Abstract:
An air displacement pipette having axially spaced annular sealing and frusto-conical lateral support zones and regions on the pipette&#39;s mounting shaft and tip, respectively, in combination with structure for insuring uniform depth of mounting shaft penetration into the pipette tip to maintain uniform tip interference with the mounting shaft as successive tips are mounted on and ejected from the mounting shaft whereby the pipette tip is easily and firmly mountable on and ejectable from the pipette tip mounting shaft by the application of reduced user generated axial forces.

Description:
RELATED APPLICATION 
     This application is a continuation-in-part application of U.S. patent application Ser. No. 09/188,032 filed Nov. 6, 1998, now abandoned assigned to the same assignee as the this patent application. 
    
    
     FIELD OF INVENTION 
     The present invention relates to improvements in pipettes and, more particularly, to air displacement pipettes including a unique pipette tip tailored to the distal end of the pipette&#39;s tip mounting shaft such that the tip is easily insertable by a pipette user onto the mounting shaft to a fluid tight position in which the tip is secured against undesired lateral rocking on or displacement from the shaft and, after use, is easily ejectable from the shaft by the pipette user. 
     BACKGROUND OF INVENTION 
     During the development of the unique pipette tip described in U.S. patent application Ser. No. 09/188,030, filed Nov. 6, 1998 now U.S. Pat. No. 6,197,259 and entitled “Easy Eject Pipette Tip” and the development of the novel pipette tip and tip mounting shaft combination described in U.S. patent application Ser. No. 09/188,031, filed Nov. 6, 1998 now U.S. Pat. No. 6,168,761 and entitled “Pipette With Improved Pipette Tip and Mounting Shaft”, both applications being incorporated herein by this reference, a special pipette tip and mounting shaft combination was discovered which provides for easier tip mounting, improved lateral tip stability and easier tip ejection than standard commercially available pipette tip and tip/shaft combinations. A brief description of the newly discovered pipette tip and mounting shaft combination is as follows. 
     SUMMARY OF INVENTION 
     The present invention incorporates in an air displacement pipette the concept of similar frusto-conical distal and proximal end portions on a pipette tip mounting shaft and pipette tip respectively. The frusto-conical distal and proximal end portions have substantially parallel inwardly and downwardly tapering surfaces incorporating axially spaced annular sealing and lateral support zones and regions on the mounting shaft and tip, respectively. Further, the present invention incorporates cooperative means on the shaft and tip for insuring uniform depth of mounting shaft penetration into the pipette tip to maintain uniform tip interference with the mounting shaft as successive tips are mounted on and ejected from the mounting shaft. 
     In particular, the present invention comprises a combination of a pipette tip mounting shaft and pipette tip in an air displacement pipette. The mounting shaft comprises an axially elongated body including a frusto-conical distal end portion having an axially tapering outer surface with annular axially spaced outer surface regions defining an annular sealing zone and an axially tapering annular lateral support zone. The pipette tip is an elongated tube comprising an open frusto-conical proximal end portion, an open conical distal end and annular axially spaced inner surface regions on the axially tapering frusto-conical inner surface of the proximal end portion defining an annular sealing region and an axially tapering annular lateral support region. The axial tapering of the mounting shaft and pipette tip are one and one-half degrees or more from the longitudinal axis of the shaft and preferably between one and one-half and five or six degrees. The outer diameter of the annular sealing zone on the mounting shaft is slightly greater than the inner diameter of the annular sealing region on the pipette tip and the sidewall of the tip in the area of the annular sealing region is sufficiently thin that the annular sealing region expands slightly to form an interference fit and air tight seal between the mounting shaft and the pipette tip when the sealing zone penetrates the sealing region. The axial spacing of the sealing and support zones is substantially equal to the axial spacing of the sealing and support regions. Also, the outer diameters of the mounting shaft in the axially tapering lateral support zone are slightly less than or substantially equal to corresponding inner diameters of the proximal end portion of the tip in at least some circumferential portions of the axially tapering lateral support region. This allows for some minimal contact between the support zone and region without creating a secondary air tight seal which would result in an undesired increase in the axial forces required to mount and eject the pipette on and from the shaft. With such a structural configuration, as the sealing zone penetrates the sealing region, the support region receives the support zone and provides lateral support therefor which prevents transverse rocking of the pipette tip on the mounting shaft as might otherwise occur during touching off of the pipette tip and an accompanying undesired dislodging of the tip from the shaft. 
     Further, the preferred embodiment of the present invention includes the aforementioned controlled interference air tight fit and mating annular lateral support zone and region as well as cooperative means on the pipette and pipette tip for limiting the axial travel of the tip on the mounting shaft. This insures uniform depth of mounting shaft penetration into the pipette tip to maintain uniform the desired tip interference with the mounting shaft as successive tips are mounted on and ejected from the mounting shaft. 
     Still further, for pipette tip and shaft combinations wherein the interference fit between the sealing zone and region is about 0.075 mm to about 0.2 mm and the wall thickness of the pipette tip in the sealing region is between 0.2 and 0.5 mm, it has been discovered that the desired minimal tip mounting and ejection forces associated with the present invention still may be achieved and the lateral stability of the tip on the shaft further enhanced when there is a small interference fit between the support region and zone. The small interference is provided by the lateral support region of the tip having an inner diameter which is slightly less than the outer diameter of the lateral support zone of the shaft, eg. less than 0.075 mm. Further, when the shaft and tip are concentric and substantially circular in the support zone and region, a secondary air tight seal may be created between the support zone and region without creating an undesired increase in the axial forces required to mount and eject the tip on and from the shaft. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a side view of a standard manual pipette having a pipette tip mounted on a mounting shaft adjacent a lower end of a tip ejector mechanism of the pipette. 
     FIG. 2 is a cross sectional side view of one embodiment of the pipette tip and mounting shaft combination of the present invention showing the fluid tight seal between the sealing region and sealing zone, the mating relationship of the lateral support region and zone and a preferred embodiment of the cooperative means including a shoulder on the pipette tip for limiting mounting shaft penetration into the tip. 
     FIG. 3 is an enlarged fragmentary section side view of the sealing region within the circle  3  for the pipette tip of FIG.  2 . 
     FIG. 4 is an enlarged fragmentary side view of an upper portion of the pipette tip and mounting shaft combination similar to FIG. 2 showing a first alternative embodiment of the cooperative means including a shoulder on the mounting shaft for limiting mounting shaft penetration into the tip. 
     FIG. 5 resembles FIG.  2  and shows an embodiment where the axial location of the sealing zone and region is reversed relative to the axial location of the support zone and region shown in FIG.  2 . 
     FIG. 6 resembles FIG.  4  and shows an embodiment where the axial location of the sealing zone and region is reversed relative to the axial location of the support zone and region shown in FIG.  4 . 
     FIG. 7 resembles FIG.  2  and is a cross sectional side view of an embodiment of the pipette tip and mounting shaft combination of the present invention showing the fluid tight seal formed by an interference fit between the sealing region and sealing zone, a small interference fit between the lateral support region and zone and a preferred embodiment of the cooperative means including a shoulder on the pipette tip for limiting mounting shaft penetration into the tip. 
     FIG. 8 is an enlarged fragmentary side view of an upper portion of the pipette tip and mounting shaft combination similar to FIG. 7 showing a first alternative embodiment of the cooperative means including a shoulder on the mounting shaft for limiting mounting shaft penetration into the tip. 
     FIG. 9 resembles FIG.  7  and shows an embodiment where the axial location of the sealing zone and region is reversed relative to the axial location of the support zone and region shown in FIG.  7 . 
     FIG. 10 resembles FIG.  8  and shows an embodiment where the axial location of the sealing zone and region is reversed relative to the axial location of the support zone and region shown in FIG.  8 . 
    
    
     DETAILED DESCRIPTION OF INVENTION 
     FIG. 1 illustrates a standard manual pipette resembling the PIPETMAN pipette sold exclusively in the United States by the Rainin Instrument Co. Inc., assignee of the present invention. The manual pipette is designated in FIG. 1 by the number  10  and includes a pipette tip ejector mechanism  12  described in U.S. Pat. No. 3,991,617 issued Nov. 16, 1976, which is incorporated herein by this reference. 
     The pipette  10  comprises a push button  14  connected by a rod  16  to a piston (not shown) located in the body or housing  18  of the pipette. The push button  14  may be depressed by a user exerting a downward force on the push button to cause downward movement of the piston of the pipette. When the push button  14  is released, a quantity of liquid to be sampled is sucked into a disposable pipette tip  20  releasably secured to a lower end of a pipette tip mounting shaft  22  of the pipette. The sample then may be transferred into another vessel by once more exerting a downward force on the push button  14 . After such use, it is common practice to eject the pipette tip  20  from the mounting shaft  22  and replace it with a new pipette tip for repeated operation of the pipette  10  in aspirating and dispensing a new sample fluid. 
     The pipette tip mechanism ejector  12  is employed to eject the tip  20  from the mounting shaft  22 . In this respect, the mechanism  12  comprises a push button  24  connected to a rod located in a passage (not shown) provided in an upper part of the hand holdable housing  18  of the pipette  10 . The passage and rod are arranged so as to be able to impart to the rod a movement of translation parallel to an axis of the pipette in opposition to a spring (not shown) normally urging the rod in an upward position. A removable tip ejector member or arm  26  including a tubular upper end extends from a lower end of the rod and from the rod follows the general exterior contour of the housing  18  of the pipette to terminate in a sleeve  28 . The sleeve  28  encircles a conical lower end  30  of the pipette tip mounting shaft  22  which tightly receives the upper end of the disposable pipette tip  20 . To eject the pipette tip  20  from the lower end of the mounting shaft  22 , a user grips the pipette housing  18  and using his or her thumb presses downward on the push button  24 . The downward force on the push button is translated by the rod to the tip ejector arm  26  and hence to the sleeve  28  which presses down on an upper end of the pipette tip. When the downward force transferred by the sleeve  28  exceeds the friction between the pipette tip  20  and the mounting shaft  22 , the pipette tip is propelled from the mounting shaft. Upon a release of the push button  24 , the spring returns the tip ejector mechanism  12  to its normal position with the sleeve spaced slightly from the upper end of a replacement pipette tip which is inserted onto the mounting shaft  22  readying the pipette  10  for its next aspiration and dispensing operation. 
     A preferred embodiment of the structure of the pipette tip and mounting shaft combination of the present invention is depicted in FIG.  2 . As there illustrated, the mounting shaft  32  comprises an axially elongated body including a frusto-conical distal end portion  34  having an outer surface which tapers axially inwardly from a main or upper portion of the shaft. The axially tapering outer surface of the distal end portion  34  comprises annular axially spaced outer surface regions defining an annular sealing zone  36  adjacent an upper end of the distal end  34  and an annular axially and downwardly and inwardly tapering lateral support zone  38  on the distal end portion  34  near the lower end of the mounting shaft  32 . 
     The pipette tip is represented by the numeral  40  and is an elongated plastic tube comprising an open frusto-conical proximal end portion  42 , an open conical distal end portion  44  and annular and axially spaced inner surface regions on the axially downwardly and inwardly tapering inner surface  43  of the proximal end portion  42  defining an annular sealing region  46  and an axially tapering annular lateral support region  48  for mating with the sealing and support zones  36  and  38  respectively, on the mounting shaft  32 . As illustrated, the frusto-conical inner surface of the proximal end portion  42  of the tip  40  is similar to and slightly larger than the frusto-conical outer surface of the distal end portion  34  of the shaft  32 . Also, in any axial vertical plane, the outer surface of the frusto-conical distal end portion of the shaft  32  is substantially parallel to the inner frusto-conical surface of the proximal end portion  42  of the tip  40 . As used herein, “substantially parallel” means that the outer surface of the axially tapering outer surface of the distal end portion  34  is within one and one-half degrees of the axial taper of the inner surface  43  of the proximal end portion  42  of the tip  40 . 
     FIG. 3 illustrates in enlarged detail a preferred embodiment of the sealing region  46  and comprises the portion of the pipette tip  40  of FIG. 2 within the circle  3 . As shown, the sealing region  46  is formed by an inwardly extending substantially V-shaped bead  49  extending radially inward from the sidewall  50  of the pipette tip  40 . The innermost surface of the bead  49  forms a very narrow annular sealing band or line for engaging the sealing zone  36  of the pipette tip mounting shaft  32  to form the previously described air-tight seal between the tip and mounting shaft. 
     As illustrated in FIG. 2, the outer diameter of the annular sealing zone  36  is slightly greater than the inner diameter of the annular sealing region  46  on the pipette tip  40  and the sidewall  50  of the tip in the area of the annular sealing region  46  is sufficiently thin that the annular sealing region expands slightly to form an interference fit and air tight seal between the mounting shaft  32  and the pipette tip  40  when the sealing zone  36  penetrates the sealing region  46 . In practice, it has been found that the desired interference fit is formed when the difference in the outer diameter of the annular sealing zone and the inner diameter of the annular sealing region is at least 0.075 millimeters (mm). Further, it has been found that in practice that the wall thickness of the pipette tip in the area of the sealing region  46  is preferably between 0.20 and 0.50 mm. 
     Also as illustrated in FIG. 2, the axial spacing of the sealing and support zones is substantially equal to the axial spacing of the sealing and support regions. Also, the outer diameters of the shaft  32  within the axially tapering lateral support zone  38  are slightly less than or substantially equal to corresponding inner diameters of the proximal end portion within at least some circumferential portions of the axially tapering lateral support region. This allows for some minimal contact between the support zone and region without creating a secondary air tight seal which would result in an undesired increase in the axial forces required to mount and eject the pipette tip on and from the shaft. With such a structural configuration, as the sealing zone  36  penetrates the sealing region  46 , the support region  48  receives the support zone  38  and provides lateral support therefor which prevents transverse rocking of the pipette tip  40  on the mounting shaft  32  as might otherwise occur during “touching off” of the pipette tip and an accompanying undesired dislodging of the tip from the shaft. In these regards, it is preferred that the axial spacing of the mating lateral support zone  38  and region  48  from the sealing zone and region ( 36 ,  46 ) is substantially equal to the inner diameter of the pipette tip  40  in the portion of the support region engaging the support zone. Such a length relationship provides excellent lateral stability for the pipette tip  40  on the mounting shaft  32 . 
     Further, as illustrated in FIG. 2, the present invention includes cooperative means  52  on the pipette of the present invention and the pipette tip  40  for limiting the axial travel of the tip on the mounting shaft  32 . This insures uniform depth of mounting shaft penetration into the pipette tip to maintain uniform tip interference with the mounting shaft as successive tips are mounted on and ejected from the mounting shaft. In the embodiment illustrated in FIG. 2, such cooperative means  52  comprises an annular, upwardly facing, inwardly directed shoulder  53  on the inner surface of the pipette tip  40  immediately adjacent the lateral support region  48 . The shoulder  53  is designed such that an upper surface thereof engages a downwardly facing surface such as the bottom  54  of the distal end  34  of the mounting shaft  32  at an outer circumferential portion thereof. 
     An alternate embodiment of the cooperative means  52  is depicted in FIG. 4 as comprising an outwardly directed downwardly facing annular shoulder  53 ′ on the pipette tip mounting shaft  32  which upon insertion of the shaft into the open proximal  42  of the tip engages the upper annular edge  56  of the tip to halt further penetration of the shaft into the tip. 
     While in the foregoing, particular preferred embodiments of the pipette tip of the present invention have been described and illustrated in detail, changes and modifications may be made without departing from the spirit of the present invention. For example, FIGS. 5 and 6 show alternative embodiments of the combinations illustrated in FIGS. 2 and 4 respectively wherein the axial location of the sealing zone  36  and region  38  is reversed relative to the axial location of the support zone  46  and region  48  respectively. 
     For further example, FIGS. 7,  8 ,  9  and  10  resemble FIGS. 2,  4 ,  5  and  6  respectively and show alternative embodiments of the present invention where there is a small interference fit between the lateral support region  48  and support zone  38  to further enhance the lateral stability of the tip  40  on the shaft  32  without introducing an undesired increase in the axial forces required to mount and eject the tip from the shaft. In this regard, and as illustrated in each of FIGS. 7-10, it has been discovered that for pipette tip and shaft combinations wherein the interference fit between the sealing zone  36  and region  46  is about 0.075 mm to about 0.2 mm and the wall thickness of the pipette tip in the sealing region  46  and in the lateral support region  48  is between 0.2 and 0.5 mm, the lateral stability of the tip  40  on the shaft  32  can be further enhanced while maintaining the desired minimal tip mounting and ejection forces associated with the present invention when their is a small interference fit between the support region and zone. The small interference is provided by the lateral support region  48  of the tip  40  having an inner diameter which is slightly less than the outer diameter of the lateral support zone  38  of the shaft  32 , eg. less than 0.075 mm. Further, when the shaft  32  and tip  40  are concentric and substantially circular in the support zone  38  and region  48 , a secondary air tight seal may be created between the support zone and region without creating an undesired increase in the axial forces required to mount and eject the tip on and from the shaft. 
     Accordingly, the present invention is to be limited in scope only by the terms in the following claims.