Robots are machines that load and unload stock, assemble parts, transfer objects, or perform other tasks.
Robots are used for replacing humans who were performing unsafe, hazardous, highly repetitive, and unpleasant tasks. They are utilized to accomplish many different types of application functions such as material handling, assembly, arc welding, resistance welding, machine tool load/unload functions, painting/spraying, etc.
Studies in Sweden and Japan indicate that many robot accidents have not occurred under normal operating conditions but rather during programming, program touch-up, maintenance, repair, testing, setup, or adjustment. During many of these operations, the operator, programmer or corrective maintenance worker may temporarily be within the robot’s working envelope where unintended operations could result in injuries.
All industrial robots are either servo or non-servo controlled. Servo robots are controlled through the use of sensors which are employed to continually monitor the robot’s axes for positional and velocity feedback information. This feedback information is compared on an on-going basis to pre-taught information which has been programmed and stored in the robot’s memory.
Non-servo robots do not have the feedback capability of monitoring the robot’s axes and velocity and comparing with a pre-taught program. Their axes are controlled through a system of mechanical stops and limit switches to control the robot’s movement.
Type of potential hazards
The use of robotics in the workplace also can pose potential mechanical and human hazards.
Mechanical hazards
Mechanical hazards might include workers colliding with equipment, being crushed, trapped by equipment, or being injured by falling equipment components. For example, a worker could collide with the robot’s arm or peripheral equipment as a result of unpredicted movements, component malfunctions, or unpredicted program changes.
A worker could be injured by being trapped between the robot’s arm and other peripheral equipment or being crushed by peripheral equipment as a result of being impacted by the robot into this equipment.
Mechanical hazards also can result from the mechanical failure of components associated with the robot or its power source, drive components, tooling or end-effector, and/or peripheral equipment. The failure of gripper mechanisms with resultant release of parts, or the failure of end-effector power tools such as grinding wheels, buffing wheels, deburring tools, power screwdrivers, and nut runners are such hazards.
Human errors
Human errors can result in hazards both to personnel and equipment. Errors in programming, interfacing peripheral equipment, connecting input/output sensors, can all result in unpredicted movement or action by the robot which can result in personnel injury or equipment breakage.
Robots in the workplace are generally associated with the machine tools or process equipment. Robots are machines, and as such must be safeguarded in ways similar to those presented for any hazardous remotely controlled machine.
Various techniques are available to prevent employee exposure to the hazards which can be imposed by robots. The most common technique is through the installation of perimeter guarding with interlocked gates. A critical parameter relates to the manner in which the interlocks function. Of major concern is whether the computer program, control circuit, or the primary power circuit, is interrupted when an interlock is activated. The various industry standards should be investigated for guidance; however, it is generally accepted that the primary motive power to the robot should be interrupted by the interlock.
The ANSI safety standard for industrial robots, ANSI/RIA R15.06, is very informative and presents certain basic requirements for protecting the worker. However, when a robot is to be used in a workplace, the employer should accomplish a comprehensive operational safety/health hazard analysis and then devise and implement an effective safeguarding system which is fully responsive to the situation. (Various effective safeguarding techniques are described in ANSI B11.19.)
Essentially, robots perform work that would otherwise have to be done by an operator. They are best used in high-production processes requiring repeated routines where they prevent other hazards to employees. However, they may create hazards themselves, and if they do, appropriate guards must be used.
The following figures show a type of robot in operation, the danger areas it can create, and an example of the kind of task (feeding a press) it can perform.
Figure 1: Robot movement capability
Figure 2: Potential danger areas in robot envelope
Figure 3: Using barrier guards to protect robot envelope
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