Modular safety relay circuit for the safe switching on and/or off of at least one machine

To enable an increase in a service life of a modular safety relay circuit, a modular safety relay circuit is provided for the safe switching on and/or off of at least one machine comprising at least one relay module to which the at least one machine is connected, wherein the relay module comprises at least two relay contacts that are connected in series and that can be brought from a first position into a second position and vice versa; and wherein one relay contact switches in advance by a delay of the other relay contact; and a control unit controlling the relay contacts that alternatingly controls the relay contacts in accordance with a state detection of the relay contacts with the delay.

FIELD

The invention relates to a modular safety relay circuit for the safe switching on and/or off of at least one machine.

BACKGROUND

In today's automation industry, a total plant is autonomously controlled by at least one safety control such that the machine carries out the work assigned to it and optionally interacts with another machine. In this respect, the total plant has to have a sufficient safety level against possible injury to persons or against a failure of the total system despite a high degree of automation and accordingly has to satisfy the specifications of the standard EN ISO 13849, for example.

To satisfy the high safety specifications, an environment of the machine, a position and/or a movement of the machine are monitored by means of sensors, for example, with the safety control actuating at least one safety relay unit circuit that switches the machine off on an unintended operating state.

The safety relay circuit is generally known and has at least one relay module having input terminals and output terminals. The safety relay circuit receives input signals at the input terminals, with the input signals being provided by at least one connected signal transmitter and with output signals being communicated to the at least one machine connected to the relay module via the output terminals, with the output signals being prepared by a control unit of the safety relay circuit in dependence on the input signals.

In other words, using the input signals of the connected signal transmitter, the relay module is able to safely switch the connected machine off and also to switch it back on. For this purpose, the relay module comprises relay contacts upstream of its output terminals, said relay contacts being activated to close or to open by means of a control winding, for example.

In this respect, one relay contact is usually loaded more than another relay contact of the relay module so that this more strongly loaded relay contact theoretically determines a service life of the entire relay module.

SUMMARY

It is therefore an object of the invention to provide a modular safety relay circuit for the secure switching on and/or off of at least one machine with which an increase in the service life of the relay module is possible.

The object is satisfied in accordance with the invention by a modular safety relay circuit for the safe switching on and/or off of at least one machine having at least one relay module to which the at least one machine is connected, wherein the relay module comprises at least two relay contacts that are connected in series and that can be brought from a first position into a second position and vice versa, and wherein a relay contact switches in advance due to a delay of the other relay contact and having a control unit that controls the relay contacts and that alternatingly controls the relay contacts with the delay in accordance with a state detection of the relay contacts.

The advantage hereby results that the relay contacts are uniformly worn so that a maximum possible number of switching procedures of the relay module can be increased.

In accordance with a preferred embodiment, the relay contacts are closed in the first position and the relay contacts are open in the second position or the relay contacts are open in the first position and the relay contacts are closed in the second position. The control unit furthermore advantageously comprises a logic module that carries out the delay on the switching of the relay contact controlled with a delay. A setting of the delay can hereby be changed in a very simple manner.

In accordance with a further preferred embodiment, the delay of the switching is in the single-figure millisecond range on a transition of the relay contacts from the first position into the second position. The relay module thus still has a safe response behavior even though the relay contacts are switched in a controlled delayed manner.

In accordance with a further preferred embodiment, the delay of the switching is in the two-figure to three-figure millisecond range on a transition of the relay contacts from the second position into the first position since a switching procedure of the machine is less time-critical than a switching off thereof.

In accordance with a further preferred embodiment, the state detection for changing the relay contact with the delay comprises a number of actuated switching cycles of the relay contacts. The control unit can monitor and control the wear of the relay contacts fully automatically in this manner.

In accordance with a further preferred embodiment, the delay can be switched on or off manually by an operator, whereby the operator can very easily choose between a high response time, namely the switching off of the delay, or a longer service life, namely switching on the delay, of the relay module or of its relay contacts.

DETAILED DESCRIPTION

FIG. 1schematically shows an automation plant that comprises a modular safety relay circuit1in accordance with the invention to which a machine is connected. The safety relay circuit1switches a load circuit on or off that supplies the machine, shown by way of example as a robot arm R, with energy. The switching on and off of the machine can here by carried out safely or only a safe switching on or only a safe switching off so that different application cases can be satisfied by the safety relay circuit1.

The safety relay circuit1shown comprises a relay module2that has input terminals2-I and output terminals2-O, with a camera K and a light grid LG, for example, being able to be connected as signal transmitters to the input terminals2-I. The robot arm R is connected to the output terminal2-O so that the relay module2can switch a power supply to the robot arm R off or on in dependence on the signals of the camera K or of the light grid LG.

The signals of the signal transmitter are supplied to a control unit CPU that evaluates the signals. The control unit CPU generates corresponding control signals with reference to the evaluation to safely control the robot arm R. This means, for example in the event that a protected field of the light grid LG is interrupted, the control unit CPU generates a corresponding control signal to disconnect the robot arm R from the power supply. If the protected field of the light grid LG remains interrupted, the control unit CPU does not permit any switching back on of the robot arm R.

For this purpose, the relay module2comprises in accordance with the invention at least two relay contacts3a,3band4a,4bthat are connected in series and that can be brought from a first position into a second position and vice versa. By way of example, the relay contacts3a,3band4a,4bare closed in the first position and are open in the second position. In the first, closed position of the relay contacts3a,3band4a,4b, the robot arm R is connected to the power supply at the output terminals2-O of the relay module2and in the second, open position of the relay contacts3a,3band4a,4bthe robot arm R is disconnected from the power supply.

This example can also be configured in the opposite manner depending on the application case required. This means that with a required disconnection of the robot arm R from the power supply in the base state, the relay contacts3a,3band4a,4bare open in the first position and are closed in the second position.

The control unit CPU that can be a computer processor moves both relay contacts3aand3bor4aand4bconnected in series from the closed position into the open position or also conversely in dependence on the signals of the signal transmitter, with the robot arm R also being reliably controlled when one of the two relay contacts3aor3bor4aor4bconnected in series has a malfunction in the form, for example, of a welding of the relay contacts3aor3bor4aor4b.

In the embodiment shown, bot output terminals2-O of the relay module2have to be connected to the power supply so that the robot arm R can move into operation. If one of the two relay contacts3a,3band4a,4bis not closed, the robot arm R remains out of operation. This means that with the shown wiring of the relay module2, a safe control of the robot arm R is achieved in a two-channel redundant manner.

In accordance with the invention, one of the two relay contacts3aor4aconnected in series switches in advance by a delay of a switching of the other relay contact3bor4bconnected in series, with the control unit CPU controlling the relay contacts3a,3band4a,4bdetermining a state of the relay contacts3a,3band4a,4band alternatingly controlling the relay contacts3aor3band4aor4bwith the delay in accordance with a state detection or the detected state of the relay contacts3a,3band4a,4b. “In advance” is understood such that one of the relay contacts3aor3band4aor4bconnected in series always switches before the other relay contact3bor3aand4bor4a.

In other words and with respect to the embodiment inFIG. 1, the control unit CPU controls the relay contacts3bor4located closer to the output terminals2-O with the delay so that the relay contacts3aor4alocated further from the output terminals2-O switch before the respective relay contacts3bor4bcontrolled with the delay. The control unit CPU in so doing detects the state of the relay contacts3a,3and4a,4band changes the control of the relay contacts3bor4bwith the delay in accordance with the state of the relay contacts3a,3band4a,4bsuch that the relay contacts3aor4aswitched in advance up to then switch after the relay contacts3bor4bswitched with a delay up to then.

This means the relay contacts3aor4aswitched in advance are controlled with the delay by the control unit CPU such that the relay contacts3bor4bconnected with the delay up to then are now switched in advance. After a repeat detection of the state of the relay contacts3a,3band4a,4b, the control unit CPU again changes the control with the delay in the relay contacts3a,3band4a,4b, whereby a uniform wear of the relay contacts3a,3band4a,4bcan be ensured to extend the service life of the relay module2or of the modular safety relay circuit1.

The control unit CPU in this respect preferably comprises a logic module that performs the delay on the switching of the relay contacts3bor4bconnected in series. The logic module enables a fast and simple adaptation of the control unit CPU as required to optionally change the alternating control of the relay contacts3a,3band4a,4bwith the delay in accordance with the state detection of the relay contacts3a,3band4a,4b.

The detection of the state of the relay contacts3aor3bor4aor4b, for example, comprises a number of actuated switching cycles of the relay contacts3aor3bor4aor4bto change an order of the relay contacts3aor3bor4aor4bcontrolled with the delay. This means that after X actuated switching cycles, where X is a natural number, the relay contacts3aor4aare controlled with the delay instead of the relay contacts3bor4bcontrolled with the delay up to then. After a further Y actuated switching cycles, where Y is a natural number, the control unit CPU again changes the order of the relay contacts3bor4bcontrolled with the delay.

The natural number Y of the actuated switching cycles of the relay contacts3a,3band4a,4bcan be the same as or smaller than the natural number X of the actuated switching cycles of the relay contacts3a3band4a,4bat the start of operation of the relay module2or of the safety relay circuit1depending on the operating time period of the relay module2or of the safety relay circuit1. A time period between the changing of the delayed control of the delayed control of the relay contacts3a,3band4a,4bcan hereby be shortened in accordance with the previous operating time period so that a wear of the relay contacts3a,3band4a,4bby the operating duration can also be taken into account in the alternating change of the delayed control of the relay contacts3a,3band4a,4b. This results in increased security against a failure of the relay module2or of the safety relay circuit1.

The delay of the switching of the relay contacts3aor3bor4aor4bis in particular in the single-figure millisecond range, preferably 1 to 5 milliseconds, on a transition of the relay contacts3a,3band4a,4bfrom the first, closed position into the second, open position. This means that on the switch-off procedure of the robot arm R, a fast switching of the relay contacts3a,3band4a,4bis relevant to safety so that the delayed control of one of the two relay contacts3a,3band4a,4bconnected in series may not effect any relevant increase of a response behavior of the relay module2or of the safety relay circuit1.

On a transition of the relay contacts3a,3band4a,4bfrom the second, open position into the first, closed position, the delay of the switching of the relay contacts3a,3band4a,4bis in the two-figure to three-figure millisecond range, preferably in the range of several 100 milliseconds. This means that the switch-on procedure of the robot arm R is less time critical so that the delayed control of one of the two relay contacts3a,3band4a,4bconnected in series can effect an increased response behavior of the relay module2or of the safety relay circuit1.

The logic module of the control unit CPU furthermore makes it possible for an operator to manually switch the delay of the switching of the relay contacts3a,3band4a,4bon or off. The operator can achieve an improved, uniform wear of the relay contacts3a,3band4a,4band thus an increase in the service life of the relay module2or of the safety relay circuit1by the switching on of the delay of the switching of the relay contacts3a,3band4a,4b. If, however, a high, unchanged response behavior of the relay module2or of the safety relay circuit1is required for safety reasons, the operator can switch off the delay of the switching of the relay contacts3a,3band4a,4bor can leave it inactivated.

REFERENCE NUMERAL LIST

1modular safety relay circuit

2-I input terminal of the relay module

2-O output terminal of the relay module

CPU control unit

K camera

LG light grid

R robot arm