WO2020193946A1

WO2020193946A1 - Metrological apparatus and method of manufacture

Info

Publication number: WO2020193946A1
Application number: PCT/GB2020/050668
Authority: WO
Inventors: Jonathan HACKETT
Original assignee: Taylor Hobson Limited
Priority date: 2019-03-22
Filing date: 2020-03-16
Publication date: 2020-10-01
Also published as: GB201903975D0; GB2582375B; CN113795724A; GB2582375A

Abstract

Metrological apparatus and method of manufacture A carriage assembly for a metrology apparatus is described herein. The carriage assembly is configured to support a measurement probe. The carriage assembly comprises an aperture configured to receive a datum rail having a longitudinal axis, and configured to allow the datum rail to slide therethrough, and a channel configured to receive a guide rail having a longitudinal axis, and configured to allow the guide rail to slide therethrough, wherein the guide rail is parallel to the datum rail. At least one of the aperture and the channel comprise a biasing means integrally formed with the carriage assembly for inhibiting movement of the carriage assembly with respect to the corresponding datum rail or guide rail in a direction other than along the corresponding longitudinal axis of the datum rail or guide rail.

Description

Metrological apparatus and method of manufacture

Field of Invention

The present invention relates to a carriage assembly for a metrological apparatus, a metrological apparatus including the carriage assembly, and a method of manufacturing the carriage assembly.

Background

Some types of metrological apparatus such as surface measurement instruments comprise a measurement probe which is used to follow the surface of a workpiece and a transducer which provides a signal dependent upon the movement of the measurement probe in response to surface characteristics such as texture or form. To follow the surface of a workpiece it is necessary for the metrological apparatus to be constructed in a manner to minimise systematic or random errors.

The Surtronic® S-100 Series Surface Roughness Tester is an example of a metrological apparatus configured to perform surface measurements of a workpiece. The S100 comprises a measurement probe mounted on a carriage assembly that slides along a datum rail and a guide rail. The carriage assembly is manufactured from several components (see Figures 1 and 2, and description below), and these components are arranged precisely to join together effectively.

The arrangement of these components and the manufacture the carriage assembly of the Surtronic® S-100 in this manner is time consuming and complicated, in particular because components such as bushes that surround the datum rail need to be carefully aligned so that the carriage assembly can smoothly slide along the datum rail. Moreover if any error is made during the manufacturing process this may result in metrological measurements having a systematic error. The problems with the prior art are therefore the time, complexity, and difficulty associated with assembling the carriage assembly. Embodiments of the present disclosure may seek to mitigate these problems.

Summary of Invention Aspects of the invention are as set out in the appended clams. Optional features are set out in the dependent claims.

In the present case, the inventors have surprisingly realised that despite the various different parts of the carriage assembly being very functionally different (and sometimes contradictory - for example providing rigid support vs providing a biasing force) they can all be made as one piece and still perform contradictory functions. For example, the structure of the carriage assembly needs to be rigid to support a measurement probe, to constrain rotation of the carriage assembly against the guide rail, and to obtain a straight traverse along the datum rail to perform accurate metrological measurements, but also flexible to accommodate, for example, the guide and/or datum rails.

According to a first aspect of the disclosure, there is provided a carriage assembly for a metrology apparatus, the carriage assembly configured to support a measurement probe for performing surface measurements of a workpiece. The carriage assembly comprises an aperture configured to receive a datum rail and to allow the datum rail to slide therethrough, and a channel configured to receive a guide rail and to allow the guide rail to slide therethrough, wherein the guide rail is parallel to the datum rail. At least one of the aperture and the channel comprises a biasing means integrally formed with the carriage assembly. Optionally the biasing means may be configured to inhibit movement of the carriage assembly with respect to the corresponding datum rail or guide rail, for example in a direction, or in some examples in all directions, other than a direction along the corresponding longitudinal axis of the datum rail or guide rail.

Because the carriage assembly 310, in use, supports a measurement probe 350, it needs to be relatively stiff. The unitary construction of the carriage assembly 310 of examples of the disclosure provide a further benefit as they enable the design to have the required stiffness such that the carriage assembly 310 is relatively inflexible.

Furthermore, by integrally forming the running surfaces (i.e. the internal surfaces of the channel and the aperture) into the carriage assembly, they are inherently aligned and this therefore removes the requirement for settling and subsequent gluing.

Optionally, the carriage assembly, including the biasing means, may be formed of a single unitary piece. Further optionally the aperture, channel and/or biasing means may be formed of the same material. Optionally, the material may be polyether ether ketone (PEEK), optionally reinforced by carbon fibres, and/or optionally further comprising polytetrafluoroethylene (PTFE).

In some examples the aperture comprises a first biasing means configured to inhibit rotation of the carriage assembly about an axis transverse to the longitudinal axis of the datum rail, so that the datum rail is secured by, but is configured to slide within, the aperture.

The carriage assembly has a horizontal axis that passes through both the aperture and the channel. In some examples the channel comprises a second biasing means configured to bias the guide rail in the channel. At least a component of the biasing from the second biasing means of the channel may be in a direction transverse to the horizontal axis, and transverse to the longitudinal axis of the guide rail. The channel of the carriage assembly may further comprise a guide pad opposing the second biasing means. Both the guide pad and the second biasing means may be integrally formed with the carriage assembly. The guide pad and the second biasing means may be configured, in use, to be in contact with the guide rail and to permit the guide rail to slide therebetween. Optionally the guide pad may be shaped to allow the carriage assembly to move along the guide rail and to reduce friction between the guide pad and the guide rail. For example, the guide pad may be configured to contact the guide rail with an at least partly rounded surface. The guide pad may be long enough to be stiff and stable, but also short enough that it is effectively a point contact and therefore only constraining the carriage’s rotation around the datum rail and not influencing the straightness of the traverse. To this end, the fixed/rigid side of the guide pad contacts the guide rail with a cylindrical surface, whose axis crosses the guide rail axis, therefore creating a single point of contact. The contact surfaces of the second biasing means may be rounded, so that as the frictional drag force applies a torque to each beam during movement causing it to rotate, it still presents the same shape of surface to the guide rail.

In some examples the carriage assembly may be configured to couple to a movement means configured to move the carriage assembly along the datum and guide rails. The carriage assembly may be configured to simultaneously bias the datum or guide rail in one direction and allow the respective datum rail or guide rail to slide through the corresponding aperture or channel in a transverse direction when the carriage assembly is moved by the movement means. For example, the biasing means may be configured to simultaneously bias and allow the respective datum rail or guide rail to slide through the corresponding aperture or channel when the carriage assembly is moved by the movement means.

The movement means may be any apparatus suitable for providing a force to the carriage assembly to force the carriage assembly to move along the datum and guide rails. The movement means may comprise a motor, an engine, a system of moving weights, a pulley system, or any other suitable means for effecting movement of the carriage assembly along the guide and datum rails.

The carriage assembly may comprise an interface, such as a slot, for receiving the movement means. The interface may be configured to releasably couple to the movement means. For example, the carriage assembly may comprise a front panel that connects the channel and aperture. The front panel may comprise a slot for receiving the movement means, such that the carriage assembly may be removed (e.g. for servicing or inspection) from the movement means.

It will be understood that the carriage assembly may support a measurement probe, and the measurement probe may be configured to move in tandem with the carriage assembly as the carriage assembly moves along the datum and guide rails. For example, displacement of the carriage assembly along the datum and guide rails may be equal to the displacement of the measurement probe. The measurement probe may be suitable for measuring the surface roughness, surface conductance, or other surface properties of a workpiece. In some examples relative movement of the carriage assembly along the datum rail may be measured to determine the displacement of the measurement probe. Movement of the carriage assembly along the datum rail may be determined using sensors and/or based on the energy supplied to the movement means, for example a current supplied to the movement means. In some examples the measurement probe may be configured to measure a workpiece by moving in a direction perpendicular to and/or parallel to the longitudinal axis of the datum and guide rails. The measurement probe may be configured to passively follow the surface height of a workpiece as the carriage assembly is moved along the datum and guide rails.

The biasing means may be any means suitable to provide a force on the guide and/or datum rails such that the guide and/or datum rails are securely held by the carriage assembly, for example such that the guide and/or datum rails have an interference fit with the respective channel and aperture. The biasing means may be in the form of, or function as, sprung arms. The sprung arms may be integrally formed with the carriage assembly and in some examples may be made from the same material as the rest of the carriage assembly. It will be understood, however, that in some examples the biasing means may be in the form of a different type of spring, or elasticated element, or any other suitable means.

Optionally, the aperture has at least one longitudinal groove situated along its inner surface. Advantageously the longitudinal grooves may allow any wear particles to migrate along the grooves and away from any running surfaces (i.e. away from any points of contact between the datum rail and the carriage assembly).

The aperture may extend along the longitudinal axis of the datum rail for a distance greater than that which the channel extends along the longitudinal axis of the guide rail. Further, optionally, the aperture extends along the longitudinal axis of the datum rail for a distance at least three times greater than that which the channel extends along the longitudinal axis of the guide rail.

Optionally, the carriage assembly comprises a reinforcement that bar may extend between the aperture and the channel. Further optionally, the carriage assembly comprises a second reinforcement bar that may extend at least partially along the length of the datum rail and/or the length of the aperture. The reinforcement bars may improve the stiffness of the carriage assembly and therefore improve the accuracy of measurements performed by the metrological apparatus in which the carriage assembly is used.

According to a second aspect of the disclosure, there is provided a carriage assembly for a metrology apparatus, the carriage assembly configured to support a measurement probe for performing surface measurements of a workpiece. The carriage assembly comprises an aperture configured to receive a datum rail and to allow the datum rail to slide therethrough. The aperture comprises a first biasing means configured to bias the datum rail into a receiving portion within the aperture. The datum rail has a longitudinal axis, and the receiving portion is configured to inhibit rotation of the carriage assembly about an axis transverse to the longitudinal axis of the datum rail, so that the datum rail is secured by, but is configured to slide within, the aperture. In some examples the receiving portion is configured to inhibit movement of the datum rail in directions other than along the longitudinal axis. At least a component of the biasing of the first biasing means may be in a direction parallel to the horizontal axis. Optionally, the receiving portion is generally v-shaped to provide at least two points of contact with the datum rail. Optionally, the receiving portion provides at least three points of contact with the datum rail in addition to a point of contact provided by the first biasing means. Providing such a receiving portion configured to receive may mean that the carriage assembly 310 can slide smoothly along the datum rail 322 regardless of orientation (for example, whether it is upright or upside down).

Optionally, the first biasing means may comprise a pair of biasing means arranged to be spaced along at least a portion of the length of the datum rail, to inhibit rotation of the carriage assembly about a plane in the horizontal axis. The first biasing means may be configured to bias the datum rail into the receiving portion in a direction parallel to the horizontal axis of the carriage assembly. In examples where the first biasing means comprises a pair of biasing means, the force to be applied by each member of this pair may not necessarily the same as the other, as the forces that they are opposing are not equal. The combination of forces (weight & friction) and the drag torque from the guide rail and/or datum rail mean that the total force at each end of the carriage assembly will likely be different. Equally, if the first biasing means comprises only a single biasing means, the location of its action on the datum rail would likely be off-centre, to balance the torque as well as the forces.

In some examples, the aperture extends along at least a portion of the longitudinal axis, and wherein the aperture comprises at least two receiving portions, each receiving portion arranged proximal to a respective end of the aperture along the portion of the longitudinal axis. In other examples the receiving portion extends along the length of the aperture in the direction of the longitudinal axis.

In some examples the carriage assembly further comprises a channel configured to receive a guide rail and to allow the guide rail to slide therethrough. The guide rail also has a longitudinal axis that is parallel to the longitudinal axis of the datum rail The carriage assembly has a horizontal axis that passes through both the aperture and the channel and the receiving portion is configured inhibit rotation of the carriage assembly about the horizontal axis.

Optionally, at least a component of the biasing of the first biasing means may be in a direction parallel to the horizontal axis. Optionally, the first biasing means may be any means suitable for providing a force on the datum rail such that the datum rail fits tightly within the aperture (for example to inhibit movement of the datum rail within the aperture in any direction other than along the longitudinal axis of the datum rail), whilst allowing the carriage assembly to move along the datum rail. For example, the first biasing means may be a spring, such as sprung arm or pair of sprung arms, or may be an elasticated element, or any other suitable means. The first biasing means may allow the carriage assembly to self-compensate for an amount of wear that may occur in use. The channel may comprise a second biasing means configured to bias the guide rail in the channel, with at least a component of the biasing from the second biasing means being in a direction transverse to the horizontal axis, and transverse to the longitudinal axis of the guide rail. The second biasing means may be integrally formed with the carriage assembly. Incorporating the biasing means into the carriage assembly may remove the need for connecting (e.g. screwing) the biasing means to the carriage assembly. This may reduce the number of points where a greater amount of wear may be expected, as well as decreasing manufacturing time and cost. In addition, the second biasing means may also allow the carriage assembly to self-compensate for an amount of wear that may occur in use.

The carriage assembly may be configured to couple to a movement means configured to move the carriage assembly along the datum rail. Optionally, the movement means may be any apparatus suitable for providing a force to the carriage assembly to force the carriage assembly to move along the datum rail.

Optionally, the movement means may comprise a motor, an engine, a system of moving weights, a pulley system, or any other suitable means.

According to a third aspect of the disclosure there is provided a metrological apparatus for performing surface measurements of a workpiece. The metrological apparatus comprises a carriage assembly (for example, the carriage assembly described above with reference to the first and/or second aspect), a datum rail situated within the channel, a guide rail situated within the aperture, a movement means detachably coupled with the carriage assembly, and a measurement probe mounted on the carriage apparatus, configured to move as the carriage assembly moves along the datum and guide rails, and to measure the surface roughness of a workpiece.

According to a fourth aspect of the disclosure there is provided a method of manufacturing the carriage assembly (for example, the carriage assembly described above with reference to the first and/or second aspect) by injection moulding, for example shutoff moulding. The method may comprise the steps of positioning a mould of the carriage assembly into a first position, passing a first material into the mould, wherein the first material is in a molten state, and is suitable for injection moulding, solidifying the first material within the mould of the carriage assembly, and removing the carriage assembly from the mould of the carriage assembly.

Brief Description of the Figures

Figure 1 shows a perspective view of a prior art metrological apparatus; Figure 2 shows a perspective view of a carriage assembly, measurement probe and guide and datum rails used in the prior art metrological apparatus of Figure 1 ;

Figure 3 shows a perspective view of an example carriage assembly of embodiments of the disclosure;

Figure 4 shows an end view of the example carriage assembly of Figure 3;

Figure 5 shows a top view of the example carriage assembly of Figure 3 and 4;

Figure 6 shows a perspective view of the example carriage assembly of Figures 3, 4 and 5 coupled to a measurement probe and guide and datum rails; and

Figure 7 is a flow diagram showing the steps for manufacturing a carriage assembly such as the example carriage assembly of Figures 3 to 6.

Detailed Description

Figure 1 shows the prior art the Surtronic® S-100 Series Surface Roughness Tester metrological apparatus discussed above in the Background section. The metrological apparatus 100 comprises a housing 125 carrying user interface comprising a screen and a user control module comprising one or more buttons. Extending from an aperture 127 in the housing 125 is a measurement probe 150. The measurement probe 150 is connected via a shaft 152 to a carriage assembly 210 contained within the housing 125. The metrological apparatus 100 may also contain within the housing 125 a control module comprising a processor, a data store and a power means. The power means may comprise a source of stored energy, or may be a means of receiving energy from an external source. The metrological apparatus 100 may also contain within the housing 125 a movement means 226 for moving the measurement probe 150 via the carriage assembly 210, powered by the power means and controlled by the control module.

The prior art carriage assembly 210 is shown in Figure 2. The body of the carriage assembly 210 is formed in an L-shape structure. The carriage assembly comprises an aperture 214 for receiving a datum rail 222, and a channel 225 for receiving a guide rail 224. The channel 225 and aperture 214 are formed in a front panel 205 on one side of the L-shape, with the aperture 214 extending through the carriage assembly 210 along the length of the other side of the L-shape. The front panel 205 of the carriage assembly 210 is further coupled to a movement means 226 and the measurement probe 150 via shaft 152 extending through a fully- round hole in the front panel 205, so the bottom of the hole prevents the carriage assembly 210 being removed unless the movement means (which is glued in to the housing 125) is removed with it.

The carriage 210 assembly is formed of multiple components. For example, two slide bushes are glued to opposing ends of the aperture 214 to allow the carriage assembly 210 to slide over the datum rail 22. Gluing the slide bushes to the carriage assembly 210 typically takes a minimum of 24 hours in order to ensure the glue is set without bending the body of the carriage assembly 210 and such that the two slide bushes are correctly aligned. The channel 225 also comprises a guide pad for contacting and sliding over the guide rail 224 that is also glued in place, and a leaf spring for biasing the guide rail 224 against the guide pad.

However, as described above, the arrangement of these components and the manufacture of the carriage assembly 210 in this manner is time consuming and complicated, in particular because components such as the bushes surrounding the datum rail 222 need to be carefully aligned so that the carriage assembly 210 can smoothly slide along the datum rail 222. In addition, because the carriage assembly 210 is manufactured from a number of separate components, variations in the design tolerances can result in undesirably bending and flexing of the carriage assembly 210, which may affect metrological measurements. Figures 3 to 6 show examples of a carriage assembly 310 of embodiments of the disclosure. The carriage assembly 310 of Figures 3 to 6 has common functionality with the prior art examples illustrated in Figures 1 and 2 and discussed above.

However, in contrast to the carriage assembly 210 of Figures 1 and 2, the carriage assembly shown in Figures 3 to 6 is constructed from a single unitary piece, which in this example is injection-moulded plastic such as polyether ether ketone (PEEK), optionally reinforced by carbon fibres, and/or optionally further comprising polytetrafluoroethylene (PTFE). As with the prior art example, the body of the carriage assembly 310 shown in Figure 3 is formed in an L-shape structure. The carriage assembly 310 comprises an aperture 314 for receiving a datum rail 322, and a channel 325 for receiving a guide rail 324. The channel 325 and aperture 314 are formed in a front panel 305 on one side of the L-shape, with the aperture 314 extending through the carriage assembly 310 along the length of the other side of the L-shape. The carriage assembly 310 has a horizontal axis that passes through both the aperture 314 and the channel 315. The channel 315 is generally U-shaped and forms a slot allowing the guide rail 324 to slide into the channel 315 in a direction along the horizontal axis.

The guide rail 324 is parallel to the datum rail 322. The datum rail 322 has a longitudinal axis, and the guide rail 324 has a longitudinal axis. Because the aperture 314 extends through the carriage assembly 310 along the length of the other side of the L-shape (but the channel 315 does not), the aperture 314 extends along the longitudinal axis of the datum rail 322 for a distance greater than that which the channel 315 extends along the longitudinal axis of the guide rail 324, and the aperture 314 itself has a longitudinal axis through the carriage assembly 310.

The aperture 314 comprises an integrated first biasing means 375 formed integrally (for example, of unitary construction) with the body of the carriage assembly 310. The aperture 314 also comprises, opposing the first biasing means 375, a receiving portion 377, which in the examples shown is approximately V-shaped and forms two fixed points of contact between the receiving portion 377 and the datum rail 322, with the first biasing means 375 forming a third point of contact with the datum rail 322. This third point, with the two above, defines a plane of kinematic contact with the datum rail 322, which retains it against the two fixed points. As can be seen in more detail in Figure 5, the first biasing means 375 comprises a pair of sprung arms, which in the example shown, are coupled together a point roughly mid-way along the longitudinal axis of the aperture 314 through the carriage assembly 310. The four fixed points (two from the receiving portion 377 when the biasing means retain them against the datum rail 322 and two from the two arms of the first biasing means 375) provide a defined traversing direction and remove four degrees of freedom, leaving only translation along the datum rail 322 and rotation around the datum rail 322 unconstrained. The channel 325 comprises an integrated guide pad 326 opposing an integrated second biasing means 328. The guide pad 326 and integrated second biasing means 328 of the channel 325 oppose each other in a direction transverse to the direction in which the first biasing means 375 and the receiving portion 377 of the aperture 314 oppose each other. In the example shown, the second biasing means 328 comprises a pair of sprung arms, each arm extending parallel to the other in a direction parallel to the horizontal axis of the carriage assembly. The guide pad 326 of the channel 325 provides a fifth point of contact and removes the fifth degree of freedom, leaving the remaining degree of freedom in only the desired direction of travel.

The front panel 305 of the carriage assembly 310 comprises an optional central U- shaped slot 340 that extends to one side (in this example, the base) of the front panel 310 of the carriage assembly 310. The central slot 340 is reinforced with a slot reinforcer 341 that bounds the slot 340.

In the example shown the carriage assembly 310 comprises an optional first reinforcement bar 342 that extends between the aperture 314 and the channel 315 and in the example shown extends along the length of the front panel 305. In the example shown the first reinforcement bar 342 has a dog-leg proximate to the aperture 314, which in the example shown accommodates the central slot 340 and slot reinforcer 341. The dog-leg shape serves two functions. It maintains a‘spine’ of material across the carriage assembly 310, which helps its overall stiffness, while the dog-leg itself allows this spine to push the left-most V feature of the aperture 314 as far to the outside of the part as possible. This gives the widest possible footprint for the aperture 314, maximising its stability in the available length. The first reinforcement bar 342 may form at least a portion of the aperture 314 and/or channel 315. In the example shown, the first reinforcement bar 342 provides one half of the circumference of the aperture 314, and also provides one half or side of the channel 315 and extends the length of the channel 315 in the horizontal axis. The half of the circumference of the aperture 314 formed by the first reinforcement bar 342 is offset along the longitudinal axis of the aperture 314 (and along the longitudinal axis of the datum rail 322 when in use) from the other half of the circumference of the aperture 314, to form a telescoping shut-off.

The first reinforcement bar 342 also supports the guide pad 326 of the channel 325 proximate to the end of the first reinforcement bar 342 and the end of the channel 315 to oppose the second biasing means 328. In the example shown, the second biasing means 328 extends along one side of the channel 315 parallel to, and to the same extent that the first reinforcement bar 342 extends along the other side of the channel 315. In the example shown, as can be seen in Figure 5, the first reinforcement bar 342 extends along the horizontal axis between the two sprung arms of the second biasing means 328, such that each sprung arm of the second biasing means 328 and the guide pad 326 coupled to the first reinforcement bar 342 are offset from each other along the longitudinal axis of the guide rail 324 in use to provide opposing moments on the guide rail 324.

The carriage assembly 310 also comprises an optional second reinforcement bar 344 that extends along the length of the aperture 314 and parallel to the longitudinal axis of the datum rail 322 when in use. In the example shown the first reinforcement bar 342 is coupled to the second reinforcement bar 344 and has the same proportions (i.e. height and thickness).

Also shown in Figures 3 to 6 is an end-stop indicator post 320 that is of unitary construction with the carriage assembly 310. The aperture 314 is configured to receive a datum rail 322 and to allow the datum rail 322 to slide therethrough. The channel 325 is configured to receive a guide rail 324 and to allow the guide rail 324 to slide therethrough.

The first biasing means 375 is configured to bias the datum rail 322 into the receiving portion 377 in a direction parallel to the horizontal axis of the carriage assembly 310. The pair of sprung arms of the first biasing means 375 are configured to exert a biasing force on the datum rail 322 at opposing ends of the aperture 314. The first biasing means 375 and receiving portion 377 are configured to inhibit movement of the carriage assembly 310 with respect to the corresponding datum rail 322 in a direction other than along the corresponding longitudinal axis of the datum rail 322.

The second biasing means 328 is configured to bias the guide rail 324 towards the guide pad 326 in a direction transverse to the horizontal axis, and transverse to the longitudinal axis of the guide rail 324 in use.

It will be understood that the first and second biasing means 375, 328 are sized such that, if the carriage assembly 310 were inflexible, the datum and guide rails 322, 324 would not fit in the gaps. The first and second biasing means 375, 328 are, therefore, inherently under load when flexed to accommodate the rails 322, 324, providing an always-present preload that resists the weight and drag forces.

The front panel 305 of the carriage assembly 310 is configured to couple to a movement means 326 and the measurement probe 350 via shaft 352. In particular, the central slot 340 and slot reinforcer 341 are configured to allow detachable coupling to a movement means 326 and/or a shaft 352 coupled to a measurement probe 350, as shown in Figure 6 and described in more detail below. This simplifies the assembly process of a metrological apparatus incorporating both the carriage assembly and a movement means and facilitates easy removal of components of the metrological apparatus for servicing and inspection. For example, it means that the carriage assembly 310 can be removed from the housing while leaving the movement means 326 in place. In the examples shown the aperture 314 is not circular (instead it is formed of two roughly triangular shaped halves to make an approximate diamond or parallelogram shape), and the first biasing means 375 together with the receiving portion 377 are configured to form a three point kinematic connection with the datum rail 322. The first biasing means 375 is configured to bias the datum rail 322 to maintain this connection within the receiving portion 377 in the aperture 314. Such a three point kinematic connection may help to inhibit movement of the carriage assembly 310 with respect to the datum rail 322 in a direction other than along, or about, the longitudinal axis of the datum rail 322. The channel 325 is configured to receive the guide rail 324. The second biasing means 328 is configured to bias the guide rail 324 against the guide pad 326 of the carriage assembly 310 in a direction transverse to the horizontal axis of the carriage assembly 310, transverse to the longitudinal axis of the aperture 314 and transverse to the longitudinal axis of the guide rail 324 and datum rail 322 in use. The second biasing means 328 is also configured to bias the guide rail 324 against the guide pad 326 of the carriage assembly 310 in a direction transverse to the direction of biasing of the first biasing means 375. The carriage assembly 310 is configured to slide (for example, effected by movement means 326) along the guide rail 324 and datum rail 322 along the longitudinal axis of the guide rail 324 and datum rail 322. The carriage assembly 310 is therefore configured to exhibit ease of motion in one degree of freedom (for example in one axis such as the axis parallel to the longitudinal axis of the aperture 314, and the longitudinal axis of the guide rail 324 and datum rail 322 in use), but inhibit motion in all other degrees of freedom. The carriage assembly 310 may be configured to provide a low degree of friction with the guide rail 324 and datum rail 322. For example, the carriage assembly 310 may be manufactured from, or comprises a proportion of, a material with a low degree of friction with metals, such as polyether ether ketone (PEEK) and/or polytetrafluoroethylene (PTFE).

The receiving portion 377 of the aperture 314 is configured to inhibit rotation of the carriage assembly 310 about an axis transverse to the longitudinal axis of the datum rail 322, so that the datum rail 322 is secured by, but is configured to slide within, the aperture 314. The receiving portion 377 and first biasing means 375 are configured such that a datum rail 322 may be used with a larger tolerance than may be used otherwise, so that after a degree of wear through continual use there still remains an interference fit between the aperture 314 and the datum rail 322. The optional telescoping shut-off arrangement of the aperture 314 shown in the examples of Figures 3 to 6 is configured to aid alignment of the datum rail 322 within the aperture 314. This means that slide bushes are no longer required, and therefore this simplifies the manufacture process as the gluing of the bushes is not required. As the glue would otherwise take 24 hours to set as described above, this reduces the manufacturing time of the carriage assembly 310 considerably. The telescoping shut-off design of the aperture 314 as shown in the example of Figures 3 to 6 may make injection moulding of the carriage assembly 310 simpler and more efficient.

The end stop indicator post 320 may be configured to stop the carriage assembly 310 being moved too far/out of range along the datum rail 322, and/or as a zero point reference for measurement, such that the relative displacement of the carriage assembly 310 to the datum rail 322 can be measured. For example, the metrological apparatus may comprise a sensor (for example, light gates) for sensing the position of the end stop indicator post 320.

In use, similar to the example described above with reference to Figures 1 and 2, the carriage assembly 310 of embodiments of the disclosure sits within a housing of a metrological apparatus. The housing comprises a guide rail 324 and a datum rail

322 coupled to the housing. The carriage assembly 310 is mounted on the guide rail 324 and datum rail 322 and supports a measurement probe 350 outside of the housing via a shaft 352 that extends through an aperture in the housing. The carriage assembly 310 is coupled to a movement means 326 and driven along the guide rail 324 and datum rail 322 by the movement means 326. As with the prior art example described with reference to Figures 1 and 2, the movement means 326 may be operated by a control module. Because the carriage assembly 310 supports the measurement probe 350, the measurement probe 350 moves (for example with respect to a workpiece being measured) as the carriage assembly 310 moves along the datum rail 322 and guide rail 324.

In some examples the aperture 314 comprises at least two receiving portions 377. For example, each receiving portion 377 may be arranged proximal to a respective end of the aperture 314 along a corresponding portion of the longitudinal axis of the datum rail 322.

The carriage assembly 310 may be formed of a single material (or may be formed of the same mixture of materials throughout such that its construction is homogenous) so that the aperture 314, channel 325 and/or biasing means 375, 328 may be formed of the same material. The carriage assembly 310 may be formed for example, from polyether ether ketone (PEEK). This may be reinforced by carbon fibres. The carriage assembly 310 may additionally or alternatively contain polytetrafluoroethylene.

In some examples it will be understood that the aperture 314 may not have a receiving portion 377. For example, the aperture 314 may be substantially circular. In such examples the aperture 314 may also not comprise a first biasing means 375.

In some examples the inner surface of the aperture 314 may comprise one or more grooves. These grooves may extend through the aperture. The grooves may be configured to allow any particles caught in the aperture, especially any particles caught between the datum rail 322 and the aperture 314, to be accommodated within the grooves. Therefore the particles will cause less friction and/or wear between the datum rail 322 and the carriage assembly 310. The particles may also be more likely to be removed from the aperture 314 by the manipulation of the carriage assembly 310 along the datum rail 322 due to the grooves. It is noted that only one groove may be required to achieve this effect, although multiple grooves may be employed in some embodiments. In some embodiments the grooves may be spaced equidistant from one another, and in other embodiments the grooves may be spaced at random intervals apart along the inner surface of the aperture. It is noted that the presence of grooves is an optional feature for the unitary carriage assembly 310.

Figure 7 is a flow diagram illustrating a method 700 for manufacturing a carriage assembly, for example the carriage assembly of Figures 3 to 6.

The method comprises the steps of positioning 710 a mould of the carriage assembly into a first position, passing 720 (for example, injecting) a first material into the mould, 730 solidifying the first material within the mould of the carriage assembly, and removing 740 the carriage assembly from the mould of the carriage assembly. The mould may be manufactured from a hard wearing material, for example a metal such as aluminium, or steel. Steel may be harder wearing, but aluminium may be cheaper to use. The material of the mould may be selected on the basis of a number of technical and commercial considerations. The first material may be any material suitable for injection moulding, and may be in a liquid form. For example the material may be a thermoplastics, thermosets and elastomers. The material may be an alloy or blend of multiple materials. Common materials for injection moulding include nylon, polyethylene and polystyrene. The material may be solidified by the temperature of the material decreasing below the melting point of the material, or by a change in the pressure.

Once the material has solidified the carriage assembly is formed. The removal of the carriage assembly may be effected by the mould being formed of two or more components that may be taken apart such that the carriage assembly can be removed. For example a mould may have an ejector pin such that it may easily, reliably and quickly be opened to allow for the removal of the carriage assembly.

It will be appreciated from the discussion above that the embodiments shown in the Figures are merely exemplary, and include features which may be generalised, removed or replaced as described herein and as set out in the claims. With reference to the drawings in general, it will be appreciated that schematic functional block diagrams are used to indicate functionality of systems and apparatus described herein. It will be appreciated however that the functionality need not be divided in this way, and should not be taken to imply any particular structure of hardware other than that described and claimed below. The function of one or more of the elements shown in the drawings may be further subdivided, and/or distributed throughout apparatus of the disclosure. In some embodiments the function of one or more elements shown in the drawings may be integrated into a single unit. The above embodiments are to be understood as illustrative examples. Further embodiments are envisaged. It is to be understood that any feature described in relation to any one embodiment may be used alone, or in combination with other features described, and may also be used in combination with one or more features of any other of the embodiments, or any combination of any other of the embodiments. Furthermore, equivalents and modifications not described above may also be employed without departing from the scope of the invention, which is defined in the accompanying claims.

Claims

CLAIMS:

1 . A carriage assembly for a metrology apparatus, the carriage assembly configured to support a measurement probe, the carriage assembly comprising:

an aperture configured to receive a datum rail having a longitudinal axis, and configured to allow the datum rail to slide therethrough;

a channel configured to receive a guide rail having a longitudinal axis, and configured to allow the guide rail to slide therethrough, wherein the guide rail is parallel to the datum rail; and

wherein at least one of the aperture and the channel comprise a biasing means integrally formed with the carriage assembly for inhibiting movement of the carriage assembly with respect to the corresponding datum rail or guide rail in a direction other than along the corresponding longitudinal axis of the datum rail or guide rail.

2. The carriage assembly of claim 1 , wherein the carriage assembly is formed of a single unitary piece.

3. The carriage of any preceding claim, wherein the aperture, channel and biasing means are formed of the same material.

4. The carriage assembly of any preceding claim, wherein the carriage assembly is configured to:

(i) couple to a movement means for moving the carriage assembly along the datum and guide rails; and

(ii) simultaneously bias the datum or guide rail in one direction and allow the respective datum and guide rails to slide through the corresponding aperture and channel in a transverse direction when the carriage assembly is moved by the movement means.

5. The carriage assembly of claim 4, wherein the carriage assembly supports a measurement probe, wherein the measurement probe is configured to move as the carriage assembly moves along the datum and guide rails.

6. The carriage assembly of any preceding claim, wherein the biasing means comprises at least one sprung arm.

7. The carriage assembly of any preceding claim, wherein the aperture has at least one longitudinal groove on its inner surface.

8. The carriage assembly of any preceding claim, wherein the aperture comprises a first biasing means configured to inhibit rotation of the carriage assembly about an axis transverse to the longitudinal axis of the datum rail, so that the datum rail is secured by, but is configured to slide within, the aperture.

9. The carriage assembly of any preceding claim, wherein the carriage assembly has a horizontal axis that passes through both the aperture and the channel, and wherein the channel comprises a second biasing means configured to bias the guide rail in the channel, with at least a component of the biasing from the second biasing means of the channel being in a direction transverse to the horizontal axis, and transverse to the longitudinal axis of the guide rail.

10. The carriage assembly of claim 9, wherein the channel of the carriage assembly further comprises a guide pad opposing the second biasing means, wherein both the guide pad and the second biasing means are integrally formed with the carriage assembly, and wherein the guide pad and the second biasing means are configured in use to be in contact with the guide rail and to permit the guide rail to slide therebetween.

1 1. The carriage assembly of any preceding claim wherein the carriage assembly is configured to couple to a movement means for sliding the carriage assembly along the datum and guide rails.

12. The carriage assembly of claim 1 1 , wherein the channel and aperture are connected by a front panel extending therebetween, wherein the front panel comprises a slot for detachably coupling the carriage assembly to the movement means.

13. A carriage assembly for a metrology apparatus, the carriage assembly configured to support a measurement probe, the carriage assembly comprising:

an aperture configured to receive a datum rail and to allow the datum rail to slide therethrough, wherein the datum rail has a longitudinal axis;

wherein the aperture comprises a first biasing means configured to bias the datum rail into a receiving portion within the aperture, wherein the receiving portion is configured to inhibit rotation of the carriage assembly about an axis transverse to the longitudinal axis of the datum rail, so that the datum rail is secured by, but is configured to slide within, the aperture.

14. The carriage assembly of claim 13, wherein the carriage assembly further comprises a channel configured to receive a guide rail and to allow the guide rail to slide therethrough, wherein the guide rail also has a longitudinal axis that is parallel to the longitudinal axis of the datum rail;

wherein the carriage assembly has a horizontal axis that passes through both the aperture and the channel; and

wherein the receiving portion is configured inhibit rotation of the carriage assembly about the horizontal axis.

15. The carriage assembly of claim 14, wherein at least a component of the biasing of the first biasing means is in a direction parallel to the horizontal axis.

16. The carriage assembly of clam 9, 14 or 15, wherein the first biasing means comprises a pair of biasing means arranged to be spaced along at least a portion of the length of the datum rail, to inhibit rotation of the carriage assembly about a plane in the horizontal axis.

17. The carriage assembly of claim 8, or any claim as dependent thereon, or any of claims 13 to 16, wherein the first biasing means is configured to bias the datum rail into a receiving portion, the receiving portion configured to inhibit movement of the datum rail in directions other than along the longitudinal axis.

18. The carriage assembly of claim 9 or 14, or any claim as dependent thereon, wherein the first biasing means is configured to bias the datum rail into the receiving portion in a direction parallel to the horizontal axis of the carriage assembly.

19. The carriage assembly of claim 17 or 18, wherein the receiving portion is generally v-shaped to provide at least two points of contact with the datum rail.

20. The carriage assembly of claims 17, 18 or 19, wherein the receiving portion provides at least three points of contact with the datum rail in addition to a point of contact provided by the first biasing means.

21. The carriage assembly of any of claims 17-20, wherein the aperture extends along at least a portion of the longitudinal axis, and wherein the aperture comprises at least two receiving portions, each receiving portion arranged proximal to a respective end of the aperture along the portion of the longitudinal axis.

22. The carriage assembly of any of claims 14 to 21 , wherein the channel comprises a second biasing means configured to bias the guide rail in the channel, with at least a component of the biasing from the second biasing means being in a direction transverse to the horizontal axis, and transverse to the longitudinal axis of the guide rail.

23. The carriage assembly of any of the previous claims wherein the aperture extends along the longitudinal axis of the datum rail for a distance greater than that which the channel extends along the longitudinal axis of the guide rail.

24. A metrological apparatus for measuring the surface of a workpiece, comprising: a carriage assembly as set out in any previous claim;

a datum rail situated within the channel;

a guide rail situated within the aperture;

a movement means detachably coupled to the carriage assembly; and

a measurement probe mounted on the carriage apparatus, configured to move as the carriage assembly moves along the datum and guide rails, and to measure the surface roughness of a workpiece.

25. A method of manufacturing the carriage assembly of any previous claim, by injection moulding comprising the steps of:

positioning a mould of the carriage assembly into a first position;

passing a first material into the mould, wherein the first material is in a molten state, and is suitable for injection moulding;

solidifying the first material within the mould of the carriage assembly; and removing the carriage assembly from the mould of the carriage assembly.