Fig. 1. Whatever shape material is being spooled, the "gauge" or thickness of the material must be measured.

By Mark Wilson

Many winding systems are dedicated to winding only one type of material. Designing these systems is straightforward once basic variables are known such as line tension, material width and spool size. If however a single winding system is going to be used to wind different materials with different "thicknesses"(wire and cable diameter, strip width, etc., see Figure 1), and will use spools of varying widths, there are a few key points to consider.

The material being spooled is wrapped around the spool core in evenly placed lines. The traversing linear actuator guides the placement of the material back and forth across the spool core. If different materials having different thicknesses are wound on the same system, the linear actuator must travel a specific linear distance per one revolution of the shaft for each different material.

While the take-up motor reduces in speed as more material is spooled onto the reel, the linear actuator must continue to traverse a specific linear distance with each shaft revolution -- regardless of the take-up motor speed. A winding system designed to handle a variety of materials and spool sizes, therefore, must provide a method of synchronizing the reciprocating movement of the linear actuator with the rotational speed of the take-up reel.

Overview of Design Goals
To ensure that a single winding system offers flexible capabilities to handle the majority of different materials, the system must be designed around application requirements for winding the largest size material, Figure 1. Additionally, a flexible winding system must be setup for using the largest spool (flange-to-flange widths). Using these setup parameters optimizes the winding system so that: A) it will accommodate the broadest range of materials; and B) linear actuator pitch and thrust capabilities are not exceeded.

Thickness of Material and "Pitch"
When the material being spooled is "thick," (a large diameter, for example) the spool core fills up faster than with smaller materials. The linear actuator guiding the thicker material onto the spool must move a longer linear distance per shaft revolution, Figure 2, than with smaller materials.

Fig. 2. The linear actuator moves a longer linear distance when spooling thicker gauge materials. The reel core fills up faster than with thinner gauge materials which must be traversed at a slower rate to permit the spool to fill up uniformly.

For an example, suppose that a wire manufacturer needs to wind 1" (25.4 mm) diameter cable and also 1/8" (3.2 mm) diameter wire on the same winding system. For any given take-up reel rotation, the traversing actuator must travel 1" (25.4 mm) per reel revolution for the thicker material, but only move 1/8" (3.2 mm) per reel revolution for the thinner material.

If the linear actuator offers variable pitch control, the linear speed of the actuator is easily increased or decreased by adjusting the pitch setting. This type of actuator is a cost-effective option.

There are alternatives for controlling the pitch of a linear actuator such as programmable winding systems, changing the gearing system, or changing the linear actuator itself. These options, however, take time and can be costly to implement and maintain.

Optimizing the System for Thrust Capacity
A further insurance step for a versatile, efficient winding system is to use the widest reel or spool (flange-to-flange width) when defining setup parameters. Assuming distance B in Figure 3 remains the same, for the take-up reel having the largest width, the angle between the payoff and the material guide on the linear actuator is at a maximum when the actuator reaches the flange.

Fig. 3. By designing around the requirements using the widest reel (flange-to-flange), when the linear actuator reaches the reel flange, the angle between the point of pay-off and the material guide on the actuator is at a maximum. This will impose the maximum thrust requirement on the linear actuator. This value is then added to the thrust requirement resulting from the innate line tension of the material being spooled. Narrower reels may then be used without concern over exceeding thrust requirements.(Note: This is true only if distance B remains the same.)

This creates the maximum line tension of the material being spooled which then imposes the maximum thrust requirement on the linear actuator. If a narrower spool is used on the same system, the angle between the point of payoff and the material guide on the actuator will be less. The thrust requirement then is also less and the thrust capacity of the linear actuator will not be exceeded.

Additional Thrust Considerations
Even with effective tension-controlling devices such as "dancers," the innate line tension in the material being spooled creates some linear actuator thrust requirements.

The combined total of all thrust requirements is used to select the linear actuator capable of meeting application requirements.

The maximum amount of thrust that will be required of the linear actuator can be calculated by the formula:
FK = (C) (FZug) / (1.6) (the square root of {C2/4 + B2})
FK is the line tension created by the angle M
C is the traverse width
FZug is the innate tension in the material being spooled
B is the linear distance from the point of pay off to the material guide mounted on the linear actuator
1.6 is the constant value for conversion
(FK and FZug are expressed in Newtons. C and B are expressed in millimeters)

The sum of FK plus FZug determines the maximum thrust capacity required of the linear actuator selected for the system. The thrust rating for the linear actuator must exceed this sum.

Synchronizing Take-Up Motor and Traversing Actuator
The basic, back-end components of a winding system include the take-up reel or spool, the take-up motor, and a traversing linear actuator used to guide the material being spooled back-and-forth onto the take-up reel.

When the winding operation begins, the core of the take up reel is empty and therefore presents its smallest diameter. The take-up motor speed is at its highest setting. As more material is wrapped around the spool core, it is necessary to reduce the take-up motor speed.

Regardless of take-up motor speed, the traversing linear actuator pitch must remain the same. The material must be guided across the spool core at a steady rate per shaft revolution. So there must be a means of synchronizing the rotation of the take up reel with the reciprocating motion of the linear actuator.

Typically, the take-up motor driving the reel is linked via a pulley system to the linear actuator drive shaft, Figure 4. This provides a means of maintaining constant synchronizing between the reciprocating motion of the traversing linear actuator with the rotating motion of the take-up reel. A mechanical, closed-loop condition exists.

Fig. 4. The take-up reel motor may be used to drive the linear actuator by employing a pulley system.

Unfortunately just any old pulley won't work. It is necessary to select the correct size wheel for the pulley system in order to create the optimum gear ratio between the motor and the linear actuator drive shaft. The correct ratio must be determined to put the traversing actuator in synch with the take-up motor. Otherwise, pitch adjustments to the linear actuator won't accomplish the desired results.

The ratio between the motor and the linear actuator drive shaft may be calculated using this formula:
iopt = (0.95) (hmax/dmax)
iopt is the ratio value being calculated
hmax is the maximum pitch setting of the linear actuator
dmax is the maximum diameter measured in step number 1 above
0.95 is the constant value for conversion
(hmax and dmax are expressed in millimeters)

The pulley wheels must be selected to create the optimum ratio, iopt. In the calculation above, if iopt is less than 1, the traversing linear actuator shaft must turn faster. The smaller pulley wheel would therefore be set-up to drive the shaft. If iopt is greater than 1, the traversing linear actuator shaft must turn slower and would then be driven by the larger pulley wheel.

The Importance of Variable Pitch
Variable pitch enables the operator to use the same winding system to wind large and small materials.

As material is wrapped around the spool core, the take-up motor slows down to accommodate the longer lengths being wound.

Because the take-up motor and traversing actuator drive shaft are linked via pulley, it follows that as the motor slows down, so does the actuator.

However, the critical parameter is the linear distance traveled, not the linear speed. This is why a linear actuator with pitch adjustment control must be used, Figure 5.

Fig. 5. This linear actuator has pitch settings from 1 to 100 thereby enabling fine pitch control and cost-effective spooling of a wide range of materials.

Once the pitch is set, and the actuator is synchronized with the take-up motor via the pulley system, the actuator will always travel the same linear distance per shaft revolution -- regardless of motor speed. Therefore the material being spooled will always be guided across the spool at the correct rate.

Calculation Sheet for Winding System Efficiency
In the form shown in Figure 6, the criteria for an efficient winding system is organized into a useful questionnaire. When preparing to design a winding system, completing this form puts information at your fingertips which you'll need when you begin discussion with a linear motion system supplier or value-added distributor. The form is also available on-line at www.amacoil.com/Amacoil/motion.html

Fig. 6. Winding system specifications form

Setting up the system to meet the specific winding application requirements for a range of materials is a more cost-effective design path than trying to modify a dedicated winding system to handle other materials.