Pen switching mechanism in drum plotters

Abstract

A drum plotter has a pen carriage movable back and forth across a sheet of print paper on a platen which is rotatable about its own axis in opposite directions. The pen carriage supports thereon a pen holder unit rotatable for bringing one of pens with differently colored inks into a writing position. The pen in the writing position is pushed by a hammer toward the platen for writing desired characters, figures or the like on the sheet of print paper. The pen holder unit is rotatably actuatable by a ratchet wheel engaged by a pawl member driven intermittently by a cam mounted on a shaft supporting the pen carriage and drivable by a solenoid-operated mechanism.