Abstract:
A hand cutter with a retractable blade guard providing an unimpaired view of the blade, when it is placed on the object. The blade guard is unlocked and retracted by a trigger mechanism, which is activated by closing the hand around the cutter handle. The blade guard remains in the retracted position until the trigger is released or a relocking mechanism is activated by putting the blade to use by cutting the object.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a hand cutter with blade guard according to the preamble to Patent-claim  1 . 
     BACKGROUND OF THE INVENTION 
     Hand cutters with safety features for protection are well known and have been present in the market for many years. The need for cutting tools with the highest possible protection for the user is increasing in today&#39;s market, where many goods are shipped throughout the world for which the packaging needs to be removed safely. Solutions range from low cost devices with integrated blades to more sophisticated hand cutters with replaceable blades. Several means are known for providing safe handling of the cutters, both for when these are in use, as well as when they are not in use. One common solution is to stow the cutting blade within the handle of the cutting tool when it is not in use. The blade is extended out of the handle for cutting before its use and can be stowed back in the handle after its use. Another known solution is the addition of a protective guard, which is placed over the blade, when the cutting tool is not in use. 
     A common solution for such a blade guard is to attach the guard to the handle at a pivot point, where it can be rotated between the extended position, where the blade is protected by the guard, and the retracted position, where the blade can be used for cutting. In order to protect the user from accidental cutting when the cutter is not in use, the blade guard of such knives is often permanently forced to the extended position by a spring. In order to allow cutting, the blade guard must be forced away from the extended position in which the blade is covered. This is commonly achieved by applying force to the blade guard. Various implementations of this are shown in U.S. Pat. Nos. 6,178,640, 6,578,266 and 6,718,637 where the blade guard is retracted by the force created when the blade guard makes contact to the object to be cut. This has the disadvantage that it is very difficult to position the cutting edge of the blade at an exact position on the object to be cut, since the cutting edge of the blade is blocked from the view of the user by the blade guard until actual contact with the object to be cut is made. 
     In addition the blade guard can create impressions or marks on the object to be cut if the spring forcing the blade guard to the closed position is too strong. This is not desirable if the cutter is used on a product that could be scratched such as a painted surface or if the object is very soft and can be deformed by the force of the blade guard. Another side effect of the known blade cutters using this mechanism is that when the force on the blade guard is suddenly released, e.g. when the cutter exits the object to be cut the spring immediately forces the blade guard back to the extended position. This creates a force on the pivot point of the blade guard and the blade guard itself and causes a vibration of the whole cutter. This vibration is absorbed by the users hand and can also cause damage to the object if the cutter is not moved away quickly. 
     SUMMARY OF THE INVENTION 
     The main object of the present invention is to provide an improved hand cutter with a retractable blade guard by allowing the user to retract the blade guard using a trigger mechanism, which moves the blade guard to the retracted position, so that the blade guard does not impair the view of the cutting edge of the blade, allowing a precise positioning of the cutting edge of the blade on the object to be cut. 
     Another object is to prevent the blade guard from coming into contact with the object to be cut, preventing marks or impressions on the object by the blade guard. 
     It is a further object of the invention to provide a means for moving the blade guard from the extended to the retracted position and back in a uniform controlled manner such that no sudden forces or vibrations on parts of the cutter and the users hand occur. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawing 
         FIG. 1  is a side view of the hand cutter in the closed position 
         FIG. 2  is a side view of the inside of the hand cutter in the closed position 
         FIG. 3  is a side view of the inside of the hand cutter in the open position 
         FIG. 4  is a perspective view of the release assembly 
         FIG. 5  is a perspective view of the lock mechanism 
         FIG. 6  is a side view of the inside of the hand cutter showing the blade holder 
         FIG. 7  is a perspective view of the blade holder and the release assembly 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  is a side view of the outside of the hand cutter. The cutter consists of a housing  10 , which has a trigger button  62  extending downwards on the lower part of the housing. At the front end of the cutter, a blade  20  extends from the housing  10  which is protected by a blade guard  30  when the hand cutter is not in use. 
     The housing  10  is formed such that it fits the users hand nicely and the trigger button  62  can be easily pushed by closing the hand or by forming a fist. Since no sliding motion is required to activate the trigger, the hand cutter can be easily held and used without a tiring effect even if the trigger button  62  is activated many times during the course of a day. 
     In  FIG. 2  the inside of the hand cutter of the preferred embodiment is shown in the closed or protected position without the housing. It shows the trigger button  62  and a trigger rack arm  63  connected to the trigger button  62 . The trigger rack arm  63  is pushed upwards as soon as the trigger button  62  is activated by the users&#39; hand. Teeth at the front edge of the upper end of the trigger rack arm  63  interlock with a rack wheel  52  connected to the housing  10  so that the rack wheel  52  rotates clockwise as soon as the trigger rack arm  63  moves upwards.  FIG. 4  shows a release wheel  53  which is coupled with the rack wheel  52  so that it rotates clockwise simultaneously. An arm extending from the upper part of the release wheel  53  is rotatably connected to the release piece  51 . As soon as the release wheel  53  rotates clockwise, the release piece  51  is moved towards the front of the hand cutter. 
     At the lower end of the release piece  51  an extension which is wider towards the back part of the hand cutter, pushes down the lock piece  40  as soon as the release piece  51  is moved forward, as can be seen in  FIG. 3 . The lock piece  40  is connected to the housing  10  at the front of the cutter, so that the rear part of the lock piece  40  can move downwards. The downward movement of the lock piece  40  releases the locking extension  371  at the lower rear end of a rack  37  from a notch in the lock piece  40  as shown in  FIG. 5 . The same forward movement of the release piece  51  pushes forward the rack  37  which is now free to move along the length of the cutter. At the lower front end of the rack  37  teeth are interlocked with a gear wheel  35 . The forward movement of the rack  37  rotates the gear wheel  35  clockwise. Below the gear wheel  35  the rear end of the blade guard  30  is also equipped with teeth that are interlocked with the gear wheel  35 . The clockwise rotation of the gear wheel  35  rotates the blade guard  30  counterclockwise, so that the front part of the blade guard  30  moves upwards around the pivot point  34 . Through this upward movement of the blade guard  30 , the blade  20  is no longer covered and the cutting edge of the blade is fully visible for an exact positioning on the object to be cut. 
       FIG. 3  shows the inside of the hand cutter in the open position. In this position the user has a clear view of the blade  20  and can position the cutting edge of the blade precisely at the desired spot, so that a cut can be made with great accuracy. As soon as the user releases the trigger button  62 , the upwards force on the trigger rack arm  63  is released and the rack wheel  52  coupled to the release wheel  53  are rotated back counterclockwise. This rotation is enhanced by a spring connected to the release wheel  53  and allows the release piece  51  to move back to the original closed position. The rearward movement of the release piece  51  moves the extension at the lower end, used to force the lock piece  40  downwards, out of the reach of the lock piece  40 . A spring forces the lock piece  40  back upwards to the original position so that the rack  37 , which is forced rearward by an additional spring, can again be locked by means of the locking extension  371 . At the same time, blade guard  30  is rotated back to the protected position via the gear wheel  35  which is rotated counterclockwise by the rack  37  during its rearward movement. In this way the blade  20  is again protected and the blade guard  30  locked as soon as soon as the trigger is released. 
     In order to protect the user of the cutter, a automatic relocking mechanism is added to the safety cutter. In  FIG. 6  the blade holder  70  is shown together with the rack wheel  52  and the release wheel  53 . As soon as the blade  20  is placed on the object to be cut, the front of the blade  20  is pushed slightly upwards and the rear end of the blade holder  70  moves downwards as it rotates around the blade holder pivot point  74 . Through this downward movement, the blade holder  70 , which extends to the rack wheel  52  and the release wheel  53 , is forced between the two wheels. This pushes the rack wheel  52  and the release wheel  53  apart from each other so that the two wheels are decoupled. As soon as the rack wheel  52  and the release wheel  53  are decoupled, the release wheel  53  is forced to rotate counterclockwise, back to the original position, by a spring  531  as can be seen in  FIG. 2 . The rack wheel  52  remains in the same position as long as the trigger button  62  remains pushed. Due to the connection of the release wheel  53  with the release piece  51 , the release piece  51  is pulled back to the original position so that the lock piece  40  is rotated back upwards by the spring. In this position the notch in the lock piece  40  returns to the original position, so that the locking extension  371  of the rack  37  can reengage with the notch as soon as the rack  37  moves back to the original position. 
     The blade guard  30  does not return to the protected position until the cutter is removed from the object to be cut. Until this occurs, the rack  37 , which is forced towards the back end of the cutter by a spring, does not move completely to the original position, preventing the locking mechanism to reengage. As soon as the blade guard  30  returns all the way to the protected position, the rack  37  returns to the original position where the locking extension  371  reengages with the notch in the lock piece  40 . In this state the blade  20  of the cutter is again protected even if the trigger button  62  is still being pressed, thus preventing accidental cutting after the cut has been completed. 
     The blade guard  30  remains in the locked position until the trigger button  62  is released and pressed again to activate the release mechanism.