Method for replacing a rack in a rack and pinion drive and jig assembly

Abstract

A method for replacing a rack in a rack and pinion drive includes providing a rack and pinion drive having a first rack (10) installed in meshing engagement with a pinion of a gearbox (20), providing a jig assembly including a second toothed rack (31) and a coupling device (40, 50, 60), positioning the second rack in longitudinal coaxial alignment with the first rack, connecting a first end (32a) of the second rack to a proximal end (11b) of the first rack by the coupling device, and linearly displacing the first and second racks to bring the second rack into meshing engagement with the pinion of the gearbox. A nominal rotational position between the respective pinion and the primary gear (23) can be calibrated when the first rack or the second rack is in meshing engagement with the pinion of the gearbox.

Description

[Technical field]

[0001] The present disclosure relates to the field of rack and pinion drives. In particular, the present disclosure relates to a method for replacing a rack in such a drive, and a jig assembly for use in performing the method. The method and jig assembly may be used, for example, in the assembly, calibration, transportation, installation, commissioning, repair and maintenance of rack and pinion drives. [Background technology]

[0002] Rack and pinion drives are often used to convert rotary motion into linear motion and / or vice versa. Such rack and pinion drives may be used, for example, in linear actuators and lift devices, where the rotary motion of a motor is converted into linear actuation or lifting motion. Another exemplary application is energy harvesting, such as wave energy harvesting, where the reciprocating linear motion of a buoy or the like is converted into rotational motion of an output shaft by a rack and pinion drive.

[0003] In applications where large forces and / or torques are transformed, the rack and pinion drive preferably comprises several pinions meshing with one and the same rack. The torque to be transmitted can be divided by this means between several pinions and a corresponding number of gears fixed to each pinion. As a result, the load on each torque transmission tooth flank can be reduced. Such rack and pinion drives comprising several pinions are over-constrained. Such over-constraint can cause problems related to the tooth flanks of different pinions and gears being simultaneously subjected to different loads in the load transmission engagement. To overcome these problems, it has been proposed to introduce a certain rotational flexibility or compliance between each pinion and its corresponding gear.

[0004] US Patent No. 5,399,633 discloses a rack and pinion drive comprising a toothed rack and a gearbox including a plurality of pinions meshing with the rack. Each pinion is fixed to a respective primary gear. The primary gears are mechanically connected to a common input or output shaft of the gearbox. To improve load distribution to all tooth flanks in simultaneous engagement, each pinion is fixed to the respective primary gear by a respective elastically deformable fixing device that allows limited relative rotation between the respective pinion and the primary gear.

[0005] In such rack and multiple pinion drives, where a means for rotational compliance between the pinions and their respective primary gears is provided, it is important that the relative nominal rotational position between each pinion and the primary gear be accurately adjusted or calibrated. In addition, any pretensioning of the elastically deformable devices that provide rotational compliance needs to be accurately adjusted or calibrated for each pair of pinion and primary gear, and for each other pair of pinion and primary gear.

[0006] Such adjustment or calibration must be performed prior to or during commissioning of the device, with the rack placed in engagement with the pinion. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] European Patent Publication No. 2921694 Summary of the Invention [Problem to be solved by the invention]

[0008] However, in many applications, the rack has a significant length relative to the gearbox. In addition, the rack often needs to be strong and durable, which results in the rack being heavy. In high-precision applications, the straightness of the rack, as well as the geometry and surface finish of the teeth, need to be kept within narrow tolerances. Therefore, the assembly and adjustment or calibration, as well as other handling of such rack-and-pinion drives with long and heavy racks, is often tedious and often involves a significant risk of rack damage.

[0009] Further problems are caused by the fact that the rack must be maintained in meshing contact with the pinion after adjustment or calibration until commissioning to avoid losing calibration, making it difficult and cumbersome to transport the racked equipment from the assembly site to the site of use, especially in applications requiring long and heavy racks.

[0010] It is an object of the present disclosure to provide a method for replacing a rack in a rack and pinion drive and a jig assembly that facilitates assembly, calibration, testing, transportation, installation, and / or commissioning of a rack and pinion drive with a means for rotational compliance between the pinion and primary gear pair.

[0011] Another object is to provide such a method which is easy to implement. A further object is to provide such a jig assembly which is simple in design. [Means for solving the problem]

[0012] In general, all terms used in the claims should be interpreted according to their ordinary meaning in the art, unless expressly defined otherwise herein. All references to "a / an / the element, apparatus, component, means, step, etc." should be openly interpreted as referring to at least one example of the element, apparatus, component, means, step, etc., unless expressly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless expressly stated otherwise.

[0013] According to a first aspect, the present disclosure provides a method of replacing a rack in a rack and pinion drive comprising a gearbox comprising a first toothed rack and a number of pinions arranged to mesh with the first rack. The pinions are connected to respective primary gears by rotational compliance devices. The method is defined in the accompanying claim 1, comprising: providing a rack and pinion drive having a first rack mounted in meshing engagement with a pinion of a gearbox; providing a jig assembly including a second toothed rack and a coupling device; placing a second rack in longitudinal coaxial alignment with the first rack; connecting a first end of a second rack to a proximal end of the first rack with a coupling device; linearly displacing the first rack and the second rack to meshing engagement with a pinion of the gearbox; and separating the first rack from the second rack. Calibrating a nominal rotational position between each pinion and the primary gear when the first rack or the second rack is in meshing engagement with a pinion of the gearbox.

[0014] The first rack may thus constitute a "utility rack", which in the following refers to a rack intended to be installed in the gearbox and to engage the pinion during normal operation of the rack and pinion drive, and the second rack may constitute an "auxiliary rack", which in the following refers to a rack intended to be used temporarily as a replacement for the utility rack, for example during assembly, calibration, testing, transportation and / or commissioning of the rack and pinion drive.

[0015] The term "jig assembly" is used herein to refer to an assemblage of components arranged to be aligned with a further component that does not form part of the jig assembly to position, guide, and / or hold one of the components. More specifically, a "jig assembly" as described herein comprises a second or auxiliary rack and a coupling device arranged to releasably connect and align the second or auxiliary rack with a first or utility rack that does not form part of the jig assembly.

[0016] The method allows the auxiliary rack to be easily fixed as a longitudinal extension to the utility rack of the rack and pinion drive. By this means the utility rack can be used during assembly and calibration of the rack and pinion drive. Using the utility rack in tooth engagement with the pinion during calibration ensures that the nominal relative rotational position between each pinion and the primary gear, as well as the pretension of any elastic compliance members, are accurately adjusted to the actual tooth geometry of the utility rack. Once calibration is achieved, the utility rack and the auxiliary rack fixed to the end of the utility rack may be linearly displaced until the pinion of the gearbox is in tooth engagement with the auxiliary rack. The utility rack can then be separated from the auxiliary rack. As long as the auxiliary rack has approximately the same tooth geometry as the utility rack, the nominal relative rotational position as well as the pretension achieved during calibration will be maintained after replacing the utility rack with the auxiliary rack in the gearbox.

[0017] The rack and pinion drive may then be transported with the utility rack decoupled from the gearbox with the auxiliary rack. This provides an important advantage since the utility rack in many applications can be very long relative to the length of the gearbox. Transport and other handling of the rack and pinion drive with the utility rack installed poses a significant risk of damaging the utility rack and / or the gearbox due to the elongated configuration of such a long and heavy utility rack. This problem is effectively eliminated or reduced by a method that allows the long and heavy utility rack to be transported and handled decoupled from the gearbox until the rack and pinion drive is finally commissioned at the site of use. The auxiliary rack, which is kept in tooth engagement with the pinion during such transport and handling, ensures that the calibration of the gearbox is maintained during transport and handling.

[0018] After transportation to the site of use, the method allows the utility rack to be easily secured as an extension to the auxiliary rack. The utility rack can then be engaged with the pinion in the gearbox without risk of losing the calibration previously achieved. Once the utility rack is finally installed, the auxiliary rack may be decoupled and removed from the utility rack. The auxiliary rack can then be used in other rack and pinion drives as well.

[0019] It is also possible to use an auxiliary rack that engages the pinion during calibration and testing of the gearbox if the auxiliary rack has the same tooth geometry as the utility rack. In such cases, the auxiliary rack may be kept engaged with the pinion until final assembly or commissioning of the rack-and-pinion drive. The auxiliary rack is replaced by the utility rack by fixing the utility rack as an extension to the utility rack and linearly displacing the rack so connected until the utility rack engages the pinion.

[0020] The method may also be used for maintenance and repair of rack-and-pinion drives where the utility rack needs to be temporarily removed or replaced. In such cases, the auxiliary rack is secured to the existing utility rack and then linearly displaced until the pinion engages the auxiliary rack. The existing utility rack is then disconnected from the auxiliary rack for repair and then reconnected to the auxiliary rack so that it reengages with the pinion by linear displacement. Alternatively, after disconnecting the existing utility rack, a replacement utility rack may be connected to the auxiliary rack and engaged with the pinion.

[0021] Thus, the method provides a simple and efficient means for calibrating the pinion and primary gear of a rack and pinion drive and / or maintaining the calibration of the pinion and primary gear of a rack and pinion drive during assembly, testing, transportation, commissioning, repair, and maintenance.

[0022] According to one embodiment, the method includes placing at least one toothed surface of the second rack in flush alignment with a corresponding toothed surface of the first rack. The method may include inserting at least one spacing member between the first end of the second rack and the proximal end of the first rack to adjust a pitch between an outermost tooth at the first end and an outermost tooth at the proximal end.

[0023] The connecting means may comprise a rod extending longitudinally within a bore through the second rack, and the method may comprise connecting the rod to the proximal end and pulling the rod longitudinally to urge the first end toward the proximal end.

[0024] The step of bringing the second rack into meshing engagement with the pinion of the gearbox by linear displacement of the first rack and the second rack may be accomplished by rotating an in- / or output shaft of the gearbox.

[0025] According to a second aspect, there is provided a jig assembly as claimed in claim 6 attached hereto. The jig assembly is intended for use in replacing a rack of a rack and pinion drive. The apparatus comprises a gearbox comprising a first toothed rack and a number of pinions arranged to mesh with the first rack. The jig assembly comprises a second toothed rack extending from a first end to a second end and a coupling device for releasably connecting the first end of the second rack to a proximal end of the first rack. The coupling device comprises guide means arranged to hold the second rack in longitudinal coaxial alignment with the first rack, a rod extending through a longitudinal bore in the second rack and having a first rod end connectable to the proximal end of the first rack, and a tensioning device connectable to the rod and arranged to engage the second rack, thereby tensioning the rod to urge the first end towards the proximal end.

[0026] The jig assembly provides an efficient means for carrying out the method according to the first aspect. The jig assembly may include at least one spacing member arranged to be interposed between the first end of the second rack and the proximal end of the first rack when the second rack is connected to the first rack. The spacing member may include a shim or similar device. Such a spacing member or multiple spacing members may be interposed between the second rack and the first rack to maintain the correct tooth geometry at the transition between the utility rack and the auxiliary rack. In particular, such a spacing member or multiple spacing members may be used to adjust the pitch between the outermost teeth at the first end and the outermost teeth at the proximal end.

[0027] The guide means may comprise a bushing arranged for radially guided reception within the bore at the first end and for connecting the rod to the proximal end. The bushing may include a first portion that is received in the bore with an intermediate fit, a clearance fit, or an interference fit.

[0028] The bushing may include male or female threads arranged to mesh with corresponding threads arranged on the proximal end of the first rack. This allows for a simple and reliable design of the jig assembly and allows the first and second racks to be connected to each other by a simple action.

[0029] The bushing may include an externally threaded portion projecting longitudinally from the first end of the second rack. The tension adjustment device may include a first threaded joint.

[0030] The first threaded joint may include male threads disposed on the second rod end of the rod and a stop member having corresponding female threads and a stop surface disposed for support by an end surface disposed on the second end of the second rack.

[0031] The jig assembly may further comprise at least one annular support member received within the bore and positioned to support and receive said rod. The rod may be securable to the bushing by a second threaded joint.

[0032] The jig assembly provides the same advantages as discussed above. Further objects and advantages will become apparent from the following description of illustrative embodiments and the appended claims.

[0033] Aspects and embodiments will now be described, by way of example only, with reference to the accompanying drawings, in which: [Brief description of the drawings]

[0034] [Figure 1] FIG. 2 is a partially exploded perspective view of a rack and pinion drive with a jig assembly according to one embodiment when secured to a utility rack of the rack and pinion drive; [Diagram 2]FIG. 2 is a partially exploded perspective view showing a portion of the jig assembly and utility rack shown in FIG. 1. [Diagram 3] 2 is an enlarged longitudinal cross-sectional view of a portion of the rack and pinion drive having the jig assembly shown in FIG. 1; FIG. [Figure 4] FIG. 4 is an enlarged longitudinal cross-sectional view of a portion of the device shown in FIG. 3. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] Aspects of the present disclosure are described more fully hereinafter with reference to the accompanying drawings, in which specific embodiments of the invention are shown. However, these aspects may be embodied in many different forms and should not be construed as limiting. Rather, these embodiments are provided as examples so that this disclosure will be thorough and complete, and will fully convey the scope of all aspects of the invention to those skilled in the art. Like numbers refer to like elements throughout the description.

[0036] 1 to 4 show a rack and pinion drive provided with a jig assembly 30 according to a first embodiment. The rack and pinion drive comprises a first rack in the form of a utility rack 10 and a gearbox 20.

[0037] The utility rack 10 extends longitudinally from a first end 11a to a second end 11b, which forms the proximal end when using a jig assembly, as described in more detail below. The utility rack 10 has a first flat toothed surface 12a and a second flat toothed surface 12b disposed opposite the first toothed surface. The first toothed surface 12a and the second toothed surface 12b extend substantially the entire length of the utility rack 10a. In particular, both toothed surfaces 12a, 12b extend all the way to the second proximal end 11b. The toothed surfaces 12a, 12b are connected by a curved circumferential surface of the rack 10 such that the utility rack presents an oval-like cross section.

[0038] The illustrated utility rack 10 is shorter than utility racks would normally have in many applications for visibility reasons. Typically the utility rack may be up to 10m long. The utility rack may be made from different materials, one example is machined cast steel. For strength and durability reasons the utility rack is typically made solid with no cavities, bores or the like. Typically the weight of a 10m long utility rack may be up to 1000kg.

[0039] The gearbox 20 comprises a housing 21 having a longitudinal channel 22 for receiving a portion of the utility rack 10. In the illustrated example, the gearbox comprises eight pinions (not shown) arranged in the housing 21 such that each pinion can mesh with one of the toothed surfaces 12a, 12b of the utility rack 10. Here, four pinions mesh with each of the toothed surfaces 12a, 12b. Each pinion is connected to a respective primary gear 23 by a shaft 24 and a rotational compliance device 25. The primary gears 23 are arranged such that two primary gears 23 connected to respective pinions meshing with the first toothed flank 12a and two primary gears 23 connected to respective pinions meshing with the second toothed flank 12b together mesh with one and the same secondary gear (not shown). Thus, the gearbox 20 comprises two secondary gears. Each secondary gear is further connected to a tertiary gear 26 by a respective shaft 27. The two tertiary gears 6 mesh with a common fourth gear (not shown). The fourth gear is connected to a single output or input shaft (not shown) of a rack and pinion drive. In the illustrated example, the device may be used as a linear actuator or lift device, and the fourth gear is connected to an input shaft (not shown), which is connected to an electric motor (not shown).

[0040] To improve load distribution between the tooth flanks of the pinions and gears which are simultaneously engaged during torque transmission, the gearbox 20 comprises means for providing rotational compliance. In the illustrated example, this is achieved by connecting each pinion to a respective primary gear 23 by a rotational compliance device 25. Each compliance device is fixed to a respective shaft 24 and primary gear 23. Each compliance device 25 further comprises an elastically deformable fixing device (not shown) which allows limited relative rotation between the primary gear 23 and the pinion.

[0041] A known rack and pinion drive comprising several compliance devices as mentioned above is disclosed in EP 22921694 and will not be described in further detail here.

[0042] The jig assembly 30 comprises a second rack forming an auxiliary rack 31a. The auxiliary rack 31 extends longitudinally from a first end 32a to a second end 32b. The first end 32b is intended to face the proximal end 11b of the utility rack 10 when the jig assembly 30 is in use. The auxiliary rack 31 has a first flat toothed surface 33a and a second flat toothed surface 33b arranged opposite the first toothed surface 33a. The first toothed surface 33a and the second toothed surface 33b extend substantially over the entire length of the utility rack 10. In particular, the toothed surfaces 33a, 33b both extend over the first end 32a. The toothed surfaces 33a, 33b are connected by a curved circumferential surface of the auxiliary rack 31, which causes the utility rack 31 to present an ellipse-like cross-section similar to the cross-sectional geometry of the utility rack 10.

[0043] The tooth geometry of the first toothed surface 33a and the second toothed surface 33b are similar to the tooth geometry of the utility rack 10. In applications where the jig assembly 30 meshes with the pinion in the gearbox 20 during calibration of the rack and pinion device, it is important that the tooth geometry of the auxiliary rack is approximately identical to the tooth geometry of the utility rack used in normal operation. If the utility rack used during normal operation is also used for calibration, as well as if the auxiliary rack is used, for example, during transportation of the rack and pinion device, it may be sufficient for the tooth geometry of the auxiliary rack to be generally similar to the tooth geometry of the utility rack. Also, in such cases, the auxiliary rack that meshes with the pinion during transportation can maintain the nominal relative rotation between the pinion and the primary gear, as well as the pretension of the elastically deformable compliant member achieved by calibration.

[0044] Typically, the auxiliary rack 31 may be significantly shorter than the utility rack 10. In general, the auxiliary rack 31 may be slightly longer than the longitudinal length of the gearbox 20. Furthermore, because the auxiliary rack is not intended to be exposed to significant loads that may occur during normal operation, the auxiliary rack may be formed from weaker, less durable, and therefore lighter and less expensive materials with lower performance than the utility rack.

[0045] The auxiliary rack 31 has a central bore 34 extending from the first end 32a to the second end 32b of the auxiliary rack 31. The central bore 34 has a central portion 34a having a first diameter and two end portions 34b disposed at each end 32a, 32b of the auxiliary rack 31. The end portions 34b have a diameter slightly larger than the diameter of the central portion 34a such that an outwardly facing annular stop surface 34c is formed adjacent each end 32a, 32b of the auxiliary rack 31.

[0046] The jig assembly 30 further comprises a coupling device for connecting the auxiliary rack 31 to the utility rack 10. In the illustrated example, the coupling device comprises guide means comprising a bushing 40. The coupling device further comprises a rod 50 and a tensioning device 60.

[0047] The bushing 40 has a first cylindrical portion 41 that is received with a close fit in the end portion 34b of the bore located at the first end 32a of the auxiliary rack 31. The first cylindrical portion 41 has a central female threaded recess 41a facing the second end 32b of the auxiliary rack 31. A second cylindrical portion 42 having a smaller diameter extends axially from the first cylindrical portion 41 and is received with a close fit in a cylindrical recess 13 located at the proximal end 11b of the utility rack 10. A third cylindrical portion 43 having an external thread extends axially from the free end of the second cylindrical portion 42 and is screwed into a female threaded recess 14 that extends axially from the bottom of the cylindrical recess 13 of the utility rack 10.

[0048] The rod 50 is received in the bore 34 and has a first rod end 51a arranged adjacent to the first end 32a of the auxiliary rack 31 and a second rod end 51b extending through the second end 32b of the auxiliary rack 31. The first rod end 51a has an axial internally threaded recess 52 and the second rod end 51b has an external thread. The rod 50 is connected to the bush 40 by a threaded joint. More precisely, in the illustrated example, the first rod end 51a is connected to the bush 40 by an externally threaded fastening member 55 which is screwed into the recess 41a of the bush and into the recess 52 of the first rod end 51a.

[0049] The tensioning device 60 also comprises a threaded joint. In the example shown, the tensioning device 60 comprises a stop member 61 in the form of an internally threaded nut which engages with the external thread of the second rod end 51b. The stop member 61 is axially supported by an end face of the second end 32b of the auxiliary rack 30. In the example shown, a washer 62 is arranged between the stop member 61 and said end face. Two additional nuts 63, 64 are threaded onto the threaded second rod end 51 and are interconnected so that the rod 50 can be rotated by a wrench or similar tool engaging one or both of the additional nuts 63, 64.

[0050] In the illustrated example, the jig assembly further comprises an alignment collar 70 that can be used to align the flat toothed surfaces 33a, 33b of the auxiliary rack 31 with the toothed flat surfaces 12a, 12b of the utility rack during fastening of the auxiliary rack 31 to the utility rack 10. The alignment collar comprises an upper half 71 and a lower half 72. Each half has a respective internal flat toothed surface 71a, 72a. The upper half 71 and the lower half 72 may be fastened to one another by fastening means, not shown, such as screws.

[0051] When replacing the utility rack 10, which is installed in engagement with the pinion of the rack-and-pinion drive by the auxiliary rack, the utility rack 10 is first linearly displaced so that the proximal end 11b protrudes accessible from the gearbox 20. The second cylindrical portion 43 of the bushing 40 is then screwed into the threaded recess 14 of the proximal end 11b of the utility rack 10. The bushing 40 is thereby fixed to the utility rack 10 in such a way that its first cylindrical portion 41 extends axially from the proximal end 11b. The first end 32a of the auxiliary rack 31 is then placed opposite the proximal end 11b of the auxiliary rack 10, thereby longitudinally aligning and rotationally oriented the auxiliary racks 31, 10 such that each flat toothed surface 33a, 33b of the auxiliary rack 31 is flush with the corresponding toothed surface 12a, 12b of the utility rack 10. To facilitate this operation, the inner flat toothed surfaces 71 a, 72 a of the alignment collar 70 may be engaged with the first toothed surfaces 12 a, 33 a and second toothed surfaces 12 b, 33 b of the utility and auxiliary racks, respectively. The two alignment collar halves 71, 72 may then be fastened together.

[0052] When the auxiliary rack 31 is so positioned relative to the utility rack 10 , the first cylindrical portion 41 of the bushing 40 is received within the end portion 34 b of the bore 34 . Thereafter or before, the rod 50 may be prepared by threading a fastening member 55 into the recess 52 of the first rod end 51a. The rod 50 may then be inserted into the bore 34 from the second end 32b of the auxiliary rack, while being linearly displaced until the first rod end 51a reaches the bush 40. To facilitate this insertion, an annular spacing member 57 for receiving the rod 50 may first be inserted into the bore 34. In the example shown, two such spacing members 57 are inserted with a tight fit into the bore 34, one at each transition from the central bore portion 34a to the respective end portion 34b of the bore 34. By this means, each spacing member 57 is supported radially and in the respective axial direction.

[0053] The rod 50 may then be fixed to the bushing 40 by rotating the rod so that the free end of the fastening member 55 threads into the threaded recess 41a of the first cylindrical portion 41 of the bushing 40. Once the rod 50 is firmly fixed to the bushing 40, the rod 50 may be axially tensioned by tightening the stop member 61 so that the washer 62 is clamped between the stop member 61 and the end face of the second end 32b of the auxiliary rod 31. Such tension on the rod 50 brings the first end 32a of the auxiliary rack into contact with the end face of the proximal end of the utility rack 10. At the same time, the auxiliary rack 31 is radially fixed to the utility rack 10 by the bushing 40 which is threadably fixed to the utility rack and received in the bore 34 of the auxiliary rack with an interference fit. By this means, the auxiliary rack 31 is rigidly and securely fixed to the utility rack 10, so that the alignment collar 70 can be removed.

[0054] After the utility rack 10 and the auxiliary rack 31 are so secured, they may be linearly displaced together until the utility rack is removed from the gearbox housing 21 and the auxiliary rack 31 is in meshing engagement with the pinion of the gearbox 20.

[0055] The utility rack 10 may then be separated from the auxiliary rack by rotating the rod 50 such that the locking members 55 disengage from the bushings 40. This allows for removal of the utility rack 10. The bushings 40 may then be unscrewed from the proximal end 11b of the utility rack 10.

[0056] As shown in FIG. 4, the jig assembly may further comprise one or more shims 58 that may be inserted between the end face of the proximal end 11b of the utility rack 10 and the end face of the first end 32a of the auxiliary rack 31. Such shims 58 may be used to ensure correct tooth geometry, and in particular correct tooth pitch, at the junction between the utility rack 10 and the auxiliary rack 31. Any suitable number of shims may be inserted depending on the tolerances of the machined surfaces of the utility rack and auxiliary rack as well as the bushing 40 to achieve the correct distance between adjacent teeth at the junction between the two racks 10, 31.

[0057] Aspects of the present disclosure have been described above primarily with reference to certain embodiments and examples thereof. However, as will be readily appreciated by those skilled in the art, other embodiments than those disclosed above are equally possible within the scope of the present disclosure as defined by the appended claims. For example, the threaded joints described above may be reversed, such that the female threads are replaced by male threads and vice versa. Furthermore, other fastening means other than threaded joints, such as bayonet couplings, may be used where applicable. Of course, the rack and pinion drive may be configured in many other ways than those shown and disclosed above. The gearbox may comprise any suitable number of pinions, such as, for example, 2, 4, 6, 10 or 12, and a corresponding number of primary gears. The methods and jig assemblies disclosed herein may find advantageous application in many different such rack and pinion drives, particularly when they are overconstrained and comprise a means for achieving rotational compliance between the pinions and the corresponding primary gears.

Claims

1. A method of replacing a rack in a rack and pinion drive, the rack and pinion drive comprising a gearbox (20) having a first toothed rack (10) and a number of pinions arranged to mesh with the first rack (10), the pinions being connected to respective primary gears (23) by rotational compliance devices (25), the method comprising: providing a rack and pinion drive having a first rack (10) mounted in meshing engagement with the pinion of the gearbox (20); Providing a jig assembly (30) comprising a second toothed rack (31) and a coupling device (40, 50, 60); Positioning the second rack (31) in longitudinal coaxial alignment with the first rack (10); connecting a first end (32a) of the second rack (31) to a proximal end (11b) of the first rack (10) by means of the coupling device (40, 50, 60); a linear displacement of the first rack (10) and the second rack (31) causing the second rack (31) to meshingly engage with the pinion of the gearbox (20); and separating the first rack (10) from the second rack (31), the method further comprising: calibrating a nominal rotational position between each pinion and the primary gear (23) when the first rack (10) or the second rack (31) is in meshing engagement with the pinion of the gearbox (20).

2. 2. The method of claim 1, comprising arranging at least one toothed surface (33a, 33b) of the second rack (31) in flush alignment with a corresponding toothed surface (12a, 12b) of the first rack (10).

3. 3. The method according to claim 1 or 2, comprising inserting at least one spacing member (58) between the first end (32a) of the second rack (31) and the proximal end (11b) of the first rack (10) to adjust the pitch between the outermost teeth at the first end (32a) and the outermost teeth at the proximal end (11b).

4. 4. The method according to claim 1, wherein the connecting means comprises a rod (50) extending longitudinally within a bore (34) passing through the second rack (31), the method comprising connecting the rod (50) to the proximal end (11b) and longitudinally pulling the rod (50) to urge the first end (32a) towards the proximal end (11b).

5. The method according to any one of claims 1 to 4, wherein the linear displacement of the first rack (10) and the second rack (31) into meshing engagement with the pinion of the gearbox (20) is achieved by rotating an input shaft or an output shaft of the gearbox (20).

6. 1. A jig assembly (30) for use in replacing a rack of a rack and pinion drive, the rack and pinion drive comprising a gearbox (20) including a first toothed rack (10) and a plurality of pinions arranged to mesh with the first rack (10), the pinions being connected to respective primary gears (23) by rotational compliance devices (25), the jig assembly (30) comprising: a second toothed rack (31) disposed to mesh with the pinion of the gearbox and extending from a first end (32a) to a second end (32b); a coupling device (40, 50, 60) for releasably connecting the first end (32a) of the second rack (31) to the proximal end (11b) of the first rack (10), guide means arranged to hold said second rack (31) in longitudinal coaxial alignment with said first rack (10); a rod (50) extending through a longitudinal bore (34) in the second rack (31) and having a first rod end (51 a) connectable to the proximal end (11 b) of the first rack (10); a tensioning device (60) connectable to the rod (50) and arranged to engage the second rack (31) thereby tensioning the rod (50) to urge the first end (32a) towards the proximal end (11b); A jig assembly (30).

7. 7. The jig assembly of claim 6, further comprising at least one spacing member (58) disposed to be interposed between the first end (32a) of the second rack (31) and the proximal end (11b) of the first rack (10) when the second rack (10) is connected to the first rack (31).

8. 7. The jig assembly of claim 6, wherein the guide means comprises a bush (40) arranged to be radially guided and received in the bore (34) at the first end (32a) and to connect the rod (50) to the proximal end (11b).

9. The jig assembly of claim 6, wherein the bushing (40) comprises a first portion (41) received within the bore (34) with an intermediate, clearance or interference fit.

10. 10. The jig assembly according to claim 8 or 9, wherein the bush (40) comprises male or female threads arranged to threadably mate with corresponding threads arranged on the proximal end (11b) of the first rack (10).

11. 11. The jig assembly of claim 10, wherein the bushing (40) comprises an externally threaded portion (43) projecting longitudinally from the first end (32a) of the second rack (31).

12. The jig assembly of any one of claims 6 to 11, wherein the tension adjustment device (60) comprises a first threaded joint.

13. 13. The jig assembly of claim 12, wherein the first threaded joint comprises a male thread disposed on a second rod end (51b) of the rod (50) and a stop member (61) having a corresponding female thread and a stop surface arranged to be supported by an end surface disposed on the second end (32b) of the second rack (31).

14. The jig assembly of any one of the preceding claims, further comprising at least one annular support member (57) received within said bore (34) and arranged to support and receive said rod (50).

15. A jig assembly according to any one of the preceding claims, wherein the rod (50) is securable to the bush (40) by a second threaded joint.

16. A rack and pinion drive comprising a gearbox (20) comprising a first toothed rack (10) and a plurality of pinions arranged to mesh with the first rack (10), the pinions being connected to respective primary gears (23) by rotational compliance devices (25), the rack and pinion drive further comprising a jig assembly according to any one of claims 6 to 15.

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