Device for detecting pressure forces between two bodies

Abstract

The invention relates to a device for detecting the pressure forces between two bodies (1) that can be brought into contact by applying a force, said device comprising a multilayer measuring sheet (3) which can be inserted into the butt joint between the two bodies (1) and, between two electrically conductive layers (5) connected to an evaluation circuit (6), has a sensor layer (4) with pressure-responsively varying electrical properties. To improve the measurement result, it is proposed for two superposed measuring sheets (3) having an electrically insulating separation layer (9) interposed therebetween to form a measuring insert (2) insertable into the butt joint, and for the two measuring sheets (3) to each be separately connected to the evaluation circuit (6), which comprises a signal processing unit (11) which, in accordance with a predetermined algorithm, combines the measurement signals from the two measuring sheets (3) into a measurement result.

Description

[0001] Device for measuring the pressure forces between two bodies

[0002] Technical area

[0003] The invention relates to a device for detecting the compressive forces between two bodies which can be brought together under the action of force, with a multi-layer measuring film which can be inserted into the butt joint between the two bodies and which has a sensor layer with pressure-dependent changing electrical properties between two electrically conductive layers connected to an evaluation circuit.

[0004] State of the art

[0005] To measure the application forces of disc or drum brakes, it is known (AT 524 872 B1) to insert a multi-layer measuring film consisting of a sensor layer with electrical properties that change depending on the pressure between the brake body and the brake rotor. With the help of two electrically conductive layers, the electrical measurement signal from the sensor layer, which changes depending on the pressure, is tapped and fed to an evaluation circuit in which the application forces that occur are determined based on the known pressure dependence of the electrical measurement signal. Due to unavoidable local irregularities in the sensor layer with regard to the pressure dependence of its electrical properties, measurement errors are to be expected. Measurement errors can also occur if the measuring film is not loaded evenly across its measuring surface.

[0006] In order to take measurement errors into account, it is known (AT 524 872 B1) to provide the measuring foil with two electrode layers connected to the evaluation circuit to determine the foil capacitance between the electrode layers in order to assign the determined application forces to the area of ​​the sensor layer exposed to the respective pressure application. If the brake body does not act on the brake rotor of a disc or drum brake over the entire surface, different distances arise between the brake body and the brake rotor, which influence the capacitance of the measuring foil clamped between the brake body and the brake rotor. With the result that the contact surface can also be determined with a corresponding capacitance measurement in order to relate the application forces recorded using the sensor layer to this contact surface.

[0007] However, an additional capacitance measurement has no influence on irregularities occurring in the area of ​​the measuring surface of the sensor layer with regard to the pressure-dependent electrical properties of the sensor layer.

[0008] Description of the invention

[0009] The invention is therefore based on the object of designing a device for detecting the compressive forces between two bodies which can be placed against one another, with a measuring film which can be inserted into the butt joint between the two bodies, in such a way that the measuring accuracy can be improved with comparatively little design effort.

[0010] Starting from a device of the type described at the outset, the invention achieves the stated object in that two measuring foils arranged one above the other with an electrically insulating separating layer in between form a measuring insert which can be inserted into the butt joint and in that the two measuring foils are each individually connected to the evaluation circuit which comprises a signal processing unit which combines the measuring signals of the two measuring foils into a measuring result according to a predetermined algorithm.

[0011] Because these measures allow the electrical quantities dependent on the compressive forces to be measured between the two bodies to be measured independently of one another by two measuring foils, and because the irregularities in the electrical properties of the sensor layers of the two measuring foils are distributed differently across the measuring surface shared by both measuring foils, the independently recorded electrical measurement signals for the compressive forces to be measured can be linked to improve the measurement result. For this purpose, the measurement signals from the two measuring foils are compared in a signal processing unit of the evaluation circuit according to a predetermined algorithm, and a measurement result processed according to the algorithm is output. In the simplest case, the algorithm can lead to averaging, which already brings about a noticeable improvement in measurement accuracy.

[0012] Providing a measuring insert with two measuring foils that provide independently recorded measurement signals can also be advantageously used to monitor the functionality of the measuring insert. If the measurement signals of the two measuring foils differ by a certain amount, this indicates that at least one of the two measuring foils is faulty. Consequently, the evaluation circuit can compare the measurement signals of the two measuring foils and output an error signal if a specified difference between the two measurement signals is exceeded.

[0013] Additionally, at least one of the two measuring foils can have two electrode layers connected to the evaluation circuit for determining the foil capacitance between the electrode layers. This allows the respective contact area between the two bodies pressed against each other to be determined from the foil capacitance in a conventional manner, and thus the effective compressive forces to be recorded as a function of the respective contact area. Since, when the two measuring foils are arranged congruently, the contact areas for both measuring foils are identical, at least in this case, the area measurement for one of the measuring foils is sufficient.

[0014] Brief description of the invention The drawing shows an example of the subject matter of the invention.

[0015] Fig. 1 shows a device according to the invention in a schematic block diagram and

[0016] Fig. 2 shows a schematic layer structure of a multi-layer measuring film which can be used according to the invention.

[0017] Ways to implement the invention

[0018] To measure the compressive forces acting between two bodies 1, according to the invention, a multilayer, foil-like measuring insert 2 is inserted into the joint between the two bodies 1. The insert consists of two matching measuring foils 3 arranged congruently one above the other. These multilayer measuring foils 3 have a sensor layer 4 made of a material whose electrical properties change with the applied pressure, as is particularly the case with piezoresistive materials, preferably appropriately doped semiconductors, e.g., silicon- or germanium-based or 111 V semiconductors.

[0019] The sensor layer 4 of the two measuring foils 3 is 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 electrical resistance of the sensor layer 4 changes with the applied pressure, the pressure load on the sensor layer 4 and thus the magnitude of the acting forces can be determined from the magnitude of the electrical current flowing through the sensor layer 4 due to the given pressure dependence of the specific electrical resistance. The area of ​​the sensor layer 4 is predetermined by the design and therefore known.

[0020] For evaluating the measurement signals, an evaluation circuit 6 is provided, to which the two measuring foils 3 are each individually connected, specifically as shown in Fig. 1 via corresponding couplings 7 for the signal lines 8 connected to the conductive layers 5. These couplings can be used to transmit not only the measurement signals to the evaluation circuit 6, but also the energy required for measurement operation from the evaluation circuit 6 to the measuring foils 3. However, the measurement signals can also be transmitted wirelessly to the evaluation circuit 6, which typically requires a separate power supply associated with the measuring insert 2.

[0021] To ensure independent measurement of the compressive forces acting between the two bodies 1 by the two measuring foils 3, the two measuring foils 3 must be electrically separated from each other by an insulating separating layer 9. Known measuring foils of this type have two electrically insulating cover layers 10, as shown in Fig. 2. The two adjacent inner cover layers 10, which in this case form a two-layer separating layer 9 when two conventional measuring foils 3 are used for a measuring insert 2 according to the invention, can advantageously be replaced by a common, single-layer separating layer 9.

[0022] Since, due to these design measures, the compressive forces prevailing between the two bodies 1 are detected independently by the two measuring foils 3, the measurement signals from these measuring foils 3 can be linked to obtain a measurement result that, in particular, compensates for irregularities in the structure of the sensor layers 4. For this purpose, the evaluation circuit 6 comprises a signal processing unit 11 in which the measured values ​​detected by the two measuring foils 3 are calculated according to a predetermined algorithm in order to output an improved measurement result and, for example, to forward it to a display 12.

[0023] If, under certain circumstances, it is to be expected that the application pressure will not be distributed evenly across the measuring surface of the measuring insert 2, an additional capacitance measurement can be carried out to estimate the size of the area of ​​the two measuring foils 3 that is each exposed to pressure. For this purpose, as shown in Fig. 2, two electrode layers 13 are provided on at least one of the two measuring foils 3, which cover the electrically conductive layers 5 with an intermediate insulating layer 14. Since the foil capacitance depends on the respective area over which the pressure is transmitted between the two bodies 1, such a capacitance measurement can be used to determine the proportion of the surface of the sensor layer 4 that is exposed to the application pressure due to the acting forces, which allows the determined forces to be assigned to the area of ​​the sensor layer 4 exposed to the respective pressurization.

[0024] The additional capacitance measurement, for which two separate electrode layers 13 do not necessarily have to be provided because one of the electrically conductive layers 5 can also be used as an electrode layer for the capacitance measurement, does not increase the handling effort. The additional design effort required by the electrode layers 13 and their connecting leads 15 also remains low. It is only necessary to ensure that the pressure-loaded area portion that can be determined as a result of the capacitance measurement is taken into account when calculating the measurement result. If both measuring foils are provided with electrode layers for separate capacitance measurements, error compensation can also be made with regard to the determination of the pressure-loaded area portion, although this generally does not have a significant influence on the measurement result.

[0025] Although the exemplary embodiment provides two matching, congruently arranged measuring foils 3, which results in simple design and measurement conditions, a mutually offset measuring foil arrangement is also conceivable. In this case, the measuring surface shared by the two measuring foils determines the comparison of the measurement results. With appropriate adjustment of the algorithm, it is also possible to use non-matching measuring foils.

Claims

Patent claims 1 . Device for detecting the pressure forces between two Force acting bodies (1 ) which can be placed against each other, with a multi-layer measuring film (3) which can be inserted into the butt joint between the two bodies (1 ), which has a sensor layer (4) with pressure-dependent changing electrical Properties between two electrically conductive layers (5) connected to an evaluation circuit (6), characterized in that two measuring films (3) arranged one above the other with an electrically insulating separating layer (9) interposed form a measuring insert (2) which can be inserted into the butt joint, and in that the two measuring films (3) are each connected individually to the evaluation circuit (6), which comprises a signal processing unit (11) which combines the measuring signals of the two measuring films (3) to form a measuring result according to a predetermined algorithm.

2. Device according to claim 1, characterized in that at least one of the two measuring foils (3) has two electrode layers (13) connected to the evaluation circuit (6) for determining the foil capacitance between the electrode layers (13).

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