JPH03204717A - Cordless tablet - Google Patents

Abstract

PURPOSE:To generate a stable magnetic field from a position indicator without using a power source such as a battery, etc. by converting temporarily a voltage inputted by a voltage input coil to a stable DC voltage, and driving a transmitter by this stable voltage and generating the magnetic field. CONSTITUTION:By allowing an AC current of a prescribed frequency to flow to a power supply grid pattern 26, an AC magnetic field of a prescribed frequency can be generated. This AC magnetic field excites the voltage input coil 15 of a position indicator 1 to which a resonance capacitor 16 adjusted in advance to tune with its frequency is connected. Accordingly, the inputted voltage is inputted to a DC converter consisting of a full-wave rectifier 14 and a smoothing capacitor 13 and converted to a DC voltage. Subsequently, this converted DC voltage is inputted to a transmitter 12 and outputs a prescribed signal, and this signal excites a magnetic field generating coil 11 of the position indicator 1 and generates a magnetic field for reading a position on a tablet side. In such a way, the magnetic field of high stability can be generated from the position indicator 1.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention provides an electronic method for reading coordinates of a designated position on a surface. The present invention relates to a tablet that utilizes an inductive phenomenon, and particularly to a so-called cordless tablet that eliminates the need for a connection cable to connect the position indicator to the tablet body for indicating the position to be read.

[Conventional technology]

One conventional method of this type of cordless tablet is a device described in Japanese Patent Application Laid-open No. 70326/1983.

This device has an X-direction grid line group (X-direction loop coil group) and an X-direction grid line group (X-direction loop coil group) installed on the tablet side, and is tuned to a specific frequency on the position indicator side. An LC resonant circuit is provided. For example, when determining the position in the X direction, first select a specific grid line in the group of grid lines in the X direction, and then apply an alternating current, for example, at a specific frequency.A so-called alternating magnetic field is generated from this specific grid line. The LC resonant circuit provided in the position indicator is excited. The LC resonant circuit self-oscillates due to this excitation and generates an alternating current magnetic field from its coil L. At this point, the supply of alternating current to the specific grid line is stopped. Even at this stage, the LC resonant circuit of the position indicator is oscillating and generating a magnetic field, so the LC resonant circuit generates a magnetic field at the specific grid line where the current supply has been stopped. An induced voltage is generated by the magnetic field. This induced voltage is detected.

The grid lines in the X direction are selected one after another to perform the current supply and the induced voltage detection operation after the stop of the current supply,
The induced voltage in each grid line of the X-direction grid line group is detected, and the processing device calculates these voltage data to determine the position in the X-direction indicated by the position indicator.

A similar operation is performed in the X direction, and the position in the X direction is determined to determine the indicated position coordinates.

In addition, another capacitor is provided in the LC resonant circuit of the position indicator, the capacitance of which changes during the on/off operation of the switch, and the phase of the voltage induced in the grid line and the basis of the supplied alternating current are determined. By detecting the phase difference between the signal and the phase, the on/off state of the switch is also determined.

As described above, the device described in Japanese Patent Application Laid-Open No. 63-70326 is an excellent system that requires only an LC resonant circuit in the position indicator and does not require a power source such as a battery.

However, when measuring position, this method requires a transmission circuit for supplying alternating current for each grid line provided on the tablet side, and a voltage induced when the supply of alternating current is stopped. It is necessary to provide a switching circuit for alternately switching between the receiving circuit and the receiving circuit, which has the drawback of complicating the configuration of the tablet.

For this reason, the present applicant proposed a solution to the above-mentioned drawbacks in Japanese Patent Application No. 199668 [Cordless Tablet] dated August 1988.

In this device, the structure of the position indicator is almost the same as the device described in the above-mentioned Japanese Patent Laid-Open No. 63-70326, and a group of grid lines in the X direction on the tablet side is a group of drive lines, and a group of grid lines in the X direction is The line group is a sense line group, and an alternating current whose frequency changes at a predetermined repetition period is sequentially supplied to the drive line group while selecting a specific drive line, and this alternating current is supplied to the specific drive line. During this period, the voltages induced in the sense line groups are switched and detected one after another, and the induced voltages in each sense line generated by the self-oscillation of the resonant circuit of the position indicator for each of these drive lines are converted into matrix data. This method determines the coordinates of the position indicated by the position indicator. Further, by detecting which frequency of the frequency band that the position indicator is tuned to which changes at the predetermined repetition period, it is possible to identify whether the position indicator is switched on or off.

[Problem that the invention seeks to solve]

Incidentally, both of the above-mentioned systems have the advantage that the position indicator has an extremely simple configuration, since the configuration of the position indicator is almost entirely composed of an LC resonant circuit that includes a plurality of switches and a plurality of capacitors. On the other hand, there was a problem in that the processing device on the tablet side was complicated. This point is particularly noticeable when performing switch identification.

Regarding the former method described above, when performing this switch identification, it is necessary to measure the phase immediately after switching the connection of the grid line from the transmitting circuit to the receiving circuit. Waiting until the voltage induced in the grid lines stabilizes will result in a reduction in position reading speed. In addition, in this case, since the supply of magnetic field from the tablet side to the resonant circuit of the position indicator is stopped, the voltage induced in the grid line gradually attenuates, and the more time passes, the more the reading accuracy is affected. affect Therefore, after the above-mentioned connection switching is performed, it is extremely difficult to decide at what point the phase measurement is to be performed, due to the transient phenomenon that accompanies the connection switching.

Furthermore, in the latter case of frequency-based identification, it is necessary to make the difference between the respective frequency bands of the alternating current supplied to the drive line relatively large. This was also because the stability of the induced voltage was not very high.

In any case, these are configured so that only the LC resonance circuit of the position indicator receives the magnetic field from the tablet side and returns it as a magnetic field to the tablet side, so the magnetic field generated by the position indicator is stabilized. There was a drawback that the degree was inevitably low.

This invention aims to improve this point.

[Means for solving problems]

For this reason, the present invention includes a voltage capture coil and its resonance capacitor as a voltage capture means that receives an alternating current magnetic field of a predetermined frequency generated from the tablet side and captures the voltage into the position indicator, and a capacitor for its resonance. A DC converter that rectifies and smoothes the voltage taken into this position indicator and converts it into DC voltage, an oscillator that receives the DC voltage from this DC converter and generates a predetermined signal, and is connected to this oscillator. A position indicator is constituted by a magnetic field generating coil that generates a magnetic field, and the magnetic field output from the magnetic field generating coil is utilized.

[Effect]

By passing an alternating current of a predetermined frequency through the power supply grid pattern, an alternating current magnetic field of a predetermined frequency can be generated.

This alternating magnetic field excites the voltage intake coil of the position indicator to which is connected a resonant capacitor pre-tuned to the frequency. The voltage thus taken in is input to a DC converter consisting of a full-wave rectifier and a smoothing capacitor and is converted into a DC voltage. This converted DC voltage is then manually input to a transmitter to output a predetermined signal. This signal excites the magnetic field generating coil of the position indicator to generate a magnetic field on the tablet side for position reading. In this way, in this method, the voltage taken in by the voltage intake coil is first converted into a stable DC voltage, and this stable voltage drives the transmitter to generate a new magnetic field, so it is highly stable. A magnetic field can be generated from the position indicator.

〔Example〕

1 to 4 show the configuration of a cordless tablet according to an embodiment of the present invention. FIG. 1 is an explanatory diagram showing the electrical configuration of the position indicator of this tablet, and FIG. An explanatory diagram schematically showing the mechanical configuration of the position indicator, Figure 3 shows the configuration of the tablet side of this tablet, Figure (a) shows the position reading configuration, and Figure (b) shows the position reading configuration. FIG. 4 is an explanatory diagram showing an example of a grid pattern for supplying power to an indicator, and FIG. 4 is a state diagram of a magnetic field or a signal at each stage.

First, the configuration of a position pointing device according to the present invention will be explained with reference to FIGS. 1 and 2.

As shown in FIG. 2, this position indicator is provided with a magnetic field generating coil 11 protruding from the front of the case, and a voltage intake coil 15 is provided on the back side of the case. Furthermore, a plurality of switches sw, , swt, and sWl are installed on the top surface of this case. An induced voltage is captured by the voltage capture coil 15 in response to a magnetic field of a predetermined frequency generated from the tablet side. This voltage is processed in a predetermined manner to create a new signal and supplied to the magnetic field generating coil to supply a highly stable magnetic field to the tablet side. When the plurality of switches sw, , swt, and SW are turned on or off, they change the circuit constants of the electric circuits involved in generating the magnetic field of the position indicator I, and change the properties of the magnetic field generated by the magnetic field generating coil 11, for example. It is used to change the frequency. By measuring the frequency of the voltage induced on the tablet side, it is possible to know which switch is acting.

These elements are connected as shown in FIG. LC with voltage intake coil 15 and resonance coil 16
A resonant circuit is configured, and a magnetic field with a frequency tuned to this resonant circuit is generated from the tablet side, thereby exciting the voltage intake coil 15 of this resonant circuit, and the induced voltage can be obtained. The voltage is input to a DC converter composed of a full-wave rectifier 14 and a smoothing capacitor 13, and is converted into a DC voltage. This DC voltage is input to the oscillator 12 and generates a predetermined signal. This signal is transmitted to the magnetic field generating coil 11 via the reference capacitor C6 to generate a magnetic field of a predetermined frequency. respective switches SW+ connected in parallel to the reference capacitor C0;
Three capacitors Ct, C with SWz, SW,
z and C3 change the capacitance value in this magnetic field generation circuit according to the on/off state of each switch, thereby changing the frequency of the generated magnetic field.

Next, the configuration of the tablet side will be explained with reference to FIG. 3.

First, the power supply grid pattern will be explained with reference to FIG. 3(b).

This power supply grid pattern 26 is composed of a first zigzag grid line 261 and a second zigzag grid line 262, which are formed by folding a single conductor in a zigzag pattern. Each of these grids @2
61 and 262 have the same shape, but they are shifted from each other by 1/4 pitch (period). 1st
, for example, As1 on the second zigzag grid line 261.
When an alternating current of nωt is supplied, an alternating magnetic field is generated by both on this power supply grid pattern. As described above, the power supply grid pattern 26 is
The phase grid configuration makes it possible to generate a magnetic field that acts on the voltage intake coil 15 no matter where the position indicator 1 shown in FIG. 1 is located. The frequency of the magnetic field generated by these is determined by the voltage intake coil 15 and resonance capacitor 16 of the position indicator 1 shown in FIG.
By setting the frequency of the alternating current supplied to each of the grid lines 261 and 262 in advance to match the tuning frequency of the resonant circuit, it is possible to always supply power to the position indicator l. Therefore, the position indicator 1 can generate a highly stable magnetic field.

The magnetic field from the magnetic field ordering coil 11 of this position indicator 1 is
It acts on the X-direction sense line group 21 and the Y-direction sense line 1s22 shown in FIG. 3(a), which are stacked and installed on the power supply grid pattern 26.

Now, if the position indicator 1 (only the magnetic field generating coil 11 is shown in the figure) exists as shown in FIG. 3(a), the magnetic field generated by the magnetic field generating coil 11 of this position indicator l will cause Of the sense lines in the X-direction sense line group 21, the largest induced voltage is generated in the sense line closest to the magnetic field generating coil 11, and similarly for the Y-direction sense line group 22, the sense line closest to the magnetic field generating coil 11 generates a large induced voltage. The largest induced voltage occurs on the sense line connected to the sensor. Each sense circuit 2
By detecting the voltages induced in each sense line one after another by 3 and 24 and subjecting them to predetermined processing in the processing device 25, the coordinates of the indicated position of the position indicator 1 can be determined. Furthermore, as shown in FIG. 1, this position indicator 1 has switches S W +, sw, , sw, which are paired with capacitors in its magnetic field generation circuit, and the on/off operation of these switches generates a magnetic field. By measuring the frequency of the induced voltage detected by the X-direction sense circuit 23 or the Y-direction sense circuit 24 in the processing device 25, it is also possible to identify whether the switch is on or off. .

FIG. 4 is a state diagram of magnetic fields or signals at each stage of the device according to the invention.

What is shown in FIG. 4(a) is a schematic representation of the magnetic field generated by the power supply grid pattern 26 shown in FIG. 3(b). Therefore, the voltage induced in the voltage intake coil 15 of the position indicator l shown in FIG. 1 is also obtained in the same manner.

What is shown in FIG. 4(b) is a state in which this taken-in voltage is input to the full-wave rectifier 14 of the position indicator 1 and rectified. FIG. 2C shows a state in which the voltage is converted into a DC voltage by the smoothing capacitor 13. This DC voltage is sent to the transmitter 12 of the position indicator l, and a predetermined signal is generated by the magnetic field generating coil 11 in Figs. 4(d) to (2).
) is generated.

FIG. 4(b) shows a state when any of the switches sw, , sw, , sw of the position indicator 1 shown in FIG.
(e) shows the magnetic field generated when only switch SW1 is acting, and (e) shows the magnetic field generated when only switch SW1 is acting.
The generated magnetic field when only switch SW2 is acting is shown in the same figure (f), and the generated magnetic field when only switch SW3 is acting is shown in the same figure (respectively shown in barrels.By changing the capacitance value in the magnetic field generating circuit) As mentioned above, by measuring the frequency of the voltage induced in the sense line group, it is possible to know which switch is acting.

Note that in the above description, the power supply pattern 260
Although it has not been mentioned that the generated magnetic field interferes with the sense line groups 21 and 22, for example, the frequency of the magnetic field for power supply, that is, the frequency shown in FIG. Set the frequency to 1/2 or less or twice or more of the frequency shown in Figure 4 (f) to 0), and insert a trap circuit (selective absorption circuit) into the sense circuits 23 and 24 that detect the induced voltage in the sense line group. This can significantly reduce these interferences.

Further, in this embodiment, an example has been described in which the voltage intake coil 15 and the magnetic field generation coil 11 are provided at different positions, but they may also be provided at almost the same position.

〔Effect of the invention〕

As described above, according to the present invention, a stable magnetic field can be generated from the position indicator without using a power source such as a battery, and the position reading configuration on the tablet side can be made relatively simple.

[Brief explanation of drawings]

1 to 4 show the configuration of a cordless tablet according to an embodiment of the present invention. FIG. 1 is an explanatory diagram showing the electrical configuration of the position indicator of this tablet, and FIG. An explanatory diagram schematically showing the mechanical configuration of the position indicator, Figure 3 shows the configuration of the tablet side of this tablet, Figure (a) shows the position reading configuration, and Figure (b) shows the position reading configuration. FIG. 4 is an explanatory diagram showing an example of a grid pattern for supplying power to an indicator, and FIG. 4 is a state diagram of a magnetic field or a signal at each stage. 11-Magnetic field generation coil 15-Voltage intake coil 26--
---Grid pattern rabbit for power supply 4

Claims (1)

[Claims] A voltage capture coil and its resonance capacitor serve as a voltage capture means that receives an alternating current magnetic field of a predetermined frequency generated from the tablet side and captures the induced voltage into this position indicator, and rectifies and rectifies the voltage captured by the voltage capture means. A position indicator is created using a DC converter that smoothes and converts the DC voltage, a transmitter that receives the DC voltage from the DC converter and generates a predetermined signal, and a magnetic field generating coil that is connected to this transmitter and generates a magnetic field. and a group of sense wires arranged on the tablet side where a voltage is induced by the magnetic field output from the magnetic field generating coil of this position indicator, and detects the necessary induced voltage of these sense wire groups. A cordless tablet, characterized in that the coordinates of the position indicated by the position indicator are determined.