Note: Descriptions are shown in the official language in which they were submitted.
1~188~3
The present invention relates to an apparatus for the measurement
of the length of an object and more particularly to ~he measurement of the
length of a tread.
Tires are made from, among other things, treads. Typically, treads
are made continuously from rubber extruder systems. The tread is extruded
through different dies in one continuous length from softened rubber and is
then conveyed over a series of belts for cooling. The treads are then cut
Erom this continuous length at a "cutting" station into specified lengths
for use in different si~es and types of tires. The treads, cut in various
sizes, are then transported over a series of belts to an area termed "booking"
station whence they, along with other items, such as cord, are taken to be
assembled into a tire.
Between the "cutting" station and the "booking" station (~ypically
between 50 to 100 feet) the treads are moved onto a series of conveyors. The
conveyors serve to accelerate the tread on it relative to the subsequent
tread. The cut treads are also moved onto weighing belts which determine the
weight of each tread. The effect of this series of conveyors is to increase
the spacing between each tread so that a requisite amount of time between
each tread for weighing and removal from conveyors is provided. A tread
failing to meet the requisite weight requirement is rejected at this point.
Although the distance between the "cutting" station and tlle "booking"
station is relatively short, this spacing is required as part of quality con-
trol ~for weight specification) and to provide time for removal from the con-
v~yors. Ilowcver, i~ has also been observecl that ~he leng~h o~ ~he tread cut
at khe "Gu~king" sta~ion i~ not the same as the leng~h of the same ~read at
the ~booking" station. Mos~ of the t:Lme the tread will have shrunk between
the "~utting" statiQn and the "booking" sta~ion The cause oE this shrinkage
s~ems ~rom ~wo ac~ors. Tho Eirst is the relaxation o~ ~onsion in ~ho trcad
as soon as it is cut. The olasticity O-e rubber, while a very much desirable
quality in tire, is a source oE objection in this part o~ the manufacturing
9;~
process. The second is that despite the cooling of the tread prior to cut-
ting~ the temperature of the tread immediately after cutting is not the same
as ambient temperature. rrhus, the tread is subject ~o further cooling
between the "cutting" station and the "booking" station.
The tread at assembly must meet certain specifications for size for
proper fitting to a tire. Thus, the shrinkage of the tread must be accounted
for during the manufacturing process, e.g. cut the tread to a size larger than
desired to allow shrinkage. However, the shrinkage of the tread is, as
discussed, uncontrollable and is to a certain degree unpredictable. The
unpredictability arises from the fact that many factors contribute to the
shrinking phenomenum, e.g. ambient temperature, type of rubber used, tempera-
ture of tread at cutting, etc.
Heretofore, the solution to this problem of production control and
~uality assurance in the manufacturing of treads to specified lengths has been
to manually and selectively measure a few treads at the "booking" station to
measure and calculate the degree of shrinkage and to control the production
of subsequent treads. Clearly, an automatic system which can measure every
tread is desirable.
A tread length sensor for measuring the length of a tread, having
a leading edge, a trailing edge and a one surface which is substantially flak,
comprises a means for generating a beam of radiation. The beam is aligned
such that it can impinge the leading edge of the tread. The beam is detected
by a sensing means which produces a first electrical signal which is res-
ponsive to the beam impinging the leading edge. The tread is supported by a
supporting means. The traillng edge o~ the trcad is illuminated by illuminat-
lng mcaTIs. Thc trailing edge is de~ccted by a detecting means which is
positloned at a fixed dlstance fr~m the beam. ~he clotecting me~ns produces
a sccond clectriGal si~nal in response to the con~rast between the supporting
means and the tread. The first electrical signal J ~hu second clectrical
signal and -the fixed distance are used by a calculating means to determine
33
the length of the trcad.
~:igure 1 ls a cross-sectional view of a typical tread.
~igure 2 is a perspective view of a typical tread.
Figure 3 is a side view of a typical tread.
~igure 4 is a schematic view of the sensor of the present invention.
Figure 5 is a schematic view of an example of an image of the trail-
ing edge of a tread detected by a digital camera at the instant -the leading
edge impinges the beam.
~ igure 6 is a block diagram of a partial system using the sensor of
the present invention to correct for the production of treads.
Referring to Figure 1, there is shown a cross-sectional view of a
typical tread 10. The tread 10 has a one surface 12 which is substantially
flat, and a top surface 15, opposite the one surface 12. The top surface 15
is substantially wavy. As the tread 10 moves in the direction shown by arrow
18, the tread 10 is characterized by a leading edge 14 and a trailing edge 16.
As can be seen from Figure 3, the leading edge 14 and the trailing edge 16
are not perpendicular to the one surface 12. In the cutting process, the
tread 10 is cut at an angle less than 90 degrees from the one surface 12.
Referring to Figure 4 there is shown the tread length sensor,
generally designatcd as 20, of the present inven~ion. The tread lO to be
measured by the tread length sensor 20 is shown as moving in a direction 18.
The sensor 20 comprises a laser 22. The laser 22 is capable of emitting a
beam 24 of radiation. The beam 2~ is aligned such that it would impinge the
leading edge 14 of the one surface 12 of the tread 10 as the tread 10 moves
in tha direction 1~. The beam 2~ is detccted by a photode~ec~or 26. Tho
photocl~ector ~6 outputs a Eirst electrical signal 28 wh:Lch :indicatos when thebeam 24 has impinged the leading edge 1~.
Tho tread 10 is suppor~ed by a bel-~ X0. The belt xn supports the
tread 10 on the one surface 12S the surEace which is subs~antially -Elat.
Lamps 32 are used ~o illuminate the traillng eclge l6 Oe the tread 10. A
893
dig:ital camera 34 detects the trailing edge 16 by detecting the contrast
between the trailing edge 16 of the one surface 12 and the belt 30. The
camera 34 produces a second electrical signal 36 in response to the contrast
between the trailing edge 16 and the belt 30. The camera 34 is at a fixed
distance from the laser 22. The ~irst electrical signal 28 and the second
electrical signal 36 are entered into a digital computer 38 which, along with
the information of the fixed distance between the camera 34 and the laser 22,
can calculate the length of the tread lO.
In general, any means to generate a beam of radiation, such as x-ray
tube, incoherent light (visible or invisible) etc., can be used in place of
the laser 22 -- so long as the beam 24 produced is capable of impinging the
leading edge 14 of the tread 10. Similarly, any sensing means, such as
ionization chamber, photomultiplier tube, photodiode~ etc., can be used in
place of the photodetector 26 -- so long as the sensing means can detect the
beam 24 impinging the leading edge 14. The ~irst electrical signal 28, pro-
duced by the photodetector 26 to indicate when the beam 24 has impinged the
leading edge 14, can be simply the output signal of the photodetector 26
passed through an inverter. The belt 30 supports the tread 10. Typically~
it is a moving belt moving ~n the direction shown by arrow 18. The require-
ment for the belt 30 is that it supports the tread 10 and provides sufficient
contrast be~ween the belt 30 and the tread 10 to be detected by the digital
camera 34. The lamps 32 illuminating the trailing edge 16 can be Oe any
illuminating means, so long as the contrast between the tread 10 and the belt
30 can be detected. Another possible use of lamps 32 is to position them
below the ~read 10 and the belt 30 to provide back light illumination. The
digl~nl camera S~ can bo o~ any klnd, such as *Rokicon LC600 manufacturod by
tho Ro~icon Corporation o~ Sunnyval~, Caliornia.
The ~h~ory o opora-tion Oe the sensor 20 Oe the prcs~nt invontion is
as ~'ollows. A~ter ~ho ~read 10 is cut by the cu-~er Cnot shown~ it conkinucs
~o move toward the beam 2~. As soon as ~he leading cclgo 14 Oe th~ tread 10
*Trade Mark
33
;mpinges the beam 24, a first signal 28 is sent to the computer 38. The com-
puter 38 then immediately receives the second signal 36 ~rom the digital cam-
era 34. The second signal 36 may be adjusted for the speed of the moving belt
30. The first signal 28, the second signal 36 and the fixed distance are used
by the computer 38 to calculate the length of ~he tread 10. A schematic view
of an example of an image received by the digital camera 34 at the instant the
leading edge 14 is impinged by the beam 24 is shown in Figure 5. There are
ten dots, each representing a photosensitive element, such as a photo-diode.
Typically, the camera 34 will have more than ten elements. The six left-most
elements are darkened to reflect the image of the tread LO. The four right-
most elements reflect the image of the belt 30. The contrast between the
tread 10 and the belt 30 is evident at the division between the fourth and
fifth right-most elements. ~ypically, the tread 10 is dark; thus, the belt
30 need be only of a light color to provide sufficient contrast. From a
predetermined measurement based upon the fixed distance between the camera
34 and the laser 22, the distance of each element from the point where the
beam 24 impinges the leading edge 14 is determined. Thus, the length of the
tread 10 that is within the view of the digital cc~mera 34 can be calculated.
There are many advantages of the sensor 20 of the present invention.
Pirst there are no moving parts; thus, the sensor 20 is not subject to
mechanical wear. Secondly~ unlike the manual system of measuring a selective
number of treads, the sensor 20 is entirely compatible with the manufacturing
process~ i.e., it can automatically and without contact or interruption
mqasure each ~read lO as each is produced. Thirdly, the treads lO comq ln
dl~eeren~ slæq5~ Thq digi~al camera 34 can a~commodate treads Oe varying sizes
so long as ~he ~railing ed~e 16 is wlkhill tho viqw o~ ~he camera 34. rrhus,
tho s~nsor 20 naqd not be adjuxtqd to accommodate limited variations in the
size Oe the ~reads lO. Measurement of varying slzes Oe treads ls possible.
Pour~hly, in the sensor 20 of tho present invention, the len~th ~-~' of the
tread 10 is measured rather than A-A' (shown in ~igure 2) as done in the prior
15 93
art. By measuring B-B' it is seen from ~igure 4 that a greater degree of con-
trast is availa~le, i.e., the camera 34 can distinguish a greater degree of
contrast between trailing edge 16 of the one surface 12 and the belt 30 than
the contrast between the trailing edge 16 and the top surface 15 opposite the
one surface 12. Fifthly, by measuring B~B' a lower probability of error is
introduced than measuring A-A'. Typically, as the tread 10 is produced~ it
may move in a skew manner. Thus, if the measurement of the length of the
tread 10 were performed on the top surface 15, a deviation of only a few
degrees ~ may result in the measurement of the length C-A'. However, that
same deviation of a few degrees ~ will result in a smaller error if the
measurement were made on the one surface 12, e.g., B'-D, as is done by the
sensor 20 of the present invention.
Referring to Figure 6, there is shown a block diagram of a partial
system using the sensor 20 of the present invention to adjust the production
of treads 10. The length sensor calculator 38 is as discussed in Figure 4.
The calculator 38 produces a third output signal 40 which is the calculation
of the measurement of the length of the tread 10. The third signal 40 enters
into a comparator 44. A fourth signal 42 is also entered into the comparator
44. The fourth signal 42 is a pre-set signal, i.e. it is the desired value of
the length of the tread 10. It can be set by the operator of the process.
The comparator 44 compares the third signal 40 to the fourth signal 42 to pro-
duce a correction signal 46. The correction signal 46 is used to adjust the
cutter ~not shown). In this manner complete feedback control of the production
o ~reads 10 based upon the length sensor 20 is accomplished.
