May 24, 2002

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 and supervised. 

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.

Accident Information

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 the following:

• 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 hand.

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.

Hazards

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 equipment.

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 robot.
  
• 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 robot.

In 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 barriers.
  
• 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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