Automatic flusher with bi-modal sensitivity pattern

In an automated flush system (10), a control circuit (12) controls a flusher (16) in response to the output of a sensor (14). The vertical sensitivity pattern (24) of the sensor (14) is angled downward. Consequently, radiation that the sensor (14) emits tends to be reflected away from the sensor (14) by relatively specular vertical enclosure surfaces such as that of a stall door (18), while more-diffuse deflectors, such as a user that the sensor (14) is intended to detect, tend to reflect greater percentages of the sensor radiation back to the sensor (14). Similarly reduced sensitivity to enclosure surfaces results from a horizontal sensitivity pattern (40) having a reduced-sensitivity central region. The sensor system can thereby more reliably avoid confusing enclosure surfaces with users, on whose detection the system's automatic flush strategy is based.

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's angle of
 incidence on a stall door is more nearly normal, than immediately to that
 region'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'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's legs, which are the sensor'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'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's advantage seems to be that it reduces
 the sensor'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's upper back, which tends to move most, and more
 to the user'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.

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'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'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's response, in
 output current per unit flux density, as a function of angle. Those
 patterns' product is the sensor's overall sensitivity pattern 24. Since
 the sensor and receiver positions do not exactly coincide, the pattern'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'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' 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'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'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'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'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' 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'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'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's
 legs, which are often the sensor'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's teachings. FIGS. 3-6 depict one such system.
 FIG. 3 depicts the illustrated embodiment'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'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's plot 22
 depicts.
 With one exception to be described below, the shapes of a receiver lens
 70's left and right faces 72 and 74 are the same as those of the
 transmitter lens 62'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'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' 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's lens 62 differs from lens 70
 in that the transmitter lens 62's surface 68 includes a central groove 78,
 which is responsible for the bimodal pattern that FIG. 2 depicts. Groove
 78's surface is concave, as FIG. 5 illustrates by exaggerated surface
 curvatures. In FIG. 5, surface 68's curvature is detectable, as is that of
 groove 78. Surface 68's curvature is not as detectable in FIG. 6, since
 FIG. 6 does not exaggerate the curvatures. As was mentioned above, though,
 surface 68'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'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.