Chapter 6 -
Robotics in the Workplace
Robotics in the Workplace
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
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 might include workers colliding with equipment, being
crushed, or 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 to name a
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.
Human errors in judgment result frequently from incorrectly activating the
teach pendant or control panel. The greatest human judgment error results
from becoming so familiar with the robot's redundant motions that
personnel are too trusting in assuming the nature of these motions and
place themselves in hazardous positions while programming or performing
maintenance within the robot's work envelope.
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
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 R15.06-1986, 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 B11.19-1990.)