Abstract:
A stop mechanism advantageously combined with a manhole cover includes a holder body having a passage which slidably receives a stop member able to be cammed in and out upon advance or retraction of a threaded drive member having an enlarged tip engaged with a down sloping channel formed in the stop member. Upper sides of the channel engage the tip upon reversal of the drive member to cam the stop member back into the holder body. The stop member when extends prevents removal of the cover from being blown completely free of the manhole vault structure in the event of an explosion.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation in part of U.S. application Ser. No. 12/357,525 filed on Jan. 22, 2009 now U.S. Pat. No. 7,712,995 which is a division of U.S. patent application Ser. No. 11/761,711 filed on Jun. 12, 2007, now U.S. Pat. No. 7,484,908. which claims benefit of U.S. provisional patent application No. 60/921,975 filed on Apr. 6, 2007 and U.S. provisional patent application No. 60/889,553 filed on Feb. 13, 2007 and No. 60/812,757 filed on Jun. 12, 2006. This application also claims benefit of U.S. provisional application No. 61/131,754 filed on Jun. 11, 2008. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention concerns retractable stop mechanisms and more particularly such mechanisms for preventing unauthorized removal of covers for catch basins and manholes installed in roadways for access to utilities, i.e., water, gas, communications, electricity, etc. These covers are provided in order to keep out debris but also to present a supporting surface for pedestrians and vehicles on the surrounding roadway surface. If the covers are removed by thieves or vandals, the opening to a catch basin or manhole presents severe hazard to vehicles and pedestrian traffic. Removal of these covers by vandals or scavengers has become an increasing problem which has created an urgent need for some means for preventing unauthorized removal of the covers. In instances where there are no existing means incorporated in existing catch basin and manhole covers, providing a simple retrofit to existing covers with a securing means is highly desirable. Such devices should preferably be designed to withstand traffic and weather and the efforts of vandals, thieves or terrorists to remove them. The large numbers involved require a simple installation method to minimize labor costs. The securing means should preferably not present an obstruction in the roadway, particularly for snow plows, nor a tripping hazard to pedestrians. 
     At the same time, any such means should be reliable in operation even after many years of exposure to the elements. 
     The present inventor has heretofore invented a retractable stop mechanism which is designed to allow a limited movement of a manhole cover out of the manhole vault structure to when an explosion occurs in the manhole space but prevents the cover from being blown free so as to avoid the hazard presented by the manhole cover when it falls back to the surface while still allowing escape of the gases so as to minimize damage to the vault structure. The stop mechanism also prevents complete removal of the manhole cover to function as a security retention for the cover. This is described in detail in U.S. Pat. No. 7,484,908 incorporated herein by reference. That mechanism relies on a spring return to retract the stop member, but due to the possibility of corrosion, causing increased resistance to movement of the parts of the mechanism, it is desirable to not rely on a spring operation of the retraction release as the mechanism since it may be exposed to the elements for many years. 
     It is an object of the present invention to provide a simple but selectively and reliably releasable stop mechanism for manhole covers and other structures which can resist attempts at unauthorized removal of the cover, but which is easily operated by an authorized person even after many years in service, which can be readily installed on existing covers, and does not present an obstruction to traffic. 
     It is a further object to provide a releasable cover stop mechanism advantageously arranged to allow a manhole cover to rise up out of a manhole cover frame to a limited extent for venting gases created in an explosion as described and claimed in U.S. Pat. No. 7,484,908. 
     SUMMARY OF THE INVENTION 
     The above recited objects and other objects which will become apparent to those skilled in the art upon a reading of the following specification and claims is achieved by a rugged tamper resist stop mechanism in accordance with the present invention which prevents complete removal of a cover from a manhole opening, which is adapted to be mounted on the underside of the cover. A holder body is provided to slidably mount an elongated stop member. A headed drive member which may be threaded comprised of a threaded bolt is received into a threaded bore in the holder body, wherein it may be advanced or retracted by being rotated in the threaded bore. An enlarged bulbous tip on the drive member is engageable with surfaces defining a downwardly sloping channel formed into the top of the stop member with both advance and return movement so as to produce a two-way camming action to advance or retract the stop member to either an extended position with one end protruding from the holder body, or to a retracted position with the one end retracted into the holder body. 
     The holder body is formed with an internal passage slidably receiving the stop member, which may be of a generally cylindrical shape, and the downwardly angled channel formed therein receives the enlarged tip of the drive member. The channel is preferably defined by rounded sides and a rounded bottom surface, the sides slightly converging towards each other at the upper ends thereof to form a slot therebetween at the top, narrower than the drive member tip which is slidable in the widest point of the channel. The slot is sized to slidably receive a shaft portion of the drive Member adjacent the tip. When the drive member is advanced into the threaded bore, by engagement of a special tool with a uniquely shaped security head on the drive member, the tip of the drive member is received within a wider entry portion of the channel and is engaged with the rounded bottom surface defining in part the downwardly angled channel in the stop member, thereby camming the stop member from a retracted position within the body into an extended position with one end protruding from the holder body. 
     In this position, the protruding one end of the locking member may be aligned with a fixed abutment located above the protruding end and preventing complete removal of the cover, although able to move up to a limited extent due to a clearance between the stop member one end and the abutment which creates an annular gap allowing venting of the gases created in an explosion. 
     When the drive member is rotated in the opposite direction so as to be backed out of the bore in the holder body, upper surfaces on the enlarged tip of the drive member engage the inside of the convergent portion of the channel sides to exert an upward camming force on the stop member positively acting on the stop member to be moved in the opposite direction, thereby retracting the stop member so that the one end of the stop member is moved back into the holder body. 
     The cover is then able to be completely removed from the opening without interference from the stop member. 
     The stop mechanism is advantageously combined with a manhole cover to prevent the cover from being completely blown free of a surface manhole vault structure or to be removed by an unauthorized person. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side elevational view of a stop mechanism according to the invention with fragmentary portions of a manhole cover and adjacent manhole vault structure shown in section with the cover shown in an elevated state and being restrained from further upward movement by a stop member included in the stop mechanism engaging a fixed abutment. 
         FIG. 2  is an enlarged top view of the stop mechanism shown in  FIG. 1  with one end of a retractable stop member shown extended to restrain the cover from moving completely free from the surrounding vault structure shown in fragmentary form and in broken lines. 
         FIG. 3  is a side view of the stop mechanism shown in  FIG. 1  in partial section with the stop member in the extended position and engaged with a fixed abutment on the vault structure after the cover has risen to a limited extent. 
         FIG. 4  is a partially sectional side view of the stop mechanism shown in  FIGS. 1-3  with the stop member shown retracted but with the outline of the stop member indicated in broken lines in the extended position and the cover at rest recessed to in the manhole opening. 
         FIG. 5  is a partially sectional side view of the stop mechanism shown in  FIGS. 1-4  with a shear pin released and a holder body tilted down to allow the cover to tilt up to increase the area available to vent gases. 
         FIG. 6  is an end view of the stop mechanism showing the mounting to the underside of the cover. 
         FIG. 7  is a pictorial view of the stop member included in the stop mechanism shown showing the drive member in position with its tip in engagement therewith. 
         FIG. 8  is an enlarged pictorial view of the drive member shown in  FIG. 7 . 
         FIG. 9  is a fragmentary transverse sectional view of the stop member shown in  FIG. 7  looking down the channel formed therein with the tip of the drive member disposed therein. 
         FIG. 10  is a fragmentary sectional view of the holder body and separated threaded drive member retainer elements able to engage the drive member to insure retention of the drive member in the holder body even after being disengaged with the threads in the threaded bore. 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, certain specific terminology will be employed for the sake of clarity and a particular embodiment described in accordance with the requirements of 35 USC 112, but it is to be understood that the same is not intended to be limiting and should not be so construed inasmuch as the invention is capable of taking many forms and variations within the scope of the appended claims. 
     As shown in the drawing Figures, an embodiment of a stop mechanism  10  according to the invention is shown, suspended between a pair of side rails  12  attached to the underside of the cover C with bolts  13  received in the threaded holes in the underside of the cover C in a generally similar manner as the mechanism shown in U.S. Pat. No. 7,484,908, incorporated herein by reference. The stop mechanism  10  includes a holder body  14 , having a longitudinal passage  15  is formed therein. The holder body  14  may be attached to the underside of a manhole cover C fit into an opening in a manhole vault and cover frame structure S, captured between the pair of side rails  12  by a pair of rods  16 A,  16 B passing completely through holes in the holder body with opposite ends received in respective blind holes  18 A,  18 B in the adjacent inside faces of the rails  12 . 
     This general arrangement is shown in U.S. Pat. No. 7,484,908 and includes a shear pin  19  which when fractured under a predetermined stress level allows a limited pivoting down of the holder body  14  as described further below. 
     A threaded bore  20  extends into the top of the holder body  14  intersecting a lengthwise passage  22 . The passage  22 , which may be lined with bronze bushing  29 , is open to the left but closed on the right as shown. A small vent hole bore  26  may be formed venting the passage  22 . 
     A recess  28  is also preferably formed into the bottom of the passage  22 , the recess  28  aligned with threaded bore  20  and may be generally cylindrical with a rounded bottom. 
     A stop member  30  is slidably received in the passage  22  and may be selectively positioned with one end  32  protruding from the holder body  14  ( FIG. 3 ) or retracted therein ( FIG. 4 ). That is, the stop member  30  is slidably movable from a retracted position to an extended position to the left ( FIGS. 1 ,  3 ) within the holder body  14 . The one end  32  of stop member  30  may be flattened to better engage the sides of a fixed stop structure F formed on the vault structure  5 . Grooves  34  may also be provided ( FIG. 7 ) extending across the flattened top of the one end  32  of the stop member  30 . The stop member  30  has formed therein a down sloping channel  36  extended in from the top surface and passing entirely through the bottom side of the stop member  30 . 
     The channel  36  is partially circular in section and has a slightly enlarged entry  38  formed at the entrance at the top end in order to be able to receive an enlarged bulbous tip  40  on the bottom end of a drive member  42 , aligned therewith in the retracted position shown in  FIG. 4 . 
     The channel  36  is defined in part by a rounded bottom surface  37  ( FIG. 9 ) engageable with the rounded bottom of the tip  40  of the drive member  42   
     The drive member  42  is also formed with a specially shaped head  44  engageable with a mating specially shaped driving tool such as a socket (not shown). The head  44  may be designed with a unique shape (not shown in the drawing), so that a special tool containing a socket having a shape mating with the head  44  complementary thereto is required to rotate the member  42  in order to provide security by preventing engagement of the head  44  with standard tools. The head  44  is accessed through an opening  45  in the cover C in which the head  44  is recessed. 
     The drive member  42  is also formed with a threaded shaft main body  46 , and a narrowed intermediate non-threaded shaft section  48 , connecting the tip  40 , the tip  40  having a greater diameter than the diameter of the intermediate shaft section  48 . 
     The main body  44  threadedly engages the threaded bore  20 . As the drive member  42  is continued to be rotated into threaded bore  20 , the tip  40  is received within the channel  36  which as noted has a slightly enlarged entry  38  sized to freely accept the tip  40 . As the drive member  42  continues to be rotated so as to be advanced along bore  20 , the tip  40  engages the down sloping bottom surface  37  of channel  36 , thereby camming the stop member  30  towards the fully extended position reached as the drive member  42  is advanced to the bottom of the channel  36 . 
     Further advance of the drive member  42  causes the tip  46  to be received within recess  28 , the drive member  42  thereby firmly holding the stop member  30  in place within the holder body  14 . 
     Stated another way, the drive member  42  exerts a camming force causing extension movement of the stop member by engagement with the sloping bottom  37  of the channel  36  with the tip  46 . The stop member  30  is thereby advanced to the left upon continued descent of the drive member  42  in engagement with the bottom surface of the channel  36  thereby pushing the stop member  30  to the left into its extended position with one end  32  fully protruding from the holder body  14  as seen in  FIG. 4 . 
     The one end  32  of stop member  30  when extended is aligned below fixed stop F on the surrounding vault structure S to be restrained thereby, preventing complete escape or removal of the cover C. 
     The channel  36  has upper sides  39  slightly converging towards each other and terminating at the upper ends to form an intervening slot  50  at the top of the channel  36 . A clearance space  43  is formed to the right beyond the channel  36  to allow the main portion  46  and intermediate section  48  to pass axially along the stop member  30  without interference as the tip  40  descends along the channel  36  and the stop member  30  is cammed to the left ( FIG. 7 ). 
     When the drive member  42  is rotated in the opposite direction, it moves up in the holder body  14 , and the rounded upper surfaces of tip  40  engage and exert an upward camming force on the inside surfaces of the converging sides  39  of the channel  36  whereby tip  46  slidably engages and cams the stop member  22  to the right until reaching its retracted position within the holder body  14  shown in  FIG. 1 . 
     The drive member  42  is retained in the bore  20  to maintain a proper alignment of the channel  36  with the tip  40  and ensuring that drive member  42  will continuously engage channel  36  for extension and retraction of stop member  30 . An arrangement to capture the member  42  is also provided as described below. 
     A shear pin  19  in a hole  21  are also provided. When forces are developed sufficient to shear the spin  19 , the holder body  14  is allowed to pivot down about the rod  16 A which motion is accommodated by the oversized hole  18 B creating a clearance with rod  16 B as seen in  FIG. 5 . 
     In this arrangement, with the one end  32  protruding, the cover C is allowed to rise up until the protruding end  32  (and another fixed abutment not shown engages another fixed stop on the cover C across from the mechanism  10 , not shown) engages a fixed stop F on the vault structures. 
     This creates a peripheral gap between the cover C and the surrounding vault structure S, which allows venting of gases through the gap while not allowing the cover to completely blow free of the manhole vault and cover frame structure. This also prevents complete removal of the cover C. 
     In order to increase the vent area, the holder body  14  is allowed to pivot down when the shear pin  19  is stressed sufficiently to be broken, which allows tilting up of one side of the cover C as seen in  FIG. 5 . 
     The stop member  30  is able to be selectively retracted in order to install and remove the cover C. 
     All components of the present invention may be formed from durable and tough materials such as tough plastics, metals, and alloys thereof. Accordingly, the constituents of the present invention may be metal-formed, extruded, molded, or otherwise formed as known in the art Zinc plating of the holder body  14  and stainless steel used to form members  42  and  30  are preferred together with bars (OILITE™) bearing  29  to keep the parts moveable even after many years of exposure The stop mechanism of the present invention may also be used in other applications to facilitate security of a closed or isolated area. A particularly advantageous use is in combination with a manhole cover as described herein. It will be appreciated that the stop mechanism  10  of the present invention may be radially or otherwise oriented on a bottom surface of the manhole cover to facilitate securement as described above. 
     Referring to  FIG. 10 , a pair of threaded retainer pins  52  with spring biased plungers  54  are received in threaded holes  56  slightly offset from each other and extending into the bore  20 . 
     The plungers  54  engage the outside of the drive member  42  while allowing its advance in for  26  when sufficiently retracted the plungers engage a groove  47  in the unthreaded section  43  and seated therein to tend to hold the member  42  in the bore  20 . 
     This prevents the member  42  from becoming separated from the holder body  14  and perhaps from being dropped into the manhole vault. 
     It will be appreciated that the features of the present invention have been described in exemplary embodiments, but are subject to modification as would be recognized by one of ordinary skill in the art. Furthermore, the use of a stop mechanism in accordance with the present invention has been exemplified but not limited to securing down manhole covers. Other securement applications such as a general panel latching are also contemplated. 
     It should be understood that a fixed stop is affixed to the underside of the cover across from the stop mechanism as shown in U.S. Pat. No. 7,484,908 so that the cover C cannot be removed until the stop mechanism is operated. 
     A second mechanism according to the invention could also be installed. 
     The movable parts are substantially entirely enclosed so as to minimize corrosion and seizing even over a period of many years.