How does a typical wind-unwind system work?
Perhaps the best way to describe this system is by examining a multiple-web converter — a handling system that converts many individual web streams into one web of manufactured product. To start, a motion controller directs four unwinds (each with its own tension control), laminator, die, nip roll, traverse axis, and rewinder (also containing its own tension control). A die-sealing axis cuts the base web into individual strips, combines some with wrapper stock, and uses the remainder to seal the stock into a finished web.
What is the primary type of motion in winding and unwinding?
Rotary motion is predominantly encountered in this application, as the traverse axis demonstrates. The traverse axis winds many products onto a small-diameter mandrel and controls where the finished web is placed on a winder mandrel. It accomplishes this by moving a ballscrew assembly a specified distance for each winder rotation. Resultant web patterns on the winder drum resemble threads on a screw. A traverse axis continually moves from one end to the other when placing web onto a mandrel. The axis is electronically geared to the winder so that as the winder mandrel's diameter increases, pitch wind remains constant.
The winder axis then takes the finished web from the nip roll and winds it onto a mandrel. A dancer maintains web tension between winder and nip roll. The winder axis also modifies its gear ratio so the dancer remains central, providing constant tension throughout the wind cycle.
What are the main challenges to implementing motion in a wind-unwind process, and why are they worth overcoming?
Some challenges in implementing rotary motion are:
Complex wind patterns — End users can program patterns into a traverse winding machine via control software for tighter electronic gearing.
Multiaxis servo control — Permits flexible software design for winding sequences. As a result, machine control development becomes more versatile.
Quick end-wind reaction — All digital servo system with multiaxis electronic gearing make end-point transitions accurate and repeatable. This increases product quality and decreases mechanical wear.
Automatic layer counting — Developed in the programming language; critical product segments wind quickly with precise sequences.
Wind angle control — High-speed controls calculate advanced math.
Fast product changes — Versatile operator-interface touchscreens and the motion controller's mass data storage permit product recipe development.
Batch processing — Full job control is programmed into a motion controller, increasing a winder's ability to manufacture products with minimum operator intervention.
Quick cycle times — Advanced servo algorithms provide stable control and agility to fast moving transport mechanisms for high throughput.
Applications that might employ the above functions include coil winding, plastic-film spooling, motor armature winding, air filters, fiberglass layups, rope spooling, fuse winding, capacitor foil and transformer cores, fiber-optic cable, and dental floss.
Where can motion technology make the biggest difference in wind-unwind applications?
Applying multiaxis servosystems to traverse winding achieves coordinated motion control through electronic gearing. Gearing must be exact, repeatable, and free of drift, which can result from rounding errors during implementation. Spontaneously creating winding patterns produces different designs that are otherwise difficult to implement mechanically. Directly downloading a mechanical-cam equivalent from CAD or a pre-configured recipe shortens changeover time and permits short, economical production runs. Problems such as dog boning — unwanted material buildup on traverse turnaround — and layer overlap (due to product width changes) can readily be adjusted without changing mechanical parts.
Three function blocks, GetWinderDiameter, GetWinderBaseSpeed, and DancerPID, control a simple winder system with a web tensioning dancer. Note that each calculates winder speed, or gearing; the actual motion block receiving this reference is omitted here to reduce example size.
To begin, GetWinderDiameter calculates the current winder diameter by comparing winder roll and master line speed. Remaining inputs initialize roll diameter and clamp the diameter calculation. Diameter output is then fed into the GetWinderBaseSpeed block.
GetWinderBaseSpeed calculates the winder's current base speed based on current roll diameter and master line speed reference. DancerPID's output then trims the base speed between 5 and 20% and calculates a speed correction based on the current roll position. A PID control sets the response for correction output.