A tray conveyor in which plastic trays with rows of embedded translators are driven by stators in multiple conveyor sections. Washing stations in cleaning zones in each conveyor section are provided to automatically clean empty trays in the conveyor's return path. Indicia on each tray identify the tray as belonging to a specific family of trays. Each of the conveyor sections conveys only conveyor trays that belong to a predetermined family assigned to that conveyor section.