Real-time Ethernet lets stitcher heal itself
The Pacesetter 1100 from Goss International Americas Inc., Durham, N.H., is a saddle stitcher that assembles pages of a magazine in the right order, staples them together, and then trims the edges before delivering finished publications for stacking. The old way of powering saddlestitching machines was with a 40-hp motor and mechanical driveshaft with take-offs for each section. Moving the saddle stitcher to a servodriven-feeder approach allows the same advantages as seen in other kinds of printing equipment that have changed over to servos: dynamic on-the-fly adjustments, less make-ready time and changeover time between jobs, and tight synchronization between operations.
Goss Senior Project Engineer Atef Massoud evaluated nine different motion-control systems for the machine before settling on a SynqNet control platform from Motion Engineering Inc., Santa Barbara, Calif. This highspeed networking scheme, basically a real-time implementation of Ethernet, can handle servocycle update rates to 8 kHz for 20 axes connected to a SynqNet stand-alone controller. In particular, the network let Goss architect the machine with self-healing fault tolerance, a quality unavailable in the other networks Massoud evaluated. The network is configured in a ring topology so if one or more stations are off-line the rest can continue operating without stopping the line. The reason is the self-healing mechanism uses the redundant link on the fly.
Software utilities from MEI also aided in the development of a customized velocity feedforward algorithm for the machine. The master axis drives a chain which moves the magazine sections, called signatures, through the line of feeder stations to stapling and trimming operations. The motor drive for the chain sends incremental encoder data out over SynqNet, where it is used as the master axis to create position and velocity commands for the respective axes to calculate commands for the servos. In Pacesetters that have more than 20 feeder stations, a second SynqNet is used to handle the additional modules. In this case, the master encoder signal is split and sent to the master axis for each of the two SynqNets.
Software tools from MEI facilitated frequency response analysis, allowing designers to shape the frequency response while maintaining desired stability margins.