Rotary encoder device and method of mounting a rotary encoder device on a machine

Abstract

A rotary encoder device comprising a stator and a rotor rotatable relative to each other about a rotation axis, one of the stator and the rotor comprising a scale and the other of the stator and the rotor comprising a readhead for reading the scale, whereby the relative rotational position of the stator and the rotor about said axis can be determined, wherein the stator and the rotor are constructed with cooperating radial alignment features configured such that, in a first relative axial position of the stator and the rotor, the cooperating radial alignment features are engageable so as to thereby constrain the stator and the rotor in a predetermined relative radial position, and in a second relative axial position of the stator and the rotor, the cooperating radial alignment features are not engageable, wherein the readhead can read the scale in said second relative axial position.

Description

[0001] The present invention relates to a rotary encoder device and a method for mounting the rotary encoder device on a machine.

[0002] A rotary encoder device includes a stator and a rotor that are rotatable relative to each other about a rotational axis. One of the stator and rotor includes a scale, and the other includes a read head for reading the scale, thereby determining the relative rotational position of the stator and rotor about the axis. Typically, the stator includes the read head, and the rotor includes the scale, but this is not always the case. In use, the rotor is mounted to a relatively rotatable part of a machine (e.g., a shaft), and the stator is mounted to a relatively fixed part of the machine, such that the axis of rotation of the relatively rotatable part of the machine and the axis of rotation of the rotary encoder device are substantially coaxial. In this way, the encoder can be used to measure the rotation of the relatively rotatable part of the machine.

[0003] During the installation of the rotary encoder device on the machine, it may be important to ensure that the stator and rotor are mounted to the machine in a preferred radial arrangement.

[0004] US 9664537 describes an encoder assembly and a separate encoder alignment structure that slides onto the stator and rotor portions of the encoder to engage them and constrain them in a predetermined relative configuration to align the indexing marks with the indexing sensor.

[0005] The present invention relates to an improved rotary encoder device and an improved method for mounting the rotary encoder device on a machine.

[0006] In particular, the present invention relates to a rotary encoder device comprising a stator and a rotor rotatable relative to each other about a rotational axis, one of the stator and the rotor including a scale and the other including a read head for reading the scale, thereby determining the relative rotational position of the stator and the rotor about the axis. The stator and the rotor are configured with cooperative radial alignment features. The cooperative radial alignment features may be configured such that, in a first relative axial position of the stator and the rotor, the cooperative radial alignment features are engageable, thereby constraining the relative radial position of the stator and the rotor to a predetermined radial position. The cooperative radial alignment features may also be configured such that, when the stator and the rotor are in a second relative axial position, they are not engageable.

[0007] According to a first aspect of the invention, a rotary encoder device is provided, comprising a stator and a rotor rotatable relative to each other about a rotation axis, one of the stator and the rotor including a scale and the other including a read head for reading the scale, thereby determining the relative rotational position of the stator and the rotor about the axis, wherein the stator and the rotor are configured with cooperating radial alignment features configured such that: in a first relative axial position of the stator and the rotor, the cooperating radial alignment features are engageable so as to thereby constrain the stator and the rotor to a predetermined relative radial position, and in a second relative axial position of the stator and the rotor, the cooperating radial alignment features are not engageable, wherein the read head can read the scale in the second relative axial position.

[0008] Therefore, the user can set the stator and rotor (and thus the scale and read head disposed thereon) to a predetermined radial position by arranging the stator and rotor such that the cooperating radial alignment features engage with each other in the first relative axial position (“setting relative axial position”). This can be useful during the installation of the rotary encoder device, whether it is the first time the rotary encoder device is installed on any machine or at any subsequent time during the reinstallation of the rotary encoder device (e.g., during installation on the same machine after maintenance, or during installation on different machines). The present invention means that no separate alignment component is required to achieve relative radial alignment, thereby simplifying manufacturing and installation, reducing costs, and / or eliminating the need for the user to maintain and find such a separate alignment component for subsequent alignment (e.g., for reinstallation of the encoder device). Once radially aligned, the user can arrange the stator and rotor in a second relative axial position (“operating relative axial position”), in which the cooperating radial alignment features are not engageable. Therefore, in the second (“operating”) relative axial position, the rotary encoder device can be used / operated without the cooperating radial alignment features engaging or becoming engaged due to the relative rotation of the stator and rotor. Therefore, in the second relative axial position, the stator and rotor can rotate freely and completely about the axis of rotation without the need for cooperative radial alignment features to engage or to engage due to the relative rotation of the stator and rotor.

[0009] Preferably, the rotary encoder device is configured such that, in a first (“set”) relative axial position of the stator and rotor, the cooperating radial alignment features are engageable to form an interference fit. In other words, when in their engaged state in the first relative axial position, preferably, the cooperating radial alignment features are configured to form an interference fit. Therefore, preferably, the stator and rotor can be held in the engaged state in the first relative axial position by the frictional force between the cooperating radial alignment features. Preferably, the rotary encoder device is configured such that the interference fit / frictional force between the cooperating radial alignment features is sufficient to support the weight of the rotor or stator, whichever is heavier, so that the cooperating radial alignment features (and therefore the rotor and stator) do not automatically disengage under their own weight. Therefore, in other words, preferably, the rotary encoder device is configured such that, when in the first relative axial position, the frictional force generated by the interference fit between the cooperating radial alignment features is sufficient to support the weight of the rotor or stator, whichever is heavier, so that the cooperating radial alignment features, and therefore the rotor and stator, do not automatically disengage under their own weight.

[0010] In a preferred embodiment, the rotary encoder device is preferably configured (e.g., the cooperating radial alignment features are configured such that the cooperating radial alignment features can be manually engaged. In a preferred embodiment, the rotary encoder device is preferably configured (e.g., the cooperating radial alignment features are configured such that the relative displacement force applied to the stator and rotor to form an interference fit between the cooperating radial alignment features is no greater than: 150 Newtons (N) (in the case of linear engagement); and / or 20 Newton-meters (Nm) (in the case of rotary engagement). Similarly, preferably, the relative displacement force applied to the stator and rotor to break / disengage the interference / friction fit between the cooperating radial alignment features is no greater than: 150 Newtons (N) (in the case of linear engagement); and / or 20 Newton-meters (Nm) (in the case of rotary engagement). In a particularly preferred embodiment, the rotary encoder device is preferably configured (e.g., the cooperating radial alignment features are configured such that the interference fit can be formed by applying a relative axial displacement force of no more than 150 N on the stator and rotor (e.g., in a first axial direction). Similarly, in a particularly preferred embodiment, the rotary encoder device is configured (e.g., the cooperating radial alignment features are configured) such that the interference / friction fit can be broken / disengaged by applying a relative axial displacement force of no more than 150 N on the stator and rotor (e.g., in a first axial direction, or in a second axial direction opposite to the first axial direction).

[0011] Preferably, the cooperative radial alignment feature of the rotor and stator is configured to provide at least one radial reference device (or feature) defining a reference (relative) radial position of the stator and rotor when the stator and rotor are in a first relative axial position, and at least one resilient radial compliant biasing device (or feature) biasing the rotor and stator into the radial reference device / feature / position. The at least one radial reference device / feature (e.g., a hard stop) may be at least positioned in the first position about the axis of rotation, and the at least one resilient radial compliant biasing device / feature (e.g., a flexure / spring) may be at least positioned in a second position about the axis of rotation different from the first position. For example, the at least one resilient radial compliant biasing device / feature may be configured such that when the stator and rotor are in the second relative axial position, the resilient radial compliant biasing device / feature adopts a default / relaxed radial configuration / state, and when the stator and rotor are in the first relative axial position, the resilient radial compliant biasing device / feature biases / deforms from its default / relaxed radial configuration / state, and in response biases the rotor and stator into the radial reference. As described in more detail below, a radial reference device / feature may be provided by one or more (radial rigid) contact points between the rotor and the stator. Similarly, a resilient radial compliant bias device / feature may be provided by one or more (resilient radial compliant) contact points between the rotor and the stator.

[0012] A rotary encoder device can be configured such that, when in its engaged state, cooperative radial alignment features provide a set (e.g., a first set) of contact points (between the stator and rotor). This set (e.g., the first set) of contact points may include contact points between the stator and rotor at at least three distinct / discrete locations, preferably around the axis of rotation, for example, at least two contact points. Preferably, at least two of these contact points are configured to be radially rigid, thereby providing a reference (relative) radial position for the stator and rotor (e.g., a hard stop that provides this reference (relative) radial position). Preferably, at least one of these contact points is configured to be resiliently radially compliant (and configured to bias / force the rotor and stator into the at least two radially rigid contact points when in their engaged state). For example, at least one of these contact points (i.e., one of the resiliently radially compliant contact points) may be configured to be part of / provided by or disposed on a radially deformable member. For example, at least one of the contact points may be configured to be part of / set by or disposed on the flexure.

[0013] A particularly preferred configuration is that at least one of the contact points is configured to be resiliently radially compliant, and at least two of the contact points are configured to be radially rigid (e.g., part of / provided by or disposed on a radially rigid member). A particularly preferred configuration is that the group (e.g., the first group) of contact points comprises only two rigid contact points (at different / discrete locations around the axis of rotation) and at least one (and preferably only one) resiliently radially compliant contact point, which is configured to bias / force the rotor and stator into the radially rigid contact point when they are in their engaged state. Thus, at least one (and preferably only one) of the contact points is configured to be radially deflected / deformed by the interaction of the stator and rotor in a first relative axial position, and in response to this, provides a radial reaction force that biases / forces one or more radially rigid contact points of the stator and rotor to engage in the first relative axial position. In contrast, the radially rigid contact points are not deflected / deformed by the interaction of the stator and rotor in the first relative axial position.

[0014] Preferably, the rotary encoder device is configured such that all contact points in the group (e.g., the first group) are located on the same axial side of the scale. Preferably, the rotary encoder device is configured such that all contact points in the group (e.g., the first group) are located in a plane extending perpendicular to the axis of rotation.

[0015] The rotary encoder device can be configured such that, when in its engaged state, cooperative radial alignment features provide a second set of contact points in addition to the first set (the first set) of contact points. The first and second sets of contact points can be located at different axial positions. For example, it is preferable that all contact points in the second set are located on the same axial side of the scale, and on a different axial side of the scale than all contact points in the first set. In other words, it is preferable that all contact points in the first set are located on a first axial side of the scale, and all contact points in the second set are located on a second axial side of the scale (i.e., on the side of the scale opposite to the first axial side).

[0016] Preferably, the contact point between the stator and rotor in this group (e.g., the first group) of contact points is located in a first plane extending perpendicular to the axis of rotation. Preferably, the contact point between the stator and rotor in the second group of contact points is located in a second plane extending perpendicular to the axis of rotation. Preferably, the first plane and the second plane are located at different axial positions (and according to the previous paragraph, the first plane and the second plane are preferably located on different axial sides of the scale, but it should be noted that they do not necessarily have to be located on different axial sides of the scale).

[0017] According to the first set of contact points, the second set of contact points may include contact points between the stator and rotor at at least three different / discrete locations, preferably around the axis of rotation, for example, at least two contact points. Preferably, at least two of the contact points are configured to be radially rigid. Preferably, at least one of the contact points is configured to be resiliently radially compliant (and configured to bias / force the rotor and stator into the at least two radially rigid contact points when they are in their engaged state). A particularly preferred configuration is that at least one of the contact points is configured to be resiliently radially compliant, and at least two of the contact points are configured to be radially rigid. A particularly preferred configuration is that the second set of contact points includes only two rigid contact points (at different / discrete locations around the axis of rotation) and at least one (and preferably only one) resiliently radially compliant contact point configured to bias / force the rotor and stator into the radially rigid contact point when they are in their engaged state. Preferably, the rotary encoder device is configured such that all contact points in the second group are located on the same axial side of the scale, and for example, in a plane extending perpendicular to the axis of rotation.

[0018] As will be understood, the cooperating radial alignment features may include one or more radial alignment features on the stator and one or more radial alignment features on the rotor, these radial alignment features being configured, for example, to provide the set (or sets) of contact points at a first relative axial position. The radial alignment features on one of the stator and rotor may include a continuous annular feature (i.e., a feature that extends continuously and completely around the axis of rotation), and the radial alignment features on the other of the stator and rotor may include discrete features at at least two, preferably at least three, different locations around the axis of rotation. According to a preferred embodiment of the invention, the effective diameter provided by the cooperating radial alignment features on the stator and rotor allows them to form an interference fit at the first relative axial position.

[0019] One or more of the radial alignment features of the stator may be disposed on a radial alignment member, which is formed separately from and attached to the stator body, for example. Multiple radial alignment features may be disposed on the radial alignment member. According to a preferred embodiment of the invention, the radial alignment member may include a resilient radially compliant (e.g., spring / flexure) portion on which at least one of the radial alignment features is disposed. Therefore, according to a preferred embodiment of the invention, the radial alignment member may be configured to provide at least one resilient radially compliant contact point and at least one radially rigid contact point. The radial alignment member may be a flat (e.g., plate-like) member. Providing multiple radial alignment features on a single radial alignment member may be preferable to providing separate radial alignment members attached to the stator body, as it helps reduce costs and improves ease of manufacture and assembly. In an advantageous embodiment of the invention, the radially rigid contact point is formed on a first portion of the stator (e.g., as an integral part of the body), and at least one resilient radially compliant contact point is provided by a radial alignment member (e.g., spring / flexure) attached to the first portion. Therefore, the radial alignment member can be radially elastically deformable, and the first part is radially rigid.

[0020] In a preferred embodiment, the cooperating radial alignment features can be engaged and disengaged solely by relative axial displacement / movement between the stator and rotor at a first relative axial position and a second relative axial position. In alternative embodiments, additional displacement / movement, such as relative rotation of the stator and rotor, may be required to engage and / or disengage the cooperating radial alignment features. However, it has been found that requiring only relative axial displacement / movement to engage and disengage the cooperating radial alignment features may be preferred and advantageous (e.g., for efficiency reasons, and for example, for ease of use and manufacture).

[0021] The rotary encoder device can be a closed rotary encoder device (also known as a "sealed" rotary encoder device). A closed ("sealed") rotary encoder device may include an integral protective housing, within which at least the rotor's scale and the stator's read head are located. One or more seals may be provided between the rotor and the stator. The integral protective housing and the seals together protect the scale and read head from external contamination. As will be understood, the invention is not limited to these closed / sealed rotary encoder devices and can also be used with unclosed / unsealed encoder devices (referred to as "open" encoders). The stator's radial alignment features may be formed as an integral part of the integral protective housing, or may be formed separately and attached to the integral protective housing. Similarly, the rotor's radial alignment features (e.g., the aforementioned radial alignment members) may be formed as an integral part of the rotor, or may be formed separately and attached to the rotor.

[0022] It is possible that the read head cannot read the scale when the stator and rotor are in the first relative axial position. As will be understood, the read head's ability to read the scale when the stator and rotor are in the first relative axial position may not be important / necessary, as the encoder device is only configured when the stator and rotor are in this configuration. However, it is possible that the read head can read the scale in the first relative axial position of the stator and rotor. It is also possible that the read head can read the scale in the first relative axial position of the stator and rotor, but when the stator and rotor are in their second relative axial position, the read head and scale have a preferred / superior (e.g., optimal) reading configuration / capability. Again, this is not necessary, and it is possible that the read head can read the scale equally well in both the first and second relative axial positions of the stator and rotor.

[0023] In a preferred embodiment, the rotary encoder device is configured such that no integral position-restraining bearing exists between the stator and rotor when they are in their second relative axial positions. In this case, a device external to the rotor and stator is required to guide the relative rotation of the rotor and stator in their second relative axial positions. Such a device external to the rotor and stator can be the machine on which the rotary encoder device is mounted. For example, such a device external to the rotor and stator may include a static portion (on which the stator is mounted) and a rotatable machine portion (e.g., a shaft) (on which the rotor is mounted). As will be understood, in embodiments where rotary seals are disposed between the rotor and stator, these rotary seals should not be considered position-restraining bearings. In fact, these rotary seals are not configured to constrain the position between them, but rather to allow for both axial and radial positional variations and still function as seals.

[0024] According to a second aspect of the invention, an apparatus is provided comprising a machine having a static portion and a rotatable shaft, and a rotary encoder device according to any of the above embodiments / aspects, wherein a stator is mounted (e.g., fixed / fastened) to the static portion of the machine, and a rotor is mounted (e.g., fixed / fastened) to the rotatable portion of the machine (e.g., a shaft). The stator may be rigidly mounted (e.g., fixed / fastened) to the static portion of the machine, and the rotor may be rigidly mounted (e.g., fixed / fastened) to the rotatable portion of the machine, such that the relative rotation of the rotor and stator in their second relative axial positions is guided only by the static portion and the rotatable portion of the machine.

[0025] According to a third aspect of the invention, a method is provided for mounting a rotary encoder device according to any of the above embodiments / aspects to a machine having a static portion and a rotatable portion (e.g., a shaft), the method comprising, in any suitable order: configuring the rotary encoder device such that the rotary encoder device is located on the machine, such that the rotor of the rotary encoder device is arranged on the rotatable portion of the machine, and such that the rotor and stator of the rotary encoder device are arranged in their first relative axial positions, such that cooperating radial alignment features of the rotor and stator engage, such that the radial position of the stator is determined by the cooperating radial alignment features; securing / fastening the stator to the static portion of the machine at the radial position determined by the cooperating radial alignment features (e.g., via one or more fastening devices / components, such as clamps, threaded fasteners, adhesives, etc.); and disengaging the cooperating radial alignment features of the rotor and stator, and arranging the rotor and stator in their second relative axial positions such that the rotor and stator are free to rotate relative to each other.

[0026] The disengagement step can be performed before, after, or during the step of securing the stator to the static part of the machine. However, to help ensure that the stator does not move relative to the rotor during the step of securing / fastening the stator to the static part of the machine, it is preferable that the disengagement step does not occur beforehand (and, for example, occurs afterward).

[0027] The method may additionally include securing / fastening the rotor to a rotatable part of the machine (e.g., via one or more fastening devices / components, such as clamps, threaded fasteners, adhesives, etc.). This can be performed before, after, or during the step of securing the stator to a static part of the machine. In a preferred embodiment, the step of securing the rotor to a rotatable part of the machine is performed simultaneously with the step of disengaging the cooperating radial alignment features of the rotor and stator. That is, for example, securing the rotor to a rotatable part of the machine can also be used to disengage the cooperating radial alignment features of the rotor and stator.

[0028] Preferably, the rotor is radially fitted onto the rotatable part of the machine, such that the radial position of the rotor relative to the rotatable part of the machine is constrained to a predetermined radial position (i.e., even before the rotor is fixed / fastened to the rotatable part of the machine).

[0029] Embodiments of the invention will now be described by way of example only with reference to the following accompanying drawings, in which:

[0030] Figure 1 This is an isometric view of an example rotary encoder device according to the present invention;

[0031] Figure 2 yes Figure 1 An exploded view of the rotary encoder device shown;

[0032] Figure 3(a) is Figure 1 and Figure 2 A side elevation view of the rotor of the rotary encoder device;

[0033] Figure 3(b) is a cross-sectional view of the rotor taken along line CC in Figure 3(a);

[0034] Figure 4 yes Figure 1 and Figure 2 An isometric view of the radial alignment plate of the rotary encoder device;

[0035] Figure 5 yes Figure 4 An isometric view of a radial alignment plate, which is mounted to a mounting plate via a retaining plate. Figure 1 and Figure 2 The stator of the rotary encoder device;

[0036] Figure 6(a) is Figure 1 and Figure 2 A cross-sectional view of the rotary encoder device taken at the plane containing the first radial alignment plate of the stator;

[0037] Figure 6(b) is a cross-sectional view taken along line BB of Figure 6(a), wherein the right-hand side of Figure 6(b) shows the relative configuration of the stator and rotor in the first (“set”) relative axial position of the cooperating radial alignment feature engagement, and the left-hand side of Figure 6(b) shows the relative configuration of the stator and rotor in the second (“operation”) relative axial position of the cooperating radial alignment feature disengagement.

[0038] Figure 6(c) is a plan view of an alternative embodiment of the radial alignment plate;

[0039] Figure 7 This is a plan view of an alternative embodiment of the radial alignment plate;

[0040] Figure 8This is a flowchart illustrating an example process for installing a rotary encoder device according to the invention into a machine;

[0041] Figures 9(a) and 9(b) show Figure 1 and Figure 2 An isometric view of the rotary encoder device and the machine on which the rotary encoder device is to be mounted, and Figure 9(c) is a cross-sectional view through the rotary encoder device mounted on the machine.

[0042] Figure 10 Alternative embodiments are described, and a plan view of the stator base plate is shown, which has three separate radial alignment features fixed thereto.

[0043] Figures 11(a), 11(b), and 11(c) relate to alternative embodiments, and Figure 11(a) shows an isometric view of the rotor according to this alternative embodiment, Figure 11(b) shows a cross-sectional view of the rotor and stator in a first (“operational”) relative axial configuration, wherein the cooperating radial alignment features are disengaged, and Figure 11(c) shows a cross-sectional view of the rotor and stator in a second (“setting”) relative axial configuration, wherein the cooperating radial alignment features are engaged; and

[0044] Figures 12(a) and 12(b) relate to another alternative embodiment, which, apart from how cooperative radial alignment features are provided, is similar to... Figure 1 The embodiments shown in Figure 6 are substantially the same, and therefore the same parts share the same reference numerals. Figure 12(a) shows an exploded view of the rotary encoder device of this embodiment, and Figure 12(b) is an isometric view of the base plate on which a set of cooperating radial alignment features are provided.

[0045] refer to Figure 1 An example rotary encoder device 100 including a stator 110 and a rotor 150 is shown. The stator 110 and rotor 150 are rotatable relative to each other about a rotation axis A. As explained in more detail below, the stator 110 and rotor 150 are axially movable relative to each other between a first (“set”) relative axial position and a second (“operation”) relative axial position. During installation, the stator 110 and rotor 150 are arranged in their first (“set”) relative axial position to engage cooperating radial alignment features, thereby arranging the stator 110 and rotor 150 in a predetermined relative radial position. During operation of the rotary encoder device, the rotary encoder device can be used to provide a measurement of the relative rotation of the static part of the machine and the rotatable shaft of the machine (i.e., the “machine shaft”). Therefore, during operation, the stator 110 can be fixed to the static part of the machine ( Figure 1 (not shown in the image), and the rotor 150 can be fixed to the machine shaft ( Figure 1(Not shown in the diagram) (wherein the rotation axis A of the rotary encoder device and the rotation axis of the machine shaft are substantially coincident). During operation, the stator and rotor will be arranged in their second (“operational”) relative axial positions, and the rotary encoder device can be used to measure the relative rotation of the machine's shaft and static parts. As described in more detail below, in the described embodiment, the rotary encoder device 100 is a “closed” (or “sealed”) rotary encoder device because its scale and read head are housed within a protective housing, but as will be understood, this is not necessarily required.

[0046] refer to Figure 2 As shown in Figure 3, the rotor 150 includes a rotor / encoder shaft 152 having a scale 156 disposed on a radially projecting portion 154 of the rotor / encoder shaft 152. For simplicity, the rotor / encoder shaft 152 will be referred to as rotor shaft 152 hereinafter. In the described embodiment, the rotor shaft 152 is hollow to accommodate the aforementioned machine shaft ( Figure 2 (Or not shown in Figure 3), but this is not necessarily the case. As depicted in Figure 3(b), in the described embodiment, the rotor bore 155 does not have a constant diameter along its axial length, but instead has two axially separated, annularly extending regions 157 with decreasing inner diameters. The diameters of the regions 157 with decreasing inner diameters are chosen such that they fit tightly against the machine shaft, thereby positioning the rotor 150 radially relative to the machine shaft. As will be understood, other configurations are also possible, including but not limited to those where the diameter of the bore 155 is constant along its axial length.

[0047] In the described embodiment, the scale is a scale commonly referred to as a "ring scale" or "edge-reading scale" because the axially extending scale feature 158 is formed on the outer cylindrical surface of the radially projecting portion 154 of the rotor shaft 152. This contrasts with a "disc scale" (where the scale includes radially extending features disposed on a flat surface of a disc-shaped member). However, as will be understood, the invention is also applicable to rotary encoder devices with disc scales. The scale 156 can be an absolute scale or an incremental scale, with or without one or more reference marks. The scale 156 can comprise a single scale track or multiple scale tracks. Suitable example scales include magnetic scales, optical scales, inductive scales, or capacitive scales. In the described embodiment, the scale is an optical scale, and particularly a reflective optical scale (although it can be a transmissive scale, which is more commonly associated with disc scales).

[0048] The rotor shaft 152 includes a first radial alignment feature 160 and a second radial alignment feature 162, which are configured to engage the radial alignment features on the stator (described in more detail below) when the rotor 150 and the stator 110 are arranged in a particular relative axial position. The radial alignment features of the rotor and the radial alignment features of the stator are referred to herein together as “cooperative radial alignment features”.

[0049] A first radial alignment feature 160 of the rotor is disposed at a first axial position along the rotor shaft 152, and a second radial alignment feature 162 of the rotor is disposed at a second axial position along the rotor shaft 152, such that they are located on opposite axial sides of scale 156. In the described embodiment, the first radial alignment feature 160 and the second radial alignment feature 162 of the rotor 150 include a radially projecting ring having a diameter D' greater than the diameter D of the main portion of the rotor shaft 152. In the described embodiment, the radially projecting ring is a continuous / unbroken ring extending around the entire circumference of the rotor shaft 152. Although this is not necessarily the case (e.g., the first and second radial alignment features may include one or more radially projecting features, such as arcs, located at discrete positions around the circumference of the rotor shaft 152), a continuous ring can be advantageous in this embodiment because, as described in more detail below, the corresponding radial alignment features on the stator are disposed at discrete circumferential positions. Therefore, providing a radial alignment feature that extends continuously around the circumference for at least one of the rotor and stator avoids the need for the user to arrange the rotor and stator in a specific rotational orientation so that the radial alignment features on the rotor and stator (described in more detail below) are aligned and engageable.

[0050] refer to Figure 1 and Figure 2 The stator 110 includes a base plate 112 and a cover 114, which are assembled via threaded fasteners 115 (see [link to stator]). Figure 2The rotor and rotor 150 are held together. Flexible rotary (e.g., radial lip) seals 116 and 118 are provided in the upper and lower portions 116 and 118, which extend across the annular gap between the stator 110 and rotor 150 during assembly to seal the interior of the stator 110 from external contaminants. The stator 110 also includes a first read head 120 and a second read head 122 mounted to a base plate 112. When the rotary encoder assembly 100 is assembled, the first read head 120 and the second read head 122 are configured to read the scale 156 at positions 180° apart from each other about the axis of rotation A. In use, the read heads 120 and 122 will be connected to a controller, etc., from which signals can be used to determine the rotational position (and / or derivatives thereof) of the rotor 150 and stator 110 (and thus the rotational position of the relatively rotating portion of the machine on which the rotary encoder assembly is mounted, and / or derivatives thereof). For clarity, wiring for such a connection is omitted in the figures. Optionally, this connection can be wireless.

[0051] As will be understood, although two read heads 120, 122 are provided in this embodiment, alternative embodiments may include only a single read head, or more than two read heads (or include read heads that extend completely around the axis of rotation, such as in the case of an inductive encoder).

[0052] The stator 110 also includes radial alignment features disposed at a first axial position and a second axial position. Specifically, the stator includes a first radial alignment plate 130 and a second radial alignment plate 132 providing the radial alignment features. During assembly, the first radial alignment plate 130 is arranged on the same axial side of the scale 156 as the first radial alignment feature 160 on the rotor 150, and the second radial alignment plate 132 is arranged on the same axial side of the scale 156 as the second radial alignment feature 162 on the rotor 150. The axial spacing between the first radial alignment plate 130 and the second radial alignment plate 132 is the same as the axial spacing between the first radial alignment feature 160 and the second radial alignment feature 162 on the rotor 150.

[0053] like Figure 4 As shown, the first radial alignment plate 130 and the second radial alignment plate 132 include an axially extending hole 134 passing through the center of the plate, through which the rotor shaft 152 can be received. The hole 134 has a generally circular shape, but has three regions 136, 138, and 140 with decreasing diameters, which will be explained in more detail below. These regions form the radial alignment features of the stator (also referred to herein as 136, 138, and 140). Fastener holes 135 are provided through which fasteners (e.g., threaded fasteners 137) pass to rigidly fasten the plates to the stator 110.

[0054] The first radial alignment feature 136 of the stator's radial alignment features is disposed on the spring member 142, which is freely radially outwardly displaced and provides resistance to such radial displacement. Therefore, the first radial alignment feature 136 is "elastically radially compliant". In contrast, the second radial alignment features 138 and the third radial alignment features 140 of the stator's radial alignment features are rigidly fixed in place. The effective diameter of the stator's radial alignment features 136, 138, and 140 (when the spring member 142 is in a relaxed, undeflected state) is greater than the diameter D of the main portion of the rotor shaft 152, but slightly smaller than the diameter D' of the radially projecting rings 160 and 162 of the rotor 150. Specifically, the second radial alignment feature 138 and the third radial alignment feature 140 (radial fixing feature) in the radial alignment features of the stator nominally have the same diameter D' as the radially projecting rings 160, 162 of the rotor 150, and when the spring member 142 is in a relaxed, undeflected state, the first radial alignment feature 136 is positioned in a radially offset position to provide a diameter smaller than the diameter D', such that when the radially projecting rings 160, 162 of the rotor 150 are positioned in a straight line with the axial direction of the radial alignment features 136, 138, 140 of the stator, the first radial alignment feature 136 deflects away from its relaxed, undeflected position to provide the aforementioned spring force.

[0055] like Figure 2 , Figure 5 As shown in Figure 6(b), during assembly, the first radial alignment plate 130 is sandwiched between the surface of the stator cover 114 and the first retaining plate 170, and the second radial alignment plate 132 is sandwiched between the surface of the stator base plate 112 and the second retaining plate 172.

[0056] The first retaining plate 170 and the second retaining plate 172 each have an axially extending bore with a diameter larger than the diameter D of the main portion of the rotor shaft 152 and also larger than the diameter D' of the radially projecting rings 160, 162 of the rotor 150. Therefore, the retaining plates 170, 172 do not contact the rotor 150 at all in their axially engaged or axially disengaged axial positions. During the engagement / disengagement process of the rotor 150, the radial alignment plates 130, 132 are clamped between the retaining plates and the stator surface, increasing the axial robustness of the radial alignment plates 130, 132. During the engagement / disengagement process, torsional forces are generated at the mating interface, which can cause the radial alignment features 136, 138, 140 to deform in the axial direction. This is of particular concern for the first radial alignment feature 136, which is mounted on the radial spring member 142 and is therefore not too stiff axially. The retaining plates provide axial support for these features and thus help reduce / prevent such axial deformation. As will be understood, these retaining plates 170, 172 (or equivalent axial support members) are optional, and may not be necessary at all, for example, if the radial alignment features 136, 138, 140 of the stator 110 are sufficiently rigid in the axial direction (e.g., if they are made of a thicker and / or harder material). As another alternative, axial support members (e.g., retaining plates) may be provided solely for the radial spring members.

[0057] Figure 6(a) shows a cross-sectional plan view of the rotary encoder device 100 in the plane containing the first radial alignment plate 130. Figure 6(b) shows a cross-sectional view along line BB shown in Figure 6(a), wherein the right-hand side of Figure 6(b) shows the relative configuration of the stator 110 and rotor 150 in a first (“set”) relative axial position, in which cooperating radial alignment features engage to thereby constrain the relative radial position of the stator and rotor to a predetermined radial position, and the left-hand side of Figure 6(b) shows the relative configuration of the stator 110 and rotor 150 in a second (“operation”) relative axial position, in which the cooperating radial alignment features disengage, and in which read heads 120, 122 (read head 122 is not shown in Figure 6(b)) can read scale 156. As will be understood, it is not necessary for the read heads 120, 122 to be able to read the scale 156 when the stator 110 and rotor 150 are in their first relative axial positions. In fact, in the described embodiment, the axial displacement between the first and second relative axial positions makes it so that when they are in their first relative axial positions, the scale 156 is no longer aligned with the reading windows of the read heads 120, 122, and therefore the read heads cannot “see” the scale. As will be understood, in alternative embodiments, it is possible that the read heads 120, 122 can still see the scale 156 when the stator 110 and rotor 150 are in their first relative axial positions. This could be due to, for example, the size of the reading window of the read head, the axial range of the scale, and / or the axial distance between the first and second relative axial positions, allowing the read heads to still see the scale in both the first and second relative axial positions. In another embodiment, and as described above, the scale may be a “disc scale,” wherein the scale includes radially extending features disposed on a flat surface of a disc-shaped member. Therefore, in this embodiment, the axial spacing or "running height" between the scale and the reading head will be different for the first relative axial position and the second relative axial position.

[0058] As shown on the right-hand side of Figure 6(b), the rotor 150 can be axially displaced (i.e., along the axis of rotation A) to a first relative axial position, in which the first radial alignment feature 160 and the second radial alignment feature 162 on the rotor 150 engage with the corresponding first radial alignment plate 130 and the first radial alignment features 136, 138, and 140 on the second radial alignment plate 132 (i.e., the first, second, and third sections with reduced diameters). When engaged / in the first relative axial position, the first radial alignment feature 160 of the rotor 150 and the first radial alignment features 136, 138, and 140 of the first radial alignment plate 170 of the stator 110 provide a first set of three contact points between the rotor 150 and the stator 110. Similarly, when engaged / in the first relative axial position, the second radial alignment feature 162 of the rotor 150 and the first radial alignment features 136, second radial alignment feature 138, and third radial alignment feature 140 of the second radial alignment plate 172 of the stator 110 provide a second set of three contact points between the rotor 150 and the stator 110 in the first axial position. In each of the first and second sets of three contact points, the contact points are equiangularly spaced around the axis of rotation A. Furthermore, although it is preferable for repeatability performance to have three contact points provided by each set of cooperating radial alignment features of the rotor / stator (these contact points are substantially equiangularly spaced around the axis of rotation), this is not necessary. For example, as few as two contact points, or, for example, four or more contact points, may be provided by each set of cooperating radial alignment features of the rotor / stator. For example, the radial alignment plates 130' / 132' of FIG. 6(c) are configured to provide four contact points with the rotor. Specifically, the radial alignment plates 130' / 132' of FIG6(c) provide a first radially compliant contact point 136a and a second radially compliant contact point 136b, as well as a third radially rigid contact point 138 and a fourth radially rigid contact point 140. Similarly, these contact points need not be spaced substantially equally about the axis of rotation.

[0059] Because the effective diameters of the first radial alignment features 136, the second radial alignment feature 138, and the third radial alignment feature 140 on the radial alignment plates 170 and 172 are slightly smaller than the diameters of the first radial alignment feature 160 and the second radial alignment feature 162 on the rotor 150, the first radial alignment feature 136 mounted on the radial spring member 142 will be radially displaced outward. This, in turn, will provide a resisting force due to the elasticity of the radial spring member, which will radially push the rotor 150 into the rigidly mounted second radial alignment features 138 and the third radial alignment feature 140. The rigidly mounted second radial alignment features 138 and the third radial alignment feature 140 define a fixed radial position of the rotor 150 when the radial alignment features of the rotor and stator engage in cooperative engagement. Therefore, due to the fixed nature of the rigidly mounted second radial alignment features 138 and the third radial alignment feature 140 on the stator 110, and due to the compliance of the first radial alignment feature 136, a high level of repeatability of the radial position of the rotor 150 relative to the stator 110 is ensured. Although this configuration may be preferred for repeatability reasons, it is not required, and for example, two or all three of the first radial alignment feature 136, the second radial alignment feature 138 and the third radial alignment feature 140 on the stator 110 may be mounted on the spring member. Figure 7 An example of this situation is shown in the figure, which illustrates a plan view of an example alternative radial alignment plate 130' / 132' having a first radial alignment feature 136', a second radial alignment feature 138', and a third radial alignment feature 140' disposed on a first radial spring member 142', a second radial spring member 144', and a third radial spring member 146'.

[0060] In the described embodiment, the rotary encoder device 100 is configured such that the cooperating radial alignment features can be manually engaged by a user axially pushing the rotor 150 relative to the stator 110 until the rotor 150 stops due to contact between the radially projecting portion 154 of the rotor 150 (on which a scale 156 is provided) and the first retaining plate 170 of the stator 110 (at which point the radial alignment features on the rotor and stator will engage with each other). As will be understood, such axial stops may be provided by other features of the rotor and / or stator, and / or such axial stops may not be provided at all, and may only require the user to determine when the cooperating radial alignment features engage. Ideally, the relative axial displacement force on the rotor and stator required to engage the cooperating radial alignment features does not exceed 150 N, such that typically no tools are required to engage them, but they can be engaged by hand alone.

[0061] In the described embodiment, the rotary encoder device 100 is configured such that the cooperating radial alignment features form an interference fit at a first relative axial position of the stator 110 and the rotor. Thus, in other words, in the described embodiment, the rotor 150 is held in its axially engaged position by the frictional force between the cooperating radial alignment features on the stator 110 and the rotor 150. Specifically, the rotary encoder device 100 is configured such that the frictional force between the cooperating radial alignment features on the stator 110 and the rotor 150 in their engaged state is sufficient to support the weight of either the rotor 150 or the stator 110 (whichever is heavier) so that they do not automatically disengage under their own weight. This can be advantageous because it avoids the need for additional tools (or user-applied force) to hold the cooperating radial alignment features on the stator 110 and the rotor 150 in their engaged state.

[0062] However, as will be understood, while the described self-holding and manual break-through configurations may be preferred for ease of use, such configurations are not essential. For example, in alternative embodiments, the rotary encoder device 100 may be configured such that tools may be required to engage, and / or hold, the cooperating radial alignment features on the stator 110 and rotor 150 into engagement, and / or disengage them. For example, in the alternative embodiment shown in FIG11, the cooperating radial alignment features may include mating tapered (e.g., truncated conical) surfaces 131, 133 on the rotor 150 and stator 110 that engage (i.e., contact) with each other in an axial position to define a predetermined radial position of the stator and rotor, but do not provide any frictional resistance to their axial disengagement in the disengagement direction. In this scenario, the rotor 150 may (e.g., depending on the mounting orientation) need to be held in its axially engaged position, while the rotor 150 and / or stator 110 are secured to the machine by something other than the cooperating radial alignment features themselves. For example, the user can manually hold the radial alignment features into engagement, and / or a clamp or other holding device / apparatus (e.g., which may utilize magnets) can be used to keep the radial alignment features pulled into engagement.

[0063] The advantage of the cooperative radial alignment features of the rotary encoder device 100 is that they can be used to assist in the installation (initial installation or subsequent reinstallation) of the rotary encoder device 100 onto a machine according to predetermined standards set by the manufacturer. For example, during the installation of the rotary encoder device 100, it may be important to ensure that the stator 110 and rotor 150 have predetermined radial positions in order to achieve the desired performance level of the rotary encoder device 100. When engaged, the cooperative radial alignment features of the rotary encoder device 100 constrain the relative radial positions of the rotor 150 and stator 110 to predetermined radial positions, the repeatability of which is defined by the configuration of the cooperative radial alignment features and can therefore be determined by the manufacturer of the rotary encoder device 100.

[0064] Therefore, now refer to Figure 8 As shown in Figure 9, the self-radial alignment capability of the rotary encoder device 100 can be utilized during installation on machine 900 (this can be the first installation of the rotary encoder device on machine 900, or for reinstallation on the same machine or another machine). Figure 8 The first stage 802 of the process of mounting the rotary encoder device on machine 900, as shown, involves the following actions: engaging the cooperating radial alignment features of the rotor and stator (action 802a) (as explained in detail above) and positioning the rotary encoder device 100 on the machine (action 802b). In the described embodiment, positioning the rotary encoder device 100 on machine 900 includes arranging the rotary encoder device 100 such that machine shaft 902 passes through hollow rotor 150 and slides it axially downward until stator 110 rests on surface 906 of static portion 904 of machine 900. In the described embodiment (which illustrates a typical scenario), the relative dimensions of the machine shaft and rotor 150 cause rotor 150 to fit tightly radially onto machine shaft 902, such that the radial position of rotor is determined and fixed by machine shaft 902, even before the shaft and rotor are secured relative to each other by additional fastening devices (such as threaded members, clamps, adhesives, etc.). In the described embodiment, the fastening device is threaded nut 905, which will be described in more detail below.

[0065] The order of these two actions, 802a and 802b, is not important, and therefore they are therefore in Figure 8This is shown as part of the same first stage 802. That is, the cooperating radial alignment features of the stator 110 and rotor 150 can be engaged to set the radial position of the stator 110 and rotor 150 before or after the rotary encoder device has been positioned on the machine. In any case, once the cooperating radial alignment features of the rotor and stator are engaged and the rotor 150 is positioned on the machine shaft 902, the user can be confident that the rotor 150 and stator 110 are in the manufacturer-predicted relative radial position.

[0066] Therefore, the process can then proceed to the second stage 804. Similar to the first stage 802, there are multiple actions 804a, 804b, and 804c. The order of these actions is not necessarily critical, but there can be a preferred order for these actions, as explained in more detail below. The actions in this second stage 804 include: securing the stator 110 to the static part of the machine (action 804a); securing the rotor to the machine shaft (action 804b); and disengaging the cooperating radial alignment features of the rotor and stator (action 804c).

[0067] Securing the stator 110 to the static part of the machine (action 804a) can be done, for example, by using fastening devices (such as clamps, adhesives) and / or, as in this embodiment, by using threaded fasteners 909 that pass through holes 180 in the stator 110 and into threaded holes 911 in the static part 904 of the machine. The size of the holes 180 in the stator for receiving the threaded fasteners 909 is too large, such that the radial / lateral position of the stator on the machine is not strictly limited by the position of the threaded fasteners 909 / threaded holes 911 on the machine, and therefore the stator 110 has a degree of lateral freedom to adopt a radial position determined by the cooperative radial alignment features of the stator 110 and the rotor 150.

[0068] Securing the rotor 150 to the machine shaft (action 804b) can be done, for example, via fastening devices (such as clamps, adhesive clamps) and / or via threaded fasteners / nuts 905 as in the described embodiments.

[0069] Disengaging the cooperating radial alignment features of the stator 110 and rotor 150 (action 804c) can be achieved by axially displacing the rotor 150 relative to the stator 110. This can be accomplished, for example, by the user (installer) pushing the rotor downward (in the orientation of the drawing).

[0070] Optionally, and in the case of the described embodiment, it is possible for the actions of securing the rotor 150 to the machine shaft (action 804b) and disengaging the cooperating radial alignment features of the rotor and stator (action 804c) to occur simultaneously. For example, in the described embodiment, the action of securing the rotor 150 to the machine shaft 902 via the threaded nut 905 causes a relative axial displacement between the rotor 150 and the stator 110. That is, the threaded nut 905 slides on and threadedly engages the corresponding threaded portion of the end 907 of the machine shaft 902. When the threaded nut 905 is tightened on the end of the threaded portion 907 of the machine shaft 902, the threaded nut travels axially downward (in the orientation of the illustrated figures), and thereby pushes the rotor 150 axially downward until the bottom of the rotor 150 abuts against the protrusion 913 on the machine shaft 902, at which point the cooperating radial alignment features of the rotor and stator will have disengaged.

[0071] The preferred sequence of actions in the second stage 804 is that action 804a is performed before action 804c. Action 804a can be performed after action 804c (i.e., the cooperating radial alignment features of rotor 150 and stator 110 can be axially disengaged before stator 110 is fixed to the static part of the machine), but this is less desirable because there is a risk that stator 110 will move radially / laterally relative to rotor 150 before or during the process of fixing stator to the static part of the machine, resulting in stator 110 no longer being in the manufacturer's predetermined radial position relative to rotor.

[0072] Whether action 804b occurs before, after, or during step 804c may not be very important. For example, the situation is usually (if not typical) that the relative dimensions of the rotor and the machine shaft cause the rotor 150 to fit tightly radially onto the machine shaft, such that the radial position of the rotor is determined and fixed by the machine shaft, even when the rotor and the machine shaft have not yet been fixed relative to each other by additional fastening devices (such as threaded components, clamps, adhesives, etc.).

[0073] In the described embodiment, there is no integral bearing mechanism between the stator 110 and the rotor 150. Therefore, in use, the position between the stator 110 and the rotor 150 is entirely controlled by the machine's shaft and static components (not shown). Thus, to ensure that the stator 110 and rotor 150 do not rattle during transport, they can be arranged in their engaged positions (and held in these positions by retaining brackets to ensure they do not accidentally disengage). As will be understood, the invention can also be used in rotary encoder devices with integral bearings (i.e., bearings between the rotor and stator), although these devices may have less need for the invention since these integral bearings are typically configured to constrain the relative position of the scale and the read head.

[0074] In the described embodiment, radial alignment features 136, 138, 140 on stator 110 are provided by plates 130, 132 such that they are provided via a single sheet of material. As will be understood, this is not necessarily the case. For example, radial alignment features may be provided by a separate sheet of material individually attached to stator 110. Figure 10 An example embodiment of this situation is illustrated, wherein the individual first radial alignment feature 136', second radial alignment feature 138', and third radial alignment feature 140' are fixed to the stator 110, and particularly to the stator base plate 112 in the illustrated view. As shown, in this particular embodiment, the first radial alignment feature 136' and second radial alignment feature 138' provide rigid contact points, and the third radial alignment feature provides radially compliant contact points. In another embodiment, the first radial alignment feature 136', second radial alignment feature 138', and third radial alignment feature 140' may be configured as features integrally formed in the stator 110 (e.g., features integrally formed in the base plate 112 or cover 114). In another embodiment depicted in Figures 12(a) and 12(b), for each of the first and second sets of cooperating radial alignment features, those radial alignment features providing rigid contact points 138, 140 on the stator are integrally formed with the stator (e.g., integrally formed with the base plate 112 or the cover 114, as shown in Figure 12(b)), and those radial alignment features providing radially compliant contact points on the stator are provided by a separate radially deformable member 142', which in this embodiment is attached to the stator via a threaded fastener 137 (e.g., attached to the base plate 112 or the cover 114, as shown in Figure 12(b)). In this embodiment, the radially deformable member 142' includes a flexure.

[0075] In the described embodiment, two sets of cooperating radial alignment features are provided; one set (provided by the first radial alignment feature 160 of the rotor and the first radial alignment plate 130 of the stator) is disposed on a first axial side of the scale 156, and the other set (provided by the second radial alignment feature 162 of the rotor and the second radial alignment plate 132 of the stator) is disposed on the opposite second axial side of the scale 156. However, this is not necessarily the case. Alternative embodiments include: providing two sets of cooperating radial alignment features (which are axially separated) on the same side of the scale; providing only one set of cooperating radial alignment features; or providing more than two sets of cooperating radial alignment features located at different axial positions.

[0076] In the described embodiment, the contact points in each set of cooperating radial alignment features are arranged in a plane extending perpendicular to the axis of rotation. While this arrangement may be preferred (to help balance forces on the rotor), it is not necessarily required, and the contact points may be arranged at different axial locations, for example.

[0077] In the described embodiments, at least one of the cooperating radial alignment features is resiliently radially compliant. While this can be beneficial (e.g., helping to avoid over-constraining the rotor and stator when engaging via the cooperating radial alignment features, which can be beneficial for repeatability reasons), it is not necessarily required. For example, all cooperating radial alignment features can be resiliently radially rigid.

[0078] In the described embodiment, the cooperating radial alignment features engage solely through the relative axial movement of the rotor and stator, i.e., no other relative movement or other means are required to induce their engagement. This arrangement is particularly preferred due to its simplicity of operation; however, as will be understood, other embodiments are also within the scope of the invention. For example, a rotary encoder device can be configured such that the cooperating radial alignment features engage by first placing the rotor and stator in a first relative axial position, and then, while in the first relative axial position, rotating the stator and rotor relative to each other, thereby engaging the cooperating radial alignment features. In this embodiment, the cooperating radial alignment features can disengage, for example, by inducing a relative rotation of the stator and rotor (e.g., in a direction opposite to the direction that caused their engagement) and then axially displacing the rotor and stator to a second position where the cooperating radial alignment features cannot engage through the relative rotation of the stator and rotor.

Claims

1. A rotary encoder device comprising a stator and a rotor rotatable relative to each other about a rotation axis, one of the stator and the rotor including a scale and the other of the stator and the rotor including a read head for reading the scale, thereby enabling determination of the relative rotational position of the stator and the rotor about the axis. in, The stator and the rotor are configured with cooperative radial alignment features, which are configured such that: At the first relative axial position of the stator and the rotor, the cooperative radial alignment feature is engageable so as to thereby constrain the stator and the rotor at a predetermined relative radial position, and In the second relative axial position of the stator and the rotor, the cooperative radial alignment feature is not engageable, wherein the read head is capable of reading the scale in the second relative axial position.

2. The rotary encoder device of claim 1, wherein the rotary encoder device is configured such that, at a first relative axial position of the stator and the rotor, the cooperating radial alignment features are engageable to form an interference fit.

3. The rotary encoder device of claim 2, wherein the rotary encoder device is configured such that when in the first relative axial position, the frictional force generated by the interference fit between the cooperating radial alignment features is sufficient to support the weight of the rotor or the stator, whichever is heavier, such that the cooperating radial alignment features and therefore the rotor and the stator do not automatically disengage under their own weight.

4. The rotary encoder device as claimed in claim 2 or 3, wherein the rotary encoder device is configured such that: i) The interference fit can be formed by applying a relative axial displacement force of no more than 150 N on the stator and / or by applying a relative rotational force of no more than 20 Newton-meters (Nm) on the stator and the rotor, and / or ii) The interference fit can be broken by applying a relative axial displacement force of no more than 150 N on the stator and the rotor and / or by applying a relative rotational force of no more than 20 Newton-meters (Nm).

5. The rotary encoder device as claimed in any of the preceding claims, wherein, The cooperative radial alignment feature can be engaged and disengaged individually by the relative axial displacement of the stator and the rotor between the first relative axial position and the second relative axial position.

6. The rotary encoder device as claimed in any of the preceding claims, wherein, The cooperative radial alignment feature of the rotor and the stator is configured to provide the following when the stator and the rotor are in the first relative axial position: At least one radial reference device, the at least one radial reference device defining a reference radial position for the stator and the rotor, and At least one resilient radially compliant biasing device biases the rotor and the stator into the radial reference device.

7. The rotary encoder device as claimed in any of the preceding claims, wherein, When in its engaged state, the cooperative radial alignment features provide a first set of contact points, which include contact points between the stator and the rotor at at least three different locations around the axis of rotation.

8. The rotary encoder device as claimed in claim 7, wherein, At least one of the contact points is configured to be elastically radially compliant.

9. The rotary encoder device as claimed in claim 7 or 8, wherein, At least two of the contact points are configured to be radially rigid.

10. The rotary encoder device according to any one of claims 7 to 9, wherein, When in its engaged state, the cooperative radial alignment feature provides a second set of contact points, with the first set of contact points and the second set of contact points located at different axial positions.

11. The rotary encoder device as claimed in claim 10, wherein, The first set of contact points and the second set of contact points are located on opposite axial sides of the scale.

12. The rotary encoder device as claimed in any of the preceding claims, wherein, The rotary encoder device is a closed rotary encoder device, which includes an integral protective housing, wherein at least the scale of the rotor and the reading head of the stator are located within the integral protective housing, and wherein one or more seals exist between the rotor and the stator to protect the scale and the reading head from external contamination.

13. The rotary encoder device of any of the preceding claims, wherein the rotary encoder device is configured such that there is no integral position constraint bearing between the stator and the rotor when the stator and the rotor are in their second relative axial position, such that a device external to the rotor and the stator is required to guide the relative rotation of the rotor and the stator in their second relative axial position.

14. An apparatus comprising a machine having a static portion and a rotatable portion, and a rotary encoder device according to any one of the preceding claims, wherein, The stator is mounted to the static part of the machine, and the rotor is mounted to the rotatable part of the machine.

15. The device as claimed in claim 14 when dependent on claim 13, wherein, The stator is rigidly mounted to the static part of the machine, and the rotor is rigidly mounted to the rotatable part of the machine, such that the relative rotation of the rotor and the stator in their second relative axial position is guided only by the static part and the rotatable part of the machine.

16. A method of mounting a rotary encoder device according to any one of the preceding claims to a machine having a static portion and a rotatable portion, the method comprising, in any suitable order: The rotary encoder device is configured such that it is located on the machine, the rotor of the rotary encoder device is arranged on a rotatable part of the machine, and the rotor and stator of the rotary encoder device are arranged in their first relative axial positions, such that the cooperating radial alignment features of the rotor and the stator engage, and the radial position of the stator is determined by the cooperating radial alignment features. The stator is fixed to the static part of the machine at the radial position determined by the radial alignment features of the cooperation; as well as The radial alignment features of the rotor and the stator are disengaged, and the rotor and the stator are arranged in their second relative axial position such that the rotor and the stator can rotate freely relative to each other.

Images