Note: Descriptions are shown in the official language in which they were submitted.
CA 02238969 1998-OS-28
WO 97/22461 PCT/US96/15953
- 1 -
METHOD AND APPARATUS OF PRODUCING BELTS WITH
PRECISE CORD LENGTH AND TENSION
Backaroun.d of the Invention
This invention pertains generally to the art of
apparatus and methods for applying cords to a rotating
structure, and more specifically to apparatus and
method for producing elastomeric belts with precise
cord length and cord tension.
Traditional methods of applying cords to a
rotating mandrel involved a cylindrical mandrel of
minimal compliance, meaning the dimensions of the
mandrel, especially the diameter and circumference,
are essentially constant. The mandrel may be a rigid
1.5 cylinder, in which case the cord length is controlled
by selecting a cylindrical mandrel with the correct
circumference. Other mandrels are not cylinders, and
the invention disclosed herein applies to such
mandrels as well.
In some prior art mandrels, the mandrel
circumference is adjusted by applying or removing
layers of material from its surface. Other mandrels
have radially telescoping elements which form a series
of arcs approximating a circle. In all of these, the
cord is applied using a guide wheel which controls the
cord tension as accurately as practical in a demand
feed mode. The length of cord per revolution of the
mandrel is dependent on the cylinder circumference
and, therefore, on the manufacturing tolerances of the
cylinder.
Mandrels are often used in the construction of
elastomeric belt products, such as timing or drive
belts for automotive applications. Most belt designs
also require layers of other belt materials be wound
onto the cylinder before the cord. The thickness,
hardness, and temperature tolerances of these
materials may also affect cord length.
- CA 02238969 1998-OS-28
WO 97/22461 PCT/US96/15953
- 2 -
The present invention controls cord length
independently of the tolerances of the cylinder or the
underlying layers. Furthermore, the present invention
is capable of controlling cord length in a highly
accurate manner, with accuracies to 30 parts per
million possible. This is of particular importance in
making toothed timing belts where a cord length error
will result in improper meshing of teeth and premature
tooth or belt failure.
Another advantage of the present invention is
that the helical cord structure made by the present
invention can be removed easily from the cylinder
without loss of length accuracy or distortion of the
helix dimensions. This allows the belt containing the
cord to be formed by internal pressure in an external
mold like a tire mold, or in a press, rotocure, or
sectional cure device. The belt is easily removable
due to the collapsibility of the mandrel. Allowing
the mandrel to collapse releases tension in the cord
and provides enough clearance for easy removal of the
belt from the mandrel.
Timing belts are traditionally made on
cylindrical molds having tooth forms on the outer
surface which are parallel to the cylinder axis. A
layer of fabric, rubber, plastic, or other flexible
material is placed over the cylinder. The cord is
wound over the outside of the assembly. Additional
materials may be placed over the cord. The belt is
formed by applying inwardly radial pressure from a
diaphragm during the curing process. The finished
product is removed by sliding it axially to disengage
the mold teeth from the belt teeth. This process can
work for belts with axial teeth or belts with a single
set of helical teeth, but it cannot work for an
interrupted tooth such as a herringbone, dual helical,
or zigzag tooth because belts with these forms of
teeth cannot slide axially off the mandrel.
CA 02238969 2004-12-22
-3-
The present invention allows these products to be made with
an external rather than an internal mold, while still retaining
cord length accuracy. It also allows these products to be made
with flat sectional molds while retaining cord length accuracy.
Both of these methods allow the belt teeth to be disengaged from
the mold by motion approximately perpendicular to the mold
surface. This allows the interrupted tooth forms to be removed
from the mold.
The present invention contemplates a new and improved
method of producing belts with precise cord length and tension
which is simple in design, effective in use, and overcomes the
foregoing difficulties and others while providing better and
more advantageous overall results.
Summary of the Invention
In accordance with one aspect of the present invention, a
new and improved method of producing belts with precise cord
length and tension is provided.
In one aspect, the invention is a method and apparatus for
applying accurate lengths of cord to a rotating mandrel by using
a geared feed capstan. The geared feed capstan measures and
meters out a selected length of cord for each revolution of the
mandrel. All real materials suitable for winding, including
cords or wires, are elastic or stretchable, so that an accurate
description of the length of the cord to be applied must also
specify the tension in the cord when its length is measured. The
feed capstan measurement and metering accuracy is affected by the
tension of the cord entering and exiting the feed capstan. This
necessitates measuring and controlling the cord tension. The
exiting tension is controlled by the expansion of the mandrel.
The entering tension is held constant by a tension control
capstan, but any other means that maintains accurate entering
tension is also suitable. In the disclosure, the exiting cord
tension control is achieved by the expanding mandrel and the
tension sensing load cells which in part control the expansion.
CA 02238969 2004-12-22
_4_
The concept of primarily controlling cord length and secondarily
controlling cord tension is a key element of the invention.
In the Japan Patent Application No. JP 63 030234 A, a
resin-impregnated filament is wound on a rotating mold jig. The
rotation of a servomotor is controlled by signals from a tension
measuring device and a speed detector and the filament is wound
at a specified tension.
For example, other cord winding machines use cord tension
as the control parameter. As the mandrel rotates, the length of
cord is determined by the mandrel circumference, a procedure
called "demand feed" for the purposes of this disclosure. The
length of the cord is dependent on the mandrel circumference and
the tolerances of that circumference. There is no means of
accurately determining the length of cord so applied.
The function of the apparatus disclosed herein may be
inverted (so that the cord length is secondarily controlled and
cord tension is primarily controlled) and the apparatus will
still provide improvements and benefits over the prior art. The
load cells which control the expansion of the flexible diaphragm
can instead be used to control cord tension directly, and the
feed capstan can be used as an accurate length measuring device
rather than as a measuring and metering device. The length
measured at the feed capstan can then be used to control the
mandrel inflation to obtain the desired metered length of cord.
More particularly, in accordance with an aspect of the
present invention, an apparatus for applying a cord to a
rotating structure, the apparatus including a capstan for
regulating the length of the cord; supplying means for supplying
the cord to the capstan; holding means for holding and rotating
the rotating structure: and applying means for applying the cord
from the capstan to the rotating structure on the holding means.
According to another aspect of the present invention,
l~tov- 10-97 11 _ 47A F- _ 06
CA 02238969 1998-OS-28
v _y
the apparatus for applying a cord to a rotating structure
further ncludes a °irst capstan
~n
2C
4~r~;....;i~.fava s.la.ahnaGaa,a 1
AMENDED SdEET
CA 02238969 1998-OS-28
WO 97/22461 PCT/US96/15953
- 5 -
between the supplying means and the applying means;
and, a second capstan between the first capstan and
the applying means.
According to another aspect of the present
invention, the applying means includes a laying wheel
and, a second tension sensor, the second tension
sensor being located between the laying wheel and the
second capstan.
According to another aspect of the present
invention, a method for applying a cord to a rotating
structure, the method includes the steps of supplying
the cord to a capstan via supplying means; positioning
the card around the capstan, thereby applying tension
to the cord; feeding the cord to an applying means;
I5 and, applying the cord around the rotating structure,
the rotating structure being connected to a mandrel
means. The rotating structure is expandable.
According to another aspect of the invention, the
method further includes the cord being positively fed
to the mandrel according to a defined algorithm where
said algorithm is based on a shape, circumference and
rotational speed of said mandrel.
According to one aspect of the invention, an
apparatus for accurately applying a cord to a
rotatable mandrel includes means for dynamically
adjusting the circumference of the mandrel in response
to a control input. The means for adjusting is an
inflatable diaphragm mounted on an outer surface of
the mandrel.
According to another aspect of the invention, the
apparatus further includes control means which
includes a control valve capable of dynamically
adjusting the mandrel circumference by selectively
inflating or deflating the diaphragm in response to
feedback control input of a measured cord tension.
According to another aspect of the invention, the
apparatus includes control means which includes a
control valve and tension control means wherein the
CA 02238969 2004-12-22
-6-
tension control means is an electronically geared tension
control capstan.
According to another aspect of the invention a cord-laying
means for laying the cord on said mandrel includes a cord-laying
wheel which isolates radially directed forces from said mandrel.
According to another aspect of the invention the belt can
be corded on first and second pulleys. The first and second
pulleys being spaced a center distance apart, and the center
distance being selectively adjustable to control cord tension in
the cord. The center distance between the first and second
pulleys is dynamically adjustable to control cord tension in the
cord during said positive-feeding of the cord onto the mandrel.
According to another aspect of the invention a position-
determining means, namely an encoder, is operatively associated
with the motor and shaft which rotates the mandrel.
According to another aspect of the invention, a method of
accurately applying a cord to a rotatable mandrel, said method
comprising the steps of rotating a mandrel, the mandrel having
means for dynamically adjusting a circumference of the mandrel
in response to a control input, the means being an inflatable
diaphragm mounted on an outer surface of said mandrel, and
sending the control input to the means to adjust the
circumference of said mandrel in order to maintain a desired
cord tension.
According to another aspect of the invention, a method of
accurately applying a cord to a rotatable mandrel, said method
comprising the steps of rotating a mandrel, feeding cord to said
mandrel, laying the cord on said mandrel, and, isolating
radially directed forces from circumferentially-directed forces.
According to another aspect of the invention, an apparatus
for applying a section of cord having a predetermined length
from a supply source to a rotatable mandrel including said
rotatable mandrel having an axis of rotation, a feed capstan for
feeding said cord to said rotatable mandrel, said cord having an
entering tension entering said feed capstan and an exiting
CA 02238969 2004-12-22
_7_
tension exiting said feed capstan, a cord laying wheel disposed
between said feed capstan and said rotatable mandrel for
positioning said cord on said rotatable mandrel in
a predetermined pattern, a first tension measuring means for
measuring said exiting tension, said first tension measuring
means contacting said cord between said feed capstan and said
laying wheel, the apparatus being characterized by:
said feed capstan positively feeding said predetermined
length of cord from said feed capstan to said rotatable mandrel;
first measuring means for measuring said length of cord
exiting said feed capstan; and,
adjusting means for dynamically adjusting a circumference
of said mandrel to maintain a predetermined cord tension in the
cord between said feed capstan and said laying wheel.
According to another aspect of the invention, an apparatus
for accurately applying a cord to a rotatable mandrel, said
apparatus including a shaft having first and second ends, a
drive motor attached to said first end of said shaft, a mandrel
attached to said second end of said shaft; said apparatus
characterized by: a position-determining means, said position-
determining means operatively associated with said shaft, motor
and mandrel and capable of accurately determining the position
of said mandrel; and, a feed capstan, said feed capstan being
electronically geared, said electronic gearing being coordinated
with said position-determining means.
According to another aspect of the invention, a method of
accurately applying a cord from a supply source to a rotatable
mandrel, said method including feeding said cord to a rotating
mandrel by rotating a feed capstan and measuring a tension in
said cord at a first predetermined position between said feed
capstan and said mandrel with a first tension measuring device,
said method being characterized by the steps of: equipping said
mandrel with means for dynamically adjusting a circumference of
said mandrel; positively feeding a predetermined length of cord
to said mandrel according to a defined algorithm; sending a
CA 02238969 2004-12-22
-7a-
control input from said first tension measuring device to said
means for adjusting said circumference of said mandrel; and,
adjusting said circumference of said mandrel in response to said
control input in order to maintain a desired cord tension.
One advantage of an aspect of the present invention is
its ability to apply a cord at a known length and tension
to a rotating structure according to a defined algorithm, such
application being made independently of the shape, size, and
speed of the rotating structure.
Another advantage of an aspect of the present invention is
its use of an accurate feed capstan in conjunction with a means
of accurately controlling tension into and out of the capstan.
Another advantage of an aspect of the present invention is
the use of a tension capstan to control the tension of a cord
into the feed capstan.
Another advantage of an aspect of the present invention is
its control of the tension from the feed capstan to the rotating
structure by making the rotating structure radially compliant to
the cord being wound.
Another advantage of an aspect of the present invention is
its ability to dynamically adjust the radius of the mandrel as
it rotates using measured tension feedback to adjust the radius
to achieve desired cord tension.
Another advantage of an aspect of the present invention is
the use of a rigid cord laying wheel to accurately control
the cord position on the mandrel and to separate the radial
forces that arise from laying the cord from the desired forces
which result from the tension in the cord.
Another advantage of an aspect of the present invention is
the use of timing belt or chains to positively feed a cord onto
a belt slab which is rotating on two or more pulleys.
Another advantage of an aspect of the present invention is
its ability to adjust the center-to-center distance between
pulleys to control cord tension during positive feeding of the
cord.
CA 02238969 2004-12-22
-7b-
Still other benefits and advantages of aspects of the
invention will become apparent to those skilled in the art upon
a reading and understanding of the following detailed
specification.
CA 02238969 1998-OS-28
WO 97/22461 PCT/US96/15953
_ g _
Brief Description of the Drawings
The invention may take physical form in certain
parts and arrangement of parts. A preferred
embodiment of these parts will be described in detail
in the specification and illustrated in the
accompanying drawings, which form a part of this
disclosure and wherein:
FIGURE 1 is a perspective view of an apparatus
according to the invention used to produce belts with
precise cord length; and,
FIGURE 2 is a perspective view of a further
embodiment of the present invention featuring two
pulleys rather than a single mandrel.
Detailed Descri._ption of the Invention
Referring now to the drawings, which are for
purposes of illustrating a preferred embodiment of the
invention only, and not for purposes of limiting the
invention, FIGURE 1 shows a perspective view of an
apparatus 10 for applying cords 12 to a rotating
mandrel 14. The mandrel 14 illustrated is cylindrical
but the herein disclosed methods and apparatus are
equally applicable to noncylindrical mandrels and such
applications are equally within the claimed subject
matter.
The invention is conveniently disclosed with
reference to three areas or spans associated with the
inventive apparatus where the cord 12 is under
tension. In a first span 12C the cord 12 is under a
tension T1. The first span 12C is the path of the
cord 12 from a feed capstan 18 to a mandrel 14. In a
second span 12B the cord 12 is under a tension T2.
The second span 12B is the path of the cord 12 from an
electronically-geared tension capstan 16 to an inlet
of the feed capstan 18. In a third span 12A the cord
12 is under a tension T3. The third span 12A is the
path of the cord 12 from the tension capstan 16 to the
supply source of the cord 12.
~t'~lov- 1 O-~ ~ 1 1 ~ 47A P - ~'
CA 02238969 1998-OS-28
_g_
Tension capstan 16 is a demand deed, tensio;~ control
dezrice tvhich changes tensiar~ in the ccrd 12 from a tensic:r~
T3 in first section. ef the cord pat.~. 12A to tension T2 in
the secon3 section of the path 12B. This charge in cord
pension CCG~~:=s wh'_le the apparatus i0 is operating at a
variable cord speed in a second section 12E of the cord
path. T~e variable cor3 speed is de-erm~.ned by '~he speed
required for the cord ?2 to enter a feed capstan 18. The
cord tension in the second path section 12B is measured by a
1C ~ension sensor 20 of conventional design- Any tension
aansor 20 chosen wi=?-: sound engineeri~g j'~dgmer_t for the
'. artiCular application -r_ question W1~.~. suffice_ The
te:~sion sensor 20 controls 'he speed of the tension capstan
16 r°lat;ve to =he s~aeed of the fe=d capstan 19 to
compensate f or an;~ change in the 1°nr~ th of the second path
section 1?E an-: to maintair_ the tens_on T2 it t=~2 second
path 5e,~ticr. 12- at G desired level.
The zensio_~_ capsta n 16 is prezer«bi~~ .:f a cc=lventional
desiwn, rr:eaning it dope nds on t%:e coeffioi~nt of =ricti on
?0 and tY:e a=c of contact between. t:~e taraion capstan 16 and
the cord 12 . T5e tension capstan. 15 further deae :ds on ='~
and T2 h.oth beir_g gr°aGex' than taro .o create a d=f fere__~_Ce
between T3 and '~2 which; is relatively independent of
variac=one ~.n ~3 and where 'T-'3 can bs gy'eater' than an less
than T3. The ailo;vGble tension T3 is determined by the
character'stics of tine cord 12 arid cord package design for
the be'_t in quast_cn. The allowable tension T3 can 'Jary
from a few grams to several hundred pounds or kilograms by
scaling' the size o= several components described.
The control system for the motor 22 which urns the
tension. capstan 16 can use feedback from the tension sensor
20 and positionai and rotational data f=om a feed capstan
encoder 24 to accurately control tensior~ T2.
Y71Umt1'.Vl4t ~W~:~kS»A~1
AMENDED S~iEET
CA 02238969 1998-OS-28
WO 97/22461 PCT/US96/15953
- 10 -
The feed capstan 18 preferably can accommodate
one, two, or more cords 12 entering the feed capstan
18 from one or more similar cord paths 12B containing
the features described. The feed capstan 18 is
preferably of a conventional design and is similar to
tension capstan 16 in that it depends on a coefficient
of friction and arc of contact between the cord 12 and
the feed capstan 18 and further depends on T2 and T1
both being greater than zero to propel a cord 12 from
the second portion of the path 12B to the third
portion of the path 12C. The ratio T1/T2 can
typically range from 0.05 to 20, and preferably is 0.5
or 2.0, and is further preferably always less than or
greater than 1.0 during operation of the apparatus.
The feed capstan 18 preferably has a cylindrical
outer surface of an accurately known circumference on
which the cord 12 rests when in contact with the feed
capstan 18. The feed capstan 18 is connected to a
servomotor 26 which can apply clockwise or
counterclockwise torque to the feed capstan 18. The
torque so supplied is of sufficient magnitude to cause
the feed capstan 18 and the cord 12 to move a desired
feed distance along the path 12B, 12C relatively
independent of tension T2 and T1.
The feed capstan 18 is electronically geared so
that the length of cord 12, rather than its tension,
can be controlled. In other words, the feed capstan
18 '"positively feeds" the cord 12 in regards to its
length, rather than "demand feeds" the cord 12 in
regards to tension in the cord 12. The expanding
mandrel 54 controls the tension in the cord 12.
An alternate method of accurately winding cord 12
onto a rotating surface might be used if the cord 12
has a well-defined and highly uniform modulus of
elasticity. In such case, the algorithm used to
electronically gear the feed capstan 18 to the mandrel
rotation can include consideration of both the desired
lengths ,~~t;~~~n~ spec ~fied tension, and the actual
. °., _.
CA 02238969 1998-OS-28
WO 97/22461 PCT/CTS96/15953
_ 1y _
tension sensed by the load cells in the third cord
span (tension T1). The algorithm can adjust the
actual length applied at the actual tension T1 to
correspond according to the cord elastic modulus to
the desired length at the desired cording tension.
This method depends on the mandrel having an elastic
compliance similar to the elastic modulus of the cord
and is applicable over a very small range of
adjustment. This method may eliminate the need for an
expanding mandrel. However, the algorithm is much
more difficult to implement and the actual modulus of
the cord can vary over time, making this method less
desirable than the preferred method described herein.
The feed capstan 18 is connected to an encoder 24
which accurately detects the position and rotation of
the feed capstan 18, and thereby accurately measures
the movement of the cord 12 from the second path
section 12B into the third path section 12C.
The third cord path section 12C extends from the
feed capstan 18 to the mandrel 14 onto which the cord
12 is to be wound. Contained within cord path section
12C is a tension measuring device 28 for each cord 12
passing through section 12C, and at least one cord
laying wheel 30. The cord laying wheel 30 contains
circumferential grooves 72. Each circumferential
groove 72 can guide one or more cords 12 onto the
circumference of the mandrel 14.
The cord laying wheel 30, tension measuring
device 28, and feed capstan 18 are mounted rigidly
with respect to one another to form an assembly 32 to
maintain a constant length in the third cord path
section 12C. The assembly 32 is mounted on a radial
positioning system 34 to form a radial assembly 36
which can accurately bring the perimeter of the cord
- 35 laying wheel 30 to a desired radial distance from the
center of rotation of the mandrel 14. The radial
positioning system 34 includes linear bearings or
slides mounted on an axial positioning system 38. The
CA 02238969 1998-05-28
WO 97/22461 PCT/LTS96/15953
- 12 -
linear bearings have only one degree of freedom, which
is linear motion in the direction perpendicular to the
axis of rotation of the mandrel 14.
The radial assembly 36 is mounted on the axial
positioning system 38 which can move the radial
assembly 36 parallel to the axis of rotation of the
mandrel 14. The axial positioning system 38 includes
a linear bearing or slide which supports the radial
positioning system 34. The linear bearings of the
axial positioning system 38 have only one degree of
freedom, which is linear motion in the direction
parallel to the axis of rotation of the mandrel 14.
The axial positioning system 38 is strong, stiff and
rigid enough to prevent linear motion in any undesired
direction or rotation of the radial positioning system
34 about any axis.
The combined motion of the radial and axial
support systems 34,38 defines a plane containing the
axis of rotation of the mandrel 14 and the centerline
of the cord laying wheel 30. This configuration
allows for easy control of the radius at which the
cord is laid on the mandrel 14. These systems can be
made to the degree of accuracy presently existing in
the known art of winding cord at a controlled tension
in a demand-feed mode. The accuracy and stiffness of
the axial and radial support systems 34,38 is critical
to enable the cord-laying device to separate radial
and circumferential forces.
The mandrel 14 is rigidly coupled to and rotates
with a mandrel support shaft 42 which has a first end
78 connected to a drive motor 44, so that the drive
motor 44 rotates the shaft 42 and mandrel 14. A
second end 80 of the shaft 42 is attached to the -
mandrel 14. The shaft 42 is also connected to a
position-determining means accurately determining the
position of said mandrel. In the preferred
embodiment, the position-determining means is an
CA 02238969 1998-OS-28
WO 97/22461 PCT/LJS96/15953
- 13 -
encoder 46 which accurately measures the position and
rotation of the shaft 42 and mandrel 14.
The shaft 42, radial positioning system 34, and
axial positioning system 38 are connected for
coordinated motion in a conventional manner,
particularly similar to a computer numerically
controlled (CNC) machine tool with the shaft 42
representing a typical rotary "C" axis. Such a system
allows the shaft 42 and axial support 38 to move
concurrently a.n a way that cause the cord laying wheel
30 to move in a helical or any other specified path
along the outer cylindrical surface of the mandrel 14.
If the radial positioning system 34 is also
controlled to move concurrently with the shaft 42 and
the axial positioning system 38, the cord laying wheel
30 can move along any definable path on a three
dimensional surface of revolution which is rotating
about the shaft 42. The three dimensional shape could
be a familiar filament wound object, such as a torus,
a tire, a convoluted air spring, a cylindrical air
spring with helical or variable angle winding, a bead
setting bladder, tire curing bladder, a pressure
vessel, or a missile casing.
The rotation of the mandrel 14 is measured by an
encoder 46 attached to the mandrel support shaft 42.
The rotation of the feed capstan 18 is measured by an
encoder 24. The control system (not shown) must
control the rotation speed and angular acceleration of
either the mandrel 14 or the feed capstan 18, and must
contain an algorithm defining the desired relative
motion of the mandrel 14 and the feed capstan 18. For
example, in the case of a cord 12 wound at constant
helical pitch on a cylindrical mandrel 14, the
relative motion is a constant gear ratio matching the
speed of the cord 12 on the feed capstan 18 to the
theoretical surface speed required to create path 12D
at the proper tension T1 on the mandrel 14.
CA 02238969 1998-OS-28
WO 97/22461 PC'f/L1S96/15953
- Z4 -
Although mechanical means can be used to control
the relative motion of the feed capstan 18 and the
mandrel 14, a much more flexible and cost effective
system is achieved when electronic controls are used.
The encoders 24, 46 can detect errors in the relative
motion or speed of the feed capstan 18 and the mandrel
14. Conventional motor speed control systems can be
used to maintain the correct relative speeds of the
motors 26, 44, but controlling the relative speeds can
result in the accumulation of small speed errors which
result in increasingly large positional errors. The
preferred control system is electronic and uses the
encoders 24, 46 to measure the relative position of
the mandrel 14 and the feed capstan 18, and thereby
detect errors in their relative position. The
preferred control system adjusts the speed of either
motor 26 or motor 44, creating an intentional small
velocity error which returns the positional error near
zero and prevents the accumulation of small positional
errors which would result in an unacceptable large
positional error.
The mandrel 14 has an outer surface 86 onto which
the cord 12 is wound along cord path 12D. Layers of
other belt materials 50 may be placed on the mandrel
14 prior to winding of the cord 12. These layers 50
may include discrete components, sheet material, or
previously applied wound cord. The circumference of
the mandrel 14 and these underlying layers 50 must be
at least large enough to maintain the minimum required
tension T1 in cord path section 12C, and must be no
larger that the circumference required to maintain the
maximum allowed tension in path 12C. If the mandrel
14 and the underlying layers 50 have sufficiently
accurate dimensions, or have compressibility or
compliance which keep tension T1 within an acceptable
tolerance range, the mandrel Z4 can be of a
conventional design.
CA 02238969 1998-OS-28
WO 97/22461 PCT/US96/I5953
- 15 -
To obtain greater precision in the control of
tension T1, the mandrel 14 may contain circumference
means for dynamically adjusting the circumference of
the mandrel 14. In the preferred embodiment the
circumference means is a layer 54 with an adjustable
radius_ The preferred construction of this layer 54
consists of a flexible diaphragm 54 attached to the
rigid structures of the mandrel 14, forming a fluid
tight cavity between the mandrel 14 and the diaphragm
54. Fluid is introduced to the diaphragm 54 by a
control means for controlling the circumference of the
mandrel 14. In the preferred embodiment the control
means is a control valve 58 which enables the
diaphragm 54 to expand radially, thereby adjusting the
radius or circumference of the underlying layers 50 of
the in-process belt to the size required to achieve
the desired tension T1. Tension capstan Z6 controls
the tension into the feed capstan 18, while the
tension out of the feed capstan 18 is controlled by
the expanding diaphragm 54. The tension sensor 28 in
cord path 12C can be used as a feedbacl~ element to the
control system which uses the valve 58 to adjust the
amount of fluid in the cavity between mandrel 14 and
the diaphragm 54.
A further improvement in the control of tension
T1 is achieved by positioning the cord laying wheel 30
at the exact required cord laying radius so that
radial forces associated with laying cord are
supported by the cord laying wheel 30, the positioning
systems 34, 38, and the frame of the machine. This
allows tension T1 to depend only on circumferential
f orces .
The above-described mandrel 14 and diaphragm 54
provide for a very small adjustment in the length of
the timing belts made on the mandrel 14. Mandrels 14
with different radii can be attached to the mandrel
support shaft 42 to make timing belts with a wide
range of timing belt length or circumference. The
CA 02238969 1998-OS-28
WO 97/22461 PCT/41S96/15953
- 16 -
mandrel 14 must have a large diameter and weight to
make a long timing belt.
With reference to F2GURE 2, an alternate
embodiment of the invention is disclosed. It is often
desirable to make belts of various length, some being
long belts, without having a large inventory of
mandrels 14. FIGURE 2 shows a machine having two
parallel shafts 42A and 42B supporting pulleys or
sprockets 14A and 14B which are placed at a specified
center-to-center distance E to make timing belts of
varying lengths. The timing belt is built around the
pulleys 14A,14B with the belt length being determined
by the circumference of a pulley 14A,14B plus two
times the center-to-center distance E between the
pulleys 14A,14B.
The positive feed system described previously can
be applied to such a building machine only if the belt
motion can be accurately measured. Since the
underlying belt structures are no longer attached to
the mandrel (see FIGURE 1), this position cannot be
measured by detecting position of the pulley 14A,14B
or shaft 42A,42B rotation_ A leader chain or timing
belt 62 running in sprockets 64 on the pulleys 14A,14B
can be used to guide the end of the cord 12 around the
pulleys 14A,14B at a known position. The tension Tl
is adjusted by either changing the center-to-center
distance E of the pulleys 14A,148, or by making one of
the pulleys 14A or 14B with an expandable diaphragm 54
(see FIGURE 1) as described above.
In the case of an expandable diaphragm 54, the
control system as described above, of course, would
also be used. The lead belt or chain 62 must change
in length as the center-to-center distance E is
adjusted. This can be achieved with proper selection
of the belt elastic modulus or by using a tooth
pressure angle which allows the belt or chain 62 to
change effective radius on the sprockets 64. (The
"tooth pressure angle" for a belt or chain is the
CA 02238969 1998-05-28
WO 97/22461 PCT/CTS96/15953
- 17 -
angle between a radial line of the sprocket passing
from the center of the sprocket through the tooth
contact point, and a normal line at the tooth contact
point. If these lines are perpendicular, the pressure
angle is zero, and the forces between the belt and
sprocket are only tangential. The belt can transmit
torque without a radial component to the normal
forces. When the pressure angle is greater than zero,
the normal force between the belt and sprocket
contains a radial component which can push the belt
radially outwardly. This outward motion allows the
belt to operate at a constant circumferential length
even when the center-to-center distance of the
sprocket is varied by a small amount.) The control
system would use feedback from the load cell 28 to
control the expanding diaphragm, and therefore, cord
tension. If the cord tension is to be controlled by
varying the center-to-center distance E. The load
cell 28 would provide feedback to the center-to-center
adjusting mechanism and therefore control cord
tension.
The invention has been described with reference
to the preferred embodiment. Obviously, modifications
and alterations will occur to others upon a reading
and understanding of the specification. It is
intended by applicant to include all such
modifications and alterations insofar as they come
within the scope of the appended claims or the
equivalents thereof.
t, it ti-;G~"~A , (~i 3 t t t'.i~'~H. ~'~ '
