Working Safely Around Industrial Robots
By Maureen Alvarez, CIH, CSP
How many times have you wanted to
have a robot around to help with your work? Just the thought
of a robotic machine doing all the work can make you smile
right? Afterall, the robot will run itself and you can head
off to do other things right? Well, it isn’t as simple as
that. The robot has “revolutionized” some industrial processes
but these pieces of equipment still need to be controlled
A robot’s movements are very predictable
yet when you place employees to work near robots – the employees
movements are not as predictable. Even with the best employee
training program there is still the risk of employees getting
too close to a working robot and becoming seriously injured
or killed. These robotic work partners can save us all a
significant amount of work as long as we understand their
limitations and the safety requirements for robots.
Industrial robots are programmable
multifunctional mechanical devices designed to move material,
parts, tools or specialized devices through variable programmed
motions to perform a variety of tasks. Robots are generally
used to perform unsafe, hazardous, highly repetitive and unpleasant
tasks. They have many different functions such as material
handling, assembly, welding, machine tool load and unload
functions, painting, spraying, etc.
The following accident information
regarding robots was taken from the OSHA Technical Manual
(http://www.osha-slc.gov/dts/osta/otm/otm_iv/otm_iv_4.html). Past studies have shown the following information:
Studies in Sweden and Japan indicate
that many robot accidents do not occur under normal operating
conditions but, instead during programming, program touch-up
or refinement, 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.
Typical accidents have included
- A robot's arm functioned erratically during
a programming sequence and struck the operator.
- A materials handling robot operator entered
a robot's work envelope during operations and was pinned
between the back end of the robot and a safety pole.
- A fellow employee accidentally tripped the
power switch while a maintenance worker was servicing an
assembly robot. The robot's arm struck the maintenance worker's
Robotic safeguarding systems protect
not only the operators but also engineers, programmers, maintenance
personnel, and any others who work on or with robot systems.
A combination of safeguarding methods may be used. Redundancy
and backup systems are especially recommended, particularly
if a robot or robot system is operating in hazardous conditions
or handling hazardous materials.
The safeguarding devices employed
should not themselves constitute or act as a hazard or curtail
necessary vision or viewing by attending human operators.
The operational characteristics
of robots can be significantly different from other machines
and equipment. Robots are capable of high-energy (fast or
powerful) movements through a large volume of space even beyond
the base dimensions of the robot. The pattern and initiation
of movement of the robot is predictable if the item being
"worked" and the environment are held constant.
Any change to the object being worked (i.e., a physical model
change) or the environment can affect the programmed movements.
Some maintenance and programming
personnel may be required to be within the restricted envelope
while power is available to actuators. The restricted envelope
of the robot can overlap a portion of the restricted envelope
of other robots or work zones of other industrial machines
and related equipment. Thus, a worker can be hit by one robot
while working on another, trapped between them or peripheral
equipment, or hit by flying objects released by the gripper.
Additional hazards can also result
from the malfunction of, or errors in, interfacing or programming
of other process or peripheral equipment. The operating changes
with the process being performed or the breakdown of conveyors,
clamping mechanisms, or process sensors could cause the robot
to react in a different manner.
Robotic incidents can be grouped
into four categories:
1. Impact or Collision Accidents.
Unpredicted movements, component malfunctions, or unpredicted
program changes related to the robot's arm or peripheral equipment
can result in contact accidents.
2. Crushing and Trapping Accidents.
A worker's limb or other body part can be trapped between
a robot's arm and other peripheral equipment, or the individual
may be physically driven into and crushed by other peripheral
3. Mechanical Part Accidents.
The breakdown of the robot's drive components, tooling or
end-effector, peripheral equipment, or its power source is
a mechanical accident. The release of parts, failure of gripper
mechanism, or the failure of end-effector power tools (e.g.,
grinding wheels, buffing wheels, deburring tools, power screwdrivers,
and nut runners) are a few types of mechanical failures.
4. Other Accidents. Other
accidents can result from working with robots. Equipment that
supplies robot power and control represents potential electrical
and pressurized fluid hazards. Ruptured hydraulic lines could
create dangerous high-pressure cutting streams or whipping
hose hazards. Environmental accidents from arc flash, metal
spatter, dust, electromagnetic, or radio-frequency interference
can also occur. In addition, equipment and power cables on
the floor present tripping hazards.
To minimize the risk of such accidents
involving robots, NIOSH (http://www.cdc.gov/niosh/85-103.html?)recommends
the following for robotic systems:
- Include physical barriers that incorporate
gates equipped with electrical interlocks so the operation
of the robot stops when the gate is opened.
- Include motion sensors, light curtains, etc.
as backups to the electrical interlocks.
- Provide barriers between robotic equipment
and any free standing objects to prevent employees from
getting caught between the robot and a pinch point.
- Provide adequate clearance distances around
all moving components of the robotic system.
- Include remote diagnostic implementation
as much as possible so that the maximum amount of troubleshooting
can be done from areas outside the operating range of the
- Provided adequate illumination in the control
and operational areas.
- Include on floors or working surfaces clearly
visible marks that indicate the zones of movement of the
addition to the above, training specific to the particular
robot in question should be provided to workers who will be
programming, operating or maintaining robots. Refresher training
should also be conducted on a regular basis. Training should
emphasize safe work practices and stress the following:
- Workers must be familiar with all working
aspects of the robot, including full range of motion, known
hazards, emergency stop buttons, programming and safety
- Operators should never be in reach of the
robot while it is operating.
- Programmers, operators and maintenance workers
should operate robots at reduced speeds to avoid hazards
during programming and be aware of all pinch points.
Robots are an important part of
business today. Please review all the safety information
related to the robots at your workplace. A thorough training
program is essential when working around robots. Please communicate
the importance of robot safety at your workplace.
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