JPH09200022A - Touch key - Google Patents

Abstract

(57) A touch key capable of outputting a reception signal having a high S / N ratio and simplifying a circuit configuration is provided. An optical axis 2 ′ of a light emitting element 2 and a light receiving element 5
And 5'indicate the inner surface 3a and the outer surface 3b of the transparent body 3.
The light receiving element 5 is arranged at a predetermined angle so that it does not exist in the range where the reflected light is reflected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a touch key, and more particularly to emitting infrared light to a reflector such as a finger and receiving infrared light reflected by the reflector to detect the presence or absence of the reflector. By doing so, the present invention relates to a touch key that outputs a key input signal.

[0002]

2. Description of the Related Art Generally, since this type of touch key does not require a mechanically operating portion and can improve the confidentiality, it can be used for various measuring devices (field devices) installed outdoors. Many. FIG. 4 is a block diagram showing a circuit configuration of a general touch key. Infrared light is emitted from the light emitting element 2 based on the pulse signal of a predetermined frequency output from the drive circuit 1. The infrared light passes through the transparent body 3 such as glass and is applied to the reflector 4 including the finger of the operator.

A part of the infrared light reflected by the reflector 4 again passes through the transparent body 3 and is detected by the light receiving element 5, and the received signal 1
Output as 0. The received signal 10 has a low-frequency component removed by the high-pass filter 6, is amplified by the AC amplifier circuit 7, and is output as an AC signal. continue,
This AC signal is integrated by the integration circuit 8 based on a predetermined time constant, and the DC signal is compared with a predetermined threshold voltage by the determination circuit 9 to determine the presence / absence of the reflector 4 and determine whether or not there is a key input. The indicated key input signal is output.

[0004]

Therefore, in such a conventional touch key, the reflected light reflected by the inner surface or the outer surface of the transparent body 3 is not taken into consideration, and the amount of light received by the light receiving element 5 is emphasized. Then, for example, when the light emitting element 2 and the light receiving element 5 are arranged at positions where the exit angle and the light receiving angle of the infrared light are substantially equal to each other with the reflector 4 as the center, the light is reflected by the transparent body 3. The infrared light is also received by the light receiving element 5, and there is a problem that it is detected as noise when the reflector 4 does not exist.

FIG. 5 is an explanatory view showing a conventional touch key. (A) is output when the reflector 4 is not present, (b) is output when the reflector is present, and (c) is output from the light receiving element 5. The received signal 10 is shown. When the reflector is present, as shown in FIG. 5B, the infrared light emitted from the light emitting element 2 is slightly refracted according to its refractive index and passes through the transparent body 3 and then the reflector. The light is reflected by the light source 4, passes through the transparent body 3 again, and is received by the light receiving element 5.

Here, when the infrared light emitted from the light emitting element 2 passes through the inner side surface 3a and the outer side surface 3b of the transparent body 3, a part of the infrared light is reflected light (broken line in FIG. 5) and equal to the incident angle. Reflects on the incident side at an angle. In this case, depending on the position of the light receiving element 5, the reflected light from the transparent body 3 is received by the light receiving element 5 as shown in FIG. 5A, and there is no reflector 4 as shown in FIG. 5C. Even when the amplitude of the received light signal 10 is increased, the difference voltage V from the amplitude when the reflector 4 is present
d becomes relatively small.

Therefore, in order to accurately determine the presence or absence of the reflector 4 based on such a relatively small difference voltage Vd, that is, the received signal having a low S / N ratio, a more precise and complicated circuit configuration is required. However, there is a problem in that the number of circuit components is increased and the cost is increased. The present invention is intended to solve such a problem, and an object of the present invention is to provide a touch key that can output a reception signal with a high S / N ratio and can simplify the circuit configuration.

[0008]

In order to achieve such an object, in the touch key according to the present invention, the light receiving element is made of a transparent material when infrared light emitted from the light emitting element passes through the transparent material. It is arranged outside the range of the reflected light reflected on the side surface of the light receiving element. Therefore, when the infrared light emitted from the light emitting element passes through the transparent body, the reflected light reflected by the side surface of the transparent body toward the light receiving element is not received by the light receiving element.

[0009]

Next, the present invention will be described with reference to the drawings. FIG. 1 is an explanatory diagram showing a touch key according to an embodiment of the present invention, and the same or similar parts as those in the above description (see FIGS. 4 and 5) are denoted by the same reference numerals.
In FIG. 1, (a) shows the case where the reflector 4 including the operator's finger does not exist, (b) shows the case where the reflector 4 exists, and (c) shows the received signal 10 ′ output from the light receiving element 5.
Is shown.

In this case, the light emitting element 2 and the light receiving element 5 are
As shown in FIG. 2, it is integrally supported as a photo sensor,
They are arranged at almost the same position. FIG. 2 is an explanatory view showing a photosensor, in which the light emitting element 2 and the light receiving element 5 are supported with a slight interval (for example, 1 to 3 mm) so that their respective optical axes 2'and 5'are substantially parallel to each other. .
The optical axis 2'of the light emitting element 2 indicates the central axis indicating the direction in which the infrared light is emitted, and the optical axis 5'of the light receiving element 5 indicates the central axis in the range in which the infrared light is received. It is assumed that

The optical axes 2'and 5'of the light emitting element 2 and the light receiving element 5 which are integrally supported as such a photosensor are arranged at a predetermined angle with respect to the inner side surface 3a and the outer side surface 3b of the transparent body 3. When the light receiving element 5 is arranged so as not to exist in the range where the reflected light is reflected, as shown in FIG. 1A, when the reflector 4 does not exist, the infrared light emitted from the light emitting element 2 is emitted. Light is reflected by the inner surface 3a and the outer surface 3b of the transparent body 3 as reflected light (see the broken line in FIG. 1). However, since the light receiving element 5 does not exist in the range where the reflected light is reflected, the reflected light is not received by the light receiving element 5.

Further, as shown in FIG. 1B, the reflector 4
In the case of the presence of, the infrared light passing through the transparent body 3 and applied to the reflector 4 is diffusely reflected on the surface of the reflector 4. Thereby, for example, the infrared light reflected in the same direction as the incident angle in the reflector 4 is reflected in the direction of the light emitting element 2 by following the same route as that emitted from the light emitting element 2 in the opposite direction. Therefore, the light is received by the light receiving element 5 arranged adjacent to the light emitting element 2.

Therefore, in the received signal 10 'output from the light receiving element 5 in response to the reception of infrared light, as shown in FIG. 1C, the reflected light cannot be detected without the reflector 4. Therefore, the difference voltage Vd between the case where the reflector 4 is not provided and the case where the reflector 4 is provided is relatively large, and a reception signal having a high S / N ratio can be obtained. This eliminates the need for a highly accurate and complicated circuit configuration as in the prior art. For example, instead of the high-pass filter 6 and the integrating circuit 8 shown in FIG. 4, a counter for counting the pulse number of the received signal 10 ′ is provided, It is possible to determine the presence / absence of a key input according to the coefficient output, and the circuit configuration can be simplified.

When the light receiving element 5 has a predetermined detection range, the relationship between the detection range of the light receiving element 5 and the optical axis is shown in FIG. In FIG. 3, the case where the light emitting point of the light emitting element 2 of the photo sensor and the light receiving point of the light receiving element 5 are arranged at the same position is shown as an example, and 31 is the light emitting point of the light emitting element 2 (that is, 32)
Is the optical axis 2 '(optical axis 5') of the light emitting element 2 (light receiving element 5),
33 is the perpendicular of the inner surface 3a (outer surface 3b) of the transparent body 3, θ
Is the angle formed by the vertical line 33 and the optical axis 32, and θd is the light receiving element 5
Is an angle from the optical axis 32 indicating the detection range of.

In this case, since the light emitting point of the light emitting element 2 and the light receiving point of the light receiving element 5 are arranged at the same position 31, in order to prevent reflected light from being detected by the light receiving element 5, a transparent material is used. The angle of the optical axis 32, that is, the angle θ may be determined so that the reflected light reflected vertically by the inner side surface 3a (outer side surface 3b) of 3 is outside the detection range of the light receiving element 5, and therefore, The relationship between the angle θ and the angle θd is θ>
θd. As a result, the degree of freedom in the arrangement position of the light receiving element is increased as compared with the case where the light receiving element is arranged outside the range of the reflected light.

The same applies to the case where the light emitting point of the light emitting element 2 and the light receiving point of the light receiving element 5 are not arranged at the same position 31 or the optical axes 2'and 5'are not parallel, The positions of the light emitting element 2 and the light receiving element 5 (for example, the elements 2 and 5 and the inner surface 3a) so that the reflected light reflected by the inner surface 3a (outer surface 3b) of the transparent body 3 is outside the detection range of the light receiving element 5. Alternatively, the distance from the outer surface 3b or the spatial position of each element) and the angles of the optical axes 2'and 5'may be determined.

[0017]

As described above, according to the present invention, when the infrared light emitted from the light emitting element passes through the transparent body, the reflected light is reflected by the side surface of the transparent body toward the light receiving element. Since the light receiving element does not detect reflected light, the voltage difference between the case where there is no reflector and the case where there is a reflector becomes relatively large, and the received signal with a high S / N ratio is obtained. Can be obtained. Therefore, there is no need for a highly accurate and complicated circuit configuration as in the past. For example, instead of using a high-pass filter or an integrating circuit, a counter that counts the number of pulses of the received signal is provided, and whether or not there is a key input depending on the coefficient output. Can be determined, and the circuit configuration can be simplified.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a touch key according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a photo sensor.

FIG. 3 is an explanatory diagram showing a relationship between a detection range of a light receiving element and an optical axis.

FIG. 4 is a block diagram showing a circuit configuration of a general touch key.

FIG. 5 is an explanatory diagram showing a conventional touch key.

[Explanation of symbols]

2 ... Light emitting element, 3 ... Transparent body, 3a ... Inner surface (transparent body),
3b ... outer surface (transparent body), 4 ... reflector, 5 ... light receiving element,
10 '... Received signal.

Claims (1)

[Claims] 1. A light-emitting element that emits infrared light to a reflector such as a finger through a transparent body, and a light-receiving element that receives infrared light reflected by the reflector through the transparent body. Then, in the touch key that outputs the key input signal by detecting the presence or absence of the reflector according to the received signal from the light receiving element, in the light receiving element, the infrared light emitted from the light emitting element passes through the transparent body. In this case, the touch key is arranged outside the range of reflected light that is reflected by the side surface of the transparent body toward the light receiving element.