Abstract: A hydraulic servomechanism for controlling the pressure of ink supplied to an ink jet printer head includes a bellows located between an ink source and the head and arranged for expansion and contraction to decrease and increase the pressure of ink in the bellows.Pressure is sensed at the bellows output connected to the ink head and the sensed pressure is compared to a desired ink pressure to produce a driving signal which excites an electromagnetic driver coupled to the bellows. The driver applies a force to the bellows to adjust the pressure to the desired pressure. A position sensing switch is responsive to the volume of the bellows and controls a valve located between an ink source and the bellows input to maintain the volume of ink in the bellows within a predetermined volumetric range.

Abstract: A hydraulic circuit and related method are provided for dynamically varying the pressure of ink supplied to an ink jet printer head to obtain consistent volume ejected ink drops despite differences in the time elapsing between successive drops. A dot rate command signal related to an actuation frequency and corresponding to the pressure of ink at the head necessary for producing an ejected drop having a desired volume is compared with the ink pressure at the head to produce a pressure control signal for varying the pressure of the ink in a variable volume fluid chamber to deliver ink to the head at the desired pressure. The pressure control signal is one chosen by experiment as that required to produce the desired ink drop volume for the specific ink supply and ink jet printer head employed.