Optical sensor

A monitor-light-emitting device and multiple light-emitting devices are mounted on a board, and a light-guiding member is disposed in front of these devices. Monitor light emitted from the monitor-light-emitting device is directly supplied to a light receiving device. Part of light emitted from the multiple light-emitting devices is incident on the light-guiding member and is used as reference light. The reference light is received by the light receiving device. Reflected detection light that has been reflected off a target object located in front of the optical sensor is transmitted through the light-guiding member and is received by the light receiving device. A condenser is disposed in front of the light receiving device and the reference light or the reflected detection light is efficiently supplied to the light receiving device.

PRIORITY CLAIM

This application claims the benefit of Japanese Patent Application No. 2012-059328, filed on Mar. 15, 2012, and which is incorporated by reference herein in its entirety.

BACKGROUND

1. Field of the Invention

The present invention relates to an optical sensor that emits light and detects the reflected light to determine if there is a target object in front of the sensor.

2. Description of the Related Art

Certain optical sensors that detect whether or not there is a human body or hand in front of an electronic device are known.

In an optical sensor described in Japanese Unexamined Patent Application Publication No. 2001-194232, a light emitting portion and a light receiving portion are arranged side by side on a substrate and a transparent board is disposed in front of the light emitting portion and the light receiving portion. When infrared rays emitted from the light emitting portion pass through the transparent board to the front and are reflected off a target object in front of the transparent board, the reflected light is received by the light receiving portion. By monitoring the amount of light received by the light receiving portion, it is determined whether or not there is a target object in front of the sensor.

In the optical sensor described in Japanese Unexamined Patent Application Publication No. 2001-194232, the light receiving portion receives not only the light reflected off the target object but natural light such as sunlight. Thus, when strong natural light is supplied to the sensor of an electronic device, the accuracy with which the sensor detects a target object decreases.

In view of the circumstances, the following configuration is conceived of in order to compensate for the decrease in detection accuracy due to the natural light. Specifically, in the configuration, a light-guiding member made of a light-transmissive material is disposed in front of the light emitting portion and the light receiving portion so as to guide some infrared rays emitted forward from a detection-light-emitting portion, so that those rays are received by the light receiving portion. Further, the light-guiding member guides infrared rays emitted from a monitor-light-emitting device to cause the light receiving portion to receive the light. The amount of light received by the light receiving portion after being emitted from the detection-light-emitting portion and the amount of light received by the light receiving portion after being emitted from the monitor-light-emitting device are compared to each other so that the decrease in detection accuracy is compensated for.

The optical sensor having the above configuration, however, needs to be adjusted such that the amount of light received by the light receiving portion after being emitted from the detection-light-emitting portion is balanced with the amount of light received by the light receiving portion after being emitted from the monitor-light-emitting device. Such an optical sensor is difficult to design. Particularly, if the optical sensor includes multiple detection-light-emitting portions, balancing of the amounts of received light becomes more difficult.

SUMMARY

Embodiments of the present invention have been made to solve the existing problems, and an object of the present invention is to provide an optical sensor employing a configuration in which a light receiving device receives light emitted from a light-emitting device and light reflected off a target object, the optical sensor being capable of receiving detection light and monitor light while achieving the right balance between the amounts of received detection light and received monitor light.

An aspect of the present invention is an optical sensor including a monitor-light-emitting device that emits light at a first timing; a detection-light-emitting device that emits light at a second timing different from the first timing; a light receiving device arranged side by side with the monitor-light-emitting device and the detection-light-emitting device; and a light-guiding member disposed in front of the detection-light-emitting device and the light receiving device. In the sensor, reference light of the light emitted from the detection-light-emitting device and penetrating into the light-guiding member propagates through the light-guiding member and is received by the light receiving device, and reflected detection light of the light emitted from the detection-light-emitting device, transmitted through the light-guiding member, and reflected off a target object located in front of the optical sensor, is guided by the light-guiding member and received by the light receiving device. A visor portion is disposed between the monitor-light-emitting device and the light-guiding member, and monitor light of the light emitted from the monitor-light-emitting device is capable of being directly incident on the light receiving device. Whether the target object is present or not is determined on the basis of an output of light received by the light receiving device when the detection-light-emitting device emits light and an output of light received by the light receiving device when the monitor-light-emitting device emits light.

In the optical sensor according to the above aspect of the present invention, the monitor light emitted from the monitor-light-emitting device is directly received by the light receiving device. Thus, adjusting of the amount of received monitor light is facilitated, and consequently, balancing of the amounts of received monitor light and received reference light is facilitated.

Preferably, a portion of the light-guiding member is formed into a condenser, which has a light-emerging surface and a slope, the light-emerging surface facing the light receiving device, the slope extending from the light-emerging surface such that the condenser is widened in a lateral direction, in which the monitor-light-emitting device and the detection-light-emitting device are arranged, toward the front. Preferably, the monitor-light-emitting device faces the slope.

Providing a condenser at a portion of the light-guiding member in the above described manner allows only a small amount of the monitor light to be incident on the light-guiding member from the monitor-light-emitting device and facilitates direct application of the monitor light to the light receiving device. On the other hand, the reference light propagating through the light-guiding member and the reflected detection light penetrating into the light-guiding member are efficiently guided to the light receiving device.

Preferably, the light-guiding member includes a detection-light transmitting portion, which faces the detection-light-emitting device, and a light-guiding portion, which is positioned between the detection-light transmitting portion and the slope. Preferably, the thickness of the light-guiding portion in a front-rear direction is smaller than the thickness of the detection-light transmitting portion in the front-rear direction.

In the above configuration, light emitted from the detection-light-emitting device is made more likely to be transmitted to the front through the detection-light transmitting portion, and the reference light emitted from the detection-light-emitting device and penetrating into the light-guiding member is guided to the light receiving device without being attenuated in the light-guiding portion by a large amount. Consequently, regarding the light emitted from the detection-light-emitting device, adjusting of the amount of reference light propagating through the light-guiding member and the amount of light passing through to the front is facilitated.

Preferably, the light-guiding portion and the detection-light transmitting portion are molded by different part-molding molds.

The use of the part-molding molds facilitates fixing of the thicknesses of the light-guiding portion and the detection-light transmitting portion in the front-rear direction in accordance with usage conditions or various other conditions.

Preferably, the detection-light-emitting device includes a first detection-light-emitting device and a second detection-light-emitting device. Preferably, the second detection-light-emitting device is disposed farther from the light receiving device than the first detection-light-emitting device is. Preferably, a guide slope is formed in a portion of the light-guiding member between the first detection-light-emitting device and the second detection-light-emitting device, the guide slope being inclined in such a direction as to become gradually separated from the second detection-light-emitting device toward the rear.

The use of multiple detection-light-emitting devices as in the above case can reduce the difference between the amounts of second reference light and first reference light that are supplied into the light-guiding member, the second reference light being emitted from the second detection-light-emitting device positioned away from the light receiving device, the first reference light being emitted from the first detection-light-emitting device positioned near the light receiving device.

In the optical sensor according to the aspect of the present invention, it is easy to balance the following amounts, that is, the amount of monitor light received by the light receiving device after being emitted from the monitor-light-emitting device and directly transmitted to the light receiving device; the amount of reference light received by the light receiving device after being emitted from the detection-light-emitting device, guided through the light-guiding member, and supplied to the light receiving device; and the amount of reflected detection light received by the light receiving device after being emitted by the detection-light-emitting device and reflected off a target object. Thus, the detecting operation can be performed highly accurately.

DETAILED DESCRIPTION

FIG. 1illustrates an in-vehicle display device1as an example of an electronic device. The in-vehicle display device1is used as a car navigation system, a driving information display device, or an interior-condition display device.

The in-vehicle display device1includes a housing and a panel3in front of the housing2. In the panel3, a display window4is open, and a display panel screen5such as a liquid-crystal display panel appears through the display window4. Push-button controllers6aand6band rotary controllers7aand7bare attached to the front surface of the panel3.

An optical sensor10is disposed on the panel3below the display window4. The optical sensor10emits infrared rays to the front of the panel3(in the Y1direction). When a human hand or another object approaches the front of the panel3, some rays are reflected off the hand or the like and the reflected rays are detected by the optical sensor10. A controller (not illustrated) disposed inside the housing2performs display controls, such as switching the content displayed on the screen5, when light reflected off the human hand or the like is detected.

In the cross sectional view of the optical sensor10illustrated inFIG. 2, the Y1direction denotes the direction to the front of the panel3, and the Y2direction denotes the direction to the rear of the panel3, that is the direction toward the housing2.

The optical sensor10includes a casing11. The casing11has a rectangular tube shape that is hollow throughout and open to the front (in the Y1direction) and to the rear (in the Y2direction). The longitudinal direction of the casing11is in the X direction.

As illustrated inFIG. 2, the casing11having a rectangular tube shape contains a first right partition wall12a,a first left partition wall12b,a second right partition wall13a,and a second left partition wall13b,which are integrally formed.

The first right partition wall12aand the first left partition wall12bdefine a light-receiving space14. The first right partition wall12aand the second right partition wall13adefine a first right light-emitting space15a,and the first left partition wall12band the second left partition wall13bdefine a first left light-emitting space15b.The second right partition wall13aand a right end wall11aof the casing11define a second right light-emitting space16a,and the second left partition wall13band a left end wall11bof the casing11define a second left light-emitting space16b.

As illustrated inFIG. 2andFIG. 3, the casing11contains a visor portion17, which is continuous with the first right partition wall12aand extends inward, toward the light-receiving space14. On the inner surface of the visor portion17, a slope17athat is inclined rightward in the Y2direction is formed. The casing11is made of a plastic material having any color such as black or dark green. The inner surface of the visor portion17and the slope17aare flat surfaces and thus easily reflect light. A small wall18is integrally formed on the left side of the first right partition wall12a,and a light passage19is open between the visor portion17and the small wall18.

As illustrated inFIG. 2, a board21is attached to the rear side (Y2side) of the casing11. The board21is tightly attached to the first right partition wall12a,the first left partition wall12b,the second right partition wall13a, the second left partition wall13b,and the right and left end walls11aand11bof the casing11. The board21covers the rear side (Y2side) of the light-receiving space14, the first right light-emitting space15a,the first left light-emitting space15b,the second right light-emitting space16a,and the second left light-emitting space16b.

A light receiving device22is mounted in a center area of a front surface of the board21facing in the Y1direction. The light receiving device22is a photodiode or a phototransistor, for example, and is disposed in a center area of the light-receiving space14. A monitor-light-emitting device23is disposed on the front surface of the board21. The monitor-light-emitting device23is positioned inside a small space defined by the first right partition wall12a,the visor portion17, and the small wall18.

A first right detection-light-emitting device24aand a second right detection-light-emitting device25aare mounted on the front surface of the board21on the right side ofFIG. 2. The first right detection-light-emitting device24ais disposed in the first right light-emitting space15aand the second right detection-light-emitting device25ais disposed in the second right light-emitting space16a.A first left detection-light-emitting device24band a second left detection-light-emitting device25bare mounted on the front surface of the board21on the left side ofFIG. 2. The first left detection-light-emitting device24bis disposed in the first left light-emitting space15band the second left detection-light-emitting device25bis disposed in the second left light-emitting space16b.

The monitor-light-emitting device23, the first right detection-light-emitting device24a, the second right detection-light-emitting device25a, the first left detection-light-emitting device24b,and the second left detection-light-emitting device25bare infrared-light-emitting diodes.

As illustrated inFIG. 2, a light-guiding member30is attached to the front side (Y1side) of the casing11. Preferably, the light-guiding member30is made of a transparent or semi-transparent material having a total luminous transmittance of 70% or higher, such as an acrylic resin.

As illustrated inFIG. 2andFIG. 3, a condenser31is formed in a center area of the light-guiding member30. The condenser31protrudes rearward (in the Y2direction) and is positioned in the light-receiving space14. A Y2-side end face of the condenser31is a flat light-emerging surface31aand faces the light receiving device22in close proximity to the light receiving device22. The light-emerging surface31amay be a convex lens surface that causes the emerging light to converge on the light receiving device22.

The condenser31has a right slope32aand a left slope32b.The right slope32ais continuous with the right end of the light-emerging surface31aand extends rightward ofFIGS. 2 and 3toward the front (in the Y1direction). The left slope32bis continuous with the left end of the light-emerging surface31aand extends leftward ofFIGS. 2 and 3toward the front (in the Y1direction).

As illustrated inFIG. 2andFIG. 3, the light-guiding member30includes a right light-guiding portion33a,which extends rightward from the end of the right slope32a.The right light-guiding portion33ahas a uniform thickness T1in the front-rear direction. A step portion34ais formed in a right end portion of the right light-guiding portion33a,and a stopper surface35ais formed on the rear-side (the Y2side) end of the step portion34a.A first right detection-light transmitting portion36ais formed on the right side of the stopper surface35a.A stopper surface37ais formed on the right side of the first right detection-light transmitting portion36a.A second right detection-light transmitting portion38ais formed on the right side of the stopper surface37a.

The first right detection-light transmitting portion36ahas a uniform thickness T2in the front-rear direction. The second right detection-light transmitting portion38ahas a uniform thickness T3in the front-rear direction. The thickness T2and the thickness T3are larger than the thickness T1of the right light-guiding portion33a.The thickness T2of the first right detection-light transmitting portion36aand the thickness T3of the second right detection-light transmitting portion38amay be the same or the thickness T3may be larger than the thickness T2.

As illustrated inFIG. 2, a left light-guiding portion33b,a step portion34b,a stopper surface35b,a first left detection-light transmitting portion36b,a stopper surface37b,and a second left detection-light transmitting portion38bare formed on the left side of the condenser31. The light-guiding member30has a bilaterally symmetric structure.

As illustrated inFIG. 3, the stopper surface35aabuts against the top end of the first right partition wall12aand the stopper surface37aabuts against the top end of the second right partition wall13a.As illustrated inFIG. 2, the stopper surface35babuts against the top end of the first left partition wall12band the stopper surface37babuts against the top end of the second left partition wall13b.

In this arrangement, the first right detection-light-emitting device24afaces the first right detection-light transmitting portion36aand the second right detection-light-emitting device25afaces the second right detection-light transmitting portion38a. In addition, the first left detection-light-emitting device24bfaces the first left detection-light transmitting portion36band the second left detection-light-emitting device25bfaces the second left detection-light transmitting portion38b.

As illustrated inFIG. 2andFIG. 3, a protrusion39a, which is a portion of the light-guiding member30protruding toward the rear (in the Y2direction), is formed integrally with the light-guiding member30at a position between the first right detection-light-emitting device24aand the second right detection-light-emitting device25a. The protrusion39ahas a right guide slope39bthat faces the second right detection-light-emitting device25a.The right guide slope39bis inclined so as to become gradually separated from the second right detection-light-emitting device25atoward the rear (in the Y2direction).

As illustrated inFIG. 2, a protrusion39cis also formed integrally with the light-guiding member30at a position between the first left detection-light-emitting device24band the second left detection-light-emitting device25b.The protrusion39chas a left guide slope39dthat faces the second left detection-light-emitting device25b.The right guide slope39bis left-right symmetric to the left guide slope39d.

FIG. 4illustrates a mold set for injection molding used for molding the light-guiding member30. A fixed mold41has a flat face41afacing a cavity. A front surface30aof the light-guiding member30facing to the front (in the Y1direction) is molded with the flat face41aof the fixed mold41so as to be flat. As illustrated inFIG. 4, fixed molds43,44,45, and46face the fixed mold41. The light-emerging surface31aof the condenser31is molded with the fixed mold43. The stopper surface35ais molded with the fixed mold44and the stopper surface37ais molded with the fixed mold45. An end surface of the protrusion39ais molded with the fixed mold46.

A part-molding mold47is placed between the fixed mold43and the fixed mold44. A part-molding mold48is placed between the fixed mold44and the fixed mold45. A part-molding mold49is placed between the fixed mold45and the fixed mold46. A part-molding mold50is placed between the fixed mold46and the fixed mold41.

Changing the shape of the part-molding mold47enables adjustments of the angle of a right slope32aillustrated inFIG. 3and the thickness T1of the right light-guiding portion33a.Changing the shape of the part-molding mold48enables an adjustment of the thickness T2of the first right detection-light transmitting portion36a.Changing the shapes of the part-molding mold49and the part-molding mold50enables an adjustment of the thickness T3of the second right detection-light transmitting portion38a.Changing the shape of the part-molding mold50enables an adjustment of the angle of the right guide slope39b. The left half of the light-guiding member30is also molded in the same manner.

As illustrated inFIG. 2andFIG. 3, the front side of the light-guiding member30is covered by a cover51. The cover51functions as a filter that preferentially allows transmission of infrared rays.

Now, a detecting operation of the optical sensor10will be described.

In the optical sensor10, the first right detection-light-emitting device24a,the second right detection-light-emitting device25a,the first left detection-light-emitting device24b,and the second left detection-light-emitting device25bsequentially emit light at different timings. Immediately after each detection-light-emitting device emits light, the monitor-light-emitting device23emits light. For example, the light emission sequence is as follows: the first right detection-light-emitting device24a,the monitor-light-emitting device23, the first left detection-light-emitting device24b,the monitor-light-emitting device23, the second right detection-light-emitting device25a,the monitor-light-emitting device23, the second left detection-light-emitting device25b,and the monitor-light-emitting device23.

As illustrated inFIG. 3, monitor light emitted from the monitor-light-emitting device23is transmitted to the light-receiving space14through the light passage19defined by the visor portion17and the small wall18. As represented by the optical path i, the majority of the monitor light is directly supplied to and received by the light receiving device22in the light-receiving space14. As represented by the optical path ii, the minority of the monitor light passes through the light passage19and hits the right slope32aof the condenser31, but is less likely to penetrate into the light-guiding member30since the incident angle θ of the monitor light to the right slope32ais less than 90 degrees.

Due to the angle of the slope17aof the visor portion17, the monitor light emitted from the monitor-light-emitting device23negligibly penetrates into the light-guiding member30but easily and directly penetrates into the light receiving device22. Thus, the intensity of the monitor light received by the light receiving device22is easily adjustable by performing operations such as controlling electric currents that are to be supplied to the monitor-light-emitting device23.

As represented by the optical path iii, part of light emitted from the first right detection-light-emitting device24apenetrates into the light-guiding member30, propagates inside the light-guiding member30, emerges from the light-emerging surface31aof the condenser31, and is supplied to the light receiving device22as first reference light. As represented by the optical path iv, the remaining part of light emitted from the first right detection-light-emitting device24apasses through the first right detection-light transmitting portion36aand emerges to the front (in the Y1direction).

As represented by the optical path v, part of light emitted from the second right detection-light-emitting device25apenetrates into the light-guiding member30and is used as second reference light. As represented by the optical path vi, since the right guide slope39bfaces the second right detection-light-emitting device25a,another part of light emitted from the second right detection-light-emitting device25apenetrates into the light-guiding member30from the right guide slope39band is used as second reference light. The second reference light propagates inside the light-guiding member30, emerges from the light-emerging surface31aof the condenser31, and is supplied to the light receiving device22. As represented by the optical path vii, the remaining part of light emitted from the second right detection-light-emitting device25apasses through the second right detection-light transmitting portion38aand emerges to the front (in the Y1direction).

Since the second right detection-light-emitting device25ais positioned farther from the light receiving device22than the first right detection-light-emitting device24ais, the second reference light emitted from the second right detection-light-emitting device25ais more likely to be attenuated inside the light-guiding member30than the first reference light emitted from the first right detection-light-emitting device24a.Despite the attenuation, since the right guide slope39bfaces the second right detection-light-emitting device25a, the amount of second reference light emitted from the second right detection-light-emitting device25aand penetrating into the light-guiding member30is larger than the amount of first reference light emitted from the first right detection-light-emitting device24aand penetrating into the light-guiding member30. By adjusting the amount of emission and the amount of attenuation of the second reference light, the difference between the amount of first reference light received and detected by the light receiving device22and the amount of second reference light received and detected by the light receiving device22can be reduced, or preferably these amounts can be made substantially equal to each other.

Between the condenser31and the first right detection-light transmitting portion36a,a right light-guiding portion33ahaving a small thickness T1in the front-rear direction is disposed. The right light-guiding portion33ahas a small area of cross section. Thus, when the first reference light that has been emitted from the first right detection-light-emitting device24a,which is located closer to the light receiving device22, and has penetrated into the light-guiding member30passes through the optical path viii, the amount of first reference light is limited in the right light-guiding portion33a.By limiting the amount of first reference light, the difference between the amount of first reference light received and detected by the light receiving device22and the amount of second reference light received and detected by the light receiving device22can be further reduced, or these amounts can be made substantially equal to each other.

Thus, it is easy to make the received amounts of three types of light coincide with one another, the three types of light being the monitor light emitted from the monitor-light-emitting device23and received by the light receiving device22, and the first reference light and the second reference light that propagates in the light-guiding member30and is supplied to the light receiving device22.

As represented by the optical paths iv and vii, part of light emitted from the first right detection-light-emitting device24aand the second right detection-light-emitting device25ais transmitted to the front (in the Y1direction) through the light-guiding member30and the cover51. When a hand or the like, which is a target object, approaches the front of the panel3illustrated inFIG. 1, part of the light that has been transmitted through the cover51is reflected off the hand or the like and becomes reflected detection light. The reflected detection light is transmitted through the cover51and is supplied to the front surface30aof the light-guiding member30. The reflected detection light, which has been reflected off the hand, converges on the condenser31from the front surface30asince the condenser31is formed at a center portion of the light-guiding member30and has the right slope32aand a left slope32bthat face each other while being spaced farther apart toward the front (in the Y1direction). The reflected detection light taken into the condenser31is converged by the right slope32aand the left slope32band finally supplied to the light receiving device22. Thus, the light receiving device22can efficiently receive the reflected detection light.

The same detecting operation as described above is performed on the light emitted from the first left detection-light-emitting device24band the second left detection-light-emitting device25b,which are disposed on the left side of the optical sensor10.

FIGS. 5A,5B,6A and6B illustrate a detecting operation performed by the optical sensor10.FIG. 5AandFIG. 6Aillustrate the amount of light received by the light receiving device22when the first right detection-light-emitting device24aemits light.FIG. 5BandFIG. 6Billustrate the amount of light received by the light-receiving device when the monitor-light-emitting device23emits light. Since the same operation is performed when the detection-light-emitting devices24b,25a,and25bemit light, the case where the first right detection-light-emitting device24aemits light is only described below.

FIGS. 5A and 5Bshow detection outputs from which the effect of the natural light such as sunlight is excluded. The waveform drawn with the solid line inFIG. 5Arepresents the light amount61received by the light receiving device22when the first right detection-light-emitting device24aemits light in the state where a human hand or another object is not present in front of the optical sensor10. The waveform drawn with the solid line inFIG. 5Brepresents the light amount62received by the light receiving device22when the monitor-light-emitting device23emits light. The controller compares the light amount61, received by the light receiving device22when the first right detection-light-emitting device24aemits light, and the light amount62, received by the light receiving device22when the monitor-light-emitting device23emits light immediately after the first right detection-light-emitting device24aemits light. Then, a current required to match the received light amount62with the received light amount61is supplied to the monitor-light-emitting device23.

In the optical sensor10, the intensity of light emission of each light-emitting device is adjusted such that the light amount61received by the light receiving device22when either one of the detection-light-emitting devices emits light coincides with the light amount62received by the light receiving device22when the monitor-light-emitting device23emits light immediately after the detection-light-emitting device emits light. For this reason, when a hand or another object is not present in front of the optical sensor10, the received light amount61and the received light amount62coincide with each other and thus the current supplied to the monitor-light-emitting device23is not changed.

When a human hand or the like approaches the front of the optical sensor10, the light that has been emitted from the first right detection-light-emitting device24aand has passed through the light-guiding member30is reflected off the hand or the like and is received by the light receiving device22. Thus, the light amount63received by the light receiving device22when the first right detection-light-emitting device24aemits light is increased further than the light amount61by61, as indicated by the broken lines inFIG. 5A. In this case, the current flowing through the monitor-light-emitting device23is increased such that the light amount64received by the light receiving device22when the monitor-light-emitting device23emits light immediately after the first right detection-light-emitting device24aemits light coincides with the light amount63. The controller recognizes an approach of a human hand or the like to the front of the optical sensor10by monitoring the amount of an increase in the current flowing through the monitor-light-emitting device23.

FIGS. 6A and 6Bshow detection outputs in which the effect of the natural light such as sunlight is included. The waveform drawn with the solid line inFIG. 6Arepresents the light amount65received by the light receiving device22when the first right detection-light-emitting device24aemits light in the state where a human hand or another object is not present in front of the optical sensor10. Since the natural light penetrates into the light-guiding member30, the light receiving device22receives not only the first reference light supplied from the first right detection-light-emitting device24a,but the natural light. Thus, the received light amount65is larger than the received light amount61illustrated inFIG. 5Aby δ2corresponding to the amount of natural light.

As illustrated inFIG. 6B, when the monitor-light-emitting device23emits light, the light receiving device22receives not only the monitor light but the natural light, and thus the received light amount66is increased. Here, the received amount of natural light remains substantially the same as in the case illustrated inFIG. 6A. Thus, the amount62of an increase in the received light amount66is the same as the amount δ2of an increase in the received light amount65illustrated inFIG. 6A. Consequently, the current supplied to the monitor-light-emitting device23is not increased, and the controller determines that a hand or the like is not present in front of the optical sensor10.

As illustrated inFIG. 6A, when a hand or the like approaches the front of the optical sensor10, the light amount67received by the light receiving device22when the first right detection-light-emitting device24aemits light is increased further than the light amount65, as indicated by the broken lines. In this case, as illustrated inFIG. 6B, the current supplied to the monitor-light-emitting device23is increased such that the light amount68received by the light receiving device22when the monitor-light-emitting device23emits light coincides with the received light amount67. The controller determines that a human hand or the like approaches the front of the optical sensor10by using an increase in the current supplied to the monitor-light-emitting device23.

Although preferred embodiments have been described in detail, the present invention is not limited to these specific embodiments. Rather, various modifications and changes can be made without departing from the scope of the present invention as described in the accompanying claims. Accordingly, all such modifications are intended to be included within the scope of this invention as defined in the following claims.