An antecedent is a word (or group of words) that a pronoun refers to. The pronoun "its" is a third-person singular pronoun that refers to an animal, an event, a place, or a non-human thing, therefore, its antecedent should be in the third person singular as well and should refer to any of those entities. In the sentence, then, the antecedent of "its" is "robot" because "robot" is a noun that refers to a singular non-human thing.
