JPS6013525B2 - Proximity detection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a nearby object detection method that detects the approach or contact of an object such as a human body as a change in oscillation frequency, and more specifically, the present invention relates to an improvement in a nearby object detection method that detects the approach or contact of an object such as a human body as a change in oscillation frequency. The present invention relates to a nearby object detection method which is suitable for use in an automatic channel selection device of a television receiver, etc., which can be used to detect changes in oscillation frequency in a binary manner.

2. Description of the Related Art Conventionally, as a so-called proximity switch device, a device as shown in FIG. 1 has been proposed for use in automatic channel selection devices for television receivers and the like. In the conventional device shown in Fig. 1,
11 is a capacitor that detects the approach of a human body as a change in capacitance; 12 is an oscillation circuit 13 that converts this change in capacitance into a change in frequency; and a frequency detection circuit 14 that detects this change in frequency. A holding circuit 15 holds the variable speed boat, and a tuner 15 automatically selects a channel based on a signal from the previous stage.

The frequency of the output A of the oscillation circuit 12 decreases as shown in FIG. 2A when a human body or the like approaches the capacitor 11, and returns to its initial state when the human body moves away from the capacitor 11. The next stage frequency detection circuit 13 outputs a signal as shown in FIG. 2B when the frequency decreases. With this signal B, tuner 15
However, as shown in FIG. 2B, when the human body leaves, the signal B also returns to its initial state.

Therefore, in order to maintain the state selected by the tuner, it was necessary to provide a holding circuit 14 and generate a signal C holding the signal B as shown in FIG. 2C. An oscillation circuit used in such an automatic tuning device is one in which the oscillation frequency is changed by touching the non-grounded side pole of a capacitor C of a Wien bridge type oscillation circuit shown in FIG. 3 with a finger. In FIG. 3, 21 is an operational amplifier;
22 is a non-inverting input terminal of the operational amplifier, 23 is an inverting input terminal, R,, R2, RT are resistors, CT is a capacitor, 24
is the output terminal. When these circuit components are connected as shown in FIG. 3 and the power is turned on, a square wave having an amplitude approximately equal to the power supply voltage Vo volts appears at the output terminal 24 as shown in FIG. 4a.

It is also known that the frequency is expressed by the following equation. At this time, if you touch the non-grounded plate of the capacitor CT with your hand, the capacitance will increase significantly and the oscillation frequency will decrease as shown in equation [1}, as shown in Figure 4b. Become.

This frequency change was detected by the next stage of circuitry, and was used to turn on a switch or automatically tune the television.
However, in this circuit, the frequency changes only at the moment of finger contact, and in order to maintain the state of the switch, etc., it was necessary to add some kind of holding circuit or holding mechanism. SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks and provide a nearby object detection device that does not require a holding circuit or holding mechanism.

The present invention takes advantage of the fact that the capacitance of a liquid crystal element changes greatly depending on the orientation state of liquid crystal molecules, and that the threshold voltage at which a change in the orientation of liquid crystal molecules starts has a significant frequency dependence. It is characterized by using a liquid crystal element as a capacitor which is a determining element of frequency in an oscillation circuit.

FIG. 5 shows an oscillation circuit of a proximity switch device according to an embodiment of the present invention, in which a resistor RT is connected to an output terminal 44 of an operational amplifier 41.
and R2 are connected, the resistor R, is grounded via a liquid crystal element 45 used as a capacitor, and the connection point with the liquid crystal element 45 is connected to the inverting input terminal 43 of the operational amplifier 41.

Furthermore, the resistor R2 is grounded via the resistor R3, and R2 and R3
The connection point of is connected to the non-inverting input 42 of the operational amplifier 41.

On the other hand, the liquid crystal element 45 has electrodes 5 on its inner surface as shown in FIG.
It has a structure in which a liquid crystal material 53 is sandwiched between two substrates 52 provided with 1.

At this time, a P-type or N-type nematic liquid crystal is used as the liquid crystal material, and the P-type is initially aligned substantially horizontally with respect to the electrode, and the N-type is initially aligned substantially perpendicularly to the electrode. The characteristics of a liquid crystal element using a P-type nematic liquid crystal will now be explained.

P-type nematic liquid crystal molecules are largely polarized in the molecular long-axis direction, with a dielectric constant in the long axis direction (normal) and a yield rate in the short axis direction (
s) has the following relationship.

GoL>GoS. ．． ．． ．． 、． ．． ．． ．． {
21 Note that in the case of ordinary liquid crystal materials, the degree of temperature is 3 to 1 (L/S). It is also known that when an alternating current voltage is applied to this liquid crystal element, the interaction between polarization and electric field causes the orientation of the liquid crystal molecules to change so that the most axes of the liquid crystal molecules approximately align with the direction of the electric field, that is, in the direction perpendicular to the electrodes. There is.

This orientation effect has a remarkable frequency characteristic, and if we define the effective value of the voltage that starts orientation as a threshold and value voltage (Vth), this threshold and value voltage are expressed as a function of frequency as shown in Figure 7. It becomes a characteristic. As is clear from the figure, the value voltage (Vth) increases rapidly when it exceeds a certain frequency. This frequency is usually about 10 kHz to 10 Hz and is defined as a cutoff frequency (nac). We will now return to the circuit shown in FIG. 5 and continue the explanation.

As explained in the conventional example, the voltage waveform appearing at the output terminal 44 of this circuit is a square wave whose amplitude is approximately equal to the power supply voltage, as shown in FIG. 8a. The frequency of the output voltage is expressed by the following equation. However, Cp is liquid crystal element 4
This is the value when the liquid crystal molecules are oriented almost parallel to the electrodes in the initial state with a capacitance of 5, and is determined by the throat s and the shape of the element.

At this time, the voltage waveform of the inverting input terminal 43 is
2 and the power supply voltage Vc, as shown in FIG. 8b, and the frequency is equal to the above p.

This means that the inverting input terminal voltage, which changes depending on the time constant determined by RT and Cp, and the output terminal voltage are connected to R. This is because the output terminal voltage is inverted when the non-inverting input terminal voltage divided by , R2 matches. This operating point is determined at point Q in FIG. 9 from the relationship with the frequency characteristics described above.

That is, one point in the region where the frequency p is equal to or higher than the cutoff frequency c, and the effective value of the voltage applied to the liquid crystal element 45 (=inverting input terminal voltage) is equal to or lower than the threshold voltage at the frequency p. Therefore, the liquid crystal molecules in the liquid crystal element do not undergo any orientation change due to the applied voltage, and the capacitance Cp remains unchanged.Next, a part of the human body (such as a finger) is connected to the non-grounded electrode of the liquid crystal element. When touched, Cp in equation '3' increases significantly due to the effect of the capacitance of the human body, and the frequency of the output terminal voltage and the voltage applied to the liquid crystal element 45 (=inverted input state voltage) increases. If the frequency at this time is nam and the operating point is set to point 8 in Figure 9, the voltage applied to the liquid crystal element 45 exceeds the threshold value of the liquid crystal element, so the liquid crystal molecules are not opposed to the electrodes. The orientation changes almost vertically.Therefore, the capacitance of the liquid crystal element becomes a value Cv determined by approximately.Furthermore, when you release your finger, the frequency of the output terminal voltage and the voltage applied to the liquid crystal element (=inverting input terminal voltage) is Although it moves to the high frequency side, it stabilizes at the frequency 〆v determined by the capacitance Cv of the liquid crystal element.

At this time, nv is as shown in the following equation. Furthermore, as shown in the equation {2), since L is larger than S, Cv>Cp holds, and Pv and Nap satisfy the following equation.

NaV<nap...[5]Furthermore,
Since L/dos=3~10, p/nav: 3~
It becomes 10.

Therefore, the operating point is represented by point y in Figure 9, and this state is maintained and continues stably until reset by some external operation such as turning off the power to the operational amplifier 41 or shorting the two electrodes of the liquid crystal element 45. . As described above, it has been explained that the circuit according to the present invention can detect the contact or proximity of a human body as a change in the oscillation frequency, and can stably maintain this state.

In order to perform this operation reliably, Nap must be greater than or equal to the cutoff frequency c, and Nav must be equal to or higher than the cutoff frequency nac.
(Region 1 in Figure 9) and the effective value of the voltage applied to the liquid crystal element (inverting input terminal voltage) is below the threshold voltage when it is above the cutoff frequency, and below the threshold voltage when below the cutoff frequency. (Region 0 in FIG. 9), and care must be taken in selecting the liquid crystal material and designing the liquid crystal element. In this specification, the operation using a P-type nematic liquid crystal has been explained, but when an N-type nematic liquid crystal is used, a liquid crystal whose long axis of the liquid crystal molecules is initially aligned perpendicular to the electrodes is used. A similar operation can be performed using an element.

In addition to the circuit shown in Figure 5, the voltage applied across the capacitor, which is the determining factor for the oscillation frequency, is an AC waveform with an average value of zero, and the frequency corresponds to the output voltage waveform. In general, similar effects can be obtained if the oscillation circuit changes with

Furthermore, in another embodiment of the present invention, a twisted nematic type liquid crystal display element, which is generally used in display elements for watches, is used as the liquid crystal element 45 described above.

If this is done, it is clear that the liquid crystal element used to detect the proximity of a human body, etc., will have the display function as is, and there will be no need for display components (such as miniature light bulbs) that were separately installed in the sub-chamber. Therefore, the effect is large. A twisted nematic type liquid crystal display element has a liquid crystal material 93 sandwiched between two glass substrates 92 each having a transparent electrode 91 such as ln203 on the inner surface, as shown in FIG. 10. A polarizing plate 94 is provided on the outside of the glass substrate. At this time, it is necessary that the liquid crystal molecules have a well-known twisted structure. By using such a liquid crystal display element as the liquid crystal element 45, it is possible to detect a change in the oscillation frequency of the oscillation circuit, that is, the approach or contact of an object to be detected, and simultaneously display the change visually, which is extremely useful in practice. . As is clear from the above detailed description, according to the proximity object detection method of the present invention, by using a liquid crystal element as a capacitor for determining the oscillation frequency, contact or proximity of a human body, etc., can be detected as a change in frequency. Since the state can be maintained stably, there is no longer a need for a holding circuit or mechanical holding mechanism that was required to be added to the subordinate proximity switch, and furthermore, by providing a display function to the liquid crystal element, display parts can be removed. Remarkable effects such as making it unnecessary can be obtained.

Brief description of the drawings Figure 1 is a circuit diagram showing a conventional proximity switch device, Figure 2 is a circuit diagram showing a conventional proximity switch device.
1 is an output voltage waveform diagram for explaining the operation of the device shown in FIG. 1, FIG. 3 is a circuit diagram showing an oscillation circuit used in the device shown in FIG. 1, and FIGS. FIG. 5 is a voltage waveform diagram for explaining the operation of the circuit shown in FIG. 5, and FIG.
The figure is a perspective view showing the structure of a liquid crystal element used in the circuit of Fig. 5, Fig. 7 is a graph showing the frequency dependence of the threshold voltage for starting molecular alignment of the liquid crystal element, and Fig. 8 is a graph showing the frequency dependence of the threshold voltage for starting molecular alignment of the liquid crystal element. 9 is a voltage waveform diagram for explaining the operation of the circuit shown in FIG. 5.
FIG. 10, which is a graph showing the operating points of the liquid crystal element during operation of the circuit shown in the figure, is a perspective view showing a liquid crystal display element used in another embodiment of the present invention.

41... Operational amplifier for oscillation circuit, 45...
Liquid crystal element for capacitor, Q, 3, y... Operating point of liquid crystal element.

group l diagram Traditional 2 illustrations Figure 3 Figure 4 Figure 6 Figure 5 Figure 7 Figure 8 Solution? figure Tsutomu'0 figure

Claims (1)

[Scope of Claims] 1. An oscillation circuit equipped with an oscillation frequency determining capacitor to which an AC voltage whose frequency changes in response to changes in the frequency of the oscillation output and whose average value is substantially zero is applied. A liquid crystal element comprising a liquid crystal material filled between a pair of electrodes in a close object detection method in which the presence of an object to be detected approaching or touching the capacitor is detected as a change in the oscillation frequency in the oscillation circuit. is connected as the capacitor, the voltage applied to the liquid crystal element and its frequency are defined so that the molecular orientation in the liquid crystal material does not change when there is no approach or contact with the object to be detected, and A nearby object detection device, characterized in that the voltage applied to the liquid crystal element and its frequency are regulated so that when an object approaches or comes into contact with it, a change in molecular orientation in the liquid crystal material occurs and the change is self-maintained. . 2. In the proximity object detection device according to claim 1, the change in the oscillation frequency is caused in the liquid crystal element by configuring the liquid crystal element so that a change in its molecular orientation can be optically discerned from the outside. A nearby object detection device characterized by visually displaying.