Abstract:
A reflection-type optical sensor is provided wherein misjudgment is prevented in detecting the existence of an object and determining whether a distance to the object is large or small. A housing is molded from white polycarbonate resin and has a light-projecting portion and a light-receiving portion. A light-projecting lens and a light-emitting device are mounted in a light-projecting chamber formed in the light-projecting portion. A light-receiving lens and a light-receiving device are mounted in a light-receiving chamber formed in the light-receiving portion. Those of the wall surfaces of the light-projecting chamber and the light-receiving chamber which are illuminated with light are light reflection-promoting surfaces that promote the reflection of light. The light reflection-promoting surfaces can be smooth surfaces, surfaces painted in white, inner surfaces of auxiliary members fabricated as separate parts from aluminum, or the like.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to an optical sensor and, more particularly, to a reflection-type optical sensor having internal light reflection-promoting surfaces to provide improved detection capabilities. 
     BACKGROUND DISCUSSION 
     As shown in FIGS.  7 ( a ) and  7 ( b ), a reflection-type optical sensor has been used as a sitting sensor for a toilet seat device A that can function also as a bidet. The optical sensor detects whether or not a person a is seated on the toilet seat b. The sitting sensor d is mounted to a fixture c to which the toilet seat b is mounted. The sitting sensor d has a light-emitting device such as an infrared diode or the like (not shown) that emits light toward the seated person a via a light-projecting lens. Light reflected by the seated person a is received by a light-receiving device such as a single position-sensitive device (PSD) via a light-receiving lens spaced from the light-emitting device by a given distance. Where the level of light received by the light-receiving device is smaller than a predetermined value, the sensor judges that no one is seated. Where the received light level exceeds the predetermined value, the sensor judges that a person is seated. 
     Where the result of the decision is that no person is seated, the device is controlled so that no water is ejected from a water nozzle even if a nozzle switch is depressed. Normally, the sitting sensor d is accommodated and held in a housing or holder (not shown). The holder is typically made of a dark synthetic resin such as a black-colored resin. The wall surface of the chamber through which passes light projected by the light-emitting device and light received by the light-receiving device pass is embossed. A cover e is swingably connected to the fixture c. 
     In the above-described prior art sitting sensor, a part of the light projected by the light-emitting device is absorbed into the holder and the amount of projected light decreases due to the color of the holder, the material of the holder, or the surface treatment of the holder wall surface. If the object (person a) to be detected is wearing clothing of low reflectivity, such as black-colored clothing, a part of the light is absorbed by the clothing due to its color. Therefore, a sufficient amount of reflected light cannot always be obtained. The reflected light is also absorbed by the holder, resulting in additional attenuation. Further attenuation is caused by the embossing of the chamber wall surface. As a result, adequate light may not reach the light-receiving device. Hence, detection is not properly performed. In this case, the result of the decision may be that no human is seated. That is, an erroneous decision occurs. Particularly in cases where the object (person a) to be detected is very close to the sensor, if reflection occurs at a short distance and the beam of the reflected light blurs, the aforementioned problem becomes even more conspicuous. This makes it impossible to detect a person in a seated state, which leads to an erroneous decision. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing shortcomings, an object of the present invention is to provide a reflection-type sensor with improved detection capabilities. 
     To achieve the foregoing object, the present invention provides a reflection-type optical sensor comprising a light-projecting portion and a light-receiving portion formed in a holder, a light-projecting lens and a light-emitting device disposed in a light-projecting chamber formed in the light-projecting portion, and a light-receiving lens and a light-receiving device disposed in a light-receiving chamber formed in the light-receiving portion. The light-projecting chamber and the light-receiving chamber have wall surfaces that receive incident light and are light reflection-promoting surfaces for promoting the reflection of light. By providing light reflection-promoting surfaces, absorption of light projected by the light-emitting device into the holder and absorption of the reflected light into the holder is prevented; whereas attenuation would otherwise take place. Reflection of light incident on the reflection-promoting wall surface is promoted. This assures that light received by the light-receiving device is maximized. Hence, an erroneous decision is prevented. 
     Preferably, the above-described light reflection-promoting surfaces are formed as inner surfaces of the holder, and may comprise painted inner surfaces of the holder. These inner surfaces of the holder may also comprise inner surfaces of auxiliary members inserted in the holder. 
     The aforementioned light-receiving device is preferably a split type that makes a decision as to whether the object is remote or near, based on the position at which light is received and the amount of received light. This prevents an erroneous decision where the object is at a rather short distance. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view illustrating one embodiment of a reflection-type optical sensor according to the present invention; 
     FIG. 2 is a plan view illustrating light reflection at a very short distance in the reflection-type optical sensor; 
     FIG.  3 ( a ) is a reduced plan view illustrating reflection in a case in which an object to be detected is located at a reference position; 
     FIG.  3 ( b ) is a reduced plan view illustrating reflection in a case in which an object to be detected is located remotely; 
     FIG.  3 ( c ) is a reduced plan view illustrating reflection in a case in which an object to be detected is located nearby; 
     FIG. 4 is a block diagram illustrating the structure of the light-receiving apparatus for making a decision as to whether the distance to an object is large or small; 
     FIG. 5 is a perspective view illustrating a reflection-type optical sensor in a second embodiment of the present invention; 
     FIG. 6 is a perspective view illustrating a reflection-type optical sensor in a third embodiment of the present invention; and 
     FIGS.  7 ( a ) and  7 ( b ) are a plan view and a side elevation, respectively, illustrating a case in which a reflection-type optical sensor is used in combination with a toilet seat. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Various embodiments of the present invention are described with reference to the drawings. 
     Referring to FIGS. 1 and 2, a holder  1  is made of a white synthetic resin such as polycarbonate resin and has a light-projecting portion  11  and a light-receiving portion  12 . A light-projecting chamber  11   a  and a light-receiving chamber  12   a  that form light passages are formed inside the light-projecting portion  11  and the light-receiving portion  12 , respectively. A light-emitting device  2  such as an infrared diode is disposed at the rear end of the inside of the light-projecting chamber  11   a . A light-projecting lens  3  is disposed at the front end of the light-projecting chamber  11   a . A light-receiving lens  4  is disposed at the front end of the inside of the light-receiving chamber  12   a . A light-receiving device  5  is disposed at the rear end of the light-receiving chamber  12   a . The light-emitting device  2  and the light-receiving device  5  are connected to circuit boards  6  and  7 , respectively. The holder  1  is mounted to a mounting board  10 . 
     The wall surfaces of the light-projecting chamber  11   a  and the light-receiving chamber  12   a  which are illuminated with light comprise light reflection-promoting surfaces  11   b  and  12   b , respectively, for promoting the reflection of light. Since the wall surfaces illuminated with light comprise the entire wall surface of the light-projecting chamber  11   a , the entire wall surface thereof comprises the light reflection-promoting surface  11   b . In the light-receiving chamber  12   a , the surface of the wall surface illuminated with light is the light reflection-promoting surface  12   b . In FIG. 2, the left-hand wall surface of the light-receiving chamber  12   a  is the light reflection-promoting surface  12   b.    
     The light reflection-promoting surfaces  11   b  and  12   b  are formed as inner surfaces of the holder  1 . Also, the light reflection-promoting surfaces  11   b  and  12   b  are formed as smooth surfaces. That is, light reflection-promoting surfaces  11   b  and  12   b  promote reflection of light because of surface processing. As shown in FIG. 5, they may be painted white, and light reflection-promoting surfaces  11   c  and  12   c  may be formed as painted surfaces that promote reflection of light. In this case, the number of degrees of freedom of the material and the color of the holder  1  is increased. In FIG. 5, substantially identical locations as their counterparts of FIG. 1 are indicated by the same reference numerals and will not be described below. 
     Because of the provision of the light reflection-promoting surfaces  11   b ,  12   b  ( 11   c ,  12   c ), if an object P to be detected is at a very short distance as shown in FIG. 2, when reflected light transmitted through the light-receiving lens  4  is again reflected off the light reflection-promoting surface  12   b  ( 12   c ), the reflection of light is promoted. Almost no loss of light takes place. This assures that adequate light is received by the light-receiving element  5 A. Consequently, no misjudgment occurs. 
     Preferably, the light-receiving device  5  is a split-type sensor that makes a decision as to whether the object is remote or near based on the position at which light is received and on the amount of received light. In the illustrated example, the light-receiving device is split into two light-receiving elements  5 A and  5 B bonded together along a given division line. This division line is next described. As shown in FIG.  3 ( a ), where an object P 0  to be detected is at a reference distance of L 0  from the light-projecting lens  3 , light emitted by the light-emitting device  2  is reflected by the detected object P. The reflected light passes through the center of the light-receiving lens  4 . The position at which the light is received by the light-receiving device  5  is taken as the division line. One side (the lower side in FIG.  3 ( a )) of this division line is taken as the light-receiving element  5 A, while the other side (the upper side of FIG.  3 ( a )) is taken as the light-receiving element  5 B. This division line is at a distance of q from the axis passing through the center of the light-receiving lens  4 . 
     FIG.  3 ( b ) shows a case in which an object P 1  to be detected is at a great distance of L 1 , greater than the reference distance L 0 , from the light-projecting lens  3 . In this case, light emitted by the light-emitting device  2  is reflected by the detected object P 1 . The reflected light passes through the center of the light-receiving lens  4 . The position at which the light is received by the light-receiving device  5  is at a distance of r from the axis. Since the distance r&lt;distance q, the light is principally received by the light-receiving element  5 B in this case. 
     FIG.  3 ( c ) shows a case in which an object P 2  to be detected is at a short distance of L 2 , shorter than the reference distance L 0 , from the light-projecting lens  3 . In this case, light emitted by the light-emitting device  2  is reflected by the detected object P 2 . The reflected light passes through the center of the light-receiving lens  4 . The position at which the light is received by the light-receiving device  5  is at a distance of s from the axis. Since distance s&gt;distance q, the light is principally received by the light-receiving element  5 A in this case. In the case of short distances, the reflected light strikes the light reflection-promoting surface  12   b  of the light-receiving chamber  12   a  and is reflected as shown in FIG.  2 . The reflected light is received by the light-receiving element  5 A. Since the reflection of the reflected light is promoted by the light reflection-promoting surface  12   b , the reflected light is not attenuated as in the prior art technique. A sufficient amount of light is received reliably by the light-receiving element  5 A. 
     FIG. 4 is a block diagram showing a structure of a circuit for making a decision as to whether an object is remote or near. The circuit is formed on circuit boards  6  and  7 . A timing signal-generating means  20  such as a clock generating circuit supplies a clock signal to a light-emitting device driver  21 , an output decision means  22 , and an output latch means  23 . The light-emitting device driver means  21  is a conventional driver circuit responsive to the clock signal produced by the timing signal-generating means  20  to control the emission of light from the light-emitting device  2  at a desired timing. The amount of light received by light-receiving elements  5 A and  5 B is judged by received light amount decision means  24 A and  24 B, respectively, each of which produces an output voltage based on the magnitude of the currents output by the corresponding light-receiving elements  5 A and  5 B. The outputs of the received light amount decision means  24 A and  24 B is supplied to a magnitude decision means  25  and an output of the received light decision means  24 A is also directly supplied to the output decision means  22 . 
     The magnitude decision means  25  is a conventional circuit, such as an error amplifier or processor used for producing an output which varies depending upon the relative magnitude of the inputs from the received light amount decision means  24 A and  24 B. In the case of FIG.  3 ( b ), for example, the magnitude decision means  25  judges that the amount of light received by the light-receiving element  5 B is greater than the amount of light received by the light-receiving element  5 A based on outputs of the received light amount decision means  24 A and  24 B, so that the output decision means  22  outputs a “remote” signal to the output latch means  23  indicating that the object is remotely located. The output latch means  23  comprises a latch circuit or memory device, where the output signal of the output decision means  22  is latched. 
     In the case of FIG.  3 ( c ), the magnitude decision means  25  judges that the amount of light received by the light-receiving element  5 A is greater than the amount of light received by the light-receiving element  5 B and the output decision means  22  produces a “near” output signal to the output latch means  23 , indicating that the object is located closely. The output latch means  23  latches the near signal. 
     In the case of FIG.  3 ( a ), the magnitude decision means  25  judges that the amount of light received by the light-receiving element  5 A is substantially equal to the amount of light received by the light-receiving element  5 B. In this case, the magnitude decision means  25  produces a near output. The output decision means  22  produces a near output signal to the output latch means  23 , where the signal is latched. 
     In the case of very short distances as shown in FIG. 2, the received light amount decision means  24 A judges whether the amount of received light is in excess of a given level. Therefore, a near output signal is directly supplied to the output decision means  22  without the need to wait for a decision to be made by the magnitude decision means  25 . The output decision means  22  produces a near output signal to the output latch means  23 , where the signal is latched. 
     Where the reflection-type optical sensor is used for a toilet seat, if a remote output signal is latched, it is assumed that no one is seated. If a near output signal is latched, it is assumed that a person is seated. In this manner, if a near output signal is latched, the machine is controlled so that water may be ejected from the nozzle. 
     FIG. 6 shows a further embodiment of the present invention. Light-reflecting cylinders  81  and  82  acting as auxiliary members are inserted into given positions in a light-emitting portion  11  and a light-receiving portion  12  of a holder  1 . Those of the wall surfaces of the light-emitting chamber  11   a  and the light-receiving chamber  12   a  which are illuminated with light are made of separate parts. In FIG. 6, those elements that are substantially identical with their counterparts of FIG. 1 are indicated by the same reference numerals and will not be described below. 
     The light-reflecting cylinders  81  and  82  acting as the auxiliary members may be made of white polycarbonate resin in the same way as the holder  1  described above. In this case, the color of the holder  1  is not limited to white. The light-reflecting cylinders  81  and  82  may be made of white polycarbonate resin, and the other portions may be made of a different color polycarbonate resin. That is, the holder  1  is molded in two colors. Furthermore, the holder  1  may be molded from a non-white polycarbonate resin, and the light-reflecting cylinders  81  and  82  may be made of sheets of aluminum and inserted into the holder  1 . Additionally, the light-reflecting cylinders  81  and  82  may be made of sheets of aluminum, and these may be insert-molded during molding of the holder  1 . 
     As described thus far, in accordance with the present invention, those of the wall surfaces of light-projecting chamber and light-receiving chamber in a holder which are illuminated with light are formed as light reflection-promoting surfaces for promoting the reflection of light. Therefore, attenuation of light emitted by a light-emitting device is suppressed by the light reflection-promoting surface of the light-projecting chamber. Attenuation of light reflected by an object to be detected is suppressed by the light reflection-promoting surface of the light-receiving chamber. Consequently, the light-receiving element receives a sufficient amount of light and erroneous detection can be avoided.