Method and apparatus for non-destructive inspection of tires

A pulsed through-transmission ultrasonic non-destructive inspection of the internal structure in a tire wall is effected. The transmitted acoustic signals preferably have a frequency of least 40 Khz, are transduced to electrical form, amplified with a relatively long time constant AGC, rectified and integrated during only the initial or leading edge portions of each pulse or burst. The resulting integrated analog signal values thus provided have relative magnitudes which may be displayed or otherwise processed to detect structural anomalies within the tire wall. If plural acoustic transmitters are utilized, they are preferably multiplexed such that only a single transducer is activated at a given time.

This invention is generally 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 electrical features of 
the preferred embodiment. The mechanical features, per se are the sole 
invention of Doyle L. Dugger and are claimed in commonly assigned 
copending application Ser. No. 31,961 filed concurrently herewith. The 
combination of mechanical and electrical features, is the joint invention 
of myself and Doyle L. Dugger and is claimed in commonly assigned 
copending application Ser. No. 31,963 filed concurrently herewith. 
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 effectively 
and rapidly practiced. There are also potential economic benefits. For 
example, during tire retreading operations, a defective 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 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 are available from the 
National Technical Information Service. They each include a complete 
chapter on ultrasonic tire testing as well as other chapters devoted to 
different tire testing procedures (e.g. holographic, infrared and X-ray). 
There are also many prior art patents relating generally to the use of 
ultrasonic waves to non-destructively test pneumatic tire casings. For 
example: 
U.S. Pat. No. 2,345,679--Linse (1944) 
U.S. Pat. No. 2,378,237--Morris (1945) 
U.S. Pat. No. 3,336,794--Wysoczanski et al. (1967) 
U.S. Pat. No. 3,604,249--Wilson (1971) 
U.S. Pat. No. 3,815,407--Lavery (1974) 
U.S. Pat. No. 3,882,717--McCauley (1975) 
U.S. Pat. No. 4,059,989--Halsey (1977) 
There are also several prior art patents relating to mechanical structures 
for chucking or otherwise physically handling pneumatic tire casings 
during various types of non-destructive testing or manufacturing 
processes. For example: 
U.S. Pat. No. 2,695,520--Karsai (1954) 
U.S. Pat. No. 3,550,443--Sherkin (1970) 
U.S. Pat. No. 3,948,094--Honlinter (1976) 
U.S. Pat. No. 4,023,407--Vanderzee (1977) 
Although a wide variety of non-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 
widespread acceptance in commercial practice. Some of the prior art 
approaches have required a liquid coupling medium on one or both sides of 
the tire wall under test. Some prior testing procedures use a so-called 
"pulse-echo" approach which gives rise to a rather complex pattern of 
echos due to normal internal tire structures as well as for abnormal 
structures. Many have used relatively low frequencies (e.g. 25 Khz) with 
resulting severe interference from normal ambient acoustic sources while 
others have used extremely high frequencies (e.g. 2 Mhz) with resulting 
rapid signal attenuation. Some have used continuous ultrasonic waves 
resulting in a confusing pattern of standing waves and the like while 
others have looked for envelope peaks in the received acoustic waves. 
Others have used individual pulses of acoustic signals for each tire 
testing site. In some cases the peak received envelope magnitude has been 
used to reach final data values. Some have also attempted to test an 
inflated tire carcass (but sometimes causing the acoustic signals to pass 
through two tire walls so as to keep all transducers external to the tire) 
although most have attempted to test a non-inflated tire carcass. There 
may have been other techniques as well. 
It has now been discovered that these earlier attempts at ultrasonic 
non-destructive inspection of tire casings can be considerably improved 
and made more commercially viable. 
For example, it has been discovered that a pulse or burst transmission mode 
may be used to reduce standing waves or unwanted reverberation effects 
within the tire. Each burst comprises only a few (e.g. 100) cycles of 
acoustic signals providing a very low overall duty cycle and extremely 
efficient transducer operation. At the same time, it has been discovered 
that the envelope of received acoustic signals may be altered by internal 
reverberation, standing wave, wave cancellation or other irrelevant wave 
effects after the initial portion or rising edge of each burst is 
received. Accordingly, in the preferred embodiment of this invention, the 
received acoustic signals are passed through a gated receiver circuit such 
that only those signals within the initial portion of each burst are 
utilized. 
Still further improvements may be possible in some circumstances by 
averaging readings taken at different frequencies thereby avoiding some 
possible adverse standing wave pattern effects and the like. Furthermore, 
non-linear analog-to-digital conversion techniques may be used to assist 
in recovering usable data. 
In the presently preferred embodiment, plural transmitting acoustic 
transducers are located inside a revolving inflated tire so as to 
acoustically illuminate the entire inside tire surfaces under test. 
However, it has been discovered that peculiar wave cancellation, standing 
wave patterns or similar wave effects may distort readings if more than 
one transmitter is activated at a given time. Accordingly, the preferred 
embodiment includes multiplexing circuitry to insure that only a single 
transducer is activated at a given time. 
Plural acoustic receiving transducers are arrayed about the outer tire 
walls so as to receive acoustic signals transmitted therethrough from the 
transmitting transducers located inside the tire. Each receiving 
transducer is preferably collimated and matched to the ambient air 
impedance with a cylindrical tube having an inner conical surface which 
tapers down to the sensing area of the actual receiving transducer. Such 
collimation helps to confine each receiver's output to represent acoustic 
signals transmitted through a limited area of the tire wall and further 
helps to reject interference from tread patterns and ambient noise. Flaws 
in the tires such as separations between cord layers and rubber layers or 
between various rubber layers attenuate the acoustic signals passing 
therethrough to a greater extent than when the acoustic signals pass 
through a normal section of the tire wall. 
It has also been discovered that leaks in in a pressurized tire (i.e. air 
passing through the tire wall) can be detected with the same ultrasonic 
receiving transducers by noting an icrease in received signal level over 
that encountered during passage by normal sections of the tire wall even 
while the ultrasonic transmitters are turned off. 
Each of the receiving transducers is connected to its own signal processing 
channel albeit plural receivers may be multiplexed to share a common 
signal processing channel in synchronization with the multiplexing of the 
plural acoustic transmitters thereby minimizing the number of necessary 
signal processing channels. A relatively long term automatic gain 
controlled amplifier is incorporated in each signal processing channel so 
as to compensate for different average signal levels from tire-to-tire and 
from channel-to-channel, depending upon different average respective tire 
wall thicknesses. After AGC amplification, the received ultrasonic signals 
are rectified and integrated during a gated period on the rising edge of 
each burst. The resulting integrated valves then truly represent the 
relative transmission capabilities of different successive sections of the 
tire wall under inspection. In one exemplary embodiment, successive 
observations at each tire wall position are averaged together to avoid 
potential standing wave null points and the like which might occur at some 
receiver locations for some particular frequency and tire geometry. Such 
values may be displayed on a CRT for visual inspection and detection of 
defects. Alternatively, such values may be digitized (possibly with a 
nonlinear exponential-law A-to-D process to enhance the effective 
signal-to-noise ratio at relatively low signal strengths) before display 
and/or process desired pattern recognition algorithms in a digital 
computer so as to automatically identify tire anomalies such as 
separations between layers. 
It has also been discovered that improved operation results when the 
acoustic signals are of a moderately high frequency (e.g. greater than 
approximately 40 Khz and, in the preferred embodiment, 75 Khz). Such 
moderately high acoustic frequencies tend to avoid unwanted spurious 
indications caused by the usual ambient acoustic sources nd, at the same 
time, provide relatively short wave lengths (e.g. approximately 1.5 inches 
or so in tire rubber) thereby improving the resolution of relatively small 
tire defects, yet without unnecessarily complicating the observed 
transmission readings by having a wave length so small that the signals 
may be affected by tire structure anomalies presenting no actual defect. 
The averaging of received signal over several cycles during the leading 
edge of each burst improves the signal-to-noise ratio of the resulting 
measured values as does the use of a non-linear A to D process. The 
averaging of data taken at different frequencies may further enhance the 
results. 
The use of an inflated tire in the preferred 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 rotation. The inflated 
tire also useful in helping to at least partially 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 five 
psi is needed to maintain a stable inflated tire structure. However, it 
has been discovered that improved signal transmission and overall 
performance occurs if 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 uniform surface 
thus minimizing spurious defect indications that might otherwise be caused 
by tread patterns and/or by uneven wear spots or patterns in the outer 
treadwall surface of the tire. In this connection, the tire buffing 
apparatus and method may be advantageously employed in combination with 
the ultrasonic non-destructive testing method and apparatus to present a 
unified, convenient and efficient overall operation. Since such a buffing 
operation is necessarily involved in tire retreading operations anyway, 
this combination is particularly attractive where the tire carcasses are 
being inspected in preparation for retreading. 
The ultrasonic bursts and receiver gating periods are preferably 
synchronized to occur at corresponding successive incremental positions of 
the rotating tire such that the final display or defect indication may be 
accurately located with respect to an index mark on the tire and/or tire 
mounting flange or the like.

Referring to FIGS. 1 and 2, two perspective views of the presently 
preferred exemplary combined tire buffer and NDI machine are shown. As 
will be apparent, the NDI 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 110 are attached to the outer rotatable 
ends of spindles 102 and 104 for mounting an inflated tire 112, 
therebetween. A conventional pneumatically operated 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 operations. 
Ring 108, and hence tire 112, is driven by a two horsepower d.c. motor 116 
through reducing gears 118. A tire surface speed of approximately 600 feet 
per minute is preferred for buffing operations while a much lower speed of 
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 operations, ring 110 is retracted by 
cylinder 120 so as to permit the tire 112 to be lifted into place on ring 
108 by lift 114. Thereafter, ring 110 is extended against the 
corresponding rim of tire 112 and the tire is inflated to a desired set 
point pressure by compressed air passed through the center of spindle 102. 
A conventional rotating tire buffing rasp 200 is mounted on a vertical 
pedestal 202 situated on the backside of the machine as seen in FIG. 2. 
The rasp 200 is controlled via a conventional panel 204 to move laterally 
along a desired buffing path 206 and horizontally towards and away from 
the tire by conventional control mechanisms including a "joy stick" used 
to control pneumatic cylinder 208, lead screws and associated drive motors 
and the like. The buffer rasp 200 is rotated by a separate motor mounted 
on pedestal 202. The buffer mechanism, per se, is of a conventional type 
as marketed by Bandag, Inc., e.g. Buffer Model No. 23A. 
An array of 16 ultrasonic acoustic receiving transducers 210 is disposed 
above and around the outer walls of tire 112. The receivers 210 preferably 
include a conically shaped collimator and/or focusing tube to help limit 
the field of view for each individual transducer to a relatively small 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 respective desired 
positions, to help protect the receivers and to help isolate the receivers 
from spurious ambient acoustic signals. The array of receivers 210 is 
radially adjusted into operative position by an air cylinder 212 having a 
coupled hydraulic control cylinder so as to define a radially extended 
operative position for the receivers 210. 
A block diagram of the combined tire buffer/NDI machine and its associated 
electrical and pneumatic circuits is shown in FIG. 3. The electrical motor 
and pneumatic cylinder controls 300 are of entirely conventional design 
and thus not shown in detail. Operator inputs depicted at the left of FIG. 
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 to 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 pressure. The 
flange 108 is spring-loaded such that during chuck engagement and tire 
inflation, 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 protected position so that it 
may subsequently be extended into an operative position under the array 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 of the transmitter before it is uncovered from its protected 
position. 
In the buffing mode, the transmitter need mot 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 desired. Although it may not be required, it is presently 
preferred to have the tire buffed to a substantially uniform outer 
treadwall surface before NDI operations are performed. Such buffing is 
believed to avoid possible spurious indications of 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 inflated tire 112 is extended into 
operative position and the array of receivers 210 is lowered into 
operative position by respectively associated pneumatic cylinders. The 
same 2 -horsepower d.c. motor which drives the tire at approximately 600 
surface feet per minute during buffing operations may be reduced in speed 
by conventional electrical circuits so as to drive the tire at 
approximately 40 surface feet per minute during the NDI mode. After the 
tire motion has reached a steady state, the operator may activate the scan 
request input switch to the ultrasonic NDI circuits 302. Thereafter the 
walls of tire 112 will be ultrasonically inspected during one or more 
complete tire revolutions to produce a display 304 which can be humanly 
interpreted directly or indirectly to reveal the condition of the tire 
(e.g. satisfactory for further buffing and retreading, doubtful or 
unsatisfactory). If questionable condition 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 FIGS. 4-10. 
AS shown in FIG. 4, the outputs from the 16 ultrasonic receivers 210 are 
amplified and multiplexed onto eight signal processing channels A-H by 
circuits 402 which are shown in greater detail in FIG. 5. Each signal 
processing channel then provides AGC amplification, rectification, 
integration and analog-to-digital conversion with the signal processing 
circuitry 404. A representative channel of such processing circuitry is 
shown in detail at FIG. 7. 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 memory 412, to a programmable read-only memory 
(PROM) 414 and to a system interface circuit 416 which is shown in detail 
at FIG. 8. A display interface 418 (shown in detail at FIG. 10) is 
directly connected to the data memory banks 412 to provide a CRT type of 
oscilloscope display. 
The system interface 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 well as to the 
transmitter drivers and multiplexing circuitry 422 used to drive plural 
ultrasonic transmitters. The operation of the entire system is 
synchronized to the rotational movements 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 424 provides 1,024 pulses per 
revolution at terminal RPGX and 1 pulse per revolution at terminals RPGY. 
As shown in FIG. 5, ultrasonic acoustic transmitting crystals 500 and 502 
are disposed inside inflated tire 112, which is chucked between rings 108 
and 110, rotatably secured to spindles 102 and 104, respectively. The 
electrical leads feeding transmitters 500 and 502 are fed out through the 
fixed spindle 102 to the transmitter activation circuits. Inflation air is 
likewise fed in through the center of spindle 102 as are pneumatic lines 
and/or other control connections for extending and retracting the 
transmitters. 
The exemplary ultrasonic transmitters 500 and 502 have a radiation field 
which substantially illuminates a sector of approximately 90.degree.. 
Hence, they are mounted at 90.degree. 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 if 
the transmitters are too close to the inside tire surfaces or too far away 
from these surfaces. In the preferred exemplary embodiment, transmitting 
crystals 500 and 502 are approximately two inches from the inner tire wall 
surfaces although this optimum distance of separation may be varied by a 
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 of the tire wall. Here 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 walls. Preferably, the 
receivers are no closer than approximately 1 inch to the outer tire 
surface but are preferably within 5.5 to 8.5 inches of the opposingly 
situated transmitting crystal. The receiving transducers 210 preferably 
each employ a conically shaped collimator and/or focusing tube as shown in 
detail at FIG. 12. These tubes are preferably machined from polyvinyl 
chloride plastic material and also help to match the impedance of the 
actual transducer crystal surface to the surrounding ambient air acoustic 
impedance. 
A moderately high ultrasonic frequency is employed so as to help avoid 
interference from spurious ambient acoustic signals and to obtain 
increased resolution by using shorter wavelength acoustic signals while at 
the same time avoiding ultra-high frequency acoustic signals and the 
problems associated therewith. Frequencies above 40 kHz are desirable with 
75 kHz being chosen as the presently preferred optimum frequency. 
Ultrasonic transducing crystals operating at 75 kHz are conveniently 
available. For example, receiving crystals are available as the MK-111 
transducer from Massa Corporation, Windom, Massachusetts, having the 
following specifications: 
Frequency of Maximum Impedance (fm): 75 kHz.+-.3 kHz 
Impedance at fm (min): 6 K Ohms 
Receiving Sensitivity (O.C.) at Frequency of Max Output Db re 1 
Volt/microbar: -70DB min. 
Transmitting Sensitivity Db re 1 microbar at 1 ft./10mw: -12DB Min. 
Maximum Power Input: 100 MW 
Directivity: -10 DB Max. at 90.degree. Total Angle 
Temperature Stability: 10% Change in Frequency -30.degree. F. to 
+150.degree. F. 
Capacitance: 1200.+-.20% PF 
A suitable transmitting crystal tuned to approximately 75 kHz is available 
from Ametek/Straza, California under No. 8-6A016853. 
The electrical leads from each of the transducers 210 are preferably 
connected through coaxial cables 506 to their respectively associated 
pre-amplifiers 508. The outputs from each of the 16 amplifiers 508 are 
connected to an eight pole double throw electronic switch comprising 
Signetics SD5000 integrated circuits, controlled by the HIGH CHAN 
multiplexing signal provided by system interface 416. The eight resulting 
multiplexed output channels are connected through transistor buffer 
amplifiers to signal processing channels A-H.Accordingly, in the absence 
of a HIGH CHAN multiplex signal, the outputs from the first eight 
preamplifiers 508 are coupled to respective corresponding signal 
processing channels A-H. However, when the HIGH CHAN multiplexing signal 
is present, the outputs from the last eight of the pre-amplifiers 508 are 
connected to respectively corresponding signal processing channels A-H. 
The circuitry of each pre-amplifier 508 is shown in more detail at FIG. 6. 
It includes a first transistorized stage having a gain of approximately 
150 followed by a cascaded integrated circuit amplifier having a gain 
factor of approximately 11. 
The signal processing circuit 404 for each of channels A-H are identical. 
Accordingly, only the circuitry for channel A is shown in FIG. 7. The 
waveforms shown in FIG. 11 will be useful in understanding the operation 
of the circuitry in FIG. 7. 
The generation of a pulsed or bursted ultrasonic waveform for driving the 
transmitters 500 and 502 will be described later. However, by reference to 
FIG. 11, it may be seen that each transmitter is driven to provide at 
least one approximately 30 cycle burst of 75 kHz acoustic output signals 
each time an RPGX trigger pulse occurs (e.g., 1,024 times per tire 
revolution). After a transmission delay, which will depend upon the 
separation between transmitter and receiver and the characteristics of the 
intervening ambient air and tire rubber, the transmitted acoustic signals 
are received. The received and transduced acoustic signals may have a 
complex amplitude envelope (rather than the well-behaved one shown in FIG. 
11) depending upon the type of multiple reflections, internal 
reverberations, wave cancellations, and/or other peculiar wave effects 
which take place along the transmission path. Accordingly, it is only the 
leading edge or initial portion of each such ultrasonic pulse or burst 
(e..g. where the amplitude envelope is initially increasing) that provides 
the best and most accurate indication of the transmission path quality 
(i.e. its included tire structural defects). Accordingly, the signal 
processing circuitry shown in FIG. 7 is adapted to effectively utilize 
only such initial or leading edge portions of each burst of ultrasonic 
signals. In one embodiment, data for each tire measurement area is 
obtained by averaging measurements taken at different respective acoustic 
frequencies. 
As explained in U.S. Pat. No. 3,882,717, it is necessary to provide 
automatic gain control amplification of through-transmission ultrasonic 
test signals to compensate for different average tire casing thicknesses. 
This earlier patented system had but a single signal processing channel 
with AGC employed to compensate for differences in average tire casing 
thicknesses over the cross-section of a given tire. However, it has been 
discovered that automatic gain controlled amplification must also be 
included in each of the plural testing channels of this invention so as to 
compensate for differences in average tire casing thickness from 
tire-to-tire. 
Accordingly, an AGC amplifier 700 (e.g. integrated circuit MC1352) is 
included within channel A as shown in FIG. 7. The ultrasonic signals 
passing through channel A are fed back to pin 10 of the AGC amplifier 700 
and input to a relatively long time constant (e.g. 10 seconds) RC circuit 
702 connected to pin 9 of amplifier 700. Accordingly, the average of 
signals passing through the channel over the last several seconds (during 
the included periods that the amplifier is enabled) is compared to a 
constant reference AGC bias presented at pin 6 so as to maintain a 
substantially constant average output level at pin 7 over the RC time 
constant period. Amplifier 700 in the preferred exemplary embodiment has a 
gain which may vary automaticlally betwen a factor of 1 and 1000. 
Amplifiers 704 and 706 are connected in cascade within channel A and each 
provide a gain factor of approximately 2. Additionally, amplifier 706 had 
diodes 708 and 710 connected so as to effect a full wave rectification of 
its output signals as presented to the FET gate 712. 
Referring back to FIG. 11, an integrate reset signal INTGRST is generated 
during the first transmission delay period for a given test tire position 
and presented to FET gate 714 (FIGURE 7) so as to discharge the 
integration capacitor 716 connected across amplifier 718 (forming a 
Miller-type integrator). Furthermore, the AGC amplifier 700 is enabled by 
the AGCEN signal at some point during each testing cycle so as to sample 
the received signals. The integrator enabling signal INTGEN is timed so as 
to enable the FET switch 712 only during the initial portions or leading 
edge of the ultrasonic burst (e.g. approximately 130 microseconds or about 
the first 10 cycles of the 75 kHz burst). If desired, two or more received 
bursts at respective differrent frequencies may be sampled and the results 
integrated together so as to effectively aveage measurements taken at 
different frequencies (and hence having different acoustic standing wave 
patterns). 
Therreafter, the output of integrator 718 is converted to a digital signal 
under program control by CPU 408 generating suitable analog DAC inputs to 
comparator 720 and conversion gating signals CONV to gate 722 which 
interfaces with one of the conventional data bus lines (in this case 
DB.phi.. Such program controlled analog-to-digital conversion is 
conventional and involves the CPU program controlled conversion of 
reference digital signals to refernce analog DAC signals which are then 
successively compared in comparator 720 with the results of such 
comparisons being made available to the CPU via data bus lines and gates 
722. By a process of successive comparisons to different known reference 
signals, the programmed CPU is capable of determining a digital value 
corresponding to the input integrated analog value from amplifier 718. 
This process is of course repeated simultaneously in channels A-H and 
successively in each channel for each burst or group bursts of ultrasonic 
signals occurring at a given tire wall test site. 
Referring now to FIG. 8, the RPGX (1,024 pulses per revolution) and RPGY (1 
pulse per revolution) signals from the rotary pulse generator are passed 
through tri-state buffers 800 to data bus lines DBO and DB1 respectively 
in response to the IN3 and Q4 addressing signals provided by the CPU. 
Other addressing outputs from the CPU are input to an output decoder 802 
so as to provide signals OUT320.00 through OUT320.70 under appropriate 
program control. 
Just prior to a scan cycle, the CPU is programmed to repetitvely poll data 
bus line DB2 looking for a scan request signal SCANRQ generated by an 
operator manipulation of the scan request switch 804 which causes 
flip-flop 806 to be set at the next occurrence of OUT320.60. 
Once a scan request has been detected by the CPU via data bus line DB2, the 
CPU is programmed to poll the RPGX and RPGY signals which are then 
presented on data bus lines DB0 and DB1 by address inputs IN3 and Q4. An 
actual measurement cycle is not started until the second RPGY signal is 
detected so as to insure that the tire is running true at a substantially 
steady state speed and that the AGC circuits are operating properly. 
Thereafter, each occurrence of an RPGX signal detected by the CPU is 
programmed to cause the generator of an OUT320.10 signal. The OUT320.10 
signal triggers one shot circuits 808 and 810 and also enables the latch 
812 to accept the ditigal values presented on data bus lines DB0 through 
DB4. 
Just prior to the generation of the first burst of ultrasonic waves at a 
given tire wall test site, the CPU generates OUT320.70 which triggers 
reset one shot 822 and provides an integrator reset signal INTGRST via 
addressable flip-flop 823 and NAND gate 825. 
The 4 bit binary counters 814 and 816 are connected in cascade to count the 
18.432 Mhz clock signals input from the CPU board and to divide these 
clock pulses by a numerical factor reresented by the contents of latch 
812. The result is an approximately 75 kHz clock signal, (both 74 kHz and 
76 kHz frequencies are used successively in one embodiment with the two 
results averaged together) which is used to trigger one shot 818 having an 
adjustable time period such that its output can be adjusted to a 
substantially square wave 50% duty cycle signal. As shown in FIG. 8, one 
shot 818 is controlled by a pulser enabling signal from the addressable 
flip-flop 819. thus if desired (e.g. to listen for leaks), the ulrasonic 
transmitters may be selectively disabled by the CPU. 
The approximately 75 kHz 50% duty cycle signal is then buffered through 
amplifier 820 and presented as square wave output MB (see FIG. 11) to 
conventional transmitter driver amplifiers (providing approximately 200 
volts peak-to-peak electrical output) which, in turn, cause a generally 
sinusoid type of 75 kHz acoustic output from the transmiter as shown in 
FIG. 11. 
This generation of the approximately 75 kHz output MB will continue until 
one shot 808 times out (e.g. approximately 1 millisecoond). During that 
interval, a burst of ultrasonic acoustic signals is caused to emanate from 
one fo the transmitting crystals. 
The period of one shot 810 is adjusted for a delay approximately equal to 
but slightly less than the transmission delay between acoustic 
transducers. The delayed output from one show 810 resets the data ready 
flip-flop 828 and triggers the integrate timing one shot 826 which 
produces the integrate enable signal INTGEN. At the conclusion of the 
integrate enable signal from one shot 826, the data ready flip-flop 828 is 
set to provide a data ready signal to the CPU via data bus line D84. If 
more than one analog data value is to be combined at the output of the 
integrator, the CPU is simply programmed to ignore the data ready signal 
until the requisite number of measurement cycles have been completed. 
Ultimately, however, the data ready signal indicates to the CPU that 
analog-to-digital conversion of the integrated analog signal is now ready 
to be performed. The CPU, under conventional program control, then begins 
to produce various analog reference signals DAC from the digital-to-analog 
converter 830 under control of the digital data latched into latch 832 
from the data bus lines by the addressing signal OUT320.00. At the same 
time, the CPU is programmed to provide proper conversion gating signals 
CONV via the addressing inputs to ates 834, 836 and 838. 
The DAC may be a linear type 08 or a non-linear exponential type 76 or 
other known non-linear types of DAC circuits. The non-linear DAC-76 is 
believed to improve the effective signal-to-noise ratio for lower level 
signals. 
The CPU is programmed so as to normally produce the multiplexing HIGH CHAN 
outpu by setting and resetting the addressable flip-flop 840 via the 
address lines A.phi.-A2, OUT320.30 in accordance with the data value thne 
present on data line DB.phi.. However, manula override switch 842 has been 
provided so thateither the low channels .phi.-7 or high channels 8-15 may 
be manually forced via tri-state buffes 844 with outputs connected to the 
data bus lines DB6 and DB7. 
The flow diagram for an exemplary CPU control program is shown in FIGS. 
15-16. Conventional power-up, resetting and initialization steps are shown 
at block 1500. After the START entry point, the scan request flip-flop 806 
(FIGURE 80 is reset, the integrators are disabled (via flip-flop 823, 
FIGURE 8), and the data memory circuits are disabled at block 1502. 
Thereafter polling loop 1504 is entered and maintained until a SCANRQ on 
DB2 is detected. 
Once a scan request has been detected, the indicator lamps are tested, the 
integrators are enabled for normal operation (via flip-flop 823), the data 
memory is enabled for access by the CPU (and conversely, the display 
interface is disabled from access to the data memory) at block 1506. The 
high/low/normal switch 842 (FIGURE 8) is also checked via DB6 and DB7. If 
the low or normal mode is indicated, the HIGH CHAN multiplex signal is 
maintained equal to zero via flip-flop 840. Thereafter, polling loop 1508 
is entered to test for a RPGY transition. A similar polling loop 1510 is 
subsequently entered to issue at least one tire revolution before 
measurements are taken. Then a software counter .theta..sub.current is set 
to zero and the LOOP1 testing subroutine (FIG. 16) is entered. As will now 
be explained in more detail, the step within LOOP1 are executed 1024 times 
to collect and record 1024 data values in each of eight transducer 
channels corresponding to 1024 tire testing sites distributed over a whole 
360.degree. of tire rotation in each of the eight channels. 
After entry of LOOP1, te RPGX signal on DB.phi. is tested for a transition 
from 1 to .phi. at loop 1600. Once this transition occurs, all te 
integrators are reset (via one shot 822, FIGURE 8), the latch 812 is set 
to produce a 74 kHz MB drive signal and the transducers are driven with a 
burst of 74 kHz MB drive signals via one shot 808 and a pulser enabling 
signal via flip-flop 819. Since one shot 810 is also triggered, the leding 
edge of the received burst is gated and integrated in each channel. 
While this test at 74 kHz is being performed, the CPU is in a wait loop 
1602. Thereafter, latch 812 is reset to produce a 76 kHz MB signal and the 
transmitters are again pulsed. The result is another gated integration of 
the leading edge of a received burst at 76 kHz. As soon as this second 
integration is completed, the data ready signal on DB4 is detected at 
waiting loop 1604. After the analog data has thus been accumulated for two 
different frequencies at a given tire test site, the AGC circuits are 
keyed (to keep them actively sampling the channel signal level within the 
relevant RC time constant period) and a conventional analog-to-digial 
conversion routine is entered. This routine converts each integrator 
output to a six bit digital value which is then stored in te dat memory 
412. The data for each channel is stored in a separate section of the 
memory so that similar data points for each channel can be later addressed 
using the same lower order memory addressing signals. 
The .theta..sub.current software counter is thereafter incremented by one 
and LOOP1 is re-entered unless data measurements at all 1024 tire test 
sites have already been taken. 
After the first exit from LOOP1, a pattern recognition subroutine may be 
entered, if desired, at block 1512. The pattern recognition results may 
then be tested at 1514 and 1516 to determine which of status indicator 
lamps 846 (FIGURES 8) should be lighted. Altenatively, the pattern 
recognition steps may be skipped as shown by dotted line 1518 to flip the 
HIGH CHAN multiplex signal, if operation is in the normal mode. (If only 
high or low channel testing has been forced by switch 842, return can now 
be made to the START entry point). Thereafter, measurementsare taken for 
the higher group ofeight channels as should now be apparent. 
While LOOP1 in FIG. 17 causes measurements at 74 kHz and 76 kHz to be 
combined, it should also be apparent that block 1606 can be skipped if 
measurements at only a single frequency are desired. Similarly, 
measurements at more than two frequencies can be combined if desired. 
Furthermore, the combination of plural data values can be initially made 
either in analog form (as in the exemplary embodiment) or in digital form 
as should now be apparent. 
As already discussed, the CPU may be programmed, if desired, to 
automatically analyze the digitized data collected during a complete 
scanning cycle with pattern recognition algorithms and to activate one of 
the indicator lamps 846 (e.g. representing acceptance, rejection or air 
leakage) via conventional lamp driving circuits 848 as controlled by the 
contents of latch 850 which is filled from data bus lines DB.phi. 
throughDB4 under control of the address generated OUT320.20 signal. Air 
leakage can be detected, for example, by perfomring a complete scanning 
and measurement cycle while disabling the ultrasonic transmitters. 
Detected increases in received signals are then detected as leaks. 
The central processing unit shown in FIG. 9 is conventionally connected to 
decode the various address lines and provide addressing inputs already 
discussed with respect to the system interface shown in FIG. 8. The CPU 
itself is a conventional integrated circuit 8080 microprocessor having 
data input and output lines D.phi. through D7 which are connected to the 
data bus lines DB.phi. through DB7 through conventional bi-directional bus 
driver circuits 900. Address lines A.phi. through A9 and A13 are alos 
directly connected through buffer amplifiers 902 to the system interface, 
memory circuits, etc. Address lines A10, A11 and A12 are decoded in 
decoder 904 to provide addressing outputs Q.phi. through Q7. Similarly, 
addressing lines A14 and A15 are decoded together with the normal writing 
and data bus input signals from the CPU in decoder circuitry 906 to 
provide IN.phi. through IN3 and OUT.phi. through OUT3 addressing outputs. 
The normal data bus input CPU signal DBIN and the addressing lines 814 and 
815 are also connected through gates 908 and 910 to conventionally provide 
a directional enabling input to the bidirectional bus drivers 900. The 
approximately 18 Mhz clock 912 is also conventionally connected to the 
8080 CPU. However,pin 12 of the 3G8224 integrated circuit is brought out 
to deliver an 18.432 Mhz clock to the frequency dividing circuits of the 
system interface already discussed with respect to FIG. 8. 
The data memory circuits are provided by a conventional connection of 25 
integrated circuitsof the 4045 type so a s to provide 8,192 eight bit 
bytes or words of data storage capability. 
The programmable read-only memories may be provided by three integrated 
circuits of the 2708 type, each providing 1,024 bytes of programmed 
memory. 256 eight bit words of read/write memory are also preferably 
connected to the CPU as part of the programmable memory circuits. An 
integrated circuit of te type 2111-1 may be used for this purpose. 
The CRT display interface is directly connected to the data memory board. 
Once an entire measure cycle has been completed (e.g. when the third RPGY 
signal has been detected after a scan request), there are 1,024 data 
values available for each of the 16 measurement channels representing the 
relative magnitudes of ultrasonic signals transmitted through the tire at 
1,024 successive respectively corresponding positons about the tire 
circumference within the area monitored by the receiving transducer for a 
given channel. This digital data may be converted to conventional video 
driving signals for a CRT and displayed as shown in FIGS. 13 and 14. 
Alternatively, te 8080 computer may be programmed to analyze (e.g. by 
pattern recognition algorithms) the available digital data and to activate 
appropraite ones of the indicator lamps 846 shown in FIG. 8. 
The display interface shown in FIGURE 10 is conventionally connected 
directly to the data memory 412 via memory data bus lines 1000, memory 
quadrant selection bus lines 1002, memory address bus lines 1004 and data 
latch strobe line 1006. The whole display can be selectively disabled or 
enabled asdesired under CPUcontrol via CPU addressing outputs A13, Q3, 
OUT3 and A.phi. via flip-flop 1008 and the associated inverter and gates 
shown in FIG. 10. In the preferred embodiment, the display interface is 
disabled whenever other parts of the system are accessing the data memory 
412 so as to prevent possible simultaneous activation of the data memory 
circuits. 
The display interface is driven by a 11.445 MHz clock 1010. Its output 
drives counter 1012 which is connected to divide the clock signals by a 
factor of 70. The first 64 counts of couner 1012 are used by comparator 
1014 which also receives 6 bits of data (i.e. 64 differeent numerical 
values) from the addressed data memory location representing the magnitude 
of ultrasonic signals transmitted through a particular tire testing site. 
Thus the output from comparator 1014 on line 1016 will occur at a specific 
time within 64 clock periods corresponding to the magnitude of the input 
digital data via lines 1000. The clock pulse during data coincidence will 
cause flip-flop 1018 to transition momentarily and produce a video output 
pulse via gate 1020 having one display dot time width and spaced within 
its respectively corresponding channel time slot according to the 
magnitude of the recorded data. Flip-flop 1022 is triggered by counter 
1012 upon counting a 65th clock pulse and generates an inter-channel 
separation blanking video pulse out of gate 1020. The counter 1012 then 
continues to count 5 more clock pulses before resetting itself and 
starting another cycle using data from the next adjacent channel. 
The 70th count form counter 1012 also drives a three bit channel counter 
1024 which, through the 3-to-8 decoder 1026, successively addresses eight 
different sections of the data memory corresponding respectively to eight 
of the sixteen ultrasonic receiver channels. A selection between display 
of the higher or lower eight channels is made via switch 1028. 
At the end of a complete horizontal scan line, 8.times.70 clock pulses 
(2.times.70 clock pulses are counted during horizontal retrace period) 
will have been counted by counters 1012 and 1024 and a carry pulse will go 
to the 12 bit counter 1029 so as to increment the addresses on line 1004 
(via decoder 1030) for the next horizontal scan line. In the case of the 
usual interlaced CRT scanning raster, every other horizontal line will 
actually be skipped and picked up during a second vertical seam raster as 
will be appreciated. The states of counters 1024 and 1029 provide all 
requisite timing information for conventionally generating the usual CRT 
horizontal synchronization, vertical synchronization and vertical and 
horizontal retrace blanking video signals at 1032. 
The various video signals are conventionally mixed in video amplifier 1034 
and output to a CRT display. 
Since there are 1024 data values in each channel but many fewer horizontal 
scan lines in the usual CRT raster, switch 1036 is provided so as to 
select only the odd or even addresses for data values in a given channel. 
Thus the complete 360.degree. of scanned tire surface, within a given 
channel, is displayed in an assigned time slot over 512 vertically-spaced 
horizontal scan lines. 
As thus described, the data values for a given channel would be distributed 
within a vertical segment of the CRT display and displaced in a horizontal 
sense from a vertical base datum line in accordance with the stored data 
values. However, in the preferred embodiment, the CRT deflection yoke is 
rotated by 90.degree. so that the final CRT display for a channel is 
presented horizontally as shown in FIGS. 13 and 14. 
As depicted in FIGS. 13 and 14, the signal traces in each individual 
channel are deflected upwardly to represent reduced ultrasonic signal 
magnitudes. Accordingly, in FIG. 13, it can be seen that a defect has 
occurred in channels 12 and 13 at approximately 20.degree. from the index 
marker. Similarly, a defect is shown in FIG. 14 at channels 12, 13 and 14 
at approximately 280.degree.. 
Although not shown in FIGS. 13 and 14, if a leak had been present, it would 
have been indicated by an increased signal magnitude which, in the 
representation of FIGS. 13 and 14, would have resulted in a downward 
deflection of the signal trace for the corresponding channel. 
The tracing for channels 0 through 3 and 12-15 is caused by wire ends, 
transitions between various normal tire layers and a periodic pattern of 
remaining tire tread structures about the outer edges of the tire 
treadwall. The data actually shown in FIGS. 13 and 14 was taken using a 
linear DAC circuit in the analog-to-digital conversional process. 
FIG. 17 shows another circuit for generating the AGC amplifier and 
integrator channels. The circuit permits generation of INTGEN, AGCEN, 
INTGRST, and MBT pulses from RPGX pulses at 1605 or simulated RPG pulses 
from addressable latch 1608 under program control. 
When the RPG simulator is enabled, 1608 output labeled 5 is a 50% duty 
cycle pulse train which is selected by multiplexor 1611 to trigger 
one-shots 1612 and 1613. One-shot 1612 is triggered by the rising edge of 
the output of 1611 and times out in 300 ns. One-shot 1613 is triggered by 
the falling edge of 1611 and also times out in 300 ns. 
The outputs of 1612 and 1613 are combined to trigger DELAY one-shot 1614 
and MB one-shot 1615. The generation of 75 KHz bursts by 1615, 1620, 1621, 
1622 and 1623 has been previously described. DELAY one-shot 1614 triggers 
INTEGRATE one-shot 1616 and resets DATA READY flip flop 1617. 
Flip flop 1617 signals that the analog outputs of the AGC 
amplifier/integrator channels are ready for digitizing. Flip flop 1617 is 
only set while RPG is high. 
Flip flop 1617 triggers AGCEN flip flop 1619 which is level shifted and 
sent to the AGC amplifiers. 
A delayed RPG signal appears at the output of flip flop 1618 and it is used 
by the software for synchronizing to tire rotation. 
When the simulator is disabled, multiplexor 1611 sends the logical output 
of 1605 to one-shots 1612 and 1613. The input source for 1611 now comes 
from the tire-rotation generated RPGX pulses, and the generation of the 
required outputs, i.e., INTGEN, is accomplished by controlling multiplexor 
1611 outputting pulses to one-shots 1612 and 1613. 
The sequence of one-shot firings follows the same pattern as described in 
the previous paragraphs when the RPG simulator is activated. 
The DAC comprised of 1624 and 1625 generate an analog voltage used by the 
CPU for analog-to-digital conversion of the integrated values of received 
signals. 
Decoder 1609, flip flop 1610, register 1627 and lamp driver 1628 perform 
functions already described. Latch-decoder 1629 and display 1630 provide 
status information during program execution. 
During air-leak detection, PULSEN generated by software at 1608 is low, 
thus inhibiting MB excitation pulses to the pulser unit by clearing 
one-shot 1620. 
FIGS. 18, 19a and 19b illustrate a program sequence which searches for air 
leaks then searches for separations in two eight-channel groups. 
Blocks 1631 and 1632 initialize states of the system and 1633 selects the 
RPG simulator to trigger the one-shot timing elements. The RPG simulator 
switches alternately high and low at a 8 ms rate while the SCAN RQ flip 
flop is tested in the loop 1634 and 1635. The RPG simulator refreshes the 
AGC levels so when SCAN RQ becomes active, data acquisition for air leaks 
can begin immediately. 
When SCAN RQ becomes active, the RPG unit is selected in 1636 and data 
memory enabled in 1637. Subroutine GETDATA is called at 1638 and is 
detailed in FIGS. 20a and 20b. Next, PATTERN REC is called at 1639, and 
any air leaks present will be detected and the AIR LEAK lamp will be 
turned on by 1640 and 1641. 
Now the pulser is activated at 1642. Tests for HICHAN, LOCHAN only and 
normal scan are done at 1643, 1644 and 1645. 
Subroutines GETDATA and PATTERN REC are called at 1646. Blocks 1647, 1648, 
1649 and 1650 test for REJECT/ACCEPT status and decide whether to continue 
to scan the high channel group. GETDATA and PATTERN REC are called again 
at 1651 and the tire status is tested again by 1652 and the program 
returns to CONTINUE via 1653, REJECT status, or 1654, ACCEPT status. 
FIGS. 20a and 20b detail the flow of subroutine GETDATA. The position 
counter, .theta. CURRENT is set to zero at 1655. The tire scan begins at 
the current tire position which is assumed to be the origin. Block 1656 
tests for occurrence of the once-per-revolution INDEX pulse and stores 
.theta. CURRENT at location OFFSET. If INDEX is present, then 1657 stores 
the location in memory. 
Block 1658 waits until RPG is zero. When the condition is met, 1659 sets 
the pulsing frequency to 74 KHz and repeats the INDEX test at 1660 and 
1661, and waits until RPG is one at 1662. A new pulsing frequency is 
selected at 1663. 
When a complete RPG cycle has elapsed, the DATA READY flip flop will be 
set, and 1664 waits for this condition. When DATA READY is true, eight 
steady state voltages generated by each of the integrators are converted 
by block 1665 and stored in data memory as raw data. The tire position is 
incremented and tested for the last data point at 1666. The program 
continues to acquire data by jumping to the reentry point B. When all 
points are digitized and stored, the data is justified in memory by 1667 
so the data associated to the INDEX point is at the start of the data 
block. 
While only a few exemplary embodiments and only a few variations thereof 
have been explained in detail, those in the art will appreciate that many 
other modifications and variations may be made without departing from the 
novel and advantageous 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.