Abstract:
A novel utility knife in which the parts for securing and replacing the cutting blade are selectively movable in and out of the handle of the knife via a single track system. The blade is secured through a series of elastic metal sheets, one of which contains a projection on a metal tab. The lateral manipulation of the metal tab allows the blade to disengage from the metal sheets. Once disengaged, a user of the utility knife may remove or replace the cutting blade.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority under 35 USC 119 to Chinese Patent Application No. 200820157545.3 filed on Dec. 22, 2008, the entire contents of which application is hereby incorporated by reference. 
     TECHNICAL FIELD 
     The invention relates to a handheld cutting tool utilized in the construction industry and in households generally known as a utility knife. 
     BACKGROUND INFORMATION 
     At present, a cutting tool widely used in both the industry and the household construction is a handheld instrument with a blade commonly referred to as a utility knife. A utility knife generally has an elongated fixed handle, which is equipped with a sliding mechanism which can control the expansion of a cutting blade. The blade used by a utility knife is generally movable in and out of the elongated handle. Additionally, the handle typically houses the means for securing the blade. The rigidity of the elongated handle coupled with the placement of the securing mechanism within the handle has made the replacement of the cutting blade difficult. 
     In addition to the difficulty of blade replacement, the sliding mechanism of a utility knife generally includes a double guided rail and a column pulley system. This type of system has the shortcoming of producing a sliding of the fixed blade which lacks smoothness. Furthermore, the sliding mechanism and the means for securing the cutting blade cannot be extended from the elongated handle creating the need for a longer utility knife. A longer utility knife makes the tool less convenient to be used and carried. 
     SUMMARY 
     The present invention is intended to overcome the shortcomings existing in the current system used to secure the cutting blade of a standard utility knife. Specifically, the invention solves the difficulty in replacing the cutting blade of a utility knife by providing a mechanism for exterior blade replacement. The mechanism allows a user to replace the blade without the need for disassembling the handle of the utility knife. In addition, the invention allows the blade, the components securing the blade and the components allowing the replacement of the blade to be stored within the handle via a track system. 
     The improved utility knife contains a series of flexible metal sheets securing a removable cutting blade. The metal sheets cooperate to form a groove in which an elastic tab is located. The elastic tab further contains a projection that interacts with U-shaped grooves in the cutting blade. The interaction between the projection and the U-shaped grooves secures the cutting blade to the metal sheets. Lateral manipulation of the elastic tab disengages the projection from the U-shaped grooves allowing the cutting blade to be easily removed and replaced. A second securing structure located on the metal sheets contacts the cutting blade and pushes up against the cutting blade. This contact provides the necessary force to keep the cutting blade from falling out of the metal sheets due to the force of gravity alone. A person using the invention can overcome the force generated by the second securing structure by pulling on the cutting blade while the elastic tab is disengaged. 
     The cutting blade as well as the metal sheets securing the blade can be selectively housed in the handle of the utility knife through a sliding rail system. The system contains two fixed positions corresponding to either a fully retracted position or a fully extended position. Two sliding guide blocks are attached to the metal sheets and allow the metal sheets and cutting blade to be moved in the sliding rail system from the fully extended position to the fully retracted position. While in either position a flange on a selectively depressible button is engaged with a notch preventing movement of the two sliding blocks. The depression of the button disengages the flange from the notch and allows the user to slide the button and sliding blocks to the opposite fixed position or any position in between the two fixed positions. The cutting blade and the replacement mechanism are exposed when the utility knife is in the fully extended position. When in the fully retracted position, the cutting blade and the metal sheets are housed entirely within the handle of the utility knife. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features and advantages of the present invention will be better understood by reading the following detailed description, taken together with the drawings wherein: 
         FIG. 1  is a perspective view of the invention; 
         FIG. 2  is a right side view of the novel invention; 
         FIG. 3  is a left side view of the invention where the cover plate has been removed and the cutting blade is in a fully extended position; 
         FIG. 4  is a left side view of the invention where the cover plate has been removed and the cutting blade is in a retracted position. 
         FIG. 5  is a perspective view of the blade housing; 
         FIG. 6  is a cross-sectional view of the invention taken at line A-A of  FIG. 2 ; 
         FIG. 7  is a structural diagram of the third member shown in  FIG. 1 ; 
         FIG. 8  is a structural diagram of the first member shown in  FIG. 1 ; 
         FIG. 9  is a structural diagram of the second member shown in  FIG. 1 ; 
         FIG. 10  is a structural diagram of the sliding member shown in  FIG. 1 ; 
         FIG. 11  is a structural diagram of the cutting blade shown in  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Now referring to the drawings,  FIG. 1  shows a novel utility knife  100 . The utility knife  100  comprises an exterior shell  10 , a metal block  20  and a cutting blade  30 . The cutting blade  30  is selectively attachable within the metal block  20 . The metal block  20  further comprises a first member  22 , a second member  23  and a third member  24 . The first member  24  contains a tab  222 . Two slide guiding blocks are affixed on the metal block  20 , and are selectively slideable within a single sliding track  111  as seen in  FIG. 3 . 
     The exterior shell  10  may comprise a first cover plate  10   a , a second cover plate  10   b  and track rails  11  shown in  FIG. 6 . As is shown in  FIG. 5 , the track rails  11 , form a hollow, rigid structure in which the track rails  11  are preferably fixed to the first cover plate  10   a  and the second cover plate  10   b . A track rail bridge  12  connects the two track rails  11 , preferably at the upper front portion of the track rails  11  keeping them substantially parallel to one another. The other portions of the track rails  11  remain substantially unattached forming a slideway  13 . A single sliding track  111  is formed from the arrangement of the two track rails  11 . The upper portion of the single sliding track  111  comprises a back groove  112  and a front groove  113 . 
     As seen in  FIGS. 3 ,  6  and  10  sliding guide blocks  60  are selectively movable within the sliding track  111  through cooperation with the sliding member  50 . The two sliding guide blocks  60  are affixed to the metal block  20 , and a guide block void  61  is in cooperation with a button cavity  224 ,  234  and  244  (seen in  FIGS. 7-9 ) of metal block  20 . The sliding member  50  comprises a button  51 , a flange  52  and a spring element  53 ; wherein, the button  51  is equipped with the flange  52  preferably protruding from each side of the button  51 . 
     The metal block  20  is preferably made of elastic steel consisting of one continuous piece. As is shown in  FIG. 1  and  FIG. 6 , the metal block comprises a first member  24 , a second member  23  and a third member  22  with the second member  23  located between the first member  24  and third member  22 . The two sliding guide blocks  60  are affixed to the first member  24  and the third member  22  preferably by a metal fastener. 
     As is shown in  FIG. 7 ,  FIG. 8  and  FIG. 9 , the first member  24 , the second member  23  and the third member  22  respectively comprise a first member body  241 , a second member body  231  and a third member body  221 . In addition, the bodies contain respectively a first void  244 , a second void  234  and a third void  224 . The voids  244 ,  234  and  224  along with the guide block void  61  form a cavity for the sliding member  50  as seen in  FIG. 3 . As is shown in  FIG. 3 ,  FIG. 4  and  FIG. 6 , the button  51  and a portion of the metal block  20  are transversed by the spring member  53 . 
     Again referring to  FIG. 1  and  FIG. 3 , the metal block  20  and the sliding guide blocks  60  are then arranged in the track rails  11  and the sliding guide blocks  60  are slideable within the single sliding track  111 . Because the invention uses the single sliding track  111  to cooperate with the sliding guide blocks  60  a large contact area is created which enhances the smoothness and the stability of the sliding mechanism. 
     Now referring to  FIG. 3  and  FIG. 4 , the flange  52  extends from the external part of the button  51  and is selectively engagable with the front groove  113  or the rear groove  112  creating a snap-in connection and one of the two fixed positions. When the button  51  of the sliding member  50  is pressed, the spring member  53  is compressed causing the flange  52  to disengage from the front groove  113  or the rear groove  112 , allowing the user to slide the sliding member  50  on the slideway  13 . The sliding action also causes the sliding guide blocks  60  to slide in the single sliding track  111 . As is shown in  FIG. 3 , when the flange  52  is locked in the front groove  113 , the metal block  20  along with the cutting blade  30  is fixed at the fully extended position as is shown in  FIG. 4 , when the flange  52  is locked in the rear groove  112 , the metal block  20  along with the cutting blade  30  is fixed at the fully retracted position. 
     The third member  22 , shown in  FIG. 1  and  FIG. 7 , further comprises a flexible metal strip  225  formed by offset channels. The lower portion of the flexible metal strip  225  is connected to the third member body  221 , while the remaining portions of the metal strip  225  remain unattached from the third member body  221 . A projection  223  is stamped on the metal strip  225  such that it projects toward the first member  24  and second member  23 . A pushing tab  222  on the upper portion of the metal strip  225  also extends toward the first member  24  and second member  23 . As is shown in  FIG. 8  and  FIG. 9 , pushing tab gaps  242  and  232  are respectively arranged on the first member  24  and the second member  23  such that they correspond to the pushing tab  222 . Now referring additionally to  FIG. 1 , the pushing tab  222  is contained in the pushing block gaps  232  and  242  once the first member  24 , the second member  23  and the third member  22  are assembled together. 
     As is shown in  FIG. 9 , a blade mounting slot  233  at the front end of the second member body  231  of the second member  23  is in communication with the push block gaps  232 ,  242 . Now referring additionally to  FIG. 11 , the cutting blade  30  is arranged in the blade mounting slot  233 . U-shaped blade grooves  31  on the cutting blade  30  cooperate with the projection  223  of the metal strip  225  thereby securing the cutting blade  30  to the metal block  20  when the cutting blade  30  is placed in the blade mounting slot  223 . 
     For the front metal sheet  24  shown in  FIG. 8 , a pressure strip  243  is formed on the first member body  241  by a U-shaped cutout. The front end of the pressure strip  243  is bent slightly toward the inner surface of the first member  24  causing it to make slight contact with the cutting blade  30  when the cutting blade  30  is inserted in the blade mounting slot  233 . This contact provides enough force to prevent the cutting blade  30  from disengaging from the metal block  20  due solely to the force of gravity. The force exerted by the pressure strip  243  can be overcome by the user pulling on the cutting blade  30  while the projection  223  is disengaged from the grooves  31  of the cutting blade  30 . 
     Due to the elasticity of the first member  24  and the third member  22 , when the pushing tab  222  is pushed toward the exterior of the third member  22 , the entire metal strip  225  including the projection  223  can be driven by the lateral movement of the pushing tab  222 . The projection  223  on the metal strip  225  is thereby caused to disengage from the grooves  31  of the cutting blade  30 , thus, allowing the cutting blade  30  to be either removed or replaced. 
     In addition, as is shown in  FIG. 2  and  FIG. 6 , a clip  70  can also be fixed on the exterior shell  10  by a fastening device which allows users the convenience of carrying the utility knife  100  on a belt or other item. 
     Having thus described the invention in connection with the preferred embodiments thereof, it will be evident to those skilled in the art that various revisions can be made to the preferred embodiments described herein without departing from the spirit and scope of the invention. It is my intention, however, that all such revisions and modifications that are evident to those skilled in the art will be included within the scope of the following claims.