Zippier food pouches

A five-axis motion control system from Baldor is at the heart of what is claimed to be the first continuous ‘cross-web’ zipper applicator for continuous vertical form-fill-seal and horizontal flow-wrapping equipment.

The new machinery for manufacturing resealable pouches – developed by Line Equipment for inserting Supreme Plastics narrow zippers – is expected to achieve throughputs of over 80 pouches/minute.

By applying zippers across the web as opposed to using conventional in-line zip application techniques boosts fill ratios, saves material and allows one machine to be programmed for form-fill-seal operations on a wider spectrum of pouch sizes.

To achieve continuous manufacturing, Line Equipment’s machine uses three zip applicators mounted on looped belts, each driven by a rotary servo motor. 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. This element, which is synchronised with the plastic web and applicator seals the zippers into place.

The fifth axis uses a linear motor, because of the sheer accelerations involved. At 80 pouches/minute, the heating element can be accelerating at rates in excess of around 2.4 G, or 23 metres/sec/sec.

The motion control system uses a panel-mounting Baldor 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, and pouch size. 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 provided all the motion, I/O and human-machine interface system components required for the new machine, and wrote the application software using their MintMT motion language. Development time was reduced by means of MintMT’s built-in multi-tasking operating system. Baldor used this feature 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 allowed the control program to be written in a couple of days ready for download onto the prototype. With testing, the application software was produced within a week, helping to keep Line Equipment’s development project on target.

The availability of application-level software in the form of ‘keywords’ within the Mint language also contributed significantly to fast software creation. In particular, Baldor used FLY, a high level command which will synchronise the movement of two axes while controlling the position of one – providing an elegant solution for the continuous zip attachment process. 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.

Interest in the latest applicator is expected to come from markets which traditionally use flow-wrappers and other continuous form-fill-seal equipment; including cheese, meat, vegetables, confectionery, bakery, pharmaceuticals, and other fresh, chilled and frozen foods.

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