EP2494534B1 - Safety communication system for signaling system states - Google Patents

Description

The present invention relates to a security communication system having an evaluation unit and a number of subscribers connected in series, each having a sensor, and a method for signaling system states.

Such a security communication system is in EP0362797 A2 as in WO8101624 A1 disclosed.

To avert danger to people, machinery and equipment in automation usually emergency stop and / or other sensors are provided at appropriate facilities with which the machinery or equipment can be switched off and put in a safe state. In spatially extended systems or automation systems, it is also necessary to provide several sensors, such as emergency stop button, temperature sensors, pressure sensors, floor mats, light barriers and the like, to ensure optimum accessibility in the event of danger.

It is an object of the present invention to provide a security communication system and a method by which a signal for a critical system condition, e.g. an emergency signal, reliably signaled and the source of a signal can be clearly located.

To solve this problem, the present invention proposes a security communication system according to claim 1, which comprises an evaluation unit comprises, to which a number of subscribers connected in series is connected.

The evaluation unit has a signal output, a signal input, a ground connection and a device for providing a predetermined signal for the subscribers.

The subscribers each have a signal input, a signal output, a ground connection for a reference potential, a sensor and an electronic circuit. Each electronic circuit is configured to modulate the predetermined signal to signal the system status represented by the output of the respective sensor.

The evaluation unit is designed to evaluate the modulated predetermined signal and to control a safety function in response to the evaluation result.

The sensor may be, for example, an emergency stop switch, a temperature sensor, a pressure sensor, a step mat, a photoelectric barrier and a protective grid. The output signal of a sensor indicates a critical or a non-critical system state. A critical system status causes the evaluation unit to trigger a safety function. Advantageously, the predetermined signal is modulated by the subscribers such that the evaluation unit in response to the modulated predetermined signal or which can locate those subscribers who have signaled a critical system condition.

An advantageous embodiment provides that the electronic circuit of each subscriber comprises a logic module and at least one transistor, wherein the transistor can be controlled by the logic module. The transistor is arranged between the signal input to the signal output of the respective subscriber and adapted to modulate the predetermined signal applied to the signal input and to transmit via the signal output to the evaluation unit or a downstream subscriber.

The electronic circuit can furthermore be designed to obtain a supply voltage for the subscriber directly from the predetermined signal present at the signal input (21, 31, 41), so that no separate auxiliary power has to be provided.

The electronic circuit expediently comprises a second transistor with which the signal input can be switched to the reference potential.

The logic module of the electronic circuit is preferably equipped with an internal function monitoring, wherein over the second transistor signaling of an error condition can take place by the predetermined signal pulled to the reference potential and thus no longer transmitted to the input of the evaluation.

The above technical problem is further solved by the method steps of claim 6.

Accordingly, a method for signaling system states of multiple serially connected subscribers of a security communication system is provided.

In order for each participant to signal the activation of a sensor, the predetermined signal contains a signal pulse whose pulse length depends on the number of subscribers connected in series.

Conveniently, steps c) and e) provide for this that each participant modulates the signal pulse of the predetermined signal as a function of the system state of its sensor.

In order to be able to locate the subscriber who has signaled a critical system state, each subscriber preferably modulates the signal pulse of the predetermined signal according to their position in the security communication system. Each participant preferably modulates the signal pulse at the point assigned to it within the signal pulse and / or preferably with an individual modulation signal.

In order for the subscribers to be able to reliably recognize the predetermined signal, the predetermined signal may include a start pulse and a first pause preceding the signal pulse. Furthermore, the signal pulse may include an end pulse followed by a second pause which is longer in time than the first pause.

To be able to ensure monitoring of a system during the entire operation, the steps a) to 9) are repeated cyclically or at predetermined times, whereby the switching states of the participants can be transmitted cyclically or at the predetermined times to the evaluation unit.

Expediently, before the execution of step a), a configuration phase is run through in which the evaluation unit determines the number of subscribers within the security communication system and in which the subscribers determine their position within the security communication system.

The security communication system according to the invention is distinguished from known security systems by a localizability of all in the security communication system participants who signal a critical system state. By automatically determining the number and position of the participants, such a security communication system is particularly easy to extend.

The shape and frequency of the predetermined signal have sufficient robustness to spurious emissions so that security communication systems with line lengths greater than 1 km in length are possible. The cycle times of the signal transmission are sufficiently short for more than 20 subscribers to meet the requirements of safety technology for automation systems.

Fig. 1

einen Notausschaltreis mit drei Notauseinheiten und einer Auswerteeinheit,

Fig. 2

ein schematisches Schaltbild einer Notauseinheit mit einem an einer elektronischen Schaltung angekoppelten Notausschalter,

Fig. 3

ein Signal-Zeitdiagramm des Notausschaltkreises während einer automatischen Konfigurationsphase,

Fig. 4

ein Signal-Zeitdiagramm des Notausschaltkreises während eines normalen Arbeitsbetriebs, d.h. wenn kein Notausschalter geschaltet ist, und

Fig. 5

ein Signal-Zeitdiagramm des Notausschaltkreises bei zwei von drei aktivierten.

The invention will now be described in detail by way of an exemplary embodiment with reference to the accompanying drawings. In the drawings show:

Fig. 1

an emergency stop circuit with three emergency units and an evaluation unit,

Fig. 2

a schematic diagram of an emergency unit with a coupled to an electronic circuit emergency stop switch,

Fig. 3

a signal-time diagram of the emergency stop circuit during an automatic configuration phase,

Fig. 4

a signal-time diagram of the emergency stop circuit during a normal working operation, ie when no emergency stop switch is switched, and

Fig. 5

a signal-time diagram of the emergency stop circuit at two of three activated.

That in the FIG. 1 Security communication system 1 illustrated by way of example may be an emergency shutdown circuit which has an evaluation unit 10 and, for example, three subscribers 20, 30 and 40 connected in series, which are distributed, for example, in a field to a wide-area automation system. The participants 20, 30, 40 are also referred to below as Notauseinheiten, each having an emergency stop button 23, 33, 43 as a sensor with which a safety function can be requested on an equal basis. The series-connected participants 20, 30, 40 form a subscriber chain.

Like from the FIG. 1 it can be seen, the emergency stop switches 23, 33, 43 are each connected to an electronic circuit 24, 34, 44, which provide a secure electronic coupling to the emergency stop circuit for each emergency stop.

The evaluation unit 10 has a signal output 11 and a signal input 12, to which the three Notauseinheiten 20, 30 and 40 are connected in series.

The emergency cutouts are interconnected via signal inputs 21, 31, 41 and signal outputs 22, 32, 42 provided by the electronic circuits 24, 34, 44, respectively.

The evaluation unit 10 may have not shown further signal outputs and signal inputs to which further Notauseinheiten not shown are connected in series, which form additional parallel subscriber chains.

In order for the emergency units to be able to signal in particular the actuation of the respective emergency stop switch of the evaluation unit 10, the evaluation unit 10 generates a predetermined signal UA (see FIG Fig. 4 ) output at the signal output 11. This signal UA can essentially be embodied as a binary voltage signal which is varied between a high and a low level, wherein the low level preferably corresponds to the reference potential GND at a ground terminal 15 of the evaluation unit 10. The voltage signal UA serves to transmit information between the emergency units and the evaluation unit and advantageously also provides a supply voltage for the electronic circuits 24, 34, 44 and / or for the sensors.

The circuits 24, 34, 44 of the Notauseinheiten 20, 30, 40 of the emergency stop circuit 1 are constructed identically, so that in the FIG. 2 only the diagram of the emergency unit 20 is exemplified. The diagram illustrates in particular the structure of the circuit 24 in detail.

The circuit 24 comprises a signal input 21, a signal output 22 and a logic module 210, which can preferably be realized by a microcontroller or alternatively by an FPGA, CPLD or an ASIC.

The emergency stop switch 23 is connected via two channels to the logic module 210 via ports P8 and P9 as well as ports P11 and P12. For such a two-channel and thus secure connection to the circuit, all two-channel emergency stop switches available on the market are basically suitable, i. In principle, both emergency stop switches with two NC or two NO contacts, as well as an NC / NO pair can be used for the emergency stop unit. The appropriately used switch type must be set only by soft or hardware means to the logic device 210. Alternatively, other sensor types, such as running mats, temperature and pressure sensors, light barriers, protective grids, etc., can also be connected to an emergency stop unit. Furthermore, several sensors can be connected via an emergency stop unit via different ports of the logic module 210.

The circuit 24 comprises a transistor 220 and optionally a transistor 260, which are connected with their respective gate terminal to the logic device 210. The transistor 220 is between the signal input 21 and the Signal output 22 is connected, while the transistor 260 is connected between the signal input 21 and the ground terminal 25. Alternatively, the second transistor 260 could also be connected between the signal output 22 and the ground connection 25. The logic module 210 controls the transistors 220 and 260 in such a way that the voltage signal UA applied to the signal input 21, which is the predetermined signal, can be modulated by the transistor 220 and output to the signal output 22. By means of the transistor 260, the voltage signal UA at the input 21 can be pulled to the reference potential of the ground terminal 25, whereby all participants of Notausschaltkreises, ie the evaluation unit 10 and the other following in the series circuit Notauseinheiten 33, 43 an error condition can be signaled.

The electronic circuit 24 further has a diode 231 and a capacitor 232 which are connected in series between the signal input 21 and the ground terminal 25 to the reference potential GND and provide a power supply for the logic device 210 via a supply device 233. For example, the supply device 233 may be designed as a switched-mode power supply or as a voltage regulator.

From a signal varying between 0 V and 24 V at the signal input 21, a constant supply voltage of eg 3.3 V or 5 V can be obtained for the logic module, so that in a preferred manner no additional line for an auxiliary power of Notauseinheiten 20, 30, 40th in an emergency stop circuit is required.

Alternatively, however, can also lead an additional line, the supply voltage to the Notauseinheiten and this associated emergency stop. The power supply does not take place in this case via the signal lines, so that the diode 231 and the capacitor 232 can be omitted in favor of an additional connection.

The function of the emergency stop circuit 1 and the individual emergency units connected in series will be described below with reference to FIGS FIGS. 3 to 5 illustrated signal-time diagrams for different operating conditions explained. At this point it should be expressly noted that on the in the FIG. 1 Emergency shutdown circuit shown by way of example only three Notauseinheiten are connected. The emergency shutdown circuit 1 is basically suitable for use with a large number of emergency units distributed along a route of a spatially extended automation system and connected in series with one another. In particular, the emergency shutdown circuit 1 allows for easy expandability with additional emergency disengaging units that may be inserted, for example, between the emergency shutdown unit 30 and the emergency shutdown unit 40. The safety function of the emergency stop circuit is guaranteed from a connected emergency stop unit.

At each start-up of the emergency stop circuit 1 first passes through a configuration phase in which the number of connected Notauseinheiten 20, 30, 40 is determined by the evaluation unit 10 and determine the Notauseinheiten their position in the series circuit. At the start In this configuration phase, the transistor 220 of a respective emergency unit is initially disabled, so that the in FIG. 3 shown configuration signals at the signal inputs 21, 31, 41 of the respective Notauseinheiten initially not be forwarded to the signal outputs 22, 32, 42.

In the FIG. 3 are the voltage waveforms of the generated during the configuration phase configuration signals UAk, UBk, UCk and UDk, which abut each of the signal inputs 21, 31, 41 of the emergency unit 20, 30 and 40 and the signal input 12 of the evaluation unit 10 is shown. The configuration signal UAk is generated by the evaluation unit and transmitted via the signal output 11 to the input 21 of the first emergency stop unit 20. The configuration signal UAk is generated for example by a microcontroller in the evaluation unit 10 and follows a predetermined pulse sequence with respect to a system clock.

At time t1, a first energy pulse 311 is initially applied to the signal output 11, which remains present for a period of three clock cycles Tb and essentially serves to supply the emergency output units. The signal UAk is reset for one clock, so that a signal pause 312 follows the energy pulse 311. Subsequently, a signal pulse 313 is sent over the duration of a clock followed by a second pause 314 of two clocks.

With view on FIG. 2 It will be appreciated that the first emergency unit 20 is awakened by the energy pulse 311. The voltage signal UAk delivered by the evaluation unit 10 lies between the input 21 and the Ground connection 25. It provides a charging current over the duration of the three clocks, which flows in the flow direction through the diode 231. The capacitor 232 is charged during this time and thus provides the supply voltage for the supply device 233 and the microcontroller 210, in particular during the signal pauses. The microcontroller of the emergency unit 20 thus begins its operation and recognizes via a signal detection device, which is formed from the voltage divider of the resistors 241 and 242, consequently the individual subsequent signal pulse 313 before the second break 314. The emergency unit 20 registers itself as the first participant in the series connection of the emergency stop circuit 1 to the evaluation unit 10th

Meanwhile, the evaluation unit 10 initially detects no input voltage at its own signal input 12 and concludes that at least one emergency shutdown unit is connected in the emergency shutdown circuit.

Accordingly, the evaluation unit 10 outputs a second energy pulse 321 via the signal output 11, which is followed, after a break 322, by a second signal pulse 323, which is three clocks wide. The first emergency stop unit 20 receives at its signal input 21 the energy pulse 321 and the signal pulse 323 of the signal UAk and outputs these pulses through the now open transistor 220 to the signal output 22 as a second signal UBk, wherein the second signal UBk modulated by the emergency stop unit 20 so is that the signal pulse 323 is hidden during a clock Tb. The second signal UBk contains thus a high level 3231, a low level 3232 and a second high level 3233.

The second emergency stop unit 30 consequently receives at its signal input 31 the voltage signal UBk, which identifies the energy pulse 321 and subsequently the high level 3231, the low level 3232 and the second high level 3233. The voltage signal UBk thus corresponds to the modulated signal UAk, which has been generated by the evaluation unit 10. The emergency unit 30 is now activated by the energy pulse 321 and recognizes itself as a second party, i. as a second emergency stop unit 30 in the emergency stop circuit.

The evaluation unit 10 further detects no input signal at its signal input 12 and outputs a third energy pulse 331 via the signal output 11, followed by a signal pause 332 and a third signal pulse 333. The third signal pulse 333 is widened compared to the previous cycle second signal pulse 323 by a further two clocks, and thus comprises a total of a width of 5 clocks Tb.

The Notauseinheiten 20 and 30 respectively give a modulated signal UBk or UCk (see Fig. 3 ) via their respective signal output 22, 32. The first emergency stop unit 20 modulates the signal UAk such that the signal pulse 333 is hidden during a clock Tb. The second signal UBk thus contains a high level and a low level of the length Tb and a second high level 333 'of three times the length of Tb. The second emergency stop unit 30 receives the signal UBk and modulates its signal pulse 333 'such that the signal pulse 333' is hidden during a clock Tb. The signal UCk thus contains a high level 3333, a low level 3334 and a second high level 3335 each of the clock length Tb.

The third emergency stop unit 40 receives the signal UCk and recognizes itself as the third emergency stop unit 40 in the emergency stop circuit, while the evaluation unit 10 continues to receive no input signal at its signal input 12.

The evaluation unit 10 sends in its signal UAk another energy pulse 341 and a fourth signal pulse 343, which is extended compared to the third signal pulse 331 again by two clocks Tb, and thus comprises a total width of seven clocks Tb. The transmitted signal UAk is modulated and forwarded by each emergency stop unit 20, 30, and 40. In this case, each emergency unit modulates the signal UAk in such a way, for example, that each emergency shutdown unit inserts a low level of length Tb into the signal pulse 343, ie that one clock in each case is faded out within the signal pulse 343. The signals UBk, UCk and UDk respectively modulated by the emergency cutouts 20, 30 and 40 are in Fig. 3 shown. At the signal output 42 of the third emergency stop unit 40, the signal UDk is output, which contains the energy pulse 341 as well as the signal pulse 343 modulated by all three emergency cutouts, which contains four high levels 3431, 3433, 3435 and 3437, each by a low level from each other are separated.

The evaluation unit 10 now receives at its signal input 12 from the emergency stop unit 40 passed signal UDk and thus registers a total of three emergency cutouts 20, 30, 40 connected to the emergency stop circuit and thus completes the configuration phase.

If the configuration of the emergency stop circuit fails due to the influence of electromagnetic interference, the configuration phase can also be repeated several times until stable communication is established.

At the in the FIG. 3 shown time profiles of the differential voltages (UAk-UBk), (UBk-UCk) and (UCk-UDk) shows in which time intervals, the capacitors 323 of Notauseinheiten 20, 30 and 40 are charged.

Alternatively, at the subscribers, ie in the present example, the emergency disbursements, their respective position in a subscriber chain could be manually set, which are coded for example by DIP switches or stored in a non-volatile memory. In the same way, the number of existing Notauseinheiten can be set or stored on or in the evaluation unit 10. The configuration phase after the startup of the emergency stop circuit is replaced in this case by an initialization phase, during which the participants are supplied with energy at the same time. For this purpose, for example, a long energy pulse is provided. Preferably, after a first startup, a configuration phase can be triggered manually, after which the configuration data of the emergency stop circuit is stored in the nonvolatile memories of the users, so that after each further commissioning, only the initialization phase has to be run through.

FIG. 4 represents the normal operation of the emergency stop circuit 1 under the condition that no emergency stop switch 23, 33, 43 has been operated.

After the completion of the configuration phase, the evaluation unit 10 generates an exemplary, cyclical, predetermined signal UA, which is output via the signal output 11 to the first emergency stop unit 20. The temporal waveform of the signal UA is in the FIG. 4 shown above. The signal UA contains in each cycle a start pulse 410 having the width of a clock Tb, followed by a pause or low level 420 of length Tb. The pause 420 is followed by a signal pulse 430 whose length depends on the number of emergency cutouts present in the emergency stop circuit. The signal pulse 430 contains in each case two clocks Tb for each emergency stop unit connected to the emergency stop circuit 1 and an additional end pulse 437 of length Tb. In the present example, with a total of three connected emergency cutouts 20, 30 and 40, this corresponds to a signal width of seven clock lengths Tb Signal pulse 430 is followed by a pause or low level 440 of two clock lengths Tb, with which a signal cycle is completed.

The emergency stop unit 20 receives the above-described signal UA at the signal input 21 in each cycle and modulates the signal pulse 430, for example, such that during predetermined clocks the signal pulse 430 is hidden.

In the present example, the signal pulse 430 is modulated by means of the transistor 70 in such a way that the signal pulse 430 starts with a high level 431 of length Tb, followed by a low level 432, that is to say a hidden section, of length Tb. The remainder of the signal pulse 430, which is in Fig. 4 with 430 'is not modulated. The modulated signal UA is now transmitted as a signal UB to the emergency stop unit 30. The emergency stop unit 30 thus receives the start pulse 410, the pause 420 and the modulated signal pulses 431, 432 and 430 '. In the present example, the emergency unit 30 merely modulates the signal pulse 430 'of the received signal UB in a manner similar to the emergency unit 20. To this end, the signal pulse 430' is modulated to start at a high level of length Tb which is a low level or hidden portion of the length Tb connects. The remainder of the signal pulse 430 ', which is in Fig. 4 is not modulated, the modulated signal UB is now transmitted as a signal UC to the emergency unit 40.

The emergency stop unit 40 thus receives the start pulse 410, the pause 420 and the signal pulse modulated by the upstream emergency units 20 and 30. In the present example, the emergency unit 40 merely modulates the signal pulse 430 "of the received signal UC in a manner similar to the emergency units 20 and 30. For this purpose, the signal pulse 430" is modulated to start with a high level of length Tb. which is followed by a low level or hidden portion of the length Tb. The remainder of the signal pulse 430 ", which only contains the end pulse 437, is not modulated, The modulated signal UC now becomes the evaluation unit 10 as the signal UD. transfer. The signal pulse 430 initially generated by the evaluation unit 10 now comprises three high levels 431, 433 and 435 corresponding to the number of emergency units present and the end pulse 437 which are each separated by a hidden section. The evaluation unit 10 recognizes from the received signal DU that no emergency stop switch has been actuated. The difference signals (UA-UB), (UB-UC) and (UC-UD) show at which time intervals the capacitors 90 of the emergency cut-off units 20, 30 and 40 are recharged. To recharge the power supply, the signal pulse is used in each case, which is hidden during the transfer or during the modulation by the respective emergency unit.

The FIG. 5 shows the signal-time diagrams in the event that the first and third Notauseinheit 20 and 40 at time t3 report an actuated emergency stop, while the second emergency unit 30 of the series circuit sends no emergency stop signal. The time t3 can be understood to mean that the evaluation unit 10 has already transmitted a plurality of signals UA, wherein no actuation of an emergency stop switch has been signaled until the time t3 of the evaluation unit 10.

The evaluation unit 10 further generates the in FIG. 4 described cyclic, predetermined signal UA, which is output via the signal output 11 to the first emergency stop unit 20. The temporal waveform of the signal UA is in the FIG. 5 shown above and corresponds to that in the FIG. 4 represented signal.

The emergency shutdown unit 20 receives the already described signal UA at the signal input 21 in the current cycle and modulates the signal pulse 530, which corresponds to the signal pulse 430 of the in Fig. 4 shown signal UA, such that the operation of the emergency switch 23 of the evaluation unit 10 can be signaled. For this purpose, the in Fig. 5 represented signal pulses 530 are modulated by means of the transistor 70 such that the received signal pulse 530 starts with two low levels 531, 532, which have the length 2Tb. In other words, the signal pulse 530 in the emergency off unit 20 is blanked out for the time of a double clock length Tb. The remainder of the signal pulse 530, which is in Fig. 5 denoted by 530 'is not modulated. The modulated signal UA is now transmitted as a signal UB to the emergency stop unit 30. The emergency stop unit 30 thus receives the start pulse 510, the pause 520 and the modulated signal pulse resulting from the low levels 531 and 532 and the high level 530 '. Since the emergency unit 30 does not have to signal an emergency stop signal, it modulates the signal pulse 530 'of the received signal UB in the same way as in the example which is based on the FIG. 4 has been explained. The signal pulse 530 'is therefore modulated so that it starts with a high level 533 of length Tb, followed by a low level 534 and hidden portion of the length Tb. The remainder of the signal pulse 530 ', which is in Fig. 4 is not modulated, the modulated signal UB is now transmitted as a signal UC to the emergency unit 40.

The emergency stop unit 40 thus receives the start pulse 510, the break 520 and the signal pulse modulated by the upstream emergency units 20 and 30. The emergency unit 40 only modulates the signal pulse 530 "of the received signal UC, in such a way that the actuation of the emergency stop switch 43 can be signaled For this purpose, the signal pulse 530" is modulated in such a way that it has two low levels 535 and 536 or two blanked sections each of length Tb begins. The remainder of the signal pulse 530 ", which only contains the end pulse 537, is not modulated, The modulated signal UC is now transmitted as the signal UD to the evaluation unit 10.

The signal pulse 530 initially generated by the evaluation unit 10 now comprises a high level 533 and the end pulse 537. The evaluation unit 10 recognizes from the low levels 531, 532 and 535, 536 of the received signal UD that the emergency stop switches 23 and 43 of the emergency shutdown units 20 and 40 have been operated.

Instead of the method described above, the configuration phase could initially be followed by a reporting phase, which is not shown in the figures. Within this reporting phase, the emergency dispensers 20, 30, 40 of the evaluation unit 10 only signal whether or not the security function has to be activated at all.

For this purpose, the evaluation unit 10 sends a cyclical, predetermined signal to the first emergency stop unit 20 via its signal output 11. This signal comprises a characteristic start pulse, which preferably differs from the starting pulse of the operating mode, for example in the width, followed by a signal pulse having a predetermined width. The predetermined width the signal pulse is preferably not dependent on the number of Notauseinheiten in a subscriber circle in the reporting phase.

All Notauseinheiten 20, 30, 40 receive the predetermined signal at its signal input 21, 31, 41 and forward this non-modulated to the subsequent participants, unless an emergency stop button has been pressed. If one of the emergency units is to have a critical system status, i. an actuated emergency stop switch, are signaled, the received signal can be modulated by hiding a predetermined position in the signal pulse. During the reporting phase, all emergency units are assigned the same position in the signal pulse for signaling. The signaling of one or more critical system states by one or more participants is thus OR-linked.

The evaluation unit 10 is therefore only signaled in this reporting phase, if any critical system state, i. an actuated emergency stop switch is present and whether the safety function is to be activated.

As soon as an emergency stop unit 20, 30, 40 signals an actuated emergency stop switch, the emergency stop circuit is set by the evaluation unit 10 into the operating mode described above. The evaluation unit determines in the method described above which emergency shutdown unit signals an actuated emergency stop switch.

The reporting phase offers shorter cycle times compared to the above-described operating mode, as long as no actuated emergency stop switch is signaled. This is particularly advantageous for a large number of emergency units in the subscriber chain.

If errors occur, for example, as a result of short circuits or line breaks in the emergency stop circuit 1, then the evaluation unit 10 receives at least no complete signal UD at its signal input 12. In response to an incompletely received signal UD, the evaluation unit 10 can also trigger a safety-based function and signal an error.

The microcontroller 210 of the emergency units 20, 30, 40 can additionally determine an internal malfunction, for example a failed channel of a two-channel connected emergency stop switch, independently. Such an error can be signaled by an emergency stop unit, for example the emergency stop unit 20, of the evaluation unit 10 in that the transistor 260 of the electronic circuit 24 short-circuits the signal input 21 to the ground terminal 25. The evaluation unit 10 thus receives an incomplete signal UD and closes from the transmitted short-circuit signal to a faulty signal UD and can then trigger a safety-related function and / or an error signal. In order to control a modulated signal, a second signal recognition device comprising the resistors 251 and 250 may be provided at the signal output 22, 32, 42 of an emergency stop unit 20, 30, 40.

Claims (11)

1. A safety communication system (1) for providing a safety function, comprising:

   an evaluation unit (10) and connected thereto a plurality of subscriber devices (20, 30, 40) which are connected in series; wherein

   the evaluation unit (10) has a signal output (11), a signal input (12), a ground connection (15), and means for providing a predefined signal for the first subscriber device, the predefined signal including a signal pulse of a pulse length that depends on the number of subscriber devices connected in series;

   the subscriber devices (20, 30, 40) each include a signal input (21, 31, 41), a signal output (22, 32, 42), a ground connection (25, 35, 45) for a reference potential, a sensor (23, 33, 43), and an electronic circuit (24, 34, 44); wherein

   each electronic circuit (24, 34, 44) is adapted to modulate the signal pulse of the predefined signal according to its position in the safety communication system and to transmit the modulated predefined signal via the signal output to the next downstream subscriber device, or at the end of the series to the evaluation unit (10) in order to signal a critical or non-critical system state which is represented by the output signal of the respective sensor; and wherein

   the evaluation unit is adapted to evaluate the modulated predefined signal and to control a safety function in response to the evaluation result.
2. The safety communication system according to claim 1, characterized in that based on the modulated predefined signal the evaluation unit (10) is capable to localize the subscriber device or those subscriber devices which have signaled a critical system state.
3. The safety communication system according to claim 2, characterized in that the electronic circuit (24, 34, 44) of each subscriber device includes a logic device (60) and at least one transistor (220), wherein the transistor (210) is controllable by the logic device (210) and is arranged between the signal input (21, 31, 41) and the signal output (22, 32, 42) of the respective subscriber device, and is adapted to modulate the predefined signal applied to the signal input (21, 31, 41) and to transfer it via the signal output (22, 32, 42) to the evaluation unit (10) or to a downstream subscriber device.
4. The safety communication system according to claim 3, characterized in that each electronic circuit (24, 34, 44) is adapted to be capable to obtain a supply voltage from the predefined signal applied to the signal input (21, 31, 41).
5. The safety communication system according to claim 3 or 4, characterized in that each electronic circuit (24, 34, 44) comprises a second transistor (260) by means of which the signal input (21, 31, 42) is connectable to the reference potential (25, 35, 45).
6. A method for signaling at least one system state of a safety communication system (1) which comprises an evaluation unit (10) and a plurality of subscriber devices (20, 30, 40) connected in series, wherein each subscriber device has associated therewith at least one sensor, comprising the steps of:

   a) generating, in the evaluation unit (10), a predefined signal (UA), wherein the predefined signal includes a signal pulse whose pulse length depends on the number of subscriber devices connected in series;

   b) outputting the predefined signal (UA) from the evaluation unit (10) to the first subscriber device (20) of the safety communication system;

   c) modulating the signal pulse of the received predefined signal in the first subscriber device (10) according to the position thereof in the safety communication system and based on the output signal provided by a sensor (23) that is associated with the first subscriber device, and outputting the modulated predefined signal to a further subscriber device (30);

   d) modulating the signal pulse of the received modulated predefined signal in the further subscriber device (30) according to the position thereof in the safety communication system and in response to the state signal which is provided by a sensor (33) associated with the further subscriber device, and outputting the modulated predefined signal to a further subscriber device;

   e) repeating step d) in function of the number of subscriber devices in the safety communication system;

   f) outputting the modulated predefined signal (UD) from the last subscriber device (40) of the safety communication system to the evaluation unit (10);

   g) evaluating, in the evaluation unit, the received modulated predefined signal, and controlling a safety function if a critical system state was signaled by at least one subscriber device.
7. The method according to claim 6, characterized in that the predefined signal includes a start pulse and a first pause preceding the signal pulse, and the signal pulse includes a final pulse which is followed by a second pause which is longer in time than the first pause.
8. The method according to claim 6 or 7, characterized in that the received predefined signal or the received modulated predefined signal is modulated by masking out the signal pulse at least at one predetermined point for a predetermined time.
9. The method according to claim 8, characterized in that the masked-out portion of the signal pulse is used to generate a supply voltage of the subscriber device.
10. The method according to any of claims 6 to 7, characterized in that steps a) through g) are repeated cyclically.
11. The method according to any of claims 6 to 8, characterized in that prior to step a) a configuration phase is performed in which the evaluation unit (10) determines the number of subscriber devices (20, 30, 40) within the safety communication system and in which the subscriber devices identify their position within the safety communication system.

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