Abstract:
The present invention relates to an electrically monitored mechanical pipette which includes a microswitch in its volume delivery adjustment mechanism which operates to signal the electrical volume monitoring system of the pipette when a fluid volume delivery setting adjustment is being made. In this manner, the pipette operates in a low power mode during normal operation to display the present fluid volume delivery setting, but moves to a high power consumption mode when changes are being made to the fluid volume delivery setting. The microswitch allows the high power consumption elements in the electronic volume monitoring system, such as a Hall-effect transducer assembly, to be inactive and receive no power input until it is needed during adjustment of the fluid volume delivery setting.

Description:
This application claims benefit of Provisional application 60/025,694 filed Sep. 9, 1996. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates generally to an electronically monitored mechanical pipette. More specifically, the invention relates to an electronically monitored volume delivery adjustment mechanism for a pipette. Even more specifically the invention relates to a microswitch for signalling the electronic system of an electronically monitored mechanical pipette when volume setting adjustment is taking place. 
     2. Prior Art 
     Mechanically operated micropipettes are well known in the art as exemplified by U.S. Pat. No. 4,909,991 to Oshikubo. In such prior art devices, the volume of liquid to be dispensed by the pipette is generally indicated to the operator by means of a mechanical display. The display commonly consists of a set of rotary drums driven by a gear mechanism attached to the actuating shaft of the pipette, such that rotation of the actuating shaft causes the drums to rotate to display a new setting. However, due to unavoidable mechanical wear and tear on pipettes, the amount of fluid actually being delivered by a pipette may not actually correspond to the volume being indicated by the mechanical displayed. Further, accuracy may degrade over time as the actuating elements, such as the shaft, gears, and rotary drum, wear out. 
     Electrically driven pipettes are also well known in the art as exemplified by U.S. Pat. No. 4,905,526 to Magnussen, Jr. et al. This type of instrument commonly includes an electronic display for displaying the volume of fluid to be dispensed by the pipette, and an actuator generally comprised of an electric drive mechanism, such as a stepper motor. The stepper motor generally drives a rotor, which is attached by a threaded screw to an actuator shaft, the threaded screw changes the rotational motion of the motor into linear motion of the actuator shaft. The shaft thereafter drives a piston to displace fluid for pipetting. Although electrically operated pipettes have some advantages over mechanically operated pipettes, they nevertheless suffer from several drawbacks. First, the enlarged size of an electrically operated pipette, due to the need to accommodate the electric driving mechanism, and the added electronic hardware, make the device very difficult to handle for the operator. Further, the electronic motor can be very power demanding and thus necessitate connection of the pipette to a power source, or the use of large batteries which can be rapidly drained of power. 
     Electrically monitored mechanical pipettes are also known in the art as exemplified by U.S. Pat. No. 4,567,780 to Oppenlander et al. This type of instrument generally includes a plunger having an adjustable stroke length which is generally adjusted by rotating the plunger itself. The electrical monitoring system monitors plunger rotation and electronically displays the volume delivery setting corresponding to the plunger position. The device continuously monitors the plunger position and volume delivery setting of the pipette. Although this device overcomes several of the disadvantages of mechanical and electrical pipettes, it nevertheless fails to completely resolve the problem of high power demands during operation. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     The principal object of the present invention is to provide an electrically monitored mechanical pipette with a continuous volume delivery setting display and low power consumption. 
     Another object of the present invention is to provide an electrically monitored mechanical pipette which activates the electrical volume monitoring system thereof only when the volume delivery setting is being changed. 
     Another object of the present invention is to provide an electrically monitored mechanical pipette which includes a microswitch as a part of the volume delivery adjustment mechanism which reduces power consumption of the pipette by providing a signal to power up the electrical volume monitoring system only when the volume delivery setting is being changed. 
     Briefly, and in general terms, the present invention provides for electronically monitoring a mechanical pipette which enables low power operation of the electronics thereof during use of the device to pipette fluid, and engages high powered electronics only when necessary to provide monitoring of the pipette while the operator is resetting the desired fluid volume delivery setting and for recomputation of the new setting. 
     In the presently preferred embodiment shown by way of example and not necessarily by way of limitation, an electrically monitored mechanical pipette made in accordance with the principals of the present invention includes a volume delivery adjustment mechanism which includes a plunger, an advancer, a driver, and a threaded bushing. The volume delivery adjusted mechanism is monitored by an electrical volume monitoring system which preferably includes a transducer assembly having two Hall-effect sensors, and an electronics assembly which includes a microprocessor and a display. During volume delivery adjustment, the sensors send a set of transducer signals to the electronics assembly computes and displays the new fluid volume delivery setting. 
     A microswitch assembly is provided for detecting relative rotational motion between the volume delivery adjustment mechanism and the pipette and to signal the electronics assembly that the fluid volume delivery setting is being changed. Upon receipt of a signal, in the form of an interrupt signal from the microswitch, the electronics assembly powers up the transducer assembly which then tracks the motion of the volume delivery adjustment mechanism. The transducer sensor signals are received by the electronics assembly which computes and displays the new fluid volume delivery setting Once the volume delivery adjustment mechanism is no longer being rotated, the electronics assembly shuts down the power to the transducer assembly to minimize power use of the pipette. 
     In one preferred embodiment of the microswitch assembly a bobber mechanism is positioned such that the volume delivery adjustment mechanism causes a switch, such as a metal contact pad, in the mechanism to move up and down as the volume delivery adjustment mechanism rotates. This up and down motion of the switch causes it to intermittently contact and release a stationary switch pad mounted on the electronics assembly. In this manner, a signal such as an interrupt signal is sent by the bobber mechanism to the electronics assembly each time the bobber switch pad contacts the stationary electronics switch pad. The interrupt signal causes the electronics assembly to power up the transducer assembly for monitoring the motion of the volume delivery adjustment mechanism. 
     Another preferred embodiment of the microswitch assembly includes a bobber which is in physical contact with a spring loaded switch which is activated each time the bobber moves up and down. 
     These and other objects and advantages of the present invention will become apparent from the following more detailed description, when taken in conjunction with the accompanying drawings in which like elements are identified with like numerals throughout. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a pipette made in accordance with the principals of the present invention; 
     FIG. 2 is a front view of the pipette of FIG. 1; 
     FIG. 3 is a cross-sectional view taken along line III—III of FIG. 2; 
     FIG. 4 is a perspective view of a preferred embodiment of an electronics assembly and a transducer assembly made in accordance with the principals of the present invention; 
     FIG. 5 is a cross-sectional view of a transducer assembly made in accordance with the principals of the present invention; 
     FIG. 6 is a cross-sectional view taken along line VI—VI of FIG. 5; 
     FIG. 7 is an exploded view of a preferred embodiment of a microswitch assembly made in accordance with the principals of the present invention; 
     FIG. 8 is a perspective view of a preferred embodiment of a microswitch assembly and an electronics assembly made in accordance with the principals of the present invention with the housing of the electronics assembly removed; 
     FIG. 9 is a side view of the microswitch assembly and electronics assembly of FIG. 8; and 
     FIG. 10 is a perspective view of a second preferred embodiment of a microswitch assembly made in accordance with the principals of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     As shown in the exemplary drawings for the purposes of illustration, an embodiment of an electronically monitored mechanical pipette made in accordance with the principals of the present invention, referred to generally by the reference numeral  10 , is provided for continuous low power display of the fluid volume delivery setting of the pipette, and for temporary high power activation of the electrical volume monitoring system whenever the volume delivery setting is being changed by an operator. 
     More specifically as shown in FIGS.  1 - 3 , the pipette  10  of the present invention includes a housing  12  having a first generally cylindrical bore  14  passing longitudinally therethrough which contains a transducer assembly  20  centrally located therein, a microswitch assembly  50  positioned at the proximal end thereof and a barrel assembly  30  attached to the distal end thereof to extend outwardly in the distal longitudinal direction. The housing  12  also includes a smaller longitudinal bore  16  containing an ejector rod  18 , held in its proximal most position by ejector spring  22  and prevented from escaping the smaller bore  16  by O-ring  24 . An electronic assembly  40  is attached to the proximal end of the housing  12  and extends away from the housing  12  in a generally perpendicular direction. The housing  12  is designed to be easily gripped in a single hand of an operator such that the electronic assembly  40  remains above the operator&#39;s hand for easy viewing by the operator, and the barrel assembly  30  extends below the operator&#39;s hand for easy positioning thereof. The pipettor  10  can be operated by manipulation of the ejector rod  18  and the square plunger  26  by the user&#39;s thumb as will be explained in more detail below. 
     ASSEMBLY 
     Referring again to FIGS.  1 - 3 , assembly of the pipettor  10  of the present invention is preferably initiated with the barrel assembly  30 . First, the piston  28  is inserted into the primary spring  32 . The proximal end of the piston  28  is then affixed to the piston adaptor  34  and the distal end of piston  28  is inserted into the fluid channel  36  of the barrel housing  42 . The fluid channel  36  is sealed against leakage therepast by means of a plug  38  preferably made of Teflon, through which the piston  28  passes and which seats itself in the distal portion of the barrel housing  42  just above the fluid channel  36 . The plug  38  is secured for a fluid tight fit against the piston  28  by the seal  44 . The seal  44  and plug  38  are held in the distal portion of the barrel housing  42  by washer  46  which is biased downward by the primary spring  32 . The force of the washer  46  against the seal  44  assists the seal  44  in squeezing the plug  38  against the piston  28  and also assists in forcing the plug  38  downward against the proximal end of the fluid channel  36 . This assists in preventing fluid leakage out of the fluid channel  36 . Finally the annular disk  48  is inserted over the piston adaptor  34  and snap-fit into the distal opening of the barrel housing  42 . The enlarged end  52  of the piston adaptor  34  is larger in diameter than the annular disk opening  54  and allows the piston adaptor  34  to move longitudinally relative to the barrel housing  42  yet does not allow it to be completely removed therefrom. This completes barrel assembly  30 . 
     Turning now to the housing  12 , the primary washer  56  is inserted into the distal end of the housing  12  until it abuts with the shoulder  62  thereof. The secondary spring  60  is then inserted into the distal end of the housing  12  until it abuts primary washer  56 . The secondary washer  61  is then placed against the secondary spring  60  to abut with shoulder  58  of the housing  12 . The primary washer  56 , secondary spring  60  and secondary washer  61  are then permanently held in place within the housing  12  by press fitting the bushing barrel  64  into the distal end of the housing  12 . The bushing barrel  64  is threaded on its interior surface and the proximal end of the barrel housing  42  of the barrel assembly  30  is threaded on its exterior surface. In this manner, the entire barrel assembly  30  can be removably attached to the housing  12  by threading the barrel housing  42  into the bushing barrel  64 . A further description of the barrel assembly  30 , including alternative embodiments thereof, is included in co-pending U.S. application Ser. No. 08/926,095 entitled “Detachable Pipette Barrel” filed Sep. 9, 1997, which is incorporated herein by reference in its entirety. 
     Referring now to FIGS.  3 - 5 , the transducer assembly includes an annular magnet  116  encased in the transducer housing  118  and held in position on the transducer bearing  130  by abutment against shoulder  120 . Sensors  122  and  124  are positioned within the transducer housing  118  at positions 90° apart from each other. The sensors  122  and  124  operate to track the rotation of the annular magnet  116 . Leads  134  and  136  extend from the sensors  122  and  124  up to the electronics assembly  40  to allow the sensor signals to pass tot he electronics assembly  40 . A more detailed description of the transducer assembly  20  is located in applicant&#39;s co-pending U.S. application Ser. No. 08/925,980 entitled “Transducer Assembly for an Electronically Monitored Mechanical Pipette” filed Sep. 9, 1997 filed which is incorporated herein by reference in its entirety. 
     As best seen in FIG. 3, the square plunger  26  is next inserted through the advancer  74 . The transducer driver  76  is then inserted over the distal end of the plunger  26  and attached to the distal end of the advancer  74  by means of screws or the like. The distal end of the transducer driver  76  forms a reduced diameter threaded extension to which a small bushing  78  is threadedly attached. The small bushing  78  is of a larger diameter than the plunger  26  and thus interferes with the distal end of the transducer driver  76  to preventing the plunger  26  from being withdrawn therefrom 
     Referring now to FIGS. 3 and 7, the microswitch assembly  50  is assembled by first sliding the square opening of the bobber guide  82  over the proximal end of the square plunger  26 , and attaching the button  72  to the proximal end of the plunger  26 . Next, the bobber  80  is inserted over the bobber guide  82  and the bobber switch  84  is inserted over the bobber  80  and held in place by the retaining ring  86 . The bobber spring  88  is then inserted over the bobber guide  82  until it abuts against the retaining ring  86  and the retainer  90  is attached to the distal end of the bobber guide  82 . Threads  138  of the advancer  74  are then advanced into the threads  140  of bushing  70 . The bobber guide  82  is then inserted into the bushing  70  until the retainer  90  snap fits into a retainer slot  92  in the interior annular surface of the bushing  70  just above threads  140 . This action causes the bobber spring  88  to be biased between the retaining ring  86  and shoulder  94  in the proximal end of the bushing  70 . In this manner, the bobber  80  is always biased upward against the enlarged flange portion  96  of the bobber guide  82 . When completely assembled, the bobber  80  is prevented from rotating by the keys  142  thereon which match keyways (not shown) in bore  16 . Similarly, pin  144  prevents the advancer  74  from rotating above the threaded portion of the bushing  70 , and a key and keyway (not shown) are used to prevent rotation of the transducer housing  118 . Thus, rotation of button  72  by the operator causes the plunger  26 , advancer  74  and transducer driver  76  to rotate and translate in the upward or downward direction. Translational (longitudinal) distance is controlled by the pitch of threads  138  and  140 , and the number of rotations of the button  72 . 
     Likewise, rotation of button  72  causes rotation (but not translation) of bobber guide  82 , transducer bearing  130  and annular magnet  116 . 
     The rotational motion of the bobber guide  82  causes the bobber  80  to move downwardly Since the bobber  80  is held against rotation by the keys  142  positioned in keyways (not shown) in the bore  16 , the bobber  80  must move downwardly to unmesh bobber teeth  146  from bobber guide teeth  148 . This downward motion causes the bobber switch  84  to contact the stationary switch pad  98 , and continues until the bobber teeth  146  slip past the bobber guide teeth  148 . This downward movement distance in the preferred embodiment is approximately 0.030 inches. The bobber  80  is then biased upwardly again by bobber spring  88 . This continues as further rotation occurs, and results in a “bobbing” motion of bobber  80  until rotation of the button  72  is stopped. 
     Once the transducer assembly  20  and microswitch assembly  50  are completed, the transducer assembly  20  is inserted into the housing  12  through the proximal opening of bore  14  and held in position against shoulder  68  by bushing  70 . The bushing  70  includes flattened surfaces (not shown) which form small longitudinal channels (not shown) in conjunction with the bore  14 , through which the leads  134  and  136  pass from the transducer assembly  20  to the electronics assembly  40 . 
     The stationary switch pad  98  is held in position at the top of the housing  12  by screws or the like, and a portion thereof extends into the bore  14  to contact and assist in retaining the bushing  70  in its proper position within the bore  14 . The bobber switch  84  extends over and above the stationary switch pad  98  and is held in a spaced apart position therefrom by the bobber spring  88 . 
     As shown in FIGS. 8 and 9, the stationary switch pad  98  is in electrical contact with the electronic assembly  40  and likewise forms part of the electrical volume monitoring system by being attached to the negative side of the batteries  100  through lead  102  and to the positive side of the circuit board  104  by lead  106 . The circuit board itself is connected to the positive side of the batteries  100  by lead  108 . The circuit board  104  has attached thereto the microprocessor  110 , the LCD display  112 , the calibration buttons  113 ,  114 ,  115  and the leads  134  and  136  from the transducer assembly  20 . 
     Finally, referring now to FIG. 3, the ejector spring  22  is inserted over the ejector rod  18  and the ejector rod  18  is subsequently inserted through the small bore  16  of the housing  120 . The O-ring  24  is attached to a distal portion of the rod  18  to retain it within the small bore  16 . The distal end of ejector rod  18  is threaded and sized to receive the ejector barrel  66  which is held in place by nut  128 . 
     In use, a disposable pipette tip (not shown) is attached to the distal end of the barrel housing  42  to be in fluid flow communication with the fluid channel  36  and to abut the distal end of the ejector barrel  126 . When it is desired to dispose of the pipette tip, the operator presses down on the ejector rod  18  with the thumb of the hand holding the pipette  10 . This causes the ejector rod  18  and the ejector barrel  66  to move distally and push the pipette tip off of the distal end of the barrel housing  42 . 
     OPERATION 
     The pipette  10  of the present invention operates as follows. The operator, using the thumb of the hand holding the pipette  10 , presses down on button  72  until the small bushing  78  on the distal end of the plunger  26  touches the primary washer  132 . This motion is resisted by the primary spring  32  through the piston adaptor  34 . This motion also brings the piston  28  downwardly along the fluid chamber  36 . The operator then inserts the distal end of the pipette  10  (with a disposable pipette mounted thereon) into a fluid to be pipetted. The operator releases the button  72  and the primary spring  32  returns to its fully upwardly extended positions, and draws piston  28  in a proximal direction, causing the fluid chamber  36  to be filled with fluid. The operator then inserts the distal end of the pipette  10  into the container to receive the fluid and again forces button  72  downwardly with the thumb until the small bushing  78  touches the primary washer  56 . The user continues downward force on the button  72  to cause the primary washer  132  to also move downwardly against the force of the secondary spring  60  until it is completely compressed. At this point, the preset volume of fluid has been delivered from the fluid channel  36 . 
     If the operator desires to change the fluid volume delivery setting, the operator rotates button  72  either clockwise to reduce the volume delivery setting, or counterclockwise to increase the volume delivery setting. Rotation of button  72  causes rotation of bobber guide  82 , threaded advancer  74 , transducer drive  76 , transducer bearing  130 , and the annular magnet  116 . Rotation of the thread advancer  74  (by rotation of button  72 ) causes the threaded advancer  74  to rotate through the threads  140  on the inside of the bushing  70  and thereby move in a longitudinal direction. This longitudinal movement also forces longitudinal movement of the plunger  26  and the transducer driver  76 . 
     Rotational motion of the bobber guide  82 , causes the bobber  80  to be forced downwardly in the distal direction against the bobber spring  88  until the bobber switch  84  contacts the stationary switch pad  98 . In the preferred embodiment, the gap between the bobber switch  84  and the stationary switch pad  98  is approximately 0.010 to 0.15 inches. Since the bobber  80  is keyed to the housing  12 , and therefore cannot rotate, it moves downward to allow the meshing teeth  148  of the bobber guide  82  to pass over the meshing teeth  146  of the bobber  80  (approximately 0.030 inches). The individual teeth of the meshing teeth  146  and  148  are preferably sized to cause the bobber  80  to “bob” approximately every 6° of rotation. Each time the bobber is forced downwardly due to rotation of the bobber guide  82 , the bobber switch  84  is forced into contact with the stationary switch pad  98  (since the gap between them is only approximately 0.010 to 0.015 inches, and the downward movement of the bobber switch is approximately 0.030 inches which exceeds the gap). The bobber spring  88  then forces the bobber  80  upwardly again against the bobber guide  82  When the bobber  80  is again in its upwardmost position, the bobber switch  84  is again spaced away from the stationary switch pad  98 . The contact of bobber switch  84  with the stationary switch pad  98  sends an interrupt signal to the microprocessor  110  which it recognizes as a signal to power up the sensors  122  and  124  in the transducer assembly  20 . 
     As the annular magnet  116  rotates, the magnetic field thereof passes through the sensors  122  and  124 . The sensors  122  and  124  produce a current output based on the changing magnetic field passing therethrough which is sent to the microprocessor  110  through leads  134  and  136 . The microprocessor computes a new volume delivery setting based on the signals it receives from the sensors  122  and  124  and displays the new volume setting in display  112 . The operational features of the transducer assembly  20  and electronics assembly  40  are more completely described in applicant&#39;s co-pending U.S. application Ser. No. 08/925,980 identified above. Also, a more detailed discussion of the electronic volume monitoring system, including calibration thereof, is included in applicant&#39;s co-pending U.S. patent application Ser. No. 08/926,371 entitled “Calibration System for an Electronically Monitored Mechanical Pipette” filed Sep. 9, 1997 which is incorporated herein by reference in its entirety. 
     When the operator stops turning the knob  72 , the bobber  80  is again biased to its upward proximal position by the bobber spring  88 , and the bobber switch  84  is separated from the stationary switch pad  98 . After a short period of time, preferably approximately 100 milliseconds after receiving its last interrupt signal, the microprocessor  110  turns off the power to the transducer assembly  20 . The display  112  however remains powered, and continuously displays the current fluid delivery setting. In this manner, when the pipette  10  is not activated to change a fluid delivery setting, the power consumption thereof is limited to the power required to maintain the current fluid delivery setting displayed on the display  112  (approximately 10 microamps). The high power requirements of the transducer assembly  20 . (approximately 170 milliamps) are only being consumed therefor when the pipette  10  is actually being operated to change its fluid volume delivery setting. 
     An alternative embodiment of the microswitch assembly  50  of the present invention is shown in FIG. 10 In this embodiment, the bobber switch  84  and stationary switch pad  98  are replaced with bobber groove  150  and switch button  152  respectively When the bobber  80  is in its upwardly biased position, switch button  152  rests in bobber groove  150 . However, when the bobber is forced downwardly by rotation of bobber guide  82 , the bobber groove  150  also moves downwardly. The switch button  152  is forced out of the bobber groove  150  and into switch box  154  to make electrical contact with the circuit of the electronic volume monitoring system and send its interrupt signal to the microprocessor  110 . 
     It will be apparent from the foregoing that, while particular embodiments of the invention have been illustrated and described, various modifications can be made thereto without departing from the spirit and scope of the invention. Specifically, for example, the preferred embodiment of the monitoring assembly of the present invention is shown an described as a transducer assembly including Hall-effect sensors. However, any monitoring assembly, such as an optical encoder which will provide a pulse at known angular intervals, is also contemplated by the present invention. Accordingly, it is not intended that the invention be limited, except as by the appended claims.