Method for operating an inductive safety switch and device

Abstract

Method for operating an inductive safety switch, which serves to detect a target in a surveillance area, where the target influences the oscillation amplitude A of an oscillating circuit depending on the distance, wherein the inductive safety switch has an evaluation circuit with an adjustable electronic parameter P, where the functional dependency FA is determined via the electronics parameter P P (s) the vibration amplitude A is adjustable from the target distance s, where FA P (s) is always smaller than the maximum vibration amplitude Amax, i.e. FA P (s) < Amax, where a first parameter value NB is provided for normal operation, to which the functional dependency FA applies. NB (s) is assigned where FA is used to generate a first binary switching signal SS1 in this function NB (s) a first switching threshold C is provided, where this first switching threshold C is assigned a first switching point SC, at which a switching state change of the first binary switching signal SS1 occurs when the target reaches the switching point SC, where a second parameter value TC is provided for testing the switching threshold C or the change of the switching state at the switching threshold C, where the parameter value TC is chosen such that for distances s < SC the vibration amplitude FA TC (s) is above the threshold value C and to test the switching function at the switching threshold C in the case that the target is at target distance s0 with s0 < SC and thus the oscillation amplitude A= FA NB (s0) is smaller than the switching threshold C, The following steps will be carried out a) temporarily setting the parameter value TC and b) Checking whether a switching state change has occurred and if no switching state change occurs in step b), a fault is assumed and the safety switch assumes the state defined as safe. wherein a second switching threshold D is provided in the safety switch for generating a second binary switching signal SS2, where the second switching threshold D is assigned a second switching point SD, at which a switching state change of the second binary switching signal SS2 occurs when the target reaches the switching point SD, where a third parameter TD is provided for testing the switching state change at the switching threshold D, where the parameter TD is chosen such that for distances s > SD the vibration amplitude FA TD (s) is below the threshold D, where, to test the switching function at the switching threshold D, the target is located at a target distance s1 with s1 > SD, and thus the oscillation amplitude A = FA NB(s1) is greater than the switching threshold D, The following steps will be carried out c) temporarily setting the parameter value TD and d) Checking whether a switching state change has occurred and if, in step d), no switching state change occurs, a fault is assumed and the safety switch assumes the state defined as safe, where a test of the switching state change only takes place if the target is at target distance s0 < SC or at target distance s1 > SD.

Description

[0001] Inductive safety switches generally belong to the class of non-contact safety-related sensors.

[0002] Non-contact safety-related sensors are used in safety technology to protect dangerous positions in machines such as presses, punching machines, cutting tools, robots and the like.

[0003] The safety-related sensor monitors an impermissible movement (exiting or entering) of a defined object (e.g. metallic, electrically conductive objects) into a position defined as dangerous.

[0004] If a hazardous position is violated, the safety-related sensor emits a corresponding safety switching signal, which can, for example, be a shutdown signal for a hazardous machine. Such safe sensors must operate with exceptional reliability and therefore meet safety requirements, such as the product standard IEC 60947-5-3.

[0005] Safe, non-contact sensors are used in electronic switching devices, primarily in automation technology. They have been known for a long time and are also manufactured and distributed by the applicant, among others.

[0006] They essentially consist of a sensor for detecting preferably electrical, but also optical or other physical properties of moving objects (target), whereby the change in the relevant physical quantity serves as a measure for the approach of an object, and a control unit which generates a preferably binary switching signal when a switching threshold is reached.

[0007] Safety switches operating according to the inductive principle have at least one sensor coil and can be operated with current pulses or with continuous, usually sinusoidal alternating current. The sensor coil can be part of an LC resonant circuit (oscillator) and thus help determine its frequency.

[0008] The sensor coil can also be supplied with pulsed or sinusoidal current from a generator.

[0009] The sensor can also be constructed as a transformer, in particular as a differential transformer, and thus have additional transmitting or receiving coils.

[0010] The change in the inductance and / or impedance of a coil, or the coupling factor between two or more coils, is evaluated.

[0011] When using safe, non-contact sensors, particular attention must be paid to the function defined as safe, the so-called safety-related function (often referred to as the safety function). The safety-related function of an inductive safety sensor, for example, is currently limited to monitoring the movement (damping or undamping) of a defined object in an area defined as hazardous.

[0012] From DE 101 35 263 A1 a switching oscillator for applications in proximity sensors is known, in which partial failures of the sensor element and the amplifier are detected by means of periodically switched tests.

[0013] From the document DE 100 25 662 A1 a proximity sensor with several switching thresholds is known, but no component tests are carried out.

[0014] A safety switch with a start-up self-test is known from EP 1 363 306 A2.

[0015] EP 0 035 225 A2 discloses a proximity switch with a complex functional test.

[0016] An inductive proximity switch with a monitoring unit is known from DE 103 45 819 A1.

[0017] New digital production technologies such as Industry 4.0 are based, among other things, on the networking of machines (and their components) and on the high flexibility of production facilities. This gives rise to a number of new aspects that can impact the functional safety of machines. It may be necessary to reconfigure parts of a production facility during operation, for example, to increase efficiency and the flexibility of the entire system. With the familiar safety-related sensors, only a specific area can be monitored for safety purposes at a time.

[0018] An object of the invention is to provide a method for operating an inductive safety switch and an inductive safety switch which does not have the above-mentioned disadvantages and which is in particular very flexible.

[0019] This problem is solved by the features specified in claim 1.

[0020] Advantageous further developments of the invention are specified in the subclaims.

[0021] The main idea of ​​the invention is to safely monitor two areas in an inductive safety switch.

[0022] The inductive safety switch offers a high degree of flexibility. It allows the movement of a defined object (target) into multiple hazardous areas to be monitored, allowing for flexible response to changing safety requirements in a reconfigurable production facility.

[0023] According to the invention, two safety-related switching thresholds are defined, which are exceeded or undershot by the influence of an object / target (13) (for example metallic, electrically conductive objects) at a distance s, and at least the undershooting of the threshold value (C) and the exceeding of the threshold value (D) is safety-related.

[0024] According to the invention, the switching thresholds (C) and (D) can be congruent.

[0025] According to the invention, more than two switching thresholds are also possible.

[0026] In a further development of the invention, the exceedance or undershoot of the various safety-related threshold values ​​can be output via binary interfaces (A). The information regarding the exceedance or undershoot of the various safety-related threshold values ​​can be transmitted to a higher-level safety-related evaluation unit via a secure electronic communication interface (6).

[0027] The electronic communication interface can, for example, be a secure bus connection or a secure point-to-point communication. According to the invention, the safety-related switching thresholds can be parameterized via the secure communication interface.

[0028] According to the invention, the safety-related switching thresholds can be parameterized in the simplest way (e.g. by pressing a button on the sensor).

[0029] In further development of the invention, different physical principles can be applied for object detection.

[0030] The essential idea of ​​the invention is to integrate at least two safety-related switching thresholds and / or two safety-related output states into a safety-related inductive proximity switch.

[0031] The invention is explained in more detail with reference to the drawing. Fig. 1 shows a block diagram of the safety-related inductive proximity switch Fig. 2 shows two safety-related switching thresholds in a contactless inductive proximity switch as a sensor Fig. 3a Function diagram of oscillation amplitude as a function of target distance Fig. 3b Functional diagram of switching signals as a function of the target distance

[0032] The Fig. Figure 1 shows the essential components of the safety-related sensor, preferably an inductive proximity switch. The sensor coil 2, together with the capacitor 10, forms an oscillating circuit 11, which is damped by an oscillator circuit 3 acting as a negative resistor.

[0033] Shown is a current mirror circuit that requires no coil tapping and offers a convenient way to set different switching thresholds in the lower current mirror using resistors 7 and 8. The resistors can be activated simultaneously or alternately by a microcontroller 9. The upper current mirror serves as feedback. Further details are disclosed in DE 196 50 793 C1.

[0034] The evaluation circuit 4 controls the oscillator circuit 3 and is able to generate a binary switching signal based on the oscillator amplitude, wherein in an advantageous embodiment the quality factor of the parallel resonant circuit 11 formed by the sensor coil 2 and the resonant circuit capacitance 10 is evaluated, without limiting the invention thereto.

[0035] The oscillator circuit 3 and the evaluation circuit 4 are housed together in a customer-specific evaluation circuit 5, an ASIC, without limiting the invention thereto. As already mentioned, the ASIC 5 can contain a control module 4 with a threshold switch (trigger) and a logic component not shown here, for example, a microcontroller.

[0036] As shown, it can also be connected via signal lines to a microcontroller 9, which also performs safety-relevant functions, generates a safety-related binary switching signal and / or outputs digital measured values ​​serially or in parallel to a communication interface 6.

[0037] Since the oscillator current is determined by resistors 7 and 8, the amplitude falls or rises depending on the influence of an object / target (13) at a distance s in the monitoring area, which leads to a signal change in the evaluation circuit 4 when predetermined switching thresholds, which are determined by the microcontroller 9 with the aid of resistors 7 and 8, are exceeded or undershot. A signal change in the evaluation circuit 4, due to the exceeding or undershooting of a switching threshold, is evaluated by the microcontroller 9 in a safety-relevant manner, and the safety-relevant information of the signal change is output via safe electronic, binary switches A, without limiting the invention thereto.

[0038] The safe communication interface 6 is suitable for communication with a higher-level safety-related evaluation unit and can transmit safety-relevant information about the exceedance or undershoot of a switching threshold, without limiting the invention thereto. Furthermore, safety-related light signals can be generated using different-colored LEDs that indicate the exceedance or undershoot of a switching threshold, an error, or another signal.

[0039] The two resistors 7 and 8 in combination with the microcontroller serve according to the invention to determine the safety-related switching thresholds (C) and (D) in Fig. 2, without limiting the invention thereto.

[0040] Fig. 2 is intended to illustrate the use of the safe sensor 1, preferably an inductive proximity switch, for the safety-related monitoring of the undershoot of the safety-related threshold value (C) and the overshoot of the safety-related threshold value (D), wherein the distance s of the object (13) to the active surface (12) of the sensor can cause the safety-related threshold values ​​to be undershot or exceeded.

[0041] The procedure is described below using the functional dependencies FA P (s) according to Fig. 3a and the corresponding switching states Fig. 3b) is explained in more detail.

[0042] The inductive safety sensor 1 is used to detect a target in a monitoring area.

[0043] The evaluation circuit 5 is used to detect the distance-dependent eddy current influence due to the target, whereby the evaluation circuit 5 comprises an LC resonant circuit for generating an alternating magnetic field, an oscillator circuit to feed the LC resonant circuit and an analog logic component for determining switching states, wherein the evaluation circuit has an adjustable electronic parameter P.

[0044] The electronic parameter P can be used to determine the functional dependency FA P (s) of the oscillation amplitude A from the target distance s. Where FA P (s) always smaller than the maximum oscillation amplitude FA P (s) < Amax

[0045] For normal operation, a first parameter value NB is provided, where the functional dependency FA applies NB (s). To generate a first binary switching signal SS1, this function FA NB(s) a first switching threshold C is provided.

[0046] This first switching threshold C is assigned a first switching point SC at which a switching state change of the first binary switching signal SS1 occurs when the target reaches the switching point SC.

[0047] To test the switching threshold C or the switching state change at the switching threshold C, a second parameter value TC is provided, whereby the parameter value TC is selected such that for distances s < SC the oscillation amplitude FA TC (s) is above the threshold C. To test the switching function at the switching threshold C, in the case that the target is at the target distance s0 with s0 < SC and thus the oscillation amplitude A= FA NB (s0) is smaller than the switching threshold C, the following steps are carried out. a) temporarily setting the parameter value TC and b) Check whether a switching state change occurs

[0048] The function value changes according to the upward arrow. The function value FA TC (s T ) is correspondingly above the switching threshold C, therefore the switching state changes.

[0049] If no switching state change occurs in step b), an error is assumed and the safety switch assumes the state defined as safe.

[0050] A second switching threshold D is provided in the safety switch to generate a second binary switching signal SS2.

[0051] The second switching threshold D is assigned a second switching point SD, at which a switching state change of the second binary switching signal SS2 occurs when the target reaches the switching point SD.

[0052] A third parameter TD is provided to test the switching state change at the switching threshold D. The parameter TD is selected such that for distances s > SD the oscillation amplitude FA TD(s) is below the threshold D.

[0053] To test the switching function at the switching threshold D, in the case that the target is at target distance s1 with s1 > SD and thus the oscillation amplitude A= FA NB (s1) is greater than the switching threshold D, the following steps were carried out. a) temporarily setting the parameter value TD and b) Check whether a switching state change occurs

[0054] The function value changes according to the downward arrow. The function value FA TD (s T' ) is accordingly below the switching threshold D, therefore the switching state changes.

[0055] The function value changes according to the downward arrow, and a brief switching state change occurs. If no switching state change occurs in step b), a fault is assumed, and the safety sensor assumes the state defined as safe.

[0056] In the description of the invention, hysteresis at the individual switching thresholds was neglected. Hysteresis exists at each switching threshold, but this is not relevant to the invention, so it was essentially set to zero. List of reference symbols 1 Safe sensor, preferably inductive proximity switch 2 sensor coil 3 Oscillator circuit 4 Evaluation circuit with one trigger 5 Evaluation circuit with oscillator, trigger and logic module (ASIC, FPGA) 6 Secure communication interface 7 First resistor to set a switching threshold 8 Second resistor to set a switching threshold 9 microcontroller, control unit 10 resonant circuit capacitor, resonant circuit capacitance 11 Oscillating circuit, consisting of the sensor coil 2 and the capacitor 10 12 Active surface of a safe proximity switch through which, for example, electromagnetic fields enter and exit, ultrasound enters and exits, or a change in a magnetic field is detected. 13 Object for influencing a sound threshold in a safety-related sensor 14 Dangerous (safety-relevant) position areas where a safety-related response must be initiated.

Claims

[1] Method for operating an inductive safety switch, which is used to detect a target in a surveillance area, where the target influences the oscillation amplitude A of an oscillating circuit depending on the distance, wherein the inductive safety switch has an evaluation circuit with an adjustable electronic parameter P, where the functional dependence FA P (s) the oscillation amplitude A is adjustable from the target distance s, where FA P (s) is always smaller than the maximum oscillation amplitude Amax, ie FA P (s) < Amax, where for normal operation a first parameter value NB is provided, to which the functional dependency FA NB (s) is assigned, where to generate a first binary switching signal SS1 in this function FA NB (s) a first switching threshold C is provided, wherein this first switching threshold C is assigned a first switching point SC, at which a switching state change of the first binary switching signal SS1 occurs when the target reaches the switching point SC, wherein a second parameter value TC is provided for testing the switching threshold C or the switching state change at the switching threshold C, where the parameter value TC is chosen so that for distances s < SC the oscillation amplitude FA TC (s) is above the threshold C and to test the switching function at the switching threshold C in the case that the target is at the target distance s0 with s0 < SC and thus the oscillation amplitude A= FA NB (s0) is smaller than the switching threshold C, the following steps must be carried out a) temporarily setting the parameter value TC and b) Check whether a switching state change occurs and if no switching state change occurs in step b), a fault is assumed and the safety switch assumes the state defined as safe wherein a second switching threshold D is provided in the safety switch for generating a second binary switching signal SS2, wherein the second switching threshold D is assigned a second switching point SD, at which a switching state change of the second binary switching signal SS2 occurs when the target reaches the switching point SD, whereby a third parameter TD is provided for testing the switching state change at the switching threshold D, where the parameter TD is chosen so that for distances s > SD the oscillation amplitude FA TD (s) is below the threshold D, where to test the switching function at the switching threshold D in the case that the target is at the target distance s1 with s1 > SD and thus the oscillation amplitude A= FA NB(s1) is greater than the switching threshold D, the following steps must be carried out c) temporarily setting the parameter value TD and d) Check whether a switching state change occurs and if no switching state change occurs in step d), a fault is assumed and the safety switch assumes the state defined as safe, whereby a test of the switching state change only takes place if the target is at target distance s0 < SC or at target distance s1 > SD. [2] Method according to claim 1, characterized by that the switching thresholds C and D are congruent. [3] Method according to one of the preceding claims, characterized by that the exceedance or undershoot of the various switching thresholds via several binary interfaces A n is issued. [4] Method according to one of the preceding claims, characterized bythat the inductive safety switch is designed as a safe opener and a safe closer. [5] Device for carrying out the method according to one of the preceding claims.

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