Method for determining profile of tyres

Abstract: An apparatus and method for detecting the profile of an article comprising: mounting means for the article (4) about an X axis, a non-contact type Y distance measuring means (10) arranged to measure in the Y axis direction perpendicularly and towards said X axis and movable in the X axis direction, X detection means (7) for sensing the position of the Y measuring means in the direction of the X axis, data memory means (13) for storing the X positions and the corresponding Y distance measurement data obtained, and radius calculating means (14) for calculating the radius of at least part of the surface of the article (4) from the digital X and Y data stored in the data memory means (13), the radius calculating means (14) having division means (15) for dividing the X and Y data for a plurality of portions of the article based on predetermined reference values and arithmetic means (16) for determining the radii of the respective portions each from the corresponding data divided by the division means, the arithmetic means being operable to determine the equation of the circle of: x² + y² + ax + by + c = 0 from the X and Y data to calculate the radius of the articles, the coefficients a, b and c of the circle equation being determined by least square approximation.

Description: The present invention relates to a method for determining the profile of tyres. Japanese Utility Model Publication SHO 62-102110 discloses an apparatus for measuring the radius of a tyre tread. This comprises a means for measuring the crown radius of a tyre which is an optical sensor for measuring the distance to the crown portion of the tyre from the sensor without contact to the tyre. The sensor is mounted so that it can be moved in the direction of the axis of the tyre and thus scan across the tread region. The output signals in relation to the distance from the sensor to the surface of the tyre and the position of the optical sensor in relation to the axial direction of the tyre are both used to calculate the profile of the tyre crown portion by means of measuring three points on the tread profile and calculating from the said three points. Thus the conventional apparatus for measuring the radius of the crown of a tyre is adapted to determine the said crown radius from three points on the tread profile and is therefore unable to accurately and rapidly measure the profile of the tread shoulder portions. Furthermore the apparatus fails to give measurements of sufficiently high accuracy since it does not measure variations in crown shape and simply averages over three points. An object of the present invention is to provide a method to determine the profile of tyres which is adapted to determine the radius of curvature in short section of the tyre with higher accuracy. According to the present invention comprises mounting the tyre on a measuring apparatus with the tyre rotation axis being in parallel to an X axis, measuring perpendicularly to the X axis a Y axis distance (Yi) from a Y axis distance measuring means of the measuring apparatus to the tyre tread and storing such measurement as Y data, measuring an X axis position of the Y axis distance measuring means corresponding to the Y data measurement and storing such a measurement as X data; repeating the measurement and storing of Y axis distances and X axis positions while moving the Y axis distance measuring means along the X axis; characterised by inputting reference data (-q,-p,+p,+q) on the tyre to be measured into a data memory means, said reference data, based on a tyre equator line set at a zero X axis point, including standard X axis lengths (-p to +p, -q to -p and +p to +q) of the crown portion and shoulder portions respectively of the profile for the tyre to be measured, separating the series of X and Y data into two data sets with reference to said reference data (-q,-p,+p,+q), one set corresponding to points on the crown portion of the tyre tread, the other set corresponding to points on the shoulder portions of the tyre tread and calculating the radii of the crown portion and the shoulder portions of the tyre tread respectively using the separated data sets. The Y measuring means is preferably a laser sensor movable in the direction of the X axis. The movement in the direction of the X axis may be provided by a feed screw engaging the Y measuring means and disposed parallel to the X axis. A rotary encoder for the feed screw may be used to detect rotation of the feed screw to give the X data. The data memory means and the radius calculating means are preferably a computer. The apparatus for carrying out the invention may also include rotation means for the tyre so that it can be rotated about its X axis and angular position R detection means are provided to detect the angle of rotation of the tyre and provide an R data output. Data memory means are then provide to store said R angle data and the apparatus further comprises radial runout (RRO) calculation means to determine the radial runout of the tyre from the Y and R data in the memory means. The calculation to determine the radii of the respective crown and shoulder portions from the corresponding separated data sets is by determining the equations of the circle x² + y² + ax + by + c = 0 from the X and Y data, where the coefficients a, b and c are determined by least square approximation and this equation the radius is given by ((a/2)² + (b/2)² - c) 1/2 The method may also include computation of radial runout of the tyre using R angle data corresponding to particular X and Y values for rotation of the tyre. Further aspects of the present invention will become apparent from the following description, by way of example only, of an embodiment of the method: Figure 1(a) is a perspective diagram of an apparatus for determining the profile of tyres; Figure 1(b) is a diagram illustrating the basic concept of the apparatus; Figure 2 is a graphical display showing the profile and radius of the tyre; Figure 3 is a flow chart showing the radius measuring procedure; Figure 4 is a diagram showing a method of interpolating the data; Figure 5 is a graph showing the radial runout (RRO) of a tyre; Figure 6(a) is a diagram showing an arrangement for positioning a measuring unit; and Figure 6(b) is a sectional view along the line Z-Z in Figure 6(a). A tyre mount 2 is fixedly provided on a base 1. The tyre 4 is mounted on a rotatable shaft 3 which extends in a vertical direction. The axis of the shaft 3 will hereinafter be referred to as the "X-axis". A handle 5 is fixed to the upper end of the shaft 3 for rotating the shaft 3 and thus the tyre 4. The shaft 3 is provided at its lower end with a R detection means 6 for sensing the angle of rotation R of the shaft 3. The R detection means 6 comprises a rotary encoder. The base 1 is provided with rails (not shown) on which a movable table 7a is slidably mounted for movement in a horizontal direction (hereinafter referred to as the "direction of the Y-axis") intersecting the X-axis at right angles. The table 7a is movable by rotating a threaded rod (not shown) by a handle 7b. The movable table 7a carries a measuring unit 7 thereon. The measuring unit 7 has a rotatable feed screw 8 extending vertically parallel to the X-axis. A motor 9 for rotating the feed screw 8 is provided in the lower portion of the measuring unit 7. A Y distance measuring means 10 is mounted in the measuring unit 7 in a screw-thread engagement with the feed screw 8 and movable upwardly and downwardly by rotation of the feed screw 8. The Y measuring means 10 comprises a laser sensor and is able to measure the distance Yi from the peripheral surface of the tyre 4 in the direction of the Y-axis without contacting the tyre. Coupled to the feed screw 8 is an X detection means 11 for measuring the position Xi of the Y detection means 10 with respect to the X-direction. The X detection means 11 comprises a rotary encoder for counting the number of revolutions of the feed screw 8. The position of the Y detection means 10 in the X-direction is found by multiplying the thread pitch of the feed screw 8 by the number of revolutions. The range of movement in X-direction (widthwise of the tyre) is such that measurements can be obtained for tyres of every category. A personal computer 12 provides a data memory means 13 for storing the data from the X, Y and R detection means 11, 10 and 6, and radius calculating means 14 for calculating the radius of the tyre tread from the stored data. The calculating means 14 comprises division means 16 for dividing the Xi and Yi data into groups for a plurality of portions of the width of the tyre such for example as the crown portion and shoulder portions, and arithmetic means 16 for calculating the radii of the respective crown and shoulder portions from the corresponding data group from the division means 15. The computer 12 is connected to a display 17 and an X-Y plotter 18 to show the profile and radii of the section of the tyre tested. Also connected to the computer is RRO display means 19 for displaying the RRO (radial runout) of the tyre determined from the X and R data in the data memory means 13. The RRO display means 19 comprises an X-Y recorder. Indicated at 20 is an input unit for the personal computer 12. The radius of the tyre is measured in the following manner. First, the tyre 4 is mounted and inflated on a rim and the assembly is mounted on the shaft 3. The shaft 3 is locked against rotation. Next, the movable table 7a is moved in the Y-direction to set the distance Yi between the peripheral surface of the tyre 4 and the Y measuring means 10 to a predetermined value. The motor 9 is then continuously driven to continuously rotate the feed screw 8 and continuously move the Y measuring means 10. During this movement, measurements are taken for Yi at predetermined intervals. In this case, the distance Yi between the Y measuring means 10 and the peripheral surface of the tyre 4 is measured by the Y measuring means 10, and the position Xi of the Y detection means 10 in the X-direction is measured by the X detection means 11. Each pair of Xi and Yi data items is stored in the data memory means 13 of the computer 12 as the coordinates of a point. Using the data for a multiplicity of points thus stored, the profile of the tyre 4 is calculated by the computer 12. The profile can be monitored as displayed on the display 17 as seen in Figure 2 (I). The profile can also be displayed on the X-Y plotter 18. At least five sets of data per centimetre of tyre width are collected for the profile data. The procedure for determining the tread radius from Xi and Yi data in the data memory means 13 will be described next with reference to Figure 3. The data in the memory means 13 is first subdivided into groups by the division means 15. This can be into data for the tyre crown portion and data for the shoulder portions. The data is divided in the following manner. First of all, opposite end values of the data are detected which mean the Xi and Yi data at each of opposite ends of the tyre cross section. The value X representing each end is determined by detecting the value Y equal to or exceeding a certain reference value. More specifically, the value Y is compared with the predetermined reference value, and upon the value Y equal to or exceeding the reference value, the corresponding X value is taken as the end value of the X data. When the values X at the opposite ends of the data are thus determined, the value X at the mid-point between the opposite ends is calculated. The calculated mid-point of the X data corresponds to or represents the equator of the tyre and is used to divided the tread of the tyre 4 into the crown portion and the shoulder portions. A region is specified to either side of the centre which is the portion of the tyre equator to define the crown portion as shown in Figure 3. The regions from these limits to the sides of the tyre thus define the shoulder portions. Thus, the mid-point value of the data must be detected. The X data coordinate system is then so transformed that the mid-point value of X data serves as the origin of the X-axis. Next, reference values are entered by the input unit 20 to specify the region for which calculation is to be performed. Thus, the reference values define the width of the crown portion or shoulder portion. These values to be entered represent the distance as measured from the equator. After entering the reference values, the data between the opposite ends can be divided into the data as to the crown portion and the data as to the shoulder portions. Suppose the region of the crown portion is specified as the range of from -p to +p. Of the data between the opposite ends, the X data from -p to +p is taken as the data as to the crown portion. Further if the range of -q to -p and the range of +p to +q are entered as the regions of the shoulder portions, the X data from -q to -p and from +p to +q among other items of data between opposite ends is taken as the data for the shoulder portions. In this way, the stored data is divided by the division means 15 into groups for the crown portion and shoulder portions. Subsequently, the data for the bottoms of the grooves of the tyre pattern is deleted from the data. The bottom data represents the grooves formed in the tyre tread and if not detected and removed is an impediment to the calculation of an accurate radius of the tyre crown portion or shoulder portions and must therefore be deleted. The groove bottom data is identified by reference to Y values. For this purpose, the data for the top point of the tyre is detected first (subsequent to the detection of the opposite end values and mid-point value of the data). The Y measurements which are above a certain reference value beyond the Y measurement of the top point are interpreted as being groove data. Different reference values are used for the crown portion and the shoulder portions. The groove bottom data identified as such is deleted so as not to be used in the subsequent calculation. Next, the data for the groove wall portions and noise are deleted from the specified data since these are also an impediment to subsequent accurate calculation of the tyre radius. The data to be deleted is identified according to whether four consecutive Y values are smooth values. More specifically, the value Yi is the data to be used when the four consecutive values of Yi, Yi+1, Yi + 2 and Yi+3 fulfil the requirements of: (Yi - Yi+1)² ≦ d (Yi - Yi+2)² ≦ e (Yi - Y1+3)² ≦ f wherein d, e and f are predetermined reference values. The values failing to fulfil any one of the above requirements are deleted as inappropriate data. When the deletion of data for the groove bottoms, groove walls and noise leaves in the resulting group of data items a blank section (corresponding to the deleted data) which is greater than a certain value, the blank section is filled by interpolated date. More specifically, if the deleted blank section in the group of consecutive data items is longer than the predetermined value, this section is interpolated with data to make the data items sufficiently complete. Suppose if the data between the ith data and the (i+n)th data is deleted, producing a blank section longer than the predetermined value as seen in Figure 4. The data of Yi + h/2 is then inserted as the (i+n/2)th position. In this way, the data is divided for the crown portion and the shoulder portions by the division means 15, and the data to be used is determined. The radii of the crown portion and the shoulder portions are then calculated by the arithmetic means 16. The arithmetic means 16 determines the coefficients a, b and c for the circle equation of: x² + y² + ax + by + c = 0 from the stored X and Y data to calculate the centre of circle (-a/2, -b/2) and the radius: ((a/2)² + (b/2)² - c) 1/2 The coefficients a, b and c are determined by least square approximation. With this method, actual Xi and Yi data is substituted in the circle equation: x² + y² + ax + by + c = 0 to obtain S as expressed by: S = Xi² + Yi² + aXi + bYi + c and to find the coefficients a, b and c which make the sum ΣS² minimum, the sum of S² being calculated for all the effective data (X, Y) as to the contemplated region. The crown portion tread radius thus obtained is indicated at (III) in Figure 2, and the shoulder portion tread radius obtained at (II) in Figure 2. The display 17 shows these radii. The radius of the desired region can be determined by the method described above. At least the tread crown radius and the tread shoulder radius can be determined at the same time. Next, the calculated display of RRO will be described. First, the shaft 3 is unlocked, and the tyre 4 is rotated with the handle 5. The angle of rotation R is detected by the R detection means 6, and at the same time, the distance Y from the tyre peripheral surface is measured by the Y detection means 10. The point (R, Y) is stored in the data memory means 13. Such points over the entire periphery of the tyre are measured and stored. The R and Y data is fed to the RRO display means 19 to present a graph as shown in Figure 5. As seen in Figures 6(a) and (b), the measuring unit 7 is provided with positioning jigs (stoppers) 21 for positioning the tyre surface within the range of m ± 15mm wherein m is the fixed focal length of the Y detection means 10 to thereby regulate the measuring range. When the measuring unit 7 is moved towards the tyre, the forward ends of the stoppers 21 come into contact with the tyre surface, whereupon the measuring unit 7 is halted.

Claims: A method of determining the profile of a tyre tread comprising mounting the tyre (4) on a measuring apparatus with the tyre rotation axis being in parallel to an X axis, measuring perpendicularly to the X axis a Y axis distance (Yi) from a Y axis distance measuring means (10) of the measuring apparatus to the tyre tread and storing such measurement as Y data, measuring an X axis position (Xi) of the Y axis distance measuring means (10) corresponding to the Y data measurement and storing such a measurement as X data; repeating the measurement and storing of Y axis distances (Yi) and X axis positions (Xi) while moving the Y axis distance measuring means (10) along the X axis; characterised by inputting reference data (-q,-p,+p,+q) on the tyre to be measured into a data memory means (13), said reference data, based on a tyre equator line set at a zero X axis point, including standard X axis lengths (-p to +p, -q to -p and +p to +q) of the crown portion and shoulder portions respectively of the profile for the tyre to be measured, separating the series of X and Y data into two data sets with reference to said reference data (-q,-p,+p,+q), one set corresponding to points on the crown portion of the tyre tread, the other set corresponding to points on the shoulder portions of the tyre tread and calculating the radii of the crown portion and the shoulder portions of the tyre tread respectively using the separated data sets. A method of determining the profile of a tyre according to claim 1 characterised in that the radii of the crown and shoulder portions are calculated by determining for each separated data set of X and Y the equation of the circle x²+y²+ax+by+c = 0 determining the coefficients a, b, and c by least square approximation and calculating the radius according to radius = ((a/2)²+(b/2)²-c) 1/2 . A method of determining a tyre tread profile according to either of claims 1 or 2, characterised in that the separation of the series of X and Y data in two data sets is carried out by determining the opposite end values of the stored X data for which stored Y data exists, determining the mid-point between these opposite end X data values and comparing the X data based on the mid-point with the inputted reference data (-q,-p,+p,+q) of the crown portion (-p to +p) and shoulder portions (-q to -p and +p to +q). A method of determining the profile of a tyre tread according to any of claims 1, 2 or 3, characterised in that the tyre is rotated about its X axis and the R angle data corresponding to particular X and Y values are calculated to determine the radial runout (RRO) of the tyre with respect to the X axis.

Inventors: ASANO KAZUO, WADA YASUO, ASANO, KAZUO, WADA, YASUO
Applicants: SUMITOMO RUBBER IND, SUMITOMO RUBBER INDUSTRIES LIMITED
Application year: 1991
Main classification: G01B11
IPC codes: B60C3, G01B21, G01M17, B60C9, G01B11