DEVICE FOR MEASURING DEFORMATIONS, STRESSES, FORCES AND / OR TORQUES IN MULTIPLE AXES

Description

[0001] The invention preferably relates to a device for measuring multi-axial stresses on an object, comprising a spring body and a sensor chip which has one or more sensor elements for measuring deformation, stress, force, and / or torque, as well as an electronic circuit on a substrate. The spring body comprises a base plate on the front of which a force transmitter, preferably in the form of a pin, is installed, with the sensor chip being positioned on the back of the base plate below the force transmitter. The invention further relates to a system comprising such a device and a data processing unit, wherein the data processing unit is configured to read out the measurement data determined by the sensor chip and preferably uses this data to determine the forces and / or torques acting on the force transmitter. Background and state of the art

[0002] The invention relates to the field of sensors for measuring deformations, stresses, forces and / or torques.

[0003] Force measurements on objects are performed, for example, for the dimensioning and verification of mechanically stressed components. Proper dimensioning of mechanically stressed components requires knowledge of the nature of the stresses. The decisive parameters for the design are the maximum stresses that occur, which ultimately determine the dimensions. These stresses must be determined beforehand and then verified experimentally. Experimental stress analysis can thus be considered a link between theoretical calculations and experimental verification.

[0004] Monitoring the condition of machines also requires measuring forces and / or deformations in order to detect and document changing stresses. These can occur, for example, due to changes in boundary and operating conditions over time, as well as in material properties.

[0005] For this purpose, a particularly compact design of the force sensors is desirable to eliminate any influence on the machines or components being monitored. Furthermore, a compact design of the force sensors is desirable to resolve local (potentially multi-axial) deformation or stress / strain states. Depending on the local distribution of the deformation or stress gradients, a large-area, non-compact transducer can only provide a rough average of local states, which is disadvantageous.

[0006] The size of known force sensors is usually determined by the dimensioning of spring bodies or load cells, as well as the minimum dimensions of the measuring transducers.

[0007] The spring element or load cell is typically a suitably shaped piece of metal that serves to transmit force and whose geometry changes slightly under the influence of forces or torques. The resulting deformation is measured by a sensor, such as a strain gauge or another resistive or capacitive measuring unit.

[0008] The overall dimensions of the device are determined primarily by the minimum dimensions of the transducers. When determining multi-axial stresses, several transducers are usually required – at least one for each axis – which are arranged separately at the corresponding positions.

[0009] Placing multiple sensor transducers, for example in the form of strain gauges, requires more space.

[0010] Due to the component geometry and the load application, the stress state is a function of location. The magnitudes and directions of the principal stresses vary across the surface. Unless an additional normal load (e.g., pressure) is applied, a biaxial stress state typically prevails on the surfaces of objects under multiaxial stress. However, its principal directions are usually unknown.

[0011] Strain gauge rosettes, which feature multiple strain gauges in different directions, fulfill the important task within experimental stress analysis of fully determining a biaxial stress / strain state. This is because it has been demonstrated that the principal strains can be determined using three independent strain measurements in different directions. Even if the principal directions are known, two independent strain measurements are still required to determine them. Known arrangements from the prior art include the 45° right-angle rosette and the 60° delta rosette.

[0012] Conventional spring bodies are designed to have several zones for specific uniaxial stresses, which can be measured using multiple transducers.

[0013] Typical spring body shapes for load cells include, for example, double bending beams for small loads, shear bars for larger loads, column-shaped spring bodies (compression bar or hollow cylinder), ring torsion spring bodies for high loads, multi-bending beam spring bodies for high-quality scales, or diaphragm spring bodies, which have a small size with high stiffness.

[0014] The stress state is determined via deformation or strain measurement. Even under high component stresses (stress just before the fracture limit), only very small deformations or strains occur in typical, mostly metallic materials (approx. 1-2‰).

[0015] In particularly rigid systems, such as machine tools or linear measuring instruments, the usable strain is significantly lower. Semiconductor strain gauges that could be used for this purpose are usually only applicable with considerable effort.

[0016] Strain gauges are fundamentally based on the change in electrical resistance due to changes in length and cross-section. When a strain gauge is stretched, its resistance increases. When it is compressed (negative strain), its resistance R decreases. The following applies: DR / R = k · ε , where ε corresponds to the relative change in length.

[0017] Problem areas of metallic strain gauges are low k-factors and resulting low sensitivities, as well as large strain gauges and therefore poor spatial resolution, especially in rosettes where, due to the size of the strain gauges, measurements are taken at different locations on the different axes, which can result in both poor spatial resolution and an erroneous result.

[0018] Semiconductor strain gauges, on the other hand, allow for significantly more sensitive measurements. However, these strain gauges are also very mechanically sensitive, making installation complex, and they still frequently break. Furthermore, these semiconductor strain gauges are often rigidly bonded to the object being measured, frequently to increase the gauge's stability. In this case, the mechanical properties of the adhesive often influence and distort the strain measurement.

[0019] In general, problems often arise with the known strain gauge measurement methods, especially with the commonly used bridge circuits with only 1 or 2 active, relatively large strain gauges at different locations on the component and the addition of passive resistors to the bridge circuit, namely, in particular, poor temperature compensation and low sensitivity.

[0020] Silicon chip-based sensors, which have multiple sensor elements to measure voltage distributions, are also known in the prior art.

[0021] In Jaeger et al. 2000, voltage measurements based on the piezoresistive behavior of CMOS-integrated field-effect sensors are disclosed. The circuits provide temperature-compensated measurement results that are proportional to the normal voltage difference (σxx - σyy) and the shear voltage (σxy) in a plane. The use of silicon field-effect transistors as voltage sensors offers several advantages over conventional resistive elements due to their small size, high sensitivity, and integrability into active circuits, and allows for well-localized voltage state measurements.

[0022] Gieschke et al. (2009) propose CMOS-integrated sensors employing piezoresistive sensor bridges with analog and digital circuitry. Thirty-two piezoresistive sensor bridges are distributed as sensing elements on a single sensor chip, enabling the measurement of shear stress (σxy) or normal voltage difference (σxx - σyy) in a single plane. The sensing elements can be described as four transistors arranged in a square Wheatstone bridge configuration. The shear stress is determined by n-channel transistors, with the sensor bridge rotated by 45° relative to an (x,y) coordinate system. In contrast, p-channel transistors are arranged as a sensor bridge parallel to the coordinate system and measure the normal voltage difference.

[0023] Kuhl et al. (2013) describe sensor chips based on the technology of Gieschke et al. (2009). The piezoresistive sensor bridges are implemented as square field-effect transistors (FETs, preferably MOSFETs) with four source / drain contacts (piezo-FETs) that utilize the piezoresistive shear effect in n-type (NMOS) or p-type (PMOS) inversion layers. NMOS sensor elements are preferably used to measure the shear voltage σxy, and PMOS sensor elements are used to measure the normal voltage difference (σxx - σyy). Twenty-four such piezoresistive sensor bridges are distributed as sensor elements on a single sensor chip. Ten NMOS sensor elements measure the shear voltage, and fourteen PMOS sensor elements measure the normal voltage difference.

[0024] However, there is room for improvement regarding their use for measuring and / or monitoring multi-axial stresses on components or objects. WO 03 / 087750 A1 discloses a stress sensor comprising a substrate, a force application pin, and strain gauges. Object of the invention

[0025] The object of the invention is to provide a device without the disadvantages of the prior art. In particular, it was an object of the invention to provide a device that can determine multi-axial stresses on objects with high precision and is also characterized by a compact, robust design with low susceptibility to errors.

[0026] The problem is solved by the features of independent claim 1. Advantageous embodiments of the invention are described in the dependent claims.

[0027] The spring element advantageously allows tensions, forces, or stresses, even from multiaxial loads or external forces, to be concentrated in a small, localized area within the base plate. For example, the force transmitter can be an elongated force indicator or pin that is locally connected to the base plate at a clamping point.

[0028] A stress on the force transmitter at the end facing away from the base plate leads to a localized stress distribution at the clamping point and, through suitable design of the spring body, also on the back of the base plate, which advantageously correlates clearly with the stress on the force transmitter in terms of magnitude (height) and direction.

[0029] Preferably, the maximum stress at the measuring point is of the same order of magnitude as at the front clamping point of the force transmitter or pin, thereby reducing undesirably high notch stresses at the pin's clamping point. The stress distribution on the back side is preferably adapted to the area of ​​the sensor chip and increased. Advantageously, this makes it possible to measure external loads or forces with high sensitivity, without any limitations due to strength issues at the clamping point.

[0030] Advantageously, the sensor chip attached to the back of the base plate allows for precise, spatially resolved measurement of deformations, stresses, forces, and / or torques in the relevant area of ​​the base plate. Deformations, stresses, or forces and torques acting on the base plate are preferably transmitted to the substrate of the sensor chip, with one or more sensor elements detecting deformations or stresses of the substrate. With appropriate calibration... Summary of the invention

[0031] The problem is solved by the features of independent claim 1. Advantageous embodiments of the invention are described in the dependent claims.

[0032] In one aspect, the invention relates to a device for measuring multi-axial stresses on an object comprising a spring body and a sensor chip, comprising one or more sensor elements for measuring deformations, stresses, forces and / or torques, and an electronic circuit on a substrate, wherein the substrate of the sensor chip comprises a semiconductor material, wherein the spring body comprises a base plate on the front of which a force transmitter is installed, wherein the sensor chip is positioned on the back of the base plate below the force transmitter.

[0033] The spring element advantageously allows tensions, forces, or stresses, even from multiaxial loads or external forces, to be concentrated in a small, localized area within the base plate. For example, the force transmitter can be an elongated force indicator or pin that is locally connected to the base plate at a clamping point.

[0034] A stress on the force transmitter at the end facing away from the base plate leads to a localized stress distribution at the clamping point and, through suitable design of the spring body, also on the back of the base plate, which advantageously correlates clearly with the stress on the force transmitter in terms of magnitude (height) and direction.

[0035] Preferably, the maximum stress at the measuring point is of the same order of magnitude as at the front clamping point of the force transmitter or pin, thereby reducing undesirably high notch stresses at the pin's clamping point. The stress distribution on the back side is preferably adapted to the area of ​​the sensor chip and increased. Advantageously, this makes it possible to measure external loads or forces with high sensitivity, without any limitations due to strength issues at the clamping point.

[0036] Advantageously, the sensor chip, mounted on the back of the base plate, allows for precise, spatially resolved measurement of deformations, stresses, forces, and / or torques in the relevant area of ​​the base plate. Deformations, stresses, or forces and torques acting on the base plate are preferably transmitted to the substrate of the sensor chip, with one or more sensor elements detecting deformations or stresses of the substrate. With appropriate calibration, the forces or torques acting on the force transmitter can be inferred with extreme precision from the deformations or stresses of the substrate (which is connected to the back of the base plate).

[0037] For this purpose, the device can be kept extremely rigid, since even slight deflections or translations of the force transmitter can be reliably measured in the form of characteristic deformations or stress distribution in the base plate.

[0038] The force transmitter itself can be inserted into an object, for example a component, a control element or a machine, in a form-fit and / or force-fit manner, so that multi-axial stresses of the object are directly transferred to the force transmitter.

[0039] Stresses refer to mechanical stresses and, in the context of the invention, preferably mean deformations, tensions, forces and / or torques acting on the relevant components, such as the object, force transmitter or base plate.

[0040] The stresses can include, for example, a deflection with respect to the force transmitter, preferably a pin, for instance due to lateral forces (Fx, Fy), which preferably act at the end of the force transmitter facing away from the base plate. A (mechanical) stress preferably indicates the ratio of forces (e.g., lateral forces) per unit area. A normal mechanical stress σ on an imaginary cross-sectional area A through a body is the component Fn of an external force F per unit area A, perpendicular to that cross-sectional area. The normal stress σxx therefore preferably indicates the force acting along the x-axis (Fx) in an imaginary x,y coordinate system on a cross-sectional area A of the sensor chip or substrate (yz-plane) perpendicular to that axis.

[0041] The deflection of the force transmitter, preferably the pin, causes a deformation of the base plate, particularly in the area of ​​the clamping of the force transmitter, i.e. in an area where the force transmitter is positively and / or force-fitted to the base plate.

[0042] In the area of ​​the base plate, for example, expansions or compressions occur, which depend on the direction and amplitude of the deflection or allow conclusions to be drawn about them.

[0043] Strain (often denoted by the symbol ε) indicates a relative change in the length of a body, which can be either an elongation or a shortening. An increase in the object's size is referred to as positive strain or stretching; otherwise, it is called negative strain or compression. Strain is preferably defined as ε = ΔI / I 0 , where ΔI represents the change in length and I 0 the initial length.

[0044] According to the invention, the sensor chip is used to detect, in particular, local strains or compressions of the base plate, which allows for a precise determination of the deflections of the force transmitter in several axes. The plane (xy-plane) preferably corresponds to the plane of the sensor chip on which the sensor elements are arranged and, for example, preferably measure a shear or normal stress difference.

[0045] If the force transmitter is positively engaged in an object, such as a joystick or an axle, deformations or stresses in the object can be determined directly by measuring the smallest deflections.

[0046] Stresses can also involve axial forces (Fz) acting on the force transmitter in its axial direction (in the case of a pin, its longitudinal direction). In the case of an axial tensile or compressive force on the force transmitter, preferably in the form of a pin, characteristic deformations or stresses also occur within the clamping area of ​​the base plate. For example, in the case of a round pin, the base plate can develop a rounded bulge due to an axial tensile or compressive force on the force transmitter, with a characteristic elongation or compression pattern.

[0047] Furthermore, torques (Mz) acting on the force transmitter also advantageously lead to specific deformations or stresses in the area of ​​the base plate, for example in the form of a torsion pattern. By appropriately integrating the device, in particular the force transmitter, into a component, for example a tool spindle, torques or torsion patterns within the component or the spindle can thus be measured.

[0048] The application possibilities of the device according to the invention are diverse, with the advantages of the proposed device being particularly evident in the measurement or monitoring of multi-axial stresses.

[0049] Furthermore, the device is characterized by a compact design, as preferably exactly one sensor chip is used, which measures stresses on the force transmitter at a local area of ​​the base plate.

[0050] The device's exceptional robustness in handling is further enhanced by media separation. While the force transmitter of the spring body is connected to the object or component at the front, the sensor chip is installed separately on the back of the spring body. For example, due to its compact design, precise measurement accuracy, and media separation, the device can be used as a miniaturized flow sensor, preferably based on the impact plate or vortex principle, or combinations thereof.

[0051] Furthermore, the device according to the invention is particularly suitable for tactile control in Human Machine Interface (HMI) applications. A high stiffness of the spring element is advantageous in this regard, enabling precise, displacement-free control with preferably low forces (e.g., 5–10 N).

[0052] Integrated into a joystick, the device can be used, for example, to operate machines, vehicles, or wheelchairs. It can also be used to provide a keyboard panel. By highly sensitively measuring axial forces in the Z-axis and torques around the X or Y-axis, the location and magnitude of a force applied to a panel with an attached force sensor can be measured with exceptional precision. The device is also particularly well-suited as a "sensor probe" in 3D coordinate metrology, offering a significantly smaller, more compact, and more cost-effective solution compared to the prior art.

[0053] Furthermore, the compact and robust design of the device allows for particularly advantageous use as a force sensor in soft / sensitive robotics. Here, force-based control can complement or replace pure position control. This enables significantly more sensitive control, for example, with regard to gripping movements or the positioning of automatically guided elements, such as tools, in the case of opposing forces. The device according to the invention can therefore also be advantageously used, for example, in demanding human-machine co-working or precision machining, such as machining operations.

[0054] Purely path-controlled robot systems often lack the necessary sensitivity for such applications. While path control can be extremely precise, without precise measurement of the forces acting upon them, unwanted damage to the objects being processed can easily occur.

[0055] In a preferred embodiment, the spring body is configured such that forces and / or torques acting on the force transmitter are concentrated in a local area of ​​the base plate, so that the sensor chip installed on the rear side below the area allows conclusions to be drawn about the forces and / or torques acting on the force transmitter by measuring deformations, stresses, forces and / or torques of its substrate connected to the area of ​​the base plate.

[0056] The force transmitter is preferably a pin (or rod or pointer) which preferably stands essentially perpendicular to the surface of the base plate without being subjected to any force (without stress).

[0057] The force transmitter, particularly in the form of a pin, is preferably elongated with a cross-sectional dimension that is small compared to its length or height. The ratio of cross-sectional dimension to length or height is preferably referred to as the aspect ratio. The cross-sectional dimension preferably denotes the maximum extent in the cross-section of the force transmitter. In the case of a circular cross-section, the cross-sectional dimension preferably corresponds to a diameter. In the case of a square cross-section, the cross-sectional dimension preferably corresponds to an edge length.

[0058] Terms such as "essentially", "approximately", "about", "approximately", etc. preferably describe a tolerance range of less than ± 20%, preferably less than ± 10%, even more preferably less than ± 5%, and particularly less than ± 1%. Statements using "essentially", "approximately", "about", etc., always disclose and include the exact value stated.

[0059] In a preferred embodiment, the force conductor, preferably in the form of a pin, has a diameter of 0.5 mm to 5 mm, particularly preferably 1 mm to 3 mm and / or a length of 5 mm to 500 mm, preferably 10 mm to 100 mm.

[0060] In a preferred embodiment, the pin has an aspect ratio of diameter to length of 1:3 to 1:100, preferably 1:5 to 1:20.

[0061] In a preferred embodiment, the pin has a central bore, wherein the wall thickness of the pin with the central bore is preferably between 0.2 mm and 5 mm, and particularly preferably between 0.5 mm and 2 mm. In this embodiment, the force transmitter preferably has the form of a hollow cylinder, wherein the bore is located along the central axis and the wall thickness preferably corresponds to the difference between the outer radius (of the pin) and the inner radius (of the bore).

[0062] Providing a bore in a pin as a force transmitter leads to particularly characteristic deformations of the base plate, so that the forces or torques acting on the force transmitter can be measured with particular precision.

[0063] For the purposes of the invention, a base plate preferably refers to a substantially planar component with a front and back side, wherein the maximum extent of the front or back side (length, width) is large compared to the thickness of the base plate. In the case of a circular base plate, the maximum extent of the front or back side can, for example, correspond to a diameter. Preferably, the thickness of the base plate can be, for example, by a factor of 5, 10, 20 or more smaller than the maximum extent of the front or back side (e.g., a diameter or edge length of the front or back side).

[0064] The shape of the front or back of the base plate can vary and may, for example, correspond to a circle, a rectangle, a trapezoid, a triangle, an ellipse, without restriction.

[0065] In the context of the invention, the positioning of the sensor chip below the force transmitter preferably means that the sensor chip is positioned on the rear side of the base plate in a local area opposite the force transmitter or the clamping point. The sensor chip preferably overlaps at least partially with a projection of the front clamping point of the force transmitter. In preferred embodiments, the force transmitter and sensor chip can be axially aligned with each other.

[0066] In preferred embodiments, the base plate can be formed by a substantially homogeneous planar body. It is also preferred that the base plate is not a homogeneous body, but may have interruptions, for example in the form of slots, openings, or other topologies. The base plate can, for example, also be formed by a lattice structure that deforms in a characteristic (measurable) manner when the force transmitter is subjected to stress. The term "base structure" can therefore preferably be used synonymously with the term "base plate."

[0067] In a preferred embodiment, the base plate has a thickness between 0.1 mm and 2 mm, preferably between 0.3 mm and 0.7 mm.

[0068] In a preferred embodiment, the base plate and / or the force transmitter is formed from a metal, preferably selected from the group consisting of iron, steel, stainless steel, spring steel, brass, copper, titanium, aluminum, lead, magnesium, beryllium copper and / or other alloys of the aforementioned.

[0069] In other preferred forms, the base plate and / or the force conductor can be made from other materials used in microsystems technology, such as semiconductors, ceramics or plastics, in addition to metals.

[0070] Ceramic materials, in particular, are highly resistant to high temperatures and harsh environmental conditions, especially when used for base plates and / or force transmitters. For example, the device is also suitable for media separation due to the rear mounting of the sensor chip on the base plate. Thus, in the case of a flow sensor application, the force transmitter can be located in a flowing fluid (liquid or gas), while the sensor chip is installed on the opposite side of the base plate.

[0071] In a preferred embodiment, the base plate and / or the force transmitter can be formed from a substrate, preferably selected from the group consisting of monocrystalline silicon, polysilicon, silicon dioxide, silicon carbide, silicon germanium, silicon nitride, nitride, germanium, carbon, gallium arsenide, gallium nitride, indium phosphide and glass.

[0072] These materials are easy and cost-effective to process in semiconductor and / or microsystem manufacturing and are suitable for large-scale production. Furthermore, this allows for the device, including the spring element and sensor chip, to be provided preferably in an integrated (semiconductor) process. This simplifies manufacturing, enabling the cost-effective production of a particularly compact multi-axis force sensor.

[0073] The aforementioned dimensions and materials of the force transmitter and the base plate have proven advantageous in order to provide a particularly sensitive measuring device.

[0074] In a preferred embodiment, the base plate and / or the force transmitter has a relief line, preferably in the form of a border around the force transmitter at its clamping surface with the base plate. Relief line (also known as relief line) relieve groove(designated) refers in particular to a recess, notch or notch which is present in the form of a border on the base plate and / or the force conductor.

[0075] Particularly advantageous in this respect are the provision of a central bore within the pin and / or a clearance, preferably in the form of a border around the force transmitter at its clamping surface with the base plate.

[0076] Both features, independently of each other but particularly pronounced in combination, lead to characteristic deformations of the base plate in the clamping area, which allow particularly sensitive measurements of multi-axial stresses on the force transmitter.

[0077] In preferred embodiments, the spring body can be monolithic. That is, the force transmitter, preferably a pin, and the base plate are formed from a single block of material. However, the spring body can also be formed as a composite body, with the force transmitter, preferably a pin, fixed to the base plate.

[0078] For the purposes of the invention, a sensor chip preferably means a semiconductor component comprising at least one substrate with one or more sensor elements and preferably an electronic circuit.

[0079] In a preferred embodiment, the one or more sensor elements are configured for a resistive, preferably a piezoresistive, an optical, a magnetic, an inductive and / or a capacitive measurement of deformations, stresses, forces and / or torques of the substrate.

[0080] Resistive and piezoresistive sensor elements are generally based on a change in electrical resistance due to a change in the length of the substrate on which they are mounted. The piezoresistive change in resistance due to strain of the sensor elements is significantly greater (k-factor), particularly in (doped) semiconductors, and allows for more sensitive and accurate strain measurements. A change in resistance can preferably be measured by changing the voltage applied to the sensor element in a Wheatstone bridge.

[0081] Piezoelectric sensor elements preferably rely on the material-inherent generation of an electrical voltage by means of compressive and / or tensile forces acting on the arrangement.

[0082] An inductive measuring arrangement is preferably based on the strength of the current induced by a changing magnetic field.

[0083] An optical sensor element can preferably measure strains between different areas via distance measurement (for example, interferometric measurement, in which information about the phase difference of coherent optical signals is obtained through a superposition of these signals, which can then be read out). This phase difference, in turn, preferably contains information about the distance between the areas.

[0084] A magnetic sensor element can, for example, be based on a Hall sensor, which generates a different voltage depending on its position within a magnetic field and thus depending on the experienced magnetic flux density. Therefore, preferably with a fixed reference magnetic field, the measured voltage can be used to determine the relative position of the Hall sensor to this magnetic field. This measuring principle makes it possible, in particular, to measure distances (and thus voltage or strain) between different areas on the substrate.

[0085] A capacitive sensor element is preferably based on the principle of a measurable change in the capacitance of a capacitor when the distance between the capacitor plates (electrodes) is varied. A variety of different implementations are conceivable for this, for example, in the form of individual capacitor plates on the substrate, or by (MEMS) comb structures, in which the comb coverage and / or the comb spacing can be varied depending on the embodiment.

[0086] A person skilled in the art is familiar with various sensor elements and materials which can preferably be used to enable resistive, preferably piezoresistive, optical, magnetic, inductive and / or capacitive measurement of deformations, stresses, forces and / or torques.

[0087] MEMS sensors are preferably used here; that is, components based on MEMS technology. MEMS stands for the English term microelectromechanical system,This is a microsystem, enabling a compact (micrometer range) design with excellent functionality and ever-decreasing manufacturing costs. In particular, the entire sensor chip, including the sensor elements and electronics, is preferably fully integrated using CMOS technology.

[0088] Preferably, the sensor elements are arranged on a substrate together with an electronic circuit for evaluating and / or controlling the sensor elements and are in contact with this circuit via electrical connections, which are made, for example, by wire bonds and / or are provided in the substrate, e.g., by conductive traces. The substrate primarily serves as a mechanical support but can also perform electrical functions, e.g., provide electrical connections for the individual components.

[0089] Preferred electronic circuits include, without limitation, an integrated circuit (IC), an application-specific integrated circuit (ASIC), a programmable logic device (PLD), a field-programmable gate array (FPGA), a microprocessor, a microcomputer, a programmable logic controller and / or any other electronic, preferably programmable, circuit.

[0090] Preferably, the measurement data from the sensor elements can be read and / or pre-processed by means of an electronic circuit and / or other electronic components on the sensor chip. For this purpose, a multiplexer (MUX, for reading the signals from multiple sensor elements), an operational amplifier (e.g., a microcontroller), or a microcontroller can be integrated on the sensor chip or a circuit carrier. differential difference amplifier (DDA) with variable gain) or analog-to-digital converter ( analog-to-digital converter, ADC) are available for converting the signals into digital data.

[0091] In a particularly preferred embodiment, the one or more sensor elements comprise piezoresistive structures, preferably piezoresistive sensor bridges.

[0092] Preferably, the piezoresistive sensor bridges can be configured as Wheatstone bridges, ideally as a full bridge. Advantageously, four piezoresistive structures forming the full bridge can be positioned very close to each other. Disturbances such as temperature drift are compensated for, as the temperature drift preferably affects all piezoresistive structures equally.

[0093] Particularly preferably, the sensor chip comprises more than 3, 5, 10, 15, 20 or more sensor elements, wherein the sensor elements are distributed at different positions on the substrate.

[0094] The large number of sensor elements enables a particularly precise measurement of the two-dimensional distribution of deformations, stresses, forces, and / or torques on the substrate. Unlike, for example, semiconductor strain gauge sensors, the sensor chip does not integrate the local stress on the substrate across its entire surface, but rather, by means of the numerous sensor elements on the substrate, allows for a spatially resolved measurement of the stress or strain in the relevant area beneath the substrate surface.

[0095] In a preferred embodiment, a stress difference σxx - σyy is measured on the substrate using one or more of the sensor elements. The stresses σxx and σyy correspond to orthogonal normal stresses in the xy-plane.

[0096] In a preferred embodiment, a shear stress σ xy is measured by means of one or more sensor elements, so that shear forces acting on the substrate can also be detected.

[0097] In a preferred embodiment, the sensor elements are designed as piezoresistive sensor bridges, which are arranged in a square as Wheatstone bridges, wherein a shear voltage is determined by n-channel-based transistors and wherein the sensor bridge is rotated by 45° to an (x,y) coordinate system, while p-channel-based transistors are arranged as a sensor bridge parallel to the coordinate system and measure the normal voltage difference.

[0098] The piezoresistive sensor bridges are particularly preferably configured as square field-effect transistors (FETs, preferably MOSFETs) with four source / drain contacts (piezo-FETs) that utilize the piezoresistive shear effect in n-type (NMOS) or p-type (PMOS) inversion layers. NMOS sensor elements are preferably used to measure the shear voltage σxy, and [missing information] to measure the normal voltage difference (σxx). - σ yy ) PMOS sensor elements are used. Examples of preferred sensor chips with piezoresistive sensor bridges as sensor elements are disclosed, among others, in Gieschke et al. 2009 and Kuhl et al. 2013. Advantageously, this allows for the realization of particularly compact sensor elements with dimensions of 10 µm x 10 µm or smaller.

[0099] Particularly preferably, the sensor can have several sensor elements which create a voltage difference of the normal voltages. σ xx -σ yy is determined, as well as several sensor elements which measure a shear stress σ xy. This provides a particularly precise representation of a two-dimensional stress distribution in the substrate and thus indirectly of the area of ​​the base plate in which the force transmitter is clamped.

[0100] According to the claimed invention, the substrate of the sensor chip comprises a semiconductor material, preferably silicon, monocrystalline silicon, polysilicon, silicon dioxide, silicon carbide, silicon germanium, silicon nitride, nitride, germanium, carbon, gallium arsenide, gallium nitride, and / or indium phosphide. These materials are easy and inexpensive to process in semiconductor and / or microsystem fabrication and are also well suited for mass production. Likewise, these materials are particularly suitable for doping and / or coating to achieve the desired electrical, mechanical, thermal, and / or optical properties in specific areas.

[0101] The sensor elements for measuring mechanical deformation and / or stress acting on the sensor chip are placed on or into the substrate. Materials and / or manufacturing techniques known from the semiconductor industry can be used for this purpose, which are characterized by their efficiency, simplicity, low production costs, and suitability for high-volume production.

[0102] For example, masking (preferably photolithography) on the substrate can be used to define areas for the formation of sensor elements and / or an electronic circuit, where further semiconductor processes such as etching, doping, and / or deposition can be carried out. The substrate can also be a multilayer substrate comprising two or more layers, which are processed individually and then bonded together.

[0103] An etching and / or structuring process may preferably be selected from the group comprising dry etching, wet chemical etching and / or plasma etching, in particular reactive ion etching, reactive ion deep etching (Bosch process).

[0104] A deposition or application process may preferably be selected from the group comprising physical vapor deposition (PVD), in particular thermal evaporation, laser beam evaporation, arc evaporation, molecular beam epitaxy, sputtering, chemical vapor deposition (CVD) and / or atomic layer deposition (ALD). Doping may be carried out, for example, by known methods such as alloying, diffusion and / or ion implantation.

[0105] In a preferred embodiment, the substrate of the sensor chip has a thickness between 100 µm and 600 µm, preferably between 200 µm and 400 µm. The dimensions of the substrate are particularly suitable to ensure a good transfer function between deformations of stress or deformations of the base plate area and the sensor elements.

[0106] Preferably, the sensor chip is attached to the back of the base plate with one side of the substrate. For this purpose, an adhesive can be used, for example, which creates a direct bond between the substrate and the base plate.

[0107] Besides adhesive bonding, a variety of assembly and interconnection technologies (AET) can be used for the mechanical coupling of the sensor chip to the base plate. These include, without limitation, the use of adhesive films, soldering, brazing (welding), reactive joining (preferably with thermally reactive films, especially nanometer multilayers or reactive multilayer systems (RMS) joining), or bonding, for example, anodic bonding, direct bonding, bonding processes with intermediate layers (e.g., eutectic bonding), glass-frit bonding, adhesive bonding, and / or selective bonding.

[0108] Mechanical deformations are preferably transferred directly to the thin-film substrate via mechanical coupling using an AVT technique (for example, gluing, soldering, reactive joining, bonding, etc.), whereby the sensor elements on the opposite side of the substrate record a two-dimensional stress or deformation image.

[0109] The sensor elements are thus preferably used to determine deformations or stresses of the sensor chip itself or of the substrate. Due to the mechanical coupling with the force transmitter, the measurement data directly provides information about stresses, forces, deformations, or torques acting on the force transmitter or on the object into which the force transmitter is inserted.

[0110] Various calibration methods allow for the determination of not only relative statements about changes in mechanical stresses in the force transmitter or object, but also absolute statements about the stresses, forces, deformations, or torques acting in the component. The calibration can incorporate, for example, the mechanical properties of the sensor chip or substrate, as well as the force transmitter.

[0111] Due to the finite thickness of the substrate, the two-dimensional stress or strain image generated by the sensor elements on the free side of the substrate can deviate from the actual stress or strain distribution on the base plate. However, these differences are constant for a given sensor chip and substrate, and are therefore taken into account during calibration.

[0112] In a further preferred embodiment, the device comprises one or more inductive interfaces, preferably coils, for transmitting measured values ​​and / or for supplying energy.

[0113] Such a telemetric interface allows for particularly flexible use of an energy-autonomous device.

[0114] The electrical power required for operation can be coupled in via the inductive interface by an external reader. The integrated sensor elements can then measure the voltage or deformation distribution and wirelessly transmit the measurement data back to the reader. For data transmission via the telemetry interface, NFC, for example, may also be preferred. ( near field communication ) to use the standard.

[0115] The device can also be used advantageously, for example, to monitor rotating objects, such as tool spindles, which would otherwise not be easily possible using cable-based contact.

[0116] The inductive interface or (transponder) coils can be installed on the sensor chip itself, or separately, for example on a circuit board.

[0117] In a preferred embodiment, the sensor chip is contacted with a circuit carrier. A circuit carrier is preferably a component comprising an electrically insulating material on which electrically conductive connections (traces) and / or electronic components or assemblies are located.

[0118] In preferred embodiments, the circuit carrier is a printed circuit board (PCB). printed circuit board ) ,including both conventional (rigid) printed circuit boards and flexible printed circuit boards (English: flexible printed circuits ) can be used.

[0119] In a preferred embodiment, the sensor chip can also be contacted with a circuit carrier using a chip-on-board method, wherein electrical contacting is preferably carried out using a flip-chip assembly or chip-and-wire technique, preferably by wire bonding.

[0120] In chip-and-wire technology, the sensor chip is preferably glued directly onto the circuit carrier (e.g. a printed circuit board) and electrically connected to the circuit carrier by means of wire bonding (bridges made of fine wire).

[0121] Preferably, for example, the sensor chip can be attached to the back of the base plate using an AVT technique (e.g., gluing, soldering, reactive joining, etc.) and connected to a printed circuit board (PCB) also attached to the base plate via an electrical connection, e.g., a wire bond. Alternatively, a flip-chip assembly can preferably be used, in which the sensor chip is preferably mounted to the circuit carrier (e.g., PCB) with an active contact side on which the sensor elements and / or electronics are located. The contact is preferably made using contact pads. bumps) , for example, by means of an anisotropically conductive film. In flip-chip assembly, it is also preferred to apply the sensor chip directly to the substrate using an adhesive for optimal force transmission, with the circuit board located on the accessible side facing away from the base plate.

[0122] The sensor chip can preferably be connected to an external data processing unit via an interface on the circuit carrier, either wired or wireless.

[0123] The sensor chip can preferably be connected to an external data processing unit via an interface on the circuit carrier (e.g. a printed circuit board), either wired or wireless.

[0124] Different shapes may be preferred for the sensor chip, for example a circular shape, rectangular shape or other polygonal shape, the shape of a rectangle, in particular a square, is particularly preferred.

[0125] In a preferred embodiment, the sensor chip has a width and / or length between 0.5 mm and 10 mm, preferably between 1 mm and 5 mm, and more preferably between 1 mm and 3 mm. The thickness of the sensor chip is preferably less than 1 mm, more preferably less than 700 µm, or less than 500 µm.

[0126] In the preferred embodiment, the sensor chip is therefore essentially flat, i.e., it is characterized by a greater width and / or length in one plane (xy-plane) compared to an orthogonal dimension (z-axis, thickness). The factor can be, for example, 2, 3, 5, or more.

[0127] In a preferred embodiment, the sensor chip has an area of ​​0.25 mm² to 100 mm², preferably 1 mm² to 25 mm², and particularly preferably 1 mm² to 9 mm².

[0128] In another aspect, the invention preferably relates to a system comprising a) a described device and b) a data processing unit the data processing unit is configured to read measurement data obtained from the sensor chip.

[0129] The average person skilled in the art recognizes that technical features, definitions and advantages of preferred embodiments disclosed for the device according to the invention apply equally to the system comprising such a device, and vice versa.

[0130] Preferably, the data processing unit is configured to determine the forces and / or torques acting on the force transmitter from the measurement data obtained by the sensor chip regarding deformations, stresses, forces and / or torques of the substrate.

[0131] The data processing unit thus preferably allows an evaluation of the measurement data from the sensor chip in order to determine the actual stresses on the force transmitter or an object connected to it.

[0132] The electronic circuitry on the sensor chip itself can also perform a (pre-)evaluation of the measurement data. However, it may also be preferable for the electronic circuitry to essentially forward the measurement data unprocessed to the (external) data processing unit for further processing and / or evaluation.

[0133] The (external) data processing unit is preferably a unit that is suitable and configured for receiving, transmitting, storing, and / or processing data, preferably measurement data. The data processing unit preferably comprises an integrated circuit, a processor, a processor chip, a microprocessor, or a microcontroller for processing data, as well as a data storage device, for example, a hard drive. random access memory (RAM), a read-only memory (ROM) or also a flash memory for storing the data.

[0134] To determine the forces and / or torques acting on the force transmitter based on the measurement data of deformations, stresses, forces, and / or torques of the substrate acquired by the sensor chip, a computer program containing commands to perform the corresponding calculation steps can preferably be stored on the data storage device. Reference data obtained through suitable calibration can also preferably be stored on the data processing unit for this purpose.

[0135] A particularly preferred data processing device is a personal computer (PC), a laptop, a tablet, or the like, which, in addition to means for receiving, sending, storing, and / or processing data, also includes a data display device and an input device, such as a keyboard, a mouse, a touchscreen, etc. Furthermore, the data processing unit can preferably also be used to control the device, i.e., for example, to specify parameters for carrying out the measurements. Detailed description

[0136] The invention will be explained in more detail below using examples, without being limited to these.

[0137] Fig. 1 shows a schematic illustration of a preferred embodiment of a spring body according to the invention. 1.

[0138] The spring body 1 includes a force conductor 3,which has the shape of a pin and is clamped into a base plate 5 mechanically coupled. Without force applied, the force transmitter is stationary. 3 essentially perpendicular to the base plate 5. Forces or torques acting on the force transmitter 3 These effects lead to deflections or deformations that directly affect the clamping area of ​​the base plate. 3 transmitted

[0139] Fig. 1A shows a top view of the spring body 1, so that the front of the base plate 5 is visible. Fig. 1 B illustrates the back of the base plate 5.

[0140] In Fig. 1A is a deflection of the force transmitter 3 illustrated in one spatial direction. As in Fig. 1B As can be seen, such a deflection leads to a characteristic deformation of the back of the base plate. 5 below the pen 3.Red areas indicate stretching, while blue areas indicate compression. The arrangement and orientation of the compression and stretching areas allow for a highly precise resolution of the direction of deflection of the force transmitter. 3. The amplitude of the deformation or stress in the base plate is also important. 5 correlates very closely with the amplitude of the deflection of the force transmitter 3.

[0141] The illustrated spring body 1 This allows the force at the power inlet to be 3 acting forces and / or torques in a local area of ​​the base plate 5 are concentrated so that a sensor chip (in) is located on the back below the area. Fig. 1 (not shown) based on a measurement of deformations, stresses, forces and / or torques of its interaction with the area of ​​the base plate 5 Connected substrates allow conclusions to be drawn about the forces and / or torques acting on the force transmitter.3 allowed.

[0142] For this purpose, the shape of a round pen has been developed. 3, which is essentially perpendicular to the base plate and free of forces 5 has proven advantageous. Particularly good results can also be achieved if the pen 3 a perforation 6 features and in the base plate 5 and / or the force transmitter 3 a free stitch 7 in the form of a border.

[0143] The Fig. 2 and 3 illustrate the measurement of the resulting stresses or deformations in the area of ​​the base plate 5 below the force conductor 3.

[0144] As in Fig. 2 A and B As illustrated, the sensor chip learns 2 or its substrate through direct coupling to the base plate 5an analogous deformation or stress distribution, which is measured by means of the sensor elements (not shown) on the sensor chip 2 can be recorded.

[0145] Fig. 3 illustrates a two-dimensional stress distribution on the base plate 5, which results from a deflection of the force transmitter 3 according to the Fig. 1 results.

[0146] In Fig. 3A and 3B The two-dimensional distribution of the normal stresses Sx (or σ xx ) and Sy (or σ yy ) are shown.

[0147] The sensor chip 2 or the sensor elements installed on it preferably determine the difference between the normal voltages S x - S y (or σ xx - σ yy )

[0148] The difference is in the Fig. 3 C The voltage distribution is advantageously characterized by a series of distinctive peaks, which allow for highly precise measurement of the deflection of the force transmitter. 3 allow.

[0149] Fig. 4 illustrates a preferred embodiment of a sensor chip 2. The sensor technology and electronics located on the substrate are shown.

[0150] The sensor chip 2 comprises a total of 32 sensor elements 9, which are positioned at different locations on the substrate to ensure a two-dimensional resolution of the voltage distribution. The sensor chip 2 It itself has a length and width of approximately 2 mm x 2.5 mm and a thickness of approximately 300 µm.

[0151] The sensor chip 2 It is fully integrated using CMOS technology. Regarding the sensor elements... 9 These are piezoresistive sensor bridges, which are preferably designed as Wheatstone bridges (see...). Fig. 4 B and C ).

[0152] In Fig. 4B is a sensor element 9illustrated, which is a piezoresistive sensor bridge of type PMOS and is aligned parallel to the coordinate system (x,y) and is particularly sensitive to the difference of the normal voltages σ xx - σ yy .

[0153] Fig. 4 C shows a sensor element 9 , which is a piezoresistive sensor bridge of type NMOS and is oriented rotated by 45° to the coordinate system (x,y) and is particularly sensitive to the shear stress σ xy .

[0154] In addition to the sensor elements 9 The sensor chip has additional electronic components. In particular, the sensor chip includes 2 a control logic as an electronic circuit 11 or an analog-to-digital converter (ADC) and an operational amplifier ( differential difference amplifier (DDA)). In the preferred embodiment, an inductive interface is also provided ( telemetric interface ) for wireless reading of measurement data or for power supply.

[0155] An exemplary application of a preferred device is described in the Fig. 5 illustrated. Here, the device with the force transmitter is located 3 within a joystick. A movement of the joystick leads to a deflection of the force transmitter. 3, which can be determined based on a measurement of the stress or deformation distribution by the sensor chip (not illustrated).

[0156] To power the sensor chip and read the measurement data, the device includes an inductive interface in the form of a secondary coil. The electrical power required for operation can be supplied by an external base unit or reader, which includes a primary coil for this purpose. The integrated sensor elements can then measure the voltage or deformation distribution and wirelessly transmit the measurement data back to the base unit or reader.

[0157] The base unit or reader can already perform a (pre-)evaluation of the data using reading electronics as a data processing unit. Preferably, the measurement data is also transferred to another external data processing unit, such as a PC, notebook, or mobile device, for evaluation, visualization, and / or storage. Reference symbol list

[0158] 1 Spring body 2 Sensor chip 3 Force transmitter, preferably pin 5 Base plate 6 Through hole 7 Clear line 9 Sensor elements 11 Electronic circuit, for example ASIC 13 Inductive interface Bibliography

[0159] Gieschke P. , Y. Nurcahyo, M. Herrmann, M. Kuhl, P. Ruther and O. Paul, "CMOS Integrated Stress Mapping Chips with 32 N-Type or P-Type Piezoresistive Field Effect Transistors," 2009 IEEE 22nd International Conference on Micro Electro Mechanical Systems, Sorrento, Italy, 2009, pp. 769-772, doi: 10.1109 / MEMSYS.2009.4805496. Jaeger Richard.C., Suhling, Jeffrey C., Ramani, Ramanathan, Bradley, Arthur T. and Xu, Jianping,CMOS Stress Sensors on (100) Silicon, IEEE JOURNAL OF SOLID-STATE CIRCUITS, VOL. 35, NO. 1, JANUARY 2000. Kuhl M., Gieschke, P., Rossbach, D., Hilzensauer, S., Panchaphongsaphak, T., Ruther, P., Lapatki, B., Paul, O., Manoli, Yi, "A Wireless Stress Mapping System for Orthodontic Brackets Using CMOS Integrated Sensors," in IEEE Journal of Solid-State Circuits, vol. 48, no. 9, pp. 2191-2202, Sept. 2013, doi: 10.1109 / JSSC.2013.2264619.

Claims

1. An apparatus for measuring multi-axis loads on an object comprising: - a spring body (1), and - a sensor chip (2) comprising one or more sensor elements (9) configured to measure deformations, stresses, forces and / or torques and an electronic circuit (11) on a substrate, wherein the substrate of the sensor chip (2) comprises a semiconductor material, wherein the spring body (1) comprises a base plate (5) on the front side of which a force conductor (3) is installed, wherein the sensor chip (2) is positioned on the rear side of the base plate (5) below the force conductor (3).

2. The apparatus according to the preceding claim characterized in that the spring body (1) is configured in such a way that forces and / or torques acting on the force conductor (3) are concentrated in a localized area of the base plate (5), such that the sensor chip (2) installed on the rear side below said area enables conclusions to be drawn about the forces and / or torques acting on the force conductor (3) on the basis of a measurement of deformations or stresses of its substrate that is connected to said area of the base plate (5).

3. The apparatus according to one of the two preceding claims characterized in that the spring body (1) is monolithic.

4. The apparatus according to one of the preceding claims characterized in that the force conductor (3) is formed by a pin which is substantially perpendicular to the base plate (5) when no force is exerted upon it.

5. The apparatus according to claim 4 characterized in that the pin (3) has a diameter from 0.5 mm to 5 mm, particularly preferably 1 mm to 3 mm, a length from 5 mm to 500 mm, preferably 10 mm to 100 mm and / or an aspect ratio of diameter to length from 1:3 to 1:100, preferably 1:5 to 1:20.

6. The apparatus according to one of the preceding claims 4 or 5 characterized in that the pin (3) has a central bore, wherein a wall thickness of the pin (3) with central bore is preferably between 0.2 mm and 5 mm, particularly preferably between 0.5 mm and 2 mm.

7. The apparatus according to one of the preceding claims characterized in that the base plate (5) has a thickness between 0.1 mm and 2 mm, preferably between 0.3 mm and 0.7 mm.

8. The apparatus according to one of the preceding claims characterized in that the base plate (5) and / or the force conductor (3) has a relief groove (7), preferably in the form of a border around the area where the force conductor (3) comes into contact with the base plate (5).

9. The apparatus according to one of the preceding claims characterized in that the base plate (5) and / or the force conductor (3) are formed from a metal, preferably selected from the group of iron, steel, stainless steel, spring steel, brass, copper, titanium, aluminium, lead, magnesium, beryllium copper and / or other alloys of the aforementioned.

10. The apparatus according to one of the preceding claims characterized in that the one or more sensor elements (9) are configured for a resistive, preferably a piezoresistive, optical, magnetic, inductive and / or capacitive measurement of deformations, stresses, forces and / or torques of the substrate.

11. The apparatus according to one of the preceding claims characterized in that the one or more sensor elements (9) comprise piezoresistive structures, preferably piezoresistive sensor bridges, and / or the sensor chip (2) has more than 5, 10, 15, 20 or more sensor elements (9), the sensor elements (9) having different sensitivities for a measurement of deformations, stresses, forces and / or torques of the substrate.

12. The apparatus according to one of the preceding claims characterized in that the sensor chip (2) is configured to measure deformations, stresses, forces and / or torques in multiple axes and / or to measure a two-dimensional distribution of deformations, stresses, forces and / or torques of the substrate.

13. The apparatus according to one of the preceding claims characterized in that the substrate of the sensor chip (2) has a thickness between 100 µm and 600 µm, preferably between 200 µm and 400 µm.

14. A system comprising: a) an apparatus according to one of the preceding claims b) a data processing unit characterized in that the data processing unit is configured for reading out the measured data detected by the sensor chip (2).

15. A system according to the preceding claim characterized in that the data processing unit is configured to detect the forces and / or torques acting on the force conductor (3) from the measured data related to deformations, stresses, forces and / or torques of the substrate detected by the sensor chip (2).