JPH0582606B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a coordinate input device.

Conventionally, as a means of converting patterns such as characters and figures input by hand into electrical signals, coordinate systems electromagnetically detect the position of a pen on the input surface of a tablet and generate an electrical signal indicating the coordinates of the pen input position. An input device is used. The input surface of the tablet has two sets of conductor loops perpendicular to each other, and the input pen has a built-in coil.
By detecting the electromagnetic coupling point between the conductor loop group on the input surface and the coil of the pen during handwriting input, an electric signal indicating the coordinates of the pen input position is generated.

FIG. 7 is a block diagram showing a conventional coordinate input device, and FIG. 8 is a time chart for explaining its operation. Immediately below the input surface 12 of the tablet 1, two sets of conductor loops 10 and 11 are arranged orthogonally to each other, and the input pen 7 has a built-in coil. Each set of loops 10 and 11 is given a multiphase burst signal, which is a multiphase pulse signal modulated with a carrier signal, from scanning circuits 3X and 3Y, respectively, and travels along the X and Y coordinate axes on the input surface. Generates a magnetic field. The control circuit 5 connects the instep circuits 3X and 3
The coordinate generating circuit 8 sends a switching signal instructing switching of the scanning direction to Y, alternately switching the direction of the traveling magnetic field described above, and transmits a signal e in which a pulse rises at a timing corresponding to the origin of the X coordinate and the Y coordinate.
send to For example, within one period T for generating a traveling magnetic field in the direction of the X coordinate axis, as shown in FIG. 2, multiphase burst signals x ₁ to x _N are sent from the scanning circuit 3 generates a magnetic field that travels along the X coordinate axis. When inputting, that is, the input surface 1 as shown by the dashed arrow A with the pen 7.
2, the coil of the pen 7 interlinks with the traveling magnetic field, and a voltage signal a corresponding to the change in magnetic field strength is induced in the coil.

Switches S ₁ and S ₂ both output signal a to the detection circuit 2 during scanning in the X coordinate (or Y coordinate) direction.
This is a changeover switch to lead to 0X (or 20Y). For example, during scanning in the X coordinate direction, signal a is guided to the detection circuit 20X, amplified by the amplifier 21, and then detected by the detector 22, and the signal b
It is sent to the filter 23 as a. Filter 23 extracts the fundamental wave component of signal b and sends it to amplifier 24 . The amplifier 24 amplifies the fundamental wave component of the signal b and sends the signal c to the amplitude comparator 25. Amplitude comparator 2
5 generates a signal d whose pulse rises when the amplitude of the signal c becomes zero, and sends this to the coordinate generation circuit 8. The coordinate generating circuit 8 generates a digital signal having a value proportional to the time t of the pulse interval between the signal e and the signal d, and sends this as a coordinate signal.
Since the pulse interval time t of the signal e and the signal d is proportional to the X coordinate of the input location, the coordinate signal indicates a digital value proportional to the X coordinate of the input location.

During scanning in the Y coordinate direction, signal a is detected by the detection circuit 2.
0Y, the coordinate generating circuit 8 generates a coordinate signal of a digital value proportional to the Y coordinate of the input location in the same manner as described above.

In such a conventional coordinate input device, when switching scans in both coordinate directions, two detection circuits 2 are used in order to prevent mutual interference of signals c generated by scanning in each direction.
It is necessary to provide 0X and 20Y and switch them alternately. Furthermore, since the filter 23 extracts only the fundamental wave component, its amplitude becomes small, and an amplifier 24 is required to amplify this, and the frequency F of the fundamental wave component extracted by the filter 23 is approximately 1/(2T).
(However, T is the scanning period in each coordinate direction), the frequency is quite low, and the filter 23 becomes large. For these reasons, in the conventional coordinate input device, the circuit scale of the detection circuits 20X and 20Y is large.
As a result, the device has the disadvantage of becoming larger and more expensive.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks and to provide a coordinate input device which has a smaller circuit scale than the conventional one and is therefore small and inexpensive.

The device of the present invention includes a pen having a built-in coil that generates a magnetic field in response to an applied carrier wave signal, and two sets of conductor loops arranged below an input surface, so that the input surface by the pen is and a tablet that transmits first and second electrical signals that simultaneously scan electrical signals induced in two sets of the loops in response to the magnetic field when inputting the coordinate input device, a pair of wave amplifying means for passing and amplifying a signal component of a predetermined bandwidth including the frequency of the carrier wave of the electric signal; a pair of wave amplifying means for detecting the amplified electric signal; and a pair of wave amplifying means for detecting the amplified electric signal, and the detected electric signal. a pair of peak detecting means for detecting the peak of the waveform of and generating third and fourth electrical signals indicating the time of the peak, and a pulse signal indicating the time corresponding to the origin of the coordinates and the third and It is characterized in that it sends out a coordinate signal indicating the coordinates of the input location in response to each time difference with the fourth electrical signal.

Next, the present invention will be explained in detail with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention, and FIG. 2 is a time chart for explaining its operation.

In this embodiment, the coil inside the pen 7 (not shown)
The coordinates of the input location are detected by passing a carrier current generated by the oscillator 50 to generate an alternating magnetic field, and sequentially scanning the voltage induced in each conductor loop (not shown) of the tablet 1 at the time of input.
Scanning circuits 4X and 4Y sequentially scan the induced voltage in each conductor loop of tablet 1 and guide it to detection circuits 30X and 30Y, respectively. The wave amplifier 31X of the detection circuit 30X removes high frequency components of both side band components with respect to the carrier wave from the signal a _x , smoothes the stepped envelope of the signal a _x , and generates a signal f _x with a smooth envelope. Send to detector 32X. In order to obtain a signal f _x with a smooth envelope, let the carrier frequency be F _c and the scanning frequency be F _B (however, each scan time of signals x ₁ to x _N , that is, the burst length is T _B , and the scanning (Frequency F _B = 1/T _B ), the wave characteristics of the wave amplifier 31X are set such that the amount of attenuation in the frequency band below (F _c - F _B ) and the frequency band above (F _c + F _B ) is sufficiently large. Just set it. The detector 32X detects the signal f _x and sends the detected signal g _x to the peak detection circuit 33X. When a synchronous detector is used as the detector 32X (Fig. 5), the detected signal g _x
becomes a voltage waveform as shown by the solid line in Figure 2,
When using an envelope detector (Fig. 1), the signal g _x
has a voltage waveform as shown by the broken line, and when the carrier wave is added before the wave amplifier 31 and envelope detection is performed (Fig. 6), the signal g _x has a voltage waveform as shown by the solid line. Become. In either case, the peak detection circuit 33X generates a signal h _x whose pulse rises at the peak of the waveform of the signal _g
send to The coordinate generation circuit 8X generates a digital signal having a value proportional to the pulse interval time t between the signal i and the signal _hx , in which a pulse rises at a timing corresponding to the origin of each coordinate sent from the control circuit 6. ,
This is sent as a coordinate signal.

In FIGS. 1, 5, and 6, the detection circuit 30Y and the coordinate generation circuit 8Y operate exactly the same as the detection circuit 30X and the coordinate generation circuit 8X described above, and generate a coordinate signal for the Y coordinate.

FIGS. 3a and 3b are a block diagram showing an example of the structure of the peak detection circuits 33X and 33Y in this embodiment, and a time chart for explaining the operation thereof, respectively. The detected signals g _x and g _y are sent to an amplitude comparison circuit 34 and a differentiation circuit 35 . The differentiating circuit 35 differentiates the waveforms of the signals g _x and g _y to obtain a signal k
and sends this to the zero-crossing detection circuit 36. The zero-crossing detection circuit 36 generates a signal l whose pulse rises every time the waveform of the signal k becomes zero level, and sends this to one input terminal of the AND gate 37. On the other hand, the amplitude comparison circuit 34 generates a signal m whose pulse rises only when the voltage of the signal g exceeds a predetermined threshold voltage _Vt , and sends this to the other input terminal of the AND gate 37. . AND gate 37 sends out signals h _x and h _y that are AND signals of signals l and m.
Even when there is no _{noise , the} signals _g However, the differential value becomes zero, which causes erroneous peak detection, but in this configuration example, only the pulse of the signal l when the voltage of the signals g _x and g _y exceeds the threshold voltage V _t is detected. Erroneous peak detection can be prevented by transmitting the signal.

FIG. 4 shows the peak detection circuit 33X, 3 of this embodiment.
FIG. 3 is a block diagram showing another example of the configuration of 3Y. This configuration example is based on the amplitude comparison circuit 3 in the circuit shown in FIG. 3a.
4, the threshold voltage levels can be expressed as signals g _x , g _y
A comparator circuit 38 is used which can be varied in response to the peak of . That is, instead of the predetermined threshold voltage V _t , a threshold voltage obtained by passing the signals g _x and g _y through the peak holding circuit 40 and the amplitude adjustment circuit 41 is sent to the amplitude comparison circuit 42 . There is. This threshold voltage is a constant multiple of the peak voltage of the signals g _x and g _y , and the amplitude comparison circuit 42
A signal is generated in which a pulse rises only when the voltages of g _x and g _y exceed the threshold voltage. Therefore, by setting the ratio between this threshold voltage and the peak voltage of the signals g _x , g _y to an appropriate value in advance in the amplitude adjustment circuit 41, fluctuations in the peak voltages of the signals g _x , g _y can be controlled. The peaks of the signals g _x and g _y can be reliably detected even if

The detection circuits 30X and 30Y of this embodiment detect the peaks of the signals g _x and g _y after detection, and the large filter 23 for low frequencies unlike the conventional one is unnecessary. Furthermore, since there is no mutual interference between signals due to switching of the scanning direction as in the case where waves are waved by the filter 23, the X and Y axes can be scanned simultaneously, and the number of detections can be doubled compared to the conventional method. Note that the filter portions of the wave amplifiers 31X and 31Y only need to extract frequencies near the high-frequency carrier signal, and can be made much smaller than the conventional filter 23. Therefore, the detection circuit 30X of this embodiment,
30Y can be made smaller and cheaper than conventional detection circuits 20X and 20Y.

As is clear from the above description, the present invention has the effect of realizing a coordinate input device that has a smaller circuit scale than the conventional one and is therefore compact and inexpensive.

[Brief explanation of the drawing]

1, 5, and 6 are block diagrams showing embodiments of the present invention, FIG. 2 is a time chart for explaining the operation of the embodiment of the present invention, and FIG. 3a is a block diagram showing an embodiment of the present invention. A block diagram showing the peak detection circuit used in the embodiment, b is a time chart showing the operation of a, FIG. 4 is a block diagram showing another peak detection circuit, and FIG. The block diagram shown in FIG. 8 is a time chart for explaining the operation of FIG. 7. 1...tablet, 10,11...loop, 1
2... Input surface, 3X, 3Y, 4X, 4Y... Scanning circuit, 5, 6... Control circuit, 7... Pen, 8X,
8Y...Coordinate generation circuit, 20X, 20Y, 30
X, 30Y...detection circuit, 31X, 31Y...
Wave amplifier, 32X, 32Y...Detector, 33X,
33Y...peak detector, 34, 42...amplitude comparator, 35...differentiation circuit, 36...zero-crossing detection circuit, 37...AND gate, 40...peak holding circuit, 41...amplitude adjustment circuit , 50...oscillator,
51...Switching circuit.

Claims (1)

[Scope of Claims] 1. A pen having a built-in coil that generates a magnetic field in response to an applied carrier wave signal, and a pair of conductor loops arranged below an input surface, the input surface being connected to the input surface by the pen. A coordinate input device comprising: a tablet that simultaneously scans electrical signals induced in a pair of the loop groups in response to the magnetic field to send out first and second electrical signals; a pair of wave amplification means for passing and amplifying a signal component of a predetermined bandwidth including the frequency of the carrier wave of the electric signal; a pair of wave detection means for detecting the amplified electric signal with an envelope detector; A pair of devices that detect the peak value of the detected electrical signal by differentiating the waveform of the electrical signal and then detecting its zero crossing point to generate third and fourth electrical signals indicating the time of the peak value. peak value detection means for transmitting a coordinate signal indicating the coordinate of an input location in response to a time difference between a pulse signal indicating a time corresponding to the origin of the coordinate and the third and fourth electric signals, respectively; A coordinate input device characterized by comprising a generation circuit. 2. The coordinate input device according to claim 1, wherein the wave amplifying means has a passing bandwidth set to be twice or less the scanning frequency within the loop group. 3. The coordinate input device according to claim 1, wherein the peak detection means detects the zero crossing point only when the detected electrical signal exceeds a predetermined threshold voltage. 4. The coordinate system according to claim 3, wherein the peak detection means detects the zero crossing point only when the detected electrical signal exceeds a threshold voltage determined in response to the peak of its own waveform. input device.