JPS5828287Y2 - coordinate reading device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a coordinate reading device, and more particularly to a coordinate reading device in which the top surface of a tablet is electrostatically shielded.

Conventionally, a coordinate reading device is configured as shown in FIG.

1 is a tablet and has a sense line Xn. It consists of an insulating substrate 2 having Ym.

3X. 3Y is a scanning circuit that scans each sense line Xn, Ym, and 4Vi is a pencil type coordinate indicator, and this indicator 4 has a coil 5 at its tip for generating an induction signal to the sense lines Xn*Xrn. ing.

A crystal oscillator 6 constitutes an excitation circuit for the coil 5 together with an amplifier 7, and its AC excitation frequency is approximately 300 KHz.

8ri A pen switch that turns on when a certain pressure is applied and outputs a signal to the calculation control unit 11, 9II'i sense line Xn
, an amplification filter circuit for waveform processing the induced signal t from Xm,
10 is an AD converter for AD converting the signal from the amplification/filtering circuit 9, and is a scanning circuit 3X.

3Y, an amplification/filtering circuit 9, and an AD converter 10 constitute a scanning detection circuit.

Reference numeral 11 denotes an arithmetic control section, which includes a data memory and a CPU, and calculates the position of the coordinate indicator 4 based on the signal from the AD converter 10, as well as controls all other external inputs and outputs.

External equipment that performs input/output of the 12ri arithmetic control unit 11
3&-! This is a scan address register whose scanning is controlled by the arithmetic control unit 11.

However, when actually using the coordinate reading device shown in FIG.
The hand H holding the coordinate indicator 4 must be placed on top, that is, on the cover 2a (made of an insulating member).

At this time, stray capacitance Cs1sC between the excitation coil 5 and the hand H, and between the hand H and the sense line Xn (Ym)
Form 8z.

Then, the potential of the stray capacitance Cs1 oscillates due to the electromagnetic waves generated by the alternating magnetic field of the coil 57), and this potential oscillation is further electrostatically coupled to the sense line Xn (Xm) via the stray capacitance Cs2. .

Therefore, both electromagnetic induction from the sense line Xm(Ym)rj coil 5 and electromotive force due to electrostatic induction from the hands H7) are generated.

When this state is viewed in terms of the waveform of the scanning signal, it becomes as shown in FIG. 3, where the original scanning waveform due to electromagnetic induction is level-amplified by the electromotive force Vo due to electrostatic induction.

Normally, the peak voltage Vprj is about 6V, but on the other hand, the electrostatically induced voltage vO may reach 2Vt.

Therefore, the secondary peak P1. which is not detected under normal conditions. P2
When the voltage exceeds the threshold voltage vth, the arithmetic control unit 11 scans from the left in FIG.
There was a drawback that Pl was determined to be the peak coordinate and the position of the coordinate indicator 4 was calculated incorrectly.

The present invention was developed to quickly eliminate the above-mentioned drawbacks. By providing a thin film member of a non-magnetic conductor to cover the sense line, that is, the upper surface of the tablet on the side facing the coordinate indicator, stray capacitance caused by hand contact can be avoided. It is an object of the present invention to provide a coordinate reading device that eliminates electrostatic induction due to electrostatic induction.

The present invention will be described in detail below with reference to the drawings.

FIG. 4 shows a preferred embodiment of the present invention, and the reference numerals correspond to those in FIG. 2, respectively.

In this case, aluminum A4 is vacuum-deposited on the inner surface vc of the cover 2a, which covers the tablet 1 consisting of the solid substrate 2 and the nonce wires Xn (, , Ym) from above, to form a thin film M material.

Aluminum thin film AtrJ 0.0 with one or several vapor depositions
It has a thickness of 5-0.5μ, and its electrical resistance can be set to a sufficiently low value (several Ω or less) to serve as an electrostatic shield (its value is not constant because the electrostatic field range changes). ).

Therefore, if the thin film At is electrically connected to the ground terminal of the scanning detection circuit including the scanning circuits 3X and 3Y, even if conventional stray capacitances Cs1 and Cs2 exist, the electrostatically induced electromotive force from the hand H will be absorbed by the thin film A. Since the impedance of B is sufficiently low, it falls from the stray capacitance Cs2 to the ground via the thin film A/, and does not contribute to the electromagnetic induced electromotive force of the sense line Xn (Ym) due to the magnetic flux Φ.

On the other hand, for the AC magnetic flux Φ from the coil 5, the thin film A/
, are sufficiently thin, there is no practical problem with troubles caused by overcurrent, and the electromagnetic induced electromotive force of the sense line Xn (Ym) can be obtained at the same level as the conventional one.

Therefore, as shown in FIG. 5, only the desired scanning signal can be obtained.

Although FIG. 4 shows an example in which the thin film AA is deposited on the inner surface of the Vi cover 2a, it is sufficient to cover the upper surface of the thin film AtU tablet 1 on the side facing the coordinate indicator, so as shown in FIG. An insulating film such as a non-interresist film on the insulating substrate 2 (
Even if a thin film AA is deposited from above the sense line Xn (Ym) via the sense line The aforementioned effects remain unchanged.

Generally, as shown in FIG. 6, the circuit block Bri including the scanning circuits 3X and 3Y is shielded by a conductive frame F, and the ground terminal G of the frame F and the circuit block B.
Since the thin film At shown in FIG. 4a is electrically connected to the frame F, it can be easily electrically connected to the ground terminal of the scanning detection circuit.

Therefore, the potential of the thin film At is maintained at the same potential as that of the ground terminal.

According to experimental values, vacuum deposition was performed on the inner surface of the cover 2a for 1 to 3 times.
When a thin film At with a thickness of 0.05-0.2μ is formed by rotating the thin film A/1. Compared to when there is no electromotive force, the electromagnetic induced electromotive force does not attenuate, and from Vo=2V to Vo f
-OV”! could remove the influence of electrostatic induction.

This is 0.2V in Vo when hand H (body) is grounded.
, O in Vo when the outer periphery of the coordinate indicator 4 is shielded,
Clearly superior to tV.

This is because it is practically difficult to ground the hand H (human body), and it is necessary to disperse the alternating current magnetic field of the coordinate indicator 4ri.

Furthermore, the thin film A/ is a range that satisfies the mutually contradictory conditions of the need for low impedance and the need to eliminate electromagnetic induction interference due to eddy currents.

It has been found that a thickness gV'i of 0.01-10μ is practically excellent.

Although aluminum was used as the thin film member in the above embodiment, 1. A similar effect can be obtained using a non-magnetic conductor (for example, Cu).

It is also possible to form a thin film by electric field or electroless plating instead of vacuum deposition.

As described above, according to the present invention, a thin film member made of a non-magnetic conductor is provided to cover the top surface of the tablet on the coordinate indicator side, and is electrically connected to the ground terminal of the scanning detection circuit, so that the coordinate indicator can be Electromagnetic induction to the sense line is not obstructed, and only electrostatic induction due to stray capacitance via the hand can be removed.

In addition, since aluminum lamura vacuum-deposited on the cover or tufflet was used as the thin film member, the thickness was 0.01-1.
It becomes possible to set a practically appropriate range of 0μ, which has a great effect.

[Brief explanation of drawings]

Fig. 1 is a schematic block diagram of a conventional coordinate reading device, Fig. 2 is an explanatory diagram of main parts showing the usage state of the conventional coordinate reading device, Fig. 3 is a waveform diagram showing the scanning signal in Fig. 2, and Fig. 4 is a schematic block diagram of a conventional coordinate reading device. Diagram a
id Fig. 4 is a cross-sectional view of main parts showing another embodiment of the present invention, Fig. 5 is Fig. 4 aYc offset scanning. A waveform diagram showing signals, and FIG. 6 is a schematic cross-sectional view showing an embodiment of the present invention. DESCRIPTION OF SYMBOLS 1...Tablet, 2...Insulating substrate, 2a...Cover At...Thin film aluminum (thin film member), 3X. 3Y...Scanning circuit, 4...Coordinate indicator, 5...Coil, 6...Crystal oscillator, 7...Amplifier, 6,7.
...Excitation circuit, 9...Amplification filter circuit, 10...AD
Converter, 3X. 3Y, 9.10...Scanning detection circuit, 11...Arithmetic control section, t...Scanning signal, G...Ground terminal.

Claims (4)

[Scope of utility model registration request] (1) A tablet formed by laying a large number of sense wires at regular intervals, a coordinate indicator having a coil for indicating coordinates to the tablet, an excitation circuit that generates an alternating magnetic field in the coil, and the sense wire. A coordinate reading device consisting of a scanning detection circuit that sequentially scans and detects guidance signals generated on a line, and an arithmetic control section that calculates the position of the coordinate indicator based on this detection signal is pressed, and the coordinate indicator of the tablet is pressed. A thin film member made of a non-magnetic conductor is provided to cover the upper surface of the opposite side, and this thin film member is electrically connected to the ground terminal of the scanning detection circuit, so that the potential of the thin film member is the same as that of the ground terminal. A coordinate reading device characterized by having five precepts. (2) A utility model characterized in that a cover member is provided to cover the upper surface of the tablet, and the thin film member is constituted by a non-magnetic conductive member deposited or plated on the inner surface of the cover member on the tablet side. Scope of registration claims No. 1
Coordinate reading device as described in section. (3) The thin film member is constituted by a non-magnetic conductive member deposited or plated on the upper surface of the tablet on the side facing the coordinate indicator via an insulating film. coordinate reading device. (4) The coordinate reading device according to claim 2 or 3, wherein the non-magnetic conductive member has a thickness of go, oi-10μ.