METHOD FOR MONITORING A MULTIPLE SHORT-CIRCUIT-FORMING ALIGNMENTS AND ORDER FOR EXECUTING THE METHOD

Description

[0001] The invention relates to a method for monitoring short-circuit-forming signaling elements and an arrangement for carrying out the method.

[0002] Signaling elements such as switching mats or emergency stop switches are used in safety control systems, especially in industrial settings, to safely switch electrical devices such as presses or milling tools on and off in order to prevent hazards to people and materials.

[0003] The safety controllers typically have a number of switching inputs and outputs for connecting the working contacts of the signaling elements.

[0004] In addition to monitoring the switching position of the signaling elements, continuous functional testing of the safety controller is also required to comply with the relevant safety standards and certifications. For particularly high safety levels, this also includes continuous testing of the wiring of the connected signaling elements.

[0005] This test is typically performed by blanking intervals in the logic signals at the switching outputs. With standard digital logic circuits, the switching outputs carry either a logic 1 or a logic 0, distinguished by specific voltage values. For example, a voltage of +24 V is typically assigned to a logic 1, while ground potential represents a logic 0.

[0006] To determine whether the voltage applied to the switching inputs of the safety controller actually matches the output voltage of the safety controller, the output voltage is provided with regular blanking intervals.

[0007] In the event of a cable fault, for example a short circuit to another cable with a corresponding voltage, this blanking gap at the switching input is no longer detectable and the fault is recognizable.

[0008] This principle is frequently used not only for cross-circuit detection but also for determining the switching state of so-called short-circuit-forming signaling elements. These signaling elements have two current paths, each with an input and an output, which are short-circuited when activated.

[0009] To determine the switching state of a signaling element, both the first and second inputs of the element are supplied with a voltage signal containing blanking intervals. These blanking intervals are staggered in time, so that they always occur at different times in the two current paths. When the signaling element is activated and the current paths are thus short-circuited, the blanking intervals are bridged – just as in a cross-circuit. Therefore, they are no longer detectable at the outputs of the current paths connected to the switching inputs of the safety controller, and the safety controller can detect the activation of the signaling element.

[0010] Since actuation is detected by comparing the input and output signals, and a difference only occurs during a blanking interval when the indicator element is actuated, the detection accuracy is limited by the frequency of the blanking intervals. This always results in a delay between the actual actuation and its detection, and a very brief actuation of the indicator element will not be detected at all if it occurs between two blanking intervals. Furthermore, the system always requires knowledge of the exact position of the blanking intervals for signal evaluation.

[0011] According to the teaching of EP 2 988 419 B1, it is therefore proposed to apply symmetrical square wave signals to the two inputs of the signaling element with phase shifts of 180° and with blanking intervals and on-time of equal length.

[0012] This allows for a particularly simple and reliable detection of the activation state of a single signaling element using a simple either / or evaluation.

[0013] When using multiple signaling elements, these are usually connected in series according to the state of the art, which means that evaluation is only possible for the entirety of the signaling elements and no identification of individual elements is possible.

[0014] From US patent 2011 / 204729 A1, a safety switching device for the fail-safe control of actuators and an emergency shutdown device with a safety switching device are known. The safety switching device comprises at least one first and one second safety input for receiving a first and second input signal, at least one first and one second safety output for outputting a first and second output signal, and a control unit for evaluating the input signals and generating the output signals. The first and second safety outputs further comprise a feedback loop that feeds the output signals back to the control unit, enabling the control unit to perform a test routine for testing the output signals.

[0015] From publication DE 44 41 070 A1, a safety switch arrangement for switching the power supply of a work device on and off by means of a sensor signal is known, which is supplied to the work device via two evaluation channels, each with an actuator, wherein the actuators have switch-like means consisting of semiconductor elements, a computer unit is connected upstream of each actuator, which is connected to the actuator via two bidirectional supply lines, wherein switching pulses are transmitted back from the computer unit to the actuator via the first supply line and trigger a switching operation there, and wherein test pulses are transmitted back from the computer unit to the actuator via the second supply line for its functional testing, the computer units are connected via a bidirectional supply line for their functional testing.and the switching states of the switch-like devices are changed so briefly by the computer units for functional testing of the actuators that the operating state of the working equipment does not change due to its inertia.

[0016] The invention is based on the objective of extending the known state of the art in such a way that a simple evaluation of the actuation state and the detection of cable faults is possible with several signaling elements.

[0017] According to the invention, this is done using a method according to claim 1. Advantageous embodiments are set out in the dependent claims.

[0018] The invention is explained in more detail using figures.

[0019] They show, for example: Fig. 1 a schematic representation of a safety controller with an attached pressure mat, and FIG 2A graphical representation of the various switching signals at the switching outputs of the safety controller.

[0020] The representation according to FIG 1 Figure 1 shows a safety controller with a control unit (not shown), which may be designed as a microcontroller, for example.

[0021] The safety controller 1 has two switching outputs 4 which are inserted into the power supply of an electrical consumer which is to be safely switched off in case of danger.

[0022] A pressure-sensitive mat 2 is provided as a short-circuit-inducing signaling element, which has two parallel current paths 3, 4. The inputs of the current paths 3, 4 are connected to switching outputs 5, 6 of the safety controller 1 and the outputs of the current paths to switching inputs 7, 8 of the safety controller.

[0023] The pressure-sensitive mats 2 serve to secure larger areas. They are laid on the floor in hazardous work areas involving electrical equipment. If a pressure-sensitive mat 2 is stepped on, a short circuit occurs between the two current paths 3 and 4.

[0024] This short circuit is detected by monitoring the corresponding signal inputs 7,8 by the safety device 1 and the consumer is switched off.

[0025] According to legal regulations, not only the activation of the mats but also the proper functioning of the alarm elements must be monitored. Faults could occur, for example, due to a broken wire or a short circuit in the power supply lines.

[0026] According to the invention, when using several pressure-sensitive mats, the current paths of these mats are connected with different signal sequences S 1 ...S n , S 1 ... Sn is supplied in such a way that, within a given time frame, a readily decodable, unambiguous, binary representation of the state of the connected pressure-sensitive mats 2 is available at every point in time. The second of the two current paths 4 of a signaling element is supplied with the inverted signal sequence. S 1... S n of the first current path 3 is actuated.

[0027] Fig. 2 The diagram shows the switching signals at 12 different switching outputs 5,6 of the safety controller 1 for connection to the two parallel current paths of 6 pressure mats 2. At time t1 of this representation, for example, the (safe) state of the pressure mats 2 is defined by the binary number 10 01 10 10 01 01.

[0028] In total, 6 different binary numbers indicate the safe state of the 6 pressure-sensitive mats within the decoded timeframe.

[0029] A deviation from this indicates the presence of a triggering event. For example, the binary number 11 01 10 10 01 01 indicates that pressure mat no. 1 was stepped on at time t1 and a short circuit occurred between the two current paths 3,4 of this pressure mat.

[0030] However, this statement is not unambiguous, since in the event of a fault, for example a short circuit between the supply line to the second current path of the first mat and the supply line to the first current circuit of the third mat could also result in a corresponding binary number. 11 01 10 10 01 01 there.

[0031] To distinguish whether a triggering event or an error is present, it is therefore necessary to consider several successive time points t 1 , t 2 , t 3 in the signal history.

[0032] These would be the signal values S 1 and S 3 upon triggering by stepping onto the first mat at the three time points ( 11 , 11 , 11 ) so continuously 11, while the short circuit between the supply line to the second current path of the first mat and the supply line to the first current circuit of the third mat the signal values S 1 and S 3 (11, 11, 00) at the three times.

[0033] The switching signals are needed to quickly determine the cause. S 1 ... S n as in from Figure 2 The signal is clearly structured. Each signal periodically repeats a sequence of a short pulse and a short blanking interval, as well as a long pulse and a long blanking interval, where pulses and blanking intervals each have the same duration, and the long pulses and blanking intervals have twice the duration of the short pulses and blanking intervals, respectively.

[0034] The switching signals S 1 and 2, which are to be assigned to a single mat, S1. The signals of the different mats have a matching phase position; the signals of the different mats are phase-shifted relative to each other. The duration of the shift between 2 adjacent signals, for example between S1 and S2 or S2 and S3, corresponds in the present case with 6 mats to the duration of a narrow pulse, or one sixth of the period of the signal, and thus to a phase shift of 60°, i.e. 360° / n with n = number of mats, in the present case six.

[0035] The present signal structure is suitable for controlling up to 6 mats; for a larger number, it is possible, for example, to extend the signals by a second short pulse with a blanking interval.

[0036] It would also be conceivable to leave the basic signal with a short and a long pulse plus blanking intervals, but to reduce the phase shift or the duration of the shift between 2 adjacent signals to half of a narrow pulse. Reference symbol list

[0037] 1 Safety controller 2 Pressure mat 3 First current path 4 Second current path 5, 6 Switching outputs of the 7, 8 Switching inputs of the safety controller S 1 ... S n Signal sequence on the first current path of the first to n ten pressure mat S 1 ... S n signal sequence on the second current path of the first to n tenth foot mat t1, t2, t3: Time points in the signal waveform

Claims

1. Method for monitoring a plurality of short-circuit forming indicating elements, wherein each indicating element has at least two current paths, which are short-circuited upon actuation of the indicating element, characterised in that the current paths (3,4) of the indicating elements (2) are supplied with different signal sequences (S1...Sn, S1...Sn) in such a way that a simple, decodable, unique, binary representation of the state of the connected pressure sensitive mats (2) exists at each time instant within a predetermined time frame and that it is possible to differentiate a stepping on the pressure sensitive mat from an error in the supply lines to the current paths by several consecutive time instants (t1, t2, t3) in the signal curve being observed and a deviation in the switching signals at the switching outputs (5, 6) of the current paths (3, 4) being assigned to the presence of a tripping operation or a fault.

2. Method according to claim 1, characterised in that the respective second (4) of the two current paths of an indicating element (2) is supplied with the inverted signal sequence ( S1...Sn) of the respective first current path.

3. Method according to claim 1 or 2, characterised in that each signal has a periodically recurring sequence of a short impulse and a short blanking interval and a long impulse and a long blanking interval, that impulses and blanking intervals have the same duration in each case and the long impulse or blanking intervals have twice the duration of the short impulse or blanking intervals, and that the switching signals to be assigned to an individual mat have a concurring phase position and the signals of the different mats are phase shifted by 60° with respect to one another.

4. Method according to claim 1 or 2, characterised in that each signal has a periodically recurring sequence of a short impulse and a short blanking interval and a long impulse and a long blanking interval, that impulses and blanking intervals have the same duration in each case and the long impulses or blanking intervals have twice the duration of the short impulse or blanking intervals, and that the switching signals to be assigned to an individual mat have a concurring phase position and the signals of the different mats are phase shifted by 360° / n with respect to one another with n equating to the number of mats.

5. Method according to claim 1 or 2, characterised in that each signal has a periodically recurring sequence of two short impulses and a short blanking interval and a long impulse and a long blanking interval, that impulses and blanking intervals have the same duration in each case and the long impulse or blanking intervals have twice the duration of the short impulses or blanking intervals, and that the switching signals to be assigned to an individual mat have a concurring phase position and the signals of the different mats are phase shifted by 40° with respect to one another.

6. Method according to claim 1, characterised in that pressure sensitive mats (2) are provided as indicating elements, which is embodied so that a short circuit between the two current paths (3,4) is caused when the pressure sensitive mat (2) is stepped on.

7. Arrangement for carrying out the method according to one of claims 1 to 3, characterised in that a safety controller (1) is provided, which comprises a plurality of signal outputs (5,6) and signal inputs (7,8) and that short-circuit forming indicating elements (2) are provided, which each have at least two current paths (3,4), which are short-circuited upon actuation of the indicating element (2) and which are connected to signal outputs and signal inputs of the safety controller and a deviation in the switching signals at the switching outputs (5, 6) of the current paths (3, 4) can be assigned to the presence of a tripping operation or a fault.