Measuring system having a sensor head and an encoder wheel

Abstract

The invention relates to an encoder wheel (1) for an axial angle-measuring system. According to one exemplary embodiment: the encoder wheel has an axis of rotation; the encoder wheel is produced from a single material which is either non-magnetic and electrically conductive or magnetically soft; and the encoder wheel has, on its side face which is normal to the axis of rotation, at least one track (1.1, 1.2, 1.3) in which position information is encoded by portions of different electrical conductivity or different magnetic permeability. The encoding is obtained in that material recesses are formed in the side face.

Description

MEASURING SYSTEM WITH SENSOR HEAD AND ENCODER WHEEL TECHNICAL AREA

[0001] This patent application relates to the field of position and angle measurement using encoder wheels. BACKGROUND

[0002] Several types of measuring systems for angle measurement are known. Generally, such systems feature an encoder wheel with a scale. The scale serves as a carrier of coded information, which can be detected by a sensor head, thus enabling the measurement of the encoder wheel's angular position. The encoder wheel is typically mechanically connected to a rotating machine part whose angular position is to be measured. The scale is usually a passive component, meaning it contains no active electronic components that require a power supply.

[0003] The sensor head (sensor module) essentially comprises a sensor based on an inductive physical measurement principle. The sensor can be designed to detect the entire surface of the encoder wheel or a portion or segment thereof, and to identify specific characteristics of the scale. During this detection process, the sensor typically generates one or more analog output signals. The sensor head also includes sensor electronics that convert the analog signals generated by the sensor into digital or analog position information using appropriate methods. Depending on the sensor used, the sensor electronics may also supply power to the sensor.

[0004] In the case of the inductive measuring principle, the position information within the measuring scale is encoded on the encoder wheel by different areas with varying magnetic permeabilities (p) or electrical conductivities (G). Known systems often use gears made of soft magnetic material as the encoder wheel. An inductive sensor can detect transitions between highly magnetically permeable teeth and the non-magnetic gaps (containing air) between them. Length measuring systems can be constructed similarly to angle measuring systems, with the difference that a straight, elongated encoder is used instead of an encoder wheel.

[0005] Systems are also known in which the encoder wheel has multiple tracks. Depending on the design of the tracks, this can facilitate the measurement of the absolute position. (Angle position) or the detection of the direction of rotation are possible. With a single track, usually only incremental measurement is possible. Especially with multi-track systems, the design of the encoder wheel is generally more complex. The inventor has made it his mission to improve existing concepts. SUMMARY

[0006] The aforementioned problem is solved by the encoder wheel according to claim 1 and the system according to claim 10. Various embodiments and further developments are the subject of the dependent claims.

[0007] The following describes an encoder wheel for an axial angle measuring system. According to one embodiment: the encoder wheel has a rotational axis; the encoder wheel is made of a single material that is either non-magnetic and electrically conductive or soft magnetic; and the encoder wheel has at least one track on its side surface, which is perpendicular to the rotational axis, in which position information is encoded by sections of different electrical conductivity or different magnetic permeability. The encoding is achieved by incorporating material recesses into the side surface. BRIEF DESCRIPTION OF THE IMAGES

[0008] The invention is explained in more detail below with reference to the examples shown in the figures. The illustrations are not necessarily to scale, and the invention is not limited to the aspects shown. Rather, emphasis is placed on illustrating the principles underlying the invention. The figures show:

[0009] Fig. 1 is a block diagram of a length measuring system. An angle measuring system is essentially constructed in the same way.

[0010] Fig. 2 illustrates a 3D model of a length measuring system consisting of a measuring body, a scanning head, and an output interface.

[0011] Fig. 3 illustrates a 3D model of an angle measurement system consisting of a measuring body, a scanning head, and an output interface.

[0012] Fig. 4 illustrates a 3D model of a physical measure and a sensor element with an emitter coil and two receiver coils.

[0013] Fig. 5 is an exploded view of an axial angle measuring system, consisting of rotor (measuring element) and stator (sensor head) including its subcomponents.

[0014] Fig. 6 is a representation of a physical embodiment made from one piece a) with three parallel (or coaxial) tracks and b) with one track in the form of a periodic waveform.

[0015] Fig. 7 is a sectional view of a linear physical dimension in which a measuring track was produced by mechanical processing of (material) areas BH of high conductivity or permeability and areas BL of low conductivity or permeability (air).

[0016] Fig. 8 illustrates an example of a linear measuring system with a physical dimension according to an embodiment and a sensor element.

[0017] Fig. 9 shows an encoder wheel according to an exemplary embodiment and a representation of deviations from the ideal shape (e.g. manufacturing-related radii) due to limitations of the manufacturing process. DETAILED DESCRIPTION

[0018] Figure 1 illustrates an example of a length and angle measuring system using a block diagram. The system shown comprises a scale 1 with a measuring scale and a sensor head 2, often also referred to as a probe head. The system further includes a controller 3, which is connected to the sensor head 2 via a communication link 4, specifically to the sensor electronics 2.2 (sensor circuit or measuring circuit) of the sensor head 2, which has a suitable communication interface. The position information determined by the sensor electronics 2.2 is transmitted to the controller 3 via the communication link 4. The controller 3 can use the position information for various tasks, such as controlling position, speed, torque, or the like.

[0019] The measuring element 1 contains coded information that can be detected by the sensor head 2, thus enabling the measurement of the (angular) position of the measuring element 1. In the case of an angle measurement, the measuring element is often referred to as an encoder wheel.

[0020] The sensor head 2 includes, in particular, a sensor 2.1, which is based on an inductive physical measuring principle and can detect the position of the measuring instrument or a change in its position. The sensor can extend over the entire length or angle measuring range or only over a part or segment of the measuring instrument / encoder wheel. When the measuring instrument moves relative to the sensor 2.1, the sensor 2.1 generates one or more analog signals that depend on the encoded position. The evaluation electronics 2.2 can be configured to convert the analog sensor signals into analog and / or digital position information using analog and digital signal processing.

[0021] Fig. 2 is a perspective (three-dimensional) view of a length measuring system with a sensor head 2 and a straight, linear measuring element 1 with a (single) track. Also shown is a bus line connected to the sensor head 2 as part of the communication link 4.

[0022] Fig. 3 is a perspective (three-dimensional) view of an angle measuring system with a sensor head 2 and a measuring element 1 designed as an encoder wheel. Also shown is a plug connection on the sensor head 2 as part of the communication connection 4.

[0023] In the case of an inductive measuring principle, the coded information is represented by areas of the measuring instrument that exhibit different permeabilities p (reluctances) and / or different conductivities G. A schematic representation can be seen in Fig. 4. These areas of different permeability p or conductivity G can follow one another periodically or aperiodically and can be detected by the sensor 2.1 in the sensor head 2.

[0024] In the example shown in Fig. 4, the scale 1 consists of a periodically coded measuring track. In other embodiments, there can be several periodically coded measuring tracks arranged side by side. Aperiodically coded measuring tracks are also possible. In the case of periodic coding, the division period X is defined as one period of coding (in mm or degrees). The scale 1 is detected by the sensor 2.1, so that the measuring track(s) and changes in the coded areas due to the movement of the scale (rotation of the encoder wheel) are detected.

[0025] The sensor 2.1 contained in the sensor head 2 can be used for each measuring track of the The physical embodiment must have a sensor element assigned to this measuring track. It is possible for... Two or more sensor elements can also be assigned to a measuring track. In the example from Fig. 4, the sensor element 2.1.1 has (at least) one emitter coil 2.1.1.1 and (at least) one receiver coil 2.1.1.2. In the illustrated example, the sensor element has two receiver coils that are offset from each other (in the measuring direction x) by one quarter of a division period X / 4.

[0026] The emitter coil can extend across multiple sensor elements and thus be used jointly by several sensor elements. In one example, sensor 2.1 comprises several sensor elements for multiple measurement tracks, with each measurement track assigned exactly one sensor element. Each of these sensor elements has one or more (e.g., two) receiver coils, but the emitter coil (or emitter coils) extends across several of the sensor elements or across all of them.

[0027] In the embodiments described here, the electronic circuit 2.2 (sensor electronics) is configured to supply an alternating current to the emitter coil(s) of the sensor. This alternating current can have a constant frequency, typically in the range of 1 kHz to 10 MHz (or higher). Due to the inductive coupling (back-induction) between the emitter and receiver coils, an alternating current of the same frequency is induced in the receiver coils. This back-induction is further influenced by the position of the measuring instrument relative to the sensor head (i.e., relative to the sensor elements).

[0028] When the measuring instrument moves, the mutual induction is modulated, with the modulation depending on the information encoded on the measuring tracks of the measuring instrument. If the position information is encoded by regions of different permeabilities p0, Pi, the measuring instrument exhibits regions with higher magnetic permeability Pi > g0 and regions with lower permeability p0, with the regions of higher permeability i increasing the mutual induction or the induced alternating current. If the position information is encoded by regions of different conductivities o0, <^i, the measuring instrument exhibits regions with higher conductivity oi > c0 and regions with lower conductivity c0 (e.g., c0 ~ 0), with those regions of the measuring instrument with higher conductivity Oi decreasing the mutual induction or the induced alternating current (due to eddy current losses).

[0029] The alternating currents induced in the receiver coils, or the measured signals, are demodulated by the sensor electronics 2.2 and converted into position information using analog and digital signal processing. The acquired Position information is typically transmitted via a communication link 4 to a controller 3. This controller can use the received position information for various control tasks.

[0030] The examples described here, regardless of whether they involve length or angle measurements, can be classified as incremental or absolute measuring systems. The position information of an incremental measuring system only includes information about the relative (length or angle) offset with respect to a starting position "0" at system startup. An extension can be provided that the measuring instrument has a defined system zero point in the form of a reference mark (Reference Index Ri or Reference Mark Rni). However, this information is only available once the sensor detects this reference mark on the measuring instrument after being switched on. The position information of an absolute measuring system includes the absolute (length or angle) offset between the sensor head 2 and the measuring instrument 1 immediately after being switched on. A reference mark is not required here.

[0031] Figure 5 shows an exploded view of an axial angle measuring system with a measuring element 1 (rotor, encoder wheel) and a sensor head 2 (stator) including its subcomponents. For the sake of simplicity and clarity, the measuring element is referred to as the rotor and the scanning head as the stator, although this does not exclude other possible configurations. The designation of the angle measuring system as "axial" means that the sensor head "looks" at the encoder wheel in the axial direction (i.e., in a direction parallel to the axis of rotation of the encoder wheel). In this case, the encoded information is located on the side face of the encoder wheel (not on the circumferential / surface surface as in radial measuring systems).

[0032] In the illustrated embodiment, the rotor 1 (the encoder wheel), unlike the stator 2, consists of only a single material, which is either soft magnetic (ferromagnetic) or electrically conductive and non-magnetic. According to one embodiment, the rotor can be an integral component (i.e., made from a single piece), whose measuring track(s) are generated directly from the rotor material. The rotor 2 is mounted either directly on the shaft (which can rotate about the axis of rotation) or indirectly on the shaft using one or more adapters. The encoding of the rotor 2 can also be integrated into the shaft itself by machining it. In this case, the shaft itself acts as the rotor of the measuring system. Similarly, the area to be detected by the sensor head can be... Coding for linear measuring systems can be integrated directly into the axis of motion, for example, by machining a rail guide.

[0033] The stator / sensor head 2 consists of a mechanically stable housing 2.4, an inductive sensor 2.1, which is (optionally) protected by a cover plate 2.3, electronics that evaluate the sensor signals and convert them into position information (digital or analog signal), an output cable (communication connection 4) for the interface to the controller or PC and (optionally) a potting compound 2.6, which protects the electronics from moisture or other external influences (see also block diagram from Fig. 1).

[0034] The rotor 1 and the housing 2.4 of the stator can be connected to a protective earth. This connection ensures that both the rotor and the stator are protected against electrical interference and static charges, thereby increasing the operational safety and reliability of the entire measuring system.

[0035] The purpose of the embodiments described here is to realize a physical dimension for rotary or semi-rotary measuring systems which are resistant to thermal influences and robust against mechanical shocks and vibrations, and which, due to their design, are also cost-optimized in their manufacture.

[0036] The physical measure consists of a single machined piece of material and has one or more measuring tracks containing areas of differing conductivity or permeability. As an example, Fig. 6a shows a rotary physical measure with three measuring tracks 1.1, 1.2, and 1.3. The hatched areas represent areas of high conductivity or permeability, and the bare areas represent areas of low conductivity or permeability. In this illustration, track 1.1 contains 64 pairs of areas (division Xi) of differing conductivity or permeability, measuring track 1.2 contains eight pairs (division X2), and measuring track 1.3 contains three pairs (division X3). In the case of a rotary absolute measuring system with at least two tracks, the greatest common divisor of the division periods X2, k3 of the measuring tracks with the fewest divisions must be 1.

[0037] Fig. 6b shows an alternative form, where the areas of different conductivity or permeability are separated by a continuous (sinusoidal) wave-like contour. Inner circumference of rotor 1 is manufactured. Other geometric codings (e.g. sawtooth etc.) are also possible.

[0038] The areas or measurement tracks with differing conductivity or permeability are created by mechanically processing the material. The measurement tracks thus comprise areas of material with high permeability or conductivity (the material from which the rotor is made) paired with areas where this material has been removed (air), e.g., by machining processes such as milling, turning, punching, etching, wire EDM, casting (die casting), cutting (laser, waterjet, etc.), bending, drawing, deep drawing, or another suitable machining process. For illustration, Fig. 7 shows a cross-sectional view of a linear scale in which areas BH with high conductivity or permeability (rotor material) and areas BL with low conductivity (air) have been created by mechanically processing a material.These areas BH and BL represent the aforementioned coded information that can be detected / captured by the sensor head. The representation in Fig. 7 can also be considered part of an encoder wheel. In the case of an axial angle measuring system, the y-axis shown in Fig. 7 denotes the radial direction, the x-axis the circumferential direction, and the z-axis the axial direction. The measuring track is therefore located in the xy-plane, which is perpendicular to the axis of rotation.

[0039] Materials suitable for manufacturing a robust, one-piece (made from a single material) scale are those with the following properties: electrical conductivity G > 10 6 S / m or a magnetic (relative) permeability p > 1 and a modulus of elasticity Y > 50 GPa (or 50 kN / mm²) 2 Examples of suitable materials are: Aluminum: 2.70 g / cm³ 3 , steel: 7.85 g / cm² 3 Copper: 8.96 g / cm³ 3 , Brass: 8.50 g / cm³3 or titanium: 4.51 g / cm² 3 The thickness H of the encoder wheel material (see Fig. 7) is H > 0.80 mm. The depth T of the material recess (areas of low conductivity / permeability) is T > 0.05 mm. The width B can range from 4 to 50 mm (4 mm < B < 50 mm). For linear scales, lengths L up to 2 m are possible (L < 2000 mm). For rotary systems, the (outer) diameter D of the encoder wheel can range from 10 to 1000 mm (10 mm < D < 1000 mm).

[0040] The total length of a linear measuring instrument is not limited and can consist of several segments arranged in a row. Similarly, the rotor of an angle measuring system can also be composed of two or more segments. e.g. 2x 180°, 3x 120° etc. The individual segments, in turn, are each made from a single piece, as described.

[0041] Fig. 8 illustrates a linear measuring system with a measuring element 1 according to an embodiment of the above description and a sensor element 2.1. An axial angle measuring system can be constructed analogously, wherein in Fig. 8 the z-axis would correspond to the axial direction, the y-direction to the radial direction and the x-axis to the circumferential direction.

[0042] For dimensioning, the following conditions apply in the illustrated example, assuming the longitudinally centered state of sensor element 2.1 and scale body 1. The width A of the scale body must be greater than the width B of the active structure of sensor element 2.1. The distance C between the active sensor structure and the edge of the scale body (edge ​​of the high conductivity / permeability areas) should be greater than or equal to 0.05 mm. That is: A > B, C > 0.05 mm.

[0043] Depending on the manufacturing process chosen, deviations from the ideal shape of the measurement marks must be accepted. Figure 9 serves as an example. It illustrates that, for instance, milling cannot produce perfectly ideal edges; instead, radii Ra of at least half the cutter diameter must be accepted. The larger the radii, the faster and cheaper the manufacturing process, but the greater the impact on the signal shape of the signals generated by the sensor element. Furthermore, the edges generally cannot be produced with infinite steepness because tool wear creates a continuously increasing radius Rb between the milled edge and the milled surface as the cutter's operating time increases. For the sake of completeness, it should be mentioned that these deviations from the ideal shape can also occur with other manufacturing processes.

[0044] To minimize the influence on the generated signal waveforms of the sensor element, the following rules can be specified: Ra < 5mm, ratio a / b < 3, ratio c / d < 3, Rb < 5mm, e > 0.05mm, ratio e / f < 1. All the above information and examples can be implemented for both angle and length measuring systems as well as for rotary encoders.

[0045] Some of the exemplary implementations described here are summarized below. This is not a complete list of technical features, but merely an exemplary summary.

[0046] One embodiment relates to an encoder wheel for an axial angle measuring system, i.e., an angle measuring system in which the sensor head "looks" at the encoder wheel's scale in the axial direction (parallel to the axis of rotation). The encoder wheel has an axis of rotation and is made of a single material that is either non-magnetic and electrically conductive (variant A) or soft magnetic (variant B). The encoder wheel has at least one track on its side surface (perpendicular to the axis of rotation) in which position information is encoded by sections of different electrical conductivity (variant A) or different magnetic permeability (variant B). This encoding is achieved by incorporating material recesses into the side surface.

[0047] In one embodiment, the material recesses define those sections of the at least one track where the electrical conductivity (variant A) or the magnetic permeability (variant B) is reduced. The reduction results simply from the removal of the material, resulting in a conductivity (variant A) or permeability (variant B) that corresponds to that of air.

[0048] In one embodiment, the side surface has at least two tracks coaxial with respect to the axis of rotation, in which position information is encoded by sections of different electrical conductivity (variant A) or different magnetic permeability (variant B). The tracks can have first sections (see Fig. 7, sections BH) of higher conductivity or permeability and second sections (see Fig. 7, sections BL) of lower conductivity or permeability, the second sections (BL) being defined by the areas in which the material recesses are made.

[0049] In one embodiment, the material (variant A) from which the encoder wheel is made is non-magnetic and electrically conductive, for example, aluminum, copper, brass, or titanium.5 In another embodiment (variant B), the material from which the encoder wheel is made is soft magnetic, for example, steel, an iron-nickel alloy, or an iron-cobalt alloy.

[0050] The depth of the aforementioned recesses can be 0.05 mm or more in some embodiments. The width of the at least one track can range from 4 to 50 mm. The encoder wheel can have an outer diameter ranging from 10 to 1000 mm.

[0051] In most embodiments, the encoder wheel will be an integral component (i.e., one-piece, manufactured from a single piece). For very large encoder wheels, it may be composed of two or more (especially identically designed) segments (e.g., 180° or 120° segments), each segment being made of the same material, or

[0052] Another embodiment relates to an axial angle measuring system with an encoder wheel according to the above description and with a sensor head comprising a sensor which has at least one sensor element for each track, which is configured to detect the angular position of the at least one track or a change in the angular position.

[0053] In one embodiment, each sensor element has at least one receiver coil. The sensor can further have at least one emitter coil, wherein the emitter coil and the receiver coil are transformer-coupled, and wherein the transformer coupling depends on the angular position of the encoder wheel (corresponding to the angular position of sections BH and BL). An emitter coil can extend over several sensor elements of the sensor. The concepts described here can also be applied to linear (length) measurement systems.

Claims

PATENT CLAIMS 1. An encoder wheel for an axial angle measuring system, wherein the encoder wheel (1) has an axis of rotation, wherein the encoder wheel (1) is made of a single material which is either non-magnetic and electrically conductive or soft magnetic, wherein the encoder wheel (1) has on its side surface which is normal to the axis of rotation at least one track (1.1, 1.2, 1.3) in which position information is encoded by sections of different electrical conductivity (G) or different magnetic permeability (p), and wherein the encoding is achieved by providing material recesses in the side surface.

2. The encoder wheel according to claim 1, wherein the material recesses define those sections of the at least one track (1.1, 1.2, 1.3) in which the electrical conductivity (G) or the magnetic permeability (p) is reduced.

3. The encoder wheel according to claim 1 or 2, wherein the side surface has at least two tracks (1.1, 1.2, 1.3) coaxial with respect to the axis of rotation, in which position information is encoded by sections of different electrical conductivity (G) or different magnetic permeability (p), wherein the tracks (1.1, 1.2, 1.3) have first sections (BH) of higher conductivity (G) or permeability (p) and second sections (BL) of lower conductivity (G) or permeability (p), wherein the second sections (BL) are defined by those areas in which the material recesses are provided.

4. The encoder wheel according to any one of claims 1 to 3, wherein the material is non-magnetic and electrically conductive and is in particular one of the following: aluminium, copper, brass or titanium.

5. The encoder wheel according to any one of claims 1 to 4, wherein the material is soft magnetic and in particular one of the following: steel, an iron-nickel alloy or an iron-cobalt alloy.

6. The encoder wheel according to any one of claims 1 to 5, wherein the depth (T) of the recesses is at least 0.05 mm.

7. The encoder wheel according to any one of claims 1 to 6, wherein the width of the at least one track (1.1, 1.2, 1.3) is in the range of 4 to 50 mm.

8. The encoder wheel according to any one of claims 1 to 7, wherein the encoder wheel (1) has an outer diameter in the range of 10 to 1000 mm.

9. The encoder wheel according to any one of claims 1 to 8, wherein the encoder wheel is composed of two or more segments, each segment being made of the same material, or wherein the encoder wheel is an integral component.

10. An axial angle measuring system comprising: an encoder wheel according to any one of claims 1 to 9; a sensor head (2) with a sensor (2.1) having at least one sensor element (2.1.1) for each track (1.1, 1.2, 1.3) configured to detect the angular position of the at least one track (1.1, 1.2, 1.3) or a change in the angular position.

11. The angle measuring system according to claim 10, wherein each sensor element (2.1.1) has at least one receiver coil (2.1.1.2) and wherein the sensor (2.1) has at least one emitter coil (2.1.1.1).

12. The angle measuring system according to claim 11, wherein the emitter coil (2.1.1.1) and the receiver coil (2.1.1.2) are transformer-coupled and wherein the transformer coupling depends on the angular position of the encoder wheel.

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