SAFETY AND ROBOTIC SYSTEMS

April 19, 2014


SAFETY  WHEN USING ROBOTIC SYSTEMS:

If you follow my posting you know that I am definitely interested in robotic systems and robots themselves.   Robots represent a very interesting position in manufacturing and one that has it’s own safety rules.  This post strives to provide a brief checklist relative to the systems themselves. 

Over the past ten to fifteen years we have seen a remarkable increase in the use of robotic systems to automate manufacturing processes.  Various industries rely heavily on robotic systems for smooth and continuous operation.   Today, major technological advances,  including microprocessors, artificial intelligence techniques, and innovations in automation and control systems have ushered in a new age of robotics in which once-futuristic visions have either become realities or are on the horizon.  With these advances, much smaller manufacturers can afford to purchase, operate and maintain robotic systems on an annual basis.  There has also been much greater simplicity structured into the operation of robotic systems allowing use by operators with minimal experience.  The advent of the “teach pendant” has allowed programming without knowing how to “code” the microprocessor that drives the process.

 Without the proper precautions in place, robotic systems experiencing a fault or failure might causes serious injuries to people and damage capital equipment in or around the work cell.  Investigations in Japan indicate that more than 50% of working accidents with robots can be attributed to faults in the electronic circuits of the control system.  In the same investigations, “human error” was responsible for less than 20%. The logical conclusion of this finding is that hazards which are caused by system faults cannot be avoided by behavioral measures taken by human beings. Designers and operators therefore need to provide and implement appropriate technical safety measures.

Why can robotic systems be hazardous?  Let’s take a look.

  • Movements and sequences of movements are, at times, almost impossible to follow.   The robot’s high-speed movements within its radius of action often overlap with those of other machines and equipment.  It is not uncommon at all to have several robots operating at the same time and sequenced so that “near-misses” seem to occur.  This is THE reason operational personnel MUST be trained in all operations within a work cell.
  • Release of energy caused by flying parts or beams of energy such as those emitted by lasers or by water jets. 
  • Free programmability in terms of direction and speed.  Speed control is one valuable feature of any robotic system.  Obviously, the faster the movement, the more productivity results.  It is advantageous for the system to travel as quickly as possible providing maximum quality.
  • Susceptibility to influence by external errors (e.g., electromagnetic compatibility) and certainly human factors. Factors external to the system can, at times, affect the operation of the system.  These unknown factors must be discovered, if possible, prior to the system becoming operational.  This involves testing in a very through fashion before putting the system or work cell into production.

To address the increasing sophistication, complexity and needs of robotic systems, stake-holders in the robotics and automation industries are working to establish new international safety standards through the International Organization for Standardization (ISO) for robots and robot systems integration. ISO10218-1, the initial updated standard, published in 2006, specifies requirements and provides guidance for the assurance of safety in design and construction of the robot itself, not the entire robot system.  Part 2 of ISO10218-2 was published in 2011 and covers the integration and installation of robotic systems or cells, thereby providing a more comprehensive set of requirements for robot safety.  I have designed work cells using robotic systems and definitely recommend the following safety measures be observed at all times:

  • The work cell must be laid out in a fashion that allows access to all components and assemblies required to “function” the system.  This means front, back, sides, walls and any overhead space needed for ventilation and access.  With this being the case, it is mandatory the design engineer know the travel characteristics of the robotic structure itself.  Visualize the work cell as a cube and do the equipment layout in that fashion.
  • Always provide voltage to the robot with a switch completely accessible to the operator AND in sight of the operator.  The switch is considered an integral part of the work cell.  Label the electrical enclosure with voltage and phase.
  • Over-amperage protection, i.e. fusing, must be recommended by the manufacturer of the system and adequate to handle all operational situations.  I definitely recommend power to the robot be exclusive to the robot.  Label the breakers with voltage and amperage.
  • Make sure the electrical layout segregates lights, ventilation hoods, fans, etc from the robotic system itself.  When working on the robot, you don’t want the lights and fans on the same electrical switch and enclosure.  You need to see what you are doing with performing maintenance or making necessary repairs.
  • ONLY TRAINED PERSONNEL CAN OPERATE THE ROBOTIC SYSTEM WORK CELL. No one else.
  • Always make sure PPE is used by personnel if necessary during operation of the system.  I would DEMAND safety glasses be used at all times with operating the system.
  • Robotic systems are “dumb” devices absolutely dependent upon adequate programming.  I have never programmed a robotic system right the first time.  Everything looks good on paper and with that being the case, great caution must be observed when taking the system though its initial cycle phases and testing.  Know the reach dimensions of the arm.  Know where it travels at each point on the program and inform the operator.
  • It is recommended that a light barrier or physical barrier be designed into the system so that inadvertent contact by personnel is impossible.  Tell the operator that at no time should he or she try to bypass ANY safety measure. 
  • Only authorized personnel should attempt to modify the control features of the system.
  • The electrical system should have safeguards that “kick in” during power outages and brownouts.
  • Central processing units (CPUs) driving the system should have battery backup to preserve the program unless the memory is non-volatile.

The following must be prevented during rectification of a breakdown in the production process:

  • Manual or physical access to areas which are hazardous due to automatic movements by the robot or by peripheral equipment
  • Hazards which arise from faulty behavior on the part of the system or from inadmissible command input if persons or parts of the body are in the area exposed to hazardous movements
  • Hazardous movements or conditions initiated by the movement or removal of production material or waste products
  • Injuries caused by peripheral equipment
  • Movements that have to be carried out with the safety guard(s) for normal operation removed, to be carried out only within the operational scope and speed, and only as long as instructed. Additionally, no person(s) or parts of the body may be present in the area at risk.

Troubleshooting often requires starting the robot machine while it is in a potentially hazardous condition, and special safe work procedures such as the following should be implemented:

  • Access to areas which are hazardous as a result of automatic movements must be prevented.
  • The starting up of a drive unit as a result of a faulty command or false command input must be prevented.
  • In handling a defective part, all movements on the part of the robot must be prevented.
  • Injuries caused by machine parts which are ejected or fall off must be prevented.
  • If, during troubleshooting, movements have to be carried out with the safety guard(s) for normal operation removed, such movements may be carried out only within the scope and speed laid down and only as long as instructed. Additionally, no person(s) or parts of the body may be present in the area at risk.
  • Injuries caused by peripheral equipment must be prevented.
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