WO2022090001A1

WO2022090001A1 - Hoist cable, cable-operated device and method for measuring a tensile force

Info

Publication number: WO2022090001A1
Application number: PCT/EP2021/078965
Authority: WO
Inventors: Christian Bachmann; Gerit Ebelsberger; Reinhard Freitag; Matthias Gerlich; Christian Mose; Takeru NEMOTO
Original assignee: Siemens Aktiengesellschaft
Priority date: 2020-11-02
Filing date: 2021-10-19
Publication date: 2022-05-05
Also published as: EP4172584A1; KR20230043979A; JP2023547164A; DE102020213745A1

Abstract

The invention relates to a hoist cable (1) for transferring an axial tensile force (F_A). The hoist cable (1) comprises: - a hose-like cable sheath (3) which comprises a braid consisting of a plurality of cable strands and/or fibres (5), the individual cable strands and/or fibres (5) extending obliquely to the local cable axis (A), and - an elongate sensor element (11) which is located in a sub-portion (s) within the cable sheath (3) and has a capacitor (20) of which the capacitance depends on a radial pressure (p_r) of the cable sheath (3) on the sensor element (11), - wherein the radial pressure (p_r) on the sensor element (11) depends on the axial tensile force (F_A) on the hoist cable (1). The invention further relates to a cable-operated device having such a hoist cable as well as to a method for measuring a tensile force (F_A) which acts on such a hoist cable.

Description

description

Traction rope, rope-operated device and method for measuring a traction force

The present invention relates to a traction cable for transmitting an axial traction force. This traction cable has a tubular cable sheath which comprises a braiding of several cable strands and/or fibers, with the individual cable strands and/or fibers running at an angle to the local cable axis. Furthermore, the invention relates to a cable-operated device with such a traction cable and a method for measuring a tensile force on a traction cable.

High-strength ropes are known from the prior art, which are used to transmit tensile forces in rope-operated devices. For example, traction cables are used in robotic devices, which, like the tendons in the human body, serve to transmit power between a drive unit and a driven element remote from it. However, there are also numerous other applications in mechanical engineering and electrical engineering in which force-transmitting cable kinematics are used. With the development of high-strength plastics as rope materials, such rope kinematics can be made increasingly compact. For many of these applications, it is useful to know the current load status of the traction cable used and, in particular, to measure it continuously. In principle, methods for measuring tensile stress on ropes are known in the prior art. Various hand-held devices and also stationary tensile stress measuring devices are commercially available, in which a cable under tensile stress is typically clamped between a number of rollers, with the forces acting on the rollers being measured using force sensors. The disadvantage of this type of measurement is that the measurement requires a change in the cable routing due to the additional deflection pulleys. In addition, a relatively large amount of space is typically required for this type of measurement, since a there must be a sufficiently long free rope section in order to place the measuring device on it. However, such a long free cable section is not always available or not always available, especially in compact robotic devices and other compact cable kinematics. not accessible in all operating states . In addition, a force sensor must be installed in at least one deflection element.

The object of the invention is therefore to provide a traction cable which overcomes the disadvantages mentioned. In particular, a traction cable is to be made available which, during its operation in a cable-operated device, enables the effective tensile force to be measured in a simple and space-saving manner. Furthermore, the functionality of the traction cable and in particular its flexibility and/or its tensile strength should advantageously be influenced as little as possible by the measuring arrangement. In addition, the measurement should be as continuous as possible, possible during the entire operation. A further object is to provide a cable-operated device with such a traction cable and a method for measuring the tensile force on such a traction cable.

These objects are achieved by the traction cable described in claim 1, the cable-operated device described in claim 13 and the measuring method described in claim 15.

The traction cable according to the invention is designed to transmit an axial tensile force. It comprises a tubular rope sheath, which has a braiding of several rope strands and/or fibers, with the individual rope strands and/or fibers running obliquely to the local rope axis. According to the invention, an elongate sensor element is arranged in a section within the cable sheath. This sensor element has a capacitor whose capacity depends on the radial pressure of the cable sheath on the sensor element depends . The radial pressure on the sensor element depends on the axial tensile force on the traction cable.

The designations “axial” and “radial” each refer to the local rope axis, ie to the longitudinal direction of the rope in the particular rope section under consideration. Also in the case of traction ropes with a non-circular cross-section, the term "radial" should mean the direction from an external point to the center of the rope (or vice versa), analogous to the circular shape. The rope sheath comprises several rope strands and/or fibers lying diagonally to the rope axis, as is generally the case with ropes. For example, climbing ropes are nowadays manufactured as core-mantle ropes, in which an outer rope mantle radially surrounds an inner rope core. The rope mantle described here corresponds to the rope mantle of such a core-mantle rope, with the inner rope core can be present in principle (at least in part), but can also be omitted entirely, particularly advantageously. Instead of the rope core or possibly also in addition to it, the elongate sensor element is arranged inside the rope sheath. This sensor element enables the tensile stress to be measured in situ, namely in the cable itself The sensor element i is designed to measure a radial pressure of the cable sheath on the sensor element. This is made possible by the fact that the sensor element comprises a capacitor whose capacitance can be varied by changing this radial pressure. The structure of the cable sheath with a plurality of cable strands and/or fibers running at an angle also causes the radial pressure of the cable sheath on the sensor element to change when the axial tensile force changes. This happens because due to the inclined position to the axis, a tensile force along the rope axis always causes the rope sheath to be pressed in the direction of the middle of the rope, with the angle of the individual strands or fibers with the rope axis becomes smaller. Conversely, a decrease in tensile force leads to a reduction in tension. Depending on the installation situation, this leads to a shortening and at the same time a compression of the cable sheath due to an increase in tion of the fiber angle . If the angle of the strands or fibers to the cable axis increases in this way and the diameter of the cable sheath increases accordingly, the radial pressure on the elongated sensor element also decreases. The individual strands Fibers can be knit, woven, twisted, entangled, and/or intertwined with one another. It is only essential that at least a significant part of the fibers or Strands enclose an angle with the longitudinal axis, so that the described interaction between axial tensile force and radial pressure on the inner sensor element comes about. A single strand of rope may in turn be knitted, woven, twisted, twisted and/or braided from multiple fibers. However, individual fibers of yarn or wire can also already be assembled in a corresponding manner to form the cable sheath. The elongated shape of the inner sensor element is expedient in order to cause the sensor element to be centered in the interior of the cable sheath as the tensile force increases.

A major advantage of the traction cable according to the invention is that the internal sensor element allows the tensile stress to be measured in a simple manner at the location of the cable without requiring a great deal of additional space. Only a relatively short free rope section has to be made available, in which the sensor element can be arranged. For example, the length of this section z. B. be 20 times the rope diameter or less. For example, the length of the rope section can be between 4 times and 20 times the rope diameter. Due to the integration of the sensor inside the cable, a very compact structure for measuring the tensile stress is made available, which is particularly suitable for use in compact cable-operated devices. This enables permanent monitoring of the tension during operation of the traction cable. The configuration of the sensor element with a capacity that is variable as a function of the radial pressure enables a force measurement that is sufficiently precise for many applications at the same time Apparatus simple and space-saving construction. The mechanical properties of the traction rope are not significantly changed by the integrated sensor element, especially if the relevant rope section is within a rope-operated device in a free area of the rope - i.e. between the deflection or Attachment points - is arranged. In particular, the tensile strength of the cable and the stiffness in the axial direction are only marginally influenced by the internal arrangement of the sensor element. In this way, the invention enables permanent integration of a sensor system into the traction cable for continuous measurement of the traction force.

The cable-operated device according to the invention has a drive unit, a driven element and a pull cable according to the invention, which connects the drive unit and the driven element in a force-transmitting manner with respect to a pulling direction. The configuration of the traction cable according to the invention enables the tensile stress within the device to be measured in a simple manner, with hardly any additional installation space being required for this functionality. The described connection between the drive unit and the driven element via the traction cable does not have to be a direct connection. In other words, further connecting intermediate elements should not be ruled out. However, the force-transmitting connection should at least be mediated via the traction cable.

The method according to the invention serves to measure a tensile force which acts on a traction cable according to the invention. In this case, an electrical signal influenced by the capacitance of the capacitor is measured, the size of which depends on the radial pressure exerted by the cable sheath on the sensor element. Furthermore, the radial pressure on the sensor element depends on the tensile force on the traction cable. The advantages of the cable-operated device according to the invention and the measuring method according to the invention result analogously to the advantages of the traction cable according to the invention described above. Advantageous configurations and developments of the invention emerge from the claims dependent on claims 1 and 13 and from the following description. The described configurations of the traction cable, the cable-operated device and the measuring method can generally be advantageously combined with one another.

Thus, the elongate sensor element can generally advantageously be aligned with its longitudinal axis along the local cable axis and have an aspect ratio of at least 2:1. This aspect ratio is to be understood as meaning the ratio of length to (largest) diameter of the sensor element. A sensor element designed in this way is centered in the interior of the cable sheath by the tensile force acting on the cable.

Generally advantageous and independent of the exact shape, the cable sheath and the inner sensor element can be configured coaxially to one another. Particularly advantageously, both the outer cable sheath and the inner sensor element have a rotationally symmetrical basic shape, ie each have a circular cross-sectional geometry. With the coaxial arrangement of these two forms, which are in particular rotationally symmetrical, the properties of the cable sheath are influenced particularly little due to the symmetry. However, the above-mentioned rotationally symmetrical shape of the cable casing and sensor element is not mandatory. B. a sensor element with a flat cross-sectional shape is arranged within a correspondingly flat-shaped cable sheath.

According to a generally particularly preferred embodiment, the capacitor of the sensor element has two electrodes and an elastically deformable dielectric lying radially between them. Due to the elastic deformability, the capacitance can be changed in a particularly simple manner due to the resulting change in distance between the electrodes be effected . If the dielectric (regardless of the exact shape and arrangement of the electrodes) lies radially between the two electrodes, then a change in the radial pressure acting on it can cause a change in the radial thickness of the dielectric and an associated change in capacitance. If, for example, the tensile stress on the traction cable is increased, the radial pressure acting on the sensor element increases, which leads to compression of the elastically deformable dielectric and correspondingly to an increase in capacitance. If, on the other hand, the tensile stress that has been increased in this way decreases again, then this compression is reversed again due to the elasticity of the dielectric, the electrode spacing increases again and the capacitance falls accordingly. In this way, an electrical measurement variable dependent on the tensile force can be made available in a particularly simple manner. By measuring this variable capacitance, the tensile force on the rope can be measured with sufficient accuracy for many applications.

In this embodiment with an elastically deformable dielectric, at least one of the electrodes is expediently designed to be flexible, so that it can also be deformed in a non-destructive manner. In a particularly advantageous manner, both electrodes can even be designed to be mechanically resilient, particularly in the case of design variants with a rolled-up layer stack.

The elastically deformable dielectric can particularly preferably be in the form of an elastomer or can comprise at least one elastomer as a material component. This elastomer can, for example, be a rubber, a silicone, a silicone rubber, an acrylic and/or another z. B. be plastic made elastic by means of plasticizers or comprise such a material.

In general and independently of the choice of materials, the capacitor can advantageously be designed in the shape of a cylinder or at least be based on a cylindrical basic shape. In particular, it can have a circular-cylindrical basic shape. Deviating from the ideal cylindrical shape extending over the entire axial length, it can in principle also be beveled or have rounded end areas. This shape can be advantageous in order to protect the cable sheath from buckling loads in the area of the axial ends of the sensor element. However, it is also possible and in certain circumstances advantageous if the capacitor is oval or rectangular over a significant part of its axial length. is egg-shaped or has a longitudinal section geometry that tapers towards both axial ends in the manner of a double cone. With such a tapering capacitor geometry, the associated higher stiffness of the outer electrode can be compensated for by a correspondingly low wall thickness in order to still achieve adequate deformability. An oval longitudinal section shape of the capacitor can be supported, for example, by rounded caps located between the electrodes in the area of the axial ends and/or by dielectric protruding from the outer electrode in the axial end areas.

According to a first embodiment variant for the geometry of the capacitor, it can have an inner electrode and an outer electrode, with the dielectric coaxially surrounding the inner electrode and the outer electrode coaxially surrounding the dielectric. This embodiment variant corresponds to the construction of a coaxial cable, the core of which is provided by the inner electrode and the outer conductor by the outer electrode, with the dielectric being elastically deformable. In principle, the internal electrode can be either solid or hollow. Thus, according to a particularly simple embodiment, the internal electrode can be implemented as a simple wire or pin made of an electrically conductive material.

According to an alternative second embodiment, the capacitor can also be formed by a layer stack rolled up in a spiral shape, which has two electrodes and one intervening dielectric layer includes. The roll axis corresponds in particular to the local rope axis. An advantage of this rolled-up variant is that the plurality of windings allows a particularly high change in capacitance to be achieved for a given change in the radial pressure.

In an advantageous first sub-variant of this wound capacitor, the rolled-up layer stack can have two metal foils as electrodes and at least one elastomer element in between as a dielectric layer. This elastomeric element can be designed as a type of foil or mat, so that by superimposing the elastomeric element and the two metal foils, a stack that can be rolled up is formed. Two such elastomer elements are particularly preferably present in the layer stack - one between the two metal foils and one on the outside of the stack - so that a short circuit between the two metal foils is avoided between the turns and at the same time there is a particularly high change in capacitance as a function is reached by the tensile stress. In this embodiment, both metal foils can advantageously be designed to be resiliently deformable, so that they contribute to a reversible deformability of the entire capacitor and thus to a reversible change in capacitance. The two metal foils can protrude in the axial direction in relation to the dielectric to facilitate their electrical contacting. So e.g. B. similar to the wound paper capacitor, one electrode may protrude toward a first axial end and the other electrode may protrude toward the opposite second axial end.

In general, in this embodiment with a loosely assembled stack of layers, the elastomer element can swell out of the intermediate space between the electrodes towards the axial end regions when the radial pressure increases and its radial thickness correspondingly decreases. If, at the same time as the axial expansion of the dielectric If the two electrodes also expand in the axial direction, the increase in surface area leads to a further increase in capacitance, which further intensifies the increase in capacitance due to the reduction in the radial distance. However, the axial length of the electrodes can also be essentially constant.

In an advantageous second sub-variant of the wound capacitor, the rolled-up layer stack can in turn have at least one elastomer element, with at least one of the electrodes being formed by a coating on one of the two main surfaces of the elastomer element. In other words, in this embodiment at least one of the electrodes is connected to the elastomer element as a fixed coating. This coating can in particular be a metallic coating. Both electrodes can be formed particularly advantageously by such coatings. An elastomer element can either be coated on both sides, with either another elastomer element or another insulator being interposed before it is rolled up. Alternatively, two elastomer elements can be combined to form a stack that can be rolled up, with each of the elastomer elements being coated on one side with an electrode. The metallic coating of the electrode(s) can in particular be vapour-deposited onto the respective elastomer element. Alternatively, however, the electrodes themselves can also be designed as conductive elastomers, which are applied in particular as a coating on an adjacent dielectric elastomer element. The advantage of this variant is that a particularly flexibly deformable electrode can be obtained. Conductive elastomers are, for example, elastically deformable polymers that are filled with metallically conductive fillers. The electrical conductivity that can be achieved with this is lower than that of purely metallic materials, but measuring the change in capacitance of the capacitor does not require a particularly high conductivity of the electrodes. In this sub-variant with electrodes configured as a coating, the elasticity of the capacitor and thus the resetting in the direction of the original geometry is brought about above all by the elasticity of the dielectric. However, the electrodes applied as a coating must be flexible enough to grow or expand with the change in geometry of the dielectric. to shrink with . Thus, in this embodiment, an axial change in length of the dielectric also includes the electrodes.

In general and independently of the exact configuration of the electrodes and the dielectric, it is advantageous if the sensor element has at least one metallic spring element with a variable diameter, which either forms the outer electrode of the capacitor or is electrically connected to one of the two electrodes. This metallic spring element, together with the deformable dielectric, can bring about a return to the original geometry after reversible deformation due to a temporary change in force. It is also possible for both electrodes to be in the form of metallic spring elements, but it is particularly advantageous for at least the outer electrode to be in the form of a spring element. As an alternative or in addition to such resilient electrodes, there can be an outer sleeve acting as a spring element, which is expediently electrically conductively connected to the outer electrode and exerts a restoring effect in a similar way.

The metal spring element can be designed, for example, as a slotted clamping sleeve and/or as a spirally rolled clamping sleeve. Such clamping sleeves are well known from the prior art and are sometimes also referred to as clamping pins or spring pins. The metallic spring element advantageously has a circular-cylindrical basic shape, with the axial end regions being rounded off, chamfered or rounded off. can be tapered in another way. Such a slotted clamping sleeve can be designed, for example, as a wavy and/or toothed slotted clamping sleeve, in particular with simple slitting. A corrugated and/or toothed slit has the advantage that the cable sheath lying radially on the outside is less easily clamped in the slit. The clamping sleeve can also be designed as a multiply slotted clamping sleeve. Thus, the individual slits can be designed as axial partial slits with alternating opening direction, so that a meandering structure results for the part connected to one another. Such meandering clamping sleeves are known in the prior art. Furthermore, the slot or the slots can be designed as radial partial slots, so that the springing is effected by radially inner or radially outer recesses. Slots located radially on the outside can be filled with elastic material to protect the cable sheath.

In general and independently of the exact configuration of the capacitor, it is advantageous if the outer contour of the sensor element is convex over a predominant part of its axial length, so that the axial tensile force on the traction cable can cause radial pressure on the sensor element. As a result of this shape, a radial compressive force is generated not only locally (e.g. in the axial end regions) but over a large part of the length of the sensor element due to the tensile force on the cable sheath. The shape is advantageously such that the resulting radial pressure is as uniform as possible over the majority of the length of the sensor element. This is achieved by a convex shape that extends as far as possible. In the axial end areas, however, the convex shape of the sensor element can optionally transition into pointed end pieces in order to promote centering of the sensor element within the cable sheath.

The favorable shape of the sensor element described does not necessarily have to be due to a convex outer contour of the condensation tors can be achieved . Rather, the capacitor can be cylindrical in shape for easier production, but surrounded by an adapter sleeve to achieve the desired outer contour. Optionally, this adapter sleeve can be structured by recesses in axially spaced ribs in order to bring about a local force component on the capacitor that is aligned as radially as possible within the individual ribs. The spaces between these ribs can in turn be filled with an elastic material to protect the outer cable sheath.

In a generally advantageous manner, the traction cable can have two electrical connection lines for connecting the electrodes of the capacitor to an evaluation unit, the two connection lines being routed parallel to the cable axis, in particular in the region of the sensor element. The lines can be routed out of the area of the sensor element either at the same axial end of the subsection in question or also at opposite axial ends. In the first case, there is a particularly simple common line routing to the evaluation electronics, which can be located either in the area of the traction cable or outside. If necessary, the lines must then be electrically isolated from one another if they are routed close together. In the second case there is a lower additional capacitance due to the lines. In general, the connection lines can be implemented as wires, stranded wires or cables, for example. They can be passed through the cable sheath by passing through the braiding of the individual cable strands or cables in the connection area. Fibers pass radially outwards.

The cable sheath can generally preferably consist at least predominantly of a synthetic plastic. The synthetic plastic can advantageously be an ultra high molecular mass polyethylene (in particular Dyneema or Spectra), an aromatic polyester (in particular Vectran), an aramid (in particular Kevlar or Nomex), a poly(p-phenylene-2), 6-benzobisoxazole) (especially PBO or Zylon) or act as a polyamide. These materials are characterized by a particularly high tensile strength. In addition, they are flexible and electrically non-conductive, which is also advantageous for many applications. Generally advantageous and independent of the exact choice of material, the specific tensile strength of the material of the cable sheath can be, for example, 2500 N/mm ² or higher. Such a high tensile strength makes it possible to use traction cables with small cable diameters for the transmission of high tensile forces. For example, the rope diameter in the areas outside of the partial area occupied by the sensor element can be between 0.5 mm and 10 mm. In contrast, the rope diameter in the partial area filled with the sensor element can be increased, for example, by a factor of 3. For example, a cable sheath with a regular outer diameter of 4 mm can have an enlarged outer diameter of up to 12 mm in the area of the sensor element. In general, the factor for the cable diameter can advantageously be in a range between 1.5 and 5. With a comparatively high factor, the sensitivity of the tensile stress measurement is particularly high, but the mechanical load on the cable sheath in the area of the sensor element also increases.

The invention is not limited to cable sheaths made from high-strength synthetic plastics. As an alternative, the cable sheath can also consist of conventional materials, for example steel, copper or hemp, and be filled locally with a sensor element for measuring the tensile force in a corresponding manner.

In general, the traction cable can consist of several partial cables, each of which has a separate cable sheath. In such a case, it is sufficient if at least one of these partial cables is provided locally with an internal sensor element for measuring the tensile force.

According to an advantageous embodiment of the cable-operated device, the section with the internal sensor arranged sorelement in a free-running area of the traction cable. Such a freely running area is a section of the traction cable in which there is no mechanical contact with a deflection pulley, there are no attachment points and the traction cable is not in mechanical contact with other leading elements either.

The cable-operated device can include an evaluation unit with which the change in capacitance, which is dependent on the tensile force, can be measured. This evaluation unit can be designed either as part of the traction cable or separately from it. The evaluation unit can have a coil, for example, whose inductance forms an oscillating resonant circuit together with the capacitance of the capacitor. The evaluation unit can also be designed in such a way that it enables the frequency of this oscillator to be measured. If the capacitance of the capacitor is reduced, this frequency is increased and vice versa. In this way, an electrical measurement is made possible in a relatively simple manner, which supplies a signal dependent on the tensile stress.

The cable-operated device can be configured as a robotic device, for example. The traction cable can be used within the robotic device to transmit a tensile force, for example to move a robotic joint unit with the aid of an integrated drive device. In other words, the traction cable can assume a function analogous to a tendon in the human body. As an alternative to a "drive tendon" (which connects the drive unit and the driven element in a force-transmitting manner), such a tendon can also fulfill the function of a support bracing, through which the movable elements of the drive train are supported against the mechanical mass or other mechanically rigid elements. For example, the traction cable according to the invention be integrated into a support bracing of a so-called tensegrity structure. According to a particularly advantageous embodiment of the measurement method, this can be designed to also detect rapid changes in the tensile stress by measuring the electrical signal. In this way, vibrations in the area of the traction cable can be measured. Such a measurement can be used particularly advantageously as the basis for active vibration damping in a cable-operated device.

The invention is described below using a few preferred exemplary embodiments with reference to the attached drawings, in which:

Figure 1 shows a schematic plan view of a traction cable into which a sensor element is inserted,

Figure 2 shows a traction cable with a sensor element inserted therein,

Figure 3 shows a schematic longitudinal section through a sensor element,

Figure 4 shows a schematic longitudinal section through another sensor element,

FIG. 5 shows a schematic perspective representation of the capacitor of FIG. 4,

Figure 6 shows a schematic longitudinal section through another traction cable,

Figures 7 to 11 show different variants of clamping sleeves and

FIG. 12 shows a schematic cross-sectional illustration of a further capacitor.

Elements that are the same or have the same function are provided with the same reference symbols in the figures. FIG. 1 shows a schematic plan view of a traction cable 1 according to a first example of the invention, namely during a production step in which a sensor element 11 is inserted into the interior of the cable sheath 3 of this traction cable. The cable sheath 3 is a hose-like braid made up of several cable strands or fibers, one of which is exemplarily draws is . These individual strands Fibers each lie at an angle to the local rope axis. By upsetting the cable sheath 3 and temporarily enlarging the interstices of the mesh, the sensor element can be inserted into the interior of the cable sheath 3 in a non-destructive manner. FIG. 2 shows the state of the traction cable 1 in which the sensor element 11 is inserted into the interior of the cable sheath and the individual cable strands 5 are pushed together again to form a symmetrical braid. The two figures thus illustrate how a traction cable according to the invention can be produced in a simple manner by subsequent modification of a conventional cable which has a tubular cable sheath with an internal cavity. In this case, the sensor element is only inserted into a partial section s of the traction cable 1, in which the diameter is then correspondingly increased. In contrast, the traction cable remains unchanged in the remaining sections. Overall, the essential properties such as tensile strength and axial stiffness are changed only insignificantly by inserting the sensor element.

The sensor element 11 has an elongated shape and, when fully inserted, lies coaxially with the cable axis A. In this example, it has an outer contour 12 which is convex in shape over a significant part of its length. Nevertheless, it tapers to a point in the axial end areas. This pointed taper makes it easier to center the sensor element in the cable sheath under tensile load. When a tensile force F _A is applied to the cable sheath 3, the oblique position of the surrounding cable fibers 5 results in a radial compressive force p _r on the sensor element lying on the inside. Due to the convex outer contour 12 of the sensor element, the resulting compressive force has a high radial component over a large part of the length of the sensor element, which can be measured with the aid of the sensor element in order to obtain a measure of the magnitude of the tensile force F _A present. The measurement is carried out by measuring an electrical signal, which is influenced by a capacitance inside the sensor element. In order to enable this electrical measurement, the sensor element two connection lines 31 and 32 on. These initially run parallel to the cable axis A within the cable sheath 3, but are then led out of the interior through the cable mesh of the sheath through oblique end sections. In this way, an electrical measurement can be made possible via an evaluation unit that is not shown in detail here.

Several variants for the internal structure of the sensor element are shown as examples in the following figures. FIG. 3 shows a schematic longitudinal section according to a first example of such a sensor element 11 . As described above, the sensor element has an elongate shape and is arranged along the local cable axis A within the cable sheath, which is not shown here. It is used to measure a radial pressure p _r (or also the radial component of a compressive force acting obliquely at certain locations). For this purpose, a capacitor 20 is arranged inside the sensor element, the capacitance of which depends on the radial pressure. The capacitor has two electrodes 21 , 22 and a dielectric 25 lying radially between them. In the embodiment shown here, the first electrode 21 is designed as an internal wire. The dielectric 25 is a circular cylindrical element which concentrically surrounds this wire 21 , and the dielectric 25 is in turn surrounded concentrically by the outer electrode 22 . It is therefore a circular-cylindrical coaxial structure, analogous to a coaxial cable. The dielectric 25 is provided by an elastomer, so that its radial thickness d can change reversibly under radial pressure loading. This brings about a reversible change in capacitance, which can be measured via the connection lines 31, 32 connected to the electrodes 21, 22 via an external circuit, not shown here, for example by detecting a changed oscillation frequency together with a coil contained in the circuit. The circular-cylindrical geometry of the capacitor shown here is particularly simple to manufacture. In order to nevertheless achieve a convex outer contour 12 of the sensor element 11, the capacitor here has a convex matching sleeve 13 surrounded . The shape of this adapter sleeve 13 ensures that pressure is exerted on the capacitor with a high radial component over a larger part of the length of the sensor element due to the tensile force on the surrounding cable jacket.

FIG. 4 shows a further example of a sensor element 11 in a schematic longitudinal section. Similar to the example in FIG. 3, here too the capacitor 20 is constructed from an inner electrode 21, a dielectric 25 surrounding it in a cylindrical manner and a surrounding cylindrical outer electrode. In contrast to the previous example, here the connection lines 31 , 32 for the two electrodes are led out to the same axial end of the sensor element.

There they can, analogously to what is shown in FIG. 2, be guided to the outside through the braiding of the cable sheath, which is not shown here. A further difference from the previous example is that the dielectric formed from an elastomer protrudes in the axial direction beyond the outer electrode 22 even in the uncompressed state and is therefore longer than the actual capacitor. The dielectric is beveled in these protruding areas and thus contributes to the shaping of the convex outer contour of the sensor element. In the inner area of the condenser 20 , the convex outer contour is also achieved here by a surrounding adapter sleeve 13 . FIG. 4 shows only as an example that this adapter sleeve can in principle be configured differently. An axially continuous adjustment sleeve is shown in the lower part of the figure, similar to the example in FIG. In the upper part, on the other hand, the adapter sleeve is subdivided into axial ribs 17 by a plurality of recesses, in order to bring about the most uniform possible radial transmission of the pressure on the condenser outside of the central area as well. Optionally, the gaps between these ribs can be filled with an elastically deformable material in order to avoid wear on the cable sheath at the sharp edges. In the versions with such ribs, they should of course extend over the entire circumference of the adapter sleeve.

Referring to FIG. 5, there is shown a schematic perspective view of the capacitor 20 of the figure, shown here without the surrounding adapter sleeve. The easy-to-implement circular-cylindrical construction of this capacitor and the similarity to the construction of a conventional coaxial cable are particularly evident here. In principle, such a cylindrical capacitor could also be used inside a cable sheath without a convex adapter sleeve for measuring tensile stress, but the distribution of the radial compressive force over the length of the capacitor is then less uniform.

FIG. 6 shows a schematic longitudinal section through a traction cable 1 according to a further example of the invention.

The sensor element is essentially formed here by the capacitor 20 which is arranged inside the cable sheath 3 . In contrast to the previous examples, there is no additional adapter sleeve here, but the capacitor itself is already convex in shape. The convex shape is made clear by the lens-like cross-sectional profile of the capacitor, which should also be rotationally symmetrical in this example. Both the outer electrode 22 and the dielectric arranged therein have a convex cross-sectional shape. Various implementation options are shown in the left and right-hand parts of the drawing by way of example only, although in a real example a uniform design that is essentially the same in both axial end regions can advantageously be selected. The right-hand part shows, for example, that the convexly arched dielectric 25 can protrude from the outer electrode 22 in the axial end area 26, with this end area 26 also having a rounded shape. When the capacitor 20 is compressed in the radial direction, the proportion of the dielectric 14 that swells out increases. Due to the essentially fixed axial length of the two electrodes 21 and 22 the effective length of the capacitor does not change. The left part shows by way of example that the convex shape of the outer electrode 22 in the axial end area can be supported by an axially tapering end cap 27 arranged between the inner electrode and the outer electrode. This end cap can be made of a comparatively rigid plastic. If the elastomeric dielectric 25 is radially compressed, this end cap can optionally be displaced in the direction of the axial end. However, it is also conceivable that exactly as shown in FIG. 6, there is a combination of a rounded dielectric protruding on one side and an opposite end cap 27 .

In the examples shown so far in FIGS. 3 to 6, the outer electrode 22 in each case surrounds the dielectric 25 as a hollow body. Due to the radial compressibility of the elastomer, the radial thickness d of the dielectric can change reversibly, with its elasticity also causing a restoring force, which again leads to an expansion of the capacitor when the radial pressure action ends or decreases. In order to facilitate this reversible deformation, it is advantageous if the outer electrode can also be reversibly deformed in such a way that its diameter is variable. Ideally, such a deformation of the outer electrode also leads to a restoring force. This can be achieved in that, in the examples described, the outer electrode is implemented as a metallic spring element with a variable diameter. Such spring elements are known, for example, in the form of so-called clamping sleeves from the prior art.

FIGS. 7 to 11 show several examples of different configurations of clamping sleeves 24 , as can be used in particular as external electrodes 22 .

Thus, FIG. 7 shows a simple hollow cylindrical clamping sleeve 24 with a simple straight slot 24a in the cylinder wall. Depending on a radial pressure on this collet, the width of this slot 24a changes, resulting in a variation of the sleeve diameter. Due to the spring effect of the metallic cylinder wall, such a deformation also results in a restoring force.

In a similar way, the clamping sleeve 24 shown in FIG. 8 also acts as a cylindrical spring with a variable diameter. Here, however, the slit 24a is formed as a wavy toothed slit. This has the advantage that a smaller gap is formed on the cylinder surface with a similar spring deflection. Correspondingly, there is less risk of a cable sheath lying on the outside or an adapter sleeve arranged outside the clamping sleeve getting caught in the slot 24a and being damaged as a result.

FIG. 9 shows a spirally rolled clamping sleeve 24 which also acts as a radial spring with a variable diameter. If the diameter changes, the individual windings of the metal scroll spring slide over one another with relatively little friction, so that a spring effect can also be achieved without a continuous slot.

FIG. 10 shows a clamping sleeve 24 with a plurality of axial slits 24a, each of which is in the form of only partial slits. The remaining connecting webs alternate between the two axial ends, resulting in a meandering structure for the cylinder wall that remains stationary. Overall, the compression and opening of the slots results in a spring effect and a variable diameter of the clamping sleeve 24 here as well.

Finally, FIG. 11 shows an embodiment of a clamping sleeve 24 with a plurality of slots 24a, which are continuous in the axial direction, but are formed only as partial slots in the radial direction. By way of example, the partial slots are shown here lying radially on the outside, but an inside arrangement is also possible and may be advantageous in order to avoid jamming of the cable. Generally, the slots 24a shown and in particular the Partial slots of Figures 10 and 11 are generated by subsequent processing of a metallic hollow cylinder, for example by processing with a laser or a broach. Furthermore, these slots can be filled with an elastically deformable material.

FIG. 12 shows a schematic cross-sectional representation of a capacitor 20 according to a further example of the invention. A section perpendicular to the local cylinder axis of the condenser is shown, whereby this cylinder axis should again be aligned along the local cable axis A in the finished traction cable. A first connecting line 31 runs in the center in the axial direction, which can also be configured as a wire here. A layer stack 29 is wound around this wire in the manner of a roll. In this example, this layer stack comprises an inner first electrode

21 and an outer second electrode 22 and two elastomer elements 25a and 25b, which are formed like a mat.

The first electrode is electrically connected to the internal connection line 31, and the outer electrode

22 is electrically connected to a surrounding metallic outer sleeve 23 . In order to facilitate this electrical connection, the outer second elastomer element 25b here has one winding less than the first elastomer element 25a. However, the number of windings shown is only to be understood here as an illustration and can advantageously also be significantly larger in real embodiments. The main advantage of such a rolled arrangement is that the plurality of windings of the dielectric lying on top of one another results in an increased stroke in the change in capacitance in the event of radial compression or expansion.

Different variants are conceivable for the precise configuration of the layer stack 29 . For example, it can be a stack of two mat-like elastomer elements 25a and 25b, with a metallic foil being arranged as an electrode between these two elastomer elements and on one of the outer sides of the stack is . As an alternative to the contacting shown here, these metallic foils can also be contacted in the axial end regions of the winding, in particular if they each protrude over the elastomer elements in one of the end regions. If the metallic foils are sufficiently thick, they can also contribute to the spring effect of the rolled stack. The individual elements of this stack of layers can also slide over one another, particularly in the axial direction, so that, for example, during compression the elastomer elements 25a and 25b can be pushed out axially from the original cylinder, with the metal electrode foils essentially retaining their axial length .

In an alternative embodiment of the layer stack, however, the mat-like elastomer elements can also be firmly connected to the conductive electrodes 21, 22 as a coating. Such a coating can be, for example, a vapor-deposited metal layer or else a conductive elastomer connected to the dielectric. In principle, either one of the elastomer elements can be coated on both sides with the electrodes and only one uncoated insulation layer is provided for the adjacent turn. Alternatively, two elastomer elements lying one on top of the other and each coated on one side can form the layer stack 29 .

In any case, the rolled embodiment of FIG. 12 is particularly advantageous in order to achieve a high change in the measurement signal as a function of the radial pressure and thus of the tensile stress on the cable. The outer sleeve 23 shown can advantageously be designed as a metallic spring element with a variable diameter and thus contribute to a restoring effect of the layer stack. Particularly advantageously, this outer sleeve 23 can in turn be implemented as a clamping sleeve and, in particular, be configured similarly to one of the clamping sleeves 24 in FIGS. 7 to 11. reference character list

I pull rope

3 rope sheath

5 strands of rope or . fibers

I I sensor element

12 outer contour

13 adapter sleeve

17 ribs

20 condenser

21 first electrode (inner electrode)

22 second electrode (outer electrode)

23 outer sleeve

24 collet

24a slot

25 dielectric

25a first elastomer element

25b second elastomer element

26 end portion of the dielectric

27 end cap

29 layer stack

31 first connection line

32 second connection line

A local rope axis d radial thickness of the dielectric

F _A axial tensile force p _r radial pressure s section

Claims

26 patent claims

1. traction cable (1) for transmitting an axial tensile force (F _A ), comprising

- a tubular cable sheath (3) which comprises a mesh of several cable strands and/or fibers (5), the individual cable strands and/or fibers (5) running obliquely to the local cable axis (A), and

- a in a section (s) inside the rope sheath

(3) arranged elongated sensor element (11), which has a capacitor (20), the capacitance of which depends on a radial pressure ( _pr ) of the cable sheath (3) on the sensor element (11),

- Wherein the radial pressure ( _pr ) on the sensor element (11) depends on the axial tensile force (F _A ) on the traction cable (1).

2. traction cable (1) according to claim 1, wherein the cable sheath

(3) and the inner sensor element (11) are configured coaxially to one another.

3. traction cable (1) according to one of claims 1 or 2, wherein the capacitor (20) of the sensor element (11) has two electrodes (21,22) and an elastically deformable dielectric (25) lying radially in between.

4. Traction rope (1) according to claim 3, in which the capacitor (20) has an inner electrode (21) and an outer electrode (22), the dielectric (25) coaxially surrounding the inner electrode (21) and the outer electrode (22) surrounding the Surrounding dielectric (25) coaxially.

5. Traction rope (1) according to claim 3, in which the capacitor (20) is formed by a spirally rolled-up layer stack (29) which comprises two electrodes (21, 22) and an intermediate dielectric layer (25), with the rolling axis of the local rope axis (A) corresponds to .

6. Traction rope (1) according to claim 5, in which the rolled-up layer stack (29) comprises two metal foils as electrodes (21, 22) and at least one intermediate elastomer element as a dielectric layer (25).

7. traction cable (1) according to claim 5, wherein the rolled-up layer stack (29) has at least one elastomer element (25), wherein at least one of the electrodes (21,22) by a coating on one of the two main surfaces of the elastomer element (25) is formed.

8. traction cable (1) according to one of claims 3 to 7, in which the sensor element (11) has a metallic spring element (22,23) with a variable diameter, which either forms the outer electrode (22) of the capacitor (20) or as an outer sleeve ( 23) is electrically connected to one of the two electrodes (21,22) of the capacitor (20).

9. traction cable (1) according to claim 8, in which the metallic spring element (22,23) is designed as a slotted clamping sleeve (24) and/or as a spirally rolled clamping sleeve (24).

10. Traction cable (1) according to one of the preceding claims, in which the outer contour (12) of the sensor element (11) is convexly shaped over a predominant part of its axial length such that the axial tensile force (F _A ) on the traction cable (1st ) A radial pressure ( _pr ) on the sensor element (11) can be effected.

11. traction cable (1) according to any one of the preceding claims, which has two electrical connection lines (31,32) for connecting the electrodes (21,22) of the capacitor (20) to an evaluation unit, the two connection lines

(21,22) are guided in particular parallel to the cable axis (A).

12. traction cable (1) according to any one of the preceding claims, wherein the cable sheath (3) consists at least predominantly of a synthetic plastic.

13. Cable-operated device with a drive unit, a driven element and a pull cable (1) according to one of claims 1 to 12, which connects the drive unit and the driven element with respect to a pulling direction (A) in a force-transmitting manner.

14. Device (50) according to claim 13, which is designed as a robotic device.

15. A method for measuring a tensile force (F _A ) which acts on a traction cable (1) according to any one of claims 1 to 12,

- wherein an electrical signal influenced by the capacitance of the capacitor (20) is measured, the size of which depends on a radial pressure ( _pr ) of the cable sheath (3) on the sensor element (11),

- Wherein the radial pressure ( _pr ) on the sensor element (11) depends on the tensile force (F _A ) on the traction cable (1).