Patent Publication Number: US-2020300010-A1

Title: Door chain device

Description:
FIELD OF THE INVENTION 
     The invention relates to a door locking device that restricts the extent to which a door can be opened, with a view to restricting unauthorised entry. 
     BACKGROUND TO THE INVENTION 
     Door locking devices which allow secure limited opening of a door for permitted inspection of a caller, but prevent unwanted entry, are generally referred to as ‘door chains’. These devices usually comprise a short length of chain one end of which is secured to a door frame the other ‘free’ end of the chain is releasably secured to a guard plate fixedly attached to a door associated with the door frame. When the ‘free’ end of the chain engages the guard plate, the door chain allows the door to be opened a small amount to confirm the identity of the caller but prevents unwanted entry, after inspecting the caller, the ‘free’ end of the chain may be disengaged from the door guard plate allowing the door to be opened fully. 
     There are shortfalls associated with commercially available door chains although they do offer a degree of security, they provide little resistance to a determined intruder relying solely on the integrity of the fixing means which are typically woodscrews. The present invention provides an improved door chain device that will mitigate the above shortfall and will also be suitable for all types and styles of doors, it will be inexpensive to manufacture having few components and will also be aesthetically pleasing to even discerning consumers. Additionally, the chain can become snagged or caught on the housing of the device. 
     SUMMARY OF THE INVENTION 
     According to the present invention is directed to a door guard plate comprising:
         a main body, internal of which are located two compression springs; and   a chain holder comprising a body portion and a chain arm extending therefrom and having a free end for releasably engaging a chain and a body portion;   wherein, the main body comprises a slot and the body portion of the chain holder body is contained within the main body and the chain arm of the chain holder extends through the slot of the main body to protrude therefrom and slide therein.       

     The chain holder body may have two spring engaging limbs that can be arranged adjacent the two compression springs within the main body. This provides a reliable surface against which the springs can provide a biasing force. The main body may be a housing that is provided on the device. 
     Preferably, the main body comprises an angled face such that the thickness of the main body decreases over the length of the angled face, with the thinner end of the angled face being distal from the free end of the chain arm of the chain holder and, in use, proximal to the door. Having a chamfered, tapered or angled face provides a surface against which the chain can be guided. This reduces the risk of the chain becoming caught or snagged on the main body, which is a problem with known devices where the end surface is not angled. 
     In one arrangement, the two spring engaging limbs extend are arranged to extend from a central axis and substantially 90 degrees therefrom centrally and they may be arranged adjacent one end of the chain holder. 
     Advantageously, a first section of the chain arm of the chain holder extends at a 90 degree angle from the body portion of the chain holder and protrudes through the slot in the main body and a second section of the chain arm further extends at another 90 degree angle to form a hook shape, extending away from the angled face of the main body. The hook shape provides a mechanism for engaging a door chain. Clearly, the angles on the chain holder may be varied but still allow the chain holder to form an arm that engages the chain, when in use. For example, the arm may extend a 60 degrees from the chain holder body and then at a further 120 or 130 degrees to form the chain engaging arm. Other angles may be possible that still form the hook shape required to engage the chain. 
     A base plate may be provided to which the door guard plate may be attached. 
     In a preferred embodiment, the corners of the main body between the angled face and the side of the main body are arcuate. This reduces the risk of the chain catching on an angled corner of the main body, thereby providing a more reliable device. 
     A channel may be provided in the outer surface of the main body that extends towards the angled face. This provides a route through which the chain may pass to reduce it snagging or catching and so it provides a path for the chain. 
     The invention extends to a door chain device comprising a chain and a door guard plate as described herein. 
     The invention further extends to a system comprising a guard plate as described herein attached to a door and a chain connected to a door frame, wherein an edge of the door guard plate is adjacent the edge of the door and the free end of the chain arm of the door guard plate extends away from the door frame and towards the centre of the door. 
     Accordingly a door chain device may be provided comprising an anchor plate that is fixedly attached to a door frame for securing one end of the chain to said door frame, a door guard plate fixedly secured to a door operatively associated with the door frame and means provided to releasably secure the ‘free’ end of said chain to the door guard plate. The chain can only be engaged and disengaged from the door guard plate when the door is closed. 
     The door guard plate may incorporate at least one spring, which can act as a damper to absorb a force or forces applied to a partially opened door, when the door chain device according to the invention, is in use. 
     Preferably, the dampening means comprises two strong compression springs. 
     Preferably, the chain comprises a plurality of links with adjacent links being rotationally offset with respect to one another. 
     The door guard plate may comprise a main body which is in the form of a narrow elongated main body, or housing, which has one side open, said housing defines internally, a pair of spaced spring receiving compartments, a chain holder which is mounted within said housing and between the spring receiving compartments and is biased to a first position by the compression springs, a bent arm of the chain holder extends outward of the housing to be engageable by any available link of the chain, any force applied to the chain will cause the chain holder to move away from its first position against the force of the springs. A back plate is also provided to close the open back side of the housing, said back plate may be secured to the housing with adhesive or by other suitable means. A number of screw fixing apertures are provided in the sides of the housing by means of which the fully assembled door guard plate is secured to a door. 
     Alternatively, the back plate may be secured to the back face of a door with screws or bolts and the housing, chain holder and spring assembly then mounted on and secured to the back plate with threaded bolts. 
     The door guard plate is, preferably, fixedly securely to a door, adjacent the door edge and thereby acts to protect the edge of the door from damage by the chain. 
     The door frame anchor plate may be fixedly secured to a door frame for securing one end of the chain to said frame, alternatively the chain may be connected directly to the door frame. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the present invention will now be described further by way of example, with reference to the accompanying drawings, in which: 
         FIG. 1  is a front view of a door chain device in accordance with the present invention, secured to a door and door frame and in its operative position; 
         FIG. 2  is a view of the front elevation of the guard plate housing of  FIG. 1 ; 
         FIG. 3  is a back view of the rear elevation of the guard plate housing of  FIG. 1 ; 
         FIG. 4  is a perspective view of the chain holder of  FIG. 1 ; 
         FIG. 5  is a side view of the chain holder of  FIG. 4 ; 
         FIG. 6  is a front view of the chain holder of  FIG. 4 ; 
         FIG. 7  is a perspective view of the back plate of  FIG. 1 ; 
         FIG. 8  is a part cross sectional view of the guard plate housing of  FIG. 1 ; 
         FIG. 9  is a part cross sectional view of a partially assembled door guard plate of  FIG. 1  along line A-A; 
         FIG. 10  is an underside view of the guard plate housing of  FIG. 1  with back plate assembled thereon. 
         FIG. 11  is a view of the front end of the assembled door guard plate of  FIG. 1 ; 
         FIG. 12  is a view of the back end of the assembled door guard plate of  FIG. 1 ; 
         FIG. 13  is a cross sectional view of the guard plate housing of  FIG. 1  along line C-C; 
         FIG. 14  is a cross sectional view of the guard plate housing of  FIG. 1  along line B-B; 
         FIG. 15  is a cross sectional view of the housing of  FIG. 1  along line C-C with chain holder assembled therein; 
         FIG. 16  is a perspective view of the components of the door frame anchor bracket; 
         FIG. 17  is a part cross sectional view of a partially assembled door guard plate according to a second example of the invention; 
         FIG. 18  is a perspective view of a modified back plate for the housing of  FIG. 17 ; 
         FIG. 19  is a perspective view of a door guard plate in accordance with a third embodiment of the present invention; 
         FIG. 20  is an underside view of the assembled door guard plate of  FIG. 19 ; 
         FIG. 21  is a perspective view of an alternative chain holder for the door guard plate of  FIGS. 19 to 22 ; and 
         FIG. 22  is a part cross sectional view of the partially assembled door guard plate of  FIGS. 19 to 22 . 
     
    
    
     Where possible, the same numerals have been used throughout this specification to denote similar components. 
     Reference is now made to  FIGS. 1 to 16 , which show the first example of a door chain device according to the present invention. The illustration of  FIG. 1  shows the complete assembly  1   a  fixedly secured to a door ‘a’ and door frame ‘b’, with the door chain device in its operative or standby condition, one end of the chain  30  is secured in the door frame anchor plate  50  that is fixedly secured to the door frame ‘b’ the other, free end of the chain  30  is releasably secured to the guard plate  1 , by means of the chain link  31   b  which is engaged on the arm  22  of the chain holder  20 . The door guard plate  1  is secured to the inner surface of a door ‘a’, at the very edge of the opening side of the door ‘a’ and will therefor protect the door ‘a’ from damage by the chain  30 . 
     The door chain device  1   a  comprises a door guard plate  1 , a door frame anchor bracket  50  and a short length of chain  30 . 
     The door guard plate  1  comprises a metal housing  2 , a chain holder  20 , two compression springs  29  and a base/mounting plate  40 . 
     The housing  2  is preferably formed as a metal die casting, metal pressing or fabricated from a suitable plastic material and is in the form of a generally elongate or rectangular enclosure with an open back, the inside of the housing  2  is partitioned longitudinally to provide two spaced spring receiving compartments  5 , a long narrow aperture  6  is defined centrally and longitudinally in the front face  2   a  of the housing  2  in the space between the spring receiving compartments  5  said aperture  6  is to allow passage of the arm  22  of the chain holder  20 , and facilitates transverse movement of the chain holder  20  in the housing  2 . Two spaced screw receiving apertures  15  are provided in the back side  3  of the housing  2  by means of which said back end  3  is secured to the base plate  40  with screws  15   a , a further screw receiving aperture  15  is provided centrally and close to the front end of the housing  2  in the chain location recess  7   c , by means of which the front end of said housing  2  is secured to the base plate  40  with screws  15   a . The front end  3   a  of the housing  2  defines an angled face, the angle of said face is preferably no less than 50 degrees with large radiuses  3   c  on the front corners which are fashioned to blend with the angled face of the front end  3   a  of the housing  2 . 
     A gap  7  is provided between the ends of the partition walls  8  respectively and the back wall  3  of the housing  2  said gap  7  is to accommodate the wall  42  of the base plate  40 . 
     A chain holder  20 , as shown in  FIGS. 4 to 6 , locates in the housing  2  and is positioned between the two compression springs  29  said chain holder  20  is preferably formed as a metal die casting or may be steel and defines a flat rectangular body portion  21  from which a chain receiving arm  22  extends at 90 degrees centrally and adjacent the front end  21   a , said chain receiving arm  22  is bent at 90 degrees to provide a radius of approximately 6 mm and to be parallel with the body  21  of the chain holder  20 , the chain receiving arm  22  extending approximately 30 mm past the back end  3  of the door guard plate  1 . The chain holder  20  also defines a pair of spring engaging limbs  23  which extend outwards at 90 degrees respectively from the back end  21   b  of the body  21  said limbs  23  are fashioned and dimensioned to be a clearance or snug fit in the spring receiving compartments  5  to engage respectively one end of each spring  29 , said limbs  23 , in use, act to compress the springs  29  when force is applied to the spring holder  20  by the chain  30 . 
     An aperture  24  is provided centrally in each of the spring engaging limbs  23  said apertures  24  to allow passage of the screws  15   a  used to secure the back end of the housing  2  to the base plate  40 . The chain receiving arm  22  extends through the elongated slot  6  in the front face of the housing  2  to be accessible to the chain link  31   b  or any available link, said elongated slot  6  guides, supports and limits the transverse movement of the chain holder  20  in the housing  2 . The chain holder  20  is slidably mounted in the housing  2  between the base plate  40  and the inner dividing walls  8  of the spring receiving compartments  5 ,  FIG. 9  best illustrates the position of the chain holder  20  in its first inoperative position in which position, the springs  29  respectively, are pre-loaded against the limbs  23  of the chain holder  20  and acting to bias said chain holder  20  against the stop face  7   b  at the back end of the elongated slot  6 . 
     The base plate  40  is generally a flat, rectangular strip of metal plate with a first end portion bent at 90 degrees to form a wall  42 , the main body  41  of the base plate  40  is provided with spaced screw receiving apertures  16  to receive woodscrews  16   a  (not shown) by means of which it is secured to the inside face of the door ‘a’, a pair of spaced threaded apertures  15  are provided in the back wall  42  of the base plate  40  by means of which the back end of the housing  2  is secured to the wall  42  of the base plate  40  with screws  15   a . A hook formation  46  depends centrally from the front or second end portion of the base plate  40  said hook  46  is provided with a threaded aperture  15  by means of which the front end of the housing  2  is secured to the base plate  40  with screws  15   a . The base plate  40  locates on the shoulder  9  in the housing wall  2  and the outer surface  41   a  of the base plate  40  will be flush with the back surface of the housing  2 , the base plate  40  also acts to protect the surface of the door ‘a’ and provide a low friction metal to metal sliding surface for the chain holder  20 . 
     The chain  30  comprises a plurality of links with adjacent links being rotationally offset with respect to one another, preferably, the links  31  are stainless steel and short links fabricated from standard 4 mm wire. Preferably, the end link  31   b  on the free end of the chain  30  is releasably engaged on the arm  22  of the chain holder  20  as shown in  FIG. 1 , alternatively, a ring  36  (not illustrated), may be secured to the free end of the chain  30  for engagement of the arm  22 , alternatively, a number of chain links  31  on the free end of the chain  30  may be made available for engagement on the arm  22  of the chain holder  20 . 
     The door frame anchor bracket  50 , comprises a generally U shaped body  51  with a pair of attachment flanges  52  and  52   a , said flanges define respectively, a screw fixing aperture  16 , the bottom flange  52   a  is longer and its end is fashioned and bent at 180 degrees to form a hook  53  on which to hang the link  31   b  when the door chain device  1   a  is not in use. A deep through slot  55  is provided centrally in the U-shaped body  51  of the bracket  50  to receive the link  31   a  on the end of the chain  30 . In order to secure one end of the chain  30  to the anchor bracket  50  the link  31   a  is first inserted into the slot  55  until the link  31   a  abuts the flanges  52  and  52   a , a half link  58  is then engaged in the link  31   a  via the back of the bracket  50  to secure the chain  30  to the bracket  50 . When the anchor bracket  50  is fixedly secured to a door frame ‘b’ with screws  15  the ends  59  of the half link  58  will be abutting the door frame ‘b’ effectively locking the half link  58  against removal, alternatively, as illustrated in  FIG. 1  a headed locking rivet  56  may be used to secure the chain  30  to the anchor bracket  50 , the non-headed end of the rivet  56  being peened over to retain said rivet captive in the bracket  50 . 
     In the UK in excess of 80 percent of external doors are panelled, the maximum width of styles, that is, the distance between the opening edge of the door ‘a’ and raised panelling, on these types of doors is 100 mm, this requires that the door guard plate  1  is fixed adjacent the opening edge of a door ‘a’, there is not room to place a slide plate in front of the door guard plate  1  in order to protect the door ‘a’ from the chain  30 , as is proposed in prior art U.S. Pat. No. 4,648,642, also, the prior art device as illustrated and described is clearly intended and required to be set back from the door edge as it would not function or act as a damper if it was fixed adjacent the edge of a door ‘a’, furthermore, the chain  30  will abut and jam against the lower front corner of the housing of the device when the door ‘a’ is opened to inspect a caller due to the fact that the front end of the housing is not substantially angled and the front sides contoured. 
     For a door chain to receive broad market appeal and not be excluded from a large segment of the market it must be suitable for panelled doors and the door guard plate  1  should preferably be no longer than 95 mm, any longer and it may be encroaching onto or over door panelling, it is for this reason the door guard plate  1  of the present invention has been designed to be able to be secured at the very edge of the door ‘a’, and at the height conventional door chains are normally fixed. 
     Due to the above mentioned restraints, the chain holder  20  of the invention is positioned toward the back end  3  of the housing  2  and the forward travel of said chain holder  20  is restricted by the end wall  7   a  of the slot  7  and it is unlikely that the chain holder  20  would abut the end  7   a  of the slot  7  even in a severe attempted forced entry, the chain holder  20  would remain a chain link distance from the door edge ensuring that the door chain device  1   a  would always function effectively. The door chain device  1   a  would not function as intended if the chain holder arm  22  or any part of the chain holder  20  in its operation was allowed to project past the edge of the door ‘a’ 
     Testing has established that the front end  3   a  of the housing  2  is required to be angled at preferably a minimum of 50 degrees with large radiuses  3   c  at the sides, this ensures that the chain  30  will transition smoothly across the front  3   a  of the housing  2  to locate in the central channel  7   c , when the door ‘a’ is opened ‘on chain’ for inspection of a caller. Without such a steep angled/contoured front end  3   a  the chain  30  will abut and jam against the lower front corner of the housing  2 , which, in an extreme situation could cause the door guard plate  1  to become dislodged compromising the door chain  1   a  and security. 
     The housing  2  is mounted on and secured to the base plate  40 , said base plate  40  protects the surface of the door ‘a’ from scaring by the chain holder  20  and provides a smooth sliding surface (metal to metal) for the chain holder  20 . The base plate  40  is secured to the door ‘a’ with suitable screws or suitable threaded bolts if being fixed to plastics material doors, such as unplasticized polyvinyl chloride (uPVC). 
     To assemble the door guard plate  1 , enter the chain holder  20  into the housing  2  through its open back side, passing the arm  22  of the chain holder  20  through the aperture  6  and move said chain holder  20  toward the back of the housing  2  until it abuts the end  7   b  of the slot  6 , insert the springs  29  into their respective compartments  5 , this requires the springs  29  to be compressed against the inside surface of the front wall  3   a  while simultaneously forcing the free end of said springs respectively into engagement with the limbs  23  of the chain holder  20 . Once thus assembled, the slightly loaded springs  29  will retain said assembly together until it is required to be mounted on and secured to the base plate  40  with screws  15   a.    
     When the door chain device  1   a  is fixedly secured to a door ‘a’ and door frame ‘b’ ( FIG. 1 ), and the device is not operational, the link  31   b  on the free end of the chain  30  is engaged on the hook  53  of the anchor bracket  50 . 
     To place the door chain device  1   a  on standby or in its operational condition the chain  30  is disengaged from the hook  53  of the anchor bracket  50  and the end link  31   b , or any other available link  31 , is engaged on the arm  22  of the chain holder  20  when the components of the door chain device  1   a  will assume the position illustrated in  FIG. 1 . When a caller comes to the door ‘a’, the door ‘a’ may be opened a distance determined by the length of the chain  30 , a door movement of approximately 10 cm, sufficient to allow a caller to be identified. 
     The chain  30  is of a length that will comfortably allow the link  31   b  to be engaged on the arm  22  of the chain holder  20  but requires that the door ‘a’ must be closed in order to disengage the chain  30  from the door guard plate  1 . With the door chain device  1   a  operational and when the door ‘a’ is opened for inspection of a caller, any attempt at forced entry will cause the chain  30  to pull on the chain holder  20  against the force of the compression springs  29  said chain holder  20  being moved transversely in the aperture  6  in the housing  2 , simultaneously, the springs  29  will absorb and mitigate the applied force. Strain on all the screw fixings is dramatically reduced by the use of the damper springs  29  said springs  29  are fully supported in the housing  2  by their individual enclosures and the base plate  40 . 
     Referring now to  FIGS. 17 and 18  which illustrate an alternative method of securing the housing  2   a  to the base plate  40   a  all other aspects are the same as the previous embodiment. 
     The housing  2   a  in this example is provided with an elongated bore  10  centrally and internally in the housing  2   a  said bore  10  is to receive and locate the hook formation  46  defined centrally at the front end of the base plate  40   a , this arrangement eliminates the need for a screw fixing in the central channel  7   c  at the front of the housing  2   a.    
     Referring now to  FIGS. 19 to 22  which illustrate an alternative or modified door guard plate  1 . In this example the guard plate  1  is secured to the inner surface of the door ‘a’ with suitable wood screws or threaded bolts (not shown) by means of screw receiving apertures  16  provided in the sides of the housing  2   b.    
     The base plate  40   b  is generally a thin metal plate, a pair of spaced ribs  44  are defined centrally and depend from the inner surface  41   b  of the base plate  40   b  said raised ribs  44  act as additional transverse guides and support for the chain holder  20   a . The base plate  40   b  locates on the step  9  in the housing  2   b  when its outer side  41   a  will be flush with the back face of the housing  2   b . The base plate  40   b  may be secured to the housing  2   b  with adhesive or other suitable means. 
     The chain holder  20   a  in this example is preferably produced as a pressing or stamping from a 4 mm thick sheet of stainless steel. The body  21  of the chain holder  20   a  is provided with a pair of spaced apertures  26  and  26   a  respectively, one at each end thereof said apertures to receive hardened steel pins, or alternatively roll pins, which, in use, act as runners ( FIG. 22 ) to bear against the partition wall  8  in the housing  2   b  to retain the chain holder  20   a  in the housing  2   b . The short pin  28  locates in the front aperture  26  in the body  21 , when the pin  28  is in position it protrudes from each side of the body  21  in order to abut against the partition walls  8 , the pin  28  locks the front end  21   a  of the chain holder  20   a  in the housing  2   b.    
     The longer pin  27  locates in the rear aperture  26   a  of the body  21 , when the rear pin  27  is in position it protrudes from each side of the chain holder body  21  sufficient to allow it to engage fully the back end of the compression springs  29  said pin  27  bears against the partition walls  8  and locks the back end  21   b  of the chain holder  20   a  in the housing  2   b . In use, the springs  29  respectively, are lightly loaded against the long pin  27 , transverse movement of the chain holder  20   a  in the housing  2   b  will cause the pin  27  to compress the springs  29  and provide the damper means. The back end  21   b  of the chain holder body is spring biased against the inner surface of the back wall  3  of the housing  2   b . The chain holder  20   a  of this embodiment may be used as an alternative in the housing  2  and  2   a.    
     A narrow slot or bore  25  is provided centrally in the front surface of the housing  2   b  in the back wall  3  said slot  25  is to receive a short rectangular strip of plastic  25   a  which is thin and very flexible. When the plastic strip  25   a  is fully engaged in the slot  25  it protrudes therefrom approximately 4 mm in order to be engageable by the chain link  31   b  as said link  31   b  is being engaged on or removed from the chain holder arm  22 . A small force is required to bend the plastic strip  25   a  to allow passage of the link  31   b . The plastic strip  25   a  will prevent inadvertent removal of the chain  30  from the chain holder  20  and  20   a.    
     All other aspects of this example are similar to that of  FIGS. 1 to 16 .