Safety switch element with dual sensors

Abstract

The present invention proposes a safety switch element (1) having a tactile sensor in the form of a switch strip (2) or a switch mat, and having an electrical contact element (7), wherein at least one contact element (7) is connected as an electrode (E) of a capacitive proximity sensor in such a way that capacitive coupling (C(d)) to an surrounding object, in particular capacitive coupling that depends on the distance between such object and the capacitive proximity sensor is measured, and the present invention proposes that the electrical contact elements (7) of the tactile sensor are normally connected as a closed circuit and connected in a way that they conduct electricity to one another, and that a single contact element or a series of contact elements (7) connected in a way that conduct electricity to one another form the electrode (E) of the proximity sensor.

Description

Technical Field

[0001] The present invention relates to a safety switch element having a tactile sensor in the form of a switch strip or a switch mat. This switch strip or switch mat has electrical contact elements. For the sake of simplicity, hereinafter, an elongated switch strip will be mainly referred to as an example of the safety switch element for description, but it is not limited to the switch strip.

Background Art

[0002] A switch strip designed as a normally closed contact has a contact chain formed by a plurality of electrical contact elements connected in series. These contact elements can in principle move apart, but due to spring elasticity, they are held close to each other in an electrically conductive state. This contact chain is arranged, for example, in the cavity of an elastomeric hollow profile. When contact with an object and deformation of the elastomeric hollow profile occur, adjacent contact elements move apart against the spring force, and as a result, the flow of current is interrupted and the switching operation of the sensor occurs.

[0003] A switch strip designed as a normally open contact has, for example, two electrical contact elements that extend spaced apart from each other in the cavity of an elastomeric hollow profile. These contact elements typically extend linearly and over substantially the entire length of the hollow profile. When the switch strip contacts an object, the elastomeric hollow profile is deformed, and in this case, the two contact elements contact each other to close the circuit, causing the switching operation of the sensor.

[0004] European Patent Application Publication No. 1612822 discloses a switching element, particularly in the form of a switch strip or switch mat, which is typically designed as an open contact. One of the two electrodes, i.e., the two contact elements, also functions as an electrode of a capacitive proximity sensor, so that an object can be detected capacitively before the switching element is tactilely activated by the contact of the two electrodes.

[0005] German Patent Application Publication No. 102008005783, European Patent Application Publication No. 3287585, and International Publication No. 2010 / 012492 also disclose safety switch elements designed as normally open contacts and configured as capacitive proximity sensors in addition to tactile detection of objects.

[0006] German Patent Application Publication No. 102019132508 discloses a capacitive sensor device that enables a function to be activated during the intended operation, for example, while a finger is in contact with an operating element, but wiping the sensor with damp dirt or a damp cloth does not activate the sensor's response.

[0007] In contrast to safety switch elements designed as normally open contacts, safety switch elements designed as normally closed contacts are inherently safer because, for example, even if the current flow is interrupted due to other factors, the sensor will still switch, and as a result, the connected equipment being monitored, such as moving machine parts or autonomous vehicles, will automatically switch to a safe state.

[0008] In contrast to linear, one-dimensional switch strips, a similar operating principle can be applied to two-dimensional switch mats. Electrical contacts within a switch mat can be arranged in different paths, such as multiple parallel contacts that require multiple electrical connections but allow for a certain spatial resolution, or they can meander or extend in a meandering manner, thereby enabling the entire surface to be sensed with a minimum number of electrical connections.

[0009] Switch strips and switch mats designed as described above are "tactile" sensors that respond to contact, causing switching action by opening or closing contact elements when the corresponding elastic support or housing deforms. [Overview of the Initiative]

[0010] The present invention aims to expand the detection area of ​​a sensor, enable detection of approach to the sensor, and achieve particularly high safety.

[0011] This objective is achieved by the safety switch element described in claim 1. Advantageous configurations are claimed in the dependent claims.

[0012] In other words, rather than proposing the use of entirely different sensors or the addition of a second independent sensor to a tactile sensor, the present invention proposes continuing to use the existing contact elements of a contact chain as a tactile sensor while additionally providing them with a second function, namely, the function of a capacitive proximity sensor, thereby utilizing one or more contact elements of a tactile sensor as electrodes of a proximity sensor. According to the present invention, a safety switch element that normally operates on the closed-contact principle is used. Due to the closed-contact principle, the function of a capacitive sensor can be realized even with a safety switch element having only a single electrode, i.e., a contact chain.

[0013] To realize the capacitance measurement principle, the safety switch element comprises an electrical signal generator connected to an electrode via an electrical resistor. This electrode is formed by one or a series of contact elements of a tactile sensor, for example, one or more contact elements constituting a normally closed contact chain, or all of the contact elements in the state before the contact chain is broken. Thus, according to the present invention, both a tactile sensor and a proximity sensor are provided using these originally existing contact elements.

[0014] Because the safety switch element is designed as a normally closed contact, the proximity sensor's function is maintained even when the tactile sensor is activated, i.e., when the normally closed contact element is interrupted and switching occurs. When the normally closed contact chain is interrupted, the previously continuous contact chain is divided into two sections, one of which remains connected to the signal generator. At the time the tactile sensor is activated, the protected moving object connected to the safety switch element has already transitioned to a safe state, such as moving at a reduced speed or being stopped. However, in certain applications, it may be important and beneficial to be able to evaluate the signal from the proximity sensor even in this safe state.

[0015] Electrically conductive obstacles (objects), such as the human body, are grounded via impedance. This electrical impedance consists of ohmic resistance, capacitance, inductance, or a combination thereof, and represents the electrical coupling of the obstacle to ground. Therefore, when an obstacle enters the detection area of ​​a proximity sensor, it acts like a capacitor together with the electrodes, changing the voltage drop across the measuring resistor. From this change in electrical resistance, the presence of an obstacle within the detection area can be detected qualitatively (firstly), and quantitatively determined (at least estimated) with limited accuracy (the distance to the electrodes).

[0016] Further improvements to this safety switch element, specifically the extension of the tactile sensor with the added functionality of a proximity sensor, offer several advantages.

[0017] Firstly, the technical safety of the safety switch element is improved because it uses essentially two sensors, i.e., sensors with two different operating principles. Even with a proximity sensor alone, the position of an obstacle within the detection area can be determined based on qualitative judgment, and the idea of ​​not using a tactile sensor may seem obvious. However, compared to such a solution, the safety switch element according to the present invention has the advantage that the uncertainty of capacitive proximity measurement is complemented by highly 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 at the same distance from a capacitive proximity sensor, the larger obstacle will be 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 occur in the proximity sensor of the switch element according to the present invention, the still-existing function as a tactile sensor guarantees the safety function required of the safety switch element.

[0018] Secondly, since the wiring work required for the safety switch element according to the present invention is reduced, two different sensor types can be installed particularly easily compared to the case where two completely independent sensors are installed.

[0019] Thirdly, the safety switch element according to the present invention can be designed to save installation space compared to a sensor installation configuration that installs two completely separate sensors, such as a tactile sensor and a proximity sensor that operates completely independently of the tactile sensor. For example, there is no need to install an additional ultrasonic sensor or similar proximity sensor that is positioned laterally to the longitudinal direction of the switch strip and increases the minimum required installation depth of the switch strip.

[0020] Fourth, compared to conventional safety switch elements, such as switch strips, the safety switch element according to the present invention can also be designed to save installation space. In conventional switch strips, the deformation path must usually be dimensioned to be longer than is technically necessary for the function of the switch strip itself. This unnecessarily large installation depth is intended to allow the movable body to continue moving to a degree that it will not collide with the obstacle that caused the switch strip to be activated, even after the drive of the movable body has been cut off following the tactile activation of the switch strip. A typical example of such an application is, for example, the metal housing of an industrial truck. This housing is equipped with a switch strip, and care has been taken to ensure that a person's foot is not injured after the aforementioned obstacle, such as a person's foot, activates the switch strip. The deformation space or installation depth of the switch strip should generally correlate with the braking distance of the movable body. The function of the switch strip as a proximity sensor, which is additionally realized by the present invention, allows the speed of the movable body to be reduced in advance, i.e., before the tactile sensor is activated, and it is possible to issue an alarm before the switch strip deforms so that the braking distance to a stop is correspondingly shorter. Therefore, the installation depth of the switch strip can be kept small.

[0021] Depending on the application, it may be necessary to minimize the size of the outwardly protruding switch strip, making it crucial to design in a way that saves space for the safety switch elements. For example, when mounted on industrial trucks, it is necessary to avoid situations where the switch strip is torn or sheared during loading and unloading operations. This is similar to situations where pallets close together come into contact with the tail lift or adjacent pallets during pallet loading or unloading on industrial trucks. As a design advantage, smaller structural dimensions where necessary can also be a decisive reason for purchasing each switch strip.

[0022] Fifth, by designing a safety switch element based on the principle of normally closed contacts, even after the electrodes of the tactile sensor, i.e., the contact chain formed from multiple individual contact elements, are broken, a portion of the contact chain can continue to be used as a capacitive proximity sensor.

[0023] This relates to a single row of interconnected contact elements, i.e., the portion of the contact chain still connected to the signal generator and the measuring resistor electrode, in a configuration that is particularly easy to implement from a technical standpoint. In other configurations, two rows of interconnected contact elements, i.e., two portions of the contact chain on either side of the disconnection point, i.e., the entire but disconnected contact chain, can be used as two capacitive proximity sensors.

[0024] Therefore, in any of the configurations described above, one or more contact elements of the tactile sensor form electrodes of a capacitive proximity sensor with reduced capacitance compared to the contact chain in an uninterrupted state. The tactile sensor is already activated when the contact chain is interrupted, and thus the moving body automatically transitions to a safe state, but the continued functionality of the capacitive sensor can be advantageously utilized if the associated controller is properly configured.

[0025] For example, if an autonomous vehicle automatically reverses after contacting an obstacle, the direction of reverse movement can be selected so that the vehicle does not simply reverse in the same lane as before, but moves in an arc away from the obstacle detected by capacitive proximity sensors, for example, into a different lane. This means that obstacles such as objects that are mistakenly parked and protruding into the travel path can be avoided, especially in a short amount of time.

[0026] After the collision with the first obstacle, if a person appears at the collision point and becomes an additional second obstacle within the moving space of the movable body, the presence of this person can still be detected by an effective capacitive proximity sensor before the movable body automatically retreats. During the retreat, the contact chain is closed again, and a new movement of the movable body in the original direction is allowed again. The early detection of additional obstacles that have not yet been detected before the tactile sensor is activated provides additional safety in this case. As a result, the safety switch element according to the present invention provides a particularly high safety level.

[0027] Finally and sixthly, the design of the safety switch element based on the normally closed contact principle provides the possibility of automatically identifying the cut-off position in the longitudinal direction of the electrode after the electrode is cut off. The cut-off position can be approximately identified based on the capacitance change of the electrode. This can be advantageous, for example, in statistical evaluations. If it is found that the contact with the obstacle is concentrated in a specific area of the safety switch element, measures can be taken to avoid the collision with the obstacle or to minimize the damage caused by the collision by changing either the safety switch element itself, the movable body monitored by the safety switch element, or the environment of the movable body.

[0028] By minimizing the damage to the safety switch element, its service life can be extended, and the implementation of appropriate maintenance or repair work accompanied by the stoppage of the movable body can be minimized. This is an economic advantage provided by the safety switch element according to the present invention. The possibility of changing the environment of the movable body as needed can reduce the future probability of collision occurrence, resulting in an overall improvement or enhancement of the safety level.

[0029] In one configuration, the safety switch element includes a shield. The operating mode of the proximity sensor may be affected by the shield. When a switch strip is installed on the movable member, the shield is preferably attached so as to be disposed between the component and the contact element of the switch strip. The shield is used to reduce or completely avoid interference factors that may affect the switch strip from the component.

[0030] The shield is composed of a flat metal plate strip, a strip made of conductive fiber material or metal fiber, or, in the case of a co-extruded member, by a corresponding region formed of a material different from the base material, namely a highly conductive elastomer material.

[0031] In one configuration, the safety switch element comprises a controller having a signal input for measurement signals from at least one additional sensor. The controller may be physically integrated into the safety switch element as an internal controller, for example, arranged in the cavity of a hollow member made of elastomer where the contact element is also arranged. Alternatively, the controller may be arranged at a position remote from the safety switch element as an external controller, but is configured to be wirelessly or wiredly connected to the contact element of the safety switch element as part of the safety switch element to enable effective signal transmission. In this case, the safety switch element has a multi-component configuration.

[0032] In another configuration, the safety switch element may be part of a further component already provided for the actuation of the movable body and serving as an external controller for the safety switch element to evaluate signals from the safety switch element and / or to influence the power supply to the safety switch element, specifically, at least one controller, for example, part of a safety switch device including equipment, a vehicle, or a motor controller.

[0033] Because the functionality of non-contact proximity sensors may be affected by environmental factors that the safety switch element experiences, additional sensors can be used to provide information about these environmental influences. For example, air humidity and / or air temperature can be detected, and changes in the measurement behavior of capacitive sensors that depend on them can be compensated for by appropriate correction factors. Such additional sensors may already be present on the moving body, in which case their signals can be processed by an internal or external controller of the safety switch element. In other configurations, additional sensors may be provided on the safety switch element itself, for example, one or more in the controller area, or incorporated as additional elements in the switch strip or switch mat.

[0034] The safety switch element according to the present invention, which normally operates on a closed-contact principle, basically requires only a single electrode, i.e., a contact chain formed from individual contact elements. In one configuration, the safety switch element has an additional electrode as a so-called reference electrode. In the absence of an optional shield electrode, the reference electrode becomes the second electrode of the safety switch element. The aforementioned additional sensor can be called a specific sensor because it captures specific parameters and, accordingly, provides measured values ​​such as air humidity and / or air temperature. Instead of, or in addition to, a change in the measurement behavior of a capacitive sensor can be compensated for by a reference electrode, which in the context of this specification can be called a general sensor or general-purpose sensor to distinguish it from a specific sensor. All factors affecting the contact chain as the first electrode also affect the reference electrode, with the exception of one point: the appearance of an obstacle. The reference electrode is not used to determine whether an obstacle is present in the detection area, and in this respect, unlike the contact chain, this is the only external factor to which the reference electrode is not exposed. Thus, this electrode, additionally installed on a capacitive sensor, provides a reference measurement.

[0035] Therefore, the reference electrode may be positioned outside the detection area, or within the detection area at a point where the appearance of an obstacle is not expected, for example, behind the first electrode of the safety switch element, or behind the shield, or in the direction of movement of the movable body, such as between the first electrode of the safety switch element and the movable body. Since the reference electrode is exposed to environmental influences as well as the first electrode of the capacitive sensor formed by the contact chain, the reference measurement will change based on all of these influences, not just specific influences. This reference measurement can be used to calibrate the measurement obtained from other first electrodes.

[0036] An internal or external controller can be used to automatically act on the drive mechanism of a monitored moving object based on the switching signal from the safety switch element, for example, to automatically decelerate or completely stop the drive mechanism. The reference electrode may be located outside the safety switch element and connected to the controller. For example, one application is to design the safety switch element as a switch strip and place it on the front of an autonomous mobile industrial truck. The reference electrode may be located at least outside the switch strip, such as under the vehicle floor or on the vehicle body. Both the switch strip on which the first electrode is located and the reference electrode are connected to the controller, and as a result, the value from the reference electrode can be automatically evaluated and used to calibrate the value from the first electrode.

[0037] In one configuration, the safety circuit controller enables the movable body to automatically retract slightly, or reverse, after the tactile sensor is activated. This reversal is essentially in the opposite direction to the movement before activation and is performed only over a limited distance, not excessively far, to avoid new accident risks. If the object comes into contact with an obstacle, the reversal minimizes the contact time. [Brief explanation of the drawing]

[0038] The present invention will be described in more detail with reference to the following purely schematic drawings. [Figure 1]This diagram schematically illustrates the operating principle of a safety switch element that is normally designed as a closed contact. [Figure 2] This diagram schematically illustrates the operating principle of a safety switch element that is normally designed as an open contact and is not related to the present invention. [Figure 3] A schematic diagram of the capacitance-type measurement principle is shown. [Figure 4] This figure shows an example of a structural embodiment of a safety switch element designed as a normally closed contact. [Figure 5] This figure shows another example of a structural embodiment of a safety switch element designed as a normally closed contact. [Modes for carrying out the invention]

[0039] Figures 1 and 2 first illustrate the basic functions of each safety switch element 1. Figure 1 shows a switch strip 2 designed as a normally closed contact, and Figure 2 shows a switch strip 3 designed as a normally open contact and not belonging to the present invention. Each switch strip 2 and 3 has two electrical connections, called a transmitter "Tx" and a contact "Ct".

[0040] Secondly, the operation of the two switch strips 2 and 3 with the proximity sensor function added will be explained with reference to Figures 1 and 2. For both the normally closed contact shown in Figure 1 and the normally open contact shown in Figure 2, the detection area 4 is symbolically shown to be covered by the proximity sensor extending along the elongated switch strips 2 and 3 in each of the four steps a) to d). The switch strips 2 and 3 do not extend through the center of the detection area 4, which will be explained in more detail later.

[0041] In the first step a), approaching the obstacle (object), the obstacle is not yet within the detection area. Therefore, this step a) is not illustrated. The safety device allows, for example, the unhindered movement of the movable body to which the safety switch element 1 is assigned and attached.

[0042] In step 2b), the obstacle 5 enters the detection area 4. The obstacle 5 is represented as a symbolically shown human body part in the shape of a hand. When the obstacle 5 enters the detection area 4, a warning is issued. A controller is assigned to the safety switch element 1, which is connected to the drive unit or drive controller of the movable body, and the warning automatically limits, for example, the movement speed of the movable body.

[0043] In step 3(c), the obstacle 5 has entered the detection area 4 up to the switch strips 2 and 3, but the contact sensor systems of the switch strips 2 and 3 have not yet been activated. However, even in this step(c), the controller assigned to the safety switch element 1 can automatically activate the safety switch operation, for example, by automatically stopping the drive mechanism of the movable body.

[0044] In step 4d), the obstacle 5 further enters the detection area 4, triggering the switching operation of the tactile sensor systems of each switch strip 2,3. In this case as well, a safety switching operation similar to that known to occur when the switch strips are activated is automatically performed, typically in the form of an automatic stop of the drive mechanism of the movable body. The operation of the tactile sensor systems also reveals the different operating principles of the two switch strips 2,3.

[0045] Designed as a normally closed contact, the switch strip 2 in Figure 1 comprises a contact chain 6 consisting of multiple electrical contact elements 7 held electrically connected in close proximity to each other by spring pressure. In the symbolically simplified illustration in Figure 1, the contact elements 7 are shown as a number of conductive, for example, metal hollow cylinders supported by a tensioned elastic tension element through which they pass. The contact chain 6 is arranged purely exemplary within a cavity of a hollow member (not shown) made of elastomer material. In the event of contact with an obstacle 5 and the resulting deformation of the hollow member, adjacent contact elements 7 of the contact chain 6 separate from each other, thereby interrupting the flow of standby current and enabling the switching operation of the switch strip 2. Contact Ct indicates the position where separation of the contact chain 6 is detected.

[0046] Normally, due to the closed-contact principle, even if the standby current of the switch strip 2 is interrupted for other reasons, such as damage to the power supply line leading to either of the two electrical connection points "Tx" or "Ct", a switching operation similar to that of the contact chain 6 is triggered, causing the moving body to automatically transition to a safe state, such as the stopping of the drive unit.

[0047] The switch strip 3 shown in Figure 2 is normally designed as an open contact and has two electrical contact elements 7 that extend linearly at a constant distance from each other. The contact elements 7 may be made up of, for example, metal wires or metal threads and drawn into a cavity of an elastomer hollow member. If the elastomer hollow member is manufactured by co-extrusion, the linear contact elements 7 are made of a different material from the base material of the hollow member, i.e., a more conductive material. When an obstacle 5 collides with the switch strip 3, the two contact elements 7 come into contact with each other and close the circuit. Contact point Ct indicates the point where the two contact elements 7 come into contact with each other.

[0048] Damage to the electrical supply line connected to one of the two electrical connection points "Tx" and "Ct" does not cause the switch to operate, but rather results in the loss of function of the switch strip 3, which normally operates according to the open-contact principle.

[0049] In the two switch strips 2 and 3 schematically shown in Figures 1 and 2, the conductive contact elements 7, which are normally closed and normally open, represent only one of many possible variations of how the conductive elements may be in contact or interconnected. For example, instead of detection at each contact Ct, the separation of the contact chain 6 or the contact of two contact elements 7 can be detected at other elements such as the respective transmitter Tx or electrodes using a correspondingly adapted evaluation circuit.

[0050] The detection regions in Figures 1 and 2 extend at different lengths from the contact elements 7 of the switch strips 2 and 3, specifically longer upwards than downwards in Figures 1 and 2. This is achieved by the schematic shields 8 shown below each switch strip 2 and 3 in Figures 1 and 2. The shields 8 are schematically simplified as a single line and labeled as a "shield electrode" denoted as "SdTx," but in reality, they consist of at least one, typically two or more, separate shield electrodes. The design of the shields 8 allows for influence and definition of the measurement range throughout the three-dimensional space around the contact elements 7. The design of the shields 8 relates, for example, to their size, path or shape, material, and / or distance from the contact elements 7.

[0051] Figure 3 illustrates the capacitive measurement principle when the switch strip 2 operates as a proximity sensor, particularly before the activation of each tactile sensor. The safety switch element 1 includes a current source or voltage source that generates an alternating current voltage. This current source or voltage source is also called a signal generator, and is indicated by the symbol S in Figure 3, as it can be adjusted in terms of amplitude, phase, and frequency to generate, for example, a sine wave, a sawtooth wave, or a square wave. The signal generator S is connected to an electrode E via an electrical resistor R. In the normally closed-contact switch strip 2, multiple or all of the contact elements 7 of the tactile sensor contact chain 6 form this electrode E. In this way, the safety switch element 1 is constructed using these originally existing contact elements 7, and it includes both a tactile sensor and a proximity sensor.

[0052] An electrically partially or fully conductive obstacle 5 is grounded via an impedance Z representing the electrical coupling between the obstacle 5 and earth. When the obstacle 5 enters the detection area 4 of the proximity sensor, together with the electrode E, it functions as a capacitor C(d), shown by the dashed box in Figure 3, whose capacitance C depends on the distance d between the obstacle 5 and the electrode E.

[0053] The symbol Tx indicates a transmitter, and that electrical capacitance (capacitive coupling) is detected in "transmit" mode. Alternatively, unlike the illustrated exemplary embodiment, it is also possible to detect capacitance in "receive" mode. Therefore, the illustrated exemplary embodiment is just one of several possibilities for using the contacts of a switch element tactile sensor as electrodes for a capacitive proximity sensor.

[0054] Capacitor C(d) affects and changes the voltage drop U(R,C). Therefore, this voltage drop depends first on the electrical resistance R and second on the capacitance of 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 switch strip 2 and can be automatically evaluated, so the switch strip 2 can be used as a proximity sensor. The proximity sensor can be used to qualitatively detect the presence of an obstacle 5 in the detection area 4. Furthermore, although the accuracy is limited, it is also possible to quantitatively determine the presence of the obstacle 5 as the distance from electrode E. Therefore, a safety switching signal can be generated based on the signal from the proximity sensor before the tactile sensor of the safety switch element 1 is activated by contact of the obstacle 5 with the switch strip 2.

[0055] Figure 4 is a perspective view showing a safety switch element 1 designed as a normally closed switch strip 2. The housing 9 has a rear surface 10 which can be fixed to a movable body or directly to a support fixed to the movable body. The opposite front surface 11 of the housing 9 is oriented away from the movable body and is the side of the switch strip 2 where contact with an obstacle is expected. The illustrated contact element 7 is part of the contact chain 6. The shield 8 consists of four shield electrodes 12, two of which have a straight cross-section and two have a curved cross-section, and extends in a U-shape to encircle the contact chain 6 overall. The shield 8 oriented the proximity sensor detection area 4 substantially toward the front surface 11, i.e., upward in Figure 4.

[0056] The housing 9 is shown purely schematically. The housing 9 is made of a solid material and may be made of a deformable foam material having a longitudinal hole inside which the contact chain 6 is housed. However, the housing 9 may be designed as a deformable hollow member made of, for example, an elastomer. These two configurations allow the switch strip to be easily mounted on a curved surface. However, the housing 9 may be designed as two parts, for example, a rigid profile rail forming the rear surface 10 and a deformable cover forming the front surface 11 that can block the contact chain 6.

[0057] Figure 5 is a perspective view showing the safety switch element 1, similar to Figure 4, and the housing 9 is shown purely schematicly, similar to Figure 4. In this exemplary embodiment, the switch strip 2 has a single shield electrode 12 that forms a shield 8 for the proximity sensor. Since the shield electrode 12 is curved in a U shape, a U-shaped shield 8 is formed, similar to the switch strip 2 in Figure 4, and the detection area 4 of the proximity sensor is also shielded, here substantially in the front direction 11, i.e., extending upward in Figure 5, the rear side 10 of the contact chain 6, i.e., the movable body side.

[0058] In Figure 5, a reference electrode 13 is shown below the shield 8, which does not contribute to the capacitive detection of the switch strip 2 approaching an obstacle located in front of the front 11 by the shield 8. The reference electrode 13, like the first electrode in the form of a contact chain 6, is similarly exposed to all environmental parameters and therefore plays a role in detecting capacitance changes that may occur due to fluctuating environmental parameters. Both the contact chain 6 as the first electrode of the safety switch element 1 and the reference electrode 13 as an additional electrode are connected to a controller assigned to the safety switch element, which can then be used to automatically evaluate the value from the reference electrode 13 and calibrate the value from the contact chain 6. The reference electrode 13 may be built into the safety switch element 1 as in the illustrated exemplary embodiment, or it may be located outside the safety switch element 1 in a different configuration. [Explanation of Symbols]

[0059] 1. Safety switch element 2 Switch strips designed as normally closed contacts 3. Switch strips designed as normally open contacts 4. Detection Area 5. Obstacles (objects) 6-contact chain 7 Contact elements 8 Shields 9 Housing 10 Rear 11 Front 12 Shielding electrodes 13 Reference electrode Tx transmitter Ct contact SdTx shielded electrode S signal generator R Electrical resistor E-electrode Z Impedance C(d) Capacitor d distance U(R,C) Voltage Drop

Claims

1. Having a tactile sensor in the form of a switch strip (2) or a switch mat, Having an electrical contact element (7), At least one of the contact elements (7) is connected as an electrode of a capacitive proximity sensor in such a manner that capacitive coupling (C(d)) to a surrounding object, in particular, capacitive coupling that depends on the distance between such object and the capacitive proximity sensor, is measured. The electrical contact elements (7) of the tactile sensor are normally connected as closed contacts and are connected in a manner that allows them to conduct electricity with each other. A safety switch element (1) in which a single contact element, or a series of contact elements (7) connected to one another in a manner that conducts electricity, forms the electrode (E) of the proximity sensor.

2. An electrical signal generator (S) is connected to the electrode (E) via an electrical resistor (R), The safety switch element according to claim 1, further comprising a detector for detecting the voltage drop (U(R,C)) across the electrical resistor (R).

3. The proximity sensor is provided with a shield (8). As a result, the contact element (7) connected as an electrode (E) of the capacitive proximity sensor is partially surrounded by a shield electrode (12), as described in claim 1 or claim 2.

4. A controller having a signal input for measurement signals from at least one additional sensor, The safety switch element according to any one of claims 1 to 3, wherein the controller is configured to determine a correction coefficient based on the measurement signal from the additional sensor, and to correct the measurement value from the capacitive proximity sensor using this correction coefficient.

5. The safety switch element according to claim 4, wherein the at least one additional sensor is designed to capture environmental data that may affect the function of the capacitive proximity sensor.

6. The additional sensor comprises other electrodes of the capacitive proximity sensor that constitutes the additional sensor, The safety switch element according to claim 5, wherein the other electrode is arranged as a reference electrode (13) in such a manner that it is exposed to environmental influences in the same way as the first electrode (E) of the capacitive proximity sensor, except when the object is generated.

7. A safety switch element according to any one of claims 1 to 6, comprising a controller configured to output an inversion signal to a drive device for a movable body after a switching operation has been activated.

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