Abstract:
A hand cutter with a blade guard providing the highest possible protection from accidental cutting. The blade guard can be effortlessly activated from the locked position by a trigger, which is achieved by closing the hand around the cutter handle. The released blade guard remains in the released state until the blade has been put to use by cutting the object, when the blade guard release is removed so that the blade guard is automatically relocked as soon as the blade guard returns to the initial protected position.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a hand cutter with blade guard according to the preamble to Patent-claim  1 . 
       BACKGROUND OF THE INVENTION 
       [0002]    Hand cutters with blade guards 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. 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 can be placed over the blade, when the cutting tool is not in use. 
         [0003]    German patent DE 3 116 354 and U.S. Pat. No. 4,086,698 show solutions with a longitudinal blade guard. This blade guard is located on the side of the cutting edge of the blade. It is permanently forced to the extended position by a spring, thus protecting the blade from accidentally cutting. This solution is designed to protect the user as soon as the blade leaves the object to be cut. However it has the disadvantage, that depending on the angle at which the blade is placed on the object, the blade guard will get jammed and must be manually pushed to the retracted position to allow cutting the object. 
         [0004]    U.S. Pat. No. 5,697,157 shows another solution, where a guard is attached to the handle, which can be rotated between the extended position, where the blade is covered by the guard, and the retracted position, where the blade can be used for cutting. While this solution provides some protection, it does not protect from accidental use of the blade, nor does it provide protection, when the blade is being used and the user slips from the object being cut. German Patent DE 3 540 026, which has a similar type of blade guard, has an elastic mechanism permanently forcing the guard back to the extended position. It also shows a mechanism that can be used for locking the blade guard when the cutting tool is not in use. However this blade lock must be activated separately after the cutting process and again does not provide protection when the user accidentally slips from the object being cut. 
         [0005]    Recent developments have combined the automatic protection from accidental use of the blade as shown in German Patent DE 3 116 354 and U.S. Pat. No. 4,086,698 with an automatic relocking of the blade guard as soon as the cutter is no longer in use. This is done by providing a means permanently forcing the blade guard to the position, where the user is protected, together with an automatic locking of the blade guard in the protected position, triggered by the use of the cutter. In U.S. Pat. Nos. 6,578,266 and 6,560,873 the automatic locking is triggered by a movement of the blade guard. The blade guard can be unlocked by actively pressing a button and the relocking mechanism is activated as soon as the blade guard is moved from the protected position through a contact of the blade guard with the object to be cut. The presented trigger mechanisms in these inventions require use of the thumb, which leads to a quick tiring of the user, if there are many objects that need to be cut. Also the automatic relocking can be easily triggered, when the blade guard accidentally touches the object without actually cutting it, so that it needs to be unlocked again before a cut can be made. This can lead to additional tiring of the user. 
       SUMMARY OF THE INVENTION 
       [0006]    The main object of the present invention is to provide an improved, easy to use and safe hand cutter with a blade guard providing the highest possible protection from accidental cutting. The blade guard can be released from the protected position by a trigger, which is easily activated. The released blade guard remains in the released state until the blade has been put to use. As soon as the object has been cut the blade guard release is removed so that the blade guard is automatically relocked as soon as the blade guard returns to the initial position, in which the blade is protected. 
         [0007]    Another object of the invention is to provide an improvement to the trigger mechanism, allowing an effortless activation of the blade guard release from the locked position, so that the user does not easily get tired, when doing multiple cuts. This is achieved by providing a means to activate the trigger by closing the hand around the cutter handle, instead of requiring the use of a thumb or finger to push or slide an activation button. 
         [0008]    It is a further object of the invention to provide a means for easy and safe transportation of the cutter. This is achieved by providing a loop at the rear end of the cutter housing, which can be attached to a keychain or lanyard and a mechanism for permanently locking the blade guard in the protected position in order to prevent accidentally releasing the blade guard. 
         [0009]    A final object of the invention is to provide a simple to use means for limiting the cutting depth of the blade by limiting the movement range of the blade guard. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    In the drawing 
           [0011]      FIG. 1  is a side view of the hand cutter 
           [0012]      FIG. 2  is an internal side view of the hand cutter, from the left hand side. 
           [0013]      FIG. 3  is an internal side view of the hand cutter, from the right hand side. 
           [0014]      FIG. 4  is an internal view from the front of the cutter. 
           [0015]      FIG. 5  shows the blade holder and the trigger ramp, while the cutter is in use 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0016]      FIG. 1  is a side view of the outside of the hand cutter. The cutter consists of a compact housing  1 , which has a trigger button  6  extending downwards on the lower part of the housing. At the front end of the cutter the blade  2  is protected by a blade guard  3 . At the rear end the cutter has a loop  8 , which can be used for attaching the cutter to a keychain or lanyard, which can be attached to a belt or carried around the neck. This allows the cutter to be carried around easily without the use of the hands, and without the need to place it in a pocket and removing it from the pocket before another use. It therefore allows the use of both hands for moving the objects, which are being cut. 
         [0017]    The housing  1  is formed such that it fits the users hand nicely and the trigger button  6  can be easily pushed by closing the hand or forming a first, without much effort or the need to use the thumb. Since no sliding motion is required and gripping the handle is the way the cutter should be held for cutting in any case, this allows multiple activations of the trigger without tiring the users thumb or fingers. 
         [0018]    In  FIG. 2  the preferred embodiment is shown without the housing cover. It shows the trigger ramp  61 , which is connected to the trigger button  6  in a way that allows the trigger ramp to rotate around the trigger pivot  64 . The torsion spring  66  and the button spring  67  complete the trigger assembly. The torsion spring  66  is connected to the housing  1  and permanently forces the trigger button  6  downward, so that it moves to the relaxed position as soon as the grip on the cutter is released. The button spring  67  connects the trigger button  6  to the rear arm  612  of the trigger ramp  61 . It has a fixed length and executes a force attempting to keep the distance d between the trigger button  6  and the trigger ramp  61  constant. As soon as this distance d is either extended or reduced the button spring  67  executes a force in the opposite direction. The front arm  611  of the trigger ramp is vertically oriented and connects the trigger assembly to the release assembly. 
         [0019]    The release assembly consists of the release piece  51  and a flat spring  56 . The flat spring  56  is connected to the housing  1  and permanently creates a force pushing the release piece  51  downwards. The release piece  51  basically has the form of an arch. In  FIG. 4  the release piece  51  is shown from the front of the cutter. In a further embodiment the middle opening of the release piece  51  is narrow in the upper part and has a widening step on both sides at the bottom part  516 ,  516 ′. The top of the front arm of the trigger ramp  611  is wider that the narrow part of the opening of the release piece, but fits in the wider lower part between the bottom end  516 ,  516 ′ of the release piece  51 . If the trigger ramp  61  is pushed upwards, the top of the front arm of the trigger ramp  611  pushes against the bottom part  516 ,  516 ′ of the release piece  51  and forces it upwards in direction U against the force of the flat spring  56 . 
         [0020]    On one side the release piece  51  is slanted so that it becomes thicker towards the bottom. This increasing thickness creates an outwards force O as the release piece  51  is moved upwards, thus moving the front part of the lock piece  41  outwards towards the side of the housing  1 . The lock piece  4  is fixed to the housing  1  at the rear end  42  ( FIG. 3 ) and is made of a material that is slightly elastic. This allows the front part of the lock piece  4  to be moved outwards, while at the same time creating a force pushing it back towards the center of the cutter. The outward movement created by the slanted release piece  51  moves the front part of the lock piece  41  out of the path of the rear arm of the blade guard  32 , which releases the blade guard  3 , so that it can move freely. 
         [0021]    As can be seen in  FIG. 3  the rear arm  32  of the blade guard  3  is in contact with the front part of the lock piece  41 . If the lock piece  4  is in the regular position it prevents the rear arm of the blade guard  32  from moving to the rear of the cutter. This locks the blade guard  3  by preventing the front arm  31  from moving upwards and exposing the blade  2 . As soon as the front part of the lock piece  41  is displaced outwards, the rear arm  32  of the blade guard is free to move towards the rear of the cutter so that a force applied to the front arm of the blade guard  31  will result in the blade guard rotating around pivot point  34 . Such a force on the blade guard  3  is created as soon as the cutter is placed on the object to be cut and rotates the blade guard  3  and exposes the blade to allow cutting of the object. 
         [0022]    To ensure that the blade guard  3  returns to its original position, covering the blade  2 , a guard spring  36  is attached to the rear arm of the blade guard  32  and the housing in the front part. The guard spring  36  executes a permanent force rotating the blade guard  3  back to the closed position, so that the blade  2  is never exposed without actually being in contact with the object to be cut. 
         [0023]    A further improvement to the preferred embodiment includes a movable knob on one side of the housing in the area of the rotation of the front arm of the blade guard  31 . The knob extends on the inside of the housing, so that its end blocks the front arm of the blade guard  31  from rotating further, thus limiting the cutting depth. This knob can be further be placed in a groove so that it can be adjusted to the desired maximum cutting depth either between preset positions or by a screwing mechanism fixing it at the desired location in the groove. 
         [0024]    As can be seen from  FIG. 5  the blade holder  7  is connected to the housing  1  at a pivot point  74 . The blade  2  is placed in the blade holder  7  in a way that any movement of the blade  2  is automatically transferred to the blade holder  7 , and vice versa. 
         [0025]    Assuming that the blade guard  3  has been released as described above and the cutter is placed on the object to be cut, the front arm of the blade guard  31  will be rotated upwards as the cutting edge of the blade  21  comes into contact with the object. When the cutter is pressed into the object to be cut a force C is executed to the cutting edge  21  forcing the blade holder  7  to rotate slightly around the pivot point  74  as soon as the first cut is made. At the other end of the blade holder  7  there is an extension of the blade holder  719 , which is moved slightly to the rear and downwards D when the blade holder  7  rotates. In the preferred embodiment the extension  719  fits between the two legs of the arch of the release piece  51  and extends to a point where it is in contact with the rear arm of the trigger ramp  612 . To allow a better contact between the extension  719  and the rear arm of the trigger ramp  612  a bump  619  can be provided on the back side of the rear arm of the trigger ramp  612  as can be seen in  FIG. 5 . As the extension  719  is moved downwards by the pivoting blade holder  7  the rear arm of the trigger ramp  612  is forced rearwards. With this movement it is pushed out of the contact area with the bottom part of the release piece  516 ,  516 ′. The release piece  51  is then free to move downwards and will be forced back to its original position by the flat spring  56 . This allows the front end of the lock piece  41  to return back to the original position. Since the rear arm of the blade guard  32  is rotated to the back during the process of cutting an object, the blade guard  3  is not locked by the front end of the lock piece  41  until the rear arm of the blade guard  32  is rotated back to the front of the lock piece  41 . Due to the elasticity of the lock piece  4 , the rear arm of the blade guard  32  can pass the lock piece by temporarily moving the front of the lock piece  41  to the outside. 
         [0026]    As soon as the cutting process is done and the cutter is removed from the object, the blade guard  3  is rotated back to its original position protecting the blade, where the rear arm of the blade guard  32  is again beyond the front end of the lock piece  41  as described above. With the lock piece  4  back to the original locked position the blade guard  3  cannot be rotated again due to the presence of the front end of the lock piece  41  behind the rear arm of the blade guard  32  until the trigger button  6  is activated again, releasing the blade guard  3 . 
         [0027]    In a particular embodiment the cutter includes a mechanism preventing the user from accidentally unlocking the blade guard  3 . This provides additional safety when the cutter is carried around while not being in use. In the rear part of the housing  1  a trigger lock is introduced, which can be moved longitudinally between two positions: a locked position, when the trigger lock is in the front position and an unlocked position, when it is in the back position. The trigger lock has a knob, which extends towards the outside and is guided in a longitudinal opening on the side of the housing. This knob can be manually moved between the locked and the unlocked position. On the inside of the housing  1  the trigger lock extends in such a way that the extension is located directly above the rear arm of the trigger ramp  612 , if the trigger lock is in the locked position. If the trigger button  6  is pressed, while the trigger lock is in the locked position the rear arm of the trigger ramp  612  cannot move upwards. Therefore the trigger ramp  61  is rotated and the front arm  611  is moved towards the back, so that it does not push the release piece upwards. In this way an accidental unlocking of the blade guard is prevented if the trigger lock is placed in the locked position.