Modular safety switching device system

Details Modular safety switching device system Modular safety switching device system

2002-10-17

2004-08-17

Pope, Daryl (Department: 2632)

Communications: electrical

Condition responsive indicating system

With particular system function

C340S507000, C340S003100, C307S010800

Reexamination Certificate

active

06778080

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a modular system of safety switching devices, i.e. a modular safety switching device system, for switching on and fail-safely switching off actuators. The system comprises at least one input module for fail-safely evaluating a safety transmitter and for generating an output signal, and at least one output module for fail-safely actuating the actuator in response to the output signal from the input module. At least the input module can be operated in different operating modes.
Safety switching devices are generally known. They are generally used to evaluate a signal from a safety transmitter, such as an emergency off switch, a protective door position switch, etc. in a fail-safe manner and to drive one or more fail-safe output contacts of an output circuit. Actuators, such as contactors, valves, motors, hazardous machine parts, for example saw blades, robot arms, high-voltage equipment, etc. are brought into a safe state via these output contacts then. The present assignee distributes a large number of different safety switching device types under the common trade name “PNOZ”.
In practice, it often occurs that a plurality of switching events, for example the actuation of an emergency off switch, the opening of a protective door, or reaching through a light curtain, have to be interconnected, for example AND-linked. For this purpose, a plurality of switching devices are usually connected in series, the output terminals of one safety switching device being connected to the input terminals of the following safety switching device.
In many cases, in addition to the AND linking, a hierarchical structure of the safety switching devices is desired, in order, for example, to stop the entire machine with one switching event, for example the emergency off switch in one case, and, with other switching events, for example a protective door switch, to stop only a specific motor in the entire machine or to keep it stationary. Such a hierarchical structure has hitherto been possible by appropriate wiring and it has proved successful in practice.
Nevertheless, there remains a desire to provide a structure of safety switching devices which is more flexible, so that machine-specific evaluation of safety switching events becomes easily possible without complicated wiring.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a modular safety switching device system which permits flexible linking of the safety switching devices used, without having to perform complicated wiring for linking the individual safety switching devices and in particular without specific wiring for different operating modes of the input modules.
According to one aspect of the invention, this object is achieved by a the modular safety switching device system as mentioned at the outset having a control module for setting the operating mode of the input and output modules, and having a display for fail-safely displaying the set operating modes of the input modules and/or of the output modules.
In the new safety switching device system, therefore, the operating mode of each input and output module can be specifically set via the control module and checked via the display. In the case of the input modules, “operating mode” might include, for example, which output module the input modules are assigned to, i.e. to which output module the output signal from the input module is fed. Further operating modes of the input modules might be, for example: start-up test, acknowledgment, deactive, etc. Operating modes in the case of the output modules are, for example, different delay times for switching off the outputs with a delay, for example 0 seconds, 0.5 seconds or 1 second. The term “fail-safe” is to be understood to mean that the function of the display is checked, so that a faulty display of the operating mode can be ruled out.
The advantage of this modular safety switching device system is a simple and very flexible setting and configuration. In particular, different systems can be achieved with the same modular structure, by changing the assignment of input modules to output modules. Furthermore, hierarchical systems can also be built up, in which for example one input module acts on two output modules and other input modules act on one output module each. These settings and changes can be made without changing the wiring, which not only saves costs in the maintenance and setting up of such a system but also eliminates sources of error which can arise from erroneous wiring.
Overall, therefore, a safety switching device system can be built up which can be configured very flexibly and simply to an extremely wide range of requirements, the configuration being carried out via a central control module. In particular, the output signals from the input modules can be fed to the output modules in any desired manner. In this case, the programs for all the selectable operating modes are stored completely in the control module and are checked and approved by a certification authority, for example the professional association. By means of the configuration, the desired operating modes, preferably the desired programs, are selected and the application-specific program of the safety system is assembled from the standard programs stored in the control module. The advantage is that the checking of application-specific software is not necessary.
A further advantage of the inventive safety switching device system not only resides in the fact that the user can rely on the respective display of the operating mode when setting up the operating modes, and therefore needs no further aids or functional checks, but can also be seen in the fact that production tests can be rationalized, since the device can automatically carry out the test of the display means. A visual and therefore fault-susceptible test of the display in production control can consequently be dispensed with.
In a refinement of the invention, the display comprises a number of optical elements, preferably light-emitting diodes, corresponding to the number of selectable operating modes. Each optical element is preferably assigned a feedback element, preferably an optical conductor, the feedback element guiding the light emitted by the optical element to a light evaluation unit, which checks the state of the optical element.
These measures permit the construction of a fail-safe display with little effort and low costs. The light emitted by the optical element is guided via an optical conductor to an optical sensor, which generates a corresponding signal. This signal is then compared with the reference signal, in order to be able to make a statement as to whether the optical element is operating without faults. The use of light-emitting diodes as optical elements has proven to be particularly beneficial. Furthermore, the use of optical elements on each input and output module (decentralized display means) permits an expensive central display to be dispensed with. In systems which have a relatively large number of modules, however, this advantage decreases again. Of course, it might also be considered to test the optical element for freedom from faults in a different way. One possible way is to impress two different currents on the optical element, preferably an LED, one after the other and to measure the two different voltages. Via a comparator, it is then possible to establish whether the two voltages lie above or below a predefined threshold value. If there are deviations from a predefined result here, there must be a fault.
In another refinement of the invention, the display is implemented as a central display, preferably as a liquid crystal display device. The operating modes of the input module and/or of the output module are preferably displayed in two different types and/or in two mutually independently driven areas of the display, so that a fail-safe representation is achieved.
These measures permit the use of a display, i.e. a monitor, in order to set the operating modes of the input

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