Electrical transmission or interconnection systems – Switching systems – Condition responsive
Reexamination Certificate
1998-12-07
2001-03-20
Fleming, Fritz (Department: 2836)
Electrical transmission or interconnection systems
Switching systems
Condition responsive
C307S112000, C307S125000
Reexamination Certificate
active
06204575
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a controller of an area sensor having a plurality of optical axes provided within a detection area, each optical axis connecting a set of a light-projecting device and a light-receiving device. In particular, the invention relates to the safety of extension of a controller for use with a plurality of such area sensors.
An area sensor is a kind of switch that comprises a light projector having light-projecting devices and a light receiver having light-receiving devices, a set of one light-projecting device and one light-receiving device forming an optical axis or an optical channel. If any one of the optical axes is interrupted by a moving object, the area sensor turns on. Working as a switch, the area sensor ensures the safety of the operators of machine tools, punching machines, press machines, brakes, molding machines, automatically controlled machines, coiling machines, robots, casting machines and so forth. In the case of a press machine, the area sensor is positioned in a detection area which is the dangerous zone of the machine and when fingers or any other part of the operator's body enters the detection area and interrupts a particular optical axis, the sensor detects that phenomenon and takes an immediate protective action by shutting down the machine or issuing a warning signal.
The area sensor is also used in an automatic production line at plant, where it detects the presence or absence of a moving article and signals for a transfer to the next step upon detecting the article. In this case, the area sensor works as a sensor for automatic control.
An area sensor
1
of the type is shown in FIG.
9
and it comprises a light projector
2
in which a plurality of light-projecting devices
21
such as light-emitting diodes (LEDs) that emit infrared or other radiations are spaced on a specified pitch (in
FIG. 9
, eight light-projecting devices are provided), a light receiver
3
in which a corresponding number of light-receiving devices
31
such as photodiodes
31
that are spaced on a specified pitch in correspondence with the light-projecting devices
21
so that they receive optical axes
9
which are the infrared beams emitted from the light-projecting devices
21
in the light projector
2
, and a controller
4
that controls both the light projector
2
and the light receiver
3
via cables
7
. The light projector
2
and the light receiver
3
are provided in a face-to-face relationship such that the projector
2
is positioned on one side of the detection area where the operator of a press machine or the like must be protected whereas the receiver
3
is positioned on the other side of the detection area. Optical beams issued from the light-projecting devices in the light projector
2
travel to the corresponding light-receiving devices in the light receiver
3
and the interruption of any one optical beam is detected. The light receiver
3
is also equipped with an indicator
8
that signals the operating status of the area sensor.
In accordance with the control by the controller
4
, the light-projecting devices
21
in the light projector
2
emit cyclically in sequence (e.g. from down to up) and with synchronism being ensured between a particular light-projecting device
21
and the corresponding light-receiving device
31
in the light receiver
3
, only the corresponding light-receiving device
31
is rendered to be capable of light reception whereas the other light-receiving devices
31
are incapable of light reception. The reason for ensuring that only one corresponding light-receiving device
31
at a time is rendered to be capable of light reception is that the light from a particular light-projecting device
21
is not necessarily launched into the corresponding light-receiving devices
31
and there may be a case in which the same light is also launched into nearby light-receiving devices
31
as light of a comparatively high intensity. In other words, the conventional area sensor is of such a design that the light reception signals from all light-receiving devices
31
are collectively fed into a single binarizing circuit and, although a particular axis is interrupted by an object that has entered the detection area, the light launched into nearby light-receiving
31
causes the overall signal level to exceed a threshold and the sensor will erroneously determine that the projected light is being received by the light receiver and thus fails to achieve correct detection of the object that has entered the detection area.
On the other hand, if detection is continued with only one optical axis being cyclically rendered effective at a time, the entrance of an object or fingers or some other part of the human body into the detection area interrupts the optical axis
9
in the affected position so that it is no longer received by the corresponding light-receiving device
31
, whereupon the sensor issued a warning signal or shuts down the machine to ensure safety for the operator.
FIG. 8
is a block diagram for the area sensor under consideration. The area sensor
1
comprises the light projector
2
, the light receiver
3
and the (master) controller
4
.
The light projector
2
comprises a desired number N of light-projecting devices
21
(
211
,
212
, . . .
21
N) in the form of light-emitting diodes or the like that are spaced on a desired pitch, say, 40 mm, N light projecting circuits
22
(
221
,
222
, . . .
22
N) for driving these light-projecting devices
21
, a gate array
23
that scan controls the N light-projecting circuits
22
on a time-sharing basis to perform the necessary processing for detecting abnormalities and displaying the detected abnormality, an indicator circuit
24
for signaling the operating status of the area sensor, a clocking oscillator circuit
25
and a power supply circuit
26
. In the illustrated case, the operation of the light-projecting circuits
22
is controlled by using the gate array
23
. Needless to say, the gate array may be replaced by other control devices such as a CPU.
The lights receiver
3
comprises a desired number N of light-receiving devices
31
(
311
,
312
, . . .
31
N) in the form of phototransistors or the like that are spaced on the same pitch as the light-projecting devices
21
in the light projector
2
, N light-receiving circuits
32
(
321
,
322
, . . .
32
N) for performing I-V (current voltage) conversion on the light reception signals from the respective light-receiving device
31
, a gate array
33
that scan controls the N light-receiving circuits
32
on a time-sharing basis in synchronism with the corresponding light-projecting devices
21
, an indicator circuit
34
that displays the status of the associated area sensor, a clocking oscillator circuit
35
, a power supply circuit
36
, a light reception signal processing circuit
37
that collectively amplifies, binarizes and detects the light reception signals from the light-receiving circuits
32
, a detection signal output circuit, and an output circuit
38
for delivering sync signals. Besides synchronous scan control, the gate array
33
performs auxiliary detecting operations, abnormality detecting operations and processing for displaying the results of detection. As in the case of the gate array
23
, the gate array
33
of course can be replaced by other control devices such as a CPU.
The controller
4
includes a control circuit
41
in the form of a gate array; the control circuit
41
receives an external input from an external input circuit using an input terminal, a mode setting from a mode setting circuit using a DIP switch, and a signal indicative of the status of light projection from a sensor connector
42
to the light projector via a light projection status signal input circuit; the control circuit
41
also receives the aforementioned detection output and a system sync signal from a sensor connector
43
to the light receiver via a detection signal input circuit and a sync signal input circuit, respectively. The control circuit
41
delivers
Fleming Fritz
Keyence Corporation
Sughrue Mion Zinn Macpeak & Seas, PLLC
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