Method for determining the position of two elements relative to one another by means of an RFID system

Abstract

In a method for determining a position of a first element in relation to a second element, with both elements moving relative to one another, the position is determined using an RFID system comprising an RFID reader on the first element and a number of activatable transponders on the second element. The transponders pass through a receiving and reading region of the RFID reader and, after activation, transmit their identification data. A control device contains a programmed algorithm for controlling the RFID system and for carrying out the position determination, and a memory of the control device stores data in the form of a table in which the transmitted identification data of all the transponders have the associated position of said transponders on the second element. The identification data transmitted by the transponders located within the receiving and reading region are assigned to the respective positions of the transponders on the second element by means of the specified table, whereupon the position of the RFID reader on the first element relative to the second element is determined by way of a computation rule that the algorithm contains.

Description

[0001] Hanover, September 6, 2024

[0002] IP, Dr. Ohlendorf, Kilsch / MM

[0003] 302675-DE-NP

[0004] Method for determining the position of two elements relative to each other using an RFID system

[0005] The invention relates to a method for determining the position of a first element in relation to a second element, wherein the first and second elements move relative to each other on predetermined trajectories and the determination of the position (hereinafter: position determination) is carried out using an RFID system in which an RFID reading device or an RF ID reader is provided on the first element and a number of transponders are provided on the second element.

[0006] 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.

[0007] Measuring systems for determining the position of components moving linearly or rotationally relative to each other are known. Such systems include, for example, those that use RFID tags as transponders and an RFID reader. The transponders are attached to one of the moving components and transmit a signal containing identification information, which can be received by an RFID reader connected to the other moving component. The identification information can include position information or be listed in a table and assigned to the position information. This table is stored in memory, and the corresponding position information for each transponder can be retrieved from it.

[0008] 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.

[0009] 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.

[0010] To accurately detect even slight changes in position, transponders must be positioned relatively close to each other on one of the moving elements or components. This ensures 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 reader. With such close proximity, 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 positional data points are captured almost simultaneously, precise positioning is often impossible.

[0011] In the prior art devices for determining position using RFID systems, a conflict of objectives arises because, 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 inaccuracy when simultaneously reading a large number of transponder signals by the RFID reader and the resulting different position information.

[0012] 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 using an RFID system, which achieves high accuracy without additional apertures or shields, in which elaborate arrangements of several transponder rows can be dispensed with and in which a single RFID reader is sufficient for position determination despite a large number of closely spaced transponders.

[0013] 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 is determined using an RFID system in which an RFID reading device or an RFID reader is provided on the first element and a number of transponders are provided on the second element. Within a reception and read range of the RFID reading device or RFID reader, the transponders can be activated by the RFID reading device or RFID reader using 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 reading device or RFID reader.Once activated, the transponders within the read / receive range transmit data for their unique identification (identification data) to the RFID reader. The transponders on the second element are positioned along the length of the second element in the direction of its trajectory and are spaced apart from each other. During the movement of the second element relative to the first element, a subset of n transponders is temporarily within the read / receive range at any given time.A programmable electronic control device and an algorithm programmed in the control device are provided for controlling the RFID system and for carrying out the position determination, wherein data in the form of a predefined table (look-up table) are stored in a memory of the control device, in which the identification data of all transponders are assigned their exact position x at the second element.

[0014] The algorithm programmed in the control unit initiates the following steps for position determination: a) The RFID reader or RFID device transmits a signal or signal sequence to activate a subset of n transponders that are within the reception and read range at the time of transmission. b) The RFID reader or RFID device assigns the identification data transmitted by the n transponders located within the reception and read range to the respective positions xi, X2, ... , x n -i, x nthe transponder on the second element using the specified look-up table. c) Determining a position X of the RFID reading device or RFID reader on the first element relative to the second element by determining the position X of the RFID reading device or RFID reader relative to the positions x of the n transponders located in the receive and read range on the second element using the relationship

[0015] (xl + x2 + x3 + ••• x(n — 1) + xn) n where the following holds:

[0016] X the position of the RFID reader or the

[0017] In the RFID reader, xi, X2, ... , x"-i, Xn is the position of the n transponders located within the receive and read range on the second element, and n is the number of transponders located and activated within the receive and read 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 read range of a single reader / reading device lead to increased accuracy in position determination.

[0018] The positions xi, X2, x n -i , x n within the reception and reading area of ​​the

[0019] The n transponders located on the second element of the RFID reading device or the RFID reader, which are stored as data in a memory of the control device in the form of a predefined table, 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.

[0020] 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.

[0021] This becomes clear in the following example (Example 1). Here, a portion of the look-up table stored in the control unit is shown graphically. It lists the n transponders located within the reception and reading range of a reading device or reader (where n = 4 is chosen here), identified by their numbers 4, 5, 6, 7, and their transmitted identification data (TAG ID). These are then assigned to their respective positions X4, xs, xe, x? on the second element in the right-hand column, starting from a reference point not described in detail here.

[0022] According to the invention, the reading device or reader detects the four transponders 4 to 7 and their identification data almost simultaneously within its reading range and thus determines the exact position X of the RFID reading device or RFID reader 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 at (1,6+3,2+4,84-6,4) .

[0023] X = — — ■ — ■ — — = 4 mm.

[0024] 4

[0025] A further development of the procedure consists in the following: during the data transmission initiated by the activation of the transponders for the identification of the respective transponder, the intensity I of the signal for data transmission of the respective transponder is measured by the RFID reading device or the RF ID reader, and in process step c) the position X of the RFID reading device or the RFID reader on the first element relative to the second element is determined by weighting the transponder positions using their signal intensities , I2, L-1, l n , also known as RSSI (received signal strength indicator), whereby the position X of the RFID reading device or RFID reader relative to the positions of the n transponders located in the receive and read range on the second element is determined by the relationship where it is true that

[0026] X the position of the RFID reader or the RFID

[0027] Reader is, xi, X2, ... , x„-i, x n where the position of the transponders located within the receive and read range on the second element is, n is the number of transponders located in the receive and read range and activated, and li, I2, In-1, In are the intensities of the data transmission signals of the respective transponder.

[0028] Such a weighting is achieved by the signal intensities I1, I2, I measured during transmission by the reader. n -i, l n increases the accuracy of position determination.

[0029] This can also be illustrated using another example (Example 2), where, as above, a portion of a look-up table stored in a control device is shown graphically, alongside which the intensities currently determined by the reader are also considered. Again, the n transponders located within the reception and reading range of a reader, where n = 4, are listed with the numbers 4, 5, 6, 7, along with their transmitted identification data (TAG ID), and assigned to their respective positions X4, xs, xe, x? on the second element – ​​starting from a reference point not described in detail here.

[0030] The column to the right lists the corresponding signal intensities U, Is, le, I7) that are currently being determined and are not stored in the look-up table.

[0031] According to the invention, the reading device detects within its reading range in

[0032] Essentially, it simultaneously measures the four transponders 4 to 7 and their identification data and then uses the intensities to determine the exact position of the first element relative to the second element.

[0033] (1.6 ■ 30 + 3.2 ■ 40 + 4.8 ■ 70 + 6.4 ■ 40)

[0034] X = - - - = 4.27 mm

[0035] 180

[0036] 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.

[0037] In principle, the method according to the invention can also be carried out without a look-up table and with transponders that transmit their position information to the reading device as part of their identification data, provided that it is ensured that the position information and the actual position on the second element correspond. In this case, the transponders must be pre-programmed with their position information and then attached to the second element in the correct sequence and position. Both passive and active transponders can also be used in the method.

[0038] A further embodiment of the method according to the invention consists in the RFID reading device or RFID reader 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.

[0039] In another embodiment of the method, the alternating magnetic fields or radio waves of the RFID reading device are focused on the second element using a lens or aperture to activate the transponders. 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 reading 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.

[0040] The invention also relates to a programmable control device for operating an RFID system with an RFID reading device or RFID reader and with transponders that can be activated by the RFID reading device or RFID reader, wherein the RFID system is designed to determine the position of a first element relative to a second element, and the first and second elements move relative to each other along predetermined paths such that the transponders traverse a read and receive area of ​​the RFID reading device or RFID reader. The RFID reading device or RFID reader is permanently connected to the first element, and a number of transponders are activated by the RFID reading device or RFID reader.The RFID reader, which can be activated by means of alternating magnetic fields or radio waves, is provided on the second element, wherein the transponders located in a receiving and reading range of the RFID reading device or the RFID reader transmit data for their unique identification (identification data) to the RFID reading device or the RFID reader after their activation. The control device has an algorithm in its programming for carrying out the method according to the invention.

[0041] 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.

[0042] 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 relative 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 reading device or an RFID reader is provided on the first element and a number of transponders are provided on the second element. The device has the following features:

[0043] The RFID reading device or RFID reader (5) 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 such that the transponders on the second element pass through a reception and reading area of ​​the RFID reading device or RFID reader when the second element moves along the path.

[0044] On the second element, a number of transponders, which can be activated by the RFID reading device or RFID reader using alternating magnetic fields or radio waves, are arranged in such a way that, in the event of a relative movement between the first and the second element, a portion of the transponders are temporarily located within the reception and reading range.

[0045] The transponders are equipped with an electronic circuit and an antenna, which, after activation, allows data for the unique identification (identification data) of the activated transponder to be transmitted to the RFID reading device or RFID reader.

[0046] A programmable control device communicating with the RFID reading device or RFID reader has a memory in which data is stored in the form of a predefined table (look-up table) in which the identification data of all transponders is assigned their exact position x (position data) on the second element.

[0047] The control unit contains an algorithm which, according to the inventive method as described above, correlates the identification data transmitted by the respective activated transponder with the position data of the look-up table in memory and determines the position X of the RFID reading device or RFID reader on the first element relative to the second element.

[0048] 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.

[0049] Without reducing the accuracy of position determination within the required ranges of motion, 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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 longitudinal displacement is determined by repeatedly determining a position of the cylinder with respect to the piston rod according to the method according to the invention, in which, on the one hand, an RFID reading device or an RF ID reader is either fixedly connected 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 reading device or the RFID reader by means of alternating magnetic fields or radio waves are provided on the respective other element, i.e., on the respective 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 reading device or the RFID reader.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.

[0055] 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 change in length is determined 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 during compression. An RFID reading device is permanently connected to the damper cylinder, and a number of transponders, which can be activated by the RFID reader, are provided on the protective cover or on an element connected thereto.

[0056] A further embodiment of the device according to the invention consists in the fact that, 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, which is connected to the damper piston rod and concentrically surrounds the damper cylinder, according to the method according to the invention. During compression, the damper cylinder enters the protective cover, wherein an RFID reading device or an RFID reader is fixedly connected to the protective cover and a number of transponders, which can be activated by the RFID reading device or the RFID reader, are provided on the damper cylinder or on a substrate connected thereto.

[0057] The invention will be explained in more detail using an exemplary embodiment. The following are shown:

[0058] Fig. 1 shows a basic representation of a ruler-like arrangement of transponders on a component or element,

[0059] Fig. 2 shows a basic representation of a ruler-like arrangement of a different type of transponder on a component or element,

[0060] Fig. 3 shows a basic representation of an element which is connected to a

[0061] is equipped with a reading device or an RFID reader,

[0062] 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 an RFID reading device or RFID reader provided on another component or element, wherein the transponders pass through a receiving and reading area of ​​the RFID reading device or RFID reader.

[0063] Fig. 5 shows an enlarged side view of the one shown in Fig. 4.

[0064] Situation, presented in principle,

[0065] Fig. 6 shows a diagram of signal intensities generated by an RFID

[0066] The reading device or RFID reader is measured during the transmission of identification data of the respective transponder.

[0067] Fig. 7 shows a schematic representation of a vibration damper for a motor vehicle chassis with a device for carrying out the method according to the invention. Fig. 8 shows a schematic 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.

[0068] The figures may reference identical or similar elements using the same reference numerals. To clarify the invention, it is advantageous to view the figures together.

[0069] 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.

[0070] 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.

[0071] Fig. 3 shows, in a schematic representation, an element 1 equipped with a reading device or RFID reader 5, which also has an antenna AL and a programmable electronic control unit 6 communicating with the antenna. An algorithm for controlling the RFID system and for performing position determination is programmed into the control unit 6. The programmable electronic control unit 6 thus controls the implementation of the method according to the invention and is also constructed in the form of an electronic circuit (IC, integrated circuit).

[0072] Fig. 4, particularly in conjunction with Figs. 5 and 6, illustrates the position determination using the RFID system according to the invention with the aid of basic diagrams. Fig. 4 shows a simplified arrangement in a top view, in which a component or element 1 is located 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 the RFID reader 5 extending towards the component or element 2a.

[0073] The reception and reading area 7 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 a reading device or RFID reader 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 reading device or reader 5.

[0074] The transponders 3a can be activated by means of alternating magnetic fields via the antenna AL of the reading device or reader 5 and via the antennas AT located in the reception and reading area 7, while the component or element 2a below the component or element 1 passes through the reception and reading area 7 of the reading device or reader 5 on the trajectory 4.

[0075] After activation, the transponders 3a transmit data for their unique identification (identification data) to the RFID reader 5 within the receive and read range. The transponders 3a are positioned on the second element 2a along its extension in the direction of the trajectory 4 and are 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 there are within the receive and read range 7 of the reader 5; that is, a portion of n = 4 transponders is temporarily within the receive and read range 7.

[0076] In a memory 6a of the control unit 6, not shown in detail here, data is stored in the form of a predefined table (look-up table) in which the identification data of all transponders 3a is assigned their exact position x to the second element. The transponders, which are temporarily located within the receive and read area 7 in the illustration of Fig. 5, are located at positions X4 to x?.

[0077] The control unit contains an algorithm for controlling the RFID system, which performs the steps already shown in the example above (Example 1) for determining the position.

[0078] As described there, the identification data of the n transponders located within the reception and read range of a reader, transmitted after a signal has been sent to activate transponder 3a, are compared by the algorithm with the identification data stored in a look-up table in the control unit 6. This assigns the transmitted identification data (TAG ID) of the n transponders their respective positions X4, xs, xe, x? on the second element – ​​starting from a reference point B.

[0079] The position X of element 1, recognizable in Fig. 5, relative to the positions of the 4 middle transponders 3a located in the receive and read area on the second element 2a, is then determined by the relationship

[0080] 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 range on the second element 2a is achieved by weighting them according to the signal intensities U, Is, k, Iz shown in the diagram of Fig. 6. These intensities are measured by the reading device 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.

[0081] The position X of element 1 relative to the positions of the 4 middle transponders 3a located in the receive and read area on the second element 2a is then determined by the following relationship: „ > ( X 4 ' I4 + X 5 ' I5 + X 6 ' + X 7 ' I7)

[0082] (I4+ 15+ 16+ I7)

[0083] Fig. 7 shows a schematic representation of an 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. 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).

[0084] The device 10 in the vibration damper 13 has an RFID reading device / an RFID reader 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 which is glued to an inside of a cylindrical dust cover 21 connected to a damper piston rod 12.

[0085] The device further includes an integrated programmable control unit 6 with a memory 6a in the RFID reading device 5, as shown in Fig. 1. Data is stored here in the form of a predefined table (look-up table) in which the identification data of all transponders on the substrate 20 are assigned their exact position x (position data) along the cylindrical dust cover 21, as shown in Examples 1 and 2 above.

[0086] Using the RFID reader 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. 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, 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.

[0087] 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.

[0088] 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.

[0089] The repeated determination of the position of the outer damper cylinder 11 as first element 1 in relation to the damper piston rod 12 as 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.

[0090] The transponders attached to the substrate 20 pass through the receiving and reading area 7 of the RFID reading device 5 during compression and rebound, are thereby activated by means of alternating magnetic fields or radio waves, and then transmit data for their unique identification (identification data) to the RFID reading device 5. For the sake of clarity, the receiving and reading area 7 of the RFID reading device 5 on the damper cylinder 11 is not shown in detail in Fig. 7, but its function becomes clear when comparing Fig. 7 with Fig. 5.The identification data of the transponders attached to the substrate 20, which are located in the reception and reading area, are then assigned their positions according to the inventive method via the look-up table, after which the position of the dust cover 21, thus 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, can be determined.

[0091] 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 reading device 5 and the elements carrying the transponders are interchanged.

[0092] Fig. 8 differs from the representation in Fig. 7 only in that an RFID reading device / an RFID reader 5 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.

[0093] The RFID reader 5 also has an integrated programmable control unit 6 with a memory 6a, as shown in Fig. 1.

[0094] The fact that the reader 5 and the elements carrying the transponders are swapped here compared to Fig. 7 offers the advantage that the dimensions of the RFID reading device / RF ID reader 5 can be somewhat larger and assembly is simplified, making replacement particularly easy.

[0095] Here too, the transponders attached to the substrate 20 pass through the receiving and reading area 7 of the RFID reading device 5 during compression and rebound, are thereby activated by means of alternating magnetic fields or radio waves, and then transmit data for their unique identification (identification data) to the RFID reading device 5. 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 method according to the invention during compression and rebound, as already described above.

[0096] With reference to the method according to the invention, the damper cylinder 11 in the embodiment according to Fig. 8 is 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.

[0097] Reference mark (part of the description)

[0098] I first element

[0099] 2a, 2b second element

[0100] 3a Transponder with external antenna

[0101] 3b transponder with integrated antenna

[0102] 4. Trajectory curve

[0103] 5 RFID reading device / RFID reader

[0104] 6 Control unit

[0105] 6a storage

[0106] 7 Reception and reading area

[0107] 10. Setup

[0108] II outer damper cylinder

[0109] 12 Damper piston rod

[0110] 13 vibration dampers, gas pressure dampers

[0111] 14 Gas cushion / gas volume in the outer damper cylinder

[0112] 14a Oil volume in the outer damper cylinder

[0113] 15 valve

[0114] 16 Interior of the inner damper cylinder

[0115] 16a Oil volume inside the inner damper cylinder

[0116] 17 inner damper cylinder

[0117] 18 valve

[0118] 19 damper pistons

[0119] 20 substrates with attached transponders

[0120] 21 Dust cover

[0121] 22 body-side eye

[0122] 23 chassis-side eye

[0123] X4 position transponder 4 xs position transponder 5

[0124] X6 Position Transponder 6

[0125] X7 Position Transponder 7

[0126] X Position Element 1 k Signal intensity Transponder 4

[0127] Signal intensity transponder 5 le signal intensity transponder 6

[0128] I7 Signal intensity Transponder 7

[0129] AT antenna of the transponder

[0130] AL antenna of the RF ID reader

[0131] 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 is determined using an RFID system, wherein an RFID 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 transponders (3a, 3b) can be activated within a receive and read range (7) of the RFID reading device (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 reading device (5). pass through RFID reader (5), - wherein the transponders (3a, 3b) after their activation within the receive and read range (7) transmit data for their unique identification (identification data) to the RFID reading device or RFID reader (5), - wherein the transponders (3a, 3b) are provided on the second element (2a, 2b) along its extension in the direction of the trajectory curve (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 portion 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 determination of the position, - wherein data in the form of a predefined table (look-up table) is stored in a memory (6a) of the control device (6), in which the identification data of all transponders is assigned their exact position x on the second element (2a, 2b), characterized in that the following steps are initiated by the algorithm programmed in the control device (6) for determining the position: a) sending a signal or signal sequence by the RFID reading device or the RF ID reader (5) to activate a subset of n transponders (3a, 3b) which are located within the receive and read range (7) at the time of transmission, b) assigning the identification data transmitted by the n transponders located within the receive and read range (7) to the RFID reading device or the RFID reader (5) to the respective positions xi, X2, ..., x n -i, x nthe transponder (3a, 3b) on the second element (2a, 2b) using the specified look-up table, c) Determining a position X of the RFID reading device or RFID reader (5) on the first element (1) relative to the second element (2a, 2b) by determining the position X of the RFID reading device or RFID reader (5) relative to the positions x of the n transponders (3a, 3b) located in the receive and read range on the second element (2a, 2b) by the relationship x _ (X! + X2+ X3+ -X n 1 + X n ) n where: X is the position of the RFID reading device or RFID reader (5), xi, X2, X3, ... , x„-i, x n is the position of the n transponders (3a, 3b) located within the receive and read area (7) at the second element (2a, 2b), n is the number of transponders (3a, 3b) located and activated in the receive and read area (7).

2. Method according to claim 1, wherein, during the transmission of the identification data initiated by the activation of the transponders (3a, 3b) for the identification of the respective transponder (3a, 3b), an intensity I of the signal for data transmission of the respective transponder (3a, 3b) is measured by the RFID reading device or the RFID reader (5), and in method step c) the determination of the position X of the RFID reading device or the RFID reader (5) at 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, h, ... , I n -i, l n is carried out and the position X of the RFID reading device or RFID reader (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: X is the position of the RFID reading device or RFID reader (5), xi, X2, X3, ... , x„-i, x n is the position of the transponders (3a, 3b) located within the receive and read area (7) on the second element, n is the number of transponders (3a, 3b) located and activated in the receive and read area (7), I1, I2, I3, ... , ln-1, In is the intensity of the data transmission signals of the respective transponder (3a, 3b).

3. Method according to claim 1 or 2, wherein the RFID reading device or RFID reader (5) sends signals or signal sequences of different frequencies to activate a portion of n transponders (3a, 3b).

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

5. Programmable control device (6) for operating an RFID system for determining the position of a first element (1) relative to a second element (2a, 2b) by means of an RFID reading device or RFID reader (5) on the first element (1) on the one hand and by means of a number of transponders (3a, 3b) on the second element (2a, 2b) that can be activated by the RFID reading device or RFID reader (5), wherein the first and the second element move relative to each other on predetermined trajectories (4) such that the transponders (3a, 3b) define a receive and read area (7) of the RFID reading device or RFID reader (5), wherein transponders (3a, 3b) located in a receiving and reading area (7) of the RFID reading device or RFID reader (5) transmit data for their unique identification (identification data) to the RFID reading device or RFID reader (5) after their activation, wherein the control device (6) has a memory (6a) and in its programming an algorithm for carrying out the method according to claims 1 to 4.

6. Computer program comprising an algorithm with instructions for a control device (6) according to claim 5 for carrying out the method according to claims 1 to 4.

7. Device for carrying out the method for determining the position of a first element (1) in relation to a second element (2a, 2b) according to claims 1 to 4, wherein the first and the second element move relative to each other along predetermined trajectories (4) and the determination of the position is carried out using an RFID system, in which an RFID reading device or an RFID reader (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 reading device or the RFID reader (5) is configured as a transmitter-receiver and is arranged on the first element (1) for emitting 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 reading device or the RFID reader (5) when the second element (2a,2b) moves on the trajectory (4), the transponders (3a, 3b) passing through the reception and reading area (7) on the second element (2a, 2b) can be activated by the RFID reading device or RFID reader (5) using alternating magnetic fields or radio waves and are arranged such that, in the event of 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 area (7), The transponders (3a, 3b) are equipped with an electronic circuit and an antenna, whereby, after their activation, data for the unique identification (identification data) of the activated transponder (3a, 3b) can be transmitted to the RFID reading device or RFID reader (5). A programmable control device (6) communicating with or integrated into the RFID reading device or RFID reader (5) has a memory (6a) in which data is stored in the form of a predefined table (look-up table) in which the identification data of all transponders (3a, 3b) is assigned their exact position x (position data) on the second element. An algorithm is stored in the control device (6).which correlates the identification data transmitted by the respective activated transponder with the position data of the table in the memory (6a) and from this determines a position X of the RFID reading device or RFID reader (5) at the first element (1 ) relative to the second element (2a, 2b).

8. Device according to claim 7, 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.

9. Device according to claim 7, wherein the transponders (3a, 3b) are arranged on the second element (2a, 2b) along its extension in the direction of the trajectory (4) in predetermined sub-areas at a smaller distance from each other than in adjacent sub-areas.

10. Device according to one of claims 7 to 9, 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).

11. Device according to one of claims 7 to 10, wherein the transponders (3a, 3b) are glued or printed on the second element (2a, 2b).

12. Device according to one of claims 7 to 10, wherein the transponders (3a, 3b) are attached to a substrate which is applied, in particular glued, to the second element.

13. Device according to any one of claims 7 to 12 for determining a longitudinal displacement of a piston rod (12) in a cylinder (11), wherein the longitudinal displacement is determined by repeatedly determining a position of the cylinder (11) relative to the piston rod (12) according to the method according to any one of claims 1 to 4, wherein, on the one hand, an RFID reading device or an RF ID reader (5) is fixedly connected to and / or moves with the cylinder (11) or with the piston rod (12), and, on the other hand, a number of transponders (3a, 3b) that can be activated by the RFID reading device or the RFID reader (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) pass through at least part of a receiving and reading area (7) of the RFID reading device or RFID reader (5).

14. Device according to claim 13 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 by repeatedly determining a 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 claims 1 to 4, wherein the damper cylinder (11) dips into the protective cover (21) when the suspension is compressed, wherein an RFID reading device or an RFID reader (5) is fixedly connected to the damper cylinder (11) and a number of transponders (3a, 3b) that can be activated by the RFID reading device or the RFID reader (5) are provided on the protective cover (21) or on an element (20) connected to the protective cover (21).

15. Device according to claim 13 for determining the change in length of a vibration damper (13) in a motor vehicle chassis, wherein the determination of the change in length is carried out by repeatedly determining a position of a damper cylinder (11) with respect to a protective cover (21) connected to the damper piston rod (12) and concentrically surrounding the damper cylinder (11) according to the method according to claims 1 to 4, wherein the damper cylinder (11) dips into the protective cover (21) when the suspension is compressed, wherein an RFID reading device or an RFID reader (5) is fixedly connected to the protective cover (21) and a number of Activable transponders (3a, 3b) are provided on the damper cylinder (11) or on an element (20) connected to the damper cylinder (11).

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