The present invention relates to an air displacement apparatus and more particularly, to a liquid sealed air displacement apparatus for use in a fluid transfer device.
Fluid transfer devices (e.g., pipette mechanisms) are used to transfer small volumes of fluid in many applications. The devices may range from simple glass tubes to more elaborate mechanical displacement devices. In either case, the devices operate by displacing air and a seal is used to hold the displaced air, which facilitates the liquid transfer. Traditional devices use displacement pistons with mechanical seals such as lip seals or o-rings to prevent the air from entering the displacement chamber. These seals can be run dry, and wear eventually causes the seal to leak air and degrades accuracy of the device.
Accordingly, there is a need for a sealed air displacement apparatus that substantially prevents air leakage and that is capable of running longer without wear or leakage.
These and other features and advantages will be better understood by reading the following detailed description, taken together with the drawings wherein:
Referring to
The fluid receiving member 104 may be removably coupled to the air displacement apparatus 102. The fluid receiving member 104 includes a fluid passage or channel that is capable of receiving a volume of fluid and is in communication with the air displacement chamber. Examples of the fluid receiving member 104 include, but are not limited to, a cannula, plastic tubing, a conical pipette tip, or a stainless nozzle. Those skilled in the art will recognize that various types of fluid receiving members may be coupled to the air displacement apparatus 102 for use in various types of applications.
Referring to
The sealing fluid in the clearance 116 between the piston 110 and the cylinder 112 prevents air from entering the displacement chamber 114 formed when the piston 110 is retracted. The sealing fluid may be a silicone oil or other similar fluid. Those skilled in the art will recognize other types of sealing fluid that are capable of sealing the clearance 116 and that are capable of remaining within the clearance 116.
The air displacement apparatus 100 may also include a linear actuator 120 and a coupling 122 between the linear actuator 120 and the piston 110. The coupling 122 may be coupled directly to a drive shaft 121 of the linear actuator 120. The linear actuator 120 may be a lead screw driven captive shaft linear actuator, such as the type available from Hayden Switch & Instrument, Inc. as part no. P28H49-2.1-001. The coupling 122 may be a floating coupling that compensates for angular and lateral misalignment when driving the close clearance ceramic piston/cylinder components.
A compression spring 124 may be positioned against the piston 110 biasing the piston away from the cylinder 120 to compensate for axial backlash, which may be present in the coupling 122 and/or the lead screw in the linear actuator 120. According to one embodiment, the piston 110 may include a piston cap 126 having at least two diameters. The spring 124 may be captured between the piston cap 126 and the cylinder 112 such that the spring 124 is under compression (e.g., approx. 2 lbs.) when the piston 110 is fully inserted into the cylinder 112. The piston cap 126 may be made of metal and may be attached to the piston 110 by interference fit, adhesive bonding, or other mechanical fastener. The coupling 122 may be coupled to the piston cap 126 using a threaded stud 127 and lock-nut 128.
A housing 130 may be coupled to the linear actuator 120 and may enclose at least the piston 110, the cylinder 112, the coupling 122, and the spring 124. The linear actuator 120 may be coupled to one end 132 of the housing 130, for example, using fasteners 134. The cylinder 112 may be rigidly mounted within the other end 136 of the housing 130. The piston 110 and the coupling 122 may be located within the housing 130 in a manner that allows the piston 110 and the coupling 122 to move axially within the housing 130. Although the housing 130 is shown as generally cylindrical, the housing may have other shapes and configurations.
A port fitting connector 140 may be located at the other end 136 of the housing 130, for example, adjacent to the cylinder 112. The end of the cylinder 112 may be sealed with a static o-ring 142 held against the port fitting connector 140. The port fitting connector 140 may include a port passage 144 that provides fluid communication between the displacement chamber 114 and the fluid passage in the fluid receiving member 104. The fluid receiving member 104 may be coupled to the port fitting connector 140, for example, using a commercially available gas tight fitting. One exemplary embodiment of the port fitting connector 140 may include a ¼-28 flat bottom boss 148, although a wide variety of fluid connections may be used. The port fitting connector 140 may allow the fluid receiving device 104 to be easily changed without tools. Those skilled in the art will recognize that various types of commercially available or custom-designed port fitting connectors may be used for different applications.
The port fitting connector 140 may be retained against the cylinder 112 with a cap 150 that engages the end 136 of the housing 130. One embodiment of the cap 150 may threadably engage a straight thread on the end 136 of the housing 130. The cap 150 may include a clearance hole 152 in the center such that the port fitting connector 140 protrudes through the clearance hole 152. The cap 150 may thus secure both the port fitting connector 140 and the cylinder 112 to the housing 130.
According to one embodiment of the piston and cylinder arrangement, shown in
One method of operation of the air displacement apparatus is described in reference to
In use in a fluid transfer application, the fluid receiving member 104 may be coupled to the port fitting connector 140. The piston 110 usually starts in its fully inserted position (as shown in
The movement of the piston 110 may be precisely controlled by the linear actuator 120 to control the volume of fluid that is drawn into the fluid receiving member 104 and the volume of fluid that is dispensed from the fluid receiving member 104. Embodiments of the fluid transfer device 100 may be capable of total volumes in a range of 20 μL to 200 μL and resolutions in a range from 0.02 μL/Full Step to 0.20 μL/Full Step. The exemplary embodiment of the air displacement apparatus 100 is capable of running for millions of cycles without wear or leakage.
Consistent with one aspect of the present invention, a liquid sealed air displacement apparatus includes a linear actuator, a piston coupled to the linear actuator and a cylinder defining a displacement chamber for receiving the piston. The piston causes displacement of air when the piston retracts from the displacement chamber in the cylinder. The piston and the cylinder define a clearance configured to receive a sealing fluid. The clearance is configured with a dimension to substantially maintain the sealing fluid between the piston and the cylinder. The sealing fluid is received in the clearance between the piston and the cylinder and substantially prevents air leakage into the displacement chamber.
Consistent with another aspect of the present invention, a liquid sealed air displacement apparatus includes a linear actuator, a floating coupling coupled to the linear actuator, a piston coupled to the floating coupling, and a cylinder defining a displacement chamber for receiving the piston. The piston causes displacement of air when the cylinder retracts from the displacement chamber in the cylinder. The piston and the cylinder define a clearance configured to receive a sealing fluid, and the clearance is configured with a dimension to substantially maintain the sealing fluid between the piston and the cylinder. The apparatus may also include a compression spring configured to bias the piston away from the cylinder and a port fitting connector coupled to an end of the cylinder. A housing holds at least the linear actuator, the piston, the cylinder, the floating coupling, and the compression spring.
Consistent with a further aspect of the present invention, a fluid transfer device includes a piston configured to be coupled to a linear actuator and a cylinder defining a displacement chamber for receiving the piston. The piston causes displacement of air when the cylinder retracts from the displacement chamber in the cylinder. The piston and the cylinder define a clearance configured to receive a sealing fluid, and the clearance is configured with a dimension to substantially maintain the sealing fluid between the piston and the cylinder. The sealing fluid is received in the clearance between the piston and the cylinder to substantially prevent air leakage into the displacement chamber. The fluid transfer device also includes a fluid receiving member coupled to an end of the cylinder. The fluid receiving member includes a fluid passage in communication with the air displacement chamber such that retraction of the piston creates suction in the displacement chamber causing a fluid to be drawn into the fluid passage.
Consistent with yet another aspect of the invention, a liquid sealed air displacement apparatus includes a piston configured to be coupled to a linear actuator and a cylinder defining a displacement chamber for receiving the piston with a clearance between the piston and the cylinder. The piston causes displacement of air when the cylinder retracts from the displacement chamber in the cylinder. The cylinder includes an inner wall defining an annular groove configured to receive a sealing fluid. The clearance and the annular groove are configured with a dimension to substantially maintain the sealing fluid between the piston and the cylinder. The sealing fluid is received in the clearance and the annular groove between the piston and the cylinder to substantially prevent air leakage into the displacement chamber.
While the principles of the invention have been described herein, it is to be understood by those skilled in the art that this description is made only by way of example and not as a limitation as to the scope of the invention. Other embodiments are contemplated within the scope of the present invention in addition to the exemplary embodiments shown and described herein. Modifications and substitutions by one of ordinary skill in the art are considered to be within the scope of the present invention, which is not to be limited except by the following claims.
This application claims the benefit of co-pending U.S. Provisional Patent Application Ser. No. 60/565,108, filed on Apr. 23, 2004, which is fully incorporated herein by reference.
Number | Date | Country | |
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60565108 | Apr 2004 | US |