The rules text for Autonomous says "If the equipment provides an attack, that attack may be used once per round, as a free action, at the end of the creature's Action Phase. If the attack is a melee attack, it must follow the normal rules for guarding; however, it will not trigger a counterstrike or damage barrier, and will not remove a guard marker from its target."
I would be willing to say since it does not break guard it should not break Charm.