Patent ID: 8015866
Filing Date: 2011-09-13
Classification: B41J,G01F

Abstract:
1. A liquid detection unit comprising: a liquid detection chamber including a liquid inlet, a liquid outlet, a flexible diaphragm which is displaced according to liquid pressure between the liquid inlet and the liquid outlet, and a detection portion installation member having a surface facing the diaphragm, a volume of the liquid detection chamber changing according to the liquid pressure; a movable member provided in the liquid detection chamber; a detection portion including a detection space which communicates with the liquid detection chamber and is separated from the liquid detection chamber by the detection portion installation member, and a piezoelectric-type sensor which causes the detection space to vibrate and detects a remaining vibration waveform of vibrations, the detection portion being provided on the other surface of the detection portion installation member; an urging member which urges the movable member toward the detection portion installation member; and a piece of flexible film which is fixed to the liquid detection chamber and holds the detection portion installation member, wherein the movable member includes a pressure receiving plate attached to the diaphragm and the pressure receiving plate includes a detection space sealing surface facing the surface of the detection portion installation member, wherein when the liquid pressure is a predetermined value, the diaphragm expands until a volume of the liquid detection chamber becomes a predetermined level and separates the detection space sealing surface of the pressure receiving plate from the surface of the detection portion installation member against urging force of the urging member, wherein the movable member brings the detection space sealing surface of the pressure receiving plate into contact with the surface of the detection portion installation member by the urging force of the urging member when the liquid pressure becomes lower than the predetermined value and liquid is introduced into the liquid detection chamber for the first time, and displaces the diaphragm to a position at which the volume of the liquid detection chamber becomes smaller than the predetermined volume, wherein the movable member further includes a first liquid channel which guides the liquid from the liquid inlet to the detection space and a second liquid channel which guides the liquid from the detection space to the liquid outlet, and a part of the second liquid channel is open at a first sealing surface of the movable member, wherein the liquid detection chamber includes a second sealing surface which seals a part of the second liquid channel by being brought into contact with the first sealing surface of the movable member, wherein the liquid detection chamber includes an opening through which the surface of the detection portion installation member is exposed and an abutting surface of the detection portion installation member, and wherein when a distance from the first sealing surface of the pressure receiving plate to the detection space sealing surface is defined as L1, and a distance from the second sealing surface of the liquid detection chamber to the abutting surface is defined as L2, a relationship of L1>L2 is satisfied.