Force sensor system with overload protection

Abstract

Force sensor system (10), comprising - a housing arrangement (12) with at least one through-hole (14) having at least one diameter (D1) to accommodate at least one force measuring sensor (16); - at least one force measuring sensor (16) arranged in the at least one through-hole (14); and - at least one abutment body (18) which is arranged in the at least one through-hole (14), wherein the force sensor system (10) has radial play (RS) between the at least one abutment body (18) and the through-hole (14), characterized in that the at least one through-hole (14) has a spacing device (24) between at least one force measuring sensor (16) and at least one abutment body (18), which is designed to abut the abutment body (18) against the force measuring sensor (16) without any load.

Description

[0001] The invention relates to a force-detecting sensor system with overload protection.

[0002] It has been found that in the off-highway machinery sector, including agricultural and construction machinery, and in the trailer sector there is a constant need for a force sensor system to precisely measure forces under sometimes very different conditions.

[0003] Until now, problems for force sensor systems existed when the measuring range and the overload range were so far apart that a conventional force measuring sensor failed in the event of an overload or only measured forces inaccurately.

[0004] Particularly in the off-highway sector, machines must be constructed very robustly in order to withstand extreme loads without damage. One example is the wheel bearing forces of a construction machine. For example, the weight in the bucket of a wheel loader must be determined. For example, three tons of material can be transported in its bucket. For a wheel loader with an empty weight of around thirteen tons, this means that each wheel has a weight of around four tons. This value can be assumed to be the nominal load for which the force sensor system must be designed in order to record the weight of the material transported in the bucket as accurately as possible. However, there are situations in the operation of wheel loaders where the load is unevenly distributed across the wheels. For example, when eighty percent of the total weight rests on one wheel due to driving maneuvers. This corresponds to around thirteen tons, or more than three times the original design.If the force sensor system is designed to provide good measurement accuracy for the four-ton nominal load, it would be destroyed in the event of an overload. If the force sensor system is designed to withstand the overload without damage, the measurement accuracy at the aforementioned nominal load is significantly reduced.

[0005] DE 103 54 603 A1 describes a connecting element for force measurement. An air gap is located between a bending beam and a sleeve to provide overload protection.

[0006] DE 87 06 522 U1 describes a measuring device with a measuring bolt which can be clamped into a bearing with its first end in a cantilevered manner and which has a receiving part for a load at the second end.

[0007] US 2004 / 0 007 397 A1 describes a force transducer for absorbing the weight force introduced into a holder of a vehicle seat with a force introduction element connected to the vehicle seat, a force output element connected to the holder and an expansion body provided between the force introduction element and the force output element.

[0008] DE 10 2004 016 398 A1 describes a load measuring device for a suspended tool with at least one force sensor with a first fastening section for connection to a tool holding device and a second fastening section for connection to the tool itself.

[0009] It is therefore an object of the invention to provide a precise force sensor system with overload protection.

[0010] The object is thus achieved by a force sensor system, a housing arrangement, and a force measuring sensor having the features of the independent claims. Preferred embodiments of the invention are specified in the subclaims and the following description, each of which may represent an aspect of the invention individually or in combination.

[0011] The invention thus relates to a force sensor system comprising a housing arrangement with at least one through-hole having at least one diameter to accommodate at least one force measuring sensor; at least one force measuring sensor arranged in the at least one through-hole; and at least one abutment body arranged in the at least one through-hole, wherein the force sensor system has radial play between the at least one abutment body and the through-hole.

[0012] Below, a basic idea of ​​the invention and individual aspects of the claimed subject matter are explained, and furthermore, preferred modified embodiments of the invention are described. Explanations, particularly regarding advantages and definitions of features, are essentially descriptive and preferred, but not limiting, examples. If an explanation is limiting, this will be expressly stated.

[0013] A basic idea of ​​the invention is therefore that, as a result of the claimed design of the force sensor system, the radial play is closed above a defined load and the forces are diverted around the force measuring sensor. This is also known as force shunt. In particular, this force shunt should only become active outside the measuring range in order to avoid falsifying the measurement result and to maintain measurement accuracy. The force shunt is achieved by bridging the play, i.e. a small gap. Since only very small distances or deformations occur during strain measurements, precisely manufactured machine components are required. Depending on the amount of play and the material properties, the force, stress and / or strain at which material deformation leads to a closed gap and thus the force shunt is formed can be set or defined.

[0014] The abutment body thus forms a radial clearance with the housing assembly through the defined gap. This radial clearance can be created, for example, by precisely manufacturing the through-hole, for example, using a grinding process. The diameter of the through-hole is then measured, and the appropriate abutment body is selected and inserted. If a load acting on the housing assembly exceeds a defined value, the clearance or gap is closed, and part of the force is diverted around the force sensor.

[0015] In the sense of the invention, radial play is defined as at least such a gap which has a material distance between the inner surface of the through-hole and the outer surface of the abutment body at a specific location such that no force shunt occurs for the regular force detection of a force sensor system set to a specific value range.

[0016] For example, a second abutment body can be placed in the housing assembly in such a way that the second abutment body adjusts the housing deformation for the desired data acquisition through a correspondingly acting abutment. Additionally or alternatively, the housing assembly can be constructed with through-holes and / or grooves in such a way that the through-holes and / or grooves adjust the housing deformation for the desired data acquisition through a correspondingly acting material weakening. These measures can be advantageous for using the housing assembly for different force levels and / or for increasing the force at selected points.

[0017] According to a preferred embodiment of the invention, it is provided that the at least one through-hole has at least two different diameters, namely a small diameter and a larger diameter; the at least one force measuring sensor is arranged in the at least one through-hole in the region of the small diameter; and the at least one abutment body is arranged in the at least one through-hole in the region of the larger diameter, wherein the force sensor system has radial play between the at least one abutment body and the through-hole in the region of the larger diameter. The different diameters ensure that the abutment body and the force measuring sensor do not touch each other. This is useful in order to maintain the high measurement accuracy of the force measuring sensor. In particular, if the force measuring sensor has sensor means in the potential contact area, this can reduce the risk of false detections.

[0018] According to a preferred embodiment of the invention, it is provided that one or more force measuring sensors is or are strain gauges, preferably glued or sputtered, and / or has or have a substantially cylindrical shape with at least one end face and / or one lateral surface, wherein the at least one end face and / or the lateral surface have meandering expansion means.

[0019] A strain gauge is a sensor used to measure the strain of an object. The most common type of strain gauge consists of an insulating flexible pad supporting a metal foil pattern. The strain gauge is attached to the object with a suitable adhesive, such as cyanoacrylate. It is also possible to sputter the strain gauge onto the object to be sensed. When the object is deformed, the foil is deformed, causing its electrical resistance to change. This change in resistance, usually measured using a Wheatstone bridge, is related to the strain by a quantity known as the strain factor. A strain gauge exploits the physical property of electrical conductivity and its dependence on the geometry of the conductor.When an electrical conductor is stretched within the limits of its elasticity so that it does not break or permanently deform, it becomes narrower and longer, increasing its electrical resistance from end to end. Conversely, when a conductor is compressed so that it does not kink, it widens and shortens, decreasing its electrical resistance from end to end. The magnitude of the induced voltage can be determined from the measured electrical resistance of the strain gauge. A typical strain gauge arranges a long, thin conductive strip in a meandering pattern, a zigzag pattern of parallel lines. This does not increase sensitivity because the percentage change in resistance for a given stretch is the same for the entire zigzag line as for a single conductor. A single linear conductor would have to be extremely thin, which could cause it to overheat.This would cause its resistance to change and expand. Or the trace would have to be operated at a much lower voltage, making it difficult to accurately measure resistance changes.

[0020] Sputtering, also called cathode sputtering, is a physical process in which atoms are released from a solid, also called target, by bombardment with high-energy ions, mainly noble gas ions, and pass into the gas phase.

[0021] A force measuring sensor that essentially has a cylindrical shape with at least one end face and / or one outer surface, wherein the at least one end face and / or the outer surface have meandering strain elements, is a force measuring sensor based on thin-film sensor technology and uses the strain gauge measuring method. By way of example and not limitation, the strain elements are coated directly onto the end face and, for temperature compensation, also onto the outer surface of a small steel cylinder. The force measuring sensor is pressed into the through-hole of the housing arrangement with slight interference and thus experiences the same strain as the surrounding material. The thin-film sensor technology functionality is typically realized through a submicrometer-thin, strain-sensitive metal coating that is structured by micromachining.This measuring structure enables continuous force and torque measurement during operation. This measuring technology makes it possible, for example, to determine torque very quickly and precisely. In particular, it is a multi-layer system consisting of an insulating coating and a strain-sensitive metal coating, in particular using PVD (physical vapor deposition) technology. Unlike chemical vapor deposition, the starting material is converted into the gas phase using physical processes. The gaseous material is then fed to the substrate to be coated, where it condenses and forms the target layer. Particularly preferred for good measurement results, but not limiting, the essentially cylindrical shape of the force measuring sensor is a bolt, preferably with a diameter of eight millimeters and, for example, a length of twenty millimeters.Essentially, this means that the basic cylindrical structure can have some deviations, such as small recesses. A completely cylindrical shape is also possible.

[0022] According to a preferred embodiment of the invention, one or more abutment bodies are rolling elements. Rolling elements are known, for example, from rolling bearings as balls, rollers, cylindrical rollers, needles, cones, or other rotating bodies made of steel, ceramic, or special, extra-hard plastics. As elements of a rolling bearing or a linear rolling guide, these elements significantly reduce the friction between the various components of the bearing or guide and thus greatly facilitate the relative movement of various machine elements. Due to the completely different application, it is therefore unlikely that rolling elements would be used. It has been found that rolling elements are particularly suitable as abutment bodies because high-precision manufacturing processes for rolling elements exist, allowing the radial gap to be optimally adjusted. In particular, the rolling elements can be made of chrome steel.This material is very hard but easily rusts, with reference to the preferred steel grade 100Cr6; a steel with a carbon content of approximately one and a half percent by weight and approximately one and a half percent by weight of chromium. Other steels include 100CrMnSi6-4 and 100CrMo7, with the alloying elements manganese and molybdenum serving to improve through-hardenability. Due to its susceptibility to rust, the use of a cover element is particularly preferred. For applications in corrosive environments, the high-alloy steels X65Cr13 and X30CrMoN15-1 can also be used.

[0023] According to the invention, the at least one through-hole between at least one force measuring sensor and at least one abutment body comprises a spacing device to support the abutment body against the force measuring sensor without stress. For example, the at least one through-hole may comprise a step in the transition region from a larger diameter to a smaller diameter as a spacing device to support the abutment body. The purpose of this feature is to ensure that the measurement accuracy of the force measuring sensor is not impaired.

[0024] According to a preferred embodiment of the invention, the at least one through-hole has a cover element at one or both ends, which cover element is preferably designed in two stages such that an inner diameter segment engages in the diameter, preferably the larger diameter, of the through-hole, and that an outer diameter segment having an even larger diameter rests on an outer surface of the housing arrangement. This ensures, on the one hand, that the abutment body does not fall out of the through-hole. Furthermore, no dirt can penetrate into the through-hole. The cover element can be connected to the housing arrangement in a force-fitting and / or form-fitting manner, and in particular detachably, in order to always be able to access the force measuring sensor and / or the abutment body.

[0025] According to a preferred embodiment of the invention, it is provided that the housing arrangement has one or more through-openings and / or one or more grooves, to be connected to a component via this or these, and / or to set a force flow for force detection via this or these. On the one hand, the housing assembly must be connected to the component to be tested. A connection via one or more through holes and / or one or more grooves does not adversely affect the measurement result. On the other hand, the force flows can also be adjusted via the position of the connection of these components, thus improving the measurement quality and achieving overload protection.

[0026] According to a preferred embodiment of the invention, it is provided that the force sensor system has at least two abutment bodies in a through-hole, which are preferably arranged opposite each other along the through-hole, and / or which, in particular, surround the force sensor along the through-hole at one end each. Thus, deformations in two opposing directions can be compensated by the other abutment body. This increases the robustness and thus the measurement quality of the force sensor system.

[0027] Preferably, the housing arrangement is cuboid-shaped. It has been found that the aforementioned features can be realized particularly well with a cuboid shape. However, other shapes for the housing arrangement are also possible.

[0028] The invention will now be explained by way of example with reference to the accompanying drawings using preferred embodiments, wherein the features presented below may represent an aspect of the invention both individually and in combination. They show: Fig. 1: a longitudinal section through a force sensor system according to a first preferred embodiment of the invention, with a housing arrangement, a force measuring sensor and an abutment body, wherein a load acts on the housing arrangement in the region of the abutment body; Fig. 2: a longitudinal section through a force sensor system according to an alternative preferred embodiment of the invention, wherein the force sensor system is opposite Fig. 1 has a further abutment body and is subjected to a different load which acts on the housing arrangement in the area of ​​the abutment body; Fig. 3: a perspective view of a longitudinal section of the force sensor system according to the first preferred embodiment of the invention; Fig. 4: a perspective view of the entire force sensor system according to the first preferred embodiment of the invention; Fig. 5: a symbolic detailed view of the longitudinal section of the force sensor system according to the first preferred embodiment of the invention in the region of the abutment body; Fig. 6: a perspective view of the force sensor system according to the first preferred embodiment of the invention, mounted between two components; Fig. 7: several views of force sensor systems according to different preferred embodiments of the invention, wherein the force sensor systems have different through-openings and / or grooves; Fig. 8: a perspective view of a force sensor system according to an alternative preferred embodiment of the invention, with a Fig. 1 differently arranged force measuring sensor; Fig. 9: a perspective view of a force sensor system according to an alternative preferred embodiment of the invention, with a Fig. 1 and Fig. 8 differently arranged force measuring sensors; Fig. 10: a perspective and a sectional view of a force sensor system according to an alternative preferred embodiment of the invention, with a Fig. 1 differently arranged force measuring sensor and with a different cable connection; and Fig. 11: a sectional view of a force sensor system according to an alternative preferred embodiment of the invention, with a Fig. 1 differently arranged force measuring sensor.

[0029] The Fig. 1 to 11 show a plurality of embodiments of a preferred force sensor system 10. All force sensor systems 10 according to the teachings of the invention comprise: a housing arrangement 12 with at least one through-hole 14 having at least a diameter D1 to accommodate at least one force measuring sensor 16; at least one force measuring sensor 16 arranged in the at least one through-hole 14; and at least one abutment body 18 which is arranged in the at least one through-hole 14, wherein the force sensor system 10 has radial play RS between the at least one abutment body 18 and the through-hole 14.

[0030] The illustrated preferred embodiments of the force sensor system 10 are according to the Fig. 1 to 11 further characterized in that the at least one through-hole 14 has at least two different diameters D1, D2, namely a small diameter D1 and a larger diameter D2; the at least one force measuring sensor 16 is arranged in the at least one through-hole 14 in the region of the small diameter D1; and The at least one abutment body 18 is arranged in the at least one through-hole 14 in the region of the larger diameter D2, wherein the force sensor system 10 has the radial clearance RS between the at least one abutment body 18 and the through-hole 14 in the region of the larger diameter D2. However, these are preferred, but not limiting, features of the force sensor system 10.

[0031] The force measuring sensor 16 detects loads B acting on it and transmits this information via a cable connection 40

[0032] According to a preferred and not shown embodiment of the invention, it is provided that one or more force measuring sensors 16 is or are strain gauges, preferably glued or sputtered.

[0033] In contrast, the disclosed figures show, albeit only by preference and not by limitation, that one or more force measuring sensors 16 essentially have a cylindrical shape with at least one end face 20 and one lateral surface 22, wherein the at least one end face 20 and the lateral surface 22 have meandering expansion means. The cylindrical shape is clearly schematic in the figures. Essentially, with regard to the cylindrical shape, this means that the respective force measuring sensor 16 can be guided along the through-hole 14 and, at the same time, has sufficient contact with the through-hole 14 to perform a qualitative force measurement.

[0034] According to the illustrated embodiment, the abutment bodies 18 are rolling elements. This is also a separate feature and not limiting.

[0035] Especially in Fig. 5, the exemplary embodiment is clearly visible in which the at least one through-hole 14 between the at least one force measuring sensor 16 and the at least one abutment body 18 has a spacing device 24 designed as a step or support shoulder in order to abut the abutment body 18 without stress against the force measuring sensor 16. This is thus shown by way of example as a preferred embodiment, wherein the at least one through-hole 14 in the transition region from the larger diameter D2 to the smaller diameter D1 has a step or support shoulder as a spacing device 24 in order to abut the abutment body 18. The end face 20 of the force measuring sensor 16 is thus not stressed by the abutment body 18.

[0036] Furthermore, the exemplary embodiment in the Fig. 1 to 11 such that the at least one through-hole 14 has a cover element 26 at one or both ends, which is preferably designed in two stages such that an inner diameter segment 28 engages in the larger diameter D2 of the through-hole 14 and that an outer diameter segment 30 having an even larger diameter rests on an outer surface 32 of the housing arrangement 12. Thus, the embodiment according to Fig. 1 a cover element 26 and the embodiment according to Fig. 2 two cover elements 26. This is advantageous, for example, when a respective abutment body 18 is designed as a rolling element, since rolling element steels are prone to corrosion. This provides increased protection against corrosion and other harmful influences, such as dust particles.

[0037] Furthermore, it is preferably provided that the housing arrangement 12 has one or more through openings 34 and / or one or more grooves 36. In Fig. 6 shows, by way of example, that the force sensor system 10 is connected to two components 38 via the through-openings 34. Among other things, Fig. 7 shows in the Fig. 7a, Fig. 7c and Fig. 7d different preferred configurations of grooves 36 for setting a force flow for force detection. In Fig. 7b preferably shows that the force flow for force detection can be adjusted via a through opening 34.

[0038] For example in Fig. 2 shows that the force sensor system 10 has at least two abutment bodies 18 in a through-hole 14, which are preferably arranged opposite each other along the through-hole 14, and / or which, in particular, surround the force measuring sensor 16 along the through-hole 14 at one end each. The latter feature means that an abutment body 18 is arranged closer to the outer area than the force measuring sensor 16 to be protected.

[0039] The figures show, by way of example, that the housing arrangement 12 is cuboid-shaped. This shape has proven particularly advantageous, although other shapes for the housing arrangement 12 are also possible, provided they allow for force shunting. List of reference symbols 10 Force sensor system 12 Housing arrangement 14 Through recess 16 force measuring sensor 18 abutment bodies 20 frontal area 22 Shell surface 24 Distance device 26 Cover element 28 inner diameter segment 30 outer diameter segment 32 Outer surface of the housing assembly 34 passage opening 36 grooves 38 component 40 cable connection D1 small diameter D2 larger diameter RS radial clearance B load

Claims

[1] Force sensor system (10), comprising - a housing arrangement (12) with at least one through-hole (14) having at least one diameter (D1) to accommodate at least one force measuring sensor (16); - at least one force measuring sensor (16) arranged in the at least one through-hole (14); and - at least one abutment body (18) arranged in the at least one through-hole (14), wherein the force sensor system (10) has radial play (RS) between the at least one abutment body (18) and the through-hole (14), characterized by that the at least one through-hole (14) between at least one force measuring sensor (16) and at least one abutment body (18) has a spacing device (24) which is designed to abut the abutment body (18) against the force measuring sensor (16) without any load. [2] Force sensor system (10) according to claim 1, characterized by, that - the at least one through-hole (14) has at least two different diameters (D1, D2), namely a small diameter (D1) and a larger diameter (D2); - the at least one force measuring sensor (16) is arranged in the at least one through-hole (14) in the region of the small diameter (D1); and - the at least one abutment body (18) is arranged in the at least one through-hole (14) in the region of the larger diameter (D2), wherein the force sensor system (10) has the radial play (RS) between the at least one abutment body (18) and the through-hole (14) in the region of the larger diameter (D2). [3] Force sensor system (10) according to at least one of claims 1 or 2, characterized bythat one or more force measuring sensors (16) is or are strain gauges, preferably glued or sputtered, and / or has or have a substantially cylindrical shape with at least one end face (20) and / or one lateral surface (22), wherein the at least one end face (20) and / or the lateral surface (22) have meandering expansion means. [4] Force sensor system (10) according to at least one of the preceding claims, characterized by that one or more abutment bodies (18) are rolling elements. [5] Force sensor system (10) according to at least one of the preceding claims, characterized bythat the at least one through-hole (14) has a cover element (26) at one or both ends, which is preferably designed in two stages such that an inner diameter segment (28) engages in the at least one diameter (D2) of the through-hole (14) and that an outer diameter segment (30) having a larger diameter rests on an outer surface (32) of the housing arrangement (12). [6] Force sensor system (10) according to at least one of the preceding claims, characterized by that the housing arrangement (12) has one or more through openings (34) and / or one or more grooves (36) in order to be connected to a component (38) via these and / or to set a force flow for force detection via these. [7] Force sensor system (10) according to at least one of the preceding claims, characterized bythat the force sensor system (10) has at least two abutment bodies (18) in a through-hole (14), which are preferably arranged opposite one another along the through-hole (14).

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