Robot Safety and You: Examples of Real-Life Accidents We Can Learn From
| By: Jeff Fryman, Director, Standards Development
The Robotic Industries Association remains very involved in promoting robot safety, and for that matter, industrial safety in general. Industrial safety in North America has seen continual improvement in recent years, but even one accident is one accident too many.
I am frequently asked about robot accidents. Robot accidents specifically are not tracked by the reporting agencies; but rather are lumped in with other industrial accidents. As a result no specific statistics are available. The good news is that there are not many robot accidents (accidents where the injury is caused by direct involvement with the robot). The bad news has to be that any accident is often serious. I am only aware of one fatality in the last five years, although there were several incidents in the same period. And we need to learn from near-misses as well as accidents.
In attempting to analyze robot accidents, I will turn to one of the only definitive reports that I am aware of on the subject. This is a report that Jim Howe from the International Union UAW researched and prepared, and has presented at several of the RIA sponsored National Robot Safety Conferences. I am struck by one continuing thread in each accident – the person was performing a task in which injury was foreseeable. Foreseeable by supervision, foreseeable by the design engineer, foreseeable such that the safety-control system should have provided protection – but didn’t.
I say in my training classes that you are responsible for safety. And yes, that goes for you the reader of this article as well. I can also say that all of us are responsible for safety; particularly when we look at foreseeable events. What do I mean by foreseeable? Let’s take a look at some of the incidents.
I call this the classic example of trying to get the job done: The robot stopped because one of the parts did not make a locating switch. The victim entered the cell and attempted to locate the part. The robot activated and crushed the employee. And a variation on the theme: An electrician entered a robot cell to reposition a part on a feed chute. He repositioned the part, and as he was leaving, passed through the envelope of an adjacent robot which had completed its task and was moving to its home position to pick up another part. The robot pinned the electrician against a parts-feed conveyor with its end effector.
The next examples are also related to persons inside the restricted space with power on to the robot actuators: Four workers entered the restricted space to troubleshoot a robot with power on. One worker decided to put the part back onto the fixture and the robot assumed it was time to go! The worker was pinned to the fixture.
Another case: The victim was cleaning up when he was crushed between the back end of the robot and a ‘‘safety post’‘. And yet another victim was attempting to load parts into empty positions on three conveyors. The robot was not operating fast enough to fill all of the positions. The victim was pinned against one of the conveyors by the robot and end effector.
Then there are the issues of cell design: It was necessary to periodically wipe the dust off of two photo electric eyes that signaled the robot to perform the next task. After the robot stopped, the victim entered through an opening that had been made in the perimeter guard for this purpose. When the photo cell was wiped off it signaled the robot to move and crushed the employee. And again: Another technician was working on a robot-conveyor arm. The machine dips parts into solutions and cycles every 15 minutes. The victim forgot about the 15-minute cycle and was caught between the robot arm and the conveyor.
How about a little help from your buddy? Two electricians entered a cell which had two robots that load two assembly fixtures. A yellow caution light was on indicating that it was ‘‘safe’‘ to enter the cell. Apparently while the electricians were checking the equipment one of them hit a limit switch which caused one of the robots to move quickly to the fixture to remove a panel. One of the electricians was standing in front of the assembly machine and was pinned by the robot and end effector.
And here is direct help: Every 20 cars the robot would return to a station and the sanding paper would be replaced automatically. The sanding-paper changer was not functioning properly. An electrician entered the cell through an interlocked gate. A fellow worker reset and started the line. The electrician was looking over the sanding-paper changer and did not realize that it was the 20th car. The robot moved quickly to the station striking the employee.
And also indirect help: A worker entered a robot cell on the line and attempted to clear a fault. The worker assumed that by opening the interlocked gate the robot would not move. Over the weekend a maintenance worker had placed an object into the gate relay which essentially bypassed the interlock. The worker cleared the fault and the robot quickly moved toward her pinning her against the vehicle.
And finally a revealing quote: ‘‘I was trying to un-jam the cams and as I got the jam out, the robot cycled and squeezed me against the machine. I did not know it had to be turned off.’‘
The common theme I see in all these incidents is not only that they were foreseeable tasks, but that common safety procedures were not followed. And I don’t mean only procedures from the ANSI/RIA R15.06-1999 that allow for safe work around the robot cell, but standard lockout procedures as well. Where was the supervisor in all these cases? Is that you, or were you the victim, or were you the cell designer? YOU quickly becomes WE; all of us are responsible for safety in the work place.
On a final note, the new ANSI/ASSE Z244.1-2003 standard for Control of Hazardous Energy – Lockout/Tagout and Alternative Methods allows for safe work procedures following alternative methods for control of hazardous energy. This alternative to the classic lockout to zero-state energy is only as good as the procedure that is followed. Good supervisory oversight is essential, as well as good system design and engineering for the robotic work cell.
Practice safety everyday.