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Tube pump and liquid ejection apparatusTube pump and liquid ejection apparatus description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20080056918, Tube pump and liquid ejection apparatus. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS-REFERENCE TO RELATED APPLICATIONS [0001]This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2006-236909, filed on Aug. 31, 2006 and No. 2006-236911, filed on Aug. 31, 2006, the entire content of which is incorporated herein by reference. BACKGROUND [0002]1. Technical Field [0003]The present invention relates to a liquid ejection apparatus such as an inkjet printer and a tube pump used in a liquid ejection apparatus. [0004]2. Related Art [0005]Inkjet printers (hereinafter referred to as printers) are widely known as liquid injection apparatuses for injecting liquid from a nozzle formed in a recording head onto target. In a printer, since nozzles have openings on a nozzle-forming surface of a recording head (liquid ejection head), ink solvent evaporates from the nozzles. As a result, the viscosity of the ink increases, which may influence the ejection characteristics of the ink. Printers are therefore provided with a maintenance mechanism that performs maintenance of a recording head. [0006]A maintenance mechanism includes a cap for sealing a nozzle-forming surface of the recording head and a suction pump located in a drain passage. The maintenance mechanism drives the suction pump while sealing the nozzle-forming surface with the cap, thereby producing negative pressure in the cap. Ink having an increased viscosity is drawn out of the nozzles, and the ink ejection is prevented from deteriorating. As such suction pumps, tub pumps that are disclosed, for example, in Japanese Laid-Open Patent Publication No. 2001-301195 and Japanese Laid-Open Patent Publication No. 2002-349452 are used. [0007]The above publications each disclose a tube pump having a substantially cylindrical housing. The housing accommodates an intermediate portion of a flexible tube in the longitudinal direction, a rotor that rotates about the axis of the housing, and a roller (pressing member). When the rotor rotates in one direction, the roller moves along the inner circumferential surface of the housing while pressing the tube. [0008]The tube is accommodated in the housing in such a manner that the intermediate portion in the longitudinal direction wound one turn along the inner circumferential surface of the housing to form a circle. Thus, in the housing, different sections of the tube partially overlap. An elongated hole that extends along the circumferential direction of the rotor is formed in a side of the rotor. The inner wall of the elongated hole defines a cam surface. The elongated hole extends in such a manner that the radial distance from the axis of the rotor is gradually reduced from one end in the circumferential direction to the other end. The roller has a shaft that extends along the axis, which shaft is slidably inserted in the elongated hole of the rotor. The roller is movable relative to the rotor between one end of the elongated hole (actuation position) and the other end (non-actuation position). As the roller moves from the non-actuation position toward the actuation position, the roller moves radially outward in the rotor. [0009]When the rotor rotates in an actuation direction, which is one of the circumferential directions, the shaft of the roller slides toward the actuation position (pressing position) in the elongated hole. At the actuation position, the roller operates with the inner circumferential surface of the housing. That is, the roller moves along the inner circumferential surface of the housing, while consecutively pressing part of the intermediate portion of the tube. As the roller moves, portion of the tube that have been released from the pressing of the roller sequentially restore. Accordingly, the interior of a portion of the tube that is upstream of the intermediate portion, which is accommodated in the housing, is decompressed, so that negative pressure is produced in the cap. This draws ink with an increased viscosity from the nozzles. [0010]When the tube pump is operating, the roller shaft moves along the elongated hole, and rotates at the actuation position. In these cases, frictional resistance is generated between the roller shaft and the cam surface. Particularly, when tube pump is performing suction, the roller shaft, at the actuation position, rotates and slides on the cam surface while receiving a reactive force from the pressed tube. Therefore, the frictional resistance is particularly increased when the roller is at the actuation position. Such frictional resistance is preferably minimized from the perspective of reducing the friction of the cam surface, reducing the torque required for operating the tube pump, and improving the pump efficiency. [0011]However, the tube pumps disclosed in the above publications take no countermeasures to reduce the frictional resistance between a roller shaft and a cam surface. SUMMARY [0012]Accordingly, it is an objective of the present invention to provide a tube pump and a liquid ejection apparatus that reduce the torque required for operation and improves the pump efficiency. [0013]To achieve the foregoing objective and in accordance with a first aspect of the present invention a tube pump having a housing, a tube, a rotor, and a pressing member is provided. The housing has an inner circumferential surface. The tube has a section that is arranged in the housing in such a manner as to annularly extend along the inner circumferential surface. The rotor is rotatably arranged in the housing, and has a cam surface. The pressing member is arranged in the housing. The pressing member has a main body that selectively presses the tube toward the inner circumferential surface and a shaft that extends from the main body and contacts the cam surface. During rotation of the rotor, the pressing member moves, with the shaft contacting the cam surface, along the inner circumferential surface while pressing the tube. The shaft has a contact part that contacts the cam surface. The shaft is formed in such a manner that the frictional coefficient of the shaft is lower than the frictional coefficient of the main body at least in the contact part. [0014]In accordance with a second aspect of the present invention, a liquid ejection apparatus having a liquid ejection head, a cap, and a suction device is provided. The liquid ejection head has a nozzle-forming surface in which a nozzle for ejecting liquid is formed. The cap is capable of sealing the nozzle-forming surface. The suction device is capable of applying suction to the interior of the cap. The suction device is formed by the tube pump according to the first aspect of the present invention. [0015]In accordance with a third aspect of the present invention, a tube pump having a housing, a tube, a rotor, and a pressing member is provided. The housing has an inner circumferential surface. The tube has a section that is arranged in the housing in such a manner as to annularly extend along the inner circumferential surface. The rotor is rotatably arranged in the housing, and has a cam surface. The pressing member is arranged in the housing. The pressing member has a main body that selectively presses the tube toward the inner circumferential surface and a shaft that extends from the main body and contacts the cam surface. During rotation of the rotor, the pressing member moves, with the shaft contacting the cam surface, along the inner circumferential surface while pressing the tube. The main body has an insertion hole into which the shaft is inserted. The shaft contacts the inner surface of the insertion hole and is rotatable relative to the main body. At a contacting portions of the shaft and the main body, the frictional coefficient of one of the shaft is lower than the frictional coefficient of the other. [0016]In accordance with a fourth aspect of the present invention, a liquid ejection apparatus having a liquid ejection head, a cap, and a suction device is provided. The liquid ejection head has a nozzle-forming surface in which a nozzle for ejecting liquid is formed. The cap is capable of sealing the nozzle-forming surface. The suction device is capable of applying suction to the interior of the cap. The suction device is formed by the tube pump according to the third aspect of the present invention. [0017]In accordance with a fifth aspect of the present invention, a tube pump having a housing, a tube, a rotor, and a pressing member is provided. The housing has an inner circumferential surface. The tube has a section that is arranged in the housing in such a manner as to annularly extend along the inner circumferential surface. The rotor is rotatably arranged in the housing. The rotor has a cam surface that extends in a circumferential direction of the rotor. The pressing member is arranged in the housing. The pressing member selectively presses the tube toward the inner circumferential surface and is slidable on the cam surface between an actuation position and a non-actuation position. During rotation of the rotor, the pressing member, if at the actuation position, moves along the inner circumferential surface while pressing the tube, thereby producing negative pressure in the tube, and, if at the non-actuation position, moves along the inner circumferential surface while pressing the tube in such a manner that no negative pressure is produced. The frictional coefficient of the cam surface is partially different. [0018]In accordance with a sixth aspect of the present invention, a liquid ejection apparatus having a liquid ejection head, a cap, and a suction device is provided. The liquid ejection head has a nozzle-forming surface in which a nozzle for ejecting liquid is formed. The cap is capable of sealing the nozzle-forming surface. The suction device is capable of applying suction to the interior of the cap. The suction device is formed by the tube pump according to the fifth aspect of the present invention [0019]Other aspects and advantages of the present invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention. BRIEF DESCRIPTION OF THE DRAWINGS [0020]The invention, together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which: Continue reading about Tube pump and liquid ejection apparatus... Full patent description for Tube pump and liquid ejection apparatus Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Tube pump and liquid ejection apparatus patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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