Patent Publication Number: US-11027440-B2

Title: Self-retracting knife with replaceable blade

Description:
BACKGROUND 
     Embodiments of the present invention relate to self-retracting utility knives with replaceable blades. Such tools are sometimes referred to as box cutters and have a housing which forms a handle, and a blade may be easily removed and replaced with another blade. If the blade breaks or becomes dull, the user may remove the blade and replace it with a new blade or flip the blade to present a new edge on the blade. 
     A self-retracting knife is a tool where the blade is supported by a blade carrier that retracts into the handle for safety reasons when no outside forces are acting upon the blade carrier. A self-retracting utility knife usually includes a tension spring that pulls the blade carrier into the handle to keep the blade fully retracted. Thumb or finger pressure is used to offset the force of the spring to extend the blade. When pressure is released, the blade carrier fully retracts. Precise thumb or finger positioning is required as any movement of the activating extension button adjusts the amount of blade extension. When scoring or making heavy cuts with pressure, the knife transfers all of the pressure of the cut to the activating finger or thumb that is holding the blade extended and exposed. When a user pushes the blade carrier forward with enough force to overcome the spring, the blade will extend from the handle and remain extended as long as the user exerts a force to overcome the force of the retracting spring and any force applied to the work. Thus, with traditional self-retracting knives, when the user stops exerting a force to extend the blade, the blade will retract back into the handle or housing. 
     SUMMARY OF THE INVENTION 
     A self-retracting knife of the present invention also includes a housing enclosing a blade carrier and having a blade aperture at one end. The blade carrier extends a replaceable blade through the blade aperture in a fully extended position and encloses the blade within the housing in a fully retracted position. In accordance with the invention, the housing also supports an anti-retraction member or latch bar which allows a user to select a latching or non-latching position by applying or not applying a light pressure to the anti-retraction latch bar. The blade carrier is positioned in an extended position when the latch bar is in a latching position so that the force of the retraction spring will not retract the blade carrier. The spring returns the blade carrier to the fully retracted position when the anti-retraction latch bar is released and returns to the non-latching position. 
     According to one embodiment of the present invention, a self-retracting knife comprises a housing with a rear blade carrier aperture in addition to a front blade aperture. The blade carrier extends the blade through the front blade aperture in an extended position and the blade carrier extends through the rear carrier aperture in a retracted position. This embodiment may also include an extension limiter that prevents the rearward end of the carrier bar from moving past the end of the extension limiter when a force is applied to the end of the blade carrier. When the anti-retraction latch bar is in a latching position and a force is applied to extend the blade carrier, the blade carrier extends the blade only partially through the knife aperture of the knife housing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a self-retracting utility knife constructed in accordance with the invention; 
         FIG. 2  is an exploded view of the self-retracting knife shown in  FIG. 1 ; 
         FIG. 3  is an elevational view of the blade carrier shown in  FIG. 2 ; 
         FIG. 4  is a longitudinally center view of the knife with the blade carrier in a fully retracted and non-latched position; 
         FIG. 5  is a view similar to  FIG. 4  with the addition of a blade in the retracted and latched position; 
         FIG. 6  is a view similar to  FIG. 5  and with blade in its fully extended and latched position; 
         FIG. 7  is a view similar to  FIG. 6  and showing a two edge blade in a fully retracted and latched position, and 
         FIG. 8  is an exploded view of a modified self-retracting knife constructed in accordance with the invention. 
     
    
    
     DETAILED DESCRIPTION 
     According to one embodiment of the present invention, a self-retracting knife includes a blade carrier that projects through a rearward end of a housing of the knife. When a user wants to extend a blade attached to the blade carrier, the user grasps the knife, exerts a light finger pressure on an anti-retraction member or latch bar, and the user bumps or taps the blade carrier against a surface to extend the blade. The anti-retraction latch bar maintains the blade carrier and the blade in an extended position as long as the user maintains pressure on the bar. If the user releases pressure on the bar, the blade carrier will retract into the housing and project through the rearward end of the housing again. Thus, in this embodiment, a grasping and tapping action is required to extend the blade carrier and the force is applied to the blade carrier from outside the knife housing. In addition, a light grasping action is required on the latch bar to maintain the extension of the blade carrier. 
     Referring to  FIG. 1 , a self-retracting knife  10  includes a housing  12 , a blade carrier  14 , and an anti-retraction member or latch bar  16 . The housing is formed by two mating housing sections  12   a  and  12   b  releasably connected in an opposing relation. However, the housing  12  may be primarily one piece or created from more than two sections. The housing  12  forms a carrier aperture  13  at the rearward end and a blade aperture  15  ( FIG. 2 ) at opposite or front end. 
     The housing  12  enclosed the blade carrier  14  such that when the blade carrier  14  is in a fully retracted position, the carrier  14  projects to a maximum position through the carrier aperture  13 . To extend the blade carrier  14 , a user grasps the knife housing  12 , applies a light finger pressure to the anti-retraction latch bar  16 , and presses or taps the blade carrier  14  on a surface for example, a tabletop, the palm or leg of the user, etc. Thus, the force acting to extend the blade carrier  14  is external to the knife  10 . 
     When the blade carrier  14  is extended, a blade  17  ( FIG. 2 ), which is removably coupled to the blade carrier  14 , extends through the blade aperture  15  of the housing  12 , as shown in  FIG. 1 . As mentioned above, the blade  17  is removably coupled or secured to the carrier  14  such that a user may exchange a worn blade with a new blade or the opposite end of the same blade. 
       FIG. 2  shows an exploded view of the self-retractable knife. The latch bar  16  includes a surface  18 , where pressure on the surface  18  maintains the blade carrier  14  in an extended position. The housing  12  also encloses a blade carrier retraction member in the form of a tension spring  20  that connects the blade carrier  14  to the housing section  12   b  by a pin  23 . The forward end of the spring  20  is connected to a hook  22  on the blade carrier bar  14 . Other forms of retraction members may also be used to return the blade carrier  14  to its retracted position. 
     As shown in  FIG. 2 , the anti-retraction latch bar  16  has the surface  18  for a user to apply finger or thumb pressure to keep the blade carrier  14  in an extended position. When the user applies light pressure to the surface  18  of the latch bar  16  and the blade carrier  14  is in an extended position, one of the stop or latch teeth  28   a - c  (collectively  28 ) of the latch bar  16  interacts or catches with a projection or catch pin  46  ( FIGS. 2 &amp; 3 ) on the side of the blade carrier  14  to enter a latching position that prevents the spring  20  from returning the blade carrier  14  back to its fully retracted position. The latch teeth  28  may also be formed on the blade carrier  14  and the catch pin  46  may be formed on the latch bar  16 . The self-retracting knife  10  may also have a single latch tooth and a single catch pin. In any embodiment, as long as pressure remains on the latch bar  16  and the latch bar remains in the latching position, the blade carrier  14  remains in an extended position. 
     The anti-retraction latch bar  16  has a hole or aperture  24  ( FIG. 2 ) through which a tubular post  26  of the housing section  12   b  extends to support the latch bar  16  for slight rotation or pivoting. A torsion coil spring  30  couples a tab  31  on the latch bar  16  to the housing section  12   b  and rotates or pivots the latch bar  16  to a non-latching position when there is no pressure against the surface  18  of the latch bar  16 . 
     The latch bar  16  includes an upward projection  32  that extends to an end surface  34  ( FIG. 2 ). The blade carrier  14  has a side projection  48  ( FIG. 2 ) that engages the projection  32  so that when the blade carrier  14  is in the fully retracted position and the latch bar  16  is in the non-latching position, the end surface  34  blocks the blade carrier  14  from being extended when a force is applied to the blade carrier  14 . However, when the latch bar  16  is tilted or placed in a latching position, the end surface  34  is removed from the linear path of the projection  48  of the blade carrier  14 . Thus, when the latch bar  16  is pressed to the latching position and a force greater than the force of the retraction spring  20  is applied to the blade carrier  14 , the blade carrier  14  will be extended. 
     The self-retracing knife  10  may include an extension limiter  36  ( FIG. 2 ) that indirectly limits how far the adjacent blade carrier  14  travels by opposing the force pushing the blade carrier  14  forward. The extension limiter  36  includes a flexible spring arm  38  with a thumb adjusting head  40  and an engaging base portion  43 . The housing  12  includes three notches  42   a - c  (collectively  42 ), where each notch represents a different position for the extension limiter  36 . For example, if the base portion  43  of the extension limiter  36  is in the left-most notch  42   a , the blade carrier  14  will be able to travel to the fully extended position when light pressure is applied to the latch bar  16  and a force is applied to the end surface of the blade carrier  14 . However, if the base portion  43  of the extension limiter  36  is in the right-most notch  42   c , then the blade carrier  14  will only travel a short distance when pressure is applied to the latch bar  16  and a force is applied to the blade carrier  14 . 
     To move the extension limiter  36  from one notch  42   a  to another notch  42   b  or  c , the user presses down on the head  40  such that a base portion  43  of the head  40  is retracted into the housing  12 . Then the user slides the head  40  back to the desired notch  42   b - c . When the user releases the head  40 , the spring arm  38  forces the base portion  43  into the desired notch  42 , placing the extension limiter  36  in a locked position. 
     An end surface  44  ( FIG. 2 ) of the extension limiter  36  projects through the carrier aperture  13 , but not as far as the blade carrier  14  ( FIG. 1 ) when the carrier  14  is in the fully retracted position. When a force is applied to the blade carrier  14 , the blade carrier may slide through the housing. If the extension limiter  36  is in notch  42   b  or  42   c  and the rearward end of the blade carrier  14  reaches the end surface  44  of the extension limiter  36 , the extension limiter  36  blocks further forward movement of the blade carrier  14 . Thus, by using the extension limiter  36 , the user can adjust how far the blade carrier  14  travels when the user presses on the latch bar  16  and applies a force to the end of the blade carrier  14 . The extension limiter  36  may be used to limit how far the blade  17  attached to the blade carrier  14  will extend through the blade aperture  15 . 
       FIG. 3  shows a side view of the blade carrier  14 . The carrier  14  includes a hook  22  that receives one end of the retraction spring  20  ( FIG. 2 ). The opposite end of the spring connects to the stud or pin  23  ( FIG. 2 ). A catch pin  46  on the blade carrier  14  interacts with the retraction latch teeth  28  ( FIG. 2 ) of the latch bar  16  to prevent or stop the retraction spring  20  ( FIG. 2 ) from returning the blade carrier  14  back to the fully retracted position. The blade carrier  14  also includes a projection  48  ( FIG. 2 ) that interacts with the end surface  34  ( FIG. 2 ) so that when the self-retracting knife is in the fully retracted position and the latch bar  16  ( FIG. 2 ) is in the non-latching position, the end surface  34  ( FIG. 2 ) of the latch bar will prevent the blade carrier  14  from being extended even when a force is applied to the blade carrier  14 . The blade carrier  14  has a slot  51  and the extension limiter  36  has a slot  53  ( FIG. 2 ) through which the tubular post  26  ( FIG. 2 ) projects to align the blade carrier  14 , the latch bar  16 , and the extension limiter  36 . 
       FIG. 4  illustrates the self-retracting knife  10  in a non-latching and retracted position with the end surface  44  of the extension limiter  36  projecting from the housing. This is the position that the self-retracting knife  10  is when no outside forces are placed on the self-retracting knife. The knife  10  is in the non-latching position because the latch bar  16  is rotated downwardly by the torsion spring  30  pressing upwardly on the tab  31  of the latch bar  16 . Also, the knife  10  is in the fully retracted position with the blade carrier  14  retracted by the retraction spring  20 . When the knife  10  is in the non-latching and retracted position, the projecting stub  32  is rotated upwardly into the path of the side projection  48  of the blade carrier  14  so that forward movement of the blade carrier  14  is blocked. However, when the knife  10  does not include a stub  32  or a projection  48  or both, the knife  10  can be placed in the extended position if a force is applied to the blade carrier  14  regardless of the position of the latch bar  16 . 
       FIG. 5  illustrates the knife  10  in a fully retracted position when a light force is applied to the surface  18  of the latch bar  16  but no force has been applied to the blade carrier  14 . When a force, such as finger pressure on the surface  18  from a user gripping the knife  10 , of the latch bar  16  rotates the projection  32  and end surface  34  ( FIG. 2 ) out of the way of the projection  48  so that a force applied to the blade carrier  14  will cause the blade carrier to travel such that the blade  17  extends through blade aperture  15  ( FIG. 2 ). As the catch pin  46  of the blade carrier  14  slides past the retraction latch teeth  28   a - c , the catch pin  46  slides up inclined surfaces  54   a - c  of the latch teeth  28   a - c  to move the latch teeth  28   a - c  out of the way of the catch pin  46  of the blade carrier  14 . Thus, the blade carrier  14  repeatably tilts the latch bar  16  out of the way while the blade carrier  14  travels through the housing  2 . However, if the user grips the latch bar  16  with greater pressure or force, then the latch teeth  28   a - c  will not move out of the way. Thus, a user should not apply too much pressure to the latch bar  16  while blade carrier  14  is traveling. 
     In embodiments that include an extension limiter  36  as shown in  FIGS. 2 and 5 , the end surface  44  will limit the travel of the blade carrier  14 , depending on where the extension limiter is set. In the example of  FIG. 5 , the extension limiter is in the leftmost notch  42   a  of  FIG. 2 , so the blade carrier  14  can travel the entire distance to the fully extended position where the blade  17  projects fully out of the blade aperture  15 . However, when the extension limiter is in the middle notch  42   b , then the blade carrier  14  produces a medium extension of the blade  17  out of the blade aperture  15 . Further, if the extension limiter  36  were in the rightmost notch  42   c , the blade carrier  14  would travel less than when the extension limiter is in the middle notch, resulting in a short extension of the blade  17  out of the blade aperture  15 . 
       FIG. 6  illustrates the knife  10  in a latched and fully extended position. With pressure on the surface  18  of the latch bar  16 , a force previously applied to the blade carrier  14  resulting in the blade carrier  14  in the fully extended position, the latch teeth  28  interacts with the catch pin  46  of the blade carrier  14  and prevent the retraction spring  20  from retracting the blade carrier  14 . Thus, the knife  10  remains with the blade  17  in the fully extended position. 
     When pressure is removed from the latch bar  16 , the retraction latch teeth  28  are no longer engaged with the catch pin  46  of the blade carrier  14 , and the retraction spring  20  returns the blade carrier  14  to the fully retracted position of  FIG. 4 . As the blade carrier  14  returns to the retracted position, the projection  48  of the blade carrier  14  slides along the top surface of the latch bar  16 , which pivots the latch bar  16  out of the way, so the blade carrier  14  may return to the fully retracted position of  FIG. 4 . Once the projection  48  of the blade carrier  14  is clear of the latch bar  16 , the spring  30  returns the latch bar  16  to its home position shown in  FIG. 4 . 
     As shown in the embodiments of  FIGS. 1-6 , the self-retracting knife  10  is a utility knife. However, the self-retracting knife may be any type of knife that includes a removable blade from a blade carrier. For example, the self-retracting knife  10  may be made as a carpet knife as shown in  FIG. 7 . All of the structural components of this self-retracting knife would be similar to the structural components of the embodiments described above except for a two or double edge blade  55 . 
       FIG. 8  illustrates a modified and simpler form of a self-retracting knife constructed in accordance with the invention and operates in a manner similar to the knife of  FIGS. 1-6 . The modified knife includes an elongated housing formed by mating housing shells or sections  62  and  64  of die-cast metal or molded plastics material and which are secured together by a screw  66  threaded into a tubular boss  99  molded as a part of the housing section  64 . A conventional knife blade  65  is supported within the housing by a blade carrier  68  which slides within the housing between a fully retracted position where the blade carrier  68  and blade  65  are enclosed within the housing and a fully extended position where the blade  65  projects through a slot formed within the forward end of the housing sections  62  and  64 . 
     A biasing or retraction member in the form of a retraction tension spring  71  has a forward end portion connected to the carrier  68  by a pin  73  pressed into a hole within the top surface of the blade carrier  68 . The spring  71  has a rearward end portion connected to a hook  72  formed as part of the housing section  64 . In accordance with this modification of the invention, an anti-retraction member or latch bar  80  is pivotally supported within the housing by the tubular boss  99  which projects through a hole  82  within the latch bar  80 . The latch bar  80  has a forward finger engaging portion  84  which projects downwardly through a slot  86  formed within the bottom of the housing sections  62  and  64 . The finger engaging portion  84  is biased downwardly within the slot  86  by a coil spring  87  having one end portion interacting with the housing section  64  and an opposite end portion interacting to a side projection  88  of the latch bar  80 . The latch bar  80  has a pin  92  which projects laterally and is positioned to engage one of the surfaces formed by teeth  94  on the bottom of the blade carrier  68  when the forward portion  84  of the latch bar  80  is pressed upwardly by fingers pressing on the bottom surface of the forward portion  84 . 
     The use and operation of the self-retracting knife shown in  FIG. 8  is similar to the knife described above in connection with  FIGS. 1-6 . That is, the blade will not retract while pressure is maintained on the latch bar  80 . It differs in how the blade  65  is extended. The blade is extended by moving the thumb engaging button  96  forward which is connected to the blade carrier  68  which slides through the slot  97 . The blade is extended by exerting a force on the thumb button  96  that is sufficient to extend or stretch the tension spring  71 . The blade may be held by the thumb button  96  in the extended position against the tension of the return spring and the force of the knife blade on the work surface or can also be held in position with pressure on the surface of the latch bar  80 . If it is desired to only partially extend the blade through the housing, the thumb button should only be advanced far enough for the pin  92  to engage the tooth  94  which provides the desired amount of extension. Two or more partially extended positions for the knife blade  65  may be obtained by two or more teeth  94  with stop surfaces formed on the bottom of the blade carrier  68 . 
     It is apparent that a self-retracting knife constructed in accordance with the invention provides desirable features and advantages. For example, in reference to the embodiment of  FIG. 8 , not only is the knife blade  65  self-retracting to a fully retracted position within the housing, which is desired by many users, the knife blade may be held in a fully extended position or a partially extended position by only extending the blade carrier  68  to a partially or fully extended position. In the event it is not desired or possible to hold the thumb button  96 , the blade carrier  68  may be held in place simply pressing upwardly with light finger pressure on the forward end portion  84  of the latch bar  80  so that the pin  92  engages one of the stop surfaces on the teeth  94 . If the light finger pressure on the forward portion of the latch bar  80  is released, the coil spring  87  returns the latch bar  80  to its home position and the retraction spring  71  returns the blade and blade carrier to its fully retracted position within the housing. This permits the knife to be used in any position as long as the user&#39;s fingers are pressing on the forward portion of the latch bar  80 . 
     In the self-retracting knife described in  FIGS. 1-8 , the blade will remain exposed from the housing the desired amount while allowing the fingers or thumb to be adjusted, moved, relocated, or repositioned on the knife as long as slight pressure is maintained on the anti-retraction latch bar. Also, when scoring or making heavy cuts with the knife using pressure, the forces are transferred to the entire hand as only a slight amount of pressure is needed on the anti-retraction latch bar to keep the blade extended to its desired position. This avoids placing those forces on the activating finger or thumb. 
     As another advantage, it is easier and faster to extend the blade by bumping or tapping the rearward end of the knife on a surface (table top, wall, the users leg) than it is to pick up the knife, position a finger or thumb over the activation button, and slide it forward to expose the blade. A further advantage is provided by the preset extension stops on a knife of the present invention makes it easier to use the knife with the blade partially exposed. For example, when opening a closed cardboard box, the user would like to expose the blade enough to cut the tape but not so much as to damage the contents. Prior self-retracting knives allow for partial extension, but any movement of the activating button will adjust the blade exposure, risking the contents of the box. In comparison, the extension limiter of the invention allows the user to preset the blade to a certain depth, removing risk of damage to the contents. 
     While the forms of knives herein described constitute preferred embodiments of the invention, it is to be understood that the invention is not limited to these precise forms of knives, and that changes may be made therein without departing from the scope of the invention as defined in the appended claims.