Measuring device

Abstract

Measuring device (1) for measuring the thickness of a measuring body (2), in particular the thickness of a gas diffusion electrode, comprising - a support body (3) having a support surface (4) which is designed to receive a measuring body (2), - a pressing element (5) which is mounted to be movable relative to the support element (3), in particular translationally movable, and is designed to apply a defined contact pressure to a measuring element (2) received by the support element (3), - a sensor device (6) comprising a sensor frame (7) and at least one sensor (8) arranged movably on the sensor frame (7), in particular translationally movable, which is designed as a displacement sensor or measuring probe, - a control device (9), wherein the at least one sensor (8) is configured to detect a position value of a surface at a measuring point (P) along a measuring axis (A), and wherein the control device (9) is configured to determine the thickness of the measuring body (2) as the difference between a first position value detected on the support surface (4) and a second position value detected on the top of the measuring body (2), wherein the first position value and the second position value are detected along the same measuring axis (A).

Description

[0001] The invention relates to a measuring device for measuring the thickness of a measuring body.

[0002] Gas diffusion electrodes are known from the prior art. They are used in electrochemical processes, for example in fuel cells or in electrolysis devices designed as membrane electrolyzers.

[0003] The installation of a gas diffusion electrode in such a fuel cell or membrane electrolyzer is carried out under strict tolerance conditions with regard to the thickness of the membrane and the gas diffusion layers (GDL) on both sides, since complete surface contact of the membrane and the adjacent GDL is essential for the efficiency of the respective system.

[0004] Therefore, it is essential that every gas diffusion layer used undergoes comprehensive quality control, in particular thickness measurement. Since this must be done not just at specific points, but across the entire surface of the gas diffusion layer, or at least over a sufficiently large number of supports, very long measurement times result.

[0005] Measuring the thickness is further complicated and delayed by the fact that the measurement must be carried out under the influence of the mechanical pressure prevailing in the installed state of the gas diffusion layer. This pressure is relatively high, reaching values ​​of over 500 kPa, which, with typical areas of several thousand cm², results in significant delays. 2 Forces exceeding 350 kN can occur.

[0006] Therefore, accurately measuring the thickness of the gas diffusion layer to ensure adequate quality presents a significant challenge. The measurement process causes considerable delays in production and is also technically complex. Consequently, measurements are often performed at the lower end of the required accuracy range, particularly with regard to the measured support points on the gas diffusion layer. This, in turn, leads to high return rates, as the measurement fails to detect local thickness variations, preventing the gas diffusion layer from being installed correctly.

[0007] Therefore, starting from the prior art described above, the object of the invention is to provide a measuring device which enables the measurement of the thickness of a measuring body in a shorter time and with higher accuracy, and which also simplifies the thickness measurement.

[0008] To solve this problem, the invention proposes a measuring device for measuring the thickness of a measuring element, in particular the thickness of a gas diffusion electrode. The measuring device comprises a support body, which in turn has a support surface configured to receive a measuring element. The measuring device further comprises a pressure element, which is movably mounted relative to the support body, in particular translationally movable, and is configured to apply a defined contact pressure to a measuring element received by the support body. The measuring device further comprises a sensor device, which in turn comprises a sensor frame and at least one sensor, configured as a displacement sensor or measuring probe, which is movably arranged on the sensor frame, in particular translationally movable. The measuring device further comprises a control device.The at least one sensor is now configured to detect a position value of a surface at a measuring point along a measuring axis, and the control device is configured to determine the thickness of the measuring body as the difference between a first position value detected on the support surface and a second position value detected on the top of the measuring body, wherein the first position value and the second position value are detected along the same measuring axis.

[0009] By incorporating a support body and a pressure body, which can exert a defined contact pressure on a measuring element held by the support body, the thickness calculated from the difference between the two position values ​​directly represents the functionally relevant installation thickness under operating pressure. Complex conversions from no-load measurements or empirical load corrections are eliminated. This increases process reliability and reduces the scrap rate.

[0010] By enabling the measuring device to detect the position of the support surface and the position of the surface of the measuring body and to determine the thickness from the difference, a particularly fast and efficient measuring method is used.

[0011] Capturing the first and second position values ​​along the same measuring axis eliminates Abbe and cosine errors, as well as angular and parallelism errors between sensor guidance, the contact surface, and the press body kinematics. Since both measurements take place on the same line, the difference corresponds to the perpendicular distance between the contact surface and the top surface at the measuring point, regardless of global zero points or minor tilts of the assembly.

[0012] This approach results in a shorter measurement time and increased measurement accuracy. Furthermore, it provides a particularly simple measuring device.

[0013] The measuring body can be a flat measuring body, i.e., a measuring body whose thickness is significantly smaller, in particular by at least a factor of 10, than its thickness in the two width directions. In particular, the measuring device can be designed to measure the thickness of a gas diffusion electrode (GDL). Unlike compact, largely incompressible measuring bodies, the thickness of a GDL is pressure- and time-dependent (viscoelastic relaxation) due to its porosity and compressibility as well as its hygro- / thermo-dependent state. Furthermore, the GDL has a micro-rough, heterogeneous surface, so that probing forces and lateral shear components can distort the measured values. According to the invention, the GDL is therefore measured under a defined contact pressure, and the thickness is determined as the difference between two position values ​​acquired along the same measuring axis.This differential single-line principle suppresses Abbe / angular errors as well as offset / drift components and delivers the functionally relevant installation thickness. The axial, translational sensor guidance minimizes tapping artifacts and protects the porous structure. This makes the measuring device particularly suitable for GDL in fuel cells / membrane electrolyzers.

[0014] The support body has a contact surface designed to receive the measuring element. This can mean, in particular, that a sufficiently large, flat surface is provided, free of obstacles or local protrusions. Specifically, the contact surface can be designed to ensure largely uninterrupted surface contact between the measuring element and the support surface. The support body has sufficient thickness to keep deformations below a tolerance range, particularly below the measurement resolution of the at least one sensor, even under the load caused by the defined contact pressure. For this purpose, the support body can have a thickness of at least 100 mm, preferably at least 150 mm. Furthermore, the support body can have a width and depth, perpendicular to its thickness and to each other, of at least 450 mm and 600 mm, respectively.The support body can have a cubic shape.

[0015] The support body may, particularly on its contact surface, have means for contact and position fixation.

[0016] The pressing element is mounted in such a way that it is movable relative to the support body. For this purpose, an adjustment device with a corresponding receptacle for the pressing element may be provided. In particular, the pressing element is mounted so that it is translationally movable relative to the support body. This can mean that only translational movement with one degree of freedom relative to the support body is possible. Specifically, the translational degree of freedom can be aligned vertically, i.e., essentially along the axis of gravitational acceleration, in the intended state of the measuring device. This prevents distortions of the measurement caused by gravitational forces.

[0017] The pressing element is also designed to apply a defined contact pressure to a measuring element held by the support body. This can mean that the pressing element applies and maintains a predetermined pressure setpoint, preferably within a predefined tolerance window, to the measuring element held by the support body during the acquisition of the second position value. The pressure can be generated by force control (force / effective contact area) or by displacement control with force monitoring. The pressing element can be designed and / or arranged in the measuring device such that it can be moved from a starting position, in which it is clearly raised from the support surface, down to the support surface.In particular, it may be provided that the pressing body is arranged such that a measuring body received from the support surface is located between the support surface and a lower underside surface of the pressing body.

[0018] A displacement sensor, also known as a position sensor, is a sensor that detects the linear position or change in position of a moving sensor element or the distance to a surface along a measuring axis and provides this as a position value. The measuring principle can be tactile (e.g., plunger / spindle) or non-contact. In particular, a displacement sensor can be a linear potentiometer.

[0019] A measuring probe can refer to a tactile displacement sensor whose spring-mounted probe tip mechanically touches the surface and whose output signal represents the position of the probe tip along the measuring axis.

[0020] The term "measuring axis" refers to the straight-line direction of movement and measurement of the sensor relative to the sensor device or sensor frame, along which the position values ​​are recorded.

[0021] A "position value of a surface at a measuring point" can denote a spatially representative scalar for the location of the measuring point along the measuring axis. The measuring point is the intersection of the measuring axis with the relevant surface; in the case of an area-based measuring field, its geometric centroid is considered the measuring point. The position value can be an absolute coordinate or a distance value relative to a reference defined on the measuring device.

[0022] The phrase "along the same measuring axis" can mean that both measurements (first / second position value) take place on one and the same geometric straight line in space. Parallel offset or tilted axes can be excluded. Deviations within a predefined adjustment or measurement uncertainty tolerance range are disregarded.

[0023] The at least one sensor can be driven, in particular, mechanically and / or pneumatically or hydraulically, for example by an electric motor or a pneumatic / hydraulic piston device, especially a linear motor. For this purpose, the control device can actuate a corresponding adjustment unit of the at least one sensor. If the measuring device has more than one sensor, each sensor can be adjustable independently of the other sensors, in particular by mechanical and / or pneumatic actuation. In this case, the control device is configured to actuate the respective adjustment units separately.

[0024] To increase the precision of the adjustment of at least one sensor, a gearbox, in particular a reduction gearbox, may be provided.

[0025] According to a further feature of the invention, the press body has at least one, preferably one for each sensor, through-opening, wherein the measuring axis of the at least one sensor passes through the at least one through-opening.

[0026] This method makes it particularly easy to ensure that the defined contact pressure is present within the measuring range while at least one sensor is measuring the second position value. This increases measurement accuracy and simplifies the measuring device. Furthermore, the measuring speed is also increased, as the contact pressure and approach movement can occur simultaneously or at least overlapping.

[0027] The through-hole completely penetrates the press body, meaning that a connection exists between two opposite sides of the press body in the area of ​​the through-hole. A blind hole is therefore not a through-hole.

[0028] According to a further feature of the invention, the through-opening is designed to accommodate the sensor or a part of the sensor, in particular a stylus tip, a stylus and / or a sensor head of the sensor.

[0029] This allows the second position value to be recorded under applied pressure without having to reset the press body. This simplifies the device and increases measuring accuracy and speed.

[0030] The through-hole can, in particular, have a cross-section that is larger over its entire height than the largest cross-section of the at least one sensor. The "largest cross-section of the at least one sensor" can refer only to the part of the sensor that is to be accommodated by the through-hole. This is particularly the case if the sensor has a greater height than the thickness of the pressed body. The through-hole can have an internal cross-section over its entire length that is larger than the relevant external cross-section of the sensor section to be accommodated. An additional radial clearance can also be provided.

[0031] Preferably, the through-hole is cylindrical or stepped and aligned concentrically to the measuring axis (A); chamfers and / or radii on the edges can prevent edge contact of the sensor. Alternatively, the through-hole can be designed as a slot opening, with the vertical axis of the slot running parallel to the sensor's movement. Preferably, the coaxiality between the measuring axis (A) and the through-hole is maintained within a predetermined tolerance range, in particular ≤ 0.2 mm and / or ≤ 1 degree relative to the effective length of the opening. Preferably, a mechanical stop can be provided to limit the maximum permissible immersion stroke of the sensor into the through-hole.

[0032] According to a further feature of the invention, the sensor frame is arranged on a part of the support body and is preferably fixedly connected to it.

[0033] By positioning the sensor frame on a portion of the support body, the reference for thickness determination, particularly the support surface, remains in a constant position relative to the sensor frame during measurement. Simultaneously, the sensor frame is mechanically decoupled from the force-applying pressing body, preventing force applications, bending, or micro-movements of the pressing body from affecting the sensor. This improves measurement stability and repeatability and reduces geometric errors, especially angle effects, during the measurement period.

[0034] “Arranged on a part of the support body” can mean that the sensor frame is attached to a structural region of the support body, in particular the support surface, a side wall and / or a projection or rib of the support body, and that the measuring positions of the sensors result from this arrangement.

[0035] "Fixed connection" refers to a positionally and orientationally stable connection without any remaining kinematic degrees of freedom relative to the support body for measurement operation. Only elastic compliances within a specified tolerance range are permissible.

[0036] Preferably, the sensor frame is flush-mounted to the support body via locating surfaces and dowel pins, as well as screw connections, ensuring positional and rotational stability to enable reproducible reassembly. Additionally or alternatively, the sensor frame can be securely attached to the support body via a magnetic connection, also ensuring positional and rotational stability.

[0037] Preferably, the sensor frame is made of the same material or has a similar coefficient of thermal expansion as the support body in order to minimize thermally induced relative movements between the support surface and the sensor.

[0038] Preferably, the sensor frame is arranged on a lateral or lower region of the support body, so that the press body can be moved unhindered onto the measuring body. Alternatively, the sensor frame can be positively and force-fittedly connected to the support body via a rigid bracket, whereby the coaxiality between the sensor axes and the associated through-holes is maintained within a predetermined tolerance range.

[0039] According to a further feature of the invention, the measuring device is designed to determine the thickness of the measuring body under the influence of the defined contact pressure.

[0040] By determining the thickness under the influence of the defined contact pressure, the measuring device directly obtains the functionally relevant installation thickness. Calibration or conversion factors for idling measurements are eliminated; at the same time, time-dependent relaxation and settling effects of the measuring body are taken into account. This increases measurement accuracy and repeatability and reduces cycle time, as pressing and measuring can be performed simultaneously or overlapping.

[0041] "...determining the thickness ... under the influence of the defined contact pressure" can mean that the second position value is acquired on the top of the measuring body during a predetermined pressure window, which is set and maintained by the pressing body. The thickness is calculated from the difference between the position value previously acquired on the contact surface and the position value acquired under applied contact pressure along the same measuring axis.

[0042] Determining the thickness under contact pressure requires that the sensor's measuring path to the measuring point remains unobstructed while pressure is applied, and that the measurement is linked to the pressure condition. Openings that do not functionally serve the measuring path, or where measurement occurs without applied contact pressure, do not perform the determination according to the invention.

[0043] Preferably, the measuring device includes means for pressure or force control, in particular a force sensor in the force flow of the pressing body and / or a pressure sensor of a pneumatic / hydraulic drive unit, wherein the control device regulates the contact pressure within a tolerance range and keeps it constant during the acquisition of the second position value.

[0044] Preferably, the control device only performs the detection of the second position value if the contact pressure is within the specified window and, furthermore, preferably, a minimum dwell time has elapsed since reaching the window.

[0045] Preferably, the acquisition of the second position value can overlap with the adjustment of the contact pressure as soon as the pressure window is reached, thereby reducing the measurement time. This can particularly apply to the approach path of the sensor towards the surface of the measuring body.

[0046] Preferably a measuring channel is provided along the measuring axis, in particular a through-opening in the press body and / or a measuring window, which enables the sensor to make an unobstructed measurement at the measuring point during the application of pressure.

[0047] It may also be provided that, to determine the second position value, several samples within the print window are captured and averaged in order to suppress noise and micro-movements.

[0048] According to a further feature of the invention, the sensor frame is provided to be force-decoupled from the pressing body.

[0049] Due to the force decoupling of the sensor frame from the press body, the forces generated during the adjustment and maintenance of the contact pressure do not pass through the sensor. Elastic deflections, micro-movements, and vibrations of the press body do not affect the measured values, which improves the repeatability, long-term stability, and zero-point stability of the differential measurement. This makes the measurement faster and more accurate, and results in a simplified measurement setup.

[0050] "Force-decoupled" here can mean that during measurement operation there is no force-conducting connection between the pressing body and the sensor frame, and / or that no statically effective force path of the forces introduced by the pressing body passes through the sensor frame. Only position-guiding, non-force-bearing elements or contacts within a specified tolerance range for transverse forces are permissible.

[0051] Preferably, there is a gap between the press body and the sensor frame so that no contact surfaces exist under load. Preferably, the sensor frame is attached exclusively to the support body and / or its base plate, without any connecting elements to the press body. Preferably, alignment / fitting devices (e.g., dowel pins) are arranged so that they only secure the position and do not transmit any operating forces. Preferably, the sensor cables / hoses are routed so that they are not in the force path between the press body and the sensor frame.

[0052] According to a further feature of the invention, it is provided that the at least one measuring axis is essentially normal to the support surface.

[0053] Due to the essentially normal alignment of the measuring axis to the support surface, the thickness is measured directly in the normal direction without cosine errors. Angular and parallelism deviations thus have a minimized impact on the difference result of the thickness determination. Repeatability and measurement accuracy increase, especially with small thicknesses and high contact pressures.

[0054] "Essentially normal" means that the measuring axis exhibits an angular deviation of 90° relative to the local tangent plane of the support surface only within a predetermined limit, preferably less than 2°, and more preferably less than 1°. Deviations within the adjustment and measurement uncertainty range are disregarded.

[0055] Preferably, the measuring axis (A) runs parallel to the direction of action of the pressing body. Preferably, the through-holes of the pressing body are aligned coaxially with the respective measuring axis within a predetermined tolerance range.

[0056] According to a further feature of the invention, it is provided that the support body is hardened on its support surface, in particular plasma nitrided, ground and polished.

[0057] A hardened, especially plasma-nitrided, ground and polished, contact surface forms a stable, low-wear reference with low roughness and high dimensional accuracy. This prevents any significant indentations or micro-displacements under contact pressure. The zero level remains constant over many cycles, reducing the scatter and drift of the thickness measurement and increasing repeatability.

[0058] Preferably, plasma nitriding is carried out at ≤ 520 °C. The compound layer ("white layer") can be thin, preferably less than or equal to 10 µm. More preferably, or alternatively, the compound layer can subsequently be peeled off and / or polished. The nitrogen diffusion zone can have a sufficient depth, particularly in the range of 0.1–0.5 mm.

[0059] Preferably, the nitrided surface layer achieves a microhardness ≥ 900 HV0.1. The bearing surface can have a roughness of Ra ≤ 0.05–0.10 µm, particularly by grinding and / or polishing. The bearing surface can have a flatness of ≤ 5 µm with respect to the effective measuring area.

[0060] According to a further feature of the invention, it is provided that the press body is arranged on a press ram of a forming press, preferably in such a way that the defined contact pressure is generated by means of the press ram.

[0061] By positioning the press body on a press ram of a forming press, a rigid and precisely guided drive unit designed for high forces is available. The defined contact pressure can be set and maintained evenly and reproducibly. The stroke, installation space, and clamping options of the press allow for robust, series-production-ready implementation with short cycle times.

[0062] “Forming press” refers to a press for the plastic forming of workpieces, comprising in particular a stand / frame, a moving press ram and a counter support, whereby the drive type can be mechanical, hydraulic or servo-electric and the press is designed to apply large process forces.

[0063] "Press ram" refers to the moving, force-applying pressing element or the attached tool part that moves in the direction of action towards the counter-surface and applies the pressing pressure. The tool part can be the press body. "...arranged on a press ram" means that the press body is attached to the press ram in a positionally and orientationally stable manner, for example via an adapter / support plate, T-slots, and / or fittings, so that the press body directly absorbs the movement and force of the press ram. It can also mean that the press ram itself provides the press body.

[0064] Preferably, the press body is securely attached to the press ram via an adapter plate with dowel pins and screw connections to ensure positional and rotational stability and reproducible alignment relative to the support surface. Preferably, the direction of action of the press ram is collinear with the measuring axis. Preferably, the press control can be configured to regulate the contact pressure within a pressure window and maintain it during the acquisition of the second position value.

[0065] According to a further feature of the invention, the measuring device is designed to apply a contact pressure of at least 0.4 N / mm². 2 , preferably at least 0.5 N / mm 2 , preferably of at least 0.55 N / mm 2 , preferably of at least 0.6 N / mm 2 to produce.

[0066] The inventors have surprisingly discovered that by designing for such a contact pressure, the thickness is determined under a load at which the microscopic contact and pore structure of the measuring body, particularly in the case of porous / compressible materials such as GDLs, has largely settled. In this range, the remaining pressure dependence of the measured quantity (∂t / ∂p) is small, so that the measured thickness represents the functionally relevant installation thickness with low scatter. Conventional measuring devices with point-source probing force or low surface pressures do not achieve this state over a large area, or only inhomogeneously. This leads to cosine, contact, and settling errors, as well as increased relaxation artifacts. In contrast, the pressure limit according to the invention ensures that the contact area is saturated and the local stiffness is stable, thereby increasing reproducibility and comparability between measuring points and batches.

[0067] The contact pressure can be applied to a pressure area, i.e., the area on which the total pressure is exerted, of at least 100,000 mm². 2 or 1000 cm 2 relate.

[0068] Preferably, the pressure homogeneity in the measuring area is maintained within a relative band, for example ± 5%, during the measurement, so that all measuring points are subjected to the same load.

[0069] According to a further feature of the invention, the measuring device is designed to accommodate a measuring body with a first dimension of at least 400 mm and a second dimension of at least 350 mm lying orthogonal to the first dimension, wherein the first dimension and the second dimension are measured in the plane of the support surface.

[0070] The design for accommodating large-format measuring specimens of such dimensions enables thickness determination on the full-size component under uniform contact pressure. Compared to conventional measuring devices designed for small samples, edge and sample-cutting artifacts are avoided. The measurement results are representative of the series production installation condition. At the same time, the large accommodating capacity places increased demands on flatness, stiffness, and pressure homogeneity, which are met according to the invention by the combination of the pressed body and the contact surface, so that high repeatability and measurement accuracy are achieved despite large spans.

[0071] “First extension” / “second extension” denote two mutually orthogonal longitudinal dimensions of the measuring body in the plane of the support surface; they can be understood as the largest enclosing rectangular dimensions (projection dimensions).

[0072] "Capture" can mean that the measuring device enables the measuring body to be fixed in position and support within the specified dimensions, without specifying a particular clamping method.

[0073] Preferably, the pressing body has an effective contact surface whose projection area completely covers the measuring range over the aforementioned dimensions, so that a sufficiently homogeneous surface pressure is achieved.

[0074] Preferably, stop or reference edges are provided on which the measuring body can be positioned with repeatable accuracy along the first and / or second dimension.

[0075] According to a further feature of the invention, the sensor device has a plurality of sensors, in particular at least two, preferably four, more preferably six, each of which can be operated and read independently of one another and are configured to detect a position value of a surface along its own measuring axis at a respective measuring point.

[0076] The multiple independently operable and readable sensors allow for parallel thickness measurement at several points. Combined with the press body, which provides uniform contact pressure across the entire surface, and preferably with through-holes that create a free measuring path along the respective measuring axes, time-consuming repositioning movements and repeat measurements at successively approached points are eliminated. The cycle time decreases approximately proportionally to the number of sensors, while comparability and reproducibility increase because all measuring points are recorded under the same pressure. Such parallelization is generally not achievable in the prior art, as it either requires a single sensor to be moved serially or separate guides and pressing devices for each measuring point.

[0077] "Independently operable and readable" can mean that each sensor can be activated separately, and / or provides its own measurement signal, and / or operates without mechanical coupling to other sensors. Simultaneous (synchronized) or time-delayed readout of the sensors is possible.

[0078] A "dedicated measuring axis at each measuring point" can mean that each sensor measures along a defined straight line that passes through its measuring point. The measuring axis preferably runs coaxially to the corresponding through-opening of the press body.

[0079] Preferably, the sensors are read synchronously as soon as the contact pressure is within a pressure window, so that all measuring points are recorded under identical load conditions. Preferably, the measuring axes of the majority of sensors are parallel to each other and substantially perpendicular to the mounting surface; the associated through-holes are aligned coaxially to the measuring axes within a predetermined tolerance range. Preferably, the sensors are arranged in a grid pattern, particularly rectangular or hexagonal, within the sensor frame, so that area-representative coverage of the measuring range is achieved.

[0080] According to a further feature of the invention, the control device is designed to determine a local thickness and / or a thickness distribution over the measuring body from the position values ​​provided by the majority of sensors for each measuring point.

[0081] The calculated local thickness at each measuring point and the resulting thickness distribution across the measuring body make inhomogeneities (e.g., local thinning / over-thickness, gradients, edge zone effects) clearly visible across the entire surface. Since all measuring points are recorded under the same contact pressure, the local thicknesses are measured simultaneously and are therefore comparable.

[0082] According to a further feature of the invention, the control device is designed to store at least one position value for each existing sensor, at least temporarily, preferably permanently.

[0083] By storing the position values ​​for each sensor, the control device can assign correct value pairs—namely, those of the contact surface and the loaded upper surface—evaluate them in sync with the contact pressure window, and average multiple samples if necessary. This can reduce noise, prevent confusion between measuring points, enable traceability, and allow for subsequent recalculation (e.g., after a calibration update), thereby increasing repeatability and measurement accuracy. Furthermore, measured values ​​can be saved and reused for later quality control.

[0084] The expression "... to be stored at least temporarily, preferably permanently" can mean that the position values ​​are stored in volatile memory (e.g. buffer / ring buffer) at least until the thickness calculation is completed and are preferably stored permanently in non-volatile memory with sensor identification and timestamp.

[0085] According to a further feature of the invention, it is provided that the at least one sensor can detect the position value with a resolution of at most 10 µm, preferably at most 8 µm, more preferably at most 5 µm, and more preferably at most 1 µm.

[0086] This ensures a particularly accurate and efficient measurement.

[0087] According to a further feature of the invention, it is provided that the at least one sensor is a Mitutoyo Linear Gauge LG100-150.

[0088] The inventors have discovered that this special sensor allows for a particularly simple, fast, and accurate measurement of thickness.

[0089] According to a further feature of the invention, the support body is provided to consist of a nitridable tool / or heat-treatable steel, in particular 34CrAINi7-10, 31CrMoV9, X40CrMoV5-1, 1.2709 or 17-4 PH.

[0090] Nitridable tool or heat-treatable steels, after plasma nitriding, exhibit a very hard, wear-resistant surface layer with a tough, load-bearing core and low distortion. This enables the provision of a dimensionally stable, smooth bearing surface under high surface pressure.

[0091] If the bearing body is made of 34CrAlNi7-10 (1.8550) and plasma nitrided, the Al-assisted nitride formation provides a particularly deep, pressure-bearing surface layer with very low distortion, thereby minimizing indentations from the pressing body and maintaining the shape fidelity of the bearing surface over many cycles.

[0092] If the support body is made of 31CrMoV9 (1.8519) and plasma nitrided, the material combines a tough core with a hard, wear-resistant outer layer, so that micro-indentations under load are reduced and the flatness of the support surface is permanently ensured.

[0093] If the support body is made of X40CrMoV5-1 (1.2344 / H13) and plasma nitrided, the high heat strength and tempering resistance of the hot-work steel ensures that the dimensional and shape stability of the support surface is maintained even during thermally stressed measuring cycles and short cycle times.

[0094] If the support body is made of 1.2709 (maraging steel) and low-temperature plasma nitrided after aging, an exceptionally low-distortion, high-load-bearing reference surface is created, which maintains its zero position constantly even with frequent setup and high load cycles.

[0095] If the support body is made of 17-4 PH (1.4542) and low-temperature plasma nitrided, the material combines corrosion-resistant basic strength with a hard, wear-resistant surface layer, so that the surface quality and flatness remain stable in the long term even in humid or chemically stressed environments.

[0096] The invention further proposes a method for measuring the thickness of a measuring body using a measuring device described above. The method comprises the following steps: - Providing a measuring device according to the invention, wherein the measuring device is preferably in a state in which the pressing body exerts a defined contact pressure on the support body, - Detecting, by means of at least one sensor along a measuring axis, and / or providing from a memory of the control device, the first position value at the support surface and storing the first position value by means of the control device, - Arranging a measuring body, preferably a part of the measuring body, on the support surface, - Lowering the pressing body onto the surface of the measuring body, so that a defined contact pressure is applied to the measuring body, - Detecting, by means of at least one sensor, the second position value on the top of the measuring body along the same measuring axis along which the first position value was detected, and storing the second position value, - Determine, using the control device, the thickness of the measuring body by calculating the difference between the first position value and the second position value.

[0097] The method determines the functionally relevant installation thickness under load by calculating the thickness as the difference between two position values ​​acquired along the same measuring axis and coupling the acquisition to a contact pressure window. This geometrically suppresses Abbe, cosine, and parallelism errors, minimizes offset and drift components in the differential signal, and controls viscoelastic effects. At the same time, the cycle time is reduced because no approach to an absolute machine Z-reference is required, and pressing and measuring can be performed simultaneously.

[0098] The procedure may stipulate that the contact pressure is maintained within a predetermined pressure / force window during the acquisition of the first and / or second position value.

[0099] The procedure may stipulate that the recording of the first and / or second position value is only enabled when the pressure / force window is reached.

[0100] Preferably, after reaching the pressure / force window, a minimum dwell time is observed before the first and / or second position value is recorded.

[0101] Preferably, the second position value is formed from several samples recorded within the pressure / force window, in particular as the mean and / or median value.

[0102] Preferably, the thickness is determined as the amount of the difference between the first and second position values.

[0103] The method can provide that the initial position value on the bearing surface is recorded again before each thickness measurement and / or before and after a drift test measurement series. Preferably, however, the initial position value is recorded once during the first execution of the method within a reference period and then permanently stored, so that the initial position value can be retrieved from memory and used for a second and all subsequent thickness measurements. This significantly reduces the measurement time.

[0104] Preferably, the measuring axis is guided collinearly to the direction of action of the pressing body.

[0105] The method can provide for the synchronous reading of multiple sensors and the determination of local thickness values ​​and / or a thickness distribution from the associated position values.

[0106] Preferably, position values ​​are subjected to a plausibility and outlier check; values ​​outside specified limit criteria are discarded or replaced.

[0107] The method can provide that position values ​​with timestamp and contact pressure information are stored, at least temporarily until the thickness calculation, preferably permanently.

[0108] The method can provide that, after an initial measurement, the measuring body is moved a predetermined feed path in the plane of the support surface, and the steps of lowering, holding in the pressure window, and capturing the second position value are repeated multiple times, thus creating a measurement grid of parallel local measurements. Preferably, the reading of the majority of sensors is synchronous, so that several measuring points are captured simultaneously per feed step. This results in a surface-representative thickness distribution with a short cycle time.

[0109] Further advantages and features of the invention will become apparent from the following description with reference to the figures. These show Fig. 1 a measuring device according to the invention in an isometric view; Fig. 2 a measuring device according to the invention in a top view; Fig. 3a a measuring device according to the invention in a side view with lowered pressing body; Fig. 3b a measuring device according to the invention in a side view with the pressing body raised; Fig. 4a a measuring device according to the invention in a sectional view; and Fig. 4b a measuring device according to the invention in a sectional view.

[0110] The Fig. Figure 1 shows an isometric view of a measuring device 1 according to the invention. The measuring device 1 serves to measure the thickness of a measuring body 2. This measuring body 2 can be received by a support surface 4, which is provided by a support body 3 of the measuring device 1.

[0111] The measuring device 1 further comprises a press body 5, which in the embodiment shown here is arranged on the press ram of a forming press. The press body 5 is movably arranged with respect to the support body 3 and can be moved along a vertical axis by means of the press ram. Thus, the press body 5 can be pressed onto a measuring body 2 received by the support surface 4, thereby generating a defined contact pressure in the measuring body 2.

[0112] The measuring device 1 further comprises a sensor device 6. This consists of a sensor frame 7, which carries sensors 8 that are also arranged to be laterally movable on the sensor frame 7 and can be moved along a vertical axis.

[0113] The press body 5 has through-openings through which the sensors 8 can at least partially pass.

[0114] The measuring device 1 is further associated with a control device 9, which is shown here only schematically.

[0115] Fig. Figure 2 shows the measuring device 1 in a top view. In the embodiment shown here, the measuring device 1 has a total of six sensors 8a-f, which are arranged in a rectangular pattern.

[0116] As in Fig. 3a and Fig. As can be seen in 3b, the press body 5 can be moved vertically and thereby exert a contact pressure on the measuring body 2.

[0117] Fig. 4a and Fig. Figure 4b shows the measurement process. The sensors 8 are configured to detect a position value of a surface at a measuring point P along a measuring axis A.

[0118] In a first step, the sensors 8 detect an initial position value at a measuring point P on the support surface 4. For this purpose, they protrude through the through-opening 10 of the press body 5. The press body 5 exerts a defined contact pressure on the support surface 4. The initial position value is then stored in the control device 9. If a current initial position value is already stored there, the measuring procedure can, instead of detecting the initial position value, retrieve the initial position value from a memory of the control device 9. The press body 5 is then lifted again.

[0119] A measuring body 2 is then positioned on the support surface 4, and subsequently the pressing body 5 is lowered onto the measuring body 2 and pressed down onto it, so that a defined contact pressure is exerted on the measuring body 2. The sensors 8 then measure a second position value through the through-holes 10, along the same measuring axis A. This second position value is also transmitted to the control device 9 and stored, at least temporarily. The difference between the two position values ​​is then calculated, and the thickness of the measuring body 2 is thus determined. Reference sign 1 measuring device 2 measuring bodies 3 support bodies 4. Support surface 5 press bodies 6 Sensor device 7 Sensor rack 8 Sensor 9 Control device 10 Through opening A measuring axis P measuring point

Claims

[1] Measuring device (1) for measuring the thickness of a measuring body (2), in particular the thickness of a gas diffusion electrode, comprising - a support body (3) having a support surface (4) which is designed to receive a measuring body (2), - a pressing element (5) which is mounted to be movable relative to the support element (3), in particular translationally movable, and is designed to apply a defined contact pressure to a measuring element (2) received by the support element (3), - a sensor device (6) comprising a sensor frame (7) and at least one sensor (8) arranged movably on the sensor frame (7), in particular translationally movable, which is designed as a displacement sensor or measuring probe, - a control device (9), wherein the at least one sensor (8) is configured to detect a position value of a surface at a measuring point (P) along a measuring axis (A), and wherein the control device (9) is configured to determine the thickness of the measuring body (2) as the difference between a first position value detected on the support surface (4) and a second position value detected on the top of the measuring body (2), wherein the first position value and the second position value are detected along the same measuring axis (A). [2] Measuring device (1) according to claim 1, characterized by , that the press body (5) has at least one, preferably one for each sensor (8), through-opening (10), wherein the measuring axis (A) of the at least one sensor (8) passes through the at least one through-opening (10). [3] Measuring device (1) according to claim 2, characterized by, that the through-opening (10) is designed to accommodate the sensor (8) or part of the sensor (8). [4] Measuring device (1) according to one of the preceding claims, characterized by , that the sensor frame (7) is arranged on a part of the support body (3) and is preferably fixedly connected to it. [5] Measuring device (1) according to any one of the preceding claims, characterized by , that the measuring device (1) is designed to determine the thickness of the measuring body (2) under the influence of the defined contact pressure. [6] Measuring device (1) according to one of the preceding claims, characterized by , that the sensor frame (7) is force-decoupled from the press body (5). [7] Measuring device (1) according to one of the preceding claims, characterized by , that at least one measuring axis (A) is essentially normal to the support surface (4). [8] Measuring device (1) according to one of the preceding claims, characterized by, that the support body (3) is hardened on its support surface (4), in particular plasma nitrided, ground and polished. [9] Measuring device (1) according to any one of the preceding claims, characterized by , that the press body (5) is arranged on a press ram of a forming press, preferably in such a way that the defined contact pressure is generated by means of the press ram. [10] Measuring device (1) according to any one of the preceding claims, characterized by , that the measuring device (1) is configured to apply a contact pressure of at least 0.4 N / mm 2 , preferably at least 0.5 N / mm 2 , preferably of at least 0.55 N / mm 2 , preferably of at least 0.6 N / mm 2 to produce. [11] Measuring device (1) according to any one of the preceding claims, characterized by, that the measuring device (1) is configured to accommodate a measuring body (2) with a first dimension of at least 400 mm and a second dimension of at least 350 mm lying orthogonal to the first dimension, wherein the first dimension and the second dimension are measured in the plane of the support surface (4). [12] Measuring device (1) according to any one of the preceding claims, characterized by , that the sensor device (6) has a plurality of sensors (8a, b, c, d, e, f), in particular at least two, preferably four, further preferably six, each of which can be operated and read independently of one another and are configured to detect a position value of a surface at a respective measuring point along its own measuring axis (Aa, b, c, d, e, f). [13] Measuring device (1) according to claim 12, characterized by, that the control device (9) is configured to determine a local thickness and / or a thickness distribution over the measuring body from the position values ​​provided by the majority of sensors (8a, b, c, d, e, f) for each measuring point. [14] Measuring device (1) according to any one of the preceding claims, characterized by , that the control device (9) is configured to store at least one position value for each existing sensor (8a, b, c, d, e, f) at least temporarily, preferably permanently. [15] Measuring device (1) according to any one of the preceding claims, characterized by , that the at least one sensor (8) can detect the position value with a resolution of at most 10 µm, preferably at most 8 µm, further preferably at most 5 µm, further preferably at most 1 µm. [16] Measuring device (1) according to any one of the preceding claims, characterized by, that at least one sensor (8) is a Mitutoyo Linear Gauge LG100-150. [17] Measuring device (1) according to any one of the preceding claims, characterized by , that the support body (3) is made of a nitridable tool / or heat-treatable steel, in particular 34CrAINi7-10, 31CrMoV9, X40CrMoV5-1, 1.2709 or 17-4 PH.

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