GB2351346A

GB2351346A - Determining the uniformity of a tyre

Info

Publication number: GB2351346A
Application number: GB9914688A
Authority: GB
Inventors: Neville John Turley
Original assignee: Dunlop Tyres Ltd
Current assignee: Dunlop Tyres Ltd
Priority date: 1999-06-23
Filing date: 1999-06-23
Publication date: 2000-12-27
Also published as: GB9914688D0

Abstract

To evaluate the uniformity of a pneumatic tyre (1) in a particular direction eg along a circular path around the sidewall (4), the comparative height of a plurality of points along that direction is obtained at a fixed distance from the rotational axis (I) of the tyre eg by means of a sensor (2) for measuring the distance to the nearest point on the sidewall (4). The basic set of data formed by one or more initial scans is processed to identify specific data resulting from non-critical uniformity irregularities such as spue pips, and the identified data is removed from the basic set of data. The resulting modified basic data is processed in a secondary scan to identify any remaining uniformity irregularities eg due to sidewall bulges, and the uniformity of the tyre is graded according to the identified remaining uniformity irregularities.

Description

2351346 A METHOD OF DETERMINING THE UNIFORMITY OF A TYRE The present

invention relates to a method of determining the uniformity of a tyre and particularly but not exclusively to determining the existence of sidewall defects such as bulges.

The final operations in the tyre manufacturing process include inspection of the tyre for manufacturing defects and quality grading according to the measured level of any defects detected. Aspects of the tyre which are normally scrutinised in this process are uniformity, both radial and lateral, and also the presence of bulges in the internal tyre carcass structure which mav result from such factors as irregularities in component joints. Such bulges are most evident and easily measured on -he tyre sidewall.

In modern tvre manufacturing plants this operation - 4 of tyre scru,-.Lny is increasingly automated.

In a typical automated operation the tyre is inflated and turned about its rotational axis past stationary concentric sensors which detect the 2 distance to the tyre surface. Such sensors may be of a type which physically contact the tyre surface or may be of a non-contacting type using laser or capacitance measuring techniques. The resultant measurements provide data comparing the distance from the fixed sensor to the tyre surface at a number of points along a circular arc around the tyre. This data is then analysed automatically by predetermined routines to furnish information on uniformity and bulges which provides the basis for classifying --he quality of the product.

However a Droblem which exists with such automatic 4 uniformity inspection operations is that of distinguishing between non- uniformities which affect the quality ranking of the tyre and those nonuniformities which do not.

A particular example of a non-uniformity which does not normally debase the quality of the tyre is the witness-marks of spue-pips present o n the tyre sidewalls. Spue-pips result from the passage of rubber down air vent holes in the tyre sidewall mould plate. The venting of tyre moulds is necessary to ensure that the moulded tyre achieves 3 good contact with the mould surface. The most common form of venting comprises small-diameter holes drilled through the mould wall. After the air has vented through such holes, the uncured rubber of the tyre flows down the hole, resulting in a bristle-like cured spue-pip, in the finished tyre surface. Such spue-pips are normally removed by trimming but leave behind witness marks on the tyre surface.

Although these witness marks detract from the visual appearance of the tyre their presence may not usually be reason for downgrading the tyre quality. Whilst it is possible to position the sensor to avoid many such marks, the reality of an automated system dealing with a variety of types and sizes of tyres is such that many such marks will be detected. Witness marks which are detected by the automated uniformity screening operation may be interpreted as bulges and erroneously held to be indicative of a more serious non-uniformity of the carcass structure.

It is therefore an object of the present invention to provide a method of avoiding detecting unwanted 4 non-uniformities in an automated tyre inspection procedure.

According to the invention a method of evaluating the uniformity of a pneumatic tyre comprises obtaining from the inflated tyre a basic set of data comprising the comparative height in the particular direction of a plural number of points on the tyre surface at a fixed distance from the tyre rotational axis, processing the basic set of data in one or more preliminary scans to identify the specific data resulting from predetermined non-critical uniformity irregularities, removing the identified data from 4 the basic set of data, processing the modified basic set of data in a secondary scar, to identify any remaininQ uniformity irregularities, and grading the uniformity of the tyre according to the identified remaining critical uniformity irregularities.

Further aspects of the invention will become apparent from the following description by way of example only of one embodiment in conjunction with the following drawings in which:

Figure I shows a graphical representation of the measured sidewall uniformity of a truck tyre; Figures 2-4 show graphical representations of the data of Figure 1 after various scannings; and Figu.res SA and 5B show a schematic representation of the apparatus used in a tyre uniformity measurement.

In the tyre uniformity screening method according to the invention, as generally depicted in Figures 5A and 5B, a tyre 1 is mounted on a wheelrim 3, inflated and rotated in an anti-clockwise direction R about its rotational axis I in the proximity of a stationary sensor 2 positioned in the region of the tyre sidewall 4. The sensor 2 is capable by suitable means of measuring the distance d to the nearest point on the tyre surface. The measurement data from the sensor 2 is taken to data storage means (not shown) for subsequent analysis.

The distance measurement for a large number of points around the entire 3600 of the sidewall circumferential periphery are taken. Preferably and most conveniently for subsequent analysis these measurements are taken at equal angular spacing.

6 After a complete set of distance data has been collected, the variability in uniformity of the tyre can be obtained by determining the maximum distance value and calculating the absolute value of the maximum value subtracted from each of the distance values.

Figure 1 shows a graphical representation of the sidewall uniformity variation of a typical truck tyre. The plot is based on more than 1000 data values or points.

In a conventional automatic uniformity scrutiny, this basic set of data is screened for indications of bulges by a process in which the whole set of data is scanned sequentially and according to a predetermine_- 'window size' of a predetermined number of degrees, distance values separated by this number of degrees are averaged. This number of degrees of the 'window size' is an integer multiple of the angular spacing of the distance measurements in the basic set of data. In a conventional automated screening process a 'window-size' of 8 degrees is used and found particularly effective in identifying typical sidewall bulges. This process 7 yields a set of data which i S represented graphically by Figure 2, which shows a distribution of a number of small peaks representing bulges blb15 ranging in height from 0.1 to 0.5 mm.

According to a preferred quality standard, bulges of this magnitude of blblS would not be regarded as significant and thus would not be detrimental to the quality grading of the tyre.

However as Figure 2 additionally shows the conventional scrutiny also yields a significantly larger peak Pl at the 1950 angular position. Peak Pl has a magnitude of 1.37 mm and under the preferred quality standard would be of sufficient magnitude to downgrade the tyre.

The problem, however with such a conventional automated scrutinising operation is illustrated by the fact that the peak value P1 represents not a bulge but a spue-pip witness mark and as such should not downgrade the product quality. Since the conventional scrutiny cannot distinguish between genuine bulges and other sidewall imperfections it is clearly unsatisfactory.

8 The method according to the present invention solves this problem by introducing a preliminary step which determines those data peaks relating to non-critical non-uniformities and then removes these from the data leaving only genuine bulges.

According to the present method, in the preliminary step the data is firstly scanned using a 'windowsize' appropriate for the detection of only the nonuniformity it is desired to eliminate. Accordingly for the elimination of spue-pip-related witness marks the Inventor has found that a 'window-size' of 2 degrees is effective in identifying spue-piprelated blemishes of 0.7 mm in diameter. Thus firstly scanning the whole of the basic data set f rom 01 to 360' using a reduced 1window-sizel of 20 yields a result represent graphically in Figure 3, wherein the existence of peak P1 due to the spue-pip is the only Significant feature indicated.

The method of the invention then continues by removing from the original data that data resulting from the presence of the spue-pip detected in the previous preliminary scan. The removed original 9 data values can be ignored or replaced by the mean of the adjacent data values.

This in the final step of the present method the modified data set is scanned using the preferred 'window size' of 8 degrees which detects bulges in the normal way. The result of this operation is shown graphically in Figure 4 wherein it is evident that the non-uniformity due to the spue-pip has been eliminated.

According to the invention, non-critical uniformity irregularities can be removed f rorn the tyre uniformity data providing a proper basis for an automated grading of the tyre quality.

Whilst the above embodiment has described the elimination of spue-pip marks from tyre sidewall derived lateral data, the principle of the method of the invention may be applied to other moulding marks or features of the tyre such as mould split Ilashlines or engraving details and to data from other regions of the tyre such as radial uniformity data from the tyre tread.

Claims

1. A method of evaluating the uniformity of a pneumatic tyre in a particular direction comprising obtaining from the inflated tyre a basic set of data comprising the comparative height in the particular direction of a plural number of points on the tyre surface at a fixed distance from the tyre rotational axis, processing the basic set of data in one or more preliminary scans to identify the specific data resulting from predetermined non-critical uniformity irregularities, -removing the identified data from the basic set of data, processing the modified basic set of data in a secondary scan to identify any remaining uniformity irregularities, and grading the uniformity of the tyre according to the identified remaining cr4tical uniformity irregularities.

2. A method according to claim 1, wherein the basic set of data comprises the comparative heights of a plural number of points at a fixed distance. Lrom the tyre rotational axis wherein each point is spaced apart from its adjacent points by constant angle.

3. A method according to claim 2, wherein the one or more preliminary scans comprises selecting an 11 appropriate value in degrees of 'window-size, the value being an integer multiple of the constant angle and which can identifying the predetermined non-critical uniformity irregularity, and sequentially processing the basic set of data such that there is derived a set of mean non-critical values, each mean value being the average of the height value at a first point and the height value at a second point spaced apart in a consistent direction from the first point by the value in degrees of the 'window-size' and analysing the set of mean values to identify the existence of any of the predetermined uniformity irregularities.

4. A method according to any of claims 1 to 3, wherein the secondary scan comprises selecting an appropriate value in degrees of 'window-size', the value being an integer multiple of the constant angle and which can identify critical uniformity irregularities, and sequentially processing the modified basic data set such that there is derived a set of mean critical values, each mean value being the average of the height value at a first point and the height value at a second point spaced apart in a consistent direction from the first point by the value in degrees of the 'window-size' and analysing 12 the set of critical mean values to identify the existence of any critical uniformity irregularities.