Abstract:
An interlock assembly for a door latch mechanism of a door in a container for bulk material that has an interior lined with a membrane for holding fluid. The interlock assembly includes a plunger in an aperture formed through the door, which moves between an extended position, where the plunger extends into the interior of the container, and a locked position, where the plunger is urged outwardly from of the interior of the container. A spring is positioned to apply a force to urge the plunger to the extended position. A lock member is connected to move with the plunger between the extended position and the locked position. The spring force is selected to enable the membrane, under static pressure of fluid within the container, to urge the plunger to the locked position, thereby engaging the lock member to interlock against operation of the door latch.

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to door latch interlock mechanisms. More particularly, the present invention relates to door latch interlock mechanisms useful in conjunction with rigid containers having flexible liners for storing or processing liquids or other fluid materials. 
     Description of the Related Art 
     Storage and processing containers are in widespread use in various industries and other endeavors. Many of these are used to contain liquids and other flowable bulk materials, such as powders and granular materials. While containing many types of fluid materials, it is preferable to line the container with a polymeric membrane so that the bulk material is either impermeably contained in a suitable polymeric material, or to insure that the bulk materials does not contact the container itself. For example, in the case of pharmaceutical and food grade materials, a polymeric liner, such as PVC or polypropylene, may be used to maintain the purity and cleanliness of the bulk material. In other instances, the bulk material may react with a storage container itself, so a polymeric liner is used to prevent such reactions. 
     Even though such storage and process containers may be lined, it is still necessary to access the interior of cleaning and service. For this reason, such containers may be equipped with doors large enough for workers to access the interior. In fact, such doors may be the access port through which polymeric liners are installed. It is necessary to securely latch the doors in a closed position when they are not in use. Particularly when the container is filled with a fluid material since the static pressure produced under the force of gravity generates a substantial opening force against the interior of the door. Herein lies a risk of such designs. If the door were intentionally or inadvertently opened while the lined container was full of a fluid material, then the static pressure would push the liner outwardly through the door opening. In fact, the liner may rupture, allowing the fluid material to flow out of the container. Thus it can be appreciated that there is a need in the art for an apparatus for mitigating the potential risk of opening such a door while there is fluid in the process container. 
     SUMMARY OF THE INVENTION 
     The need in the art is addressed by the teaching of the present disclosure. The present disclosure teaches an interlock assembly for a door latch mechanism of a door in a container for bulk material that has an interior lined with a membrane for holding fluid. The interlock assembly includes a plunger located within an aperture formed through the door, which moves between an extended position, where the plunger extends into the interior of the container, and a locked position, where the plunger is urged outwardly from of the interior of the container. A spring is positioned to apply a force to urge the plunger to the extended position. A lock member is connected to move with the plunger between the extended position and the locked position. The spring force is selected to enable the membrane, under static pressure of fluid within the container, to urge the plunger to the locked position, thereby engaging the lock member to interlock against operation of the door latch. 
     In a specific embodiment of the foregoing assembly, where the door latch mechanism includes a latch bar that engages a door frame in the bulk material container, the lock member interferes with movement of the door latch mechanism, which interferes with movement of the lock bar while the lock member is at the locked position. In a refinement to this embodiment, a stop member is fixed to the door latch mechanism, and is positioned to engage the lock member while the lock member is at the locked position. 
     In a specific embodiment of the foregoing assembly, the container is a food grade or pharmaceutical grade process bin, and the membrane is an impermeable liner for the process bin. In another embodiment, the membrane is a replaceable polymeric liner. 
     In a specific embodiment of the foregoing assembly, the plunger is fabricated from a polymeric material. In another embodiment, the plunger has a distal face portion that engages the membrane, and the distal face portion is smooth and rounded to reduce possible damage to the membrane. 
     In a specific embodiment of the foregoing assembly, the spring is selected from a compression spring and a tension spring. In another embodiment, the spring couples the force to the plunger through a linkage, and the linkage may be a lever. 
     In a specific embodiment of the foregoing assembly, the plunger and the lock member are rigidly connected, and are movable in unison. In another embodiment, the plunger and the lock member are connected by a linkage, which may be through a pivot. 
     The present disclosure also teaches a membrane lined bulk material container with an interlocked door opening, which includes a container for bulk material that includes a side wall, and a membrane that holds fluid disposed within the interior of the container. A door is located in the side wall, and there is a door latch mechanism that latches the door at a closed position. An interlock assembly is used, which comprises a plunger disposed within an aperture formed through the door, that moves between an extended position, wherein the plunger extends into the interior of the container, and a locked position, wherein the plunger is urged outwardly from of the interior of the container. There is also a spring arranged to apply a force to urge the plunger to the extended position. A lock member is coupled to move with the plunger between the extended position and the locked position, and the force of the spring is selected to enable the membrane, under static pressure of fluid within the container, to urge the plunger to the locked position thereby engaging the lock member to interlock against operation of the door latch. 
     In a specific embodiment of the foregoing container, the door latch mechanism includes a latch bar that engages a door frame in the side wall, and the lock member interferes with movement of the door latch mechanism, thereby interfering with movement of the lock bar while the lock member is at the locked position. In a refinement to this embodiment, a stop member is fixed to the door latch mechanism, and it is positioned to engage the lock member while the lock member is at the locked position. 
     In a specific embodiment of the foregoing container, the membrane is a replaceable polymeric liner. 
     In a specific embodiment of the foregoing container, the plunger is fabricated from a polymeric material. In another embodiment, the plunger has a distal face portion that engages the membrane, and the distal face portion is smooth and rounded to reduce possible damage to the membrane. 
     In a specific embodiment of the foregoing container, the plunger and the lock member are rigidly connected, and are movable in unison. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view drawing of a process container according to an illustrative embodiment of the present invention. 
         FIG. 2  is an exterior view of container doors according to an illustrative embodiment of the present invention. 
         FIG. 3  is an interior view of container doors according to an illustrative embodiment of the present invention. 
         FIG. 4  is an interior view of container doors showing an interlock assembly according to an illustrative embodiment of the present invention. 
         FIG. 5  is a section view drawing of the interlock assembly according to an illustrative embodiment of the present invention. 
         FIG. 6  is a section view drawing of an interlock plunger assembly according to an illustrative embodiment of the present invention. 
         FIG. 7  is a section view drawing of an interlock plunger assembly according to an illustrative embodiment of the present invention. 
         FIG. 8  is a detail view drawing of an interlock assembly according to an illustrative embodiment of the present invention. 
         FIG. 9  is a detail view drawing of an interlock assembly according to an illustrative embodiment of the present invention. 
     
    
    
     DESCRIPTION OF THE INVENTION 
     Illustrative embodiments and exemplary applications will now be described with reference to the accompanying drawings to disclose the advantageous teachings of the present invention. 
     While the present invention is described herein with reference to illustrative embodiments for particular applications, it should be understood that the invention is not limited thereto. Those having ordinary skill in the art and access to the teachings provided herein will recognize additional modifications, applications, and embodiments within the scope hereof and additional fields in which the present invention would be of significant utility. 
     In considering the detailed embodiments of the present invention, it will be observed that the present invention resides primarily in combinations of steps to accomplish various methods or components to form various apparatus and systems. Accordingly, the apparatus and system components and method steps have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the disclosures contained herein. 
     In this disclosure, relational terms such as first and second, top and bottom, upper and lower, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. The terms “comprises,” “comprising,” or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by “comprises a” does not, without more constraints, preclude the existence of additional identical elements in the process, method, article, or apparatus that comprises the element. 
     An illustrative embodiment of the present invention is applied to the pharmaceutical industry, and in particular, processing bins that employ polymeric liners to impermeably retain a fluid content, which is commonly a liquid. Such processing and storage bins are commonly fabricated from stainless steel, for the benefits of corrosion resistance, cleanliness, and durability. As such, these bins are opaque and the contents are concealed from view. Thus, operators of such equipment may not know the extent to which such containers are filled. Also note that the polymeric liners are generally flexible bag-like structures that can be replaced from time to time. For this and other reasons, the exterior walls of such containers may have doors installed for access to the interior. Such doors contain the polymeric liner in the same fashion as the walls. Given that the container is opaque and that the doors can be opened by operators, care must be exercised not to open the door if a substantial amount of fluid is in the container. The interlock assembly of the present disclosure alleviates the risk of opening the doors while the container has a substantial amount of fluid therein. 
     Reference is directed to  FIG. 1 , which is a perspective view drawing of a liquid container  2  according to an illustrative embodiment of the present invention. This container  2  is an example of a fluid storage bin suitable for use in pharmaceutical processing and storage. The container  2  is fabricated with an exterior frame  4 , which comprises plural stainless steel structural shapes, such as rectangular tubing and angle iron shapes. The walls  6  are commonly fabricated from stainless steel sheet or plate stock. As such, the interior of the container  2  is smooth and suitable from housing a polymeric bag-type liner  12  without risk for damage or puncture. This exemplary processing bin  2  comprises a pair of access doors  8 ,  9  that swing open  10  for access to the interior of the bin  2 . The top of a polymeric bag  12  is visible at the open top of the container  2 . As the polymeric liner  12  is filled and emptied, the unfilled portion of the polymeric bag moves upwardly and downwardly with the level of the liquid contained therein. Of course, the static pressure of the liquid displaces the polymeric liner  12  firmly against the walls  6  of the bin  2 , as well as against the inside of the doors  8 ,  9 . The doors  8 ,  9  are latched in a closed position using latch handle  14  on door  9 . Door  8  is retained in the closed position by door  9 . 
     Reference is directed to  FIG. 2 , which is an exterior view of container doors  8 ,  9  according to an illustrative embodiment of the present invention. This detailed view illustrates further details about the doors  8 ,  9  used in the container  2  (not shown in this view). The doors  8 ,  9  are attached using plural hinges  16  so that they may swing open and out of the way for access. A latch handle  14  is coupled to a door latch mechanism that ultimately controls an upper and a lower latch bar  20 ,  21  that engage a door frame (not shown) to retain the doors  8 ,  9  in the closed position. A cover plate  18  is placed over the door latch mechanism of the door, exposing only the latch handle  14  for operations by an operator. 
     Reference is directed to  FIG. 3 , which is an interior view of container doors  8 ,  9  according to an illustrative embodiment of the present invention. The latch bars  20 ,  21  are visible as well as the aforementioned hinges  16 . Note that on the interior of door  9  there is a plunger  22  that extends into the interior side of the door  9 . This plunger  22  is actuated by force of the fluid in the container (not shown), and interacts with the door latch mechanism to interlock the movement of the latch bars  20 ,  21 . This arrangement will be more fully discussed hereinafter. 
     Reference is directed to  FIG. 4 , which is an interior view of container doors  8 ,  9  showing the door latch mechanism and interlock assembly according to an illustrative embodiment of the present invention. In this view, the cover plate (item  18  in  FIG. 3 ) has been removed, thereby exposing the door latch mechanism and the parts of the interlock assembly. The latch handle  14  is connected to a pivot plate  24  such that a ninety degree rotations of the latch handle  14  causes an upper latch link  26  and a lower latch link  28  to cycle in the fashion of a connecting rod, and drive a upper latch bar  20  and a lower latch bar  21  inwardly and outwardly from the edge of the door  9 . The latch bars  20 ,  21  engage corresponding slots in the door frame (not shown) and retain the door  9  in a closed position. Door  8  is retained by and overlapping edge (not shown) with door  9 . The interlock assembly includes a stop member  30  that is fixed to the lower latch link  28 , and a lock member  38 , which engages the stop member  30  to interfere with the latch bar  21  being retracted into door  9 . In the illustrative embodiment, the lock member  38  is a shaft like extension and the stop member  30  is a plate like structure. Other structures could also be employed, provided that the lock member would interfere with the opening operations of the door latch mechanism. The lock member could also be attached to other components in the door latch mechanism, such as the latch bars  20 ,  21 , the pivot  24 , or the latch handle  14 . The lock member  30  could also be an integral portion of the door latch assembly itself. 
     Reference is directed to  FIG. 5 , which is a section view drawing of the door  9  at the interlock assembly according to an illustrative embodiment of the present invention. The door  9  has a cover plate  18  in place to enclose the various components of the door latch mechanism and the interlock assembly. In particular, the door latch mechanism includes the lower latch link  28 , which is connected to the lower latch bar  21  by a pin  34 . A linear guide  36  directs the latch bar  21  along a linear path. The stop member  30  is fixed to the lower latch link  28 . The interlock assembly further includes a plunger  22  and a lock member  38 , which are supported by a frame  40  attached to the door  9 . The plunger  22  extends into the interior of the container so that the liner (not shown) can be urged against it by the fluid contents of the container. 
     Reference is directed to  FIG. 6 , which is a section view drawing of an interlock assembly according to an illustrative embodiment of the present invention. The door  9  serves as the host for the interlock assembly, and there is a round aperture  42  formed through the door  9  to accomplish this. A formed metal frame  40  is fixed to the door  9  about the aperture  42 . The frame  40  supports a guide bushing  46 , which supports a shoulder bolt  38 . The guide bushing may be a suitable polymeric material, such as Nylon, Delrin, UHMW poly, or a metallic material such as sintered bronze. The shoulder portion of the shoulder bolt  38  glides through the bushing  46 . The head of the shoulder bolt  38  serves as the lock member, which engages the stop member (not shown) attached to the door latch mechanism (not shown). The threaded portion of the shoulder bolt  38  threadably engages a hole  44  formed in a plunger  22 . The plunger  22  is formed from a suitable polymeric material. The plunger  22  is cylindrical in form with a rounded, arcuate face at the distal end, which might be referred to as a button shape. This shape presents a smooth surface to the liner (not shown) in the container (not shown). A conical spring  48  is disposed between the frame  40  and the plunger  22 , and serves to urge the plunger  22  outwardly from the interior surface of the door  9 . 
     Reference is directed to  FIG. 7 , which is a section view drawing of an interlock plunger assembly according to an illustrative embodiment of the present invention.  FIG. 7  corresponds to  FIG. 6 , however,  FIG. 7  includes the liner  50  and a quantity of liquid  52  therein. The static pressure of the liquid  52  presses the liner  50  against the plunger  22 . The force of the spring  48  is selected such that the liquid pressure overcomes the spring  48  force and urges the plunger outwardly from the interior side of the door  9 . This also pushes the should bolt  38  outwardly through the guide  46 . When the liquid level  52  drops, the spring  48  urges the plunger  22  back into the interior. 
     Reference is directed to  FIG. 8  and  FIG. 9 , which are detailed view drawings of an interlock assembly according to an illustrative embodiment of the present invention.  FIG. 8  illustrates the interlock assembly in the locked position, and  FIG. 9  illustrates the interlock assembly in the unlocked position. A stop member  30  is fixed to the lower latch link  28 . The lower latch link  28  is connected by a pin  52  to the lower latch bar  21 , which passes through guide  36 . The plunger  22  can be seen, as well as the frame  40  and the lock member  38 , which is the head of a shoulder bolt in this embodiment. In FIG.  10 , the plunger  22  and lock member  38  are urged toward the interior of the door  9 , so the stop member is free to move upwardly so that the door may be opened. On the other hand, in  FIG. 9 , the plunger and lock member have been urged outwardly so that the lock member  38  interferes with movement of the stop member  30 , and the door latch mechanism cannot be moved to the open door position. Thusly, the door latch mechanism is interlock from opening while liquid in the lined container is present at the location of the plunger  22 . 
     Note that the illustrative embodiment employs a shoulder bolt as the lock member and as the connecting link between the plunger and the lock member. This arrangement is not a require feature. The lock member and the plunger could be coupled through linked lever and a pivot, or through a cam and follower arrangement. Those skilled in the art will appreciate that the movement of the plunger and the position of the lock member could be linked in a variety of ways. So long as the plunger movement results in the interference with the door latch mechanism, then the assembly will function as intended. 
     Thus, the present invention has been described herein with reference to a particular embodiment for a particular application. Those having ordinary skill in the art and access to the present teachings will recognize additional modifications, applications and embodiments within the scope thereof. 
     It is therefore intended by the appended claims to cover any and all such applications, modifications and embodiments within the scope of the present invention.