Design News | Trend Watch: Automation & Control
Unwinding Complexity in Spooling Applications
Dynamic parameterization and integrated controls ease the complexity of spooling applications
by Douglas Parentice, Moog Animatics
Spooling is the most effective way for OEMs to conveniently package materials of exceptionally long length such as thread, film, wire and thermoplastics. One such OEM manufactures specialty and industrial wires used in toys, food service products, recycling and pulp industries; fasteners; and welded and woven wire panels for residential and agricultural fencing. Although this wire OEM is considered an expert in its field, the company’s outdated mechanical technology was unable to perform a taper pattern across a straight spool, and the cost of machine operators was rising dramatically. The wire OEM approached Jeffrey Ianno, president of Industrial Automation & Motion in Murrysville, PA, about retrofitting several old machines with a method for winding requiring a four percent taper across a 20-inch cylindrical core.
The integrity of a spool of any material is primarily based on the wind pattern and proper tension control used throughout the winding process. Typically, the spooling material is fed at a certain rate while a guide traverses the material back and forth corresponding to a desired pattern. The position accuracy of a traversing guide is best maintained when it's linked to the rotational velocity of the winding spool.
“Selection of proper traverse type for different materials is crucial, especially for profile materials that can’t twist or tolerate excessive stress,” said Ianno.
The most common problems in winding and spooling applications are over- or under-travel, inadequate or excess stress on the spooling material, and tapered patterns created with low-friction material. Closed-loop systems are an industry preference because they eliminate inconsistencies on the spool by feeding material exactly where it’s needed in the wind pattern. Fully integrated motion control systems are also gaining popularity in the converting industries because of their multi-axis capabilities while reducing the total cable costs in the machine.
Gapless Material, Uncompromised Traverse End Points
Ianno turned to Moog Animatics knowing that his OEM could use the closed-loop PID (proportional, integral, derivative) control of their integrated motion control systems to set and maintain a critical tension level while taking advantage of new commands created specifically for winding and spooling applications.
“Our latest firmware is custom tailored to the winding industry. We offer both relative and absolute position control for setting traverse points, spool widths, dwell points and more. Knowing the challenges of winding applications, we added the ability to dynamically phase adjust incoming master signals,” said Hack Summer, Applications Technology Manager at Moog Animatics. “This enables real-time offsets for variations in material width without sacrificing positioning accuracy at the traverse point, and allows for a complete, precise fill of material with no gaps or overlays.
“Take a one-inch wide ribbon, for instance. With each turn of the spool, the ribbon must move one inch across the spool surface. But what happens if the ribbon varies in width throughout its total length? Previous industry solutions required dynamically changing the electronic gear ratio of the traversing motor or offsetting its traverse speed on the fly,” Summer explained. “By utilizing a sensor to feed back material width, the effective gear ratio can be dynamically compensated within the SmartMotor to ensure there are no gaps in the material wound onto the spool, and without compromising traverse endpoint locations.”
Tapered, ‘Dog Bone” Spools Present Challenges
The wire OEM needed to create a wind pattern where the exterior shape of the finished spool was tapered while the core was straight. In this situation, traverse points are often difficult to program and control, resulting in a poor-quality wind.
Tapered wind patterns prevent the material from getting hung up while unwinding when it can only be pulled from the spool in a direction parallel to the spool’s core. “For the wire OEM, tapered steel cores cost more than cylindrical cores and complicate the winding process due to material slip,” said Ianno. “If you do use a tapered core for winding low-friction material, the material tends to slip to the smallest end of the core regardless of the tension level.”
Another frequent problem in the winding industry is avoiding the ‘dog bone spool’. In winding towards one end of the spool, the traversing mechanism decelerates as it nears the flange to prevent collision. This deceleration causes material to build up faster on either end than across the middle, creating a dog bone shape that’s wider at the two ends of the spool than it is in the middle.
“To avoid a dog bone spool, traverse points are set slightly less than the length of the spool between the flanges,” said Summer. “Dwell distance can also be set to cause the traverse mechanism to wait a certain amount of time at each end before heading back the other direction. This allows material to fill into the gap between the flange and the set spool length.”
Encoder, Actuator, SmartMotor Solve Problems
To solve the wire OEM’s problems, Industrial Automation & Motion and Moog Animatics worked together to write a program that would first build a taper pattern onto the straight spool. As material was built up, the wind width decremented in from one end to create the base taper layer. Once the taper pattern had built up, the material was traversed the full length of the spool. Since each wire revolution sits in between the grooves of the previously wound layer, the tapered pattern remained intact without the material slipping.
The solution was accomplished with an encoder to track angular position of the main spool, a screw-driven actuator to traverse the wire guide, and Moog Animatics SM23165DT Class 5 SmartMotors enhanced with the latest firmware.
The Moog Animatics servo system was programmed to calculate the traverse speed by electronically gearing the spool encoder to the traverse axis. The system also calculated the slew (traverse) rate by entering the wire diameter into a custom algorithm written by Industrial Automation & Motion. The Moog Animatics integrated SmartMotor then automatically determined slew width, calculated an appropriate method for building the requested taper, and wound the same tapered roll consistently to an appropriate diameter.
Douglas Parentice is general manager with Moog Animatics.
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