Facilitating Fiber-optic Fabrication

Spooling system for fiber-optic material reduces dependency on external controls

—edited by Stephanie Gooch

Packaging fiber-optic cable at the end of a production line is nothing like winding wire, cable, tubing or rope. Winding assemblies configured for spooling heavy gauge cable are too robust for handling the delicate fiber-optic material. In any winding or spooling operation, stopping the system to adjust controls, such as reversing the take-up drive motor, reduces productivity. In the case of some fiber optics, proper winding of the fragile, thin fibers may require ramp-down at the reversal points to assure the material “fills” correctly at the spool edges. Ramping-up the system after reversal, rather than letting the linear actuator engage immediately at full linear speed, prevents twisting or breakage of the thin fiber.

Such a system must provide automatic reversal of the traversing nut, with efficient synchronization of the traversing nut’s linear speed with the rotational speed of the take-up reel for efficiency, high production, and to meet the unique winding requirements of fiber optics. Normally these requirements mean the winding system will need a variety of sometimes costly components — control systems, sensors, clutches, en-coders, reversible variable-speed motors, gearboxes. Training personnel to operate and maintain these systems further adds to the overall investment.

Accommodating various materials

Typically, a fiber-optic manufacturer makes a range of materials with varying diameters. The winding system for each material must compensate for the different diameters, as each size must be wound onto its respective reel at a different rate. Winding 1/16-in. diameter fiber-optic cable, for instance, requires the linear traverse to move 1/16-in. per shaft rotation, while fiber with a diameter of 1/32-in. requires the linear traverse to move only 1/32-in. per shaft rotation. 

Rather than customizing different winding systems to properly wind individual sizes, it is often more efficient and economical to use the same winding system to handle a range of different fibers. However, this imposes certain requirements on the winding system design, which not all winding technologies can handle equally well.

As fiber-optic material is spooled, it is wrapped around the spool core in evenly placed lines. The traversing linear actuator in the winding system guides the placement of the material back and forth across the spool core. Assuming a constant line speed, as more and more material is spooled onto the reel, it becomes necessary for the take up drive to slow down. The linear actuator, however, must continue to traverse a specific linear distance with each shaft revolution — regardless of the take-up motor speed. 

With many winding technologies, synchronizing the back-and-forth movement of the linear actuator with the rotational speed of the take-up reel can involve programmable winding systems, changing the gearing system, or changing the linear actuator itself. These options all take time and can be costly to implement and maintain. 

Rolling ring systems

Rolling ring linear actuators, on the other hand, dramatically simplify the process. A simple pulley system may be used to join the take-up drive motor and the linear actuator drive shaft. On a rolling ring linear actuator, pitch is set simply by manually setting a pitch control. Once pitch is set, the nut will traverse the same linear distance per shaft revolution regardless of the rotational speed of the motor. As the take-up reel drive motor slows down, the linear speed of the actuator decreases proportionately. A mechanical, closed-loop condition exists. The material being spooled will always be guided across the spool at the correct rate regardless of how fast or slow the take-up drive motor is rotating.

Rolling ring technology won’t incur large up-front investments of time and resources and often offers an ideal set of design, production and maintenance advantages for fiber-optic cable manufacturers. Rolling ring systems reduce the spooling system’s dependency on external electronic controls and programming. For example, rather than having to stop the traversing system to reverse the linear actuator, as with a screw-based set-up, a rolling ring design automatically reverses while the drive motor continues to rotate at a constant speed in one direction. That eliminates the need for clutches or gears, simplifying both design and operation. It also eliminates the need to invest in a variable speed, bi-directional take-up drive motor. Alternatively, a less-expensive and simpler-to-operate single-speed, unidirectional motor may be employed. 

Protecting delicate fibers

Fiber-optic material can be fragile and prone to crimping or breakage during the winding process. If the fiber is wound too tightly, compression of the material on the spool can cause deformation, which will affect the fiber-optic cable’s performance. To compensate for these qualities, a fiber-optic winding system must often provide ramp-down and ramp-up functionality to eliminate sudden, “jerky” movements that could twist or snap the fiber. Rolling ring engineering meets these requirements using purely mechanical means. To understand how this is accomplished, it may be helpful to briefly examine how rolling ring technology works.

A rolling ring bearing has a specially contoured inner race forming a sort of “ridge.” When mounted on a smooth, threadless shaft, a rolling ring bearing contacts the shaft only on the apex of the ridge. The resulting clearance between the shaft and bearing permits angling the bearing left or right, while maintaining point contact between bearing and shaft. The shaft and bearing never lose contact, assuring no backlash. 

In a rolling ring linear actuator, an assembly of rolling ring bearings is fixed within the housing (nut). Each bearing is held at a specific angle relative to the shaft. When the shaft is rotated, compression against the central ridge surface causes the bearings to “roll” along the length of the shaft, carrying with it the load-bearing nut. The rotary input provided by the motor-driven shaft is thereby converted to linear output. 

Reversing direction smoothly

A lever, connected to the bearing assembly, is located on the bottom of the linear actuator. Turning the lever rotates the bearing assembly through sequential angled positions on the shaft. Depending on which way the bearing assembly is rotated or pivoted, this process increases or decreases the linear actuator’s pitch. If the lever is rapidly flipped through its full motion, the bearing assembly quickly pivots and assumes its “mirror” position on the shaft. The result is instantaneous, automatic reversal of traversing direction.

Various hardware stops are used to mechanically turn the lever on the bottom of the actuator. “End stops” flip the lever so direction reversal occurs. But other types of stops just partially turn the lever so the bearing assembly is pivoted, thus changing the linear actuator’s pitch. The rolling ring linear actuator manufacturer can design the assembly with the various stops in place to meet reverse or ramp-up and ramp-down requirements.

It is important to note that these changes to pitch and traversing direction are achieved without adjusting external controls and without changing the direction of the take-up drive motor. Reversing direction and adjusting pitch without slowing or stop-ping the system enhances production rates, which can therefore be maintained at higher levels than with a system that requires routine shutdowns for control adjustments. Because no electronic controls or gear systems are involved, design time is less, maintenance is reduced and operation requires no special training or skills. 

Continuous precision operation

Depending on the make and model, rolling-ring linear actuators provide from 6.75 to 800 lbs of axial thrust. For winding extremely fine diameter fiber optics requiring high precision linear traverse systems, rolling ring system accuracy may be increased up to ± 0.0004 in. using special control options. 

Since a rolling ring system operates on a smooth, threadless shaft, the system normally remains free of the clogs and jams associated with screw-based set-ups. This design generally obviates fabrication of a protective bellows assembly. Furthermore, it virtually eliminates “churning” which results from particles being caught in the threads of a screw-based system. Such churning can damage expensive equipment and result in downtime while cleaning and repairs are implemented. 

The only real maintenance required with a rolling ring system is shaft lubrication. The “workhorse” nature of a rolling ring system permits longer periods of continuous use of production machinery, which in turn helps make processes more productive (i.e. more profitable). Additionally, winding fiber optics on a rolling ring system does not require a separate load carrier. The material guide may be attached directly to the traversing nut so there is no need to invest in the design and fabrication of a load carrier.

For more information:

Connect directly to Amacoil, Inc.'s website via the Online Reader Service Program at www.rsleads.com/204df-345