Pump unit including pump frame, pump wheel and pulley and method for using the pump unit to squeeze a tube for sucking ink from a nozzle opening in a recording head

摘要

A pump unit and corresponding method for applying negative pressure to a capping device to prevent clogging of a nozzle opening in an ink jet printer includes a frame having a supporting surface on which a pump tube is disposed. A plurality of gears which are driven by a motor of the ink jet printer are disposed in the frame. A plurality of pulleys are rotatably mounted to one of the gears for applying a pressure to the pump tube to thereby generate a negative pressure in the pump tube. The maximum contact region between the pulleys and the tube in the pump frame is selected to be smaller than 180 DEG to allow for the load applied to the tube by the pulleys to be essentially constant. Damper sheets are economically disposed in the frame to position the pulleys to contact the tube when the gear on which the pulleys is driven in a certain direction. The tube is lead out of the frame in a manner so that at least one half of the tube is bent at right angles at a position where the tube separates from the tube supporting surface and is fixed in a slot formed in the pump frame. Accordingly, the frame space facing the tube supporting surface is used effectively, and the tube can be freely lead to a connection point external of the pump frame.