Abstract:
This invention provides a unique utility knife, which has at least two extendable and retractable parallel blades. The blades are easily operated with one hand by a mechanism on a non-force-bearing surface of the knife. The blade handle of this utility knife may be bent to enhance the ergonomic ease of use of the knife. As a result, the utility knife is efficient, as well as safe, convenient and economical.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to an independently retractable, double bladed, utility knife. 
     Utility knives with retractable blades have been used in a variety of applications for many years. These blades suffer from several shortcomings in certain applications. For example, in the roofing trade it is generally necessary for a roofer to carry two separate utility knives. One knife is equipped with a straight razor blade for cutting felt paper and the like, while the other knife is equipped with a hooked blade for cutting shingles which have a granulated surface. Neither of these knives is well adapted for cutting the other type of material. As a result, it is often necessary to switch knives. To accomplish this, the user must retract the first blade and put it away before retrieving the second knife and extending its blade. This is inconvenient and inefficient, as it must be repeated again and again during the workday. 
     There have been prior attempts to solve this problem. For example, U.S. Pat. No. 719,208 to Garda relates to a plurality of blades and a fork attached to a common handle which are pivotable in relation to each other to allow for individual use. U.S. Pat. No. 1,599,800 to Van Sickel discloses adjustable parallel blades extending from a common holder. U.S. Pat. No. 5,093,994 to Karas and U.S. Pat. No. 5,960,544 to Beyers disclose double bladed utility knives. These knives have a blade at opposite ends. To switch blades, the first blade must be retracted, the knife turned in the hand and the second blade extended. U.S. Pat. No. 4,578,865 to Keller relates to a double bladed utility knife having concurrent advancement and retraction of the blades. These attempts suffer from the inconvenience and inefficiencies associated with the use of two separate knives, since in each case to switch blades, the user must retract, manipulate the knife, and extend blades, switch blades entirely or again use two knives. 
     U.S. Pat. No. 5,337,481 to Mears discloses an invention which improves on the prior art but which has additional shortcomings. Mears discloses a double bladed utility knife which has parallel, individually retractable blades which extend from one end of the knife and are operated by a retraction mechanism located on the top surface of the blade housing. In use, the roofer must apply pressure to the knife to allow the blade to cut the roofing material. The only surface available for applying such pressure is the top surface of the blade, causing the retraction mechanism to injure the users&#39; fingers or at least reduce the amount of pressure available to be brought to bear on the blade. In addition, the Mears&#39; utility knife is longitudinally oriented to form a rectangular shape. This orientation does nothing to improve the ease of use, especially when combined with the placement of the retraction mechanism on the top surface of the knife. 
     None of these prior inventions features a utility knife with a pair of independently extendable blades at one end of the knife, which is ergonomically designed and oriented to be easily operable with one hand by a mechanism on the side of the knife, as well as safe, convenient and economical. 
     SUMMARY OF THE INVENTION 
     This invention provides a unique utility knife, which has two different parallel blades. The blades are independently extendable and retractable from one end of the knife by a simple mechanism located on the side of the knife. 
     More specifically, this invention consists of two handle parts, which are parallel to each other and are essentially mirror images of each other. Placed between these two handle parts and separating them is a central handle part. These parts are all pierced by openings, which are aligned in a way that allows passage of an attachment means. The attachment means maintains proper alignment of the utility knife and enables the parts to be joined or separated in order to replace the blades. In addition to attachment openings, a slot pierces the two handle side surfaces to allow passage of the lever for extending and retracting the blades. 
     In one of the preferred embodiments, the handle parts are essentially longitudinally oriented to form a parallelogram. In a second preferred embodiment, the handle assembly is shaped so that the two blades disposed therein are offset from the main, longitudinal axis of the handle parts to form an angle which reduces strain on the user. 
     The handle parts have an external surface with which the user comes in contact, a front through which the cutting blades pass, a rear opposite the front, a top surface on which the user applies pressure to cut, and a bottom surface contiguous with the cutting surface of the blades. 
     Inside the knife are two depressions, one in each handle part, each of which contains a slidable blade holder and a cutting blade. These depressions begin as openings on the front of the knife and extend inwardly towards the rear. Attached to the slidable holder is a lever, which extends through a slot in the handle to the exterior, allowing the user to operate the blades. These levers are disposed on the side surfaces, also called the external user surfaces, of the handle parts to allow the user to apply pressure more effectively to the utility blade cutting edges. 
     The central handle part has two raised tracks on each side which are parallel to each other as well as the top and bottom of the central handle part and extend inward perpendicularly from the front of the knife. These tracks match the two depressions, one in each handle to hold the blade holder and blade in position. 
     Accordingly, it is the object of the present invention to provide an improved utility knife having double blades so that a user may carry and use one knife instead of two. Another objective of the present invention is to provide a double bladed utility knife, which requires no manipulation other than extension or retraction of the blades by simple movement of the fingers. Yet another objective of the present invention is to provide a retraction mechanism placed in such a way as to allow maximum pressure to be exerted on the knife and hence, the blades, without causing pain or added exertion to the user. Still another objective of the present invention is to provide a more ergonomically correct utility knife by improving the orientation of the handle parts. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional view of the utility knife of the present invention, viewed from the entry surface of the attachment means. 
     FIG. 2 is a front view of the exterior of the utility knife of the present invention, from which end the blades extend. 
     FIG. 3 is a rear view of the utility knife of the present invention. 
     FIG. 4 is a top perspective view of the exterior of the utility knife of the present invention. 
     FIG. 5 is a bottom perspective view of the exterior of the utility knife of the present invention. 
     FIG. 6 is a cross-sectional view of the utility knife of the present invention, viewed from the entry surface of the attachment means. (See also FIG. 1) 
     FIG. 7 is a perspective view of the blade holder of the utility knife of the present invention, showing the side of the blade holder, which contacts the blade handle. 
     FIG. 8 is a perspective view of the blade holder of the utility knife of the present invention, showing the side of the blade holder, which contacts the blade. 
     FIG. 9 is a perspective view of the blade holder of the utility knife of the present invention, showing the side of the blade holder, which contacts the blade, containing a blade. 
     FIG. 10 is a perspective view of the user surface of the utility knife of the present invention, showing the raised lever extending through the slot in the handle part, which allows the user to extend or retract the blade. 
     FIG. 11 is a perspective view of alternate configuration of the utility knife of the present invention, wherein the portion of the handle parts and central parts contacting the blade mechanisms are angled. 
     FIG. 12 is a perspective view of alternate configuration of the utility knife of the present invention, wherein the portion of the handle parts and central parts contacting the blade mechanisms are angled at a ninety degree angle. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIGS. 1-10 depict one of the preferred embodiments of the present invention. The utility knife as assembled for use is illustrated by FIGS. 4,  5 , and  6 . A cross-sectional view of the utility knife of the present invention is illustrated in FIG.  1 . The utility knife comprises a first handle part  1  and a second handle part  2 , which are parallel to each other and essentially mirror images of each other. Placed between these two handle parts and separating them is a central handle part  3 . First handle part  1  is pierced by attachment openings  4  and  5 , second handle part  2  is pierced by attachment openings  8  and  9 , and central handle part  3  is pierced by attachment openings  6  and  7 . These openings are aligned in such away to allow passage of attachment means  10  and  11 . The attachment means maintains proper alignment of the utility knife and removal of the attachment means allows replacement of the blades. 
     Handle parts  1 ,  2  and  3  have six surfaces each: two side surfaces, a front, a rear, a top and a bottom surface for each part. Handle parts  1  and  2  have external user surfaces  12  and  13 , and blade holder surfaces  14  and  15  which are parallel to each other. The central handle part  3  has a first blade supporting surface  16  and a second blade-supporting surface  17 , each surface being a mirror image of the other. The first blade supporting surface  16  is in contact with blade holder surface  15  of first handle part  1  and second blade supporting surface  17  is in contact with blade holder surface  14  of second handle part  2 . 
     First handle part  1  has a front  18 , second handle part  2  has a front  19 , and central handle part  3  has a front  20 . These fronts are aligned to form a flat front face  21 , shown in FIG. 2, perpendicular to the handle external user surfaces of handle parts  1  and  2  and the blade supporting surfaces of central handle part  3 . It is from this face that the blades extend. 
     First handle part  1  has a rear  22 , second handle part  2  has a rear  23 , and central handle part  3  has a rear  24 . These rears are aligned to form a flat rear face  25 , shown in FIG. 3, perpendicular to the handle external user surfaces of handle parts  1  and  2  and the blade supporting surfaces of central handle part  3 . 
     First handle part  1  has a top  26 , second handle part  2  has a top  27 , and central handle part  3  has a top  28 . These tops are aligned to form a flat top face  29 , shown in FIG. 4, perpendicular to the handle external user surfaces of handle parts  1  and  2  and the blade supporting surfaces of central handle part  3  and at an angle to front face  21  and rear face  25  to form a three-dimensional parallelogram. 
     First handle part  1  has a bottom  30 , second handle part  2  has a bottom  31 , and central handle part  3  has a bottom  32 . These bottoms are aligned to form a flat bottom face  33 , shown in FIG. 5, perpendicular to the handle external user surfaces of handle parts  1  and  2  and the blade supporting surfaces of central handle part  3  and at an angle to front face  21  and rear face  25  to form a three-dimensional parallelogram. The bottoms  30 ,  31 , and  32  and bottom face  33  are easily differentiated from tops  26 ,  27 , and  28  and top face  29 , since the bottom sides are nearest the cutting edge  35  of blade  34 . 
     In addition to attachment openings, a slot pierces each of the two handle surfaces. First handle part  1  is pierced by slot  36 ; second handle part  2  is pierced by slot  37 . These slots are parallel to top face  29  and bottom face  33 . 
     First blade supporting surface  16  of central handle part  3  has two raised tracks, top track  38  and bottom track  39 . These tracks are parallel to each other as well as the top and bottom of the central handle part  3  and extend inwardly from the front end  20  of central handle part  3 . Second supporting surface  17  of central handle part  3  has an identical but mirror image set of tracks, top track  40  and bottom track  41 , also extending inwardly from front end  20 . These tracks support blade  34  as it moves, bottom track  39  supporting cutting edge  35  of blade  34 , and top track  38  supporting the notched edge  42  of blade  34 . 
     Blade holder surface  14  of second handle part  2  is notched to contain a rectangular blade holder depression  43 , which is parallel to the top and bottom of handle part  1  and extends inward from front end  18  of first handle part  1 . The blade holder depression  43  is large enough to contain blade  34  plus blade holder  46 , and the top edge  44  of blade holder depression  43  matches and runs parallel to top track  40  of central handle part  3 . The bottom edge  45  of blade holder depression  43  matches and runs parallel to bottom track  41  of central handle part  3 . Fitting into blade holder depression  43  of second handle part  2  is blade holder  46 . 
     The blade holder  46 , pictured separately in FIGS. 7,  8 , and  9  has a blade surface  47 , illustrated in FIG. 7, a handle surface  48 , illustrated in FIG. 8, a tab end  49  and a raised lever  50 . Blade surface  47  has a top  51  and a bottom  52 . Top  51  of blade surface  47  is bent at a greater than ninety-degree angle to overhang blade  53  and the notched edge  54  of blade  53  is fitted under the overhanging top  51 . This works with the tracks of the central handle part to hold the blade in position. 
     The raised lever  55 , pictured in FIG. 10 is sized to fit through the slot  56  in first or second handle portion  57  to provide the mechanism which, when moved toward the front face  58  extends the blade  59  and when moved towards the rear face  60  retracts the blade  59 . 
     FIG. 11 depicts another of the preferred embodiments, wherein top face  61  and bottom face  62  are angled. Maintaining the alignment described above results in a utility knife assembly which has a bend in the handle rearward of the blade holder depression  63  and the retraction/extension mechanism  64 . This bend greatly enhances the ergonomic ease of use of the utility knife. 
     FIG. 12 depicts another embodiment, wherein the angle of the bend of the handle assembly is ninety (90) degrees.