Monitoring system for a bending elastic strip element and bending elastic strip element

Abstract

The invention relates to a monitoring system for a flexurally elastic strip-like element and a flexurally elastic strip-like element. The invention relates to a monitoring system for monitoring the bending load of at least one strip-like element (16) which is subjected to bending stress during operation and which extends in the longitudinal direction and has a sheath (16) in which recesses (30) are introduced at least in sections on the circumferential side, in which recesses (30) pressure-sensitive sensor elements (32) are inserted, the sensor element emits a sensor signal when subjected to a pressure load.

Description

[0001] This application is a divisional application of the Chinese invention patent application filed on March 26, 2020, which entered the Chinese national stage on September 27, 2021, with PCT application number PCT / EP2020 / 058622, national application number 202080025254.2, and invention name "Monitoring system for bending-elastic strip elements and bending-elastic strip elements". Technical Field

[0002] The invention relates to a monitoring system for a flexurally elastic strip-shaped element and to a flexurally elastic strip-shaped element, the monitoring system being used to monitor the bending load of at least one strip-shaped element which is subjected to bending stress during operation. Background Art

[0003] Such a strip-shaped element which is subjected to bending stress is, for example, a supply set, with which two machine parts which can move relative to each other are connected to each other. The term "supply set" is generally understood here to mean a guide element which has individual supply lines inserted therein, for example electrical, hydraulic and pneumatic individual lines. The guide element is, for example, a hose-shaped element which has an inner cavity in which the individual supply lines are guided, in particular loosely.

[0004] Such supply sets are also called hose sets and are used, for example, in multi-axis industrial robots. Such hose sets are usually guided along a robot arm in the direction of a robot arm, to which the tool is fastened. Typically, the hose set is fastened with one end to a device for length compensation, which has a return mechanism.

[0005] Such hose sets in industrial robots are subject to very strong alternating bending stresses. Accordingly, the service life of the hose sets is limited and must be replaced regularly.

[0006] It would be desirable to be able to correctly estimate the useful life of such a hose set, or also to be able to identify improper operation or mishandling of a hose set in use. Summary of the invention

[0007] Based on this, the object of the present invention is to obtain information about the bending stress to which a strip-shaped element, in particular such a hose set, is subjected.

[0008] According to the invention, this object is achieved by a monitoring system which is designed to monitor the bending load of at least one strip-shaped element which is subjected to bending stress during operation. The strip-shaped element is usually arranged and fastened to a unit to be monitored, for example an industrial robot, during operation. The monitoring system has:

[0009] - a strip-shaped element which extends in the longitudinal direction and has a jacket in which at least one recess is introduced at least in sections on the circumference,

[0010] a pressure-sensitive sensor element which is inserted into the recess and which is designed to emit a sensor signal when subjected to pressure load,

[0011] - a local measuring unit for receiving the sensor signal,

[0012] Furthermore, an evaluation unit is provided for evaluating a sensor signal which is related to the bending stress to which the strip-shaped element is subjected, based on the bending-induced pressure load of the sensor element, and which is part of the monitoring system.

[0013] In this case, in a first embodiment variant, the evaluation unit is directly part of the unit to be monitored. For example, the evaluation unit forms a common local structural unit arranged on the device together with the local measuring unit. Alternatively to this, the evaluation unit is arranged away from the device to be monitored and is only connected to the measuring unit or at least can be connected thereto in terms of data technology in order to be able to receive sensor signals. The connection in terms of data technology is particularly wireless here, for example also via the Internet. "Arranged away from the unit to be monitored" should be understood in particular to mean that the evaluation unit is not arranged in the immediate vicinity of the unit and preferably is not arranged in a building or operating site where the unit to be monitored is arranged.

[0014] It is particularly important to arrange the pressure-sensitive sensor element in the lateral recess. The sensor element is inserted here with a precise fit so that (in the event of bending of the strip-shaped element and thus also of the sheath) it is subjected to a pressure load due to the compression of the sheath. Since (depending on the direction of the bending of the element) the recess is compressed, a pressure load is applied to the sensor element in the event of bending, to which the sensor element is sensitive.

[0015] The recess on the peripheral side is usually understood as a recess in the wall of the sheath. It can be a recess on the outer periphery of the sheath or a recess on the inner periphery.

[0016] This measure makes it possible to detect the bending load of the strip-shaped element in a simple manner, so that, in conjunction with the sensor signal and a suitable evaluation, conclusions can be drawn, for example, about impermissible loads or the remaining service life.

[0017] In a suitable embodiment, the recess is a groove which is at least partially helical. The helical groove thus extends at least partially around the circumference of the jacket. The groove is introduced into the jacket material. The groove expediently extends over the entire length of the jacket or at least over almost the entire length of the jacket (for example at least 90% of the total length). It is also preferred that the groove is designed to be continuous and helical.

[0018] Furthermore, the sensor element is designed as a sensor line which is inserted into the groove and preferably extends over the entire length of the groove or at least over the width of the groove (for example more than 50%).

[0019] The sensor line has a conductor surrounded by a dielectric. The sensor line is connected to a measuring unit, i.e., in particular, coupled to the measuring unit. Preferably, in addition to receiving the sensor signal, the measuring unit is also configured to feed the measuring signal into the sensor line and to feed the measuring signal for measurement. The received sensor signal is formed by a reflected signal component of the measuring signal. The reflected signal component is generated in such a way that the measuring signal is reflected at a disturbing position. The disturbing position is configured here at a position where the dielectric is subjected to a pressure load and in particular is squeezed due to the bending of the strip-shaped element.

[0020] The measurement signal is in particular a high-frequency signal with a typical frequency of several tens or several hundred MHz. The frequency is preferably changed during operation within a predetermined frequency range. In particular, a periodic variation between two frequency values ​​(so-called "swing") is provided. Alternatively, the measurement signal is a step signal or a measurement pulse, as described, for example, in WO 2018 / 086949A1.

[0021] The sensor line usually has an impedance which is determined to a large extent by the dielectric. The deformation of the dielectric due to the compressive stress usually leads to a local impedance change at the stress point. The measurement signal propagating in the sensor line is at least partially reflected at this stress-exposed point (hereinafter also generally referred to as interference point). The reflected component then returns again in the direction of the measuring unit, where it is detected.

[0022] The sensor line is a transverse pressure-sensitive element, since the application of pressure perpendicular to the direction of propagation of the sensor line is detected.

[0023] The particular advantage of this measure is that the bending stresses to which the strip-shaped element is subjected can be monitored simply by simply inserting the sensor line into the spiral groove. When the strip-shaped element is bent, the compressive load is exerted on the sensor line in that the lateral groove walls delimiting the groove narrow the receiving space of the groove and thus compress the sensor element inserted therein and designed as a sensor line.

[0024] The sheath is preferably a so-called corrugated hose. At least one supply line is preferably guided in the corrugated hose. Alternatively, a medium is guided in the hose. In such a corrugated hose, the spiral groove preferably extends continuously from one end of the sheath to the other end.

[0025] The sheath is preferably a guide or protective element, in which at least one supply line is guided. The supply line is, for example, an electrical, pneumatic or hydraulic line. Typically, a plurality of supply lines are guided within the corrugated hose, wherein different types of supply lines can also be guided.

[0026] In a particularly preferred embodiment, the strip-shaped element is a so-called hose set of a multi-axis industrial robot. The hose set is therefore designed for installation in such an industrial robot. The hose set is expediently fastened to such an industrial robot. During operation, the hose set is used to supply tools arranged on a manipulator. The hose set extends along the manipulator arm, more precisely preferably to a device for length compensation. In this device, changes in length caused by the movement of the manipulator arm or other manipulator arms are compensated. The individual supply lines are typically led out of the corrugated hose to an interface and there, for example, are connected or can be connected to the corresponding further-leading supply lines via a releasable coupling point.

[0027] The sensor line preferably extends along the entire sheath and the slot, at least over a majority of the length of the sheath or the slot.

[0028] The sensor line usually has an outer diameter and the slot has a slot width, wherein the outer diameter is matched to the slot width. This is to be understood as meaning that the slot width and the outer diameter are identical or at least substantially identical. At least substantially identical is to be understood as meaning that the slot width and the outer diameter correspond with a tolerance range of maximum + / - 15% and more preferably maximum + / - 10% or maximum + / - 5%. "Slot width" is to be understood as the clear distance between two opposite slot walls in the unloaded state, in particular when the sheath is not bent.

[0029] The outer diameter expediently has a slight excess, for example a maximum of 5% or a maximum of 10% compared to the groove width. This makes it possible, for example, for the sensor line to be held in the groove in a purely frictional manner. Additional fastening elements are preferably omitted.

[0030] In a practical embodiment, the dielectric is elastically deformable and is in particular designed as a foamed dielectric. A particularly suitable material for this is thermoplastic rubber, since it has a high restoring force. In addition, polyurethane (PUR) or thermoplastic elastomers, in particular crosslinked thermoplastic elastomers, such as TPV (thermoplastic polyolefin sulfide), are preferably used as the material for the dielectric.

[0031] These materials generally have good elasticity and therefore good restoring forces. This is essential in order to be able to detect the often frequently occurring alternating bending stresses in real time without excessively long relaxation times that would be disruptive to the measurement.

[0032] The material preferably has a relative humidity of 0.9-1.0 g / cm 3 In the range of 0.9-0.95 g / cm 3 The density of the plastic material used is within a range of . These values ​​apply to the unfoamed state. In a preferred embodiment variant, a foamed plastic is used. The foaming allows the density to be adjusted appropriately on the one hand, and also the sensitivity, since the (lateral) force required for extrusion is reduced as the foaming increases.

[0033] The sensor line is designed, for example, as a core or a core pair. The core is a metallic conductor that is surrounded by a core sheath as an insulation. The core sheath forms a dielectric.

[0034] Preferably, the sensor line is designed as a coaxial line. The sensor line itself therefore has an inner conductor, which is directly surrounded by a dielectric. An outer conductor is again arranged directly around the dielectric. Typically, the outer conductor is a dielectric sheath in the manner of a shield, for example in the form of a braided shield.

[0035] The evaluation of the reflected component of the measurement signal is usually based on the fact that, under local pressure load, the impedance value changes at this local location, so that a disturbance point is formed at this local location, at which the signal component is reflected.

[0036] For example, the evaluation of such a reflected signal component can be carried out here with the aid of so-called time measurement methods (time domain reflectometry, TDR (Time Domain Reflectometry)). In this case, the travel time of the signal is usually known, from which, in combination with the (measured) travel time and the known propagation speed, for example, the position of the interference point can then be inferred. If the geometrical course of the sensor line and the slot is known, the position of the interference point on the sheath can then be inferred and thus also the direction of the bend. Preferably, a simplified time measurement method is used, as described, for example, in WO 2018 / 086919 A1.

[0037] Alternatively, there is also a feasible solution for evaluation in the frequency domain. For this purpose, the so-called frequency reflection measurement method (FDR Frequency Domain Reflectometry) is known. This FDR method is preferably used. The measuring unit is configured here to feed a so-called swing signal so that this FDR method can be performed. The evaluation of the reflected signal component is carried out in the evaluation unit. The reflected signal component (also referred to as the reflected signal) is therefore forwarded to the evaluation unit, where the reflected signal is evaluated. The term "swing signal" is generally understood to be a signal with a typically constant amplitude, whose frequency varies between an upper frequency and a lower frequency. Within this frequency band between the upper frequency and the lower frequency, there is a main frequency that is unique to the line, and in addition, the main frequency is also related to the length of the sensor line. Typically, the measurement signal is fed in at one end of the sensor line and reflected at the opposite end of the sensor line, such as a short-circuited or open end, and returned to the measuring unit again, where it is received. This frequency that is unique to the line is particularly consistent with the following simplified formula:

[0038] f [MHZ] = 150 * v r / d [m] ;

[0039] Where f = frequency (in MHz), d = length of the signal path (in meters), v r = Measures the relative propagation speed of a signal.

[0040] The relative propagation velocity is typically between 0.66 and 0.8. It is defined as the ratio of the propagation velocity to the speed of light (in a vacuum).

[0041] The frequency is usually related to the dielectric constant ε rThe length of the signal path typically corresponds to twice the length of the sensor line (round trip from the feed point to the line end where the signal is reflected and travels back to the feed point = measuring unit).

[0042] In a suitable embodiment, the evaluation unit is designed to resolve the position of the bend in conjunction with the sensor signal. This is therefore a position-resolved measurement. In the case of a direct measurement of the travel time, for example via a TDR measurement, this is derived directly from the travel time given a known propagation velocity and known geometrical factors. The known geometrical factors include the diameter of the jacket at the bottom of the groove and the slope of the helical groove. In conjunction with these geometrical factors, the position along the jacket at which there is a disturbing position that causes the reflected signal to be reflected can be determined.

[0043] When measuring in the frequency domain, the measured frequency spectrum is converted into a time-dependent profile, for example by inverse Fourier transformation. The travel time is then determined again in conjunction with this time profile. There is also the possibility of determining the position of the interference along the length of the sensor line by determining the phase of the reflected signal. For this purpose, so-called vector network analyzers (VNA) are used, for example, in a manner known per se.

[0044] Preferably, the evaluation unit is also designed to determine the direction of the bending of the sheath in conjunction with the sensor signal. This is preferably done by determining the position of the interfering location in the course of the sensor line as accurately as possible. In conjunction with known geometric data, it is then possible to determine at which angular position the interfering location is located, i.e., whether the location is, for example, on the upper side of the sheath, at a lateral position or at the bottom. The direction of the bending is then determined based on this angular position.

[0045] In an expedient development, the current bending radius is inferred by means of the evaluation unit in conjunction with the sensor signal.

[0046] Different bending radii usually lead to different compressions, which in turn influence the component of the reflected signal. Therefore, the degree of bending can be inferred based on the level of the reflected signal component.

[0047] For example, according to a first embodiment variant, the bending radius is determined by comparing the variation curve of the reflection signal with a previously measured reference variation curve, in particular a reference spectrum, which is respectively assigned to a specific bending radius. Therefore, a reference variation curve or a reference spectrum is stored for different bending radii.

[0048] In addition or as an alternative, the number of interference points present is determined in conjunction with the sensor signal, wherein the current bending radius is derived in conjunction with the number of interference points. This is based on the idea that the number of interference points varies depending on the bending radius, i.e., more winding sections are compressed at smaller bending radii than at larger bending radii, so that they act as interference points. Therefore, there is a relationship between the current bending radius and the number of interference points.

[0049] In addition to or in addition to the number of interference locations, the bending radius can also be inferred, for example, from the amplitude ratio or the absolute amplitude of the sensor signal for the individual interference locations (in each case a maximum in the signal curve). In the case of a bend, the maximum compression occurs in the middle of the bend, which results in a maximum with the highest amplitude in the sensor signal.

[0050] Preferably, the spectrum detected during the measurement is viewed and evaluated. Such a spectrum is obtained, for example, in the FDR (Frequency Reflectometry) method, in which a so-called wobble signal is fed in as the measurement signal. In particular, the degree of curvature / curvature radius is inferred from the amplitude ratio between the main maximum and the secondary maximum in the spectrum and from the number of maxima.

[0051] In a preferred embodiment, the evaluation unit is configured as a central unit, which is arranged spaced apart from the flexural elastic element to be monitored, and in particular also spaced apart from a possible unit to be monitored, in particular an industrial robot, on which the flexural elastic element is fastened. The local measuring unit is configured to forward the sensor signal, and the central unit is configured to receive the sensor signal. The transmission of the sensor signal is preferably performed wirelessly, but in principle can also be performed wired. In the case of a wireless connection, the forwarding is performed, for example, via the Internet, and in particular involves a cloud-based evaluation. This is understood to mean that the data from the sensor signal is forwarded to a cloud storage, i.e., to a central storage location connected via the Internet, and is read from there for evaluation by the evaluation unit.

[0052] “Remote” is understood here in particular to mean that the evaluation device is not arranged in the same operating position as the strip-shaped element to be monitored. Preferably, the central unit is arranged at the manufacturer or at another service provider independent of the operator of the system.

[0053] In a suitable manner, a plurality of strip elements to be monitored, i.e., in particular a plurality of hose kits to be monitored, can be connected or connected to a central unit in terms of data technology. The central unit is designed to evaluate data from a plurality of elements to be monitored. Thus, data from a large number of elements to be monitored are received and evaluated via the central unit. This provides a broad data basis for a large number of installations and applications. By this measure, the acquired data can form a starting point for a data-based model, which is used, for example, to simulate the stress, wear resistance or service life of the hose kit used. More precise conclusions about the service life, probability of failure, etc. can thus be derived based on a broad data basis. Weak points can also be identified in advance and then avoided, for example, by changes in the design structure or changes in the process flow.

[0054] According to the invention, this object is also achieved by a strip-shaped element which is subjected to bending stress during operation and is flexurally elastic, and which is particularly designed for use in a unit to be monitored. The element extends in the longitudinal direction and has a flexurally elastic sheath, in which recesses are introduced at least in sections on the circumference. In addition, a pressure-sensitive sensor element is provided, which is inserted into the recess and is designed to emit a sensor signal in the event of a pressure load caused by the bending of the strip-shaped element. In addition, a local measuring unit is provided for receiving the sensor signal, wherein the measuring unit is additionally also designed to forward the sensor signal to an evaluation unit.

[0055] The advantages and preferred embodiments cited with regard to the monitoring system can also be transferred to the flexurally elastic element. In particular, this is a hose set for an industrial robot, which has a corrugated hose as a sheath, which has a spiral groove in which a sensor line is inserted as a sensor element. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] The following is a more detailed description of the embodiments in conjunction with the accompanying drawings. These embodiments are shown in partially simplified diagrams:

[0057] Figure 1 shows a simplified diagram of an industrial robot;

[0058] Figure 2 A simplified sectional view of a section of a corrugated hose having a spiral groove, in which a sensor line is inserted, is shown;

[0059] Figure 3 A cross-sectional view of a coaxial line is shown.

[0060] Figure 4 An exemplary measurement structure is shown;

[0061] Figures 5A to 5Eshows exemplary signal profiles for different numbers of interference locations, and;

[0062] Figure 6 Simplified diagram showing a plurality of units to be monitored transmitting sensor signals to a central unit.

[0063] In the figures, parts having the same function are provided with the same reference symbols. DETAILED DESCRIPTION

[0064] exist Figure 1 , an articulated arm robot is shown, which is designed as a multi-axis industrial robot 1, in particular a six-axis industrial robot 2. The articulated arm robot has a first section, also referred to as a rocker arm 4, which is connected to a base 6 via a first joint connection R1. The rocker arm 4 can be pivoted around the base around a horizontal axis. In addition, the rocker arm 4 can usually be pivoted around a vertical line. At the second joint connection R2, a second section, usually referred to as a robot arm 8, is connected to the rocker arm 4 so that it can be pivoted around the so-called (horizontal) "axis 3". Finally, a robot arm 10 as a third section is connected to the robot arm 8 via a third joint connection R3. Finally, a processing tool 12, such as a welding tongs, etc., or a holder for medical equipment, for example, is arranged on the robot arm 10.

[0065] In order to supply power and / or fluid and / or data signals to the processing tool 12, the industrial robot 2 has a supply line kit 14, which is guided along the robot arm 2 and connected to the base 6 from there. In the area of ​​the robot arm 6, the supply line kit 14 is guided in a sheath (protective hose) configured as a corrugated hose 16. The supply line kit 14 and the corrugated hose 16 are also collectively referred to as a hose kit 18. The hose kit is a bending elastic element, which is subjected to alternating bending stresses during operation. Typically, a separation position for the supply line kit 14 is arranged in the area of ​​the second joint connection R2, and the hose kit 18 is guided to the separation position as a replaceable wear unit.

[0066] Furthermore, a device 20 for guiding and returning the hose set 18 is fastened to the robot arm 6, in particular in the region of the second articulation R2. The device serves for length compensation during robot arm movements. The hose set 18 is held on the device 20 via a holding element (hose clamp) 22. Preferably, a measuring unit 24 is integrated on or in the holding element 22.

[0067] The measuring unit 24 is also connected in terms of data technology to an evaluation unit 26 , which is designed at least for forwarding data in the evaluation unit 26 .

[0068] The measuring unit 24 and the evaluation unit 26 are part of a monitoring system for monitoring the flexural elasticity of a hose set 18 which is subjected to bending stresses during operation. The hose set 18 itself is also part of the monitoring system. Figure 2 and 3 The hose kit is described in more detail.

[0069] Combination Figure 2 , again in a fragmentary cross-sectional view, a hose kit 18 is shown having a corrugated hose 16 and a supply line kit 14 inserted therein. The hose kit generally extends in a longitudinal direction L. The supply line kit 14 comprises a plurality of supply lines 28 , which are arranged loosely within the corrugated hose 16 , for example.

[0070] The corrugated hose 16 has spirally extending grooves 30 on the circumference, i.e. on its outer jacket. Usually, due to the wavy design of the wall of the hose jacket (viewed in the longitudinal direction), external grooves (grooves 30) open to the environment are formed on the (radial) outer side of the hose jacket and internal grooves open to the interior of the corrugated hose 14 are formed on the (radial) inner side. At least in one of these grooves, in the exemplary embodiment in the external groove 30 (e.g. Figure 2 ), a sensor line 32 is guided. The groove 30 is delimited here by opposite groove walls and a groove bottom. The clearance between the groove walls of the groove 30 defines the groove width a and corresponds here at least largely to the diameter D of the sensor line 32. The sensor line 32 is therefore inserted into the groove 30 with a precise fit.

[0071] The groove 30 and thus the sensor line 32 are wound relatively tightly around the circumference of the corrugated hose 16. Due to the helical configuration of the groove 30, the sensor line is thus helical and is thus guided along the thread line. The lead angle α, which characterizes the slope of the groove 30, is relatively small. Preferably, the lead angle α is generally in the range between 5° and 30° and in particular in the range between 10° and 20°. The diameter of the hose set 18 is typically in the range of a few centimeters, for example in the range of 3 cm to 8 cm.

[0072] The sensor line 32 is in particular a coaxial line, as exemplarily shown in Figure 4 . Thus, it has a central conductor 34 which is directly surrounded by a dielectric 36 made of plastic. The dielectric is an elastic, in particular foamed material. The dielectric 36 is in turn concentrically surrounded by an outer conductor 38 which is formed by a shield, for example a braided shield. The outer conductor is ultimately surrounded by a line sheath 40.

[0073] Especially from Figure 4 It can be seen that the sensor line 32 is connected to the measuring unit 24 .

[0074] During operation, the measuring unit 24 feeds a measuring signal M into the sensor line 32 at the feed-in position. The measuring signal is, for example, a high-frequency, for example, sinusoidal signal. The measuring signal M passes through the sensor line 32. The measuring signal M is completely reflected at the end of the sensor line 32 opposite the feed-in position, which end is, for example, configured as a short-circuited or open end, and returns again in the direction of the measuring unit 24 as a (reflected) sensor signal S and is detected by the measuring unit 24. The first evaluation of the sensor signal S can already be performed in the measuring unit 24. The data D generated here is forwarded to the evaluation unit 36, for example, for further evaluation. In principle, there is also the possibility of forwarding the sensor signal S directly to the evaluation unit 26, that is, the sensor signal forms the data D. In addition, there is the possibility of integrating the evaluation unit 26 and the measuring unit 24 directly into a common structural unit.

[0075] When the hose set 18 is subjected to bending stress, the inside of the curved portion of the corrugated hose 16 is compressed as a whole, thereby reducing the groove width a. As a result, the sensor line 32 inserted therein is subjected to pressure loads at the curved location and is also squeezed in particular. This pressure-loaded location forms a disruptive location.

[0076] Due to the relatively tight winding of the sensor line 32, typically multiple winding sections of the sensor line 32 are compressed simultaneously, so that typically multiple interference locations are generated simultaneously when bending occurs. Due to the compression of the sensor line 32 and thus the dielectric 36, an impedance change occurs locally at the bending location (interference location). This impedance change or impedance step causes the propagated measurement signal M to be at least partially reflected at this location and return to the measuring unit 24 again and can be evaluated there.

[0077] According to a first preferred variant, the frequency reflection method (FDR) is used in particular for the evaluation. For this purpose, a so-called wobble signal is fed in as the measurement signal M by means of the measuring unit 24. This measurement signal is a signal with a constant amplitude, the frequency of which varies between an upper limit frequency and a lower limit frequency. Within the frequency range determined by these two limit frequencies there is a main frequency which, depending on the propagation speed of the measurement signal M and the signal path (twice the length of the sensor line 32), varies according to the formula f [MHZ] = 150 * v r / d [m](see above). Typically, the length of the sensor line 32 is in the range of 5 m to 30 m, and in particular in the range of 15 m to 25 m. The length of the sensor line 32 preferably typically exceeds the length of the hose set 18 by 5 to 15 times. The length of the hose set 18 is typically in the range of 0.5 m to 3 m, and in particular in the range of 1 m to 2 m.

[0078] exist Figures 5A to 5E 1 and 2 show different idealized profiles of the sensor signal S for different numbers of interference locations. In the individual diagrams, the amplitude is plotted against the frequency of the sensor signal S. The fed-in wobble signal varies in the present case, for example, in the range between 0 and 400 MHz.

[0079] Each location of a disturbance point is assigned a defined frequency of the reflected sensor signal S. According to the above formula, the frequency is dependent precisely on the distance between the feed point and the disturbance point at which the signal component is reflected.

[0080] Figure 5A The situation is shown here for the case where there is only one interfering location. Figure 5B shows the situation with two interfering locations, Figure 5C shows the situation with three interference locations, Figure 5D shows the situation with four interference locations, while Figure 5E Finally, the situation is shown for a case with ten interference locations. Due to the presence of multiple interference locations, reflected signal components are generated at each interference location. Due to the spatial spacing of the interference locations, the signal components are superimposed (due to phase differences, superposition in phase or inverse phase due to distance), resulting in the characteristic spectrum shown with maximum and secondary maxima. Due to this superposition of reflections, the sensor signal becomes clearer and more concise as the number of interference locations increases.

[0081] In particular, from the shape of the sensor signal, i.e. in particular from the location of the maxima and minima, the number of secondary maxima per main maximum and from the level of the signal levels at the maxima and minima, for example the number and size of the interference locations, the distances of the interference locations from one another and therefore also the degree of the curvature can be inferred.

[0082] The spectrum obtained during the measurement is usually characterized by a special frequency associated with the sensor line length. In addition, the spectrum is characterized by further special frequencies, which are in particular associated with further distances. For example, in this case, these further distances are the distance to the first interference location and the distance to the first interference location or the distance to further interference locations or the distance between these interference locations. In addition, the spectrum is characterized by multiple reflections between interference locations or multiple reflections between interference locations and conductor ends.

[0083] Typically, the hose set 18 is checked with respect to the current bending load using the evaluation unit 26 in conjunction with the received sensor signal S.

[0084] This check is preferably carried out continuously during operation, i.e. when the industrial robot 2 is in use. Continuously is to be understood here in particular as meaning that the respective measurement initiated by the feeding of the measurement signal M is carried out continuously. For this purpose, the measurement signal is fed in permanently, i.e., for example, the sway signal is "tuned" uninterruptedly at different frequencies. Alternatively, the feeding is carried out at repeated time intervals, for example in the range of a few seconds. Or in the range of tenths of a second. This continuous monitoring makes it possible to carry out real-time monitoring during movements and bending stresses of the hose set 18.

[0085] In particular, it is known at which locations the bending loads occur, in which direction the hose set bends and how large the resulting bending radius is in conjunction with the detected sensor signal S. Thus, the actual bending stresses experienced by the hose set during operation can be known in conjunction with the evaluation.

[0086] Since regularly recurring process cycles are typically carried out with the hose set 18 , the profile of the bending stresses to which the hose set is subjected during such a process cycle can be simulated with a high degree of accuracy.

[0087] Based on these data, conclusions are then preferably drawn about the actual loads, wear and possible remaining service life of the hose set 18 and, in particular, recommendations are made, such as replacement of the hose set 18. Operating situations that lead to impermissible bending loads can thus also be identified in advance, so that measures can be taken in a timely manner by appropriate warnings.

[0088] In a preferred embodiment, the data D are evaluated in a central unit 42 which is provided as a common evaluation unit 26 for a plurality of devices to be monitored, in particular for industrial robots 2 to be monitored or hose sets 18 to be monitored. Figure 6. The individual measuring units 24 of the individual units to be monitored, i.e. the hose sets 18 of the industrial robot 2, first forward their data D, for example, to the cloud and then call up and evaluate them from there via the central unit 42. This measure enables the central unit 42 to provide a very extensive data basis. Based on this extensive data basis, a data model can then be created which reflects the loads to which the hose sets 18 are subject as realistically as possible and thus provides important information for the future development and design of further hose sets 18.

[0089] The invention is described in the present case in conjunction with a hose set 18 as an example of a flexurally resilient element, but is not limited to application in a hose set 18 .

Claims

1. A monitoring system for monitoring the bending load of at least one strip-shaped element which is subjected to bending during operation, the monitoring system comprising - the strip-shaped element, which extends in the longitudinal direction and has a jacket, in which a recess is introduced at least in sections on the circumference, a pressure-sensitive sensor element, which is inserted into the recess and is designed to emit a sensor signal when subjected to pressure load, - a local measurement unit, the local measurement unit being configured to receive the sensor signal, - an evaluation unit for evaluating the sensor signal relating to the bending stress to which the strip-shaped element is subjected, based on a pressure load of the sensor element caused by a bending of the element, - in, The recess is designed as a groove which is spiral-shaped at least in sections, and the sensor element is designed as a sensor line which is inserted into the groove and has a conductor surrounded by a dielectric and is connected to the local measuring unit. - and wherein the sheath is a corrugated hose having helical grooves.

2. The monitoring system according to claim 1, wherein: The helical groove has a pitch angle (α) in the range between 5° and 30°.

3. The monitoring system according to claim 1 or 2, wherein: The local measuring unit is also designed to feed a measurement signal into the sensor line and to receive a signal component of the measurement signal reflected at a disturbance location, wherein the reflected signal component forms the sensor signal and wherein the measurement signal is at least partially reflected at the disturbance location due to a pressure load on the dielectric caused by bending.

4. The monitoring system according to claim 1 or 2, wherein: At least one supply line is guided in the sheath.

5. The monitoring system according to claim 1 or 2, wherein: The strip-shaped element is a hose kit for a multi-axis industrial robot.

6. The monitoring system according to claim 1 or 2, wherein: The sensor line has an outer diameter and the slot has a slot width, wherein the outer diameter is matched to the slot width.

7. The monitoring system according to claim 1 or 2, wherein: The dielectric is an elastically deformable dielectric.

8. The monitoring system according to claim 1 or 2, wherein: Thermoplastic rubber, PUR or TPV is used as the material of the dielectric.

9. The monitoring system according to claim 1 or 2, wherein: The sensor line is designed as a coaxial line.

10. The monitoring system according to claim 3, wherein: The measuring unit is designed to feed in a wobble signal in order to carry out a frequency reflection measurement method.

11. The monitoring system according to claim 1 or 2, wherein: The evaluation unit is designed to detect the position of the bend using the sensor signal.

12. The monitoring system according to claim 1 or 2, wherein: The evaluation unit is designed to determine a direction of bending of the sheath using the sensor signal.

13. The monitoring system according to claim 1 or 2, wherein: The evaluation unit is designed to infer a current bending radius using the sensor signal.

14. The monitoring system according to claim 1 or 2, wherein: The evaluation unit is designed as a central unit which is situated at a distance from the device to be monitored and is designed to receive the sensor signal.

15. The monitoring system according to claim 14, wherein: A plurality of devices to be monitored can be connected to the central unit in terms of data technology, and the central unit is designed to evaluate data from the plurality of devices to be monitored.

16. A strip-like element which is subjected to bending during operation and is flexurally elastic, the strip-like element extending in a longitudinal direction and having - a sheath in which a recess is introduced at least in sections on the circumference, a pressure-sensitive sensor element, which is inserted into the recess and is designed to emit a sensor signal when subjected to pressure load, - a local measuring unit for receiving the sensor signal and forwarding it to an evaluation unit, - in, The recess is designed as a groove which is spiral-shaped at least in sections, and the sensor element is designed as a sensor line which is inserted into the groove and has a conductor surrounded by a dielectric and is connected to the local measuring unit. - and wherein the sheath is a corrugated hose having helical grooves. 17 . The flexurally elastic element according to claim 16 , which is designed as a hose kit and is fastened to an industrial robot.

Images