Including In-Depth Analysis of Light Curtains vs. Laser AOPD
Press brakes are unforgiving machines and a common source of workplace amputations of hands, fingers and arms. United States Department of Labor statistics indicate an average of 368 instances of amputations annually from press brake accidents. And these are only the reported accidents.
WHY ARE PRESS BRAKES SO DANGEROUS?
The primary reasons are access to the point of operation at the front of the machine, as well as reaching around the safety device to get to the point of operation at the ends of the machine. In addition, there are pinch points and hazardous motion created by the back-gauge system.
But the dangers don’t stop there. However well intentioned, fabricators often employ lower cost, used or refurbished press brakes where the primary controls and/or condition of the machine and safety system may be suspect. Plus, original equipment manufacturers (OEM’s) generally consider the point of operation aspect of the press brake safety system to be the end-user’s responsibility. The end-user may assure, incorrectly, that the machinery arrived into the shop ready for commissioning. Lastly, press brakes have always been operator intensive, sometimes involving multiple operators, and operator behavior is not always predictable. That is why it is good practice to make one operator the leader of the crew.
OSHA/ANSI SAFETY REGULATIONS
OSHA’s machinery and machine guarding regulations (29 CFR 1910 Subpart O) require one or more guarding methods to protect employees from exposure to hazardous machine energy during the operation of press brakes. There isn’t a great deal of detail to the OSHA regulations so fabricators in search of answers would be better served by turning to ANSI B11.3-2012 which covers safeguarding of power press brakes. The B11.3 adopted EN 12622 (European standard), giving it even more specific instructions to follow and minimizing any vague, grey areas.
ANSI B11.3 is the only safety system standard specifically applicable to power press brakes used in America, and it excludes mechanical power presses; hydraulic power presses, hand brakes; tangent benders; apron brakes; and other similar types of metal bending machines. It discusses hazards associated with the point of operation at length and identifies alternative guards and devices. For example, the ‘close proximity point of operation AOPD’ safeguarding devices, which we will discuss later in this blog, and a means of safeguarding referred to as ‘Safe Speed.’ We should note that ANSI B11.0-2015 recommends risk assessments of press brakes among other equipment, offered by Rockford Systems.
PRESS BRAKE PROTECTION OPTIONS
Today, there several ways to safeguard a press brake, some better than others. All have advantages and drawbacks.
The most basic type of safeguarding is a fixed and interlocked barrier guard coupled with two-hand controls. This is not a functional solution for fabricators as a work piece is hand held in close proximity to the point of operation during the braking process and can potentially whip up as bending is taking place.
Another approach are pull backs and restraints. Both are restrictive and have limitations and for that reason, operators dislike them. Both devices shackle the operator to a machine and restricts mobility. Yet another approach is the two-hand down/foot-through device. In some cases, this will work. However, this method raises ergonomic issues and it is very slow. Not what you want in a busy, production-driven fabrication shop.
SHEDDING LIGHT ON SAFETY
A modern light curtain is a photoelectric presence-sensing device that protects against access into hazardous points and areas of the press brake. They can range from very compact to larger, more robust and resistant models that can withstand demanding ambient conditions. We should note that a stop-time measurement (STM) device is needed to calculate the safety distance on a regular basis, just as it is needed with two-hand controls.
Safety Light Curtains safeguard personnel using an LED transmitter and receiver. Any interruption of the plane of light by an object equal to/or larger than the “minimum object sensitivity” initiates an output signal. That could be a hand or a finger or a misplaced tool that will either cause the machine to stop or prevent a cycle until the blockage is removed. The operator must be outside the protected area through the entire stroke of the press brake ram. The safety distance between the light curtain and the machine depends on the application, the type of light curtain, and the machine’s stopping performance.
OSHA has a set of regulations for light curtains that are listed here:
1. The machine must be able to stop the movement of the ram anywhere in the stroke.
2. The stopping time of the ram must be known.
3. The stopping time of the ram must be monitored for deviation in stopping time on each stroke.
4. The minimum distance the light curtains can be located to the pinch point must be known.
5. The light curtains must be control reliable.
6. The machine stop circuit with which the light curtains are interfaced, must be control reliable.
7. The light curtains must be self checking for proper operation on each stroke.
8. There should be no easy way to disable the safety system without special tools.
9. If the safety system is disabled there should be a clear indication that it is disabled.
10. The operator and setup person should be properly trained in the operation of the safety system.
LASER FOCUSED ON SAFETY
The newest entry into the press brake safety category is probably its most revolutionary, the Laser Active Optic Protective Device, more commonly referred to as the AOPD. Four manufacturers now make AOPD systems including LazerSafe™ a partner of Rockford Systems. Inclusion of Laser AOPD technology in the B11.3 is a welcome addition to the standard that now gives press brake manufacturers, dealers and users a clear guideline to implementing this technology safely. (B11.3 sub-clause 8.8.7 – Close Proximity Point of Operation AOPD Safeguarding Device)
The biggest advantage of AODP is that operators can hand-hold piece parts up close to the dies, while using a foot-switch to actuate the machine-cycle, which is almost impossible to safely accomplish using a light curtain. Another advantage is for larger piece parts with tall side-legs that would be difficult when using a vertically mounted light curtain for safeguarding. For those familiar with using light curtains, those two situations often require excessive “Channel Blanking” which “yes” allows for production of those parts, but often lets the hands and fingers to reach too close to the dies.
LIGHT CURTAINS or AODP?
Laser AOPD protects the point of hazard whereas light curtain systems restrict operator access to the point of hazard. Operators can hand-hold piece parts up close to the dies with AOPD, while using a foot-switch to actuate the machine-cycle. This is virtually impossible to safely accomplish using a Light Curtain. But that doesn’t make AODP perfect for every application. AOPD systems are well suited for applications such as box bending, bending with flanges, or where light curtain effectiveness is diminished due to excessive blanking or muting.
There are advantages and drawbacks to both systems. And we would stress that it is not an “either-or” situation between light curtains and AODP. The two can be used, and often are, on the same machine. Light curtains provide for die configurations that the AODP won’t handle like compound bends, for instance. This is done to ensure that safeguarding is provided for all die setups. For die setups where neither light curtains or AOPD can offer effective safeguarding, but the part can be fixture in place, that is it does not require hand-support, a two-hand control can be used for safeguarding.
The diagram below sums up the two systems.