Patent Publication Number: US-6212697-B1

Title: Automatic flusher with bi-modal sensitivity pattern

Description:
BACKGROUND OF THE INVENTION 
     The present invention concerns automatic flush systems and is directed particularly to sensor apparatus that they employ. 
     Technological advances in recent years have made the use of automatic flushers quite popular in public facilities. Although they have been employed for both toilets and urinals, their use for urinals has been much more widely accepted than for toilets, because automatic urinal flush systems have tended to be more reliable than automatic toilet flush systems. 
     One reason why toilet flushers tend to be less reliable is that toilets tend to be placed in stalls. This requires the object detectors on whose operation automatic flushers are based to distinguish between actual users and stall surfaces. Although ways of making this distinction exist, they tend to be relatively complicated, costly, and inconvenient. 
     SUMMARY OF THE INVENTION 
     We have found that the difficulty presented by such enclosures can be greatly reduced by employing a sensor system that in plan view has a bimodal sensitivity pattern. Specifically, the sensor is significantly less sensitive in a central region, where the sensor radiation&#39;s angle of incidence on a stall door is more nearly normal, than immediately to that region&#39;s left and right, where it is less so. This tends to reduce responsiveness to enclosure surfaces in comparison with user surfaces. The reason for this result appears to be that surfaces such as those of stall doors tend to reflect more specularly than those of the desired target, namely, the user. This means that the stall door reflects less light back to the source than a user does when the incident light forms a large angle with the surface normal. This feature is particularly beneficial if the sensor&#39;s sensitivity-pattern maxima that flank the central region are spaced apart in front of the toilet bowl by an amount that matches the spacing of a typical user&#39;s legs, which are the sensor&#39;s typical targets. 
     Another aspect of the present invention takes further advantage of the tendency of enclosure surfaces to be more specular than user surfaces. According to this aspect of the invention, the sensor system&#39;s sensitivity pattern is directed at a downward angle rather than horizontally. This, too, tends to result in angles of incidence that differ significantly from perpendicular and therefore produce relatively little retroreflection from surfaces that reflect somewhat specularly. 
     A further reason for this aspect&#39;s advantage seems to be that it reduces the sensor&#39;s sensitivity to motions of a user seated on the toilet. Since the sensor pattern is directed at a downward angle, the sensor tends to respond less to the user&#39;s upper back, which tends to move most, and more to the user&#39;s lower back, which tends not to move as much. 
     We have found that employing such directional sensitivity patterns greatly reduces the difficulties of implementing automatic flush systems in enclosed environments. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention description below refers to the accompanying drawings, of which: 
     FIG. 1 is a side view of an automatic-toilet system that embodies the present invention&#39;s teachings; 
     FIG. 2 is a plan view of the automatic-toilet system; 
     FIG. 3 is a side elevation of the lenses employed in the sensor system that the automatic-toilet system employs; 
     FIG. 4 is a front elevation of the sensor system&#39;s transmitter lens; 
     FIG. 5 is cross-section taken at line  5 — 5  of FIG. 4 with curvatures exaggerated for the sake of explanation; and 
     FIG. 6 is cross-section taken at line  6 — 6  of FIG.  4 . 
    
    
     DETAILED DESCRIPTION OF AN ILLUSTRATIVE EMBODIMENT 
     An automatic toilet system  10  includes a control circuit  12  that responds to a sensor system  14  in determining when to trigger a solenoid-operated flusher  16 . The particular control strategy that circuit  12  employs is not relevant to the invention, but it typically involves assuming an armed state when a user is detected and then, from the armed state, triggering a flush when it no longer detects a user&#39;s presence. 
     To detect a user, the sensor emits some type of wave disturbance, typically an infrared beam, that will be reflected by a user back to the sensor. The problem presented by enclosure-system surfaces, such as that of a stall door  18 , is that they, too, can reflect radiation and thereby confuse the control circuit  12 . 
     The illustrated embodiment reduces such confusion by employing two aspects of the present invention. FIG. 1 illustrates one of those aspects. It shows the sensor&#39;s receiver tansmitter radiation pattern  20  as well as its transmitter pattern  22 . The latter pattern gives the relative values of radiant flux density, i.e., radiant power per unit area, as a function of angle. The former pattern gives the radiation detector&#39;s response, in output current per unit flux density, as a function of angle. Those patterns&#39; product is the sensor&#39;s overall sensitivity pattern  24 . Since the sensor and receiver positions do not exactly coincide, the pattern&#39;s shape depends somewhat on distance from the sensor. But plot  24  reasonably approximates the pattern at most locations beyond the front of the toilet bowl  26 . 
     As FIG. 1 indicates, the sensor transmits relatively little radiation horizontally, i.e., toward objects at the same height as the sensor  14 . Its sensitivity to radiation reflected from such objects is similarly low. So it is not as sensitive to objects located at that height as it is to objects lower down. (As those skilled in the art will recognize, of course, a downward tilt in the overall sensitivity pattern can be achieved by directing only one or the other pattern downward, but having both incline downward is preferable.) 
     An advantage of this downward direction results from the fact that the reflection from stall doors tends to be relatively specular. That is, the angle of reflection of a very large percentage of radiation that a stall door receives tends to be nearly equal to its angle of incidence. Light ray  28 , for instance, tends to be reflected in a relatively narrow plume centered on ray  30 . This means that very little of the sensor radiation that strikes the stall door  18  is reflected back to the sensor. In a more-conventional system, on the other hand, a large percentage of the light would shine at the stall door  18  in directions not far from the one that ray  32  illustrates. The plume that would result from such a ray would be centered on the sensor, making it relatively sensitive to the stall door  18 &#39;s presence. 
     Because the radiation pattern is directed downward, the radiation will tend to strike the user at angles similar to those at which it strikes the stall door  18 . But users&#39; clothes tend to reflect more diffusely, i.e., less specularly, than a stall door or other enclosure wall. So the reflection plume will tend to be wider, making the sensor more sensitive to users than to, say, a stall door. 
     Much of the advantage of this aspect of the invention can be obtained through sensitivity patterns that differ markedly from the one that FIG. 1 depicts. Preferably, though, less than 12% of its sensitivity pattern should extend above the horizontal. That is, if the pattern is integrated through all angles in a vertical plane, the portion of the result that upward angles produce should be less than 12%. In most embodiments, the center of the pattern will form an angle of at least 5 degrees with the horizontal. 
     The sensor system&#39;s downward tilt has another advantage. Criteria in many control strategies involve target-position changes in some fashion. It turns out that motions of a user&#39;s upper back tend to be less informative for this purpose than those of his lower back. By using a downward inclination, the sensor can make the system more responsive to the latter than to the former. To maximize this effect, we arrange the sensor system so that the percentage of the pattern between 3 inches and 12 inches above the toilet seat is at least 1.5 times the percentage of the pattern between 12 inches and 21 inches above the toilet seat in a region somewhere in a range between 2 inches and 15 inches behind front of the toilet. 
     Further reliability results if the sensor&#39;s sensitivity to the toilet itself is suppressed. For this reason, we prefer that less than 20% of the sensitivity pattern extend below the angle that intersects the toilet edge  34 . 
     As FIG. 2 illustrates, the present invention takes advantage of the above mentioned tendency of enclosure surfaces to reflect more specularly than users. Plot  40  can be thought of as a plane view of the sensitivity pattern. More precisely, it is the component of the pattern in a plane normal to a vertical plane and containing in a line such as the one that FIG.  1 &#39;s ray  28  represents. According to the invention, the sensitivity pattern has a local minimum  42  in a central region of the pattern, i.e., in a region of the pattern for which the percentage of the pattern to its left equals the percentage of the pattern to the right. The pattern exhibits maxima  46  and  48  to the left and the right of the central portion. Both maxima have values that are greater than any value within the central region. 
     Because of enclosure surfaces&#39; tendency to reflect in a relatively specular manner, plumes resulting from incident rays  50  and  52 —and therefore centered on rays  54  and  56 , respectively—tend to be relatively narrow. That is, most resultant reflection is directed away from the sensor  14 . In contrast, although the reflection from ray  58  tends to be centered in a direction that leads toward sensor  14 , the amount of radiation transmitted in directions near to ray  58  is small, and the sensor&#39;s sensitivity to rays that reach it from that direction is low. Moreover, FIG. 2 shows the directions only in plane view, and, as FIG. 1 shows, even the rays that appear to be directed back toward sensor  14  actually tend to be directed downward, away from it. 
     The particular relationship of the central minimum to the maxima on either side is not critical to achieving the present invention&#39;s advantages. Of course, it is desirable to suppress the central part of the sensitivity pattern to as a great a degree as possible. As the drawing indicates, though, sensitivity in that region need not be suppressed entirely. Still, the central minimum should be no greater than 80% of the maximum outside the central region. 
     Additionally, there is no particularly critical angular offset that is required between the two maxima. The angle will depend greatly on the particular sensor placement and other details of the individual installation. But it is best for the maxima to be between 3 and 14 inches apart somewhere within 30 inches in front of the toilet bowl. This corresponds to a typical distance between the center points of a user&#39;s legs, which are often the sensor&#39;s primary targets. 
     Those skilled in optics can readily produce patterns that have the salient features emphasized above. Various systems of lenses, reflectors, baffles, etc., can be employed to achieve such a result and implement the present invention&#39;s teachings. FIGS. 3-6 depict one such system. 
     FIG. 3 depicts the illustrated embodiment&#39;s sensor arrangement. A source  60  in the form of, say, an infrared-light-emitting-diode is disposed behind a lens  62 . FIG. 4 is a front view of lens  62 . In that view, the optically useful part of the lens is generally circular, being centered within a flange portion  64  employed for mounting the lens in a housing that FIGS. 3 and 4 omit. That central circular portion is approximately half an inch in diameter. FIG. 3 shows that lens  62  forms rear surface  66 . That surface is spherically convex, having a 0.63-inch radius of curvature and a peripheral edge that defines a plane normal to a line that extends downward to the right at an angle of 18.6 degrees with the horizontal. The lens&#39;s front, exit surface  68  is also spherically convex, having a 2.0-inch radius of curvature and a peripheral edge that defines a plane normal to a line that extends downward to the left at an angle of 9.8 degrees with the horizontal. With the source positioned as shown, this results in a radiation pattern similar to the one that FIG.  1 &#39;s plot  22  depicts. 
     With one exception to be described below, the shapes of a receiver lens  70 &#39;s left and right faces  72  and  74  are the same as those of the transmitter lens  62 &#39;s corresponding surfaces  66  and  68 . They collect light received from the target and tend to direct it toward a radiation detector  76 , such as a photodiode. This arrangement is responsible for FIG.  1 &#39;s receiver pattern  20 . 
     Although the illustrated positions of the source  60  and detector  76  with respect to their respective lenses contribute to determining the sensor pattern, it is sometimes desirable to locate those elements and the other electronics remotely from the lenses&#39; somewhat hostile environment. In such cases, it may be preferable to produce similar patterns by running fiber-optic cables from the lens positions to a remote source and detector. 
     As FIG. 4 shows, the illustrated embodiment&#39;s lens  62  differs from lens  70  in that the transmitter lens  62 &#39;s surface  68  includes a central groove  78 , which is responsible for the bimodal pattern that FIG. 2 depicts. Groove  78 &#39;s surface is concave, as FIG. 5 illustrates by exaggerated surface curvatures. In FIG. 5, surface  68 &#39;s curvature is detectable, as is that of groove  78 . Surface  68 &#39;s curvature is not as detectable in FIG. 6, since FIG. 6 does not exaggerate the curvatures. As was mentioned above, though, surface  68 &#39;s curvature is spherical, so it actually has the same curvature in both cross sections. That curvature in the FIG. 6 view makes the surface groove  78 &#39;s surface actually toroidal, although it appears cylindrical in FIGS. 5 and 6. 
     We have found that directing the sensor pattern downward and making it bimodal can markedly increase the reliability of a simple sensor system employed inside an enclosure. The present invention therefore constitutes a significant advance in the art.