PC motion card simplifies automated
loading upgrade for printing press: The PC-compatible motion controller card, NextMove PC, proved the ideal tool for Dangel Robots' add-on loading system for one of the USA's highest-throughput printing presses. The 10-colour Flexo press from Kidder Inc (Agawam, MA) produces high-volume packaging and wrapping for consumer goods such as beverages. The robot unloads, then reloads printing impression and ink rolls weighing up to 2000 pounds. Previously, each roll was exchanged manually using a block and tackle hoist, an operation taking two press operators 15-20 minutes. The Dangel robot automates the process, cutting it to around three minutes.

The NextMove PC is an upgrade to an existing machine control system based on programmable controllers. Dangel Robots decided to employ a PC platform to provide a graphical user interface for the motion control system. Consultant control systems designer Craig Deady chose Baldor's NextMove PC motion controller card for the motion and machine control because it provided an economic solution with all the necessary hardware, and because of previous experience with the Mint software development environment - which gave him confidence that the software could be developed rapidly to meet the project's tight timescales.

For this application, the motion system necessitated X and Z servo motor axes for each of two robot arms which grip the roll, plus a considerable amount of I/O, much of which Deady was able to locate remotely on the robot arms at low cost thanks the NextMove PC's CAN fieldbus interface.

The real-time motion part of the application is controlled by NextMove PC. The user interface is based on a touch screen, which allows the operator to program robot moves by touching the graphical image of the roll they want to exchange from the printing press deck, and the roll storage cart position.

These paths are taught using a 'teach pendant' peripheral and Mint's teach and replay commands, with NextMove PC then computing a smooth movement path using point-to-point motion functions and electronic gearing between the master and follower robot arms. During normal operation, the operator always has instant shut-down capability thanks to the incorporation of a 'live man's handle'.

As the motion system is only one element of a larger control system, Deady uses NextMove PC as an autonomous sub-system, exploiting Mint's interrupt handling to create an event-driven rather than polled system for software simplicity.

"The motion control program runs independently of the user interface and other host PC software, making the overall system modular and easier to develop," notes Deady. "This allowed me to adopt a 'divide and conquer' strategy to simplify debug and system integration, using the Mint software development workbench tools to test the program in isolation by reading and writing values via dual port RAM." Thanks to this approach he managed to develop the motion software in less than three weeks, and notes that the robot arms were also commissioned on site very quickly, in under a week following the mechanical construction phase.