JPH05289806A - Coordinate input device - Google Patents

Abstract

PURPOSE:To increase the number of position coordinates read per unit time by detecting a position coordinates in accordance with the coordinate of the middle point of two intersections between a function, which is obtained by interpolation with a representative value in a prescribed period as a function value for the corresponding coordinate value, and a threshold. CONSTITUTION:A driving circuit 2 is operated in accordance with the control signal of a CPU 31 to successively select X and Y electrodes for every certain period. Simultaneously, the signal inputted from a coordinate pointing pen 5 to an A/D converter 32 through a waveform shaping and amplifying circuit 7 is converted to digital data and is stored in a RAM 34. The CPU 31 retrieves a maximum value in the period, and the pen 5 is approximated to or brought into contact with a tablet 1, and an experimentally determined threshold or large is obtained in consideration of an influence of ambient noise or the like, and the position coordinate of the pen 5 is obtained in accordance with the coordinate value of the middle point of two intersections between the function, which is obtained by interpolation with he maximum value as the function value for the corresponding coordinate value, and the threshold. Position coordinate data is sent from an I/O port 33 to a host computer 8.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coordinate input device.

[0002]

2. Description of the Related Art A conventional coordinate pointing pen in which a scanning signal is sequentially applied to a plurality of electrodes formed so as to be orthogonal to each other, and which changes stepwise according to the degree of electrical coupling depending on the spatial distance from the scanning electrodes. As a method of obtaining the position coordinates by using the detected signal intensity in, the signal intensity detected corresponding to the scanning electrode is regarded as a function value in the coordinate value of the center position of the scanning electrode, and the vicinity of the maximum value is appropriate. There is a known method of approximating with a simple function and obtaining the coordinates at which the function has a maximum value.

[0003]

However, in the above-mentioned prior art, in order to obtain the necessary resolution and accuracy, it is necessary to use a high resolution A / D converter for converting the signal strength into a digital value. Also, the processing in the CPU also has a problem that the processing time is long because the approximation is performed by the function of the second or higher order that frequently uses multiplication and division, and the number of position coordinate readings per unit time is limited.

Therefore, the present invention solves such a problem, and an object of the present invention is to provide a coordinate input device in which a large number of position coordinate readings are made per unit time while ensuring necessary resolution and accuracy. It is in.

[0005]

The coordinate input device of the present invention comprises X electrodes arranged in parallel at a predetermined interval, Y electrodes arranged in parallel in a direction orthogonal to the X electrodes at a predetermined interval, and the Y electrodes arranged in parallel. A tablet including an insulating layer that insulates the Y electrode and the X electrode, an electrode driving circuit that sequentially applies a predetermined signal to the X electrode and the Y electrode for a predetermined period, and the tablet by bringing the tablet into close proximity or contact with the tablet. A coordinate input device having coordinate indicating means having an electrode for detecting a predetermined detection signal from above, and position detecting means for receiving the detection signal and outputting position coordinates of the coordinate indicating means, which are sequentially obtained. A function obtained by interpolating a representative value of the detection signal in each of the predetermined periods as a function value in a coordinate value uniquely corresponding to each of the predetermined periods; And detecting the position coordinates of the uniquely coordinate pointing means from the coordinate value of the midpoint of the intersection two places to a threshold that is uniquely determined from the maximum value in the.

[0006]

EXAMPLES The present invention will be described below with reference to examples.

[Embodiment 1] As an embodiment, a pixel pitch of 0.
A transparent type which can be combined on a liquid crystal display device having a display capacity of 640 × 480 pixels of 3 mm is shown.

First, the configuration of this embodiment will be described with reference to FIG. The tablet 1 is a 1.1 mm thick glass substrate (a) on which 80 transparent electrodes having a pitch of 2.5 mm and a width of 0.1 mm are formed as the X electrodes, and a pitch of 2.5 mm as the Y electrodes.
A glass substrate (b) on which 60 transparent electrodes having a width of 2.4 mm are formed has the transparent electrode surface inside, and a polyester film having a thickness of 0.2 mm is sandwiched between the X electrodes and the Y electrodes so that they are orthogonal to each other. Combined, glass substrate (a)
Is the input surface, that is, the surface with which the coordinate pointing pen 5 described later approaches or abuts. The drive circuit 2 has each X electrode, Y
One-chip microcomputer 3 which will be described later and is connected to each electrode
This is for applying a predetermined signal to each X electrode and Y electrode in accordance with a control signal generated by the control signal. In this embodiment, a liquid crystal common driving IC having 80 outputs is used. The 1-chip microcomputer 3 is an 8-bit CPU 31, an 8-bit A / D converter 32, an I / O port 33, and a RAM 34, which are all contained in a single chip. ROM
Reference numeral 4 is connected to the one-chip microcomputer 3 and stores a program. The coordinate pointing pen 5 has a metal detection electrode 51 covered with resin as a tip, and an amplification circuit 52 for receiving a signal from the detection electrode 51 as an input. In addition,
The input of the amplifier circuit 52 is grounded via a resistor 53 of 1 MΩ. The cable 6 is for electrically connecting the coordinate indicating pen 5 and the main body, and is made of a thin and soft material so as not to hinder the operation of the coordinate indicating pen 5. The waveform shaping amplifier circuit 7 is composed of an amplifier circuit using a general-purpose operational amplifier, an integrating circuit, and a level shift circuit.
Signal is converted into a signal that meets the input specifications and is input to the A / D converter 32 described above. The host computer 8 is the receiver of the position coordinate data from the coordinate input device. The above is the overall configuration of the present embodiment.

Next, the operation will be described with reference to FIG. First, the nth X electrode from the left is defined as X (n), and the nth Y electrode from the top is defined as Y (n). That is, from the X (1) electrode to X
There are (80) electrodes and Y (1) to Y (60) electrodes. The voltage waveform applied to the X (n) electrode is Xn, Y (n)
The voltage waveform applied to the electrodes is shown as Yn in FIG. First, by the operation of the drive circuit 2 in accordance with the control signal of the CPU 31 described above, the X (1) electrode to the X (80) electrode are sequentially selected for each fixed period t. Only one electrode is selected at the same time during this series of X electrode scanning periods, and the other electrodes are unselected. The period t is 30
μs, and +5 V and −5 V are applied to each electrode in the selection period and the non-selection period, respectively. At the same time, the signal input from the coordinate indicating pen 5 to the A / D converter 32 via the waveform shaping amplifier circuit 7 is sequentially converted into digital data by the CPU 31 in accordance with a conversion command issued at a rate of once per period t, The data is CPU
The data is stored in the RAM 34 in such a manner that the data corresponding to which electrode during the selection period can be identified by 31. When the X electrode scanning period ends, the CPU 31 operates the RAM 3 during the period.
The data stored in 4 is searched for the maximum value.
If the obtained maximum value does not reach the constant threshold value Vth empirically determined by taking into consideration the influence of ambient noise,
The coordinate pointing pen 5 judges that it is not in proximity to or in contact with the tablet 1, and repeats the above operation until the maximum value obtained exceeds the threshold value. During this period, if the coordinate pointing pen 5 is close to or in contact with the tablet 1, a voltage signal due to capacitive coupling with each electrode appears on the detection electrode 51, and as a result, the above-mentioned maximum value is equal to or higher than the threshold value. Becomes When this condition is satisfied, the CPU 31 starts the calculation for obtaining the X position coordinate of the coordinate indicating pen 5.

Here, the coordinate pointing pen is connected to the X (3) electrode and the X (3) electrode.
(4) Between the electrodes, A is the voltage signal waveform at the detection electrode when positioned near the X (3) electrode, B is the input signal waveform to the A / D converter 32, and the timing when the conversion command is issued from the CPU 31 It is shown as C in FIG. The change of the voltage value at the timing C of the signal waveform B is X
(1) The period from the selection of the electrode to the selection of the X (6) electrode is large, and the subsequent selection of the X (7) electrode to the X (80)
It can be seen that there is almost no change in the period up to selection of the electrodes. From this, it can be seen that the X position coordinate of the coordinate indicating pen 5 can be determined from the maximum value of the above-mentioned data and a total of five data of two data before and after the maximum value.

A calculation method for obtaining the X position coordinate of the coordinate indicating pen will be described below. First, the maximum value of the above-mentioned data is D
max, the electrode that was selected when this data was acquired is the X (n) electrode,
The data values obtained when selecting the (n + 2) electrode are defined as D (n-2) to D (n + 2), respectively. By this definition, Dn = Dmax.

Dc is calculated as Dc = Dn × 0.6, and D (m−2) to D (n−1) are sequentially set as D (m), and D (m) <Dc ≦ D (m + 1) or Find m that satisfies the condition of D (m)> Dc ≧ D (m + 1). From D (n-2) to D (n
If up to +2) is normal data, there are two of this m, so let m1 and m2 be ΔX = [m1 + m2 + {Dc-D (m1)} / {D (m1 + 1) -D (m1)}. + {Dc-D (m2)} / {D (m2 + 1) -D (m2)}] / 2 is calculated. If ΔX when the coordinate indicating pen 5 is located at the origin 0 of the X coordinate is obtained in advance, and this value is used as a constant ΔX (0), X = ΔX−ΔX (0) is calculated. The X position coordinate of the coordinate indicating pen 5 can be obtained.

After the X position coordinate of the coordinate indicating pen 5 is determined, the same operation is performed for the Y electrode. After determining the Y position coordinate, the position coordinate data is sent to the host computer. This completes the one-cycle operation. After that, the position coordinates of the coordinate indicating pen 5 can be sequentially obtained by continuously performing the above cycle operation.

According to this embodiment, 8-bit C which is low cost
Input device capable of reading position coordinates of 200 points or more per second with a resolution and accuracy of 4% or 20% or less of the electrode pitch, despite using a 1-chip microcomputer with a PU and 8-bit A / D converter Was realized.

[Embodiment 2] In the embodiment 1, at the start of work, the user instructs the origin with a coordinate pointing pen, and ΔX and ΔY obtained at that time are ΔX (0) and ΔY.
By setting it to (0), the parallax of the user can be easily corrected.

[Embodiment 3] In the embodiment 1, as the tablet 1, the X electrode is formed on the input surface of the glass having a thickness of 0.7 mm, and the Y electrode is formed on the back surface thereof in the same shape as the embodiment 1, respectively.
When a non-glare film was applied on the X electrodes, it was observed that the voltage value at the timing C of the signal waveform B changed greatly between the X electrode scanning period and the Y electrode scanning period. By performing the same calculation as that of 1, it was possible to obtain the same performance and achieve the thinning.

[Embodiment 4] Although Dc = Dn / 2 was set in Embodiments 1 and 3, similar performances were obtained.

[0018]

As described above, according to the coordinate input device of the present invention, it is possible to realize a coordinate input device with high resolution and high accuracy and a large number of coordinate readings per unit time by using low-priced general-purpose components. It has the effect of being possible.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a configuration of a coordinate input device according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram of the operation of the coordinate input device according to the first embodiment of the present invention.

[Explanation of symbols]

 1. Tablet 2. Drive circuit 3.1 Chip microcomputer 4. ROM 5. Coordinate pointing pen 6. Cable 7. Waveform shaping amplifier circuit 8. Host computer

Claims (1)

[Claims] 1. An X electrode arranged in parallel at a predetermined interval, a Y electrode arranged in parallel at a predetermined interval in a direction orthogonal to the X electrode, and an insulating layer for insulating the Y electrode from the X electrode. A tablet, an electrode drive circuit that sequentially applies a predetermined signal to the X electrode and the Y electrode for a predetermined period, and an electrode that detects a predetermined detection signal from the tablet by approaching or contacting the tablet. In a coordinate input device comprising coordinate pointing means and position detecting means for inputting the detection signal and outputting the position coordinates of the coordinate pointing means, a representative value of the detection signals sequentially obtained in each of the predetermined periods is calculated. A function obtained by interpolating as a function value at coordinate values uniquely corresponding to each predetermined period, and a threshold value uniquely determined from the maximum value of the representative values. Coordinate input apparatus and detecting the position coordinates of the uniquely coordinate pointing means from the coordinate values of the middle point of intersection at two locations with values.