The first usage of “automaton” meant “contrivance with a hidden mechanism that appears to operate on its own.” In modern contexts, however, there are two usages. You might apply the word to a self-operating device, such as your robot vacuum, but it’s also used in a more figurative sense, meaning “an individual who acts in a robotic manner.” It comes from the Greek “autómatos,” meaning “of one’s own accord, acting without external intervention, natural.”