Grammatical function of "as"

What's the grammatical function of "as" in the following sentence?

The furniture makers in those early decades of the 1600’s were known as “joiners,” for the primary method of constructing furniture, at least among the English of this time, was that of mortise-and-tenon joinery.

Any response would be appreciated.

Its grammatical function is of a preposition, introducing the preposition phrase as joiners, which is a complement of known.