A vision of safety
By Michelle Morra
By Michelle Morra
Canadian manufacturer uses camera sensors as an alternative safeguarding solution
Imagine that you are operating a press brake, a machine roughly the size of a small car. The upper die, with a punch that must fall heavily and fast enough to bend metal, will come crashing down every time you activate it with a foot pedal. The flat piece of metal you start with may be no bigger than a door hinge, and your job is to push, turn and readjust it with your fingers as the punch bends the part, one end at a time, into the shape of a box. All this time, your fingers are just an inch away from the pinch point Ã³ the danger zone where the punch meets the part.
You perform this operation hundreds of times a day, or until the work order is completed. One of those times your thumb gets too close to the pinch point. How can the machine be stopped in time?
ItÃs a matter of millimetres and milliseconds. ThereÃs a whole industry built around ultra-precise safeguarding systems for machines used in manufacturing. The sole purpose is to ensure that a machine will stop when a workerÃs body, limb or appendage gets in harmÃs way. Safeguarding systems are more than just fancy safety gadgets. They are required by law.
Since 2002, when the Canadian Standards AssociationÃs new Z142-02 safety standard for power press operation came into effect, several Canadian jurisdictions have begun to reflect the code by mandating it as part of their occupational health and safety regulations. Companies are getting the message and finding ways to comply.
Melitron Corporation, a Guelph, Ont.-based manufacturer of precision metal products, recently upgraded its press brakes, which previously had no safety beyond the standard emergency stops built into the machines. The company researched the market and invested close to $250,000 to purchase 10 V 4000 units, a vision-based safeguarding system from Minneapolis, Minn.-based SICK Inc.
The system mounts on the upper beam of the press brake, providing safeguarding during the fast downward movement of the punch. It uses vision-based technology for point-of-operation safeguarding on press brake machines in metalworking and automotive applications.
Rated as “Category 4” under the CSA standard, the V 4000 also monitors the speed of the press. It knows how fast it is supposed to move. The machine does this anyway, and slows down when it gets closer to the part, but the safeguarding system constantly monitors its speed.
Sean Spencer, MelitronÃs operations manager, says the company considered installing other types of safeguarding, including light curtains.
“They would have cost us about a third or a quarter of what this has cost us,” he says. “But we liked this from the productivity standpoint, because itÃs more flexible for various types of parts.”
The V 4000 consists of two cameras, one on each end of the press brake. The cameras are aligned with each other, and with the tooling that is used to bend the parts. The system monitors a 25-mm high to 40-mm wide area. Never taking its “eyes” off the pinch point, it looks for a foreign object in the danger zone. It is programmed to know what the piece of metal should look like, and what its measurements should be. When a foreign object Ã³ such as the operatorÃs finger Ã³ gets in harmÃs way, the V 4000 stops the machine.
“Light curtains arenÃt so good for small parts,” says Spencer. “My understanding is that when an operator sets up the machine to create a part, if the part is small enough that their hands will then pass the light curtain, they have to program the light curtain to recognize their arms so it wonÃt trigger the light curtain. Whereas [the V 4000] actually detects right along where the pinch point is, so the operator can have his fingers within an inch of the pinch point.”
Steve Aamodt, the machine tools market manager at SICK Inc., further explains how it works. “No matter how long the press brake is, itÃs going to look down the whole length of the tool, at the pinch point. So as that ram comes down, the V 4000 is travelling with it, and the whole time itÃs looking at the tip of that tool. If it sees something intruding with that field, itÃs going to stop the machine. It doesnÃt get in the way,” he says. “The V 4000 is underneath the press, underneath the ram, but it allows operators to work as if they donÃt have safeguarding.”
That, however, is a matter of perspective. When one of the first users of the V 4000 reported several complaints from its operators, Aamodt hopped on a plane to see how he could assist them. The operators said that the system slowed down production. They were accustomed to working without any safeguarding.
Aamodt asked one of the operators to turn off the safety device, and timed him while he made two parts, one in each hand, as he usually did. Then he turned on the V 4000 and asked the operator to make two more parts. “It was a difference of 15 seconds,” he says.
“Safety is going to slow down any operation if you didnÃt have safety on it before,” says Aamodt, “because thereÃs an extra step in there. Yes, youÃre going to lose a little bit of productivity, but our job is to minimize that. YouÃre still losing time, but youÃre going to go home with your fingers intact at the end of the day.”
Melitron has a very low accident rate, says Miranda Corman, the companyÃs human resources officer, except for the occasional medical aid case.
“ThatÃs largely related to the fact that we work with steel, and you can walk by a piece, or if a piece slips, it can cut your arm,” she says. “But in terms of general housekeeping and following company rules and regulations, we have very few issues here.”
Despite its low accident rate, the company decided to be proactive in buying a safety solution.
“The Act requires you, as an employer, to take every precaution reasonable to ensure the safety of the workers,” says Corman. “ItÃs such a broad definition that the more guarding you can implement in your facility, the safer you are from orders or charges if anything were to happen.”
Besides safety, the company was looking for a solution that would cause the least disruption in workflow. When they were researching the market, they considered a system that used lasers as opposed to cameras.
“It was similar but required more operator intervention,” says Spencer. “We found that [the V 4000] allowed you to work more smoothly with fewer interruptions, plus it covers a larger safety area. The other one was just a flat line. This covers a 25-mm high region.”
Aamodt explains that, because the V 4000 is able to make such precise calculations on the position and speed of the press brake, it doesnÃt have to stop the machine every time the ram drops.
“The laser-based system will physically stop the machine,” says Aamodt. “Every single time, itÃs going to stop. Even if thereÃs nothing in the way, it stops.”
He says stopping is the machineÃs way of making sure it is safe to proceed. Just before reaching the pinch point it stops so the operator can acknowledge, by pressing the foot pedal, that his hand is out of harmÃs way.
“ThereÃs extra wear and tear on the machine,” says Aamodt, “and itÃs a pain for operators. TheyÃre used to hitting the foot pedal and already concentrating on the next part.”
The V 4000 creates a safety volume below the die that is constantly monitored for intrusion. It uses the machineÃs existing linear scales to calculate machine-relevant information such as the upper beamÃs position, velocity, direction and stopping distance. It knows when it is safe to proceed and does not need the extra “okay” from the operator. When the V 4000 detects a foreign object at the pinch point, it pauses the machine, but will proceed with the job as soon as the object is out of the way and the operator presses the “Start” button.
Another reason Melitron chose vision-based safeguarding, says Spencer, was its flexibility. The V 4000 provides multiple protection “modes” for different bending tasks. It can accommodate parts of various types and sizes, including thick sheet metal, bent metal shapes and thin plate with side walls. For each new type of part, the machine takes about 10 to 15 minutes to set up.
“ItÃs just another adjustment that needs to be made when theyÃre doing a setup,” says Corman. “They have to change the tooling on the machine and set the camera.”
It has been a year since Melitron went from no safety on its press brakes to the vision-based safeguarding system. Operators who had to learn how to use, relocate and reprogram the system for different parts have gotten over any growing pains they might have felt at first. Training and refresher training helped. And though the manufacturer was all the way in Minnesota or California, SICK tech support was available by phone, and by way of the help system on the machineÃs diagnostic software. Operators have gotten the hang of it.
“Like anything new, at first they didnÃt like it. TheyÃd still prefer not to have it,” says Spencer. “ItÃs just less convenient [than working without safeguarding].”
But for Melitron, which Spencer says is a “fairly progressive-minded company,” zero safeguarding was no longer an option. And with the V 4000, the companyÃs vision of a safer workplace has come to fruition, with minimal impacts on productivity.
Michelle Morra is a Toronto-based freelance writer.