Ink jet printer

Abstract

An ink jet printer having an ink supply tank and a constant volume fluid pump which pumps ink through a supply line to a print head and, during a start up sequence, to a pressurizing line having a fluid accumulator which rapidly increases the line pressure of the system until a predetermined ink pressure within the print head is reached. The pressure is sensed by a transducer adjacent the print head, and an outlet valve is actuated to close the flow of ink through the head abruptly, thereby creating a pressure wave which initiates ink flow through the orifices of the print head. In order to minimize contamination of ink in the supply line, the pressurizing line conveys ink back to the supply tank. The printer also includes an air system having a constant volume vacuum pump which is connected to draw air from the ink supply tank, thereby creating a vacuum within the tank, a pair of inlet lines connected to the vacuum pump inlet, each having a valve thereof which can be opened or closed to vary the amount of vacuum created within the tank by the supply pump, and an ink removal line which is connected to the ink supply line such that atmospheric air is drawn through the ink removal line, ink supply line and print head to the ink supply tank, thereby purging the print head of ink.