Abstract:
The present invention relates to an electrical switch including an arcuate cavity partially filled with an electrically conducting fluid. The fluid is adapted to move into electrical contact with a pair of electrodes positioned within the cavity in response to a rotational force acting thereupon. The switch is electrically connectable to a rotatable platter. When connected to the platter, the switch is positioned radially outward from the platter&#39;s axis of rotation, such that the forces generated by the platter upon rotation urge the electrically conducting fluid into contact with the electrodes and thus complete a circuit.

Description:
TECHNICAL FIELD OF THE INVENTION 
     The present invention relates generally to electrical switches and, more particularly, to an apparatus for automatically switching an electrical circuit when a platter is rotated. 
     BACKGROUND OF THE INVENTION 
     Many medical analytical techniques, such as blood and urine analysis, rely on centrifugation as part of the testing procedure. Generally, automated devices designed to perform these tests include a built-in centrifuge having a rotatable platter or carousel in which fluid samples are mounted. It is often desirable to separate the carousel rotating function from the analytical functions, in order to conserve resources such as power and/or computer time. Power conservation is especially important if the device is battery operated. To this end, it is attractive to include switching means in the rotatable platter capable of switching on the analytical functions only after the platter has achieved a predetermined rotational rate. 
     One way of performing this switching function is to rely on the user to activate the analytical function when the platter is rotating at the proper speed. This switching method suffers from the disadvantages of requiring the user to spend valuable time and attention manually actuating the analytical functions of the device. Moreover, manual actuation is not as reliable as an automatic switching means. 
     One automatic switching means involves the connection of a mechanical switch to the platter. While more reliable than manual switching, mechanical switches are prone to error arising from dirty electrical contacts, broken or worn springs, and broken or worn actuators. Moreover, mechanical switches rely on moving parts with lifetimes adversely affected by the rotational forces generated by the rotating platter. 
     There is therefore a need for a non-mechanical switch usable with a rotatable platter capable of actuating an electrically connected device, such as an analytical device, upon rotation of the platter to a predetermined speed. The present invention addresses this need. 
     SUMMARY OF THE INVENTION 
     The present invention relates to an electrical switch including an arcuate cavity partially filled with an electrically conducting fluid. The fluid is adapted to move into electrical contact with a pair of electrodes positioned within the cavity in response to a rotational force acting thereupon. The switch is electrically connectable to a rotatable platter. When connected to the platter, the switch is positioned radially outward from the platter&#39;s axis of rotation, such that the forces generated by the platter upon rotation urge the electrically conducting fluid into contact with the electrodes and thus complete a circuit. 
     One form of the present invention relates to an electrical switch including a cavity partially filled with an electrically conducting fluid adapted to move into electrical contact with a pair of electrodes positioned within the cavity in response to a rotational force acting thereupon. The switch is adapted to be operationally connected to a rotatable platter and spaced radially from the platter&#39;s axis of rotation, such that the forces generated upon rotation of the platter urge the electrically conducting fluid into contact with the electrodes, thus completing a circuit. 
     Another form of the present invention relates to an electrical switch formed as part of a modular cartridge and including a cavity formed in the cartridge and partially filled with an electrically conducting fluid. The electrically conducting fluid is adapted to move in response to a rotational force acting thereon and into electrical contact with a pair of electrodes positioned within the cavity. The cartridge is operationally connectable to a rotatable platter through matable electrical contacts positioned in both the cartridge and the platter. Rotation of the platter urges the electrically conducting fluid into contact with the pair of electrodes, thus completing a circuit. 
     One object of the present invention is to provide an improved apparatus for electrical switching in response to a change in angular momentum. Related objects and advantages of the present invention will be apparent from the following description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective schematic view of a rotatable platter containing a first electrical switch embodiment of the present invention. 
     FIG. 2 is a cross-sectional illustration of the electrical switch of the embodiment of FIG.  1 . 
     FIG. 3 is a perspective view of a cartridge containing a second electrical switch embodiment of the present invention. 
     FIG. 4 is a perspective schematic view of the cartridge of FIG. 3 inserted in a rotatable platter. 
     FIG. 5 is a perspective schematic view of a rotatable platter containing a third electrical switch embodiment of the present invention. 
     FIG. 6A is a cross-sectional illustration of the electrical switch of the of FIG. 5 having electrically conducting fluid occupying a first position. 
     FIG. 6A is a cross-sectional illustration of the electrical switch of the of FIG. 5 having electrically conducting fluid occupying a second position. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiment illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated device, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates. 
     The present invention relates to an apparatus for closing an electrical circuit in a rotatable member in response to rotation of that member. FIGS. 1 and 2 illustrate one embodiment of the present invention, a rotation-actuated electrical switch  10  positionable in a rotatable platter  12 . FIG. 1 illustrates the preferred positioning of switch  10  within platter  12 . Rotatable platter  12  preferably has a generally circular shape and rotates about shaft  13 . Platter  12  is more preferably generally planar and includes a primary axis of rotation  14  substantially colinear with shaft  13  and substantially perpendicular to platter  12 . Switch  10  is preferably formed integrally within platter  12 , but may also be formed separately from platter  12  and connected thereto by any convenient means, such as through a modular cartridge (see FIGS.  3  and  4 ). Switch  10  preferably extends generally radially outward from axis of rotation  14 . More preferably, axis of rotation  14  does not intersect switch  10 . 
     FIG. 2 illustrates switch  10  in greater detail. Switch  10  comprises an elongated enclosure or compartment  20  defining a cavity, at least a portion of which is generally arcuate or substantially arch-shaped. Preferably, enclosure  20  has a simple arcuate shape, but may also have any convenient shape incorporating an arched or likewise bent portion, such as a “dogleg” shape or the like. The generally arcuate enclosure  20  has a proximal portion (or inner leg)  22 , a middle portion  24 , and a distal portion (or outer leg)  26 . Middle portion  24  may range in size from large enough to occupy a majority of enclosure  20  to just large enough to connect proximal portion  22  to distal portion  26 . Enclosure  20  is preferably positioned relative axis of rotation  14  such that proximal portion  22  is the closest portion to axis of rotation  14 . More preferably, proximal portion  22  extends upwardly through platter  12  to middle portion  24 . Middle portion preferably extends from proximal portion  22  away from axis of rotation  14  to distal portion  26 . Distal portion  26  extends from middle portion  24  downwardly through platter  12  and away from axis of rotation  14 . As used herein, the term “upwardly” indicates a direction generally opposite the pull of gravity, such that a body moving upwardly would gain gravitational potential energy. Likewise, the term “downwardly” indicates a direction generally congruent with the pull of gravity, such that a body moving downwardly would lose gravitational potential energy. 
     Switch  10  also includes a pair of spaced electrical contacts  28 ,  29  adapted to electrically connect the interior of distal portion  26  to the exterior of switch  10 . Switch  10  further includes an electrically conducting fluid  30  (such as mercury or an aqueous electrolytic solution) partially filling the enclosure  20 . Fluid  30  preferably rests in proximal portion  22  of switch  10  when platter  12  is at rest. Preferentially, switch  10  is oriented such that distal portion  26  is positioned generally radially outward from proximal portion  22  relative to primary axis of rotation  14 . More preferentially, switch  10  is also oriented such that proximal portion  22  and distal portion  26  are positioned below (i.e., having less gravitational potential energy than) middle portion  24 . 
     Rotation of platter  12  generates a radially outwardly acting force (represented by arrow  36 ) urging fluid  30  into distal portion  26  of switch  10  and into contact with the pair of spaced electrical contacts  28 ,  29 . Force  36  is proportional to the rate of rotation of platter  12 . As platter  12  is rotated beyond a predetermined threshold rate, the value of force  36  becomes sufficient to displace fluid  30  from proximal portion  22  to distal portion  26  of switch  10  and into electrical contact with the pair of spaced electrical contacts  28 ,  29 , thus completing an external electrical circuit (not shown) coupled to spaced electrical contacts  28 ,  29  and enabling current to flow between spaced electrical contacts  28 ,  29 . 
     The threshold rate of rotation at which fluid  30  becomes displaced into distal portion  26  may be predetermined by varying the amount of fluid  30 , the composition (specifically, the viscosity and/or density) of fluid  30 , and/or varying the curvature of enclosure  20 . Generally, as the density and/or viscosity of fluid  30  increases, a greater force  36  will be required to displace fluid  30  into distal portion  26 . Likewise, as enclosure  20  becomes more arcuate (or as the slope from inner leg  22  to middle portion  24  becomes steeper), a greater force  36  will be required to displace fluid  30  into distal portion  26 . By choosing the appropriate degree of curvature of enclosure  20  and amount and composition of fluid  30 , the rotation rate of platter  12  at which switch  10  trips may be predetermined. After switch  10  has been subjected to rotational force  36  and tripped, switch  10  may be disengaged and reset by repositioning enclosure  20  such that fluid  30  flows from distal portion  26  back into proximal portion  22 . This operation may be performed manually or automatically. 
     FIGS. 3 and 4 illustrate a second embodiment of the present invention, a switch  10  formed in a modular cartridge  40 A adapted to be electrically connected to a rotatable platter  12 A. FIG. 3 illustrates cartridge  40 A in detail. Cartridge  40 A includes a substantially arcuate or generally arch-shaped elongated enclosure or compartment  20 A defining a cavity having an upwardly-inclined proximal portion or inner leg  22 A, a middle portion  24 A, and a downwardly-inclined distal portion or outer leg  26 A, whereas the inclinations of the proximal and distal portions  22 A,  26 A are relative to the cartridge  40 A orientation when electrically connected to rotatable platter  12 A (see FIG.  4 ). Switch  20 A also includes a pair of spaced electrical contacts  28 A,  29 A adapted to electrically connect the interior of distal portion  26 A to the exterior of the switch  10 A. First and a second electrical lead  28 A and  29 A extend from within distal portion  26 A of enclosure  20 A to the exterior of cartridge  40 A and terminate in cartridge electrodes  42 A and  43 A. Switch  10 A further includes an electrically conducting fluid  30 A partially filling the enclosure  20 A. 
     FIG. 4 illustrates cartridge  40 A as operationally connected to platter  12 A. Fluid  30 A preferably rests in proximal portion  22 A of switch  10 A when cartridge  40 A is inserted into resting platter  12 A. Preferentially, switch  10 A is oriented such that distal portion  26 A is positioned generally radially outward from proximal portion  22 A, relative to primary axis of rotation  14 A. In other words, as positioned within cartridge  40 A as inserted into platter  12 A, switch  10 A extends generally radially outward from axis of rotation  14 A and has the form of an elongated enclosure  20 A having an upwardly-inclined elongated proximal portion  22 A and a downwardly-inclined elongated distal portion  26 A and is positioned relative to platter  12 A such that upwardly-inclined proximal portion  22 A lies radially inward relative to middle portion  24 A and downwardly-inclined distal portion  26 A lies radially outward middle portion  24 A. 
     Rotatable platter  12 A includes a recess  50 A adapted to receive cartridge  40 A. Recess  50 A also preferably includes platter electrodes  52 A and  53 A adapted to make electrical contact with cartridge electrodes  42 A and  43 A when cartridge  40 A is inserted into platter recess  50 A. As with the previous embodiment, rotation of platter  12 A generates a radially outwardly acting force  36 A urging fluid  30 A into distal portion  26 A of switch  10 A and into contact with pair of spaced electrical contacts  28 A and  29 A (see FIG.  3 ). Force  36 A is proportional to the rate of rotation of platter  12 A, and as a threshold rate of rotation is achieved, the value of force  36 A becomes sufficient to displace fluid  30 A from proximal portion  22 A to distal portion  26 A and into electrical contact with spaced electrical contacts  28 A and  29 A, thus completing an external electrical circuit (not shown) coupled to platter electrodes  52 A and  53 A. After rotational forces  36 A have tripped switch  10 A, switch  10 A may be reset by orienting cartridge  40 A such that fluid  30 A returns to proximal portion  22 A. This may be accomplished by automatically reorienting cartridge  40 A while in platter recess  50 A, or by manually removing cartridge  40 A from platter recess  50 A and orienting cartridge  40 A such that fluid  30 A flows from distal portion  26 A. 
     FIGS. 5 and 6 illustrate yet another embodiment of the present invention, a rotation-actuated electrical switch  10 B positionable in a rotatable platter  12 B, wherein switch  10 B has a generally linear configuration. FIG. 5 illustrates the preferred positioning of switch  10 B within platter  12 B. Rotatable platter  12 B is preferably generally circular, and is more preferably generally planar and includes a primary axis of rotation  14 B oriented substantially perpendicular to the plane of platter  12 B. Switch  10 B is preferably positioned within platter  12 B, but may also be attached externally thereto by any convenient means. Switch  10 B preferably extends generally radially outward from axis of rotation  14 B and more preferably does not intersect axis of rotation  14 B. 
     FIGS. 5 and 6 illustrate yet another embodiment of the present invention, a rotation-actuated electrical switch  10 B positionable in a rotatable platter  12 B, wherein switch  10 B has a generally linear configuration. FIG. 5 illustrates the preferred positioning of switch  10 B within platter  12 B. Rotatable platter  12 B is preferably generally circular, rotates about shaft  13 B, and is more preferably generally planar and includes a primary axis of rotation  14 B oriented substantially colinear with shaft  13 B and substantially perpendicular to the plane of platter  12 B. Switch  10 B is preferably positioned within platter  12 B, but may also be attached externally thereto by any convenient means. Switch  10 B preferably extends generally radially outward from axis of rotation  14 B and more preferably does not intersect axis of rotation  14 B. 
     Switch  20 B also includes a pair of spaced electrical contacts  28 B,  29 B adapted to electrically connect the interior of distal portion  26 B to the exterior of switch  10 B. Switch  10 B further includes an electrically conducting fluid  30 B (such as mercury or an aqueous electrolytic solution) partially filling enclosure  20 B. Fluid  30 B preferably rests in proximal portion  22 B of switch  10 B when platter  12 B is at rest. Switch  10 B is preferably oriented such that distal portion  26 B is positioned generally radially outward from proximal portion  22 B relative to axis of rotation  14 B. More preferentially, switch  10 B is also oriented such that proximal portion  22 B is positioned below distal portion  26 B such that while platter  12 B is at rest, gravity acts to retain fluid  30 B in proximal portion  22 B. 
     FIG. 6B illustrates the effects of rotation of platter  12 B on switch  10 B. Rotation of platter  12 B generates a radially outwardly acting force (represented by arrow  36 B) urging fluid  30 B into distal portion  26 B and into contact with the spaced electrical contacts  28 B and  29 B. Force  36 B is proportional to the rate of rotation of platter  12 B, such that when a threshold rate of platter  12 B rotation is achieved, force  36 B becomes sufficient to displace fluid  30 B from proximal portion  22 B into distal portion  26 B and thus into electrical contact with spaced electrical contacts  28 B and  29 B to complete an external electrical circuit (not shown). 
     The rate of rotation at which fluid  30 B becomes displaced into distal portion  26 B may be predetermined by varying the amount of fluid  30 B in enclosure  20 B, the composition (specifically, the viscosity and/or density) of fluid  30 B, varying the inclination of enclosure  20 B with respect to the plane of platter  12 B, and/or varying the positioning of electrical contacts  28 B and/or  29 B within distal portion  26 B. Generally, as the density and/or viscosity of fluid  30 B increases, a greater force  36 B will be required to displace fluid  30 B into distal portion  26 B. Likewise, as the inclination of enclosure  20 B becomes steeper, a greater force  36 B will be required to displace fluid  30 B into distal portion  26 B. Moreover, the farther the electrical contacts  28 B and  29 B are positioned from proximal portion  22 B, the greater the amount of force  36 B necessary to move fluid  30 B into electrical communication therewith. The precise rotational rate at which fluid  30 B electrically connects electrical contacts  28 B and  29 B may therefore be determined by choosing the appropriate inclination of enclosure  20 B, the appropriate amount and composition of fluid  30 B, and/or the appropriate positioning of electrical contacts  28 B and  29 B in distal portion  26 B in the appropriate combination. 
     While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiment has been shown and described and that all changes and modifications that come within the spirit of the invention are to be desired to be protected.