Field of the Invention

The present invention relates to wheel recutting. Embodiments of the present invention relate to a wheel recutting apparatus, a wheel recutting method and a refinished wheel.

Background of the Invention

Modern alloy vehicle wheels have become more prevalent with a finish commonly known as "diamond turned". This finish involves mounting the wheel onto a lathe during manufacture and turning usually the front face of the wheel to leave a mirror like finish. This finish is then preserved by applying a transparent lacquer coating to the lathe-turned face rather than using a coloured paint finish.

Unfortunately, after exposure to the environment, this lacquer may become damaged due for example to ultra violet sunlight or mechanical impact. This damage to the lacquer then allows water and air to come into contact with the machined aluminium face, which in turn oxidises (corrodes) and ruins the aesthetic appearance of the wheel.

It is possible to repair this damage by using a lathe and cutting tool to follow the radial profile of the wheel to remove the lacquer and top layer of oxidised alloy. This repair process is currently carried out using either a manual lathe and an operator to guide the cutting tool across the radial profile of the wheel (using X-Y slides) or from a semi-automated process that uses a touch (contact) probe to "map" a user selected radial profile and then to automatically follow the mapped profile with a cutting tool. There are a number of drawbacks to these processes, as outlined below:

• The manual method is time consuming and requires a skilled machinist to operate the lathe.

• In the manual method, if a misjudgement is made throughout the process of moving both the X & Y slides together, then the wheel can be irreparably damaged.

• The automated process using a touch probe relies on repeatedly moving a contact probe mounted on the lathe, up to the face of the wheel along an operator-selected-and-aligned wheel radial and mapping the point of contact with respect to the radial distance to obtain a wheel profile. It will be appreciated that this requires the wheel to be held stationary. It will further be appreciated that since the probe tool is aligned with the wheel radial, the process can fail if a double spoke style wheel is being probed.

• The physical size of the touch probe makes it difficult to get an accurate mapping of wheel profile where there are profile changes which are similar in size to the physical dimensions of the touch probe.

Summary of the Invention

According to a first aspect of the present invention, there is provided an apparatus for recutting the surface of a wheel, the apparatus comprising: a rotatable mount, for holding and rotating the wheel about its axis;

a surface profiler, operable during rotation of the wheel to detect surface elevations at different radial positions on the wheel; a surface elevation profile generator, operable to generate a 3D surface elevation profile of at least a portion of the surface of the wheel from the detected surface elevations;

a cutting profile generator, operable to calculate a cutting profile for the wheel from the 3D surface elevation profile, the cutting profile defining a cutting elevation with respect to radial position; a cutting tool; and a cutting controller, operable to control the position of the cutting tool with respect to the wheel to recut the surface of the wheel in accordance with the generated cutting profile.

The surface profiler may detect surface elevations at different radial positions while the wheel is being continuously rotated. There is no need to hold the wheel stationary while a surface elevation is being detected at a particular position on the wheel - the surface elevation can be detected while the wheel is actually in motion. This dramatically increases the speed at which it is possible to generate a surface profile for the wheel, and thus dramatically reduces the time required. This process can be completely or substantially automated, with the operator optionally specifying a cutting depth (i.e. the amount of material to be cut away from the surface of the wheel). It will be appreciated that the cutting depth would be applied to the cutting profile generated by the cutting profile generator. In order to ensure that the entire surface of the wheel is recut, the cutting profile which is used should be based on appropriate data within the surface elevation profile of the wheel for each radius. The present invention can readily derive this information for any given radius from the surface elevation profile.

It will be appreciated that the cutting profile may be generated in respect of the complete top surface of the wheel using the entirety of the surface elevation profile, or may alternatively be generated in respect of a radial portion of the top surface of the wheel using a subset of the surface elevation profile. Equally it will be appreciated that the apparatus may be configured to only generate the surface elevation profile for a radial portion of the top surface of the wheel where only that portion requires refinishing.

In accordance with one profiling pattern, the surface profiler may be operable to detect and output surface elevations around a plurality of concentric rings at different radial positions on the surface of the wheel. In accordance with another profiling pattern, the surface profiler is operable to detect surface elevations while the radial position at which the surface elevation is being detected is being continuously varied and while the wheel is being rotated (in other words, in a spiral pattern).

An angular encoder may be provided, operable to detect and output a current angular position of the wheel with respect to a reference position. In this case, the surface elevation profile generator generates the surface elevation profile using the angular positions output by the angular encoder in combination with the radial position at which the surface elevation is being detected and the surface elevation measured by the surface profiler.

The cutting tool may be moveable both to different radial positions with respect to the wheel and parallel to the axis of rotation of the wheel. The cutting control circuitry is operable to control the position of the cutting tool and the rotation of the wheel to recut the surface of the wheel. The rotation of the wheel during the cutting process may be at the same or a different angular velocity than the rotation of the wheel during the surface profiling stage. A linear drive mechanism may be provided, operable to reposition the surface profiler at different radial positions with respect to the wheel. The cutting tool and the surface profiler may be co-mounted on the linear drive mechanism, in which case the cutting control circuitry may be operable to control the axial position of the cutting tool using the linear drive mechanism (which is therefore used for both the profiling and cutting stages, thereby reducing the size of the apparatus). Co-mounting the surface profiler and cutting tool is also likely to result in improved accuracy when compared with a system in which the surface profiler and cutting tool are moveable separately. However, a separate linear positioner could be used for each of the profiler and the cutting tool, or alternatively only the cutting tool may be moved linearly, with the profiler sampling different radii by keeping the surface profiler at a single position and targeting different radii of the wheel by rotation of the surface profiler.

A 3D map generator may also be provided, to generate and display to an operator a 3D representation of the surface of the wheel based on a set of surface elevation profiles of concentric rings at different radial positions. In this way, the whole wheel radial profile can be mapped though 360 degrees allowing the computer system to find buckles or other problems with wheel geometry which may affect vehicle safety or the subsequent cutting process, thus allowing the operator to correct a problem before an irreversible cut is made to the wheel.

The 3D map generator may itself be operable to automatically detect abnormalities in the surface of the wheel from the 3D representation, and to highlight any detected abnormalities to the operator. Pattern recognition techniques could be used. Wheels typically make use of repeating patterns of spokes, nuts and apertures, and therefore an isolated (i.e. non-repeating) occurrence of a shape can be assumed to relate to an abnormality, which could then be brought to the attention of the operator.

Taking this a step further, the cutting profile generator may be operable to calculate a cutting elevation at a given radial position at which abnormalities have been detected based on the detected depth of the abnormality below the surface elevation profile at that radial position.

Similarly, an isolated abnormality may be excluded (masked) for the purposes of generating the cutting profile, so that any raised material resulting from surface damage does not feed into the selection of a cutting elevation for a particular radial position.

The 3D map generator may be operable to detect an outer rim of the wheel or other normally concentric feature of the wheel, to detect a discontinuity in the surface around a ring at the radius of the normally concentric feature, and if a discontinuity is detected, to highlight the discontinuity to the operator. This is a concentricity test, which will highlight if the wheel has been distorted. While in this example the normally concentric feature is automatically detected, in an alternative example the radial position of the normally concentric feature may be marked on the 3D representation by the operator, and discontinuities identified at the marked radial distance.

The cutting profile generator may be operable to calculate a cutting elevation at a given radial position at which abnormalities have been detected without taking into account the height of any detected abnormality above the remainder of the surface elevation profile at that radial position. As a result, raised surface damage will not result in a cutting profile being generated based on an artificially high surface elevation. The 3D map generator may be operable to identify whether the surface elevation profile of a concentric ring at a predetermined radius has a consistent elevation within a predetermined tolerance, or to identify whether a set of positions on the surface elevation profile at regular intervals from each other have a consistent elevation within a predetermined tolerance. If the profile or set of positions do not have a consistent elevation within the predetermined tolerance, the operator is notified that the wheel is either not properly mounted on the rotatable mount, or is distorted. It will be understood that it is important, both for the generation of a surface profile, and for recutting, that the wheel be accurately mounted in a level position. If the wheel is sat on a small piece of debris then the results of scanning and recutting will be inaccurate. This test indicates to the operator that there may be a problem in this regard. If the operator finds no problem then this may indicate that the wheel is itself deformed.

The 3D representation may be colour coded to indicate which portions of the wheel are to be cut based on the current cutting profile, and which portions of the wheel are not to be cut based on the current cutting profile. This lets the operator see at a glance where the wheel is to be cut, and gives him the opportunity to manually intervene if he considers that this would give undesirable results.

The cutting profile generator may be responsive to the user inputting start and end radial distances for cutting to set the cutting profile such that the wheel will be recut only at radial distances between the user inputted start and end radial distances. This enables the operator to exclude certain portions of the wheel from the recutting process, which may be important if the wheel comprises parts or materials which cannot be recut, or features which are intended to be preserved. The operator can input multiple start and end positions so that plural radial bands of the wheel can be recut.

The 3D map generator may be operable to detect the reflectance at different radial positions on the surface of the wheel during the generation of the surface elevation profile, and to automatically mark up the 3D representation of the surface of the wheel to indicate areas of the surface of the wheel having a detected reflectance above a predetermined threshold. The recutting process is typically carried out on diamond turned areas of the wheel, which can be expected to have a relatively high reflectance compared with non-diamond turned areas of the wheel (which are not to be recut). This characteristic can be used to automatically determine areas of the wheel which can be recut. Optionally, start and end radial distances for cutting can be set based on this determination. The reflectance may be detected using the automatic gain control system of a laser used as the surface profiler.

The apparatus may be operable to compare the generated surface profile with a surface profile for the wheel which is stored in a wheel profile database, and if a match is found, to obtain wheel-related information from the database. A variety of different wheel-related information could be envisaged. For example, the wheel-related information may comprise a minimum safe elevation profile for the wheel, and the apparatus may be operable to compare the detected surface elevation profile with the minimum safe elevation profile for the wheel, and to determine whether cutting is possible based on the comparison. The apparatus may be operable to constrain the cutting profile generator to generate the cutting profile so that the wheel is not cut to below the minimum safe elevation profile. Moreover, the 3D map generator may be operable to indicate to the user if the wheel cannot be satisfactorily recut without cutting below the minimum safe elevation profile.

The wheel-related information may comprise one or more test parameters for the operator to test the wheel. The test parameters may indicate to the operator certain things which need to be checked (for safety reasons) on that type of wheel, or may indicate to the operator issues with recutting on that type of wheel, which the operator can take into account in controlling the setting of the cutting profile.

The 3D map generator may be operable to identify damage to the wheel from differences between the generated surface profile and the version of the surface elevation profile stored in the wheel profile database.

The 3D map generator may be responsive to the wheel being rotated on the rotatable mount to rotate the view of the 3D representation presented to the user. This enables the operator to interact with the 3D representation by physically interacting with the wheel, and means that if the operator can readily understand which part of the 3D representation corresponds to which part of the physical wheel. The 3D representation may be aligned such that the part of the 3D

representation which appears (for example in an isometric view) to be closest to the operator corresponds to the part of the physical wheel which is closest to the operator. It will be appreciated that this association will be strongest if the display device upon which the 3D representation is presented is mounted near to, and preferably directly above, the mounted wheel. The orientation of the view provided of the 3D representation may be determined from an output of an angular encoder used to determine the orientation of the wheel.

An angular encoder may be used to detect and output a current angular position of the wheel with respect to a reference position. This information can be used to generate the 3D representation.

While the surface profiler could in principle be a contact-based profiler, preferably the surface profiler is a non-contact profiler. Such a non-contact profiler enables free rotational movement of the wheel during profiling, enabling the speed of profiling to be increased. More preferably the non-contact profiler is an optical profiler. Still more preferably the optical profiler is a laser. A laser based profiler is capable of a much better imaging resolution than a physical probe for example.

The rotatable mount may be operable to rotate the wheel at a constant angular velocity for all radii. This arrangement is simple from a mechanical and control perspective, but results in a higher spatial sampling density towards the centre of the wheel than near the perimeter of the wheel. As a result, the constant angular velocity should be selected in dependence on the maximum radius for surface elevation measurement and the sampling rate of the surface profiler so that an acceptable spatial sampling density is achieved towards the outside of the wheel.

Alternatively, the rotatable mount may be operable to rotate the wheel at a variable angular velocity, the angular velocity being decreased incrementally as the linear drive mechanism increases the radial distance of the surface profiler from the centre of the wheel. In this way a substantially constant spatial sampling density can be achieved across the full surface of the wheel, but at the cost of increased mechanical and control complexity.

The surface of the wheel may include both relatively flat or slowly undulating portions, and also relatively sharp changes in elevation. To take account of this, the linear drive mechanism may be operable to incrementally reposition the surface profiler by a first radial distance following the completion of a surface elevation profile of each concentric ring, and to detect a high frequency change between the surface elevation profiles of adjacent concentric rings, and if such a change is detected, to incrementally reposition the surface profiler by a second radial distance smaller than the first radial distance at, near or around the radius at which the high frequency change was detected. In this way, the concentric rings sampled by the surface profiler may be spaced apart more in areas where there are no changes or only low frequency changes in the surface elation than in areas where high frequency changes occur. More generally, the radial sampling resolution may be increased in regions where higher frequency changes in elevation are found to occur. The same principle may also be applied to the spiral scan pattern, with the variation of radial position occurring more slowly where high frequency changes in elevation occur (or alternatively the radial position may not be varied at a different rate but the rate of rotation of the wheel may be reduced instead - or a combination of the two).

In one way of implementing this for concentric ring scanning, the surface profiler is operable to detect a high frequency change when the a change in surface elevation on a radial line between a first surface elevation profile and a second surface elevation profile exceeds a first predetermined magnitude, to rewind the surface profiler position and incrementally reposition the surface profiler by the second radial distance from the radial position corresponding to the first surface elevation profile, and to continue to incrementally reposition the surface profiler by the second amount until a change in the surface elevation between adjacent surface elevation profiles falls below a second predetermined magnitude, whereupon the linear drive mechanism reverts to incrementally repositioning the surface profiler by the first amount.

Further benefits of embodiment of the invention are as follows:

• An accurate radial profile can be extracted irrespective of number and type of spokes.

• Small radius curves can accurately be mapped since laser displacement spot size can be orders of magnitude smaller than a touch probe diameter.

• Wheel digitisation resolution is many orders of magnitude higher than using a touch probe due to laser displacement sensor spot size the repetition rate of the sensor (a laser displacement sensor can take thousands or even millions of samples per second compared with the ~1 sample a second of a usual touch probe approach).

• The whole process from scan through to cutting can be completely automated requiring no skilled machinist or manual X-Y portions of the cutting process as with a touch probe approach when a small radius is encountered.

According to a second aspect of the present invention, there is provided a method of recutting the surface of a wheel, the method comprising the steps of: rotating the wheel about its axis; detecting, during rotation of the wheel, surface elevations at different radial positions on the wheel;

generating a 3D surface elevation profile of at least a portion of the surface of the wheel from the detected surface elevations;

calculating a cutting profile for the wheel from the 3D surface elevation profile, the cutting profile defining a cutting elevation with respect to radial position; and controlling the position of a cutting tool with respect to the wheel to recut the surface of the wheel in accordance with the generated cutting profile.

Following the cutting operation, a step of applying a lacquer finish to the recut surface may be provided.

According to a third aspect of the present invention, there is provided an apparatus for profiling the surface of a wheel, the apparatus comprising: a rotatable mount, for holding and rotating the wheel about its axis;

a surface profiler, operable during rotation of the wheel to detect surface elevations at different radial positions on the wheel; a surface elevation profile generator, operable to generate a 3D surface elevation profile of at least a portion of the surface of the wheel from the detected surface elevations.

Preferably, the profiling apparatus comprises a cutting profile generator, operable to calculate a cutting profile for the wheel from the 3D surface elevation profile, the cutting profile defining a cutting elevation with respect to radial position. However, the cutting profile could instead be generated by an apparatus completely separate to the profiling apparatus.

According to a fourth aspect of the present invention, there is provided an apparatus for recutting the surface of a wheel, the apparatus comprising: a cutting tool; and a cutting controller, operable to control the position of the cutting tool with respect to the wheel to recut the surface of the wheel in accordance with a cutting profile generated by either the profiling apparatus described above, or generated at another device based on the surface elevation profile generated by the profiling apparatus described above.

It will be appreciated that, while preferably a single device carries out the profiling, the generation of a cutting profile, and the cutting process itself, it is possible to achieve similar results using separate devices for the profiling, the generation of the cutting profile, and the cutting process.

Various further aspects and features of the present invention are defined in the claims. In particular, a computer program for causing an apparatus to execute the method described above is envisaged, as is a wheel refinished by the above apparatus or the above method. It will be appreciated that such a wheel will have a different surface profile than a wheel refinished by traditional methods.

Brief Description of the Drawings

Embodiments of the present invention will now be described with reference to the following drawings, in which like reference numerals are used to denote like parts, and in which:

Figures 1A and IB schematically illustrate a wheel refinishing apparatus according to an embodiment of the invention;

Figure 2 schematically illustrates a 3D representation of a wheel images by the apparatus of Figure 1;

Figure 3 is a schematic flow diagram of the operation of the wheel refinishing apparatus of Figure 1;

Figure 4 is a schematic flow diagram showing a variable increment radial sampling routine; and

Figures 5A and 5B schematically illustrate the concentric circle scan pattern and the spiral scan pattern respectively.

Description of the Example Embodiments

Referring first to Figure 1A, a view of a recutting apparatus for a wheel is schematically illustrated. The apparatus comprises a frame 10 which supports a rotating mount 20. The rotating mount 20 receives a wheel 5, and can be driven to rotate by a motor 30 which drives the rotating mount 20 via a belt 40. The motor 20 is controlled by a controller 100. The rotational position of the mount 20 (and by inference the angular position of the wheel 5) is detected by an angular encoder 50, which outputs the rotational position to the controller 100. A horizontal linear positioner 60 and a vertical linear positioner 70 are also shown. These position a laser displacement sensor 80 and a cutting tool 90 with respect to the wheel 5. The horizontal linear positioner 60 and the vertical linear positioner 70 are controlled by the controller 100. The laser displacement sensor 80 measures an elevation of the surface 5a of the wheel 5, and is controlled by, and passes data to, the controller 100.

The recutting apparatus effectively operates in a scan mode to map the surface 5a of the wheel 5 and generate a cutting profile for the wheel, and in a cutting mode, in which the surface 5a of the wheel 5 is recut based on the cutting profile generated in the scan mode. In the scan mode, the mount 20 (and thus the wheel 5) is rotated under the control of the controller 100, and the horizontal linear positioner 60 is controlled to position the laser displacement sensor 80 at a desired radial distance from the centre of the wheel 5. During the scan mode the vertical linear positioner 70 is locked into a fixed position. The wheel 5 is rotated about 360° while the laser displacement sensor 80 measures the surface elevation at the current radial position to form a surface elevation profile for a concentric ring at the desired radial distance. Once a surface elevation profile for a given radius has been completed, the horizontal linear positioner 60 is controlled to reposition the laser displacement sensor 80 to a different radial distance from the centre of the wheel 5. Again, the wheel 5 is rotated about 360° while the laser displacement sensor 80 measures the surface elevation at the new radial position to form a surface elevation profile for a concentric ring at the new radial distance. This process continues until the complete surface 5a of the wheel 5 has been mapped to form a surface elevation profile for the entire wheel, or at least for a portion of interest. In order to generate the 3D map, the controller 100 receives (at a given instant of scanning) an elevation measurement from the laser displacement sensor 80, and a rotational position of the wheel 5 (with respect to a reference position) from the angular encoder 50. The controller 100 is also aware of the radial distance of the laser displacement sensor 80 (either by virtue of its role controlling the horizontal linear positioner 60 or by way of a radial position detector (not shown)). These three elements of information are sufficient for the controller to construct a 3D (relief) representation of the surface of the wheel. The elevation data measured at each radial distance is used to form a radial profile. A cutting profile may then be generated from the radial profile by subtracting a desired cutting depth from the radial profile. The cutting depth may be user selected based on operator preference or based on an amount of material required to be removed to obliviate signs of damage. Abnormalities in one or both of the 3D representation and the radial profile can be either automatically detected by the controller 100 and drawn to the attention of the operator, or spotted by the operator prior to the cutting mode being engaged. Each of the 3D representation, the cutting profile and any automatically detected abnormalities can be presented to the operator on a display device (not shown). If damage is observed, the operator is able to modify the cutting profile in a manner which will remove or reduce the severity of the damage. In some embodiments the system may be operable to generate a recommended cutting profile which would remove the damage or reduce the severity of the damage. The 3D representation may be colour coded to indicate which portions of the wheel are to be cut based on the current cutting profile, and which portions of the wheel are not to be cut based on the current cutting profile.

The controller 100 may provide all processing functions and output display information directly to a display device, or alternatively the controller 100 may be connected to a computer upon which control and display software is installed and operating. In the latter case the computational and display aspects described above (such as generating the surface elevation profile, generating the radial profile and the resulting cutting profile, and rendering the 3D representation to a display) may be carried out by the computer, with the controller 100 simply serving to control and receive data from the various hardware elements of the apparatus.

It will be understood that the only component of the surface elevation profile data which is of interest for forming a cutting profile is that which describes the substantially planar top surface of the wheel, including the top surface of the spokes. In order to determine an appropriate elevation value for a given radial position from the surface elevation profile, the following steps are conducted:

(A) A maximum elevation for the radial position is determined;

(B) Elevation data greater than a predetermined distance lower than the maximum elevation is masked (ignored) - e.g. the area between spokes;

(C) An average elevation for the remaining data is determined;

(D) Elevation data outside the central 50% of data points is masked (to remove data relating to spoke edges and other structures); and (E) An average value (mean, mode or median) is determined from the remaining (unmasked) data.

It will be appreciated that the above is merely one technique for determining an appropriate elevation value for each radial position. Each determined elevation value for each radial position forms part of the radial profile from which a cutting profile is to be generated. A simpler technique would be to simply use the maximum elevation at each radial distance. However, this would result in a spuriously high elevation where ridges are formed by surface damage, or by any noise present in the data. Some improvement could be achieved by filtering or averaging, or by identifying and masking from the data any surface damage. It will also be appreciated that the cutting profile could be determined directly rather than via a radial profile, particularly if a fixed cutting depth is used.

In the cutting mode, the cutting tool 90 is lowered to a desired cutting position by the vertical linear positioner 70 based on the cutting profile. It will be appreciated that the cutting profile could be smoothed (for example using a low pass filter), and that the number (and separation) of radial positions at which cutting takes place may be different to (larger or smaller) than the number (and separation) or radial positions at which surface sampling takes place.

Referring now to Figure IB, a top plan view of the apparatus shown in Figure 1A is schematically illustrated. Clearly visible in Figure IB is the top surface 5a of the wheel 5, including spokes 7. Also visible are the horizontal linear positioner 60 and the vertical linear positioner 70, which serve to position the laser displacement sensor 80 and the cutting tool 90 at a desired radial and vertical position.

In summary of the above, it will be understood that, with the laser displacement sensor at a fixed radial distance, the system rotates the wheel slowly whilst taking distance measurements from the sensor. When 360 degrees of distance and angular data has been acquired, the system moves the displacement sensor mounted on a linear stage a small distance along the radial and repeats the data acquisition. Data is collected and modelled using a computer or other data processing apparatus.

By using the depth data coupled with an angular encoder and linear positioning stage position, a 3 dimensional model can be generated within the computer. From this 3 dimensional mapping, a wheel radial profile can be extracted and then used as directions to move a cutting tool along the same (or derived) profile.

In one example, a scan rate of 3kHz, a laser spot size of 30μιτι and a wavelength of 650nm are used for the laser displacement sensor and a rotation rate of 0.5Hz is used for rotating the wheel. It will be appreciated that the overall mapping rate which can be achieved in this way is likely to be superior to that of a touch probe having an approximate dimension of 1mm and limitations on its speed of safe operation. It will be appreciated that other laser profiling and rotation

characteristics could also be used.

Referring now to Figure 2, an example 3D representation of a wheel as generated by the scanning mode of the apparatus of Figure 1 is shown.

Referring to Figure 3, a schematic flow diagram is provided which illustrates the scanning and cutting process. The system is initialised at a step SI. This includes setting the horizontal linear positioner 60 and vertical linear positioner 70 to a starting position for scanning. This involves setting the horizontal linear positioner 60 to position the laser displacement sensor 80 to a starting position either at or near the centre of the wheel 5 (if the laser displacement sensor 80 is to be moved incrementally outwards) or at the outer circumference of the wheel 5 (if the laser displacement sensor 80 is to be moved incrementally inwards). The vertical linear positioner 70 will be locked into a fixed position for the duration of the scan mode.

At a step S2, a first elevation profile ring is generated for a first radial position by rotating the wheel 5 360° on the mount 20 while sampling the elevation measurement generated by the laser displacement sensor 80. At a step S3 it is determined whether the generated elevation profile ring corresponds to the final concentric ring to be sampled (which of course it will not for the first elevation profile). If it is determined that the generated elevation profile ring does not correspond to the final concentric ring to be sampled, then the radial position of the laser displacement sensor 80 is incremented at a step S4. Optionally, at a step S5 the angular velocity of the rotation of the wheel 5 may be modified if it is desired to preserve a substantially constant spatial resolution across the surface of the wheel. This could be achieved by providing a slower angular velocity towards the outside of the wheel than towards the centre of the wheel. Otherwise, the step S5 can be omitted and an appropriate fixed angular velocity can be used which will provide a satisfactory level of resolution at the outside of the wheel (at the expense of oversampling towards the centre of the wheel). The process can then return to the step S2, where a further elevation profile ring is generated at the new radial position. The steps S2 to S4/S5 continue until it is determined at an instance of the step S3 that the final concentric ring has been sampled. The process then moves on to a step S6, where a 3D representation of the surface 5a of the wheel 5 is generated and displayed.

A radial profile based on the measured elevation at each radial position is also generated at a step S7, either directly from the raw data or indirectly from the 3D representation. The 3D representation and the radial profile are then provided to the operator for user review at a step S8. The 3D representation may include highlighted "problem" regions automatically detected by a computer. These may relate to damage to the wheel which might prejudice vehicle safety (giving the recutting technique a secondary benefit as a safety diagnostic tool) or which might cause problems for recutting. Also at the step S8 the user is able to set a cutting depth (how much material is to be removed from the surface of the wheel). Where surface damage is automatically identified by the system, for example by identifying non-repeating raised and/or depressed features, a proposed cutting depth at least for a radial portion of the wheel at which damage has occurred may be flagged to the operator, assisting the user in selecting the cutting depth. It will be appreciated that the cutting depth need not necessarily be uniform for all radii - a deeper cutting depth could be selected for a damaged region. At a step S9, the selected cutting depth(s) is applied to the radial profile to set a cutting profile. The step S9 also receives operator approval for the cutting mode to be engaged, leading to recutting taking place at a step S10. The recutting process causes the cutting tool 90 to be moved with respect to the (rotating) wheel to follow the cutting profile set at the step S9. The recutting process is completed when the cutting tool 90 has been applied throughout at least one complete rotation of the wheel for each radial position at which cutting is to take place.

Referring now to Figure 4, a schematic flow diagram is provided which explains how fine surface detail can be sampled at a different radial resolution than coarse surface detail. At a step S101, the radial increment which separates the concentric circles to be scanned is set to a first value, a. Then, at a step S102, an elevation profile ring is generated for a current radial position. At a step S103, it is determined whether the current concentric ring is the final one to be sampled. If it is the final ring then at a step S104 the steps S6 to S10 described in Figure 3 are conducted. If it is not the final ring then the radial position of the laser displacement sensor 80 is incremented by the first value a at a step S105, and a further elevation profile ring is generated at the step S106. At a step S107 it is determined whether there has been a high frequency change between adjacent elevation profiles. This could be determined where the magnitude of a change in elevation between adjacent concentric circles exceeds a predetermined threshold. If there has not been a high frequency change then the radial increment is set (or retained) at the value a at a step S108 whereupon the process returns to the step S103. The steps S103 to S107 are then repeated. If at the step S107 it is determined that there has been a high frequency change between adjacent elevation profiles then the radial increment is set to a second value b and the position of the laser displacement sensor 80 is "rewound" back to the previous radial position and then incremented by the value b (which is less than the value a) at a step S110. The process then returns to the step S102. It will be appreciated that the process (steps S103 to S110) will continue using the increment value b until the step S107 determines a low frequency change between adjacent elevation profiles. This could be determined where the magnitude of a change in elevation between adjacent concentric circles falls below a predetermined threshold. It should be understood that the respective thresholds for detecting high frequency and low frequency changes may be different. By way of the above process it is possible to sample (in the radial direction) planar areas at a relatively coarse level and edged and detail areas at a relatively fine level. As an example, a radial step size of 2mm could be used for coarse detail and a step size of 0.1mm could be used for fine detail. It will be appreciated that other step sizes could also be used.

In an alternative embodiment, the scanning process does not scan concentric rings, but instead continuously varies the radial position at which depth is being measured by the surface profiler while the wheel is being rotated, resulting in a spiral scanning path. The scanning spiral may start either at the outside edge of the wheel surface of the inside edge of the wheel surface. A problem with the concentric circle method described above is that a single rotation may be wasted while the radial position of the surface profiler is repositioned from one ring position to another ring position if the starting circumferential position for each scan is the same. Even if a different (staggered) circumferential start position can be used for each successive ring, a slight delay results for each ring, which accumulates over time. This issue does not arise for the spiral scanning pattern, since sampling occurs while the radius at which the surface position is being sampled is being continuously varied. In other words, the spiral pattern removes or at least reduces dead time in the sampling process because there is no pause in sampling while the surface profiler is repositioned.

Referring to Figures 5A and 5B, a concentric ring scanning pattern and a spiral scanning pattern respectively are schematically illustrated. In particular, Figure 5A shows the concentric circle scan method, with the concentric circles at various radii being visible, and the sampling points being identified by the spots disposed around the circle. Figure 5B shows the spiral scan method, with the continuous spiral path from the outside to the inside of the wheel being visible, and the sampling points being identified by the spots disposed on the continuous path. In both cases the spots on the rings/spiral are at the same circumferential position at all sampling radii. However, this need not necessarily be the case - provided that sufficient resolution of coverage is provided across the surface of the wheel such that an accurate representation of the surface of the wheel can be generated and used to form a cutting profile.

Again for either scan pattern, the sampled elevation (Z depth) along with the rotational angle (provided by the angular encoder) and the laser axis X position (radial position) are used to form a 3D matrix (or to populate a 2D matrix populated with depth values for each x, y position). A polar to Cartesian conversion will be required in this case because the wheel angle and laser X position define the x, y position as a polar measurement.

The resulting matrix effectively forms a depth map which may be rendered as a 2D or 3D image on a display. The depth map represents a surface, and is formed of volume (x, y, z) elements (voxels) - the 3D equivalent of pixels. Various operations may be applied to the depth map, for example low pass filtering, averaging, interpolation, morphological operations and the like. For example, low pass filtering could be used to remove noise from the depth map. Other operations may be used to pick out surface damage - for example a high pass filter could be used to identify candidate features which may represent surface damage. The candidate features could be narrowed down by removing those that feature repeatedly at regular intervals around the wheel (since these are likely to be structural features of the wheel such as nuts or spokes). The thus identified portions of the depth map may then be highlighted to the operator. Surface damage identified in this way (or any other way) may be analysed to identify the height of any ridged components of the damage and/or the depth of any gouged components. This could be achieved in a partly automated way in which the operator "draws around" a damaged area on the display, and the system then analyses the selected portion to identify its height and/or depth. The identified height of a ridge may be used to assist in identifying the original surface elevation at a given radii (thereby feeding in to the generation of a radial profile), while the identified depth of a gouge may be used to identify a cutting depth required to remove the gouge and recover a smooth surface.

Various operations to automatically pick out wheel damage or other irregularites from the 3D representation are possible. For example, in one embodiment an outer rim of the wheel or other normally concentric feature of the wheel is detected or specified by the operator. In order to determine whether the wheel is distorted (in which case recutting may be impossible and/or the wheel may need to be discarded on safety grounds), any unexpected discontinuities in the surface eleveation around a ring at the radius of the normally concentric feature are detected. In the case of a wheel rim, or other structure which can be expected to be continuous, a discontinuity is detected if the surface elevation changed by more than a threshold amount. In the case of a structure which can be expected to be present at regular intervals around the circumferential direction of the wheel (for example spokes), a discontinuity is detected if the elevation at an expected position of the structure differs by more than a threshold amount from the measured elevation at other parts of the structure at different circumferential positions. If a discontinuity is detected in this way it is highlighted to the operator.

In order that scanning and cutting can be conducted accurately, the top surface (to be cut) of the wheel should be level. In order to ensure that this is the case, the 3D map generator is operable to select a suitable radial position, for example the outer rim of the wheel, and to identify whether the surface elevation profile of a concentric ring at the radius corresponding to the outer rim has a consistent elevation within a predetermined tolerance. If the elevation varies outside of this tolerance, it can be determined that either the wheel is not mounted in a level position, or that the wheel is distorted. The distortion in this sense may be a large scale distortion across the entirety of the wheel rather than the localised damage referred to above. As a result, the analysis conducted may be smoothed or otherwise filtered to ignore surface damage. Alternatively, since this type of irregular mounting or distortion can be expected to occur gradually, the analysis may look for a particular elevation gradient around the concentric ring which exceeds a predetermined threshold. While a continuous structure is ideal for the performance of this analysis, is can also be achieved with regular structures (such as spokes) by identifying whether a set of positions on the surface elevation profile at regular intervals from each other in a circumferential direction at a fixed radius have a consistent elevation within a predetermined tolerance. In either case, if the profile or set of positions do not have a consistent elevation within the predetermined tolerance, the operator is notified that the wheel is either not properly mounted on the rotatable mount, or is distorted, and can take the necessary action to either remount the wheel or check whether it needs to be discarded.

The operator is able to specify ranges of radial distances at which cutting should take placed. This enables the operator to have overall control of the cutting process, and to be able to elect not to recut certain portions of the wheel. The cutting profile generator is responsive to the user inputting start and end radial distances for cutting to set the cutting profile such that the wheel will be recut only at radial distances between the user inputted start and end radial distances. The portion to be recut may be displayed to the operator on the 3D representation. To assist with this process, the apparatus may be configured to detect the reflectance at different radial positions on the surface of the wheel during the generation of the surface elevation profile. Diamond-turned portions of the wheel (which are the portions of interest for recutting) typically have a relatively high reflectance. The apparatus can then automatically mark up the 3D representation of the surface of the wheel to indicate areas of the surface of the wheel having a detected reflectance above a predetermined threshold. This may result in the start and end cutting radial distances being automatically populated (although the operator can override these if required). Conveniently, the automatic gain control system of a laser used as the surface profiler can be used to identify the reflectance without the need for additional hardware to be provided.

A surface elevation profile for a wheel is likely to be distinctive, and can be used to determine the type of the wheel by referring to either a local or external database storing elevation profiles for various wheels and information regarding those wheels. By comparing the generated surface profile with a surface profile for the wheel which is stored in a wheel profile database, wheel-related information relating to the wheel mounted in the apparatus can be extracted from the database if a match can be found. Even if the wheel has been damaged, image processing techniques can be used to recover sufficient information to characterise the wheel. For example, signatures could be used based on radial profiles and/or circumferential profiles at one or more radial/circumferential positions on the wheel. Even if certain portions of the wheel have been damaged, it is likely that at least some of the signature data will be unaffected, allowing a best match to be made. The wheel- related information may comprise a minimum safe elevation profile for the wheel. This can be compared with the detected surface elevation profile to determine whether cutting is possible. In other words, it may not be acceptable to continue to reduce the thickness of the wheel indefinitely by recutting, for safety reasons. In order not to breach safety parameters, the apparatus can constrain the cutting profile generator to generate the cutting profile so that the wheel is not cut to below the minimum safe elevation profile. Further, the 3D map generator is able to indicate to the user if the wheel cannot be satisfactorily recut (for example to remove surface damage) without cutting below the minimum safe elevation profile.

In addition, the wheel-related information may comprise one or more test parameters for the operator to test the wheel. The 3D map generator can also identify damage to the wheel by identifying differences between the generated surface profile and the version of the surface elevation profile stored in the wheel profile database. These automatically identified differences can be visually flagged to the operator.

It is useful for the operator to be able to inspect not only the 3D representation of the wheel, but also the wheel itself, and to be able to immediately appreciate those parts of the 3D representation and the physical wheel which correspond to each other. This is particularly important because a wheel will have multiple degrees of rotational symmetry. In order to assist the operator, the 3D map generator is responsive to the wheel being rotated on the rotatable mount to rotate the view of the 3D representation presented to the user. Preferably the orientation of the view provided of the 3D representation is determined from an output of an angular encoder used to determine the orientation of the wheel. In this way, if the user is viewing the 3D representation and wants to physically inspect a part of the wheel corresponding to a highlighted portion of the 3D

representation, he can rotate the wheel until the 3D representation shows the highlighted portion to be closest to him, and then inspect the physical wheel knowing that the part of the wheel closest to him corresponds to the area of interest indicated in the 3D representation.