Device for detecting pressure between two objects

Abstract

The invention relates to a device for detecting a pressure between two objects (1) which can abut against each other under the action of a force, comprising a multi-layer measuring membrane (3) which can be inserted into a butt seam between the two objects (1) and which has a sensor layer (4), the sensor layer has an electrical characteristic that varies as a function of pressure between two electrically conductive layers (5) connected to an evaluation circuit (6). In order to improve the measurement results, it is proposed that two measuring films (3) which lie one on top of the other with an electrically insulating barrier layer (9) therebetween form a measuring insert (2) which can be inserted into the butt seam, and that the two measuring films (3) are each connected to an evaluation circuit (6) which comprises a signal processing unit (11), the signal processing unit combines the measurement signals of the two measurement membranes (3) into a measurement result according to a predetermined algorithm.

Description

Technical Field

[0001] The invention relates to a device for detecting the pressure between two objects that can be brought together under the action of a force, the device comprising a multilayer measuring membrane that can be inserted into a joint between the two objects and that has a sensor layer with electrical properties that vary as a function of pressure between two electrically conductive layers that are connected to an evaluation circuit. Background Art

[0002] To detect the clamping force of a disc or drum brake, it is known (AT 524 872 B1) to introduce a multilayer measuring membrane composed of a sensor layer with pressure-dependent electrical properties between the brake body and the brake rotor. With the help of two conductive layers, the pressure-dependent electrical measurement signal of the sensor layer is tapped and fed to an evaluation circuit, where the resulting clamping force is determined based on the known pressure dependence of the electrical measurement signal. Due to the inevitable local inhomogeneities in the pressure dependence of the sensor layer's electrical properties, measurement errors are to be expected. Furthermore, measurement errors can occur if the measuring membrane is unevenly loaded across its measuring surface.

[0003] In order to take measurement errors into account, it is known (AT 524 872 B1) to provide a measuring membrane for distributing a determined clamping force to the surface of a sensor layer exposed to the corresponding pressure application, with two electrode layers connected to an evaluation circuit for determining the membrane capacitance between the electrode layers. If the brake body does not act on the entire surface of the brake rotor of a disc or drum brake, different distances occur between the brake body and the brake rotor, which influences the capacitance of the measuring membrane sandwiched between the brake body and the brake rotor. Therefore, the contact surface can be determined by a corresponding capacitance measurement, so that the clamping force detected using the sensor layer can be associated with this contact surface.

[0004] However, the additional capacitance measurement has no influence on irregularities occurring in the measurement surface region of the sensor layer with regard to the pressure-dependent electrical properties of the sensor layer. Summary of the Invention

[0005] The object of the present invention is therefore to design a device for detecting the pressure between two objects that can be placed against each other, having a measuring membrane that can be inserted into the joint between the two objects, so that the measurement accuracy can be increased with relatively little design effort.

[0006] Based on a device of the type described at the outset, the present invention solves the problem in that two measuring membranes arranged one above the other with an electrically insulating separating layer between them form a measuring insert that can be inserted into a joint, and the two measuring membranes are each connected to an evaluation circuit, which includes a signal processing unit that combines the measurement signals of the two measuring membranes to form a measurement result according to a predetermined algorithm.

[0007] As a result of these measures, the electrical variable dependent on the pressure to be measured between the two objects is measured independently by the two measuring membranes. Since irregularities in the electrical properties of the sensor are distributed differently across the common measuring surface of the two measuring membranes, the independently recorded electrical measurement signals of the pressure to be recorded can be combined to improve the measurement result. To this end, the measurement signals from the two measuring membranes are compared in a signal processing unit of an evaluation circuit according to a predetermined algorithm, and a measurement result processed according to this algorithm is output. In the simplest case, this algorithm can generate an average value, which already leads to a significant improvement in measurement accuracy.

[0008] Providing a measuring insert with two measuring membranes, which provide independently recorded measurement signals, can also be advantageously used to monitor the functional performance of the measuring insert. If the measurement signals of the two measuring membranes differ from each other by a certain degree, this indicates that at least one of the two measuring membranes is faulty. Therefore, the measurement signals of the two measuring membranes can be compared in an evaluation circuit, and a fault signal can be output if a predetermined difference between the two measurement signals is exceeded.

[0009] As a supplement, at least one of the two measuring membranes can have two electrode layers connected to an evaluation circuit for determining the membrane capacitance between the electrode layers, so that conclusions can be drawn from the membrane capacitance in a manner known per se about the respective contact surface between the two objects pressed against one another, and thus the effective pressure can be determined from the respective contact surface. Since the pressing surfaces of the two measuring membranes coincide when the two measuring membranes are arranged congruently, at least in this case, surface detection of one of the measuring membranes is sufficient. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The subject matter of the invention is illustrated by way of example in the accompanying drawings. In the drawings:

[0011] Figure 1 A schematic block diagram showing an apparatus according to the present invention, and

[0012] Figure 2 A schematic layer structure of a multilayer measuring membrane that can be used according to the invention is shown. DETAILED DESCRIPTION

[0013] In order to detect the pressure acting between two objects 1, according to the invention, a multilayer, membrane-like measuring insert 2 is introduced into the joint between the two objects 1, the measuring insert consisting of two identical, congruent measuring membranes 3 placed one above the other. These multilayer measuring membranes 3 have a sensor layer 4 made of a material whose electrical properties change with the applied pressure, in particular a piezoresistive material, preferably a suitably doped semiconductor, for example based on silicon or germanium or a III-V semiconductor.

[0014] The sensor layers 4 of the two measuring membranes 3 are arranged between two electrically conductive layers 5, via which an electrical measuring voltage is applied to the preferably piezoresistive sensor layer 4. Since the specific resistance of the sensor layer 4 changes with the applied pressure, the pressure load on the sensor layer 4 and, therefore, the magnitude of the applied force, can be inferred from the magnitude of the current flowing through the sensor layer 4 due to the pressure dependence of a given specific resistance. The area of ​​the sensor layer 4 is structurally predetermined and therefore known.

[0015] For evaluating the measurement signals, an evaluation circuit 6 is provided, to which the two measuring membranes 3 are each connected, i.e. according to Figure 1 Via corresponding couplers 7 for signal lines 8 connected to the conductive layer 5, not only the measurement signal can be transmitted to the evaluation circuit 6, but also the energy required for the measuring operation can be transmitted from the evaluation circuit 6 to the measuring membrane 3. The measurement signal can also be transmitted wirelessly to the evaluation circuit 6, which generally results in a separate energy supply being assigned to the measuring insert 2.

[0016] In order to ensure that the two measuring membranes 3 independently measure the pressure acting between the two objects 1, the two measuring membranes 3 must be electrically isolated from each other by an insulating isolation layer 9. Known measuring membranes of this type have two electrically insulating cover layers 10, such as Figure 2 When two conventional measuring membranes 3 are used for the measuring insert 2 according to the invention, the two inner cover layers 10 adjacent to one another (in this case forming a two-layered insulating layer 9 ) can advantageously be replaced by a common single-layer insulating layer 9 .

[0017] Due to these design measures, the pressure present between the two objects 1 is recorded independently of one another by the two measuring membranes 3, so that the measurement signals from these measuring membranes 3 can be linked to one another to obtain a measurement result, in particular to compensate for irregularities in the structure of the sensor layer 4. For this purpose, the evaluation circuit 6 includes a signal processing unit 11, in which the measurement values ​​recorded by the two measuring membranes 3 are calculated according to a predetermined algorithm in order to be able to output an improved measurement result and forward it to, for example, a display 12.

[0018] If in certain cases the applied pressure is not expected to be uniformly distributed over the measuring surface of the measuring insert 2 , a capacitance measurement can additionally be performed to estimate the dimensions of the surfaces of the two measuring membranes 3 exposed to pressure. Figure 2 In at least one of the two measuring membranes 3, two electrode layers 13 are provided, covering the conductive layer 5 with an insulating layer 14 between them. Since the membrane capacitance depends on the respective area over which the pressure is transmitted between the two objects 1, this capacitance measurement can be used to determine the proportion of the area of ​​the sensor layer 4 exposed to the applied pressure caused by the applied force, which allows the determined force to be associated with the area of ​​the sensor layer 4 exposed to the respective application of pressure.

[0019] For the additional capacitance measurement, it is not necessary to provide two separate electrode layers 13, since one of the conductive layers 5 can also serve as an electrode layer for the capacitance measurement. The additional capacitance measurement does not increase the processing effort. The additional construction effort required by the electrode layer 13 and its connecting lines 15 is also kept low. It is only necessary to ensure that the pressure-exposed area ratio detectable based on the capacitance measurement is appropriately taken into account when calculating the measurement result. If both measuring membranes are provided with electrode layers for separate capacitance measurements, errors in determining the pressure-exposed area ratio can still be compensated, but this generally has no significant impact on the measurement result.

[0020] Although the exemplary embodiment provides two identical, congruently stacked measuring membranes 3, which simplifies the construction and measurement conditions, arrangements of the measuring membranes offset from one another are also conceivable. In this case, the shared measuring surface of the two measuring membranes is crucial for comparing the measurement results. By appropriately adjusting the algorithm, non-identical measuring membranes can also be used.

Claims

1. A device for detecting the pressure between two objects (1) that can be brought into contact with one another under the action of a force, the device comprising a multilayer measuring membrane (3) that can be inserted into a butt joint between the two objects (1), the multilayer measuring membrane comprising a sensor layer (4) having electrical properties that vary depending on the pressure between two conductive layers (5) connected to an evaluation circuit (6), characterized in that Two measuring membranes (3) placed one above the other with an electrically insulating separating layer (9) between them form a measuring insert (2) which can be inserted into a joint, and the two measuring membranes (3) are each connected to an evaluation circuit (6), which includes a signal processing unit (11) which combines the measurement signals of the two measuring membranes (3) into a measurement result according to a predetermined algorithm.

2. The device according to claim 1, characterized in that At least one of the two measuring membranes (3) has two electrode layers (13) connected to an evaluation circuit (6) for determining the membrane capacitance between the electrode layers (13).

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