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Uniform flow displacement pumpRelated Patent Categories: Pumps, Expansible Chamber Type, Elongated Flexible Chamber Wall Progressively Deformed, Deformation By Rolling Or Sliding Engagement MemberUniform flow displacement pump description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070077158, Uniform flow displacement pump. Brief Patent Description - Full Patent Description - Patent Application Claims
[0001] This application is a continuation of U.S. Pat. No. 7,150,607, filed on Oct. 29, 2003, which claims the benefit of U.S. Provisional Application No. 60/427,468, filed Nov. 18, 2002. FIELD OF THE INVENTION [0002] The present invention relates to methods and systems for analyzing particles in a dilute fluid sample, and more particularly to pumps utilized by such systems to manipulate the fluid samples. BACKGROUND OF THE INVENTION [0003] Methods and systems for analyzing particles and particularly sediments are well known in the art, as disclosed in U.S. Pat. Nos. 4,338,024 and 4,393,466, which are incorporated herein by reference. Such systems utilize a flow cell though which fluid samples are passed, and a particle analyzer for capturing still frame images of the fluid passing through the flow cell. Thus, the flow cell positions and presents the sample fluid containing particles of interest for analysis. The more accurately that the sample fluid is positioned by flow cell, the better the analysis of the particles therein that can be made. [0004] Typical flow cells cause the sample fluid, and a sheath fluid that buffers the sample fluid, to flow together from a large entry chamber into a small cross sectional examination area or region. The transition from the inlet or entry chambers to the examination region forms a hydrodynamic lens that squeezes both the sample fluid and the sheath fluid proportionally into the smaller space. Where the particles of interest are microscopic particles, the resulting cross-sectional space occupied by the sample fluid must be positioned within the depth of field of the analyzer, such as an optical system or a laser system, to obtain the best analytical information. For the best hydrodynamic focus, a large area of sheath flow must envelop the small area of sample fluid without any swirling or vortices. Thus, uniform flow of sample and sheath fluids through the flow cell is essential for optimal operation of particle analyzers. [0005] Displacement pumps, (e.g. tubing or peristaltic pumps), are well known in the art and have been used to pump fluid samples and sheath fluids through flow cells. Conventional peristaltic pumps include multiple rollers that roll along flexible tubing containing fluid. The rollers push the fluid along the length of the tubing, drawing fluid into an input end of the tubing and forcing fluid out an output end of the tubing. A common configuration includes a rotating hub with rollers on its periphery, and an annularly shaped housing against which the tubing is pressed. With each rotation of the hub, each roller engages with, rolls along the length of, and disengages from, the tubing. At least one of the rollers is in contact with the tubing at all times so that fluid cannot flow backwards through the tubing. [0006] Conventional peristaltic pumps have several drawbacks. For example, multiple rollers engaging with and disengaging from the flexible tube cause pulsations in the fluid flow through the pump, which can be problematic for proper operation of flow cells. Moreover, the amount of fluid delivered by the pump for n degrees of rotation is dependent on the starting angle of the rollers. Most pump designs only retain the tube at its ends, relying on the multiple rollers engaged with tubing to hold it in its circular path along the housing. Thus, the tube can stretch and contract as the rollers move across its length, which again can cause varying flow and uncertainty in the volume moved by rollers. Lastly, when the pump is shut down, rollers are left in contact with the tube, causing compression setting (flat spotting) of the tube, which adversely affects the uniform flow of the fluid after the pump is activated again. [0007] There is a need for a displacement pump that provides uniform fluid flow of known and repeatable quantities, and which does not produce flat spots on the tube during non use. SUMMARY OF THE INVENTION [0008] The present invention is a pump that includes a compression surface, a hollow compression tube secured to the compression surface, and compression means for incrementally compressing the compression tube against the compression surface to create a moving occlusion of the compression tube that uniformly pushes fluid through the compression tube, wherein the compression means has at least one rest position in which the compression means does not compress the compression tube. [0009] In another aspect of the present invention, a pump includes a pump assembly and a cassette assembly. The pump assembly includes a pump housing that defines a cavity, a roller disposed in the cavity, and a motor for moving the roller relative to the housing. The cassette assembly is removably disposed in the cavity and includes a cassette housing having a compression surface, and a hollow compression tube secured to the compression surface. As the motor moves the roller, the roller presses the compression tube against the compression surface to create a moving occlusion of the compression tube for pushing fluid through the compression tube. [0010] Other objects and features of the present invention will become apparent by a review of the specification, claims and appended figures. BRIEF DESCRIPTION OF THE DRAWINGS [0011] FIG. 1A is an exploded view of the pump assembly of the present invention. [0012] FIG. 1B is a perspective view of the pump assembly of the present invention. [0013] FIG. 2A is an exploded view of the cassette assembly of the present invention. [0014] FIG. 2B is a perspective view of the cassette assembly (without compression tube) of the present invention. [0015] FIG. 2C is a perspective view of the cassette assembly of the present invention. [0016] FIG. 3 is a top view of an alternate embodiment of the present invention. [0017] FIG. 4 is a top view of a second alternate embodiment of the present invention. [0018] FIG. 5 is a side view of a third alternate embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [0019] The uniform displacement pump of the present invention is illustrated in FIGS. 1A-1B and 2A-2C, and includes a pump assembly 10 and a cassette assembly 12. Continue reading about Uniform flow displacement pump... Full patent description for Uniform flow displacement pump Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Uniform flow displacement 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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