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Multi-tasking motion control system

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AN advanced five-axis motion control system, available from Australian Baldor , is at the heart of 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 more than 80 pouches/minute, providing a breakthrough in food packaging technology.

By applying zippers across the web, food producers gain considerable packaging flexibility compared with conventional in-line zip application techniques - boosting fill ratios, saving material, and allowing one machine to be programmed for form-fill-seal operations on a much wider spectrum of pouch sizes.

To achieve continuous manufacturing, Line Equipment's innovative 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 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 in excess of around 2.4G, 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, 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 provides all motion, I/O and human-machine interface system components required for the new machine, and wrote the application software using the MintMT motion language.

Development time was greatly 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 greatly simplified software development, allowing 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.

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