Providing Protection around Robotic Devices
You’ve probably seen it many times in science fiction movies: a robot goes berserk and wreaks havoc on its human masters. While real life is not quite that dramatic, and today’s industrial robots may not be as amazing as their counterparts from the movies, those robots are quite capable of causing injuries and damage.
Robotic devices have become a fixture in many industries, making substantial contributions to the nation’s productivity. However, like any machine, they can malfunction. Robots also lack human awareness of nearby hazards and may not realize that a worker has inadvertently placed himself in harm’s way. Most robot-related injuries are related to such situations.
How do we define robots?
“Robot” is a collective term for a variety of programmable mechanical devices that automate repetitive and/or precise tasks. Robots can be used to handle and assemble materials, paint, weld, and perform other functions. The specific task that a robot performs determines its configuration and the space in which it works, which we refer to as its working envelope.
Most robots are made up of four primary systems: the mechanical unit, a source of power, controls, and tooling for specific tasks. The mechanical unit is what is typically considered to be the “working” part of the robot, often a mechanical arm with a variety of linkages, sensors, controls, and other components.
The robot’s power is typically provided electrically, pneumatically, hydraulically, or through some combination, each of which presents its own safety concerns. For example, hydraulic systems may use flammable oil, while electrical systems may create the potential for shocks or electrocution.
Most industrial robots use computer- or microprocessor-based control systems interfacing with and managing all aspects of the robot’s operation. Some have servo-based controls that employ sensors to provide continuous monitoring of activities and allow for automatic adjustments. Non-servo robots may be controlled by limit switches and mechanical devices such as stops. Robots can be programmed to follow a specific path within the working envelope, travel from point to point through a route that may vary, or in a continuous path along several points.
Robots are usually programmed through a teach-and-repeat technique in which a trained programmer uses a control device to guide the robot through each step of the desired operation. The robot stores those steps and the corresponding physical locations, then repeats them in the correct order.
Inherent hazards of robots
Robots need to be monitored and adjusted as needed, a task which is often handled by maintenance workers. Studies suggest those workers may be at the greatest risk for injury, because many robot-related accidents happen outside of normal operations — typically when the robots are being maintained, cleaned, adjusted, or tested.
Maintenance workers normally perform their tasks within the robot’s working envelope, so they’re potentially in the path of unexpected or unintended movements. They may be struck by moving parts such as the robot arms, pinned between the arm and other parts of the robot or nearby equipment, or hit by flying objects released by the robot.
Most incidents associated with robots fall into one of four categories: collisions and impacts, crushing and trapping, mechanical failures, and any others, which includes everything from ruptured hydraulic lines to tripping over power cables.
Other contributing factors
Incidents involving robots may also be the result of other issues such as simple human error. A programmer may make a mistake in entering a sequence that subsequently causes an unexpected action and an injury. Or a worker carelessly enters the work envelope and is struck by the arm. Incorrect installation of a robot may lead to later problems such as premature component failure.
Controls may fail or be impaired by outside factors such as electromagnetic interference. A component that fails in one part of the robot may trigger more catastrophic failures or problems in other areas. Problems with pneumatic, hydraulic, or electrical power sources can also create unexpected effects.
Protection starts with assessment
Safeguarding workers from issues related to robotic devices begins by developing a thorough understanding of the potential risks. That involves a detailed hazard assessment of all aspects of the robot’s operations, including programming, the environment in which it will work, how it will be installed, the tasks it will perform, maintenance procedures, and how it will interact with other equipment and human workers.
Safeguards should be developed for everyone who will work with the robot, from the installers, to the programmers, to the operators, and anyone who works nearby. Those safeguards may include any combination of limiting devices, barriers, sensing equipment, and awareness devices such as lights and horns.
Programmers and maintenance personnel may need additional safeguards when performing their functions within the work envelope, incorporating protection from both the robot itself and any other workers whose actions may inadvertently cause unexpected operations. One safeguard to consider is a dramatically reduced operating speed during the programming period.
Safety policies and safety training specific to issues related to robotics are also critical. Anyone who works with or around the robots — or who may encounter them in the course of his or her normal job — should receive training about the potential risks and correct procedures. The more everyone understands the potential for problems, the less likely anyone will encounter them.