A device for detecting pressure between two objects

Abstract

The present invention describes a device for detecting the pressure between two objects (1) that can be pressed together under the action of a force by means of a multi-layer measuring sheet (3) that can be introduced into the butt joint between the two objects (1), the multi-layer measuring sheet having a sensor layer (4) with pressure-dependent electrical properties between two conductive layers (5) connected to an evaluation circuit (6). To improve the measurement result, it is proposed that two measuring sheets (3) arranged one above the other via an electrically insulating separating layer (9) constitute a measuring insert (2) that can be introduced into the butt joint, and that both measuring sheets (3) are each individually connected to an evaluation circuit (6) that has a signal processing unit (11) that correlates the measurement signals of both measuring sheets (3) to 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 pressed together under the action of a force by means of a multi-layer measuring sheet that can be introduced into the butt joint between the two objects, the multi-layer measuring sheet comprising a sensor layer between two conductive layers connected to an evaluation circuit and having an electrical property that varies depending on the pressure. [Background technology]

[0002] To detect the clamping force of a disc or drum brake, it is known to install a multi-layer measuring sheet between the brake body and the brake rotor, consisting of a sensor layer whose electrical properties vary depending on the pressure (Australian Patent No. 524872). The pressure-dependent electrical measurement signal of the sensor layer is picked up by two conductive layers and fed to an evaluation circuit, which determines the clamping force based on the known pressure dependence of the electrical measurement signal. Due to unavoidable local irregularities in the sensor layer with respect to the pressure dependence of its electrical properties, measurement errors are to be expected. Additionally, measurement errors can occur if the measuring sheet is not evenly loaded across its measurement surface.

[0003] To take measurement errors into account, it is known to provide a measuring sheet for allocating a specific clamping force to the respective pressure-exposed surfaces of the sensor layer with two electrode layers connected to an evaluation circuit for determining the sheet capacitance between the electrode layers (AU Patent No. 524872).If the brake body does not act on the brake rotor of a disc or drum brake over its entire surface, different distances arise between the brake body and the brake rotor, which distances affect the capacitance of the measuring sheet clamped between the brake body and the brake rotor.By corresponding capacitance measurements, the contact surface can additionally be determined and the clamping force detected by the sensor layer can be related to this contact surface.

[0004] However, the additional capacitance measurement does not affect the irregularities in the pressure-dependent electrical properties of the sensor layer that occur in the region of the measurement surface of the sensor layer. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Austrian Patent Invention No. 524872 Summary of the Invention [Problem to be solved by the invention]

[0006] The problem underlying the present invention is therefore to design a device for detecting the pressure between two objects that can be pressed against one another by means of a measuring sheet that can be introduced into the butt joint between the two objects in such a way that the measurement accuracy can be improved with relatively few structural changes. [Means for solving the problem]

[0007] Based on the device of the type mentioned at the beginning, the present invention solves the problem posed by the fact that two measuring sheets arranged one above the other via an electrically insulating separating layer constitute a measuring insert that can be introduced into the butt joint, and that both measuring sheets are each connected separately to an evaluation circuit which has a signal processing unit that correlates the measurement signals of both measuring sheets to a measurement result according to a predefined algorithm.

[0008] As a result of this configuration, the electrical quantities that depend on the pressure between the two objects to be measured are measured independently by the two measuring sheets, and due to the fact that irregularities in the electrical properties of the sensor layers of the two measuring sheets are distributed differently across the measuring surface common to both measuring sheets, the independently detected electrical measurement signals related to the pressure to be detected can be correlated with each other in order to improve the measurement result. For this purpose, the measurement signals of the two measuring sheets are compared in a signal processing unit of the evaluation circuit according to a predetermined algorithm, and a measurement result processed according to this algorithm is output. In the simplest case, the algorithm can result in averaging, which already leads to a significant improvement in the measurement accuracy.

[0009] The provision of a measuring insert with two measuring sheets that provide measurement signals detected independently of each other can also be advantageously used to monitor the functionality of the measuring insert. If the measurement signals of the two measuring sheets differ from each other by more than a predetermined amount, this means that at least one of the measuring sheets is defective. Therefore, the measurement signals of the two measuring sheets can be compared in an evaluation circuit, and an error signal can be output if the difference between the two measurement signals exceeds a predetermined value.

[0010] Additionally, at least one of the measuring sheets can have two electrode layers connected to an evaluation circuit for determining the sheet capacitance between these electrode layers, so that the respective contact areas between the two objects pressed against each other can be deduced from the sheet capacitance in a manner known per se, and thus the effective pressure, which depends on the respective contact areas, can be determined.When the measuring sheets are arranged flush with each other, the contact areas of the two measuring sheets coincide, so that, at least in this case, it is sufficient to detect the surface of one of the measuring sheets.

[0011] The drawings show exemplary diagrams of the subject matter of the invention. [Brief explanation of the drawings]

[0012] [Figure 1] Schematic block diagram of an apparatus according to the present invention [Figure 2] Schematic layer structure of a multi-layer measuring sheet that can be used according to the invention DETAILED DESCRIPTION OF THE INVENTION

[0013] To detect the pressure acting between two objects 1, according to the invention, a multi-layer sheet-like measuring insert 2 is introduced into the butt joint between the two objects 1, which measuring insert consists of two identical measuring sheets 3 arranged flush one above the other. The multi-layer measuring sheets 3 comprise a sensor layer 4 made of a material whose electrical properties change depending on the applied pressure, in particular a piezoresistive material, preferably a suitably doped semiconductor, for example a silicon-based or germanium-based or III-V semiconductor.

[0014] The sensor layer 4 of both measuring sheets 3 is arranged between two conductive layers 5, via which an electrical measurement voltage is applied to the preferably piezoresistive sensor layer 4. Since the specific electrical resistance of the sensor layer 4 changes with applied pressure, the pressure load on the sensor layer 4, and therefore the magnitude of the acting force, can be deduced from the magnitude of the current flowing through the sensor layer 4 based on the given pressure dependence of the specific electrical resistance. The area of ​​the sensor layer 4 is predetermined by design and is therefore known.

[0015] For evaluating the measurement signals, an evaluation circuit 6 is provided, to which both measuring sheets 3 are individually connected, and according to Fig. 1 via corresponding couplings 7 for signal lines 8 connected to the conductive layers 5, via which not only can the measurement signals be transmitted to the evaluation circuit 6 but also the energy required for the measurement operation can be transmitted from the evaluation circuit 6 to the measuring sheets 3. However, the measurement signals can also be transmitted wirelessly to the evaluation circuit 6, which normally involves a separate power supply assigned to the measuring inserts 2.

[0016] To ensure that the pressure acting between the two objects 1 is measured independently by the two measuring sheets 3, the two measuring sheets 3 must be electrically separated from one another by an insulating separating layer 9. Known measuring sheets of this type comprise two electrically insulating cover layers 10, as shown in Figure 2. The two inner cover layers 10 which are located adjacent to one another when using two conventional measuring sheets 3 for the measuring insert 2 according to the invention constitute two separating layers 9 in this case, but can advantageously be replaced by one common single separating layer 9.

[0017] As a result of these design measures, the pressure acting between the two objects 1 is detected by the two measuring sheets 3 independently of one another, so that the measurement signals of these measuring sheets 3 can be correlated with one another to obtain measurement results that compensate, in particular, for irregularities in the structure of the sensor layer 4. For this purpose, the evaluation circuit 6 has a signal processing unit 11 in which the measured values ​​detected by the two measuring sheets 3 are calculated according to a predetermined algorithm in order to output an improved measurement result that can be transmitted, for example, to a display 12.

[0018] If it is expected that the applied pressure will not be distributed evenly over the measuring surface of the measuring insert 2, additional capacitance measurements can be carried out to estimate the area of ​​each of the two measuring sheets 3 that is exposed to the pressure action. For this purpose, according to Fig. 2, at least one of the two measuring sheets 3 is provided with two electrode layers 13, which cover the conductive layer 5 via an insulating layer 14. Since the sheet capacitance depends on the respective areas through which the pressure is transmitted between the two objects 1, such capacitance measurements make it possible to estimate the area proportion of the sensor layer 4 that is exposed to the applied pressure due to the acting force, and thus to assign the specified force to the surface of each of the sensor layers 4 that is exposed to the pressure action.

[0019] The additional capacitance measurement, which does not necessarily require two separate electrode layers 13, does not increase the cost of installation, since one of the conductive layers 5 can also be used as an electrode layer for the capacitance measurement. The additional construction costs due to the electrode layers 13 and their connecting lines 15 also remain low. It is only necessary to ensure that the area proportion subjected to pressure load, which can be detected based on the capacitance measurement, is taken into account accordingly when calculating the measurement result. If both measuring sheets are provided with electrode layers for the capacitance measurement that are separated from each other, error compensation is also possible with regard to the determination of the area proportion subjected to pressure load, but this generally does not have a significant effect on the measurement result.

[0020] According to the present embodiment, two identical measurement sheets 3 are provided, which are arranged one above the other and are flush with each other, which results in simple construction and measurement conditions, but a measurement sheet arrangement offset from one another is also conceivable. In this case, the common measurement area of ​​both measurement sheets is important for the adjustment of the measurement results. In addition, it is also possible to use non-identical measurement sheets by correspondingly adapting the algorithm.

Claims

1. 1. A device for detecting the pressure between two objects (1) which can be pressed together under the action of a force by means of a multi-layer measuring sheet (3) which can be introduced into the butt joint between the two objects (1), the multi-layer measuring sheet comprising a sensor layer (4) between two conductive layers (5) connected to an evaluation circuit (6) and having an electrical characteristic which varies depending on the pressure, 1. A device characterized in that two measuring sheets (3) arranged one above the other via an electrically insulating separating layer (9) constitute a measuring insert (2) that can be introduced into a butt joint, and that both measuring sheets (3) are each individually connected to an evaluation circuit (6), which has a signal processing unit (11) that associates the measurement signals of both measuring sheets (3) with a measurement result according to a predetermined algorithm.

2. 2. The device according to claim 1, wherein at least one of the measuring sheets (3) comprises two electrode layers (13) connected to an evaluation circuit (6) for determining the sheet capacitance between the electrode layers (13).

Images