Abstract:
An improved filter mounting mechanism for laboratory work cabinets, especially biological safety cabinets, enables simple and quick removal and replacement of a filter supported in the cabinet housing between a work chamber and a filtration chamber. The filter mounting mechanism comprises a stationary filter support surface between the work chamber and the filtration chamber, and a filter clamping surface movable toward and away from the filter support surface between a clamping position relatively proximal to the filter support surface for holding the filter in an operational disposition against the filter support surface and an installation position relatively distal to the filter support surface for permitting insertion and removal of the filter between the filter support and clamping surfaces. An extensible and retractable linkage mechanism, e.g., a scissors mechanism, is connected to the filter clamping surface for selectively actuating movement of the clamping surface between the clamping and installation positions.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates generally to laboratory work cabinets such as exhaust hoods, fume hoods, and biological safety cabinets and, more particularly, to means for the mounting, installation and removal of contaminant filters in such cabinets. 
         [0002]    Various forms of work cabinets are commonly utilized in laboratories in many diverse industries ranging from educational and research institutions to chemical, medical and pharmaceutical concerns. Such cabinets may include, for example, fume hoods, other exhaust hoods, and biological safety cabinets. While such cabinets may differ in varying structural and operational respects, the common purpose and use of such cabinets is to provide scientists and associated personnel with access to a work chamber for performing various scientific tests, reactions, experiments and like operations while protecting the operator and the ambient laboratory environment from exposure to potentially dangerous contaminants. 
         [0003]    All such cabinets necessarily include an air circulation system for controlling airflow within the cabinet and for filtering contaminants from the airflow. In turn, all such cabinets have the periodic need to replace air filters as they become loaded with accumulated filtered materials. In some cabinets, the removal and replacement of contaminant laden filters can be a time consuming process involving extended downtime in the normal operation of the cabinets. In biological safety cabinets which provide a biohazard containment means which enables laboratory personnel to perform various procedures utilizing biologically hazardous substances while protecting the personnel, the work product and the ambient environment from exposure to and contamination by such substances, that issue is particularly prevalent because such cabinets typically include two filters requiring periodic replacement, one for filtering air recirculating within the cabinet and another for filtering air being exhausted from the cabinet, and because each of the filters must be installed with highly secure seals to protect against the dangerous biologically hazardous substances typically being handled. 
         [0004]    Thus, while the present invention is applicable to the mounting, installation, removal and replacement of filters in virtually any laboratory work cabinet, the present invention is particularly applicable to biological safety cabinets. For example, one class of biological safety cabinet referred to as Class II, Type A2 cabinets basically have a work chamber that is mostly enclosed except for a front access opening sufficient for a user&#39;s hands to perform procedures within the work chamber. An air circulation system maintains a continuously circulating positive air flow within the work chamber which is controlled to move laminarly in parallel relation to the front access opening to prevent escape of the internal cabinet air outwardly through the forward access opening to protect the user and the ambient area from contamination. The air circulation system utilizes a fan to continuously withdraw air from the work chamber into an adjacent filtration chamber from which a portion of the air is recirculated into the work chamber through a first high efficiency particulate air filter, commonly referred to as a HEPA filter, while the balance of the withdrawn air is exhausted outside the cabinet through a second HEPA filter. Typically, a ratio of about 70% recirculated air to 30% exhausted air is maintained in Class II A2 cabinets. The exhausted air is replaced by ambient air from the surrounding room drawn first into the filtration chamber before entering the work chamber through the first filter, thereby to prevent room air contamination of the work chamber and also to maintain the integrity of the laminar air flow along the front access opening. 
         [0005]    It is important that the full perimeter of each filter in such biological safety cabinets be securely sealed to prevent any portion of the recirculating or exhausting airstreams from bypassing the filters and thereby contaminating either the work chamber or the exhausted air with biological materials. It is equally important that the filters in such biological safety cabinets be replaced with sufficient frequency to maintain uniformity in the laminar velocity of the circulating air and to minimize airborne contaminants in the circulating air. In turn, therefore, it is desirable that downtime in operation of the cabinets be minimized when accomplishing filter replacement but that objective is outweighed by the necessity that filters be installed precisely with secure perimeter seals. Hence, there is a continuing need in the industry for a simple and quick yet reliable means of removing and replacing filters in such cabinets. 
       SUMMARY OF THE INVENTION 
       [0006]    The present invention seeks to address the foregoing needs of the industry by providing an improved means for the mounting, installation and removal of contaminant filters in laboratory work cabinets, but especially in biological safety cabinets. 
         [0007]    Briefly summarized, the present invention provides a novel filter mounting mechanism which can be adapted to essentially any laboratory work cabinet having a housing defining a work chamber and a filtration chamber, a filter between the filtration chamber and the work chamber for removing contaminants from air passing between the work chamber and the filtration chamber, and an air circulation system for directing air flow between the work chamber and the filtration chamber and through the filter. According to the invention, the filter mounting mechanism comprises a stationary filter support surface disposed between the work chamber and the filtration chamber, and a filter clamping surface movable toward and away from the filter support surface. More particularly, the filter clamping surface is movable between a clamping position relatively proximal to the filter support surface for holding the filter in an operational disposition against the filter support surface and an installation position relatively distal to the filter support surface for permitting insertion and removal of the filter between the filter support and clamping surfaces. An extensible and retractable linkage mechanism is connected to the filter clamping surface for selectively actuating movement of the clamping surface between the clamping and installation positions. 
         [0008]    In a contemplated embodiment, the linkage mechanism is a pantograph linkage, such as a scissors linkage which may comprise, for example, pivoted scissors links connected by a common drive rod for moving the scissors links in coordinated extending and retracting movements relative to one another. 
         [0009]    As mentioned, the invention may be advantageously embodied in a biological safety cabinet wherein the air circulation system includes a fan interposed between the work chamber and the filtration chamber for drawing air under negative pressure from the work chamber and directing the air under positive pressure into the filtration chamber and therefrom through the filter for return into the work chamber for recirculating air between the work and filtration chambers. 
         [0010]    In such an embodiment, the biological safety cabinet may further comprise a second filter between the filtration chamber and an exhaust opening in the housing for exhausting a portion of the pressurized air delivered by the fan to outside the housing and a second filter mounting mechanism may be provided for such filter. 
         [0011]    For example, a second stationary filter support surface may be provided adjacent the exhaust opening, with a second filter clamping surface movable toward and away from the second filter support surface between a second clamping position relatively proximal to the second filter support surface for holding the second filter in an operational disposition against the second filter support surface and a second installation position relatively distal to the second filter support surface for permitting insertion and removal of the second filter between the second filter support and clamping surfaces. A second extensible and retractable linkage mechanism is connected to the second filter clamping surface for selectively actuating movement of the second clamping surface between the second clamping and installation positions. 
         [0012]    The second linkage mechanism may also be a scissors linkage or other pantograph linkage, for example, also having pivoted scissors links connected by a common drive rod for moving the scissors links in coordinated extending and retracting movements relative to one another. 
         [0013]    The filtration chamber may be defined by first and second plenum sections which are movable relative to one another, with the first plenum section including the first-mentioned filter clamping surface and the second plenum section including the second filter clamping surface. 
         [0014]    Additional features and characteristics of the present invention will be described in and apparent from the following disclosure of a contemplated embodiment, with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  is a partially exploded and partially broken-away perspective view of a biological safety cabinet according to a contemplated embodiment of the present invention; 
           [0016]      FIG. 2  is a vertical cross-sectional view of the biological safety cabinet of  FIG. 1 , taken along line  2 - 2  thereof; 
           [0017]      FIG. 3  is another vertical cross-sectional view of the biological safety cabinet of  FIG. 1 , taken along line  3 - 3  thereof; and 
           [0018]      FIG. 4  is a partially exploded and partially broken-away perspective view of the air recirculation chamber of the biological safety cabinet of  FIG. 1 , depicting each filter mounting mechanism in its clamping condition holding the filters in their operational dispositions; and 
           [0019]      FIG. 5  is a partially exploded and broken-away perspective view similar to  FIG. 4 , depicting the upper filter mounting mechanism in its installation condition for removal and installation of a replacement filter. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0020]    Referring now to the accompanying drawings, and initially to  FIG. 1 , a biological safety cabinet in accordance with one contemplated embodiment of the present invention is indicated generally at  10 . The safety cabinet  10  basically comprises a housing  12  supported on a trestle stand  14 , which may include a set of casters (not shown) for moveability of the cabinet structure. The housing  12  is a generally rectangular structure having spaced-apart end walls  18 , a bottom wall  20 , a rear wall  22 , a partial front wall  24 , and a top wall  26 , collectively defining an open interior which is divided by a horizontal intermediate wall  28  into a lower work chamber  30  and an upper air recirculation chamber  32 . The housing  12  may preferably be fabricated of sheet metal, such as stainless steel. 
         [0021]    The partial front wall  24  predominately encloses only the air recirculation chamber  32 , leaving open front access by users into the work chamber  30 . A transparent sash  34  is supported by and extends downwardly from the front wall  24  to partially enclose the work chamber  30  except for a narrow front access opening  36  into the work chamber  30  between the bottom wall  20  and the lower edge of the sash  34  through which users may have manual access into the work chamber  30 . The transparency of the sash  34  permits visual access into the work chamber  30  by users. The sash  34  may also be retractable as necessary to permit greater access into the work chamber  30  by users. 
         [0022]    In  FIG. 1 , the front wall  24  is shown in exploded relation to the remainder of the cabinet  10  for illustration of the air recirculation chamber  32 , but as seen in  FIGS. 4 and 5  the front wall  24  is preferably mounted by hinges to the top wall  26  for upward pivoting when access to the recirculation chamber  32  is necessary or desirable. As shown in  FIG. 1  and further seen in  FIGS. 2-5 , the majority of the air recirculation chamber  32  is occupied by a hollow sub-housing  40  defining a plenum within its open interior which serves as an air filtration chamber  42 . The sub-housing  40  is formed collectively by a lower plenum section  40 A and an upper plenum section  40 B which telescopes slidably into the lower plenum section  40 A. A seal  41  ( FIG. 4 ) is mounted to the lower plenum section  40 A in sealing contact around the entire telescoping surface of the upper plenum section  40 B. An air circulation fan  38  is mounted within one end of the recirculation chamber  32  with the output side of the fan  38  mounted to one end of the lower plenum section  40 A of the sub-housing  40  to discharge blown air under positive pressurize into the air filtration chamber  42 . 
         [0023]    The lowermost bottom side of the lower plenum section  40 A of the sub-housing  40  is open and the intermediate wall  28  of the main housing  12  is formed with a corresponding opening for air flow communication therebetween. A first air filter  44  is disposed between the bottom side of the lower plenum section  40 A and the intermediate main housing wall  28  in full covering relation to their respective openings. Similarly, the uppermost topside of the upper plenum section  40 B of the sub-housing  40  is open in facing relation to and communication with an exhaust duct  55  in the top wall  26  of the main housing  12 . A second air filter  46  is disposed between the topside of the upper plenum section  40 B and the top main housing wall  26  in full covering relation to their respective openings. Each air filter  44 ,  46  includes seals  44 A,  46 A extending fully about their upper and lower perimeters for sealing engagement with the respective housing walls  26 ,  28  and plenum sections  40 A,  40 B. The two air filters  44 ,  46  are preferably high efficiency particulate air filters, more commonly referred to as HEPA filters, for their ability to capture molecular-sized microorganisms and like biological matter. 
         [0024]    The intake side of the fan  38  draws air from within the work chamber  30  and also from the ambient air surrounding the safety cabinet  10  through hollow interior channels defined within the bottom and rear walls  20 ,  22  of the housing  12 . More specifically, as best seen in  FIG. 2 , each of the bottom and rear walls  20 ,  22  are formed by dual spaced wall panels defining a continuous interior airflow channel  48  within the bottom wall  20  and continuing upwardly within the rear wall  22  to open into the air recirculation chamber  32 . A series of perforations  50  are formed along substantially the full length of the forward edge of the bottom wall  20  to open into the forwardmost end of the airflow channel  48 . A similar series of perforations  52  are formed along the lowermost end of the rear wall  22  adjacent its juncture with the bottom wall  20 , also opening into the airflow channel  48  thereat. 
         [0025]    The housing  12  of the safety cabinet  10  will thus be understood to provide a controlled air recirculation system which operates as follows. The fan  38  continuously creates a negative pressure condition within its end of the air recirculation chamber  32  which acts through the airflow channel  48  to draw air from within the work chamber  30  through the perforations  52  and into the airflow channel  48 . To a somewhat lesser extent, surrounding ambient air is drawn into the airflow channel  48  through the perforations  50 . The fan  38  pressurizes the in-drawn air and discharges it under positive pressure into the filtration chamber  42  from which a portion of the air passes downwardly through the filter  44  into the work chamber and a portion of the air passes upwardly through the filter  46  into the exhaust duct  55 . The filter  44  is of a substantially larger size than the filter  46  such that the majority of the airflow, for example approximately 70%, returns into the work chamber  30  through the filter  44 , with only a smaller proportion, for example approximately 30%, of the airflow being exhausted. 
         [0026]    Within the work chamber  30 , the air passing downwardly through the filter  44  moves predominantly vertically downwardly in a laminar manner which, together with the constraint of the sash  34 , the constraint of incoming ambient air into the perforations  50 , and the negative pressure exerted from the fan through the rearward perforations  52 , substantially prevents the escape of any of the airflow outwardly through the access opening  36 . Thus, users may perform laboratory procedures within the work chamber  30  utilizing hazardous substances, e.g., microorganisms, particulate toxic chemicals, etc., without risking escape of such substances into the ambient area outside the cabinet. Moreover, as such procedures are ongoing, the continuous recirculation of the air internally within the housing  12  progressively filters airborne contaminants so as to maintain sufficient cleanliness within the internal air to prevent contamination of the procedure. 
         [0027]    As will be understood, the filters  44 ,  46  will progressively become loaded with filtered contaminants over time as the cabinet is operated whereby the filters must be replaced on a periodic basis. Conventionally, the filters are secured in place by a series of bolts, screws or other fasteners, that are difficult and time consuming to remove and reinstall, often requiring hours to accomplish. The present invention provides a uniquely simple and reliable means of removing loaded filters  44 ,  46  and installing new replacement filters with minimal downtime. 
         [0028]    As depicted in  FIGS. 3, 4, and 5 , a first filter mounting mechanism, indicated generally at  60 , for installing and supporting the lower filter  44  comprises a pair of extensible and retractable pantograph linkage mechanisms, for example in the form of a pair of scissors-jack mechanisms  62 ,  64 , mounted within the recirculation chamber  32  to act between the lower plenum section  40 A of the sub-housing  40  and the lower filter  44 . Each scissors-jack mechanism  62 ,  64  comprises a pair of mounting bars  66 ,  68  supported in parallel spaced relation adjacent opposite ends by two pairs of pivoted scissors links  70 . A threaded drive nut  72  is affixed to the pivot between each pair of scissors links  70  and a threaded drive rod  74  extends in threaded engagement through the drive nuts  72 . The drive rod  74  has a hexagonal head  76  on its forward end for actuation of drive rotation via a common socket drive tool or wrench. The scissors jack mechanisms  62 ,  64  are mounted at opposite ends of the lower plenum section  40 A, with each upper mounting bar  66  affixed to the inside face of a respective end wall  18  of the main housing  12  and with each lower mounting bar  68  affixed to the respective end of the lower plenum section  40 A. 
         [0029]    Similarly, a second filter mounting mechanism, indicated generally at  80 , for installing and supporting the upper filter  46  comprises a pair of extensible and retractable pantograph linkage mechanisms in the form of identical scissors-jack mechanisms  82 ,  84 , mounted within the recirculation chamber  32  to act between the upper plenum section  40 B of the sub-housing  40  and the upper filter  46 . The scissors jack mechanisms  82 ,  84  are mounted at opposite ends of the upper plenum section  40 B, with each upper mounting bar  68  affixed to the adjacent end face of the upper plenum section  40 B and with each lower mounting bar  66  affixed to the top face of the lower plenum section  40 A. 
         [0030]    Thus, the heads  76  of the respective drive rods  74  of the scissors-jack mechanisms  62 ,  64 ,  82 ,  84  are conveniently accessible to an operator or service technician upon lifting of the front wall  24  and sash  34 . By selective clockwise or counterclockwise rotation of the drive rods  74 , coordinated extending or retracting movements of the mounting bars  66 ,  68  are effected toward or away from one another so as to move either or both of the respective plenum sections  40 A,  40 B telescopically relative to one another. The scissors-jack mechanisms  62 ,  64 ,  82 ,  84  may include one or more guide elements (not shown), e.g., in the form of a plate or other link connecting the respective mounting bars  66 ,  68 , to synchronize and guide their extending and retracting movements in a vertical direction and prevent any tendency for the mechanisms to undergo any horizontal or inclined vector of motion. 
         [0031]    The upwardly facing surface of the intermediate wall  28  of the main housing  12  surrounding the opening in the wall  28  serves as a stationary support surface for the lower filter  44 , and the downwardly facing perimeter edge  40 C of the lower plenum section  40 A serves as a filter clamping surface for exerting a clamping retention force on the filter  44  against the wall  28 , as depicted in  FIG. 4 . The wall  28  is provided with spaced-apart flanges  29  for slidable insertion and positioning of the filter  44  on the wall  28  in proper alignment relative to the lower plenum section  40 A. By simple rotational actuation of the respective drive rods  74  of the scissors-jack mechanisms  62 ,  64  to retract the mechanisms, the lower plenum section  40 A may be elevated sufficiently from the intermediate wall  28  to permit the filter  44  to be quickly removed and replaced with a new filter  44  when necessary. Once the replacement filter  44  is properly positioned on the intermediate wall  28 , reverse rotation of the drive rods  74  extends the scissors-jack mechanisms  62 ,  64  to lower the plenum section  40 A into clamping engagement with the new filter  44 , thereby effecting a secure seal along both the upper and lower perimeters of the filter  44 . 
         [0032]    Similarly, the downwardly facing surface of the top wall  26  of the main housing  12  surrounding the exhaust duct  55  serves as a stationary support surface for the upper filter  46 , and the upwardly facing perimeter edge  40 D of the upper plenum section  40 B serves as a filter clamping surface for exerting a clamping retention force on the filter  46  against the wall  26 , as depicted in  FIG. 4 . The wall  26  is likewise provided with spaced-apart flanges  27  for slidable insertion and positioning of the filter  46  between the wall  26  and the upper plenum section  40 B in proper alignment relative thereto. By rotational actuation of the drive rods  74  of the scissors-jack mechanisms  82 ,  84  to retract the mechanisms, the upper plenum section  40 B may be lowered sufficiently from the top wall  26  to permit the filter  46  to be quickly removed and replaced with a new filter  46  when necessary, for example as depicted in  FIG. 5 . Once the replacement filter  46  is properly positioned between the wall  26  and the upper plenum section  40 B, reverse rotation of the drive rods  74  extends the scissors jack mechanisms  82 ,  84  to raise the upper plenum section  40 B into clamping and sealing engagement with the new filter  46 . 
         [0033]    As will thus be readily understood, the filter mounting mechanisms  60 ,  80  of the present invention enable simple, easy and rapid removal and installation of filters with minimal downtime in laboratory work cabinets, and especially in biological safety cabinets having multiple filters in which heightened safety and security concerns mandate that the filters must be precisely secured and sealed in place. Whereas in conventional biological safety cabinets removal and replacement of filters can be difficult and take several hours, the exchange of filter in cabinets according to the present invention can be reduced to a matter of minutes with equal or even greater filter security. 
         [0034]    It will therefore be readily understood by those persons skilled in the art that the present invention is susceptible of a broad utility and application. Many embodiments and adaptations of the present invention other than those herein described, as well as many variations, modifications and equivalent arrangements will be apparent from or reasonably suggested by the present invention and the foregoing description thereof, without departing from the substance or scope of the present invention. Accordingly, while the present invention has been described herein in detail in relation to its preferred embodiment, it is to be understood that this disclosure is only illustrative and exemplary of the present invention and is made merely for purposes of providing a full and enabling disclosure of the invention. The foregoing disclosure is not intended or to be construed to limit the present invention or otherwise to exclude any such other embodiments, adaptations, variations, modifications and equivalent arrangements, the present invention being limited only by the claims appended hereto and the equivalents thereof.