WO2023227481A1

WO2023227481A1 - Multi-track assembly for length- and angle-measuring systems

Info

Publication number: WO2023227481A1
Application number: PCT/EP2023/063489
Authority: WO
Inventors: Bernhard LINDNER; Paul TUTZU; Victor Vasiloiu
Original assignee: Flux Gmbh
Priority date: 2022-05-21
Filing date: 2023-05-19
Publication date: 2023-11-30

Abstract

The invention relates to a device for a length- or angle-measuring system, comprising: a first measuring track with a periodic coding that has a first number of division periods, said first measuring track being arranged on a first plane; and at least one second measuring track with a periodic coding which has a second number of division periods, said second measuring track being arranged on a second plane. The first number of division periods and the second number of division periods differ, the first plane and the second plane are parallel to each other, and the first measuring track and the second measuring track at least partly overlap.

Description

MULTI-TRACK ARRANGEMENT FOR LINEAR AND ANGLE MEASURING SYSTEMS

TECHNICAL FIELD

[0001] The invention relates to a multi-track arrangement for measuring systems for position determination, a sensor head for scanning the multi-track arrangement and a corresponding measuring system consisting of a multi-track arrangement and a sensor head.

BACKGROUND

[0002] Various measuring systems for position determination are known from the prior art, in particular linear/length measuring systems, angle measuring systems or rotary encoders. Linear measuring systems or length measuring systems are designed to determine the position along a route with different end points. In contrast, angle measuring systems are designed to determine the position along a closed circular path. A measuring system for position determination includes a measuring standard, which contains coded position information, and a scanning head with a sensor. In addition, the measuring system can include a physical evaluation channel and an evaluation circuit. The position information from the measuring system is usually forwarded via an interface to a servo controller for regulation or control (for example to regulate/control position, speed or torque).

The position measurement is carried out by the relative movement of the scanning head and the material measure. The sensor measures a physical property, for example a magnetic or an electrical measurement variable, which depends on the encoded position information. Position information is then calculated by the evaluation circuit from the change in the physical property. The position information obtained can either be relative if it depends on a starting position, or absolute if each point of a trajectory is uniquely defined by the coded position information of the measuring standard. Depending on the measuring system, the scanning head or the measuring scale moves. In the case of a circular measuring scale, we speak of rotor and stator.

[0004] So-called vernier-coded measuring standards are known for absolute position measurement. The measuring standard has at least two periodically coded measuring tracks, which have different graduation periods, so that a unique signal combination of the tracks is available for each position on the measuring standard. [0005] Known systems use, for example, coded measurement tracks which are arranged in the same plane parallel to the scanning surface or to the scanning point of the sensor or the sensor elements. The publication DE 10 2021 205036 A1 discloses a scanning element for a system with several tracks arranged in parallel in the same plane. The publication EP 2329225 B1 discloses an inductive position sensor for a system with several tracks arranged in parallel in the same plane. The publication EP 0845659 B1 discloses a scanning element for a position measuring device in which several tracks with different periodicities are arranged in parallel in the same plane.

[0006] Theoretically, such arrangements and systems can be expanded to include any number of tracks in order to increase the measurement accuracy. However, the parallel positioning of two or more vernier channels in the same plane, as is known from the prior art, results in a number of disadvantages, which are briefly discussed below.

The width of the arrangement increases with each additional parallel measurement track. In the case of an angle measuring system, this means that either the inside diameter becomes smaller, which is particularly disadvantageous for systems that require a large through hole, for example for cable harnesses, or the outside diameter increases, which in turn leads to increased space requirements. The disadvantage of increased space requirements also applies to linear measuring systems.

[0008] The different lengths of the division periods lead to different operating points of the individual sensor elements. The distance between the measuring standard and the sensor element, also called the air gap, is defined as the operating point. In addition, the behavior of the generated signal amplitude of the sensor element is usually not linear.

The system resolution is largely determined by the measurement track which has the largest number of division periods, ie the smallest division length. The higher the requirement regarding system resolution, the higher the number of division periods of this track must generally be. However, a track with many division periods drastically limits the work area. The larger tracks are generally used to generate the absolute position of the system. However, the greater the difference in the division periods of the individual tracks, the greater the difference in their amplitude curve. [0010] When designing the sensor, it is advantageous to vary the number of division periods of the individual measurement tracks only minimally or to define them in the same order of magnitude. This means that the working areas of the measurement tracks would not limit each other and their amplitude curves would only differ insignificantly from one another. However, it must be noted that this makes the requirements for the accuracy of the measuring channels for determining the absolute position of the system significantly more stringent.

[0011] In summary, it can be stated that for a system with high resolution, which corresponds to a track with many pitch periods, the higher the result of multiplying the number of pitch periods of the measurement tracks, the higher the requirements regarding the position detection of the individual tracks apply. In addition, the greater the difference in the number of division periods, the greater the difference in the working range of the individual sensor elements. This in turn limits the working area of the entire system.

[0012] A further disadvantage of tracks of the measuring scale running parallel in the same plane is the robustness of the system against assembly errors. Assembly errors include, in particular, vertical tilting, horizontal twisting or horizontal offset of the scanning head or the sensor and the sensor elements relative to the tracks of the measuring standard.

[0013] The wider a multi-track arrangement is, the greater the effect of tilting on the working area or the air gap of the sensor, in particular on the outermost tracks. These usually include those with the most division periods and thus those with the smallest working area. The tilting changes the relative phase between the sensor and the measuring scale. If this phase error becomes greater than the maximum permitted error, the absolute position can no longer be determined correctly.

[0014] A horizontal rotation as well as a horizontal offset of the scanning head relative to the measuring standard leads to a change in the relative phase between the position signals of the individual measuring channels and in turn reduces the working range of the system. If, in combination with the accuracy of the track, the phase change is greater than the maximum permitted position error, the absolute position can no longer be determined correctly. It also applies that the influence of the phase shift is more pronounced the wider or more tracks the system has. [0015] The inventors have set themselves the task of providing a measuring system for position determination which overcomes the above disadvantages, in particular significantly reduces the influence of assembly errors (tilting, twisting, offset, eccentricity, etc.) and at the same time remains particularly compact.

SUMMARY

[0016] The stated object is achieved by a device with the features of claim 1, a system with the features of claim 7 and a sensor head with the features of claim 18. Various embodiments and further developments of the present invention are described in the dependent claims.

[0017] An arrangement is described which comprises: a first measurement track with a periodic coding, which has a first number of division periods, the first measurement track being arranged in a first plane, and at least one second measurement track with a periodic coding , which has a second number of division periods, the second measurement track being arranged in a second level. The first number of division periods and the second number of division periods differ from each other. The first level and the second level are parallel to one another and the first measurement track and the second measurement track at least partially overlap.

[0018] A system is also described which comprises: an arrangement according to the previous paragraph, and a sensor head with a first sensor element, which forms a first measurement channel together with the first measurement track, and at least one second sensor element, which together with the second measurement track forms a second measurement channel. The first and second sensor elements cover at least one pitch period of the first and second measurement track, respectively.

[0019] In addition, a sensor head for an arrangement as shown above is described, which has the following: a first sensor element which is arranged in a third plane and is designed to form a first measurement channel with the first measurement track; and at least one second sensor element, which is arranged in a fourth plane and is designed to form a second measurement channel with the second measurement track. The third level and the fourth level are parallel to one another and spaced apart from one another, with the first sensor element and the second sensor element at least partially overlapping one another. This makes it possible in particular to create a configuration which minimizes the otherwise different influence of errors in the execution or assembly of the multi-track arrangement on the respective measuring channels. Errors in execution or assembly include, in particular, tilting, twisting, offset, eccentricity of the measuring tracks and/or sensor elements. In addition, such an arrangement has the advantage that any phase errors that may occur have the same geometric effect on all measuring channels. Furthermore, such a configuration enables a compact design, particularly with regard to the ratio of the outside diameter to the inside diameter in the case of an angle measuring system. It also makes it possible to optimize the working area and to better scan the coded information of the measurement tracks. In addition, it becomes possible to reduce the effort involved in producing and operating a multi-track arrangement.

BRIEF DESCRIPTION OF THE FIGURES

[0021] For a better understanding of the features and advantages of the invention, some embodiments of the invention will be described in more detail below with reference to the attached FIGS. 1 to 19. However, the representations of the figures only illustrate some embodiments and should not be viewed as limiting, since there may also be other, equally effective embodiments. It should be noted that some of the details and/or features shown in the figures are not reproduced to scale for reasons of clarity.

[0022] Figure 1 shows a block diagram of a position measuring system.

[0023] Figure 2 shows a perspective view of a length measuring system according to the prior art.

[0024] Figure 3 shows a perspective view of an angle measuring system according to the prior art.

[0025] Figure 4 shows a perspective view of a length measuring system with a periodically coded measuring standard and a periodic sensor element.

[0026] Figure 5 shows two views from above of an embodiment of a vernier arrangement with two parallel tracks with 16 or 3 graduation periods, where the sensor only has one Part of the measuring standard covers (Fig.5a) or covers the entire surface of the measuring standard (Fig.5b).

[0027] FIG. 6 shows the output signals of a sensor element of a track with 16 graduation periods depending on the angle.

[0028] FIG. 7 shows the output signals of a sensor element of a track with 3 graduation periods depending on the angle.

[0029] Figure 8 shows the starting position of the sensor elements in comparison to the absolute position of the measuring system depending on the angle.

Figure 9 shows a side view of an embodiment of a material measure for a linear vernier coding with 3 tracks.

[0031] FIG. 10 shows a diagram that shows the signal amplitude of an inductive sensor depending on the air gap or working area for different pitch lengths.

[0032] FIG. 11 shows views from above of two embodiments of a measuring scale for vernier coding with two tracks, each with different graduation periods.

[0033] FIG. 12 shows a cross-sectional view of a measuring system with an assembly error in the form of a tilt.

Figure 13 shows a view from above of a measuring system with an assembly error in the form of a twist.

[0035] FIG. 14 shows a view from above of two overlapping vernier tracks of a measuring standard with 16 or 3 graduation periods.

15 shows a schematic cross-sectional view of an embodiment of a measuring system with two overlapping measuring channels.

Figure 16 shows a perspective view of a measuring system with two parallel vernier measuring channels in the same plane (Figure 16a) and a measuring system with overlapped vernier measuring channels in different planes (Figure 16b). [0038] FIG. 17 shows a simplified, perspective view of an embodiment of an angle measuring system with three completely overlapping measuring channels.

Figure 18 shows a diagram that shows the signal amplitude of three measurement tracks with 32, 8 and 3 graduation periods depending on the air gap.

19 shows views from above of a material measure for an angle measuring system with (1) a magnetic track, (b) a geometric track and (c) a combination of a magnetic and a geometric track.

DETAILED DESCRIPTION

The following definitions apply to the description of the drawings.

A material measure comprises one or more measurement tracks. A measurement track includes periodically or aperiodically coded information, which can be introduced in a variety of forms. A measuring standard or a measuring track of a measuring standard can be designed as both a passive and an active element. The measuring standard or the one or more measuring tracks of a measuring standard can be scanned by a scanning head or a sensor.

[0044] A multi-track arrangement refers to a material measure which comprises two or more measuring tracks.

[0045] In the case of periodic coding of a measuring track of a material measure, a division period refers to the period of the coding, i.e. the smallest unit or distance of the coded measuring track, after which the coded information repeats itself.

[0046] A scanning head includes a sensor, which can include one or more sensor elements. A sensor can be based on one or more physical measuring principles, in particular magnetic, inductive, optical, capacitive measuring principles and/or Giant Magneto-Impedance (GMI) as a measuring principle. A sensor can scan the entire length or surface of a measuring standard as well as just a part or a segment of a measuring standard. A sensor element covers at least one division period of the measurement track. During scanning, the sensor generates one or more analog signals, which are influenced by the coded information contained in the measuring standard or the one or more measuring tracks. In particular, a sensor or a sensor element can comprise an emitter coil and a receiver coil. An emitter coil can emit an electromagnetic emitter signal with a predefined emitter signal frequency, which can induce a signal in the receiver coil. Depending on the conductivity or permeability of an area of the measurement track to be scanned, the induced signal is amplified or reduced. The signal amplitude, which refers to the amplitude of the induced sensor signal, depends in particular on the working range or operating point of the sensor or sensor element.

A measuring channel refers to the combination of a measuring track of a material measure with a sensor element assigned to the measuring track, which is suitably arranged to completely or partially scan the measuring track to determine the position.

[0049] A physical evaluation channel refers to a physical channel via which the one or more analog signals generated during scanning are forwarded to evaluation electronics.

[0050]An evaluation electronics converts analog sensor signals into digital or analog position information using suitable methods and can in particular include a circuit, controller or microcontroller.

[0051] Overlapping of measurement tracks refers to the geometric overlap of the measurement tracks in the direction of the sensor scanning them or the sensor elements scanning them. Overlap of sensor elements refers to the geometric overlap of the sensor elements in the direction of the measurement tracks they scan.

[0052] In the case of a multi-track arrangement for a linear or length measuring system, completely or completely overlapping means that the edges of the smallest squares, which each have one of two adjacently overlapping measuring tracks or one of two adjacent overlapping sensor elements orthogonal to the overlapping direction, are essentially congruent in the overlapping direction, i.e. at least 95% of the area enclosed by them.

[0053] In the case of a multi-track arrangement for an angle measuring system, complete or complete overlap means that the rings or partial rings, which consist of the largest inner full or partial circle or the inner full or partial ellipse and the smallest outer full or partial circle or the outer full or partial ellipse are formed, each of which delimits one of two adjacently overlapping measurement tracks or one of two adjacently overlapping sensor elements orthogonally to the overlapping direction, in the overlapping direction essentially, ie to at least 95 % of the area between the inner and outer boundaries are congruent.

In contrast, a partial overlap occurs if a track does not extend over the entire angle or over the entire length of the other track(s), so that the overlap is less than 95%, or if, for example, in an arrangement with four tracks, each with two completely overlapping tracks running in parallel.

[0055] A mechanical change refers to the change, in particular the change in the shape, surface and/or structure of an object, through the action of a force. Geometric modulation means the change in the shape of an object through the action of a force.

[0056] Magnetic measurement variables include, for example, the field strength, the flux density, the reluctance, the permeability, the saturation magnetization, the dipole moment and the polarization.

[0057] Electrical measurement variables include, for example, current, voltage, charge, capacity, energy, power, resistance and conductivity.

[0058] Figure 1 shows a general block diagram of a position measuring system, in this case a length measuring system. The measuring system includes a material measure 1 and a scanning head 2 (sensor head). The position information of the measuring system is forwarded via an interface 4 to a servo controller 3 for regulation, for example of the position, the speed and/or the torque, or for control.

[0059] The material measure 1 contains coded information which can be introduced in a wide variety of forms. The material measure 1 can be designed as both a passive and an active element. Examples of active elements for the measuring scale are angular position encoders (resolvers) and rotary encoders, which have a meander-shaped structure that is supplied with an alternating current signal.

The scanning head 2 includes a sensor 2.1. The sensor 2.1 can be based on various physical measuring principles, for example on a magnetic, inductive, optical, capacitive or the “Giant Magnetic Impedance” (GMI) measuring principle. The sensor 2.1 can scan (capture) the entire length or surface of the measuring standard 1 or only a part or a segment of it. The sensor 2.1 generates one or more analog signals during scanning.

[0061] The scanning head 2 also includes an electronic circuit with evaluation electronics 2.2 (sensor circuit), which converts the analog sensor signals into digital or analog position information using suitable methods. The sensor circuit 2.2 can have an evaluation circuit with a multiplexer, the multiplexer being connected to the sensor elements and being designed to provide measurement signals via a single physical evaluation channel.

The position measuring system can be a linear measuring system or a length measuring system. Figure 2 shows a representation of a linear or length measuring system. The material measure 1 is designed as a linear, band-shaped element which extends along a length direction x, which also represents the measuring direction. It has a linear coding, which also extends in the measuring direction x. The sensor head 2 is arranged above the material measure 1 and can move along the measuring direction x in order to detect the material measure 1.

3, on the other hand, shows a representation of an angle measuring system with an annular measuring standard 1 and a corresponding, also annular sensor head 2. The measuring standard 1 has a circular coding along a radial direction, which corresponds to the measuring direction. In the example shown, the sensor head 2 is arranged parallel to and spaced from the material measure 1. In addition, both elements have one and the same axial axis, which is arranged perpendicular to the planes in which the material measure 1 and the sensor head 2 each extend and passes through a center of the material measure or the sensor head. During the measurement, the sensor head can rotate around the axial axis and thus serve as a rotor, while the measuring scale remains rigid and serves as a stator. Alternatively, the measuring scale can rotate around the axis and the sensor head can remain rigid.

Typically, the material measure 1 and the sensor head 2 are at a substantially constant distance in a direction which is perpendicular to the plane in which the material measure 1 extends, spaced apart, as shown in Figures 1 to 3. This means that optical as well as magnetic, capacitive or inductive measurements can be carried out.

4 shows a schematic representation of a linear measuring system according to the prior art, which is based on an inductive measuring principle. The coded information is introduced into the material measure 1 (the scale) through different areas with different permeabilities p (reluctances) and/or different conductivities σ. In the example shown, the linear-shaped measuring scale 1 extends along a measuring direction x, with two adjacent areas in the measuring direction having different permeability or conductivity. The coding is periodic, with a period comprising a sequence of a first region with a permeability po or conductivity σo and a second region with a permeability μ1 or conductivity σ1 and having a division period λ. By relative movement of the material measure 1 and a sensor head, an incremental position measurement can be carried out starting from a starting position of the sensor head.

[0066] Basically, the material measure 1 comprises one or more periodically or aperiodically coded measurement tracks. In the case of periodic coding, the division period λ corresponds to a period of coding. The measuring scale 1 is controlled by a sensor

2.1 sensed. The scanning is therefore not a matter of sampling, but rather a detection of the material measure. It applies that the sensor 2.1 is a sensor element

2.1.1 for each track of the measuring scale contains. A sensor element 2.1.1 is formed from at least one emitter coil 2.1.1.1 and one or more receiver coils 2.1.1.2. It applies that a sensor element 2.1.1 can have one or more emitter coils 2.1.1.1 and an emitter coil 2.1.1.1 can be shared by both just one sensor element 2.1.1 and by several sensor elements 2.1.1.

[0067] The sensor element 2.1.1 covers at least one graduation period λ of the measurement track. The sensor element can also cover several division periods n λ (with n ∈ N), where n denotes the number of division periods. This means that any errors that may occur can be averaged, which reduces the general measurement error. The emitter coils 2.1.1.1 and the receiver coils 2.1.1.2 can be implemented, for example, as conductor tracks in the form of a meander structure (flat coils) in or on a rigid or flexible substrate (eg a printed circuit board). In the example shown, the sensor element 2.1.1 comprises a single emitter coil 2.1.1.1, which has the shape of a cuboid, and two meandering, offset receiver coils 2.1.1.2, which are arranged within the emitter coil 2.1.1.1.

[0068] A measuring track of the material measure 1 forms a measuring channel in combination with the sensor element 2.1.1. The electronic circuit 2.2 feeds an alternating current into the generator coil(s) 2.1.1.1 of the sensor element 2.1.1, for example with a frequency in the range from a few kHz to 100 MHz. Due to the inductive coupling (counter-induction) between the emitter 2.1.1.1 and receiver coils 2.1.1.2, an alternating current of the same frequency is induced in the receiver coils 2.1.1.2. The counter-induction is modulated during a relative movement of the material measure 1 with respect to the scanning head 2 (the sensor structure).

[0069] In the case of different permeabilities p, those areas of the measuring scale 1 with higher magnetic permeability (μ1 ≥ μ0) will amplify the counter-induction or the alternating current induced in the receiver coils 2.1.1.2.

[0070] In the case of different conductivities σ, those areas of the measuring scale 1 with higher conductivity (σ1 ≥ σ0) will reduce the mutual induction or the alternating current induced in the receiver coils 2.1.1.2.

[0071] The alternating currents induced in the receiver coils 2.1.1.2 or the measured signals are demodulated by the evaluation electronics 2.2 and converted into position information. The position information obtained in this way is forwarded via an interface 4 to a servo controller 3 for various regulations and controls. In one example, the interface is a synchronous serial interface (SSI, Synchronous Serial Interface) and includes a power amplifier (line driver), e.g. of type RS485, as well as a cable and a connector.

As described above, for position measurement, the sensor head can move along the measuring direction above the surface of the measuring standard and thereby detect changes in one or more physical variables, such as the inductance or the magnetic field strength, with the evaluation circuit calculating position information from the sensor signals. Alternatively, the sensor head can be rigid while the measuring scale itself moves, for example rotates.

A distinction is made between incremental and absolute measuring systems. [0074] The position information of an incremental measuring system only contains information about the relative offset in relation to the starting position “0” at system start. An extension can contain a defined system zero point in the form of a reference mark (Reference Index Ri or Reference Mark Rm). However, this information is only available when the sensor scans this corresponding mark on the measuring scale after switching on.

[0075] The position information of an absolute measuring system includes the absolute offset between the scanning head and the measuring standard immediately after switching on. There are various options for coding and recording an absolute position.

For example, the material measure can be coded using a Pseudo Random Code (PRC). A PRC is a digital code (encoded with N bits). In this case, the material measure usually only includes one measurement track to be scanned. A corresponding sensor records a specific length or segment of this track. Each recorded partial area of the coding, which corresponds to a combination of “ones” and “zeros”, may occur exactly once over the entire length or the entire angle. This means that an absolute position can be obtained with appropriate evaluation electronics.

[0077] The execution using Pseudo Random Code (PRC) is particularly suitable for long measuring distances, but requires very complicated sensor structures and evaluation electronics in order to decode the plurality of the code (N bits). The advantages of execution using PRC can be seen as the fact that theoretically and mathematically any system length can be coded and thus made possible. In addition, only one measurement track is required. The disadvantages are that a complex sensor structure and evaluation electronics are required and this complexity increases with the measuring length.

[0078] Alternatively, the measuring standard can be designed as a vernier-coded measuring standard. In this case, the material measure comprises two or more periodically coded tracks with different periodicities or pitch periods, which are also referred to as incremental tracks. As a rule, these tracks are guided parallel to the scanning surface or to the scanning point. A division period is the smallest unit of the coded measuring standard and indicates the distance after which the coded pattern repeats itself. [0079] It applies here that the greatest common divisor (ggT) of the number of division periods of at least two measuring tracks of a vernier-coded measuring standard, which are used to obtain the absolute position, must be equal to 1. This ensures that each combination of the measurement tracks within the scanning areas of the sensor only exists once over the entire measuring scale, in particular length and/or angle, of a corresponding sensor. This means that an absolute position can be obtained with appropriate evaluation electronics.

[0080] A comparatively simple sensor structure and evaluation electronics are required for a vernier version, but the measuring length is limited. This version is therefore particularly suitable for angle measurements because the maximum length, the arc length, is predefined. The fundamentally very compact physical implementation can be viewed as a further advantage. The maximum length, which is often limited in practice, can be seen as a disadvantage. Another disadvantage is that a compromise between measuring length and accuracy is often necessary. The higher the accuracy requirement for long distances, the more complex a vernier implementation becomes.

A simplified, absolute vernier-coded angle measuring system with a multi-track arrangement is shown schematically in FIG. The system is composed as follows.

The material measure 1 consists of two parallel (or concentric) tracks 1.1 and 1.2 with different graduation periods in an XY plane. In the example of Figure 5, the first track 1.1 contains sixteen division periods λ ₁ (number of division periods of the first track m=16) and the second track 1.2 contains three division periods ₂ (number of division periods of the second track n ₂ =3). The condition gcd(n ₁ , n ₂ ) = 1 is fulfilled (gcd = greatest common divisor). The sensor 2.1 consists of two sensor elements 2.1.1 and 2.1.2 arranged next to each other (and above the associated tracks), each of which has the same graduation periods as the associated tracks 1.1 and 1.2, also in the XY plane. The sensor 2.1 can cover both only a part of the material measure 1, as shown in FIG. 5a, and the entire area, as shown in FIG. 5b. [0083] This principle can be expanded to include any number of measurement tracks and the associated sensor elements by adding additional, also parallel and concentric tracks. For the sake of simplicity and for a clear representation, a system with only two tracks is presented in the example in FIG.

[0084] In FIG. 6 and FIG. 7, the respective output signals of the sensor elements 2.1.1 and 2.1.2 of FIG. 5 are shown as examples. Figure 6 shows the output signal from sensor element 2.1.1 and Figure 7 shows that from sensor element 2.1.2. In this example, the two sensor elements 2.1.1 and 2.1.2 each generate two sinusoidal signals that are offset by 90° to one another, i.e. a sine and cosine signal. The sensor element 2.1.1 generates sixteen sine and cosine periods for a complete 360° rotation of the measuring scale 1, which correspond to the number of graduation periods of the first track 1.1. The sensor element 2.1.2 generates three sine and cosine periods according to the division periods of track 1.2.

[0085] All output signals generated by the sensor elements 2.1.1 and 2.1.2 pass through evaluation electronics or circuit 2.2. Position information, in particular angle or length information, is obtained from the output signals through various mathematical operations (such as demodulation). The absolute position is determined by combining the position information generated on the output signals of the sensor elements 2.1.1 and 2.1.2. This is shown in Figure 8. The absolute position is given in radians in Fig. 8 (in the interval ± π radians, corresponding to ±180°). The absolute position, which is shown as a dot-dash line, is obtained over the entire mechanical position of 360° due to the uniqueness of the pairs of the starting positions of the sensor element 2.1.1 shown as a solid line and the starting position of the sensor element 2.1.2 shown as a dashed line .

An example of linear vernier coding with three parallel tracks is shown in Figure 9. Figure 9 shows a side view of a material measure of an absolute length measuring system. The material measure comprises three periodic measuring tracks 1.1, 1.2 and 1.3 with a periodicity λ ₀ , λ ₁ or λ ₂ and along a measuring direction x. The measuring tracks 1.1, 1.2 and 1.3 are arranged parallel to each other and next to each other in a direction that is perpendicular to the measuring direction. The lengths λ ₀ , λ ₁ and λ ₂ of the divisions are different and the number of division periods n ₁ , n ₂ and n ₃ of the tracks for the same length is also different. The measuring track 1.1 of the measuring scale 1 has n ₁ =7, the measurement track 1.2 112 =5 and the measurement track 1.3 has n ₃ = 3 graduation periods. The following relationship applies between the period length and the number of graduation periods of the respective measuring track: λi = 1/ni, where 1 stands for the total length of the measuring standard.

[0087] The relationship gcd(n _i , n _j , n _k , ...) = 1 only has to apply to each of the tracks that are used to obtain the absolute position (the indices i, j, k denote the tracks). Typically, those measurement tracks that have the lowest number of division periods are used. In the example in FIG. 9, the three tracks fulfill the condition gcd (n ₁ , n ₂ , n ₃ ) = 1. The uniqueness of the coding is therefore given.

Figure 10 shows a diagram showing the signal amplitude (in volts) of an inductive sensor depending on the air gap (in millimeters) for different pitch lengths λ=0.25; 0.5; 1; 2; and shows 4 mm. The air gap is the distance between the material measure and the sensor element in a direction that is perpendicular to the measuring direction and to the plane of the material measure. It is also called the working point. It is desirable that the signals from the various tracks have sufficient amplitude in order to minimize measurement errors as much as possible. However, it is clear from FIG. 10 that the different lengths of the division periods lead to very different operating points and that the behavior of the generated signal amplitude of the sensor element is non-linear. In addition, the system resolution is largely determined by the measurement track that has the largest number of division periods, i.e. the smallest division length. As can be seen in Figure 7, however, a track with many pitch periods, for example the track with the pitch length λ = 0.25 mm, drastically limits the working area. Furthermore, it can be seen that the greater the difference in the division periods of the individual tracks, the greater the difference in their amplitude curve.

[0089] When designing the sensor, it is therefore advantageous to vary the number of division periods of the individual measurement tracks only minimally or to define them in the same order of magnitude. This means that the working areas of the measurement tracks would not limit each other and their amplitude curves would only deviate insignificantly from one another. However, it must be noted that the requirements for the accuracy of the individual measuring channels for determining the absolute position of the system are becoming significantly stricter.

This can be seen in Figure 11, which shows two examples of a material measure for a

Represent angle measuring system. The system in Figure 11a has two measuring channels, one with a first measuring track 1.1, which has a pitch length λ ₁ = 360°/16, and with a corresponding sensor element, and one with a second measuring track, which has a second pitch length ü = 360°/15, and with the associated one Sensor element. The maximum permitted error e for the first measuring channel relative to the second measuring channel over a total revolution of 360° is calculated as follows: e = angle/ ( λ ₁ · λ ₂ ) = 360°/(16 • 15) = 1 .50° (1)

[0091] If the two measuring channels exceed this error, the measuring system can no longer generate a clear and therefore valid absolute position with this vernier coding. In comparison, consider the system in Fig.10b. This has a first measuring track 1.1 with a pitch length λ ₁ = 360°/16 and a second measuring track 1.2 with a pitch length λ2 = 360°/3. The maximum permitted error is calculated analogously to e = 360° / (16 3) = 7.50°. The permitted error band is significantly larger in this case, but with the disadvantage that the operating points of the individual sensor elements differ more.

[0092] It is therefore clear that for a system with high resolution, which has at least one track with a high number of division periods, the requirements with regard to the position detection of the individual tracks are particularly high. In addition, a large difference in the number of division periods between the different tracks leads to a correspondingly large difference in the working range of the individual sensor elements, which in turn limits the working range of the entire system (air gap).

[0093] Another point to consider is the robustness of the system against assembly errors. Figure 12 shows a schematic representation of an angle measuring system with an assembly error in the form of a tilt. The sensor head 2, which should ideally be arranged parallel to the material measure 2, is inclined relative to the material measure 1 by an angle alpha with respect to an axis A, which runs perpendicular to the plane of the material measure 1.

[0094] It can be seen that the larger or wider a system is, the greater the effect tilting has on the working area (=air gap) of the sensor. The greatest influence is felt by the outermost track (+/- dz), usually the one with the most division periods and thus the one with the smallest working range. The tilting changes the relative phase between the sensor and the measuring standard. If this phase error becomes larger than the maximum permitted error, the absolute position can no longer be determined correctly. [0095] Further forms of assembly errors include an offset and a rotation of the scanning head 2 or the sensor element relative to the material measure. Figure 13 shows a length measuring system with three measuring channels, which has such an assembly error. The sensor head 2 (and thus also the sensor elements contained therein) is ideally arranged so that it is arranged parallel to the edges of the material measure. In the example of Figure 13, these edges are arranged at an angle alpha relative to an axis A, which runs parallel to an edge of the measuring standard, and thus relative to the measuring standard 1 itself.

A rotation or an offset of the scanning head 2 relative to the material measure 1 leads to a change in the relative phase between the position signals of the individual measuring channels and in turn reduces the working range of the system. If the phase change is greater than the maximum permitted position error (in combination with the accuracy of the track itself), the absolute position can no longer be determined correctly. Again, the influence of the phase shift is greater the wider (or the more tracks) the system has.

14 shows a view from above of a first and a second measuring scale for an angle measuring system with a single, circular measuring track with 16 or 3 graduation periods (FIG. 14, left and middle) and with a third measuring scale, which che forms a device with two overlapping measuring tracks due to the complete overlap of the first and second measuring scales 1.1 and 1.2. Since the largest common divisor of the number of these tracks is equal to 1, it is also a vernier arrangement, which can be used for absolute position measurement. In contrast to the arrangements of Figures 5 and 11, the measurement tracks are not arranged next to each other in the same plane, but are arranged overlapping in different planes. The measurement tracks are therefore congruent and have the same dimensions in the respective plane. In another example, the measurement tracks only partially overlap.

[0098] Analogously, the corresponding sensor elements 2.1.1 and 2.1.2 are also overlapped. A schematic sectional view of an angle measuring system with overlapping measuring channels is shown in Figure 15. The measuring track arrangements 1.1 and 1.2 correspond to the measuring track arrangements of Figure 14. The first measuring channel includes the sensor element 2.1.1 and the measuring track 1.1. The second measuring channel includes the sensor element 2.1.2 and the measuring track 1.2. Both the measuring track arrangements 1.1 and 1.2 as well as the sensor elements 2.1.1 and 2.1.2 are arranged one above the other in a direction z, which is perpendicular to the plane xy is running. The first measuring channel, which has the measuring track 1.1 with the larger number of graduation periods, is thus arranged between the sensor element 2.1.2 and the measuring track arrangement 1.2 with the smaller number of graduation periods. The measuring scales and the sensor elements are each arranged in a plane which is parallel to the xy plane. In the z direction, the overlapping measuring scales on the one hand and the sensor elements on the other hand are spaced apart by a distance z. In another example, the sensor elements only partially overlap.

[0099] Figure 16 shows a perspective view of an angle measuring system with two concentric, parallel vernier measuring channels in the same z-plane (Figure 16a) and an angle measuring system with overlapping vernier measuring channels in different planes (Figure 16b). For the sake of simplicity and for a clear representation, the sensor elements 2.1.1 and 2.1.2 are shown in Figure 16 and subsequently also in Figure 17 only with the respective receiver coils of the sensor elements. The emitter coils, however, are not shown. As shown, the receiver coils are designed as sinusoidal conductor tracks. The number of periods of a receiver coil corresponds to the number of periods of the corresponding measurement track. In turn, the systems can be expanded to include any number of measurement channels. The emitter coils and/or the receiver coils of the different measurement channels can be arranged on the same substrate.

[0100] In the embodiments of FIGS. 14-16, both the measurement tracks and the sensor elements are not arranged in parallel, but rather either completely or partially overlapped. By axially overlapping (Z direction) two or more measuring channels both in the rotor (measuring track) and in the stator (sensor elements), a configuration can be created that has the above-described disadvantages of vernier coding next to each other arranged measurement tracks can be significantly reduced. In particular, the entire system becomes significantly more compact and the influence of assembly errors (tilting, twisting, misalignment, eccentricity, etc.) can be significantly reduced. A major advantage of this arrangement is that any phase errors that may occur have the same geometric effect on all measuring channels. In addition, as described below, the working area of the measurement tracks can be easily optimized. The effort required to produce and operate the measuring system can also be reduced. Although Figures 14-16 show angle measuring systems, it is clear that the overlapping of measuring channels can also be implemented in length measuring systems with the same advantages. [0101] Figure 17 shows a perspective view of an angle measuring system with three completely overlapping measuring channels, and thus an extension of the solution from Figures 14-16 by one measuring channel. The system includes a sensor and a measuring body. The sensor comprises a first sensor element 2.1.1 with a number m=32 of division periods and a division period λ ₁ = 360°/32, a second sensor element 2.1.2 with a number n ₂ =8 of division periods and a division period λ ₂ = 360°/8 and a third sensor element 2.1.3 with a number n ₃ =3 of division periods and a division period ü = 360°/3. The sensor elements are arranged in different levels and spaced apart from one another.

[0102] Analogous to the sensor elements 2.1.1, 2.1.2 and 2.1.3, the measuring standard has three measuring tracks with a first measuring track 1.1 with the graduation period λ ₁ = 360 °/32, a second measuring track 1.2 with the graduation period λ ₂ = 360 °/8 and a third measuring track 1.3 with the graduation period ü = 360°/3. The measurement tracks and the corresponding sensor elements therefore have the same number of graduation periods. The measurement tracks are arranged in different levels and spaced apart from each other.

[0103] In the example in FIG. 17, the first measurement channel (m=32) determines the resolution of the system. The second and third channels are used to determine the absolute position, whereby the condition gcd (n ₂ , n ₃ ) = gcd (8, 3) = 1 is fulfilled.

[0104] If the measurement channels overlap, care must be taken to reduce or eliminate cross-talk between the individual measurement channels. According to one exemplary embodiment, the distances between the sensor elements and the associated measurement tracks are selected depending on the number of graduation periods. In particular, the distances between a measurement track and the respective sensor element can be selected such that the distance du between the sensor element 2.1.1 with the most graduation periods, ie with the smallest graduation length, and the associated measurement track 1.1 on the measuring scale 1 am is smallest and the distance d33 between sensor element 2.1.3 with the fewest graduation periods, ie with the largest graduation length, and the associated track 1.3 on the measuring scale 1 is the largest. The larger the number of division periods of a measuring channel, the smaller the distance between the measuring track and the sensor element of this measuring channel. This situation is shown, for example, in FIG. 17. In particular [0105] As a result, the conflict regarding the different operating points of the individual measuring channels, as already shown above with regard to FIG. 10, can be resolved and can also be used advantageously in order to bring signal amplitudes of the individual measuring channels to a similar level. In this way, the sensor electronics in particular can be simplified, for example by only requiring one physical channel for each sensor signal instead of separate evaluation channels, which switches between the individual sensor elements using a multiplexer.

In a further exemplary embodiment, the number of division periods of a measurement track with a larger number of division periods is greater by at least a factor of 1.5 than the number of division periods of a further measurement track with a smaller number of division periods. For the arrangement of FIG. 17 this means the following: λ ₂ ≥ 1.5 · λ ₁ and ta ≥ 1.5 · λ.2. The conditions for the number of division periods are: n ₁ ≥ 1.5 · n ₂ and n ₂ ≥ 1.5 · n ₂ . As stated above, these conditions are met in the example of FIG. 17, because the following applies: m = 32 ≥ 1.5 · n ₂ (= 1.5 · 8 = 12) and n ₂ = 8 ≥ 1.5 · n ₃ (= 1.5 · 3 = 4.5 ). Since, in Figure 17, the number of pitch periods of the measurement tracks becomes higher along the z-direction, the number of pitch periods of a given measurement track is 1.5 times higher than the number of pitch periods of the measurement track immediately below it.

[0107] According to one example, the number mi of graduation periods of the sensor elements is equal to the number n _i of graduation periods of the associated material measure, where i is the index of the measuring channel. For an arrangement with three measuring channels, λ ₁ ·n ₁ = λ ₁ ·m ₁ = 1 and λ ₂ ·n ₂ = λ ₂ ·m ₂ = 1 and λ ₃ ·n ₃ = λ ₃ ·m ₃ = 1, where 1 represents the total length of the measuring body 1. The example in Figure 17 also satisfies these conditions, because λ ₁ ·n ₁ = λ ₁ ·m ₁ = 11.25°-32 = 360° and λ ₂ ·n ₂ = λ ₂ ·m ₂ = 45°-8 = 360° and λ ₃ ·n ₃ = λ ₃ ·m ₃ = 120°-3 = 360°. This is particularly advantageous when there is a complete geometric overlap of the sensor elements of the sensor.

[0108] According to a further example, the distances bi2, b23 between the individual sensor elements and the distances ai2, a23 between the measuring tracks of the measuring standard are selected such that, at a given distance between the sensor and the measuring standard (nominal distance), on the one hand the mutual influence of the measuring channels (cross-talk) is minimized and, on the other hand, the amplitudes of the signals of the measurement channels are essentially the same. In particular, the amplitudes of the signals of the measuring channels can lie within a predetermined tolerance band. The distances between the sensor elements ments and between measurement tracks also depend on the number of division periods for each measurement track as well as the differences in the numbers of division periods. In any case, the distances bij between two sensor elements i and j are in the range from 0.01 to 1.00 mm and the distances aij between two measurement tracks i and j are in the range from 0.01 mm to 1.00 mm.

18 shows a diagram which shows the signal amplitude of three measuring channels with measuring tracks which have 32, 8 or 3 graduation periods, depending on the air gap (working area) of the measuring channel. The signal amplitude corresponds to the amplitude of the signal induced by the emitter signal of the emitter coil in the receiver coil. The signal amplitude was set to the interval [0; 1] normalized. In order to ensure a constant signal amplitude, the distance parameters a ₁₂ , a ₂₃ , b ₁₂ and b ₂₃ of the arrangement in FIG Measuring channels d ₁₁ = 0.50 mm and d ₂₂ = 1.00 mm and d ₃₃ = 2.00 mm are the same. This is represented by a solid line in Figure 18, which represents an ideal operating point AP = 0.55.

[0110] Due to manufacturing tolerances and technical limitations in manufacturing, the permissible working range of the measuring channels can be defined in such a way that a fluctuation ±A of the signal amplitudes (tolerance band) around the ideal working point AP is permitted. In the example of Figure 18, a fluctuation A = 0.1 around the operating point AP = 0.55 was chosen, which is shown by two dashed lines. The operating point for the three measurement tracks is therefore between 0.45 and 0.65. From Figure 18 it is particularly clear that the requirements for the air gap of the measuring channel with the largest number of division periods are higher than the requirements for the air gap of the measuring channel with the smallest number of division periods.

[0111] In one example, the lower limit of the tolerance band is at least 70%, preferably at least 80% and more preferably at least 90% of the operating point. In a further example, the upper limit of the tolerance band is not more than 130%, preferably not more than 120% and more preferably not more than 110% of the operating point.

An arrangement with partially or completely overlapping measuring tracks or sensor elements has the advantage that the distances between the measuring tracks and the sensor elements can be selected flexibly, so that a similar signal amplitude can be achieved for all measuring channels. You are also particularly flexible when choosing work area. As can be seen from FIG. 10, this is not the case in conventional arrangements in which the measuring tracks are arranged in the same plane.

By appropriately selecting the distances between the measurement tracks and the sensor elements, crosstalk or mutual interference between the measurement channels can be significantly reduced.

[0114] According to a further example, the measuring channels are based on different measuring principles and the corresponding sensor elements measure different sizes. This means that the mutual interference between the various measurements can be reduced. For example, a first sensor element can measure a change in the conductivity of the corresponding measurement track and a second sensor element can measure a change in the permeability/reluctance of the corresponding measurement track. For this purpose, the sensor circuit can be designed to generate a first signal for the first measurement track with a first emitter signal frequency f ₁ and to feed it into the emitter coil of the first sensor element, and a second signal with a second emitter signal frequency f ₂ to generate and feed into the emitter coil of the second sensor element, whereby the first emitter signal frequency and the second emitter signal frequency differ. In one example, the first emitter signal frequency is at least twice greater than the second emitter signal frequency. The following applies: f ₁ ≥ 2 ·f ₂ . For example, a permeability or reluctance is measured with the sensor element whose emitter coil is excited with the smaller emitter signal frequency, while a conductivity is measured with the sensor element whose emitter coil is excited with the larger emitter signal frequency.

19a shows a view from above of a material measure for an angle measuring system with a magnetic track. Figure 19b shows a view from above of another measuring standard for an angle measuring system. The width of the annular measuring standard in the radial direction changes depending on the angle, such that the measuring standard has three identical sections radially, each of which has a wider and a narrower area. These sections thus form a periodic measurement track with three periods, which can be referred to as a geometric track. The change in the width of the material measure can be effected by a mechanical method, for example by milling, etching, cutting and/or turning. Figure 19c shows a view from above of a further measuring standard for an angle measuring system, which is formed by superposition of the effects from Figures 19a and 19b. The measuring standard therefore has both the magnetic track of Figure 19a and the geometric track of Figure 19b. Both tracks overlap and are arranged in the same axial plane (plane xy). Since the magnetic field generated by the magnetic track is influenced by the geometry of the measuring scale, and thus by the geometric track, a change in the geometry and thus the geometric track can be detected by a corresponding sensor. The additional, geometric measurement track therefore plays the same role as the additional, magnetic track in the examples above. The first, magnetic measuring track and the second, geometric measuring track can thus be formed from a single measuring track molding, the geometric measuring track being formed by deforming the molding. In the example shown, the largest common divisor of both tracks is equal to one, so that both tracks form a vernier coding, which can be used for absolute position measurement. The example of Figure 19c can be used for any number of periods of the magnetic and geometric track. It can also be implemented in a measuring scale of a length measuring system.

A particularly compact design can be achieved with a position measuring system in which the various measuring tracks or the sensor elements are arranged at least partially overlapping. In addition, the influence of design errors on the arrangement can be reduced. Since the measuring channels have different distances between the measuring track and the sensor element, the working area can be selected particularly flexibly and thus easily optimized.

Claims

PATENT CLAIMS

1. A device (1) for a length or angle measuring system, which has the following: a first measuring track (1.1) with a periodic coding which has a first number of graduation periods, the first measuring track being arranged in a first plane, and at least one second measurement track (1.2) with a periodic coding which has a second number of division periods, the second measurement track being arranged in a second level, the first number of division periods and the second number of division periods differing from one another, and wherein the first plane and the second plane are parallel to one another and the first measurement track (1.1) and the second measurement track (1.2) at least partially overlap.

2. Device according to claim 1, wherein the first level and the second level are spaced apart from one another.

3. Device according to claim 1, wherein the first and second measuring tracks are formed from a single measuring track molding.

4. Device according to claim 3, wherein the second measuring track is formed by deforming the measuring track molding.

5. Device according to one of claims 1 to 4, wherein the first measurement track (1.1) and the second measurement track (1.2) completely overlap.

6. Device according to one of claims 1 to 5, wherein the greatest common divisor of the first number of division periods and the second number of division periods is equal to 1.

7. System, which comprises: a device according to one of claims 1-6, and a sensor head (2). a first sensor element (2.1.1), which forms a first measuring channel together with the first measuring track (1.1), and at least one second sensor element (2.1.2), which forms a second measuring channel together with the second measuring track (1.2), wherein the first and second sensor elements cover at least one pitch period of the first and second measurement tracks, respectively.

8. The system of claim 7, wherein the first and second sensor elements are arranged in a third and fourth plane, respectively, the third plane and the fourth plane being parallel to one another and spaced apart from one another.

9. System according to claim 8, wherein the first sensor element (2.1.1) and the second sensor element (2.1.2) at least partially overlap.

10. System according to one of claims 7 to 9, wherein the first number of division periods of the first measurement track (1.1) is greater than the second number of division periods of the second measurement track (1.2), with a first distance between the first measurement track (1.1 ) and the first sensor element (2.1.1) is designed to be smaller than a second distance between the second measuring track (1.2) and the second sensor element (2.1.2).

11. System according to one of claims 7 to 10, wherein the first number of division periods of the first measurement track is greater by at least a factor of 1.5 than the second number of division periods of the second measurement track (1.2).

12. System according to one of claims 7 to 11, wherein distances between the measurement tracks and the corresponding sensor elements are selected such that signal amplitudes of the sensor elements are the same within a given tolerance band.

13. System according to one of claims 7 to 12, wherein a distance between two immediately adjacent measuring tracks is in the range of 0.01 mm to 1.00 mm, and / or wherein a distance between two immediately adjacent sensor elements is in the range from 0.01 mm to 1.00 mm.

14. System according to one of claims 7 to 13, wherein the first and the second sensor element have a receiver coil which is designed as a periodic conductor track and has a first and second number of division periods, respectively, and wherein the number of division periods of the first or the second sensor element is equal to the number of graduation periods of the first or second measurement track.

15. System according to one of claims 7 to 14, wherein the first and the second sensor element each have an emitter coil, the sensor head having a sensor circuit (2.2) which is designed to generate a first signal with a first emitter signal frequency and into the emitter coil of the first sensor element, and wherein the sensor circuit (2.2) is further designed to generate a second signal with a second emitter signal frequency and to feed it into the emitter coil of the second sensor element, and wherein the first emitter signal frequency and the second emitter signal frequency differentiate.

16. The system of claim 15, wherein the first emitter signal frequency is at least two times greater than the second emitter signal frequency.

17. System according to one of claims 7 to 16, wherein the sensor circuit (2.2) has an evaluation circuit with a multiplexer, the multiplexer being connected to the sensor elements and being designed to provide measurement signals via a single physical evaluation channel.

18. Sensor head (2) for a device according to one of claims 1-6, which has the following: a first sensor element which is arranged in a third level and is designed to provide a first measurement channel with the first measurement track (1.1). form, at least one second sensor element, which is arranged in a fourth level and is designed to form a second measurement channel with the second measurement track (1.2), the third level and the fourth level being parallel to one another and spaced apart from one another, wherein the first sensor element (2.1.1) and the second sensor element (2.1.2) at least partially overlap.