JPS6154524A - Handwritten input tablet - Google Patents

Abstract

PURPOSE:To obtain an accurate handwritten input device by detecting the voltage at both ends of a resistor connected in series to a constant current diode. CONSTITUTION:When a pen 9 is pressed down, a circuit conducts to flow a fixed current (about 1mA) to a constant current diode 10. This current is refered to as I0 and branched into currents I1 and I2 in the direction X according the position where a planar resistance 2 for detection of X direction. The current I2 flows through a resistance 4 for detection of X direction and is increased and decreased quantitatively in the direction X according to the pressed position. Then I0=I1+I2 is satisfied. In the same way, a current I4 flows to a resistance 5 for detection of Y direction with a quantitative change. Thus I0=I3+I4 is satisfied. Here X:Y=I2:I4 is satisfied since the current I0 is fixed. This secures accurate detection of both positions of X and Y axis directions.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a handwriting input device, and particularly to a handwriting input tablet that allows input with a pen or the like.

[Prior art]

Figure 2 is a conceptual diagram of a conventional handwriting input tablet.

1d constant current circuit, which supplies power to the taglet position detection section. 2.3 are an X-direction position detection surface resistor and a Y-direction position detection surface resistor, respectively. When inputting by pressing both sheet resistors with the pen 9, the X direction position detection resistor 4 and the Y direction position detection resistor 5 detect the
The current flowing in the Y direction is detected, and the subtraction amplifier 37vt
The current is made into an absolute value current and sent to the A/D converter 8, where the pen position in the X and Y directions is detected. At this time, a signal indicating that the pen has been pressed is taken out from the end of the Y-direction position detection resistor 5, sent to the A/D converter 8, and detected.

[Problem that the invention seeks to solve]

However, in the prior art, after the pen is pressed until a certain pressing pressure is reached, the contact resistance of the X-direction position detection surface resistor 2 and the Y-direction position detection surface resistor 3 of the pressed portion of the pen increases. Due to the characteristics of the constant current circuit, the current passing through the X-direction position detection resistor 4 and the Y-direction position detection resistor 5 becomes small, and when the pen is pressed. There was a problem in that the actual location could be detected as being different from the actual location. The present invention is intended to solve these drawbacks, and its purpose is to provide a tablet that can reproduce accurate handwritten input.

[Means to solve the problem]

Handwritten input tape of the present invention) d, a constant current diode,
A resistor connected in series and a voltage comparator are provided at both ends of the resistor to detect the pressing force during handwriting input.

(Function) The present invention utilizes the constant current characteristics of a constant current diode.The constant current diode has a characteristic that exhibits constant current characteristics above a certain voltage.The characteristic diagram is shown in Fig. 3. In this embodiment, a constant current is supplied regardless of the resistance value of the load.

〔Example〕

FIG. 1, which shows an embodiment of the handwriting input tablet of the present invention, is a conceptual diagram of the present invention. In the figure, there are 10 digit constant current diodes and 11 digit pressing pressure detection resistors. The details of the circuit will be explained below.

When the pen 9 is not pressed, the X-direction position detection surface resistor 2 and the Y-direction position detection surface resistor 3 are not in contact with each other, so they are electrically insulated and act as constant current diodes. Since no current flows through 10, there is no difference in K and T between both ends of the pressing force detection resistor 11. pen 9
When pressed, the two circuits conduct and the constant current diode causes
A constant current flows. In this example, 1 mA flows. Let this current be 0. Depending on the pressed position of the X-direction position detection surface resistor 2, the current is branched into negative and 2 in the X direction. Here, 1 flows through the X-direction position detection resistor 4. It is a flow. Focusing on work 2, it quantitatively increases or decreases in the X-axis direction depending on the pressed position. Therefore, ko = ko 1 0 k 2. The same can be said for the Y direction. Since the Y-direction position detection resistor 5 and the current 4 change quantitatively, Io = 4 s + I4. As mentioned earlier, Io is a constant current, so X: Y = I
2: Step 4, and the position in the X-axis and Y-axis directions is detected. Engineering 2. 41-t each, X-direction position detection resistor 4
A potential difference is generated across the Y-direction position detection resistor 5, and the subtraction amplifier 6.7 converts the current into an absolute value current, which is sent to the VD converter and converted into a digital value.
considered to be location data. When the pen 9 is pressed with a certain pressure or more, as described above, when the pen starts to be pressed or is being pressed gently, the X-direction position detection surface resistor 2 and the Y-direction position detection surface resistor are activated, respectively. When the contact resistance between the two terminals 3 and 3 becomes large enough to not be ignored, a constant current cannot flow from the constant current diode 10. This current is determined by the supply power voltage, but in this embodiment, the power supply is 5V, so assuming that 1mA is flowing, if the contact resistance becomes 5Ω or more, the constant current will no longer be supplied and the current will drop.

At this time, the voltage at both ends of the pressing force detection resistor 11 drops at the same time, so the voltage comparator 12 detects a voltage shortage, and A
/D converter 8 is not allowed to read or read data. As a result of the above, the data sent to the A/D converter is always a value at a constant current. Note that in this embodiment, the pressing force detection resistor 111-t is inserted between the constant current diode 10 and the position detection surface resistor.
Needless to say, as a method of ``, it is also possible to insert the resistor between the position detection surface resistor and the ground.

〔Effect of the invention〕

As described above, the handwriting input tablet of the present invention detects the pressure of the pen, so it has the following advantages.

(1) Since position detection errors do not occur when the pen touches the tablet, it is possible to manually generate data with clean hands.

(2) Accurate data can be obtained manually, improving recognition efficiency during character recognition.

(3) Since a constant current diode is used instead of a constant current circuit, costs can be reduced. Moreover, the structure can be easily made.

There are advantages as mentioned above.

[Brief explanation of drawings]

FIG. 1 is a conceptual diagram of a handwriting input tape of the present invention. FIG. 2 is a conceptual diagram of a conventional handwritten input tape recorder. FIG. 5 is a characteristic diagram of the constant current diode of the present invention. 2.. X direction position detection surface resistor 3.. Y direction position detection surface resistor 10.. Constant current diode 11.. Pressure detection resistor or more

Claims (1)

[Claims] A constant current diode, a resistor connected in series between the constant current diode and a sheet resistor, and a voltage comparator provided at both ends of the resistor are provided to detect input pressing pressure of input by a pen. Handwriting input tablet.