Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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METHOD AND APPARATUS OF PRODUCING BELTS WITH
PRECISE CORD LENGTH AND TENSION
Reference to Related Application
s This application is a divisional of copending Canadian application No.
2,238,969, filed October 3, 1996.
Background of the Invention
This invention pertains generally to the art of apparatus and methods
to 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
is mandrel, especially the diameter and circumference, are essentially
constant.
The mandrel may be a rigid 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.
2o 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
2s 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
3o before the cord. The thickness, hardness, and temperature tolerances of
these materials may also affect cord length.
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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
s 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.
io 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.
is 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
2o 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
2s slide axially off the mandrel.
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
3o 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.
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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.
s
Summary of the Invention
In accordance with one aspect of the present invention, a new and
improved method of applying a cord to a rotating mandrel producing belts
with precise cord length and tension is provided.
io In one aspect, the invention is directed to 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
is 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
20 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. The concept of primarily controlling cord length and
2s secondarily controlling cord tension is a key element of the invention.
In 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.
3o 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
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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
s 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
io 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, there is provided an apparatus for accurately applying a cord to a
is 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
2o 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 present invention, the apparatus for
applying a cord to a rotating structure further includes a first capstan
between
2s 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
3o 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
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supplying the cord to a capstan via supplying means; positioning the cord
around the capstan, thereby applying tension to the cord; feeding the cord to
an applying means; and, applying the cord around the rotating structure, the
rotating structure being connected to a mandrel means. The rotating structure
s 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.
io 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.
is 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
2o control means which includes a control means which includes a control valve
and tension control means wherein the 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
2s radially directed forces from said mandrel.
According to another aspect of the invention the belt can be corded on
first and second pulleys. Th,e 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
3o pulleys is dynamically adjustable to control cord tension in the cord
during
said positive-feeding of the cord onto the mandrel.
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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
io 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
is forces.
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.
2o 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.
2s 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
3o 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
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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
s 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.
Still other benefits and advantages of an aspect of the invention will
io become apparent to those skilled in the art upon a reading and
understanding
of the following detailed specification.
Brief Description of the Drawings
The invention may take physical form in certain parts and arrangement
is 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,
ao FIGURE 2 is a perspective view of a further embodiment of the present
invention featuring two pulleys rather than a single mandrel.
Detailed Description of the Invention
Referring now to the drawings, which are for purposes of illustrating a
2s 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
3o 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
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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
s 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.
Tension capstan 16 is a demand feed, tension control device which
changes tension in the cord 12 from a tension T3 in the first section of the
to cord path 12A to tension T2 in the second section of the path 12B. This
change in cord tension occurs while the apparatus 10 is operating at a
variable cord speed in a second section 12B of the cord path. The variable
cord speed is determined by the speed required for the cord 12 to enter a
feed capstan 18. The cord tension in the second path section 12B is
is measured by a tension sensor 20 of conventional design. Any tension sensor
20 chosen with sound engineering judgment for the particular application in
question will suffice. The tension sensor 20 controls the speed of the tension
capstan 16 relative to the speed of the feed capstan 18 to compensate for any
change in the length of the second path section 12B and to maintain the
2o tension T2 in the second path section 12B at a desired level.
The tension capstan 16 is preferably of a conventional design, meaning
it depends on the coefficient of friction and the arc of contact between the
tension capstan 16 and the cord 12. The tension capstan 16 further depends
on T3 and T2 both being greater than zero to create a difference between T3
2s and T2 which is relatively independent of variations in T3 and where T2 can
be greater than or less than T3. The allowable tension T3 is determined by
the characteristics of the cord 12 and cord package design for the belt in
question. The allowable tension T3 can vary from a few grams to several
hundred pounds by scaling the size of several components described.
3o The control system for the motor 22 which turns the tension capstan 16 can
use feedback from the tension sensor 20 and positional and rotational data
from a feed capstan encoder 24 to accurately control tension T2.
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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
s a coefficient of friction and arc of contact between the cord 12 and the
feed
capstan 18 and further depends on T2 andT1 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
to 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
is 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
20 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
2s 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 length at some specified tension, and the actual tension sensed
by the load cells in the third cord span (tensionT1 ). The algorithm can
adjust
the actual length applied at the actual tensionT1 to correspond according to
3o 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
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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.
s 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
io 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.
is 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 laying
2o 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 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.
2s 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
3o 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
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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
s 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
io 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
Is position-determining means accurately determining the position of said
mandrel. In the preferred embodiment, the position-determining means is an
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
20 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 in a way that cause the
cord laying wheel 30 to move in a helical or any other specified path along
the
2s 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
3o 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
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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
s 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
to 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 tensionT1 on the mandrel 14.
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
Is 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
2o 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
2s 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
3o 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 tensionT1 in
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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 tensionT1 within an acceptable
s tolerance range, the mandrel 14 can be of a conventional design.
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
to 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
is 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 16 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
2o path 12C can be used as a feedback 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 tensionT1 is achieved by
positioning the cord laying wheel 30 at the exact required cord laying radius
2s 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 tensionT1 to depend only on circumferential forces.
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.
3o 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
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circumference. The mandrel 14 must have a large diameter and weight to
make a long timing belt.
With reference to FIGURE 2, an alternate embodiment of the invention
is disclosed. It is often desirable to make belts of various length, some
being
s 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
io 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
is 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 pulleys14A,14B at a known position. The tension T1
is adjusted by either changing the center-to-center distance E of the pulleys
20 14A,14B, 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
2s 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 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
3o 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
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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
s 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.
to 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.
