Improving worker safety in robotic welding
By Carrie Halle
By Carrie Halle
May 30, 2019 – Robot density in Canada has been on the rise for more than a decade and reached 145 units per 10,000 employees last year.
Growth was mainly driven by installations in the automotive industry. In Canada, as in around the world, one of the most common uses for industrial robots is arc and spot welding.
Robotic welding provides Canadian manufacturers with several competitive advantages. Most importantly, it makes them more productive while generating more consistent, higher quality welds and reducing waste. Robots also empower manufacturers to address the current shortage of skilled welders to recruit.
In addition, by taking the human element out of the welding process, robots eliminate operator dangers such as electric shock, exposure to gases and toxic fumes and flash burns to the eye’s cornea. Ironically, with the implementation of these robots, new dangers have replaced the old ones – which is why it is critical for manufacturers to follow best safety practices when implementing a robotic welding program.
Are industrial robots safe?
Robotics professionals are quick to point out that while industrial accidents involving robots and robotic welders do happen, they are infrequent. But when they do happen, they are usually fatal.
The first recorded death by robot happened in 1979 when a worker collecting parts from a storage facility was hit and killed by a one-ton robotic arm. Fast forward to June 2015, when a German Volkswagen factory employee was crushed to death when setting up an industrial robot. A month later, a similar type of accident involving a robot occurred in India. And yet another accident happened later that same year at a Michigan auto parts manufacturer where a robotic arm swung and crushed the head of a maintenance worker between a hitch assembly. In December of last year, a Chinese worker was impaled in a horrific accident by a rogue robot in a porcelain factory.
Closer to home, in August 2016, a maintenance worker in an Ontario manufacturer entered a robot cell without locking off the power. While carrying out the repair, the worker felt pressure and saw it was the robot pressing the back of his body. Although two colleagues were able to retrieve him, the worker still suffered serious and permanent injury.
Robot accidents typically occur during non-routine operating conditions, such as programming, maintenance, testing, setup, or adjustment, when the employee is temporarily within the working envelope. In most cases, safeguards are either absent, improperly installed, or were bypassed by the employee.
Who is responsible for robot safety?
In Canada, robot safety is shared between all stakeholders ranging from manufacturer to end user, as outlined in CAN/CSA-Z434-14, Industrial Robots and Robot Systems. It is an adoption, with Canadian deviations, of ISO 10218-1 & 2 from the International Organization of Standardization. By adopting ISO 10218-1 & 2 the robot standards for Canada’s CSA, USA ANSI, ISO and EN ISO are harmonized with the goal of moving toward a single global standard that is consistent from country to country in the design and application of robotic cells. The measures and procedures of the Industrial Establishments Regulation also may apply.
According to the standard, the manufacturer, integrator and installer have the shared requirement to provide “information for use” to the user of the robot and robot system. The user has the responsibility to apply this information in developing training and safe work practices. That said, the standards largely speak to the supply chain and do not tell end users how to safely run robots or even how to turn them on. Canada did add value by offering user-directed information in annexes to its standard rather than in separate technical reports like in the U.S. version.
Understanding robotic safeguarding
The first step in developing a safety strategy for a robotic welder or any type of robot is to conduct a risk assessment that takes into account the severity of potential injury, frequency of exposure to a hazard and the probability of injury. Once an option, a thorough risk assessment is today required in CSA-Z434.
Once completed, an action plan must be implemented to take on the hazards identified by the risk assessment. Typically, an effective safeguarding system for robotic welders is a combination of electrically interlocked perimeter guards, safety light curtains, safety laser scanners and pressure-sensitive safety mats. Automatic weld curtains and high-volume ventilation systems can also minimize exposure to hazards in the welding environment. Torch length and robot reach must to be factored in when designing the system. Here is a review of suggested equipment:
- Perimeter guards are designed to keep machine operators and other plant employees safely away from the robotic welding cell other than when they must enter for loading and unloading workpieces or maintaining the welding equipment, robot and other machinery. Perimeter guards are positioned around a robot work envelope and incorporate gates equipped with interlocks so that all automatic operations of the robot and associated machinery will stop when any gate is opened. Robotic welders tend to do the same thing again and again, and cannot generally tell if a worker is in vicinity. That’s why factories establish “danger” or “kill” zones with perimeter guards that people have to stay out of while the robot is operating.
- A laser scanner is a reliable, cost-effective safeguard installed around robotic welders. These are fully programmable devices that use an infrared laser to scan their surroundings and measure distances. A laser scanner can be set up to scan on a horizontal or vertical plane. Should a person or object come into contact with the infrared beam, any hazardous machine motion stops.
- A light curtain system is another common safeguard used with robotic welding equipment, especially in situations where an operator requires frequent access to a cell. Most systems include a transmitter that emits infrared light to the receiver that, when triggered, stops hazardous machine motion. The transmitter and receiver can be installed top to bottom (vertical protection field) or side to side (horizontal protection field). The sensing field can be desensitized to ignore some objects but respond to other objects of a defined size, or muted for temporary suspension to allow material feeding.
- Pressure-sensitive safety mats are yet another option for robotic welding equipment. They can be used around the perimeter of the cell, or more commonly, installed as a secondary safety device inside of perimeter guarding systems. When a worker stands on the mat, the metal plates make contact and hazardous motion stops. Pressure-sensitive safety mats are not be used as primary safeguarding except when all other means are not applicable. Also, when installing mats, ensure they’re located so that an operator or other employee, when stepping onto the mat, cannot reach into the point-of-operation hazard prior to the machine’s hazardous motion coming to a complete stop.
Along with these measures, it is critical to remember the human variable. For instance, if a safeguard prevents the operator from loading or unloading parts from the cell, they may remove it without understanding the dire ramifications. Improperly designed safety equipment frustrates workers or, worse yet, leads to a false sense of security, and ultimately can create accidents.
Training is essential: Employees must be familiar with all operational aspects of a robot welder, including the full range of motion, known hazards, programming information, locations of emergency stop buttons and power sources, and the importance of safety barriers, as well as procedures for freeing a colleague who becomes trapped.
Welding has always been a dangerous job, and there is no doubt that robots are making it safer by performing hazardous, repetitive tasks. But given the fact that tens of thousands of industrial robots are now working in close proximity with employees and often do not have the sensory ability to detect if those employees are in their vicinity, safety must to be kept top of mind.