Machine Design

Siemens PLC Runs Converting Machine Servos

Curt G. Joa Inc.,

Siemens Energy & Automation Inc.,
(800) 964-4114,

Making disposable products can be particularly demanding. Manufacturers of baby diapers, tissues, and other singleuse consumer goods frequently switch production lines from one product to another. And small innovations drive market share, so specifications can change quickly.

Curt G. Joa Inc., Sheboygan Falls, Wis., a company that builds and modifies equipment for turning web-based nonwoven materials into such products uses modular machines to shorten product changeover times. The machines range from simple rotary cut-off devices to 50-m long machines with over 150 servoaxes. Some equipment makes disposable products at up to 1,200 units/min.

A manufacturer asked Joa to upgrade one of its machines. Joa’s engineers built an 8-m section of the upgrade to test and verify it.

The challenge came when Joa attempted to translate the program the client’s machine was running. Engineers tried to paste modifications into the core software of the client’s machine. The problem, however, was that the old hardware and software would not accept it.

The need for new controls led to installing a Siemens Simatic S7-400 PLC in the new machine. The S7-400 is designed for highperformance machines and factory automation using centralized and distributed architecture. It has a CPU with integral I/O and communications interfaces.

At first glance, the S7-400 seemed like overkill. However, the new PLC would assume all aspects of machine operation when the new and old sections were joined.

The PLC also monitors the system, taking action on faults. And interlocks networked to the PLC via ProfiNet replace hard-wired ones.

The new module needed drivecontrol as well, a task that called for 34 additional servodrives on top of the 300 to 400 servomotors already on the equipment. The existing servomotors were Siemens Masterdrive units, so Joa engineers used similar units to ensure compatibility.

The Masterdrives handle some tasks the PLC once did, letting the PLC run faster. The Siemens FM458 drive-controller module in the S7-400 PLC exchanges operating parameters and status information with the 34 new servodrives.

The single master drive cascades to multiple virtual masters that control groups of drives. The drives synchronously move at speeds defined by their parameters, eliminating the need for gear-ratio corrections, synchronized speed changes, and phase advances.

The PLC uses a high-speed link to synchronize all drives and controllers from a single external master, thus ensuring data is acted upon in every drive at the same time. The network operates at 11 Mbit/sec with little overhead; 100 pieces of 32-bit data can be transmitted in 0.63 msec.

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