A method for synchronizing clocks in a packet transport network. A dual power supply system provides a mechanical lock-out functionality, and the control system is protected from electrostatic build-up on the surface of the feed roller. The cap includes a tubular portion having such an inside diameter as to allow the tube to pass therethrough, a protrusion protruding inward from an inner surface of the tubular portion, and an extending portion extending toward the hole from an end of the tubular portion confronting the surface of the passage component.