Safety switch element with duo sensor

Abstract

The invention relates to a safety switch element (1) which has a tactile sensor in the form of a switch rail (2) or switch mat that has electric contact elements (7), wherein at least one contact element (7), in the form of electrodes (E) of a capacitive proximity sensor, is switched such that the capacitive coupling to obstacles (5) located in the surroundings is measured, said coupling being based on, among others, the distance of such obstacles to the capacitive proximity sensor. The invention proposes that the electric contact elements (7) of the tactile sensor, in the form of openers, are switched, or a series of contact elements (7) which are connected together in an electrically conductive manner form the electrodes (E) of the proximity sensor. Optionally, a shielding electrode (8) can be provided.

Description

[0001] "Safety switching device with duo sensor"

[0002] Description:

[0003] The invention relates to a safety switching device comprising a tactile sensor in the form of a switch strip or switch mat, wherein this switch strip or switch mat comprises electrical contact elements. For the sake of simplicity, the invention will be explained below using an elongated switch strip as an example of a safety switching device, without, however, being limited to switch strips.

[0004] A switch strip designed as a normally closed contact contains a contact chain formed from a plurality of electrical contact elements connected in series. While they can in principle be moved apart, they are held tightly together in electrically conductive contact by spring elasticity. The contact chain can be arranged, for example, in the cavity of an elastomer hollow profile. Upon contact with an obstacle and corresponding deformation of the rubber hollow profile, neighboring contact elements are separated from each other by overcoming the spring force, interrupting the current flow and thus generating a switching operation of the sensor.

[0005] A switch strip designed as a normally closed contact has two electrical contact elements spaced apart from each other, for example, in the cavity of an elastomer hollow profile. The contact elements are typically linear and extend over virtually the entire length of the profile. When the switch strip comes into contact with an obstacle, the elastomer profile is deformed, and the two contact elements come into contact with each other, closing an electrical circuit and thus triggering the sensor's switching process.

[0006] EP 1 612 822 A1 discloses a switching element, particularly in the form of a switch strip or switch mat. This switching element is designed as a normally closed contact. Of the two electrodes, namely the two contact elements, one also serves as an electrode of a capacitive proximity sensor, so that obstacles can be detected capacitively before the switching element is triggered tactilely by contact between the two electrodes.

[0007] Safety switching elements are also known from DE 10 2008 005 783 A1, EP 3 287 585 A1 and WO 2010 / 012492 A1, which are each designed as a closer and act as a capacitive proximity sensor in addition to the tactile detection of an obstacle.

[0008] From DE 102019 132 508 A1, a capacitive sensor device is known which enables the triggering of a function when operated as intended, for example by an outstretched finger on a control element, while moist dirt or wiping the sensor with a damp cloth should not trigger a reaction of the sensor.

[0009] In contrast to a safety switching device that is designed as a normally open contact, a safety switching device designed as a normally closed contact is inherently safe because, for example, even in the event of an interruption in the current flow caused by another reason, a switching operation of the sensor is generated and accordingly a connected device to be monitored, such as a moving machine part, an autonomously moving vehicle or the like, is automatically switched to the safe state.

[0010] In contrast to linear, one-dimensional safety edges, similar functional principles can be applied to two-dimensional safety mats. The electrical contacts in a safety mat can be laid out in different configurations, for example, a large number of parallel contacts, which requires a large number of electrical connections but also allows for a certain degree of spatial resolution, or they can be arranged in a meandering or serpentine pattern, allowing the entire surface to be covered by sensors with a minimum number of electrical connections.

[0011] The switch strips and switch mats designed as described above are “tactile” sensors that react to contact and, when a correspondingly elastic carrier or housing is deformed, trigger the switching process by opening or closing the contact elements.

[0012] The invention is based on the object of extending the detection range of the sensors so that even an approach to the sensor can be detected and, moreover, of enabling a particularly high level of security.

[0013] This object is achieved by a safety switching device according to claim 1. Advantageous embodiments are described in the subclaims.

[0014] In other words, the invention proposes neither using a completely differently constructed sensor nor supplementing the tactile sensor by adding a second, independent sensor. Instead, the existing contact elements of the contact chain continue to be used as tactile sensors, but also assigning them a second function, namely to create a capacitive proximity sensor, and thereby using one or more contact elements of the tactile sensor as the electrode of the proximity sensor. According to the invention, a safety switching element operating according to the break contact principle is used. The function of the capacitive sensor is also enabled with a safety switching element that, due to the break contact principle, has only a single electrode, namely the contact chain.

[0015] To implement the capacitive measuring principle, the safety switching device has an electrical signal generator connected to an electrode via an electrical resistor. One or a series of contact elements of the tactile sensor form this electrode, e.g., one, several, or—namely, before an interruption of the contact chain—all of the contact elements forming the contact chain of the opener. Accordingly, the invention creates both a tactile sensor and a proximity sensor using these already present contact elements.

[0016] Since the safety switching element is designed as an opener, the function of the proximity sensor is still maintained even if the tactile sensor is triggered, i.e. if the contact elements of the opener are interrupted and cause a switching operation. If the contact chain of the opener is interrupted, two sections of the previously uninterrupted contact chain result, one section of which is still connected to the signal generator. Because the tactile sensor has been triggered, an object to be protected, which is typically movable and is connected to the safety switching element, has now been brought into a safe state, for example by moving at a reduced speed or having been brought to a standstill. For certain applications, it can nevertheless be important and advantageous to be able to evaluate signals from the proximity sensor even in this safe state.

[0017] An electrically partially or fully conductive obstacle—e.g., a human body—is grounded via an impedance. The electrical impedance can consist of an ohmic resistance, a capacitance, an inductance, or a combination thereof and represents the electrical coupling of the obstacle to the ground. Therefore, when the obstacle enters the detection zone of the proximity sensor, it acts together with the electrode like a capacitor, changing the voltage drop across a measuring resistor. From these changes in electrical resistance, the presence of the obstacle in the detection zone can be firstly detected qualitatively (presence in the detection zone) and secondly, with limited accuracy, also determined quantitatively (distance to the electrode), or at least estimated.

[0018] This described further development of the safety switching device, in which a tactile sensor is extended by the additional function of a proximity sensor, has several advantages:

[0019] Firstly, the safety switching device offers improved technical safety because it essentially uses two sensors, namely two different operating principles. Even with the proximity sensor alone, the position of the obstacle in the detection zone could be determined based on its qualitative information, so it might be logical to dispense with the tactile sensor. Compared to such a solution, the safety switching device according to the invention has the advantage that uncertainties in the capacitive proximity measurement are offset by the reliable tactile measurement. Capacitive proximity measurement is uncertain in that the proximity measurement depends on the size of the obstacle. If two obstacles of different sizes are the same distance from a capacitive proximity sensor, the larger obstacle is determined to be closer.Or, if a large obstacle is very close to the capacitive proximity sensor, a small obstacle may not be detected by the capacitive proximity sensor. Even if these phenomena should occur with the proximity sensor of the switching device according to the invention, the continued function as a tactile sensor ensures the safety function required of the safety switching device.

[0020] Secondly, a particularly simple installation of two different sensor types is made possible compared to the installation of two completely separate sensors, because less cabling is required for the safety switching device according to the invention.

[0021] Thirdly, the safety switching device according to the invention can be designed to save space compared to a sensor installation in which two completely separate sensor types are installed, for example, a tactile sensor and, in addition, a proximity sensor that operates completely independently of the tactile sensor. For example, it is not necessary to install additional ultrasonic sensors or similar proximity sensors, which would be aligned transversely to the longitudinal direction of the safety edge and would increase the required minimum installation depth of the safety edge.

[0022] Fourthly, compared to a conventional safety switching device, e.g., a safety edge, the safety switching device according to the invention can be designed to save space: the deformation path of a conventional safety edge must usually be dimensioned as long as is technically unnecessary for the function of the safety edge itself. The purpose of this unnecessarily large installation depth is to ensure that after the tactile activation of the safety edge, when the drive of a moving object is switched off, this moving object can continue to move far enough without colliding with the obstacle that triggered the switching process of the safety edge.A classic example of such an application is a metal housing of an industrial truck equipped with a safety edge. A person's foot must not be damaged after the foot, as the aforementioned obstacle, has triggered the safety edge. The deformation space or the installation depth of the safety edge must approximately correlate with the braking distance of the moving object. Due to the additional function of the safety edge as a proximity sensor, which is implemented according to the invention, an alarm can be triggered before the safety edge is deformed, so that the speed of the moving object can be reduced in advance, namely before the tactile sensor is triggered, and the braking distance to a standstill is correspondingly shorter. Accordingly, the installation depth of the safety edge can be kept small.

[0023] The space-saving design of the safety switching device is important because, depending on the application, outwardly protruding contact edges must be kept as small as possible. For example, when used on industrial trucks, the aim is to prevent the contact edges from being torn off or sheared off in harsh operating conditions, such as when the industrial truck brushes against tail lifts or adjacent pallets when loading or unloading a truck where pallets are positioned close together. The smaller structural dimensions may also represent a decisive factor in selecting the respective contact edge due to a design advantage.

[0024] Fifthly, the design of the safety switching element according to the opening principle makes it possible to continue to use part of the contact chain as a capacitive proximity sensor even after the interruption of the tactile sensor electrode, namely the contact chain formed by several individual contact elements.

[0025] In one embodiment, which is particularly easy to implement technically, this involves a single row of interconnected contact elements, namely the portion of the contact chain that is still connected to the signal generator and the measuring resistor of the electrode. In another embodiment, two rows of interconnected contact elements, namely the two portions of the contact chain on either side of the interruption point—i.e., still the entire, albeit interrupted, contact chain—can be used as two capacitive proximity sensors.

[0026] In both of the aforementioned configurations, one or more contact elements of the tactile sensor thus form the electrode of a capacitive proximity sensor, with reduced capacitance compared to the uninterrupted contact chain. Although the tactile sensor has already triggered in the event of an interruption of the contact chain, and the moving object has therefore been automatically brought into a safe state, the continued functionality of the capacitive sensor can be advantageously utilized if the associated control system is designed accordingly:

[0027] For example, if an autonomous vehicle automatically reverses after encountering an obstacle, the direction of travel during the reversal can be selected so that the vehicle does not simply reverse in the same lane, for example, in the opposite direction to its original direction of travel, but instead moves in a different lane in an arc away from an obstacle detected by the capacitive sensor. This allows obstacles such as incorrectly parked objects protruding into the vehicle's path to be avoided with a particularly short amount of time.

[0028] If, after a collision with a first obstacle, a person has approached the collision point, thus creating an additional, second obstacle within the movement range of the moving object, the presence of this person can be detected by the still-effective capacitive sensor before the moving object is automatically reversed. During reversal, the contact chain closes again, and the moving object is permitted to move again in the original direction. The early detection of an additional obstacle, which had not been detected before the tactile sensor was triggered, offers additional safety in this case, so that a safety switching device according to the invention offers a particularly high level of safety.

[0029] Sixthly, the design of the safety switching device according to the break contact principle offers the possibility of automatically determining the location of the interruption in the longitudinal direction of the electrode after it has been interrupted. Based on the change in the electrode's capacitance, the location of the interruption can be approximately determined. This can be advantageous for statistical analysis, for example. If it turns out that a large proportion of contacts with obstacles occur in a specific area of ​​the safety switching device, measures can be taken to modify either the safety switching device itself, a moving object monitored by the safety switching device, or the surroundings of the moving object in such a way that collisions with obstacles are either avoided or cause as little damage as possible.

[0030] Minimizing damage to the safety switching device can extend its service life, so that maintenance or repair work, which would otherwise involve operational downtime for the moving object, is required as infrequently as possible. This represents an economic advantage offered by a safety switching device according to the invention. The ability to also modify the environment of the moving object, if necessary, creates an overall improved or increased level of safety because it can reduce the likelihood of future collisions.

[0031] In one embodiment, the safety switching device has a shield. The operation of the proximity sensor can be influenced by the shield. If a safety edge is installed on a moving component, the shield can preferably be mounted so that it is located between the component and the contact elements of the safety edge. Interference that could affect the safety edge from the component is reduced or completely eliminated by the shield.

[0032] The shielding can be created by flat sheet metal strips, by strips of an electrically conductive textile material or metallic fibers, or in the case of a co-extruded profile by corresponding areas made of a material other than the base material, namely an (elastomer) material with higher electrical conductivity.

[0033] In one embodiment, the safety switching device has a controller that has a signal input for the measurement signals of at least one additional sensor. The controller can be physically integrated into the safety switching device as an internal controller, e.g., arranged in a cavity of an elastomer hollow profile in which the contact elements are also located. Or the controller can be arranged remotely as an external controller, but as part of the safety switching device, it can be wirelessly or wired connected to the contact elements of the safety switching device for signal transmission, so that in this case the safety switching device is designed in several parts.

[0034] In another embodiment, the safety switching device can be part of a safety switching arrangement which contains further components, namely at least one control, for example a system, vehicle or engine control, which is already present for the operation of the movable object and which, in addition, evaluates signals from the safety switching device as an external control with respect to the safety switching device and / or influences the electrical energy supply of the safety switching device.

[0035] Since the function of the non-contact proximity sensor can be influenced by environmental influences to which the safety switching device is subject, additional sensors can be used to provide information about these environmental influences. For example, the air humidity and / or air temperature can be measured in order to compensate for dependent changes in the measurement behavior of the capacitive sensor using suitable correction factors. Such additional sensors may already be present on the moving object, so that in this case their signals can be processed by the internal or external control of the safety switching device. In another embodiment, the safety switching device itself has one or more additional sensors, which can be installed, for example, in the area of ​​the control system or which can be integrated as additional elements into the safety edge or safety mat.

[0036] The safety switching device according to the invention, which operates according to the break contact principle, essentially requires only a single electrode, namely the contact chain formed by the individual contact elements. In one embodiment, the safety switching device has a further electrode, known as a reference electrode. Without an optional shielding electrode, the reference electrode represents the second electrode of the safety switching device. The additional sensors mentioned above can be referred to as specific sensors because they detect specific parameters and provide corresponding measured values, such as air humidity and / or air temperature.Instead of the specific sensors, or even in addition to them, changes in the measurement behavior of the capacitive sensor can be compensated using the reference electrode, which in this context can be referred to as a general sensor or universal sensor to distinguish it from the special sensors. All influences that act on the contact chain as the first electrode – except for one, namely the occurrence of an obstacle – also affect the reference electrode. It is not used to determine whether or not an obstacle is in the detection range, so this is the one external influence to which the reference electrode, unlike the contact chain, is not exposed. This additional, additionally installed electrode of the capacitive sensor thus provides a reference measurement value.

[0037] The reference electrode can therefore be located outside the detection zone or within the detection zone at a location where an obstacle is not expected to occur, for example, in the direction of movement of the moving object behind the first electrode of the safety switching element or behind a shield, e.g., between the first electrode of the safety switching element and the moving object. Since the reference electrode is also exposed to environmental influences like the first electrode of the capacitive sensor formed by the contact chain, the reference measured value changes depending on all of these influences and not just depending on a certain, specific influence. The measured values ​​obtained with the remaining first electrode can be calibrated using the respective reference measured value.Based on a switching signal from the safety switching device, the internal or external control system can automatically act on the drive of the monitored moving object, for example, automatically slowing down the drive or shutting it down completely. The reference electrode can also be located outside the safety switching device and connected to the control system: for example, one application could be that the safety switching device is designed as a contact strip and mounted on the front of an autonomously driving industrial truck. The reference electrode can be located, for example, under the vehicle floor or on the vehicle body, but in any case outside the contact strip.Both the switch bar with the first electrode located therein and the reference electrode are connected to the control system so that the values ​​of the reference electrode can be automatically evaluated and used to calibrate the values ​​of the first electrode.

[0038] In one embodiment, the safety circuit's control system allows the moving object to be automatically moved back a small distance after the tactile sensor is triggered, i.e., reversed. This backward movement, which is essentially opposite to the direction of movement before triggering, is only carried out over a limited, not excessively long distance to prevent any new accident hazards. The reversing minimizes the duration of contact, should the object come into contact with the obstacle.

[0039] The invention is explained in more detail below using purely schematic illustrations. Figures 1 and 2 schematically show the operating principle for a safety switching device configured as an opener and for a safety switching device configured as a closer, not part of the invention.

[0040] Fig. 3 is a schematic representation of the capacitive measuring principle, and the

[0041] Fig. 4 and 5 show two examples of structural designs for safety switching devices designed as openers.

[0042] First, Figs. 1 and 2 illustrate the basic function of each safety switching element 1. Fig. 1 shows a switch strip 2 configured as a normally closed contact, and Fig. 2 shows a switch strip 3 configured as a normally closed contact, which is not part of the invention. Each switch strip 2, 3 has two electrical connections, designated as transmitter "Tx" and contact "Ct."

[0043] Second, the functionality of the two switching edges 2 and 3 when they have been expanded to include the function of a proximity sensor is explained below using Figs. 1 and 2. For both the normally closed contact shown in Fig. 1 and the normally closed contact shown in Fig. 2, it is symbolically visualized in four steps a) to d) that a detection zone 4 runs along the elongated switching edge 2, 3, which the proximity sensor covers. The switching edge 2, 3 does not run centrally through the detection zone 4, as will be explained in more detail later.

[0044] In the first step a) of approaching an obstacle, the obstacle is not yet within the detection zone. It is therefore not shown in this step a). The safety device permits the unhindered movement of a moving object to which the safety switching element 1 is assigned and to which it is, for example, attached. In a second step b), an obstacle 5 penetrates the detection zone 4. The obstacle 5 is represented as a human body part in the form of a symbolically indicated hand. The penetration of the obstacle 5 into the detection zone 4 leads to an advance warning: the safety switching element 1 is assigned a control system which, in turn, is connected to the drive or drive control system of the moving object, so that, based on the advance warning, for example, the movement speed of the moving object can be automatically restricted.

[0045] In a third step c), the obstacle 5 has penetrated the detection zone 4 and reached the safety edge 2, 3, but has not yet triggered the tactile sensor system of the safety edge 2, 3. Nevertheless, already in this step c), the control system assigned to the safety switching device 1 can automatically trigger a safety switching operation, for example, by automatically switching off the drive of the moving object.

[0046] In a fourth step d), the obstacle 5 has penetrated further into the detection zone 4 and triggers a switching operation of the tactile sensors of the respective safety edges 2, 3. In this case, too, the same safety switching operation is automatically triggered that is provided in a conventional manner when a safety edge is triggered, typically in the form of the automatic shutdown of the drive of the moving object. The triggering of the tactile sensors also clearly illustrates the different functional principles of the two safety edges 2, 3:

[0047] The switch strip 2 in Fig. 1, designed as an opener, contains a contact chain 6 made up of a plurality of electrical contact elements 7, which are held close together in electrically conductive contact by spring pressure. In the symbolically simplified representation in Fig. 1, the contact elements 7 are shown as a plurality of electrically conductive, e.g. metallic, hollow cylinders, which are threaded onto an elastic, tensioned tension element. The contact chain 6 is arranged purely by way of example in the cavity of a hollow profile (not shown) made of an elastomer material. Upon contact with the obstacle 5 and a resulting deformation of the hollow profile, adjacent contact elements 7 of the contact chain 6 are separated from one another, so that the flow of a quiescent current is interrupted and a switching operation of the switch strip 2 is thus effected.The Contact Ct represents the point at which the separation of the contact chain 6 is detected.

[0048] Due to the opening principle, an interruption of the quiescent current of the safety edge 2 for another reason, e.g. due to damage to an electrical supply line leading to one of the two electrical connections "Tx" and "Ct", triggers the same switching process as an interruption of the contact chain 6, so that the movable object is automatically brought into a safe state, e.g. by switching off its drive.

[0049] The switch strip 3 shown in Fig. 2, designed as a normally open contact, has two electrical contact elements 7 running linearly at a distance from one another. The contact elements 7 can be designed, for example, as metallic wires or threads that are drawn into the cavity of an elastomer hollow profile. If the elastomer hollow profile is produced using a coextrusion process, the contact elements 7 can consist of lines made of a different material, namely one that is more electrically conductive than the base material of the hollow profile. When the obstacle 5 strikes the switch strip 3, the two contact elements 7 come into contact with one another and close an electrical circuit. The contact Ct represents the point at which the two contact elements 7 come into contact with one another.Damage to an electrical supply line leading to one of the two electrical connections “Tx” and “Ct” does not cause a switching operation, but rather renders the safety edge 3, which operates according to the normally open principle, inoperative.

[0050] In the two schematically illustrated switch strips 2, 3 in Figs. 1 and 2, the electrically conductive contact elements 7 of the normally closed contact and the normally closed contact are each just one of many conceivable variants of how the contacting or interconnection of conductive elements can be realized. For example, instead of the respective contact Ct, the separation of the contact chain 6 or the contact between the two contact elements 7 can be detected at the respective transmitter Tx, or even at another element such as an electrode, with a correspondingly adapted evaluation circuit.

[0051] The detection range in Figs. 1 and 2 extends at different distances from the contact elements 7 of the switching strips 2, 3, namely further upwards than downwards in Figs. 1 and 2. This is achieved by a schematically indicated shield 8, which is shown below the switching strips 2, 3 in Figs. 1 and 2. The shield 8 is schematically simplified by a single line and labeled "Shield Electrode" with "SdTx", while in reality it has at least one, but typically two or more separate shielding electrodes. By designing the shield 8, the measuring range can be influenced or determined in all three dimensions around the contact elements 7. The design of the shield 8 affects, for example, its size, its course or shape, its material and / or its distance from the contact elements 7.

[0052] Fig. 3 illustrates the capacitive measuring principle when the safety edge 2 is operated as a proximity sensor - particularly before the respective tactile sensor is triggered. The safety switching element 1 has an electrical current or voltage source that generates an alternating voltage and is adjustable in terms of amplitude, phase and frequency, so that it can generate, for example, sine, sawtooth or rectangular curves, which is why it can also be referred to as a signal generator and is marked S in Fig. 3. The signal generator S is connected to an electrode E via an electrical resistor R. In the normally closed safety edge 2, several or all of the contact elements 7 of the contact chain 6 of the tactile sensor form this electrode E. In this way, using these already existing contact elements 7, a safety switching element 1 is created which has both a tactile sensor and a proximity sensor.

[0053] The electrically partially or fully conductive obstacle 5 is grounded via an impedance Z, which represents the electrical coupling of the obstacle 5 to the ground. When the obstacle 5 enters the detection zone 4 of the proximity sensor, it acts together with the electrode E like a capacitor C(d), which is indicated in Fig. 3 by a dashed frame and whose capacitance C depends on the distance d between the obstacle 5 and the electrode E.

[0054] Tx denotes the transmitter and indicates that the electrical capacitance (capacitive coupling) is measured in "transmit" or sending mode. Alternatively, and in contrast to the illustrated embodiment, the capacitance can be measured in "receive" or receiving mode, so the illustrated embodiment represents only one of several possibilities for using the contacts of tactile sensors of switching devices as electrodes of a capacitive proximity sensor.

[0055] The capacitor C(d) influences and changes the voltage drop U(R,C), which thus depends firstly on the electrical resistance value R and secondly on the capacitance of the capacitor C(d). This voltage drop U(R,C) and its changes generate the actual sensor signal, which is output as a signal by the safety edge 2 and can be automatically evaluated, thus enabling the use of the safety edge 2 as a proximity sensor. The proximity sensor can be used to qualitatively detect the presence of the obstacle 5 in the detection area 4. In addition, albeit with limited accuracy, the presence of the obstacle 5 can also be quantitatively determined as the distance to the electrode E, so that a safety switching signal can be generated based on the signals from the proximity sensor before the tactile sensor of the safety switching element 1 is triggered by contact between the obstacle 5 and the safety edge 2.

[0056] Fig. 4 shows a perspective view of a safety switching element 1 designed as a normally closed contact switch strip 2. A housing 9 has a rear side 10 with which it can be attached directly to a movable object or to a support which is in turn fixed to the movable object. An opposite front side 11 of the housing 9 is accordingly aligned such that it faces away from the movable component and represents the side of the switch strip 2 which is expected to come into contact with an obstacle. The contact element 7 shown is part of a contact chain 6. The shield 8 is formed by four shielding electrodes 12, two of which have a straight cross-section and two of which have a curved cross-section and which extend in an overall U-shape around the contact chain 6. The shield 8 ensures that the detection range 4 of the proximity sensor is directed essentially in the direction of the front side 11 - in Fig.4 is oriented upwards.

[0057] The housing 9 is shown purely schematically. It can be made of a solid material, e.g., a deformable foam material having a longitudinal bore in which the contact chain 6 is accommodated. However, the housing 9 can also be designed as a deformable hollow profile, e.g., made of an elastomer material. These two designs enable uncomplicated installation of the safety edge, even on curved surfaces. However, the housing 9 can also be designed in two parts, e.g., with a rigid profile rail forming the rear side 10 and with a deformable cover forming the front side 11 and allowing the contact chain 6 to be interrupted.

[0058] In Fig. 5, a safety switching element 1 is shown in perspective similar to Fig. 4, and the housing 9 is purely schematic as shown in Fig. 4. In this exemplary embodiment, the switching strip 2 has a single shielding electrode 12, which forms the shield 8 for the proximity sensor. Since the shielding electrode 12 is bent in a U-shape, a U-shaped shield 8 is created, similar to the switching strip 2 in Fig. 4, which shields the contact chain 6 towards the rear side 10 and thus towards the movable component, so that the detection area 4 of the proximity sensor also extends essentially in the direction of the front side 11 - i.e. upwards in Fig. 5.

[0059] Below the shield 8, Fig. 5 shows a reference electrode 13 which, due to the shield 8, does not contribute to capacitively detecting the approach of the safety edge 2 to an obstacle located in front of the front side 11. Since the reference electrode 13 is otherwise exposed to all environmental parameters in the same way as the first electrode in the form of the contact chain 6, the reference electrode 13 serves to detect capacitance changes that can arise due to fluctuating environmental parameters. Both the contact chain 6 as the first electrode of the safety switching element 1 and the reference electrode 13 as a further electrode are connected to a controller assigned to the safety switching element, so that the values ​​of the reference electrode 13 can be automatically evaluated and used to calibrate the values ​​of the contact chain 6.The reference electrode 13 can either be integrated into the safety switching element 1 as in the illustrated embodiment or, in a different embodiment, it can be arranged outside the safety switching element 1.

[0060] Reference symbol:

[0061] 1 safety switching device

[0062] 2 safety edges designed as openers

[0063] 3 safety edges designed as closers

[0064] 4 Detection range

[0065] 5 Obstacle

[0066] 6 Contact chain

[0067] 7 Contact element

[0068] 8 Shielding

[0069] 9 housings

[0070] 10 Back

[0071] 11 Front

[0072] 12 Shielding electrode

[0073] 13 Reference electrode

[0074] Tx Transmitter

[0075] CT Contact

[0076] SdTx Shield electrode

[0077] S signal generator

[0078] R Electrical resistance

[0079] E Electrode

[0080] Z Impedance

[0081] C(d) Capacitor d Distance

[0082] U(R,C) voltage drop

Claims

Claims:

1. Safety switching device (1) which has a tactile sensor in the form of a switching strip (2) or switching mat which has electrical contact elements (7), wherein at least one contact element (7) is connected as an electrode (E) of a capacitive proximity sensor in such a way that the capacitive coupling (C(d)) to obstacles in the environment is measured, which depends, among other things, on the distance of such obstacles to the capacitive proximity sensor, characterized in that the electrical contact elements (7) of the tactile sensor are connected as break contacts and are electrically conductively connected to one another, wherein a single one or a row of the electrically conductively connected contact elements (7) forms the electrode (E) of the proximity sensor.

2. Safety switching device according to claim 1, characterized in that an electrical signal generator (S) is connected to the electrode (E) via an electrical resistor (R), and the safety switching device (1) has a detector which detects the voltage drop (U(R,C)) across the electrical resistor (R).

3. Safety switching device according to claim 1 or 2, characterized in that the proximity sensor is provided with a shield (8) such that the contact element (7) connected as the electrode (E) of the capacitive proximity sensor is partially surrounded by a shielding electrode (12).

4. Safety switching device according to one of the preceding claims, characterized by a control which has a signal input for the measuring signals of at least one additional sensor, wherein the control is designed in such a way that a correction factor is determined on the basis of the measuring signals of the additional sensor and the measured value of the capacitive proximity sensor is corrected by means of this correction factor.

5. Safety switching device according to claim 4, characterized by at least one additional sensor which is designed to detect environmental data which influence the function of the capacitive proximity sensor.

6. Safety switching device according to claim 5, characterized by a further electrode of the capacitive proximity sensor, which forms the additional sensor, wherein the further electrode is arranged as a reference electrode (13) in such a way that it is exposed to environmental influences - except for the occurrence of an obstacle - in the same way as the first electrode (E) of the capacitive proximity sensor.

7. Safety switching device according to one of the preceding claims, characterized by a control which is designed in such a way that, after triggering a switching operation, it outputs a reversing signal to the drive of a movable object.

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