Patent ID: 8794138

Claim:
A screen printing apparatus for printing deposits of a print medium on workpieces, the apparatus comprising: a frame support unit for supporting a printing screen unit in first and second printing positions, wherein the printing screen unit comprises a screen sheet which includes first and second sets of print apertures and a positioning mechanism for positioning the printing screen unit in one of the first and a second printing positions; a workpiece support unit operable to support a workpiece adjacent an underside of the screen sheet; a print head unit which includes a print head for driving a print medium through one of the first and second sets of print apertures in the screen sheet to print a pattern of deposits on a workpiece supported on the workpiece support unit; and at least one single screen cleaning unit which includes a cleaning head unit for cleaning the underside of the screen sheet, wherein the cleaning head unit is movable between first and second screen cleaning locations at opposite sides of the workpiece support unit, whereby the cleaning head unit is operative to clean the underside of the screen sheet at a location corresponding to the second set of print apertures when in the first screen cleaning location and with the printing screen unit in the first printing position and a location corresponding to the first set of print apertures when in the second screen cleaning location and with the printing screen unit in the second printing position; wherein the screen cleaning unit and the print head unit are operable in parallel, whereby, when the printing screen unit is in the first printing position, the screen cleaning unit is in the first screen cleaning location and cleans the underside of the screen sheet at a location corresponding to the second set of print apertures and at the same time the print head unit prints print medium onto workpieces through the first set of print apertures, and, when the printing screen unit is in the second printing position, the screen cleaning unit is in the second screen cleaning location and cleans the underside of the screen sheet at a location corresponding to the first set of print apertures and at the same time the print head unit prints print medium onto workpieces through the second sets of print apertures.