Position measuring system for a movable element using RFID

Abstract

The invention relates to a method for determining a position of a first element relative to a second element, the two elements moving relative to one another. In this method, the position is determined in situ with the aid of an RFID system using an in situ RFID reading device on the first element and a number of activatable transponders on the second element. The transponders are each calibrated separately beforehand by the in situ RFID reading device or an ex situ RFID reading device with their respective positions on the second element, and the position data are linked to their identification data. The transponders run through a receiving and reading region of the in situ RFID reader and transmit their identification and position data after being activated. An algorithm for controlling the RFID system and for determining the positions in situ is programmed in a control device. The transmitted identification data and position data are used to determine the position of the in situ RFID reader on the first element relative to the second element by means of a calculation rule contained in the algorithm.

Description

[0001] Hanover, September 6th, 2024 IP, Dr. Ohlendorf, Kilsch / MM 000006494-DE-NP

[0002] Method for determining the position of two elements relative to each other in situ using an RFID system

[0003] The invention relates to a method for determining the position of a first element in relation to a second element, wherein the first and the second element move relative to each other on predetermined trajectories and the position determination is carried out in situ using an RFID system, in which an RFID in-situ reading device is provided on the first element and a number of transponders are provided on the second element.

[0004] The invention also relates to a programmable control device with an algorithm for carrying out the method, a computer program for the control device, and a device particularly suitable for determining the longitudinal displacement of a first element relative to a second element.

[0005] Measuring systems for determining the position of components moving linearly or rotationally relative to each other in situ, i.e., directly at their point of use, application, or working environment, are known. Such systems include, for example, those that use RFID labels (also called RFID tags) as transponders and an RFID reading device or RF ID reader (also called a reader or RFID reader).

[0006] The transponders are attached to one of the moving components and, after activation by the RFID reader, transmit a signal containing identification information, either actively or passively. This information can be received by the RFID reader connected to the other moving component. The identification information can include position data or be listed in a table and assigned to position data. This table is stored in memory, allowing the corresponding position data for each transponder to be retrieved.

[0007] Depending on the design of the RFID systems, the RFID reading devices can be configured as transmitters and receivers for transmitting and receiving alternating magnetic fields or radio waves and for transmitting and receiving data to and from the transponders. EP 3 505 874 A1 discloses a measuring system, in particular an RFID system for determining a change in position between two moving components during a linear or rotary movement relative to each other. In this system, one or more layers or plates with openings are positioned as apertures between a reader and a transponder. The openings are arranged and dimensioned in such a way that the transmission of transponder signals can be influenced or controlled in order to determine the position of a transponder more accurately from the entire arrangement and multitude of transponders.

[0008] EP 2 263 966 A1 discloses a transport vehicle or industrial truck, such as a forklift, in which a change in position during a relative movement between a first and a second element is determined by attaching an RFID reader to the first element and RFID transponders to the second element, and assigning a position identification transmitted by the transponder. To increase the accuracy of the position determination, RFID transponders can be arranged in several adjacent rows or several RFID readers can be provided.

[0009] Methods for determining position using an RFID system are technically demanding and require, in addition to considering problem areas such as interference-free signal transmission and electronic equipment, also and especially ensuring high reliability and accuracy in position determination.

[0010] The position data of the transponders, when stored in the transponder electronics and sent along with their identification data to an RFID reader or RF ID reader, must precisely correspond to the actual positions of the transponders on the element or component. This means that utmost care must be taken to ensure that the transponders, which already contain position data, are placed in the correct location.

[0011] The same applies to measuring devices and methods for position determination using RFID systems, where the identification data of the transponders are listed in a table stored in memory, assigned to the position information, and retrievable for position determination. Here, too, the accuracy of the position determination depends on the positions retrievable from a stored table corresponding exactly to the actual positions of the transponders on the component / element.

[0012] A further, significant problem arises from the fact that, in order to detect even slight changes in position, the transponders on one of the moving elements or components must be arranged at relatively close intervals. This means that multiple transponders are always within the reception and read range of an RFID reader located on the other element or component, transmitting their identification information to the RFID reader. With such close proximity of the transponders, a multitude of identification data points are received by the RFID reader more or less simultaneously during the relative movement of the two elements.Even if the individual identification information transmitted by the transponders can be recognized separately by the RFID reader, for example by an anti-collision algorithm programmed into the reader that identifies all transponders within the reception range in a very short time, accurately determining the position of the two elements relative to each other remains a problem. Since multiple pieces of position information are captured almost simultaneously, precise positioning is often difficult or only partially possible.

[0013] With the devices known in the prior art for determining position using RFID systems, a conflict of objectives arises, namely that on the one hand, to increase accuracy, the transponders should be arranged at the smallest possible intervals on one of the elements, but on the other hand, the small intervals lead to an inaccuracy when simultaneously reading a large number of transponder signals by the RFID reader and the resulting different position information.

[0014] The object of the invention was therefore to provide a method for determining the position of a first element in relation to a second element in situ and with the aid of an RFID system, which achieves high accuracy without additional apertures or shields, in which complex arrangements of several transponder rows can be dispensed with, in which a single RFID reader is sufficient for position determination despite a large number of closely spaced transponders, and in which a discrepancy between the actual position of the transponders on a component or element and their position data to be transmitted to the RFID reading device can be prevented as far as possible in an RFID system for position determination.

[0015] This problem is solved by the inventive method for determining the position of a first element relative to a second element, wherein the first and second elements move relative to each other along predetermined trajectories and the position determination is carried out in situ using an RFID system in which an RFID in-situ reading device (reader) is provided on the first element and a number of programmable transponders are provided on the second element. The transponders can be activated within a reception and read range of the RFID in-situ reading device by means of alternating magnetic fields or radio waves, and the trajectory of the second element is designed such that the transponders traverse the reception and read range of the RFID in-situ reading device.Once activated, the transponders transmit data for their unique identification (identification data) to the RFID in-situ reading device within the reception and reading range.

[0016] The transponders on the second element are arranged along an extension of the second element in the direction of the trajectory and spaced apart from each other, and during the movement of the second element relative to the first element, a portion of n transponders is temporarily located within the reception and reading range.

[0017] A programmable electronic control device and an algorithm programmed in the control device are provided for controlling the RFID system and for performing the position determination in situ.

[0018] Prior to in-situ position determination, the transponders are first calibrated with respect to their position on the second element, according to the invention. This is achieved by having the RFID in-situ reading device or an RFID ex-situ reading device, each configured as a transmitter-receiver, determine the position xi, X2, X3, ... , x"-i, x n The second element of each transponder is linked to its identification data in the form of data (position data) and transmitted separately to the respective transponder.

[0019] After all transponders have been calibrated and when the second element moves relative to the first element, the following steps are initiated by the in-situ position determination algorithm programmed in the control unit: a) Emitting a signal or signal sequence by the RFID in-situ reader to activate a subset of n transponders that are within the reception and reading range of the RFID in-situ reader at the time of transmission.b) Transmission of the identification data of the transponders, triggered by their activation, together with their position data transmitted by the calibration, to the RFID in-situ reading device; c) Determining a position X of the RFID in-situ reading device on the first element relative to the second element by determining the position X of the RFID in-situ reading device relative to the positions x of the n transponders located in the receiving and reading area on the second element by the relationship.

[0020] (xl + x2 + x3 + ••• x(n — 1) + xri) n where the following holds:

[0021] X is the position of the RFID in-situ reading device, xi, X2, ... , x„-i, x nThe position of the n transponders located within the reception and reading range on the second element is transmitted by the prior calibration of the transponders, and n is the number of transponders located and activated within the reception and reading range. The method according to the invention resolves the conflict of objectives often encountered in the prior art, namely reduced reading accuracy at small transponder spacings, and reverses this conflict by having a larger number of transponders arranged close together within the reading range of a single reader / reading device lead to increased accuracy in position determination.

[0022] On the other hand, prior calibration of the transponders increases the accuracy of position determination by ensuring a particularly precise match between the data transmitted to the transponders during calibration, which describes their position, and their actual positions on the element or component. Depending on the details described below, calibration can be performed and updated multiple times, for example, before the start of a measurement cycle.

[0023] The positions xi, X2, ... , x n -i , x nThe n transponders located within the reception and reading range of the RFID reading device or RFID reader on the second element correspond, for example, to distances of the respective transponders from a reference point on the second element, such as distances from a starting point of movement or zero point, if one imagines the distances arranged parallel and in the same direction as the path of movement.

[0024] In this way, micro-RFID tags, i.e., very small transponders, can be arranged in a ruler-like pattern at very small intervals on an element or component, for example, at intervals of 1 to 5 mm between the individual transponders. The position determination using the method according to the invention is correspondingly precise.

[0025] This becomes clear in the following example (Example 1). Here, a table graphically displays the positions X4, xs, xe, x? of n = 4 transponders (numbers 4, 5, 6, 7) on the second element, transmitted as data (position data) during calibration prior to position determination. These positions are located within the reception and read range of an RFID in-situ reader at a specific time. The positions in the right-hand column of the table are assigned their respective identification data (TAG ID) of transponders 4 to 7 in the middle column.

[0026] According to the invention, the RFID in-situ reading device activates the n = 4 transponders 4 to 7 within its reading range almost simultaneously and detects their identification data and positions / position data transmitted by activation. Using the algorithm programmed in the control unit, the exact position X of the RFID in-situ reading device on the first element relative to the positions of the transponders on the second element, and thus ultimately the position of the first element relative to the second element, is then determined.

[0027] (1.6+3.2+4.84-6.4) .

[0028] X = — — ■ — 4 ■ — — = 4 mm.

[0029] A further development of the procedure consists in the following: during the transmission of identification and position data of the respective transponder initiated by the activation of the transponders, the intensity I of the signal for data transmission of the respective transponder is measured by the RFID in-situ reading device, and in process step c) the determination of the position X of the RFID in-situ reading device on the first element relative to the second element by weighting the transponder positions using their signal intensities h, I2, I n -i, l n , also known as RSSI (received signal strength indicator), whereby the position X of the RFID in-situ reader relative to the positions of the n transponders located in the receive and read area on the second element is determined by the relationship where X is the position of the RFID in-situ reading device, xi , X2, x„-i, Xn is the position of the transponders located within the receive and read range on the second element, transmitted by the prior calibration of the transponders, n is the number of transponders located in the receive and read range and activated, and li, I2, ... , ln-1, In are the intensities of the data transmission signals of the respective transponder.

[0030] Such a weighting is achieved by the signal intensities h, I2, ... , I measured during transmission by the reader. n -i, l n increases the accuracy of position determination.

[0031] This can also be illustrated using another example (Example 2), where, as above, a table graphically displays the positions X4, xs, xe, x? of a number n = 4 transponders (numbers 4, 5, 6, 7) on the second element, which are transmitted as data (position data) during calibration prior to position determination. These positions are located within the reception and read range of the RFID in-situ reader at a specific time. The corresponding identification data is assigned to each position in the table. The signal intensities currently determined by the reader, as taken into account in the process, are also shown.

[0032] Here again, the n = 4 transponders with the numbers 4, 5, 6, 7 located within the reception and reading range of a reader, along with their identification data (TAG ID) transmitted upon activation and positions X4, xs, xe, x? on the second element – ​​starting from a reference point not described in detail here – are listed and assigned. The corresponding signal intensities k, Is, h, I7) are listed in the column to the right, each currently determined by the RFID in-situ reading device.

[0033]

[0034] According to the invention, the RFID in-situ reading device activates the four transponders 4 to 7 within its reading range and detects their identification data and positions transmitted by activation, as well as the respective intensity I of the signal for data transmission (signal intensity). Using the algorithm programmed in the control device, the exact position of the first element relative to the second element is then determined, taking the signal intensities into account.

[0035] (1.6 ■ 30 + 3.2 ■ 40 + 4.8 ■ 70 + 6.4 ■ 40)

[0036] X = - - — - - = 4.27 mm.

[0037] 180

[0038] This results in even greater accuracy in position determination. Weighting by signal intensity particularly increases the accuracy of position determination when the first and second elements move along equidistant trajectories relative to each other.

[0039] One embodiment of the method according to the invention consists in the calibration of the transponders in situ and during the movement of the second element relative to the first element. In such an embodiment, the calibration, in which the position of each transponder on the second element is linked to its identification data in the form of data (position data) and transmitted separately to the respective transponder, is carried out by the RFID in-situ reading device, which is then configured as a transmitter and receiver in a known manner.

[0040] Such in-situ calibration can be performed, for example, before a single or a series of position measurements, particularly if there is concern that geometric changes to the first or second element could lead to a system-related change in their relative positions, such as those caused by adjustment mechanisms on the elements or by thermal expansion. To increase the reliability of the position measurements, recalibration can also be performed regularly after a cycle or after a predetermined number of measurements.

[0041] A further embodiment of the method according to the invention consists in the calibration of the transponders on the second element ex situ and during the movement of the second element relative to an RFID ex situ reading device. This allows the second element to be equipped with transponders whose identification data are already correlated with and programmed into its position data before it is installed or used at its destination.

[0042] In another embodiment, the transponders are calibrated ex situ on a calibration element corresponding to the second element, and this calibration takes place while the calibration element is moving relative to an RFID ex situ reader. For this to work, however, the transponders must be removed from the calibration element and correctly positioned on the second element, which is used in situ. Such an embodiment can be advantageous for the automated mass production of measuring devices.

[0043] The same applies to a further embodiment of the inventive method, which consists in the calibration of the transponders after or during their manufacture in the form of assembly and the transponders being placed correctly on the second element after their calibration.

[0044] A further embodiment of the method according to the invention consists in the separate transmission of the position data linked to the identification data to the respective transponder by restricting the receive and read range of an RFID reader used for calibration during the calibration process, such that only one transponder is present in the receive and read range at any given time. This is advantageous for both in-situ and ex-situ calibration in order to best achieve the inventive advantage of resolving / reversing the aforementioned conflict of objectives, namely that a larger number of transponders arranged close together in the read range leads to increased accuracy when the position is determined by only one RFID in-situ reader.

[0045] A further development of the method according to the invention consists in limiting the reception and reading range of an RFID reading device used for calibration by means of a lens or aperture arranged between the RFID reading device and the respective transponder. Such a design can be achieved with relatively simple and cost-effective devices, wherein the lenses or apertures are designed in the same or a similar manner as the lenses or apertures described below, which can be used for activating the transponders.

[0046] A further embodiment of the method according to the invention consists in the RFID in-situ reading device transmitting signals or signal sequences of different frequencies to activate a subset of n transponders. On the one hand, different frequencies offer the possibility of utilizing different ranges for determining the position of two elements relative to each other; on the other hand, different frequencies can reduce or prevent interference in the transmission of identification data.

[0047] In another embodiment of the method, the alternating magnetic fields or radio waves of the RFID in-situ reader are focused to activate the transponders at the second element using a lens or aperture. For example, perforated or openwork flat metal structures or sheets can be used as apertures, restricting the reading area, i.e., the radiation beam of a reader / device, and thus allowing a smaller number of transponders to be activated. Lenses for radar radiation are typically made of plastic, function similarly to optical lenses, and have a comparable effect on the radiation beam and reading area.

[0048] The invention also relates to a programmable control device for operating an RFID system with an RFID in-situ reading device and with transponders that can be activated by the RFID in-situ reading device, wherein the RFID system is provided for determining the position of a first element in relation to a second element in situ and the first and second elements move relative to each other on predetermined trajectories such that the transponders pass through a receiving and reading area of ​​the RFID in-situ reading device.The RFID in-situ reader is permanently connected to the first element, and a number of transponders, which can be activated by the RFID in-situ reader using alternating magnetic fields or radio waves, are provided on the second element. The transponders located within the reception and read range of the RFID in-situ reader transmit identification and position data to the RFID in-situ reader after activation. The control unit includes an algorithm in its programming for carrying out the method according to the invention.

[0049] The invention also relates to a computer program comprising an algorithm with instructions for a programmable control device for carrying out the method according to the invention.

[0050] The invention also relates to a device particularly suitable for carrying out the method according to the invention for determining the position of a first element in situ with respect to a second element, wherein the first and the second element move relative to each other along predetermined trajectories and the position determination is carried out using an RFID system in which an RFID in-situ reading device is provided on the first element and a number of transponders are provided on the second element. The device has the following features:

[0051] The RFID in-situ reading device is designed as a transmitter-receiver and is arranged on the first element for the transmission and reception of alternating magnetic fields or radio waves in such a way that the transponders on the second element pass through a reception and reading area of ​​the RFID in-situ reading device when the second element moves along the trajectory.

[0052] On the second element, a number of transponders, which can be activated by the RFID in-situ reader using alternating magnetic fields or radio waves, are arranged such that during relative movement between the first and second elements, some of the transponders are temporarily within the reception and reading range. The transponders are equipped with an electronic circuit and an antenna, enabling the transmission of identification and position data from the activated transponder to the RFID in-situ reader after activation.

[0053] In a programmable control device communicating with the RFID in-situ reading device, an algorithm is stored which, according to the method according to the invention as described above, determines the position X of the RFID in-situ reading device on the first element relative to the second element from the identification data and position data transmitted by the respective activated transponder.

[0054] Such a device allows the relative position of one element or component to be determined to another, whereby position determination is possible for any linear or rotational movement paths of the two elements. In a relatively simple design, the transponders are arranged on the second element along its length in the direction of the trajectory and at a constant distance from each other.

[0055] Without reducing the accuracy of position determination within the required movement ranges, design measures make it possible to provide a more economical version of the device. In a further embodiment of the device according to the invention, the transponders on the second element are arranged closer together in predetermined sections along its length in the direction of the trajectory than in adjacent sections. In those sections of the trajectory where position determination in larger steps or intervals is sufficient, fewer transponders can then be used.

[0056] A further embodiment of the device according to the invention aims in the same direction, in which the transponders on the second element are only provided in partial areas of its extension in the direction of the trajectory curve.

[0057] Another embodiment, which facilitates the assembly of a device according to the invention, consists in the transponders and / or their antennas being glued or printed onto the second element. For this purpose, transponders can be provided which are equipped with an adhesive film on their back and can be easily glued onto one of the two elements, here the second element, e.g., using predefined markings.

[0058] A further development of the device according to the invention consists in the transponders being attached to a substrate which is applied, in particular glued, to the second element. This allows the transponder arrangement, even with varying spacing in individual areas, to be prepared by the manufacturer and very easily applied to the components or elements.

[0059] Transponders, even those with built-in antennas, can now be manufactured in extremely small sizes in the form of microchips, for example as so-called p-chips with an area of ​​less than 0.5 mm x 0.5 mm.

[0060] A further embodiment of the device according to the invention is provided for determining a longitudinal displacement of a piston rod in a cylinder, wherein the determination of the longitudinal displacement is carried out by repeatedly determining the position of the cylinder in relation to the piston rod in situ and according to the method according to the invention, in which, on the one hand, an RFID in-situ reading device is fixedly connected either to the cylinder or to the piston rod and / or moves with one of the two elements cylinder or piston rod, and, on the other hand, a number of transponders that can be activated by the RFID in-situ reading device by means of alternating magnetic fields or radio waves are provided on the respective other element, i.e., on the other of the two elements cylinder or piston rod, wherein the transponders at least partially pass through a receiving and reading area of ​​the RFID in-situ reading device.By repeatedly determining the cylinder position in relation to the piston rod, longitudinal displacements of the piston rod in the cylinder can be detected much more precisely than via individual position sensors or limit switches.

[0061] This applies particularly to a further development of the device according to the invention when used to determine the change in length of a vibration damper in a motor vehicle chassis, wherein the determination of the change in length is carried out in situ by repeatedly determining the position of the damper cylinder as the first element relative to a (dust) protective cover as the second element, which is connected to the damper piston rod and concentrically surrounds the damper cylinder. The damper cylinder dips into the protective cover when the suspension compresses. An RFID in-situ reading device is permanently connected to the damper cylinder, and a number of transponders that can be activated by the RFID in-situ reading device are provided on the protective cover or on an element connected thereto.

[0062] A further embodiment of the device according to the invention consists in the following: when used to determine the change in length of a vibration damper in a motor vehicle chassis, the change in length is determined by repeatedly determining the position of a damper cylinder (as a second element) relative to a protective cover (as a first element) connected to the damper piston rod and concentrically surrounding the damper cylinder, in situ and according to the method according to the invention. During compression, the damper cylinder enters the protective cover, wherein an RFID in-situ reading device is fixedly connected to the protective cover and a number of transponders, which can be activated by the RFID in-situ reading device, are provided on the damper cylinder or on an element or substrate connected thereto.

[0063] The invention will be explained in more detail using an exemplary embodiment. The following are shown.

[0064] Fig. 1 shows a basic representation of a ruler-like arrangement of transponders on a component or element,

[0065] Fig. 2 shows a basic representation of a ruler-like arrangement of a different type of transponder on a component or element,

[0066] Fig. 3 shows a general representation of an in situ or ex situ element equipped with an RFID reading device,

[0067] Fig. 4 shows a schematic representation of an arrangement in a top view, in which a component or element equipped with transponders is located below another component or

[0068] The element is located in the RFID reading device provided according to Fig. 3, wherein the transponders pass through a receiving and reading area of ​​the RFID reading device,

[0069] Fig. 5 shows an enlarged side view of the figure shown in Fig. 4.

[0070] Situation, presented in principle for an in-situ application,

[0071] Fig. 6 shows a diagram of signal intensities measured by an RFID in-situ reading device during the transmission of identification data of the respective transponder.

[0072] Fig. 7 shows a basic representation of a vibration damper of a motor vehicle chassis with a device for carrying out the method according to the invention in situ,

[0073] Fig. 8 shows a basic representation of the vibration damper according to Fig. 7 with a different embodiment of the device for carrying out the method according to the invention in situ.

[0074] The figures may reference identical or similar elements using the same reference numerals. To clarify the invention, it is advantageous to view some of the figures together.

[0075] Figures 1 and 2 illustrate, in a purely schematic representation, a ruler-like arrangement of transponders 3a on a component or element 2a and a similar ruler-like arrangement of transponders 3b on a component or element 2b. The components or elements 2a and 2b each move along a predetermined path 4, which is defined as a straight line.

[0076] Figures 1 and 2 differ only in that element or component 2a is equipped with transponders 3a, which have external antennas AT, while component or element 2b is equipped with transponders 3b with integrated antennas, which are not shown here. The transponders themselves are not shown in detail here, but are known to consist of an antenna, an electronic circuit for receiving and transmitting, and a digital circuit, possibly with memory, which are usually integrated in a microchip.

[0077] Fig. 3 shows in a similarly basic representation an element 1 which is equipped with an RFID reading device 5 which also has an antenna AL and a programmable electronic control device 6 communicating with the antenna.

[0078] The RFID reading device shown in Fig. 3 can be arranged in situ and then used for the procedural position determination and calibration of the transponders. Alternatively, the RFID reading device can be arranged ex situ and then used only for the calibration of the transponders.

[0079] A program stored in the control unit 6 controls, on the one hand, a calibration of the transponders 3a, 3b and, on the other hand, has an algorithm for controlling and carrying out the position determination in situ using the RFID system.

[0080] The calibration of the transponders 3a, 3b with respect to their position on the second element takes place before the position determination, namely by using an RFID in-situ reader 5 or an RFID ex-situ reader to determine the position xi, X2, X3, ... , x n -i , x n of each transponder 3a, 3b on the second element in the form of data (position data) linked with its identification data and transmitted separately to the respective transponder.

[0081] The programmable electronic control device 6, which is also constructed in the form of an electronic circuit (IC, integrated circuit), thus controls the implementation of the position determination according to the invention with the help of the algorithm stored therein.

[0082] Fig. 4 shows a simplified top view of an arrangement in which a component or element 1 is positioned vertically above another component or element 2a arranged below it, such that the transponders 3a are located within a receiving and reading area 7 of an RFID reader 5, which is configured as a transmitter-receiver and extends towards the component or element 2a. As described above, the RFID reader 5 shown in Figs. 3 and 4 can be either an RFID in-situ reader or an RFID ex-situ reader.

[0083] However, in the combination of Fig. 4 with the further Figs. 5 and 6, the in situ position determination according to the invention is illustrated in the form of principle representations, wherein an RFID in situ reading device 5 is provided in the RFID system.

[0084] The receiving and reading area 7 of an RFID in-situ reading device 5 is shown in Fig. 5 in a purely schematic representation, but without qualitative or quantitative characteristics of the radar radiation. Fig. 5 shows an enlarged side view of the situation depicted in Fig. 4, in which a component or element 1 with an RFID in-situ reading device 5 is arranged above a component or element 2a equipped with transponders 3a such that the antennas of the transponders 3a pass through the reading area 7 of the RFID in-situ reading device.

[0085] The antenna AL of the RFID in-situ reading device and the antennas AT of the transponders 3a located in the receiving and reading area 7 can be activated by means of alternating magnetic fields, while the component or element 2a below the component or element 1 on the path 4 passes through the receiving and reading area 7 of the RFID in-situ reading device 5.

[0086] After activation, the transponders 3a transmit data for their unique identification (identification data) and the data transmitted during calibration to describe / identify their position on the second element 2a (position data) to the RFID in-situ reader 5 within the receive and read range 7. The transponders 3a are positioned along the second element 2a in the direction of the trajectory 4 and spaced apart from each other. At the time shown in Fig. 5, during the movement of the second element 2a relative to the first element 1, the four central transponders shown therein are within the receive and read range 7 of the RFID in-situ reader 5; that is, a portion of n = 4 transponders 3a are temporarily within the receive and read range 7. The calibration, which must be performed before the position determination, assigns each transponder 3a its position xi, X2, X3, x separately.n -i, x n The position data is transmitted to the second element 2a and linked to its identification data. This is done by the RFID in-situ reading device 5, which is configured as a transmitter-receiver. This transmits the positions X4, xs, xe, x? to the n=4 transponders 3a within the reception and read range 7 on the second element and assigns them to their identification data. The transponders, which are temporarily located within the reception and read range 7 as shown in Fig. 5, thus receive their data to identify their positions X4 to x?.

[0087] The algorithm programmed in the control unit then initiates the steps shown in the example above (Example 1) for position determination.

[0088] As described there, the identification data (TAG ID) of the n = 4 transponders located within the reception and reading range of a reader, transmitted after sending a signal to activate the transponders 3a, as well as their position data to describe their respective positions X4, xs, xe, x? on the second element - starting from a reference point B - are processed by the algorithm according to the inventive method for position determination.

[0089] The position X of element 1 relative to the positions of the 4 middle transponders 3a located in the receive and read range on the second element 2a is then determined by the relationship > (x4+x5+x6+x7) 4

[0090] A more precise determination of the position X of element 1 relative to the positions of the four middle transponders 3a located in the receive and read area 7 on the second element 2a is achieved by weighting them according to the signal intensities k, Is, k, I7 shown in the diagram of Fig. 6. These intensities are measured by the RFID in-situ reader 5 during the transmission of its identification data by the respective transponder (RSSI, received signal strength indicator). Reference is made here to Example 2 described above and the signal intensities assigned to the individual transponders listed there.

[0091] The position X of element 1 relative to the positions of the 4 middle n = 4 transponders 3a located in the receive and read area 7 on the second element 2a is then determined by the following relationship: (X4-I4+ X5-I5+X6-I6+X7-I7)

[0092] (I4+ 15 + 16+ 17)

[0093] Fig. 7 shows a schematic representation of an embodiment of a device 10 installed in a vibration damper 13 of a motor vehicle chassis (not shown in detail here) for carrying out the method according to the invention in situ. The left side of Fig. 7 shows the state of the vibration damper 13 during compression, and the right side shows it during rebound. The vibration damper is arranged in the motor vehicle between a body (not shown here) and a chassis support (also not shown).

[0094] The device 10 in the vibration damper 13 has an RFID in-situ reading device 5 designed as a transmitter-receiver on the outside of an outer damper cylinder 11 and a number of transponders, not shown in detail here, which are attached to a substrate 20 that is glued to the inside of a cylindrical dust cover 21 connected to a damper piston rod 12.

[0095] The device also features an integrated programmable control device 6 in the RFID in-situ reading device 5, as shown in Fig. 1.

[0096] Using the RFID in-situ reading device 5 on the outside of the outer damper cylinder 11 and the transponders on the substrate 20, the longitudinal displacement of the damper piston rod 12 relative to the outer damper cylinder 11 is determined. This is done by repeatedly determining the position of the outer damper cylinder 11 as the first element 1 with respect to the dust cover 21 and the associated damper piston rod 12 as the second element 2a.

[0097] The outer damper cylinder 11 belongs to the vibration damper 13, which is designed as a gas pressure damper, and contains a gas cushion / gas volume 14 above an oil volume 14a. The vibration damper 13, which is designed as a gas pressure damper, also has an inner damper cylinder 17, in the interior 16 of which there is an oil volume 16a on both sides of a damper piston 19.

[0098] The oil volume 14a of the outer damper cylinder 11 communicates with the oil volume 16a in the interior 16 of the inner damper cylinder 17 via valves 15 in the base of the inner damper cylinder 17. During compression or rebound, the oil volume 16a of the inner damper cylinder 17 also flows via valves 18 in the damper piston 19 from the respective compression side of the damper piston 19 to the opposite tension side. Damping, which will not be discussed in detail here, occurs, in short, through the dissipation of the oil volumes 14a and 16a flowing through the valves 15 and 18, in conjunction with a concomitant compression of the gas volume 14.

[0099] The vibration damper 13 is connected to a mounting point on the body by means of an eye 22 and to a mounting point on the chassis carrier by means of an eye 23.

[0100] The repeated determination of the position of the outer damper cylinder 11 as the first element 1 in relation to the damper piston rod 12 as the second element 2 is carried out according to the inventive method during compression and rebound, in which the outer damper cylinder 11 dips into and out of the dust cover 21.

[0101] The transponders attached to the substrate 20 pass through the receiving and reading area 7 of the RFID in-situ reader 5 during compression and rebound. They are thereby activated by means of alternating magnetic fields or radio waves and then transmit their identification and position data to the RFID in-situ reader 5. The position data was transmitted to the respective transponders by means of a prior calibration, as described above. For the sake of clarity, the receiving and reading area 7 of the RFID in-situ reader 5 on the damper cylinder 11 is not shown in detail in Fig. 7, but its function becomes clear when considering Fig. 7 in conjunction with Fig. 5.

[0102] The identification data and the position data of the transponders attached to the substrate 20, which are located in the reception and read area, are then processed according to the inventive method using the algorithm, whereby the position of the piston rod 12 in relation to the outer damper cylinder 11 and ultimately a change in length of the vibration damper between the eyes 22 and 23, i.e. between its mounting points on the body and chassis, is determined.

[0103] Fig. 8 shows in principle a further embodiment of a device 10 used in a vibration damper 13 of a motor vehicle chassis not shown in detail here for carrying out the method according to the invention, wherein the elements carrying the RFID-in-situ reading device 5 and the elements carrying the transponders are interchanged.

[0104] Fig. 8 differs from the representation in Fig. 7 only in that an RFID in-situ reading device designed as a transmitter-receiver is arranged on the dust cover 21, while a substrate 20 is glued to the outside of an outer damper cylinder 11, on which a number of transponders, not shown in detail here, are attached.

[0105] The RFID in-situ reader 5 also has an integrated programmable control unit 6, as shown in Fig. 1.

[0106] The fact that the RFID in-situ reading device 5 and the elements carrying the transponders are interchanged here compared to Fig. 7 offers the advantage that the dimensions of the RFID in-situ reading device 5 can be somewhat larger and assembly is simplified, making replacement particularly easy.

[0107] Here too, the transponders attached to the substrate 20 pass through the receiving and reading area 7 of the RFID-in-situ reading device 5 during a compression and rebound, are thereby activated by means of alternating magnetic fields or radio waves and then transmit their identification data as well as their position data to the RFID-in-situ reading device 5.

[0108] The determination of the change in length by repeatedly determining the position of the outer damper cylinder 11 in relation to the dust cover 21, and thus in relation to the damper piston rod 12 moving with the dust cover 21, is carried out according to the inventive method during compression and rebound, as already described above. With reference to the inventive method, the damper cylinder 11 in the embodiment shown in Fig. 8 is therefore to be regarded as the "second" element 2a, while the dust cover 21 is to be regarded as the "first" element 1 in this embodiment.

[0109] Reference symbol (part of the description)

[0110] I first element

[0111] 2a, 2b second element

[0112] 3a Transponder with external antenna

[0113] 3b transponder with integrated antenna

[0114] 4. Trajectory curve

[0115] 5 RFID reading device, in situ or ex situ

[0116] 6 Control unit

[0117] 7 Reception and reading area

[0118] 10. Setup

[0119] II outer damper cylinder

[0120] 12 Damper piston rod

[0121] 13 vibration dampers, gas pressure dampers

[0122] 14 Gas cushion / gas volume in the outer damper cylinder

[0123] 14a Oil volume in the outer damper cylinder

[0124] 15 valve

[0125] 16 Interior of the inner damper cylinder

[0126] 16a Oil volume inside the inner damper cylinder

[0127] 17 inner damper cylinder

[0128] 18 valve

[0129] 19 damper pistons

[0130] 20 substrates with attached transponders

[0131] 21 Dust cover

[0132] 22 body-side eye

[0133] 23 chassis-side eye

[0134] X4 position transponder 4 xs position transponder 5

[0135] X6 Position Transponder 6

[0136] X7 Position Transponder 7

[0137] X Position Element 1 k Signal intensity Transponder 4

[0138] Signal intensity transponder 5 le signal intensity transponder 6

[0139] I7 Signal intensity Transponder 7

[0140] AT antenna of the transponder

[0141] AL antenna of the RF ID reader

[0142] B Reference point, starting point of movement, zero point

Claims

Patent claims 1. Method for determining the position of a first element (1) relative to a second element (2a, 2b), wherein the first and second elements move relative to each other along predetermined trajectories (4) and the position determination is carried out in situ using an RFID system, wherein an RFID in-situ reader (5) is provided on the first element (1) and a number of programmable transponders (3a, 3b) are provided on the second element (2a, 2b), wherein the transponders (3a, 3b) can be activated within a receive and read range (7) of the RFID in-situ reader (5) by means of alternating magnetic fields or radio waves, and the trajectory (4) of the second element (2a, 2b) is configured such that the transponders (3a, 3b) are within the receive and read range (7) of the RFID in-situ reader (5). pass through the situ reading device (5), whereby the transponders (3a,3b) after their activation within the receive and read area (7), transmit data for their unique identification (identification data) to the RFID in-situ read device (5), wherein the transponders (3a, 3b) are provided on the second element (2a, 2b) along its extension in the direction of the trajectory (4) and are spaced apart from each other, and during the movement of the second element (2a, 2b) relative to the first element (1), a subset of n transponders is temporarily located within the receive and read area (7), wherein a programmable electronic control device (6) and an algorithm programmed in the control device are provided for controlling the RFID system and for carrying out the position determination in situ, characterized in that, prior to the position determination in situ, the transponders (3a, 3b) are first calibrated with respect to their position on the second element (2a, 2b) bythat the position xi , X2, X3, ... , x, is determined by the RFID in-situ reading device (5) or an RFID ex-situ reading device, each configured as a transmitter-receiver. n -i , x n of each transponder (3a, 3b) The second element (2a, 2b) is linked to its identification data in the form of data (position data) and transmitted separately to the respective transponder (3a, 3b). After the calibration of all transponders (3a, 3b) and upon movement of the second element (2a, 2b) relative to the first element (1), the following steps are initiated by the algorithm programmed in the control unit (6) for in-situ position determination: a) Emitting a signal or signal sequence by the RFID in-situ reader (5) to activate a subset of n transponders (3a, 3b) that are within the reception and read range (7) of the RFID in-situ reader (5) at the time of transmission; b) Transmission of the identification data of the transponders, together with their position data transmitted by the calibration, to the RFID in-situ reader (5) is triggered by activation.c) Determining a position X of the RFID in-situ reader (5) on the first element (1) relative to the second element (2a, 2b) by determining the position X of the RFID in-situ reader (5) relative to the positions x of the n transponders (3a, 3b) located in the receive and read area on the second element (2a, 2b) by the relationship x _ fol + X2+ X3+ - X, n 1 + X n ) n where: X is the position of the RFID in-situ reader. (5), xi , X2, X3, ... , x“-i , x n is the position of the n transponders (3a, 3b) located within the receive and read range (7) on the second element (2a, 2b), transmitted by the prior calibration of the transponders, n is the number of units in the reception and reading area (7) located and activated transponder (3a, 3b).

2. The method according to claim 1, wherein, during the transmission of the identification data and the position data of the respective transponder (3a, 3b) initiated by the activation of the transponders (3a, 3b), an intensity I of the signal for data transmission of the respective transponder (3a, 3b) is measured by the RFID in-situ reading device (5), and in method step c) the determination of the position X of the RFID in-situ reading device (5) on the first element (1) relative to the second element (2a, 2b) by weighting the positions xi , X2, ... , x n -i , x n the transponder (3a, 3b) by means of their signal intensities h, I2, ... , I n -i, l n is carried out and the position X of the RFID in-situ reading device (5) relative to the positions of the n transponders (3a, 3b) located in the receive and read area (7) on the second element (2a, 2b) is determined by the relationship where: is the position of the RFID in-situ reading device (5), xi , X2, X3, x„-i, x n is the position within the reception and reading area (7) located transponders (3a, 3b) on the second element, transmitted by the prior calibration of the transponders, n is the number of transponders (3a, 3b) located and activated in the receive and read area (7), I1, I2, I3, ..., In-1, In is the intensity of the data transmission signals of the respective Transponders (3a, 3b).

3. Method according to claim 1 or 2, wherein the calibration of the transponders (3a, 3b) on the second element is carried out in situ and during the movement of the second element (2a, 2b) relative to the first element (1 ).

4. Method according to claim 1 or 2, wherein the calibration of the transponders (3a, 3b) on the second element is performed ex situ and during a movement of the second element (2a, 2b) relative to an RFID ex situ reading device.

5. Method according to claim 1 or 2, wherein the calibration of the transponders (3a, 3b) is carried out on a calibration element corresponding to the second element ex situ and during a movement of the calibration element relative to an RFID ex situ reading device.

6. Method according to claim 4 or 5, wherein the calibration of the transponders (3a, 3b) is carried out after or during their manufacture in the form of assembly and the transponders (3a, 3b) are placed correctly on the second element after their calibration.

7. Method according to one of the preceding claims, wherein the separate transmission of the position data linked to the identification data to the respective transponder (3a, 3b) is carried out by restricting the receive and read range (7) of an RFID reading device used for calibration during the calibration process, such that only one transponder (3a, 3b) is located in the receive and read range (7) at any given time.

8. Method according to claim 7, wherein the restriction of the reception and reading range (7) of an RFID reading device (5) used for calibration is effected by a lens or aperture arranged between the RFID reading device (5) and the respective transponder (3a, 3b).

9. Method according to one of the preceding claims, wherein the RFID in-situ reading device (5) emits signals or signal sequences of different frequencies to activate a portion of n transponders (3a, 3b).

10. Method according to one of the preceding claims, wherein the alternating magnetic fields or radio waves of the RFID in-situ reading device (5) are focused to activate the transponders (3a, 3b) on the second element (2a, 2b) by means of a lens or aperture.

11. Programmable control device (6) for operating an RFID system for determining the position of a first element (1) in relation to a second Element (2a, 2b) in situ, by means of an RFID in-situ reading device (5) on the first element (1) on the one hand and by means of a number of transponders (3a, 3b) activatable by the RFID in-situ reading device (5) on the second element (2a, 2b) on the other hand, wherein the first and the second element move relative to each other on predetermined trajectories (4) such that the transponders (3a, 3b) pass through a receive and read area (7) of the RFID in-situ reading device (5), wherein transponders (3a, 3b) located in the receive and read area (7) of the RFID in-situ reading device (5) transmit identification data and position data to the RFID in-situ reading device (5) after their activation, wherein the control device (6) has in its programming an algorithm for carrying out the method according to one of claims 1 to 10.

12. Computer program comprising an algorithm with instructions for a control device (6) according to claim 11 for carrying out the method according to any one of claims 1 to 10.

13. Device for carrying out the method for determining the position of a first element (1) in relation to a second element (2a, 2b) in situ according to any one of claims 1 to 10, wherein the first and the second element move relative to each other on predetermined trajectories (4) and the position determination is carried out using an RFID system, in which an RFID in-situ reading device (5) is provided on the first element (1) and a number of transponders (3a, 3b) are provided on the second element (2a, 2b), wherein the device has the following features: the RFID in-situ reading device (5) is configured as a transmitter-receiver and is arranged on the first element (1) for transmitting and receiving alternating magnetic fields or radio waves such that the transponders (3a, 3b) on the second element (2a, 2b) pass through a receive and read area (7) of the RFID in-situ reading device (5), when the second element (2a, 2b) moves along the trajectory (4),The transponders (3a, 3b) passing through the receiving and reading area (7) on the second element (2a, 2b) can be activated by the RFID in-situ reading device (5) using alternating magnetic fields or radio waves and thus, arranged such that during a relative movement between the first and the second element, a portion of the transponders (3a, 3b) is temporarily located within the reception and reading range (7), the transponders (3a, 3b) are equipped with an electronic circuit and an antenna, whereby, after their activation, identification data and position data of the respective activated transponder (3a, 3b) can be transmitted to the RFID in-situ reading device (5), an algorithm is stored in a programmable control device (6) communicating with or integrated into the RFID in-situ reading device (5), which determines a position X of the RFID in-situ reading device (5) on the first element (1) relative to the second element (2a, 2b) from the identification data and position data transmitted by the respective activated transponder.

14. Device according to claim 13, wherein the transponders (3a, 3b) are arranged on the second element (2a, 2b) along its extension in the direction of the trajectory curve (4) and at a constant distance from each other.

15. Device according to claim 13, wherein the transponders (3a, 3b) on the second element (2a, 2b) are arranged at a smaller distance from each other in predetermined sub-areas along its extension in the direction of the trajectory curve (4) than in adjacent sub-areas.

16. Device according to one of claims 13 to 15, wherein the transponders (3a, 3b) are provided on the second element (2a, 2b) only in partial areas of its extension in the direction of the trajectory curve (4).

17. Device according to one of claims 13 to 16, wherein the transponders (3a, 3b) are glued or printed on the second element (2a, 2b).

18. Device according to one of claims 13 to 16, wherein the transponders (3a, 3b) are attached to a substrate which is applied, in particular glued, to the second element.

19. Device according to one of claims 13 to 18 for determining a longitudinal displacement of a piston rod (12) in a cylinder (11), wherein the The longitudinal displacement is determined by repeatedly determining the position of the cylinder (11) in relation to the piston rod (12) in situ and according to the method of one of claims 1 to 10, wherein, on the one hand, an RFID in-situ reading device (5) is fixedly connected to either the cylinder (11) or the piston rod (12) and / or moves with the cylinder (11) or the piston rod (12), and, on the other hand, a number of transponders (3a, 3b) that can be activated by the RFID in-situ reading device (5) by means of alternating magnetic fields or radio waves are provided on the other of the two elements, cylinder (11) or piston rod (12), wherein the transponders (3a, 3b) at least partially pass through a receiving and reading area (7) of the RFID in-situ reading device (5).

20. Device according to claim 19 for determining a change in length of a vibration damper (13) in a motor vehicle chassis, wherein the determination of the change in length is carried out in situ by repeatedly determining the position of a damper cylinder (11) in relation to a protective cover (21) connected to a damper piston rod (12) and concentrically surrounding the damper cylinder (11) according to the method according to one of claims 1 to 10, wherein the damper cylinder (11) dips into the protective cover (21) when the suspension is compressed, wherein an RFID in-situ reading device (5) is fixedly connected to the damper cylinder (11) and a number of transponders (3a, 3b) that can be activated by the RFID in-situ reading device (5) are provided on the protective cover (21) or on an element (20) connected to the protective cover (21).

21. Device according to claim 19 for determining a change in length of a vibration damper (13) in a motor vehicle chassis, wherein the determination of the change in length is carried out in situ by repeatedly determining the position of a damper cylinder (11) in relation to a protective cover (21) connected to the damper piston rod (12) and concentrically surrounding the damper cylinder (11), and according to the method according to any one of claims 1 to 10, wherein the damper cylinder (11) dips into the protective cover (21) when the suspension is compressed, wherein an RFID in-situ reading device (5) is fixedly connected to the protective cover (21) and a number of transponders (3a, 3b) that can be activated by the RFID in-situ reading device (5) are provided on the damper cylinder (11) or on an element (20) connected to the damper cylinder (11).

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