Patent Publication Number: US-6219923-B1

Title: Retractable knife

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to hand-held cutting knives, and more particularly to knives having retractable blades. 
     Hand-held utility knives such as those used by hobbyists, artists, draftsman, and those used for odd jobs around the home and office have long been known. A well-known form of such knife has a small metal blade detachably secured at one end of an elongate cylindrical handle and is ideal for detailed cutting work where tight control of the knife blade is required. Examples of such knives are sold under the X-Acto® trademark. 
     While known knives are excellent tools for detailed cutting, there is believed a need for a less expensive, more compact and disposable knife for the odd cutting job around the home or office. For some applications, the typical elongate handle can be a hindrance to the job at hand. Furthermore, the typical knife may not be practical for carrying and storage where a smaller sized knife would be preferable. 
     These and other limitations of known knives establish a need for a simple, compact, inexpensive and relatively safe utility knife. 
     SUMMARY OF THE INVENTION 
     One object of the present invention is to provide a utility knife having a blade that automatically retracts upon activation by the user. In this manner the blade defaults to a safe position and is extended only when desired by the user. 
     It is another object of the invention to provide a knife that has few parts, is simple to assemble, and is relatively inexpensive to produce. Reducing costs and minimizing the materials of production would make such knives more disposable, thereby avoiding the necessity of changing blades as required with known types of knives. 
     A further object of the invention is to provide a relatively small utility knife easily gripped with the fingertips for detailed cutting. 
     These objects are accomplished by providing a retractable knife having a housing which has a front and a rear and which forms an internal cavity. Disposed within the internal cavity is a coil spring which defines a longitudinal passage within the spring. The spring has first and second ends, the first end being substantially fixed relative to the housing between the front of the housing and the second end of the spring. Positioned for longitudinal movement within the longitudinal passage of the spring is the blade. Being retractable, the blade is movable between an extended position relative to the housing and a retracted position within the housing. The spring biases the blade towards the retracted position. A manually operable push rod extends through the housing and is in contact with the blade for movement therewith. 
     The knife can further include a release switch positioned on the housing to engage the push rod when the blade is in the extended position. The switch is moveable to a position disengaged from the push rod for releasing the blade. The switch preferably has an integral resilient shaft about which it can pivot to release the blade. 
     The knife may also include a safety switch positioned on the push rod to engage the housing when the blade is in the extended position. The safety switch is moveable to a position disengaged from the housing to release the push rod. 
     Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows and in part will become apparent to those skilled in the art or may be learned by practice of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The features, aspects and advantages of the present invention will become better understood with reference to the following description, claims and drawings where: 
     FIG. 1 is a top view of a knife of a preferred embodiment shown with the blade in the retracted position; 
     FIG. 1A is a bottom view of the knife of FIG. 1 shown with the blade in the retracted position; 
     FIG. 1B is a side view of a knife of FIG. 1 shown with the blade in the retracted position; 
     FIG. 2 is a side view of a knife of FIG. 1 shown with the blade in the extended position; 
     FIG. 3 is a perspective exploded view of the knife assembly of FIG. 1; 
     FIG. 4 is an enlarged view of the push rod and rear end of the blade; 
     FIG. 5 is an elevational view of the housing showing the two halves in an unassembled form; 
     FIG. 6 is a cross sectional view taken along line  6 — 6  as shown in FIG. 1; and 
     FIG. 7 is a cross sectional view similar to FIG. 6 showing the blade in the extended position. 
    
    
     DETAILED DESCRIPTION 
     Illustrated in FIGS. 1 to  7  is a preferred embodiment of the present invention—a finger held knife  10  having a manually operable retractable blade  14  movable between a retracted position as shown in FIG. 1, and an extended position as shown in FIG.  2 . As further explained below, the blade is biased towards the retracted position and is extended by manually moving the blade against the bias of a spring. This provides a safety feature in that the blade automatically defaults to the retracted position upon release and remains there unless manually moved to the extended position. 
     With particular reference to FIGS. 3,  6  and  7 , it is seen that the knife  10  includes a housing  12 , the blade  14 , a spring  16 , and a push rod  18 . The housing  12  is formed of two halves, a top-half  20   a  and a bottom-half  20   b  connected together by a hinge  22  of thin foldable material. The housing  12  is preferably formed of suitable plastic such as PET, ABS, and PVC which allows the two halves  20   a,    20   b  to be molded as a unitary piece foldable about a living (foldable) hinge  22  for final assembly. 
     Resilient snap tabs  24  extending from the housing half  20   a  and having a lip  24   a  extend through corresponding receiving openings  26  in the housing half  20   b  where the lips  24   a  engage shoulders  26   a  on the outside of the housing  12  to hold the two halves together. Additional or alternative closure means such as adhesives may be used to fixedly secure the two halves together in the final closed position. 
     The housing  12  defines an internal cavity  28  configured to hold the blade  14 , spring  16  and push rod  18 . The front  30  of the housing  12  has a slotted opening  32  through which the blade  14  movably extends. The rear  34  of the housing  12  has a rectangular opening  36  through which the push rod  18  movably extends. Internal walls  38  form a slotted blade guide  39  in the front of the housing adjacent the slotted opening  32 . A top edge  41  and lower edge  43  of the blade guide  39  limits the upward and downward movement of the blade. See FIGS. 6 and 7. 
     The blade  14  has an elongate body  40  formed of metal, upper and lower edges  42   a,    42   b  respectively, and front and rear ends  44   a,    44   b  respectively. Formed along the front end  44   a  is an angled knife edge  46 . Formed at the rear  44   b  of the blade is a notch  48  and upper and lower tabs  50   a,    50   b  which engage the spring  16  as further described below. 
     Referring to FIGS. 3 and 6, the spring  16  of the preferred embodiment is a helical coil spring having a first end  52 , a second end  54 , and which defines a longitudinal passage  56  within the coil between the first and second ends  52 ,  54 . The spring  16  is positioned within the cavity  28  longitudinally between the front  30  and the rear  34  of the housing  12 . 
     As best illustrated in FIGS. 3,  6  and  7 , the blade  14  is positioned for longitudinal movement within the longitudinal passage  56  of the spring  16 . The first end  52  of the spring is substantially fixed relative to the housing  12  by abutting an internal wall  58  of the housing(the wall  58  being formed of two half walls in each housing half  20   a,    20   b ). A slot  58   a  through the wall  58  and opening to the guide slot formed by the internal wall  38  is provided through which the blade moves. The spring is “substantially fixed” in that the spring is not fixedly attached to the wall  58  and thus may have some play. 
     The second end  54  of the spring  16  engages and moves with the upper and lower tabs  50   a,    50   b  of the blade  14  to bias the blade  14  towards the rear of the housing  12 . Here, the spring&#39;s second end  54  simply abuts the tabs  50   a,    50   b  without physical connection. 
     The push rod  18  extends through the opening  36  in the rear  34  of the housing  12  and is manually operable to move the blade  14  from the retracted position to the extended position. With reference to FIGS. 3,  4 ,  6  and  7 , it is seen that the push rod  18  has a front end  60  having a channel  62  in which the rear end  44   b  of the blade  14  fits to prevent side-to-side movement of the rear end  44   b.  A key  64  within the channel  62  fits into the blade notch  48  to prevent vertical movement of the rear end  44   b.  It is seen that the spring  16  biases the push rod  18  towards the rear  34  of the housing  12 . In the illustrated embodiment, this is done through the blade  14  which, biased rearward into contact with the push rod  18  by the spring, in turn biases the push rod rearward. Other possible configurations include a push rod fixedly connected to the blade  14  through means such as adhesives or molding the push rod onto the blade  14 . In such configurations, the spring  14  could physically engage either the blade or push rod to engagingly bias the blade towards the retracted position. 
     The front end  60  of the push rod further has upper and lower catch tabs  66  and  68  respectively (FIGS. 3 and 4) extending beyond the main body  70  of the push rod. Both tabs  66 ,  68  abut respective ledges  67 ,  69  of the housing when the blade  14  is fully retracted to hold the push rod  18  within the housing  12 . The lower catch tab  68  also holds the blade  14  in the extended position as further described below. 
     Formed on the top of the push rod  18  is a safety switch  72  which prevents accidental extension of the blade  14 . With reference to FIGS. 3,  4  and  6 , the illustrated switch  72  is integrally formed in the top surface of the push rod and is separate therefrom by a gap  74 . The switch  72  is attached to the push rod via an integral shaft  76  about which the switch pivots. The shaft, being of the same material as the push rod, e.g. PTE, ABS, etc., is resilient and thus biased to return the switch  72  to its original position once moved. A raised catch  78  is formed on the front of the switch so as to extend vertically beyond the top  71  of the rush rod and engage the rear  34  of the housing  12  as shown to prevent forward movement of the push rod and the blade (see FIG.  6 ). A button  80  extends downward from the underside of the switch where it is manually operable to be pushed upward. Upward movement of the button  80  disengages the switch from the push rod by causing the catch  78  to pivot downward about the shaft  76  to release the push rod  18  for extending the blade. 
     Once the button  80  is manually operated to release the push rod  18 , the blade  14  is extended by pushing the push rod forward against the bias of the spring  16 . It is seen that the blade moves within the longitudinal passage  56  defined by the spring  16  as the blade front  44   a  exits through the slotted opening  32 . The internal wall  58  and the length of the compressed spring  16  limits the forward movement of the blade. 
     With reference to FIGS. 1A,  5 ,  6  and  7 , a release switch  82  locks the blade in the extended position, and, upon manual operation, releases the blade  14  for biased movement back to the retracted position. The release switch  82  is similar to the safety switch  72 , being integrally formed as part of the bottom of the housing  12  and separated therefrom by a gap  84 , and pivots about a resilient integral shaft  86  connecting the switch  82  to the housing  12 . A button  88  extending from the bottom of the switch  82  allows convenient access for manual operation. At a forward section of the switch  82  is a catch  90  extending into the cavity  28  to engage the catch tab  68  of the push rod  18 . As the push rod  18  moves forward to extend the blade  14 , the catch tab  66  rides over the top surface  92  (within the cavity  28 ) of the switch  82 , pushing the catch  90  downward about the shaft  86  against the natural bias of the shaft  86  until the catch tab  68  clears the switch at which point the catch  90  biasly snaps back into place behind the catch tab  68 , thereby preventing retraction of the push rod and thus the blade. (Tab  68  is not shown in FIGS. 6 and 7 since the figures are cross sectional views. However, it is understood that the tab  68  engages the ledge  90  on both sides of the blade tab  50   b  which is shown in FIG. 6.) Manual operation of the button  88  upward rotates the catch  90  downward about the shaft  86  to releasably disengage the catch tab  66  and allow the spring  44  to retract the blade  14 . 
     The push rod  18  of the present invention includes additional features such as a support ring  94  which can be used to support the knife  10 , and contoured slots  96  providing convenient access to the button  80 . Portions of the sides and top of the housing  12  are shaped ergonomically as shown to be comfortably grasped by the user. 
     The present invention provides a unique and novel compact knife that is inexpensive to make, disposable and easy to use. In operation, the knife  10  is moved into the blade extended position of FIG. 2 by simply pushing upward the button  80  of the push rod and then pushing the push rod forward until the blade is locked in its extended position by the release switch  82 . For cutting, the knife  10  is preferably grasped on opposite sides  98   a,    98   b  between the thumb and the middle finger, the index finger being placed on the top  100 . 
     To release the blade to its retracted position, the button  88  is simply pushed to release the spring. 
     While the foregoing description is intended to describe a preferred embodiment of the present invention, it is not intended to limit it in any way. The invention is to be read as limited only by the scope of the appended claims.