Novel ethernet-based motion control architecture improves plastic bag machine
Modern plastic bag-making machines often have two servomotor based axes - web feed and cut/seal - plus a mechanically linked third axis for ‘picking off’ the finished bags. UK machine builders Hartech Engineering and GPL Machinery have cooperated in a joint development of a machine that also implements servo control on this third axis to provide programmable ‘electronic cam’ control of pick-off action.
Allowing users to finely adjust pick-off, the machine can avoid the sealing problems that commonly arise as machines are set up to handle different types of blown or cast film materials, thus minimising scrap and downtime.
The machine (known as BBM1100) is built on the mechanical framework of a common bag-making machine from Woodbank (which ceased production around a decade ago). There are many of these old machines in the UK, which GPL and Hartech have been servicing and refurbishing for more than a decade. During this time, the two companies have developed numerous add-ons and upgrades based on ABB motion control technology, including replacement servomotor axes and a new user interface. Based on ABB’s Ethernet Powerlink compatible motion control range, the new machine features an all-servomotor architecture and a user interface developed from the operator’s point of view.
The re-engineered all-servo machine not only offers inherently finer control over manufacturing - and as a result quality and productivity - than previous machines, it is also price-competitive, costing up to 30% less than a brand new machine.
The machine’s three axes are powered by drives from ABB’s 3-phase MotiFlex family, linked to the company’s BSM brushless servomotors. Control is provided by the ABB NextMove e100 machine controller with a touch-screen colour operator panel.
The Ethernet Powerlink interfaces of ABB’s drives and machine controller provide one major benefit. Through their single network cable interface they substantially reduce cabling to speed system building and lower hardware costs, and simplify subsequent machine commissioning as well.
The ABB NextMove controller also includes enough onboard digital and analog I/O to satisfy the bag-making machine’s I/O requirements. In addition, a high-speed digital input on the drives provides a direct interrupt that captures positions to within a microsecond resolution. This feature is used to support high-speed print registration on the BBM1100 - which will operate right up the machine’s fastest production rate.
The developers also greatly value ABB’s MINT programming language, which provided the machine with high-level keywords for many of the motion control operations employed during the bag-making cycle. For instance, one of the keywords used in the control software for this new machine architecture is SENTINEL, which allows events to be triggered under software control. In this case, SENTINEL synchronises the pick-off axis to a virtual line shaft acting as a ‘master clock’ for the machine cycle. This allows users to program the profile of the electronic cam with high resolution and precision, rather than being limited by a fixed-profile mechanical cam. It ensures that the machine can be configured to operate in the optimal way for the exact type, grade and thickness of plastic material being processed.
“ABB provides us with motion components offering genuine real-time performance, plus support for the complete motion control package - all from a single point,” says GPL Machinery’s Graham Levine. “It’s helped us to bring our new machine to market both efficiently and rapidly.”
In addition to implementing core performance features in the new machine, the design team has emphasised usability and reliability throughout the design. For example, the user interface has been developed from the point of view of the operator. The machine can be set up for a new batch with just a few touches on the control menus. Operators can also change action on the fly, to adjust the print registration for instance, or the dwell time of the cut and seal bar. Users also have access to deeper configuration possibilities via a password-protected screen. This can be used for purposes such as changing the action of the pick-off belts - the grip speed, acceleration and deceleration profile, for example. Such settings can be saved and renamed so that operators are able to load a proven bag-making setting for any particular job or material within seconds.
A number of hardware features also endow the new machine with high reliability. Bag-making machines have an inherent stop/start movement and there is always a degree of vibration. So, the machine builders avoided some of the more modern but more fragile feedback technologies and instead chose to use resolver feedback to measure rotational position.
The re-engineered BBM1100 machine is a first step for GPL Machinery and Hartech Engineering. The two companies already have plans for an all-new own-brand machine, which will feature a mechanical chassis of their own design and a number of new advanced features for this segment of the packaging marketplace.
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