JPH10300861A - Liquid drop detecting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid drop detecting device with improved sensitivity to detect liquid drops such as rain drops. SOLUTION: A liquid drop detecting device 10 has an emission part 20 to inject a detecting light 14 at a preset crossing angle to the back 13 of a window shield 11 for detecting rain drops deposited on the surface 12 of the window shield 11 and a receiving part 21 to receive the detecting light 14 which is reflected from detection parts 11A, 11B set on the surface 12 of the window shield 11 and then emitted from the back 13 of the window shield 11, the receiving part 21 outputting a signal in accordance with the receiving strength of the detecting light 14. For the liquid drop detecting device 10, the detection parts 11A, 11B draw circular tracks with the integral rotation of the emission part 20 and the receiving part 21.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a droplet detecting device, and more particularly to a droplet detecting device for detecting raindrops or the like attached to a windshield in order to automatically operate a wiper of an automobile according to the weather.

[0002]

2. Description of the Related Art In recent years, various devices have been proposed for detecting raindrops attached to a windshield of a vehicle in order to automatically start and stop a wiper of the vehicle according to the weather. For example, the liquid detector 60 shown in FIG. 6 detects a raindrop adhering to the front surface 62 of the windshield 61 (the upper side of the vehicle in the figure), and therefore detects the back surface 63 of the windshield 61.
A light-emitting portion 65 and a light-receiving portion 66 are provided on the lower surface (in the drawing) via a light guide plate 64 (see Japanese Patent Application Laid-Open No. 59-44641).

The light guide plate 64 has a pair of supporting portions 64A and 64B formed in a substantially triangular cross section connected via a connecting portion 64C. The light guide plate 64 is made of a suitable translucent material having the same light refractive index as the window shield 61, and
A, 64B and the connecting portion 64C are integrally formed, and are fixed in surface contact with the back surface 63 of the window shield 61. Such a light guide plate 64 is provided on the back surface of the window shield 61 via an appropriate translucent adhesive (not shown) having the same light refractive index as that of the window shield 61, for example.
Affixed to 63. The back 63 of the windshield 61
A reflection plate 64D made of aluminum or the like is interposed between and the connecting portion 64C.

The light emitting section 65 has a light emitting element such as a near infrared light emitting diode, and the light receiving section 66 has a light receiving element such as a near infrared photodiode. The light emitting section 65 is arranged such that the detection light 67 emitted from the light emitting element is incident on the rear surface 63 of the window shield 61 at a predetermined angle. The detection light 67 incident on the rear surface 63 of the window shield 61 is totally reflected at the location where the raindrop does not adhere to the detection unit 61A set on the front surface 62 of the window shield 61.
After the detection light 67 is totally reflected by the reflection plate 64D, the detection unit 61B set on the surface 62 of the window shield 61 again.
If no raindrops are attached to the window shield, the light is totally reflected at the position and exits from the rear surface 63 of the window shield 61. Therefore, the light receiving section 66 is arranged at an appropriate position and at an angle capable of receiving the detection light 67 emitted from the back surface 63 of the window shield 61 by the light receiving element, and outputs a signal based on the received light intensity. I have.

In such a liquid detector 60, if raindrops adhere to the detecting section 61A or 61B, the detecting light 67 is transmitted or scattered at these locations, so that the light receiving section 66
And the signal output from the light receiving unit 66 changes accordingly. Therefore, according to the liquid detector 60, if the wiper is controlled based on the signal output from the light receiving unit 66, the start / stop of the wiper can be automated according to the weather.

[0006]

However, in the above-described liquid detector 60, since the detectors 61A and 61B set for detecting raindrops are point-shaped and fixed, even if it starts to rain, It is extremely unlikely that raindrops will adhere to the detection unit 61A or the detection unit 61B. In other words, it is highly likely that it will take a long time to detect raindrops after rain starts. That is, there is a problem that the liquid detector 60 is not suitable for automatically controlling the operation interval by controlling the wiper that operates intermittently because the sensitivity of detecting the raindrop is low.

In order to solve this problem, it is conceivable to set a large number of detecting portions for detecting light.
There is no change in what is fixed, so it is not a fundamental solution. SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a droplet detecting device capable of improving sensitivity for detecting a droplet such as a raindrop.

[0008]

According to the first aspect of the present invention, there is provided a method for detecting a droplet attached to a surface of a plate-shaped transparent body. A light-emitting unit that causes detection light to enter the rear surface of the light-transmitting unit at a predetermined intersection angle, and receives the detection light emitted from the rear surface of the transparent body after being reflected by the detection unit set on the front surface of the transparent body A light-receiving unit, wherein the light-receiving unit outputs a signal based on the light-receiving intensity of the detection light, wherein the light-emitting unit and a line along the thickness direction of the transparent body as a rotation axis. This can be solved by a droplet detecting device, wherein the light receiving unit rotates integrally, so that the detecting unit draws a circular locus.

Here, a structure having a light emitting element such as a near-infrared light emitting diode as in the prior art can be adopted as the light emitting section, and a structure having a light receiving element such as a near infrared photodiode in the same manner as the conventional light receiving section. Etc. can be adopted. In addition, the light emitting unit and the light receiving unit are oriented so that the optical axis is oblique to a transparent body such as a windshield of an automobile, for example, and relatively fixed via an appropriate connecting member. The connecting member may be rotated by a driving means such as a motor. When a plurality of detecting units are set, the light emitting unit and the light receiving unit may be integrally rotated so that each detecting unit draws the same circular locus, or the light emitting unit may emit light so that each detecting unit draws a concentric circular locus. The unit and the light receiving unit may be integrally rotated.

[0010] In the droplet detecting device configured as described above, since the detecting portion draws a circular locus, if it is attached to, for example, a windshield of an automobile, there is a possibility that raindrops can be detected earlier than in the past. In other words, the sensitivity for detecting raindrops can be improved as compared with the related art. Here, if a plurality of detection units are set in advance, since each detection unit draws the same circular locus or concentric locus, the detection sensitivity of raindrops can be further improved.

In the present invention, one of the light emitting section and the light receiving section may have a bending member for bending the detection light. Here, as the bending member, for example, a mirror, a prism, an optical fiber, or the like can be adopted, and the shape, arrangement, and the like are arbitrary as long as the detection light can be bent in a desired direction. In the droplet detecting device configured as described above, since the detection light can be bent in a desired direction by the bending member, the arrangement form of the light emitting unit or the light receiving unit can be arbitrarily selected, and the design is smaller than the conventional one. Fewer constraints.

Further, according to the present invention, the bent member is formed in an annular shape,
The peripheral surface may be a tapered mirror surface capable of reflecting the detection light. Here, as the bending member, one or both of the outer peripheral surface and the inner peripheral surface may be a tapered mirror surface, and one or both of the light emitting portion and the light receiving portion can reflect the detection light to the mirror surface. Should be fine. The light emitting unit and the light receiving unit may be arranged so that the light emitting axis and the light receiving axis are along the surface passing through the axis of the bending member, and may be rotated about the axis of the bending member.

[0013] In the droplet detecting device thus configured, since the circumferential surface of the bent member formed in an annular shape is a tapered mirror surface, for example, a light emitting axis and a light receiving surface are provided on a surface passing through the axis of the bent member. If the light emitting part and the light receiving part are arranged along the axis and the light emitting part and the light receiving part are rotated about the axis of the bent member, it is necessary to rotate the bent member following the light emitting part and the light receiving part. There will be no. Therefore, in this droplet detecting device, it is not necessary to rotate the bending member, so that the rotating mass can be reduced, and the load on driving means such as a motor provided for rotating the light emitting unit and the light receiving unit can be reduced, and Vibration caused by rotation of the light emitting unit and the light receiving unit can be reduced.

According to a fourth aspect of the present invention, the mirror surface is formed on an inner peripheral surface of the bent member, and the light emitting section and the light receiving section are formed on an inner peripheral surface of the bent member. It may be arranged on the surface side. Here, the light emitting unit and the light receiving unit may be arranged so that the light emitting axis and the light receiving axis are along the surface passing through the axis of the bent member. In the droplet detecting device configured as described above, since the turning radius of the light emitting unit and the light receiving unit can be made smaller than when the light emitting unit and the light receiving unit are arranged on the outer peripheral surface side of the bent member, the overall shape is reduced. The size can be reduced, and the load on the driving means such as a motor can be further reduced.

According to the present invention, a plurality of light emitting units and a plurality of light receiving units may be provided. Here, as the light-emitting unit and the light-receiving unit, for example, a structure in which the light-emitting unit or the light-receiving unit is fixed to each end of a frame formed in a substantially X-shape and rotated about the intersection of the frame is adopted. it can. In the present invention, a plurality of detectors that draw a circular locus are set by a set of the light emitting unit and the light receiving unit. However, these detectors may draw the same circular locus, or may draw the concentric circular locus. Good. In such a droplet detection device, since a plurality of detection units are set, the possibility of early detection of a droplet such as a raindrop is further increased, in other words, the detection sensitivity of the droplet can be significantly improved. become.

[0016]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is an exploded perspective view showing a first embodiment of the present invention, FIG. 2 is a sectional view taken along an axis of the first embodiment, FIG. 3 is a sectional view orthogonal to the axis of the first embodiment, and FIG. FIG. 5 is a cross-sectional view taken along the axis of the second embodiment, and FIG. 5 is a cross-sectional view orthogonal to the axis of the third embodiment.

FIG. 1 shows a first embodiment of the present invention. The liquid drop detection device 10 of the first embodiment includes a windshield 11 for starting and stopping a wiper of an automobile according to the weather, or for automatically adjusting an interval of an intermittent operation.
This is to detect raindrops attached to the surface 12 (upper side in the figure). As shown in FIG. 2, the droplet detecting device 10 includes a light emitting unit 20 that causes the detection light 14 to enter the back surface 13 (the lower part in the figure) of the window shield 11 at a predetermined intersection angle, And a light receiving unit 21 for receiving the detection light 14 emitted from the back surface 13.
And outputs a signal based on the received light intensity.
Such a droplet detection device 10 includes a light guide plate 16 fixed to the back surface 13 of the window shield 11 via a silicon gel 15.
And a case 17 provided so as to cover the light guide plate 16. The light emitting unit 20 and the light receiving unit 21 are built in the case 17.

The silicon gel 15 is applied to the windshield 11
Is formed in a substantially disk shape having the same light refractive index as
The window shield 11 is adhered to the rear surface 13 of the window shield 11 in a state of surface contact so as to prevent air bubbles and foreign matter from entering. The light guide plate 16 has a substantially cylindrical shape, is chamfered along the periphery of one end face (the lower end face in FIG. 2), and has a flange 16A on the other end side. The light guide plate 16 has a flange 16A integrally formed of an appropriate synthetic resin, and a silicone gel.
15 is attached in a state of surface contact so that air bubbles and foreign substances are not mixed. A reflection plate 18 made of aluminum or the like is interposed between the silicon gel 15 and the light guide plate 16 on the axis. In addition, this reflector
18 is the back surface 13 of the windshield 11 and silicone gel 15
May be interposed.

The case 17 is made of an appropriate metal having a light shielding property,
It is formed in a cylindrical shape with a bottom by a synthetic resin or the like, and its opening (upper side in the figure) is fitted to the periphery of the flange 16A of the light guide plate 16. A disk-shaped support member 22 is fitted inside the case 17. A motor 23 as a driving unit is fixed to the support member 22, and a rotation member 24 is connected to a rotation shaft of the motor 23. The rotating member 24 is formed in a substantially quadrangular prism shape, and has a motor
23 rotating shafts are connected, and a light emitting section 20 and a light receiving section 21 are provided at both ends in the longitudinal direction, respectively.

The light emitting section 20 has a light emitting element 25 such as a near infrared light emitting diode, and the light receiving section 21 has a light receiving element 26 such as a near infrared photodiode. Then, the light emitting unit 20 and the light receiving unit
Numeral 21 is arranged so that the optical axes of the light emitting element 25 and the light receiving element 26 are on the same line perpendicular to the rotation axis of the motor 23, and are directed away from each other. In other words, the light emitting unit 20 and the light receiving unit 21 are arranged such that the light emitting element 25 and the light receiving element 26 are arranged toward the inner peripheral surface of the case 17 and can be integrally rotated by driving the motor 23. ing.

Here, the light emitting section 20 can emit the detection light 14 only in the direction orthogonal to the rotation axis of the motor 23, and the light receiving section 21 emits the detection light 14 in the direction orthogonal to the rotation axis of the motor 23. The light emitting unit 20 and the light receiving unit 21 are bent members that bend the detection light 14 because only the detection light 14 can be received.
Light is emitted or received through 30. The bent member 30 is pressed into the case 17 to
An annular shape is provided so as to surround the light emitting unit 20 and the light receiving unit 21, and an inner peripheral surface thereof is a tapered mirror surface 31 capable of reflecting the detection light 14. The inclination angle of the mirror surface 31 with respect to the axis of the bending member 30 is such that the detection light 14 reflected on the mirror surface 31 is incident on the back surface 13 of the window shield 11 at a desired intersection angle and is emitted from the back surface 13 of the window shield 11. The detection light 14 is appropriately set so as to be reflected on the mirror surface 31 and travel toward the light receiving element 26.

The light emitting section 20 and the light receiving section 21 as described above.
Are ring terminals 22A to 22D provided on the support member 22.
And the connection terminals 24A to 24D provided on the rotating member 24, respectively, so that signal output based on light emission or reception intensity accompanying power feeding can always be performed regardless of rotation of the rotating member 24. ing. As shown in FIG. 3, four ring-shaped terminals 22A to 22D are provided concentrically around the rotation shaft of the motor 23 on one surface (upper side in FIG. 2) of the support member 22. The ring terminals 22A and 22C are positive terminals, and the ring terminals 22B and 22D are negative terminals.

On the other hand, the rotating member 24 is
Connection terminals 24A to 24A are provided on the side (lower side in FIG. 2) opposite to 22.
24D is provided. The connection terminals 24A and 24B are
The light emitting unit 20 is connected to the light emitting unit 20 regardless of the rotation of the rotating member 24 by contacting the ring terminals 22A and 22B. The connection terminals 24C and 24D are
And the light emitting section 21 can output a signal based on the received light intensity regardless of the rotation of the rotating member 24 by contacting the ring-shaped terminals 22C and 22D.

Returning to FIG. 2, such a droplet detecting device 10 will be described.
, The detection light 14 emitted from the light emitting section 20 is
After being bent into the mirror surface 31 of the window 30, the light passes through the light guide plate 16 and the silicon gel 15, and passes through the window shield 11 at a predetermined intersection angle.
Incident on the back surface 13 of. The detection light 14 incident from the back surface 13 of the windshield 11 is
If raindrops do not adhere to the detection unit 11A set in the above, the light is totally reflected at the location. Then, after the detection light 14 is totally reflected by the reflection plate 18, the window shield 11 is again reflected.
If no raindrops are attached to the detecting portion 11B set on the front surface 12 of the window shield, the light is totally reflected again at that portion, and transmitted through the silicon gel 15 and the light guide plate 16 from the back surface 13 of the windshield 11, and then bent. The light is bent by the mirror surface 31 of the member 30 and received by the light receiving unit 21.

The point-like detection units 11A and 11B set on the surface 12 of the window shield 11 are driven along a circle by driving the motor 23 to rotate the light emitting unit 20 and the light receiving unit 21 integrally. Move in a circular locus. Therefore,
According to the above-described droplet detecting device 10, since the light emitting unit 20 and the light receiving unit 21 can be integrally rotated, the detecting units 11A,
Even if 11B is point-shaped, the substantial range for detecting raindrops can be widened, and there is a possibility that raindrops can be detected earlier from the beginning of rainfall as compared with the conventional method, in other words, compared to the conventional method. To improve the sensitivity of detecting raindrops.

Further, in the above-described droplet detecting device 10, since the detection light 14 is bent by the bending member 30, the arrangement of the light emitting section 20 and the light receiving section 21 can be arbitrarily selected. There are few restrictions. Further, the droplet detecting device 10
In this embodiment, since the bending member 30 is formed in an annular shape and its peripheral surface is a mirror surface 31, the bending member 30 is
In addition, it is not necessary to follow the light receiving unit 21 and rotate it. That is, the droplet detection device 10 can reduce the rotating mass, so that the load on the motor 23 can be reduced, and the vibration caused by the rotation of the light emitting unit 20 and the light receiving unit 21 can be reduced.

In particular, according to the droplet detecting device 10, the mirror surface
Since the light emitting section 20 and the light receiving section 21 are arranged on the inner peripheral surface side of the bent member 30 on which the 31 is formed, the light emitting section 20 and the light receiving section
Compared to the case where 21 is arranged on the outer peripheral surface side of the bending member 30,
The radius of rotation can be reduced, whereby the overall shape can be further reduced, and the load on the motor 23 and the vibrations associated with rotation can be further reduced.

FIG. 4 shows a second embodiment of the present invention. In the second embodiment described below, the members and the like already described in FIGS. 1 to 3 are denoted by the same reference numerals or corresponding reference numerals in the drawings to simplify or omit the description. In the droplet detecting device 40 according to the second embodiment, the light emitting unit 20 and the light receiving unit 21 are provided at both ends in the longitudinal direction of the rotating member 44, respectively, as in the first embodiment. The light-emitting element 25 of the light-emitting section 20 and the light-receiving element 26 of the light-receiving section 21 are provided such that the light-emitting axis or the light-receiving axis intersects the rear surface of the window shield 11 at a predetermined angle, respectively. The bent member illustrated in the example is omitted.

According to such a droplet detecting device 40, the light emitting section 20 and the light receiving section 21 can be rotated about the line along the thickness direction of the window shield 11 by the motor 23, so that the detecting sections 11A, 11B Moves in a circular locus along the same circle, whereby the same effect as in the first embodiment described above can be obtained, in which a substantial range for detecting raindrops can be widened as compared with the related art. And this droplet detecting device
According to 40, since a bending member for bending the detection light 14 is omitted, the number of components can be reduced as compared with the first embodiment, and the manufacturing cost can be reduced.

FIG. 5 shows a third embodiment of the present invention. In the third embodiment described below, the members and the like already described in FIGS. 1 to 4 are denoted by the same reference numerals or corresponding reference numerals in the drawings to simplify or omit the description. The droplet detection device 50 according to the third embodiment differs from the first embodiment in that the rotating member 54 has a substantially X-shape, and the light emitting units 20 and 20 and the light receiving units 21 and 21 are provided at the respective ends. This is the difference.

The light emitting elements 25, 25 of the light emitting sections 20, 20 are fed in parallel by ring terminals 22A, 22B. On the other hand, the light receiving elements 26, 26 of the light receiving sections 21, 21 independently output signals based on the received light intensity through the ring-shaped terminals 22C to 22F. In the droplet detection device 50, the detection units for detecting raindrops are set at four locations, and move so as to draw a circular locus along the same circle.

According to such a droplet detecting device 50, the light emitting units 20, 20 and the light receiving units 21, 21 can be rotated by the motor 23 about the line along the thickness direction of the window shield. The portion moves in a circular locus along the same circle, thereby making it possible to widen a substantial range for detecting raindrops as compared with the related art, similar to the first embodiment and the second embodiment described above. The effect is obtained. According to the droplet detecting device 50, since the detecting portions are set at four places, when the rotation speed of the driving means such as the motor is the same, the liquid droplet detecting device 50 is compared with the first embodiment and the second embodiment. Thus, the time interval for detecting a specific portion on the surface of the window shield is halved. That is, the droplet detection device 50
According to this, raindrops can be detected earlier than in the first embodiment and the second embodiment, and the detection sensitivity can be improved.

It should be noted that the droplet detecting device of the present invention is not limited to the embodiments described above, but can be appropriately modified and improved. For example, the bent member is not limited to the shape or form illustrated in the above-described first embodiment,
The outer diameter, the inner diameter, the shaft length, the inclination angle of the mirror surface, and the like may be appropriately selected.

In each of the above-described embodiments, the droplet detecting device is mounted on the windshield of the vehicle, but is mounted on a side screen, a rear screen, a glass roof, an inclined headlight cover, or the like as a mounting place. Is also good. However, in order to quickly stop the wiper when the weather recovers, the droplet detection device of the present invention is preferably attached to a windshield or a rear screen having a wiper. Furthermore, the droplet detection device of the present invention is applicable not only to automobiles but also to various flying objects such as airplanes and airships, ships, railways, and the like, and is used by being attached to a flat window, a skylight, a bay window, or the like of a house. It is also possible.

[0035]

As described above, according to the first aspect of the present invention, the light emitting section for allowing the detection light to enter the rear surface of the transparent body at a predetermined intersection angle, and the light emitting section set on the front surface of the transparent body. The light-emitting unit and the light-receiving unit that receive the detection light emitted from the back surface of the transparent body after being reflected by the detected detection unit are integrally rotated with a line along the thickness direction of the transparent body as a rotation axis. Accordingly, since the detection unit draws a circular locus, the possibility of detecting the droplet earlier is increased as compared with the related art, in other words, the sensitivity of detecting the droplet can be improved as compared with the related art.

According to the second aspect of the present invention,
Since the bending member for bending the detection light is provided, the arrangement of the light emitting unit or the light receiving unit can be arbitrarily selected, and the design restriction can be reduced as compared with the related art. Further, claim 3
According to the invention described in (1), since the bending member is formed in an annular shape and its peripheral surface is a tapered mirror surface capable of reflecting the detection light, the bending member rotates following the light emitting unit and the light receiving unit. Therefore, the rotating mass can be reduced, the load on the driving means such as a motor provided for rotating the light emitting unit and the light receiving unit can be reduced, and the vibration caused by the rotation of the light emitting unit and the light receiving unit can be reduced. Can be reduced.

According to the fourth aspect of the present invention,
Since the mirror surface is formed on the inner peripheral surface of the bending member and the light emitting unit and the light receiving unit are arranged on the inner peripheral surface side of the bending member, the light emitting unit and the light receiving unit are arranged on the outer peripheral surface side of the bending member. As compared with the case, the turning radius of the light emitting unit and the light receiving unit can be reduced, so that the overall shape can be reduced and the load on the driving means such as the motor can be further reduced. According to the fifth aspect of the present invention, since a plurality of light emitting units and a plurality of light receiving units are provided, the possibility of early detection of a droplet is further increased. In other words, the detection sensitivity of the droplet is increased. It can be dramatically improved.

[Brief description of the drawings]

FIG. 1 is an exploded perspective view showing a first embodiment according to the present invention.

FIG. 2 is a sectional view taken along a rotation axis of a light emitting unit and a light receiving unit.

FIG. 3 is a cross-sectional view along a radial direction of a rotation axis of a light emitting unit and a light receiving unit.

FIG. 4 is a sectional view taken along a rotation axis of a light emitting unit and a light receiving unit according to a second embodiment;

FIG. 5 is a cross-sectional view orthogonal to a rotation axis of a light emitting unit and a light receiving unit according to a third embodiment.

FIG. 6 is a cross-sectional view illustrating a conventional droplet detecting device.

[Explanation of symbols]

 10, 40, 50 Droplet detector 11 Windshield (transparent) 11A, 11B Detector 12 Front surface 13 Back surface 14 Detected light 20 Light emitting unit 21 Light receiving unit 30 Bending member 31 Mirror surface

Claims (5)

[Claims] A light-emitting unit for causing detection light to enter a rear surface of the transparent body at a predetermined crossing angle in order to detect droplets attached to a front surface of the plate-shaped transparent body; A light receiving unit for receiving the detection light reflected from the detection unit set on the front surface of the body and then emitted from the back surface of the see-through body, wherein the light reception unit receives a signal based on a light receiving intensity of the detection light. A droplet detection device that outputs a circle, wherein the light emitting unit and the light receiving unit rotate integrally with a line along the thickness direction of the transparent body as a rotation axis, whereby the detecting unit draws a circular locus. A droplet detection device characterized by the above-mentioned. 2. The droplet detecting device according to claim 1, wherein one of the light emitting unit and the light receiving unit has a bending member that bends the detection light. 3. The droplet detecting device according to claim 2, wherein the bent member is formed in an annular shape, and a peripheral surface thereof is a tapered mirror surface capable of reflecting the detection light. . 4. The apparatus according to claim 1, wherein the mirror surface is formed on an inner peripheral surface of the bending member, and the light emitting unit and the light receiving unit are arranged on an inner peripheral surface side of the bending member. Item 3. A droplet detecting device according to Item 3. 5. The droplet detecting device according to claim 1, wherein a plurality of the light emitting units and the plurality of the light receiving units are provided.