JPS6261967B2 - - Google Patents

Description

Detailed Description of the Invention (Technical Field) The present invention uses a resistive film, applies voltage to the resistive film in the x and y directions in a time-sharing manner, and determines the coordinates of an arbitrary pressure point on the resistive film. This invention relates to an improvement in a coordinate input method that detects potentials output by resistor division.

(Background Art) A block diagram of a conventional coordinate input device is shown in FIG.

In FIG. 1, 1 is a resistive film, 2 to 5 are a group of diodes, 6 and 7 are switches, and switches 6 and 7 are interlocked. Further, 8 is a DC power supply, 13 is a general term for the entire tablet section, 14 is an analog/digital converter (hereinafter referred to as ADC), and 15 is configured like a pen. Also, the tablet 13 in FIG.
The configuration is shown in Figure 2.

In FIG. 2, 9 is an insulating substrate, 10 is a pressure sensitive rubber, 11 is a conductive film, and 12 is an insulating film.

A conventional coordinate input device will be described below with reference to FIGS. 1 and 2. As shown in the figure, terminals are provided at the left and right top and bottom ends of a resistive film formed on an insulating substrate, as shown in the figure, and each terminal is connected to one diode of diode groups 2 to 5 as shown in Figure 1.
The anodes of diode group 2 are connected in common and connected to the normally closed contact (hereinafter referred to as NC contact) of switch 6, and the anodes of diode group 2 are connected to
The cathode sides of are commonly connected and connected to the NC contact of switch 7. The common contacts (hereinafter referred to as COM contacts) of switches 6 and 7 are connected to the positive voltage side and OV side of the DC power supply, respectively, so Figure 1 shows the state in which voltage is applied to the resistive film 1 in the y direction. show. At the next timing, switch 6 and switch 7 are simultaneously switched to the normally open contact (hereinafter referred to as NO contact) side, so a voltage is applied in the x direction of resistive film 1, and at the next timing, switch 6 and switch 7 switch to the normally open contact (hereinafter referred to as NO contact) side. To return to the solid line state, a voltage is applied in the y direction, x,
The voltage is applied in the y direction in a time-division manner.

Here, when a point on the insulating film 12 is pressed with the pen 15, the pressure-sensitive rubber 10 is electrically connected to the conductive film 11 under the insulating film 12 only in the vertical direction where the pressure is applied.
is conductive between the resistive film 1 and the pressure point, and the potential divided by the resistance on the resistive film 1 is connected to the pressure sensitive rubber 10,
It is led out to the ADC 14 through the conductor film 11 and converted into a digital value, but the x, y values are
Since the voltage is applied in a time-divisional manner in the directions, the potential resulting from resistance division in both the x and y directions at the pressurizing point is obtained, and as a result, the coordinate values of the pressurizing point are obtained. Here, a case in which coordinate values are input at a sampling rate of 150 points per second will be explained in more detail. To give a more specific explanation, the input panel is A4 size (effective
210 x 297 mm) and the resolution of coordinate values is 0.1 mm, it must be divided into 2971 points in the longitudinal direction, and for this purpose, the ADC 14 needs to be 12 bits. Currently, the full range input is DC10V analog.
If a digital converter is used, the analog voltage corresponding to a digital unit quantity is 10/4095≒2.
44mV. Therefore, the longitudinal direction of the resistive film is 2.44
A voltage of x2970=7246.8mV will be applied.

Now, if the pen 15 is pressurizing a certain point A from above the insulating film 12 and the switches 6 and 7 are in the state shown by the dotted lines in FIG. 1 (the COM contact and the NO contact are closed), the diode group 4 A voltage from a DC power source 8 is applied to the diode group 5 from the source. As explained above, this voltage is 7.2468V plus twice the forward voltage drop of the diodes of diode groups 4 and 5 at the required current. The explanation will proceed assuming that the same voltage is applied in the lateral direction, and the coordinate values are calculated proportionally after conversion into digital quantities. Now, as a coordinate component in the x direction, the x-component potential of the pressurizing point A (this is referred to as A _x [V]) appears at the input of the ADC 14 . Currently, the sample plate is 150 samples/second, so the period is 6.6 m.
sec, and during this time coordinate values in both the x and y directions are required, so they are converted into digital quantities by the ADC 14 within 3.3 msec, switches 6 and 7 are turned on, and the potential of the component in the y direction (this is A _y [V )
is detected and led to the ADC 14 where it is converted into a digital quantity. Although FIG. 1 is schematically drawn close to a square, assuming that the longitudinal direction is x and the transverse direction is y, if the pressure point A is at the lower right on the resistive film 1, then A _x
[V] is a large voltage value, and A _y [V] is a small voltage value. Also, the resistive film is composed of a large resistance value in order to reduce the current flowing through the resistive film, so ADC1
The input section No. 4 is in a high impedance state. For that state, a large voltage A _x appears and 3.3
Since the voltage A _y becomes small after msec, the charge due to the large voltage A _x is accumulated in the stray capacitance from the resistive film 1 to the ADC 14 and is completely discharged by the time the small voltage A _y is converted by the ADC 14. That was difficult. Furthermore, as shown in Fig. 2, since the tablet 13 is composed of various substrates, rubber, films, etc., noise voltages are often generated.In order to reduce the influence of these noises, it is recommended to add a sample and hold circuit to the input section of the ADC 14. , or it was necessary to smooth out the noise voltage. Naturally, the integral effect of stray capacitance and conductor impedance is not effective at all in blunting these noise voltages.
However, if a capacitor with a constant value that produces an integral effect on the noise voltage is inserted in front of the ADC 14, for example, even the stray capacitance will be in trouble, making it even more difficult to discharge the accumulated charge. As a result, the essential drawback was that the sample rate had to be reduced considerably.

In addition, in FIG. 1, the voltage applied to the resistive film 1 is instantaneously switched between the x direction and the y direction by switches 6 and 7, but if the voltage is switched instantaneously using a transistor or the like, the switch 6 and Due to a difference in the operation timing of switch 7, current flows not only in the x and y directions but also in unexpected directions, which confuses the potential distribution on the resistive film 1 and makes it noisy overall. There are also drawbacks such as the risk of causing potential to appear, and as a result, it is difficult to maintain a desired sample rate.

The above-mentioned drawbacks have been one of the major reasons why coordinate input devices using resistive films have been attracting attention, but have been difficult to put into practical use satisfactorily.

(Problems to be solved by the invention) In order to eliminate these drawbacks, the purpose of the present invention is to insert an integrating circuit into the output section of the tablet 13 to remove noise, and to provide a discharge circuit for discharging the charge accumulated in the integrating circuit. A new discharge timing is provided between the timings of detecting coordinate values in the x and y directions of No. 13, and the discharge circuit is made to function at this discharge timing, which will be described in detail below.

(Structure and operation of the invention) FIG. 3 is a block diagram showing an embodiment of the invention, in which numerals 16 and 17 are switches having three contacts, and the switches 16 and 17 operate synchronously. 18 is an integration circuit, 19 is a discharge circuit, and as shown in FIG. 3, switches 16 and 17 apply a voltage in the y direction of the resistive film inside the tablet 13, and then pass through the contact point in the middle.
At this point, the charges in the tablet 13 and the integrating circuit 18 are discharged by the discharge circuit 19, and then a voltage is applied to the resistive film in the x direction.

The operating conditions will be explained in more detail below.

Switches 16 and 17, like switches 6 and 7 in FIG. 1, are schematic representations of switching circuits in terms of timing, and are actually realized by elements such as transistors. If we choose the sample rate to be 150 samples/second, the cycle is 6.6 msec, and during this period, it is necessary to sample the potential, perform analog/digital conversion, and discharge twice.
Allocate 2.5 msec each for digital conversion and discharge
It is appropriate to allocate 0.8 msec each. The time constant of the integrator circuit 18 is the time for the conversion, here 2.5 msec, excluding the conversion time and data acquisition time, and 2 msec with some margin added.
I'll leave it at that. By choosing such a constant
When ADC 14 starts conversion, tablet 13
The output potential from the converter is stabilized, and even if a small disturbance noise enters, it is suppressed by the integrating circuit 18 and does not adversely affect the conversion of the ADC 14.
After converting the tablet 13 in the y direction in this way, for example, the next 0.8 msec is the time for discharging. A signal is sent from the middle contact of the switch 16 to the discharge circuit 19 to activate the discharge. Since the discharge time is 0.8 msec, it is desirable to set the time constant of the discharge circuit 19 to about 0.5 msec with some margin. However, since the charges stored in the integrating circuit 18 are discharged in a short time by the discharging circuit 19, it goes without saying that consideration must be given to current considerations.

(Effects of the Invention) As explained above, in the embodiment, the allowed sampling period is divided into four, the timing is divided into sampling and conversion of voltage of each x and y component, and discharge, and the circuit is set at the discharge timing. A discharging circuit 19 for discharging only the stored charge is provided, and at the same time, an integrating circuit 1 is provided.
8, all the drawbacks of the prior art are eliminated.

In other words, since the sampling period is divided into four timings: sampling and converting the potential in the x direction, discharging, sampling and converting the potential in the y direction, and discharging,
There is an advantage that the current flowing through the resistive film 1 is orderly, and as a result, the risk of sampling an incorrect potential is extremely reduced.

Furthermore, by providing the discharge circuit 19, it is not only possible to provide the integrating circuit 18, but also the charges accumulated in the stray capacitance of the tablet 13, including the charges of the integrating circuit 18, can be periodically discharged. This has the advantage of stabilizing the circuit.

Next, by providing the integrating circuit 18, not only can noise be removed, but also a sample and hold circuit is required between the tablet 13 and the ADC 14 in order to stably convert the output voltage from the tablet 13 into a digital value by the ADC 14. By providing the integrating circuit 18, the integrating circuit 18 also has the function of a sample and hold circuit, which has the advantage that conversion to a more stable digital value becomes possible. Therefore, it has the advantage of being able to convert an analog voltage into a digital value in a stable state, and also ensuring a desired sampling and conversion cycle, which will greatly contribute to the practical application of coordinate input devices using resistive films. It is something that makes a contribution.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a conventional coordinate input device, FIG. 2 is a block diagram of a tablet section, and FIG. 3 is a block diagram showing an embodiment of the present invention. 1...Resistive film, 2-5...Diode group, 6,
7...Switch, 8...DC power supply, 9...Insulating substrate, 10...Pressure sensitive rubber, 11...Conductor film, 12...
...Insulating film, 13...Tablet part, 14...Analog-digital converter, 15...Pen, 1
6, 17...Switch, 18...Integrator circuit, 19
...discharge circuit.

Claims (1)

[Claims] 1 A tablet having a resistive film, a means for time-divisionally applying voltage in the vertical and horizontal directions of the resistive film, and a voltage potential of the coordinates of an arbitrary pressure point on the resistive film by resistance division on the resistive film. In a coordinate input device having a means for outputting a potential as a first timing for detecting the potential in one of the vertical and horizontal directions corresponding to a point and converting the potential into a digital amount; a second timing for discharging, a third timing for detecting the potential in the other of the vertical and horizontal directions corresponding to the pressurizing point and converting the potential into a digital quantity, and integrating at the timing. A coordinate input method characterized in that a fourth timing for discharging charges accumulated in a circuit by the discharge circuit is switched in a time division manner.