MEASURING DEVICE FOR ARRANGEMENT IN A CYLINDER-SHAPED INTERNAL SECTION OF A HOLLOW BODY

Description

[0001] The invention relates to a measuring device for detecting a mechanical stress on a hollow body having a cylindrical interior section, wherein the measuring device has a deformation body which can be fixed in the cylindrical interior section in a force-transmitting manner and has a deformation region, and a sensor device which is fixed in the deformation region and can detect a mechanical stress transmitted to the deformation body due to the mechanical stress on the hollow body and a deformation of the deformation region thereby forced.

[0002] Modern technologies are known from practice, for example, known as the Internet of Things or Industry 4.0. They aim, among other things, to network physical objects, individual machine components, or entire systems and to enable them to work together automatically using information and communication technologies. This should enable the networked and collaborating components to be controlled and monitored more efficiently and specifically, thereby increasing the productivity of the resources used. A necessary prerequisite for the successful use of these technologies is the recording of the relevant physical measured variables for the individual components. Based on these measured variables, machine elements or processes can be monitored or controlled, and, for example, predictive maintenance of machines and systems can be carried out.These forecasts can focus on the current load or utilization of the component and the functionality of the machine or system, allowing impending failures to be identified early or potential causes of faults in the system to be more easily identified. Similarly, the physical measured variables can also be recorded to control a motor depending on the load exerted by a person, so that, for example, a hand-operated, electrically assisted vehicle can be operated with assistance.

[0003] Many applications require so-called intelligent machine elements or system components that can record the relevant physical measurement variables and transmit them as digital information to a data processing device. Examples of relevant physical measurement variables can include forces acting on the machine elements, torques, position parameters, or even rotational speeds.

[0004] As an example of an intelligent component, WO 2013 / 012870 A1 describes a torque sensor that is housed in a spindle, at the opposite ends of which a crank arm can be attached. The torque sensor records the forces and torques acting on the spindle from the crank arms using strain gauges and processes them in an electronic system. The force-fitting attachment of a torque sensor in a cylindrical interior of a hollow body, such as a pedal crank, generally requires a fit in the hollow body that is as precise as possible, into which the sleeve-shaped torque sensor can be pressed. Due to the usually unavoidable manufacturing tolerances in tubular hollow bodies, such aswelded, drawn or pressed pipes, the shape of an inner wall of the hollow body is not specified with sufficient precision, so that a sleeve-shaped or rod-shaped sensor body cannot easily be fixed in the interior of the hollow body in a force-fitting manner and a separate fit is always required.

[0005] For example, it is known from US Pat. No. 5,402,689 A that a sleeve-shaped deformation body has axially protruding and radially outwardly projecting clamping tongues at its opposite ends, which can be displaced radially outward with the aid of an insertable clamping element and pressed against a surrounding inner wall of a cylindrical recess in a component. However, for reliable fastening of the sleeve-shaped deformation body with the projecting clamping tongues, it must be possible to insert a clamping element between the clamping tongues from both opposite sides, so that this press-in sensor can only be secured in recesses that are accessible from opposite sides.

[0006] Various practical application examples for press-in sensors are known in which a pill-shaped measuring device is pressed into a corresponding fit, for example in a press frame, with a form-fitting or positive fit. The precision requirements for the manufacture of both the fit and the sleeve-shaped sensor bodies that have to be pressed into the fit are high and result in correspondingly high manufacturing costs. In addition, a fit can only be created in areas of the machine component that are directly accessible from the outside, so that the spatial arrangement of the torque sensors on the machine components is considerably restricted. For example, the arrangement of a torque sensor at a distance from the end faces in the interior of a tubular hollow body is generally not possible because a suitable fit cannot be formed in the cylindrical interior section.This is particularly the case if it is a welded, drawn or pressed pipe section which, given the technically possible manufacturing tolerances, does not have sufficient basic accuracy for a press connection and further machining is also excluded due to roundness deviations, wall thickness variations and eccentricity in the pipe area.

[0007] DE 10 2015 106 933 A1 describes a method for arranging and securing a torque sensor in the interior of a tubular hollow body. However, this requires the tubular hollow body to be manufactured using a special process and suitable tools, and the torque sensor must be secured in the interior at the same time, making the production of the hollow body very complex. Furthermore, the torque sensor cannot be positioned anywhere within an already manufactured tubular hollow body, making it impossible to arrange torque sensors in certified hollow bodies, which must be manufactured using a certified process.

[0008] In US 3 861 203 A or US 2008 / 0184818 A1, measuring sensors are shown and described in which a disc-shaped deformation body can be fixed in a cylindrical cavity of a component in such a way that forces and torques can be transferred to the disc-shaped deformation body via the lateral edge of the disc-shaped deformation body and can be recorded there.

[0009] Another measuring device is known from DE102010027959A1.

[0010] It is therefore an object of the invention to provide a measuring device for detecting mechanical stress on a hollow body, which can be placed robustly and cost-efficiently in tubular cavities of semi-finished products or machine elements with high tolerances.This object is achieved according to the invention in that an elastically deformable press-in ring element is arranged at each of two opposite ends of the deformation body and the press-in ring element has, at least in sections, such a small ring element thickness that the press-in ring element adapts to an inner wall of the hollow body and is pressed force-fittingly against the inner wall, so that a mechanical stress on the hollow body is transmitted to the deformation body via the press-in ring elements and causes a deformation of the deformation region of the deformation body that can be detected by the sensor device, wherein the deformation region of the deformation body consists of deformation webs connecting the two press-in ring elements, to which the sensor device is fixed, and wherein a diameter of the deformation region is smaller than a ring element diameter of the press-in ring elements.The ring element thickness corresponds to a distance measured in the radial direction between a radially inner press-in ring element inner surface and a radially outer press-in ring element outer surface.

[0011] The measuring device according to the invention comprises a deformation body with press-in ring elements arranged thereon, with which the deformation body can be fixed in a force-fitting manner in a cylindrical interior section of a hollow body without the need for a precisely specified interference fit. The deformation body is introduced into the interior of the hollow body with the press-in ring elements and positioned in the desired area or in the specified interior section. This is achieved, for example, by pressing in the end face with or without thermal shrinkage, i.e., an additional temperature adjustment of the joining partners.The elastically deformable press-in ring elements adapt to the contour of the inner wall of the hollow body and generate a sufficiently high contact pressure against the inner wall, so that the deformation body is firmly fixed in the interior of the hollow body via the press-in ring elements, and mechanical stress on the hollow body is transferred to the deformation body of the measuring device. The hollow body has an at least approximately cylindrical interior or cavity. Due to the thin ring elements, the press-in ring elements can adapt to a circumferential contour of the inner wall that is not ideally circular, but rather irregular and, for example, more oval due to tolerances.The ring element thickness is expediently specified in such a way that a deformation which changes the shape of the press-in ring elements and adaptation to the surrounding inner wall is possible and at the same time a sufficiently high restoring force is generated with which the contact pressure of the press-in ring element in question against the surrounding inner wall is effected.

[0012] It is advantageous if the press-in ring elements or the deformation body are made of the same material as the hollow body, so that temperature differences do not lead to significantly different expansions of the press-in ring elements and the hollow body, thereby weakening or impairing the force-locking connection between the press-in ring elements and the surrounding hollow body to such an extent that accurate measurement with the measuring device is no longer possible.

[0013] The seamless and force-locking connection between the measuring device according to the invention and the hollow body causes mechanical forces acting on the hollow body to be transmitted from the press-in ring elements directly to the deformation area of ​​the deformation body, so that the sensor device can detect the mechanical forces acting on the deformation area as physical measurement variables via the deformation of the deformation body caused thereby in the deformation area.

[0014] Particularly advantageously, the invention provides that the low ring element thickness of the press-in ring elements is specified in a range of 3% to 25% relative to the respective ring element diameter of the press-in ring elements. Due to the low ring element thickness, the press-in ring elements advantageously have a large predetermined elastic deformability. During a press-in process, the press-in ring elements can utilize their elastic deformability up to a certain elastic limit.

[0015] Furthermore, the press-in ring elements can be made of a suitable material that allows for plastic deformation upon forced deformation beyond the elastic limit before damage to the press-in ring elements is feared. In practice, the elastic limit is also known as the yield point of a material. The press-in ring elements can utilize an elastic deformation capacity up to an elastic limit in order to further enable plastic deformation of the press-in ring elements. In this way, the press-in ring elements can utilize their full inherent elastic deformation capacity for radial force closure, regardless of the given condition of the interior section of the hollow body.The subsequent plastic deformation enables an even greater radial adaptability of the press-in ring elements to an inner wall of the interior section of the hollow body.

[0016] Deformations of the press-in ring elements of an additional 200% to 300% compared to elastic deformations are readily possible with a suitable choice of material. The ring element thickness, which is reduced at least in some sections and ranges from 3% to 25%, advantageously allows the press-in ring elements to be adapted to almost all practical tubular hollow bodies with an at least approximately cylindrical interior section. Depending on the proportion of one or more circumferential sections with a low ring element thickness relative to the overall circumference of the press-in ring element, the restoring force of the elastically deformable press-in ring element can be specified within a wide range and thus individually adapted to the respective hollow body.The greater the ring element thickness, the stiffer the press-in ring element and the higher the restoring force of the press-in ring element and thus the contact pressure of the press-in ring element against the surrounding inner wall of the hollow body. Optionally, with a favorable design of the press-in ring elements, targeted work hardening of the press-in ring elements can also be achieved when they are radially formed, which increases the mechanical stability of the measuring device according to the invention in the hollow body.

[0017] For many applications, it is advantageous for both press-in ring elements to have the same ring element diameter. However, to be able to secure the measuring device, for example, in the conically tapered interior of a hollow body, it is also conceivable for the two press-in ring elements to each have an individual and different ring element diameter. Optionally, it is also possible for the press-in ring elements to have a profile corresponding to the profile cross-section if the inner contour is different, for example, if the hollow body has an oval profile cross-section.

[0018] Ideally, the radial stiffness of the press-in ring elements is specified to be sufficiently high that the required frictional connection can be maintained over the intended service life of the hollow body or measuring device. By applying the highest possible contact pressure of the press-in ring elements against the inner wall of the tubular hollow body, while still allowing damage-free insertion of the measuring device into the interior of the hollow body, a linear response of the measuring device can be achieved over a wide measuring range. This can facilitate the evaluation of the sensor signals of the measuring device and, if necessary, also yield more accurate measurement results.

[0019] In order to better ensure a damage-free pressing-in process of the measuring device according to the invention, it can be provided according to a particularly advantageous embodiment of the invention that the end of the deformation body lying in the pressing-in direction has at least one contact surface projecting radially inwards to a longitudinal axis of the preforming body, so that the measuring device can be pressed into the interior section in the pressing-in direction using a pressing tool resting on the at least one projecting contact surface.

[0020] During the press-in process, considerable press-in forces must typically be exerted on the measuring device according to the invention, especially on the deformation body and the deformation area. These press-in forces can even be considerably greater than the mechanical stresses to be detected by the sensor device and acting on the deformation area, so that it is possible that the deformation area and the sensor device may be permanently deformed or damaged during the press-in process, which is detrimental to their intended use, if the press-in forces act on the end of the deformation body that last penetrates the hollow body and is opposite the direction of press-in.

[0021] With the contact surface formed according to the design, which lies within the deformation body and protrudes radially from its longitudinal axis, a press-in tool can be applied to the contact surface and press the measuring device or the deformation body into the end located in the press-in direction, so that only reduced tensile forces and no compressive press-in forces act on the deformation area and the sensor device. The contact surface can encompass the entire circumference of the deformation body or consist of individual or multiple contact surfaces only in sections along the circumference.

[0022] The press-in tool then has a smaller diameter than the inner diameter of the preforming body and can be designed, for example, as a press-in mandrel or a press-in punch, so that the press-in tool can press against the contact surface(s) through the deformation body.

[0023] When the hollow body is subjected to stress, the force transmitted from the press-in ring elements to the deformation body can advantageously be converted into a deformation of the deformation body if the deformation region of the deformation body consists of thin-walled deformation webs connecting the two press-in ring elements, to which the sensor device is attached. If the deformation region consists of deformation webs, or if the press-in ring elements are connected via these deformation webs to form a deformation body, possibly formed in one piece, the forces transmitted via the press-in ring elements from the surrounding hollow body to the deformation body are concentrated on the deformation webs and can cause a greater deformation of the individual deformation webs than, for example, in a sleeve-shaped deformation region between the two press-in ring elements, which is comparatively rigid.The arrangement of four or six deformation webs between the two press-in ring elements is considered particularly advantageous, since the deformation area is thereby designed to be torsionally soft and a particularly large deformation of the deformation area of ​​the deformation body formed by the deformation webs can be achieved by the mechanical action on the hollow body.

[0024] The advantageous design of the webs as thin-walled cross-sections with a small cross-sectional area, which is advantageous for recording the stress variables, results in low rigidity, which is beneficial for the sensor properties but complicates the press-in process. During press-in, the axial compressive strength or buckling stability must not be overstressed if the force transmission during press-in is directed via the deformation webs. For this reason, measures can be taken to reduce the required press-in force.

[0025] According to a particularly advantageous embodiment of the thin-walled deformation webs, the deformation webs connecting the two press-in ring elements can be tapered at least in sections along a respective longitudinal axis of the deformation webs. This design of the deformation webs causes an excessive stress on the strain gauges attached to the deformation webs, which also reduces the stiffness of the deformation webs. This also significantly improves the linearity of the desired measuring range, since the strain gauges have to detect a lower deformation or elongation under equally acting forces.

[0026] For easier and non-destructive insertion of the measuring device according to the invention, it can be provided that at least one peripheral edge of each of the two press-in ring elements has a press-in chamfer, so that the deformation body can be inserted into the cylindrical interior of the hollow body with the press-in chamfer of the press-in ring elements first. The press-in chamfer is expediently formed in a press-in direction on the same peripheral edge of each of the two press-in ring elements, so that insertion and pressing of the measuring device is facilitated, which is pressed into the interior in the press-in direction. The press-in chamfer expediently has a very slight inclination for this purpose, so that a strong wedge effect is created during the press-in process. This means that a low press-in force can produce a high radial force.This ensures that the initial press-in force, which is necessary to ensure that the larger outer diameter of the press-in ring elements matches the shape of the inner contour of the interior section, is so low that buckling of the deformation body is avoided.

[0027] For an additional easier centering of the measuring device according to the invention at the beginning of the insertion into the hollow body, it can optionally be provided that a centering ring element with a smaller diameter than the ring element diameter is fixed to at least one end of the deformation body, so that the centering ring element can be inserted more easily into the cylindrical interior of the hollow body and specifies an advantageous positioning and alignment of the press-in ring element subsequently pressed into the cylindrical interior.A centering ring element at at least one end of the deformation body also ensures that the deformation body has a greater axial extension and that there is a lower risk of the deformation body becoming jammed in the interior of the tubular hollow body during the pressing-in process, while the pressing force exerted on the deformation body during the pressing-in process into the interior of the hollow body does not have to be increased.

[0028] According to the invention, the diameter of the deformation region is smaller than the ring element diameter of the press-in ring elements. A radially inwardly offset arrangement of the deformation region ensures that an outer surface of the deformation region is spaced from the inner wall of the surrounding hollow body. This enables uncomplicated arrangement of sensor elements even on the outer surface of the deformation region, without the sensor elements resting against the inner wall of the tubular cavity, which could result in them being abraded and / or damaged. The deformation region can thus be completely decoupled from the inner wall of the hollow body and is connected to it only via the press-in ring elements.

[0029] For an advantageous detection of mechanical effects on the hollow body, it can optionally be provided for the measuring device according to the invention that the sensor device comprises strain gauges, wherein the strain gauges are fixed in the deformation region of the deformation body and optionally on the deformation webs.

[0030] Strain gauges are known to be well suited to detecting and measuring the mechanical forces acting on them due to their electrical resistance, which changes under pressure or strain. Multiple strain gauges can be attached, aligned, and interconnected at the deformation area or the deformation webs of the deformation area in such a way that the acting mechanical forces can be broken down into bending forces, torques, and axial forces according to their respective components and evaluated. Any disruptive force components or force components that are not relevant for a given evaluation can be easily compensated for or masked out so that, for example, only torques acting on the hollow body are detected and measured by the sensor device. Optionally, it is also possible to combine two strain gauges mounted opposite one another on the deformation webs to form a full bridge or a full bridge.to be connected to a Wheatstone measuring bridge so that unwanted force components and measured variables can be compensated when evaluating the measured values.

[0031] The processing of the measured variables can be carried out particularly advantageously in the measuring device according to the invention if the measuring device comprises an electronic processing device that prepares and processes measurement signals from the sensor device. The electronic processing device can be, for example, a measuring electronics unit or a circuit board with a microcontroller. The electronic processing device can pre-process, filter, and / or perform calculations on the recorded measured variables. This allows the measured variables to be recorded at a high sampling rate, while the information can be forwarded using reduced, pre-processed data. In addition, an electronic processing device with a microcontroller can, for example, activate actuators or send information via data transmission devices as soon as the recorded measured variables exceed or fall below certain limit values.

[0032] The measuring device according to the invention can advantageously be supplied with electrical energy if the measuring device has an electrical supply line with a connector, which can be used to continuously supply the electronic components of the measuring device with electrical energy. The connector can, for example, protrude from the hollow body at an end face or through a recess in a lateral surface of the hollow body, so that the measuring device according to the invention can be supplied with electrical energy via the connector.

[0033] Optionally and particularly advantageously, the measuring device according to the invention can have an electrical energy storage device so that the electronic components of the measuring device can be supplied with electrical energy without an external power supply for a limited time or depending on the charge level of the electrical energy storage device. This allows the measuring device according to the invention to be operated in an energy-autonomous manner, since a temporary interruption in the electrical supply from outside the hollow body can be bridged by the energy storage device. Depending on the electrical energy requirement and the available space in the interior of the hollow body, rechargeable batteries or capacitors are suitable as energy storage devices. Optionally, in addition to charging the energy storage device using a connector, the energy storage device can also be charged contactlessly using an induction coil.This eliminates the need for a connector and wired contact with an external power supply.

[0034] It is also possible for the measuring device to have a device for converting kinetic energy into electrical energy, which can be used to charge the energy storage device with electrical energy. Such a design of the measuring device is particularly advantageous when used in hollow bodies that are regularly or continuously moved during their intended use, such as rotating hollow shafts.

[0035] To ensure that the measuring device according to the invention can be operated as energy-autonomously as possible, it can optionally be provided that a permanent-magnet rotor is attached to a generator weight. The generator weight and the permanent-magnet rotor are mounted within the measuring device by means of roller bearings, so that a rotational movement of the measuring device around the permanent-magnet rotor mounted in roller bearings can generate an electrical voltage in at least one coil winding attached to the rotatable measuring device. Thus, the measuring device according to the invention can be encapsulated in the hollow body without the need for externally supplied electrical energy and thus be energy-autonomously arranged and operated without a mechanical connection to the environment.An electrical energy storage device can be attached to the electronics, which continuously charges the electrical energy storage device through the rotational movement, while the electronic processing device can be powered from the electrical energy storage device when stationary. Additional electronic circuits can condition and / or smooth the voltage induced by the permanent magnet rotor before it is used in the measuring device.

[0036] For communication and transmission of the measurement signals, according to an advantageous embodiment of the measuring device according to the invention, the measuring device can be provided with a radio transmission module with which wireless communication can take place. The radio transmission module can establish a communication channel to a receiver outside the hollow body, allowing information about physical measurement variables, for example, to be transmitted to the receiver. According to a particularly advantageous embodiment, the radio transmission module can have an antenna recessed into a transverse bore, thus ensuring the mechanical robustness of the entire system and preventing damage to the electronic components even in the event of mechanical impact on the hollow body.

[0037] According to one embodiment of the invention, a particularly advantageous feature for communication and transmission of the measurement signals can be provided in the hollow body, into which an antenna device adapted to the recess and mounted on a circuit board is fitted. The antenna device is enclosed by a sleeve sealing the recess. The recess can again be a transverse hole or bore extending transversely to the longitudinal axis of the hollow body. Advantageously, this provides a particularly effective radiation characteristic of the antenna device without contaminating the interior section with external contamination.

[0038] In both designs, communication and transmission of the measurement signals can advantageously be carried out via Bluetooth (Low Energy), which ensures a certain degree of compatibility with smartphones and tablets.

[0039] For rotating applications of the measuring device according to the invention, it can advantageously be provided that the measuring device has a balancing mount, with which a balancing mass element can be secured to the deformation body. Optionally, an otherwise asymmetrical mass distribution of the measuring device according to the invention can be compensated for by at least one balancing mass element, wherein the balancing mount preferably encapsulates the at least one balancing mass element. The unbalance mount can advantageously be made of plastic.

[0040] Expanded application possibilities can arise for the measuring device according to the invention if the measuring device has at least one inertial measuring unit that can record yaw rate and / or acceleration measured values. From the yaw rate and / or acceleration measured values, the electronic processing device can calculate and provide, for example, positional positions, rotational speeds, or other calculated parameters such as energy or power, etc. Advantageously, the inertial measuring unit can be arranged 5 mm to 30 mm radially spaced from the rotation axis of the measuring device according to the invention, so that rotation of the measuring device according to the invention leads to significant accelerations, which can then be converted into a rotational speed.Furthermore, decentralized calculations for identifying states of the machine components can be carried out in advance via a sensor fusion from the various sensor sources (strain gauges, inertial measuring unit) in a microcontroller accommodated in the measuring device according to the invention - e.g. the announcement of necessary maintenance of a cardan shaft or an intention detection of operating handles.

[0041] The measuring device according to the invention is shown below in exemplary schematic representations. They show: Figure 1 a perspective view of a measuring device according to the invention in a cylindrical interior of a tubular hollow body shown partially in section, Figure 2 and Figure 3ain a sectional view, a schematic representation of a steel tube as a hollow body and a press-in ring element of the measuring device, each in a non-connected state and in a connected state in which the press-in ring element is pressed into the approximately cylindrical interior of the hollow body, Figure 3b a radial strain curve ε of the press-in ring elements plotted over an oversize ΔD to Figure 2 or Figure 3b , Figure 4 a perspective view of another measuring device in a hollow body, also shown partially in section, which has a smaller diameter than the one in Figure 1 shown hollow body, Figure 5a a side view and a perspective view of a deformation body of the measuring device with two press-in ring elements formed at two ends of the deformation body, with a centering ring element and with two press-in chamfers, Figure 5ba design of a deformation body with contact surfaces in perspective view, Figure 5c a force curve F over a time t of a pressing process of a deformation body into the interior section of a hollow body, Figure 6 a partially sectioned view of a measuring device of a different design in a torque sensor for a drive shaft with an unbalance sensor, a generator weight and an electric generator, Figure 7 an application example of a measuring device according to the invention in a universal joint shaft, and Figure 8 an application example of a measuring device according to the invention in a rolling transport trolley.

[0042] Figure 1shows a measuring device 1 configured according to the invention in an approximately cylindrical interior section 2 of a tubular hollow body 3, which in this embodiment is a steel tube. The hollow body 3 can be part of a machine or a larger system. The measuring device 1 can detect, process, transmit, and optionally also record physical measured variables and forces acting on the hollow body 3.

[0043] In order for the measuring device 1 to be able to precisely record the desired measured variables in the approximately cylindrical interior section 2 of the hollow body 3, the measuring device 1 must be firmly fixed in the hollow body 3 so that it can be deformed accordingly when the hollow body 3 is subjected to mechanical stress, so that this deformation can be detected with suitable sensors. After the measuring device 1 has been inserted and secured in the hollow body 3, there must be no further significant relative movement of the measuring device 1 to the hollow body 3, which could falsify the measurement of the mechanical stress acting on the hollow body 3.

[0044] The measuring device 1 has a deformation body 4, at each of whose opposite ends 5 a press-in ring element 6 is formed. During the insertion of the measuring device 1 into the cylindrical interior section 2, the press-in ring elements 6 are subjected to elastic deformation by a press-in process and thereby press with a restoring force against an inner wall 7 of the approximately cylindrical interior section 2. Both press-in ring elements 6 each have such a small ring element thickness 11 over their entire circumference that the press-in ring element 6 adapts to a shape of the inner wall 7 of the hollow body 3 and presses itself forcefully against the inner wall 7 due to the restoring forces generated by the elastic deformation.This elastic deformation makes it possible to fix the measuring device 1 even in hollow bodies 3 which do not have a fit adapted to the measuring device 1, but have the manufacturing tolerances which are usual in many areas.

[0045] Figure 2 and 3a illustrate the effect of the press-in ring elements 6 designed according to the invention, in that they each schematically show the only approximately cylindrical interior section 2 of the tubular hollow body 3, which is shown with an exaggerated oval shape for clarity, the inner wall 7 of the hollow body 3 and only a single press-in ring element 6 of the measuring device 1 in a sectional view. Figure 2shows the hollow body 3 and a press-in ring element 6 shown next to it individually, even before the measuring device 1 has been introduced into the interior section 2 of the hollow body 3. A ring element diameter 8 is larger than a smallest diameter 9 of the oval tubular hollow body 3 shown. If the press-in ring element 6 is inserted or pressed into the interior section 2 of the tubular hollow body 3 through a press-in opening 10, the press-in ring element 6 is elastically and possibly also plastically deformed and nestles force-fittingly against the inner wall 7 of the tubular hollow body 3, wherein the press-in ring element 6 presses radially against the inner wall 7. Figure 3ashows the hollow body 3 and the press-in ring element 6 fixed therein after the press-in process, wherein the force-locking connection is maintained by a ring element thickness 11 of the press-in ring element 6 being at least 3%, but not more than 25% of the ring element diameter 8. The restoring forces of the

[0046] Press-in ring elements 6 can be increased with a larger ring element thickness 11. With a smaller ring element thickness 11, a greater deformation of the press-in ring elements 6 and thus a better adaptation to the inner wall 7 can be achieved if the inner wall 7 deviates significantly from an ideal circular shape in cross-section.

[0047] Figure 3b shows the pressing process of the measuring device 1 in the form of a radial expansion curve ε of the press-in ring elements to Figure 2 or Figure 3b, plotted against an excess ΔD. With an elastic design of the press-in ring elements 6 with a small excess, the press-in ring elements 6 are located in an elastic region 41 of the curve. If the press-in ring elements 6 are designed such that the ring element diameters exceed a certain excess, the press-in ring elements 6 are located in a plastic region 42 of the curve, whereby a lasting residual compression 43 and a plastic deformation occur in the press-in ring elements 6, even if the press-in ring elements 6 are removed again from the interior section 2.

[0048] Figure 1further shows that the one-piece deformation body 4, in addition to the press-in ring elements 6, has four deformation webs 12 that form a deformation region 13 of the preforming body 4. A strain gauge arrangement 14 is attached to each deformation web 12, with two opposing strain gauge arrangements 14 being electrically connected to form a full bridge known as a Wheatstone bridge, so that unwanted force components acting on the strain gauges 14 can be determined and, if necessary, compensated. All strain gauge arrangements 14 together form a sensor device 15 that can detect mechanical effects on the hollow body 3 via the press-in ring elements 6 and via the deformation region 13 to which the sensor device 15 is attached.

[0049] Figure 1also shows that the measuring device 1 has an electrical energy storage device 16, which can supply an electronic processing device 17. The electronic processing device 17 has Figure 1 an evaluation electronics system that reads and processes the physical measured variables of the sensor device 15. All of these components, namely the electrical energy storage device 16 and the electronic processing device 17, are mechanically secured and held together by a plastic holder 18. The electrical energy storage device 16 is charged via a supply line 19, which leads to a connector 20, which is accessible from the outside via a borehole 21 formed in the hollow body 3.

[0050] Figure 4shows an alternative embodiment of the measuring device 1 in a likewise approximately cylindrical interior section 2 of a tubular hollow body 3. Since the diameter of the cavity circumference 9 in this hollow body 3 is smaller than in the Figure 1As is the case with the hollow body 3 shown as an example, the components of the measuring device 1 are arranged one behind the other in an axial direction to save space, and are held together by the plastic holder 18. From the press-in opening 10, the measuring device 1 can be guided far into the interior section 2 of the hollow body 3 and pressed in, with a centering ring element 22 ensuring better guidance of the measuring device 1 during pressing in. Due to the centering ring element 22, the deformation body 4 to be inserted cannot tilt so easily, thereby preventing the measuring device 1 from being pressed in crookedly. In addition to the centering ring element 22, the press-in ring elements 6 each have a press-in chamfer 24 directed in the press-in direction 23, with which the press-in ring elements 6 of the deformation body 4 can be pressed more easily into the interior section 2 of the hollow body 3.

[0051] The measuring device 1 in Figure 4also has a radio transmission module (not shown in detail), to which an antenna 25 is connected near the connector 20, with which wireless communication can take place between the measuring device 1 and an external data receiver outside the hollow body 3.

[0052] Figure 5ashows the deformation body 4 of the measuring device 1 in more detail in a side view and in a perspective view. The deformation body 4 has a ring element thickness 11 that lies in a range from 3% to 25% of the ring element diameter 8, whereby the force-fitting connection with the inner wall 7 of the tubular hollow body 3 is more robust and reliable the greater the ring element thickness 11. In the side view of the deformation body 4, starting from the right, the centering ring element 22 is shown, the diameter of which is smaller than the ring element diameter 8 of the press-in ring elements 6, so that this area can be inserted into the cylindrical interior section 2 of the hollow body 3 without the application of force and serves as a centering aid so that the deformation body 4 does not tilt during insertion into the hollow body 3.The press-in chamfers 24 on the press-in ring elements 6 are also shown in the press-in direction 23, wherein the press-in ring elements 6 delimit the deformation region 13 on both sides and transmit mechanical forces acting on the hollow body 3 to the deformation region 13. The deformation region 13 comprises four deformation webs 12, on each of which a strain gauge arrangement 14 is arranged, which converts the acting force components into a change in electrical resistance.

[0053] Figure 5b shows in addition to Figure 5aa deformation body 4 in a perspective view, in which a radially inwardly projecting contact surface 40 can be seen, which is assigned to the end 5 of the deformation body 4 lying in the press-in direction 23, so that a press-in tool can be applied to the at least one projecting contact surface 40 and can press the measuring device 1 in the press-in direction 23 into the interior section 2. As a result, the deformation body 4 can be pressed into the interior section 2 of the hollow body 3 without damage. Figure 5b shown how the deformation webs 12 have several section-wise tapers 46 of the deformation webs, so that the linearity of the measuring device can be improved.

[0054] Figure 5c shows in addition to Figure 5a and 5ba force curve F over a time t during the pressing-in process of the deformation body 4. Initially, a first force peak 44 must be applied until the deformation body 4 enters the interior section 2 of the hollow body 3. Thereafter, a force lower than the first force peak 44 must be applied for pressing until the second press-in ring element 6 must be pressed into the interior section 2 of the hollow body 3. For this purpose, a second force peak 45 must be applied, which must be even higher than the first force peak 44. Subsequently, a reduced force F is required to move the deformation body 4 to its target position.

[0055] Figure 6shows an alternative embodiment of the measuring device 1 for rotating applications, wherein the measuring device 1 is arranged and fixed within a torque transducer 26, which can be connected to the latter via two opposing flanges 27, for example, between two drive shaft sections (not shown). The asymmetrical distribution of the components of the measuring device 1 can lead to dynamic imbalances during the rotation of the torque transducer 26, which is why the measuring device 1 has a plastic balancing mount 28 for a balancing mass element (not shown in detail), so that the imbalance is at least partially compensated and the rotation of the torque transducer 26 is not unduly impaired by the measuring device 1.The plastic balancing mount 28 is particularly advantageous because it does not hinder the insertion and pressing in of the measuring device 1 and torques acting on the torque transducer 26 are cushioned or are only transmitted to the deformation area 13 via the press-in ring elements 6.

[0056] Decoupled via two roller bearings 29, the balance mount 28 additionally has a generator weight 30, to which a permanent-magnet rotor 32 is attached. The permanent magnets induce a voltage in a coil winding of the rotatable measuring device 1. The rotational energy generated during rotation of the torque sensor 26 can thus be converted into electrical energy, which can be used to operate the electrical processing device 17. This enables autonomous operation of the measuring device 1, which is no longer dependent on electrical energy from outside the torque sensor 26.

[0057] The Figure 7 shows an application example of the measuring device 1, which is integrated into a universal joint shaft 33. The measuring device 1 can be accommodated in a semi-finished steel tube of the universal joint shaft 33, which can then be further processed into a component of the universal joint shaft 33 as part of the production process. The measuring device 1 is protected within the semi-finished product from subsequent production steps such as welding, painting, sandblasting, drilling, milling, turning, pipe bending, crimping, etc. An inertial measuring unit in the measuring device 1 can, for example, record a kink angle 34 of the universal joint shaft 33 during operation, whereby the fatigue strength of the universal joint shaft 33 can be monitored.

[0058] The Figure 8shows an alternative application example of the measuring device 1, wherein the latter is located in a handle 35 of a rolling transport cart 36. If a user presses the handle 35 with a specific force in the desired direction of movement, the measuring device 1 detects the force acting on the hollow body 3 formed as the handle 35, processes the measured value, and can send a corresponding output signal to a drive motor 37, which can drive at least one of the cart wheels 38. As a result, the measuring device 1, together with the drive motors 37, provides driving support. The application example is not limited to rolling transport carts 36, but can easily be adapted to electrically powered bicycles or strollers, for example. List of reference symbols

[0059] 1. Measuring device 2. Cylindrical interior section 3. Hollow body 4. Deformation body 5. Ends of the deformation body 6. Press-in ring element 7. Inner wall of the tubular cavity 8. Ring element diameter 9. Cavity circumference 10. Press-in opening 11. Ring element thickness 12. Deformation webs 13. Deformation area 14. Strain gauge arrangement 15. Sensor device 16. Electrical energy storage device 17. Electronic processing device 18. Plastic holder 19. Supply line 20. Connector 21. Borehole 22. Centering ring element 23. Press-in direction 24. Press-in chamfer 25. Antenna 26. Torque sensor 27. Flange 28. Balancing device 29. Roller bearing 30. Generator weight 31. Gravity 32. Permanent magnet rotor 33. Universal joint shaft 34. Articulation angle 35. Handle 36. Rolling trolley 37. Drive motor 38. Trolley wheels 39. Longitudinal axis of the deformation body 40. Contact surfaces for a pressing tool 41. Elastic region 42. Plastic region 43.Residual compression 44. First force peak 45. Second force peak 46. Tapering of the deformation webs.

Claims

1. Measuring apparatus (1) for detecting mechanical stress on a hollow body (3) comprising a cylindrical interior portion (2), wherein the measuring apparatus (1) comprises a deformation body (4) that can be fixed in a force-transmitting manner in the cylindrical interior portion (2) and comprises a deformation region (13) and a sensor apparatus (15), which is fixed in the deformation region (13) and can detect mechanical stress transmitted to the deformation body (4) due to the mechanical stress on the hollow body (3) and thereby forced deformation of the deformation region (13) of the deformation body (4), wherein one elastically deformable press-in ring element (6) each is arranged at two opposite ends (5) of the deformation body (4) and the press-in ring element (6) has a ring element thickness (11) at least in some regions that is so low that the press-in ring element (6) adapts to an inner wall (7) of the hollow body (3) and is pressed in a force-fitting manner against the inner wall (7), such that mechanical stress on the hollow body (3) is transmitted via the press-in ring elements (6) to the deformation body (4) and causes a deformation of the deformation region (13) of the deformation body (4) that can be detected by the sensor apparatus (15), wherein a diameter of the deformation region (13) is less than a ring element diameter (8) of the press-in ring elements (6), characterised in that the deformation region (13) of the deformation body (4) consists of deformation webs (12) that connect the two press-in ring elements (6) and to which the sensor apparatus (15) is fixed.

2. Measuring apparatus (1) according to claim 1, characterised in that the low ring element thickness (11) of the press-in ring elements (6) is predetermined in a range of 3% to 25% relative to a relevant ring element diameter (8) of the press-in ring elements (6).

3. Measuring apparatus (1) according to claim 1 or claim 2, characterised in that the press-in ring elements (6) consist of a material that allows plastic deformation when deformation is forced beyond an elastic limit.

4. Measuring apparatus (1) according to any of the preceding claims, characterised in that the end (5) of the deformation body (4) lying in the pressing-in direction (23) comprises at least one contact surface (40) projecting radially inwards relative to a longitudinal axis (39) of the deformation body (4), such that the measuring device (1) can be pressed into the interior portion (2) in the pressing-in direction (23) by a press-in tool bearing against the at least one projecting contact surface (40).

5. Measuring apparatus (1) according to any of the preceding claims, characterised in that the deformation webs (12) connecting the two press-in ring elements (6) are tapered at least in portions along a relevant longitudinal axis of the deformation webs (12).

6. Measuring apparatus (1) according to any of the preceding claims, characterised in that at least one circumferential edge of each of the two press-in ring elements (6) comprises a press-in chamfer (24), such that the deformation body (4) can be introduced into the cylindrical interior (2) of the hollow body (3) with the press-in chamfer (24) of the press-in ring elements (6) in front.

7. Measuring apparatus (1) according to any of the preceding claims, characterised in that a centring ring element (22) having a smaller diameter than the ring element diameter (8) is fixed to at least one end face (5) of the deformation body (4), such that the centring ring element (22) can be introduced more easily into the cylindrical interior (2) of the hollow body (3) and provides advantageous positioning and alignment of the press-in ring element (6) that is subsequently pressed into the cylindrical interior (2).

8. Measuring apparatus (1) according to any of the preceding claims, characterised in that the sensor apparatus (15) comprises strain gauges (14), wherein the strain gauges (14) are fixed in the deformation region (13) of the deformation body (3) and, where applicable, to the deformation webs (12).

9. Measuring apparatus (1) according to any of the preceding claims, characterised in that the measuring apparatus (1) comprises an electronic processing apparatus (17), which prepares and processes measurement signals from the sensor apparatus (15).

10. Measuring apparatus (1) according to any of the preceding claims, characterised in that the measuring apparatus (1) comprises a radio transmission module with which wireless communication can take place.

11. Measuring apparatus (1) according to any of the preceding claims, characterised in that a recess is made in the hollow body (3), into which recess an antenna device adapted to the recess and mounted on a printed circuit board is fitted, wherein the antenna device is enclosed by a sleeve sealing the recess.

12. Measuring apparatus (1) according to any of the preceding claims, characterised in that the measuring apparatus (1) has an imbalance receptacle (28), by means of which a compensating mass element can be fixed to the deformation body (3).

13. Measuring apparatus (1) according to claim 12, characterised in that a permanent-magnet rotor (32) is fixed to a generator weight (30), wherein the generator weight (30) and the permanent-magnet rotor (32) are mounted inside the measuring apparatus (1) by means of rolling bearings (29), such that a rotational movement of the measuring apparatus (1) about the permanent-magnet rotor (32) mounted in rolling bearings (29) can generate an electrical voltage in at least one coil winding fixed to the rotatable measuring apparatus (1).

14. Measuring apparatus (1) according to any of the preceding claims, characterised in that the measuring apparatus (1) comprises at least one inertial measuring unit that can record rotation rate and / or acceleration measurement values.