Safety switching device with dual sensor

Abstract

In a safety switching device (1) which has a tactile sensor in the form of a switching strip (2, 3) or switching mat which has electrical contact elements (7), the invention proposes that 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.

Description

[0001] 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. The electrical contact elements can be configured either as normally closed or normally closed contacts. 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.

[0002] When designed as a normally closed contact, a switch strip contains a contact chain consisting of a plurality of electrical contact elements. Although these elements can in principle be moved apart, they are held tightly together in electrically conductive contact by spring-elastic means. 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 triggering a switching operation of the sensor.

[0003] A switch strip designed as a normally open contact has two electrical contact elements spaced apart from one another, for example in the cavity of a hollow elastomer profile. The contact elements are typically linear and extend over practically the entire length of the profile. The contact lines can be designed, for example, in the form of copper threads, or in the case of a co-extruded profile, as lines made of a different material, namely one that is electrically conductive than the base material primarily used for the profile and has a considerably higher electrical resistance. 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 causing the sensor to switch.

[0004] 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.

[0005] The switch strips and switch mats designed as described above are “tactile” sensors that react to contact and, when a correspondingly elastic housing is deformed, trigger the switching process by opening or closing the contact elements.

[0006] 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.

[0007] This object is achieved by a safety switching device according to claim 1. Advantageous embodiments are described in the subclaims.

[0008] In other words, the invention proposes neither to use a completely differently constructed sensor nor to supplement the tactile sensor by adding a second, independent sensor, but rather to continue to use the existing contact elements as tactile sensors, but also to assign them a second function, namely to create a capacitive proximity sensor, and to use one or more contact elements of the tactile sensor as electrodes of the proximity sensor.

[0009] 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 more of the contact elements of the tactile sensor form this electrode, e.g., the multiple contact elements that form the contact chain of the normally closed contact, or a single linear contact element of the normally closed contact. Accordingly, the invention creates both a tactile sensor and a proximity sensor using these already present contact elements.

[0010] If the safety switching device 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 element connected to the safety switching device, which is to be protected and is typically movable, has now been brought into a safe state, for example by moving at 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.

[0011] 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 detected firstly qualitatively (presence in the detection zone) and secondly, with limited accuracy, also quantitatively determined (distance to the electrode), or at least estimated.

[0012] 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: 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.

[0013] 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.

[0014] 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.

[0015] Fourthly, in comparison to a conventional safety switching device, e.g. a safety edge, the safety switching device according to the invention can be designed to save installation 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 safety edge has been triggered, when the drive of a movable element is switched off, this movable element can still move far enough that it does not strike 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 which is equipped with a safety edge, whereby the foot of a person 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 element. The additional function of the safety edge as a proximity sensor, which is implemented according to the invention, allows an alarm to be triggered before the safety edge is deformed, so that the speed of the moving element 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.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] 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, e.g., arranged in a cavity of an elastomer hollow profile in which the contact elements are also arranged, or the controller can be arranged remotely but, as part of the safety switching device, can be wirelessly or wired connected to the contact elements of the safety switching device for signal transmission.

[0020] 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 control system 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.

[0021] In one embodiment, the safety switching device has a reference electrode. Instead of the additional sensors mentioned above, or even in addition to them, changes in the measurement behavior of the capacitive sensor can be compensated using the reference electrode: an additionally installed electrode of the capacitive sensor provides a reference measured value. This additional electrode is referred to as the reference electrode because it is not used to determine whether or not an obstacle is present in the detection zone. Since this reference electrode is also exposed to environmental influences, the reference measured value changes depending on these influences. The measured values ​​obtained with the other electrodes can be calibrated based on the respective reference measured value.

[0022] 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.

[0023] The invention is explained in more detail below using purely schematic representations. Fig. 1 and Fig. 2 schematically shows the operating principle for a safety switching device designed as an opener and a safety switching device designed as a closer, Fig. 3 a schematic representation of the capacitive measuring principle, and the Fig. 4 and Fig. 5 two examples of structural embodiments for a safety switching device designed as an opener and for a safety switching device designed as a closer.

[0024] In the Fig. 1 and Fig. 2 firstly shows the basic function of a respective safety switching device 1. Fig. 1 shows a switch strip 2 designed as an opener and Fig. 2 shows a switching strip 3 designed as a normally open contact. Each switching strip 2, 3 has two electrical connections, which are designated as transmitter “Tx” and contact “Ct”.

[0025] Secondly, the following will be based on the Fig. 1 and Fig. 2 explains the functionality of the two safety edges 2 and 3 when they have been extended by the function of a proximity sensor. Both for the Fig. 1 shown opener as well as for the one in Fig. The normally closed contact shown in Figure 2 is symbolically visualized in four steps a) to d) that a detection zone 4 runs along the elongated switching strip 2, 3, which the proximity sensor covers. The switching strip 2, 3 does not run centrally through the detection zone 4, as will be explained in more detail later.

[0026] In the first step a) of approaching an obstacle, the obstacle is not yet within the detection range. It is therefore not shown in this step a). The safety device allows the unhindered movement of a movable element to which the safety switching element 1 is assigned and to which it is attached, for example.

[0027] In a second step b), an obstacle 5 enters the detection zone 4. The obstacle 5 is represented as a human body part in the form of a symbolically indicated hand. The entry of the obstacle 5 into the detection zone 4 triggers a pre-warning: a control unit is assigned to the safety switching element 1, which in turn is connected to the drive or drive control of the movable element, so that, for example, the movement speed of the movable element can be automatically restricted based on the pre-warning.

[0028] 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 element 1 can automatically trigger a safety switching operation, for example, by automatically switching off the drive of the movable element.

[0029] In a fourth step d), the obstacle 5 has penetrated even 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 movable element. The triggering of the tactile sensors also clearly illustrates the different functional principles of the two safety edges 2, 3: The switch strip 2 of the Fig. 1 contains a contact chain 6 consisting of a plurality of electrical contact elements 7, which are held tightly together in electrically conductive contact by spring pressure. In the symbolically simplified representation of the 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, interrupting the flow of a quiescent current and thus causing a switching operation of the switching strip 2. The contact Ct represents the point at which the separation of the contact chain 6 is detected.

[0030] The Fig. The switch strip 3 shown in Figure 2, which is 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 manufactured 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.

[0031] In the two schematically shown switching strips 2, 3 of the Fig. 1 and Fig. 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.

[0032] The detection range in the Fig. 1 and Fig. 2 extends at different distances from the contact elements 7 of the switch strips 2, 3, namely in the Fig. 1 and Fig. 2 further upwards than downwards. This is achieved by a schematically indicated shield 8, which is Fig. 1 and Fig. 2 is shown below the contact strips 2, 3, respectively. The shield 8 is schematically simplified by a single line, marked as a "shield electrode" with "SdTx," while in reality it has at least one, but typically two or more separate shield electrodes. By designing the shield 8, the measuring range in all three dimensions around the contact elements 7 can be influenced or determined. 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.

[0033] Fig. Figure 3 illustrates the capacitive measuring principle when the safety edges 2 and 3 are operated as proximity sensors – especially 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 in Fig. 3 is marked with S. The signal generator S is connected to an electrode E via an electrical resistor R. In the case of an NC switch edge 2, several or all of the contact elements 7 of the contact chain 6 of the tactile sensor form this electrode E. In the case of a NO switch edge 3, a single linear contact element 7 forms the 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.

[0034] 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 range 4 of the proximity sensor, it acts together with the electrode E like a capacitor C(d), which Fig. 3 is indicated by a dashed frame and whose capacity C depends on the distance d between the obstacle 5 and the electrode E.

[0035] 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.

[0036] 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 and can be automatically evaluated, thus enabling the use of the safety edge 2, 3 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, 3.

[0037] In Fig. 4 shows a perspective view of a safety switching device 1 designed as a normally closed contact strip 2. A housing 9 has a rear side 10, with which it can be attached directly to a movable element or to a support which is in turn attached to the movable element. 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 contact 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 a 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.

[0038] 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.

[0039] In Fig. 5 is a safety switching device 1 similar to Fig. 4, which is, however, designed as a normally open contact strip 3, with two lens-shaped contact elements 7. The lower contact element 7, closer to the rear side 10, is not only a component of the tactile sensor formed by the contact strip 3, but, while the contact strip 3 is operated as a proximity sensor, forms, together with two further shielding electrodes 12, the shield 8 for the proximity sensor. Since the other two shielding electrodes 12 are curved, similar to the contact strip 2, the Fig. 4 a U-shaped shield 8 is created, which shields the upper contact element 7 towards the rear side 10 and thus towards the movable component, so that the detection area 4 of the proximity sensor also extends here essentially towards the front side 11 - in Fig. 5 thus extends upwards.

[0040] The housing 9 is in Fig. 5 purely schematic and similar to Fig.4. It has a cavity between the two contact elements 7 to allow the two contact elements 7 to come closer together until they come into contact when the front side 11 is deformed. Reference symbol: 1 safety switching device 2 safety edges designed as openers 3 safety edges designed as closers 4 Detection range 5 Obstacle 6 Contact chain 7 Contact element 8 Shielding 9 housings 10 Back 11 Front 12 Shielding electrode Tx Transmitter CT Contact SdTx Shield electrode S signal generator R Electrical resistance E Electrode Z Impedance C(d) capacitor d distance U(R,C) voltage drop

Claims

[1] Safety switching device (1), which has a tactile sensor in the form of a switch strip (2, 3) or switch mat, which has electrical contact elements (7), characterized by , that 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. [2] Safety switching device according to claim 1, characterized by that an electrical signal generator (S) is connected to the electrode (E) via an electrical resistance (R), and the safety switching element (1) has a detector which detects the voltage drop (U(R,C)) across the electrical resistance (R). [3] Safety switching device according to claim 1 or 2, characterized by , that the electrical contact elements (7) of the tactile sensor are connected as openers and are electrically connected to one another, wherein a row of electrically conductively connected contact elements (7) forms the electrode (E) of the proximity sensor. [4] Safety switching device according to claim 1 or 2, characterized by , that the electrical contact elements (7) of the tactile sensor are connected as normally open contacts and are electrically separated from each other, wherein a contact element (7) forms the electrode (E) of the proximity sensor. [5] Safety switching device according to one of the preceding claims, characterized by , that the proximity sensor is provided with a shield (8), such that the contact element (7) connected as electrode (E) of the capacitive proximity sensor is partially surrounded by a shielding electrode (12). [6] Safety switching device according to one of the preceding claims, characterized by a controller having a signal input for the measurement signals of at least one additional sensor, wherein the controller is designed in such a way that a correction factor is determined on the basis of the measurement signals of the additional sensor and the measured value of the capacitive proximity sensor is corrected by means of this correction factor. [7] Safety switching device according to claim 6, characterized by at least one additional sensor designed to detect environmental data that influences the function of the capacitive proximity sensor. [8] Safety switching device according to one of the preceding claims, characterized by a second electrode of the capacitive proximity sensor, wherein the second electrode is arranged in such a way that it is exposed to environmental influences in the same way as the first electrode (E) of the capacitive proximity sensor, and wherein the safety switching element (1) has a control to which the second electrode is connected to provide measured values, and which is designed in such a way that the measured values ​​supplied by the second electrode are evaluated as reference measured values and measured values ​​supplied by the first electrode (E) are corrected using the reference measured values. [9] Safety switching device according to one of the preceding claims, characterized by a control system designed in such a way that, after a switching operation has been triggered, it outputs a reversing signal to the drive of the movable element.

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