Abstract:
A method and apparatus for filling one or more of a plurality of media plates each with a given quantity of media fluid. The media plates may be arranged in a self- supporting stack. The method comprises moving a carriage along a height of the stack of media plates to a position of a media plate to be filled and causing gripping means of said carriage to grip a lid of said media plate or, if said media plate has no lid, to grip a media plate directly above said media plate to be filled. The carriage is caused to rise to lift said lid, if present, and lift any media plates arranged above said media plate to be filled to provide access to an interior of said media plate. The interior, i.e. basin, of said media plate is filled with a given quantity of media fluid such as agar which may subsequently solidify to provide a growth medium for biological agents such as bacteria, yeast or the like. The carriage is caused to descend to replace said lid, if present, and return any lifted media plates to their former positions arranged above said media plate to be filled. The method does not require a media plate to be removed from the stack in order to fill it.

Description:
[0001]    The invention relates generally to a method and apparatus for filling a plurality of media plates in a self-supporting stack and more particularly, but not exclusively, to filling a plurality of media plates in a self-supporting stack by working up the plurality of media plates in turn starting from the lowermost plate in the stack. 
       BACKGROUND 
       [0002]    Most conventional plate pourer apparatuses work on the same general principle which is described in U.S. Pat. No. 4,170,861. Stacks of Petri dishes or plates are loaded into a magazine, for example a rotating turret, which sits on top of a plate-handling apparatus base. A mechanism at a dish-drop station lowers one dish from the bottom of a stack of empty dishes into a filling chamber. As the dish is lowered, the lid or cover is separated from the dish. A turntable transfers the dish and lid from the dish-drop station to the filling station, where the media fluid, e.g. liquid agar, is dispensed into the dish through a fixed horizontal nozzle. Once the dish is filled, the dish and the lid are transferred to an elevating station, where the dish is raised to close it with the lid and then pushed into the bottom of a stack of already filled dishes. The entire stack of filled dishes is moved up when another dish is added. 
         [0003]    The conventional plate pourer apparatuses of this type are designed to handle only round Petri dishes. There do not appear to be any commercially available plate pourer apparatuses which can handle non-Petri dish media plates, e.g. rectangular or square plates which are increasingly being used, especially in automated sampling apparatuses. Furthermore, the conventional plate pourer apparatuses appear to be able to handle only one specific size, i.e. diameter, of Petri dishes, typically 100 mm or 60 mm. Some apparatuses can be re-tooled to handle another Petri dish size, but switching to a different plate size normally requires stopping the apparatus and replacing the plate magazine and several other components of the apparatus. 
         [0004]    A consequence of the plate handling method used in most conventional apparatuses is that the apparatuses can accept plates only within a very narrow range of diameters very close to their “nominal” size, which severely limits the choice of consumables. Moreover, spills from plates within the apparatuses are often very difficult to clean as the plate stacks tends to sit directly on top of the plate pourer&#39;s main body, which contains most moving parts, electronics, etc. In addition to being difficult to clean and sterilize, the media fluid filling chamber is often not completely enclosed, which introduces the risk of contaminating the media with airborne microorganisms. 
         [0005]    U.S. Pat. No. 4,468,914 discloses an apparatus for filling Petri dishes or plates whereby plates to be filled are moved continuously from a stack towards a dispensing nozzle. The covers or lids of the plates engage a ramp which tilts said lids away from the plates to provide access to an interior of the plates for filling purposes. After the plates are filled, their lids are dropped back into place. 
         [0006]    U.S. Pat. No. 3,719,023 describes a similar plate filling apparatus to U.S. Pat. No. 4,468,914. 
         [0007]    U.S. Pat. No. 3,704,568 describes an apparatus for filling Petri dishes in which a dish and a lid are fed forward in rectilinear paths in different levels from a stack of closed dishes in a hopper at one end of a sterile chamber, the dish being caused to drop down on the bottom of the chamber between slide rails that catch the edge of the lid. In one position of the travelling path the dish is filled with substrate, and in a subsequent position the lid is caused to drop down on the dish. 
         [0008]    It can be seen that all of the above described apparatuses require plates to be moved from a stack for filling and/or returned to a stack after filling. 
       GENERAL  
       [0009]    Preferably the invention mitigates or obviates to some degree one or more problems associated with known plate pourer apparatuses. 
         [0010]    This may be met by the combination of features of the main claims; the sub-claims disclose further advantageous embodiments of the invention. 
         [0011]    Preferably the invention provides a method and apparatus for pouring media into any type and/or size of media plates without requiring the media plate to be removed from a stack for filling or returned to a stack after filling. 
         [0012]    Preferably the invention provides a method and apparatus for pouring media into any type and/or size of standard media plates without stopping the apparatus and without having to make any hardware or software modifications or adjustments to the apparatus so that the apparatus can handle plates that differ from their nominal size, as is commonly encountered with commercially available consumables. 
         [0013]    Preferably the invention assures that airborne contaminants are prevented from entering the open plates during pouring. 
         [0014]    Preferably the invention produces excellent surface quality of the solidified media with uniform thickness and wall-to wall flatness and therefore to eliminate disturbing already poured plates while remaining plates are processed. 
         [0015]    One skilled in the art will derive from the following description other objects of the invention. Therefore, the foregoing statements of object are not exhaustive and serve merely to illustrate some of the many objects of the present invention. 
       SUMMARY 
       [0016]    In a first main aspect, the invention may provide a method of filling one or more of a plurality of media plates each with a given quantity of media fluid. The media plates may be arranged in a self-supporting stack. The method comprises moving a carriage along a height of the stack of media plates to a position of a media plate to be filled and causing gripping means of said carriage to grip a lid of said media plate or, if said media plate has no lid, to grip a media plate directly above said media plate to be filled. The carriage is caused to rise to lift said lid, if present, and lift any media plates arranged above said media plate to be filled to provide access to an interior of said media plate. The interior, i.e. basin, of said media plate is filled with a given quantity of media fluid such as agar which may subsequently solidify to provide a growth medium for biological agents such as bacteria, yeast or the like. The carriage is caused to descend to replace said lid, if present, and return any lifted media plates to their former positions arranged above said media plate to be filled. 
         [0017]    Consequently, the method does not require a media plate to be removed from the stack in order to gain access to its interior, i.e. in order to fill it. Furthermore, the method does not require a media plate to be returned to the stack after filling. The stack can be considered as being stationary in that, during the automatic filling process, no plates are removed, returned or added to the stack. 
         [0018]    Preferably, the method includes performing the steps of the first main aspect for each of a plurality of media plates in the stack and preferably doing so by starting with the lowermost plate and moving to each plate in turn up the height of the stack. Consequently, the only movement of plates in a stack during an automatic filling process is the raising up a short distance of not yet filled plates above already filled plates and a plate being filled and the return of the raised plates to their former positions. 
         [0019]    In a preferred embodiment, the carriage is parked at a position above the stack of plates, especially when a program of filling plates is completed. However, in another embodiment the carriage is parked below a support for the stack of media plates. In either embodiment, parking the carriage above or below the stack of media plates makes loading a stack of clean plates or removing a stack of filled plates more efficient than would be the case otherwise. 
         [0020]    The apparatus of the invention may comprise a support for a single stack of media plates, but preferably it comprises additional stack support units and the carriage is provided with sufficient gripping means such that the method may include performing the steps of the first main aspect of the invention simultaneously on two or more stacks of media plates. Where the apparatus supports more than one stack of plates, the carriage may be provided with only one media fluid dispensing means such as a nozzle, whereby the dispensing means is movable relative to the carriage and stacked plates so as to be able to fill corresponding plates in different stacks one after the other prior to the step of lowering the carriage to replace said lid, if present, and return any lifted media plates to their former positions. 
         [0021]    Preferably, the carriage is provided with means for determining a size and/or a type of a media plate in the stack. This means may comprise contact means which engage the lid of a media plate to be filled, the plate itself or another plate adjacent thereto in order to establish data describing the plate to be filled. Additionally or alternatively, it may comprise non-contact sensor means which establishes data describing the plate to be filled through non-contact means such as optical sensors and/or proximity sensors. The data from the contact means or non-contact sensor means may enable a process controller of the apparatus to determine a size and/or type of the media plate to be filled. 
         [0022]    The method may further comprise determining an operating parameter for filling said media plate based on a determined size and/or type of said plate. The operating parameter may comprise one or more of: volume of media to be filled in the plate; pumping speed for media filling; and location of delivery of media to the interior of the plate. 
         [0023]    In a second main aspect, the invention provides an apparatus for filling one or more of a plurality of media plates each with a given quantity of media fluid. The apparatus comprises: a media plate stack support on which a plurality of media plates can be arranged in a self-supporting stack; a carriage movable along a height of the stack of media plates to a position of a media plate to be filled, the carriage carrying gripping means for gripping a lid of said media plate or, if said media plate has no lid, to grip a media plate directly above said media plate to be filled. The carriage is arranged to rise to lift said lid, if present, and lift any media plates arranged above said media plate to be filled to provide access to an interior of said media plate. A media fluid dispensing means is provided for filing the interior of said media plate with a given quantity of media fluid. Once said dispensing means has dispensed a given quantity of media fluid to the interior of the media plate, said carriage is arranged to descend to replace said lid, if present, and return any lifted media plates to their former positions arranged above said media plate to be filled. 
         [0024]    In a third main aspect, the invention provides a method of filling a media plate with a given quantity of media fluid using a media plate filling apparatus having a process controller for controlling operations of the apparatus, the method comprising the steps of: automatically determining a size and/or a type of a media plate to be filed; determining an operating parameter for filling said media plate based on the determined size and/or type of said plate; and filling said media plate with a given quantity of media fluid in accordance with said determined operating parameter. 
         [0025]    Preferably, the steps of automatically determining a size and/or a type of a media plate and determining an operating parameter comprise: arranging gripping means of said apparatus to engage a lid of a media plate to be filled or to engage the media plate itself; receiving at the process controller an input signal from the gripping means; and determining from said input signal a size and/or a type of a media plate to be filled. 
         [0026]    In a fourth main aspect, the invention provides an apparatus for filling a media plate with a given quantity of media fluid having a process controller for controlling operations of the apparatus, the apparatus comprising: means for automatically determining a size and/or a type of a media plate to be filed; means for determining an operating parameter for filling said media plate based on the determined size and/or type of said plate; and dispenser means for filling said media plate with a given quantity of media fluid in accordance with said determined operating parameter. 
         [0027]    In a fifth main aspect, the invention provides a carriage for a media plate filling apparatus, said carriage comprising: a first gripping member; and a second gripping member; the first and second gripping members defining therebetween a gripping space and being arranged to be movable relative to one another so as to close said space to grip a media plate or a lid of a media plate located in said space, the second gripping member having at least one first gripping finger member and at least two second gripping finger members, said second gripping finger members being arranged on either side of the at least one first gripping finger member and ends of said second gripping finger members being positioned further into the gripping space than an end of the at least one first gripping finger member. 
         [0028]    In a sixth main aspect, the invention provides a method of filling a media plate, the method comprising: providing a media plate filling apparatus having the carriage of the fifth main aspect of the invention; and controlling said media plate filling apparatus to perform the steps of the method of the first main aspect of the invention and/or the method of the third main aspect of the invention. 
         [0029]    In a seventh main aspect, the invention provides a computer readable medium carrying machine readable instructions executable by a processor of a computer, said machine readable instructions for implementing in a media plate filling apparatus the steps of the method of the first main aspect of the invention and/or the method of the third main aspect of the invention. 
         [0030]    The summary of the invention does not necessarily disclose all the features essential for defining the invention; the invention may reside in a sub-combination of the disclosed features. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0031]    The foregoing and further features of the present invention will be apparent from the following description of preferred embodiments which are provided by way of example only in connection with the accompanying figures, of which: 
           [0032]      FIG. 1  is a perspective view of a plate pourer apparatus according to the invention; 
           [0033]      FIG. 2  is a top perspective view of a carriage for the apparatus of  FIG. 1 ; 
           [0034]      FIG. 3  is a bottom perspective view of a carriage for the apparatus of  FIG. 1 ; 
           [0035]      FIG. 4  is a an above perspective view of a front gripping member of the apparatus of  FIG. 1 ; 
           [0036]      FIG. 5  is a an above perspective view of a rear gripping member of the apparatus of  FIG. 1 ; 
           [0037]      FIG. 6  is a perspective view of a base and elevator means for the apparatus of  FIG. 1 ; 
           [0038]      FIG. 7  is a partial view of the carriage showing the gripping members engaging a 60 mm diameter Petri dish lid; 
           [0039]      FIG. 8  is a partial view of the carriage showing the gripping members engaging a 90 mm diameter Petri dish lid; 
           [0040]      FIG. 9  is a partial view of the carriage showing the gripping members engaging a 150 mm diameter Petri dish lid; 
           [0041]      FIG. 10  is a partial view of the carriage showing the gripping members engaging a rectangular lid of a media plate; and 
           [0042]      FIG. 11  is a partial view of the main cabinet of the apparatus showing a double stack of rectangular media plates being processed for filling. 
       
    
    
     DETAILED DESCRIPTION  
       [0043]    The following description is of embodiments by way of example only and without limitation to the combination of features necessary for carrying the invention into effect. 
         [0044]    Reference in this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. Moreover, various features are described which may be exhibited by some embodiments and not by others. Similarly, various requirements are described which may be requirements for some embodiments but not other embodiments. 
         [0045]    The definition of a self-supporting stack as used herein does not preclude the use of one or more vertical guides such as a vertically extending guide plate or guide rod(s) against which the stack of plates may rest when loaded into the apparatus, the vertical guide also possibly acting as a means to enable a user to accurately position the stack of plates within the apparatus. Generally speaking, a self-supporting stack refers to a stack of media plates placed one on top of another where each upper plate rests upon the lid of a plate directly below it or, if the lower plate does not have a lid, the upper plate rests on a rim of the lower plate. 
         [0046]    Reference herein to a dish is a reference to a plate. Reference herein to a cover is a reference to a lid. 
         [0047]    The interior of a media plate or dish is considered as comprising the basin formed by the base and side wall(s) of the plate which enable a given quantity of growth media or the like to be received and contained within the plate. 
         [0048]    Referring to  FIG. 1 , a plate pourer apparatus  10  according to the invention comprises a main cabinet  12  having a base  14  with an elevator mechanism  16  ( FIG. 6 ) provided on the underneath of the base  14 . A control cabinet  18  is provided on the base  14  besides the main cabinet  12 . The control cabinet  18  houses various components including a process controller (not shown) which runs custom software to control the automatic or custom operation of the apparatus  10 . The main cabinet  12  contains a carriage  20  supported by carriage mounting brackets  21  ( FIG. 6 ) on three vertical lead screws  22  ( FIG. 6 ), which are hidden behind interior panels  21  of the main cabinet  12 . A lead screw (or leadscrew), which is sometimes referred to as a power screw or a translation screw, is a screw designed to translate turning motion into linear motion. The elevator mechanism  16  causes synchronous rotation of the lead screws  22  which translate said rotating motion to linear movement to lower or raise the carriage  20  within the main cabinet  12 . It will be understood that other types of elevation mechanism for the carriage  20  are within the scope of the invention. 
         [0049]    The cabinet  12  also contains two removable stack support units  24   a,b.  Each stack support unit  24   a, b  comprises a support base plate  26  which is adapted to support a stack of media plates in a self-supporting manner. Each support base plate  26  is spaced above the top surface of the base  14  by a short distance, being mounted on legs  28 . Each stack support unit  24   a,b  has one or more vertically extending guide rods  30  adapted to enable a user to position a stack of media plates accurately in the apparatus on one of the support base plates  26 . The guide rods  30  extend up through the carriage  20  such that the carriage surrounds the guide rods  30  and a stack of media plates placed adjacent or against the guide rods  30  when the carriage  20  moves along the height of the stack of plates. It will be appreciated that the apparatus  10  may use one or more guide plates rather than guide rods  30 , but guide rods  30  are preferred as they give more unhindered access than guide plates to the stack of media plates positioned in the stack support units  24 , b.  In some embodiments, there are no guide plates or guide rods. 
         [0050]    At the top of the cabinets  12 ,  18  there may be some LED indicator lights and a germicidal UV light providing indications of certain operations of the apparatus  10  to a user. 
         [0051]    In the bottom of the cabinet  12  there may be two level indicators  32  visible through transparent sections of a bottom liner of the cabinet  12 . A door  34  of the cabinet  12  may have a magnet that activates a safety switch on the cabinet frame as a form of door interlock. 
         [0052]    Some working components of the carriage  20  may be enclosed by a cover  36 . Referring to  FIGS. 2 and 3 , it can be seen that the carriage  20  has four plate grippers comprising a first pair of front and rear gripper members  40   a,b  and a second pair of front and rear gripper members  42   a,b  that engage right and left (as viewed in the drawings) stacks of plates  44   a,b  ( FIG. 11 ) respectively. The first pair of gripper members  40   a,b  define therebetween a first gripping space  41   a.  The second pair of gripper members  42   a,b  define therebetween a second gripping space  41   b.  The gripper members  40   a,b,    42   a,b  are supported on respective rails  46   a,b,    48   a,b  mounted underneath a main plate member  50  of the carriage  20  so as to be movable towards each other. Each of the four gripper members  40   a,b,    42   a,b  is independently actuated by an actuator preferably comprising a dedicated linear stepper motor  52   a,b,    54   a,b.    FIGS. 2 and 3  show the right pair of gripper members  40   a,b  moved to a fully closed position, and the left pair of gripper members  42   a,b  in a fully open position. Each gripper actuator is equipped with a force switch  56   a,b,    58   a,b  located towards the back of the main plate  50  that detects overload on the gripper members in either the gripper-closing or gripper-opening directions. 
         [0053]    The front gripper members  40   a,    42   a  have a much larger distance of movement from their open to closed positions than the distance of movement of the rear gripper members  40   b,    42   b.  This is because the rear gripper members  40   b,    42   b  are generally located behind the guide rods  30  and advance into the gripping spaces  41   a,b  by a small distance such that their protrusions  82   a,b,    84   a,b  and finger member protrusions  86   a,b,    88   a,b  extend between the guide rods  30  into the gripping spaces  41   a,b  in front of the guide rods  30 . 
         [0054]    The right-front gripper member  40   a  as seen in  FIG. 4  comprises a generally L-shaped support bracket  60  comprising a thin metal plate with two semi-circular finger-like protrusions  62   a,b  which in use face the plate stack  44   a  and can be moved into engagement with a media plate lid or a media plate itself. Directly above these protrusions  62   a,b  are two movable finger members  64   a,b  of a matching shape to the protrusions  62   a,b.  When the front gripper member  40   a  engages a media plate&#39;s lid, the protrusions  62   a,b  on the gripper support bracket  60  enter the space directly underneath the lid&#39;s bottom edge. As the movable finger members  64   a,b  are pushed by the lid they activate respective finger switches  66   a,b  which confirm that the gripper member  40   a  is in position to support and lift the media plate&#39;s lid. In  FIG. 4 , the finger member  62   a  on the left hand side is shown released and the finger member  62   b  on the right hand side is shown activated, i.e. pressed by a media plate lid. As an alternative to engaging a media plate lid, the protrusions  62   a,b  and the finger members  64   a,b  could be arranged to engage the bottom and sides of a media plate in order to support and lift it. This arrangement is useful where a stack of plates is arranged without plate lids such that a bottom of an upper plate rests on a rim of a lower plate with perhaps only the uppermost plate in the stack having a lid. 
         [0055]    In addition to the finger switches  66   a,b  that provide tactile feedback during plate handling, the right-front gripper member  40   a  has a photoelectric thru-beam sensor system comprising a receiver  68  and a transmitter  70 , which is used to locate the bottom edge of the plate&#39;s lid or the bottom edge of the plate before the right pair of gripper members  40   a,b  are moved towards each other to engage the lid or plate. The transmitter  70  and receiver  68  of this sensor system are mounted on opposite sides of the gripper member bracket  60  so as to provide a sensing beam across and in front of the finger members  64   a,b.  The left-front gripper member  42   a  is functionally similar to the right front gripper member  40   a,  except that it may not have a sensor system such as the photoelectric sensor system described above. 
         [0056]    Whilst the front gripper members  40   a,    42   a  are described as having two protrusions  62   a,b  and two movable finger members  64   a,b,  in other embodiments, there may be only one protrusion and one matching finger member or more than two protrusions and matching finger members. The finger members can be considered as comprising gripping means. 
         [0057]      FIG. 5  shows the right side rear gripper member  40   b  which is generally C-shaped in plan. The left rear gripper member  42   b  is functionally similar to the right rear gripper member  40   b.  The right rear gripper member  40   b  comprises a plate support bracket  80  having four finger-like protrusions  82   a,b,    84   a,b:  two on each side of the gripper member  40   b.  The protrusions  82   a,b,    84   a,b  are arranged such that at least one protrusion on each side will support the lid of a media plate or a media plate itself of any plate type and/or plate size within a range of sizes that can be handled by the plate pourer apparatus  10 . Rectangular, square and large-diameter round plates (Petri dishes) or lids are supported by the outer pair  84   a,b  of protrusions as illustrated by  FIGS. 9 and 10  and small square or round plates or lids are supported by the inner pair of protrusions  82   a,b  as illustrated by  FIG. 7 . For example, the 60 mm diameter round plate or lid ( FIG. 7 ) is supported by the inner pair of protrusions  82   a,b  whereas the 150 mm diameter round plate or lid ( FIG. 9 ) is supported by the outer pair of protrusions  84   a,b.  Round plates or round plate lids in the size range of 90 to 100 mm in diameter may be supported by both pairs of protrusions  82   a,b,    84   a,b  simultaneously ( FIG. 8 ), depending on the actual diameter of the plate or lid. 
         [0058]    Consequently, the gripper members  40   a,b,    42   a,b  of the carriage  20  are adapted to accommodate not only different types and/or sizes of media plates/lids, but also handle variations in size of plates or lids of a specific type and/or size thereby making it easier to source plates/lids of a specific type and/or size from the consumables market. Similarly to the front gripper members  40   a,    42   a,  the rear gripper members  40   b,    42   b  have movable finger members that are pushed back when the gripper member engages a plate&#39;s lid or a plate&#39;s sides. In  FIG. 5 , it can be seen that the right rear gripper member  40   b  has two moveable finger members  86 ,  88  each with two protrusions  86   a,b,    88   a,b  of matching shape to the protrusions  82   a,b,    84   a,b.  Unlike the front finger members  64   a,b  which are pivot mounted, the rear finger members  86 ,  88  slide in elongated slots in a gripper member cover  90 . There is only one finger switch  92   a,b  per side of the right rear gripper member  40   b.  Each finger switch  92   a,b  is activated by pushing on either the inner or outer protrusion of its movable finger member  86 ,  88 .  FIG. 5  shows the finger member  88  on the left hand side activated (pressed) and the finger member  86  on the right hand side released. 
         [0059]    Whilst the rear gripper members  40   b,    42   b  are described as having four protrusions  82   a,b,    86   a,b  and four matching finger member protrusions  86   a,b,    88   a,b,  the four finger member protrusions being arranged two to each of two slidable finger members  86 ,  88 , it will be appreciated that in other embodiments the protrusions and matching finger member protrusions may be differently arranged. For example, it is only necessary for gripping different types and sizes of media plates for the rear gripper members to have at least one central protrusion and two outer protrusions arranged to either side of the at least one central protrusion with matching finger member protrusions, although it is preferred to have two central protrusions as depicted in  FIG. 5 . It is also necessary that the gripping ends of the two outer protrusions extend further into the gripping space  41   a,b  than the gripping end of the central protrusion. Furthermore, the matching finger member protrusions may be arranged on a single sliding finger member or provided on three respective slidable finger members with respective finger switches. Other arrangements are also possible. 
         [0060]    Referring again to  FIGS. 2 and 3  and  FIG. 11 , the liquid media dispensing system preferably comprises a nozzle arm  100  pivot mounted close to a centre of the carriage main plate member  50 . The nozzle arm  100  extends below the carriage main plate member  50 . The nozzle arm  100  is driven by a stepper motor  102  mounted underneath the carriage  20  through a belt-and-pulley arrangement  104  provided above the main plate  50 . The nozzle arm  100  rotates directly underneath the gripper members  40   a,b,    42   a,b.    
         [0061]    The location of the nozzle arm pivot point and the distance between the pivot point and the dispensing tip  101  of the nozzle arm  100  are such that the nozzle tip  101  is positioned close to the centre of each type and/or size of media plates by rotating the arm to a specific angular orientation relative to the carriage  20 . The nozzle arm  100  draws media fluid or liquid such as an agar solution via an intake tube from a media flask in the apparatus  10 . 
         [0062]    A reflective optical encoder mounted on a PCB  106  above the nozzle arm pulley system  104  is used to find the arm&#39;s centre position and to measure its angular orientation when the stepper  102  motor is activated. 
         [0063]    In another embodiment, a separate movable nozzle arm is provided for each side of the carriage  20 , each nozzle arm being movable to a position such that a dispensing tip thereof is positioned over the basin of a media plate of any type and/or size arranged adjacent to or held in respective gripper members  40   a,b,    42   a,b  of the carriage  20 . 
         [0064]    It will be understood that, whilst the carriage is described as having left and right side pairs of gripper members, the carriage  20  may have a single set or pair of gripper members, the apparatus  10  being arranged to process only a single stack of media plates. In another embodiment, the carriage may be adapted to have two, three or more sets of gripper members, the apparatus  10  being arranged to process one, two, three or more stacks of media plates simultaneously. 
         [0065]    Referring to  FIGS. 2 and 6 , it can be seen that the carriage is supported on the three lead screws  22  which are arranged to the front-right, front-left and rear-centre of the frame of the main cabinet  12 . The rotation of the three lead screws  22  by the elevator mechanism  16  is synchronized. Respective pulleys  110  of the three lead screws  22  are connected by a single timing belt  112  to the elevator stepper motor  114  mounted inside the control cabinet  18 . 
         [0066]    The carriage mounting brackets  21  rest on nuts  116  of the lead screws  22 , but can separate slightly from the nuts  116  when the carriage  20  is raised or lowered. Respective switches  118  are provided to detect when any of the support brackets  22  separates from its corresponding nut  116 , which indicates that the carriage  20  has crashed into an object and is unable to move farther down. 
         [0067]    The control cabinet  18  contains most of the control electronics including the process controller  15 , as well as the stepper motors that power the elevator mechanism  16  and a media fluid pump unit  17  for the media flask. The cabinet  18  has a power switch  13 , a touch-screen  19  for user control inputs, the pump unit  17  and a liquid sensor unit  122  mounted on its front wall. 
         [0068]    Referring to  FIGS. 1 and 6 , the base plate  14  of the plate pourer apparatus  10  rests on three adjustable feet  120 , which are each height adjustable to enable the apparatus to be levelled. The two level indicators  32  on the base plate  14  are provided one at each corner of the main cabinet  12  such that an axis of each indicator  32  is parallel to a line connecting its corresponding front foot  120  and the rear foot  120  of the apparatus  10 . Therefore, adjusting the foot  120  at one corner, only affects the reading of the level indicator  32  on the same side of the apparatus  10 . 
         [0069]    The plate pourer apparatus  10  is preferably fully automated, but can be arranged to run custom plate filling routines. To fill a batch of plates with media the operator inserts the intake tube of the nozzle arm  100  into the media flask, loads the plates into the main cabinet  12  and activates the apparatus  10 . Under normal circumstances, no further action is required on the operator&#39;s part as the apparatus  10  automatically completes the plate filling/pouring process. 
         [0070]    The operator can control the apparatus  10  through the touch-screen and receives feedback through the touch-screen. 
         [0071]    After power-up the operator is prompted to start the initialization procedure of the apparatus  10 . The apparatus  10  is configured to go through a sequence of moves to find the reference, i.e. home, positions of the moving stages of the apparatus  10 , namely: carriage  20  at the top of the cabinet  12 ; all gripper members open; nozzle arm  100  in a centre position. 
         [0072]    The apparatus  10  is configured to then ask the operator to confirm that the media fluid is ready and that a batch of plates have been loaded into the apparatus  10 . Once confirmed, the apparatus  10  starts a new plate pouring run. 
         [0073]    With reference to  FIG. 11 , the carriage  20  is caused to move down to the height in the plate stack where the lid of the lowermost plate is expected to be found. Both front gripper members  40   a,    42   a  close until the plate detect sensor  68 ,  70 , i.e. the photoelectric thru-beam sensor on the right-front gripper member  40   a,  is activated showing that the lid of the lowermost plate is detected. The position of the front gripper members  40   a,    42   a  is registered for plate type and/or size identification purposes. 
         [0074]    The carriage  20  is then caused to move down slightly until the plate detect sensor  68 ,  70  is released, which indicates the position of the bottom edge of the lid. The carriage height is further re-adjusted relative to the lid bottom edge to position the gripper members at the height suitable for engaging the plate lid. Both front gripper members  40   a,    42   a  close again until their finger switches  66   a,b  are activated. At this point, the position of the front gripper members  40   a,    42   a  is again registered for plate identification purposes. If the finger switches  66   a,b  on both right and left front gripper members  40   a,    42   a  are activated, the apparatus  10  will simultaneously process two stacks of plates. If only the right-gripper finger switches  66   a,b  are activated, the apparatus  10  will process one stack of plates. 
         [0075]    Once the front gripper members  40   a,    42   a  are positioned for lifting the lids of the lowermost plates in their respective plate stacks, the rear gripper members  40   b,    42   b  close (one if only one stack of plates has been detected) until their finger switches  92   a,b  are activated. The position of both front and rear gripper members  40   a,b,    42   a,b  is then slightly re-adjusted to move the lids away from the stack holder guide rods  30  and/or to reduce deformation of the lids caused by the gripper action. 
         [0076]    The apparatus  10  is now ready to pour a given quantity of media fluid into the basin of the lowermost plate(s). At this point, both registered positions of the front gripper members  40   a,    42   a  are used to identify the type and/or size of plates being processed. A set of type-specific operating parameters such as media volume, pump speed, nozzle arm delivery location, etc. is selected based on the detected type and/or size of plates. 
         [0077]    With front and rear gripper members  40   a,b,    42   a,b  closed, the carriage  20  moves up, thus lifting the lid(s) of the lowermost plate(s) together with all empty plates of the stacks resting on them. This creates a space for the nozzle arm  100  to access the interiors of the plates between the plate and lid. 
         [0078]    The nozzle arm  100  rotates to position the nozzle tip  101  close to the centre of one of the plates. The carriage  20  may be moved down to bring the nozzle tip  101  closer to the bottom of the plate before the pump causes the tip  101  of the nozzle arm  100  to dispense media fluid into the plate. Once that plate is filled, the carriage  20  moves up and the nozzle arm  100  pivots to position the tip  101  over the second plate where the dispensing sequence is repeated (if both stacks are present), or to the centre position of the carriage  20  (if only one stack is present). 
         [0079]    The carriage  20  then moves down to deposit the lids back onto the plates and both front and rear gripper members  40   a,b,    42   a,b  open to release the lid(s). The carriage advances to the next plate(s) up the stacks, where the sequence of finding the bottom edge of the lid(s), closing the front and rear gripper members, lifting the lid(s), dispensing the media and depositing the lid(s) back onto plates is repeated. The apparatus  10  continues to process the plate(s) until the top of the stack(s) is reached. At this point, the gripper members are open fully and the carriage  20  moves up to the parking position at the top of the main cabinet  12 , although an alternative parking position may be below the stack base plate  26 . 
         [0080]    If the left stack  44   b  of plates is lower than the right stack  44   a,  the apparatus  10  will recognize this condition through feedback from the finger switches and will continue processing the remaining plates in the right stack  44   a  only. 
         [0081]    Once all plates have been processed, the operator is alerted by an audio and/or visual indicator. The operator may then decide to load another batch of empty plates and initiate another pouring run, or to purge the media tube. 
         [0082]    At the beginning of each pouring run and until the point when the plates have been identified and the apparatus  10  is cleared to go, the operator can activate or deactivate a UV lamp cycle-before-pouring, and automatic filling of the media tube (after the UV lamp cycle and before the pouring cycle). At any point during the pouring run the operator can modify any of the programmable parameters (e.g. dispensed volume, UV light timer). The new parameters become effective immediately once the changed settings are confirmed. 
         [0083]    Whilst the above description of the operation of the apparatus is given with respect to self-supporting stacks of plates which have lids, it will be understood that the apparatus can be used to process self-supporting stacks of plates where the plates do not have lids, but where each upper plate rests on a rim of a lower plate. In this case, the above described operation is modified such that the carriage is initially moved to near the height of the lowermost plate by way of detecting the bottom of the next plate up which is resting on to rim of the lowermost plate. The gripping members are then controlled to engage the bottom of the next plate up from the lowermost plate in order to lift it and other plates in the stack to provide access to the interior of the lowermost plate for filling. 
         [0084]    The apparatus  10  according to the invention provides a number of benefits over know plate pourer apparatuses in that it can handle rectangular and square plates in addition to round Petri dishes; it can handle a wide range of dimensional variations within each nominal size of plate; and it does not require any adjustments for, or even defining of the type of plate being processed. The apparatus  10  automatically detects the type of plates and performs pouring according to a specific pre-programmed set of parameters for the detected type and/or size of plate. It also maintains sterility throughout the pouring process with all plates being contained inside an enclosed cabinet with a programmable germicidal UV light procedure. Furthermore, spills are easy to clean, because the entire cabinet is easily accessible and there are no moving parts below the media dispensing nozzle arm. The apparatus  10  can produce excellent quality agar surface with a minimum meniscus as the already filled plates are not disturbed or moved while remaining plates in a stack are being filled. 
         [0085]    In general, the invention discloses a method of filling media plates as follows: at least one stack of plates is loaded into the stack holders  24   a,b  of the apparatus  10 . The vertically moving carriage  20  which contains plate gripper members  40   a,b,    42   a,b  with sensors moves to the approximate location of the lowermost plate within the stack. One or more sensor(s) are used to locate the bottom edge of the lowermost lid within the stack by moving the carriage  20  up and down and by moving the sensor-equipped gripper members toward and away from the plate. Based on the position of the moving stages during the locating process, the controller  15  determines the type and/or size of plate being used and selects the set of pre-programmed parameters specific for the type and/or size of plate. The carriage  20  moves to a suitable elevation and the gripper members close to engage the lowermost lid(s). The carriage  20  moves up thus elevating the lowermost lid(s) together with all empty plates within the stack(s) that rest on the lowermost lid(s). The dispensing nozzle arm  100  enters the space between the lowermost plate and lid and a quantity of media (agar) is dispensed into the plate from the nozzle arm tip  101 . If there is more than one stack of plates present, the nozzle arm  100  then moves over the next available plate and the media dispensing process is repeated. The carriage  20  moves down to deposit the lid(s) onto the plate(s) and the grippers open to disengage from the lids. The carriage  20  moves up to the approximate location of the next plate within the stack and the process of locating the edge of the lid(s), lifting the lid(s), dispensing media, lowering the lid(s) and disengaging the lid(s) is repeated until the top of the stack(s) is reached. 
         [0086]    The entire working head of the apparatus  10  comprising the carriage  20  moves up and down a stationary stack (or stacks) of plates. The apparatus gets access to a plate by lifting its lid together with all plates resting on the lid. The method works without re-organizing plates in the stack(s) and without disturbing (moving) the already processed plates. 
         [0087]    The carriage has a set of at least two gripper members  40   a,b,    42   a,b,  each with one or more finger members to engage and support a lid (or plate) in a stack. The finger members are arranged such that at least three finger members engage and support each type and/or size of plate/lid. The support points are spaced around the circumference of the plate/lid to assure stability of the stack above. Each finger may have a sensor that indicates whether the finger is engaged with the plate/lid. At least one gripper member has a sensor  68 ,  70  that detects the presence of a lid/dish as the gripper approaches the stack. This sensor may be of a non-contact type such as a through-beam optical type. Each gripper member is preferably equipped with an overload-detect sensor. 
         [0088]    The liquid sensor unit  122  may comprise a photoelectric thru-beam sensor which may be configured to detect three conditions: no media tube present; media tube empty; or media tube filled with liquid. 
         [0089]    When an “empty tube” condition is detected during operation, the apparatus may be configured to a refill procedure comprising: run the pump unit  17  back by an intake section volume; ask operator to check/refill the media container; run the pump unit  17  forward by an intake section volume; check if the media tube full; if yes, run the pump unit  17  forward to refill the entire tube; if not, repeat the refill procedure. 
         [0090]    The plate stack support units  24   a,b  with the guide rods  30  are removable from the main cabinet  14  without the need to use tools. 
         [0091]    The carriage  20  is supported by three lead screws  22  synchronized by a common drive mechanism (timing belt)  112 . The three lead screws provide both vertical and horizontal support to the carriage. 
         [0092]    Sensors  118  at the support points of the carriage  20  detect no-load condition on each individual screw  22  for crash sensing. 
         [0093]    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 exemplary embodiments have been shown and described and do not limit the scope of the invention in any manner. It can be appreciated that any of the features described herein may be used with any embodiment. The illustrative embodiments are not exclusive of each other or of other embodiments not recited herein. Accordingly, the invention also provides embodiments that comprise combinations of one or more of the illustrative embodiments described above. Modifications and variations of the invention as herein set forth can be made without departing from the spirit and scope thereof, and, therefore, only such limitations should be imposed as are indicated by the appended claims. 
         [0094]    In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word “comprise” or variations such as “comprises” or “comprising” is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention. 
         [0095]    It is to be understood that, if any prior art publication is referred to herein, such reference does not constitute an admission that the publication forms a part of the common general knowledge in the art.