Patent Publication Number: US-2010120597-A1

Title: Centrifuge with non-synchronous drive system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a national phase application of PCT application PCT/EP/2008/051368 filed pursuant to 35 U.S.C. §371, which claims priority to GB 0701942.5 filed Feb. 2, 2007. Both applications are incorporated herein by reference in their entirety. 
    
    
     TECHNICAL FIELD 
     This invention relates to non-synchronous drives for centrifuges, in particular centrifuges for use in counter current chromatography. 
     BACKGROUND ART 
     Countercurrent chromatography (CCC) machines are used to separate particles in liquid mixtures. For an example of a CCC machine see WO 2003/086639. When separating polymers such as proteins, two aqueous phases are used for separation. However, the liquid aqueous phases currently used do not easily separate using current CCC machines. For polymers, it is an advantage to spin the coils more slowly than the rotation of the rotor, however using traditional CCC machines the flying leads will twist. The rotational speed of the rotor provides a base-line gravity gradient across the coil which contributes to retention of the stationary phase. The rotation speed of the coil column governs settling times and the tangential accelerations that promote mixing. In current CCC machines these speeds are linked by a 1:1 gearing requirement imposed by the flying leads, as using different gear ratios will result in the flying leads twisting as the columns rotate. 
     In the most common versions of the coil planet centrifuge the axis of the helical column is parallel and offset from the axis of the rotor. There are two basic types of parallel axis machines, I and J types—defined by their flying-lead characteristics and depend on the speed of the bobbin relative to the rotor. However these two basic machines only allow two different rotor speed/bobbin speed possibilities. Counter current chromatography machines that attempt to allow for variable rotation-revolution speed ratios are described in U.S. Pat. Nos. 4,277,017 and 4,287,061. However, for these machines the bobbins are still rotated synchronously around a main axis of rotation with a column to avoid twisting of the flying leads. 
     Therefore, a need remains for a non-synchronous centrifuge in which the speed of rotation of the bobbin and rotor can be independently changed. 
     SUMMARY OF THE INVENTION 
     An embodiment of the invention is a centrifuge having a main drive system having a first axis of rotation, a bobbin carrier for mounting a bobbin so as to have an axis of rotation that is parallel to and offset from the first axis of rotation, a first transmission system connected to the main drive system and the bobbin carrier to transmit power from the main drive system to rotate the carrier bobbin around the first axis of rotation and to rotate the carrier around the bobbin axis of rotation and a first bobbin drive system connected to the transmission system for driving the carrier around the bobbin axis of rotation. 
     The first transmission system is connected to the bobbin carrier by a differential such that the bobbin can rotate around the first axis of rotation at a different speed than the bobbin rotates around the bobbin axis of rotation. Having the differential allows the bobbin to rotate around the bobbin axis of rotation at a different speed and direction from the rotation of the bobbin about the main axis of rotation. The differential will compensate for the twisting of the flying leads that would otherwise occur due to the difference between the speed that the bobbin rotates around the bobbin axis of rotation and the speed the bobbin rotates around the main axis of rotation. 
     In some embodiments, the centrifuge includes a second bobbin drive system connected to the bobbin carrier to drive the carrier around the bobbin axis independently of the first bobbin drive system. This allows the rotation of the bobbin about its own axis of rotation to be controlled independently from the revolution of the bobbin around the main axis of rotation and therefore prevent the flying leads from twisting when the bobbin is rotating about its axis at a different speed and/or direction from what it is revolving around the main axis. The bobbin carrier can be part of the bobbin through which it connects to the drive systems of the centrifuge or may be a separate carrier which holds the bobbin in the centrifuge. The carrier allows the bobbin to be removably attached to the centrifuge. 
     In some embodiments, the first bobbin drive system includes a main drive gear through which it connects to the main drive system, an intermediate drive gear connected to the first drive, and a differential gear that is connected to the intermediate drive gear and to the bobbin carrier. 
     The bobbin carrier can include a bobbin gear through which it connects the bobbin to the differential gear of the first bobbin drive system. 
     The differential gear can have a smaller diameter than the first drive gear and bobbin gear. This allows the centrifuge to be more compact. 
     In some embodiments, the gear ratio of the bobbin gear and the intermediate drive gear is 1:1. In some cases, the intermediate drive gear can have a smaller diameter than the main drive gear. 
     In some embodiments the bobbin carrier can rotate around the first axis of rotation at a faster speed than the bobbin carrier rotates around the bobbin axis of rotation. 
     Another embodiment of the invention is a centrifuge including a main drive system having a first axis of rotation, an outer carrier that is connected to the main drive system and that rotates around the first axis of rotation and a bobbin carrier within the outer carrier for mounting a bobbin so as to have a bobbin axis of rotation that is parallel to and offset from the first axis of rotation. The centrifuge includes a first bobbin drive system that is connected to the outer carrier for driving the bobbin carrier about the bobbin axis of rotation, a first differential that is connected to the first bobbin drive system, a second bobbin drive system connected to the bobbin carrier so as to drive the bobbin carrier around the bobbin axis of rotation independently of the first bobbin drive system, and a second differential connected to the second drive system. The first and second differentials are connected to the first and second bobbin drive systems such that the bobbin is rotatable about the first axis of rotation at a different speed than the bobbin is rotatable about the bobbin axis of rotation. 
     The first bobbin drive system includes a bobbin drive gear and the bobbin carrier has a bobbin gear, the bobbin drive gear being connected to the bobbin gear. 
     A centrifuge can further include a casing wherein the first differential is connected to a stationary gear, the stationary gear being connected to the casing of the centrifuge. 
     The second bobbin drive system includes a second bobbin drive gear, the second differential being connected to the second bobbin drive gear and to a second bobbin gear connected to the bobbin carrier. 
     A third embodiment of the invention is a countercurrent chromatography machine comprising the centrifuge described above. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of a counter current chromatography apparatus. 
         FIG. 2  is a schematic diagram of another embodiment of a counter current chromatography. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows an embodiment of a “J” type coil centrifuge for counter current chromatography. The centrifuge  1  allows the bobbin  2  to rotate around the first axis of rotation at a different speed and direction than the bobbin rotates around the bobbin axis of rotation without the flying leads twisting. 
     The centrifuge  1  includes a casing  3  to protect the components and to allow control of environmental conditions such as temperature. The centrifuge  1  includes a main drive system  4  that is attached to a transmission system. The main drive system  4  includes a main drive motor  6  that drives the drive belt  9  which in turn rotates the main drive shaft  5  of the transmission system around its axis of rotation. The main drive shaft  5  is connected to a stationary gear  7  that is non-rotatably attached to a support tube  8  holding the main drive shaft  5 . 
     The main drive shaft  5  is connected to the first bobbin drive system  10  such that rotation of the main drive shaft  5  causes the first bobbin drive system to rotate about the axis of rotation of the main drive shaft. 
     The first bobbin drive system  10  includes a main drive gear  11 , an intermediate drive gear  12  that is attached to the main drive gear  11  by a support shaft  13 , and a differential bevel gear  14 . The first bobbin drive system  10  is attached to a bobbin carrier  15  via the differential bevel gear  14 . The bobbin carrier  15  holds the bobbin  2  including the coiled assembly to which the flying leads  16  are attached to. 
     As the first bobbin drive system rotates around the main axis of rotation, the bobbin carrier rotates around the main axis of rotation and around the bobbin axis of rotation, which is parallel to and offset from the first axis of rotation. In some embodiments, instead of the bobbin drive system rotating the bobbin about the bobbin axis of rotation via rotation of the bobbin carrier it is mounted in, the bobbin drive system may directly connect to the bobbin to rotate the bobbin about the bobbin axis of rotation. In this situation the bobbin carrier is part of the bobbin. 
     The second bobbin drive system  17  includes a bobbin drive shaft  18  powered by a motor (not shown) and a bobbin drive gear  19 . The bobbin drive system  17  is connected to the bobbin carrier  15  via the second bobbin drive gear  19  and as the drive shaft  18  rotates the drive shaft  18  drives the bobbin carrier about the bobbin axis of rotation. 
     As the main drive gear  11  is rotated around the main axis of rotation by the main drive system  4 , the main drive gear  11  rotates the bobbin carrier  15  and bobbin  2  around the main axis of rotation. The main drive gear  11  of the first bobbin drive system  10  is rotatably engaged with the stationary gear  7  of the transmission system such that as the first bobbin drive system  10  is rotated about the main axis of rotation, the main drive gear  11  rotates, which in turn causes the intermediate gear  12  to rotate. Rotating the intermediate gear rotates the differential gear  14  which causes the bobbin gear  20  and therefore the bobbin carrier  15  to rotate about the bobbin axis of rotation as the bobbin carrier  15  revolves around the main axis of rotation. 
     Therefore the bobbin carrier  15  is rotated simultaneously around the bobbin axis of rotation by two drive systems, directly by the second bobbin drive system  17  and indirectly by the main drive system  4  through the transmission system and first bobbin drive system  10 . This allows for non-synchronous driving of the centrifuge. 
     In another embodiment, the differential can be a unit mounted on a rotor separate from the bobbin, with the rotor being driven around a first axis of rotation by the main drive system. The differential receives inputs from the rotor main drive system and a second bobbin drive system creating an output to the bobbin, causing the bobbin to rotate about its axis as the rotor rotates about the main axis of rotation. In this arrangement the bobbin is not directly connected to the second bobbin drive system instead the second bobbin drive system is directly connected to the differential. 
     As the bobbin is rotated about the bobbin axis of rotation by a drive system that is independent from the drive system that is rotating the bobbin around the main axis of rotation, the speed and direction of the bobbin&#39;s rotation can be changed independently of the speed and direction of the rotation of the bobbin around the main axis of rotation. The rotation about the second axis of rotation provided by the transmission system is dependant on the speed and direction of rotation round the main axis of rotation. 
     The differential gear allows for the bobbin gear carrier to rotate at a different speed than the main drive gear, but still maintain a 1:1 gear ratio between the bobbin gear and intermediate drive gear. Therefore even though the bobbin gear and intermediate drive gear can rotate at different speeds, as the 1:1 gear ratio is maintained between the two gears, the flying leads will not twist as the bobbin carrier rotates around the first axis of rotation and the bobbin axis of rotation. The differential gear automatically compensates for the twisting difference of the flying leads between the speed of the bobbin&#39;s rotation around the main axis of rotation and the speed of the bobbin&#39;s rotation around the bobbin axis of rotation. Therefore this allows the transmission system and the bobbin drive system to rotate the bobbin at different speeds and in different direction. In  FIG. 1  the differential is shown as a bevel gear, however other arrangements may be used to achieve the differential action, such as spur gears or belt drives. 
     Referring to  FIG. 2  a second embodiment of a “J” type coil centrifuge for counter current chromatography is shown. 
     The centrifuge  30  includes a main drive system (not shown) that rotates a shaft  42 . Rotating the first shaft  42  in turn rotates an outer carrier  33  through which the flying leads  41  pass. A stationary shaft  31  is connected to a stationary gear  32 . The stationary shaft is connected to the casing of the centrifuge and through which the flying leads  41  pass. The outer carrier  33  is connected to the first bobbin drive system such that rotating the outer carrier  33  causes rotation of the first bobbin drive system. 
     The gear  35  of the first bobbin drive system is connected to the stationary gear  32  via a first differential gear  34 . The bobbin drive gear  36  of the first bobbin drive is connected to the bobbin carrier  38  via a bobbin gear  39 . 
     The bobbin carrier  38  holds the bobbin  40  including the coiled assembly to which the flying leads  41  are attached. As the first bobbin drive system is rotated around the main axis of rotation by the main drive system, the first bobbin drive system rotates the bobbin carrier  38  and bobbin  40  around the main axis of rotation. 
     The differential gear  34  allows the bobbin to rotate about the central axis of the bobbin at a different speed from the rotation of the outer carrier  33  around the axis of rotation of the first shaft  42 . 
     The second bobbin drive system is powered by a motor (not shown). The second bobbin drive system includes a main drive shaft  43  having a drive gear  48  and through which the flying leads pass. A second differential bevel gear  49  connects the drive gear  48  to a bobbin gear  44 . The bobbin gear  44  is connected via a shaft  50  to the inner carrier  51 . The bobbin carrier  38  is connected to the bobbin drive gear  44  via the inner carrier  51  and as the bobbin drive shaft  43  rotates about its axis it drives the bobbin carrier  38  about the bobbin&#39;s axis of rotation. 
     The first and second differential gears  34 ,  49  allow the input speeds of the rotating shafts  42  and  43  to be varied relative to one another without the flying leads becoming twisted as the centrifuge rotates. 
       FIG. 1  exemplifies the differential bevel gear  14  and the bobbin gear  20  having a gear ratio of 1:1. However various gear ratios may be used, such as using a smaller differential bevel gear which would allow the machine to be more compact, as long as the ratio of the bobbin gear  20  and the intermediate drive gear  12  remains at 1:1.  FIGS. 1 and 2  exemplify “J” type coil centrifuges, however by altering the speed and the direction of rotation of the bobbins the centrifuge can run as either an “I” or a “J” type machine. 
     Current parallel axis centrifuges only allow limited relative speeds of the rotor and bobbin. For an “I” type centrifuge the relative bobbin speed to rotor speed is −1 while for “J” type centrifuges the relative bobbin speed to rotor speed is +1. But as the centrifuge of the invention allows the bobbin speed and rotor speed to be changed independently, it increases the configurations that the centrifuge can be ran at. 
     The centrifuge can include more than one bobbin as shown in  FIG. 1  where the main drive system  4  is connected to a further bobbin drive system  21  which is connected to a second bobbin carrier  22  connected to the bobbin drive system  17 . 
     Although the non-synchronous machine is particularly useful for separating polymers such as proteins, the machine can be used to separate other types of compounds.