Abstract:
A water bath for laboratory use capable of two mixing motions is disclosed. Master magnets are mounted on eccentric shafts turned in a circular orbit by an electric motor beneath the bath. Slave magnets are mounted on a basket within the bath. The basket rides on spherical bearings within the bath. The bearings are received within tracks on the basket. A first set of the tracks are linear. A second set of the tracks are endless. When the bearings are received in the linear tracks, the basket moves in linear reciprocal motion in response to motion of the master magnets. When the bearings are received in the endless tracks, the basket moves in an orbit in response to motion of the master magnets. The tracks and the bearings are positioned so that a particular motion may be selected by orienting the basket within the bath.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention concerns water baths capable of dual mixing modes for laboratory use. 
       BACKGROUND OF THE INVENTION 
       [0002]    Various laboratory procedures, such as Northern and Southern hybridizations, the de-staining of gels, the incubation of cells or bacteria cultures and wash processes require mixing of constituents while maintaining the constituents at a constant temperature. For many applications, this is conveniently accomplished through the use of a water bath device wherein a basket which holds containers filled with the constituents, such as test tubes or flasks, is positioned within a tub containing water held at a constant temperature by heating elements. The basket is moved within the bath to agitate the contents of the containers as required according to the procedure. The speed of the motion as well as its duration, and the temperature of the water within the bath are all controlled by the device. 
         [0003]    It is advantageous to be able to vary the type of motion which the basket executes within the bath, as some procedures require a gentle agitation afforded by orbital motion of the basket. In contrast, other procedures require vigorous mixing normally associated with reciprocal basket motion. Prior art water bath devices capable of both orbital and reciprocal motion have complicated mechanisms which require various adjustments be made to the components to switch between the two types of motion. There is clearly a need for a water bath device which can be easily and conveniently switched between the orbital and reciprocal modes of motion without extensive adjustments or modifications to the mechanisms of the device. 
       SUMMARY OF THE INVENTION 
       [0004]    The invention concerns a device for agitating a miscible material in a container. The device comprises a plurality of spherical bearings positioned in spaced relation to one another. A supporting structure for holding the container, is positionable overlying the spherical bearings and is supportable thereon. A plurality of tracks are mounted on the supporting structure and are positioned in spaced relation to one another. Each of the tracks receives one bearing of the plurality of spherical bearings. The supporting structure is movable along a path defined by the tracks when the spherical bearings are received within the tracks. 
         [0005]    In one embodiment, a first group of tracks defines a first path of movement for the supporting structure, and a second group of tracks defines a second path of movement for the supporting structure. 
         [0006]    In a particular embodiment, the bath device comprises four of the spherical bearings and four of the tracks. The first group of tracks are linear tracks arranged parallel to one another and define a linear path. A first two of the spherical bearings are positioned separated from one another by a first distance. A second two of the spherical bearings are positioned in spaced relation to the first two spherical bearings. The second two spherical bearings are separated from one another by a second distance greater than the first distance. A first two of the linear tracks are separated from one another by the first distance for receiving the first two of the spherical bearings. A second two of the linear tracks are positioned in spaced relation to the first two linear tracks. The second two linear tracks are separated from one another by the second distance for receiving the second two spherical bearings. The supporting structure is movable along the linear path when the spherical bearings are received within the linear tracks. 
         [0007]    Each of the linear tracks may comprise a plate having a linear groove therein. The groove has an arcuate cross section with a radius of curvature substantially equal to the radius of curvature of the spherical bearings. 
         [0008]    The second tracks are comprised of a first two endless tracks mounted on the supporting structure and separated from one another by the first distance for receiving the first spherical bearings. A second two endless tracks are mounted on the supporting structure in spaced relation to the first two endless tracks. The second two endless tracks are separated from one another by the second distance for receiving the second spherical bearings. The first two linear tracks are positioned between the second two endless tracks, and the first two endless tracks are positioned between the second two linear tracks. The supporting structure is movable along the linear path when the spherical bearings are received within the linear tracks, and is movable along an endless path defined by the endless tracks when the spherical bearings are received within the endless tracks. 
         [0009]    Each of the endless tracks may comprise a plate having a circular groove therein. The groove has an arcuate cross section with a radius of curvature substantially equal to the radius of curvature of the spherical bearings. 
         [0010]    The device according to the invention may further comprise an electric motor positioned beneath the supporting structure. An eccentric shaft is coupled with the motor. The motor rotates the shaft. A master magnet is mounted on the eccentric shaft. The master magnet moves in a circular path when the shaft is rotated by the motor. A slave magnet is mounted on the supporting structure and is in spaced relation to the master magnet. The slave magnet is magnetically coupled to the master magnet. The supporting structure moves along the endless path when the spherical bearings are received within the endless tracks and the motor rotates the master magnet. The supporting structure moves along the linear path when the spherical bearings are received within the linear tracks and the motor rotates the master magnet. 
         [0011]    The device also comprises a tub having a plurality of sidewalls attached to a bottom. The bottom is positioned between the master and the slave magnets. The spherical bearings are mounted on the bottom within the tub. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a perspective view of an orbital and reciprocal water bath device according to the invention; 
           [0013]      FIG. 2  is a cross-sectional view taken at line  2 - 2  of  FIG. 1 ; 
           [0014]      FIG. 3  is a sectional-view taken at line  3 - 3  of  FIG. 2 ; 
           [0015]      FIG. 4  is an exploded perspective partial view showing the device in a linear motion configuration; 
           [0016]      FIG. 5  is an exploded perspective partial view showing the device in an orbital motion configuration; and 
           [0017]      FIG. 6  is an exploded perspective partial view of another embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0018]      FIG. 1  is a view of an orbital and reciprocal water bath device  10  according to the invention. Bath device  10  comprises a housing  12  which contains a tub  14  for holding water or other liquid to be used in the bath. A control panel  16  is conveniently mounted on the housing for controlling the operation of the bath device, for example, activation of the bath device, setting the bath temperature and the frequency and duration of the agitation of the bath contents. As best shown in  FIG. 2 , the control panel  16  interfaces with a control system  18 , preferably in the form of a microprocessor and associated electronic circuitry, which controls the various components of the bath device as described below. 
         [0019]    As further shown in  FIG. 2 , a container supporting structure  20  is positionable within the tub  14 . In this example, the container supporting structure  20  takes the form of a basket  22  having spring elements  24  for holding a flask  26  or other containers to be immersed within the bath. The basket is perforated with various openings  28  to promote flow of bath water through the basket and over the containers held therein. Basket  22  is supported on a plurality of spherical bearings  30  which are mounted on a bearing plate  32  attached to the bottom  34  of the tub  14 . A plurality of plates  36  are mounted on the bottom of the basket  22 . The plates  36  have tracks (described below) which receive the spherical bearings  30  which support the basket. The basket rides on the bearings, its motion guided by the tracks in plates  36 , and is readily removable for adding and removing containers as well as changing the mode of motion of basket  22  within the bath as described below. 
         [0020]    The tub  14  is heated by electrical resistive heaters  38  mounted on the underside of the tub. Heaters  38  are controlled by the control system  18  to maintain the bath at a constant temperature. Temperature measurement of the bath is effected preferably by means of a thermistor (not shown) which returns electronic signals indicative of the bath temperature to the control system to afford feedback for positive temperature control. The control system maintains temperature stability and uniformity within +/−0.1° C. over a temperature range between 5° C. above ambient to 99° C. 
         [0021]    Motion of the basket  22  is effected by an electric motor  40  mounted beneath the tub  14 . Motor  40  is controlled by the control system  18  and rotates an eccentric shaft  42 . A master magnet  44  is attached to the eccentric shaft by means of an intervening plate  46 . Use of the intervening plate  46  allows additional master magnets  48  to be positioned beneath the tub as well. The additional master magnets  48  are each secured to the intervening plate  46 . The motor  40  is attached to a fixed plate  52  mounted to the housing  12 . Additional eccentric shafts  50 , also mounted on the fixed plate  52 , support the intervening plate  46  (see  FIGS. 2 and 3 ). Motor  40  rotates the eccentric shaft  42 , which moves in an orbital motion  43  and causes the intervening plate  46  to which it is attached to move in an orbital motion due to the eccentricity of shafts  42  and  50 . The various master magnets  44  and  48 , being fixed to the intervening plate, also execute orbital motion. 
         [0022]    As shown in  FIG. 2 , the master magnets  44  and  48  are magnetically coupled through the bottom  34  of tub  14  with corresponding slave magnets  54  mounted on the bottom of basket  22 . It is, therefore, advantageous to make the tub from non-magnetic material. Non-magnetic stainless steel alloys are preferred for durability and corrosion resistance. Preferably, there are four master and slave magnet sets within the device  10  to ensure that coupling between the magnets is maintained and the basket performs the required motion at the desired frequency without significant lag or loss of coupling due to inertial effects. To additionally enhance magnetic coupling, the master and slave magnets  44 ,  48  and  54  are preferably multi-pole magnets having a plurality of N-S poles  55  spaced angularly around the magnet as shown in  FIG. 4 . Six N-S poles are preferred. A washer  57  formed of a magnetic material is mounted behind each magnet and used to direct the magnetic fields of the magnets toward one another. 
         [0023]      FIGS. 4 and 5  show detailed views of the track plates  36  which are mounted on the bottom of the basket  22 . The path which the basket takes in its motion is determined by the shape of the tracks  56  in the plates  36 . Two forms of tracks are advantageous, linear tracks  58 , and endless tracks  60 . The tracks may comprise grooves  62  which have an arcuate cross-section  64  having a radius of curvature substantially equal to the radius of curvature of the spherical bearings  30 . Matching of the radii between the grooves and the bearings prevents excessive motion of the basket on the bearings. 
         [0024]    To permit the basket to execute either linear reciprocal motion or orbital motion in response to the motion of master magnets  44  and  48 , both linear tracks  58  and endless tracks  60  are positioned on the basket. As shown in  FIG. 4 , four spherical bearings  30  are used in the example device. A first two of the spherical bearings,  30   a  and  30   b , are positioned in spaced apart relation to one another at a first distance  66 . A second two of the spherical bearings  30   c  and  30   d , are positioned spaced from the first two bearings, and spaced apart from one another at a second distance  68  greater than the first distance. The endless tracks  60  mounted on the underside of basket  22  are arranged on the basket so that a first two of the tracks,  60   a  and  60   b , are spaced from one another at the first distance  66 . A second two of the endless tracks,  60   c  and  60   d  are spaced from one another at the second distance  68 . This track spacing conforms with the bearing spacing and permits the basket  22  to be placed on the spherical bearings  30  with the bearings riding within the endless tracks  60 . The tracks cooperate with the bearings to permit orbital motion of the basket in response to the orbital motion of the master magnets. Thus, when the motor  40  rotates the master magnets  44  and  48  the magnetically coupled slave magnets  54  force the basket  22  to move, and the tracks  60   a - 60   d  constrain the motion of the basket to orbital motion along a path defined by the endless tracks  60 . In this example, the endless tracks are circular, resulting in circular orbital motion, but other shapes, such as ellipsoidal or oval, are also feasible. 
         [0025]    As shown in  FIG. 5 , the linear tracks  58 , also mounted on the underside of basket  22 , are arranged on the basket so that a first two of the tracks,  58   a  and  58   b , are spaced from one another at the first distance  66 . A second two of the linear tracks,  58   c  and  58   d  are spaced from one another at the second distance  68 . This track spacing also conforms with the bearing spacing and permits the basket  22  to be placed on the spherical bearings  30  with the bearings riding within the linear tracks  58 . The tracks cooperate with the bearings to permit linear reciprocal motion of the basket along a path defined by the tracks in response to the orbital motion of the master magnets. Thus, when the motor  40  rotates the master magnets  44  and  48 , the magnetically coupled slave magnets  54  force the basket to move, and the linear tracks  58  constrain the motion of the basket to a linear, reciprocal motion defined by the linear shape of the tracks  58 . 
         [0026]    It is noted in  FIGS. 4 and 5  that the positions of the first and second linear tracks  58   a - b  and  58   c - d  respectively, are reversed on the basket  22  from the first and second endless tracks,  60   a - b  and  60   c - d  respectively. As shown in Figures, the more closely spaced linear tracks  58   a  and  58   b  are positioned between the more widely spaced endless tracks  60   c  and  60   d , whereas the more closely spaced endless tracks  60   a  and  60   b , are positioned between the more widely spaced linear tracks  58   c  and  58   d . This configuration of the track spacing permits the motion of the basket  22  to be determined depending upon which way it is positioned within the tub  14 . For linear motion, the basket is oriented relatively to the bearing plate  32  as shown in  FIG. 5 , with the linear tracks  58  aligning with the bearings  30 . For orbital motion, the orientation of the basket relative to the bearing plate is merely reversed, as shown in  FIG. 4 , so that the endless tracks  60  align with the bearings  30 . 
         [0027]    For a practical device  10 , the orbital radius of the basket is about 10 mm and the frequency of the basket motion may be continuously adjusted between about 20 and about 200 cycles per minute. 
         [0028]    When the basket  22  is supported on spherical bearings  30  received within the linear tracks  58  as shown in  FIG. 5 , it is observed that the basket may bump the opposing sidewalls  70  of the tub  14  (see  FIG. 2 ) for certain linear motion frequencies. This action is avoided by positioning a pair of stop surfaces  72  beneath the basket. As shown in  FIGS. 2 and 5 , the stop surfaces may comprise an elastic loop  74  stretched between two posts  76  attached in spaced relation on the bearing plate  32 . The stretched elastic loop  74  presents oppositely disposed segments  74   a  and  74   b  which are oriented transversely to the motion of the basket  22 . A pin  78  projects from the bottom of basket  22  toward the bearing plate  32 . The pin  78  is located on the basket  22  and the loop  74  is located on the bearing plate  32  such that the pin is positioned between the segments  74   a  and  74   b  only when the spherical bearings  30  are received within the linear tracks  58  ( FIG. 5 ). When the bearings are received within the endless tracks  60 , the pin  78  is spaced away from the elastic segments so that it does not make contact with them, and the motion of the basket is not affected by the presence of the stop surfaces  72 . 
         [0029]    In another embodiment, shown in  FIG. 6 , the bath device  80  has three spherical bearings  30   a ,  30   b  and  30   c  spaced in a triangular plan form with two of the bearings  30   a  and  30   b  in spaced relation along a line  72  and the third bearing  30   c  positioned spaced from the first two along a line  74  which bisects the first line  72 . The basket  22  in this embodiment has three linear tracks  58   a ,  58   b  and  58   c , and three endless tracks  60   a ,  60   b  and  60   c . The tracks are arranged so that one orbital track,  60   c  is positioned between two linear tracks  58   a  and  58   b , and one linear track  58   c , is positioned between two orbital tracks  60   a  and  60   b . This triangular configuration of bearings and tracks again makes it possible to select the type of motion of the basket  22  merely by the orientation of basket  22  within the tub  14 . If, as shown in  FIG. 6 , the basket  22  is oriented to present the linear tracks  58   a - 58   c  to the bearings  30   a - 30   c , then the basket will execute linear motion when motor  40  rotates the eccentric shaft  42 . If the orientation of the basket is reversed, then the orbital tracks  60   a - 60   c  will receive the bearings  30   a - 30   c  and the basket will execute orbital motion determined by the shape of the tracks. 
         [0030]    Orbital and reciprocal bath devices according to the invention provide improved versatility over prior art bath devices in permitting either one of two different mixing modes to be executed based upon the orientation of the container support device within the tub of the bath. The invention eliminates complicated mechanisms that must be adjusted to switch form one mixing mode to the other, thereby simplifying operation and improving reliability.