Method and apparatus for detecting ply defects in pneumatic tires

Abstract: In a method and apparatus for detecting ply defects in a pneumatic tire, measurements on the tire are obtained at two levels of tire inflation, and the data obtained in the two measurements are compared. Broken reinforcement cords in the tire cause changes in the peaks of the data obtained at the two inflations that is out of proportion when compared to data changes observed in non-damaged tires. The apparatus of the invention provides means for inflating tires to predetermined pressures and has displacement sensors for measuring peaks and valleys in the sidewall of a tire. The apparatus may also include a computer for collecting data, analyzing data, and providing a signal when a defective tire is recognized.

Description: BACKGROUND The invention relates to a method and apparatus for detecting broken reinforcement cords in a tire sidewall. When a tire goes flat, is run long periods of time underinflated or hits road objects, the reinforcement cords in the carcass ply are sometimes broken without any visible change in the tire. When the cords are broken, however, eventually there is a separation that manifests itself in what is called a zipper break (because it looks like an open zipper) in the sidewall. Unseen cord breaks are particularly a problem when retreading tires, because the expense and time needed to retread a defective carcass is wasted. Although some experienced individuals have acquired the ability to recognize such sidewall defects with good precision on observation, such individuals are scarce, and it is important that a correct diagnosis be made each time a tire carcass is inspected prior to retreading. X-ray inspection has been used in retreading operations, but x-ray equipment is expensive, requires extra safety precautions to use, and some breaks, where the broken ends are not displaced, may not be observable on the x-ray screen. Commercial ultrasonic units are believed to be used by Bandag in retreading operations. EP-A- 84 514 discloses an automated tire measurement apparatus having means for testing through different combinations of testing algorithms and tire sensors. The tire is rotated and measured for lateral runout of both sidewalls. US-A- 5 060 173 discloses a method for detecting defects in a pneumatic tire wherein the tire is rotated at a constant speed and a displacement sensor is urged at different pressures against an outer surface of the tire. It is an object of the present invention to provide a reliable, inexpensive method of detecting cord breaks in the carcass of a pneumatic tire, and to provide an apparatus to be used in the method. SUMMARY OF THE INVENTION A method for detecting defects in a pneumatic tire and an apparatus for implementing the method is provided, as defined in the appended claims. During testing, the apparatus is adapted to rotate the mandrel between 3 and 30 rpm. The apparatus comprises also an air regulator for maintaining air pressure within the tire at a constant pressure during testing. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 illustrates the apparatus of the invention. Fig. 2 illustrates a closeup of the tire mounting portion and sensor portion of the apparatus with a mounted tire. Fig. 3 illustrates a closeup of the tire mounting portion and sensor portion of an embodiment using laser displacement sensors. Fig. 4 illustrates a portion of the apparatus in breakaway illustrating a pressure switch and an encoder. Fig. 5 illustrates plots of sidewall runout at 3 psi and 20 psi on the same graph. Fig. 6 illustrates a graph showing the results of the difference between the two plots in Fig. 5. Fig. 7 illustrates Fourier treatment of the plots in Fig. 5. DETAILED DESCRIPTION OF THE INVENTION With reference now to Fig. 1, the apparatus of the invention 10 comprises a tire retreading machine (basically represented by base 14) which has been modified by the addition of vertical support strut 16, cross support 18, displacement sensors 20, and computer 26 (for collecting and analyzing data from displacement sensors 20). Support strut 16 is geared so that cross support 18 moves up and down, and cross support 18 has slides so that displacement sensors 20 move laterally independently. When a tire 30 (see Fig. 2) is mounted on mandrel 22, the mobility of the displacement sensors, up and down and side to side, make it possible for the displacement sensors to accommodate any size tire. Fig. 2 illustrates a tire 30 mounted on the apparatus and contacts 21 of displacement sensors 20 in the proximity of sidewalls 32. In the method of the invention, when a tire 30 is mounted on mandrel 22, air is pumped into the tire 30 through hose 24, to a pressure at least sufficient to provide tension between tire 30 and mandrel 22, so that the tire does not move on the mandrel. It is believed that such sufficient air pressure is about 3,45 kPa (0.5 psi), and when used in the method of the invention, minimum air pressure (for obtaining baseline measurements) is between 3,45 and 69 kPa (0.5 and 10 psi). In the illustrated embodiment, 20 kPa (3 psi) inflation is used to establish a baseline in the testing of a tire. The desired pressure in the tire is selected by controls 12, and regulator 28 maintains the pressure precisely as selected. In a preferred embodiment, a minimum pressure differential of 138 kPa (20 psi) between the baseline measurement and the elevated pressure measurement, provides broadest use of the invention over a wide range of tire sizes. In the illustrated embodiment, the apparatus is equipped with two regulators 28. With reference now to Figs. 3 and 4, in addition to air regulators 28, the illustrated apparatus is also equipped with a pressure switch 36 which is used to convey pressure data to the computer. The pressure switch makes it possible for the computer to recognize conditions where air pressure is not maintained at the desired level, such as when there is a hole or a break in a tire. An elevated pressure measurement is obtained by inflating the tire 30 on mandrel 22 to a pressure of 38 to 276 kPa (5.5 to 40 psi), preferably 103 to 172 kPa (15 to 25 psi), and in the illustrated embodiment 138 kPa (20 psi), rotating the tire in proximity to displacement sensors 20, and collecting the data generated by the displacement sensors. It is preferred that a lower inflation, such as 138 kPa (20 psi) is used, since sufficient data is obtained, and there will be minimal impact if the tire ruptures during testing at this pressure. Those skilled in the art will recognize that if proper safety cages are used, more exaggerated results will be obtained at higher pressures. An encoder 38 (Fig. 4) is used (2048 pulses in the illustrated embodiment) to pinpoint the position of the tire in its rotation so that points on a tire related to the baseline measurement can be precisely coincided with the position of the same points in the elevated pressure measurement. Those skilled in the art will recognize that the order of obtaining a baseline measurement and an elevated pressure measurement is not important and either one may be obtained first. After the baseline measurement and the elevated pressure measurements are obtained, the measurements are compared. The amplitude of the data generated in the elevated pressure measurement is greater than the amplitude of the data obtained in the baseline pressure measurement, but in a sound tire, all the peaks and valleys will show a proportional change. In a tire in which carcass cords are broken, the differences in the peaks corresponding to the broken cords will be significantly exaggerated in the elevated pressure measurement. When such differences are noted, the tire is scrapped. In a preferred embodiment, the software in computer 26 will be adapted to recognize significant differences in the baseline measurement and the elevated pressure measurement and will automatically provide a reject signal, in the form of flashing lights, buzzers or bells, when predetermined logic conditions are met. Or, the apparatus may be adapted to automatically spray the tire with ink or paint when a failed tire is recognized. In its analysis of the data, the computer is used to provide a Fourier transformation of the data and the first nine harmonics are removed. Those skilled in the art will recognize that the method is operable if anywhere from 1 to 20 harmonics are removed. The data is then passed through an inverse Fourier transformation and normalized to zero, which causes normal data to fall within a narrow band of values which is determined by testing, for example between ± 0,254 mm (± 0.010 in). The logic in the software is set so that when data outside a preselected range is seen in the inverse Fourier transformation, the reject sequence is initiated. In the embodiment illustrated in Fig. 1, displacement sensors 20 are magnetostrictive displacement sensors and readings are obtained by contact between the tire sidewall and the contact elements 21. The contact elements 21 are loaded with a spring tension sufficient to provide a response in contact element 21. The spring tension will be in the range of less than 4,45 N (1 lb) and up to 44,5 N (10 lbs), preferably less than 4,45 to 22,2 N (1 lb to 5 lbs) tension. In order to obtain as smooth a measurement as possible, the displacement sensors can be aligned to make contact with the scuff rib on the sidewall, or another smooth surface. Non-contact displacement sensors, such as ultrasonic displacement sensors, laser displacement sensors, and transducer displacement sensors can be used on the apparatus. The displacement sensors can be easily changed by removing displacement sensors 20 and substituting in their place the non-contact displacement sensors, transducer displacement sensors, or other types of displacement sensors known in the art. Fig. 3 illustrates the apparatus equipped with laser displacement sensors 20a. Laser displacement sensors are relatively inexpensive, and since there are no moving parts, are usually more responsive and accurate than contact displacement sensors. Low intensity diode lasers do not require stringent safety features of the kind seen on lasers used for surgery or for cutting metals. Examples of laser displacement sensors that can be used in the invention are available from Aromat, 629 Central Ave., New Providence, NJ, and Keyence Corp., 17-17 Route 208, North Fairlawn, NJ. The apparatus of the invention can also be used to test new tires for ply gaps. The invention is further illustrated with reference to the following example. EXAMPLE With reference now to Figs. 5, 6, and 7, data was obtained and analyzed on a tire with broken carcass reinforcement cords. This example is particularly interesting since x-ray analysis failed to detect any broken cords in this tire. In Fig. 5, the measurements obtained on the tire at 20 kPa (3 psi) inflation and at 138 kPa (20 psi) inflation are plotted on the same graph, illustrating the difference in amplitude of the peaks encountered. In Fig. 6, the data from the two graphs are subtracted to provide a composite graph of the two measurements. Fig. 7 illustrates the graphed results of passing the data through a Fourier transformation, removing the first nine harmonics and passing the resulting data through an inverse Fourier transformation and normalizing to zero. It is noted that this treatment of the data has the effect of leveling out the normal displacement data to a range between ± 0,127 mm (± 0.005 in). The peaks corresponding to the broken reinforcement cords, however, even after the broken reinforcement cords, however, even after the Fourier transformation and inverse Fourier transformation and normalization to zero, are substantially treater than ± 0,127 mm (± 0.005 in).

Claims: A method for detecting defects in a pneumatic tire (30) comprising the steps of: (a) inflating said tire (30) at a minimal pressure in the range of 3,45 to 69 kPa (0.5 to 10 psi); (b) rotating said tire (30) in proximity to a fixed displacement sensor (20,20a), thereby obtaining a continuous baseline measurement around said tire; (c) inflating said tire (30) to an elevated pressure of 38 to 276 kPa (5.5 to 40 psi); (d) rotating said tire (30) in proximity to said fixed displacement sensor (20,20a), thereby obtaining a continuous elevated pressure measurement around said tire; and (e) comparing the minimal pressure measurement with the elevated pressure measurement and noting significant differences. The method of claim 1 in which said minimal pressure is 6.9 to 69 kPa (1 to 10 psi) and said elevated pressure is 103 to 172 kPa (15 to 25 psi). The method of claim 1 in which said minimal pressure is 34 kPa (5 psi), and said elevated pressure is 138 kPa (20 psi). The method of claim 1 in which the pressure difference between minimal and elevated pressure measurements is selected to be 138 kPa (20 psi). An apparatus for detecting damage to a pneumatic tire comprising (a) a base unit (14) having a rotatable mandrel (22) mounted thereon, said mandrel being adapted for holding a tire (30); (b) support means for supporting displacement sensors in the proximity of said tire (30) attached to said base (14), said support means comprising a vertical support strut (16) attached to said base unit (14) and cross support (18) attached to said vertical support strut (16); (c) displacement sensor means (20,20a) attached to said support means wherein the support strut (16) is geared so that said cross support (18) moves up and down and said cross support (18) has slides so that said sensor means (20, 20a) can move laterally independently such that said sensor means (20, 20a) can be moved up and down and side to side into the proximity of a tire sidewall (32) when said tire (30) is mounted on said mandrel (22); and (d) means (24) for inflating said tire (30) on said mandrel (22) to different specific pressures during testing; and (e) computer means (26) programmed to compare the measurement data obtained from tne displacement sensor means (20,20a) when the tire (30) is inflated to a minimal pressure with the measurement data obtained from said displacement sensor means (20,20a) when the tire (30) is inflated to an elevated pressure. The apparatus of claim 5 wherein said displacement sensor means (20, 20a) are contact displacement sensors adapted to contact the sidewall (32) of the tire (30) when mounted on said mandrel (22). The apparatus of claim 5 wherein said displacement sensor means (20, 20a) are non-contact displacement sensors which measure anomalies in a tire (30) without contacting said sidewall (32) when the tire (30) is mounted on the mandrel (22). The apparatus of claim 5 wherein said displacement sensor means (20, 20a) are selected from the group consisting of magnetostrictive, laser, ultrasonic, and electronic transducer displacement sensors. The apparatus of claim 5 comprising software adapted to compare data and provide a yes/no indication of the condition of the tire.

Inventors: YOVICHIN ALBERT JAMES, YOVICHIN, ALBERT JAMES
Applicants: GOODYEAR TIRE & RUBBER, THE GOODYEAR TIRE & RUBBER COMPANY
Application year: 1993
Main classification: G01M17
IPC codes: G01M17, B60C25