find the ratio of the detection voltages of the three electrode lines near the pointing point of the input pen, calculate the pointing position from the geometric relationship, and achieve the minimum resolution of the device. A method has been proposed in which the pitch is made smaller than the pitch between the electrode lines (Japanese Patent Publication No. 19380/1983). This is the so-called three-point potential detection method.

However, in the three-point potential detection method according to the prior art described above, since the position is calculated from three data, calculations are complicated and signal processing lacks speed.

To explain this in more detail, in the above conventional example, for example, the strength V of the detection voltage and the distance d between the electrode line and the input pen are expressed as: V=β/α・d (α and β are constants) It is assumed that the relationship (1) holds approximately, and furthermore, it is attempted to avoid fluctuations in constants caused by non-uniformities in the mechanical dimensions, materials, etc. of the device by determining the ratio of detection voltages. However, experiments have shown that even when there is no mechanical deviation of the device, there is a large error between the distance calculated based on equation (1) above and the actual measured value, making the approximation questionable and the measurement accuracy poor. Shortcomings have long been pointed out. Furthermore, since a fractional formula with a quadratic voltage ratio as the denominator and numerator is used to determine the position, the calculation and circuit configuration are complicated, and a separate calculation formula is required especially near the edge of the tablet. It was hot.

[Purpose of the invention]

The present invention has been made in view of the drawbacks of the prior art, and an object of the present invention is to provide a graphic input device that can improve measurement accuracy and resolution with a simple configuration.

[Means for solving problems]

The present invention includes a tablet comprising a plurality of X and Y electrode lines laid at regular intervals, means for applying a scanning pulse to each of the electrode lines, and an input for detecting the potential induced in the tablet in response to the scanning pulse. The device includes a pen and coordinate position calculating means for calculating the position of the input pen on the tablet based on the signal detected by the input pen. Between the input pen and the coordinate position calculation means, there is a potential storage means for storing the potentials of the top two signals among the plurality of signals detected by the input pen; It is equipped with an L _S calculation section that calculates the ratio of sum and difference, and a distance calculation means that calculates the distance from the electrode line corresponding to the maximum potential to the pen touch position based on the output of this L _S calculation section. Then, the coordinate position calculation means has a function of calculating the coordinate position on the tablet touched by the input pen based on the output from the distance calculation means and the signal related to the maximum potential among the detection signals from the input pen. The company has adopted a structure in which it is equipped with the following. This aims to achieve the above-mentioned purpose.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIGS. 1 to 7.

First of all, the principle of this embodiment will be explained based on FIGS. 1 to 4.

As shown in FIG. 1, the tablet 1 has a plurality of X electrode lines X ₀ to X _o and Y electrode lines Y ₀ above and below a substrate 2.
- Y _n are orthogonally arranged in parallel to each other at equal intervals, and an insulating layer 3 is integrally attached above the X electrode lines X ₀ -X _o . This tablet 1
When the input pen 5 is touched directly or indirectly through the drawing paper 6 and the scanning pulses shown in Fig. 2 are sequentially applied to each electrode line X ₀ to X _o or Y ₀ to _Yo , a The signal strength induced in the input pen 5 is as shown in FIG. 3, for example. The detection signal a _i related to the electrode line X _i closest to the input pen 5 is at the maximum level
V _nax , and the level of the detection signals a _i-1 , a _i+1 , a _i-2 gradually decreases as the distance from the input pen 5 increases. Here, the signal level related to the two electrode lines X _i and X _i-1 that sandwich the input pen 5, that is, the maximum level
For V _nax and the second largest signal level V _oext ,
Calculate the distance functions L _S , L _S =V _nax −V _oext /V _nax +V _oext (2), and calculate the horizontal distance from the midpoint between the electrode lines X _i-1 and X _i to the touch point of the input pen 5. When examining the correspondence between s and s, a substantially linear relationship was obtained as shown in FIG. In other words, the inventor calculated the sum of the two detected voltages
It has been newly discovered that the position indicated by the input pen 5 (specifically, the position from the electrode at the shortest distance) can be determined by calculating the ratio of the differences.

Next, this will be explained in more detail based on FIGS. 5 to 7.

FIG. 5 is a block diagram showing a tablet input device according to the present invention. In FIG. 5, the input pen 5 for drawing figures on the tablet 1 or inputting figures by following the figures on the drawing paper 6 is equipped with a pen switch 5A. When the input pen 5 is pressed down on the tablet 1, the pen switch 5A is closed and the entire device is put into operation. The pen switch 5A is connected to a control circuit 10, and when the pen switch 5A is closed, a pen switch signal is sent to the control circuit 10. Control circuit 10
is activated by a pen switch signal to start a control operation, and first performs pulse scanning of the tablet 1 according to a predetermined sequence. That is, the control circuit 10
sends a start signal to the counter 11, causing the counter 11 to count the clock signal output by the oscillator 12.

The count value of the counter 11 is set to x by the control circuit 10.
Alternatively, the signal is sent to an X decoder 14 or a Y decoder 15 via a gate 13 which is switched in the y direction. The X, Y decoders 14, 15 have X, Y electrode lines X ₀ to X _o , respectively, of the tablet 1.
_Y0 to _Yn are connected. The X, Y decoders 14 and 15 selectively select the electrode line corresponding to the count value and sequentially apply scanning pulses (second
(see figure).

In the following, we will discuss scanning in the x direction as an example. The scanning pulse is such that the input pen 5, which is capacitively coupled to the tablet 1, detects the pulse applied to the electrode wire in the vicinity of which the input pen 5 is brought into contact. The detection signal detected by the input pen 5 is amplified by the amplifier 16, and then the first comparator 17 extracts one detection signal of the maximum level related to the electrode line closest to the input pen 5, and the pen touch point of the input pen 5. The signals are sorted by a second comparator 18 that extracts a group of detection signals related to the electrode lines on both sides of the electrode line, that is, the maximum level detection signal and the second and third level detection signals. .

Now, when the pentouch point on the tablet 1 is changed in the x direction in the range of electrode lines X _i-2 to _{X i+1,} the detected signal level after amplification is as shown in FIG. The threshold values of the first comparator 17 and the second comparator 18 are set to levels indicated by T ₁ and T ₂ in the figure, respectively. Therefore, the number of detection signals passing through the first comparator 17 is always one, and the number of detection signals passing through the second comparator 18 is two or three.

A shaping circuit 1 is provided on the output side of the first comparator 17.
9 is connected to the latch circuit 2, where the waveform of the detection signal is shaped and then the count value of the counter 11 is input as the latch strobe signal.
sent to 0. The latch circuit 20 is configured to latch the count value of the counter 11 at that timing when a latch strobe signal is input. The data latched in the latch circuit 20 indicates the position i of the electrode line closest to the input pen 5, and the data is sent to the coordinate determining section 2, which will be described later.
9 is output.

An A/D converter 22 is connected to the output side of the amplifier 16 via a hold circuit 21.
The level of each detection signal is sequentially A/D converted.

The A/D converted detection signal level data is
The first one connected to the output side of the A/D converter 22
- Stored in the storage section 23 consisting of third registers _M1 to _M3 . The input sides of the first to third registers _M1 to _M3 are connected in series, and data is sequentially shifted from the first register _M1 to the third register _M3 by a clock pulse synchronized with the detection signal. It is completed. The clock pulse for this shift operation is used to convert the output of the second comparator 18 into the shaping circuit 2.
It is created by shaping the waveform in step 4 and applying a predetermined delay in delay circuit 25. Each of the first to third registers M ₁ to _{M 3} of the storage unit 23 is cleared before starting scanning of the tablet 1 in the x direction. When the detection signal is output, the data that was output earlier is stored in the second register _M2 , and the data that was output earlier is stored in the first register _M1.
The data output later is stored. The third register _M3 remains at "0".

When the second comparator 18 outputs three detection signals, data related to the previous detection signal is stored in the order of the third to first registers M ₃ to _{M 1} .

In FIG. 6, when the touch point of the input pen 5 is considered in the range from directly above the X electrode line X _i-1 to directly above the X _i on the tablet 1, two detection signals are output from the second comparator 18. The output is in the range I, and the three detection signals are output in the range I. The levels of the detection signals a _i-2 and a _i-1 for the touch points P ₁ to P ₇ and the storage states in the first to third registers M ₁ to _{M 3} are shown in (1) to (7) in FIG. ).

The output sides of each of the first to third registers M ₁ to _{M 3} of the storage section 23 are connected in parallel to the comparison circuit 26,
This comparison circuit 26 selects the first to third registers _M1 to _M3.
The maximum detection signal level V _nax and the second highest detection signal level V _oext are selected from among the data stored in the data. these two levels
V _nax and V _oext are related to two electrode lines X _i-1 and X _i that sandwich the touch point of the input pen 5.

Moreover _, this comparison circuit ₂₆ is
Determine whether the pentouch point is on the left or right side when viewed from the midpoint BO between electrode wires X _i-1 and X _i , and press "+"
Alternatively, it has a function of outputting an addition signal or subtraction signal of "-" to the coordinate determining section 29. The two data V _nax and V _oext output from the comparison circuit 26 are sent to the L _S calculation section 27 . This L _S calculation section 27
is based on the input data of V _nax and V _oext (2)
Find the ratio of the sum/difference of the detection signal voltage according to the formula and calculate L _S
(≧0) and outputs the result to the distance calculation unit 28.

The distance calculation unit 28 calculates the distance s (≧0) from BO corresponding to the value of L _S by reading data from the memory whose address is L _S according to the diagram in FIG. 4, and calculates the value. It is sent to the coordinate determining section 29.
Here, the thickness h of the drawing paper 6, etc. on the tablet 1 is assumed to be constant, and calculations are made according to the L _S -S line with respect to this h. The s value calculated in this way is sent to the coordinate determining section 29.

The coordinate determination unit 29 calculates the addition signal from the comparison circuit ₂₆ using the point directly above the electrode line When it is outputting (i=i-1) and the pen is touched to the left of BO shown in Figure 6, x=i・l+(1/2-s)...Equation (3) Accordingly, when the comparator circuit 26 outputs a subtraction signal (i.e., when i=i and the pen is touched to the right of BO), x=i・l−(1/2−s)... The position is determined by calculating the x-coordinate according to equation (4). The coordinates in the y direction can also be determined in exactly the same manner.

In the above embodiment, the thickness h of the drawing paper, etc.
The explanation has been made on the case where the thickness is constant, but if the thickness changes, the L _S -S line in FIG. 4 will also change, and therefore it will be necessary to perform correction. Therefore, as shown in FIG. 8, for example, the comparison circuit 26 outputs
Since the average value of V _nax and V _oext is approximately proportional to the thickness h, the thickness detection circuit 30 calculates h=C・V _nax +V _oext /2 (5) where C is a constant calculation. The height h from the top surface of the tablet 1 to the tip of the input pen 5 is calculated based on the value of h.
8 and the coordinate determination unit 29, linear approximation such as s'=(a・h+1)・s...(6) (however, a is positive and determined experimentally) is performed.・Multiply by correction term such as quadratic approximation
s' is determined and the horizontal position is corrected. When this thickness correction is performed, measurement errors caused by nonuniform mechanical dimensions of the tablet 1 or dents caused by pressing the input pen 5 are also removed.

Apart from this, as shown in FIG.
8A may be prepared with a plurality of L _S -S line tables divided by h, and the table corresponding to h determined by the thickness detection circuit 30 may be extracted to determine the s value. Also, instead of finding the thickness h using equation (5), a rotatable paper presser 41 is attached to the casing 40 that supports the tablet 1, as shown in FIG. The thickness of the drawing paper 6 may be determined by detecting the distance between the attached metal plate 42 and the top surface of the tablet 1 using a proximity sensor 43 or the like.

〔Effect of the invention〕

As described above, according to the present invention, the position coordinates of the input pen when the pen is touched on the tablet are
The touch position of the input pen, which could not be determined without using three signal levels in the prior art, can be calculated with high precision from only the top two detected signals, but with the present invention, the touch position of the input pen can be calculated based on the top two signals. Therefore, it is possible to provide an unprecedented and excellent graphic input device that can significantly shorten the time for signal detection and processing.

[Brief explanation of the drawing]

Figure 1 is a sectional view showing a partial structure of the tablet, Figure 2 is a timing chart of scanning pulses,
FIG. 3 is a diagram showing a detection signal after amplification by an input pen, FIG. 4 is a diagram related to the principle of the present invention, and FIG. 5 is a block diagram showing a tablet input device according to an embodiment of the present invention. Fig. 6 is an explanatory diagram showing the detection signal level at each point when the input pen is moved in the x direction on the tablet, and Figs. 1 to 7 in Fig. 7 show the state of the data stored in the storage unit. FIG. 8 is a block diagram showing another embodiment; FIG. 9 is a block diagram showing another embodiment.
This drawing is a block diagram showing a modification of FIG. 8, and FIG. 10 is a schematic partial sectional view showing an example of a method for detecting the thickness of drawing paper. 1...Tablet, 5...Input pen, 6...Drawing paper, 14...X decoder, 15...Y decoder, 23...Storage section as potential storage means, 27
...L _S calculation unit, 28...Distance calculation unit as distance calculation means, 29...Coordinate determination unit as coordinate position calculation means, 30...Thickness detection circuit, 31...Correction circuit section, 41... Paper presser, 42...Metal plate, 43
...Proximity sensor.

Claims (1)

[Scope of Claims] 1. A tablet comprising a plurality of X and Y electrode lines laid at regular intervals, means for applying a scanning pulse to each of the electrode lines, and a means for applying a scanning pulse to each of the electrode lines, and an input pen that detects potential;
A graphic input device comprising: a coordinate position calculation means for calculating a position of a pen touch on a tablet by the input pen based on a signal detected by the input pen; a potential storage means for storing the potentials of the top two signals among the plurality of signals detected by the input pen; and an L _S calculation section that calculates the ratio of the sum and difference of the two potentials stored in the potential storage means. , is equipped with a distance calculation means for calculating the distance from the electrode line corresponding to the maximum potential to the pen touch position based on the output of this L _S calculation section, and the output from this distance calculation means and the detection signal from the input pen are combined. A graphic input device characterized in that said coordinate position calculation means has a function of calculating a coordinate position on a tablet touched by said input pen based on a signal related to a maximum potential in said input pen. 2. A tablet comprising a plurality of X and Y electrode lines laid at regular intervals, means for applying a scanning pulse to each of the electrode lines, and an input pen for detecting the potential induced in the tablet in response to the scanning pulse. and,
A graphic input device comprising: a coordinate position calculation means for calculating a position of a pen touch on a tablet by the input pen based on a signal detected by the input pen; a potential storage means for storing the potentials of the top two signals among the plurality of signals detected by the input pen; and an L _S calculation section that calculates the ratio of the sum and difference of the two potentials stored in the potential storage means. , a distance calculation means for calculating the distance from the electrode line corresponding to the maximum potential to the pentouch position based on the output of the L _S calculation section; and a distance calculation means for calculating the distance from the electrode wire corresponding to the maximum potential to the pentouch position, and the distance calculation means according to the thickness of the sheet placed on the tablet. and a correction circuit section for correcting the output of the input pen, and the coordinate position calculation means is equipped with a correction circuit section for correcting the output of the input pen, based on the output from the distance calculation means and a signal related to the maximum potential of the detection signals from the input pen. A graphic input device characterized by having a function of calculating the coordinate position on a tablet that is touched with a pen.