New Safety for Old Press Controls

Press controls with diverse redundancy now are cost-effective and can make the difference that prevents tragedies from occurring on such a regular basis

Around the world, machine safety concerns are gaining prominence. In no industry is this more relevant than metal stamping.

 

In the U.S. alone, power presses are reported to be the cause of 650 worker amputations every year, which is a totally unacceptable number for irreversible worker injuries.

Many times the culprits are older and aging power presses built when worker safety was not as high a design priority. Many power presses operating today are decades old yet still producing effectively.

So how do you bring these old workhorses up to today's safety standards without breaking the company bank?

The difference-maker today is technology. Modern controllers provide more effective and reliable monitoring and control of press safety devices. Press controls with diverse redundancy now are cost-effective and can make the difference that prevents tragedies from occurring on such a regular basis.

OSHA in the U.S. and the CSA in Canada recently developed and introduced safety codes that should soon make these technologies mandatory. Plant operators who ignore these requirements will leave themselves exposed, liable for any resulting accidents that will ultimately cost them far more than bringing their power press equipment into compliance.

Our Command Stamp press control unit has twice been third-party verified to meet the CSA Z142-02 standard, which comes into fulleffect in December 2004.

This unit uses dual processors from different manufacturers and different program versions to provide a press control safety solution that incorporates diverse redundancy. Diverse redundancy is defined as the use of different components and/or programs in the redundant monitoring of safety circuits in order to eliminate "common cause" or "common mode" failures and provide heightened safety module reliability as a result.

To provide diverse redundancy our control system incorporates two different and individually-configured 8-Bit processors with flash memories. The master processor is a Motorola MC68HC908GP32 processor with John Von Neumann Architecture and a full instruction set. The second processor, a Microchip PIC16F877, has Harvard Architecture with reduced instruction set computer (RISC) as the slave.

To learn more about diverse redundancy and review specific algorithms and software models for reducing common-mode failures in diverse program versions, you can review Reducing Uncertainty About Common-Mode Failures, by Jeffrey Voas, Anup Ghosh, Frank Charron and Lora Kassabi online at http://www.cigital.com/papers/download/ISSRE97.pdf

When you investigate new press controls, ask whether or nor each unit provides diverse redundancy solutions for both hardware and software. Some units use the same processor and different software programs, which leaves these systems open to common-mode failures caused by the hardware. The design of the Command Stamp unit incorporates diverse redundancy in both hardware and software as recommended by the ANSI B11.1 standard.

A further layer of protection is added through the constant monitoring of these two different processors on the clutch/brake board by the screen processor, which is set to send an inhibit message to the other (still-functioning) processor whenever a communications fault is detected with either processor. The screen processor is a Motorola HC11 series high-end 8-bit processor.

Control devices also can increase the operational productivity of power press operations. Through automated batch counting and operation, simplified error messaging and troubleshooting, operators are able to more quickly understand and correct press fault conditions and get back to production sooner.

In addition, device network links from press controls can network equipment for centralized data collection, operations monitoring and enable the delivery of die recipe control/updates from remote PCs. Modern press controls can also provide early identification of potentially serious mechanical malfunctions, allowing for a fix before a major breakdown.

Additionally, to support automated shop-floor data collection as well as upload and download die recipes and other settings, we designed the press control to support DeviceNet, which allows seamless networking of the press control with other manufacturing automation equipment and shop-floor data collection systems.

To date, our press control unit is the only dedicated press control system we know of that has built-in DeviceNet capabilities and can be networked directly using RS-232 or USB. Likewise, AS-i and other networking solutions can be supported through third-party DeviceNet adapters.

There's no longer any doubt that with the advent of technologically advanced, flexible and cost-effective power press control solutions, companies can increase worker safety and security. At the same time companies can gain additional benefits from improved operational productivity and mechanical fault monitoring.

In light of these two powerful drivers it's clear that the time for making any "reasonable" excuses for not upgrading power press equipment has now, simply stated, run out.

Jeff Ashcroft is with Penmar Automation (http://www.penmarautomation.com), Newmarket, Ontario, a designer and installer of commissioned systems controls for industrial equipment. Reach Jeff at jeff@penmarautomation.com

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