Gantry robot fatally strikes mold setter at Michigan plastics plant

What happened

The employer was a custom plastic injection molding company. One of its 1,500-ton horizontal injection molding machines had been fitted, six to eight months earlier, with a single-side gantry robot that traveled along a frame on top of the machine, picked each finished part out of the mold and dropped it on a conveyor. The cycle took about 50 seconds.

The 29-year-old worker had changed the mold on the machine a few days before. According to the Michigan FACE report, a colleague reminded him on January 19, 2001, to return some borrowed tools. After clocking out he went back to the machine, which was running in automatic mode along with the robot. Video shows him first looking through the closed operator gate and then, about 20 seconds later, climbing on top of the purge guard and leaning over the stationary platen to see into the mold area.

That position put his head between the robot’s home position and the vertical support of its frame. When the robot moved toward the mold to collect the next part, it struck the right side of his head and crushed it against the support. A passing employee noticed him and called for help. Coworkers stopped the machine and began first aid, and he was pronounced dead on arrival at a local hospital. The medical examiner recorded the cause as blunt force head trauma.

The system involved

The robot was a single-side gantry unit used to unload molded parts. Its controls were tied to the molding machine’s sliding operator gate, so opening the gate stopped the robot. The machine also had hydraulic, electrical and mechanical interlocks and a safety mat in the molding area.

The Michigan FACE investigators wrote that the robot was not safeguarded in line with the voluntary ANSI/RIA R15.06 robot safety standard: the space the robot traveled through above the machine had not been identified as hazardous or guarded. The employer had told workers not to enter the area on the purge-guard side while the machine and robot were running.

Investigation and response

MIOSHA was notified the same day through its fatality reporting system, and a Michigan FACE researcher accompanied the MIOSHA compliance officer to the plant on February 5, 2001. MIOSHA did not issue citations.

The FACE report recommended that the robot and the point of operation be safeguarded to prevent entry during automatic operation, that users carry out a risk assessment of the robot system, and that everyone who interacts with a robot be trained on the hazards of the specific task and system.

What is not established

The report does not name the company or the city. The worker’s reason for climbing onto the machine is inferred by investigators from the video and from a colleague’s reminder about borrowed tools.