Communications: electrical – Condition responsive indicating system – Specific condition
Patent
1993-09-09
1997-05-13
Mullen, Thomas
Communications: electrical
Condition responsive indicating system
Specific condition
250221, 2502221, 364461, 377 6, 377 9, 381 56, G08B 1318
Patent
active
056296746
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention concerns an alleyway monitoring device.
BACKGROUND ART
In warehouses with high shelf units special fork-lift trucks have to be used to reach the higher shelves and to move heavier objects. It is easier to place smaller items onto and remove them from the shelves by hand. As the driver of a fork-lift truck often does not have an adequate view of the alleyway from behind the lift and the load there is the danger of collision between the fork-lift truck and persons doing manual order-picking work.
To avoid such accidents it has already been proposed to provide a barrier at the end of each alleyway which, in conjunction with a light barrier and associated electronics, guarantees that only one person or one truck can be in the alleyway at any time. Such barriers greatly impede work, however, because even when the alleyway is empty its opening must be awaited. This is why the personnel often disconnect such barriers so that they can work more quickly. Furthermore, with these known monitoring devices, access to the alleyway is not possible if a person doing manual order-picking work is in the alleyway and a second person, also working manually, wishes to enter the alleyway.
The risk of accidents in alleyways between shelf units could also be remedied in another way by, for example, providing for each fork-lift truck a monitoring device operating on the basis of ultrasound which monitors the space immediately in front of the truck for foreign objects. This possibility does, however, have the disadvantage that many false alarms are generated by other obstacles adjacent to the alleyway. The equipping of the various fork-lift trucks with a monitoring device of this kind also involves high costs.
SUMMARY OF THE INVENTION
The object of the invention is therefore to provide a monitoring device for an alleyway between shelf units which does not normally impede access to an alleyway but triggers an alarm if a non-permitted combination of fork-lift trucks and/or persons is present in the alleyway.
In the monitoring device according to the invention the distinction between persons and fork-lift trucks is made by two light barriers which are mounted at different heights. An upper light barrier operates at such a height that it can only be broken by the high fork-lift trucks. A lower light barrier is mounted at such a height that it can also be broken by persons walking in the alleyway. Both light barriers are so designed that they report not only the fact that they have been broken but also the direction of motion of the object breaking them. This can, for example, be achieved by means of two light barriers spaced apart in the longitudinal direction of the alleyway, whose output signals are evaluated via a suitable signal connection circuit. The output signals of the light barriers processed in this way can then be transmitted direct to an up/down counter whose counter reading directly corresponds to the number of fork-lift trucks in the alleyway and/or the number of objects in the alleyway (=trucks plus persons). A monitoring circuit supplied with the counter readings then generates, according to a pre-set table supplied to it, an alarm signal whenever a non-permitted combination "number of fork-lift trucks to number of objects" is determined.
The monitoring device according to the invention can also be installed in existing alleyways between shelf units with little technical outlay. Barriers and other obstacles which impede work are not required. Work in the alleyway is completely unimpeded until an alarm is triggered. In this case, which is not very frequent in practise, the driver of the fork-lift truck must then stop his truck until the alarm has been cancelled by an authorized person after the situation has been verified.
Advantageous further embodiments of the invention are disclosed as follows.
In a monitoring device using two light beams in wide alleyways it is also possible separately to detect two persons entering or leaving an alleyway alongside each other.
A monitoring
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patent: 4866423 (1989-09-01), Anderson, II et al.
patent: 5011358 (1991-04-01), Andersen et al.
patent: 5298738 (1994-03-01), Gebert et al.
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