Measuring arrangement for detecting a relative rotational movement

Abstract

A measuring arrangement for detecting a relative rotational motion is specified, wherein the measuring arrangement detects a force (F) acting on a magnet (20) according to the operating principle of an eddy current brake, wherein the measuring arrangement comprises a magnet (20), means for force detection (15) and / or means for detecting the magnetic field strength (16) and an evaluation unit (AE), wherein the relative rotational speed (v) to an electrically conductive material, the rotational motion (n) and the direction of rotation of a shaft (4) can be determined from the force measurement.

Description

The invention relates to a measuring arrangement for detecting a relative rotational movement according to claim 1.Various measuring arrangements for determining rotational movements or for detecting the rotational speed or speed of a shaft are known. Frequently, switching cams provided on the shaft are used for this purpose (FIG. 2 ).DE 102010042142 A1 discloses a measuring arrangement for optically detecting the rotational movement of a shaft. A disadvantage here is that an optical element has to be fixed on the shaft. Optical systems often cannot be used in harsh environments due to contamination of the optics.DE 102017214166 A1 discloses a rotational speed sensor arrangement which detects switching cams running radially around a shaft by means of Hall sensor elements in order to determine the rotational position. A disadvantage here is that switching cams must necessarily be present on the shaft. In addition, the shape of the cams must be matched to the respective detection system.Measuring arrangements are also known in which, in order to determine the rotational speed, a special cam wheel with switching cams must first be mounted on the shaft in order to then align a rotational speed sensor with it. For this purpose, a cam wheel is inserted onto the shaft and the shaft must be machined accordingly for the cam wheel. Overall, adapting the shaft, mounting a cam wheel on the shaft and aligning the rotational speed sensor is too cumbersome and impractical.It is therefore an object of the invention to provide a measuring arrangement for detecting a relative rotational movement which does not require cams or additional elements to be attached to the shaft.The object is achieved by the features specified in claim 1. Advantageous embodiments of the invention are specified in the dependent claims.The essential idea of the invention is to detect a force with a measuring arrangement which acts on a magnet according to the functional principle of an eddy current brake.The invention is explained in more detail below on the basis of exemplary embodiments with reference to the drawings.They show schematically: FIG. 1 shows a measuring arrangement for optically detecting the rotational movement of a shaft according to the prior art; FIG. 2 shows a shaft whose rotational speed is monitored by a rotational speed sensor; FIG. 3 shows a measuring arrangement according to the invention FIG. 4 shows a measuring arrangement according to the invention with a shaft in a schematic illustration.In the following description of the preferred embodiments, like reference numerals designate like or comparable components.FIG. 1 shows an arrangement for measuring the rotational speed of a shaft 4. A retroreflector 5 is seated on the end face 3 of the shaft 4, that is to say in the axis of rotation. A reflected light barrier 1, hereinafter a reflected light barrier, which has a polarizer 8 and an analyzer 9, is partially shown in exploded illustration for improved understanding. The polarizer 8 and the analyzer 9 are of course located inside the apparatus. The unpolarized light 2 of a transmitting diode is first collimated and linearly polarized by the polarizer 8. The linearly polarized light 2 impinges on the retroreflector 5. It now passes through the analyzer 9, which likewise belongs to the reflected light barrier, and is focused on the receiver. Because of the above-explained properties of the retroreflector 5, the signal experiences an amplitude modulation upon rotation of the shaft 4. The switching point of the reflected light barrier 1 is set such that at least one switching change per revolution takes place. With optimum setting, the above-mentioned reflex film produces switching changes during one revolution. The reflected light barrier 1 does not have to be aligned exactly in the axis of rotation. It is sufficient if it is situated at the angle of acceptance of the retroreflector 5.FIG. 2 shows a shaft 4 whose rotational speed n is monitored by a sensor 11. A metallic element is fixed to the shaft 4 and has at least one lug or a switching cam 13, which generates corresponding pulses when the shaft 4 moves, which pulses are evaluated in a speed monitor 11, for example the DI6004 of the ifm group. The speed monitor 11 is connected via an IO link to a higher-order unit PLC. From the time t between the damping, the rotational speed n is calculated and output by the sensor 11. Advantageously, at least one damping element 13 is required on the rotating shaft.FIG. 3 shows a measuring arrangement according to the invention for detecting a relative rotational movement with a magnet 20, the measuring arrangement having means for force detection 15 and / or means for detecting the magnetic field strength 16, which are connected to an evaluation unit AE. According to the invention, no switching cam 13 is required here in order to detect the relative movement of a shaft 4. The shaft 4 is made of an electrically conductive material. The movement n and the direction of movement of the shaft 4 are determined from the direction of the force F which acts on the magnet 20 according to the functional principle of an eddy current brake. Over time t, the force F acting on the magnet 20 is detected. According to the invention, the force F is used to determine the relative rotational speed v with respect to an electrically conductive material and / or the rotational movement n and the rotational direction of the shaft 4. The sensor 11 is connected, for example, via an IO link to transmit the signals or for control to a superordinate unit PLC, or supplies, via a high or low level at a digital switching output, whether the speed is in the desired parameterized setpoint range. The diagram shows the speed curve over time t, which is determined from the force F. The evaluation takes place via the switching point SP. If the rotational speed n exceeds the shift point SP, the digital shift output, which is illustrated in the lower graph, signals the overspeed. If the rotational speed n falls below the switching point SP, the switching output switches off again accordingly. A high / low level is thus output at the digital output, which indicates whether the rotational speed n is in the parameterized setpoint range.FIG. 4 shows a measuring arrangement according to the invention with a shaft 4 in a schematic illustration according to FIG. 3. The sensor 11 according to the invention is used as the detection unit. From the force F, the rotational speed of the movement n and thus the direction of movement of the shaft 4 is determined.The function of the invention is explained in more detail below.If a magnet 20 is moved or rotated relative to an electrically conductive material, eddy currents are produced in this material. These eddy currents in turn generate a further magnetic field. These two magnetic fields produce a force F on a magnet 20 and on the electrically conductive material. The force F counteracts the relative or rotational movement. This force F is also referred to as the Lorentz force. This force F depends on several factors. Among other things, the speed v of the relative or rotational movement. If all other factors are kept constant, the speed v of the relative or rotational movement can be determined from the force F.The invention offers the following advantages over solutions with switching cams 13 or switching lugs: a.) Compared to the determination of the rotational speed via the switching cams 13 and pulses, no special constructive measures or additional components on the shaft 4 are required here. No cam wheel is required. Accordingly, the shaft 4 does not have to be adapted for a cam wheel, for example). When determining the rotational speed via switching cams 13, two sensors 11 are usually required in order to determine the direction of rotation. With the measuring arrangement according to the invention, the direction of rotation is determined directly. A reversal of the direction of rotation also rotates the determined force F.The measuring arrangement is constructed in such a way that it has means for force detection 15 and an evaluation unit AE for evaluation. For force measurement, a sensor element 12 is used, which detects the force F acting on a magnet 20 that arises due to the functional principle of an eddy current brake. From this force F, a measured value is generated which is related to the rotational speed v with respect to an electrically conductive material or to the rotational movement and direction of rotation of a shaft 4. In the case of a shaft 4, a rotational speed n can be deduced therefrom, which is monitored by the measuring arrangement. The detected values are evaluated via the evaluation unit AE and passed on to a superordinate unit PLC.Possible data values which can be detected, evaluated and output by the measuring arrangement are the rotational speed v, the rotational speed n of a shaft 4, the direction of movement or rotation and the rotational speed n or speed v in a desired range.Advantageously, a desired range is monitored by the speed measurement or the speed detection, and a corresponding signal is output when the desired range is exceeded or undershot.In addition to the force F which arises from the eddy current braking effect, the magnet 20 is additionally acted upon by the force of gravity, other acceleration forces and the force of attraction to other magnets, magnetized and unmagnetized articles. The force of gravity or the acceleration forces can either be compensated mechanically or can be calculated out by a second force measurement on an unmagnetized object of the same mass which is also located in the measuring arrangement.According to the invention, a measuring arrangement is provided, having a sensor element 12 and an evaluation unit AE for monitoring the relative speed, which measures the rotational speed n or rotational speed v of an object via the force F, and also via the magnetic field strength, which acts on a magnet 20 in the arrangement by the functional principle of an active current brake. The magnet 20 can be designed as a permanent magnet or as a stimulable coil.Alternatively or additionally to the measurement of the force F on the magnet 20 in the sensor 11, the strength of the magnetic field that arises can be determined, so that the relative rotational speed v to an electrically conductive material or the rotational movement n and rotational direction of a shaft 4 can be detected therefrom.List of reference characters1 Reflected light barrier 2 Light 3 End face 4 Shaft 5 Reflector 8 Polarizer 9 Analyzer 10 Measuring arrangement 11 Sensor 12 Sensor element 13 Switching cam 15 Means for force detection 16 Means for detecting the magnetic field strength 20 Magnet AE Evaluation unit PLC Superordinate unit F Force t Time v Rotational speed n Rotational movement, rotational speed SP Switching pointReferences included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedDE 102010042142 A1

[0003] DE 102017214166 A1

[0004]

Claims

Measuring arrangement for detecting a relative rotational movement, wherein the measuring arrangement detects a force (F) which acts on a magnet (20) according to the functional principle of an eddy current brake, the measuring arrangement has a magnet (20), means for detecting the force (15) and / or means for detecting the magnetic field strength (16) and an evaluation unit (AE), characterized in that the relative rotational speed (v) with respect to an electrically conductive material, the rotational movement (n) and the rotational direction of a shaft (4) can be determined from the force measurement.Measuring arrangement according to Claim 1, characterized in that the magnet is a permanent magnet or a coil.Measuring arrangement according to one of the preceding claims, characterized in that a desired range is monitored with the rotational speed (v) or the rotational movement (n), and a corresponding signal is output if the desired range is exceeded or undershot.Measuring arrangement according to one of the preceding claims, characterized in that a compensation of gravity and / or acceleration forces takes place mechanically or by a second force measurement on a non-magnetic object of the same mass within the measuring arrangement.Measuring arrangement according to one of the preceding claims, characterized in that instead of the force measurement, the strength of the magnetic field which is produced is measured and from this the relative rotational speed (v) to an electrically conductive material or the rotational movement (n) and the rotational direction of a shaft (4) can be determined.

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