Object sensing apparatus having filter member

An object sensing apparatus comprises a distance measuring device for measuring a distance to an object to be sensed, and a filter member having a surface disposed in confronting and spaced-apart relation to the distance measuring device. The distance measuring device has a light projecting element for projecting light toward the object and a light receiving element for receiving the light projected by the light projecting element and reflected by the object. The filter member is disposed at a preselected angle of inclination with respect to the distance measuring device. When the light projecting element projects light toward the object, light reflected or scattered by the surface of the filter member is directed in a direction away from the light receiving element.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to object sensing apparatuses and, more 
particularly, to an object sensing apparatus for accurately sensing an 
object, such as a human body or the like, approaching an automatic door or 
the like. 
2. Background of the Invention 
Conventionally, there is known a trigonometric distance measuring device in 
which light projected from a light projecting element, such as an 
infrared-ray diode, is projected through a projecting lens, and light 
reflected from an object to be sensed, such as a human body, is received 
by a light receiving element, such as a PSD (position sensitive detector) 
placed behind a light receiving lens at a predetermined distance from the 
light projecting element. 
An object sensing apparatus for a safety apparatus utilizing such 
conventional distance measuring device is also known. The distance 
measuring device is disposed, for example, in the vicinity of an automatic 
door, or is attached to the door itself. By this construction, when the 
object sensing apparatus senses an object, such as a human body, passing 
or approaching the automatic door, the distance measuring device measures 
the distance from the door to the object and an appropriate determination 
is made to open or close the door, or to prevent the door from closing 
when someone is passing through. 
FIG. 7 shows a conventional object sensing apparatus employing a distance 
measuring device a of the type described above. Using this conventional 
apparatus, it is impossible to obtain an accurate distance measurement of 
an object T at a particular distance Z. The distance measuring device a is 
attached to an installation site S in a retracted location thereof at a 
distance c from a front end surface b of the installation site, thereby 
providing a cavity d in front of the distance measuring device a. With 
this structure, there is a necessity that a distance measurement be 
positively made on a left side of the front end surface b or over an 
entire range where there is a possibility that an object or an individual 
may approach. If the distance measuring device a is installed at a 
retracted location as set forth above, dust or the like tends to 
accumulate within the cavity d or in the vicinity of an opening of the 
installation site S. In order to avoid this, and thereby prevent 
malfunction of the object sensing apparatus, a protection cover, filter or 
the like (hereinafter referred to as a filter member e) is provided at a 
location close to the front end surface b of the installation site S. 
A particular example where a filter member is provided in front of a 
distance measuring device as described above is in an auto-focusing 
camera. If the filter member e is instead provided at a distance of 
approximately c from the front end surface b of the installation site S 
and in parallel relation with the distance measuring device a, a light 
beam La projected from a light projecting element f of the distance 
measuring device a passes through a light projecting lens g and is 
projected onto the object T to be sensed. A light component Lb reflected 
by the object T then transmits through a light receiving lens h and is 
received by a light receiving element i of the distance measuring device 
a. In this process, part of the light beam La is scattered by an inner 
surface of the filter member e, causing a light component Lc. Also, a 
light beam Ld transmitted through an end of the light projecting lens g 
similarly causes a reflected light component Le or a scattering light 
component Lf by the inner surface of the filter member e. These light 
components transmit through the light receiving lens h and are received by 
the light receiving element i. This extra reflected or scattering light, 
when received by the light receiving element i, causes error in a 
measurement result obtained by the distance measuring device a, thereby 
rendering accurate distance measurements impossible. 
A detailed explanation of light reflected by an inner surface of the filter 
member e is provided with reference to FIG. 8(a). The light projecting 
element f is usually arranged behind a focal point F of the light 
projecting lens g so that an image thereof is focused at a point distant 
by a predetermined distance from the light projecting lens g. The light 
transmitting through the light projecting lens g involves light beams from 
secondary light sources, such as reflection by a substrate fixed with the 
light projecting element f, a stem, and a surface of a case, in addition 
to direct light from the light projecting element f. If an outer 
peripheral point thereof is taken at P, the point P is focused at Pa due 
to light beams Ld,Lg transmitting through the light projecting lens g. 
With the filter member e arranged in parallel with a plane vertical to the 
light projecting axis of the light projecting element f, a study was 
conducted on the reflecting direction of light from light components Ld,Lg 
which is reflected by the inner surface of the filter member. The study 
was conducted for respective cases where a filter member el was at a 
location closer to the light projecting lens g than a location of the 
filter member e, and where a filter member e2 was at a location more 
distant from the light projecting lens g than a location of the filter 
member e. Scattering light from the reflecting surface was considered 
negligible and excluded from the study. 
The light components resulting from reflection of the light component Ld 
and the light component Lg by the inner surface of the filter members e1, 
e, e2 are Le1,Lh1, Le,Lh and Le2,Lh2, respectively. 
The reflected light components Le1 and Lh1 by the filter member e1 closest 
to the lens did not transmit through the light receiving lens h and did 
not arrive at the light receiving element i, thereby having no effect upon 
a measurement result. 
However, the reflected light components Le and Lh by the filter member e 
both transmitted through the light receiving lens h and arrived at the 
light receiving element i, thereby having an effect upon a measurement 
result. 
The reflected light Le2 by the filter member e2 did not transmit through 
the light receiving lens h and did not arrive at the light receiving 
element i. However, the reflected light Lh2 transmitted through the light 
receiving lens h and arrived at the light receiving element i, thereby 
having an effect upon a measurement result. 
The degree of effect on a measurement result depends upon various 
conditions such as an aperture of the light projecting/receiving lens, the 
base line length (distance between the light projecting and receiving 
lenses), the size of the light projecting element, the location of the 
light projecting element (distance from the lens), the magnitude of 
secondary light, the condition of the reflecting surface of the filter 
member (magnitude and direction of diffusing reflection due to difference 
in smoothness), the size and arrangement of the light receiving element, 
and the location of the reflecting surface of the filter member. However, 
qualitatively, as shown in FIG. 8(b), where the magnitude of an effect on 
a measurement result is taken in a vertical axis and a distance from the 
lens is taken in a horizontal axis, there is almost no effect on a 
measurement result for the filter member e1 located at a distance R from 
the lens. In contrast, the effect on measurement result gradually changes 
as the distance R is exceeded and the lens becomes distant. The effect 
becomes maximum at the location of the filter member e, it decreases as 
the distance from the lens increases, and it becomes small at a location 
of the filter member e2. 
In view of the foregoing, there is a necessity to place the entire range 
that a passer or object may approach at a distance between the filter 
member and the lens in order to positively perform distance measurement. 
If the filter member e is placed in parallel relation with a plane 
vertical to the light projecting axis, errors occur in the measurement 
result, thereby rendering it difficult to obtain an accurate distance 
measurement. 
SUMMARY OF THE INVENTION 
In order to solve the foregoing problems in the conventional art, the 
object sensing apparatus according to the present invention has a filter 
member provided at an angle of inclination at which light projected from a 
light projecting device and emitted or scattered by an inner surface of 
the filter member is reflected in a direction different from a direction 
toward a light receiving device. By this construction, a distance over an 
entire range in which there is a possibility that a passer or an object 
may approach can be accurately and efficiently measured. Furthermore, 
accurate distance sensing is possible without errors occurring in a result 
of a distance measurement to the passer or object to be sensed. 
It is therefore an object of the present invention to provide an object 
sensing apparatus which can sense an object and perform a distance 
measurement to the object with high accuracy and efficiency. 
The foregoing and other objects of the present invention are achieved by an 
object sensing apparatus comprising distance measuring means for measuring 
a distance to an object to be sensed, and a filter member disposed in 
confronting and spaced-apart relation to the distance measuring means. The 
distance measuring means includes light projecting means for projecting 
light toward the object and light receiving means for receiving the light 
projected by the light projecting means and reflected by the object. The 
filter member is disposed at a preselected angle of inclination with 
respect to the distance measuring means. When the light projecting means 
projects light toward the object, light reflected or scattered by the 
filter member is directed in a direction different from a direction toward 
the light receiving means (i.e., in a direction away from the light 
receiving means). 
In another embodiment, the filter member has a surface portion or spot area 
for reflecting light projected by the light projecting means having a 
preselected brightness, the surface portion being disposed at the angle of 
inclination with respect to a light projecting axis of the light 
projecting means. 
In another embodiment, the light projecting means and the light receiving 
means are disposed in a plane in juxtaposed relation. A distance between a 
first end of the filter member and the light projecting means is greater 
than a distance between a second end of the filter member opposite the 
first end and the light receiving means. 
In yet another embodiment, the light projecting means and the light 
receiving means are disposed in a plane in juxtaposed relation. The filter 
member has first and second portions, one of the first and second portions 
being disposed at the angle of inclination with respect to a light 
projecting axis of the light projecting means. 
Preferably, the filter member is disposed within a distance measurable 
range of the distance measuring means and in the vicinity of a boundary of 
the distance measurable range.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
While this invention is susceptible of embodiments in many different forms, 
this specification and the accompanying drawings disclose only preferred 
embodiments of the invention. The invention is not intended to be limited 
to the embodiments so described, and the scope of the invention will be 
pointed out in the appended claims. 
A first embodiment of the object sensing apparatus according to the present 
invention is shown in FIGS. 1-2. A distance measuring device 1 is 
accommodated in and attached to an inner surface of support or attaching 
member 2. The attaching member 2 has a depth which is deeper than a 
thickness of the distance measuring device 1. When the distance measuring 
device 1 is fixed to the inner surface of the attaching member 2, as shown 
in FIG. 1, a cavity 2b exists between a front surface 2 of the attaching 
member 2a and a front surface of the distance measuring device 1. The 
cavity 2b has, at a front end, an opening 2c arranged with a filter member 
3 disposed in confronting and spaced-apart relation to the distance 
measuring device 1. 
The distance measuring device 1 has a light projecting element 11 and a 
light receiving element 12, such as a PSD, juxtaposed at a predetermined 
spacing in a plane. A light projecting lens 11a and a light receiving lens 
12a are arranged in front of the light projecting element 11 and the light 
receiving element 12, respectively. A distance between a center of the 
lenses 11a, 12a and a center of the filter member 3 is designated by X, so 
that the distance measuring device 1 has a distance measurable range Z 
beginning from a position that is closer to a lens side than a center of 
the filter member 3. Consequently, since the front surface 2a of the 
attaching member 2 is at within the distance measurable range Z close to a 
boundary thereof, the distance to an object T to be sensed can be 
sufficiently measured even where it approaches the front surface 2a. 
The filter member 3 is arranged with an inclination at a predetermined 
angle .theta. so that the light from the light projecting element 11 which 
is reflected or scattered by an inner surface 3a of the filter member 3 is 
reflected in a direction different from a direction toward the light 
receiving element 12 (i.e., reflected in a direction away from the light 
receiving element 12). That is, in this embodiment, the filter member 3 is 
inclined at an angle .theta. with respect to a vertical plane M normal to 
the light beam La along a light projecting axis of the light projecting 
element 11. The filter member 3 is arranged at an inclination to the 
vertical plane M so that the distance between one end (upper end in FIG. 
1) of the filter member 3 and the light receiving element 12 is smaller 
than the distance between the other end (lower end in FIG. 1) of the 
filter member 3 and the light projecting element 11. 
By inclining the filter member 3 with respect to the vertical plane M as 
set forth above, the direction of light which is reflected at the inner 
surface of the filter member 3 differs from the direction of light which 
is reflected at the inner surface of the filter member e described above 
for the conventional object sensing apparatus of FIG. 8. A comparison of 
such different reflected light directions is shown in FIG. 2. With the 
filter member e placed perpendicular to light beam La, the reflected light 
beams Le,Lh (shown in sold lines) pass through the light receiving lens 
12a and arrive at the light projecting element 12 as described above with 
respect to FIG. 8. In contrast, according to the present invention, with 
the filter member 3 inclined at the angle .theta., the reflected light is 
directed downward as light components Le0, Lh0 and Lc0, as shown by dotted 
lines in FIG. 2(a), and do not pass through the light receiving lens 12a 
and to the light projecting element 12. 
Consequently, the light from the light projecting element 11 passing 
through the filter member 3 is reflected by the object T to be sensed as 
light beam Lb. The reflected light beam Lb passes through the filter 
member 3 and the light receiving lens 12a and arrives at the light 
receiving element 12. Thus it is possible, according to the present 
invention, to accurately and efficiently obtain a distance measurement to 
the object T to be sensed without being affected by reflected light or 
scattered light from the filter member 3. Even where the filter member is 
moved close to the lens side, as shown by the one-dot chain lines 
designated at 13, if the filter member 3 is arranged at an inclination at 
the predetermined angle .theta., as set forth above, an accurate distance 
measurement to the object T can also be obtained. 
As shown in FIG. 2a, a light beam Ld that passes through the light 
projecting lens 11a and is incident on the inner surface of the filter 
member 3 is partially reflected as a light Le0. The light from an upper 
portion of a point P of the light projecting element 11 is projected 
downward with respect to the light beam Ld. Accordingly, the angle .theta. 
of the filter member 3 may be set to an angle such that the reflected 
light Le0 is not directed through the light receiving lens 12a and to the 
light receiving element 12 in order to avoid an effect on a distance 
measurement. 
There is also the case that diffused reflection occurs due to the light Ld 
at the inside of the filter member 3. The effect of this diffused 
reflection increases as the distance at which the filter member 3 is 
placed is increased. As shown in FIG. 2b, the required angle of 
inclination .theta. is qualitatively given by an angle .theta. taken in a 
vertical axis and a distance from the lens taken in a horizontal axis. If 
the filter member 3 is placed at a position near the light projecting lens 
11a, there is no necessity to incline the filter member. However, as the 
filter member 3 is moved to a position away from the distance measuring 
device 1, there is a necessity to gradually increase the angle .theta.. As 
the filter member 3 is moved in a direction away from the distance 
measuring device 1, exceeding the position where a maximum angle of 
inclination is required, the inclination may be at an angle smaller than 
the maximum angle. 
As described above, since an optimum angle of inclination .theta. is 
determined by various structural conditions and the diffusing reflection, 
a predetermined angle .theta. is required to be determined by 
experimentation. For example, if a diameter of the light projecting lens 
is 13 mm and a focal distance thereof is 13 mm, a diameter of the light 
receiving lens is 13 mm and a focal distance thereof is 9 mm, a base line 
length is 20 mm, a spot diameter of the light projecting element main 
projecting light is 0.6 mm, and the filter member is installed at distance 
remote from the light projecting lens, the angle of inclination .theta. is 
appropriately set at 23 degrees. Where the filter member is installed at a 
distance of 70 mm, the angle of inclination .theta. is appropriately set 
at 18 degrees. 
FIGS. 3(a) and 3(b) shows a second embodiment of the object sensing 
apparatus according to the present invention. In this embodiment, the 
filter member 23 has a bent central portion 23b with respect to left and 
right directions. That is, the central portion 23b has, on a left side, a 
left portion 23c disposed opposite to the light receiving lens 12a and 
extending perpendicular to the light projecting axis of light beam La of 
the light projecting element 11. The central portion 23b of the filter 
member 23 has, on a right side thereof, a right portion 23d disposed 
opposite to the light projecting lens 11a. 
As shown in FIG. 3(b), the right portion 23d of the filter member 23 has a 
surface portion at which an emitted light beam from the light projecting 
element 11 includes a spot area 23e with a predetermined brightness. In 
the spot area 23e, the reflected light due to the inner surface 23a of the 
filter member 23 has a brightness having an effect upon a distance 
measurement result. The right portion 23d is inclined by a predetermined 
angle with respect to a vertical plane to the light projecting axis. More 
specifically, the center of each lens 11a and 12a is disposed at a 
distance X to the central portion 23b of the filter member 23, and the 
right portion 23d of the filter member 23 is disposed at an angle of 
inclination defined by a distance a from the central portion 23b. 
Since the right portion 23d of the filter member 23 where the spot area 23e 
is located is inclined by bending or deviating the filter member 23 as 
shown in FIGS. 3(a), 3(b), the reflected light at the spot area 23e within 
the inner surface of the filter member 23 is reflected downwardly, thereby 
avoiding passage through the light receiving lens 12a. Accordingly, the 
reflected light does not arrive at the light receiving element 12 and no 
error in a distance measurement results. 
FIG. 4 shows a third embodiment of a filter member 33 according to the 
present invention. The filter member 33 is bent or deviated at a central 
portion 33b in a direction toward the projecting lens by a distance 
.alpha. in a manner similar to that shown in FIG. 3, and a right portion 
33d is inclined similarly to the second embodiment in order to align the 
left and right ends of the filter member 33 at a same level. A left 
portion 33c of the filter member 33 is similar to the left portion 23 of 
the second embodiment. Therefore, like in the second embodiment, a spot 
area 33e on the right portion 33e of the filter member 33 is inclined so 
that light within the surface of the spot area 33e is reflected downward. 
Accordingly, there is no transmission of reflected light through the light 
receiving lens 12a and, therefore, the reflected light is not incident on 
the light receiving element 12. By this construction, errors in distance 
measurement results are effectively prevented. 
FIG. 5 shows a fifth embodiment of the object sensing apparatus according 
to the present invention. In this embodiment, a filter member 43 has a 
vertically inclined angle with respect to the vertical plane perpendicular 
to the light projecting axis of the light beam La projected from the light 
projecting element 11. The filter member 43 has an upper portion inclined 
in a direction toward the distance measuring device 1. However, the 
inclination direction of the filter member 43 is not limited to the 
direction shown in FIG. 5, and the upper portion of the filter member 43 
may be inclined in a direction away from the distance measuring device 1. 
FIGS. 6(a) and 6(b) show a fifth embodiment of the object sensing apparatus 
according to the present invention. In this embodiment, a filter member 
53, has a central boundary portion 53b, a left portion 53c opposite to the 
light receiving element and extending perpendicular to the light 
projecting axis of the light beam La projected from the light projecting 
element. The filter member 53 also has a right portion 53d including a 
spot area 53e and extending at an inclined angle to the light projecting 
axis. The right portion 53d may be inclined in a direction toward the 
distance measuring device 1, or in a direction away from the distance 
measuring device 1. 
In the filter members 43, 53 of the fourth and fifth embodiments, 
respectively, the spot area is inclined so that the light within the 
surface of the filter members is reflected downward and upward. Thus the 
reflected light will not be incident on the light receiving element 1, 
thereby preventing errors from occurring in distance measurement results. 
In the embodiments of FIGS. 3(a)-3(b) and FIGS. 6(a)-6(b), although the 
central portions of the filter member are sharply bent to define the 
angles of inclination, it is preferred that the angles of inclination be 
varied by a moderate curved surface. 
The object sensing apparatus according to the present invention described 
above has the following advantages. 
The filter member is provided in confronting and spaced-apart relation to 
the distance measuring device. Thus, where there is a possibility that the 
passer or object to be detected will approach the object sensing 
apparatus, it is possible to define an entire sensing range within a 
distance measurable range without excluding distances which have been 
impossible to measure with conventional object sensing apparatuses. This 
will avoid a failure to measure a distance when an object or passer to be 
sensed approaches the sensing apparatus. 
The filter member is provided at an angle of inclination to the light 
projecting axis of a light beam projected by the light projecting element. 
By this construction, the light projected from the light projecting 
element and reflected or scattered by an inner surface of the filter 
member can be reflected in a direction different from a direction toward 
the light receiving element. Thus, there is less possibility that light 
other than the light reflected by an object or passer to be sensed is 
received by the light receiving element, thereby enabling distance 
measurements with high accuracy. 
The inclination of the filter member can be achieved by inclining only a 
portion of the filter member which includes a spot area with a 
predetermined brightness, or by slanting the entire filter member in left 
and right directions or in upper and lower directions. It is therefore 
possible to select a slanting state of the filter member which is optimal 
for a particular application, thereby providing greater freedom of design. 
The filter member is provided within a distance measurable range by the 
distance measuring device in the vicinity of a boundary thereof. Thus it 
is possible to reduce the spacing between the distance measuring device 
and the filter member to a required minimum, thereby making it possible to 
reduce the overall size of the object sensing apparatus. 
From the foregoing description, it can be seen that the present invention 
comprises an improved object sensing apparatus. It will be appreciated by 
those skilled in the art that obvious changes can be made to the 
embodiments described in the foregoing description without departing from 
the broad inventive concept thereof. It is understood, therefore, that 
this invention is not limited to the particular embodiments disclosed, but 
is intended to cover all obvious modifications thereof which are within 
the scope and the spirit of the invention as defined by the appended 
claims.