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Intelligent MSI safety interface from Leuze lumiflex closes the gap between EMERGENCY STOP relays and safety PLC technology
Author: Heinz Schreyer, Marktmanager of Leuze lumiflex GmbH + Co. KG, Fürstenfeldbruck
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Not just in Europe but internationally as well, the introduction of the European Machine Directive has had a significant effect on the safety standards to which manufacturing plant has to conform. European safety standards based on the Machine Directive that point to detailed safety aspects and safety solutions are now paving the way towards consistent international safety standards which will soon need to be observed worldwide.
While machine plant safety levels are rising, at the same time a tendency towards the integration of safety components can also be observed. This may involve taking them into consideration as early as in the planning phase. Protective sensors like safety light curtains, multi-beam safety light curtains and safety laser scanners, safety switching mats and switching strips, two-hand controls and safety switches can now be obtained in various different safety categories. Ongoing technological progress, and to some extent the expanding market as well, have been responsible for the high level of reliability and minimal need of maintenance, coupled with scaled-down dimensions and improved cost-efficiency, which safety components have already succeeded in achieving today.
Highly sophisticated sensors, some of them redundantly equipped with microprocessors, likewise need to have intelligent safety interfaces if their full capacity is to be exploited. Hitherto electronics designers have had two possible options open to them.
They can make use of the traditional relay-based Emergency Stop switching device, more often than not designed to deal with specific safety components and conform to a definite safety category. In this variant, practically every sensor needs a switching device of its own. This means that the space the equipment takes up, and the costs when machines incorporate two or more safety components, are likely to mount up rapidly. And if the machine needs servicing, it is a very lengthy business to identify the fault.
When it comes to larger units (e.g. complete assembly lines with a whole battery of Emergency Stop buttons, light curtains and safety switches), redundantly laid out safety-related PLC systems may prove to be the best solution- or more recently the further option of resorting to safety bus systems has become available. Hitherto, however, there have been no cost-effective solutions offered for individual machines with a relatively small number of safety components that come under the same or dif-ferent safety categories.
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THE SOLUTION
MSI (Modular Safety Interface) a solution in the middle ground between Emergency Stop relays and safety-related PLC systems
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With its tried and tested MSI safety interface - a family of microprocessor-controlled safety interfaces - Leuze lumiflex has filled the gap between traditional relay-based Emergency Stop components and highly sophisticated safety-related PLC controls or bus systems.
The safety interfaces have a multi-channel layout, so that they conform to category 4 as defined by EN 954-1.
Microprocessor controlled MSI interfaces recognise automatically the type of safety light curtain or multi-beam safety light curtain that is connected, irrespective of whether they are equipped with semiconductor output channels or with relays. This happens without any complicated parameterisation, following automatically when the equipment is connected. So it is possible to guide identical or different paths of safety categories through the MSI system (see Illustration 1 below). MSI is available with two or with three relay outputs, as well as with safety-related semiconductor output channels.
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| Illustration 1: MSI from Leuze lumiflex of Fürstenfeldbruck, a versatile performer in connection with applications embodying different safety components and categories |
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MSI diagnosis - getting to grips with faults!
MSI modular interfaces are provided with an RS 232 diagnosis interface for PC-supported graphics display. This gives a visual display of input and output status data and shows the internal status of the system. The data recorder of the MSI diagnosis software makes it possible to record and save data sequences, which can then be sent by e-mail to the Leuze lumiflex hotline for purposes of evaluation and analysis. In this way cable problems, faulty connections or missing sensor signals can be quickly and reliably identified (see Illustration 2). |
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| Illustration 2: MSI's comprehensive diagnosis function is a useful tool in the installation phase and simplifies mainte-nance. |
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A MULTIPLICITY OF APPLICATIONS
The modular design of the MSI series means that it can be adapted to the widest possible range of different tasks. All MSIs have a number of basic functions such as test signal outputs, selectable startup/restart interlock, EDM device monitoring, LED display and status outputs. The following section describes the standard functions, optional special functions and add-ons that are available.
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MSI-sx, a light curtain interface and Emergency Stop switching device combined!
As shown in Illustration 3, MSI-sx processes the output signals of the light curtain at the front of the machine and the locking system for the side entrance. The safety category of the safety path in each case depends on the category of the safety component, and the way in which the safety components are wired with MSI-sx. In the present example the light curtain cannot be ranked higher than category 4 at most; the locking system (with two positive action opening switches and one push rod) con-forms to category 3 standards.
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Illustration 3: MSI-sx - the example shows an appli-cation involving a type 4 safety light curtain for access protection and protective door locking facility in connection with an automated workstation.
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MSI-ix, a controlling light curtain that also secures the back area of presses and punching machines
Illustration 4 shows an application involving a mechanical or hydraulic press. Two category 4 light curtains can be connected to an MSI-ix system. While the safety curtain at the front is responsible for protection and control functions (single cycle or dual cycle operation, for example), the second light curtain serves to protect the back area of the press. Instead of this second light curtain, a safety switch for a protective door would be another possible option.
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| Illustration 4: MSI-ix - the light curtain located at the fron serves for the cyclic control of the hydraulic press. A sec-ond light curtain protects the back area of the press. |
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MSI-mx, a muting function for automated production cells
Muting is the suppression of the safety function under specified conditions, e.g. during the transportation of materials through the protective field of an access control system. In this case there is no need for the production process to be interrupted. But MSI-mx is more than just a common or garden muting controller! As may be seen in Illustration 5, MSI-mx makes it possible for two separate muting zones to be triggered independently of one another, as is the case with the incoming and outgoing stations of production or packaging cells. Additional inputs for further safety components, like Emergency Stop buttons or locking systems, are also available.
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Illustration 5: MSI-mx - showing two muting zones for the incoming and outgoing station of a production or packag-ing assembly line. These can be controlled from just one safety interface.
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MSI-mix, a combination of control and muting functions
MSI-mix has been specially developed for standard presses and bending presses. It makes it possible to control the system in either single cycle or dual cycle operation, or to suppress the safety function while non-hazardous movements are being carried out. In the case of a bending press, for instance, the safety function can be switched off when the tool has closed to a distance of less than 6 mm. Consequently the bending process can be continued, even if the material breaches the protective field as a result. A further light curtain for monitoring the back area of the press, Emergency Stop buttons and/or locking systems are further connection options.
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Illustration 6: MSI-mix - combined cyclic controls and muting functionality in connection with a bending press. Safety light curtain, multi-beam safety light curtain to protect the back area, safety switch and safety interface all from Leuze lumiflex.
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| MSI warning output signals help prevent unwanted machine stoppages. The extended design variants (Rx versions) are equipped with LED displays as well as with warning outputs. They give off the appropriate signal before the expected life cycle of the output relay has been completed. |
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SMALL MEASUREMENTS AND HIGH AVAILABILITY
MSI saves space in the switch cabinet!
In spite of the wide range of functions it provides, the MSI safety interface only takes up very little room in the switch cabinet, with a width of just 35 to 53 mm. As an ex-ample of performance specifications we may refer here to MSI-mx, a component measuring 53 mm in width to which two type 4 safety light curtains or multi-beam safety light barriers, four muting sensors, two muting display lamps and two safety door switches can be connected if desired.
MSI: EU Prototype Testing and Declaration of Conformity
MSI has been subjected to tough testing procedures at the Test Institute of the BIA (Berufsgenossenschaftliches Institut für Arbeitssicherheit [Professional Institute for Health and Safety in the Workplace]) in St. Augustin, as well as EU prototype testing for safety and electromagnetic compatibility, and came through all the tests success-fully. It is supplied with a Declaration of Conformity showing that it conforms to all the relevant European directives.
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Editorial contact
Leuze lumiflex GmbH + Co. KG
Liebigstrasse 4
D-82256 Fürstenfeldbruck
Matthias May
Presse- und Öffentlichkeitsarbeit |
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