CA1161154A - Method and apparatus for non-destructive inspection of tires - Google Patents

Abstract

METHOD AND APPARATUS FOR
NON-DESTRUCTIVE INSPECTION OF TIRES

ABSTRACT OF THE DISCLOSURE

A pulsed through-transmission ultrasonic non-destructive inspection of the internal struc-ture in a tire wall is effected. The ultrasonic in spection is preferably carried out through the walls of a rotating inflated tire with the ultrasonic trans-ducers being automatically moved toward the inner and outer tire wall surfaces to optimum relative distances of separation during an inspection cycle. The trans-ducers disposed inside the inflated tire are preferably mounted for automatic retraction into a protected space during tire mounting and demounting operations. Such ultrasonic inspection techniques may be combined with conventional tire buffing methods and apparatus as practiced in tire retreading operations.

Description

This invention is gener'ally directed to methods and apparatus for non-destructive inspection of rubber tires. Such inspection techniques may also be combined' with conventional tire buffing operations in accordance with this invention.
The invention here'claimed is directed to certain mechanical features of the prefer'red embodiment. The electrical features, se, are'tha'sol'e invention of Morris D. ~o and are disclosed and claimed' in United' States Patent No. 4,266,428 dated ~ay 12, ' 1981. The'combination of mechanical and electrical features is the joint invention of Doyle L. Dugger and Morris D. Ho and is disclosed and claimed in United States Patent No. 4,275,589 dated June 30, 1981.
There has long been an urgent need for cost effective, efficient, non-destructive'inspection (NDI~ of rubber tire casings.
- There are'obvious safety benefits to be had by such techniques if they can be efficiently and rapidly practiced. There are also potential economic benefits. For example, during tire retreading operations, a de~ective tire carcass can be discarded before wasting further expenditures of time and money if it can be accurately, efficiently and quickly detected.
In fact, the need for improved NDI methods and apparatus relating to the testing of tire casings is so great that the U.S.
Army Materials and Mechanics Research Center has sponsored special symposia devoted entirely to this subject in 1973, 1974, 1976 and 1978. The'proceedings of the first three of these symposia have now been published and .~

( -- 2 ~
are available from the National Techniczl In.orma-tion Se~vice~ They each include a complete chap-ter on ultrasonic tire testing as well as other . chapters devoted to different tire testing pro-cedures ~e.g. holographic, infrared and X-ray~.
There are also many prior art patents relating generally to the use of ultrasonic waves ko non-destructively test pneumatic tire casings.
For example:
U.S. Patent No. 2,345t679 - Linse (1944) " " " 2,378,237 - Morris (1945) " " " 3,336,794 - Wysoczanski et al (19673 " " " 3,604,249 - Wilson (1971?
" " 3,815,407 - Lavery (1974) " " " 3,882/717 - McCauley (1975 " " " 4,059,989 - Halsey (1977) There are also several prior art patents - relating to mechanical structures for chuck;ng or .
otherwise physically handling pneumatic tire casings during various types of non destructi~e testing or manufacturing processes; For`example:
U.S. Patent No. 2,695,520 - Karsai (1954) " " " 3,550,443 - Sherkin (I970) " " " 3,948,094 - Honlinter (1976) 4,023,407 - Vanderzee tl977) Although a wide variety of no~-destructive ultrasonic tests have been performed on tires in the past as shown by these prior art patents, they have each suffered serious deficiencies and have failed to achieve wid~spread acceptance in commercial prac-tice.

Prior tire chucking mechanisms in gen~-al hzve included axially movable tire mounting rims Lor quickly mounting and inflating a test tire. ~rior NDI machines have located an ultrasonic ~rans~itter inside a rotatable inflated, tire, albeit such have been only fixed or manually adjustable mounting ar-rangements~ Othex NDI machines have included arti-culated transmitter mounting arrangement in conjunc~
tion with a spread-open non-inflated test tire.
However, there has not yet ~een a commercially via-ble mechanism arrangement for quickly positioning ultrasonic transducers about an inflated test tire wall while at the same time facilitating ~uick tire mounting/de mounting procedures and also pro~
tecting the transducers from physical harm.
It has been discovexed that these earlier attempts at ultrasonic non-destructive in~pection of tire casings can be considerably im-proved and madè more commercially viable.
In accordance with the present invention a non-destructive tire testing apparatus having an ultrasonic acoustic transmitter and an ultrasonic acoustic réceiver opposingly mounted on the inside and outside respectively of a relatively movable inflated tire wall and spaced therefrom by predetermined distances so as to achieve acoustic coupling therebetween through a gaseous medium interrupted by said tire wall and including electronic circuits connected to said transmitter and receiver so as to obtain and display a measurement of the condition of the thus tested portion of the tire wall, said apparatus being characterized by:
opposing circular rings adapted to sealingly engage _ 3a -the corresponding rims of the tire when placed therebetween;
and adjustable transmitter mounting means mechanically mounted between said rings for retracting said transmitter radially toward the center of the circular rings while mounting and ~e-mounting the tire from between said rings and for extending said transmitter radially away from the center of the circular rings and toward the t;re tread wall to a fixed active position during a testing cycle.
A further aspect of the invention includes, a non-destructive tire testing method comprising mounting an ultrasonic acoustic transmitter and an ultrasonic acoustic receiver opposingly on the inside and outside respectively of a relatively movable inflated tire wall and spaced therefrom by predetermined distances so as to achie~e acoustic coupling therebetween through a gaseous medium interrupted hy said tire wall, co~necting electronic circuits to said transmitter and receiver so as to obtain and display a measurement of the condition of the thus tested portion of the tire wall, sealingly engaging the corresponding rims of the tire with opposing circular rings when placed therebetween; and retracting said transmitter radially toward the center of the circular rings while mounting and de-mounting the tire from between said rings and extending said transmitter radially away from the center of the circular rings and toward the tire tread wall toa fixed active position during a testing cycle.

- 3b The use of an inflated tire in the pre-ferred embodiment has been discovered to assist in maintaining a true running tire surface and thus avoids signal variations that might otherwise be caused by wobbling or other relative axial motions of the tire walls during rotating. The inflated tire is also useful in helping to at least par-tially stress the tire walls, as they will be stressed during normal use, and to open up leakage passageways through the tire walls so that they may be detected by ultrasonic detection of air passing therethrough. Approximately only ~ive psi is needed.
to maintain a stable inflated tire stxucture. ~ow, ever, it has been discovered that improved signal transmission and overall performance occurs i~ the tire is inflated within the range of approximately 15-18 psi.
Although it may not be required, it is preferred that the outer treadwall of the tire under inspection first be buffed to present a uni-form surface thus minimizing spurious defect in-dications that might otherwise be caused by tread patterns and/or by uneven wear spo s or patterns in the outer treadwall surface of the tire. In this connection, the tire buffing apparatus and method may ~e advantageously employed in combina-tion with the ultrasonic non-destructive testing method and apparatus to present a unified, conven-ient and efficient overall operation. Since such a buffing operation is necessarily involved in tire retreading operations anyway, this combina-tion is particularly attractive where the tire carcasses are being inspected in preparation for retreading.
The preferred exemplar~ embodiment of this invention includes special mechanical features for automatically moving the acoustic transducers into and out of operative position with respect to the inflated tire walls. During tire mounting and demounting operations, the acoustic transmitters are retracted inwardly both radially and axia}ly with respect to at least one tire mounting ring or flange so as both to facilitate the tire mounting and de-mounting operations and to protect the acoustictransmitters from possible physical damage. During or after ti~e inflation, these acoustic .ransmitters are moved radially outwardly inside the infla~ed tire in~o an operative position with respect to the inside tire walls. At the same time, the array of acous~ic 5 receivers is moved radially inwardly towards the outer inflated tire walls to a desired operative position~
In the preferred exemplary embodiment, the relative axial movement of the acoustic trans-mitters with respect to a tire mountiny flange orring is achieved by spring loading the tire ring so that it axially moves away from the acoustic transmitters thereby uncovering t~em during the tire mounting operation and thus providing prope~.clear-ance for subseguent radially outward movement into the inflated tire carcass. Such spring loading also . helps in properly seating the tire rims with the mounting flanges or rings during mounting and in-flation operations.
' Thesa and other objects and advantages o this invention will be better appreciated by r.eading the following detailed dèscription of the presently'preferred exemplary embodiment in con-junction with the accompanying drawings, of which:
FIGURES 1 and 2 are pexspective views of a combined NDI/buffer machine constructed in accordance with this invention;

FIGU~E 3 is a block diagram o~ the inven-tlon shown in FIGURES 1 and 2;

FIGURE 4 is a block diagram of the ultra-sonic NDI circuits which may be used in the NDI~bu~f~r machine of FIGURES 1~3 or in a machine having,only N~I capabilities; and .

~s~
( - 6 FIGURE 5 is a detailed cut-away cross-sectional view of the fixed spindle and transmit-ter mounting arrangement used in ~he embodiment of FIGURES 1 and 2.

! ~ 7 -Referring to FIGUP~S 1 znd 2, two per-spective views of the presently preferred exemplary combined tire buffer and NDI machine are shown. As will be apparent, the N3I features of the machine may be provided, if desired, without including the tire buffing capability.
The major mechanical components of the machine are mounted to an open frame 100 having a fixed spindle 102 and an axially movable spindle 104 opposingly aligned along horizontal axis 106.
Conventional circular tire mounting rings or flanges 108 and llO are attached to the outer rotatable ends of spindles 102 and 104 for mounting an lnrlated tire 112, therebetween. A conventional pneumatically opera-ted tire lift mechanism 114 is conveniently provided so as to assist the human operator in lifting and swinging a tire into and out of place between rings 108 and 110 during tire mounting and demounting opera-tions.
Ring 108, and hence tire 112, is driven by a two horsepower d.c. motor 116 thxough reducing gears 118. A tire surface speed of approximately 600 feet per minute is preferred for buffing operations while a much lower speed o~ approximately 40 feet per minute is preferred for NDI operations. Spindle 104, and hence ring 110, is axially extended and retracted by pneumatic cylinder 120. During tire mounting opera-tions, ring 110 is retracted by cylinder 120 so as to permit the tire 112 to be li~ted into place on ring 108 by lift 114. Thereafter, ring 110 is ex~
tended against the corresponding rim of tire 112 and ( the tire is inflated to a desirec se'_ point pressure by compressed air passed through the center o spin-dle 102.
A conventional rotating tire buffing xasp 200 is mounted on a vertical pedestal 202 situated on the backside of the machine as seen in FIGURE

2. The rasp 200 is controlled via a conventional panel 204 to move laterally along a desired buff--ing path 206 and horizontally towaxds and away ~rom the tire by conventional control mechanisms in-cluding a "~oy stick" used to control lead screws and associated drive motors and the like. The buffer rzsp 200 is rotated by a separate motor mounted on ped~stal 202. The buffer mechanism, ~ se, is of a conventional type as marketed by Bandag, Inc., e.g. Buffer Model No. 23A.
An array of 16 ultrasonic acoustic receiv-ing transducers 210 is disposed above and around the outer walls of tire 112. The receivers 210 prefer-ably include a conically shaped collimator and/or focusing tube to help limit the field of view for each individual transducer to a relatively sm~ll and unique area across the tire wall. The receivers 210 may be conveniently potted either individually or in groups in a polyurethane foam or the like to help mechanically fix the receivers in their re-spective desired positions, to help protect the xe-ceivers and to help i~olate the rec~ivers from spurious ambient acoustic signals. The array of receivexs Z10 is radially adjusted into operative position by an air cylinder 212 having a coupled 5?¢
g hydraulic control cylinder so as ~o define a radi-ally extended operative position Lor the receivers A block diagram of the combined tire buffer/NDI machine and its associated electrical and pneumatic circuits is shown in ~IGUXE 3. The electrical motor and pneumatic cylinder controls 300 are of entirely conventional design and thus not shown in detail. Opexator inputs depicted at the left of FIGURE 3 are made directly or indirectly by the operator via conventional electrical switches, relays, air valves and/or liquid control valves.
In operation, a tire is placed on lift 114 and raised into position between the rings 108 and 110.
Preferably, a predetermined index position on the tire is aligned with a physical index position on flange 108. Thereafter, the chucking apparatus is engaged by causing flange 110 o move into the tire 112 so as to pinch the tire beads together in preparation for tire inflation. The tire is then inflated to a desired set point pxessure~ As will be explained in more detail below, the flange 108 is spring-loaded such that durins chuck engagement and tire infla-tion, it is caused to move axially outwardly against the spring-loading (e.g. by approximately 2 inches).
This facilitates the tire inflation process and simultaneously uncovers an ultrasonic transmitter located within the tire from a relatively protec~ed position so that it may subsequently be extended into an operative position under the axray of receivers 210. An interlock switch activated by air pressure and/or by the physical movement of flange 108 may ( be used to prevent any premature extension o~ the transmitter before it is uncovered from its pro-tected position.
In the buffing mode, the transmitter need not be extended. The buffing rasp drive motors are conventionally activated and controlled (e.g.
with a "joy stick" and conventional push button controls) to buff the tire tread surface as de-sired. Although it may not be required, it is 0 presently preferred to have the tire buf~ed to a substantially uniform outer treadwall surface be~
fore NDI operations are performed. Such buf~ing is believed to avoid possibIe spurious indications o~ defects caused by normal tread patterns and/or by uneven wear about the tire surface.
When the operator selects the NDI mode of operation, an ultrasonic transmitter located inside the in lated tire 112 is extended into opera-tive position and the array of receivers 210 is lowered into operati~e position by respectively asso-ciated pneumatic cylinders~ The same 2-horsepower d.c. motor which drives the tire` at approximately 600 surface feet per minute during buffing opera~ions may be reduced in speed by conventional electrical circuits so as to drive the tire at approximately 40 surface feet pex minute during the NDI mode. After t~e tire motion has reached a steady state, the operator may activate the scan request input switch to the ultra-sonic NDI cixcuits 302. Thereafter ~he walls o~ tire 112 will be ultrasonically inspected duri~g one or ` more complete tire revolutions to produce a display 304 which can be humanly interpreted directly or 5'~

îndirectly to reveal the condition of the tire (e.g.
satisfactory for further buffing and retreading, doubtful or unsatisfactory). If questionable con-dition is indicated, the tire may be discarded or may be additionally buffed and retested.
The ultrasonic NDI circuits 302 are shown in greater detail at ~IGURE 4. The outputs ~rom the 16 ultrasonic receivers 210 are amplified and multi-plexed onto eight signal processing cha~nels A-H by circuits 402. Each signal processing channel then pro-vides AGC amplification, rectification, integration and analog-to-digital conversion with the signal pro-cessing circuitry 404. The resulting digitized outputs are presented to a conventional eight bit data bus 406 which is interconnected to a conventional micro-computer CPU (e.g. an 8080 type of eight bit computer~ 408. The CPU 408 is also connected via a conventional address bus 410 and data bus 406 to a data mem~ry 412, to a programmable read-only memory (PROM) 414 and to a sys-tem interface circuit 416. A display intex~ac~ 418 is directly connected to the data memory banks 412 to pro-vide a CRT type of oscilloscope display.
The system interace 416 provides the necessary gating and other control signals to the signal processing circuitry 404 and also provides HIGH CHAN multiplexing signals to the preamplifier circuits 402 as we}l as to the transmitter ~rivers and multiplexing ci ~ itry 422 used to drive plural ultrasonic transmitters. The operation of ~he en-tire system is synchronized to the rotational move-ments of tire 112 through a rotary pulse generator 424 directly driven with the tire (e.g. geared to the reducer gears). The rotary pulse generator 4~4 .5~e provides 1,024 pulses per revolu~ion a~ terminal ~GX
znd 1 pulse per revolution at terminals RPGY.
Ultrasonic acoustic transmitting crystals 500 and 502 are disposed inside inflated tire 112, which is chucked between xings 108 and 110, rotatably secured to spindles 102 and 104, respectively. The elec~rical leads ~eeding transmitters 500 and 502 are fed out through the fixed spindle 102 to the trans-mitter activation circuits. Inflation air is likewise fed in through the center of spindle 102 as are pneu-matic lines and~or other control connections for ex-tending and retracting the ~ransmitters.
The exemplary ul~rasonic t~ansmitters S00 and 502 have a radiation field which substantially illuminates a sector o~ approximately 90. Hence, they are mo~nted at 90 with respect to one another on block 504 which may, for example, be formed from polyvinyl chloride plastic materials. It has been found that acceptable operation will not result 2Q if the ~ransmittexs are too close to the inside tire surfaces or too far away from these surfaces.
In the preferred exemplary embodiment, trans~itting crystals 50Q and 502 are approximately two inches from the inner tire wall surfaces although this optimum distance of separation may be varied by z considerable amount (e.g. plus or minus approximately one inch).
The arrayed receiving transducers 210 are located about an arc generally corresponding to the outside shape o the tire wall. Hexe again, it has been found that acceptable operation does not result if the receivers are too close or too far away from the outer tire w211s . Prererably, ~he receivers are no closer than a?pr~ximately 1 inch to the outer tire surface b~ are preferably within 5.5 to 8.5 inches of the opposingly situAted trznsmitting crystal. The receivins transducers 210 pre~erably each employ a conically shaped collimator and/or focusing tube. These tubes are preferably machined from polyvinyl chloride plastic material a~d also help to match the impedance of the actual transducer crystal surface to the sux-rounding ambient air acoustic impedance.
A moderately high ul~rasonic frequency is employed so as to help avoid interference from spurious ambient acoustic si~nals and to obtain increased resolu-tion by using shorter waveleng~h acoustic signals while.
at the same time avoiding ultra-high frequency acoustic signals and the pro.~lems associated therewi~h. ~re-quencies above 40 ~z are desirable with 75 kHz being chosen 2S the presently preferred optimum frequency.
Greater de~ail of the fixed spindle 102 and of the associa.~d transmitter mounting arrange-ment is shown in the cross-section of FIGURE 5~
The transmitti~g crystals 500 and 502 are d~rected at 90 with respect to one another ~rom the face of a PVC moun~ing block 1500. The block 1500 is, in turn, attached to a retractable rod 1502 con-nected to the pisto~ of a pneuma~ic cylinder 1~04.
As shown in FIGURE 5, the pneumatic cylinder lS04 has retracted the transmitting cxy-stals 500 and 502 into a protected area de~ined by an annular plate 1506 attached to the tire mounting ring or flange 108. The tire mounting ring 108 is rotatably secured to the fixed spindle 102 through ball-bearing assemblies 1508 and 1510. This rota-table connection is maintained airtight by rotating seal assembly 1512. The center of the spindle 102 is hollow so as to permit passage of pneumatic con-trol line 1514 and of the transmitter electrical leads there~hrough.
~0 The rotating ring 108 and its connected assembly is spring-loaded via spring 1517 to its axially extended position, However, the ring 108 may be moved axially to the position shown in dotted lines against the spring force. In the preferred exemplary embodiment, such motion begins to occur when the ring 108 has approximately 1500 lbs. of lateral force applied thereto. The sliding joint which permits such mo-tion,is also maintained a~rtight by "O" ring 1516.
In the exemplary embodiment no more ~han approxi-mately two inches of axial movement are permitted before the spring force is sufficient to xesist further movement even when the tire is inflated to approximately 15-18 psi.
When the ring 108 is axially moved to the left as shown by dotted lines in FIGURE 5 against the force of spring 1517, transmittexs 500 and 502 are then exposed and the pneumatic cylinder 1504 can be activated to extend the trans-mitter into the position shown by dotted lines inFIGURE 5 for an operative measurement cycle. Suit-able interlocking switches activated by the internal pressure of the inflated tire and/o~ by t'ne ~hysical axial posi.ion of ring 108 can be employed to insuxe that pneumatic cylinder 1504 is not orroneously extended and damaged while the transmitters 500 and 502 are still enclosed and pxotected by the flange 1506.
While only a few exemplary embodiments and only a few variations thereof have been ex-plained in detail, those in the art will appreciate that many other modifications and variations may be made without departing from the no~el and advan-tageous features of this invention. Accordingly, all such modifications and variations are intended to be included within the scope of this invention as defined by the appended claims.

Claims (2)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY OR
PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method of non-destructive inspection of a tire casing comprising mounting an ultrasonic acoustic transmitter and an ultrasonic acoustic receiver on opposite sides of a wall of said casing, said transmitter and receiver being spaced apart a pre-determined distance to achieve acoustic coupling therebetween through a gaseous medium interrupted by said wall, sealingly engaging the corresponding rims of the tire with opposing circular rings when placed therebetween, inflating said tire to a predetermined pressure buffing away the outer tread wall surfaces of said tire energizing said transmitter, and obtaining and displaying a measurement of the condition of tested portion of the tire wall.

2. Apparatus for non-destructive inspection of a tire casing comprising an ultrasonic acoustic transmitter, an ultrasonic acoustic receiver, said transmitter and receiver being mounted on opposite sides of a wall of said casing and spaced apart a predetermined distance to achieve acoustic coupling therebetween through a gaseous medium interrupted by said wall, a pair of circular rings for sealingly engaging the rims of the tire, means to inflate said tire to a predetermined pressure, means to buff away the outer tread wall surfaces of said tire, and means for energizing said transmitter and for obtaining and displaying a measurement of the condition of the tested portion of the tire wall.