Electrical transmission or interconnection systems – Personnel safety or limit control features
Reexamination Certificate
2000-09-27
2001-09-04
Fleming, Fritz (Department: 2836)
Electrical transmission or interconnection systems
Personnel safety or limit control features
C307S328000
Reexamination Certificate
active
06285096
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a safety switch arrangement.
BACKGROUND OF THE INVENTION
A safety switch arrangement of this type is known from German Patent 198 15 150 A1. This patent discloses an arrangement of sensors for monitoring a tool, wherein the tool is put into operation in dependence on the switching states of the sensors. The sensors function as slaves in a bus system operating according to the master-slave principle. The master is a control unit, which cyclically polls the slaves under predetermined addresses.
The sensors are light barriers having, respectively, one transmitter and one receiver, wherein each transmitter transmits light rays with an individual coding to the associated receiver. A redundant evaluation unit is connected to the bus system, which continuously monitors the signals transmitted via the bus system. The tool is made operational by the evaluation unit only in case of an error-free identification of the coding transmitted by the receivers via the bus system.
The arrangement has the advantage that errors in the transmission of signals via the bus system can be detected with a high degree of certainty by evaluating the coding in the evaluation unit.
For this, the sensors advantageously are not required to have a redundant design, but can still monitor the transmission of signals via the bus system with the level of safety that is required for using the arrangement in the area of protection of persons.
In place of sensors, actuators such as emergency-off switches can, in principle, also be connected as slaves in the bus system. Emergency-off switches of this type are designed to have two channels for safety reasons. Thus, each emergency-off switch has two contacts which are opened when the emergency-off switch is actuated. The state of a non-actuated emergency-off switch corresponds to the interference-free operation. Given a clear beam path and this operative state, the codings are transmitted to the evaluation unit in the same way as for a light barrier. The codings can be transmitted, for example, in the form of a 4-bit wide numerical word for which the value changes continuously according to a specific sequence. If the emergency-off switch is activated, it corresponds to an interference that is identical to an object interfering with the beam path of a light barrier. In that case, the emergency-off switch transmits a fixed value for the numerical word, which differs from the codings, to the evaluation unit so that the tool is shut down. The value for the numerical word for a 4-bit numerical word, for example, is “0000”.
It is sufficient to open up one contact of the emergency-off switch to shut down the tool. However, a possible defect in the second contact of the emergency-off switch is not detected in that case. If the second contact of the emergency-off switch also fails, this can result in danger to the operating personnel for the tool, since the tool can no longer be shut down with the emergency-off switch.
BRIEF DESCRIPTION OF THE INVENTION
It is the object of the invention to design a safety switch arrangement of the aforementioned type in such a way that the tool cannot be put into operation if defective safety switches are present.
According to the invention, the safety switch arrangement comprises at least two actuators for switching on or switching off the power supply for the tool, wherein the power supply is activated only if both actuators are activated simultaneously.
The actuators are connected to a code generator. This code generator can issue a numerical word divided into two partial words, wherein the value of a partial word can be influenced respectively by one actuator. In order to test the switching states of the actuators, the partial words of the numerical word are read synchronously into the evaluation unit.
The values of the partial words respectively change continuously if the actuators are activated. The continuous change of the values of the partial words is recorded in the evaluation unit, whereupon the tool is put into operation.
As soon as one of the actuators is deactivated, the assigned partial word assumes a fixed value. In that case, only the values of the partial word that is assigned to the activated actuator still change. Accordingly, the two partial words assume a fixed value if both actuators are deactivated. Thus, it is easy to check which of the actuators is activated at specific points in time by evaluating the values for the two partial words.
The tool is released for operation only if both actuators are activated. As soon as at least one of the actuators is deactivated, the evaluation unit will record this deactivation as the value for the partial word does not change over time. As a result, the tool is shut down.
Owing to the division of the numerical word into partial words, it is possible to monitor each actuator separately via the code generator by using the safety switch arrangement according to the invention, which ensures a high error protection.
The two actuators in particular can also be the switching outputs of light barriers with a redundant design, light grids, and similar sensor devices which are used in the area of protection of persons. In particular, the two actuators can be redundant contacts of an emergency-off switch.
With applications of this type, particularly with emergency-off switches, malfunctions can occur as a result of line defects, so that individual actuators can no longer be switched off or deactivated. With emergency-off switches, this problem can result from a short circuit in the feed lines to one contact for the emergency-off switch. If this error occurs during or following the actuation of the emergency-off switch, then both contacts for the emergency-off switch are initially opened up or switched off. However, due to the short circuit in the feed lines of one of the emergency-off switch contacts, the value of short-circuited partial word continues to change while the value of the other partial word is held to a fixed value when its actuator is deactivated. The numerical word value consequently differs from a predetermined value, resulting in the tool being shut down.
If the tool is to be released again after a specified period of time, the emergency-off switch is actuated and thus released by the operating personnel. Since a short circuit is present in the feed line for one emergency-off switch contact, the value for the partial word assigned to the feed lines with the short circuit had already changed continuously prior to the activation of the emergency-off switch. This is recognized in the evaluation unit. A restart is thus prevented and an error message is issued, even though the values for both partial words change, owing to the activation of the emergency-off switch, which equals an error-free operation. A restart is possible only if both partial words have first assumed the fixed value “0000”.
In principle, an error that occurs can also be stored non-volatile in the evaluation unit. In that case, a restart of the tool, e.g., following a repair, is possible only after a start-up test in which initially the emergency-off switch is not activated, then the emergency-off switch is activated and finally the emergency-off switch is deactivated. The tool is restarted only if the values for the partial words respectively correspond to the predetermined values.
REFERENCES:
patent: 5583386 (1996-12-01), Meixner et al.
patent: 5666010 (1997-09-01), Stratiotis
patent: 5796341 (1998-08-01), Stratiotis
patent: 5796571 (1998-08-01), Wetzel et al.
patent: 198 15 150 (1998-10-01), None
Werner R. Kriesel at al., ASI-Das Aktuator-Sensor Interface für die Automation, Carl Hans Verlag München Wien, 1999.
Muller Bernhard
Schiffmann Michael
Wiesgickl Bernhard
Fleming Fritz
Kinberg Robert
Leuze Electronic GmbH & Co.
Venable
Voorhees Catherine M.
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