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04/09/2003
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A multi-tasking motion controller is at the heart of the first continuous 'cross-web' zipper applicator for food packaging equipment. Dean Palmer reports
An advanced five-axis motion control system from Baldor is helping food manufacturers package their products into re-sealable pouches, in fast, continuous vertical form-fill-seal and horizontal flow wrapping applications.
The new machinery for manufacturing re-sealable pouches was developed by a company called Line Equipment, for inserting Supreme Plastics' narrow zippers and is something of a breakthrough in the industry. The companies expect to achieve throughputs of more than 80 pouches/minute.
By applying 'zippers' across the web, food producers gain considerable packaging flexibility compared with conventional in-line zip application techniques. It boosts fill ratios, saves material, and allows one machine to be programmed for form-fill-seal operations on a much wider range of pouch sizes.
Line Equipment's innovative machine uses three zip applicators mounted on looped belts, each driven by a rotary servomotor. The applicators work in a sequence: while one is applying a zip – accelerating to web speed and synchronising with a registration mark – the next is having a zip loaded, and the third is moving into the start position. A fourth rotary motion control axis feeds and cuts zip lengths into the applicators as they reach the loading point in the loop.
A fifth axis, located under the plastic web material, controls the movement of a heating element that synchronises with the plastic web and applicator and seals the zippers into place. This axis uses a linear motor because of the sheer accelerations required to track the zipper applicator, before applying heat, and then return to the start position in readiness for the next applicator. At 80 pouches/minute, this axis can be accelerating at rates of more than 2.4G or 23 m/sec/sec.
The system uses Baldor's panel mounted 'NextMove' BX motion controller to manage the zipper applicator and linear motor axes, plus a standalone intelligent 'Flex+Drive' to control the zip feed and cut axis. The two motion control subsystem elements link to a Baldor operator panel using a CANopen fieldbus which allows the operator to define zip length, pouch size, etc. Both units include the I/O required for the various sensing and actuation functions associated with the process such as registration mark detection and zipper knife control.
Baldor also wrote the application software for the new machine using MintMT motion language. Development time was therefore reduced by using this software's built-in multi-tasking operating system. This feature was used to divide the major control functions of the machine, controlling the belt and linear motor axes, and the man-machine interface into separate tasks. This simplified software development and enabled the control programme to be written in just a few days ready for download onto the prototype. With testing, the application software was produced within one week, helping to keep Line Equipment's development project on schedule.
As Line Equipment's MD, John Blashkiw, explained: "The consumer-friendly virtues of re-sealable packaging formats are being pushed by retailers and food producers, creating a demand for higher speed and retrofittable automation." The availability of application-level software in the form of 'keywords' within the Mint language also contributed to a faster development time. Baldor used FLY, a high level command which synchronises the movement of two axes while controlling the position of one. A further keyword then allowed Baldor to correlate the zip-attach and linear motor heating element axes to the web material so that the applicator automatically tracks the web speed. This command has the additional facility of being able to operate virtually, allowing the machine to be set up without wasting material.
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Author
Tom Shelley
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