Communications: electrical – Visual indication
Reexamination Certificate
1999-06-02
2002-07-02
Tong, Nina (Department: 2632)
Communications: electrical
Visual indication
C340S555000, C250S221000, C250S222100
Reexamination Certificate
active
06414603
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a multi-optical-axis photoswitch incorporating a light emitting unit and a light receiving unit between which a multiplicity of optical axes exist which are realized by pairs of light emitting devices and light receiving devices in a detection area thereof, and more particularly to a state display method for displaying a light shielding state or the like of the multi-optical-axis photoswitch and a multi-optical-axis photoswitch adapted to the method.
2. Description of the Related Art
The multi-optical-axis photoswitch is a switch having a plurality of optical axes formed by pairs of light emitting devices of a light emitting unit and light receiving devices of a light receiving unit and arranged to be operated when any one of the optical axes is shielded by an object. Hitherto, the multi-optical-axis photoswitch has been known as an “optical area sensor” which is capable of detecting existence of an object in a wide detection area. The multi-optical-axis photoswitch is used to improve safety of an operator of a machine tool, a punching machine, a pressing machine, a controller, a molding machine, an automatic controller, a winding machine, a robot, a casting machine or the like. The foregoing multi-optical-axis photoswitch is disposed in a dangerous region for a pressing machine or the like to form a detection area and to detect shielding of an optical axis which is caused when a portion of the body of an operator, for example, the finger or the hand of the operator, enters the detection area. Thus, the operation of the machine is interrupted or an alarm is issued to protect the operator.
Further, the multi-optical-axis photoswitches are disposed along automatic manufacturing lines in a plant to detect existence of moving articles. Thus, the multi-optical-axis photoswitches are employed as sensors in an automatic control system with which a next step is started if an article is detected.
A multi-optical-axis photoswitch of the foregoing type, as shown in
FIG. 8
, incorporates a light emitting unit
2
constituted by disposing a plurality of (eight in the structure shown in
FIG. 8
) light emitting devices
21
, such as light emitting diodes (LED) which emit infrared rays, at predetermined pitches. Moreover, the multi-optical-axis photoswitch incorporates a light receiving unit
3
constituted by disposing light receiving devices
31
, such as photodiodes, at predetermined pitches to correspond to the light emitting devices
21
in order to receive optical axes
5
which are infrared beams emitted from the light emitting devices
21
of the light emitting unit
2
. The light emitting unit
2
is disposed at one end of a detection area which is provided for a pressing machine or the like and which must be protected. On the other hand, the light receiving unit
3
is disposed at the other end of the detection area such that the light emitting unit
2
and the light receiving unit
3
are disposed opposite to each other. Light beams are emitted and received between the pairs of the light emitting devices and the light receiving devices of the light emitting unit
2
and the light receiving unit
3
. Thus, whether or not each light beam is shielded is detected. The light emitting unit
2
and the light receiving unit
3
are connected to each other through a signal line
8
.
The light emitting unit
2
is controlled by a light-emitting-unit control circuit so that the light emitting devices
21
of the light emitting unit
2
sequentially and cyclically emit light from one end of the light emitting devices
21
to the other end of the same (for example, in an upward direction from the lowest device). In synchronization with the light receiving devices
31
of the light receiving unit
3
corresponding to the light emitting devices
21
, only the corresponding light receiving device
31
is enabled to receive light and the other light receiving devices
31
are made to be impossible to receive light. The reason why only one light receiving device
31
is always enabled to receive light lies in that light emitted from a light emitting device
21
is not always received by only a corresponding light receiving device
31
. Therefore, a case can be considered that relatively intense light is made incident on also light receiving devices
31
adjacent to the correspond light receiving device
31
. That is, the structure is formed such that light receipt signals from all of the light receiving devices
31
are collectively supplied to one binarizing circuit. Therefore, even if one optical axis is shielded because of introduction of an object, light made incident on the adjacent light receiving devices
31
causes the overall intensity level of light to exceed a threshold value. Thus, an incorrect determination is made that the state is a state in which light can be received. Thus, introduction of an object cannot accurately be detected.
Only one optical axis is cyclically and always made to be effective as described above to continue detection. If an object or fingers or hand of a human being is introduced into the detection area, an optical axis
5
at that position is shielded. Thus, the light receiving device
31
cannot receive light. Therefore, an alarm is issued or the operation of the machine is interrupted to improve safety.
FIG. 9
is a block diagram showing a sensor portion of the multi-optical-axis photoswitch
1
shown in FIG.
8
. The multi-optical-axis photoswitch
1
is composed of the light emitting unit
2
and the light receiving unit
3
.
The light emitting unit
2
incorporates N light emitting devices
21
(
211
,
212
to
21
N) disposed at required pitches, for example 40 mm and comprising light emitting diodes or the like, N being a required number. Moreover, the light emitting unit
2
incorporates N light emitting circuits
22
(
221
,
222
to
22
N) for operating the light emitting devices
21
; a light-emitting-device switching circuit
23
to scan the N light emitting circuits
22
in a time division manner; a light-emitting-unit control circuit
24
; and a display unit
6
for displaying a state of the multi-optical-axis photoswitch
1
.
The light-emitting-unit control circuit
24
employs a gate array in this case to perform control. As a matter of course, another control device, for example, a CPU, may be employed in place of the gate array.
If the display unit
6
is composed of one display lamp which displays, for example, red and green light, green light is displayed when all of the optical axes are ensured. In the other cases, red light is displayed. If a monochrome display lamp is employed, the lamp is turned on when all of the optical axes are ensured. In the other cases, the lamp is turned off.
The light receiving unit
3
incorporates N light receiving devices
31
(
311
,
312
to
31
N) disposed at the same pitch as that in the light emitting unit and comprising phototransistors or the like, N being a required number. Moreover, the light receiving unit
3
incorporates N light receiving circuits
32
(
321
,
322
to
32
N) for I-V converting light receipt signal from each of the light receiving devices
31
; and a light-receiving-device switching circuit
33
for scanning the N light receiving circuits
32
in a time division manner in synchronization with the light emitting devices
21
forming pairs with the N light receiving circuits
32
. In addition, the light receiving unit
3
incorporates an amplifying circuit
361
for collectively amplifying light receipt signals from the light receiving circuits
32
; and a binarizing circuit
362
for converting the amplified signals into
1
or
0
with respect to a predetermined threshold value. Moreover, the light receiving unit
3
incorporates a detection circuit
363
for determining a state of incident light by using the binarized signal; a light-receiving-unit control circuit
34
for controlling the light receiving unit
3
; and an output circuit
35
for interrupting the operation of the pressing machin
Murakami Keisuke
Okada Toshio
Yamaguchi Akiji
Keyence Corporation
Morgan & Lewis & Bockius, LLP
Tong Nina
LandOfFree
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