Patent Publication Number: US-8534905-B2

Title: Adjustable orbit imbalance compensating orbital shaker

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a CIP of U.S. application Ser. No. 13/114,280 now U.S. Pat. No. 8,226,291,filed on May 24, 2011 by Zamirowski, et al. entitled “ADJUSTABLE ORBIT IMBALANCE COMPENSATING ORBITAL SHAKER”, which claims priority to U.S. Provisional Application No. 61/347,484 filed on May 24, 2010 by Zamirowski, et al. entitled “ADJUSTABLE ORBIT IMBALANCE COMPENSATING ORBITAL SHAKER”, which are incorporated herein by reference in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Statement of the Technical Field 
     This invention generally relates to orbital shaker apparatus and, more specifically, to an apparatus for reducing the instability generally caused by static imbalance between a counterweight and the load of flasks or other vessels on the platform, and an apparatus for varying the orbit diameter of the shaker. 
     2. Description of the Related Art 
     An orbital shaker apparatus is a mixing or stirring device used especially in scientific applications or mixing or stirring containers, such as beakers and flasks holding various liquids on a platform. Specifically, an orbital shaker translates a platform in a manner such that all points on the upper surface, in the X-Y plane, of the platform move in a circular path having a common radius. Generally, beakers, flasks, and other vessels are attached to the upper surface of the platform such that the liquid contained therein is swirled around the interior side walls of the vessel to increase mixing and increase interaction or exchange between the liquid and local gaseous environment. Conventionally, the apparatus which drives the platform in an orbital translation includes one or more vertical shafts driven by a motor with an offset or crank on the upper end of an uppermost shaft such that the axis of the upper shaft moves in a circle with a radius determined by the offset in the shaft, i.e., by the “crank throw”. The upper shaft or shafts are connected to the underside of the platform via a bearing to disconnect the rotational movement between the upper shaft or shafts and the platform. 
     In operation, the mass of the shaft above the offset or crank throw, the platform with its mounting hardware and the load consisting of the filled flasks or vessels, and the clips or fasteners which hold the vessels to the platform all translate at the rotational velocity of the driven shaft in a circle with a radius equal to the crank throw. The mass of the liquid within the vessels translates at the shaft rotational velocity in a circle with a radius equal to the crank throw plus the distance from the center of the vessel to the center of mass of the liquid contained in the vessel. 
     The forces resulting from the total orbitally-rotating mass can often cause motion of the base of the shaker which can superimpose additional motion components into the liquid in the vessels and lead to undesirable turbulence or splashing. These forces can also cause the base unit to move or “walk” along its support surface. 
     In order to reduce this motion, the mass of the non-rotating supporting structure must be increased to resist the forces generated by the rotating mass. This leads to the undesirable effect of increasing the overall weight of the shaker simply to address for stabilization. Alternatively, counterweights have been employed to oppose or compensate for the forces generated from the orbitally-rotating mass. 
     For example, U.S. Pat. No. 3,430,926 to Freedman, et al., entitled “Counterweight System for Shaker Apparatus,” describes the use of multiple fixed counterweights situated about a shaft which counteract the imbalance forces generated by a rotating platform. 
     U.S. Pat. No. 5,558,437 to Rode, entitled “Dynamically Balanced Orbital Shaker,” addresses the issue of static and dynamic imbalance by positioning various fixed masses in the plane of the crank arm such that their masses and placement exactly cancel out the effects of the rotating platform&#39;s mass contribution. 
     Similarly, European Patent Application No. EP1854533 to Hawrylenko, entitled “Shaker,” describes a crank arrangement where two balancing masses can be adjusted radially and vertically to compensate for a given loading condition. 
     These arrangements all undesirably require selecting specific masses and locations, vertically as well as radially, which vary depending upon the platform load conditions. In addition, in order to correct for large mass imbalances statically and dynamically, these devices require considerable space to place the correcting weights in the appropriate locations relative to the platform load, and also increase the overall product weight. 
     U.S. Pat. No. 6,106,143 to Nickel, et al., entitled “Vibrating Device for Vibrating Liquid Provided in Vessels,” provides a means to adjust a static counterweight to compensate for a range of platform loads by advancing or retracting a mass radially along an axis. The distance between the center of mass of the counterweight and the axis of rotation increases or decreases, and thus generates an increased or decreased amount of balance compensation. This is a practical solution for modest platform loads but is not feasible for providing a large dynamic compensation range. For example, if a large counterweight mass is selected, it may not be positioned close enough to the axis of rotation to achieve a minimal balance compensation. If a small counterweight is selected, it is difficult to position it far enough from the axis of rotation to balance a large platform load without using considerable additional space. Also, this device does not provide any feedback to the user that the onset of detrimental instability is imminent, which would require a compensating adjustment. 
     U.S. Patent Application Publication Serial No. US2008/0056059 to Manera, et al. describes the use of a vibration sensor to detect an unbalanced loading condition and reduce the shaking speed to a stable magnitude, but it does not provide a means for the counterweight of the orbital shaker to be adjusted, or a process which can be applied, in order to achieve the desired speed. 
     There are rotating equipment in other technical fields that use balancing heads to correct for rotor imbalances using two arms with weights. See, for example, Mechanical Vibrations, J. P. Den Hartog 1934, pp. 236-237 ISBN 0-486-64785-4. However, orbital shakers tend to differ because the platform load includes not only a static mass component, but also a dynamic component, namely the fluid in the flasks or other containers. This fluid generates a variable imbalance depending upon the geometry of the container, amount of fluid in the container, the orbit diameter of the shaker, and the speed of the shaker which could result in a different amount of resultant balance compensation depending upon the operating conditions. Furthermore, automatic balancing techniques, whereby balancing masses migrate to the correct positions to minimize vibrations, are not generally applicable to orbital shakers because orbital shakers operate much slower than the critical speeds required to enable these techniques. 
     The eccentric throw for an orbital shaker is typically fixed by precisely machining a single component. The offset between the two eccentric journals defines the orbit radius. This radius is not adjustable. Adjusting the eccentric throw by separating the two journals into independent bearing housings whose centers of rotation can be fixed at different eccentric offsets relative to each other is a method which is known in prior art, such as, for example, the Kuehner shaker. What has not been achieved is a means of manually or automatically adjusting the eccentric throw within a continuously variable range. Furthermore, a change in the eccentric throw for a given platform load results in a change in the amount of counterweight needed to compensate for it. Thus, it is desired to combine the ability to adjust the eccentric throw with the ability to adjust the compensating counterweight simultaneously. 
     It is also desirable for an orbital shaker device to provide feedback to the user, or, in the case of a shaker with automatic adjustment, to provide feedback to its controller that the onset of detrimental instability which would require a compensating adjustment is imminent. 
     It is also desirable to provide an orbital shaker capable of balancing a large platform using counterweights of intermediate size without requiring a device of unreasonable size or weight. 
     SUMMARY OF THE INVENTION 
     An aspect of the present invention provides an orbital shaker apparatus including a first shaft rotatable about a first axis with a mounting portion, a first bearing assembly receiving the first shaft and mounted to the shaker chassis, a second shaft rotatable about a second axis offset from said first axis and including a platform portion, a second bearing assembly receiving the second shaft, a counterweight rotor assembly mounted between the mounting portion of the first shaft and the mounting portion of the second shaft, the counterweight rotor assembly extending radially around the first shaft. A platform is connected to the bearing assembly of said second shaft such that rotation of the platform occurs in an orbital manner about the first axis. Two equal counterweights are positioned in the counterweight rotor assembly, the counterweights having a fixed radial position but being adjustable in the circumferential direction to facilitate a variable counterweight balance such that a static balance between the platform load and the counterweights about the first shaft axis may be achieved. Also provided is a means of detecting static imbalance between the platform load and the counterweights. 
     In another aspect of the invention, these features allow the user to adjust the position of the counterweights in response to the noticeable imbalance of the system or information provided by the orbital shaker controller to minimize the static imbalance or reduce it to an acceptable level. 
     Additionally, a sliding connection placed between the mounting portions of the first and second shafts allows adjustment of the eccentric orbit by moving the shaft axes relative to each other. 
     In another aspect of the invention, actuators and sensors can be added to the system, which, under the direction of the controller, allow automatic adjustment of the counterweights in response to detected static imbalances, as well as automatic adjustment of the eccentric orbit to a user-specified distance. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself, however, as well as a best mode of use, further purposes and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, where: 
         FIG. 1  is a schematic elevation section view depicting the general arrangement of the components, in accordance with an embodiment of the invention. 
         FIG. 2  is a top view of the embodiment of the invention depicted in  FIG. 1 . 
         FIG. 3A  is a top view of a counterweight rotor assembly with the platform removed for clarity, to illustrate the principles of imbalance compensation using counterweight wedges, in accordance with an embodiment of the invention. 
         FIG. 3B  is another top view of the counterweight rotor assembly with counterweights moved to another position, in accordance with an embodiment of the invention. 
         FIG. 3C , is another top view of the counterweight rotor assembly with counterweights moved to another position, in accordance with an embodiment of the invention. 
         FIG. 4  is an isometric view of the rotor assembly illustrating the components involved in manually adjusting the counterweight wedges, in accordance with an embodiment of the invention. 
         FIG. 5  is an isometric view of the rotor assembly illustrating an alternate embodiment for adjusting the counterweight wedges, and includes a view of the motor which is used for automatic counterweight adjustment, in accordance with an embodiment of the invention. 
         FIG. 6  is a top view of the embodiment depicted in  FIG. 5 , in accordance with an embodiment of the invention. 
         FIG. 7A  is a cross section view of an elevation of the counterweight rotor assembly showing the method of manual adjustment of the eccentric offset, and a detail of the end of the adjustment rod, respectively, in accordance with an embodiment of the invention. 
         FIG. 7B  is a cross section view of an elevation of the counterweight rotor assembly showing the method of manual adjustment of the eccentric offset, and a detail of the end of the adjustment rod, respectively, in accordance with an embodiment of the invention. 
         FIG. 8  illustrates the typically observed value of the acceleration parameter for a range of loading and operating conditions, in accordance with an embodiment of the invention. 
         FIG. 9  is a flowchart for the operation of the manually-adjusted counterweight and eccentric orbit system, in accordance with an embodiment of the invention. 
         FIG. 10  is a system block diagram for the electronics of the manually adjustable embodiment, in accordance with an embodiment of the invention. 
         FIG. 11  shows a detail view of the eccentric actuator which is used to automatically adjust the orbit diameter of the orbital shaker, in accordance with an embodiment of the invention. 
         FIG. 12  is the system block diagram for the automatically-adjusted counterweight and eccentric orbit system, in accordance with an embodiment of the invention. 
         FIG. 13  is a cross section elevation view of the rotor assembly showing the position of the inductive coupling which supplies power and transfers electronic signals to and from the rotor, in accordance with an embodiment of the invention. 
         FIG. 14  provides the process flowchart for automatic adjustment of the eccentric offset and counterweight wedges, in accordance with an embodiment of the invention. 
         FIG. 15  is a further, graphical explanation of the automatic counterweight adjustment routine, in accordance with an embodiment of the invention. 
         FIG. 16  is an isometric view of a method for manual fixing and adjustment of counterweight positions, in accordance with an embodiment of the invention. 
         FIG. 17  is an isometric view of a method for manual fixing and adjustment of counterweight positions, in accordance with an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The description of the present invention has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. 
     During the course of this description like numbers will be used to identify like elements according to the different views which illustrate the invention. 
     The present invention advantageously provides an orbital shaker device with the ability to adjust the eccentric throw and to adjust the compensating counterweights simultaneously. 
     The present invention also advantageously provides an orbital shaker device that provides feedback to the user, or, in the case of a shaker with automatic adjustment, that provides feedback to it&#39;s controller that the onset of detrimental instability which would require a compensating adjustment is imminent 
     The present invention also provides an orbital shaker capable of balancing a large platform using counterweights of intermediate size without requiring a device of unreasonable size and weight. 
       FIG. 1  illustrates the preferred embodiment of the invention  10  which allows manual adjustment of the counterweights and the eccentric crank throw. This embodiment includes a first shaft  12  and first bearing assembly  18 , a second shaft  26  and second bearing assembly  32 , a shaft slide  42 , and a counterweight rotor assembly  38 . Also included is the first bearing housing  20  and first shaft bearings  22 , as well as second shaft mounting portion  30 , the second bearing housing  34  and second shaft bearings  36 . 
     The first bearing assembly  18  is preferably rigidly coupled to the shaker chassis  24  and is thereby constrained from rotation. The first shaft  12  is connected to the first bearing assembly  18  by bearings so that it is free to rotate about the first shaft axis  14 . The mounting portion  16  of the first shaft  12  is rigidly coupled to the counterweight rotor assembly  38 , visible in  FIG. 2 , so that the rotor can rotate in unison with the first shaft  12 . 
     As seen in  FIG. 2 , the counterweight rotor assembly  38  is centrally located, and is rotated by a belt  29  which is driven by a pulley  27  connected to the rotating shaft of a motor  25  mounted to the chassis  24 . The rotor consists of a drum with a pulley groove  37  around its circumference at the lower edge. This drum has a central raised area which forms a pedestal  39 . This pedestal portion is rigidly coupled to the first shaft  12 . 
     The counterweight rotor assembly  38  also contains two counterweight bearings  41  which are attached to the counterweight wedges  40 . Counterweight bearings  41  are free to rotate about the rotor assembly pedestal but constrained from vertical motion by a cap  43  on the pedestal  39 . 
     A platform  44  for supporting flasks  46  or other containers (not depicted) to be shaken is mounted to the second shaft bearing assembly  32 . The platform  44  assembly could be further subdivided into a subplatform which is reinforced for stiffness and connected to the second bearing assembly  32 , as well as a tray where the flasks are mounted. A subplatform and tray can be connected by lockable, linear guides so that the tray can be moved to a more ergonomically acceptable position closer to the user in the typical case where the orbital shaker is enclosed in a cabinet with a door to maintain the atmosphere to which the agitated samples are exposed. 
     The second shaft axis  28  is offset from the first shaft axis  14  by a distance R. As the counterweight rotor  38  turns, the second shaft  26  and second bearing assembly  32  describe a circular orbit with diameter 2R about the first shaft axis  14 . Platform  44  is constrained to a circular orbit by virtue of this offset as well as its connection to a flexure assembly  48 . Flexure assembly  48  is a typical leaf spring linkage to limit the platform&#39;s remaining degrees of freedom to pure rotation. The pairs of flexure springs are orthogonal to each other and constrained so that they may move in only one direction, e.g., left/right or front/back. One pair is connected to the platform  44 , while the other pair is connected to the chassis  24 . Both pairs are connected and kept orthogonal to each other through a rigid mechanical frame. For compactness, to consolidate all the springs in one plane, and to increase the axial stiffness of the springs in the longer platform direction and eliminate a cantilever, the leaf springs which move in the front/back direction connect to the chassis at their ends, and connect to the mechanical frame in the middle. 
     In an alternate embodiment, the platform&#39;s unconstrained degrees of freedom are limited by at least two additional eccentric shafts and bearing assemblies (not depicted) mounted between the platform  44  and chassis  24 , as is typical in triple eccentric bearing housing designs. 
       FIGS. 3A ,  3 B and  3 C illustrate exemplary distributions of the various system loads and a method whereby the present invention accomplishes static balancing. Normally, a single counterweight is selected to balance the static moment generated by the dead and live platform loads. The dead load is defined as the portion of the total system mass which is rigidly coupled to the rotating platform. The live load is defined as the portion of the total system mass which is enclosed by the containers on the rotating platform and is typically a liquid solution. The necessary static balance from the counterweight can be expressed as a torque (in-lb) and is determined by multiplying the weight in the vertical direction by the distance between the line of action of the weight and the first shaft axis  14 . For the dead load, this is simplified as a vertically-oriented force acting at the orbit radius R. For the live load, it is a vertically-oriented force acting at an orbit larger than R based upon agitation speed, the geometry of the media container (e.g., usually an Erlenmeyer flask) and the amount of fluid or the fill level of the container. Since the live and dead load weights and positions can vary depending upon the user&#39;s desires, a single counterweight acting at a fixed position may only statically balance one loading condition. 
     Instead of a single fixed counterweight, one aspect of the present invention is to divide this component into two equal counterweight wedges  40  which can be translated circumferentially about the rotor assembly  38 . The benefits of this feature may best be observed in the top view of the rotor assembly. 
       FIG. 3A  illustrates the relative positions of the live load L, dead load D, and individual centers of mass of the counterweight wedges, C 1  and C 2 . The vertical line is the symmetry plane through the shaft axes  14 ,  28 . The distances R, RL, and Rc are the static moment distances of the dead load, live load, and counterweight, respectively. In order to provide a static balance between the platform load and the counterweights, the following equation must be satisfied:
 
 D×R+L×RL=Rc ×( C 1 +C 2)  (1)
 
where D=Dead load weight, L=live load weight, and C 1  and C 2  are the weights of the individual counterweight wedges.
 
     The effective balancing contribution may be considered as the sum of the masses of the individual wedges multiplied by the distance from the axis of rotation of the first shaft of the rotor. As each counterweight wedge is moved, its center of mass also shifts. As the wedges are moved in unison away from each other, the effective center of mass of the combination of the two slides toward the center of the rotor. This decreases the moment arm over which the counterweight&#39;s mass acts, as shown in  FIG. 3B , where Rc&lt;Rc max, and thus reduces the static balancing contribution. In the extreme case, as shown in  FIG. 3C , Rc shrinks to zero and the two counterweights cancel each other&#39;s contributions, thus providing no static balancing whatsoever. 
     The counterweight masses are designed such that Rc max×(C 1 +C 2 ) is greater than or equal to the maximum conditions of R, RL, D, and L for a given orbital shaker. Based upon this, there will always be a counterweight position which can provide the proper static balance for any loading condition. 
     Since the platform load and counterweights orbit in different horizontal planes, they generate a dynamic imbalance which cannot be compensated by the two aforementioned counterweight wedges. In an embodiment of the invention, a second set of counterweights could be added to the system in a different vertical plane and adjusted in such a manner to compensate for the dynamic imbalance. These weights would be disposed in the same direction as the second shaft axis  28  relative to the first shaft axis  14  and be sized to accommodate the desired range of platform loads. 
       FIGS. 16 and 17  illustrate an embodiment in which the position of the counterweights are fixed and adjusted manually. In this embodiment, the rotor drum  47  is eliminated and the position markings or gradations  92  are applied to a bracket  94  which is rigidly coupled to the rotor  38 . This bracket  94  also has integral slots, grooves  96 , or teeth which are spaced periodically around the circumference. An indicator  86  with a spring pin assembly  82  including a spring  88  and pin  90  is rigidly coupled to the counterweight C 1 , C 2 . The spring pin diameter is sized so that it can engage the integral slots/grooves/teeth  96 . When the handle  84  is depressed, the pin  90  is displaced from the grooves  96  and the counterweight C 1 , C 2  can be freely rotated as in other embodiments. When the handle  84  is released, the spring  88  forces the pin  90  into one of the slots  96  and fixes the position of the counterweight C 1 , C 2 . This eliminates the need for the locking bolts described in other embodiments. This embodiment also allows the counterweights C 1 , C 2  to be manually adjusted from the side of the rotor  38  instead of from above the rotor  38 . 
     There are several alternatives for manually adjusting the position of the counterweight wedges. In  FIG. 4  illustrates an exemplary embodiment of the invention in which the counterweight wedges are vertically supported by the counterweight bearings  41  and a shoulder bolt  49  connection to the rotor drum  47 . As described previously, the counterweight wedges are radially and vertically constrained but are free to move in circumferential rotation. The shoulder bolt connection passes through a slot  51  in the drum so that by tightening the bolt  49  and compressing a backing washer  53  the counterweight can be held at any circumferential position along the slot  51 . The slot  51  can be provided with marks or gradations adjacent to it to assist the user in selecting the correct position for the counterweights  40  as a function of the platform load. In alternate embodiments, the bolt  51  may be replaced by a draw latch or compression latch for easier adjustment. In operation, the user could readily loosen the counterweight bolts to allow free rotation, make an adjustment to both counterweight wedges according to the load requirements, and tighten the bolts to fix the position of the counterweights. 
       FIGS. 5 and 6  illustrate another exemplary embodiment of the invention for manually adjusting the position of the counterweight wedges. In this embodiment, gears  63  are added to the counterweight bearings  41 , and a geartrain  64  is added to the counterweight rotor  38 . The input shaft  65  of the geartrain is oriented vertically and is accessible through a hole  33  in the platform  44 . The geartrain  64  meshes with the counterweight gears  63  and is designed so that the counterweights rotate in opposite directions from each other. Evenly-spaced markings or gradations  67  are added to the upper counterweight bearing ring  41  and a notch  61  is placed in the bearing cap  43  so that these marks can be seen by the user during adjustment. By turning the input shaft  65  clockwise or counterclockwise, the counterweights move closer to or further away from each other circumferentially and thus either increase or decrease the amount of imbalance compensation. In this embodiment, the counterweights  40  are supported vertically by rollers or low friction materials instead of the shoulder bolt  49  connections to the rotor drum  47 . 
     In order to address varying user demands for effectively agitating a range of flasks and other samples on the platform, the crank throw/eccentric offset dimension, R, may be adjusted. This will change the amount of counterweight compensation necessary, as the effective radial load will increase or decrease as R is modified. Thus, allowing the adjustment of the crank throw must necessarily involve being able to adjust the static balance correction from the counterweights. The present invention provides this eccentric adjustment in an embodiment, as illustrated in  FIGS. 7A and 7B . 
       FIG. 7A  shows that the second shaft  26  which has a second axis  28  offset from the first shaft axis  14  is rigidly coupled to a shaft slide  42 . The shaft slide  42  has a flange with a nut  45  having a main axis oriented perpendicular to the second shaft axis  28  and parallel to the allowable direction of travel of the shaft slide. The shaft slide  42  is constrained laterally by a recess in the rotor pedestal  39  and is constrained vertically by the bearing cap  43 . In an alternate embodiment, a dovetail slide can be substituted for the shaft slide  42 . The shaft slide  42  has two pins  35  to provide a positive travel stop when they interfere with the bearing cap. The threaded nut  45  portion of the shaft slide  42  is connected to a threaded rod  58  which serves as a lead screw. The rod  58  is captured by the rotor drum  47  with a snap ring  59  so that the rod can rotate but cannot translate. Thus, as the rod  58  is turned the shaft slide  42  is free to move within its travel limits in the radial direction. This radial travel shifts the first and second shaft axes  14 ,  28  closer to or further away from each other, which results in an increased or decreased eccentric crank throw, R. A jam nut  60 , when tightened, prevents the rod from rotating during operation of the orbital shaker, which would alter the orbit radius. A scale can be provided on the platform  44  for an indication to the user of the current eccentric offset, or the number of turns of the rod  58  can be correlated with this offset distance based upon the thread pitch. 
     In order to detect the onset of undesirable static imbalance, an embodiment of the invention requires an additional element. The preferred embodiment incorporates an accelerometer  54  mounted to the chassis  24  of the orbital shaker. This accelerometer  54  is sensitive to static and dynamic imbalances in three principal directions X, Y, Z. While the orbital shaker is operating, a supervisory electronic controller  56  reads the output signals from the axes and calculates an acceleration parameter, which can be defined as the following:
 
Acceleration Parameter=(( X −accel) 2 +( Y −accel) 2 +( Z −accel) 2 ) 1/2  
 
     The allowable limit for this parameter, hereinafter “the stability limit”, permitted by the controller  56  will vary depending upon the load requirements, mass, and geometry of the orbital shaker.  FIG. 8  provides a demonstration of the typically observed value of the acceleration parameter for a range of loading and operating conditions. The chart shows the measured acceleration parameter against the counterweight angle, where an increasing angle corresponds with increasing imbalance compensation. 
     The measured value of the acceleration parameter for a given loading condition and speed is roughly parabolic. A portion of this parabola lies below the stability limit and is called the stability zone. Any selected counterweight angle within this stability zone will yield acceptable operation. The stability zone decreases with increasing speed, and the minimum of the parabola increases with increasing platform load as the magnitude of the dynamic imbalance increases. Also, typically the minimum of the parabola for a given loading condition is within the stability zone for higher speed operation. 
       FIG. 9  provides an exemplary flowchart  90  for the operation of the manually-adjusted counterweight and eccentric orbit system according to an embodiment of the invention. In an embodiment of the invention, the user first adjusts the eccentric orbit  92 . Next, through a user interface  55 , such as, for example, a touchscreen, the user specifies the eccentric offset, the platform/flask configuration, and the desired speed (RPM)  94 . Since the controller  56  monitors the onset of instability, it is not necessary to provide platform information except to reduce the time necessary to manually adjust the counterweights to the correct position. The controller  56  then calculates a first counterweight position  96 , and the user adjusts the counterweights to this position  98  using the aforementioned method(s). The controller starts the motor  25  and increases the speed  100  while monitoring the acceleration parameter  102 . So long as this parameter does not exceed the stability limit  104 , the speed is increased until the desired speed is achieved  106 . If the parameter exceeds the stability limit, then the motor is stopped  108  and the controller revises its calculation for the proper counterweight position  96 . 
       FIG. 12  depicts an exemplary system block diagram  120  for manual adjustment and monitoring of the counterweights and eccentric crank throw. In addition to these components needed for manual adjustment and monitoring, elements may be added for sensing and actuation of the counterweights and eccentric offset. 
       FIG. 10  provides an exemplary system block diagram  110  for various embodiments of the invention. It is understood that the main controller  56  includes at least one processor and associated computer memory (not depicted) specially configured to perform the described functionality. Persons of skill in the arts of processors understand that various alternative processors using various operating systems and memory configurations may be used to implement the systems and methods described. The main controller  56  is accessible to the user via a user interface  55 . At a minimum, the user interface  55  includes a display providing information to the user and a keyboard or other input device allowing the user to communicate instructions and data to the controller  56 . In a preferred embodiment of the invention, the user interface  55  is a touchscreen. The controller is also in operative communication with the motor  25 , accelerometer  54 , rotor PCB  57  counterweight motor  62 , counterweight travel limit sensor (high)  78 , counterweight travel limit sensor (low)  79 , counterweight position sensor  76 , eccentric actuator  72 , and eccentric actuator position sensor  74  via inductive stationary coupling  66 /inductive rotating coupling  69 . All electrical components of all embodiments, including but not limited to the main controller  56 , motor  25 , accelerometer  54 , and user interface  55  are provided electrical power by a DC power supply  71 . Power and control signals are also provided to the rotor PCB  57  counterweight motor  62 , counterweight travel limit sensor (high)  78 , counterweight travel limit sensor (low)  79 , counterweight position sensor  76 , eccentric actuator  72 , and eccentric actuator position sensor  74  via inductive stationary coupling  66 /inductive rotating coupling  69 . A preferred embodiment of the invention uses a Dayton permanent magnet gearmotor 2L005 as counterweight motor  62 , a Honeywell HOA1405 reflective sensor for the counterweight position sensor  76 , a Firgelli Automation Linear Actuator FA-240-S-12-1″ as the eccentric actuator  72 , and a MESA Systems DON100 HE30 for the inductive stationary coupling  66 /inductive rotating coupling  69 . Those of ordinary skill in the electronic arts understand that alternative means of providing power and control to the various electronic elements of the invention may be employed. It is also understood that alternatives to the preferred motors, sensors, actuators and couplings listed above may be employed. 
     A preferred embodiment for the invention which allows for automatic adjustment of the counterweights and the eccentric crank throw is now described. For automatic adjustment of the counterweights and the eccentric crank throw, a counterweight motor  62  is preferably added to the counterweight rotor  38  as indicated in  FIG. 5  for adjusting the counterweights. The counterweight motor  62  engages one of the counterweight bearing gears  63  in order to cause it to rotate about the first shaft axis  14 . The counterweight geartrain  64  ensures that both bearing gears  63  counter rotate in unison. This counter-rotation results in counter-translation of the counterweights, which is the desired motion for proper static balancing. Limit switches  78 ,  79  prevent operating the gear motor when the counterweights reach their travel limits. A counterweight position sensor  76 , such as, for example, an optical encoder, or retroreflective sensor mounted to one of the counterweight wedges and capable of detecting the reflective/non-reflective transitions between the teeth of the counterweight geartrain  64 , determines the location of the counterweights. The counterweight motor  62  is sized so that when the rotor accelerates or decelerates the counterweights do not generate enough torque to overcome the gear train and motor&#39;s inertial resistance. 
     For changing the eccentric crank throw, an actuator  72  as in  FIG. 11  is placed between the rotor drum and the shaft slide  42 . This actuator replaces the rod  58  and contains a lead screw which is sized to resist the maximum centripetal force generated by the platform without turning, which would change the crank throw dimension, R. The actuator can contain or be used in conjunction with position sensor  74 , such as an LVDT or potentiometer so that the position of the actuator can be determined and sent to the main controller. 
     As shown in  FIG. 13 , in order to provide electrical power and control signals to the actuators on the spinning rotor in an embodiment of the invention, an inductive coupling is placed in the space between the rotor pedestal and the lower shaft housing. One half of the coupling is fixed to the housing, while the other is connected to the rotor. Signal and power are transmitted across an air gap between the two components. In other embodiments, this electrical connection can be made using a slip ring, or an electrically conductive fluid coupling. 
       FIG. 14  describes an exemplary process  140  for automatic adjustment. In an embodiment of the invention, the user inputs  142  the desired speed and eccentric offset into the user interface  55 . The controller  56  automatically adjusts the eccentric offset to the desired position  144  using the eccentric actuator  72  and the position sensor  74 . The controller calculates the desired counterweight starting position given the eccentric offset  146 . This calculation is performed using a formula where the cosine of half the angle between the counterweight wedge centers of mass equals the eccentric offset R multiplied by the known system dead load, divided by the product of the total counterweight mass multiplied by the fixed radial distance to the known counterweight center of mass, according to  FIG. 3A  This position balances the system neglecting the additional contributions of any containers, their contents, and the mounting hardware attached to the platform. The controller then actuates  148  the counterweights to their initial position using the counterweight motor  62  and travel low limit sensor  79 . Next, the controller starts the shaker motor  25  and increases the speed to the adjustment limit  150 , which is the speed at which the counterweight motor  62  is still capable of repositioning the counterweights without exceeding its torque/current limitations. The controller measures  152  and calculates the acceleration parameter while increasing the angular position of the counterweights in order to minimize the acceleration parameter  154 . The controller increases the motor speed  156 , while checking that the acceleration parameter remains below the stability limit  158 . If the acceleration parameter exceeds the stability limit, the controller then decreases the speed and adjusts the counterweights  160 , and then increases the speed again  156 . Otherwise, the shaker reaches the desired speed  162 . 
       FIG. 15  graphically demonstrates this automatic counterweight adjustment routine. Once a suitable minimum value has been achieved, the controller increases the motor  25  speed without additional counterweight adjustment, and monitors the stability parameter while the shaker approaches the desired operating speed. If the parameter is exceeded, the controller decreases the speed and makes a further adjustment to the counterweights, compensating for live-load imbalance contributions which can change in magnitude depending upon rotational speed. 
     For improved positioning of the counterweights, a load cell or strain gauge (not depicted) may be mounted to the eccentric adjusting rod or included in the eccentric actuator, so that the centripetal force generated by the platform load can be measured. 
     Having thus described the invention of the present application in detail and by reference to illustrative embodiments thereof, it will be apparent that modifications and variations are possible without departing from the scope of the invention defined in the appended claims.