Modular safety switching

Details Modular safety switching Modular safety switching

1999-08-05

2001-06-12

Hofsass, Jeffery (Department: 2736)

Communications: electrical

Land vehicle alarms or indicators

Internal alarm or indicator responsive to a condition of the...

C340S567000, C340S507000, C340S508000

Reexamination Certificate

active

06246318

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
As production or manufacturing sequences are becoming automated by using complex machines or robots, the safety requirements are becoming more stringent. Modern conventional machines and robots largely run under fully automatic control, but nevertheless have no intelligence allowing them to identify whether people may be located in dangerous proximity. In order nevertheless to preclude hazards, the systems or system parts are protected by protective fences, covering shrouds and the like. In order to gain access to the appropriate machine parts for servicing and setting up, the protective fences have doors in them, and the covering shrouds can be opened.
The safety provided by the protective fence is, of course, lost as soon as the door is opened, for which reason the state of the doors must be monitored by independent safety switching devices, in order to stop the machine in good time. A similar situation applies to machine shrouds, for example in blow molding devices, injection molding or die casting machines, or machining centers.
The requirements for safety based on state identification differ from one machine type to another and from one system to another, for which reason different signaling devices are used for state monitoring. The simplest signaling device comprises a simple break contact, which is used to monitor servicing panels that need to be opened occasionally. The most complicated signaling device contains two sets of switches, with each set having a break contact and a make contact. Such complicated signaling devices are used where the safety requirements are particularly stringent and if, for example, a switch test also has to be carried out when voltage is returned.
Similar requirements apply to emergency-stop switches, for which there are likewise various safety levels, resulting in correspondingly complicated signaling devices.
2. Description of the Related Art
The actual safety device which is intended to evaluate the operating state of the signaling devices is, fundamentally, largely independent of the type of signaling device. This applies in particular to those functions which relate to and monitor the safety of the safety switching device itself. Nevertheless, in the past, an appropriate safety switching device has been provided for each type of signaling device, and is matched to it. This has resulted in increased storage requirements and repair problems since only the respective safety switching device that is matched to the corresponding type of signaling device can be used.
Another approach that has been taken was to use jumpers in order to match the safety switching device to the respective type of signaling device, although this can lead to errors.
Against this background, the object of the invention is to provide a safety switching device which is suitable for connection of signaling devices from a set of signaling devices, and which requires no additional programming means.
This object is achieved according to the invention by a safety switching device having the features of claims
1
,
2
or
3
.
The safety switching device according to the invention has a set of inputs and/or outputs, in which case each signaling device in the set of signaling devices which may possibly be connected is assigned one or more inputs and/or outputs. An identification device is used to check whether the inputs and/or outputs associated with the relevant signaling device type, and otherwise no inputs and/or outputs are connected. In this way, the safety switching device identifies the respective type of signaling device, and internally controls its signal processing or relaying.
The identification device can be implemented relatively simply by containing a table which indicates which inputs and/or outputs may permissibly be connected in combination in each case. The identification device checks all the inputs and/or outputs and compares the signals recorded during the test with the table which contains the permissible association. The safety switching device is released only when the check has confirmed that only permissible inputs and/or outputs are connected, and that the inputs and/or outputs which are associated with a signaling device type are absolutely all connected to the signaling device. In this case, it may be necessary to close the make contacts briefly by operating the protective door or the emergency-stop switch.
In the case of simple safety switches for servicing panels that are used occasionally and for Category 1 emergency-stop switches, it is sufficient for the signaling device to be formed by a switch having one break contact. In configurations having a plurality of signaling points, a corresponding number of signaling devices of this type are provided.
For protective door monitoring at a high safety level, including possible cross-connection identification in the connecting cable, the signaling device contains two break contacts, which are either controlled separately from one another by means of a cam, or are positively coupled to one another. Such signaling devices are also used for Category 4 emergency-stop switches.
If a high safety level is desired, signaling devices having a make contact and a break contact are used for protective door monitoring and the two are coupled to one another such as they are interlocked in an opposing manner. The same type of signaling device is also used for a start-up test although, in this case, the protective door must be operated, for example.
Protective devices for injection molding or die casting machines or blow molding machines require signaling devices with a total of three break contacts per channel, in which case one of the break contacts is mechanically coupled to a main shut-off valve, in order to detect its position, while the other two break contacts monitor the protective door.
Finally, signaling devices for protective door safety are known which contain two sets of contacts, in which case one switch is a break contact and the other switch is a make contact. Contacts in each set are positively coupled to one another.
It is self-evident that this identification device is present in each channel in multi-channel safety switching devices, in order that each channel can check the connected signaling devices independently of the other. The two channels expediently compare the result of their checks, and do not release the safety switching device until it has been confirmed that both channels are correctly connected to the same type of signaling device.
In addition, developments of the invention are the subject matter of dependent claims.


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