JP2005181157A - Reflection-type photosensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a reflection-type photosensor capable of detecting accurately a genuine detection object, without wrongly detecting contamination, water drops or the like as the detection object, even when contamination, the water drops or the like are deposited on a translucent window part. <P>SOLUTION: In this reflection-type photosensor 12 arranged coaxially with a light emitting element 22 for emitting a light toward the detection object 10, and a photoreception element 24 for receiving the reflected light from the detection object 10, the reflection type photosensor 12 is constituted, to bring detection sensitivity into a peak at a position, separated by a prescribed distance from the position of the window part 20. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a reflection type optical sensor in which a light emitting element that emits light toward a detection target and a light receiving element that receives reflected light from the detection target are arranged coaxially.

Conventionally, a reflection type optical sensor (hereinafter simply referred to as an optical sensor) that emits light from a light emitting element toward a detection target and receives the reflected light from the detection target by a light receiving element to detect the detection target is known. It is.
For example, Patent Document 1 below discloses this type of optical sensor.
Patent Document 1 discloses an invention relating to a photoelectric switch (optical sensor), in which a light emitting element 202 and a light receiving element 204 are arranged adjacent to each other on different axes on the front surface of a substrate 200 as shown in FIG. In addition, infrared light is emitted from the light emitting element 202 toward the detection target, and reflected light from the detection target is received by the light receiving element 204 after removing visible light by the visible light cut filter 206, and the presence or absence of the detection target is determined. The point made to judge is disclosed.

  However, in the case of this optical sensor, since the light emitting element 202 and the light receiving element 204 facing in the same direction are arranged next to each other, a space for arranging the light emitting element 202 and the light receiving element 204 is widened. There was a problem that it was difficult to reduce the size sufficiently.

Further, in this optical sensor, since the light emitting element 202 and the light receiving element 204 are arranged side by side in the same direction, the light emitted from the light emitting element 202 goes directly to the light receiving element 204 side and is received. Therefore, there is a problem that noise is generated by the light that travels around, and the detection sensitivity to the detection target is adversely affected.
In addition, in this optical sensor, since the light receiving area of the reflected light from the detection target that can be received by the light receiving element 204 is small, it is difficult to sufficiently increase the detection sensitivity. Then, the whole sensor will be further increased in size.

On the other hand, an optical sensor in which a light emitting element and a light receiving element are arranged coaxially and in opposite directions and back to back is disclosed in, for example, Patent Document 2 below.
FIG. 10 shows a specific example thereof.
In the figure, 202 is a light emitting element, 204 is a light receiving element disposed back to back, 207 is a concave mirror (reflecting mirror), and 208 is a reflecting mirror disposed in front.
In the case of this optical sensor, the irradiation light from the light emitting element 202 is reflected by the front reflecting mirror 208 and received by the light receiving element 204, and received when the detection target enters the optical path and the light is blocked. A detection target is detected based on a decrease in the amount of light at the element 204.

On the other hand, without providing the front reflecting mirror 208 as described above, the light from the light emitting element 202 is directly reflected by the detection target and received by the light receiving element 204 and detected based on the increase in the amount of light received. It is also possible to detect the presence or absence of a target.
In particular, this type of light sensor is suitable for detecting a detection target at a close distance.

FIG. 11 shows a specific example thereof.
FIG. 11 shows a specific example of the optical sensor proposed by the present applicant in a previous patent application (Japanese Patent Application No. 2003-126064: unpublished). , Human finger), 212 a visible light cut filter, 214 a substrate, the light emitting element 202 on the front surface, and the light receiving element 204 on the back surface arranged back to back.

In this optical sensor, light emitted from the light emitting element 202 toward the detection target is reflected by the detection target 210, and the reflected light passes through the visible light cut filter 212 and then is reflected and collected by the reflecting mirror 207. Light is received by the light receiving element 204.
That is, when the detection target 210 enters the front of the light emitting element 202, the amount of light received by the light receiving element 204 increases, and the detection target 210 is detected based on this.

As described above, in the case of an optical sensor in which the light emitting element 202 that irradiates light toward the detection target 210 and the light receiving element 204 are coaxially arranged, the space occupied by the light emitting element 202 and the light receiving element 204 can be reduced. It is possible to reduce the size of the optical sensor itself.
Further, direct wraparound of light from the light emitting element 202 to the light receiving element 204 can be suppressed, and the detection sensitivity of the optical sensor can be increased.

By the way, in the case of this kind of light sensor in which the light emitting element 202 and the light receiving element 204 are coaxially arranged, the light from the light emitting element 202 is reflected by the detection target 210 as shown in FIG. In the case of the optical sensor that detects the detection target 210 by receiving the light and increasing the amount of received light, it is considered that the detection sensitivity increases as the detection target 210 is closer to the optical sensor.
However, in this case, the following problem occurs.

  That is, for example, when a light sensor is placed inside a light-transmitting window portion, if the window portion is soiled or has water droplets attached to it, the light sensor detects dirt or water droplets at the shortest distance. There is a problem that the detection is performed with high sensitivity and erroneous detection is performed as if the detection target 210 exists.

JP-A-5-274967 JP 49-11154 A

  The present invention is based on such circumstances, and even when dirt or water droplets adhere to the light-transmitting window portion, it is possible to accurately detect the original detection target without erroneously detecting it as a detection target. The present invention has been made for the purpose of providing a reflective optical sensor that can be used.

  Thus, the first aspect of the present invention is a reflection in which a light emitting element that irradiates light toward a detection target through a window portion and a light receiving element that receives reflected light from the detection target are arranged coaxially. The type optical sensor is characterized in that the detection sensitivity reaches a peak at a position separated from the position of the window portion by a predetermined distance.

  According to a second aspect of the present invention, in the first aspect, the light emitting element is an LED that emits infrared light.

  According to a third aspect of the present invention, in any one of the first and second aspects, the light emitting element and the light receiving element are arranged back to back in opposite directions, and the reflected light from the detection target is received by the reflector. It is characterized by reflecting and condensing toward the element.

Effects and effects of the invention

As described above, according to the present invention, in the optical sensor (reflection type optical sensor) in which the light emitting element and the light receiving element are coaxially arranged, the detection sensitivity reaches a peak at a position separated by a predetermined distance from the position of the window portion. An optical sensor is configured.
As described above, in the optical sensor in which the light emitting element and the light receiving element are coaxially arranged, the detection sensitivity is considered to be higher as the detection target is closer to the optical sensor. In various researches, when the irradiation angle of the light emitting element was changed in various ways, the detection sensitivity of the photosensor having the window became maximum at a position away from the position of the window, that is, the window It has been found that the detection sensitivity reaches a peak at a position away from the position, the detection sensitivity decreases at positions before and after that, and the peak position changes depending on the irradiation angle of the light emitting element.
The present invention has been made based on such findings.

  That is, the present invention is an optical sensor in which a light emitting element and a light receiving element are arranged coaxially, and the optical sensor is configured such that the detection sensitivity reaches a peak at a position somewhat away from the position of the window. According to the invention, by appropriately setting the position where the detection sensitivity reaches a peak, that is, by setting the position so that the peak is generated in the target detection area, the light-transmitting window portion is formed. Even if dirt, water droplets, or the like adhere, this is not erroneously detected as a detection target, and can be accurately detected only when the detection target exists in front of the window portion.

Here, the light emitting element may be an LED that emits infrared rays.
In addition, the light emitting element and the light receiving element can be arranged in the opposite directions back to back so that the reflected light from the detection target is reflected and collected by the reflector toward the light receiving element. ).
In the present invention, the irradiation angle of the light emitting element is set to 20 ° or less (an angle at which the light amount is a half of the maximum light amount in the optical axis direction (which may not be strictly the optical axis direction) at one side angle of the optical axis). It is desirable that the angle is 10 ° or less.

Next, embodiments of the present invention will be described in detail with reference to the drawings.
In FIG. 1, reference numeral 10 denotes a detection target (in this example, a human finger), and reference numeral 12 denotes an optical sensor (reflection type optical sensor) of this example that detects the detection target 10.
The optical sensor 12 has a main body 14 having a container shape. Here, the main body 14 is divided into a first member 16 and a second member 18.

Reference numeral 20 denotes a substrate that holds the light emitting element 22 and the light receiving element 24, and has a circular shape as shown in FIG.
A pair of arms 25 extend from the substrate 20 in opposite directions, and these arms 25 are inserted into holding grooves 26 formed at two locations in the circumferential direction of the first member 16, so that the first member 16 and the second member It is clamped by the member 18 in the axial direction.
That is, in this embodiment, the substrate 20 is attached to the main body 14 by a pair of arms 25 so as to be positioned at the center of the opening of the first member 16.

The light emitting element 22 that irradiates light toward the detection target 10 is attached to the front surface and the central portion of the substrate 20, and the light receiving element 24 is disposed on the rear surface and the central portion as shown in FIG. The light-emitting element 22 is mounted coaxially and in the rearward direction opposite to the light-emitting element 22.
Here, the light emitting element 22 is made of an infrared LED, and the light receiving element 24 is made of a photodiode.
The bottom surface of the main body 14 is a reflecting mirror (reflector) 28 having a concave curved surface, and a circular window 30 is provided in the opening 29 at the front end of the main body 14. The window part 30 is comprised by the visible light cut filter.

In the present embodiment, light (infrared light) is emitted at a predetermined irradiation angle forward from the light emitting element 22 (α in the partially enlarged view of FIG. 1 and an angle on one side of the optical axis that is a half light amount of the maximum light amount). Is transmitted through the window 30 and irradiated.
The light irradiated forward is reflected by the detection target 10 when the detection target 10 is present, and the reflected light passes through the window portion 30 formed of a visible light cut filter and is reflected and collected by the reflecting mirror 28. The light receiving element 24 receives the light.
And the front detection object 10 is detected based on the magnitude of the amount of received light.

  In the present embodiment, strictly speaking, the light irradiation angle of the light emitting element 22 is selected so that the detection sensitivity becomes maximum (peak) at a position 35 mm forward from the front surface of the window portion 30.

FIG. 3 illustrates the relationship between the irradiation angle and the position where the detection sensitivity is maximized (peak) when the irradiation angle of the light emitting element 22 is variously changed.
In FIG. 3, the horizontal axis represents the distance to the detection target, strictly speaking, the distance from the rear surface of the substrate 20 to the detection target, with the window 30 as a reference, and the vertical axis represents the output relative value. Here, the output relative value is expressed as 100% when the output is maximum, and the others are expressed as relative values with respect to the maximum value.

The result shown in FIG. 3 represents the result measured under the conditions shown in FIG.
Specifically, as the optical sensor 12, the diameter of the reflecting mirror 28 is 30 mm, the diameter of the substrate 20 is 15 mm, the distance from the bottom position (center position) of the reflecting mirror 28 to the rear surface of the substrate 20 is 30 mm, and the window portion from the rear surface of the substrate 20 The distance from the front surface of the substrate 30 to 25 mm, the distance from the front surface of the window 30 to the plate-shaped detection target 10A is 35 mm (therefore, the distance from the rear surface of the substrate 20 to the detection target 10A is 60 mm), and the irradiation angle varies. The result of measuring the amount of received light using the light emitting element 22 is shown.

As shown in FIG. 3, in this experimental result, when the irradiation angle of the light emitting element 22 is 5 °, a peak of the output relative value appears at a position 35 mm from the window 30 (at a distance of 60 mm from the substrate). Yes.
As the irradiation angle is increased, the peak position is shifted to the near distance side.
The presence of a special peak was not observed for the irradiation angle of 50 °.

  As described above, the reason why the peak appears depending on the irradiation angle of the light emitting element 22 and the position of the peak changes is not necessarily confirmed at this stage, but as one reason, if the position of the detection target 10A is too close, the substrate 20 It is conceivable that the amount of reflected light incident on the reflecting mirror 28 and, consequently, the amount of light received by the light receiving element 24 decreases due to light shielding by the light receiving element.

FIG. 5 schematically shows this.
In FIG. 5, (B) shows when the detection target 10 is at a position where the detection sensitivity is at a peak, (A) shows a case where the detection target 10 is too close, and (C) shows that the detection target 10 is at a peak. Each represents a position far from the position (the window 30 is omitted in the figure).

As shown in FIG. 5A, when the detection target 10 is too close to the window portion 30, most of the reflected light is blocked by the substrate 20, and the amount of light received by the light receiving element 24 is reduced (P in the figure). Represents a ring of reflected light passing through the substrate 20).
On the other hand, as shown in FIG. 5C, if the distance of the detection target 10 is far, the amount of light blocked by the substrate 20 is reduced, but the detection target 10 is far away from the detection target 10. As a result of the reflected light being radiated (reflected) over a wide range, the amount of reflected light incident on the reflecting mirror 28 is also reduced, and the amount of received light received by the light receiving element 24 is reduced.

In FIG. 5A, the decrease in the amount of reflected light received by the light receiving element 24 is affected by the irradiation angle of the light emitting element 22, and this tendency is promoted as the irradiation angle of the light emitting element 22 decreases.
On the other hand, if the irradiation angle becomes wider, the shielding effect of the substrate 20 against the reflected light incident on the reflecting mirror 28 becomes relatively small, and this shows a peak of detection sensitivity due to a change in the irradiation angle of the light emitting element 22. In addition, this is considered to be one reason that the position of the peak shifts to the near side or the far side.

The above is an example in which the position of the peak of detection sensitivity is set as the set position by changing the irradiation angle of the light emitting element 22, but the irradiation angle of the light emitting element 22 is kept constant and the size of the substrate 20 is large. It is also possible to set the detection sensitivity peak at a predetermined position by changing the height and to change the position.
Alternatively, the same purpose can be achieved by changing the curvature or focus of the reflecting mirror 28.

FIG. 6 schematically shows this (the window portion 30 is omitted in the figure).
FIG. 6B shows a state in which the reflected light is well imaged on the light receiving element 24 when the detection target 10 is at the set position, that is, when the curvature or focal length of the reflecting mirror 28 is set as such. Represents.
In this case, in the state of FIG. 6A, that is, in the state where the position of the detection target 10 is closer than this, the reflected light from the detection target 10 does not form a good image on the light receiving element 24 and the sensitivity is low. .

Conversely, as shown in FIG. 6C, when the detection target 10 is at a position farther than the position shown in FIG. 6B, the reflected light is imaged well on the light receiving element 24 in the same manner. Also, the detection sensitivity is low.
Therefore, by changing the curvature or focal length of the reflecting mirror 28 as described above, it is possible to change the position where the detection sensitivity reaches a peak.

According to the present embodiment as described above, the position where the detection sensitivity of the optical sensor 12 reaches the peak is set appropriately, that is, the peak is set so that the peak occurs in the target detection area. Thus, even if dirt or water droplets adhere to the translucent window part, the detection object 10 existing in front of the window part 30 can be accurately detected without erroneously detecting it as the detection object 10. it can.
In addition, since the light sensor 12 can take a large incident area of the reflected light to the reflecting mirror 28, characters or the like can be put on the sensor surface (a place where light emission is not hindered), thereby improving the sensor visibility. It can be improved.

FIG. 7 shows another embodiment of the present invention.
This embodiment is an example in which the second member 18 is provided with a radially inward projecting portion 32 and the opening of the main body 14 is narrowed within a range that does not affect the optical path of the reflected light.
The inner peripheral surface of the projecting portion 32 is a tapered surface 34 having a small diameter on the front side.
By doing so, the influence of disturbance light can be reduced.

FIG. 8 shows still another embodiment of the present invention.
In this example, the light emitting element 22 and the light receiving element 24 are attached to separate substrates 20 and 36, respectively, and are arranged coaxially in the same forward direction.
In this embodiment, the reflected light from the detection target 10 is collected by the lens 38 and then received by the light receiving element 24 behind it.

  Although the embodiment of the present invention has been described in detail above, this is merely an example, and the present invention can be configured in various forms without departing from the spirit of the present invention.

It is a figure which shows the reflection type optical sensor which is position embodiment of this invention. It is a perspective view which decomposes | disassembles and shows the reflection type optical sensor in FIG. It is a figure showing the relationship between the irradiation angle of the light emitting element in FIG. 1, and the peak of detection sensitivity. It is the figure which showed the conditions when the relationship of FIG. 3 was measured. It is explanatory drawing showing the relationship between the irradiation angle of a light emitting element, the position of a detection target, and light reception amount. It is explanatory drawing showing the relationship between the focus of a reflective mirror, the distance of a detection target, and light reception amount. It is a figure which shows other embodiment of this invention. It is a figure which shows other embodiment of this invention. It is a figure which shows the example of the conventional reflection type optical sensor. It is a figure which shows an example of the conventional reflection type optical sensor different from FIG. It is a figure which shows an example of the reflection type optical sensor which concerns on the prior application of this applicant as a comparative example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10,10A Detection object 12 Reflection type optical sensor 22 Light emitting element 24 Light receiving element 28 Reflecting mirror 30 Window part

Claims (3)

In a reflection type photosensor in which a light emitting element that irradiates light toward a detection target through a window portion and a light receiving element that receives reflected light from the detection target are arranged coaxially,
A reflection type optical sensor configured to have a peak detection sensitivity at a position separated by a predetermined distance from the position of the window portion.   The reflective optical sensor according to claim 1, wherein the light emitting element is an LED that emits infrared light.   3. The light emitting device and the light receiving device according to claim 1, wherein the light emitting device and the light receiving device are arranged back to back, and the reflected light from the detection target is reflected and collected by the reflector toward the light receiving device. A reflection-type optical sensor characterized by being configured to emit light.

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