Safety switch

Abstract

Safety switch (1), which works as an opener, with a sensor and evaluation unit (2) and a switching element (3), wherein the sensor and evaluation unit (2) can be influenced by an influencing element (4) in the monitoring area of ​​the safety switch (1), wherein the sensor and evaluation unit (2) can detect the influence state of the safety switch (1), wherein the sensor and evaluation unit (2) switches the switching element (3) to the “operation” state or to the “safe” state depending on the detected influence state, and wherein the switching element (3) is open in the “Safe” state, characterized by that a switching range (8) in the monitoring area is limited by two switching distances SA1 and SA2, that the sensor and evaluation unit (2) switches the switching element (3) to the "operation" state when the influencing element (4) is located in the switching range (8), and to the "safe" state when the influencing element (4) is outside the switching range (8), that in the "installed" assembly state, the switching range (8) extends through the switching distance SA2 to infinity, so that the sensor and evaluation unit (2), in the event that the influencing element (4) is located in the switching range (8), switches the switching element (3) to the "operation" state regardless of the distance of the influencing element (4), and that in the assembled state “not installed” the switching range (8) is finally limited by the switching distance SA2.

Description

[0001] The invention relates to a safety switch with a sensor and evaluation unit and a switching element, wherein the sensor and evaluation unit can be influenced by an influencing element in the monitoring area of ​​the safety switch, the influencing state of the safety switch can be detected with the sensor and evaluation unit, and the sensor and evaluation unit switches the switching element to the "operational" state or the "safe" state depending on the detected influencing state - in particular by comparison with at least one predetermined influencing threshold - and wherein a second sensor and evaluation unit is integrated into the safety switch. Such a safety switch is known from DE 101 24 079 C2. The invention also relates to the use of such a safety switch.

[0002] DE 10 2004 002 438 A1 discloses a safety switch consisting of a sensor and evaluation unit and a switching element. These elements, mounted on two relatively movable parts, enable their monitoring. The switching element and the sensor and evaluation unit each have an antenna through which the two elements are transformer-coupled. The antenna of the sensor and evaluation unit has a magnetic directional characteristic that enables a transformer-coupled connection to the switching element in at least two mutually perpendicular spatial directions.

[0003] From DE 10 2004 016 632 B4 a safety switch for monitoring the closed position of two parts which are movable relative to one another is known, comprising an actuator and a sensor which can each be fixed to one of the parts, wherein the actuator has at least one component which is designed to generate a transmission signal which is dependent on the closed position of the parts and wherein the sensor is designed to evaluate the transmission signal in order to detect the closed position and wherein the actuator has at least one fastening means for fastening to one of the parts, wherein the fastening means is connected to the component in such a way that the component is inoperative without the fastening means or becomes inoperative when the fastening means is released.

[0004] From DE 102 22 186 C1 a safety switch is known, having a detection device for an actuator, which is coupled to a switching device and comprises a transmitting element for emitting electromagnetic signals and an evaluation circuit which, depending on electrical signals induced at a receiving element, generates a switching signal for activating the switching device, wherein the evaluation circuit comprises an integrator which is coupled to a timer for detecting the amount of electrical energy induced in the receiving element during a time period following the emitting, and a comparison device which provides the switching signal when the amount of energy exceeds or falls below a predetermined threshold value.

[0005] From DE 29 710 694 U1 a contactless proximity switch is known which consists of at least two parts, whereby for its switching or signaling function it requires data transmission via an electromagnetic field between these parts when they approach each other.

[0006] Safety switches of the type in question have been known for some time and are used wherever strict safety regulations must be met in an industrial work environment, particularly safety regulations for tamper-proof occupational safety. For example, the EN 292-2 standard concerning the safety of machinery stipulates that moving areas and protective devices separating safety areas must be equipped with safety switches. For example, the position of a protective grille intended to prevent access to a hazardous work area (e.g., punching, pressing, milling) must be monitored using safety switches. Safety switches must be installed so that the position of the object to be monitored—in this example, the position of the protective grille—is within the monitoring range of the safety switch.The protective grid acts as the influencing element, and the degree of influence on the safety switch varies depending on the distance of the influencing element from the safety switch. In inductive safety switches, which are typically equipped with a dampable oscillating circuit, the damping of the oscillating circuit of the sensor and evaluation unit changes continuously with the distance of the influencing element from the safety switch.The continuous recording of the influence state of the safety switch and a repeated comparison of the determined influence state with a specified influence threshold – or with several specified influence thresholds – ultimately leads to a decision about how the switching element of the safety switch should be switched, i.e., whether it should be switched to the "operation" or "safe" state. Whether the "operation" state—which refers to the operation of the safety-relevant system that may need to be switched off by the safety switch, i.e., transferred to the "safe" state—corresponds to a closed switching element or an open switching element—is initially merely a question of definition.This is because the safety switch often does not directly switch off the safety-relevant system, but indirectly via various power levels, which in turn are only controlled by small signals, whereby these small signals are switched by the safety switch in question here; it is therefore quite conceivable that the "safe" state of the system is represented by a closed safety switch.

[0007] In the previously described case study, the safety switch operates as a normally open contact, which can, however, have a significant disadvantage: If a fault occurs in such a safety switch operating as a normally open contact, for example, due to welding of the switching contacts, the switching signal from the safety switch can no longer be transmitted. For this reason, safety switches are required to reliably interrupt an electrical circuit if an undesired influence on the safety switch is detected by the sensor and evaluation unit; the safety switch then operates as a normally closed contact, with the mechanism being designed to ensure positive opening, i.e., the switching element is opened if necessary, even if this means destroying the switching element.

[0008] Regardless of the technological implementation of a safety switch—that is, whether the safety switch is electromechanical or contactless, whether it is implemented in a contactless design with a separate read head (magnetically coded with reed switches or using transponder technology), or whether it is implemented without a read head as a safety switch based on the inductive, capacitive, or optical principle—safety switches are often subject to tampering attempts with the aim of circumventing the safety switch's protective mechanism. This is often done for reasons of convenience, to bypass operating procedures intended for occupational safety (two-hand buttons), or, for example, to prevent a machine stop during assembly processes in order to increase production speed.The most commonly used technique for deliberately overriding or circumventing protective devices is simply dismantling safety switches, i.e., removing them from their proper installation position. Current technology often attempts to prevent this by using special, difficult-to-remove fasteners to secure safety switches to their bearings, or by creating a redundant design with multiple safety switches covering the same monitoring area. In reality, however, the available options for "safely" securing safety switches using mechanical precautions are limited, and the redundant use of safety switches is comparatively costly.

[0009] The object of the present invention is therefore to prevent, as far as possible, or at least to make it more difficult, to circumvent the functionality of the safety switch by manipulation - in particular by disassembly.

[0010] The previously derived and indicated object is achieved according to the invention, firstly and essentially in the safety switch in question, in that a second sensor and evaluation unit is integrated into the safety switch, the assembly state of the safety switch, for example on a bearing ("installed", "not installed") can be detected by the second sensor and evaluation unit, and the second sensor and evaluation unit, in the case of the detected assembly state "not installed", switches the switching element - with priority over the first sensor evaluation unit - to the "Safe" state.

[0011] It was previously assumed that the safety switch, for example, "is or is mounted on a bearing" and that if the safety switch is mounted on a bearing, the assembly state is "installed"; if the safety switch is not mounted on a bearing, the assembly state is "not installed". On the one hand, the safety switch does not necessarily have to be mounted "on a bearing". Instead of mounting "on a bearing", any other operational mounting is of course also included, e.g. on a protective grille, on a machine, on a door or gate, or wherever. The terms "installed" and "not installed" are also not to be taken literally; the safety switch can therefore also be "installed" or "not installed" or, more generally, "provided" or "not provided".In the following, the previously used expressions “on a bearing” as well as “installed” and “not installed” are used in the broader sense explained above.

[0012] The inventive concept is completely independent of how the mounting state of the safety switch on its bearing is determined; it is only important that an undesired removal of the safety switch from its bearing does not go undetected and that the output of the safety switch, i.e. the switching element of the safety switch, is switched to the "Safe" state by the second sensor and evaluation unit, with a higher priority than the first sensor and evaluation unit can actuate the switching element.

[0013] When it is mentioned that a second sensor and evaluation unit is integrated into the safety switch, this should be understood in a functional sense, namely in the sense that the sensor data provided by the second sensor to the safety switch is evaluated, specifically with regard to the assembly status of the safety switch. This does not necessarily require a second evaluation unit separate from the first sensor and evaluation unit; rather, the functionality of the evaluation unit of the second sensor and evaluation unit can also be implemented by a single evaluation unit.

[0014] Preferably, in the safety switch according to the invention, the switching element is open in the "safe" state; the safety switch therefore operates as an opener and thus offers the safety-related advantages explained above.

[0015] In one of the preferred embodiments of the safety switch according to the invention, at least one influence threshold can be specified for the second sensor and evaluation unit. The predeterminable influence threshold specifies the boundary between the installation states of the safety switch ("installed," "not installed"). The predeterminable influence threshold makes it possible, for example—depending on the underlying sensor concept for the second sensor and evaluation unit—to adapt the second sensor and evaluation unit to different sizes and / or materials of the bearing or to different installation situations of the safety switch on the bearing.

[0016] A particularly advantageous development of the safety switch according to the invention is characterized in that the monitoring area of ​​the first sensor and evaluation unit and the monitoring area of ​​the second sensor and evaluation unit are different, namely the monitoring area of ​​the second sensor and evaluation unit extends to the side of the safety switch on which fastening elements of the safety switch are provided for attaching it to a bearing. In a particularly preferred embodiment, the monitoring area of ​​the second sensor and evaluation unit is even adjustable relative to the monitoring area of ​​the first sensor and evaluation unit, so that the safety switch according to the invention can be adapted to different installation situations while maintaining the functionality of detecting the mounting state of the safety switch on a bearing.

[0017] In a preferred embodiment of the safety switch according to the invention, the second sensor and evaluation unit includes an inductive proximity switch with an oscillating circuit. The oscillating circuit is pre-influenced by the bearing in the "installed" assembled state of the safety switch due to damping of the oscillating circuit, which corresponds to a change in the quality of the oscillating circuit. The pre-determinable influence range is defined, in particular, by two pre-determinable values ​​for the quality of the oscillating circuit or by two variables related to the quality of the oscillating circuit. This embodiment makes it clear what is meant by the fact that the sensor and evaluation unit is pre-influenced in the "installed" assembled state.In the case of the inductive proximity sensor, the pre-damping of the sensor and evaluation unit corresponds to a pre-damping of the oscillating circuit of the inductive proximity sensor by the bearing of the safety switch in the "installed" state. This means that the quality of the oscillating circuit is impaired solely by the "installed" state. Therefore, an influencing element in the "installed" state needs to approach the proximity switch less closely to reach a specified influence threshold or a specified influence range than an influencing element in the "not installed" state, in which the safety switch or the oscillating circuit of the sensor and evaluation unit is not pre-damped.

[0018] A safety switch according to the invention, in which the second sensor and evaluation unit has an inductive proximity sensor, is used in such a way that a metallic base serves as the bearing, wherein the metallic base is arranged directly adjacent to the second sensor and evaluation unit, namely in the monitoring area of ​​the second sensor and evaluation unit. The metallic bearing can, for example, be a machine element of the machine that is to be monitored for safety reasons. Since the monitoring area of ​​the second sensor and evaluation unit does not necessarily have to be aligned with the side of the safety switch on which its fastening elements are arranged, the safety switch can also be mounted in such a way that it is laterally delimited by a metallic body, in particular by a metallic machine element.

[0019] In the event that no suitable surface or lateral boundary is available for the correct functioning of the second sensor and evaluation unit, a preferred embodiment of the invention provides a separate, damping metallic mounting element to hold the safety switch, so that the metallic mounting element is arranged either between the safety switch and the bearing or to the side of the safety switch. It has proven particularly advantageous for the design of the second sensor and evaluation unit with an integrated inductive sensor element if steel, in particular stainless steel, is used for the metallic mounting element.

[0020] If, in the safety switch on which the invention is based, the sensor and evaluation unit switches the switching element to the "operational" or "safe" state depending on the detected interference state, in particular by comparison with at least one predetermined interference threshold, then it is immediately obvious that the predetermined interference threshold in the monitoring range of the safety switch corresponds to a switching distance. However, the switching distance also divides the monitoring range of the safety switch into two switching ranges: a first switching range between the proximity switch and the predetermined switching distance, and a second content range starting at the predetermined switching distance.The following assumes a safety switch that switches the switching element to the "operational" or "safe" state, depending on the detected influence state by comparison with at least one predetermined influence range that corresponds to a switching range in the monitoring range of the safety switch. With such a safety switch, the object underlying the invention is achieved in that in the "installed" assembled state, i.e. with a safety switch mounted on a bearing, the sensor and evaluation unit is pre-influenced by the bearing and that the switching range in the "not installed" assembled state - i.e. in the absence of pre-influence - is smaller than in the "installed" assembled state.

[0021] The inventive design of the safety switch makes unauthorized manipulation, specifically by disassembling the safety switch, extremely difficult. To overcome the safety measure implemented by the safety switch, simply removing the safety switch is not sufficient; rather, the safety switch must also be manipulated in such a way that the switching element also switches to the "operation" state. Because the switching range(s) in the "not installed" state is / are fundamentally smaller than in the "installed" state, it is considerably more difficult to appropriately manipulate the disassembled safety switch.This is particularly evident for a particularly preferred embodiment of a safety switch according to the invention, in which the switching range in the “installed” assembly state extends virtually one-sidedly to infinity and is finitely limited in the “not installed” assembly state.

[0022] In a further advantageous embodiment of the safety switch according to the invention, the sensor and evaluation unit can be pre-influenced from a direction other than the main extension direction of the monitoring area of ​​the safety switch, so that the safety switch can also be pre-influenced from a lateral direction in the "installed" assembled state, whereby this lateral direction does not have to correspond to the side of the safety switch with which the safety switch is fastened to its bearing, but rather it can also be an element of the bearing that laterally limits the safety switch.

[0023] In the last-described embodiment of a safety switch according to the invention, the switching element is preferably open in the “safe” state, i.e. the safety switch is designed as an opener.

[0024] In detail, there are numerous possibilities for designing and developing the safety switch according to the invention. Reference is made, on the one hand, to the claims subordinate to claims 1 and 8, and, on the other hand, to the following description of exemplary embodiments in conjunction with the drawings. The drawings show: Fig. 1 an embodiment of a safety switch according to the invention according to the first teaching of the invention and Fig. 2 an embodiment of a safety switch according to the invention according to the second teaching of the invention.

[0025] Fig. Figure 1 shows a schematic representation of a safety switch 1 with a sensor and evaluation unit 2 and a switching element 3. This – first – sensor and evaluation unit 2 of the safety switch 1 can be influenced by an influencing element 4 in the monitoring area of ​​the safety switch 1, and the influencing state of the safety switch 1 can be detected by the sensor and evaluation unit 2. Depending on the detected influencing state, the sensor and evaluation unit 2 switches the switching element 3 to the "operational" state or the "safe" state. For this purpose, the detected influencing state is compared with a predetermined influencing threshold. The influencing threshold is therefore a value specified for the sensor and evaluation unit 2, i.e., an internal value of the safety switch 1.This influence state corresponds to a specific switching distance in the monitoring range of the safety switch 1 for a specific influencing element 4.

[0026] Regardless of the functionality of the sensor and evaluation unit 2 of the safety switch 1, the Fig. 1, protection against manipulation, in particular against dismantling of the safety switch 1, is achieved in that a second sensor and evaluation unit 5 is integrated into the safety switch 1, the assembly state of the safety switch 1 on a bearing 6 can be detected by the second sensor and evaluation unit 5 and, in the case of the detected assembly state “not installed”, the second sensor and evaluation unit switches the switching element 3 to the “Safe” state, with priority over the sensor and evaluation unit 2.

[0027] An influence threshold can be specified for the second sensor and evaluation unit 5, whereby the influence threshold defines the boundary between the assembly states "installed" and "not installed" of the safety switch 1. By specifying an influence threshold, the safety switch 1 shown can be adapted to different materials and sizes of the bearing 6. Fig. The safety switch 1 shown in Figure 1 includes an inductive proximity sensor with an oscillating circuit 7, the oscillating circuit 7 being damped in the "installed" state of the safety switch 1. In this case, the predeterminable influence threshold is a predetermined value for the quality of the oscillating circuit 7. In other embodiments not shown here, the predetermined influence value is a variable related to the quality of the oscillating circuit 7; this can be, for example, the feedforward gain of a control loop required to excite the damped oscillating circuit 7 to oscillate at a specific amplitude.

[0028] The safety switch after Fig. 1 is designed as an opener, ie the switching element 3 is open in the “safe” state, so that the disadvantages described in connection with a safety switch designed as a closer are avoided here.

[0029] It is particularly advantageous in the Fig. 1 shown safety switch 1, that the monitoring range of the sensor and evaluation unit 2 and the monitoring range of the second sensor and evaluation unit 5 are different. In Fig. 1, the monitoring area of ​​the sensor and evaluation unit 2 extends to the right in the direction of the influencing element 4 and the monitoring area of ​​the second sensor and evaluation unit 5 extends in the direction of the bearing 6 of the safety switch 1. In Fig. 1 shows, on the one hand, the assembly state “installed”, namely the case in which the safety switch 1 is directly adjacent to the bearing 6, and, on the other hand, the assembly state “not installed”, i.e. the case in which the safety switch 1 is spaced apart from the bearing 6.

[0030] The Fig. The safety switch 1 used in the device 1 is mounted on a metallic base as a bearing 6, wherein the bearing 6 is a metallic machine part of the machine to be monitored for safety reasons. In another embodiment of the use of the safety switch, not shown here, the safety switch is mounted on a bearing with one side, but the second sensor and evaluation unit is influenced or dampened by a limiting element projecting from another side of the safety switch.

[0031] The Fig. 2a, Fig. 2b show a safety switch 1 according to a further teaching of the invention, wherein here too the safety switch 1 has a sensor and evaluation unit 2 and a switching element 3, and the sensor and evaluation unit 2 can be influenced by an influencing element 4 in the monitoring area of ​​the safety switch 1. The sensor and evaluation unit 2 can again detect the influencing state of the safety switch 1, wherein the sensor and evaluation unit 2 switches the switching element 3 to the "operation" state or the "safe" state depending on the detected influencing state by comparing it with at least one predetermined influencing area - corresponding to a switching area 8 in the monitoring area of ​​the safety switch 1.The safety switch 1, from which the second teaching of the invention is based, does not differ fundamentally from the safety switch 1, from which the first teaching of the invention is based; the different wording merely takes into account the fact that the safety switch 1 according to the . Fig. 2a, Fig. 2b it is more descriptive to speak of a given range of influence rather than a given threshold of influence.

[0032] The Fig. The safety switch 1 shown in Figure 2a is in the "installed" state, whereby the sensor and evaluation unit 2 is pre-influenced by the bearing 6 in this state. The special feature is that the switching area 8 in the "not installed" state, which is shown in the Fig. 2b, i.e. in the absence of pre-influence, is smaller than in the assembled state “installed” according to the Fig. 2a.

[0033] In the Fig. 2a, Fig. 2b shows the same safety switch 1 with the same specified influence range, wherein the specified influence range is an internal size of the safety switch 1. In the "installed" state, the influence range specified for the safety switch 1 corresponds to the switching range 8 in the monitoring range of the safety switch 1, wherein the switching range 8 is limited by the switching distances SA 1 and SA 2. In the embodiment according to Fig. 2a, the switching distance SA 2 is virtually infinite, ie the sensor and evaluation unit 2 is pre-influenced by the bearing 6 to such an extent that no further influence by the influencing element 4 is necessary in order to achieve the influence value corresponding to the switching distance SA 2.

[0034] In Fig. 2b, the safety switch 1 is removed from its bearing (not shown), so that the sensor and evaluation unit 2 is no longer pre-damped by the bearing 6. This means that the pre-damping of the sensor and evaluation unit 2 provided by the bearing 6 in the "installed" state must now also be effected by the influencing element 4, i.e., the influencing element 4 must be brought closer to the safety switch 1 in order to effect the same influencing state of the safety switch 1 as in the "installed" state of the safety switch 1. Fig. 2b, it is therefore indicated that the two switching distances SA 1 and SA 2 in the monitoring range of the safety switch 1 in the “not installed” assembly state are moved towards the safety switch 1, whereby the switching range 8, which in the “installed” assembly state extends practically to infinity, extends in Fig. 2 b has a finitely extended switching range 8.

[0035] If it is assumed that the switching range 8 characterizes the area in the monitoring range of the safety switch 1 in which the sensor and evaluation unit 2 switches the switching element 3 to the "Safe" state, the aim of the invention to make it more difficult to circumvent the functionality of the safety switch 1 by dismantling the safety switch 1 is achieved, since sufficient damping of the safety switch 1 is only possible in a smaller - possibly much smaller - switching range 8 of the safety switch 1 in the "not installed" assembled state.

[0036] In the Fig. 2a and Fig. The safety switch 1 shown in Figure 2b includes an inductive proximity sensor with an oscillating circuit 7, which belongs to the sensor and evaluation unit 2. In the "installed" state, the oscillating circuit 7 is pre-influenced by the bearing 6 due to damping—i.e., a change in the quality—of the oscillating circuit 7. The predeterminable influence range is defined here by two predefined values ​​for the quality of the oscillating circuit 7.

[0037] It is advantageous in the Fig. 2a and Fig.2b, that the sensor and evaluation unit 2 can be pre-influenced from a direction other than the main extension direction of the monitoring area of ​​the safety switch 1, because in the illustrated embodiment the monitoring area of ​​the safety switch 1 extends to the right in the direction towards the influencing element 4, and the influencing of the sensor and evaluation unit 2 takes place in a direction perpendicular thereto by the bearing 6.

Claims

[1] Safety switch (1), which operates as an opener, with a sensor and evaluation unit (2) and a switching element (3), wherein the sensor and evaluation unit (2) can be influenced by an influencing element (4) in the monitoring area of ​​the safety switch (1), wherein the sensor and evaluation unit (2) can detect the influence state of the safety switch (1), wherein the sensor and evaluation unit (2) switches the switching element (3) to the “operation” state or to the “safe” state depending on the detected influence state, and wherein the switching element (3) is open in the “Safe” state, characterized by , that a switching range (8) in the monitoring area is limited by two switching distances SA1 and SA2, that the sensor and evaluation unit (2) switches the switching element (3) to the "operation" state when the influencing element (4) is located in the switching range (8), and to the "safe" state when the influencing element (4) is outside the switching range (8), that in the "installed" assembly state, the switching range (8) extends through the switching distance SA2 to infinity, so that the sensor and evaluation unit (2), in the event that the influencing element (4) is located in the switching range (8), switches the switching element (3) to the "operation" state regardless of the distance of the influencing element (4), and that in the assembled state “not installed” the switching range (8) is finally limited by the switching distance SA2. [2] Safety switch according to claim 1, characterized bythat in the “not installed” assembly state the switching range (8) is smaller and closer to the safety switch (1) than in the “installed” assembly state. [3] Safety switch according to claim 1 or 2, characterized by that in the “installed” assembly state the safety switch (1) is mounted on or at a bearing (6) and the sensor and evaluation unit (2) is pre-influenced by the bearing (6). [4] Safety switch according to one of claims 1 to 3, characterized by that the sensor and evaluation unit (2) comprises an inductive proximity sensor with an oscillating circuit (7), that the oscillating circuit (7) is pre-influenced in the "installed" assembled state due to damping by the bearing (6).

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