Abstract:
A volume adjustable pipette, comprising a plunger mounted for movement in a housing to and from a stop to aspirate a fluid into and dispense the fluid from a tip extending from the housing. The movement of the plunger is damped to reduce sudden plunger movements. An axially moveable volume setting member in the housing defines the stop and a volume setting for the pipette and is axially moveable by a user turnable volume setting member. Turning of the volume adjusting member also controls a coarse volume setting means and a fine volume setting means, the course volume setting means being responsive to a relatively small turning of the volume adjusting member for moving the volume setting member a relatively large axial distance and the fine volume setting means being responsive to a relatively large turning of the volume adjusting member for moving the volume setting member a relatively small axial distance.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to volume adjustable manual pipettes and, more particularly, to a manually-operated pipette equipped with a quickly settable volume adjustment mechanism and a plunger having damped axial movement. 
     U.S. Pat. No. 3,827,305 (“the &#39;305 patent”) describes one of the earliest commercially available digitally adjustable air displacement pipettes. To provide for volume adjustment, the pipette includes a threaded shaft extending through a fixed nut. Manual turning of the shaft produces axial movement of a stop member for limiting axial movement of a plunger to define a volume setting for the pipette. The volume setting is displayed on a mechanical micrometer display comprising a series of indicator rings each encircling the threaded shaft. 
     U.S. Pat. No. 4,909,991 describes a later commercially available single channel manual pipette manufactured by Nichiryo Co. Ltd., Tokyo, Japan. The Nichiryo pipette includes an elongated hand-holdable housing for an upwardly spring biased plunger. An upper end of the plunger extends above a top of the housing and carries a control knob for thumb and finger engagement in manually turning the plunger and for axially moving the plunger in the pipette housing between an upper stop and a lower stop at which all liquid within a tip secured to a lower end of the housing is expelled by the downward movement of the plunger. The upper stop is axially adjustable within the housing in response to a turning of a hollow volume adjustment screw or shaft keyed to the plunger. The axial adjustment of the upper stop adjusts the volume of liquid that the pipette is capable of drawing into the tip in response to upward movement of the plunger to the upper stop. The pipette also includes a lock mechanism including a lock knob for locking the plunger against rotation to thereby set the upper stop in a fixed position and hence set the volume adjustment for the pipette. 
     For a more complete understanding of the current state of the art relative to the volume adjustability of manual pipettes, each of the above-identified patents is incorporated by reference into this application. 
     In each of the foregoing prior manual pipettes, volume setting requires the repeated turning of either the threaded volume setting shaft or the turning of the displacement plunger of the pipette while viewing the volume display of the pipette. Where successive volume setting for a pipette are of values of considerable difference, appreciable time and physical effort are required to accomplish the volume settings. 
     Thus, one of the shortcomings of prior manual pipettes is the time, physical effort and care required to accurately manually set the volume of such pipettes. In an attempt to reduce the time required to change the volume settings of a manual pipette, the Socorex Micropipette Calibra 822 includes a volume setting mechanism including two cylindrical cams. A larger one of the cams shows numbers on a left side of a window of a mechanical volume display for the pipette while a smaller one of the cams shows numbers on a right side of the window. After locking of a plunger-button of the pipette, a turning of a setting wheel turns the larger cam to change the numbers displayed thereby. Then a pulling out of the setting wheel followed by a turning thereof produces a turning of the smaller cam and numbers displayed thereby. Such turning of the cams sets mechanical stops within the pipette to control the volume of liquid, which the pipette will aspirate and dispense. While the volume setting structure of the Calibra pipette may reduce the time required to set the volume of a manual pipette, the volume setting structure is relatively complex and costly when compared to conventional manual pipette volume setting mechanisms as described above. Also, the volume setting provided by the Calibra pipette is not as fine a setting as is provided by conventional volume setting mechanisms. 
     U.S. Pat. No. 6,428,750 issued Aug. 6, 2002 to the assignee of the present invention (“the &#39;750 patent”), and U.S. Pat. No. 7,175,813 issued Feb. 13, 2007 also to the assignee of the present invention (“the &#39;813 patent”), describe an improved volume adjustable manual pipette having a quick set volume adjustment mechanism and a plunger position sensor. The volume setting of the pipette is monitored by the sensing and control circuitry to provide a real time display of the volume setting of the pipette on the electronic digital display. 
     In particular, the &#39;813 patent describes a manual handheld pipette capable of being adjusted with both coarse and fine volume setting capabilities, capable of being adjusted by sequentially turning a single volume adjustment member. This pipette has been found to be particularly easy and intuitive to use, as no tools are necessary to make coarse or fine volume adjustments, and only a single control need be handled, as in traditionally adjustable pipettes. 
     The quick set feature in the &#39;750 and &#39;813 patents referenced above represents a considerable advance in the art of manual pipettes. However, it has been found that when volume settings are advantageously adjusted with small and relatively easy movements, the stability of the volume setting becomes less resistant to drift and more susceptible to bumps and accidental movements. 
     There is a continuing need for a volume adjustable manually operated pipette including a quickly and easily adjustable volume setting mechanism that remains stable when perturbed. A pipette with a reliable mechanism capable of changing the volume setting relatively rapidly and without unnecessary manipulation would enable enhanced functionality over traditional manually operated pipettes. 
     SUMMARY OF THE INVENTION 
     Accordingly, a manually operated pipette according to the invention addresses the shortcomings of presently commercially available handheld pipettes, and adds additional functionality not practicable using traditional manual pipettes. 
     Manual pipettes have continued to be popular systems of choice due to their lower cost and ultimate control that the user has in choosing how to manually push the plunger down. Traditional manual pipettes, however, can be tedious to adjust, requiring up to twenty turns (and typically eighteen turns) of the wrist from minimum to maximum volume, or vice versa. The pipette according to the invention requires as little as two and one half turns in one embodiment to adjust the volume setting the same amount, and such a pipette can be set just as accurately and precisely as traditional manual pipettes. 
     The volume adjustable pipette of the present invention comprises a plunger mounted for movement in a housing to and from a stop to aspirate a fluid into and dispense the fluid from a tip extending from the housing. An axially moveable volume setting member in the housing defines the stop and a volume setting for the pipette and is axially moveable by a user turnable volume adjusting member. Turning of the volume adjusting member also controls a coarse volume setting means and a fine volume setting means. The coarse volume setting means is responsive to a relatively small turning of the volume adjusting member for moving the volume setting member a relatively large axial distance while the fine volume setting means is responsive to a relatively large turning of the volume adjusting member for moving the volume setting member a relatively small axial distance. Thus, the present invention provides a rapid setting of the volume of a pipette simply by sequential turning of a volume adjusting member. 
     In a pipette according to the present invention, the movement of the plunger is damped to reduce the occurrence of sudden, abrupt changes in the piston position driven primarily by the spring-biased piston being accidentally released by the user, for example when the user&#39;s thumb is quickly removed from the plunger button while the plunger button is depressed. The plunger mechanism may then impact the volume setting mechanism, overcoming a user-actuated frictional lock intended to keep the volume setting in place. The damped plunger reduces the tendency of the volume setting mechanism to drift under such adverse (but occasionally expected) circumstances. 
     One embodiment of a pipette according to the present invention is provided with a real-time electronic sensor, a low-power microcontroller, and a simple yet flexible user interface. The electronic sensor permits the position of a piston to be sensed and communicated to the user in real time via a user interface, and for the volume setting of the pipette to be read reliably without any dependence on a mechanical link between the interface and the coarse and fine volume setting means. 
     In an embodiment of the invention, a processor integral with the pipette not only allows the volume setting and the real-time piston position to be communicated to the user via a display, it further allows various calculations to be performed on the piston position, including the advantageous use, communication, and manipulation of liquid volume measurements, pipetting technique analysis, use observation and auditing consistent with preferred laboratory practices, performance optimization, calibration offsets, multi-point non-linear calibration, and cycle counting, as set forth in U.S. patent application Ser. No. 11/906,180, filed on Sep. 27, 2007 and published on Jan. 1, 2009 as Publication No. 2009/0000351, which is hereby incorporated by reference as though set forth in full herein. 
     As described herein, the invention is particularly applicable to air-displacement pipettes, though it should be noted that the structures and functions described herein are also applicable to positive-displacement pipettes. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other objects, features, and advantages of the invention will become apparent from the detailed description below and the accompanying drawings, in which: 
         FIG. 1  is an external view of a quick-set pipette according to the invention, with a disposable tip mounted to a liquid end of the pipette; 
         FIG. 2  is an enlarged external view of the quick-set pipette of  FIG. 1 , illustrating the functionality of a volume-setting mechanism according to the invention; 
         FIG. 3  is a simplified external view of the quick-set pipette of  FIG. 1 ; 
         FIG. 4  is a schematic view illustrating a rigid linkage between a plunger assembly and a sensor assembly of the pipette of  FIG. 3 ; 
         FIG. 5  is a schematic view illustrating a portion of the pipette of  FIG. 3  with a plunger assembly in a released position against an upper stop; 
         FIG. 6  is a schematic view illustrating a portion of a pipette of  FIG. 3  with a plunger assembly in a partially-depressed home position; 
         FIG. 7  is a schematic view illustrating a portion of a pipette of  FIG. 3  with a plunger assembly in a fully-depressed blowout position; 
         FIG. 8  is a view of a user interface display in a quick-set pipette according to the invention with a volume setting lock in an unlocked condition; 
         FIG. 9  is a view of a user interface display in a quick-set pipette according to the invention with a capacity set to an exemplary value of 123.6 microleters; 
         FIG. 10  is a view of a user interface display a user interface display in a quick-set pipette according to the invention in a tracking mode with the pipette piston in a position representing an exemplary value of 25.8 microleters of capacity; 
         FIG. 11  is a cutaway view of a volume adjustment mechanism in a quick-set pipette according to the invention; 
         FIG. 12  is a view of an exemplary intermediate sleeve of a volume adjustment mechanism in a quick-set pipette according to the invention; 
         FIG. 13  is a view of an exemplary inner sleeve of a volume adjustment mechanism in a quick-set pipette according to the invention; and 
         FIG. 14  is a view of an assembly comprising an intermediate sleeve and an inner sleeve of a volume adjustment mechanism in a quick-set pipette according to the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention is described below, with reference to detailed illustrative embodiments. It will be apparent that a system according to the invention may be embodied in a wide variety of forms. Consequently, the specific structural and functional details disclosed herein are representative and do not limit the scope of the invention. 
     Referring initially to  FIG. 1 , an overview illustration of a handheld quick-set pipette  110  according to the invention is presented. In general configuration, the quick-set pipette  110  is similar to a traditional pipette, in that a user grips a handheld body  11   2  of the pipette  110  and manipulates a spring-loaded plunger button  114  to control the intake and discharge of fluids through a disposable tip  116 , which is coupled to a liquid end  118  of the pipette  110 . 
     As in traditional air displacement pipettes, the plunger button  114  operates a piston configured to displace air within the liquid end  118 ; movement of air causes a corresponding movement of a liquid, provided an air-tight seal is present between the tip  116  and the liquid being handled, between the tip  116  and the liquid end  118 , and between the piston and a seal (as illustrated in  FIG. 4  and described below). 
     The quick-set pipette  110  further includes a tip ejector  120  mounted for longitudinal movement over the liquid end  118  and coupled to a tip ejector button  122 . After the tip  116  is mounted to the pipette  110  and used, it can be ejected and disposed of by depressing the ejector button  122 ; this functionality is again comparable to the functionality of traditional pipettes. 
     Where the disclosed embodiment of the quick-set pipette  110  begins to differ from traditional handheld pipettes, however, is in the presence of a user interface  124  including an electronic display  126  and button panel  128 . In the pipette  110  according to the invention, the display  126  and button panel  128  add very little weight to the pipette, are easily operated, and enable improved performance and added functionality to the pipette  110  that are not generally practical with traditional pipettes. These differences will be discussed in further detail below. It should be noted, however, that an alternative embodiment of a quick-set pipette according to the invention may be made as described herein without any electronic features whatsoever, and accordingly no electronic display  126  and no button panel  128 . The utility of such an alternative embodiment may well be limited, however, as there would be no electronic display to indicate the volume setting for the pipette, and a mechanical volume counter (such as found in traditional handheld pipettes) would be difficult to implement. 
     As shown in  FIG. 2 , the disclosed user interface  124  is designed and configured to be intuitive and easy to use. In the disclosed embodiment, the display  126  is a small LCD  230 , and the button panel includes a “MODE” button  232 , a “CC” (cycle count) button  234 , and a recessed “OPTION” button  236  accessible via a small opening  238 . As will be discussed in further detail below, the MODE button  232  is generally used to scroll through pipette operating modes and CC button  234  operates the cycle counter. The recessed OPTION button  236  is generally used to access an options menu, which gives access to advanced features and capabilities of the quick-set pipette  110 . 
     The user interface further includes a piston plunger shaft  240  upon which the plunger button  114  is mounted, which also serves as a volume-setting knob when rotated as indicated by the arrows  242  and a volume set lock lever  244 . The volume set lock lever is movable from a left-most unlocked position  246  and a right-most locked position as indicated by an arrow  248 . In the left-most unlocked position  246 , the plunger button is free to rotate and change the volume of the pipette  110 , as in traditional pipettes, while in the right-most locked position (arrow  248 ) the plunger button is restricted from rotational motion (hence fixing the volume) but still permitted to be pushed by the user&#39;s thumb to control the intake and discharge of liquids as desired by the user. The design and operation of the locking apparatus is set forth in U.S. Pat. No. 5,849,248, owned by the assignee of the present invention, which is hereby incorporated by reference as though set forth in full. Mechanisms of this sort are commonly known. 
     As is visible in the simplified drawing of  FIG. 3 , a finger hook  310  is further provided to allow the user to maintain a light grip on the body  112 . The plunger button  114 , the plunger button shaft  240 , the pipette body  112 , and the liquid end  118  are all coaxial with respect to a centerline  312 , thereby permitting a single linkage  410  ( FIG. 4 ) between the plunger button and the operative portion of the pipette  110  in the liquid end  118  that operates without substantial slack or backlash. And, because the mass of the pipette  110  is centered around the centerline  312 , and the display  126  and button panel  128  above the finger hook  310  contain very little mass, the quick-set pipette  110  according to the invention remains as easy to handle as a traditional pipette. 
     The linkage  410 , as illustrated functionally in  FIG. 4 , enables the plunger button  114  to act directly through the plunger button shaft  240  to a piston  412 , which maintains an air-tight seal with the liquid end  118  via a seal  413 . The seal  413  remains in a fixed position with respect to the liquid end  118  and further forms an air-tight seal with respect to an interior portion of the liquid end  118 . Accordingly, as the plunger button  114  is manipulated, the piston  412  is caused to move through the seal  413  and displace an air volume within the liquid end. As an orifice  150  ( FIG. 1 ) is provided at a distal end of the tip  116 , and a substantially air-tight seal is maintained at all other places, the only path for a liquid (or any fluid) to enter or exit the tip  116  is via the orifice  150 , and there is a deterministic relationship between the volume of air displaced by the piston  412  and the volume of liquid manipulated by the pipette  110 . As will be discussed in further detail below, this relationship between air displacement and liquid manipulation is generally linear but subject to some correction. Traditional handheld manual pipettes treat the relationship as exactly linear with a correctable zero offset. 
     The coaxial linkage  410  and connection between the plunger button  114  and the piston  412  enables a position sensing transducer  414  to be connected thereto, allowing the precise and specific position of the plunger button  114  (and hence the tightly coupled piston  412 ) to be determined at all times. The position sensing transducer  414  is small in size and requires very little battery power to operate. Accordingly, a handheld quick-set pipette  110  according to the invention has a comparable feel to traditional manual pipettes, and any battery used to power the position sensing transducer  414  and the display  126  can be quite small. In the disclosed embodiment, a protruding portion  415  of the pipette body  112  ( FIG. 1 ) between the display  126  and the finger hook  310  ( FIG. 3 ) houses a primary (i.e. non-rechargeable) button-cell battery sufficient to power a pipette  110  according to the invention for at least several months, though it will be recognized that rechargeable batteries and other battery form factors may also be employed, or the pipette  110  may be powered from an external source. 
     As illustrated, the position sensing transducer  414  includes two components: a sliding component  416  affixed to and moving with the piston plunger shaft  240 , and a fixed component  418  affixed to the pipette body  112 . Accordingly, then, the position sensing transducer  414  is able to detect and calculate the longitudinal displacement between the sliding component  416  and the fixed component  418 . It will be recognized that there are numerous configurations of sensing components that can accomplish this function, including but not limited to a variable resistor (potentiometer), an optical sensor, a capacitive sensor, an inductive sensor, or a magnetic field sensor; these options are discussed in detail in U.S. patent application Ser. No. 11/906,180, incorporated by reference above. There are advantages to keeping the sliding component  416  passive and not directly energized, thereby eliminating the need to provide any electrical connection to the moving part, which might tend to bend, break, or otherwise fail over the course of time. 
     As in traditional manual pipettes, the plunger button  114  ( FIG. 1 ) is spring-biased relative to two positions, namely a released and extended position  510  shown in  FIG. 5 , and a home position  610  shown in  FIG. 6 . With no pressure applied to the plunger button  114 , a plunger spring  420  ( FIG. 4 ) biases the plunger button  114  upward against an upper volume-setting stop, the position of which is adjusted by turning the plunger button  114  and a stop position adjustment mechanism as discussed above. In this position, the piston plunger shaft  240  and plunger button  114  are at the released and extended position  510  with respect to the body  112  of the pipette  110  as graphically illustrated in  FIG. 5 . 
     At the fixed home position  610  illustrated in  FIG. 6 , with the plunger button  114  partially depressed, the resistance to depression of the plunger button increases. As is common in handheld pipette construction, a secondary blowout spring adds to the resistance offered by the plunger spring  418 . The increased resistance is sensed by the pipette user and defines the home position  610 . Between the released and extended position  510  and the home position  610 , only the plunger spring  420  biases the plunger button position upward toward its extended position  510 , and a relatively light first force level is required to act against the spring bias. Between the home position  610  and a fully-depressed blowout position  710  illustrated in  FIG. 7 , both the plunger spring  420  and the blowout spring act upward against the plunger button  114 , and a higher second force level is required to act against the spring bias. This configuration including a primary plunger spring  420  and a secondary blowout spring is common in handheld pipettes. 
     Accordingly, at the home position  610 , the user feels a tactile transition between the two spring forces, and by exerting a force between the first level and the higher second level, the user can easily keep the plunger button at the home position. As will be discussed in further detail below, the ability of the user to identify and maintain the piston  412  at the home position  610  is a requirement for certain desirable pipetting operations. 
       FIGS. 8-10  set forth illustrative aspects of the user interface display  126  of one embodiment of a quick-set pipette  110  ( FIG. 1 ) according to the invention, when such a user interface display is present. 
     Initially, and as shown in  FIG. 8 , the user slides the volume set lock lever  244  ( FIG. 2 ) to an unlocked position  246  to allow the pipette  110  to be adjusted. The volume set lock lever  244  is equipped with a lock state switch that indicates the state of the lock to a processing unit contained in the pipette  110 . In an embodiment of the invention, the processing unit comprises a low-power microcontroller capable of running on a small battery for long periods of time, and further capable of operation in a very-low-power “sleep” state while the pipette  110  is not being used. The MSP430 series of ultra-low-power microcontrollers from Texas Instruments Inc. includes integrated circuits that meet these needs, many of which further provide additional digital and mixed-signal system-on-a-chip functionality that can be advantageously employed in a quick-set pipette  110  according to the invention; other vendors also have products that might easily be substituted. 
     In certain operating modes, while the volume set lock lever  244  is in its unlocked position  246 , the display  126  displays a flashing “UNLOCKED” indication  810  and the currently set volume of the pipette  812 , which in the illustration is 123.6 microleters. By turning the plunger button  114 , sequentially actuating coarse volume adjustment and fine volume adjustment mechanisms as described below (with reference to  FIGS. 11-14 ), the user can adjust the position of the upper volume-setting stop as in traditional pipettes. However, because the plunger button  114  is spring-biased to its extended position  510  against the adjusted upper volume-setting stop, the display  126  will be updated with the position of the piston  412  as it moves with the stop. In any event, any volume reading obtained while adjusting the volume of the pipette  110  can only be considered accurate if no longitudinal pressure is being applied to the plunger button  114 . 
     When the user locks the volume setting by sliding the volume set lock lever  244  to the locked position  248 , a lock state switch actuates, causing the “UNLOCKED” indication to disappear from the display  126  and as illustrated in  FIG. 9  the display  126  displays the fixed volume setting  910  regardless of the position of the piston  412 . The display  126  is decoupled from the real-time position of the piston  412 , allowing the user to determine the capacity of the pipette at a glance, regardless of what stage of pipetting the user is engaged in. Of course, it will be observed that the processing unit still receives measurements of the position of the piston  412 ; they are simply not being displayed. 
     When the volume set lock lever is actuated, an accurate and precise measurement is taken of the position of the piston  412  and calibrated by the processing unit as set forth in greater detail below. Because of the tight coupling among the plunger button  114 , the sliding component  416  of the position sensing transducer  414 , and the air displacement piston  412 , and further because of the capability of the position sensing transducer  414  to accurately and precisely read the position of the piston, and of the processing unit to adjust that observed position and apply both linear and non-linear compensation, calibration, and adjustment functions as necessary, this volume reading is considered more precise and more accurate than is generally possible using a manual pipette with a mechanical rotary position readout. In particular, the electronic display is not subject to slack or backlash; further advantages will be detailed below. 
     In a tracking mode, with the volume set lock lever  244  is in its unlocked position  246  ( FIG. 2 ), the display  126  shows the real-time position of the piston  412  in terms of volume (as in  FIG. 8 ), with zero being at the home position  610  and the maximum capacity of the pipette being at the fully-released position  510  of the plunger button  114 . But as set forth in  FIG. 10 , with the volume set lock lever  244  in its locked position  248  ( FIG. 2 ), the display  126  continues to show the real-time position of the piston  412  in terms of volume  1010 . If the user wishes, the volume of liquid in the tip  116  at any time can be determined by reading a value on the display. 
     Many other operating modes and display features are possible in a quick-set pipette according to the invention, and are described in detail in U.S. Pat. No. 7,175,813, which is hereby incorporated by reference as though set forth in full herein. 
     The volume adjustment mechanism is described below, with particular reference to  FIGS. 11-14 . The overall volume adjustment mechanism is illustrated in  FIG. 11 . 
     Basically, the quick set volume adjustment mechanism comprises a volume setting upper stop, internal to the quick-set pipette  110 , for limiting upward axial movement of a plunger unit (comprising the plunger shaft  240  and the piston  412 ) in a housing  1110  to define the volume setting for the pipette  110 . In the present invention, the volume setting upper stop preferably is supported for axial movement in the housing  1110  only in response to a user turning of a volume adjustment knob, which in the disclosed embodiment is the plunger button  114 . In this regard, a turning of the volume adjustment knob activates operation of either a coarse volume setting means or a fine volume setting means, each of which is described in further detail below. 
     The coarse volume settings means is supported in the housing  1110  such that when activated, a relatively small turning of the volume adjustment knob produces a relatively large axial movement (i.e. coarse adjustment) of the volume setting upper stop. Similarly, the fine volume setting means is supported within the housing  1110  such that when activated, a relatively large turning of the volume adjustment knob produces a relatively small axial movement (i.e. fine adjustment) of the volume setting upper stop. Thus, by sequentially activating the coarse and fine volume setting means through a sequential turning of the volume adjustment knob, a user of the pipette of the present invention is able to quickly and accurately set and reset the volume of the pipette simply by turning the plunger button  114 . In these regards, a sequential turning of the volume adjustment knob is defined as a turning of the volume adjustment knob which will sequentially activate the coarse and fine volume setting means described herein. 
     The volume adjustment mechanism  1112  comprises, in the disclosed embodiment, a nested arrangement of finely and coarsely threaded sleeves. Turning the volume adjustment knob (the plunger button  114  in the disclosed embodiment) preferentially turns a finely threaded inner sleeve  1114 . The inner sleeve  1114  bears relatively fine external threads engaging with corresponding internal threads on an intermediate sleeve  1116 . Accordingly, then, for fine volume adjustments, the inner sleeve  1114  is caused to rotate by turns of the volume adjustment knob, and the fine external threads of the inner sleeve translate rotation of the plunger shaft  240  to relatively small axial movements of the inner sleeve  1114 , which is coupled to and axially moves the volume setting upper stop for the pipette  110 . This rotation of the inner sleeve  1114  within the intermediate sleeve  1116  is only permitted over a short range of angular motion, as will be described in further structural detail below. In the embodiment described herein, the inner sleeve  1114  is free to rotate within the intermediate sleeve  1116  over a range of approximately only 180 degrees. 
     When the plunger shaft  240  is rotated further, the inner sleeve  1114  stops rotating within the intermediate sleeve  1116 , and the inner and intermediate sleeves  1114  and  1116  rotate together within a fixed outer sleeve  1118 . The fine external threads of the inner sleeve  1114  and the corresponding internal threads of the intermediate sleeve  1116  remain in a fixed relationship, and a set of relatively coarse external threads on the intermediate sleeve  1116  traverse corresponding coarse internal threads on the fixed outer sleeve  1118 . Accordingly, with the inner sleeve  1114  and the intermediate sleeve  1116  locked together, the relatively coarse external threads of the intermediate sleeve will translate the turns of the volume adjustment knob into relatively large axial movements of both the intermediate sleeve  1116  and the inner sleeve  1114 , and hence the volume setting upper stop. 
     The inner sleeve  1114  and the intermediate sleeve  1116  are illustrated in greater detail in  FIGS. 12-14 . 
     The intermediate sleeve  1116 , shown in  FIG. 12 , is formed from a single integral molded or machined piece of polymer. In the disclosed embodiment, it is fabricated from an appropriate grade of polyester such as HYDEX® (A.L. Hyde Co.). The intermediate sleeve  1116  is generally cylindrical in shape, with a raised upper shoulder-shaped projection  1210  that serves to limit the rotation of the inner sleeve  1114  as described below. As described herein, the relatively coarse external thread  1212  is a four-start thread with a pitch of approximately 32 threads per inch. Accordingly, each revolution along the external thread  1212  traverses approximately ⅛ inch axially along the intermediate sleeve  1116 . The relatively fine internal thread  1214  is a single-start thread with a pitch of approximately 32 threads per inch. Accordingly, while a traditional manual pipette using only a 32 thread per inch volume setting mechanism may require twenty full turns to adjust from zero to full capacity (0 to 100%), a quick-set pipette according to the invention would require only approximately five turns of the coarse volume setting means to move the volume setting mechanism over the same distance. 
     The inner sleeve  1114 , shown in  FIG. 13 , is also an integral single molded or machined polymer piece. In the disclosed embodiment, it is fabricated from an appropriate grade of polyetherimide (PEI), such as ULTEM® (SABIC Innovative Plastics, formerly GE Plastics). The inner sleeve  1114  is generally cylindrical in shape, with a radially projecting limiter pin  1310 . A portion of the inner sleeve  1114  bears an relatively fine external thread  1312 , which as disclosed is a single-start thread with a pitch of approximately 32 threads per inch, to mate with the corresponding internal thread  1214  of the intermediate sleeve  1116 . The inner sleeve  1114  further has an elongated body  1314 , defining a hexagonal shaft-receiving channel  1316 . A lower end of the elongated body  1314  either serves as or is coupled to the volume setting upper stop for the pipette  110 . When assembled, the channel  1316  receives the plunger shaft  240  (which also has a hexagonal cross-section), permitting rotational movement of the shaft  240  to act also upon the inner sleeve  1114 . 
     The fixed outer sleeve  1118  ( FIG. 11 ) is fabricated, in the disclosed embodiment, from any suitable material, such as an appropriate grade of polyester (PET). 
     The inner sleeve  1114  and the intermediate sleeve  1116  are assembled as shown in  FIG. 14 . The limiter pin  1310  of the inner sleeve  1114  is somewhat flexible and deformable, and may be urged inward (into the channel  1316 ), allowing the external threads  1312  of the inner sleeve  1114  to be screwed into the internal threads  1214  of the intermediate sleeve  1116  starting at a lower end  1410  of the intermediate sleeve  1116 . When the inner sleeve  1114  is fully screwed into the intermediate sleeve  1116 , an upper end  1412  of the inner sleeve  1114  extends from an upper end  1414  of the intermediate sleeve  1116 , and the limiter pin  1310  returns back to its normal unbiased position. 
     The initial rotational position of the inner sleeve  1114  relative to the intermediate sleeve  1116  will determine which of the coarse or fine volume setting means is initially operational. It will be seen in  FIG. 14  that the limiter pin  1310  of the inner sleeve  1114  is resting against a first end  1416  of the projection  1210  of the intermediate sleeve  1116 . Any attempt to rotate the shaft  240 , and hence the inner sleeve  1114 , clockwise (as viewed from the upper ends  1412  and  1414 ) will urge the limiter pin  1310  against the projection  1210 , causing the intermediate sleeve  1116  to rotate along with the inner sleeve  1114  and the shaft  240 . When the intermediate sleeve  1116  is mounted within the fixed outer sleeve  1118 , the relatively coarse external threads  1212  of the intermediate sleeve  1116  will move with respect to the corresponding internal threads of the fixed outer sleeve  1118 , and the volume adjustment mechanism  112  will move axially approximately ⅛ inch per rotation of the volume adjustment knob. 
     In contrast, rotating the shaft, and hence the inner sleeve  1114 , counterclockwise from the position shown in  FIG. 14  (as viewed from the upper ends  1412  and  1414 ) will allow the inner sleeve  1114  to rotate within the intermediate sleeve  1116 , as the two sleeves are uncoupled. The relatively fine external threads  1312  of the inner sleeve  1114  will move with respect to the corresponding internal threads  1214  of the intermediate sleeve  1116 , and the volume adjustment mechanism  1112  will move axially approximately 1/32 inch per rotation of the volume adjustment knob. 
     This condition will persist for approximately 180 degrees of counterclockwise rotation of the volume adjustment knob, at which time the limiter pin  1310  will contact a second end  1418  of the projection  1210  of the intermediate sleeve  116 , thereafter coupling the inner sleeve  1114  and the intermediate sleeve  1116  together for further rotation, which will result (again) in approximately ⅛ inch of axial movement per rotation of the knob. 
     It will be apparent, then, that rotating the volume adjustment knob over a range of approximately 180 degrees will preferentially engage the fine volume setting means, while rotating it further (in either direction) will engage the coarse volume setting means. It is stated above that the fine volume setting means (i.e., the inner sleeve  1114 ) is preferentially moved within that 180-degree interval. This is accomplished by maintaining a relatively low coefficient of friction in the thread interface between the inner sleeve  1114  and the intermediate sleeve  1116 , and a relatively higher coefficient of friction between the intermediate sleeve  1116  and the fixed outer sleeve  1118 . This may be facilitated through precise part dimension tolerances and material choices, as will be apparent to an engineer having ordinary skill. 
     It will be recognized that the inner sleeve  1114  either acts as or cooperates with an axially movable structure that serves as the upper stop, described above, for plunger movement in a pipette according to the invention. Accordingly, a volume setting for the pipette  110  may be performed by repeated turning of the plunger button  114 , which engages both the inner sleeve  1114  and the intermediate sleeve  1116  to accomplish a coarse volume setting. The plunger button  114  may then be backed off, reversing the direction of initial rotation, which disengages the intermediate sleeve  1116  and accomplishes a fine volume setting over a 180 degree interval. If more than 180 degree rotation is made at this stage, the coarse volume setting means is re-engaged. 
     As discussed above in connection with FIGS.  4  and  8 - 10 , a position sensor is advantageously coupled to the plunger button  114 , the plunger shaft  240 , or the piston  412  (or some other component coupled thereto), allowing the pipette  110  to read the position of the piston  412  as desired. When the plunger button  114  is not depressed, the position of the piston  412  corresponds to the volume setting for the pipette  110 . In an alternative embodiment of the invention, the position sensor may be coupled to the upper volume-setting stop, which may comprise a portion of the inner sleeve  1114  or a component coupled to the inner sleeve  1114 . 
     A conventional volume lock mechanism (the operation of which is described with reference to  FIG. 2 , above) employs a cam-and-collet arrangement to fix the rotational position of the volume adjustment mechanism  111   2  within the housing  1110 . Details of this arrangement are set forth in the &#39;813 and &#39;248 patents, incorporated by reference above. 
     It has been found, however, that at least in part as a result of the particularly steep thread angles in the coarse volume setting means, strong impacts to the plunger button  114  and other portions of the plunger mechanism of the pipette  110 , even when the lock lever  244  is positioned to engage the lock apparatus, may result in undesired movements of the volume adjustment mechanism  1112 . 
     A quick-set pipette  110  according to the invention therefore incorporates structures and features to minimize the possibility and consequences of such undesired movements of the volume adjustment mechanism  1112 . In particular, it has been found that damping the axial movement of the plunger shaft  240  by applying a frictional or viscous damping influence to that structure will tend to avoid such abrupt movements by limiting the velocity of the plunger within the pipette  110 . This has the effect of reducing the incidence of strong impacts of the plunger mechanism against the volume setting upper stop. Such strong impacts tend to dislodge the lock apparatus, and accordingly reducing the strength and incidence of impacts by the structures and methods set forth herein will also reduce unintended movements of the volume adjustment mechanism  1112 . 
     Such damping influence may be applied by a structure (such as a friction pad) mechanically interfering with the axial movement of the plunger shaft  240 , or by fluid damping. An air dashpot mechanism for damping plunger movement is disclosed in U.S. Pat. No. 5,364,596, which is hereby incorporated by reference as though set forth in full. Such a dashpot mechanism may be advantageously employed in a pipette according to the invention. However, in the disclosed embodiment, damping is accomplished in a simple and economical manner by applying a viscous fluid between a component that is axially fixable relative to the housing  1110  and a component coupled to the axially moving plunger shaft  240 . 
     In the disclosed embodiment, a fluoroether or silicone grease, such as KRYTOX® grease (DuPont), is applied between the plunger shaft  240  and the hexagonal shaft receiving channel  1316  of the inner sleeve  1114 . When the locking apparatus is in the locked configuration, the axial position of the inner sleeve  1114  is fixed relative to the housing  1110 . Alternatively, such a grease may be applied to a narrow gap between the sliding component  416  and the fixed component  418  of the position sensing transducer  414 . Other locations within the pipette  110  may also be suitable. 
     The grease is selected to be sufficiently viscous in all operating temperatures and conditions to avoid substantial migration out of the desired location, for the duration of the operating life of the pipette. The grease should not be overly viscous, however, to avoid adversely impacting the operation and “feel” of the pipette when relatively quick piston movements are desired. Greases meeting these criteria are well known. In alternative embodiments of the inventive pipette  110 , the grease may be applied between the sliding component  416  and the fixed component  418  of the position sensing transducer  414 , or at any other suitable location where there exists relative axial motion between the components. 
     In practice, the damped action of the plunger shaft  240  reduces the effect of accidental and otherwise undesired impacts upon the volume adjustment mechanism  111   2 , without substantially compromising the operation of the pipette in other ways. With such damping in place, the volume lock mechanism has been found to be secure and reliable, comparable in practice to traditional pipettes without the quick-set volume adjustment capability described herein. 
     It should be observed that while the foregoing detailed description of various embodiments of the present invention is set forth in some detail, the invention is not limited to those details and a pipette made according to the invention can differ from the disclosed embodiments in numerous ways. In particular, it will be appreciated that embodiments of the present invention may be employed in many different fluid-handling applications. It should be noted that functional distinctions are made above for purposes of explanation and clarity; structural distinctions in a system or method according to the invention may not be drawn along the same boundaries. Hence, the appropriate scope hereof is deemed to be in accordance with the claims as set forth below.