Radiant energy – Photocells; circuits and apparatus – Housings
Reexamination Certificate
2003-10-27
2004-08-10
Le, Que T. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Housings
C250S559400
Reexamination Certificate
active
06774357
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a photoelectric switch device for detecting an object in a specified region of detection.
2. Description of Related Art
Typically, various photoelectric switch devices are widely used to detect an object in a specified region of detection in, for example, a manufacturing line in a factory. Such a photoelectric switch device projects light rays toward a specific field of detection in which an object is expected to be present and detects an object in the specific region of detection on the basis of a value relating to light rays reflected by the object. A conventional triangulation method is used for some of this kind of photoelectric switch devices. The triangulation type photoelectric switch device is also referred to as a distance setting type of photoelectric switch device. Reference is made to
FIGS. 25 through 27A
to
27
C which show the structure and operation of one of the conventional triangulation type photoelectric switch devices for the purpose of providing a brief background that will enhance an understanding of the present invention.
Referring to
FIG. 25
, a triangulation type photoelectric switch device
800
comprises a light emitting diode
801
as a light source, a projection lens
802
, a focusing lens
803
and a photoelectric position sensing device (PSD)
804
. The light emitting diode
801
is coaxially aligned with the optical axis Xp of projection lens
802
. The projecting lens
802
and the focusing lens
803
are arranged with a specified separation in the same vertical plane including the optical axis Xp of the light projection lens
802
. The light projecting lens
802
directs light rays emanating from the light emitting diode
801
toward an object
900
located remotely from the photoelectric switch device
800
in the optical axis Xp of the light projection lens
802
. The light rays are then reflected back by the object
900
and focused on the photoelectric position sensing device
804
by the focusing lens
803
to form a light spot on the photoelectric position sensing device
804
.
The position of the light spot Lp on the photoelectric position sensing device
804
varies according to the distance of the object
900
from the photoelectric switch device
800
, and more particularly to the photoelectric position sensing device
804
. This distance is hereafter referred as switch-to-object distance. Specifically, the light spot Lp is formed at one of opposite ends, for example, an end e
1
, of the photoelectric position sensing device
804
when the object
900
is at the closest switch-to-object distance of a specified field of detection D
0
and shifts in position towards another end e
2
of the photoelectric position sensing device
804
as the object
900
moves away from the photoelectric switch device
800
, i.e. as the switch-to-object distance increases.
The photoelectric position sensing device
804
generates two position signals N and F having levels according to positions of the light spot Lp formed thereon. Specifically, the position signal N has a photoelectric signal (current) level proportional to the distance of the light spot Lp from the end e
1
of the photoelectric position sensing device
804
. The position signal F has a photoelectric signal (current) level proportional to the distance of the light spot Lp from the other end e
2
of the photoelectric position sensing device
804
. Accordingly, the switch-to-object distance of the object
900
is found on the basis of these two position signals N and F.
The photoelectric switch device
800
has a specified field of detection or axial detectable region of detection D
0
that is defined between the closest axial position P
1
and the remotest axial position P
2
which are axial limit positions for light rays incident upon the photoelectric position sensing device
804
through the focusing lens
803
. The axial detectable region of detection D
0
is divided into two sub-regions on both sides of a specific axial position ST that is variably preset, namely a front half axial region D
1
that is on a side of the specific axial position ST close to the photoelectric switch device
800
and is used as an effective detection region and a rear half axial region D
2
that is on a side remote from the photoelectric switch device
800
with respect to the specific axial position ST and is excluded from detection as an ineffective detection region.
The photoelectric switch device
800
is configured so as to detect an object
900
in the axial detectable region D
0
. However, the photoelectric switch device
800
determines that the object
900
is present within the effective detection region D
1
only when light rays incident upon the photoelectric position sensing device
804
are from the object
900
positioned in the effective detection region D
1
.
Referring to
FIGS. 26A and 26B
showing a method of determining whether an object
900
is present within the effective detection region D
1
on the basis of position signals N and F from the photoelectric position sensing device
804
, a difference in level between N and F position signals (N−F) represents an axial position of the object
900
within the axial detectable region D
0
and can be used as a position signal. In practice, the position signal is expressed as a ratio of the position signal level difference (N−F) relative to the total level of N and F position signals (N+F) for the purpose of normalization. The normalized position signal {(N−F)/(N+F)} is examined with respect to a threshold value TH, which meets with the position signal relating to the specific axial position ST, to determine whether an object
900
is present within the effective detection region D
1
. That is, it is determined that an object
900
is present within the effective detection region D
1
when the position signal {(N−F)/(N+F)} is greater than the threshold value TH as shown in
FIG. 26A
or that an object
900
is not present within the effective detection region D
1
but is within the ineffective detection region D
2
when the position signal {(N−F)/(N+F)} is smaller than the threshold value TH as shown in FIG.
26
B. The threshold value TH may be varied to shift the limit axial position ST so as to change, expand or narrow, the effective detection region D
1
and the ineffective detection region D
2
.
FIGS. 27A
to
27
C illustrates a process of presetting a threshold value TH in the prior art photoelectric switch device
800
. The prior art photoelectric switch
800
is provided with a threshold value trimming dial
810
, a detection indicator lamp
811
and a detection stability indicator lamp
812
. As shown in
FIG. 27A
, after putting an object
900
at a specified axial position in the optical axis Xp of the photoelectric switch device
800
and powering on the photoelectric switch device
800
to project light rays to the object
900
, the threshold value trimming dial
810
is continuously turned clockwise until the detection indicator lamp
811
turns on. Then, the threshold value trimming dial
810
is set to a position indicated by a reference numeral “
1
”. Subsequently, as shown in
FIG. 27B
, after removing the object
900
from the optical axis Xp which turns off the detection indicator lamp
811
and directs the light rays to a reflective reference object
901
, the threshold value trimming dial
810
is further continuously turned clockwise until the detection indicator lamp
811
turns on again. The threshold value trimming dial
810
is set to a position indicated by a reference numeral “
3
”. If there is no reflective reference object
901
, the threshold value trimming dial
810
is turned clockwise until it reaches an extreme position. Finally, as shown in
FIG. 27C
, the threshold value trimming dial
810
is turned back counterclockwise to a midpoint, namely a position indicated by a reference numeral “
2
”, between the positions “
1
” and “
3
”. As a
Fukumura Koji
Sugiyama Kazutoshi
Keyence Corporation
Le Que T.
Smith Patent Office
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