Safety equipment is an essential part of any robotic system or work cell to ensure the safety of your workers while your robot is in operation. There are a variety of safety options on the market today that will keep workers safe – physical barriers like fencing, arc glare and dividers, as well as invisible barriers like light curtains and area scanners.
The most common safety option is a physical barrier like fencing, arc glare, or dividers. Fencing provides a physical barrier that basically closes off the area around the robot itself, allowing people to see the set perimeter of the work cell or system. These cages are several feet tall, and their design depends on the application and how much area needs to be safeguarded.
Like many other types of steel fencing, robot system cages usually have many holes in it. Fencing may be covered with curtains to keep debris from being thrown outside of the perimeter of the work cell or system. Some curtains protect against debris and arc glare. According to an article from NASA.gov, the brilliant light present during an arc welding process can cause eye irritation or retinal damage if it is observed for long periods of time. The article states that these welding curtains protect your eyes in a way similar to a pair of sunglasses. Arc glare curtains, like Wilson Spectra curtains, are available in shades of yellow, orange, grey and brown, and they are usually fixed to the three sides of the work cell fencing. This safety option will absorb, filter and scatter the light from the arc weld, reducing the glare and improving the working environment for everyone in a welding shop.
While arc glare curtains are transparent, fixed to the robot fencing, and filter light before it impacts the eyes, metal dividers work in a different capacity to protect a worker’s eyes from the impact of arc glare. One side of the robot system is sometimes open, especially if parts have to be loaded and unloaded manually. When a 180-degree indexing table is fixed inside the system, it will have a tall, vertical metal divider fixed in the center of the table, which blocks out the robot from the operator while it is in operation. This protects the operator’s eyes during the welding process, even without arc curtains.
As mentioned above, fencing tends to have three sides, with one area open for loading parts. This area needs a different set of robotic safety options, like light curtains or an area scanner. SICK makes a variety of light curtains used by RobotWorx in several of their work cells and robot systems.
According to SICK, safety light curtains are a cost effective way to protect the access point for your robot system entry point. They come in several different sizes, from compact to robust, and even have different resistance variants. Light curtains have an emitter and receiver that are lined up across from each other. Once the light curtains are lined up and functional, they send an invisible beam across the area and give the robot a signal that it is okay to operate. If this area is invaded, the light curtains send a signal to the robot to stop. This is caused by a break in the fence circuit between the robot and the light curtains. When the fence circuit is broken, the robot can still be moved with a teach pendant.
An area scanner is similar to light curtains. However, instead of having one specific area where light is transmitting from an emitter to receiver, an area scanner is one small device that is can scan an entire area. SICK also makes area scanners, and their scanners are programmable, allowing companies a high level of performance that can work for a variety of applications. Since they can be programmed, area scanners have a higher level of versatility than light curtains, because they can have a more precise area muted out (a load zone for example), making it easier to load and unload parts in a particular system or work cell.
Emergency stop, or e-stop, is a function that is used in case of emergency. There are usually one or more e-stop buttons around a robotic work cell or system, and these buttons cause the robot to stop motion immediately. Unlike the fence circuit, when the e-stop circuit is broken, the robot is unable to be moved at all, even with the teach pendant.
Whenever something breaks the e-stop or fence circuit for a robot system, the safety reset light will come on. This light is usually located on the operator station. Once you have corrected the safety situation, the operator can press the safety reset button and then press start to resume operation. If the safety situation has not been corrected, the reset will not work, and the system will not work until the situation is corrected.
Safety equipment, like that featured above, is required under the OSHA directive regarding robotics. OSHA Directive STD 1-12-002 states that one or more of these safety methods, be it barrier guards or electronic safety devices, shall be provided to protect the operator and employees from hazards of operation, such as flying chips, sparks, rotating parts, etc. While this is a typical regulation for all machinery, there are other regulations from OSHA and other organizations that are geared directly toward robots.
In 2012, the Robotics Industry Association (RIA) completely reassessed and rewrote their standard practices for safety when dealing with industrial robotics. One of those changes was to the functional safety guidelines for robotics. Basically, according to RIA R15.06:2012, companies must perform risk assessments on their integrated systems and work cells and ensure that they are outfitted with a function safety design to reduce risk to users. This can incorporate one or many of the products listed above.