Abstract:
An apparatus for recutting the surface of a wheel is described. The apparatus comprises a rotatable mount, for holding and rotating the wheel about its axis, a surface profiler, configured to detect and output a surface elevation profile of a concentric ring at a current radial position on the surface of the wheel, a linear drive mechanism, configured to reposition the surface profiler radially with respect to the wheel, a radial profile generator, configured to calculate a cutting profile for the wheel based on the surface elevation profile for each concentric ring, a cutting tool, and cutting control circuitry, configured 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.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority under 35 U.S.C. §119 to United Kingdom patent application serial no. 1221742.8, filed Dec. 3, 2012, the disclosure of which is incorporated herein by reference in its entirety. 
       FIELD OF THE INVENTION 
       [0002]    The present invention relates to wheel recutting. 
       BACKGROUND OF THE INVENTION 
       [0003]    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 colored paint finish. 
         [0004]    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 allows water and air to come into contact with the machined aluminum face, which in turn oxidizes (corrodes) and ruins the aesthetic appearance of the wheel. 
         [0005]    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 oxidized 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. 
         [0006]    However, there are a number of drawbacks associated with these processes. For example, the manual method is time consuming and requires a skilled machinist to operate the lathe. Furthermore, in the manual method, if a misjudgment is made during the process of moving both the X &amp; Y slides together, then the wheel may 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. Still further, the physical size of the touch probe makes it difficult to obtain an accurate mapping of wheel profile particularly where there are profile changes which are similar in size to the physical dimensions of the touch probe. 
         [0007]    Alternative systems and methods are desired. 
       SUMMARY 
       [0008]    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, configured to detect and output a surface elevation profile of a concentric ring at a current radial position on the surface of the wheel; a linear drive mechanism, configured to reposition the surface profiler radially with respect to the wheel, a cutting profile generator, configured to calculate a cutting profile for the wheel based on the surface elevation profiles of at least some of the concentric rings; a cutting tool; and cutting control circuitry, configured 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. 
         [0009]    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 corresponding surface elevation profile. 
         [0010]    It will be appreciated that the cutting profile may be generated in respect of the complete top surface of the wheel using all of the surface elevation profiles, 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 profiles. Equally it will be appreciated that the apparatus may be configured to only generate surface elevation profiles for a radial portion of the top surface of the wheel where only that portion requires refinishing. 
         [0011]    The cutting tool may be moveable both radially with respect to the wheel and parallel to the axis of rotation of the wheel. The cutting control circuitry is configured to control the position of the cutting tool and the rotation of the wheel to recut the surface of the wheel. The cutting tool and the surface profiler may be co-mounted, in which case the cutting control circuitry may be configured 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). 
         [0012]    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 a irreversible cut is made to the wheel. 
         [0013]    The 3D map generator may itself be configured 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. 
         [0014]    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. 
         [0015]    While the surface profiler could in principle be a contact-based profiler, preferably the surface profiler is a non-contact profiler. More preferably the non-contact profiler is an optical profiler. Still more preferably the optical profiler is a laser. 
         [0016]    The rotatable mount may be configured 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. 
         [0017]    Alternatively, the rotatable mount may be configured 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. 
         [0018]    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 configured 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. 
         [0019]    In one way of implementing this, the surface profiler is configured to detect a high frequency change when the 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. 
         [0020]    Further benefits of embodiments of the invention include but are not limited to: an accurate radial profile can be extracted irrespective of the 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 digitization 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. 
         [0021]    According to a another 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 and outputting a surface elevation profile of a concentric ring at each of a set of different radial positions on the surface of the wheel; calculating a radial profile of the wheel based on the surface elevation profiles of at least some of the concentric rings; controlling the position of a cutting tool with respect to the wheel to recut the surface of the wheel in accordance with the generated radial profile. 
         [0022]    Following the cutting operation, a step of applying a lacquer finish to the recut surface may be provided. 
         [0023]    Various further aspects and features of the present invention are shown and described herein. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]    Exemplary 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: 
           [0025]      FIGS. 1A and 1B  schematically illustrate a wheel refinishing apparatus according to an embodiment of the invention; 
           [0026]      FIG. 2  schematically illustrates a 3D representation of a wheel images by the apparatus of  FIG. 1 ; 
           [0027]      FIG. 3  is a schematic flow diagram of the operation of the wheel refinishing apparatus of  FIG. 1 ; and 
           [0028]      FIG. 4  is a schematic flow diagram showing a variable increment radial sampling routine. 
       
    
    
     DETAILED DESCRIPTION 
       [0029]    Referring first to  FIG. 1A , a side 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 driven 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 measures an elevation of the surface  5   a  of the wheel  5 , and is controlled by, and passes data to, the controller  100 . 
         [0030]    The recutting apparatus effectively operates in a scan mode to map the surface  5   a  of the wheel  5  and generate a cutting profile for the wheel, and in a cutting mode, in which the surface  5   a  of the wheel  5  is recut based on a 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 degrees (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 position the laser displacement sensor  80  at 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  5   a  of the wheel  5  has been mapped. 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 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 cutting profile. The cutting profile may be modified 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). 
         [0031]    It will be understood that the principal 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);   (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.       
 
         [0037]    It will be appreciated that the above is merely one technique for determining an appropriate elevation value for each radial position. 
         [0038]    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. 
         [0039]    Referring now to  FIG. 1B , a top plan view of the apparatus shown in  FIG. 1A  is schematically illustrated. Clearly visible in  FIG. 1B  is the top surface  5   a  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. 
         [0040]    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 modeled using a computer or other data processing apparatus. 
         [0041]    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. 
         [0042]    It is further understood that the controller may be implemented using one or more corresponding computer processors (e.g. CPU) and associated data storage devices (e.g. memory). The data storage device(s) may store, for example, (i) a program (e.g., computer program code and/or a computer program product) adapted to or configured to direct the processor to perform the functions described herein in accordance with embodiments of the present invention, and (ii) a database adapted to store information that may be utilized or required by the program. One or more computer programs may be stored, for example, in a compressed, an uncompiled and/or an encrypted format, and may include computer program code. The instructions of the program may be read into a main memory of the processor from a non-transitory computer-readable medium other than the data storage device, such as from a ROM or from a RAM. While execution of sequences of instructions in the program causes the processor to perform the process steps described herein, hard-wired circuitry may be used in place of, or in combination with, software instructions for implementation of the processes of embodiments of the present invention. Thus, embodiments of the present invention are not limited to any specific combination of hardware and software. The computer program code required to implement the functions described herein can be developed by a person of ordinary skill in the art, and is not described in detail herein. The term “computer-readable medium” as used herein refers to any medium that provides or participates in providing instructions to the processor of the computing device (or any other processor of a device described herein) for execution. Such a medium may take many forms, including but not limited to, non-volatile media, non-transitory media, tangible media, volatile media, and transmission media. Non-volatile media and tangible media include, for example, optical or magnetic disks, such as memory. Volatile media include dynamic random access memory (DRAM), which typically constitutes the main memory. Common forms of computer-readable media include, for example, a floppy disk, a flexible disk, hard disk, magnetic tape, any other magnetic medium, a CD-ROM, DVD, any other optical medium, punch cards, paper tape, any other physical medium with patterns of holes, a RAM, a PROM, an EPROM or EEPROM (electronically erasable programmable read-only memory), a FLASH-EEPROM, other memory chip or cartridge, or other medium from which a computer can read. The process steps for carrying out the recutting of the surface of the wheel as described herein may be automatically performed according to the computer executing program instructions. 
         [0043]    Various forms of computer readable media may be involved in carrying one or more sequences of one or more instructions to a processor (or any other processor of a device described herein) for execution. For example, a remote computer can load instructions into dynamic memory and send the instructions over an a connection (e.g. Ethernet), cable line, or even telephone line using a modem. A communications device local to a computing device (or, e.g., a server) can receive the data on the respective communications line and place the data on a system bus for the control processor. The system bus carries the data to main memory, from which the processor retrieves and executes the instructions. The instructions received by main memory may optionally be stored in memory either before or after execution by the processor. In addition, instructions may be received via a communication port as electrical, electromagnetic or optical signals, which are exemplary forms of wireless communications or data streams that carry various types of information. 
         [0044]    Embodiments of the present invention may also interact and/or control one or more user devices or terminals. The user device or terminal may include any one or a combination of a personal computer, a mouse, a keyboard, a computer display, a touch screen, LCD, voice recognition software, or other generally represented by input/output devices required to implement the above functionality. The program also may include program elements such as an operating system, a database management system and “device drivers” that allow the processor to interface with computer peripheral devices (e.g., a video display, a keyboard, a computer mouse, and the like). 
         [0045]    In one example, a scan rate of 3 kHz, a laser spot size of 30 μm and a wavelength of 650 nm are used for the laser displacement sensor and a rotation rate of 0.5 Hz 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 1 mm and limitations on its speed of safe operation. It will be appreciated that other laser profiling and rotation characteristics could also be used. 
         [0046]    Referring now to  FIG. 2 , an example 3D representation of a wheel as generated by the scanning mode of the apparatus of  FIG. 1  is shown. 
         [0047]    Referring to  FIG. 3 , a schematic flow diagram is provided which illustrates the scanning and cutting process. The system is initialized at a step S 1 . 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. 
         [0048]    At a step S 2 , a first elevation profile 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 S 3  it is determined whether the generated elevation profile 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 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 S 4 . Optionally, at a step S 5  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 S 5  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 S 2 , where a further elevation profile is generated at the new radial position. The steps S 2  to S 4 /S 5  continue until it is determined at an instance of the step S 3  that the final concentric ring has been sampled. The process then moves on to a step S 6 , where a 3D representation of the surface  5   a of  the wheel  5  is generated and displayed. 
         [0049]    A radial profile corresponding to the elevation data at each radial position is also generated at a step S 7 , 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 S 8 . 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 might cause problems for recutting. Also at the step S 8  the user is able to set a cutting depth (how much material is to be removed from the surface of the wheel). At a step S 9 , the selected cutting depth is applied to the radial profile to set a cutting profile. The step S 9  also receives operator approval for the cutting mode to be engaged, leading to recutting taking place at a step S 10 . 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 S 9 . 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. 
         [0050]    Referring now to  FIG. 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 S 101 , the radial increment which separates the concentric circles to be scanned is set to a first value, a. Then, at a step S 102 , an elevation profile is generated for a current radial position. At a step S 103 , 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 S 104  the steps S 6  to S 10  described in  FIG. 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 S 105 , and a further elevation profile is generated at the step S 106 . At a step S 107  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 S 108  whereupon the process returns to the step S 103 . The steps S 103  to S 107  are then repeated. If at the step S 107  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 S 110 . The process then returns to the step S 102 . It will be appreciated that the process (steps S 103  to S 110 ) will continue using the increment value b until the step S 107  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 2 mm could be used for coarse detail and a step size of 0.1 mm could be used for fine detail. It will be appreciated that other step sizes could also be used. 
         [0051]    While the foregoing invention has been described with reference to the above embodiments, various modifications and changes can be made without departing from the spirit of the invention. Accordingly, all such modifications and changes are considered to be within the scope of the appended claims.