Robots can indeed take over the hazardous, tough, and dirty jobs, but sometimes, they can also create new risks to humans, especially in a human-robot collaborative environment.
Accidents involving these automated and very sophisticated machines can happen just as with other machinery. People may not be aware of the danger of the moving manipulator, and therefore, the robot workplace must be watched to prevent operators from hurting themselves through carelessness.
Initially, all robots were caged up, distancing them from the operators to prevent injuries. If the operators needed to enter the work area and interface with the robots to load or unload parts, they had to activate the safe mode in the safety control system. This often meant a full stop for the robot, resulting in reduced productivity.
Today, new software-based safety systems slow down a robot to a safe speed or direct the robot’s motion to a safe position, allowing people to share the same workspace with far less risk of injury. New technologies allow the robot and the people to share the same workspace and work side-by-side.
Studies indicate that many robot accidents do not occur under normal operating conditions but rather during maintenance, repair, testing, or programming. During these operations, an operator, programmer, or maintenance worker temporarily enter the robot’s working area where the injuries occur.
Robotic safety incidents occur due to multiple reasons. A robot typically places an individual in a risk circumstance when an accessory or the mechanical part fails, or the power supplies go uncontrolled. In general, robotic incidents can be grouped into four categories:
- Collision or contact accidents due to unpredicted movements, component malfunctions, or unpredicted program changes.
- Crushing and trapping accidents in which a worker’s limb or other body parts is trapped or driven into the robotic arm and other peripheral equipment.
- Mechanical part accidents in which broken drive components, tooling, or end-effectors (e.g., grinding wheels, deburring tools, buffing wheels, power screwdrivers, and nut runners), lead to a mechanical mishap.
- Other accidents, including potential electrical and pressurized fluid hazards and environmental accidents from arc ash, metal spatter, dust, and electromagnetic or radio-frequency interference. Ruptured hydraulic lines can create dangerous high-pressure cutting streams or whipping hose hazards. Besides, equipment and power cables on the floor present tripping hazards.
Sources of hazards
The potential hazards posed by robots to humans can be broken down by source/cause, as follows: human interaction, control error, unauthorized access, mechanical failure, environmental source, power system fault, and improper installation.
- Human interaction: This includes hazards, dangerous, unpredicted movement or action due to human interaction associated with programming, incorrect activation of the teach pendant, interfacing activated peripheral equipment, connecting live input-output sensors to a microprocessor, etc. One of the most significant hazards is over-familiarity with the robot’s redundant motions so that the individual places herself/himself in a dangerous position while programming or performing maintenance.
- Control errors: This includes intrinsic faults within the control system, software errors, and electromagnetic interference. These errors can occur due to defects in the hydraulic, pneumatic, or electrical sub-controls in the robot system.
- Unauthorized access: Entry into the safeguarded area is potentially hazardous. This hazard is more pronounced when the person involved is not familiar with the safeguards in place or the current activation status.
- Environmental sources: Electromagnetic interference (transient signals) can exert an undesirable influence on the automatic operation, causing a potential for injury.
- Power systems: This occurs when pneumatic, hydraulic, or electrical power sources with malfunctioning control elements disrupt the electrical signals to the control or power-supply lines. The causes a fire risk due to the potential for electrical overloads and the use of flammable hydraulic oil. It can also result in electrical shock to personnel.
- Improper installation: If the design requirements and layout of equipment are inadequate, it can lead to inherent hazards.
Robot safety measures
The use of robots necessitates hazard analysis, risk assessment, and safety measures. The following guidelines can help to remove hazardous situations to robot personnel, factory workers, visitors, and the robot itself.
- The robot work area should be closed by permanent barriers (e.g., fences, rolls, and chains) to prevent people from entering. The robot’s each envelope diagram should be used in planning the barriers. The advantage of a fence-type barrier is that it can stop a part that might be released by the robot’s gripper while in motion.
- Access gates to the closed working area should be interlocked with the robot control. Once such a gate is opened, it automatically shuts down the robot system.
- An illuminated sign stating “robot at work” should be automatically turned on when the robot is switched on. This lighted sign warns visitors not to enter the closed area when the robot is switched no, even if it does not move.
- Emergency stop buttons must be placed in easily accessible locations and on the robot’s teach box and control console. Hitting the emergency button stops power to the motors and causes the brakes on each joint to be applied.
- Pressure-sensitive pads can be placed on the floor around the robot that, when stepped on, can turn the robot controller off.
- Emphasize safety practices during robot maintenance. The arm can be blocked up on a specially built holding device before any service work begins.
- Great care should be taken during programming with the manual reaching mode. The reach box must be designed so that the robot can move as long as a switch is pressed by the operator’s finger. Removing the finger must cease all robot motions.
- The electrical and hydraulic installation should meet proper standards. This includes efficient grounding of the robot body. Electric cables must be located where they cannot be damaged by the movements of the robot. This is especially important when the robot carries electrical tools such as a spot-welding gun.
- Power cables and signal wires should not create hazards if they are accidentally cut during the operation.
- If a robot works alongside a human operator, it must be programmed to extend its arm to the maximum so that the worker can stand beyond the reach of the arm.
- Mechanical stoppers, interlocks, or sensors can be used to limit the robot’s reach if the maximum range is not required.