This invention relates to an apparatus and method for maintaining tension in strands during tangential withdrawal from a spool. More particularly, this invention relates to a tension control device which maintains constant tension in strand materials over variances in operating parameters such as decreasing spool diameter as well as variances of withdrawal speed.
Strands are unwound from spools in many industrial manufacturing operations. For many of these applications it is important that the tension in the withdrawn strands remain constant during the whole process. Numerous tension control devices for regulating the withdrawal of strand material from a spool exist. Many use a simple brake with a constant brake force applied to the rotating spool. This results is an increase of the strand tension as the spool diameter decreases during the unwinding operation. Other devices employ a force-loaded dancer roll around which the strands are deflected. These dancer rolls are connected to a brake which in turn are applied to the rotating spool. More sophisticated strand tensioning systems use complex and expensive electronic means to measure the strand tension and electronically vary the applied tension with a close-loop feedback or an open-loop control system to achieve constant output tension.
The invention disclosed in this application employs a simple, mechanical tension device consisting of a movable spool-mounting, a spool-brake and a selectable loading force applied to the spool and against the spool-brake. These elements work together in such a manner as to result in constant strand-tension which is not affected by the size of the spool or the operation speed. It is in fact a mechanical, close-loop tension control system. The maintaining of constant withdraw tension at any spool-diameter can be mathematically proven.
Accordingly it is an object of the present invention to provide constant strand tension by means of a mechanical controller for maintaining uniform strand tension for delivery to a downstream strand processing station.
It is another object of the invention to provide a strand tension controller which allows to select a desired tension level and tension uniformity downstream from the strand tension controller.
It is another object of the invention to provide a strand tension controller which includes means for uniformly and simultaneously setting the strand tension on a plurality of strands being processed.
It is another object of the invention to provide a multiple set of strand tension controllers for which the desired tension level in all strands can be changed simultaneously to fit a specific need in a downstream strand processing station. It is another object of the invention to provide a multiple set of strand tension controllers for which the desired tension level in all strands can be changed simultaneously.
It is an additional object of this invention and its simultaneous changing of tension levels on a multiple set of units to enable each unit to be fine-adjusted individually to make it suited for specific needs in a downstream strand processing station.
It is an additional object of this invention to sense a tension which exceeds the set tension, as for example through a snag of the strand material on the spool, and apply a signaling system for such an occurrence.
Some of the objects of the invention have been set forth above. Other objects and advantages of the invention will appear as the description of the invention proceeds when taken in conjunction with the following drawings, in which:
Referring now specifically to the drawings,
In
In the exploded view in
“F”=Tension in the unrolling strand 10
“L”=Force of the spring 7 on the swing lever 4
“N”=Tangential friction-force
“P”=Radial force component on the brake shoe 9
“R”=Resultant of “N” and “P” in the force-triangle.
“T”=Loading-force generated by the force of the spring 7
“T”=(L*e)/a
a=Center-distance between the rotating shaft 2 and the pivot shaft 5
b=Radius of the brake drum 3
e=Lever length between the spring 7 and the pivot shaft 5
r=Radius of the spool 1
“f”=Axis through the center of the rotating shaft 2 and the pivot shaft 5
Let-Off Calculations
Input Formulas:
[1]
Moments around “Pivot”:
(((L*e)/a)*a)−(P*a* cos β)−(F*(a−r))+(N* sin β*(a−(b* sin β))−(N* (cos β)2*b)=0
[2]
Moments Around Package-Center:
(N*b)−(F*r)=0
[3]
Friction Relationship:
N=P*μ
Calculation:
Substituting “N” by (F*r)/b (from [2] and inserting in [1]:
[4]
(((L*e)/a)*a)−(P*a* cos β)−(F*(a−r))+((F*r)/b)* sin β*(a−(b* sin β))−((F*r)/b)*(cos β)2* b)=0
Using Constants in Spread-Sheet:
(a−r)=k1
(r/b)* sin β*(a−(b* sin β))=k2
(r/b)*(cos μ)*b)=k3
New Formula [5]:
(((L*e)/a)*a)−(P*a* cos)−(F*k)+(F*k2)−(F*k3)=0
Substitute “P” with Function of (F):
a) P=(N/μ) (from [3]
b) N=(F*r)/b (from [2]
c) P=(F*r) (b*μ)
Resulting Formula [6]:
(((L*e)/a)*a)−(F*r)/(b*p)*a* cos)−(F*k)+(F*k2)−(F*k3)=0
Using New Constant [k4):
k4=(a* cos β*r)/(b*μ)
Solving for “F”[7]:
F=(((L*e)/a)*a)/(k1−k2+k3+k4)
Substituting T=(L*e)/a Gives:
F=(T*a)/(k1−k2+k3+k4)
or:
F=(T*a)/ {[a−r]−[(r/b)* sin β*(a−(b* sin β))]+[(r/b)*(cos β)2*b)]+[(a* cos β*r)/(b* μ)]}
Requirement for the Tension of the Unrolling Strand 10 to be Constant it Must Follow That:
a/{[a−r]−[(r/b)* sin β*(a−(b* sin β))]+[(r/b)*(cos β)2*b)]+[(a* cos β* r)/((b* μ)]}=constant
Through Further Calculation it can be Proven that:
F=T=(L*e)/a=constant if
β=90°−arctg μ
For Example:
If the friction coefficient p of the brake shoe 9 is 0.3, the angle β has to be 73.3° to satisfy the condition of constant withdrawal tension of the unrolling strand 10. It should be noted that for constant tension in the unrolling strand 10 the direction of the Resultant “R” of tangential friction-force “N” and the radial force component on the brake shoe “P” should be parallel to the centerline “f” through the center of the swing lever 4 and the center of the rotating shaft 2. It also is noteworthy that the length of the center distance “a” as well as the length of the radius “r” have no bearing on the theoretically perfect tension control.
Although the invention has been described with reference to specific example embodiments, it will be appreciated that it is intended to cover all modifications and equivalents within the scope of the appended claims. It should also be understood that the present disclosure includes all possible combinations and applications of any individual features recited in any of the appended claims.
spool 1
rotating shaft 2
brake drum 3
swing lever 4
pivot shaft 5
creel channel 6
spring 7
tensioning bar 8
brake shoe 9
unrolling strand 10
collar 11
collar pin 12
lever pin 13
bar pin 14
brake housing 15
mounting screws 16
brake holder 17
dampening spring 18
dampening pivot 19
bore 20
over-tension switch 21
Number | Date | Country | |
---|---|---|---|
60619597 | Oct 2004 | US |