Abstract
A method of mounting a rotary scale member on a part, the rotary scale member including a body on which a series of position features defining a scale is provided, and at least one mounting flexure configured to engage the part, the method including: force-fitting the rotary scale member and the part together, whereby the at least one flexure is displaced by the part and thereby urged via a radial reaction force into engagement with the part so as to form a friction fit with the part such that the body of the rotary scale member self-locates at an initial default radial location with respect to the part; and tweaking the radial location of the body relative to the part away from its initial default radial location to a new radial location.
Claims
1. A method of mounting a rotary scale member on a part, the rotary scale member comprising a body on which a series of position features defining a scale is provided, and at least one flexure, the method comprising: force-fitting the rotary scale member and the part together, whereby the at least one flexure is displaced and thereby urges the rotary scale member via a radial reaction force into engagement with the part so as to form a friction fit with the part such that the body of the rotary scale member self-locates at an initial default radial location with respect to the part; and tweaking the radial location of the body relative to the part away from its initial default radial location to a new radial location.
2. A method as claimed in claim 1, in which the body comprises a planar disc, and in which the at least one flexure is provided substantially in plane with the planar disc.
3. A method as claimed in claim 1, in which the at least one flexure is configured to be compliant both radially and tangentially.
4. A method as claimed in claim 1, in which the rotary scale member comprises at least two flexures.
5. A method as claimed in claim 4, in which the at least two flexures are annularly spaced.
6. A method as claimed in claim 1, in which tweaking the radial location comprises manipulating at least one radial adjustment device.
7. A method as claimed in claim 6, in which tweaking the radial location comprises rotating at least one rotatable radial adjustment device to control a radial adjustment force on the rotary scale member.
8. A method as claimed in claim 7, in which the rotatable radial adjustment device directly engages the rotary scale member.
9. A method as claimed in claim 7, in which the radial adjustment force is applied to the rotary scale member via an intermediate member located between the rotatable radial adjustment device and the rotary scale member.
10. A method as claimed in claim 9, in which the intermediate member comprises a temporary jig member configured to fit with the rotary scale member at one or more predetermined configurations, in which the method comprises: mounting the temporary jig member with respect to the rotary scale member, tweaking the radial location of the body by manipulating at least one radial adjustment device which controls the radial adjustment force applied to the rotary scale member by the temporary jig member along a predetermined direction relative to the at least one flexure; securing the body at its adjusted radial location, and removing the temporary jig member.
11. A method as claimed in claim 1, in which the at least one flexure is located radially inward of the scale.
12. A method as claimed in claim 1, in which the at least one flexure is integrally formed on the body.
13. A method as claimed in claim 1, in which: the at least one flexure comprises a radial adjustment flexure member, wherein the radial adjustment flexure member is connected to the body by at least one tangentially compliant support.
14. A method as claimed in claim 1, in which: at least one flexure is radially deflectable in a plane perpendicular to the axis about which the scale features are formed on the rotary scale member, a radial adjustment device acts on said at least one flexure so as change the extent of deflection of the flexure in said plane and thereby facilitate adjustment of the radial position of the rotary scale member relative to the part on which it is mounted, and there is a smaller than 1-to-1 relationship between i) the effect the radial adjustment device has on the extent of displacement of the flexure in said plane at their point of interaction in the plane perpendicular to the axis about which the scale features are formed on the rotary scale member; and ii) the extent of the resulting radial displacement the flexure has on the body of the rotary scale member.
15. A method as claimed in claim 1, in which the body comprises an annular body.
16-36. (canceled)
Description
[0068] FIG. 1 is an isometric view of scale disc member mounted according to the present invention on a shaft, with a readhead arranged to read the scale;
[0069] FIG. 2 is a plan view of the arrangement of FIG. 1;
[0070] FIG. 3 is a side view of the arrangement of FIG. 1;
[0071] FIG. 4 is a plan view of the scale disc member of FIG. 1 shown in isolation;
[0072] FIG. 5 is a detailed view of the region M of the scale disc member of FIG. 4;
[0073] FIG. 6 is a cross-sectional view of the scale disc member mounted on the shaft, taken along line I-I of FIG. 2;
[0074] FIG. 7 schematically illustrates the steps of installing the scale disc member of FIGS. 1 to 6 in accordance with the present invention;
[0075] FIG. 8 shows an alternative embodiment of a scale disc member adapted for mounting in accordance with the present invention;
[0076] FIG. 9 shows a scale disc adjustment tool for adjusting the radial position of the scale disc member of FIG. 8;
[0077] FIG. 10 shows a plan view of the scale disc adjustment tool mounted on top of the scale disc member of FIG. 9, which in turn is mounted on a shaft of a machine;
[0078] FIG. 11 shows a cross-sectional view of the scale disc adjustment tool of FIG. 9;
[0079] FIG. 12 shows a cross-sectional view of the scale disc adjustment tool, scale disc member and shaft of FIG. 10, taken along line II-II of FIG. 10;
[0080] FIG. 13 schematically illustrates the steps of installing the scale disc member of FIG. 8 using the tool of FIG. 9 in accordance with the present invention;
[0081] FIGS. 14 to 22 show alternative embodiments of a scale disc member adapted for mounting in accordance with the present invention;
[0082] FIGS. 23 to 25 schematically illustrate a radial adjustment of a scale disc member according to the present invention via a radial adjustment device which is partially decoupled from the part on which the scale disc member is mounted;
[0083] FIGS. 26a and 26b illustrate another alternative embodiment of a scale disc member adapted for mounting in accordance with the present invention along with a plurality of nudge blocks used for adjustment of the radial position of the disc scale; and
[0084] FIG. 27 another alternative embodiment, wherein the flexures are provided on the outer edge of the planar body.
[0085] Referring to FIGS. 1 to 3 and 6, there is shown an encoder apparatus 2 mounted on a machine, i.e. on a rotatable shaft 6 and on a component 12 of the machine (not shown). FIGS. 1 to 3 (and 6) show the encoder apparatus subsequent to it having been mounted in accordance with the process of the invention which is described in more detail below. FIGS. 4 and 5 show the scale disc member 4 in isolation.
[0086] As shown, in this embodiment, the encoder apparatus comprises a scale disc member 4 which is planar in configuration and mounted on the machine's shaft 6.
[0087] The scale disc member 4 comprises a body 5 (in this embodiment a planar annular body 5) on which a scale track 8 is provided on one of its planar faces, and a plurality of flexures 16a, 16b, 16c, 16d configured to engage the shaft 6. In this embodiment, the body 5 on which the scale track 8 is provided, and the plurality of flexures 16 are formed from a single piece of material. This can be advantageous, especially for thin planar scale disc, as it can help to ensure the compactness of the scale disc, as well as help to ensure that the flexures 16 are contained within the same plane as the annular body. In particular, the scale disc member 4 (i.e. the annular body and the flexures) is formed from a thin sheet of material, in this embodiment, from stainless steel, which is about 1 mm thick. For context, the external diameter of the scale disc member 4 in this embodiment is about 55 mm. As will be understood, the invention is not limited to discs of such a size, and such dimensions are given merely as an example of a disc. Also, the disc could be made from other metallic materials, such as aluminium. As will be understood, the disc could be made from non-metallic materials or could comprise two or more separate parts made from different materials (e.g. a glass disc mounted on a metallic hub which comprises the flexures). However, the invention is particularly concerned with single-piece thin planar discs (in particular metallic discs), for which (until the advent of the present invention), there had been significant challenges in being able to mount them on a part and avoid significant eccentricity error.
[0088] As shown in FIG. 1, the scale track 8 extends completely annularly around the scale disc member 4. Although not shown in detail in FIG. 1, the scale track 8 comprises a series of features which a readhead 10 can read to determine the relative position/motion of the scale disc 4 and the readhead 10.
[0089] The readhead 10 is mounted on a component 12 of the machine which is fixed such that the cylindrical shaft 6 can rotative relative thereto about an axis A.
[0090] In the embodiment described, the encoder apparatus 2 is an optical encoder apparatus, but this need not necessarily be the case. For instance, the encoder apparatus could be a magnetic, inductive or capacitive encoder apparatus. Furthermore, in the embodiment described, the encoder apparatus 2 is a reflective optical encoder apparatus (in that the light from the readhead is reflected by the scale back toward the readhead, and in that the readhead's illumination and scale detection components are on the same side of the scale). However, this need not necessarily be the case, and the encoder apparatus could be a transmissive optical encoder.
[0091] In this embodiment, the encoder apparatus 2 is an incremental encoder apparatus. Accordingly, in this embodiment the scale disc 4 is an incremental scale disc and the scale track 8 comprises a series of periodically arranged features which the readhead 10 can read in order to provide a count of the relative position/movement of the scale disc 4 and the readhead 10. As is common in the field of incremental encoder apparatus, the scale disc member 4 could comprise one or more reference marks which can be read by the readhead when it passes the readhead, so that the readhead can identify a reference position on the scale disc member. An example reference mark 15 is shown in FIG. 4. In this case, the reference mark 15 is shown in a track 17 separate to the incremental scale track 8, but this need not necessarily be the case. The reference mark 15 could be embedded within the incremental scale track 8. Of course, the encoder apparatus could be an absolute encoder apparatus instead of an incremental encoder apparatus. Accordingly, the scale disc 4 could be an absolute scale disc, in which the scale track(s) thereon comprises features defining a series of unique absolute positions such that the absolute position of the scale disc and readhead can be determined on start-up without requiring relative motion of the scale disc member and the readhead.
[0092] As shown most clearly in FIG. 4, the scale disc member 4 comprises a hole 14 through its middle, through which the cylindrical shaft 6 extends when the scale disc 4 is mounted on the cylindrical shaft 6. The scale disc member 4 comprises four flexures 16 which are provided in plane with the planar disc and are spaced equiangularly around the hole 14. The flexures 16 are shaped and sized such that the effective diameter D of the hole 14 is slightly smaller than the diameter D of the disc receiving portion of the shaft 6 onto which it is to be mounted by approximately 20-40 m. The flexures 16 are resiliently compliant in the radial direction (with respect to the scale disc member 4). Accordingly, the flexures 16 could be referred to as radial spring members. Due to the effective diameter D of the hole 14 being slightly smaller than the diameter D of the shaft 6 onto which it is to be mounted, the scale disc member 4 has to be force fitted onto the shaft 6. Accordingly, once the scale disc member 4 has been forced onto the shaft 6, there is a natural/default/automatic tight fit between them. This is because the process of force fitting the scale disc member 4 onto the shaft 6 causes the flexures 16 to radially deflect, wherein the elasticity of the material of the flexures 16 causes a reaction force on the shaft 6. This causes them to be biased into the shaft 6 along the radial direction, so as to thereby engage, and radially locate the scale disc 4 on, the shaft 6 (at a predetermined/default radial location).
[0093] On the assumption that the four flexures 16 are nominally identical, they should ensure that scale disc member 4 is nominally centred on the shaft 6in other words, the action of force fitting the scale disc member 4 on the shaft 6 should cause the scale disc member to self-centre on the shaft 6. However, relying on the self-centring ability of the scale disc member might not be sufficient, and it might be advantageous to be able to ever-so-slightly tweak the radial position of the scale disc member so as to achieve an optimised radial location which in turn can optimise the performance of the encoder (in particular so as to reduce eccentricity error).
[0094] In the applications and apparatus in which the inventor's discs are likely to be used, it is unlikely that adjustments of greater than 50 m would ever be required, and it could be that the extent of the adjustment is a small as a couple of microns. It needs to be borne in mind that not only is the extent of adjustment required miniscule, but that the installer also needs to be able to effect such an adjustment in a predictable and consistent manner. Being able to effect such an adjustment in a predictable and consistent manner means that the installer does not need to work on a trial-and-error basis, which is very time consuming and could also result in making the set up worse.
[0095] The inventors found that the effects of friction and stiction between the flexures 16 and the shaft 6 are a significant issue when trying to effect such tiny adjustments in a predictable manner. For instance, it is likely that the stiction between the flexure and shaft is not perfectly equal for all flexures. Accordingly, when trying to push or pull the scale disc member in a particular direction, the flexure/shaft interface might give-way/slip at one of the flexures, but not another, causing the whole scale disc member to rotate unpredictably.
[0096] To counteract this issue, the inventors invented new scale disc members and new methods of mounting a scale disc member.
[0097] For instance, in the example embodiment of FIGS. 1 to 6, as well as the flexures 16 being radially compliant (e.g. along the direction R in FIG. 5), they are also configured with tangential compliance (e.g. along the direction T in FIG. 5). As explained in more detail below, being both radially and tangentially compliant helps to ensure that the radial position of the annular body 5 can be adjusted in a predictable and consistent manner.
[0098] In the currently described embodiment, tangential compliance is achieved by providing a specially shaped flexure. In particular, the flexure 16 comprises a seat or foot portion 18 which is configured to engage the shaft 6. The foot portion 18 extends between a pair of elongate flexure legs 20, which themselves extend from the annular body 5, into the hole 14. The foot portion 18 and the flexure legs 20 are formed from the same piece of material as the annular body 5, and define a flexure void 22. As shown in FIG. 5, a first contact face 24 is provided on the void-side of the flexure foot 18, and a second contact face 26 is provided on opposite side of the void, facing the first contact face 24. As explained in more detail below in connection with FIGS. 6 and 7, an adjustment bolt 28 can be located through the flexure void 22 such that a tapered head 31 of the adjustment bolt 28 can engage and push against the contact faces 24, 26 so as to adjust their separation distance L.
[0099] The foot portion 18 is resiliently compliant in the radial direction R, by virtue of it being able to bend along its length, within the plane of the disc, and the foot portion 18 is resiliently compliant in the tangential direction T, by virtue of the pair of flexure legs 20 being able to bend along their length, within the plane of the disc.
[0100] The flexures 16, in particular, the flexure foot 18 and elongate legs 20 (and the flexure void 22) can be formed, for instance, by etching and/or machining (e.g. laser cutting) the annular body 5. Optionally, the annular body 5, along with its flexures 16, is formed by a moulding, casting and/or additive process.
[0101] A method of mounting the scale disc member 4 of FIGS. 1 to 6 will now be described with reference to FIG. 7. As schematically illustrated in steps (A) and (B) of FIG. 7, the method begins by an installer force fitting the scale disc member 4 onto the shaft 6. This involves the user approximately aligning the scale disc member 4 such that it is substantially co-axial with the shaft 6, and then pushing the scale disc member 4 onto the shaft by applying a force AF, substantially along the axial direction, such that the shaft 6 protrudes through the hole 14 in the scale disc member 4. In this embodiment, the installer keeps pushing scale disc member 4 along the shaft 6 until the underside of the scale disc member 4 comes to rest on a ledge 7 on the shaft, as shown in step (B) of FIG. 7.
[0102] As mentioned above, the inner diameter D of the hole 14 is slightly smaller than the diameter D of the disc receiving portion of the shaft 6. Accordingly, the scale disc member 4 will not simply loosely fit over and slide down the shaft 6 by itself. Rather, the installer has to force-fit them together such that the flexures 16 deflect from their natural rest position so as to open up the hole 14 to thereby accommodate the shaft, and also so as to overcome the friction between the flexures 16 and the shaft 6 so as to move the scale disc member 4 along the shaft's axis to the desired axial position on the shaft 6.
[0103] Once the scale disc member 4 is at the desired axial position on the shaft 6, the installer can check the radial position of the scale disc member 4 at step (B). This could be achieved mechanically, for example using a Dial Test Indicator (DTI) on the outer edge of the disc as it is rotated. Optionally, an optical method could be used. For example a microscope could be used to look at the edge of the scale lines. As another example, a pair of readheads could be configured to read the scale features and the count difference between them can provide a measure of eccentricity. If the radial position is not satisfactory, then the installer can fine tune the radial position of the scale disc member 4 at step (C). This is achieved in this embodiment via the use of one or more adjustment bolts 28. As shown in more detail in FIG. 6, the adjustment bolt 28 comprises a threaded portion 29 and a tapered head 31. As shown in FIG. 6, the adjustment bolt can be received through the flexure void 22 of a first flexure 16a, such that a threaded portion 29 of the adjustment bolt is received within a threaded hole 32 in the ledge 7 of the shaft 6. As per a normal threaded member, the adjustment bolt 28 can be rotated so as to change its axial position. FIG. 6 shows the configuration where the adjustment bolt 28 has been located in the threaded hole 32 and rotated until its axial position is such that the tapered side of the tapered head 31 is just touching the first 24 and second 26 contact faces (described above in connection with FIG. 5) of the first flexure 16a. With reference back to FIG. 5, it should be noted that the distance L between the first 24 and second 26 contact faces is smaller than the width W of the flexure void, such that it is certain that the tapered head 31 will engage the first 24 and second 26 contact faces and not the insides of the flexure legs 20. Accordingly, as the adjustment bolt 28 is further rotated to cause it to penetrate further into the threaded hole 32, the tapered head 31 will push against first 24 and second 26 contact faces with increasing force, thereby causing the distance L between the first 24 and second 26 contact faces to increase. In view of that the flexure's foot portion 18 is butted up against the shaft 6, the flexure's foot portion 18 is fixed in place and cannot move. Accordingly, any increase in the distance L between the first 24 and second 26 contact faces causes the whole annular body 5 to move (in this example in the Y-dimension).
[0104] Such radial motion of the annular body 5 is facilitated in a predictable manner due to the flexing of the other flexures 16b, 16c, 16d. In particular, the flexure foot 18 of the flexure 16c which opposes the first flexure will flex such that the distance L of said flexure 16c will decrease to accommodate the change in radial position of the annular body 4 in the Y-dimension. Also, the other two flexures 16b, 16c will laterally bend/distort (in the Y-dimension) in order to accommodate the change in radial position of the annular body 4 in the Y-dimension (in particular, the flexure legs 20 of the other two flexures 16b, 16c will bend along their length within the plane of the scale disc member). Such flexing of the flexures 16 means that the radial position of the annular body 5 relative to the shaft 6 can be adjusted without needing to overcome the stiction between the shaft 6 and the foot portions 18 of the flexures 16.
[0105] When the annular body 5 is in the desired radial position, then as illustrated in step (D) of FIG. 7, the adjustment bolt 28 can be left in place so as to hold the annular body 5 in position. Also, in this case, as shown in Figures (C) and (D), it can be advantageous to locate further bolts 28a (which could be identical to the adjustment bolts 28) in the voids 22 of the other flexures (16c, 16d) such that they help to clamp the annular body 5 in place. If so, then it is desired that they are not over tightened because doing so will cause the flexures (16a, 16b, 16c, 16d) to fight one another and/or distort the annular body. Additionally (or alternatively), the radial position of the annular body 5 could be fixed in place by other means, such as adhesive and/or a different mechanical fastener. For instance, one or more supplemental fastener hole(s) 9 (see FIG. 4) could be provided on the annular body 5 through which a fastener such as a clamping bolt can be passed and secured to the shaft (e.g. via a hole in the ledge 7), so as to clamp the annular body 5 in place. The bolt(s) 28(a) could then be removed.
[0106] In the above described embodiment, the problems associated with stiction causing unpredictable adjustment of the radial position has been overcome via the use of flexures which are both radially and tangentially compliant. Another embodiment of the invention, which has been found to reduce the stiction problem, will now be described with reference to FIGS. 8 to 13.
[0107] FIG. 8 shows an example scale disc member 104 which is similar to that described above in connection with the FIGS. 1 to 7 in that it comprises a planar annular body 105 on which a scale track 108 is provided on one of its planar faces, and a hole 114 through its middle, through which the cylindrical shaft 6 can extend when the scale disc 104 is mounted on the cylindrical shaft 6. The scale disc member 104 comprises a plurality of flexures 116, but in this embodiment, they do not have any tangential compliance. Rather, the scale disc member 104 comprises four pairs of cantilevered flexures (or spring members) 116a, 116b, 116c, 116d, which are radially compliant, but not tangentially compliant. Each pair of cantilevered spring members 116a, 116b, 116c, 116d is provided in plane with the planar scale disc 104 and spaced around the edge of the hole 114. Also, each pair of cantilevered spring members 116a, 116b, 116c, 116d is configured such that their free ends are proximal each other and their fixed ends are distal each other. In other words, the cantilevered spring members in each pair 116a, 116b, 116c, 116d point toward each other, rather than away from each other.
[0108] As shown in FIG. 8, each cantilevered spring member 116 is tapered such that it narrows towards its free end. Accordingly, the width of a cantilevered spring member is greater at its fixed end than its width at its free end. As will be understood, the exact desired dimensions of the cantilevered spring member will depend on a number of factors including the material, size of the disc, and the desired spring force. Our inventors have found a good desired spring force of each flexure in a pair can be about 20 Newtons, which provides a good balance between providing sufficient self-locating ability and not over gripping the shaft.
[0109] In the embodiment described, each cantilevered spring member 116 is formed by creating, in the same piece/sheet of material as the annular body 104, a slot 122 (which sits behind the cantilevered spring members 116) and a gap (which sits between the free ends of the cantilevered spring members). The slot 122 and gap enable the cantilevered spring members to flex along their length, into the slot 122. Such a slot 122 and gap can be formed, for instance, by etching and/or machining (e.g. laser cutting) the annular body 105. Optionally, the annular body 105, along with its cantilevered spring members, is formed by a moulding, casting and/or additive process.
[0110] When the scale disc member 104 is push-fit onto a shaft 6 (which is slightly larger than the space between the pairs of the cantilevered spring members 116a, 116b, 116c, 116d), the shaft 6 engages the side of each of the cantilevered spring members 116 facing the middle of the hole 114, and causes each of them to bend slightly into the slot 122. The elasticity of the material of the cantilevered spring members 116 causes a reaction force on the shaft 6. Preferably, the reaction force provided by each cantilevered spring member 116 is nominally the same, such that the annular body 105 substantially self-centres on the shaft 6. Such nominally identical reaction forces can be achieved by configuring the cantilevered spring members 116 such that they are nominally identical in shape and size.
[0111] Further details of such flexures, including further details on the advantages of providing pairs of cantilevered flexures is described in co-pending UK patent application GB1918002.5.
[0112] Similar to the embodiment of FIGS. 1 to 7, relying on the self-centring ability of the scale disc member might not be sufficient, and it might be advantageous to be able to ever-so-slightly tweak the radial position of the scale disc member so as to achieve an optimised radial location which in turn can optimise the performance of the encoder (in particular so as to reduce eccentricity error).
[0113] As mentioned above, the inventors found it incredibly difficult to adjust the radial position of such a scale disc member by such a small amount in a reliable and predictable way without tangentially compliant flexures. However, what they found was that the level of control (in particular the predictability) of the adjustment of the radial position varied significantly depending on the relationship between the radial adjustment force applied to the scale and the flexures. In particular, it has been identified by the inventors that in cases where the shaft must slide against a flexure in order to adjust the radial position, it is uncertain exactly how and when it will start to move.
[0114] The inventors found that with a scale disc member which has flexure(s) with no tangential compliance more deterministic, precise radial adjustment can be achieved by ensuring that the radial adjustment force is applied at an angle to such flexures (in other words, by ensuring that the radial adjustment force is not applied tangentially or parallel to the interface of the shaft and any such flexures, or, for instance, by ensuring that the radial adjustment force is not applied perpendicularly to the direction of the flexure force).
[0115] In particular, it has been found that it can be preferable to apply the radial adjustment force (or displacement) to the scale disc member, such that, for each of the annularly spaced mounting flexures (or pairs of mounting flexures), the angle between the direction along which the force (or displacement) is applied and a line extending perpendicular to the radial reaction force of the annularly spaced mounting flexure (or pairs of mounting flexures), is greater than the inverse tan of the coefficient of friction between the flexure and the part (e.g. shaft/hub) (e.g. of the articulated joint).
[0116] For instance, in the embodiment of FIG. 8, if we imagine a situation in which the installer wants to adjust the radial position of the annular body 105 to a new position in the Y-dimension, the logical step for the installer would be apply a force F parallel along Y dimension direction. However, it has been found that it more deterministic and precise adjustment can be achieved by applying a first force F which adjusts the radial position in both the X and Y dimensions, and then applying a second force F which further adjusts the radial position of the annular body 105 in the Y dimension, and brings the radial position of the annular body back to its original position in the X dimension. As shown, the directions of the first F and second F forces are at an angle to the tangentially stiff flexures (and are not perpendicular to the flexure/radial reaction force).
[0117] FIGS. 9 to 12 illustrate an example jig member 200 which can be used to ensure that the radial position of the scale disc member 104 of FIG. 8 is adjusted by forces/displacements which are applied at an angle to the flexures in accordance with the above described principle. The jig 200 comprises a ring-shaped body 202 which is configured to sit temporarily on top of the scale disc member 104 after the scale disc member 104 has been force-fitted onto the shaft 6 and removed once the adjustment of the radial position of scale disc member 104 is complete. In this embodiment, the ring-shaped body 202 comprises a hole 204 for receiving the shaft 6. The diameter of the hole is 204 configured to be slightly smaller than the shaft 6 such that it is a snug fit thereon. In particular, the jig 200 comprises four flexure arms 216a, 216b, 216c, 216d, the free ends of which are configured to engage the shaft 6 and radially resiliently deflect when the jig is mounted onto the shaft 6. The jig 200 also comprises a plurality of flexible adjustment arms 218a, 218b, 218c, 218d. In this embodiment there is one flexible adjustment arm associated with each flexure arm. Each adjustment arm 218 comprises a threaded channel 220 extending therethrough, and a lug 222 protruding from its underside (e.g. see FIG. 11). Also, channels 224a, 224b, 224c, 224d are provided in the jig's body 202, co-axial with each adjustment arm channel 220. This facilitates the insertion of a grub screw 230 therethrough, the thread of which can engage the thread on the adjustment arm's channel 220. When the end of the grub screw 230 engages the flexure arm 216 (which is butted up against the rigid shaft 6), the flexible adjustment arm 220 will be pushed radially outward as the grub screw 230 is tightened, into the small gap between the flexible adjustment arm 220 and the annular body 202 of the jig 200.
[0118] As illustrated in FIG. 8, the scale disc member 104 comprises four lug-receiving features 130a, 130b, 130c, 130d. In this embodiment, each lug receiving feature 130 comprises a flat face on the inside edge of the hole 114 of the scale disc member's annular body 105. When assembled together, the lugs 222 are received within the hole 114 of the scale disc member, wherein each lug 222, sits adjacent a corresponding lug receiving feature (e.g. see FIG. 12 which shows the lugs 222b, 222d sitting adjacent to the corresponding lug receiving features 130b, 130d).
[0119] A method of mounting the scale disc member 104 and adjusting its radial position will now be described with reference to FIG. 13. As illustrated in steps (A) and (B) of FIG. 13, the method begins by an installer force-fitting the scale disc member 104 onto the shaft 6. This comprises the user approximately aligning the scale disc member 104 such that it is substantially co-axial with the shaft 6, and then pushing the scale disc member 104 onto the shaft by applying a force AF, substantially along the axial direction, such that the shaft 6 protrudes through the hole 114 in the scale disc member 104. In this embodiment, the installer keeps pushing scale disc member 104 along the shaft 6 until the underside of the scale disc member 104 comes to rest on a ledge 7 on the shaft, as shown in step (B) of FIG. 7.
[0120] As mentioned above, the inner diameter of the hole 114 is slightly smaller than the diameter of the disc receiving portion of the shaft 6. Accordingly, the scale disc member 104 will not simply loosely fit over and slide down the shaft 6 by itself. Rather, the installer has to force-fit them together such that the flexures 116 deflect from their natural rest position so as to open up the hole 114 to thereby accommodate the shaft, and also so as to overcome the friction between the flexures 116 and the shaft 6 so as to move the scale disc member 104 along the shaft's axis to the desired axial position on the shaft 6.
[0121] Once the scale disc member 104 is at the desired axial position on the shaft 6, the installer can check the radial position of the scale disc member 104 at step (B), e.g. via by using a DTI on the outer edge of the disc as it is rotated. If the radial position is not satisfactory, then the installer can fine tune the radial position of the scale disc member 104 at step (C).
[0122] At step (C), the installer can push the precision adjustment tool 200 onto the shaft 6, and down along the shaft 6 until the lugs 222 become adjacent corresponding lug receiving features 130. In the described embodiment, the jig sits on/contacts the scale disc member 104 but this need not necessarily be the case. To adjust the radial position of the annular body 105 of the scale disc member 104 (e.g. along the direction illustrated by force arrow F in FIG. 8), a grub screw 230 (e.g. grub screw 230d) can be inserted through an appropriate channel 224 (e.g. channel 224dsee FIGS. 11) until its thread engages the thread of the threaded channel 220 of the corresponding flexible adjustment arm (e.g. threaded channel 220d of flexible adjustment arm 218dsee FIGS. 11 and 12). At this point, the grub screw 230 can be rotated so as to cause the grub screw (e.g. 230d) to progress axially through the channel (e.g. 220d) of the flexible adjustment arm until its end comes into engagement with the corresponding flexure arm 216 (e.g. flexure arm 216d). At this point, any further rotation of the grub screw (e.g. 230d) will cause the flexible adjustment arm (e.g. 218d) to be forced radially outwards/backwards. As this happens, the corresponding lug 222 (e.g. lug 222d) will engage the corresponding lug receiving feature (e.g. lug receiving feature 130d) on the scale disc member's body 105, and will thereby apply a force thereto, in a direction parallel to the grub screw's and channel's axis (e.g. in this case, along the direction of the arrow F shown in FIG. 8). If desired, the installer can use another grub screw to further adjust the radial position of the scale disc member's body 105. For instance, as illustrated in step (C), a second grub screw 230a can be used to pull the annular body 105 in the direction of arrow F shown in FIG. 8.
[0123] Once the installer is happy with the radial position of the annular body 105, they can secure the annular body in place. As illustrated in step (D), in this embodiment, this is achieved via the use of one or more bolts 240 which can be passed though bolt holes 250 in the tool 200 such that the annular body 105 can be secured with the tool 200 still in place. As per a standard bolt, the bolts 240 can have a threaded portion and a head portion. The threaded portion passes through the bolt holes 250 in the tool 200 and the bolt holes 160 in the annular body 105 so as to engage threaded holes (not shown) in the ledge 7 of the shaft 6, and the underside of the head portion engages the upper face of the annular body 105 of the scale disc member so as to clamp the annular body 105 to the ledge 7.
[0124] Once secured, the grub screws 240 can be removed, and then, as illustrated in step (E), tool 200 can be lifted off the shaft 6. As shown, the radial position of the annular body 105 is held in place by the bolts 240. As will be understood, alternative ways of holding the annular body in place are available, such as via an adhesive, in which case the tool 200 will stay in place until the adhesive has cured.
[0125] FIG. 14 illustrates an alternative adjustable scale disc member 304 which is configured to ensure that its radial position is adjustable by forces which are applied at an angle to the flexures in accordance with the above described principle. Similar to the other embodiments described above, the scale disc member 304 comprises a round, planar, annular body 305 on which a scale track 308 is provided on one of its planar faces, and a hole 314 through its middle, through which the cylindrical shaft 6 can extend when the scale disc 304 is mounted on the cylindrical shaft 6. The scale disc member 304 comprises three pairs of flexures (or spring member) 316, but in this embodiment, they do not have any tangential compliance. Rather, the scale disc member 304 comprises three pairs of cantilevered spring members 316a, 316b, 316c which are radially compliant, but not tangentially compliant. As shown, the cantilevered spring members 316a, 316b, 316c extend in a substantially tangential or circumferential direction relative to the disc (e.g. as opposed to substantially radially). Each pair of cantilevered spring members 316a, 316b, 316c is provided in plane with the planar scale disc 304 and spaced equidistantly around the edge of the hole 314. Also, each pair of cantilevered spring members 316a, 316b, 316c is configured such that their free ends are proximal each other and their fixed ends are distal each other. In other words, the cantilevered spring members in each pair 316a, 316b, 316c point toward each other, rather than away from each other. A flexure void 318a, 318b, 318c is provided directly behind each pair of cantilevered spring members 316a, 316b, 316c.
[0126] Similar to the other above described embodiments, the flexure pairs 316 are shaped and sized such that the effective diameter of the hole 314 is slightly smaller than the diameter of the disc receiving portion of the shaft 6 onto which it is to be mounted. Accordingly, the scale disc member 304 has to be force-fitted onto the shaft 6. Once the scale disc member 304 has been force-fitted onto the shaft 6, there is a natural/default/automatic tight fit between them.
[0127] Similar to embodiment of FIGS. 1 to 6, the flexure voids 318 are configured to receive an adjustment bolt 28 (having a threaded portion 29 and a tapered head 31). After the scale disc 304 has been force fitted onto the shaft an adjustment bolt 28 can be used in the same way as that described above in connection with FIG. 6 to effect an increase in the distance between the back of a flexure pair 316 and the back wall of its flexure void 318 (e.g. distance D shown in FIG. 14). For example, using an adjustment bolt 28 in the flexure void 318a of the first flexure pair 316a of FIG. 14a will cause the radial position of the annular body 305 to shift along the arrow A in FIG. 14. Such a shifting is facilitated by the radial deflection of the other two pairs of cantilevered spring members 316b, 316c. However, like the embodiment of FIGS. 8 to 13, the cantilevered spring members 316a, 316b, 316c are not tangentially compliant. Accordingly, it will be necessary to overcome an element of stiction between the other two pairs of cantilevered spring members 316b, 316c and the shaft 6. To reduce the effect of above described problem of stiction causing unpredictable radial adjustment, the scale disc 304 is configured to ensure that the radial adjustment force applied by an adjustment bolt 28 will be applied at an angle to the flexures (in other words, is configured to ensure that the radial adjustment force will not be applied tangentially or parallel to the interface of the shaft and any such flexures).
[0128] Further alternative adjustable scale disc members are also illustrated in FIGS. 15 to 22 and briefly described below.
[0129] The adjustable scale disc member 400 of FIG. 15 is similar to that of the embodiment of FIGS. 1 to 7, except that the flexures 416 are configured without any tangential compliance. Whilst this design does not have the benefit of tangential compliance, it is simpler in design than that of FIGS. 1 to 7. It has also been found that this design can be beneficial over the design of FIG. 14, especially for designs in which the disc is smaller, and/or the flexures are closer together, because the flexures are more isolated from each other. Similar to the embodiments of FIGS. 1 to 7 and 14 to 19, adjustment of the flexures can be effected by use of a radial adjustment device (not shown) (such as a screw with a tapered head) which can be inserted in the flexure void and tightened so as to expand the flexure (i.e. so as to increase the width w of the flexure void) and thereby laterally displacing the disc.
[0130] The adjustable scale disc member 500 of FIG. 16 comprises four flexures, 516a, 516b, 516c and 516d, only two of which 516a and 516b are configured to be directly adjustable. As per the other designs, the flexure defines a default inner periphery diameter which is smaller than the diameter of the part 6 on which it is to be mounted. Also, similar to the embodiments of FIGS. 1 to 7 and 14 to 19, adjustment of the flexures can be effected by use of an adjustment device 528 (such as a screw with a tapered head) which can be inserted in the flexure void 530 and tightened so as to expand the flexure.
[0131] The adjustable scale disc member 600 of FIG. 17 comprises four, tangentially/circumferentially extending, cantilevered flexures 616. The cantilevered flexures 616 each have a foot portion 618 configured to engage the part/shaft inserted in the hole through the disc, and which define a default inner periphery diameter which is smaller than the diameter of the part 6 on which it is to be mounted. In this embodiment, the radial adjustment devices 628 are configured to act at a tangentially/circumferentially distant point from the foot portion 618. In other words, the radial adjustment devices 628 are configured such that they do not sit directly radially behind the foot portion, but rather at a point further from the root of the cantilevered flexure than its foot portion 618. This helps to provide a lever-ratio effect which can help to provide even more precise control over the adjustment force applied to the disc. Accordingly, such a configuration can provide a smaller than 1-to-1 relationship between i) the effect the manually manipulable radial adjustment devices 628 has on the extent of displacement of the adjustment flexure 618 in said plane at their point of interaction in the plane perpendicular to the axis of rotation; and ii) the extent of the resulting radial displacement the adjustment flexure has on the annular body of the rotary scale member.
[0132] A similar lever-ratio effect can be achieved via other designs, such as that shown in FIG. 18, in which the adjustable scale disc member 700 of FIG. 18 comprises three radially extending cantilevered flexures 716, the free ends of which engage the part/shaft 6 inserted through the hole in the disc. In this design, the tightening of adjustment screws which have tapered heads causes the radially extending cantilevered flexures 716 to deflect sideways (e.g. substantially tangentially). The end faces of the free ends of the radially extending cantilevered flexures 716 have a slight angle to them such that when the flexure is pushed sideways, it effects a lateral displacement of the disc (with the other flexures flexing in response thereto). As will be understood, the extent by which the disc is laterally displaced by any given unit of sideways displacement of the flexure will depend on the angle of the end face of the radially extending cantilevered flexures 716. Accordingly, the angle of the end face of the radially extending cantilevered flexures 716 can be selected at the design and manufacturing stage to provide the desired lever-ratio effect.
[0133] The adjustable scale disc member 800 of FIGS. 19a and 19b comprises a plurality of radially extending cantilevered flexures 816, each which has a naturally bent shape and a hole 817 therethrough for receiving an adjustment screw 828 (see FIG. 19b). The free ends of the radially extending flexures defines a default inner periphery diameter which is smaller than the diameter of the part 6 on which it is to be mounted. Accordingly, when the disc member 800 is force fitted onto the part 6, they deflect and radially self-locate the disc member onto the part. As illustrated in FIG. 19b, the lateral position of the disc could be changed by the use of an adjustment screw 828 so as to change the extent of the bend in the flexure 816, thereby controlling the lateral position of the disc.
[0134] The adjustable scale disc member 900 of FIG. 20 comprises four flexures 916 which define a default inner periphery diameter which is smaller than the diameter of the part 6 on which it is to be mounted. Similar to the embodiment of FIGS. 1 to 7, the flexures 916 are configured with both radial and tangential compliance. However, in this embodiment (and in the embodiment of FIG. 21 described below), the tangential compliance is provided in a way which is isolated/independent from the radial adjustment device 928. In particular, in the embodiment of FIGS. 1 to 7, there is a concern that once a radial adjustment device 28 has been located in one of the flexure voids 22, the radial adjustment device 28 will affect the performance of radial adjustment of the disc in another direction. For example, the embodiment of FIGS. 1 to 7 above was described in connection with adjusting the radial position of the disc in the Y-dimension. If further adjustment of the radial position was desired in the X-dimension then a second adjustment screw would be needed to be inserted in flexure void of either the second 16b or fourth 16d flexure and tightened as appropriate in order to effect a change in radial position in the X-dimension. However, there is a concern that the presence of the adjustment screw located in the flexure void 22 of the first flexure 16b might interfere with the radial adjustment, and in particular might impact the ability of the first flexure 16a to flex tangentially.
[0135] In the embodiment of FIG. 20 the radial compliance of a flexure 916 is provided by an elongate seat portion 918 of the flexure and the tangential compliance is provided by a leg portion 920. The tangential compliance of the leg portion 920 is not affected by the presence of the adjustment screw 928. Accordingly, a first adjustment screw 928a can be used in the flexure void of a first flexure 916a to effect a radial adjustment in Y-dimension (which will cause the flexure void of the first flexure 916a to expand, the flexure void of the third flexure 916c directly opposite the first flexure 916a to contract, and cause the leg portions 920 of the second 916b and fourth 916d flexures to bend along their length). A second adjustment screw 928b can subsequently be used in the flexure void of the fourth flexure 916d to effect a radial adjustment in X-dimension (which will cause the flexure void of the fourth flexure 916d to expand, the flexure void of the second flexure 916b directly opposite the fourth flexure 916d to contract, and cause the leg portions 920 of the first 916a and third 916c flexures to bend along their length).
[0136] Similar to the embodiment of FIG. 20, the flexures 1016 of the adjustable scale disc member 1000 of FIG. 21, are also configured in a way such that they provide both radial and tangential compliance, and wherein the tangential compliance is not affected by the presence of a radial adjustment device 928 which is used to control another one of the flexures. In particular, the radial compliance in provided by the elongate seat portion an elongate seat portion 1018 of the flexure 1016 and the tangential compliance is provided by a pair of legs 1020 which can bend along their length.
[0137] Accordingly, in the embodiments of FIGS. 20 and 21, the flexure comprises a radial adjustment flexure member comprising (e.g. front and back) sides against which a radial adjustment device can engage and push so as to effect a radial adjustment of the disc, wherein the radial adjustment flexure member is connected to the main body of the disc member by at least one tangentially compliant support (e.g. leg).
[0138] FIG. 22 illustrates an alternative adjustable scale disc member 1100. This disc member 1100 differs substantially from the other disc members described above in that it is not a planar disc made from sheet material. Rather, the disc member comprise a hub 1102 which protrudes from the face 1104 of the disc member on which the scale features (not shown) are provided. In this case, the hub comprises four tangentially/circumferentially extending cantilevered flexures 1116, each having a foot portion 1118 which define a default inner periphery diameter (which is intended to be smaller than the diameter of a part/shaft on which it is to be mounted). Once mounted on a shaft extending through the hole defined by the feet portions 1118, the radial position of the face 1104 of the disc member can be adjusted by one or more radial adjustment devices (not shown) (for example grub screws) which can pass through holes 1120 in the hub so as to push against the free end of the cantilevered flexures 1116. Similar to the embodiment of FIG. 17, the point at which the radial adjustment device engages and pushes against the cantilevered flexure 1116 is tangentially/circumferentially distant from the foot portion 618. In other words, the radial adjustment devices will not engage the cantilevered flexure 1116 at a point directly radially behind the foot portion, but rather at a point further from the root of the cantilevered flexure than its foot portion 1118. This helps to provide a lever-ratio effect which can help to provide even more precise control over the adjustment force applied to the disc.
[0139] It has been found that the performance of all of the embodiments of FIGS. 1 to 7 and 14 to 21 can be significantly improved by use of a radial adjustment device which at least partially decouples the radial adjustment device from the part on which the disc is installed, at least in the radial direction with respect to the scale disc member, so as to avoid/reduce the radial adjustment device fighting the change in radial location of the main body of the disc. In particular, the extent or range by which the radial position of a disc can be adjusted whilst minimising the distortion of the part of the disc on which the scale is provided (e.g. the main body or annular body of the disc) can be increased by using radial adjustment devices which are at least partially decoupled from the part on which the disc is installed, at least in the radial direction. This will be explained in more detail with reference to FIGS. 23 to 25. FIG. 23 is a schematic plan drawing of the scale disc member 4 of FIGS. 1 to 7, mounted on a shaft 6. In FIG. 23, the scale disc member 4 is in it default radial location, which is controlled by the radial deflection of the flexures 16a, 16b, 16c and 16d which was caused by the force fitting of the scale disc member 4 onto the shaft 6.
[0140] FIG. 24a shows a schematic plan drawing of the same scale disc member 4, after an adjustment bolt 28 (as per FIG. 6) has been inserted into the flexure void 22 of the fourth flexure 16d and tightened such that its tapered head engages front and back contact faces of the void 22 of the flexure 16d (and as described in more detail above in connection with FIGS. 5 and 6). As the adjustment bolt 28 is further rotated to cause it to penetrate further into the threaded hole 32, the tapered head 31 will push against front and back contact faces of the void 22 of the flexure 16d (as schematically illustrated in FIG. 24b) with increasing force, thereby causing the distance between them to increase. In view of that the flexure's 16d foot portion 18 is butted up against the shaft 6, the flexure's foot portion 18 is fixed in place and cannot move. Accordingly, any increase in the distance between the front and back contact faces of the void 22 of the flexure 16d causes the whole annular body 5 to move (in this example in the Y-dimension) as illustrated in FIG. 24a (with the dotted line illustrating the annular body's 5 initial/default location).
[0141] As illustrated in FIG. 24b (and FIG. 25b), similar to the embodiment of FIG. 6, the adjustment bolt 28 is received within a hole 32 in the ledge 7 of the shaft 6. However, in contrast to the embodiment of FIG. 6, the thread of the adjustment bolt 28 engages a threaded portion of the hole 32 only at its end distal the tapered head (as opposed to substantially along its entire length). As illustrated in FIG. 25b, this means that the adjustment bolt 28 is able to tilt (in other words pivot or cant) and/or bend along its length (the dotted line in FIG. 25b illustrating the non-titled arrangement of the adjustment bolt 28). In other words, such a configuration means that the adjustment bolt 28 is more wobbly, or has more play at its tapered head end compared to the configuration shown in FIG. 6. In particular, in the embodiment described, the tapered head of the adjustment bolt 28 is free to move by up to +/200 m from its default/central position. As will be understood, there is little or no axial play, but rather only radial play. Accordingly, in the embodiment of FIGS. 23 to 25 the radial position of the tapered head of the adjustment bolt (with respect to the scale disc member 4) is decoupled from the shaft 6 and ledge 7. This means that the adjustment bolt can tilt with respect to the shaft 6 and ledge 7, thereby enabling its tapered head portion to follow the change in the radial location of the centre point of the flexure void 22 as length L of the flexure 16 (see FIG. 5) is increased. (The radial location of the centre point of the flexure void 22 changes as length L of the flexure 16 is increased because the radial position of the foot portion 18 is fixed due to being pressed against the fixed shaft 6).
[0142] This has been found to be advantageous because it means that increased radial adjustment of the annular body 5 can be achieved. For instance, as shown in FIGS. 25a and 25b, further axial driving of the adjustment bolt 28 will pull the tapered head of the adjustment bolt into the flexure void 22 of the fourth adjustment flexure 16d. If (as per the embodiment of FIG. 6) the radial position of the adjustment bolt 28 were fixed at its point of contact with the adjustment flexure 26d (i.e. at its tapered head), there would need to be substantial mechanical distortion of the foot portion 18 of the flexure 16d and/or of tapered head of the adjustment bolt in order to facilitate such further axial penetration of the adjustment bolt 28.
[0143] In contrast, with the present invention, the tapered head of the adjustment bolt 28 is free to move radially relative to the shaft 6 and ledge 7. Accordingly, rather than causing significant mechanical distortion of the foot portion 18 of the flexure 16d, the adjustment bolt 28 is free to tilt such that the tapered head of the adjustment bolt 28 can radially shift outwardly, which in turn causes it to push the disc body 5 radially outward, providing an even further radial displacement from the initial default radial location (shown by the dotted line in FIG. 25a).
[0144] As will be understood, such a configuration also means that the manufacturing tolerance of the various parts of the assembly need not be so tight, whilst still enabling sufficient range and control of the radial adjustment.
[0145] The above solution relies on the threaded hole 32 having a large, or long, counter-sunk portion, such that the thread of the adjustment bolt 28 engages a threaded portion of the hole 32 only at its end distal the tapered head (as opposed to substantially along its entire length). As will be understood, instead of a large/long counter-sunk portion, the hole 32 could have a uniform diameter, but only be threaded towards its distal/bottom end. In another alternative embodiment, the hole 32 could have a uniform diameter and be threaded along its entire length, but the adjustment bolt 28 could be configured such that it only has a threaded portion towards its end distal its tapered head. Another solution is where the hole 32 has a uniform diameter and is threaded along its entire length, and the adjustment bolt 28 is threaded along its entire length, but where the hole 32 is oversized such that the adjustment bolt 28 is a substantially loose fit so as to enable the tapered head to free displace by up to +/100 m from its default/central position, even when the adjustment bolt 28 is fully engaged in the position shown in FIG. 24b (i.e. with the tapered head engaged with the mounting flexure).
[0146] Another way of radially decoupling the radial adjustment device from the part (e.g. the shaft 6) on which the disc is mounted is to use a deformable member such as a plastic or rubber O-ring between the tapered head of the adjustment bolt 28 and the flexure 16d. In such a case it is not necessary to provide for tilting of the adjustment bolt 28. Another way is to use a radial adjustment device which does not engage the part (e.g. the shaft 6 or ledge 7). For instance, a cam element could be located within the flexure void 22 and its orientation within the flexure void could be manipulated so as control the amount by which it causes the flexure void to expand. However, it has been found that radial adjustment devices in the form of a threaded member having a tapered head, such as the adjustment bolt 28 described above, is advantageous over such cam devices because they can provide for finer control of the radial tweaking.
[0147] The above described embodiments comprise three of more flexures. However, as will be understood, this need not necessarily be the case. For instance, it is possible for the rotary scale member to comprise only one or two flexures, which facilitate adjustment of the lateral/radial position of the annular body of the rotary scale member. For instance, the at least one (or two) flexures could be configured such that the lateral/radial position of the annular body in at least one dimension can be achieved, and for example in two orthogonal dimension. For example, two opposing flexures which both have radial and tangential compliance can provide for adjustment of the lateral/radial position of the annular body in two orthogonal dimensions. In an alternative embodiment, such two opposing flexures could have only radial compliance (or tangential compliance), thereby facilitating lateral/radial adjustment in one dimension. Furthermore, in another embodiment, the rotary scale member could have just one flexure member. For instance, the rotary scale member could comprise a clamp part which is pushed over the shaft (e.g. a tight-fitting ring), and which is attached to the annular body of the rotary scale member via a single flexure which provides at least one of radial and tangential compliance. However, the above described embodiments providing three or more (e.g. pairs of) flexures have been found to be preferred solutions, which provide predictable and repeatable adjustment. Furthermore, solutions involving three or more flexures can be easier to manufacture, and help to maintain the compactness of the flexures and/or rotary scale member.
[0148] In the above described embodiments, the scale disc members are configured such that they require force-fitting onto the shaft, because the diameter of the hole defined by the mounting flexures is slightly smaller than the diameter of the shaft onto which they are mounted. However, as will be understood, the above described features are also useful for apparatus where the scale disc members do not require force-fitting onto the shaft. For example, the wobbly adjustment bolt features described in connection with FIGS. 23 to 25, could be used with apparatus in which the scale disc's hole diameter (e.g. defined by the mounting flexures) is slightly larger than the diameter of the shaft onto which they are mounted. Also, the concept of providing a scale disc member with mounting flexures which have both radial and tangential compliance could also be useful for situations in which the scale disc member is not force-fitted onto the shaft (e.g. in situations in which the diameter of the hole defined by the mounting flexures is slightly larger than the diameter of the shaft onto which they are mounted).
[0149] Furthermore, the concept of providing an adjustment mechanism with a lever-ratio effect can also be useful with apparatus in which the scale disc's hole diameter defined by the mounting flexures is slightly larger than the diameter of the shaft onto which they are mounted.
[0150] FIGS. 26a and 26b illustrate an alternative embodiment. Similar to the other embodiments described above, the scale disc member 1300 of this embodiment comprises a planar, annular body 1302 on which a scale track 1304 is provided on one of its planar faces, and a hole 1306 through its middle through which the cylindrical shaft 6 can extend when the scale disc 1300 is mounted on the cylindrical shaft 6. Similar to the embodiment of FIG. 14, the scale disc member 1300 comprises three pairs of radially compliant cantilevered spring members 1308a, 1308b, 1308c which are provided in plane with the planar scale disc 1300 and spaced equidistantly around the edge of the hole 1306. A flexure void 1310a, 1310b, 1310c is provided directly behind each pair of cantilevered spring members 1308a, 1308b, 1308c.
[0151] Similar to the other above-described embodiments, the flexure pairs 1308 are shaped and sized such that the effective diameter of the hole 1306 is slightly smaller than the diameter of the disc receiving portion of the shaft 6 onto which it is to be mounted. Accordingly, the scale disc member 1300 has to be force-fitted onto the shaft 6, thereby causing the flexures 1308 to deflect into their respective flexure voids 1310. Once the scale disc member 1300 has been force-fitted onto the shaft 6, there is a natural/default/automatic tight fit between them.
[0152] In contrast to the embodiment of FIG. 14, the flexure voids 1310 are not configured to receive an adjustment bolt via which the radial position of the disc can be adjusted. In contrast, the embodiment shown in FIG. 26a is provided with one or more nudge blocks 1320a, 1320b. These are rigid blocks having a threaded hole 1322 extending therethrough and an abutment feature in the form of a lip 1324 having a thickness which is small enough to fit in the gap between the shaft 6 and the inner edge of the hole 1306 of the scale disc member 1300. In order to adjust the position of the scale disc member 1300, a nudge block 1320 is placed such that its lip 1324 is received in the gap between the shaft 6 and the inner edge of the hole 1306 of the scale disc member 1300, and then a grub screw 1326 is inserted in the threaded hole 1322 and tightened via a tool 1328 until it engages the shaft 6. At that point, further tightening of the grub screw 1326 via the tool causes the nudge block to be pushed radially outwardly, resulting in the lip 1324 pushing the scale disc member 1300 radially outwards. As will be understood, in the embodiment shown two nudge blocks 1320a, 1320b are shown in place/in engagement with the scale disc member 1320 and shaft 6. A third nudge block 1320c is shown out of engagement with the scale disc member 1320 and shaft 6 to illustrate the various parts thereof and the grub screw 1326 and tool 1328. It might be that only one nudge block is required to provide the desired radial adjustment. Optionally, three nudge blocks could be used if desired.
[0153] FIG. 27 shows another embodiment. The scale disc member 1400 of this embodiment has features similar to those of the above-described embodiment in that it has a planar body 1402 on which a scale track 1404 can be provided on one of its faces. In contrast to the above-described embodiments, the flexures 1406a, 1406b, 1406c are provided on the outer edge 1410 of the planar body, i.e., are provided radially outward of the scale track 1404. Also, in contrast to the above-described embodiments, the planar body 1402 has does not have a central hole extending therethrough, although this need not necessarily be the case.
[0154] In this embodiment, the encoder scale disc comprises three flexures arrangements 1406a, 1406b, 1406c, which are used to locate and maintain the encoder scale disc 1000 in a part 2000. As can be seen the part 2000 comprises three mounting spaces 2010 which correspond to the three flexures 1406 of the scale disc member1400.
[0155] In this embodiment the flexure arrangements 1406 have a first member 1420 and a second member 1430 arranged such that when located within a space 2010 of the part 2000 the first member 1420 exerts a force substantially tangential to an outer edge 1410 of the scale disc member 1400 on the part 2000 (e.g. in the direction of arrow C) and the second part 1430 exerts a force on the part 2000 having both tangential and radial components relative to the outer edge 1410 of the scale disc member 1400 (e.g. in the direction of arrow D). The first 1420 and second 1430 parts of the flexures 1406 are shaped and sized such that they are a tight fit within the space 2010 of the part 2000 in which they are received, thereby requiring the scale disc member 1400 and part 2000 to be force fitted together so as to form a friction fit between the scale disc member 1400 and the part 2000 such that the planar body 1402 self-locates at an initial default radial location with respect to the part. The radial location of the planar body 1402 can be altered in line with the above-described embodiments, for instance via the use of the nudge blocks 1320 described above in connection with FIG. 26, the lip 1324 of which could be inserted in the gap 1440 between the part 2000 and the outer edge 1410 of the planar body 1404 of the scale disc member 1400.
