Multi-Tasking Software Passes the Bar
Machines successfully refurbished to flow-wrap chocolate treats

-edited by Richard Mandel

Those enticing colors. Those smooth lines. Suggestions of what delights lie within that come-hither package. That’s the goal of product wrapping designers, particularly in the case of chocolate bars bound for the impulse rack next to a grocer’s check-out counter. It’s up to machines, though, to quickly sheathe the confections, seal them tightly and stack them in shipping boxes without creases or scratches on the wrappers.

The candy wrapper

Premier Packaging, Norfolk, UK, manufactures new packing systems and refurbishes older systems to new uses. A more recent project for the upgrade division involved three wrapping/cartoning machines for a chocolate bar manufacturer. The refurbished machines were destined for a production line where the manufacturer was switching to flow wrappers on a popular milk chocolate bar, in place of a foil wrapper and paper label. The project was extremely time sensitive, and Premier Packaging refurbished the machines in around four months, imposing a tight schedule on its sub-contractors — which Baldor Electric Co, Fort Smith, AR, met by employing the multi-tasking features of the MintMT motion control language.

In this instance, help came from Baldor’s Mint Motion Center in Bristol, UK. Their role in this project was to provide a motion control subsystem to transfer and carton flow-wrapped chocolate bars. Three multi-axis servo motor systems axes are employed for this. One controls a ‘paddle’ that sweeps bars through 90 degrees into a flighted conveyor. Two further axes collate bars into groups on a feedchain, and then actuate paddles that transfer the group into a ‘lowerator’ — simultaneously moving the lowerator onto a step for depositing the group into a carton. The system is controlled by the Mint-compatible NextMove-BX, a standalone motion controller that comes with I/O, allowing it to also handle the various sensors in this application.

Development time was greatly reduced by means of MintMT’s multi-tasking capability. Baldor used this feature to divide the transfer-and-cartoning process into five separate tasks: start paddles; stop paddles (for rejects); feed feedchain; lower lowerator; and manage the man-machine interface. These software tasks were then worked on, in parallel, by several application engineers, allowing a software prototype to be written and trialed in less than a week. This design was then optimised and integrated with the hardware — including three BSM brushless AC servo motors, three Flex drives, a NextMove BX motion controller and various sensors — and delivered to Premier Packaging for commissioning. The three new machines are capable of flow wrapping and cartoning around 1000 bars per minute.

“This project demonstrates that it’s possible to refurbish older mechanically-based packaging machines easily,” says Peter Broughton, sales engineer with Premier Packaging. “In this instance the machines were renovated with advanced electronic controls supporting software-based reconfiguration, for an outlay at just a small fraction of the cost and time it would have cost to develop a new solution from scratch. For us, speed was an overriding objective, and Baldor’s application engineering service played an important role in keeping the project on track.”

Applying the MintMT

The availability of ready-to-use application examples played a key role in Baldor’s rapid turnaround of the transfer and cartoning system. This was simplified by the high level ‘keywords’ in MintMT, which offer a ready-programmed basis for many commonly required movements. Amongst the keywords used in this project was one of the FOLLOW group to control the sweep paddle; an electronically clutched gear ratio is implemented to allow a following task with ramped starts and stops via the FOLLOWMODE keyword. FLY is also used for control of the feedchain axis. This keyword provides a flying shear action, which gives an idealized multi-segmented motion profile for controlling the action of the lugs that collate the bars into groups.

“Mint’s multi-tasking trimmed several weeks development time off this project,” adds Stuart Bratton, Project Engineer for Baldor. “The asynchronous aspects of the axes on this process would have made it quite a complex problem to deal with using traditional software techniques. This kind of software advance is key to reducing the time to market for complex projects, as OEMs build more and more features into their machinery.”

He also noted that NextMove-BX’s built in I/O and fieldbus capabilities allowed the motion controller to provide a complete solution, including the user interface and the inputs and outputs needed for the various sensing tasks. In this instance, one of the controller’s dual CAN ports is used to interface to a remote man-machine interface panel using the CANopen protocol.

Magnetic Particle Brakes for Packaging Machines
An Overview

Precision tension control is needed for many types of packaging machinery. Stretch-wrap machines wrap thin plastic around boxes stacked tall on a pallet, to keep the boxes secure and prevent pilfering during shipping. To control tension of the stretch wrap material, a slip brake is used to apply torque to the center of the supply spool.

Friction brakes are used on low cost machines. Torque is not very smooth, or consistent. Torque varies with slip speed, usage, and even humidity. The friction plates wear, and need replacement often.

Magnetic particle brakes are used in higher end machines for better tension control and long, maintenance-free life. Slip torque for these brakes is very smooth, controllable, and consistent. Magnetic particle brakes do not use friction plates. Instead, a disk is centered in a chamber that is filled with powder-sized microscopic stainless steel balls. The powder is free flowing, until a magnetic field is applied from the stationary coil. The powder then forms chains along the magnetic field lines, linking the disk to the chamber wall. The torque is proportional to the magnetic field, and likewise to the applied DC input current.

Only a simple DC power supply is needed to control the brake. However, to keep tension constant when unwinding rolls of material, a follower arm potentiometer or ultrasonic sensor is recommended, along with a variable power supply, to alter torque based on roll diameter. The diameter of the roll decreases as the roll of material is used up. As the diameter decreases, torque must be decreased proportionally, to keep tension constant.

A follower arm potentiometer can be used to measure the roll diameter by means of a mechanical arm, sometimes with a roller on the end, riding on the roll. As the roll diameter changes, the arm moves towards the center of the roll, rotating a potentiometer shaft and, in turn, changing the resistance. This causes the power supply to output less current to the brake, which automatically decreases braking torque.

Alternatively, an ultrasonic sensor can be used instead of a follower. The ultrasonic sensor bounces ultrasonic sound off the roll’s surface — as the roll size decreases, the return echo takes longer to return to the sensor. This non-contact method is needed if the roll is sticky or scratches easily. The ultrasonic sensor controls the power supply powering the brake, keeping tension constant, based on roll diameter.

Typically, soda bottles are wrapped with a decorative label, or sometimes a thick, insulating label for comfort. Automatic machines apply labels from a large supply roll onto each bottle. Magnetic particle brakes are often used to tension the supply roll of labels.