WO2008076817A1

WO2008076817A1 - Pipette seal

Info

Publication number: WO2008076817A1
Application number: PCT/US2007/087415
Authority: WO
Inventors: Robert J. Dubiel
Original assignee: Parker-Hannifin Corporation
Priority date: 2006-12-18
Filing date: 2007-12-13
Publication date: 2008-06-26

Abstract

A pipette with a low friction one-piece pipette seal that can reduce the amount of force required to actuate the pipette. The one-piece pipette seal does not suffer from the tolerance stacking issues that can effect other prior art seal assemblies. The pipette seal is also easily installed and/or replaced as a unit thereby making assembly and/or servicing of the pipette more efficient.

Description

PIPETTE SEAL

Related Applications

This application claims the benefit of U.S. Provisional Application No. 60/870,439 filed December 18, 2006, and U.S. Provisional Application No. 60/912,182 file on April 17, 2007, which are both hereby incorporated herein by reference in their entireties.

Field of the Invention The present invention relates to pipettes. More particularly, the present invention relates to a seal for a pipette.

Background of the Invention A pipette is a fluid handling device that is used to transfer fluids from one device to another, for analysis purposes, for example. One type of pipette that is particularly useful is a piston-driven air displacement pipette. Such pipettes can be used to transfer a precise quantity of fluid and are typically found, for example, in laboratories and research facilities.

A typical piston-driven air displacement pipette, herein referred to simply as a pipette, operates by generating a vacuum to draw fluid into a fluid chamber of the pipette. To dispense the fluid, a positive pressure is then generated to expel the fluid from the fluid chamber the pipette. In general, a piston-driven air displacement pipette includes a spring loaded plunger that drives a piston within a barrel to generate the vacuum and/or positive pressure. The piston of a pipette is typically depressed by finger action and returns by spring action. The primary components of the force that must be overcome to depress the plunger are the return spring force and frictional forces of the pipette seal acting on the piston. These forces are interrelated because the spring force must be, at a minimum, greater than the friction force exerted on the piston by the pipette seal in order to return the plunger to its starting position when released by an operator. For example, with very light springs the piston can become stuck in the middle of its travel. Thus, the greater the pipette seal friction force, the greater the return spring force needs to be to ensure the piston fully returns.

A primary concern in pipette design and use relates to the dispensing accuracy of a pipette over time. As pipette failure typically occurs gradually over time, such failure may not be detected and, thus, experiments and/or processes can be tainted. To address pipette failure, it is common practice to frequently test and/or calibrate pipettes to ensure continued fluid dispensing accuracy.

Failure of a pipette to accurately deliver an amount of fluid is often due to failure or degradation of the pipette seal. Conventional pipette seals typically consist of three components: an O-ring, a seal member, and a seal assembly holder that supports and/or retains the O-ring and seal member in the pipette. An example of a conventional pipette seal assembly is disclosed in U.S. Patent No. 6,926,867. In conventional pipettes, failure of the pipette seal can be attributed to a combination of wearing of the seal with repeated use (abrasion), separation of the seal from the piston over time due to "cold flow" or creep, and elasticity characteristics of the seal material. Also, pipette seals utilizing multiple components are subject to tolerance "stacking" that can result in the seals being less effective or require tighter production tolerances to ensure that the seal assembly functions effectively. Another concern when designing a pipette relates to the ergonomics of using these devices repeatedly through the course of a normal day. Of particular concern is the development of repetitive stress injuries, such as carpal tunnel syndrome, in operators of the devices.

Summary of the Invention

The present invention provides a pipette with a low friction one-piece pipette seal that can reduce the amount of force required to actuate the pipette.

The one-piece design does not suffer from the tolerance stacking issues that can effect other prior art seal assemblies. The pipette seal is also easily installed and/or replaced as a unit thereby making assembly and/or servicing of the pipette more efficient. Accordingly, a pipette comprises a barrel, a piston rod supported for axial movement within the barrel, and a one-piece pipette seal for sealing the piston rod to the barrel. The one-piece pipette seal has a body portion having a bore through which the piston rod can extend, an inner cylindrical surface of the bore being configured to seal against an outer surface of the piston. An annular end face of the pipette seal is configured to seal against an axial end face within the barrel.

More specifically, the bore through the body of the one-piece pipette seal can have a diameter that is less than the diameter of the piston rod when the piston rod is not extended into the bore such that when the piston rod is extended into the bore the bore expands radially. The annular end face of the one-piece pipette configured to seal against the axial end face within the barrel can be a resilient seal overmolded on the body.

The resilient seal, which can be made of a rubber material, can be overmolded in an annular recess in the body. At least a portion of the inner surface of the bore that seals against an outer surface of the piston rod is disposed radially inward from the annular groove such that when the resilient seal is compressed against the axial end face within the barrel the resilient seal applies pressure to the body in a manner that tends to constrict the bore against the piston rod. The body of the pipette seal can be made of polyethylene and the seal can be biased against the axial end face within the barrel.

In accordance with another aspect of the invention, a one-piece pipette seal for sealing a piston rod of pipette comprises a body portion having a bore through which the piston rod can extend, an inner cylindrical surface of the bore being configured to seal against an outer surface of the piston rod when extended therein, and an annular end face of the pipette seal configured to seal against an axial end face within a barrel of the pipette.

More specifically, the bore through the body of the one-piece pipette seal can have a diameter that is sized so that when a piston is extended into the bore, the bore expands radially. The annular end face of the one-piece pipette seal configured to seal against an axial end face within a barrel can be a resilient seal overmolded on the body portion. The resilient seal, which can be made of a rubber material, can be overmolded in an annular recess in the body portion. At least a portion of the cylindrical inner surface of the bore can be disposed radially inward from the annular groove such that when the resilient seal is compressed against an axial end face within a barrel, the resilient seal applies pressure to the body portion in a manner that tends to constrict the bore. The body portion of the one-piece seal can be made of polyethylene.

Further features of the invention will become apparent from the following detailed description when considered in conjunction with the drawings.

Brief Description of the Drawings

Fig. 1 is a cross-sectional view of an pipette in an un-depressed position with an exemplary seal in accordance with the invention.

Fig. 2 is a cross-sectional view the pipette of Fig. 1 in a partially depressed position. Fig. 3 is a cross-sectional view of the exemplary seal of Figs. 1 and 2.

Fig. 4 a cross-sectional view of pipette in an un-depressed position with another exemplary seal in accordance with the invention.

Fig. 5 is a cross-sectional view the pipette of Fig. 4 in a partially depressed position. Fig. 6 is a cross-sectional view of the exemplary seal of Figs. 4 and 5.

Detailed Description

Referring now to the drawings in detail and initially to Figs. 1 and 2, a pipette 10 for drawing a measured quantity of a fluid from a first, source location, transferring the fluid to a second location, and discharging the fluid at the second location is illustrated. The pipette 10 includes a pipette body 12 having a shaft portion 14 which extends from a tip (not shown) to a housing portion 16. The shaft portion 14 has a bore 18 that is coaxial with a cylindrical shaped cavity 20 of the housing portion 16. The diameter of the cavity 20 is greater than the diameter of the bore 18, forming a shoulder 22 at the junction of the shaft and housing portions 14 and 16. The pipette 10 also includes a piston rod 24 supported for axial movement within the body 12, and a plunger (not shown) connected to the piston rod 24 that extends from the body 12 and can be depressed by an operator.

In accordance with the invention, the piston rod 24 extends through a bore 26 in a body portion 30 of a one-piece pipette seal 28. An annular lower surface 34 of the pipette seal 28 is configured to seal against an axial end face of shoulder 22. The body portion 30 can be made of any suitable material, such as polyethylene or PTFE, for example. An inner cylindrical surface 32 of the bore 26 is configured to seal against an outer surface of the piston.

As will be appreciated, the bore 26 extending through the body 30 of the one-piece pipette seal 28 can have a diameter that is slightly smaller than the diameter of the piston rod 24. Thus, when the piston rod 24 is extended into the bore 26, the bore can expand slightly to accommodate the piston rod 24. The radial expansion of the bore 26 can facilitate a tight seal between the piston rod 24 and the body 30 of the one-piece pipette seal 28. In the illustrated exemplary embodiment, the annular end face of the one-piece pipette seal 28 that is configured to seal against the axial end face of shoulder 22 is a resilient rubber seal material overmolded on the body 30. The resilient seal 36 is overmolded in an annular recess 38 in the body 30 of the seal 28. At least a portion of the cylindrical inner surface 32 of the bore 26 that seals against an outer surface of the piston rod 24 is disposed directly radially inward from the annular recess 38. Thus, when the resilient seal 36 is compressed against the axial end face of the shoulder 22 as in Fig. 2, the resilient seal 36 is compressed and can apply pressure to the body 30 in a manner that tends to constrict the bore 26 against the piston rod 24 thereby facilitating and/or maintaining the seal therebetween.

The one-piece pipette seal 28 is biased against the axial end face of shoulder 22 by a spring 40. Spring 40 extends between a spring retainer 42 associated with the piston rod 24 and an annular spring groove 44 in the upper surface of the one-piece pipette seal 28. Accordingly, when the piston rod 24 is depressed the spring 40 is compressed thereby increasing the force applied to the axial end face of the shoulder 22 by the resilient seal 34. The spring retainer 42 may also contact an inner surface of the housing 12 to limit the extent that the piston rod 26 can be withdrawn from bore 18 (as shown in Fig. 1 ).

Referring to Fig. 2, the pipette 10 is shown in a partially depressed position. In this position, the piston rod is extended through the bore 26 in seal 28. The spring 40 is compressed thereby applying an increased force to the resilient seal 34 thereby sealing against the shoulder 22. As will be appreciated, in operation the plunger would be fully depressed to expel air from the shaft segment 14. Then, with the tip (not shown) inserted into a fluid to be transferred, the plunger would be released allowing the spring 40 to urge the piston rod 24 to withdraw from bore 18 back to the position of Fig. 1 thereby creating a suction force (vacuum) to draw the fluid into the pipette 10. To discharge the fluid, the plunger would be depressed again to thereby force the fluid from the tip.

It will be appreciated that the one-piece pipette seal 28 forms a seal to prevent fluid exchange between bore 18 and chamber 20. As mentioned, the slightly larger diameter of the piston rod 24 tends to radially expand the bore 26 by compressing the material of the body 30 to form a tight seal. Spring 40 applies force to the pipette seal 28 to compress resilient seal 36 against the axial end face of shoulder 22. It will be appreciated that as the resilient seal 36 is compressed against the axial end face of the shoulder 22, it tends to apply pressure to the surfaces of the annular groove 38 in the body 30. Because the annular groove 38 is disposed radially outwardly of the cylindrical surface 32 of the bore 26, the pressure applied to the surfaces thereof can act on the surfaces 32 of the bore 26 generally counter to the pressure applied to the surfaces 32 of the bore 26 by the piston rod 24. This pressure not only can further enhance the seal with the piston rod 24, but also can compensate for small changes in the dimensions of the bore 26 in the body 30 due to abrasion, creep, etc.

It will be appreciated that the resilient seal can be an overmolded rubber seal, for example. The resilient seal can also be molded such that it applies a force to the surfaces of the annular groove even when the pipette seal 28 is not compressed against the shoulder 22. By prestressing the body 30 in such fashion, the sealing surface 32 of the body 30 can be biased against the piston rod 24. This feature can lessen the amount of interference between the piston rod 24 and bore 26 needed to form an adequate seal and, thus, lessen the force required to actuate the pipette.

Turning now to Figs. 4-6, and initially to Figs. 4 and 5, a pipette 10 is illustrated with another exemplary one-piece pipette seal 28. The pipette 10 of Figs. 4 and 5 is similar to the pipette of Figs. 1 and 2 with the exception of the features of the one-piece pipette seal 28. As in the pipette seal of Figs. 1-3, the pipette seal 28 in Figs. 4-6 includes both a resilient seal material 36 and a body 30, as best seen in Fig. 6. The resilient seal material in this embodiment, which may be a rubber material overmolded on the body 30, is formed with a radially inwardly turned lip 72 for sealing against the piston rod 24.

As will be appreciated, in this embodiment the resilient seal material 36 seals against the piston rod 24 rather than the body 30 of the seal 28 as in the embodiment of Figs. 1-3. Thus, the lip 72 is generally configured to have an inside diameter that is slightly smaller than the outside diameter of the piston rod 24 to ensure a good seal when the piston rod 24 extends through the seal 28. A portion of the resilient seal material 36 can extend to seal against the axial end face of the shoulder 22 in a manner similar to that described in connection with Figs. 1-3. Alternatively, the body 30 of the seal 28 can be configured to seal against the barrel.

As the resilient seal material 36 is generally more flexible and/or compressible than the body 30, and typically not as prone to creep as the body 30, a more reliable seal with the piston rod 24 can be formed. Further, because the resilient seal material conforms to the piston rod 24, the body 30 need not interfere with the piston rod 24 to effect a seal which can reduce the amount of effort required to actuate the pipette 10.

It will now be appreciated that the one-piece pipette seals described herein reduce the amount of force required to actuate the pipette while also reducing the complexity of the sealing system relative to pipettes utilizing multiple component seal assemblies. Unlike conventional seal assemblies wherein the dimensions of the components (e.g., seal, o ring, assembly holder) combine to provide a final amount of interference between the piston rod and the sealing surface, the single piece construction of the invention avoids tolerance stacking and enables the potential for tighter controls as to the amount of force required for both aspiration and dispensing of fluids as compared to conventional seal assemblies. The one-piece designs also simplify assembly and/or rebuilding of pipettes by reducing the number of individual components that must be handled.

Although the invention has been shown and described with respect to a certain preferred embodiment or embodiments, it is obvious that equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In particular regard to the various functions performed by the above described elements (components, assemblies, devices, compositions, etc.), the terms (including a reference to a "means") used to describe such elements are intended to correspond, unless otherwise indicated, to any element which performs the specified function of the described element (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary embodiment or embodiments of the invention. In addition, while a particular feature of the invention may have been described above with respect to only one or more of several illustrated embodiments, such feature may be combined with one or more other features of the other embodiments, as may be desired and advantageous for any given or particular application.

Claims

What is claimed is:

1. A pipette comprising: a barrel; a piston rod supported for axial movement within the barrel; and a one-piece pipette seal for sealing the piston rod to the barrel; wherein the one-piece pipette seal has a body portion having a bore through which the piston rod can extend, an inner cylindrical surface of the bore being configured to seal against an outer surface of the piston; and wherein an annular end face of the pipette seal is configured to seal against an axial end face within the barrel.

2. A pipette as set forth in claim 1 , wherein the bore through the body of the one-piece pipette seal has a diameter that is less than the diameter of the piston rod when the piston rod is not extended into the bore such that when the piston rod is extended into the bore the bore expands radially.

3. A pipette as set forth in any one of claims 1 -2, wherein the annular end face of the one-piece pipette seal is configured to seal against the axial end face within the barrel is a resilient seal material overmolded on the body.

4. A pipette as set forth in any one of claims 1 -3, wherein the resilient seal is overmolded in an annular recess in the body.

5. A pipette as set forth in any one of claims 1 -4, wherein at least a portion of the inner surface of the bore that seals against an outer surface of the piston rod is disposed radially inward from the annular groove such that when the resilient seal is compressed against the axial end face within the barrel the resilient seal applies pressure to the body in a manner that tends to constrict the bore against the piston rod.

6. A pipette as set forth in claim in any one of claims 1-5, wherein the overmolded resilient seal is rubber.

7. A pipette as set forth in any one of claims 1 -6, wherein the one-piece pipette seal is biased against the axial end face within the barrel.

8. A pipette as set forth in any one of claims 1-7, further comprising a resilient seal material supported by the body for sealing against the outer surface of the piston.

9. A pipette as set forth in any one of claims 1 -8, wherein the resilient seal material includes a radially inwardly turned lip portion.

10. A pipette as set forth in claim in any one of claims 1-9, wherein the body is made of polyethylene.

11. A one-piece pipette seal for sealing a piston rod of pipette, comprising a body portion having a bore through which the piston rod can extend, an inner cylindrical surface of the bore being configured to seal against an outer surface of the piston rod when extended therein, and an annular end face of the body configured to seal against an axial end face within a barrel of the pipette.

12. A one-piece pipette seal as set forth in claim 11 , wherein the bore through the body of the one-piece pipette seal has a diameter that is sized so that when a piston is extended into the bore, the bore expands radially.

13. A one-piece pipette seal as set forth in any one of claims 11-12, wherein the annular end face of the body includes a resilient seal material supported by the body portion.

14. A one-piece pipette seal as set forth in any one of claims 11-13, wherein the resilient seal material is overmolded in an annular recess in the body portion.

15. A one-piece pipette seal as set forth in any one of claims 11-14, wherein at least a portion of the cylindrical inner surface of the bore is disposed radially inward from the annular groove such that when the resilient seal material is compressed against an axial end face within a barrel, the resilient seal material applies pressure to the body portion in a manner that tends to constrict the bore.

16. A one-piece pipette seal as set forth in any one of claims 11-15, wherein the resilient seal material is rubber.

17. A one-piece pipette seal as set forth in any one of claims 11-16, wherein the body portion is made of polyethylene.

18. A one-piece pipette seal as set forth in any one of claims 11-17, further comprising a resilient seal material supported by the body for sealing against the outer surface of the piston.

19. A one-piece pipette seal as set forth in any one of claims 11-18, wherein the resilient seal material includes a radially inwardly turned lip portion.