JPH052447A - Writing pressure detecting pen - Google Patents

Abstract

PURPOSE:To obtain a writing pressure detecting pen which has a small moved variable of the pen point and has the high detecting accuracy by using a piezoelectric element which generates the electric charge in response to the applied compressive force. CONSTITUTION:The writing pressure F applied to the tip of a pen 9 is transmitted to a piezoelectric element 3, and the element 3 generates the electric charge in response to the compressive force. An operational amplifier performs a negative feedback operation to generate the voltage having the polarity that eliminates the electric charge of the element 3. Then the electric charge of the element 3 is neutralized by the current flowing to a resistance. Thus the electric charge of the element 3 is eliminated after the lapse of a fixed time. Therefore the writing pressure applied by the pressure of the pen 9 corresponds to the electric charge of the element 3. As a result, the detecting accuracy is improved and the moved variable of the pen point, i.e., an operating stroke can be set at about zero. Them the operability of a writing pressure detecting pen is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a writing pressure detection pen suitable for detecting writing pressure applied to the tip of a pen.

[0002]

2. Description of the Related Art Conventionally, a pen pressure detecting pen using a strain gauge as a sensor for measuring pen pressure, or a pen pressure detecting using a pressure sensitive resistance element as disclosed in Japanese Patent Laid-Open No. 64-2125. The pen is known.

[0003]

However, although the one using the above-mentioned strain gauge has a high detection accuracy, it has a problem that it is difficult to operate because the mechanism is large and the movement of the pen tip is large. Further, in the case of using the pressure-sensitive resistance element, the mechanism is small and the amount of movement of the pen tip can be made small, but there is a problem that the detection accuracy is low and the secular change is large. The present inventor has focused on a piezoelectric element that is elastically deformed by a compressive force, generates an electric charge according to the deformation, and has a very small deformation amount, as a sensor suitable for the above purpose. However, since the piezoelectric element is a charge output type element, its output impedance is extremely large.
It is more than 00 megohms. Therefore, in order to obtain a stable signal output, conventionally, as shown in FIG. 4, a charge amplifier circuit 4 having a MOS FET 1 in the input section to increase the input impedance and a temperature compensation circuit 2 to stabilize the characteristics is provided. However, the circuit for signal processing is expensive and complicated. In the figure, 3 is a piezoelectric element and 5 is an operational amplifier. The object of the present invention is to solve the above-mentioned problems and to reduce the amount of movement of the pen tip,
Moreover, it is to provide a pen pressure detection pen with high detection accuracy.

[0004]

Means for Solving the Problems The above-mentioned problems are solved by a pen, a piezoelectric element which generates an electric charge according to an applied compressive force, and a current which is connected to the piezoelectric element and neutralizes an electric charge generated in the piezoelectric element. The problem is solved by providing a power supply circuit for supplying and a conversion circuit for integrating the current supplied to the piezoelectric element and converting it into a voltage, fixing one side surface of the piezoelectric element and abutting the pen on the other side surface. ..

[0005]

[Operation] When a compressive force is applied to the piezoelectric element to generate an electric charge,
The power supply circuit supplies a current for neutralizing the generated charges to the piezoelectric element. Therefore, the value obtained by converting the value obtained by integrating the supplied current into a voltage corresponds to the amount of deformation of the piezoelectric element.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described with reference to FIGS. FIG. 1 is a configuration diagram of a writing pressure detection pen used in a digitizer. It should be noted that the components for detecting the coordinate position are not shown in the figure. 8 is a case. Reference numeral 9 denotes a pen, which is a core of a steel rod or a ball-point pen, and is movable with respect to the case 8. Reference numeral 10 is a spring that biases the pen 9 to the right in the figure. 11 is a retaining ring fixed to the pen 9. Reference numeral 12 denotes a conductive terminal plate, which is provided on both side surfaces of the piezoelectric element
They are arranged one by one. A pressing block 13 is fixed to the case 8. Reference numeral 14 is a control board on which the writing pressure detection circuit and the circuit for coordinate detection shown in FIG. 2 are arranged. 15 is a cap. Reference numeral 16 is a cable, which sends a writing pressure signal and a coordinate detection signal to a control circuit of a digitizer (not shown). FIG. 2 is a block diagram of the writing pressure detection circuit. In the figure, 20 is an operational amplifier, the inverting input terminal a is connected to the piezoelectric element 3 via one terminal plate 12, and the output terminal b is connected to the piezoelectric element 3 via the resistor 21 and the other terminal plate 12. The non-inverting input terminal c is grounded. 22 is an operational amplifier. A resistor 23 connects the output terminal b of the operational amplifier 20 and the inverting input terminal e of the operational amplifier 22. A switch 24 and a capacitor 25 are connected to the inverting input terminal e and the output terminal f of the operational amplifier 22, respectively. In addition,
The switch 24 is for making the accumulated charge of the capacitor 25 zero. The non-inverting input terminal g of the operational amplifier 22 is grounded.

The operation will be described below with reference to the timing chart of FIG. The writing pressure F applied to the tip of the pen 9 is transmitted to the piezoelectric element 3, and the piezoelectric element 3 generates an electric charge corresponding to the compressive force. Then, the operational amplifier 20 performs a negative feedback operation to generate a voltage V ₁ having a polarity that cancels the charges generated in the piezoelectric element 3. Then, the electric charge generated in the piezoelectric element 3 is neutralized by the current i flowing through the resistor 21,
After a certain period of time, the electric charge of the piezoelectric element becomes zero. Note that the above relationship is expressed by Equation 1.

[0008]

[Equation 1]

Here, C is the charge amount of the piezoelectric element, X is the writing pressure application time, T is the time constant of the circuit, R ₁ is the resistance value of the resistor 21. On the other hand, the voltage V ₁ is integrated by the integrator composed of the resistor 23, the operational amplifier 22 and the capacitor 25, and the voltage V ₂ is output. When the accumulated charge of the capacitor 25 is initialized to zero, the above relationship is expressed by the equation 2.

[0010]

[Equation 2]

However, R _{2 is} the resistance value of the resistor 23 D is the capacitance of the capacitor 25 x is the elapsed time since the initialization of the capacitor 25 By the way, since the voltage V ₁ is zero after the time X + T, the parentheses of the equation 2 are used. The third term in is zero and the second term in parentheses is
The term is equal to −R ₁ · C from Equation 1. Therefore, Equation 2 is Equation 3
Can be rewritten as

[0012]

[Equation 3]

Here, if R ₁ = R ₂ = R

[0014]

[Equation 4]

[0015] The first term in the parentheses in the equation 4 indicates that the piezoelectric element 3 is operated after the initialization of the capacitor 25 is completed, that is, after the switch 24 is opened until the writing pressure application time X due to the pressing force of the pen 9. The second term in parentheses corresponds to the integrated value of the output charge amount, and corresponds to the charge amount output by the piezoelectric element 3 in response to the writing pressure applied at time X. Since the spring 10 initializes the piezoelectric element 3 in a pressurized state, the pressing force of the spring 10 is taken into consideration in advance, and the pressing force of the spring 10 does not affect the equation 4. Further, in the present embodiment, the writing pressure F is made constant and changed stepwise in order to make the explanation easy to understand, so the first term in parentheses becomes zero.

By the way, the actual writing pressure F changes gently. However, if the time interval of measurement is set to about 1/1000 second (1 millisecond), sufficient accuracy can be obtained for practical use. Further, the voltage V ₂ in FIG. 3 changes with a time delay T of the circuit with respect to the change of the writing pressure F, but the time constant T should be set to about 1,000,000 seconds (1 microsecond). For example, the time delay error becomes a negligible value. When the writing pressure F applied to the tip of the pen 9 becomes zero, electric charges in the opposite direction to the above are generated in the piezoelectric element 3, but the output terminal b of the operational amplifier 20 has a polarity opposite to the above. Voltage V ₁ is generated,
The charges generated in the piezoelectric element 3 are neutralized in the same manner as above. The capacitor 25 may be initialized when the pen is away from the coordinate detection surface, for example.

[0017]

As described above, according to the present invention, there is an effect that the detection accuracy is high and the movement amount of the pen tip, that is, the operation stroke can be close to zero and the operability is excellent. Further, there is no need for an operational amplifier with high input impedance, and an inexpensive general-purpose operational amplifier can be used, so that there is an economical effect.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a writing pressure pen according to the present invention.

FIG. 2 is a block diagram of a writing pressure detection circuit.

FIG. 3 is a timing chart.

FIG. 4 is an explanatory diagram of a conventional technique.

[Simple explanation of symbols]

 3: Piezoelectric element 9: Pen 13: Presser block 20, 22: Operational amplifier 21, 23: Resistor 24: Switch 25: Capacitor

Claims (1)

Claim: What is claimed is: 1. A pen, a piezoelectric element that generates an electric charge according to an applied compressive force, and a power supply that is connected to the piezoelectric element and that supplies a current that neutralizes the electric charge generated in the piezoelectric element. A writing pressure, characterized by comprising a circuit and a conversion circuit for integrating a current supplied to the piezoelectric element and converting it into a voltage, wherein one side surface of the piezoelectric element is fixed and a pen is brought into contact with the other side surface. Detection pen.