Inductive encoder device

Abstract

An inductive rotary encoder comprises a first member and a second member capable of relative rotation about a rotation axis, wherein the first member has at least first and second scale tracks extending around a scale track axis, and the second member comprises i) an excitation coil through which alternating current passes to generate an alternating magnetic field operated by the at least first and second scale tracks, and ii) at least a first receiving coil for detecting a magnetic field operated by the first scale track and a second receiving coil for detecting an alternating magnetic field operated by the second scale track, thereby configuring such that the relative rotational position of the first member and the second member about the rotation axis can be measured. The inductive rotary encoder device is also configured such that the excitation coil and the receiving coil extend around a coil axis at different radii, and the excitation coil is a unidirectional excitation coil, so that when in use, the current flowing through the excitation coil flows in only one direction around the coil axis at any given point in time.

Description

Technology Field

[0001] The present invention relates to an inductive encoder, in particular to an inductive rotary encoder. Background Technology

[0002] Inductive encoders are known and generally comprise i) a first member for mounting on a first part of a machine (e.g., a shaft rotatable about a static part of the machine about an axis) (e.g., commonly referred to as a “rotor” in the case of a rotary encoder), and ii) a second member for mounting on a second (e.g., static) part of the machine (e.g., commonly referred to as a “stator” in the case of a rotary encoder). Generally, one of the members (e.g., the second member / “stator”) is an active / powered component and comprises a transmitting (or “excitation”) coil and a receiving coil (and associated electronic devices) for generating and detecting an alternating magnetic / electromagnetic field. In this invention, the terms “magnetic field” and “electromagnetic field” are used interchangeably because the magnetic field referred to is generated by an electric current and may therefore also be referred to as an electromagnetic field. Additionally, as is understood, references herein to a magnetic field generated by an excitation coil or a transmitting coil refer to an "alternating" magnetic field generated by it, and for brevity, it is often simply referred to as a "magnetic field" in this application. Generally, another component (e.g., a first component / "rotor") is a passive / unpowered component and includes scale features that manipulate the electromagnetic field detected by a sensor coil of the second component (e.g., a stator) such that the output(s) of the receiving coil(s) of the second component (e.g., a stator) depend on the relative position of the first and second components about an axis (e.g., relative rotational orientation about an axis in the case of a rotary encoder).Accordingly, the relative (e.g., rotational) position (and / or derivative of that position) of the second member / stator and the first member / rotor (and other parts of the machine) can be measured from the output(s) of the receiving coil(s) of the second member / stator. means of solving the problem

[0003] The present invention relates to improvements related to inductive encoders. In particular, this document describes an inductive rotary encoder comprising a first member and a second member that are rotatable relative to a rotation axis. The first member may have at least a first scale track and a second scale track that extend annularly around a scale track axis. The second member may have i) an excitation coil through which alternating current passes to generate an alternating magnetic field operated by the at least first and second scale tracks, and ii) at least a first receiving coil for detecting a magnetic field operated by the first scale track and a second receiving coil for detecting an alternating magnetic field operated by the second scale track, thereby allowing the relative rotational position of the first member and the second member around the rotation axis to be measured. The inductive rotary encoder may also be configured such that the excitation coil and the receiving coil extend annularly around a coil axis at different radii.

[0004] Accordingly, according to a first aspect of the present invention, an inductive rotary encoder is provided, wherein the encoder comprises a first member and a second member rotatable relative to a rotation axis, the first member having at least first and second scale tracks extending annularly around a scale track axis, and the second member having i) an excitation coil through which alternating current passes to generate an alternating magnetic field operated by the at least first and second scale tracks, and ii) at least a first receiving coil for detecting the magnetic field operated by the first scale track and a second receiving coil for detecting the alternating magnetic field operated by the second scale track, thereby configuring such that the relative rotational position of the first and second members around the rotation axis can be measured, and the inductive rotary encoder is further configured such that the excitation coil and the receiving coil extend annularly around a coil axis at different radii, the excitation coil is a unidirectional excitation coil, and accordingly, when in use, the current flowing through the excitation coil at any given time is the coil axis It flows around the circumference in only one direction (e.g., clockwise or counterclockwise).

[0005] The above at least first scale track and second scale track may extend annularly around the axis of the scale track. The excitation coil may extend annularly around the axis of the coil. The receiving coil may extend annularly around the axis of the coil. As is understood, the reference that the scale track, excitation coil and / or receiving coil extend annularly (around their respective axes) includes extending completely annularly and substantially completely annularly (e.g., around at least 75% of the entire annular range, more preferably around at least 90% of the entire annular range).

[0006] Preferably, the excitation coil extends circularly around the coil axis with a constant radius. Preferably, the excitation coil extends circularly around the coil axis with a constant single radius.

[0007] Preferably, the excitation coil is a single-turn coil, and / or the first receiving coil is a single-turn coil, and / or the second receiving coil is a single-turn coil.

[0008] The first and second receiving coils may be located on both radially opposite sides of the excitation coil. Accordingly, the excitation coil may be located radially between the first receiving coil and the second receiving coil. Thus, for example, the radius of the first receiving coil may be smaller than the radius of the excitation coil, and the radius of the excitation coil may be smaller than the radius of the second receiving coil.

[0009] The first receiving coil and the second receiving coil may be located on the same radial side of the excitation coil. For example, the first receiving coil may be radially spaced from the excitation coil by the second receiving coil. Accordingly, for example, the radius of the first receiving coil may be smaller than the radius of the second receiving coil, and the radius of the second receiving coil may be smaller than the radius of the excitation coil.

[0010] The first member may include a third scale track extending around the scale track axis (e.g., annularly). The second member includes a third receiving coil extending around the coil axis (e.g., annularly) at a radius different from the radius of the first and second receiving coils and the radius of the excitation coil, and for detecting a magnetic field manipulated by the third scale track, thereby allowing the relative rotational positions of the first and second members about the rotation axis from the first, second, and third receiving coils to be measured. The third receiving coil may be located on the radial side opposite to the first and second receiving coils of the excitation coil. Thus, for example, the first and second receiving coils may be located radially inside the excitation coil, and the third receiving coil may be located radially outside the excitation coil. Thus, for example, the excitation coil may be located radially between the second receiving coil and the third receiving coil. Accordingly, for example, the radius of the first receiving coil may be smaller than the radius of the second receiving coil, the radius of the second receiving coil may be smaller than the radius of the excitation coil, and the radius of the excitation coil may be smaller than the radius of the third receiving coil.

[0011] The above alternating current may pass through the excitation coil at a predetermined operating frequency. The excitation coil may include a capacitor configured to cause the excitation coil to operate as a resonant circuit. The capacitor may be positioned in alignment with the annular / circular extension of the excitation coil (i.e., positioned at the same radius as the radius of the conductor of the excitation coil).

[0012] The above-mentioned inductive encoder, e.g., the first member and / or second member, may include a magnetic flux increaser, wherein a current flow is generated by the magnetic field of the excitation coil within the magnetic flux increaser, and the magnetic flux increaser itself generates a magnetic field that acts to increase the magnetic flux of the magnetic field detected by one or more of the receiving coils in one or more regions of the receiving coils.

[0013] In a preferred embodiment, the excitation coil that generates a magnetic field generating a current flow within the magnetic flux enhancer is identical to the excitation coil that generates an (alternating) magnetic field operated by the scale track and detected by the receiving coil(s) (from which the relative rotational position of the first member and the second member can be measured).

[0014] The magnetic flux enhancer comprises at least one (electrical) conductor located radially outside the scale track of the first member and the receiving coil and excitation coil of the second member (which is hereinafter referred to as at least one "outer" conductor); and / or at least one (electrical) conductor located radially inside the scale track of the first member and the receiving coil and excitation coil of the second member (which is hereinafter referred to as at least one "inner" conductor). In a preferred embodiment, the electrical conductivity of the outer conductor and / or the inner conductor is such that they are 1×10⁻⁶ -6 They are designed to have a resistivity of less than Ω·m (for example, these are approximately 1.7 × 10⁻⁶ -8 It may include copper having a resistivity of Ω·m).

[0015] In a particularly preferred embodiment of the present invention, the magnetic flux enhancer comprises both an outer conductor and an inner conductor. In this embodiment, the receiving coil and the excitation coil may be positioned radially between the outer conductor and the inner conductor (e.g., with respect to the axis of rotation). Likewise, the scale track(s) may be positioned radially between the outer conductor and the inner conductor.

[0016] Preferably, these outer conductors and inner conductors are separate from each other. The outer conductors and inner conductors may be physically separate. The outer conductors and inner conductors may be electrically separated / insulated from each other.

[0017] The above flux enhancer, for example, the at least one "outer" conductor may comprise a closed annular (electrical) conductive loop. In a preferred embodiment, the "outer" conductor has a substantially constant radius, i.e., a circular shape.

[0018] The above flux enhancer, for example, the "outer" conductor, may include a metal loop. Copper is one suitable metal, but as is understood, other metals may also be used. The "outer" conductor may include a metal loop. The (e.g., closed) annular conductive loop of the "outer" conductor may be centered on the "outer conductor axis" and extend around it (e.g., annularly).

[0019] The at least one "inner" conductor may comprise a closed annular (electrical) conductive loop or a conductive disk. In a preferred embodiment, the "inner" conductor has a substantially constant radius, i.e., a circular shape.

[0020] The "inner" conductor may include a metal loop. Copper is one suitable metal, but as is understood, other metals may also be used. The "inner" conductor may include a wire-like loop. An (e.g., closed) annular conductive loop or conductive disk of the "inner" conductor may be centered on the "inner conductor axis" and extend around it.

[0021] The inner conductor may be substantially planar. The outer conductor may be substantially planar. In a preferred embodiment, the planes of the inner conductor and / or the outer conductor are substantially parallel. The inner conductor and the outer conductor may be substantially coplanar. Preferably, the planes of the inner conductor and / or the outer conductor, the plane of the scale track, and the planes of the excitation coil and the receiving coil are all substantially parallel to each other (e.g., so that the angle between any of these planes is 5° or less, more preferably 3° or less, particularly preferably 2° or less, e.g. 1° or less).

[0022] As is understood (and as described herein), the magnetic flux enhancer (e.g., inner conductor and / or outer conductor) does not necessarily have to be located in the same plane as the receiving coil and the excitation coil (not necessarily coplanar with the receiving coil and the excitation coil), or does not necessarily have to be located in the same plane as the scale track (not necessarily coplanar with the scale track).

[0023] Optionally, the first member comprises a flux enhancer (e.g., at least one "outer" conductor and / or at least one "inner" conductor). In this case, it may be preferable that the flux enhancer (e.g., at least one "outer" conductor and / or the at least one "inner" conductor) is substantially coplanar with the at least one scale track. For example, if the outer conductor and / or the inner conductor are closed annular loops (which will be described in more detail below), preferably i) the plane of the flux enhancer (i.e., the outer conductor or the inner conductor) and ii) the plane of the scale track(s) is 7.5% or less (more preferably 5% or less, particularly preferably 2% or less) of the diameter of the flux enhancer, i.e., the outer conductor or the inner conductor.

[0024] Optionally, the second member comprises a flux enhancer (e.g., at least one "outer" conductor and / or at least one "inner" conductor). In this case, it may be preferable that the flux enhancer (e.g., at least one "outer" conductor and / or the at least one "inner" conductor) is substantially coplanar with at least one of the excitation coil and the receiving coil. For example, if the outer conductor and / or the inner conductor are closed annular loops (this is described in more detail below), preferably i) the plane of the flux enhancer (i.e., the outer conductor or the inner conductor) and ii) the plane of the excitation coil and the receiving coil is 7.5% or less (more preferably 5% or less, particularly preferably 2% or less) of the diameter of the flux enhancer, i.e., the outer conductor or the inner conductor.

[0025] Optionally, the first and second members include a magnetic flux enhancer (e.g., at least one "outer" conductor and / or at least one "inner" conductor).

[0026] Preferably, the magnetic flux enhancer does not extend or exist directly behind or directly forward of the scale track, and also does not extend or exist directly behind or directly forward of the receiving coil and the excitation coil.

[0027] For example, the magnetic flux enhancer (e.g., at least one "outer" conductor and / or the at least one "inner" conductor) may be provided on the first member and located within the plane of the first member, and the receiving coil and the excitation coil may be provided on the second member and located within the plane of the second member (the first member and the second member and their respective planes are axially offset with respect to the axis of rotation and are therefore not coplanar).

[0028] As is understood, the reference herein stating that a flux enhancer (e.g., inner conductor and / or outer conductor) is positioned "radially" (e.g., "radially outer," "radially inner," or "radially between") with respect to the scale track and / or excitation coil and / or receiving coil is not intended to limit the relative configuration / arrangement of these features in the axial direction (with respect to the axis of rotation), but rather to indicate only the relative configuration of those features in the radial direction (with respect to the axis of rotation). In other words, the use of the terms "radially outer," "radially inner," or "radially between" is not intended to require that such features be in the same plane. For example, in an embodiment where the first member comprises a magnetic flux enhancer including an "outer" (e.g., closed) annular conductive loop and an "inner" (e.g., closed) annular conductive loop, and the second member is axially offset with respect to the first member, the receiving coil and the excitation coil (and any at least one magnetic field sensor) of the second member may still be positioned "radially" between the "outer" (e.g., closed) annular conductive loop and the "inner" (e.g., closed) annular conductive loop by their respective radial positions and dimensions. In fact, this is the situation illustrated in the embodiment described above in relation to the drawings (see Fig. 7 in particular). Likewise, in the embodiment illustrated in Fig. 17c, it can still be said that the scale track of the first member (rotor) is positioned radially between the outer and inner annular loops provided as part of the second member (stator).

[0029] As is understood, another term commonly used for "excitation coil" in the field of inductive encoders is "transmit coil." Therefore, the term "transmit coil" may be used herein instead of the term "excitation coil."

[0030] A scale track may include a series of (electrically) conductive / non-conductive scale features, for example, in the form of an array. In other words, a scale track may include a series of alternately arranged (electrically) conductive scale features and non-conductive scale features. A scale track may include scale features in a periodic arrangement. Thus, a scale track may include (electrically) conductive / non-conductive scale features in a periodic arrangement. In other words, a scale track may include a periodic series of alternately arranged (electrically) conductive scale features and non-conductive scale features. As is understood, references to conductive and non-conductive herein relate to electrical conductivity, and for the sake of simplification, they will be referred to simply as conductive and non-conductive. As is understood, the required or desirable levels of resistivity for conductive and non-conductive features may vary depending on the application. Nevertheless, in relation to a preferred embodiment of the present invention, the electrically conductive scale feature is 1x10 -6 Having a resistivity of less than Ω·m (e.g., the resistivity of copper is approximately 1.7 x 10⁻⁶ - 8 Ω·m), the resistivity of the non-conductive characteristic part is 1x10 - 4 It is greater than Ω·m, for example, can be significantly larger than that, for example, can be much larger than 1Ω·m, for example, 1x10 3 It can be larger than Ω·m.

[0031] As is understood, the scale track may be configured to manipulate the magnetic field depending on the relative positions of the first member and the second member, which are rotatable relative to each other around the axis of rotation.

[0032] The scale track can be configured so that the manipulation effect on the magnetic field varies in a spatially periodic manner. The spatial frequency of this spatially periodic effect may depend on the period of the scale feature.

[0033] The first and second scale tracks may be configured to manipulate the amplitude of an alternating magnetic field (generated by the excitation coil). Accordingly, the scale track may be configured to manipulate / modulate the amplitude of the (alternating) magnetic field depending on the relative positions of the first and second members, which are rotatable relative to each other around an axis of rotation. The scale track may be configured to manipulate the amplitude of the (alternating) magnetic field in a periodic manner in which the spatial frequency depends on the period of its scale feature.

[0034] The above at least first and second scale tracks (e.g., their features) may be contained within a first plane. The excitation coil(s) may be contained within a second plane. The receiving coil(s) may be contained within a third plane. Preferably, the second plane and the third plane may be substantially parallel and optionally substantially coplanar. When assembled together, the first plane and the second / third plane may be preferably substantially parallel (e.g., so that the angle between any of these planes is 5° or less, more preferably 3° or less, particularly preferably 2° or less, e.g. 1° or less).

[0035] As is understood, generally, and in a preferred embodiment of the present invention comprising an inductive rotary encoder, the inductive rotary encoder is configured or intended to be configured such that, in use, all axes (i.e., scale track axis, excitation axis and receiving axis (or "coil axis"), and rotation axis) are arranged to be substantially parallel to each other (at least to the extent that the first member and the second member do not physically come into contact with each other during operation). As is understood, the degree of parallelism actually required will depend on various aspects such as the dimensions of the inductive rotary encoder and the required level of accuracy. Nevertheless, generally, i) it will be desirable that the angle between any two of the scale track axis, excitation axis and receiving axis (or "coil axis") be 5° or less, more preferably 3° or less, particularly preferably 2° or less, e.g. 1° or less. In addition, generally, it is desirable that the angle between any of the scale track axis, excitation axis and receiving coil axis (or "coil axis") and ii) the rotation axis be 5° or less, more preferably 3° or less, particularly preferably 2° or less, e.g. 1° or less.

[0036] In a preferred embodiment, the inductive rotary encoder is configured or intended to be positioned so that, when in use, the axes (i.e., scale track axis, excitation axis, and receiving axis (or "coil axis")) and the rotation axis are all substantially aligned / coaxial (e.g., aligned / coaxial) (e.g., offset from each other by less than 10% of the receiving coil diameter, more preferably less than 5% of the receiving coil diameter).

[0037] Likewise, in an embodiment comprising an inner and / or outer conductor, preferably, when assembled, the scale track axis, the coil axis, the outer conductor axis and / or the inner conductor axis are all substantially parallel to each other, and optionally all substantially coincident / coaxial.

[0038] Generally, in use, for an inductive rotary encoder, the first member will be mounted on a rotating part of the machine and the second member will be mounted on a static part of the machine (thus, the first member may be referred to as a "rotor" and the second member as a "stator"). Nevertheless, as is understood, this is not necessarily required, and the members may be mounted in the opposite way, or both the first member and the second member may be mounted on rotatable parts.

[0039] As understood, the device may be configured to determine the relative rotational position of the first member and the second member about an axis of rotation and / or its derivative (e.g., velocity and / or acceleration) from the output of the receiving coil. Such rotational position may be the absolute relative rotational position of the first member and the second member about an axis of rotation. Accordingly, the device may include means for determining information regarding the relative rotational position of the first member and the second member about an axis of rotation and / or its derivative from the receiving coil. The means may include one or more "processing" or "processor" devices.

[0040] As is understood, "processing" or "processor" devices may include custom processing devices configured for a specific application (e.g., Field Programmable Gate Arrays "FPGAs"), as well as more general processing devices that can be programmed (e.g., via software) according to the requirements of the application in which they are used. Accordingly, suitable "processing" or "processor" devices may include, for example, a CPU (Central Processor Unit), an FPGA (Field Programmable Gate Array), an ASIC (Application Specific Integrated Circuit), etc.

[0041] The above means, for example, "processing" or "processor" device(s), may be provided as part of one or both of the first member or the second member (in this case, preferably provided as part only of the second member). However, this is not necessarily required, and such means may be provided by one or more components distinct from the first member and the second member. For example, the inductive rotary encoder device may include the first member and the second member and a separate interface unit comprising the means.

[0042] Accordingly, for example, the device may include a controller comprising such "processing" or "processor" device(s). The controller may be a controller of a machine on which or to which the first member and the second member are mounted. Accordingly, for example, the device may include a machine on which or to which the first member and the second member are mounted.

[0043] As is understood, the means for determining the rotational position and / or derivatives (e.g., velocity and / or acceleration) of the first member and the second member about the axis of rotation from the output of the receiving coil may be shared or distributed between the means provided on the first member and / or the second member and another device (e.g., a machine controller) separate from the first member and / or the second member.

[0044] According to a second aspect of the present invention, an inductive encoder is provided, said encoder comprising a first member and a second member that are movable relatively along a measurement direction (e.g., around a rotation axis), and

[0045] ● The first member comprises at least a first scale track extending along the measurement direction (e.g., extending annularly around the scale track axis), and

[0046] ● The above second member is,

[0047] ○ An excitation coil for generating a magnetic field operated by the above at least first scale track; and

[0048] ○ It includes at least a first receiving coil for detecting a magnetic field manipulated by the first scale track, through which the relative rotational position of the first and second members along the measurement direction (e.g., around the rotation axis) can be measured, and

[0049] ● The above inductive encoder device is configured to pass alternating current through the excitation coil at a predetermined operating frequency, and

[0050] ● The above-mentioned excitation coil includes a capacitor arranged so that the excitation coil operates as a resonant circuit.

[0051] The excitation coil may extend substantially circularly with respect to the axis of the excitation coil, and the capacitor is positioned in alignment with the circular extension of the excitation coil. The excitation coil may be a single-winding coil, and / or the first receiving coil is a single-winding coil, and / or the second receiving coil is a single-winding coil. The features described above in relation to the first aspect of the invention are applicable to the second aspect of the invention and are therefore not repeated herein for the sake of brevity.

[0052] According to a third aspect of the present invention, an inductive (e.g., rotary) encoder is provided, said encoder comprising a first member and a second member movable relative to each other along a measurement direction (e.g., around a rotation axis), and

[0053] ● The first member comprises at least a first scale track and a second scale track (extending annularly around the scale track axis),

[0054] ● The above second member is,

[0055] ○ Excitation coil for generating a magnetic field operated by at least the first and second scale tracks; and

[0056] ○ At least, it includes a first receiving coil for detecting a magnetic field manipulated by the first scale track and a second receiving coil for detecting a magnetic field manipulated by the second scale track, thereby allowing the relative rotational position of the first and second members around the rotation axis to be measured.

[0057] ● The second receiving coil is spaced apart from the excitation coil (e.g., radially) by the first receiving coil.

[0058] In an embodiment where the encoder is a rotary encoder, the excitation coil and the receiving coil extend annularly around the coil axis. The features described above in relation to the first aspect of the invention are applicable to the third aspect of the invention and are therefore not repeated herein for brevity. In particular, the magnetic flux enhancer described above in relation to the first aspect of the invention may be particularly beneficial for the configuration of the third aspect of the invention. Brief explanation of the drawing

[0059] Now, embodiments of the present invention will be described only by way of example with reference to the following drawings. FIG. 1 is a perspective view of an inductive rotary encoder according to the present invention. Figure 2 is a schematic cross-sectional view of the inductive rotary encoder of Figure 1 mounted on a machine. Figure 3 is a plan view of the rotor of the inductive rotary encoder of Figure 1. Figure 4 is a plan view of the stator of the inductive rotary encoder of Figure 1. Figure 5 is a plan view of the quadrant of the stator of Figure 4. FIG. 6 is a plan view of the quadrants of the stator and rotor, in which the substrate of the stator is transparent so that the rotor below the stator can be seen. Figure 7 shows a schematic cross-sectional view of the stator and rotor taken along the CC line of Figure 6. FIG. 8 is a plan view showing the excitation coil of the stator and the outer and inner conductive loops of the rotor separated. Figure 9 is a block diagram of a system for calculating the scale of the relative rotational position of the rotor and the stator. Figure 10 is a graph showing how the output of the arc tangent calculator for each receiving coil changes according to the relative rotation of the stator and rotor. FIGS. 11a and FIGS. 11b illustrate schematic partial cross-sectional views of the stator and rotor and are intended to explain the effect of changes in the lateral / radial position of the stator and rotor (e.g., eccentricity) on the electromagnetic field detected by the sensor of the stator. FIGS. 12a, FIGS. 12b, and FIGS. 12c illustrate schematic partial cross-sectional views of the stator and rotor and are intended to explain the effect of relative tilt on the electromagnetic field detected by the relative tilt sensor of the stator. FIG. 13 is a schematic plan view of the outer and inner quadrant sensors of the stator. FIGS. 14a and FIGS. 14b illustrate examples of Lissajous figures obtained from outer and inner quadrant sensors. FIGS. 15a and FIGS. 15b illustrate plan views of alternative stator configurations. FIGS. 16(a) and FIGS. 16(b) separately illustrate the isometric and planar views of an exemplary excitation coil. FIG. 16(c) schematically illustrates how the magnitude of the magnetic flux density component perpendicular to the scale (i.e., the component parallel to the axis (D) through which the scale extends around it), generated by the circular unidirectional excitation coil of FIG. 16(a) and FIG. 16(b), changes over a limited radial cross-section (indicated by the dashed line in FIG. 16(b)) with and without inner and outer conductor loops (dotted line). FIG. 16(d) shows a plan view of an exemplary excitation coil having a folded-rectangular loop. FIG. 16(e) schematically illustrates how the magnitude of the magnetic flux density component perpendicular to the scale (i.e., the component parallel to the axis (D) through which the scale extends around it), generated by the folded rectangular loop of the excitation coil in FIG. 16(d), changes over a limited radial cross-section (indicated by the dashed line in FIG. 16(d)) with and without inner and outer conductor loops (dotted line) and (solid line). FIG. 17a shows a front view of a stator (i.e., a side view of the stator facing the rotor during use) according to another embodiment of the present invention, and FIG. 17b shows a front view of a rotor (i.e., a side view of the rotor facing the stator during use). FIG. 17c shows a schematic cross-sectional view of the stator and rotor taken along the CC line of FIG. 17a and FIG. 17b. Specific details for implementing the invention

[0060] Referring to FIGS. 1 and 2, an exemplary inductive rotary encoder (100) according to the present invention comprises a rotor (200) and a stator (300). As schematically illustrated in FIG. 2, in use, the rotor (200) is mounted on a mechanical part, such as a shaft (500), which is rotatable about a static part (600) of the machine about an axis (A), and the stator (300) is mounted on a static part of the machine. Similar to a known inductive rotary encoder, the stator (300) is an active power-supplied component and includes an excitation coil and a receiving coil (described in more detail below) and associated electronics for generating and detecting an alternating electromagnetic field. Also, similar to a known inductive rotary encoder, the rotor (200) is a passive / unpowered component including a scale feature. The scale feature above manipulates the electromagnetic field detected by the receiving coil of the stator (300) (and in this example, manipulates / modulates the amplitude of the alternating electromagnetic field), so that the specific output of the receiving coil of the stator depends on the relative rotational orientation of the stator (300) and the rotor (200) around the axis (A), and thus the relative rotational position (and / or derivative thereof) of the stator (300) and the rotor (200) (and thus the relative rotational position of the static part (600) and the rotating part (500) of the machine) can be measured from the electromagnetic field. As is understood, the rotor (200) and the stator (300) can be configured in opposite ways (i.e., the rotor may have active components, i.e., an excitation coil and a receiving coil, and the stator may have passive components, i.e., a scale feature). However, due to the need for electrical connections, it may be simpler and easier for the stator to be an active power-supplied component.Additionally, since the rotor may be subjected to significant forces due to its movement and changes in speed, and thus the electronics on the active component may be vulnerable to damage caused by such forces, it may be advantageous to make the rotor a passively unpowered component. As is understood, in other embodiments, both members may be rotatable, that is, both the "stator" and the "rotor" may be rotatable, in which case both the "stator" (300) and the "rotor" (200) may be referred to as "rotors," for example, "rotor 1" and "rotor 2," or "active rotor" and "passive rotor." Nevertheless, for the sake of simplicity and convenience of explanation, the described embodiment comprises a static "stator" (300) and a "rotor" (200) rotatable relative to the stator (300).

[0061] Referring to FIG. 3, a plan view of the rotor (200) is shown. In the described embodiment, the rotor (200) comprises a disc-shaped substrate (202) provided with scale features. In the described embodiment, the substrate is formed of glass fiber, has a circular shape overall, and has a hole (203) extending through the center to allow a shaft of the machine (not shown in FIG. 3) to pass through. As is understood, the rotor substrate (202) may be formed of other materials (e.g., non-conductive materials) and does not necessarily have to have a circular shape or a hole extending through it.

[0062] The scale feature of the rotor (200) is centered on the axis (B) and extends annularly around it. In the described embodiment, the scale feature is conductive (in this embodiment, it is copper and is formed by removing a copper coating on the glass fiber substrate (202) by etching / milling, but it may also be formed by other processes such as copper plating). In an alternative embodiment, the substrate (202) may include a conductive material, in which case a non-conductive feature may be formed thereon to provide the scale feature.

[0063] In the described embodiment, the rotor (200) includes a first scale track (204), a second scale track (206), and a third scale track (208). Each scale track includes a periodic series of scale features. The periods of the first scale track (204), the second scale track (206), and the third scale track (208) are different from each other, and each scale track is configured to have an integer number of periods per rotation, and is also configured such that the phase relationship between the scale features of the three scale tracks at any angle around the axis (B) is not the same as the phase relationship at any other rotation angle. As illustrated, the first scale track (204), the second scale track (206), and the third scale track (208) are arranged concentrically with respect to each other, and thus all are centered on the same axis (B).

[0064] In the described embodiment, the rotor (200) also includes an outer conductive loop (210) made of a conductive material (copper in this embodiment) and an inner conductive loop (212) made of a conductive material (again, copper in this embodiment). The outer conductive loop (210) and the inner conductive loop (212) are centered on an axis (D) and extend annularly around it. As described in more detail below, the outer conductive loop (210) and the inner conductive loop (212) help increase the magnetic flux density in the radial space between them, thereby helping to increase the signal strength and system sensitivity of the receiving coil (described below) of the stator. As most clearly illustrated in FIGS. 6 and 7, in the described embodiment, the outer conductive loop (210) is located radially outward of all three scale tracks (204, 206, 208) and also radially outward of all coils on the stator (i.e., i) the excitation coil, ii) the first, second, and third receiving coils, and iii) the quadrant coils). Additionally, as most clearly illustrated in FIGS. 6 and 7, in the described embodiment, the inner conductive loop (212) is located radially inward of all three scale tracks (204, 206, 208) and also radially inward of all coils on the stator (i.e., i) the excitation coil, ii) the first, second, and third receiving coils, and iii) the quadrant coils). Thus, in other words, the three scale tracks (204, 206, 208) and all coils on the stator (i.e., i) the excitation coil, ii) the first, second, and third receiving coils, and iii) the quadrant coil) are positioned radially between the outer conductive loop (210) and the inner conductive loop (212).

[0065] In the described embodiment, the outer conductive loop (210) and the inner conductive loop (212) are simple circular copper loops of a closed single winding. However, they are not necessarily required to be so, and the outer conductive loop (210) and the inner conductive loop (212) may take other forms. For example, the outer conductive loop (210) and the inner conductive loop (212) may have a multiple-turn helical form (e.g., a form having a constant radius but extending axially through the substrate), include a multiple-turn spiral form (e.g., a form with a continuously changing radius), and proceed in a waveform (e.g., sinusoidal) form / path around the axis. Optionally, a plurality of distinct outer conductive loops (210) may be provided, and / or a plurality of inner conductive loops (212) may be provided.

[0066] The presence of an outer conductive loop (210) has been found to be particularly beneficial to an embodiment (described in more detail below) comprising a sensor for detecting the relative tilt of the stator and / or rotor. This is because, in addition to having the effect of increasing the signal strength of the receiving coil, at least some of the sensors used for detecting tilt and / or lateral / radial position (e.g., eccentricity) are made substantially more sensitive to the relative tilt of the rotor and stator, thereby making it easier to extract relative tilt measurements from such sensors. In particular, as described in more detail below, due to the outer conductive loop (210), an inductive rotary encoder device can be configured such that the output of the outer quadrant coil (described below) measures only the relative tilt of the rotor (200) and stator (300) and is assumed to be related only to this.

[0067] Additionally / alternatively, the presence of one or both of the outer conductive loop (210) and / or the inner conductive loop (212) may be particularly useful in an embodiment where the number of excitation coils is less than the number of scale tracks and each receiving coil (e.g., to improve magnetic flux and consequently signal strength).

[0068] Additionally / alternatively, the presence of one or both of the outer conductive loop (210) and / or the inner conductive loop (212) is particularly useful for increasing the magnetic flux density perpendicular to the scale in a radially distal region relative to the excitation coil, which may be desirable when it is desirable to increase the radial width of the scale track and / or the receiving coil and / or in an embodiment where the receiving coil and the corresponding scale track cannot be located immediately radially next to the excitation coil (e.g., where there is another receiving coil and a corresponding scale track radially between the excitation coil and the receiving coil and the corresponding scale track that generate the electromagnetic field configured to sense) and / or configured to exist only on one radial side of the receiving coil and the corresponding scale track, such as when the excitation coil is a "single-direction" excitation coil (described in more detail below). In fact, the above cases are the cases of embodiments of FIGS. 4 to 7, FIG. 15, and FIG. 16(a) and FIG. 16(b), in which i) a unidirectional excitation coil (330) is used, ii) the first scale track (204) and the first receiving coil (304) have a relatively large radial width, and iii) the second receiving coil (306) and the corresponding second scale track (206) are radially positioned between the third receiving coil (308) / third scale track (208) and the excitation coil (330). In this embodiment, the inner conductive loop (212) is particularly useful for increasing the magnetic flux density perpendicular to the scale in the area of ​​the third scale track (208) and the associated third receiving coil (308) that is located radially further from the excitation coil (330) compared to the first scale track / first scale coil (204, 304) and the second scale track / second receiving coil (206, 306) (since the second scale track (206) and the second receiving coil (306) are located radially between the third scale track (208) and the third receiving coil (308) and the excitation coil (330).Likewise, the outer conductive loop (210) is particularly useful for increasing the magnetic flux density perpendicular to the scale in the radially distal region of the first scale track (204) and the first receiving coil (304) (which has a significantly larger radial width compared to the second scale track / second receiving coil (206, 306) and the third scale track / third receiving coil (208, 308)). This will be explained in more detail below in relation to FIGS. 16(b) and FIGS. 16(c).

[0069] As is understood, for whatever reason, increasing the magnetic flux density of the electromagnetic field in the region of the scale track increases the eddy currents generated within the conductive scale feature, which in turn provides a larger amplitude modulation effect for the alternating electromagnetic field detected by the corresponding receiving coil.

[0070] Now, referring to FIGS. 4 and 5, FIG. 4 illustrates a top view of a stator (300), and FIG. 5 illustrates a detailed view of one quadrant of the stator (300). The stator (300) comprises a disc-shaped substrate (302) on which an excitation coil and a receiving coil are provided, together with the associated electronic device provided on the substrate (302) on the opposite side of the illustrated side. (In FIG. 5, the shading of the stator substrate is omitted so that other features of the stator can be seen better.) In the described embodiment, the stator substrate (302) is made of glass fiber, has a circular shape overall, and has a hole (203) extending through the center to allow the shaft (500) of the machine to pass through. According to another embodiment of the present invention, the stator substrate (302) may be made of another non-conductive material (e.g., ceramic), does not necessarily have to have a circular shape, nor does it necessarily have to have a hole extending through the substrate.

[0071] The stator (300) comprises a first scale receiving coil (304), a second scale receiving coil (306), and a third scale receiving coil (308), which are arranged concentrically and each is centered on an axis (D) and extends substantially in a complete annular shape around it. As illustrated, the width measured in the radial direction of the first scale receiving coil (304) (e.g., "radial width" R) w )) is larger than the width of the second scale receiving coil (306) and the third scale receiving coil (308). In the illustrated embodiment, the radial width (R) of the first scale receiving coil (304) w ) is about twice the radial width of the second scale receiving coil (306) and the third scale receiving coil (308). As is understood, since the receiving coil extends along a waveform (e.g., sinusoidal) path around the axis (D), another appropriate term for the radial width of the receiving coil is "coil amplitude".

[0072] In the described embodiment, each of the first scale receiving coil (304), the second scale receiving coil (306), and the third scale receiving coil (308) actually comprises a differential copper coil extending in a first sinusoidal waveform and a differential copper coil extending in a second sinusoidal waveform. The first and second differential coils are superimposed and phase-shifted by 90° relative to each other. Thus, the first differential coil may be referred to as the SIN coil, and the second differential coil may be referred to as the COS coil. Accordingly, each of the first scale receiving coil (304), the second scale receiving coil (306), and the third scale receiving coil (308) actually outputs a pair of signals in a quadrature relationship (i.e., signals phase-shifted by 90°), and thus the pair of signals may be represented, for example, as a SIN signal and a COS signal. As is understood, other configurations, such as a three-phase system comprising three sets of coils phase-shifted by 60°, are also possible. In other embodiments, each track / channel may include only a single coil, but such a system may have lower accuracy.

[0073] As illustrated in FIGS. 4 and 5, the first scale receiving coil (304), the second scale receiving coil (306), and the third scale receiving coil (308) are sinusoidal in that they extend around the axis (D) along a substantially sinusoidal path. In fact, in the described embodiment, the SIN coil and COS coil of the first scale receiving coil (304), the second scale receiving coil (306), and the third scale receiving coil (308) are each actually differential coils and have clockwise and counterclockwise windings in each period to cancel out residual magnetic fields. The coil shape is sinusoidal for harmonic suppression. Of course, the coil shape / path does not necessarily have to be sinusoidal. For example, the coil may have a different periodic shape / path to capture modulation from the scale. Also, it does not necessarily have to be a differential coil. In the described embodiment, the periods of the sinusoidal waveforms of the first scale receiving coil (304), the second scale receiving coil (306), and the third scale receiving coil (308) are different from each other (and in the described example, the periods of the sinusoidal waveforms of the first scale receiving coil (304), the second scale receiving coil (306), and the third scale receiving coil (308) are configured to match the period of the corresponding scale track). As is understood, this is not strictly necessary, but doing so may be advantageous in terms of processing and signal quality.

[0074] In the described embodiment, the first scale receiving coil (304), the second scale receiving coil (306), and the third scale receiving coil (308) each comprise a single winding (or "single loop") coil (in that it is wound around, extends around, or turns around only once, rather than being wound around the axis (D) multiple times (e.g., overlapping). In another embodiment, one or more of the receiving coils may comprise multiple winding (or "multiple loop") coils, in which case the coil is wound around the axis (D) two or more times, i.e., multiple times (e.g., overlapping).

[0075] As described in more detail below, when in use / assembled, the inductive encoder device is arranged such that i) the first scale receiving coil (304) and the first scale track (204) are positioned directly in front of each other (i.e., "directly facing") (in other words, the first scale receiving coil (304) is positioned axially aligned with respect to the first scale track (204) and directly above it in the orientation shown in FIG. 7), ii) the second scale receiving coil (306) and the second scale track (206) are positioned directly in front of each other (i.e., "directly facing") (in other words, the second scale receiving coil (306) is positioned axially aligned with respect to the second scale track (206) and directly above it in the orientation shown in FIG. 7), and iii) the third scale receiving coil (308) and the third scale track (208) are positioned directly in front of each other (i.e., "directly facing") (in other words, the third scale receiving The coil (308) is configured to be aligned axially with respect to the third scale track (208) and placed directly above it in the orientation shown in FIG. 7.

[0076] The stator (300) also includes an excitation coil (330) (which may also be referred to as a "transmitting coil") centered on the axis (D) and extending annularly around it. In the described embodiment, the excitation coil (330) is positioned radially between the first scale receiving coil (304) and the second scale receiving coil (306).

[0077] According to an embodiment of the present invention, the excitation coil (330) is a “single-direction” excitation coil in that it comprises a conductor wire extending along a circular path in a single direction around an axis (D), so that at any given point in time, current flows in only one direction around the axis (D) (e.g., clockwise or counterclockwise only). According to a preferred embodiment of the present invention, in the specific embodiment described, the conductor has a substantially constant single radius and therefore follows a single substantially circular path. In the specific embodiment described, the conductor has only one identifiable radius. A suitable exemplary excitation coil (330) having a conductor extending along a circular path in a single direction around the axis (D) and having a constant single radius is shown separately in FIG. 16(a) and FIG. 16(b).

[0078] In the specific embodiment illustrated in FIG. 16(a) and FIG. 16(b), the excitation coil (330) is a single-winding (or "single-loop") excitation coil. Thus, the excitation coil is "wound" / "extended" / "rotated" only once rather than being wound multiple times (e.g., overlapping) around the axis (D). In the described embodiment, the single-winding / loop excitation coil comprises two single-winding (copper) wires (330a, 330b) extending circularly / annularly around the axis (D), which are arranged in parallel on adjacent layers of the substrate (302) with the same radius "r" (thus spaced apart from each other along a direction parallel to the axis (D) as illustrated in FIG. 16(a)). Each end of these is connected to a single pair of terminals (+ / -). Accordingly, by being configured in this way, the two wires (330a, 330b) extend around the axis (D) and form an excitation coil that extends in a circular / annular manner in a single direction, single winding, concentric with the first scale receiving coil (304), the second scale receiving coil (306), and the third scale receiving coil (308). The advantage of using two wires configured as described is that the resistance is reduced compared to an equivalent excitation coil having only one wire (of the same dimensions), which increases the quality (Q factor) of the excitation coil. As is understood, in an equivalent embodiment, a similar reduction in the resistance of the excitation coil can be achieved with a single wire by using a thicker wire and / or using a wire made of a material with lower intrinsic resistance.

[0079] As is understood, in other embodiments, the excitation coil (330) may comprise multiple windings or "loops," in which case the conductor of the excitation coil may be wound two or more times around the axis (D) and take on a helical shape having, for example, a substantially constant radius. However, to minimize the inductance of the excitation coil and to relatively lower the driving voltage required to achieve the desired magnetic field, it may be preferable for the excitation coil to be a single-winding or "loop" excitation coil. However, as is understood, for a given desired magnetic field generated by the excitation coil, reducing the number of windings of the excitation coil implies that the level of current / ampere required through the excitation coil must be increased. This can be achieved by providing a power / drive circuit that directly provides the required level of current / ampere passing through the excitation coil (330), but the current (ampere) requirement of the power / drive circuit can be reduced by configuring the excitation coil to operate as a "resonant circuit" (also known as an "LC circuit," "tank circuit," or "tuned circuit"), for example, by allowing the excitation coil to store energy vibrating at the same frequency as the vibrating power / drive circuit. In this case, the power / drive circuit only needs to supply enough current to overcome the losses occurring in the excitation coil (330). An effective method of configuring the excitation coil (330) to operate as a resonant circuit is to configure a suitable capacitor (331) in the excitation coil (330), for example, as schematically illustrated in FIG. 16(a) and FIG. 16(b) (in this case, the capacitor may be referred to as a "resonant capacitor"). In the described embodiment, the operating / driving frequency of the excitation coil of the alternating magnetic field / stator is about 3 MHz, and thus the capacitor is selected accordingly based on the inductance of the wire extending in the circle of the excitation coil.

[0080] In the specific embodiment described, due to space constraints, the ("resonant") capacitor (331) is provided on a layer of the stator substrate (302) different from the layer where the conductors (330a, 330b) of the excitation coil (330) are located (thus, in FIG. 16(a), it is shown as being at a different location from the conductors (330a, 330b) along a direction parallel to the axis (D). However, in the described embodiment, the capacitor (331) is advantageously physically positioned to be located on substantially the same radius as the conductors (330a, 330b). This is because the capacitor (331) contributes to the electromagnetic field generated by the excitation coil (330), and thus placing the capacitor (331) on substantially the same radius as the conductors (330a, 330b) of the excitation coil helps to reduce distortion of the electromagnetic field generated by the excitation coil (330) in the region of the capacitor (331).

[0081] As is understood, the use of a resonant capacitor is not limited to the single-winding, single-direction embodiment described and illustrated in relation to FIG. 16(a) and FIG. 16(b), and may be useful in other excitation coil configurations. For example, the resonant capacitor may be used in an embodiment in which the coil comprises multiple windings, and may also be used in an embodiment in which the excitation coil extends and / or is wound in both clockwise and counterclockwise directions around an axis (as described below in relation to FIG. 16(d)).

[0082] In the described embodiment, there is only one excitation coil (330) shared among the three receiving coils (i.e., one excitation coil (330) is used to generate the electromagnetic field for the three receiving coils). As is understood, other excitation coil configurations are also possible. For example, two or more excitation coils may be provided, in which case ideally they would all be in a resonant state. As another example, the / each excitation coil may include a multi-winding (or "multi-loop") coil. As yet another example, the / each excitation coil may include a "folded rectangular loop."

[0083] During use / operation, the power / drive circuit causes alternating current to flow through the excitation coil (330), thereby generating an alternating electromagnetic field. Since the excitation coil (330) of the embodiment of FIG. 16(a) has a configuration that extends around the axis (D) in only one direction (i.e., a configuration that does not fold back on itself, such as in the case of a “folded rectangular loop”), at any given point in time, the current flows in only one direction around the axis (D). For example, as schematically illustrated by the arrows on the wires (330a, 330b) in FIG. 16(a), at a first point in time, the current flows through the wires (330a, 330b) in only a clockwise direction around the axis (D). As is understood, at another point in time when the current flows through the wires (330a, 330b) in the opposite direction due to the alternating current, the direction of the arrows points in the opposite direction.

[0084] The profile of the magnitude of the magnetic flux density component passing perpendicularly (i.e. parallel to the axis (D)) through the scale, generated by a unidirectional excitation coil (330) (schematically illustrated in FIG. 16(c)), contrasts with the profile of the magnitude of the magnetic flux density component passing perpendicularly (i.e. parallel to the axis (D)) through the scale, generated directly by an excitation coil (430) (schematically illustrated in FIG. 16(d)) composed of a folded rectangular loop, in which current flows in both clockwise and counterclockwise directions around the axis (D) at any given point in time (indicated by arrows on wire (430a)). As schematically illustrated by the solid line in FIG. 16(e), in this configuration, the magnitude of the magnetic flux density component passing perpendicularly (i.e. parallel to the axis (D)) through the scale is significantly larger and more uniform on the inside of the folded rectangular loop compared to the outside. In this configuration, as schematically illustrated in FIG. 16(d) and FIG. 16(e), the first scale receiving coil (304) may be located inside the folded rectangular loop, and the second scale receiving coil (306) and the third scale receiving coil (308) may be located on both radial sides of the folded rectangular loop. As is understood, in this case, the radial positions of the first scale track (204), the second scale track (206), and the third scale track (208) on the rotor must be changed / rearranged accordingly. As schematically illustrated in FIG. 16(d), the folded rectangular loop excitation coil (430) may optionally include a resonant capacitor (431), and if desired, as schematically illustrated in FIG. 16(d), the resonant capacitor may be positioned radially aligned with the excitation coil's conductor (430a) (this is to minimize disturbance to the magnetic field generated by this, but this is less important in the folded rectangular loop design because the magnetic field is not uniform in the folded / back-turns region).

[0085] As described above, the outer / inner conductive loop increases the magnetic flux density (magnitude of the component) passing perpendicularly into the scale, which is schematically illustrated in FIG. 16(c) and FIG. 16(e) through solid and dashed lines that schematically illustrate the magnetic flux density perpendicular to the scale for equivalent systems with and without the outer / inner conductive loop. That is, in FIG. 16(c) and FIG. 16(e), the solid line schematically represents a representative profile of the magnetic flux density passing perpendicularly into the scale in a system without the outer and inner conductive loops (210, 212), and the dashed line schematically represents a representative profile of the magnetic flux density perpendicular to the scale in a system that is identical in all respects except that it has the outer and inner conductive loops (210, 212). As is understood, increasing the magnetic flux density passing vertically into the scale feature increases the eddy currents generated therein, which in turn provides a larger amplitude modulation effect on the electromagnetic field detected by the receiving coil.

[0086] Regardless of the specific configuration of the excitation coil (330) and regardless of the presence of an outer and / or inner conductive loop, the first scale receiving coil (304), the second scale receiving coil (306), and the third scale receiving coil (308) are arranged to detect the electromagnetic field generated by the excitation coil (330) and provide an output in response. As is understood, and as described in more detail below, the electromagnetic field generated by the excitation coil (330) is affected by the presence of scale features of the first scale track (204), the second scale track (206), and the third scale track (208) on the rotor (200) (i.e., the electromagnetic field is changed) (in this embodiment, this is due to eddy currents generated within the scale features, said eddy currents having an amplitude modulation effect on the alternating electromagnetic field generated by the excitation coil (330)), and this phenomenon is used to determine the relative rotational position of the rotor (200) and the stator (300) around the axis (B / D).

[0087] In the specific embodiment described, the stator (300) also includes a first outer quadrant coil (310), a second outer quadrant coil (312), a third outer quadrant coil (314), and a fourth outer quadrant coil (316), and a first inner quadrant coil (320), a second inner quadrant coil (322), a third inner quadrant coil (324), and a fourth inner quadrant coil (326). The angle occupied by each quadrant is substantially 90°. As is understood, the length of each quadrant coil may be shorter so that the angle it occupies is less than 90°, but it may be desirable to maximize the angle occupied by each quadrant coil (within the range of the quadrants) to maximize signal strength and prevent blind spots. As described in more detail below in relation to FIGS. 13 and 14, the inner and outer quadrant coils can be used to detect the relative tilt and / or lateral / radial position (e.g., eccentricity) of the rotor (200) and the stator (300). As shown in FIGS. 6 and 7, at assembly / use, the outer quadrant coil (only the fourth outer quadrant coil (316) is shown in FIGS. 6 and 7) is positioned axially aligned with the blank region of the rotor substrate (202) (e.g., directly above in the orientation shown in FIG. 7), and the inner quadrant coil (only the fourth inner quadrant coil (326) is shown in FIGS. 5, 6 and 7) is positioned axially aligned with the third scale track (208) / directly above (in the orientation shown in FIG. 7).

[0088] As also illustrated in FIGS. 6 and 7, the radial width of the third scale track (208) is selected such that both the third scale receiving coil (308) and the inner quadrant coil (only the fourth inner quadrant coil (326) is shown in FIGS. 6 and 7) are positioned axially aligned with respect to the third scale track (208) (e.g., directly above in the orientation shown in FIG. 7).

[0089] Now, with reference to FIG. 8, the effect of the outer conductive loop (210) and the inner conductive loop (212) on the electromagnetic field generated by the excitation coil (330) is explained. In summary, the outer conductive loop (210) and the inner conductive loop (212) have the effect of "folding back" the electromagnetic field generated by the excitation coil (330) into the region where the receiving coils are located, thereby increasing the magnetic flux density in the radial space between them and helping to increase the magnetic field strength between the two coils.

[0090] According to the above description, the excitation coil (330) is located on the stator (not shown in FIG. 8), and alternating current flows within it, thereby generating an electromagnetic field around it. An arrow on the excitation coil (330) indicates the direction of the current flowing through the excitation coil (330) at a specific point in time (indicated clockwise in FIG. 8). According to the right-hand rule of electromagnetism, the excitation coil (330) is on the inner side of the loop A magnetic field is generated with polarity (inward direction of the figure) on the outside of the loop and polarity (outward direction of the figure). For convenience of explanation, only the polarity for a single half-cycle of the alternating / alternating electromagnetic field is shown in FIG. 8.

[0091] Additionally, according to the above description, an outer conductive loop (210) and an inner conductive loop (212) are provided on the rotor and are located radially outward and radially inward, respectively, of the scale tracks of the rotor (this is also not shown in FIG. 8). Both the outer conductive loop (210) and the inner conductive loop (212) pass through their loops They experience a net magnetic flux of polarity. According to Lenz's Law, they all induce a current flow opposing the magnetic field that generated it (i.e., at a specific point in time illustrated in FIG. 8, it is counterclockwise, as indicated by the arrows on the outer conductive loop (210) and the inner conductive loop (212). As a result, both the outer conductive loop (210) and the inner conductive loop (212) have ● polarity on the inner side of the loop, and on the outer side of the loop It generates polarity. Thus, within the shaded area (800, 802) of FIG. 8, the magnetic flux from the outer conductive loop (210) and the inner conductive loop (212) opposes the magnetic flux from the excitation coil (330) and reduces the magnetic flux density, whereas, in contrast, within the unshaded area (804) of FIG. 8 (the area where the scale tracks of the rotor and the scale receiving coils of the stator are located), the magnetic flux from the outer conductive loop (210) and the inner conductive loop (212) is in phase with the excitation coil (330) and acts to increase the magnetic flux density in that area.

[0092] Now, the operation of the inductive rotary encoder device (100) will be described. As described above, alternating current flows through the excitation coil (330), thereby generating an alternating electromagnetic field around it, and the first scale receiving coil (304), the second scale receiving coil (306), and the third scale receiving coil (308) are arranged to detect the alternating electromagnetic field and provide an output in response. The alternating electromagnetic field is affected (e.g., changed) by the presence of scale features on the first scale track (204), the second scale track (206), and the third scale track (208) on the rotor (200).

[0093] The effect (amplitude modulation effect in the described embodiment) of the first scale track (204), second scale track (206), and third scale track (208) on the rotor (200) on the alternating electromagnetic field detected by the respective first scale receiving coil (304), second scale receiving coil (306), and third scale receiving coil (308) varies according to the relative rotation of the rotor (200) and the stator (300) about the axis (B / D). In particular, this (amplitude modulation) effect on the alternating electromagnetic field varies in a cyclic manner, and its spatial frequency depends on the period of the scale feature. Additionally, the effect of the first scale track (204), the second scale track (206), and the third scale track (208) on the rotor (200) on the alternating electromagnetic field detected by the respective first scale receiving coil (304), the second scale receiving coil (306), and the third scale receiving coil (308) is different because their scale periods are different from each other.

[0094] Accordingly, the scale features of the first scale track (204), the second scale track (206), and the third scale track (208) on the rotor (200) impart cyclic fluctuations to the alternating electromagnetic field (e.g., in its amplitude) at different spatial frequencies, and accordingly, the spatial frequency of the cyclic fluctuation of the electromagnetic field caused by the first scale track and detected by the first scale receiving coil (304), the spatial frequency of the cyclic fluctuation of the electromagnetic field caused by the second scale track and detected by the second scale receiving coil (306), and the spatial frequency of the cyclic fluctuation of the electromagnetic field caused by the third scale track and detected by the third scale receiving coil (308) are all different from each other. Accordingly, the cyclic fluctuation of the signal generated from the first scale receiving coil (304), the second scale receiving coil (306), and the third scale receiving coil (308) has different spatial periods / space frequencies. The significance of this is explained in the following paragraph with reference to Figures 9 and 10.

[0095] As previously described in relation to FIGS. 4 and 5, each of the first scale receiving coil (304), the second scale receiving coil (306), and the third scale receiving coil (308) actually comprises superimposed differential coils, which have sinusoidal waveforms and are phase-shifted by 90° relative to each other. Accordingly, each of the first scale receiving coil (304), the second scale receiving coil (306), and the third scale receiving coil (308) actually outputs a pair of orthogonal signals (i.e., signals phase-shifted by 90°), and thus the pair of signals can be represented, for example, as a SIN signal and a COS signal. This is schematically illustrated in FIG. 9, where the first coil of the pair of coils is given the suffix "s" and the other coil of the pair is given the suffix "c". Thus, FIG. 9 shows that the first scale receiving coil (304) is a (differential) SIN coil (304 s ) and (differential) COS coil (304 c ) including, and the second scale receiving coil (306) is the SIN coil (306 s ) and COS coil (306 c ...including ) and the third scale receiving coil (308) is the SIN coil (308 s ) and COS coil (308 c It schematically illustrates the inclusion of ).

[0096] As described above, in the specific embodiment described, the first scale track (204), the second scale track (206), and the third scale track (208) on the rotor (200) impart cyclic variations (at different spatial frequencies) to the amplitude of the alternating electromagnetic field. Thus, the (differential) SIN coil (304 s , 306 s , 308 s ) and COS coil (304 c , 306 c , 308 c ) detects amplitude-modulated alternating electromagnetic signals. Accordingly, according to this specific embodiment of the present invention, the signals can be demodulated to obtain a demodulated (baseband) signal. Accordingly, in this embodiment, the stator has a SIN coil (304 s , 306 s , 308 s ) and COS coil (304 c , 306 c , 308 c It includes demodulators associated with each of ), said demodulators demodulate the signal detected by them. Thus, in FIG. 9, the SIN and COS coils (304 s , 304 c, 306 s , 306 c , 308 s , 308 c The SIN signal and COS signal output by each of ) are actually demodulated (baseband) signals.

[0097] As described, the output from each of the pair of SIN coils and COS coils corresponds to the corresponding arctangent calculator (i.e., the first arctangent calculator (304) A / Tan ), 2nd Arctangent Calculator (306 A / Tan ) and the third arctangent calculator (308 A / Tan )) provided, and the arctangent calculator calculates an angle from the pair of SIN and COS signals (e.g., in this embodiment, from the pair of demodulated / baseband SIN and COS signals). FIG. 10 shows a first arctangent calculator (304 A / Tan ), 2nd Arctangent Calculator (306 A / Tan ) and the third arctangent calculator (308 A / Tan It illustrates how the angle calculated by each of ) changes according to the relative rotation of the stator and rotor around the axis (B / D).

[0098] As described above in relation to FIG. 3, the periods of the first scale track (204), the second scale track (206), and the third scale track (208) are different from each other. In particular, the first scale track (204), the second scale track (206), and the third scale track (208), and the first scale receiving coil (304), the second scale receiving coil (306), and the third scale receiving coil (308) are configured so that the signal phases of at least three individual signal channels have a unique combination for each rotation angle of the rotor and stator around the axis (B / D). This allows the absolute rotation position to be determined from the output of three arc tangent calculators.

[0099] As is understood, each scale track, the associated scale receiving coil, and the electronic device (e.g., an arctangent calculator) form a "signal channel." In this embodiment, the first scale track (204), the first scale receiving coil (304), and the first arctangent calculator (304 A / Tan ) forms a first signal channel; a second scale track (206), a second scale receiving coil (306) and a second arc tangent calculator (306 A / Tan ) forms a second signal channel; a third scale track (208), a third scale receiving coil (308) and a third arc tangent calculator (308 A / Tan ) forms a third signal channel.

[0100] In this embodiment, the first scale track (204) has the largest integer number of cycles per rotation and may be referred to as the "incremental track" (and thus the associated channel may be referred to as the "incremental channel"). The signal channels of the second scale track (206) and the third scale track (208) have fewer cycles per rotation compared to the first scale track (204). The second and third scale tracks (208) (and thus the associated signal channels) may be referred to as the (first and second) "vernier tracks" (and thus the associated second and third signal channels may be referred to as the "vernier channels"). In the described embodiment, the first scale track (204), the second scale track (206), and the third scale track (208) are configured such that the only common integer factor of the number of cycles of all scale tracks is 1. As is understood, other terms used for "number of periods" in the field of inductive encoders include "number of features" and "number of lines."

[0101] Compared to a 2-channel system, a 3-channel system offers significantly greater degrees of freedom in selecting the number of periods for each channel and provides greater error tolerance in channel phase calculation. This error tolerance allows a large number of incremental periods per revolution to be used, thus enabling large-diameter encoders.

[0102] The relatively large error tolerance for phase detection allows small signal amplitudes to be used for vernier channels with lower signal-to-noise ratios. In fact, it has been found that in a 3-channel system, filtering and automatic / dynamic signal correction on the vernier channels may be applied only restrictively or not at all, thereby simplifying the design of the inductive rotary encoder system and reducing costs. Accordingly, as illustrated in FIG. 9, in the described embodiment, only the SIN signal and COS signal from the first scale receiving coil (304) correspond to the arctangent calculator (304 A / Tan Before being transmitted to the ), it passes through an automatic / dynamic signal corrector (305), and the automatic / dynamic signal corrector (305) performs automatic / dynamic gain correction (AGC), automatic / dynamic offset correction (AOC), automatic / dynamic balance correction (ABC), and automatic / dynamic phase correction (APC) on the output of the first scale receiving coil (304) in this embodiment.

[0103] Referring again to FIG. 9, the signals from each of the three channels (i.e., the first arctangent calculator (304) A / Tan ), 2nd Arctangent Calculator (306 A / Tan ) and the third arctangent calculator (308 A / TanEach output of the respective channel is passed to a position calculator (900), which calculates the absolute position of the stator and rotor around the axis of rotation from the signals. For example, this can be performed via a function or a look-up table based on the values ​​of each channel / outputs of the three arctangent calculators. However, in the described embodiment, the absolute position is calculated by a loop that iterates through all possible incremental cycles in turn and compares the actual vernier phase for each cycle with the expected vernier phase for that cycle. When the loop is completed, only one detected position should exist. Using an iterative loop to determine the position is particularly preferable to using other techniques, such as the technique using a look-up table. For example, an iterative loop can be more efficient, particularly in terms of memory, and can also have higher versatility (e.g., when the process is used across inductive rotary encoders of different sizes).

[0104] For example, the position calculator (900) is the first arctangent calculator (304 A / Tan After taking the value output by ), for each scale period of the first scale track / incremental channel (each of the 64 scale periods in the described embodiment), the second arctangent calculator (306 A / Tan ) and the third arctangent calculator (308 A / Tan It can be configured to identify what value is expected from ). Then, the position calculator (900) uses the expected values ​​from the second arctangent calculator (306 A / Tan ) and the third arctangent calculator (308 A / TanThe actual values ​​output by ) are compared, and it is checked whether they match. Whether they match is recorded. As described above, this is repeated for each scale cycle of the first scale track / incremental channel (each of the 64 scale cycles in the described embodiment). Only one match must exist, and in such case, the matched location is provided to the output unit (902). If there is no match or if two or more matches exist, an error status is reported to the output unit (902). The output unit (902) may be any suitable unit for outputting / communicating location information / error status via a wired or wireless connection to an external device, such as a location controller, for example.

[0105] As is understood, the arctangent calculator (304 A / Tan , 306 A / Tan , 308 A / Tan The ) and position calculator (900) may include any suitable processing unit, including but not limited to a custom processing unit configured for a specific application (e.g., a field programmable gate array ("FPGA")) as well as a more general-purpose processing unit that can be programmed (e.g., via software) according to the requirements of the application being used. Accordingly, suitable processing units include, for example, a microprocessor, CPU, FPGA, ASIC, etc.

[0106] As described above, in the described embodiment, the stator (300) comprises a first outer quadrant coil (310), a second outer quadrant coil (312), a third outer quadrant coil (314), and a fourth outer quadrant coil (316), and a first inner quadrant coil (320), a second inner quadrant coil (322), a third inner quadrant coil (324), and a fourth inner quadrant coil (326). These are optional sensors and may be used to detect or provide a measure of the relative lateral / radial position (e.g., eccentricity) and / or relative tilt of the rotor (200) and the stator (300). According to the present invention, it is neither necessary nor essential to provide such sensors or other sensors that detect or provide a measure of the relative lateral / radial position (e.g., eccentricity) and / or relative tilt of the rotor (200) and the stator (300). Nevertheless, doing so may have advantages, as explained in more detail below.

[0107] As is understood, if the above axis (B)—around which the scale tracks of the rotor extend and are centered—does not coincide with the above axis (D)—around which the receiving coil of the stator extends and is centered—relative eccentricity may be said to exist between the rotor (200) and the stator (300). During operation / use, such eccentricity may exist, for example, because the rotor (200) is not positioned concentrically with the axis of rotation of the machine shaft, and / or because the stator (300) is not positioned concentrically with the axis of rotation of the machine shaft, and / or because the scale tracks and / or receiving coil are not actually centered on their assumed axes (B / D). Accordingly, the eccentricity of the rotor (200) and the stator (300) is related to the lateral / radial position of the rotor (200) and the stator (300) (i.e., related to their relative position in a degree of freedom / direction / plane perpendicular to the axis of rotation (and thus also perpendicular to the axis (B) and the axis (D))).

[0108] Relative tilt is a measure of how parallel the rotor (200) and the stator (300) are to each other. During operation / use, this relative tilt may occur, for example, because the rotor (200) is mounted on the machine such that its axis (B) (where the scale track extends and centers on that axis) is not parallel to the rotation axis (A) of the machine shaft, and / or because the stator (300) is mounted on the machine such that its axis (D) (where the scale receiving coil of the stator extends and centers on that axis) is not parallel to the rotation axis (A) of the machine shaft.

[0109] As is understood, since the scale receiving coils (304, 306, 308) are full ring sensors (i.e., substantially fully extended around the axis), the effect of having only eccentricity of the rotor (200) and / or stator (300) (i.e., having no relative tilt between the rotor (200) and the stator (300)) is offset and thus does not cause an error, and likewise, the effect of having only relative tilt between the rotor (200) and the stator (300) (i.e., having no eccentricity) is offset and thus does not cause an error.

[0110] However, it was found that when both i) eccentricity of the rotor (200) and / or the stator (300); and ii) relative tilt of the rotor (200) and the stator (300) are present, a system error is introduced into the rotational position measurement once per rotation. In particular, the error can be expressed functionally as follows: Error = (Stator Eccentricity × Rotor Tilt) + (Stator Tilt × Rotor Eccentricity) (where "×" represents the vector cross product). Thus, for example, when the stator is tilted but the rotor is not eccentric, no error occurs.

[0111] The above error of once per rotation can be calculated for a given relative tilt value and eccentricity value. In fact, it has been found that the above error of once per rotation follows the following equation.

[0112]

[0113] ζ is the relative tilt vector, ε is the relative eccentricity vector, and "x" represents the vector cross product.

[0114] Accordingly, by measuring the relative tilt and relative lateral / radial position (e.g., eccentricity) of the stator and rotor, it becomes possible to compensate for or eliminate errors during installation. To this end, as described above, the stator (300) includes two sets of quadrant coils. In particular, the stator (300) includes a first set of quadrant coils comprising a first outer quadrant coil (310), a second outer quadrant coil (312), a third outer quadrant coil (314), and a fourth outer quadrant coil (316); and a second set of quadrant coils comprising a first inner quadrant coil (320), a second inner quadrant coil (322), a third inner quadrant coil (324), and a fourth inner quadrant coil (326).

[0115] An example of how the outer quadrant coil and the inner quadrant coil can be used to detect the relative tilt and / or relative lateral / radial position (e.g., eccentricity) of the rotor (200) and the stator (300) is now explained with reference to FIGS. 11 through 14.

[0116] In relation to the detection of the relative lateral / radial position (e.g., eccentricity) of the rotor (200) and the stator (300), it should be noted that in this embodiment, the first inner quadrant coil (320), the second inner quadrant coil (322), the third inner quadrant coil (324), and the fourth inner quadrant coil (326) are arranged axially in line / directly above the scale feature (e.g., see FIG. 6 and FIG. 7). In particular, the first inner quadrant coil (320), the second inner quadrant coil (322), the third inner quadrant coil (324), and the fourth inner quadrant coil (326) are arranged axially in line / directly above the third scale track (208). Additionally, in this embodiment, the length of each of the first inner quadrant coil (320), the second inner quadrant coil (322), the third inner quadrant coil (324), and the fourth inner quadrant coil (326) corresponds to an integer number of periods of the third scale track. As a result, the axial separation between the stator (300) and the rotor (200) does not substantially affect the strength of the magnetic field detected by the first inner quadrant coil (320), the second inner quadrant coil (322), the third inner quadrant coil (324), and the fourth inner quadrant coil (326), and thus these coils are substantially unaffected / insensitive to any relative tilt of the stator (300) and the rotor (200). This is due to eddy currents generated within the scale feature that are opposite to the transmitting magnetic field. The opposing magnetic field generated by the eddy current is forced downward through the gap between the scale features, and thus the net magnetic field detected by the first inner quadrant coil (320), the second inner quadrant coil (322), the third inner quadrant coil (324), and the fourth inner quadrant coil (326) remains the same within the expected range of axial separation between the stator and the rotor during normal installation and operation conditions.

[0117] However, as schematically illustrated in FIGS. 11a and 11b, the first inner quadrant coil (320), the second inner quadrant coil (322), the third inner quadrant coil (324), and the fourth inner quadrant coil (326) are sensitive to the relative lateral position of the rotor (200) and the stator (300) (Meanwhile, for convenience of explanation, FIGS. 11a and 11b only show the excitation coil (330) and inner quadrant coils (320, 322, 324, 326) of the stator (300), and only the third scale track of the rotor (200)). For example, as illustrated in FIG. 11a, which illustrates a state where there is no relative eccentricity "ε" between the rotor (200) and the stator (300), the net magnetic flux exposed to the opposing inner quadrant coils (illustrated by the "magnetic field envelope" line) is the same. In contrast, as illustrated in FIG. 11b, which illustrates a state where there is a relative eccentricity "ε" between the rotor (200) and the stator (300), the net magnetic flux exposed to the opposing inner quadrant coils is different. Thus, the difference in output between the opposing inner quadrant coils can be used to obtain a reliable measure of the relative lateral / radial position (e.g., eccentricity) of the stator (300) and the rotor (200).

[0118] Regarding the detection of relative tilt between the rotor (200) and the stator (300), it should be noted that in this embodiment, the first outer quadrant coil (310), the second outer quadrant coil (312), the third outer quadrant coil (314), and the fourth outer quadrant coil (316) are positioned axially in line / directly above the empty area of ​​the rotor (200) (see, for example, FIG. 6 and FIG. 7). Due to this configuration, within the degree of eccentricity typically expected for the rotor (200) and the stator (300) during normal installation and operation, the first outer quadrant coil (310), the second outer quadrant coil (312), the third outer quadrant coil (314), and the fourth outer quadrant coil (316) have been found to be substantially insensitive to any relative eccentricity between the rotor (200) and the stator (300). This is schematically illustrated in FIGS. 12a and 12b, where it can be seen that there is almost no change in the state of the magnetic flux exposed to the outer quadrant coil when there is a change in the degree of eccentricity of the rotor (200) and the stator (300). In contrast, as illustrated in FIGS. 12a and 12c, there is a significant change in the state of the magnetic flux exposed to the outer quadrant coil when there is a change in the relative tilt of the rotor (200) and the stator (300). In fact, for the outer quadrant coil that is closer to the rotor due to the relative tilt, not only does the magnetic flux density (expressed as the number of magnetic flux lines) increase, but the angle of incidence of the magnetic flux passing through the outer quadrant coil decreases, and thus a greater inductive effect occurs in the quadrant coil(s) closer to the rotor (200). Therefore, the difference in output between the opposing outer quadrant coils can be used to obtain a reliable measure of the relative tilt of the stator (300) and the rotor (200).

[0119] Meanwhile, for convenience of explanation, only the excitation coil (330) and outer quadrant coils (310, 312, 314, 316) of the stator (300) are shown in FIG. 12a, FIG. 12b, and FIG. 12c, and only the outer conductive loop (210) of the rotor (200) is shown.

[0120] With the above-mentioned phenomenon in relation to FIGS. 11 and 12 in mind, now refer to FIG. 13, which schematically illustrates the outer quadrant coil, inner quadrant coil, and excitation coil (330) of the stator (300). For convenience of reference, the first outer quadrant coil (310), the second outer quadrant coil (312), the third outer quadrant coil (314), and the fourth outer quadrant coil (316) are labeled A, D, C, and B, respectively, and the first inner quadrant coil (320), the second inner quadrant coil (322), the third inner quadrant coil (324), and the fourth inner quadrant coil (326) are labeled E, K, J, and F, respectively.

[0121] By subtracting the outputs of the quadrant coils located on opposite sides, a quadrature output can be obtained from each set. For example, the following signals can be obtained from the outer quadrant coil and the inner quadrant coil.

[0122]

[0123]

[0124]

[0125]

[0126] As illustrated in FIG. 14a, plotting x1 against y1 generates a Lissajous that indicates the relative tilt of the rotor (200) and the stator (300). The center of the Lissajous in FIG. 14a is due to the tilt of the stator (300) (the effect is static), and the radius of the Lissajous in FIG. 14a is due to the tilt of the rotor (200). At a specific point in time, the position of the Lissajous (x1, y1 value) represents the tilt error vector.

[0127] As illustrated in FIG. 14b, plotting x2 against y2 generates a Lissajous that indicates the relative eccentricity of the rotor (200) and the stator (300). The center of the Lissajous in FIG. 14b is due to the eccentricity of the stator (300) (the effect is static), and the radius of the Lissajous in FIG. 14b is due to the eccentricity of the rotor (200). At a specific point in time, the position of the Lissajous (x2, y2 values) represents the eccentricity error vector.

[0128] Accordingly, the x1, y1, x2, and y2 values ​​can be used to determine the current state of relative tilt and lateral / radial position (e.g., eccentricity), and can be used to correct the position calculated by the position calculator (900). For example, as illustrated in FIG. 9, an inductive rotary encoder device may include a tilt / lateral position (e.g., eccentricity) calculator (901), said calculator (901) transmits the x1, y1, x2, and y2 values ​​to the position calculator (900), and the position calculator (900) can use them to correct the position provided to the output unit (902). Additionally, as illustrated in FIG. 9, the x1, y1, x2, and y2 values ​​may instead / additionally transmit to the output unit (902) and output to an external device. For example, the external device can use the x1, y1, x2, and y2 values ​​to correct the received position. Additionally / alternatively, instead of being used to correct position values, the x1, y1, x2, and y2 values ​​may be used to trigger a warning / error condition or to provide an indication of the relative tilt and / or lateral / radial position (e.g., eccentricity) of the stator and rotor. For example, the indication may be a visual display, thereby allowing the installer to verify that the stator and rotor are properly configured. Optionally, if the x1, y1, x2, and y2 values ​​indicate relative tilt / lateral position (e.g., eccentricity) exceeding a predetermined threshold, an error signal may be generated. Optionally, this error signal may be used to control a machine equipped with an inductive rotary encoder in a predetermined manner (e.g., causing the machine to stop upon receiving this error signal).

[0129] As is evident from the description above, in the specific embodiment described, the outer quadrant coil is primarily sensitive to and used to determine the relative tilt of the rotor (200) and the stator (300), whereas the inner quadrant coil is primarily sensitive to and used to determine the relative lateral / radial position (e.g., eccentricity) of the rotor (200) and the stator (300). As is understood, this is not necessarily required, for example, the outer quadrant coil may be configured to be primarily sensitive to and used to determine the relative lateral / radial position (e.g., eccentricity) of the rotor (200) and the stator (300), while the outer quadrant coil may be configured to be primarily sensitive to and used to determine the relative lateral / radial position (e.g., eccentricity) of the rotor (200) and the stator (300). Additionally, in another embodiment, one or both of the outer quadrant coil and the inner quadrant coil may be sensitive to both the relative tilt and lateral / radial position (e.g., eccentricity) of the rotor (200) and the stator (300). Although it is still possible to extract measurements of the relative tilt and lateral / radial position (e.g., eccentricity) from these quadrant coils, this requires more complex electronics and / or processing, and therefore it may be desirable to have one of the inner quadrant coil and the outer quadrant coil primarily sensitive to the relative tilt of the rotor and the stator, and the other primarily sensitive to the relative lateral / radial position (e.g., eccentricity) of the rotor and the stator. In another embodiment, only one set of quadrant coils is provided. In this case, the set of quadrant coils may be configured to be primarily sensitive to and used to determine the relative lateral / radial position (e.g., eccentricity) of the rotor (200) and the stator (300), or may be configured to be primarily sensitive to and used to determine the relative tilt of the rotor (200) and the stator (300).In an optional embodiment, the set of quadrant coils may be configured to be sensitive to both relative tilt and lateral / radial position (e.g., eccentricity). Although it may not be possible to extract measurements of the relative tilt and lateral / radial position (e.g., eccentricity) of the stator and rotor from only the set of quadrant coils sensitive to both relative tilt and lateral / radial position (e.g., eccentricity), the output of such a set of quadrant coils may still be useful for determining the presence of relative tilt and / or lateral / radial position (e.g., eccentricity). For example, the output may be used to indicate / determine whether the rotor and stator are relative tilted and / or eccentrically positioned during installation / setup and / or operation, which may serve as a warning that the rotor and stator are not properly set up / configured (e.g., may function as a go / no-go signal).

[0130] In the above-described embodiment, the magnetic field detected by the quadrant coil is generated by the same excitation coil that generates the magnetic field detected by the receiving coils (304, 306, 308) of the stator. However, this is not necessarily the case. For example, FIG. 15a and FIG. 15b illustrate an alternative embodiment in which the stator includes a first excitation coil (330′) and a second excitation coil (330″) that are radially spaced apart from each other. In these embodiments, the first excitation coil (330′) is operated by the scale track (204, 206, 208) of the rotor and generates the magnetic field detected by the receiving coils (304, 306, 308) of the stator. The second excitation coil (330″) generates a magnetic field that is detected by the quadrant coils (310, 312, 314, 316, 320, 322, 324, 326) and determines the relative tilt and / or lateral / radial position (e.g., eccentricity) of the rotor (200) and the stator (300). As is understood, in this embodiment, the stator (200) includes one or more conductive features configured to manipulate the magnetic field generated by the second excitation coil (330″) in the region of the quadrant coils, so that the output of the quadrant coils varies according to the relative tilt and / or lateral position (e.g., eccentricity) of the stator (300) and the rotor (200).

[0131] In the above-described embodiments, the quadrant coil was described in relation to detecting / determining the relative tilt and / or lateral / radial position (eccentricity) of the stator and / or rotor. As is understood, the output of the quadrant coil may also be used to detect / determine the surface flatness and / or non-circularity of the rotor. Also understood, in other embodiments, in addition to or alternative to the above function, the device may be configured to determine a measure of the axial separation between the stator member and the rotor member (or at least a signal indicating such separation) through, for example, i) any one or more quadrant coils; and ii) the signal strength / amplitude of any one or more receiving coils.

[0132] As is understood, the aforementioned specific radial positions of the scale tracks (204, 206, 208) and the corresponding excitation coil (330) and scale receiving coil (304, 306, 308) are not mandatory and may be arranged to have different radial positions / combinations. For example, the rotor (200) may be configured such that the first scale track (204) is radially positioned between the second scale track (206) and the third scale track (208) (thus, the stator (300) may be configured such that the corresponding first scale receiving coil (304) is radially positioned between the second scale receiving coil (306) and the third scale receiving coil (308)).

[0133] In the above-described embodiment, a plurality of scale tracks and a plurality of receiving coils are provided. However, as is understood, this is not strictly necessary, and, for example, only a single scale track and a corresponding single receiving coil may be provided.

[0134] As described above, the first outer quadrant coil (310), the second outer quadrant coil (312), the third outer quadrant coil (314), and the fourth outer quadrant coil (316), and the first inner quadrant coil (320), the second inner quadrant coil (322), the third inner quadrant coil (324), and the fourth inner quadrant coil (326) are optional sensors used to detect or provide a measure of the relative lateral / radial position (e.g., eccentricity) and / or relative tilt of the rotor (200) and the stator (300). FIG. 17 illustrates another embodiment of the present invention (wherein the same parts are given the same reference numerals as in the other embodiment described above). As illustrated in FIG. 17a, in this embodiment, the optional outer conductive loop (210) and inner conductive loop (212) are provided on the stator (300) instead of on the rotor (200) in this case. Also, in this embodiment, the stator (300) does not include any sensor used to detect or provide a measure of the relative lateral / radial position (e.g., eccentricity) and / or relative tilt of the rotor (200) and the stator (300). As illustrated, in this embodiment, the radial widths of the second scale track (206) and the third scale track (208) are equal to each other (and are about half the radial width of the first scale track (204)), and similarly, the radial widths of the second scale receiving coil (306) and the third scale receiving coil (308) are equal to each other (and are about half the radial width of the first scale receiving coil (304)).

[0135] As illustrated in FIG. 17c, in this embodiment, the rotor (200) may comprise a flat disc-shaped member (202) made of a single layer of glass fiber and having, for example, a thickness of about 1.6 mm (for example, this may be a printed circuit board (PCB) made of a single layer of FR-4). Scale features (204, 206, 208) are electrically conductive (in this embodiment, these are copper and are formed on the first flat member (202) by etching / milling off a copper coating on the glass fiber material of the first flat disc-shaped member (202), but may also be formed through other processes such as copper plating). In an alternative embodiment, the first flat rotor member (202) may comprise an electrically conductive material, in which case non-conductive features may be formed thereon to provide scale features.

[0136] As illustrated in FIG. 17c, in this embodiment, the stator (300) includes a first planar disk-shaped member (302), and on its front side (i.e., the side facing the rotor (200) during use), the excitation coil (330) and receiving coil (304, 306, 308) of the stator are provided. As illustrated in FIG. 17c, the excitation coil (330) includes the parallel conductor wire configuration illustrated in FIG. 16(a).

[0137] The rear surface of the first planar disk-shaped member (302) is attached (via adhesive) to another / second planar disk-shaped member (303), and an electronic component (320) for driving an excitation coil (330) and processing a signal received from a receiving coil (304, 306, 308) is provided on the back surface of said member (303) (i.e., the side facing away from the rotor (200) when in use). In the embodiment of FIG. 17, the first and second planar stator members (302, 303) are made of a plurality of layers (six layers in this embodiment) of glass fiber. In an alternative embodiment, the stator (300) comprises only a single planar member (302 / 303), and, for example, the coil and the electronic component are provided on opposite sides thereof.

[0138] As illustrated in FIG. 17c, the receiving coils (304, 306, 308) may occupy two or more glass fiber / PCB layers. FIG. 17c shows the outer conductive loop (210) and the inner conductive loop (212) provided on the same layer as the excitation coil (330) and the receiving coils (304, 306, 308), but this is not necessarily required.

[0139] As is understood, the rotor (200) and / or stator (300) may be made of a material other than that described (e.g., ceramic).

[0140] As is understood, the rotor (200) and stator (300) of the other embodiments described above may include a structure similar to that of FIG. 17 (e.g., may include one or more glass fiber / PCB layers).

[0141] Also, as is understood, the rotor (200) and / or stator (300) of the above embodiments do not necessarily have to have a circular or disc-shaped configuration, nor do they necessarily have to have a hole extending through it, and they do not even necessarily have to be flat. However, the front surface where the scale feature (204, 206, 208) and the excitation coil (330) and the receiving coil (304, 306, 308) are provided is most preferably flat.

Claims

Claim 1 An inductive rotary encoder comprising a first member and a second member rotatable relative to a rotation axis, wherein the first member comprises at least a first scale track and a second scale track extending around a scale track axis, and the second member, ○ An excitation coil through which alternating current passes to generate an alternating magnetic field operated by at least the first and second scale tracks above; and ○ An inductive rotary encoder comprising at least a first receiving coil for detecting a magnetic field manipulated by a first scale track and a second receiving coil for detecting a magnetic field manipulated by a second scale track, thereby allowing the relative rotational positions of the first and second members around the rotation axis to be measured, ● the excitation coil and the receiving coil extend around the coil axis at different radii, ● the excitation coil is a unidirectional excitation coil, and thus configured such that when in use, the current flowing through the excitation coil flows only in one direction around the coil axis at any given point in time. Claim 2 An inductive rotary encoder according to claim 1, wherein the excitation coil extends circularly around the coil axis with a constant single radius. Claim 3 An inductive rotary encoder according to claim 1 or 2, wherein the excitation coil is a single-winding coil and / or the first receiving coil is a single-winding coil and / or the second receiving coil is a single-winding coil. Claim 4 An inductive rotary encoder according to any one of claims 1 to 3, wherein the first and second receiving coils are located on both radial sides of the excitation coil, and the first and second receiving coils are radially spaced apart from each other by the excitation coil. Claim 5 An inductive rotary encoder according to any one of claims 1 to 3, wherein the first and second receiving coils are located on the same radial side of the excitation coil, and the first receiving coil is radially spaced from the excitation coil by the second receiving coil. Claim 6 An inductive rotary encoder according to any one of claims 1 to 5, wherein ● the first member comprises a third scale track extending annularly around the scale track axis, and ● the second member comprises a third receiving coil extending around the coil axis at a radius different from the radius of the first and second receiving coils and the radius of the excitation coil, and for detecting a magnetic field operated by the third scale track, thereby enabling the relative rotational position of the first member and the second member around the rotation axis from the first, second, and third receiving coils to be measured. Claim 7 An inductive rotary encoder according to claims 5 and 6, wherein the third receiving coil is located on the radially opposite side of the excitation coil with respect to the first and second receiving coils, and the third receiving coil is radially spaced from the first and second receiving coils by the excitation coil. Claim 8 An inductive rotary encoder according to any one of claims 1 to 7, configured such that alternating current flows through the excitation coil at a predetermined operating frequency, and the excitation coil includes a capacitor configured such that the excitation coil operates as a resonant circuit. Claim 9 In claim 7, the inductive rotary encoder wherein the capacitor is positioned in alignment with the circular extension of the excitation coil. Claim 10 An inductive rotary encoder according to any one of claims 1 to 9, comprising a magnetic flux enhancer, wherein a current flow is generated by the magnetic field of the excitation coil within the magnetic flux enhancer, and the magnetic flux enhancer itself generates a magnetic field that acts to increase the magnetic flux of the magnetic field detected by the one or more receiving coils in a region of one or more of the receiving coils. Claim 11 In claim 10, the magnetic flux enhancer comprises: at least one conductor located radially outside the scale track of the first member and the receiving coil and excitation coil of the second member, - said at least one conductor is hereinafter referred to as at least one "outer" conductor -; and / or at least one conductor located radially inside the scale track of the first member and the receiving coil and excitation coil of the second member, - said at least one conductor is hereinafter referred to as at least one "inner" conductor - an inductive rotary encoder. Claim 12 An inductive rotary encoder according to any one of claims 1 to 11, wherein the first and second scale tracks are configured to manipulate the amplitude of the magnetic field generated by the excitation coil according to the relative positions of the first member and the second member around the rotation axis. Claim 13 As an inductive encoder, it comprises a first member and a second member movable relatively along a measurement direction (e.g., around a rotation axis), ● the first member has at least a first scale track extending along the measurement direction (e.g., extending annularly around a scale track axis), and ● the second member is: ○ An excitation coil for generating a magnetic field operated by the above at least first scale track; and ○ The inductive encoder comprises at least a first receiving coil for detecting a magnetic field manipulated by a first scale track, thereby allowing the relative rotational position of a first and second member along the measurement direction (e.g., around the rotation axis) to be measured, and ● the inductive encoder device is configured to pass an alternating current through the excitation coil at a predetermined operating frequency, and ● the excitation coil comprises a capacitor arranged so that the excitation coil operates as a resonant circuit. Claim 14 In paragraph 13, an inductive encoder wherein the excitation coil extends substantially in a circular shape around the axis of the excitation coil, and the capacitor is positioned in alignment with the circular extension of the excitation coil. Claim 15 An inductive encoder according to claim 14, wherein the excitation coil is a single-winding coil and / or the first receiving coil is a single-winding coil and / or the second receiving coil is a single-winding coil. Claim 16 An inductive encoder comprising a first member and a second member movable relatively along a measurement direction, ● the first member having at least first and second scale tracks, and ● the second member, ○ Excitation coil for generating a magnetic field operated by at least the first and second scale tracks; and ○ At least, an inductive encoder comprising a first receiving coil for detecting a magnetic field manipulated by a first scale track and a second receiving coil for detecting a magnetic field manipulated by a second scale track, wherein the relative rotational positions of the first and second members around the rotation axis can be measured, and the second receiving coil is separated from the excitation coil by the first receiving coil.

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