AT the heart of most packaging applications lies motion control, usually defined as the accurate positioning or movement of items at high speed. Whether specialising in palletising, filling, sorting or cartoning, Australian packaging OEMs are continually challenged to achieve more flexible, higher-speed packaging lines without sacrificing accuracy.
The migration from mechanical links - such as line shafts, gears and cams - to electronic servo-control systems has provided greater speed, reliability, accuracy, and flexibility to packaging lines. These motion control solutions have already proved their economic worth.
Recent developments in control technology seamlessly merge motion and sequential control into one controller platform that uses a single point of programming. This results in a simplified, cost effective system providing higher system performance, faster applications development and easier maintenance. Packaging performance is enhanced because all system control elements not only reside on the same hardware chassis, but work together within the same multi-tasking, multi-processor control architecture; this provides built-in motion/logic/communications interlocking and synchronisation, which is impossible in a multi-device architecture.
A step closer to achieving a complete control platform for packaging applications involves the integration of external servo drives with the motion/logic controller. With this is mind, the International Electrotechnical Commission (IEC) has prepared a technical standard describing the Serial Real-time Communications System (SERCOS), an industry-standardised means of realising high-speed serial communications between smart digital servo drives and controllers.
Using the SERCOS interface, the closed-loop smart servo drives receive move-profile information from the controller and ensure that the motor accurately follows the position/speed or torque profile. It does this by monitoring motor current and position feedback, and comparing it with the command reference from the controller.
In performing the high-level motion commands and planner functions, and generating the motion move profiles, the controller provides all the interlocking and path data needed to integrate multiple motion axes into a single, cohesive system.
The fully integrated solution described above may be contrasted with traditional systems offering only one function per device. In cases where a dedicated controller is used for logic and I/O control, and another for motion control, each requires its own software package, hardwiring, communications, and synchronisation logic for system integration. The result is an application that is difficult to program and maintain, exhibits inadequate reliability, and may not meet performance requirements - the system may use upwards of 25 percent of the code in each controller to achieve interlocking of motion and logic. In addition, remote access to monitoring, configuration and programming is usually limited to the logic controller only, with any modifications to motion code or servo drives configuration requiring site attendance.
As fiercer competition drives companies to address broadening market needs, packaging OEMs and end-users need every competitive advantage they can find to achieve flexible, high-speed packaging lines that are scalable for responsive expansion.
Eugene Mayevsky is product manager for motion control, Rockwell Automation Australia.
Rockwell Automation Australia (03) 9896 0221QUOTE 12/3201 ON CARD