Abstract:
A utility knife has a protective guard that moves from a locked position to an unlocked position. Preferred mechanisms utilize a pawl that cooperates with a stop to reduce movement of the guard while the guard is in a locked position, and a simple latching mechanism that allows the pawl to bypass the stop. The pawl is disposed with respect to other elements of the mechanism such that the blade guard can only pulled back to a retracted position after operation of a trigger or other actuator, and then only for a single use. Both the stop and the catch can advantageously be carried in a fixed special relation to one another by operation of a trigger or other actuator.

Description:
FIELD OF THE INVENTION 
   The field of the invention is utility knives. 
   BACKGROUND OF THE SUBJECT MATTER 
   Utility knives typically have a sharp cutting blade that can either (a) be retracted into a housing, or (b) released to an operating disposition by movement of a protective blade guard. In either case problems arise where the blade is left in an unprotected disposition where it can accidentally cause injury to a user. 
   The problem of accidental injury has been long recognized, with numerous solutions being put forward at various times. U.S. Pat. No. 4,980,977 to Matin et al. (January 1991), for example, describes a knife having a safety guard that guards the blade when not in use, and automatically retracts as the blade is removed from the workpiece. The guard has a manually triggered self-locking release assembly that automatically relocks the guard when retracted. Unfortunately, Matin&#39;s locking mechanism is external to the housing housing, which is dangerous because the mechanism is readily subjected to debris that could jam or otherwise interfere with both the locking and unlocking functions. In addition, Matin&#39;s safety guard pivots off the blade externally to the housing housing, rather than being retracted into the housing. That operation is dangerous because the pivoted guard can readily interfere with operation of the knife. 
   U.S. Pat. No. 5,878,501 to Owens et al. (March 1999) uses an internal locking mechanism, but leaves the blade in the “use” position for multiple uses. There is no automatic re-locking mechanism, and withdrawal of the blade into the housing is entirely manual. 
   More recently the present inventor pioneered utility knives having a mechanism that automatically re-locks the protective blade guarding to prevent more than a single use of the blade. Pending applications include Ser. No. 09/804,451, published in September 2002 as 2003/0131393, and Ser. No. 10/300,382, published in May 2004 as 2004/0093734. These and all other referenced patents and applications are incorporated herein by reference in their entirety. 
   While providing considerable improvement over the prior art, the preferred embodiments of the utility knives described in the Ser. Nos. 09/804,451 and 10/300,382 applications have more “play” in the blade guard than might be desired in some circumstances. In the Ser. No. 10/300,382 application, for example, a preferred locking mechanism utilizes a pawl that rides in a looped pathway. Two ramped steps on the pathway limit the pawl&#39;s travel to a one-way direction, so that once the pawl starts along the pathway, it must finish a complete loop. The mechanism, however, allows some slight backward motion of the pawl, and thus introduces potentially undesirable play in the blade guard. 
   Thus, there is a need for an improved locking/releasing mechanism that automatically re-locks the protective blade guarding to prevent more than a single use of the blade, while reducing the play in the blade guard. 
   SUMMARY OF THE INVENTION 
   The present invention provides methods and apparatus in which a utility knife has a protective guard that moves from a locked position to an unlocked position. Preferred mechanisms utilize a pawl hat cooperates with a stop to reduce movement of the guard while the guard is in a locked position, and a simple latching mechanism that allows the pawl to bypass the stop. The pawl is disposed with respect to other elements of the mechanism such that the blade guard can only pulled back to a retracted position after operation of a trigger or other actuator, and then only for a single use. The guard cannot be retracted a second time until the actuator is released, and then operated anew. 
   In preferred embodiments pawl has a finger portion that juxtaposes the stop and operates against a pin. Both the stop and the catch can advantageously be carried in a fixed special relation to one another by operation of a trigger or other actuator. 
   “Play” of the protective guard is limited by the distance between the joint and the stop in the locked position, which distance is preferably less than 5 mm, more preferably less than 3 mm, still more preferably less than 2 mm, and most preferably less than 1 mm. 
   Various objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the invention, along with the accompanying drawings in which like numerals represent like components. 

   
     BRIEF DESCRIPTION OF THE FIGURES 
       FIG. 1  is a side view of a portion of an opened utility knife case, with the blade guard in the deployed (protecting) position, and the pawl in a locked position. 
       FIG. 2  is a side view of the opened utility knife case of  FIG. 1 , showing the trigger in a depressed (actuated) position, and the pawl in an unlocked position. 
       FIG. 3  is a side view of the opened utility knife case of  FIG. 1 , showing the pawl in an unlocked position, and the blade guard moving away from the deployed position. 
       FIG. 4  is a side view of the opened utility knife case of  FIG. 1 , showing the pawl reverted to the locked position upon slight movement of the blade guard. 
       FIG. 5  is a side view of the opened utility knife case of  FIG. 1 , showing the blade guard in a retracted position, with the blade exposed. 
       FIG. 6  is a side view of the opened utility knife case of  FIG. 1 , showing the blade guard reverted back to a deployed position, and the pawl in a locked position. 
       FIGS. 7 ,  8  are side views of an alternative opened utility knife case, with components removed to show the pawl and pawl spring. 
   

   Various objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the invention, along with the accompanying drawings in which like numerals represent like components. 
   DETAILED DESCRIPTION 
   In  FIG. 1  a utility knife  1  generally comprises a housing  10  (only the front portion of which is shown), a blade  20 , a blade guard  30 , a pawl  40 , a carriage that carries a stop  52  and a catch  54 , and a trigger  60 . 
   Housing  10  is preferably sized and dimensioned to fit comfortably in the hand of a user. Housing  10  can be made of any suitable material, including metals, alloys, and plastics, and can have a hollowed out section (not shown) for storing spare blades. Housing  10  is preferably ambidextrous, but alternatively can include contours that would tend to make the device more acceptable to right or left handed use. The reader will note that housing  10  includes numerous structural elements that are not labeled. 
   Blade  20  is preferably triangular shaped at one or both ends, and has at least one cutting edge  22 . Blade  20  is preferably made of non-rusting alloy, but can also be made of other materials, including for example various plastics. Blade  20  is shown here as being held by blade holder  24 . 
   Blade guard  30  generally guards the blade  20  when the guard is in a fully deployed position (as show), and allows use of the blade when the guard is in the retracted position (see  FIG. 5 ). To that end blade guard  30  has a slit along one edge  31  through which at least a portion of the edge  22  of blade  20  can extend. Guard  30  is continuous with guard arm  32 , and pivots about pivot  34 . The pin  35  for pivot  34  is preferably fixed to or extending from the housing  10 . Guard arm  32  also carries a pin or pin portion  36  about which the pawl  40  pivots. Blade guard  30  is preferably made of transparent or at least translucent plastic, so that the user can see the blade being protected. Alternatively, blade guard  30  can be made of metal or any other suitable material or materials. 
   Pawl  40  has a first pawl arm  42  that pushes against the guard arm  32  at area  37 , and thereby biases the blade guard  30  into the deployed position shown in the Figure. To that end first pawl arm  42  is should have some degree of springiness, whether inherently or through addition of an additional spring (not shown). Pawl  40  also has a second pawl arm  44  that cooperates with stop  52  to prevent guard arm  32  from pivoting about pin  35 , and thereby prevents the blade guard  30  from retracting. Second pawl arm  44  has a joint  45  (which could also be called an elbow), and extending from the joint  45  is a finger  46  (which is also referred to herein as a latch) that cooperates with catch  54  in a latching motion. It is the finger  46  and in part the joint  45  that actually juxtapose the stop  52 . Pawl  40  is preferably constructed of a single, continuous piece of metal alloy, or plastic. 
   Carriage  50  pivots about pin  56 , which is attached to or extending from housing  10 . The pivoting motion is controlled by depression and release of trigger  60 . Stop  52  and catch  54  are each preferably attached to or extending from the carriage  50 , with their respective positions fixed at a distance of less than 2 cm., depending on the width of second pawl arm  44 . Carriage  50 , stop  52 , and catch  54  can be made from any suitable material or materials, and can be shaped as shown or can have any other suitable shapes. 
   Trigger  60  is shown on the underside of the housing  10 , and is positioned relatively forward so that the trigger is easily operated by the users forefinger. All other suitable positions are contemplated, including positions on the top or side of the housing  10 . Those skilled in the art will also appreciate that the trigger  60  is merely emblematic of a more general actuator, which could take the form of a push button, a slider, and so forth. Trigger  60  is preferably constructed from metal or plastic. 
   In  FIG. 1  the utility knife  1  is shown with the blade guard  30  in the deployed (protecting) position, and the pawl  40  in a locked position. Locking is accomplished by the approximate juxtaposition of joint  45  and finger  36  against stop  52 . In this position the maximum distance between finger  36  and stop  52  determines the play (slight movement) that blade guard  30  can undergo. As such it is beneficial if the distance  55  is less than 5 mm, more preferably less than 3 mm, even more preferably less than 2 mm, and most preferably less than 1 mm. 
   In  FIG. 2  the trigger  60  has been depressed (squeezed) against the housing  10  in the direction of arrow  12 , with the effect that the carriage  50  has rotated upwards (from the point of view of the drawing). That motion has disengaged the finger  46  from the stop  52 , which will subsequently allow the second pawl arm  44  to move to the right past the stop  52 . The pawl is thus in an unlocked position in this Figure. 
   In  FIG. 3  the blade guard  30  has been pushed back slightly, enough to displace the joint  47  and finger  46  past the stop  45 , but not enough for the blade  22  to protrude through the slit  31  in the blade guard  30 . If, from this position the pressure against the blade guard  30  is removed, so that the blade guard  30  reverts back to the fully deployed position of  FIG. 1 , then the pawl arm  44  at joint  45  and finger  46  would re-lock against the stop  52 . That situation is shown in  FIG. 4 . 
   In  FIG. 5  the blade guard  30  has been pushed back to its greatest extent, as limited by the guard arm  32  striking rest  70  attached to or formed as part of the housing  10 . In this position the blade  20  extends through slot  31  to a maximal extent, which in preferred embodiments exposes the cutting edge  22  of the blade  20  to depth of at least 8 mm, more preferably at least 9 mm, still more preferably at least 10 mm, and most preferably almost 11 mm. Movement of the blade guard  30  is presumably caused by the user pushing the guard  30  against a cardboard box or other surface being cut (not shown), with the blade guard  30  being retracted and the blade  20  being forced into the box material. 
   In  FIG. 6  the pressure on the blade guard  30  has been removed, and the guard  30  has returned to its fully deployed position. This presumably occurs because the user has made the needed cut, and removed the blade  20  from the surface being cut. Since the blade guard  30  is continuous with guard arm  32 , pivoting about pin  35 , the portion of guard arm  32  containing pin  36  is also returned to its native position, which carries joint  45  and finger  46  back to engage stop  52 . 
   In this position the blade guard  30  cannot be retracted because there is nothing to disengage the joint  45  and finger  46  from the stop  52 . To disengage and restart the cycle, the trigger  60  must be released, which would carry the hooked end  47  of finger  46  to where it would latch against catch  54 . This brings us full cycle back to  FIG. 1 . Of course, the trigger  60  need not be operated during the entire cutting cycle, and can be release as soon as the latching mechanism is unlocked. 
   In an alternative embodiment of  FIGS. 7 and 8 , a utility knife  100  generally comprises a housing  100  (only the front portion of which is shown), a blade  120 , a blade guard  130 , a pawl  140 , a carriage that carries a stop  152  and a catch  154 , and a trigger  160 . Except as noted below, all of the components are substantially similar to those in  FIGS. 1-6 , with component numbering of  FIG. 7  being higher by  100  relative to those of  FIGS. 1-6 . 
   Pawl  140  has a first pawl arm  142  that pushes against the guard arm  132  at area  137 , and thereby biases the blade guard  130  into the deployed position shown in  FIG. 7 . To that end first pawl arm  142  is should have some degree of springiness, whether inherently or through addition of an additional spring (not shown). Pawl  140  also has a second pawl arm  144  that cooperates with stop  152  to prevent guard arm  132  from pivoting about pin  135 , and thereby prevents the blade guard  130  from retracting. Second pawl arm  144  has a joint  145  (which could also be called an elbow), and extending from the joint  145  is a finger  146  (which could be utilized as a latch, but which is not necessarily utilized in this embodiment). It is the finger  146  and in part the joint  145  that actually juxtapose the stop  152 . Pawl  140  is preferably constructed of a single, continuous piece of metal alloy, or plastic. In  FIG. 7 , the latch and catch are embodied not by the finger  146 , but by a catch  180  operating on spring  182 . As will be appreciated, spring  182  exerts a force on the pawl  140  during at least some portion of the operation of the blade guard  130 . 
   It should therefore be appreciated that the two embodiments shown in the Figures are merely exemplary, and only depict one of many possible embodiments corresponding to the disclosed subject matter. What is contemplated herein is the entire class of embodiments of utility knives where a blade guard automatically re-locks after each use, and in which a pawl is used in conjunction with a stop and a catch to limit the play in the blade guard. 
   Thus, several specific embodiments and applications of utility knives have been described. It should be apparent, however, to those skilled in the art that many more modifications besides those already described are possible without departing from the inventive concepts herein. The inventive subject matter, therefore, is not to be restricted except in the spirit of the appended claims. Moreover, in interpreting both the specification and the claims, all terms should be interpreted in the broadest possible manner consistent with the context. In particular, the terms “comprises” and “comprising” should be interpreted as referring to elements, components, or steps in a non-exclusive manner, indicating that the referenced elements, components, or steps may be present, or utilized, or combined with other elements, components, or steps that are not expressly referenced.