Retracting Cutter

This invention relates to cutting tools and more particularly to hand held tools with retractable blades.

Knives date from the Stone Age and are important to the present day. Exposed blades on knives can be a hazard and thus sheaths were developed to cover the blade. As early as the Roman Empire folding knives were developed. Such folding knives are called pocket or army knives and provide a safe means of carrying and storing bladed tools.

U.S. Pat. No. 2,037,914 discloses a knife offering razor sharpness. Such knives are now known as utility, shop or trimming knives. A variety of these knives have been developed including ones with retractable blades such as U.S. Pat. No. 4,733,734, which employs a button for retracting the blade. Crosses between pocket and utility knives are known.

A scalpel is a small lightweight knife used to cut tissue during dissection or surgery. For such use it is essential to control the depth of the cut since the number of layers or thickness of tissue to be cut varies. For a surgery, it is desirable to have a blade that automatically retracts to protect health care personnel against serum transmitted diseases such as AIDS and hepatitis B. Most scalpels use a disposable blade and holder. One such holder is described in U.S. Pat. No. 4,930,220, incorporated herein by reference.

Coupon cutters, designed to cut sections from newspapers and magazines also require control of the blade depth to avoid cutting extra pages. Additionally, it is desirable that such cutters be small enough to be carried about in a pocket or purse. Hook coupon cutters place a guide between the blade and the layer that is not to be cut. Others have a very small exposure of a nonadjustable blade.

Presently, sheathed blades require a specific movement by the user such as folding, unfolding or sliding a button. Operation takes conscious effort on the part of the user and sheathing mechanisms add substantially to the cost of manufacture.

However, the inventor is unaware of a self-retracting, adjustable depth knives of reasonable cost.

The subject invention of the application is a self-retracting, adjustable knife which operates by displacement due to compression. The handle of the knife is comprised of two legs of unequal length. The legs are attached to each other at one end and a blade is located at the unattached end of the longer leg. At least one of the legs is made from a resilient material. The longer leg is curved so that the blade's cutting edge rests against the shorter leg. The shorter leg is less curved, preferably straight. To use the knife the legs of the handle are compressed between the digits of the user, causing a displacement of the legs. If the longer leg is resilient, compression toward the shorter leg lengthens the effective length of the longer leg. The effective length refers to the length of a chord from the point of attachment to the unattached end of the shorter leg or the blade edge of the longer leg. If the shorter leg is resilient, compression into the curve of the longer leg shortens the effective length of the shorter leg. At rest, that is, not compressed, the effective length of the long leg is less than the effective length of the short leg, and the blade is retracted and unexposed. Under compression, the effective length of the long leg exceeds the effective length of the short leg, and the blade is exposed for use. The amount of blade exposed can be adjusted by controlling the amount of compression. When the compression is released, the knife automatically resumes its original safe position.

FIG. 1 is a perspective view of a retracted utility knife in accordance with the invention.

FIG. 1a is a perspective view of a retracted utility knife having a non-straight shorter leg

FIG. 2 is a perspective view of the knife shown in FIG. 1 in a displaced or exposed position.

FIG. 3 is a side view of the knife shown in FIG. 1.

FIG. 4 is a side view of the knife as shown in FIG. 2

FIG. 5 is a perspective view of a retracted utility knife having an integral blade in accordance with the invention.

FIG. 6 is a perspective view of the knife shown in FIG. 5 in a displaced or exposed position.

FIG. 7 is a front perspective view of a scalpel having a in the retracted position in accordance with the invention.

FIG. 8 is a perspective of the removable stop 7 shown in FIGS. 7 and 10.

FIG. 9 is a front perspective view of a commercially available scalpel blade.

FIG. 10 is a back perspective view of the scalpel shown in FIG. 7.

FIG. 11 is side view of a scalpel having a screw to control the depth of the cut.

FIG. 12 is a side view of a knife with a roller.

FIG. 13 is a detail of a tab for attachment for a scalpel blade.

FIG. 14 is a perspective view of a detail of a tension holder for a blade before bending.

FIG. 15 is a perspective view of a detail of a knife showing the completed tension holder with disposable blade

FIG. 16 is a side view of the detail shown in FIG. 15.

FIG. 17 is a perspective view of a combination knife-clip.

FIG. 18 is a side view of a combination knife-clip.

FIGS. 1, 2, 3 and 4 show a self-retracting cutting tool having a rigid, straight leg 1 and a longer, resilient bent or bowed leg 2 attached at one end 3. FIG. 1a shows a similar tool having a non-straight shorter leg 1a. Both legs are angled at the unattached end 4 to facilitate holding the tool at an angle. A blade 5 is located at the unattached end of the longer leg 2. Although the blade and leg may be integral, it is preferable some means of attachment 6 be used. The length of the longer leg 2 must be such that when fully bowed or bent, that is, in a resting state, no line from a point on attached end of the longer, resilient leg 2 to a point on the blade 5 is greater than a corresponding line from the same point of attachment to a corresponding point on the unattached end of the short leg 1 thus shielding the blade. In other words, the effective length of the longer leg is less than the effective length of the shorter leg at rest. Also, in this position the cutting edge of blade 5 is pressed against the shorter, rigid leg 1, so the blade does not catch on an unintended object. Suitable materials for resilient legs are spring metals such as steel, brass, and aluminium, or a resilient plastic such as polyethylene or polypropylene. Suitable materials for the rigid legs are steel, brass, aluminium, plastic or ceramic. Both legs may be made of the same material, however, it is preferable that the thickness of shorter leg 1 be greater than the thickness of the longer leg 2 for added resiliency of the longer leg 2. Commercially available blades, such as breakaway blades available from Stanley tools may be attached by a cement such as super-glue, solder, spotwelding, by a screw, molded in, by a tab such as shown in FIG. 13, by the tension holder disclosed in FIGS. 14, 15 and 16, or any convenient method which does not obstruct the use of the knife. Since most blades are flat, the section of the longer, resilient leg 2 resting against the blade 5 is flat. In use the legs are compressed between the user's digits, displacing the longer leg 2. When compressed the effective length of the longer, resilient leg 2 (that is from the attachment point along the curve to the cutting edge of the blade) must be greater than the effective length of the shorter, rigid leg 1. As the longer leg 2 is displaced, the blade 5 is exposed for use. If light pressure is used, the blade 5 is displaced only slightly, allowing for a shallow cut, heavier pressure exposes more of the blade for a deeper cut. The depth of the cut is adjusted by varying the amount of compression. When compression is released, the blade 5 automatically retracts to its safe position.

FIGS. 5 and 6 show a knife made from one piece of material. In this embodiment the blade 5 has been formed from the unattached end of the longer leg 2. Tapering the material results in a more resilient leg with less thickness than the rigid leg. If steel is used, the blade edge can be heat treated to retain sharpness.

The relationship between the amount and placement of the bowing or bending of the curved leg 2 and the amount of blade 5 exposed can be estimated by inscribing a right triangle having a height from the point of pressure on the curved leg to the nearest point on the straight leg, having a base along the straight leg from the blade to the point formed by the intersection of the height with the base, and having a hypotenuse from the point of pressure to the blade. As the height is decreased, by pressure, and the hypotenuse remains constant, the base of the triangle increases. The change in height of the triangle defines the displacement at the pressure point, and the change in the base of the triangle defines the displacement of the blade. The ratio of blade displacement to displacement of the pressure point can be approximated by the ratio of the difference between the sines to the difference between the cosines of the angles formed by the first triangle leg and the hypotenuse at the initial and final positions. It has been found that knives having a blade to pressure point displacement ratio of 1:4 are satisfactory. The amount of bending or bowing may be adjusted to give a degree of control of depth suitable for the desired application. Metal can be bent for the knife on a bending machine such as described in U.S. Pat. No. 5,007,269 incorporated herein by reference. Alternatively the knife could bemolded from a resilient plastic. By placing a blade in the plastic, the plastic could serve as a stop to further control the depth of the cut.

The scalpel shown in FIGS. 7 and 10 has a stopping device 7 for precise control of displacement and therefore the depth of a cut. The stopping device 7 is a clip which slides on the leg of the scalpel and can be preset to a particular displacement. The clip can be easily removed. Such displacement control devices can be used with other embodiments. The scalpel is designed to take advantage of commercially available blades such as those shown in FIG. 9. In this embodiment, the longer leg 2 is tapped for a screw 6 which fits through opening 8 in the blade. Access to the head of the screw 6 is made via an aperture 9 in the rigid leg 1. Any suitable means of attaching blades could be used such as tab, or holder such as described in U.S. Pat. No. 4,930,220. The preferred material for scalpels is stainless steel. The scalpel of FIG. 10 is provided with textured legs to provide a better grip.

The scalpel of FIG. 11 has a similar means of securing 6 the blade 5 to that in FIGS. 7 and 10, but the means of controlling the amount of displacement is a screw 11.

The knife shown in FIG. 12 has a roller 12 attached to the shorter leg 1. This wheel reduces friction when the knife is used on soft material such as rubber or tissue.

The detail in FIG. 13 shows a tab 6 for attaching a commercially available scalpel blade 5 as shown in FIG. 9. The tab has a "T" shaped cross section. The cross bar of the T is slightly narrower than the width of the widest part of the slot 8 in the blade 5. The stem is substantially the same as the width of the narrow section of the slot 8 in the blade 5.

FIGS. 14 and 15 show a blade holder based on tension and method of making the same. An aperture 13 is drilled or stamped in the unattached end of the longer leg 2. The leg 2 is then bent to form a U having a ridge 14 at the upper end. The blade 5 is then installed by pressing against a wood or a soft metal to force it into the aperture. Upon being forced in the blade will bend slightly. The blade 5 can be removed with pliers.

The knife can be modified to combine with other useful objects such as a paper clip, pocket clip, bookmark, money clip or tweezers. FIGS. 17 and 18 show one such modification for clipping to a lapel or the top of a shirt pocket 16 or as a business card holder. In the knife shown, the knife is clipped with a outer resilient handle 15, which may be removable. The handle also serves to stiffen the shorter leg 1.

Although the tool thus far described is a knife, the retracting handle could be modified for other tools such as a punch, writing implement, string cutter, micro probe or gauge. If the tip of the tool cannot slide over the surface of the shorter leg, the longer leg could be grooved or notched to allow for protection of the tool.

A string cutter could be formed by cutting a notch in the shorter leg to guide the string.

The tools disclosed in this invention are inexpensively manufactured, easy to use, and require no complicated adjustments. Automatic retraction ensures the tool is safely out of the way when not in use. These tools could be carried in the purse or pocket of the user, being handy for clipping items from newspapers, plastic unopened seals from containers, bubble wrap, leather, and layers of tissue.