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Bellows pumpRelated Patent Categories: Pumps, Expansible Chamber Type, Bellows-type ChamberBellows pump description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060165541, Bellows pump. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to, among bellows pumps for transporting a liquid with using a bellows which axially extends and contracts, a so-called internal-liquid type bellows pump in which an air chamber is formed outside a bellows and a liquid to be transported is sucked into the bellows. [0003] 2. Description of the Prior Art [0004] Conventionally, a bellows pump of such a kind is used as a pump for transporting a liquid such as a chemical liquid, a solvent, or pure water in a semiconductor manufacturing factory. For example, bellows pumps of such a kind are classified into the following two categories. [0005] The first one is a bellows pump such as disclosed in Japanese Patent Application Laying-Open No. 2001-317449. The conventional bellows pump comprises: a pump body in which suction and discharge ports for a liquid to be transported (hereinafter, referred to as transported liquid) are formed; a pump unit which is placed on one side of the pump body; and an accumulator unit which is placed on the other side of the pump body. The pump unit comprises: a bottomed cylindrical pump bellows which is placed so that an open end portion is joined to one side portion of the pump body to internally form a pump chamber, and which can axially extend and contract; a pump cylinder configured by a cylinder head portion which is placed opposingly to the pump body in the axially outside of the pump bellows, a first cylinder section which is projected on the same axis as the pump bellows from the cylinder head portion toward the pump body so as to internally accommodate the pump bellows, which is opposed in an open end portion to the pump body across the open end portion of the pump bellows, and which cooperates with the cylinder head portion to form a pump air chamber outside the pump bellows, and a second cylinder section which is projected on the same axis as the pump bellows from the cylinder head portion toward the side opposite to the first cylinder section, and into which a piston is axially slidably fitted; a coupling shaft which slidably passes through a center portion of the cylinder head portion in the axial direction to couple the pump bellows with the piston; and suction side and discharge side check valves which are attached to the pump body in the pump chamber. The pump bellows, the coupling shaft, and the piston are integrally reciprocated by air which is alternately supplied to the pump air chamber and the second cylinder section. The pump bellows repeatedly extends and contracts so that, when the pump bellows extends, the transported liquid is sucked from the suction port of the pump body into the pump chamber via the suction side check valve, and, when the pump bellows contracts, the transported liquid is discharged from the discharge port of the pump body via the discharge side check valve. By contrast, the accumulator unit comprises: a bottomed cylindrical accumulator bellows which is placed so that an open end portion is joined to another side portion of the pump body to internally form an accumulator chamber for temporarily storing the transported liquid that is discharged from the pump chamber via the discharge side check valve, and which can axially extend and contract; and a bottomed cylindrical accumulator cylinder which is placed outside the accumulator bellows, which is opposed in an open end portion to the pump body across the open end portion of the accumulator bellows, and which forms an accumulator air chamber into which air is filled, outside the accumulator bellows. Pulsation of the discharge pressure of the pump unit is absorbed by extension and contraction of the accumulator bellows. [0006] The second one is a bellows pump such as disclosed in Japanese Patent Application Laying-Open No. 2002-174180. The conventional bellows pump comprises: a pump body in which suction and discharge ports for a transported liquid are formed; and a pair of pump units which are placed on both sides of the pump body, respectively. Each of the pump units comprises: a bottomed cylindrical pump bellows which is placed so that an open end portion is joined to one side portion of the pump body to internally form a pump chamber, and which can axially extend and contract; a pump cylinder configured by a cylinder head portion which is placed opposingly to the pump body in the axially outside of the pump bellows, and a first cylinder section which is projected on the same axis as the pump bellows from the cylinder head portion toward the pump body so as to internally accommodate the pump bellows, which is opposed in an open end portion to the pump body across the open end portion of the pump bellows, and which cooperates with the cylinder head portion to form a pump air chamber outside the pump bellows; a coupling shaft which slidably passes through a center portion of the cylinder head portion in the axial direction to couple the one end with the pump bellows; a coupling plate which is coupled with the other end of the coupling shaft; and suction side and discharge side check valves which are attached to the pump body in the pump chamber. The coupling plates of the pump units are coupled together. Suction valve ports of the suction side check valves of the pump units are communicatingly connected to the suction port of the pump body, and discharge ports of the discharge check valves are communicatingly connected to the discharge port. The pump bellows, the coupling shafts, and the coupling plates of the pump units are integrally reciprocated in the same direction by air which is alternately supplied to the pump chambers of the pump units. The pump bellows repeatedly extend and contract in alternate manner so that, when the pump bellows of one of the pumps extends and the transported liquid is sucked from the suction port of the pump body into the pump chamber of the pump via the suction side check valve, the pump bellows of the other pump unit contracts and the transported liquid is discharged from the discharge port of the pump body via the discharge side check valve. [0007] In both the conventional bellows pumps, flanges and bolts which are made of a metal are used in coupling of the pump bellows with the coupling shafts, and metal nuts and bolts are used in coupling of the coupling shafts with the pistons or the coupling plates. [0008] In order to eliminate contamination caused by metal ions and minimize contamination of a transported liquid due to a pump, a countermeasure to form components by a resin is advancing. In some pumps, liquid-contacting components, i.e., a pump body, a pump bellows, a suction side check valve, a discharge side check valve, and an accumulator bellows are made of a resin such as a fluororesin. In other pumps, also a pump cylinder and an accumulator cylinder which are non-liquid-contacting components are made of a resin, and a coupling shaft which is a metal component of a pump air chamber, and a flange and bolts which are used for coupling a pump bellows with the coupling shaft are covered with a resin, so that, even when the pump bellows or the accumulator bellows is broken, corrosion or metal ion efflux due to immersion does not occur. SUMMARY OF THE INVENTION [0009] In a conventional bellows pump, a flange and bolts are used for coupling a pump bellows with a coupling shaft. When several of the bolts are loosened or fastening torques of the bolts are uneven, the axis of the pump bellows is deviated from that of the coupling shaft, thereby causing the following problems. A sliding portion of the coupling shaft is unevenly worn, and therefore the life period of the pump is shortened. The sliding resistance is increased, and therefore the pump performance is lowered. Moreover, there is a fear that loosened bolts may slip off. In this case, the pump fails to normally operate. Furthermore, the numbers of components and assembly steps are increased, and the torques of fastening portions must be managed. Therefore, there are further problems such as that they may produce causes of impeding improvement of the productivity of the pump, and cost reduction. [0010] Moreover, nuts and bolts are used in coupling of a coupling shaft with a piston or a coupling plate. Therefore, a gap is produced between the coupling shaft and the piston or the coupling plate by dimensional tolerances. This gap may cause the coupling shaft and the piston or the coupling plate to be fastened in a state where their axes are deviated from each other. Therefore, a sliding portion of the piston is unevenly worn, or the coupling plate obliquely applies a load to the coupling shaft, so that a sliding portion of the coupling shaft is unevenly worn, and the life period of the pump is shortened. The sliding resistance is increased, and therefore the pump performance is lowered. Moreover, there is a fear that loosened bolts may slip off. In this case, the pump fails to normally operate. Furthermore, the numbers of components and assembly steps are increased, and the torques of fastening portions must be managed. Therefore, there are further problems such as that they may produce causes of impeding improvement of the productivity of the pump, and cost reduction. [0011] It is a first object of the invention to provide a bellows pump in which a shaft that is to couple a pump bellows with a piston or a coupling plate can be coupled with the pump bellows on the same axis without using a flange and a plurality of bolts, whereby the life period of the pump can be prolonged, the pump performance can be maintained for a long term, and compactification and cost reduction of the pump can be realized. It is a second object of the invention to provide a bellows pump in which a shaft that is to couple a pump bellows with a piston or a coupling plate can be coupled with the piston or the coupling plate on the same axis without using nuts and bolts in the piston or the coupling plate, whereby the life period of the pump can be prolonged, the pump performance can be maintained for a long term, and compactification and cost reduction of the pump can be realized. [0012] The bellows pump of the invention is a bellows pump that comprises a pump bellows which axially extends and contracts, which sucks a transported liquid by extension of the pump bellows from a suction port of a pump body into the pump bellows via a suction side check valve, and which discharges the transported liquid by contraction of the pump bellows from a discharge port of the pump body via a discharge side check valve, wherein one end side of a shaft can be directly coupled with a center portion of the pump bellows by thread joining. [0013] Specifically, the pump comprises a shaft which has an external thread on an external face on one side, the pump bellows has a bottomed cylindrical shape, and a bottomed cylindrical shaft screwed portion which is projected from a center portion of a bottom into the pump bellows on a same axis, and which has an internal thread on an inner face is disposed. [0014] Preferably, a recess is disposed in a center portion of the pump body, and the shaft screwed portion has a length at which a tip end side of the shaft screwed portion is always fitted into the recess of the pump body. [0015] When the pump bellows and the piston are to be coupled together by the shaft, preferably, an engagement head having a diameter which is larger than a diameter of the shaft is disposed in another end of the shaft, a center hole through which the shaft is to be passed in a center portion is disposed in the piston, the shaft is fitted into the center hole in a contracting direction of the pump bellows, and an annular sealing member which is made of an elastic material, such as an O-ring is attached to a portion of the shaft which is to be fitted into the center hole. Alternatively, the annular sealing member which is made of an elastic material may be attached to the center hole into which the shaft is to be fitted. More preferably, the center hole of the piston has a step which allows the other end of the shaft including the engagement head to be fitted into the hole. [0016] When the pump bellows and the coupling plate are to be coupled together by the shaft, preferably, an engagement head having a diameter which is larger than a diameter of the shaft is disposed in another end of the shaft, a center hole through which the shaft is to be passed is disposed in a center portion of the coupling plate, the shaft is fitted into the center hole in a contracting direction of the pump bellows, and an annular sealing member which is made of an elastic material such as an O-ring is attached to a portion of the shaft which is to be fitted into the center hole. Alternatively, the annular sealing member which is made of an elastic material may be attached to the center hole into which the shaft is to be fitted. BRIEF DESCRIPTION OF THE DRAWINGS [0017] FIG. 1 is a section view showing an internal structure of a bellows pump of a first embodiment of the invention; [0018] FIG. 2 is an enlarged view of a pump unit of the bellows pump of FIG. 1; [0019] FIG. 3 is a section view showing an internal structure of a bellows pump of a second embodiment of the invention; [0020] FIG. 4 is an enlarged view of one of pump units shown in FIG. 3; [0021] FIG. 5 is a section view showing an internal structure of a bellows pump of a third embodiment of the invention; and Continue reading about Bellows pump... Full patent description for Bellows pump Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Bellows pump 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. 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