Radiant energy – Photocells; circuits and apparatus – With circuit for evaluating a web – strand – strip – or sheet
Reexamination Certificate
2000-04-17
2002-01-29
Kim, Robert H. (Department: 2882)
Radiant energy
Photocells; circuits and apparatus
With circuit for evaluating a web, strand, strip, or sheet
C250S200000, C250S559430, C250S221000, C250S222100
Reexamination Certificate
active
06342706
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to retroreflective detectors which are arranged to emit a beam of light from a transmitter, reflect the light beam by a retroreflector and receive the reflected beam of light by a receiver. In particular, the present invention is directed to an improvement for preventing false signalling operation in response to the presence of objects.
As a detector for detecting persons or the like, Japanese Patent Laid-open Publication No. H8-265130 (JP-A-265130/1996) discloses a retroreflective detector. A detector of this type comprises a detection unit housing a transmitter and a receiver, and a retroreflector positioned opposite to the detection unit with a prescribed distance therebetween. This retroreflector comprises a prism called corner cube reflector for reflecting a beam of light emitted from the transmitter. The retroreflector functions to reflect (retroreflect) the incident light emitted from the transmitter in the direction opposite to the incident direction.
Where no object is present in the space between the detection unit and the retroreflector, a light beam (e.g. infrared ray) emitted from the transmitter is reflected by the retroreflector and then the reflected light is received by the receiver. On the other hand, where an object (e.g. a person) is present in or passes through the space between the detection unit and the retroreflector, the object interrupts the light beam emitted from the transmitter, causing the intensity of light received by the receiver to change. Hence, the presence or passage of an object is detected by evaluating changes of the intensity of the reflected light beam which is received by the receiver. To be specific, when the receiver receives no light beam reflected by the retroreflector, the detector signals the presence of an object.
Such a detector is distinguished in emitting a narrow beam of light from the transmitter. Therefore, a light beam reflected by the retroreflector is directed to the receiver with certainty. False operation is avoided by not expanding the width of emitted and reflected light beams excessively.
The narrow beams of light, on the other hand, cause the detector to recognise a passing object which should not be detected. For example, a detector originally installed for detecting the passage of persons is operated by mistake, when a leave, insect or the like passes near the transmitter and interrupts a narrow beam of light.
Another detector suggested to solve this problem comprises two transmitters and receivers each.
FIGS. 6 and 7
illustrate two types of detection units
100
,
110
each of which comprises two transmitters
101
,
101
and two receivers
102
,
102
. In the detection unit
100
of
FIG. 6
, transmitters
101
,
101
are horizontally disposed on the upper part of a light emitting/receiving surface
103
, and receivers
102
,
102
are horizontally disposed on the lower part thereof. In contrast, in the detection unit
110
of
FIG. 7
, transmitters
101
,
101
are vertically disposed on one side (on the right in the figure) of the light emitting/receiving surface
103
, and receivers
102
,
102
are vertically disposed on the other side thereof (on the left in the figure). Arrows in each figure indicate emitted and reflected beams of light.
Each of these detection units
100
,
110
causes a detector to signal the presence of an object only when light beams emitted from the transmitters
101
,
101
are both interrupted at the same time. In other words, the detector does not signal the presence of a small passing object which interrupts only either of the light beams, but it signals the presence or passage of an object when both beams of light are interrupted at the same time. False operation is avoided accordingly.
Nevertheless, the above detection units
100
,
110
still have some problems. The detection unit
100
of
FIG. 6
, which applies a horizontal arrangement of the identical elements, is operated by mistake when an object
104
shown by an imaginary line in
FIG. 6
passes near the light emitting/receiving surface
103
(e.g. when an object
104
whose longitudinal sides extend in the horizontal direction falls down), because the light beams emitted from both transmitters
101
,
101
are interrupted at the same time. In such circumstances, although the light emitting/receiving surface
103
is covered only by half, the detector wrongly signals the presence of an object.
Likewise, the detection unit
110
of
FIG. 7
, which applies a vertical arrangement of the identical elements, is operated by mistake when an object
104
shown by an imaginary line in
FIG. 7
passes near the light emitting/receiving surface
103
(e.g. when an object
104
whose longitudinal sides extend in the vertical direction crosses), because the light beams emitted from both transmitters
101
,
101
are interrupted at the same time. In these circumstances, too, although the light emitting/receiving surface
103
is covered only by half, the detector wrongly signals the presence of an object.
Such false signalling can be avoided by disposing two detection units each comprising a transmitter and a receiver and spaced from each other by a predetermined distance. This arrangement is intended to prevent simultaneous interruption of the light beams emitted from both transmitters even when an object having the above-specified shape may fall or cross.
However, since this arrangement involves an additional step of disposing the two detection units at two separate locations, it increases the installation steps of the detector and raises the production cost.
Alternatively, the detection unit may be enlarged such that the optical elements can be disposed on the edges of a large light emitting/receiving surface with proper distances. False signalling may be prevented by separating the optical elements from each other.
Yet again, this arrangement is not a practical solution. This is because the large detection unit occupies a greater installation space, and also because of its poor appearance and higher production cost.
OBJECTS AND SUMMARY OF THE INVENTION
The present invention has been made in view of the above problems and intends to provide a retroreflective detector comprising a plurality of transmitting elements and receiving elements which can effectively prevent false signalling without increasing the size of the detector.
To achieve this object, the present invention presupposes that the retroreflective detector comprises a detection unit housing a plurality of transmitting elements and a plurality of receiving elements on a light emitting/receiving surface, and retroreflective means disposed opposite to the detection unit with a predetermined distance, the retroreflective detector determining the presence, passage or absence of an object in a space between the detection unit and the retroreflective means based on whether a beam of light emitted from each transmitting element is reflected by the retroreflective means and the reflected beam of light is received by each receiving element. In this retroreflective detector, the detection unit houses a plurality of pairs of a transmitting element and a receiving element in a matrix arrangement, such that every row and column of the matrix includes at least one transmitting element.
In this arrangement, every row and column of the matrix also includes at least one receiving element. Then, the transmitting elements and the receiving elements disposed in such matrix arrangement can define the maximum of widths both in the row direction and the column direction. When a relatively small object which need not be detected may fall or pass through a detection space, beams of light emitted from the transmitting elements are partially interrupted by the falling or passing object. The emitted light beams are interrupted completely only when a falling or passing object covers all of the transmitting elements. It is understood that all transmitting elements are covered by an object which is greater than the dimension of horizontally
Hobden Pamela R.
Kim Robert H.
Optex Co. Ltd.
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