Considerations on the Structure of Safety Control for Machine and Application to the Maintenance Work

The safety of machine for normal operation mode has been logically examined by applying the “principle of safety confirmation”. However, the maintenance work, especially the test operation which is done in energized condition such as the position adjustment for the machine movements, has not been examined logically until now. Basically, the hazardous situation is caused by the failure of the objective control. This paper proposes the principle of the safe control structure that the safe control should be structured by the multistage safe control. And each control compensates the incompleteness of the safe control of previous stage. Also, by applying this principle to the test operation, this paper proposes the principle of safety maintenance work that two persons should be deployed for the test operation in addition to the actual work person. The first person is an informant of the work person for preventing hazardous situation. The second person is a safety confirming person for stopping the work when the safety situation cannot be confirmed.