JPS6213687B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a weight sensing type coordinate input device (hereinafter referred to as a touch panel), that is, a device for accurately determining the coordinates of a weight application point. A touch panel, like a tablet input device using a light pen, is a device that, when combined with a display device, detects the selection of items and figures displayed on the panel and inputs them into a computer system. FIG. 3 is a model diagram showing the principle of operation. The principle of determining the coordinates of the weight application point using the touch panel will be explained below with reference to FIG.

In FIG. 1, when a force F in a direction perpendicular to the face plate is applied with a finger or a writing instrument to a point P on the face plate 1 made of a rigid body such as a glass plate, fulcrums A, B and C on the lower side of the face plate 1 are Component forces f _a , f _b , f _c are generated corresponding to the positions of the force detectors 2a, 2b, and 2c installed at each fulcrum.
The coordinates of point P can be determined by detecting at.

The coordinates of the fulcrums A, B, and C in the face plate 1 are A (x _a , y _a ), B (x _b , y _b ), and C (x _c , y _c ).
Then, the coordinates (X, Y) of point P can be determined by the following equation.

X=x _a f _a +x _b f _b +x _c f _c /f _a +
f _b + f _c (1) Y=y _a f _a +y _b + f _b +y _c f _c /f _a
+f _b +f _c (2) Therefore, when selecting items in combination with a display device such as a CRT, the coordinates of the finger can be obtained from the above formula, and by inputting this into the computer system, it is possible to determine which item is selected. You can find out if it has been selected.

For details, see, for example,
This is shown in Publication No. 34247.

Next, we will discuss errors when determining coordinates using equations (1) and (2) above.

For simplicity, the coordinates of the three supporting points are A(-L, 0), B(L, 0), C(0,
H), equations (1) and (2) become as follows.

X=f _b −f _a /f _a +f _b +f _c L (3) Y=f _c /f _a +f _b +f _c (4) Generally, a strain gauge or a piezoelectric element is used as a force detector, and each The force detected at the fulcrum is converted into an electrical signal, and after necessary analog processing such as amplification is performed, the values of X and Y are determined by an analog calculation circuit. In addition, the signal that has undergone the necessary analog processing such as the above amplification can be AD
After converting into digital signals using a converter, the values of X and Y can also be obtained using a digital computer. At this time, the values of X and Y do not change depending on the magnitude of the applied force, but there are noises in the force detector and amplifier, noise and calculation errors in the analog calculation circuit, and quantization errors in the AD converter. Varies depending on factors such as The values obtained by converting these noises and errors into the force applied on the input side are △f _a , △f _b , △f _c for each force detector. △f ₂ = △f _a + △f _b △F = △f If we set _a +△f _b +△f _c F=f _a +f _b +f _c , then X+△X=f _b -f _a +△f ₂ /F+△F・L
(5) Y+△Y=f _c +△f _c /F+△F・H (6) Therefore, from equations (3), (4), (5), and (6), the error of X and Y is △X, △Y is △X≒△f ₂ /F・L−(f _b − f _a + △f ₂ ) △f/
F ²・L(7) △Y≒△f _c /F・H− (f _c +△f _c ) △F/F ²・
It becomes H(8).

From equations (7) and (8), it can be seen that in order to reduce △X and △Y, the applied force F can be increased.

Therefore, if we start calculating X and Y using equations (3) and (4) after the force F applied to point P in Fig. 1 reaches a certain level, △
It should be possible to reduce X and ΔY.

The present invention has been made with this point in mind, and the calculation for determining X and Y is started when the magnitude of the electric signal obtained from the force detector becomes larger than a predetermined threshold value.

Hereinafter, the present invention will be explained in detail with reference to Examples.

FIG. 3 is a block diagram of a circuit showing a first embodiment of the present invention.

Molecules f _a , f _b , f _c at fulcrums A, B, and C due to applied force F in FIG. 1 are converted into electrical signals by force detectors 2 a, 2 b, and 2 c in FIG.
The signals are further amplified by amplifiers 3a, 3b, and 3c, and then added by an adder 6. The result of the addition is compared with the threshold voltage V _REF in the comparator 7,
The applied force F increases and the addition result becomes V _REF
If it is larger, flip-flop 8 (hereinafter referred to as
It is abbreviated as FF8. ) is turned on. The ON output of the FF 8 becomes a calculation start command signal to the computer 5, and upon receiving this, the computer 5 sends a signal to the A/D converter 4 indicating that calculation can be started. In response to this, the A/D converter 4 samples and holds the output signal of the amplifier, performs A/D conversion, and starts calculating X and Y. When the calculation is completed, the control signal from the computer 5
FF8 is turned off and A/D converter 4 is disconnected from computer 5.

FIG. 4 is a circuit configuration diagram showing a second embodiment of the present invention, in which the component forces f _{a and f} at each fulcrum of the applied force F
Thresholds are set independently for _b and _fc .

That is, each output of the amplifiers 3a, 3b, 3c is set to an independent threshold voltage (which may be equal to each other) in the comparators 7a, 7b, 7c, V ^a _REF , V
^b _REF and V ^c _REF are compared.

As the applied force F increases, the component forces f _a , f _b , f _c increase, and when they become larger than the value corresponding to the threshold voltage, the corresponding outputs of the comparators 7a, 7b, 7c become 1.

When the output of at least one comparator becomes 1, the output of the logic section 9 consisting of a 3-input OR gate causes the FF
8 is turned on.

Further, even if the FF 8 is to be turned on when the output of the comparator corresponding to the maximum threshold voltage becomes 1, this can be easily realized by changing the logic section 9. The processing after FF8 is turned on is exactly the same as in the first embodiment.

In the above two embodiments, the adder 6, the comparator 7,
7a to 7c, logic section 9, and FF8 are not provided, A/
The signal digitized by the D converter 4 is input to the computer 5, and addition and comparison processing is performed according to the computer program. When the addition result becomes larger than the value corresponding to the threshold voltage V _REF , X, Y Further, an analog calculation circuit may be provided in place of the A/D converter 4 and the computer 5, and the amplifier 3
The outputs of a, 3b, and 3c are directly input to this analog calculation circuit, and the output of the adder 6 is set to the threshold voltage V _REF
It is also possible to perform calculations to obtain X and Y in response to the ON output of FF8 indicating that the size has become larger.

As is clear from the above explanation, according to the present invention,
Calculation is always started when a constant force F determined by the threshold voltage is applied, so the threshold voltage is set to a value that does not saturate the amplifiers 3a to 3c and the A/D converter 4. By doing so, the errors in X and Y can be suppressed to below a certain value. Furthermore, it is possible to eliminate malfunctions caused by minute inputs such as vibrations and wind pressure.

Furthermore, even if a force _Fs large enough to saturate the amplifiers 3a to _3c and the A/D converter 4 is applied, as shown in FIG _. If you select _s , the analog signal will be sampled and held at timing t ₀ before saturation and the calculation to find the coordinates will start, so the errors in X and Y can be kept below a certain value regardless of the magnitude of the applied force. It can be suppressed.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the operating principle of the touch panel, Fig. 2 is a diagram showing an example of the position coordinates of the force application point and three supporting points, and Fig. 3 is a diagram showing the circuit configuration of the first embodiment of the present invention. 4 are diagrams showing the circuit configuration of a second embodiment of the present invention, and FIG. 5 is a diagram showing the relationship between the magnitude of applied force and the timing at which coordinate calculation is started. 1: Face plate, 2a to 2c: Force detector, 4: A/D
Converter, 6: Adder, 7: Comparator.

Claims (1)

[Claims] 1. In a weighted detection type coordinate input device that detects the component forces at three fulcrums of a force applied to one point on a face plate to determine the coordinates of the point to which the force is applied, the component force at the three fulcrums is means for respectively generating three electrical signals corresponding to the three electrical signals; and an operation for detecting that at least one of the three electrical signals exceeds a predetermined threshold value and starting an operation for determining the coordinates of the point to which the force is applied. A weight detection type coordinate input device characterized by having a start command generating means. 2. In a weighted detection type coordinate input device that detects the component forces at three fulcrums of a force applied to one point on the face plate and calculates the coordinates of the point to which the force is applied, three electric currents corresponding to the component forces at the three fulcrums are used. The method includes means for generating respective signals, and a calculation start command generating means for detecting that the sum of the three electric signals exceeds a predetermined threshold value and starting a calculation for determining the coordinates of the point to which the force is applied. Features a weighted detection type coordinate input device.