JPH0340858B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field to which the invention pertains] The present invention relates to a tablet input device, and in particular, detects the coordinates of one contact of a signal detection pen at least twice, collates the results, and performs detection. This relates to tablet input that determines whether the result is valid or invalid.

[Prior art and its problems]

In order to prevent malfunctions caused by noise, etc., tablet input devices usually detect coordinates at least twice.
This is repeated several times, and when the results match, the detected coordinates are considered valid for subsequent processing (see Japanese Patent Publication No. 53-37163). However, with conventional devices, such as capacitively coupled tablets,
If the wave height of the detection pulse is slightly higher than the threshold value, such as when a pen touch is made at the boundary between electrodes, slight movement of the pen tip or slight change in the indentation of the sheet may occur. Therefore, during coordinate detection operation for data check, the peak value of the detection pulse may become lower than the threshold value, and coordinate re-detection may not be performed accurately.
In particular, in devices that perform coordinate detection while changing the threshold value (see Japanese Patent Applications 1983-135839 and 1984-135838), the threshold value is controlled so that it approaches the wave height of the detection pulse, so this tendency was strong.

[Purpose of the invention]

The present invention has been made in view of the above-mentioned disadvantages of the prior art, and an object of the present invention is to provide a tablet input device that can accurately detect coordinates when checking data.

[Summary of the invention]

Therefore, in the present invention, in a tablet input device that detects the coordinates of one pen contact at least twice, collates the results, and determines whether the detection result is valid or invalid, the coordinate detection at the time of data check is performed. A control circuit that sends out a threshold designation signal and switches the threshold based on this threshold designation signal so that the threshold is slightly lower than the threshold for coordinate detection during data latch. In order to achieve the above object, the present invention adopts a configuration in which a threshold value switching circuit is provided to perform the switching operation.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be described based on FIGS. 1 to 6.

FIG. 1 is an electrical block diagram showing a tablet input device according to the present invention. In the diagram, 1 is X
This is a tablet on which electrode groups X ₁ to Xn and Y electrode groups Y ₁ to Yn are arranged. When the input pen 4 is brought into contact with the tablet 1, the pen switch 4A is closed and the counter 7 is activated by the action of the control circuit 20.
The counted value of the counter 7 is sent to the X electrode drive circuit 2 or the Y electrode drive circuit 3 via the gate 8, and each of the X electrodes X ₁ to Xn or Y electrodes Y ₁ to Yn is scanned. There is. The input pen 4 detects the scanning pulse through capacitive coupling with the tablet 1, and sends its output signal to one input terminal of the comparator 21 via the amplifier 9. The other input terminal of the comparator 21 is connected to a DA converter 22 as a threshold switching circuit. The D-A converter 22 generates an analog signal corresponding to the digital signal based on a threshold designation signal (digital signal) sent from the control circuit 20, and outputs an analog signal to the comparator 21.
It has a function of outputting a predetermined threshold voltage to. To explain this in more detail, the D-A converter 2
2 is specified by the control circuit 20 as shown in FIG.
…) The threshold voltage is set to an equally divided value,
As will be described later, threshold voltages lower by Δs than these threshold voltages are switched and generated.

The output of the comparator 21 is sent to the gate 12 and the counter 23 via the shaping circuit 11.
This counter 23 detects a detection signal that is selected by the comparator 21 as a detection signal equal to or higher than a threshold level while one electrode group of the X electrode group X ₁ to Xn or the Y electrode group Y ₁ to Yn is scanned once. It has a function of counting detected signals, and this counted value is sent to the control circuit 20. Then, this control circuit 20 determines that the count value of the counter 23 is "1".
In other cases, a threshold designation signal different from the previous one is sent to the D-A converter 22 according to the counted value, and the threshold level of the comparator 21 is raised or lowered, and the same electrode group as the previous one is It will force you to rescan. By repeating this operation until the number of detection signals output from the comparator 21 becomes one (the count value of the counter 23 is "1") by one period of scanning of the same electrode group, the detection signal of the maximum level is obtained. Obtainable. This maximum level detection signal is due to the scanning pulse of the electrode closest to the contact area of the input pen 4 (the key segment designated by the input pen 4). When the detection signal of the maximum level is obtained, the control circuit 20
In order to perform the next data check, a threshold designation signal is sent to the D-A converter 22 so that the threshold is set slightly lower than the threshold at which the maximum level detection signal was obtained. , comparator 2
This allows the threshold level of 1 to be varied.

Note that details of this threshold level variable operation will be explained later.

The gate 12 is switched and connected to the latch circuit 13 by the control circuit 20 until the above-mentioned operation of selecting the maximum level detection signal is completed. Therefore, this latch circuit 13 latches the count value of the counter 7 every time a detection signal is input through the gate 12, but ultimately,
The count value of the counter 7 at the timing when the maximum level detection signal is input is latched. The data latched by the latch circuit 13 is position data relating to the contact portion of the input pen 4, as described above. When the above-described operation of selecting the maximum level detection signal, that is, the data latch operation, is completed, the control circuit 20 lowers the threshold level slightly as described above for data checking, and moves the gate 12 to the comparator 14 side. At the same time, the electrode group is rescanned. As a result, the detection signal is input as a comparison timing signal to the comparator 14 via the gate 12, and the comparator 14 compares the count value of the counter 7 and the output data of the latch circuit 13 at the timing when the detection signal is input, When a match occurs, a match signal is output. Therefore, the output data of the latch circuit 13 when the comparator 14 outputs a coincidence signal is outputted to the computer main body or the like (not shown) as correct coordinate data.

The operation of varying the threshold level of the comparator 21 described above is performed as follows.

Here, the threshold value at the time of data latch is the output level width of the amplifier 9, 8 between Qmax and Qmin.
Assume that the levels S ₁ to _{S 8} (see FIG. 2) are equally divided, and a case will be taken as an example in which the X coordinate data related to the contact area of the input pen 4 is detected.

First, the control circuit 20 specifies a threshold level of S ₅ =(Qmax-Qmin)·1/2 before applying a scanning pulse. Then, the gate 8 is connected to the X electrode drive circuit 2 side, the counting operation of the counter 7 is started, and a scanning pulse is sequentially applied to each of the X electrodes X ₁ to Xn. At this time, when the signal detected by the input pen 4 becomes as shown in 1 in FIG. 2 to 1 in FIG. 4 depending on the contact position or state of the input pen 4, the counter 23 respectively The value counted is
They become "1", "2", and "0". In other words, 1 in FIG. 2 indicates that the input pen 4 is in the key segment KS (x=i)
(See P ₁ in Figure 5)
There is only one detection signal that exceeds the threshold value _S5 (see 2 in FIG. 2). This detection signal ai is detected by the electrode Xi at the contact area of the input pen 4.
This is due to the scanning pulse applied to the At this time, "1" is input from the counter 23 to the control circuit 20, indicating that the selection of the detection signal of the maximum level has been completed, and the data check operation then begins.

On the other hand, 1 in Fig. 3 is a case where the input pen 4 is brought into contact near the boundary of the key segment KS (Fig. 5).
(see P ₃ ), and the signal exceeding the threshold S ₅ is 2
There is one (see Figure 3 2). At this time, the count value is “2”
is sent to the control circuit 20, so the control circuit 2
0 raises the threshold and S ₇ = (Qmax − Qmin)・3/4
Specify the threshold level of , and apply the scanning pulse to the X electrode group again. This time, there is only one detection signal that exceeds the threshold value _S7 (see FIG. 3), so the count value becomes "1", and the selection of the detection signal of the maximum level is completed in the same way as described above. This detection signal is due to the scanning pulse applied to the electrode Xi closer to the input pen 4 (the key segment KS designated by the input pen 4).

1 in FIG. 4 is a case where the overall detection level has decreased for some reason, and the detection signal exceeding the threshold value _S5 is 0 (see FIG. 4, 2). At this time, the count value "0" is input to the control circuit 20, so the control circuit 20 lowers the threshold value, specifies S ₃ = (Qmax - Qmin) · 1/4, and scans the X electrode group again. Apply pulse. Then, the threshold
There is one detection signal exceeding S ₃ (see Figure 4, 3),
Therefore, the count value becomes "1", and the key segment KS (x=
The scanning pulse applied to the electrode Xi according to i) is detected.

In this way, for a certain threshold value, the counter 23
When the count value is "2" or more, the threshold value is increased, and when it is "0", the threshold value is lowered, and the threshold value is changed asymptotically to detect the maximum level signal. be able to.

As described above, when "1" is input from the counter 23 to the control circuit 20, it is known that the selection of the detection signal of the maximum level, that is, the data latch has been completed, and the data check operation then begins. At this time, the control circuit 20 sets the threshold value S _Co (where n = 1 to 8) is slightly ΔS lower than the threshold value S _Lo (in this embodiment, n = 1 to 8) at the time of data latch. A threshold designation signal is output to the D-A converter 22. In other words, during data check, the threshold value is operated in stages from 1 to 8 in the same way as during data latch, and this stage is expressed by the general formula S _Co = S _Lo - ΔS (for example, S _C1 = S _L1 - ΔS). It is required. As a result, for example, even if the height of the detection pulse P _L which was H _L at the time of data latch becomes the height H _C at the time of data check, the detection pulse P _C at that time passes through the comparator and is controlled. The circuit 20 is a data check, that is, a detection pulse P _L
and the coordinates related to the detection pulse P _C ,
Be able to judge discrepancies (Chapter 6)
(see figure).

After a series of processes related to the X coordinate data are performed in this way, the control circuit 20 then connects the gate 8 to the Y electrode drive circuit 3 side, scans the Y electrode group, and performs the same operation as described above. After selecting the maximum level detection signal related to the Y coordinate,
A data check is performed, and a series of processes regarding the Y coordinate data of the contact area of the input pen 4 are performed.

In the above-mentioned embodiment, a detection method in which the threshold value is varied when data is latched has been described, but the present invention is not limited to this, and the threshold value is fixed when data is latched. It's okay.
Further, the present invention is applicable not only to the capacitive coupling method but also to other methods such as the electromagnetic coupling method.

〔Effect of the invention〕

As described above, according to the present invention, in a tablet input device that detects the coordinates of one pen contact at least twice, collates the results, and determines whether the detection results are valid or invalid, Set the threshold value for coordinate detection to be slightly lower than the threshold value for coordinate detection during data latch.
Since we have adopted a configuration that includes a control circuit that sends out a threshold designation signal and a threshold switching circuit that switches the threshold based on this threshold designation signal, it is possible to easily detect coordinates when checking data. It is possible to provide a tablet input device which can accurately perform the above operations and does not cause an error to be detected even if the pen is touched correctly unlike the conventional devices.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the tablet input device according to the present invention, and 1 in FIG. 2 indicates the point in FIG. 5.
A schematic explanatory diagram of the detection signal when touching P ₁ with a pen, 2 in Figure 2 is an operation diagram of the comparator when the threshold value is S ₅ at that time, 1 in Figure 3 is the signal at point P ₃ in Figure 5. A schematic explanatory diagram of the detection signal when touching the pen, 2 and 3 in Fig. 3 indicate the threshold value at that time.
A diagram explaining the operation of the comparator when S ₅ and S ₇ ,
1 in FIG. 4 is a schematic explanatory diagram of the detection signal when the overall detection level has decreased, and ₂ and ₃ in FIG. 5 is a partial plan view of the tablet, and FIG. 6 is a schematic explanatory diagram showing an example of the transition of the threshold value and detection signal during data latch and data check. 20... Control circuit, 22... D-A converter as a threshold switching circuit.

Claims (1)

[Claims] 1. In a tablet input device that detects the coordinates of each pen contact at least twice and compares the results to determine whether the detection result is valid or invalid, a threshold value is set when detecting the coordinates during data check. A control circuit that sends out a threshold designation signal so that the threshold is slightly lower than the threshold for coordinate detection during data latch, and a threshold switching circuit that switches the threshold based on this threshold designation signal. A tablet input device characterized by being equipped with a circuit.