Device for detecting a rotary movement or setting position on a shaft

Abstract

Device for detecting a rotary movement or setting position of a shaft, with an electrically conductive elastomer element (1) which is connected on one side to a drive pin of the shaft (3), wherein the drive pin is eccentrically connected to the shaft (3) with a first and a second electrical contact (N1, N2) which are electrically conductively applied to at least one outer side of the elastomer element (1), with a third electrical contact (N3) which is arranged within the elastomer element (1) in an electrically conductive manner between the first and second contacts (N1, N2), wherein the shaft (3) and the electrical contacts (N1, N2, N3) are arranged and connected to the elastomer element (1) in such a way that a rotational movement of the shaft (3) leads to a directed deformation of the elastomer element (1) and to a change in resistance between the third contact (N3) and first contact (N1) as well as between the third contact (N3) and second contact (N2).

Description

The invention relates to a device for detecting a rotational movement or setting position of a shaft. Such sensors are particularly suitable for detecting the position of flaps or doors whose opening movement is guided via a shaft.The use of elastomers, such as, for example, silicone switching mats with so-called contact pellet made of carbon or other materials, in order to be able to detect switching processes by inputs of an operator, is fundamentally known from patents EP 2 777 056 B1, EP 2 024 982 B1 and EP 1 878 033 B1. Disadvantages are the partly irregular or abrupt response characteristic and the technology-dependent, poorly definable compression properties.Furthermore, the documents DE 11 2013 004 512 T5, DE 197 44 527 A1 and DE 100 06 089 A1 disclose the use of conductive elastomer elements as pressure sensors, the internal molecular structure or filling technology of which generates a pressure-dependent resistance upon deformation. Disadvantages here are the partly irregular or abrupt response characteristic and the technology-dependent, poorly definable compression properties.WO 2001 / 042 754 A1 describes a tactile sensor (tactile sensor) with a pressure-dependent contact resistance between two conductive workpieces. The sensor is particularly suitable for large contact surfaces, such as for detecting seat occupancy or as impact protection and in connection with the deployment of an airbag. Preferably, it consists of a continuous metal surface and a conductive elastomer piece such as a foam buffer which is contacted by flexible electrodes. When using several electrode pairs, it is suitable for position determination. By measuring transition resistances and their subsequent A / D conversion, applied forces and / or pressures are determined.DE 10 2016 106 651 A1 shows a mechanism for actuating a tailgate for an electric vehicle, which is fastened to a supporting structure by a four-bar linkage arrangement and can be moved between a closed position and an open position.It includes a push-pull element combined with a spring arrangement belonging to the four-joint arrangement. The considerable outlay for the mechanics and the absence of an electrical report signal are considered disadvantageous.DE 10 2013 016 376 A1 shows a device for charging an electric vehicle. Here, a detection unit detecting the position of the tailgate is provided. A Hall sensor is proposed as a sensor, which can be embodied either as a digital sensor or as an analog sensor with an additional threshold value switch. This requires a magnetic transducer, which entails additional material and adjustment complexity. In addition, a pressure exerted on the tailgate is not readily recognizable.EP 2 696 163 A1 describes a displacement sensor comprising a long elastic element and a piezoelectric element. The piezoelectric element is composed of a rectangular piezoelectric film of poly-L-lactic acid stretched at least in one direction and electrodes formed on both major surfaces of the film. The piezoelectric element is attached so that the stretching direction of the film forms an angle of 45° to the longitudinal direction of the elastic element. When the elastic member is bent in the longitudinal direction, the piezoelectric film is stretched and generates a stress. The document further describes various configurations and applications of the sensor including a displacement detection device and an operation device. A disadvantage of the described sensor is that the configuration of the sensor may be complex, especially if additional functionalities such as temperature compensation are required.JP H01-110 203 A describes a rotation angle detecting apparatus using an elongated conductive rubber or elastomer. In the case of torsion, the electrical resistance of the material changes in proportion to the angle of rotation. The device is made of a conductive elastomer having a plurality of electrodes that measure resistance. This construction is simple, cost-effective and space-saving in comparison with conventional rotational angle sensors such as potentiometers or rotary transformers. The sensor can also derive the angle of rotation from the torque. An example shows a cylindrical conductive rubber having a resistance change upon rotation.US 2016 / 0 087 375 A1 discloses a power receiving port device for vehicles. This apparatus includes a power receiving port disposed in a storage space of the vehicle body, and a cover for opening and closing the port. The cover consists of a first and a second cover, which together form a planar cover. During the power supply, these lids prevent movement of a connected supply gun in the direction of its removal. The first cover is moved by rotation and the second by sliding. This configuration ensures that the supply gun is securely fixed during the power supply and cannot be removed.US 2016 / 0 083 981 A1 discloses a control device for opening and closing a vehicle cover. This apparatus controls a cover covering a connection part of a vehicle, and includes a driving unit that moves the cover, an operation posture detecting unit that detects the position of the cover, and a control unit that controls the driving unit based on the connection of the connection part, the detected operation posture, and the on / off state of the vehicle. The control is effected by a signal from an operating element or a remote key. The cover may be adjusted to various positions including fully open, restricted and fully closed positions to provide safety and operation.DE 100 40 069 C2 shows a bending measuring element comprising a mechanically deformable carrier with a plastic surface. A meander-shaped, electrically conductive resistance track of a strain gauge is applied as a foil on this surface. The plastic surface consists of thermoplastic material and the film is directly applied by the hot stamping process. The support may be a membrane or a bending beam. The bending beam can be divided along the central region and have bulges at the ends. The bending measuring element can be used in a rotary angle sensor, wherein the deflectable front end of the bending beam is acted upon by an eccentric or a gear mechanism for bending.DE 29 00 614 A1 discloses a strain gauge load transducer in the form of a parallelogram-shaped arm. The surfaces of the arm to which the strain gauges are attached are concave along the major axis to minimize measurement errors due to load point displacements. The transducer uses four strain gauges electrically connected in a Wheatstone bridge. This construction enables accurate measurements even when the load point is displaced perpendicular to the principal axis. The arm of the transducer can be used in an electronic balance, the concave shape of the surfaces increasing the accuracy of the measurements and reducing measurement errors.DE 10 2019 126 008 A1 shows a tactile position sensor for a tailgate of an electric vehicle. The sensor consists of a first rigid electrode, a second rigid electrode and an electrically conductive elastomer arranged therebetween, which acts as a seal. The elastomer is mechanically prestressed, and the electrical resistance of this arrangement is evaluated in order to identify an operating process. The electrodes are connected to a capacitor which together with the sheet resistor forms a discharge circuit. A microcontroller detects the time constant of this circuit and converts it into a binary switching signal which serves to detect the operating process.DE 10 2019 126 005 A1 discloses a tactile force-displacement sensor for a charging flap of an electric vehicle. The sensor consists of an axle, at least one electrical contact and an electrically conductive elastomer molded part which is mechanically prestressed. The electrical path resistance of this arrangement is evaluated in order to identify an access attempt. An electrical contact is connected to a capacitor which, together with the track resistor, forms a discharge circuit. The time constant of this circuit is detected and converted into a switching signal which serves to detect the operation. The sensor can detect obstacles and trapping situations and can be flexibly adapted to different types of tailgates.It is an object of the present invention to provide a cost-effective solution for detecting a mechanical actuating position which obviates the known disadvantages. In addition, the solution should be as trouble-proof and robust as possible, should have as few interactions as possible with other sensor principles, and should be flexibly adaptable to different designs of flaps or doors or should be integratable into their drive mechanism.The object is achieved by the device of the independent claims.Advantageously, a device for detecting a rotational movement or adjustment position on a shaft is provided, having an electrically conductive elastomer element which is connected on one side to a drive pin of the shaft, wherein the drive pin is eccentrically connected to the shaft, having a first and a second electrical contact which bear electrically conductively at least on an outer side of the elastomer element, having a third electrical contact which is arranged within the elastomer element in an electrically conductive manner between the first and second contacts, wherein the shaft and the electrical contacts are arranged and connected to the elastomer element in such a way that a rotational movement of the shaft leads to a directed deformation or to a torsion of the elastomer element and to a change in resistance between the third contact and first contact and the third contact and second contact.In a further embodiment, an evaluation circuit is configured such that the electrical resistances between the electrical contacts are ratiometrically evaluated, wherein a control position of the flap or door is determined on the basis of a resistance ratio.The evaluation of the resistance conditions has the advantage that absolute resistance changes, which could possibly occur as a result of component tolerances, ageing or other environmental influences, do not have a relevant influence on the measurement and the actuating position of the flap or door can thus be reliably determined.It is useful if the third electrical contact is simultaneously designed as a mechanical rotational or fixed point of the elastomer element.They show schematically FIG. 1 shows a control position-resistance diagram on which the invention is based, FIG. 2 shows an arrangement according to the invention in a simplified sectional illustration, FIG. 3 shows an arrangement according to FIG. 2 with torsion of the elastomer element, FIG. 4 is an overall view of the arrangement with movable flap and rotatable shaft, FIG. 5 shows an arrangement with an eccentric pin FIG. 6 shows an arrangement according to FIG. 5, with the eccentric pin deflected, FIG. 7 is an overall view of the eccentric pin arrangement, FIG. 8 shows a circuit for a ratiometric evaluation.The idea of the invention is now to evaluate the position of a shaft by sensor and to detect a rotational movement or a position of a shaft and in particular a flap or door connected to the shaft.In particular, the two end positions "fully closed" and "fully opened" should also be recognized, but also any desired adjustment position between these two end values.One possible application is in particular charging flaps in electric vehicles. Such a tailgate can be motor-driven or can also be moved non-motorally solely by the action of force of an operator and spring forces. Usually, the position of the tailgate is not hard-coupled to the position of a servomotor, but is equipped with certain sprung free travel or force limitations, so that in each position of the tailgate an external force effect also causes an additional influence on the position of the tailgate. Thus, both operating processes with the flap at a standstill and obstacles and trapping situations with the flap moved by motor can be detected.The effect utilized according to the invention is based on a change in resistance of at least one electrically conductive elastomer molded part made of plastic, referred to below as elastomer element, which is in constant contact with a plurality of contact surfaces and which is compressed to a greater or lesser extent by directed deformation and which results in compression-dependent contact surfaces, the transfer resistances of which are evaluated as a measure of the position of the tailgate.FIG. 1 shows the basic mode of operation and the characteristics used in the arrangement according to the invention. The position of a door or flap brings about a position of the shaft connected to this door or flap. This results in a dependence of the transition resistances R 12, R 23 in the limits between R_min and R_max as a function of the adjustment positions d 1, d 2 of the shaft. D1 indicates a specific direction of rotation and d2 the opposite direction of rotation. These adjustment positions, which act on the elastomer element 1 via the shaft, deform the elastomer element 1 and thus influence the resistance that can be measured at the respective adjustment position.FIG. 2 shows an exemplary arrangement according to the invention in a simplified sectional illustration with an electrically conductive elastomer element 1, with three electrical contacts N 1, N 2, N 3 and two contact surfaces K 1, K 2 dependent on the position of setting a part of the elastomer element 1.The dashed vertical line is intended to indicate a neutral position of the rotatable part of the elastomer element 1, which is mechanically connected to the rotatable shaft, which in turn changes its position of adjustment depending on the position of adjustment of the tailgate, wherein the prestressed rest position is shown here in the neutral position. The rotatable shaft itself is not shown in this figure for reasons of clarity.N 3 is an electrical contact which is connected at a central point to the conductive elastomer element 1 and here simultaneously forms a mechanical pivot point for the elastomer element 1. The contact N 3 can simultaneously serve as a carrier element to which the elastomer element 1 is fastened, for example by injection molding, adhesive bonding, clipping, clamping. N 1 and N 2 are further electrical contacts, the contact surfaces K 1, K 2 of which with respect to the elastomer element 1 are dependent on the setting position of the elastomer element 1. The elastomer element 1 is rotatable within certain limits in the sense of torsion, without this suffering structural damage. This property is particularly appropriate for charging flaps, since these can generally be adjusted between the closed position and the fully open position only over an angular range of approximately 90° or + / - 45°.The dashed line represents the profile of the current distribution, representatively represented by a plurality of current path lines, caused by a resistance measurement. The sub-resistor R 13 is formed between the contacts N 1 and N 3, and the sub-resistor R 23 is formed between the contacts N 2 and N 3. These partial resistances can be determined electronically in a simple manner, wherein a ratiometric measurement method is preferably used and thus the position of the tailgate can be deduced. N1 and N2 form the outer contacts, while N3 is arranged essentially electrically between N1 and N3 as a center tap, so that at least a substantial part of the current path lines run over N3 and thus essentially an electrical series connection of the resistors R13 and R23 is achieved.The third electrical contact N 3 does not necessarily have to be arranged within the elastomer element, however, but can also be electrically connected to the elastomer element 1 on an outer surface thereof.For example, the third electrical contact N 3 can be electrically connected to the elastomer element 1 above or below the latter. In principle, the contacts N 1, N 2, N 3 should be arranged in such a way that a substantial part of the current path lines run via the third electrical contact N 3, so that in principle the desired electrical series connection is achieved.FIG. 3 shows the same arrangement according to the invention as in FIG. 2, but here an additional torsion of the elastomer element 1 is shown, which is caused by a setting position d 1 of the shaft that is changed in comparison to FIG. 1. The front part of the elastomer element 1 schematically shows the electrical contacts N 1, N 2, N 3. The rear part of the elastomer element 1 spatially indicated in the image is rotated to the right, which is indicated by the arrow. As a result, a torsional deformation of the elastomer element 1 takes place, wherein the contact surface K 1 between the contact N 1 and the elastomer element 1 is reduced. For this case, only one current path line is shown in dashed lines. The contact area K 2 between the contact N 2 and the elastomer member 1 is increased. On this side, compression takes place with enlargement of the contact surface or contact surface K 2.The resistance ratio (R 13 / R 23) that can be measured from the outside is now greater than without torsional deformation. The position of the tailgate or the position of the shaft caused thereby can thus be measured via a change in resistance in both partial resistances R 13 and R 23, wherein the measurement is preferably carried out ratiometrically. With ratiometric measurement, the factors affecting the overall resistance of the elastomer member 1 can be suppressed effectively.As already mentioned with reference to FIG. 2, the third electrical contact N 3 can also be arranged inside or outside at other positions; in particular, it is not absolutely necessary for the third contact N 3 to be the point of rotation or tangency of the torsion.FIG. 4 shows a simplified schematic illustration of the arrangement according to the invention as in FIG. 3, having a movable tailgate 2 and a rotatable shaft 3, wherein the shaft 3 is connected to the tailgate 2 in a force-fitting manner. The tailgate 2 can be driven purely mechanically by the user or by a motor mechanism. This is not shown here. The tailgate shown here serves only as an example; in principle, instead of the tailgate, other elements, in particular also doors, can also be mechanically connected to the shaft. It is likewise conceivable for the shaft to be connected to further elements via a force connection, for example gearwheels or belts.The variable adjustment positions of the shaft d 1, d 2 cause a directed torsional deformation at the conductive elastomer element 1, wherein the electrical resistance is changed, which is measurable between the electrical contacts N 1, N 2, N 3. The setting position d 1 is shown, as is also shown in FIG. 3, which brings about a torsional deformation on the elastomer element 1, indicated here by the oblique dashed lines.This electrically produces a combination of two sub-resistors R 13, R 23 of the elastomer element, which can preferably be ratiometrically evaluated by a measurement circuit M.FIG. 5 shows a further arrangement according to the invention, in which the actuating position of the shaft 3, which is connected to the tailgate 2, can be detected via an electrically conductive, mechanically prestressed elastomer element 1 via a change in resistance. The position of the shaft 3 in this figure has a zero position, indicated by the vertical dashed line.Similar to FIG. 2, three electrical contacts N 1, N 2, N 3 and the partial resistors R 13 and R 23 formed by the elastomer element 1 are shown, indicated by dashed current path lines.These partial resistances can be determined electronically in a simple manner, wherein a ratiometric measurement method is preferably used and thus the position of the tailgate can be deduced. N1 and N2 form the outer contacts, while N3 is arranged essentially electrically between N1 and N3 as a center tap, so that at least a substantial part of the current path lines run over N3 and thus essentially an electrical series connection of the resistors R13 and R23 is achieved.The prestressed elastomer element 1 forms a contact surface with all three contacts N 1, N 2, N 3. In the example shown, N 3 simultaneously forms a mechanical pivot point of the elastomer element 1. In the example shown, the contact N 3 can simultaneously also serve as a carrier element to which the elastomer element 1 is fastened, for example by injection molding, adhesive bonding, clipping, clamping.In principle, the carrier function can also be assumed by another element.Also shown is a drive pin Ex, which is arranged eccentrically on the shaft 3, not shown here, and which can deform the elastomer element 1 in a directed manner via a bearing bush 4 that may be required.As already explained with reference to FIGS. 2 and 3, the third electrical contact can also be arranged here at different positions inside or outside the elastomer element 1. It is essential that, in the case of a directed deformation of the elastomer element 1, changes in resistance between the contacts N 1, N 2, N 3 can be determined.FIG. 6 shows the same arrangement according to the invention as in FIG. 5, but here a deflection of the shaft is shown, which causes a directed deformation of the elastomer element 1 via the drive pin Ex arranged eccentrically on the shaft, indicated by the angle of rotation shown to the right, caused by a setting position d 1. The apex of this angle is the pivot point of the shaft.By suitable placement of the eccentrically arranged drive pin Ex, a dimensioning adapted to the construction of the elastomer element 1 is possible within wide limits. The larger the eccentric radius is selected, the larger the deformation of the elastomer element 1.The deflection causes a mechanical relaxation of the elastomer element 1 at the contact N 1 and thus a reduction of the contact area and a compression of the elastomer element 1 at the contact N 2 and thus an enlargement of the contact area. Between N1 and N3, fewer current path lines are formed, associated with an increase in the resistance value R13. More current path lines are formed between N2 and N3, associated with a reduction in the resistance value R23.FIG. 7 shows a simplified schematic illustration of the arrangement according to the invention according to FIG. 5, having a movable tailgate 2 and a rotatable shaft 3, wherein the shaft 3 is connected to the tailgate 2 in a force-fitting manner. The tailgate 2 can be driven purely mechanically by the user or by a motor mechanism. This is not shown here. The variable adjustment positions of the shaft d 1, d 2 cause a displacement of the drive pin Ex eccentrically connected to the shaft 3, whereby a directed deformation is produced at the conductive elastomer element 1 and the electrical resistance is changed, which can be measured between the electrical contacts N 1, N 2, N 3. A neutral setting position is shown here, as is also shown in FIG. 5, without directed deformation.This electrically produces a combination of two sub-resistors R 13, R 23 of the elastomer element 1, which can preferably be ratiometrically evaluated by a measurement circuit M.FIG. 8 shows a particularly simple evaluation circuit with which it is possible to ratiometrically evaluate the sub-resistors R13, R23 according to an arrangement according to the invention.One problem in the measurement of the resistance of contact surfaces with a conductive elastomer element 1 is the great variance of the measurement values. Thus, only the production-related variation of the conductivity of the elastomer element 1 itself is already very large. This is accompanied by the mechanical tolerances of the arrangement and of the elastomer element 1, as a result of which even very different degrees of deformation can occur. This is accompanied by largely undefined temperature effects on the conductivity of the elastomer element 1 and on the temperature-induced deformation of the entire arrangement.A very simple evaluation method consists in the electrical arrangement of the sub-resistors R 13, R 23 as a resistive voltage divider. N1 is connected with a low impedance to the supply voltage VCC or to the logic high potential, and N2 is connected with a low impedance to the reference potential GND, 0 volts or to the logic low potential. At the center tap N 3 electrically substantially between the contacts N 1 and N 2, a voltage may be measured according to the electric dividing ratio of the division resistors R 13, R 23.By measuring the voltage at the center tap of the voltage divider, all influencing factors which affect the absolute resistance value of the elastomer element 1 are suppressed, since this ratiometric evaluation method does not measure the individual resistance value, but rather the ratio of the individual resistances to one another. In addition, in this way, an absolute actuating position can be derived from the ratio measurement even after the supply voltage fails and without nonvolatile memory.N1 and N2 are each applied to a digital output of a microcontroller (logic), while N3 is applied as a center tap to an analog-to-digital converter ADC. The low-pass function of the components R 1, C 1 is not required for the actual function, but enables an interference-resistant evaluation of the elastomer element 1, even if the latter is situated spatially far from the ADC input. The use of an ADC for voltage measurement offers the additional advantage that the measured voltage and the internal reference voltage of the ADC generally equally depend on the same operating voltage and thus the digitally readable measurement value is independent of the operating voltage.For further suppression of offset influences during the ADC measurement, the logical states can be inverted and the mathematical difference between the two measurements can be used for the evaluation. The disclosed arrangements relate to particularly simple exemplary embodiments in which only a single elastomer element 1 is used. The ratiometric method of the evaluation functions, however, also when the measured partial resistances consist of two or more identical elastomer elements and care is taken that the undesired influencing factors act equally on all elastomer elements used. The ratiometric method of the evaluation is also not only limited to the particularly advantageous and simple exemplary embodiments shown here, in which the ratiometric evaluation method is already given by the electrical arrangement, but can also be carried out by individual measurements of the elastomer elements 1 and by purely mathematical processing of the measurement results.List of reference charactersADC analog-to-digital converter VCC supply voltage Ex drive pin d 1, d 2 control positions of shaft K 1, K 2 contact surfaces M measurement circuit, evaluation circuit N 1, N 2, N 3 electrical contacts logic logic, microcontroller 1 elastomer element, elastomer molded part 2 charging flap 3 shaft 4 bearing bush

Claims

Device for detecting a rotational movement or setting position of a shaft, having an electrically conductive elastomer element (1) which is connected on one side to a drive pin of the shaft (3), wherein the drive pin is eccentrically connected to the shaft (3), having a first and a second electrical contact (N1, N2) which bear electrically conductively on at least one outer side of the elastomer element (1), having a third electrical contact (N3) which is arranged within the elastomer element (1) in an electrically conductive manner between the first and second contacts (N1, N2), wherein the shaft (3) and the electrical contacts (N1, N2, N3) are arranged in such a way and are connected in such a way to the elastomer element (1), a rotational movement of the shaft (3) leads to a directed deformation of the elastomer element (1) and to a change in resistance between the third contact (N3) and first contact (N1) and also the third contact (N3) and second contact (N2).Device according to claim 1, wherein the first and second electrical contacts (N1, N2) are in an electrically conductive contact with the outer side of the elastomer element (1) such that the torsion of the elastomer element (1) leads to a change in size of the contact surfaces (K1, K2) between the electrical contacts (N1, N2) and the elastomer element (1).Device according to one of the preceding claims, having an evaluation circuit (M) which is designed in such a way that the electrical resistances (R13, R23) between the electrical contacts (N1, N2, N3) are ratiometrically evaluated.Device according to one of the preceding claims, in which the third electrical contact (N3) is simultaneously designed as a mechanical turning or fixing point of the elastomer element (1).Device according to one of the preceding claims, in which the mechanical coupling of the drive pin (Ex) to the elastomer element (1) takes place via a bearing bush (4).Device according to one of the preceding claims, wherein the shaft is included with the eccentric drive pin, wherein the shaft (3) is mechanically connected to a further element such that a movement of the further element results in a rotational movement of the shaft (3).Device according to claim 5, wherein the further element is a flap (2) or door.Door or flap (2) with a device according to one of the preceding claims.

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