printable version 

SAFETY TECHNOLOGY

Labour-saving Logic

Building state-of-the-art safety into existing assembly operations is a complex process. Duff McCutcheon discovers how International Automation shaved time, engineering, and manpower off its integration projects.

Up until recently, International Automation engineer Joe Quigg was working on big integration projects for his Tier One and Two automotive clients, the thought of having to wire up the scores of safety relays necessary to secure everything was the cause of many sleepless nights.

International Automation, a division of International Machine, builds and integrates new and used machine systems and controls that have to do with tandem lines, assembly cells, welding, and assembly – much of it for the automotive industry. Its customers include Magna and Martin Rea.

“Here’s an example of working with relays,” says Quigg who is based in Windsor, Ontario. “A couple of years ago we were working on a seven [stamping] press line with eight cells for a Tier One operation. The relay panel that we had to build for that was a very large, three-door cabinet that had two of the doors devoted almost exclusively to safety relays to monitor all the safety devices on the line.”

Not only did that kind of wiring require a team of four electricians going non-stop for 14 days, but the client had to shut down parts of its operations for the duration of the integration. Not to mention the grey hairs it caused Quigg having to engineer-in all the safety.

The problem with safety relays, says Quigg, is that there are too many opportunities for people to disrupt the process, and there are too many ways for someone to not fix a problem: “There’s too much to touch; from an end user point of view, they’re just intimidating to look at.”

Since discovering Rockwell Automation’s GuardLogix, life has become considerably simpler for the engineer – and for the end users.

GuardLogix advantages

More recently Quigg was working on a five-press line with a number of robot cells between presses for moving workin-progress along the line. Each robot cell was protected by one or two interlocked gates to allow technicians to enter and work on the robots. “You have an e-stop on every cell, as well as a gate switch on the front and back of every cell, which totals up to 18 points of monitoring just for the robots, and we haven’t even started talking about the presses,” he says.

All would have been wired with their own e-stops and various other safety devices like light curtains. Now using GuardLogix, instead of just releasing electrical drawings and babysitting electricians through the wiring process, a controls engineer can actually have more control over the project before it’s released to the floor. “With GuardLogix you just wire the e-stop or safety device to the GuardLogix and use software to do the interlocking. It means someone sitting at a computer as opposed to someone stripping wire and interlocking relays; it’s great for savings,” says Quigg. Another advantage Quigg particularly liked was the pre-programming Rockwell had designed into the system in  anticipation of most standard logic functions. “With GuardLogix a lot of the commands are provided in a function block format. You can pick from a list of predefined items and pop them in there. Instead of reinventing the wheel, part of the work’s already been done for you. Rockwell set aside a number of commands that help the designer get to the end result a little quicker. You don’t have to think as much.”
 

DeviceNet Safety

Instead of traditional relays, GuardLogix relies on DeviceNet Safety as the network for all safety blocks. Using the same trunk line and processor as a system’s standard controls architecture, engineers like Quigg are able to add safety related I/Os on an as-needed basis. Depending on the project it can be customized to any size machine, whether it’s a single press or a seven or eight press tandem line. “The trunk just runs throughout the line through all the devices and you drop the block where you require it,” says Quigg.

“So instead of running cable train and conduit, and pulling tons of individual conductors, you run a DeviceNet trunk throughout your entire process and just drop devices where you need them.”

Floor space savings
 

With GuardLogix, it has since been replaced with a single cabinet less than a third of the size. You can stick it within one of the cells. In previous, pre-GuardLogix, designs, Quigg had to design-in a separate line control panel to house all the relays and PLCs required for monitoring safety devices, plus a remote panel with industrial PC for an operator to oversee and control operations. In factory environments where floor space is a precious commodity, this amounted to a very expensive bit of real estate being set aside to house electronics. By using GuardLogix and doing away with safety relays, Quigg has since been able to combine everything and fit them all into the operator console, at a huge savings in floor space.

“And that doesn’t include the amount of junction boxes that are saved, because the DeviceNet trunk just runs to all the devices, as opposed to running a conduit.”

Integration
 

The first time Quigg used GuardLogix as part of an integration project for a client, what had normally taken 14 days, with a team of four electricians, had been reduced to just five days. The client was obviously very pleased because not only were they able to reduce their shutdown time by nine days, the smaller footprint of a logic-based integration meant they could continue production all around the floor space undergoing integration.

“The client was actually able to run at 70 per cent capacity for five days while International Automation was putting the system in,” says Rockwell Account Manager Michael Cundari. “If you were doing that with hardwired relays you would have to shut everything down because you’d be compromising safety throughout the line”.

From the boardroom’s point of view, that translated into some big money savings.

According to Cundari, if you take the nine days of full available production that International Automation was able to save, it equates to:

9 days of available production

7.5 hour day

500 parts an hour @ $7 a part

= $685,125.
 

“When you add that with the numbers from running production concurrently with the start up, and you’re right there at $1m in production savings.” And that doesn’t take into account the actual savings in materials, says Quigg.

He says the most complicated line he’s ever worked on was a five-press line that had left-right exit bolsters: “Basically the press had windows on all four sides and need safety monitoring on all sides,” he explains. “You take that down a line, 5x4 = 20, plus two robots in each cell, times all the gates and e-stops, and there’s something like 85 points that have to be monitored by safety. You take that 85 figure anywhere between $400-700 per safety relay and that’s huge dollars.

Using GuardLogix worked out to be a third of the cost of using relays, plus “it’s basically infinite how you could expand (within reason of network scan time), because you’re dealing with logic,” says Quigg.

“And when you’re dealing with a programmable safety PLC, you have the ability to go online to fix a problem immediately. Integration becomes so simple because the controls designer gets to handle all the integration aspects. If there’s an error, you don’t have to unwire the panel to fix it; you can just change the logic, which can be done in seconds, as opposed to three or four hours with an electrician.”

Safety compliance
 

GuardLogix has also provided an increase in safety compliance for users, not because it’s caused any standards to be changed, but because it “allows people that might not be competent to meet those standards because Rockwell provides approved blocks that have been tested so an end user can feel more comfortable designing a system,” says Quigg. “Someone who might not have known the difference between right and wrong will be able to use the software to get to that point and not have as many roadblocks; it promotes people being able to try things.”

Plus, it’s tamper proof. With relays, if things aren’t wired properly, operators sometimes modify circuits so they can by-pass safety systems in the belief that they can do their job faster, and it’s impossible to track, apart from going through with a multimeter and wringing out the whole system. GuardLogix provides a security key that generates a safety signature code, so after anyone changes any safety logic, you can lock it out with a password. If there’s been a change to it, it will generate a different safety signature that identifies who made the change.”

Production efficiencies
 

Production efficiency was another area of major improvement. Prior to GuardLogix, one International Automation customer’s five tandem lines were 40 percent efficient and produced between 85 and 120 parts per hour. Using GuardLogix, International Automation was able to boost efficiency to 90 per cent, with each tandem producing an average of 500 parts each hour.

“We also saved the company a bundle on operators, says Cundari. “On a five-press line you’ll typically have anywhere between two and four operators per press. By automating it with robotics, combined with GuardLogix, they went from 20 operators down to about two or three. The savings alone from operators pays for the entire project.”