Tread depth measurement

Abstract

A method of generating a three-dimensional topological surface representation of a tyre on a vehicle, the method comprising: using a tread depth measurement device to record tread depth data for a tyre surface moving relative to the tread depth measurement device; generating a movement profile of the tyre surface; and using the movement profile of the tyre surface to map the tread depth data onto a base tyre structure, thereby generating a three-dimensional topological surface representation of the tyre.

1 . A method of generating a three-dimensional topological surface representation of a tyre on a vehicle, the method comprising:
 using a measurement device comprising a sensor to record tyre surface data for a tyre surface during a relative movement between the measurement device and the tyre surface; and   matching respective times at which the tyre surface data were recorded to corresponding respective positions on a curved base tyre structure and assembling the tyre surface data into said corresponding respective positions on the curved base tyre structure to construct the three-dimensional topological surface representation of the tyre.   
     
     
         2 . The method as claimed in  claim 1 , further comprising recording the tyre surface data as the vehicle moves towards or away from the measurement device. 
     
     
         3 . The method as claimed in  claim 1 , further comprising generating a movement profile and using the movement profile to match said respective times to said corresponding respective positions, wherein the movement profile comprises or is derived from a trace defined by a set of data representing the positions at given times traced by a part of the tyre surface as the relative movement takes place. 
     
     
         4 . The method as claimed in  claim 3 , further comprising one or more of:
 i) discarding portions of the trace corresponding to one of more of: tread grooves, sipes, and tyre shoulders;   ii) filtering noise from the trace;   iii) smoothing the trace; and   iv) using spline interpolation to remove discontinuities in the trace.   
     
     
         5 . The method as claimed in  claim 3 , further comprising obtaining a plurality of traces, each corresponding to a respective position on the tyre surface. 
     
     
         6 . The method as claimed in  claim 5 , further comprising extrapolating one or more traces corresponding to respective positions on the tyre surface to extend said one or more traces to a length that is the same as a length of a further trace corresponding to a further position on the tyre surface. 
     
     
         7 . The method as claimed in  claim 5 , further comprising at least one of:
 discarding any trace that shows more than a defined variation from a median of the other traces of the plurality of traces; and   taking an average of the plurality of traces to obtain a movement profile comprising a single trace.   
     
     
         8 . The method as claimed in  claim 1 , further comprising recording tyre surface data as the tyre turns relative to the measurement device while the vehicle is stationary. 
     
     
         9 . The method as claimed in  claim 8 , further comprising generating a movement profile and using the movement profile to match said respective times to said corresponding respective positions, wherein the movement profile is determined from a rotation speed of the tyre. 
     
     
         10 . The method as claimed in  claim 8 , wherein the three-dimensional topological surface representation is generated by mapping the tyre surface data onto the curved base tyre structure based on a frame rate of the measurement device. 
     
     
         11 . The method as claimed in  claim 1 , wherein the tyre surface data is obtained using a handheld device. 
     
     
         12 . The method as claimed in  claim 11 , wherein the device is adapted to generate a movement profile by measuring movement of the device relative to the tyre. 
     
     
         13 . The method as claimed in  claim 11 , wherein the handheld device comprises an accelerometer. 
     
     
         14 . The method as claimed in  claim 13 , further comprising using feedback from the accelerometer to determine the curvature of the tyre. 
     
     
         15 . The method as claimed in  claim 1 , further comprising correcting for an angle of a scan relative to an axis of the tyre. 
     
     
         16 . The method as claimed in  claim 1 , further comprising improving the generated three-dimensional topological surface representation using one or more of a combination of spatial low pass filters and a bilateral filter for preserving edges of the tyre. 
     
     
         17 . The method as claimed in  claim 1 , wherein the measurement device is a tread depth measurement device, and the tyre surface data is tread depth data. 
     
     
         18 . The method as claimed in  claim 17 , wherein the tread depth measurement device comprises an optical sensor. 
     
     
         19 . The method as claimed in  claim 1 , wherein the measurement device is arranged to use a sensing arrangement both for determining a distance to the tyre surface and for measuring the tyre surface. 
     
     
         20 . An apparatus for generating a three-dimensional topological surface representation of a tyre on a vehicle, the apparatus comprising:
 a measurement device comprising a sensor arranged to record tyre surface data for a tyre surface during a relative movement between the measurement device and the tyre surface; and   a processing system configured to match respective times at which the tyre surface data were recorded to corresponding respective positions on a curved base tyre structure and to assemble the tyre surface data into said corresponding respective positions on the curved base tyre structure to construct the three-dimensional topological surface representation of the tyre.