Knife with spring-assisted blade articulation mechanism

[0001] This is a Continuation-in-part of U.S. patent application Ser. No. 10/745,793 filed Dec. 29, 2003, now abandoned and names the same inventor.

[0002] Not Applicable

[0003] Not Applicable

[0004] 1. Field of the Invention

[0005] This invention relates to the field folding knives. More specifically the present invention comprises a folding knife with a mechanism for assisting the articulation of the blade in and out of the pocket.

[0006] 2. Description of the Related Art

[0007] Retractable knives, those knives that have blades that retract into the liner of the particular knife, come in a variety of shapes and sizes. Retractable knives fall into one of two broad categories. Some knives feature a blade which is retracted into and extended from its liner in a straight fashion. These knives are often referred to as stilettos. Stilettos utilize a spring to eject the blade from the liner when a button is pressed. Most jurisdictions prohibit the sale and possession of these types of knives.

[0008] A second type of retractable knife is the folding variety. These types of knives are commonly referred to as folding knives or pocket knives. Folding knives have blade which is pivotally connected to its liner at one end. The blade pivots between an unfolded position where the blade is extended out from the liner and a folded position where the blade rests within the pocket of the liner. Many folding knives are manual in that folding and unfolding of the blade is performed entirely by the user. Other folding knives are spring assisted where a spring assists in unfolding of the blade from the liner.

[0009] Spring assisted folding knives also come in different varieties. In one variety, the blade is held under a constant spring force while the blade is in the folded position within the pocket of the liner. The blade is held in place by some form of lock, typically some form of button. When the lock is released, the blade rapidly flips to the extended position by the action of the spring. Such knives, commonly called switchblades, are also illegal to sell and possess in many jurisdictions.

[0010] Another type of spring assisted folding knives utilizes a spring to assist in the unfolding operation after the user begins the unfolding process manually. The spring starts to assist the user once the user has partially unfolded the blade from the liner. The combined forces of the user and the spring work to fully unfold the blade into the open position.

[0011] While many different types of spring-assisted unfolding mechanisms are known, much less attention has been given to features which assist in the blade folding process. In addition, less attention has been given to features which keep the blade in the folded position. Such a feature requires some active force in order to fully fold the blade into its pocket in order to prevent the blade from accidentally unfolding in the user's pocket or onto the user's fingers.

[0012] It is therefore desirable to provide a spring-assisted folding mechanism that will assist the user in articulating the blade in and out of the pocket. It would also be desirable to provide a spring-assisted folding mechanism that helps retain the blade in the pocket. By helping keep the blade in the fully folded position, such systems help prevent the accidental partial unfolding of the blade and the attendant possibility for injury that can result from a blade being unexpectedly unfolded from its liner.

[0013] The present invention comprises a knife with a spring-assisted articulation mechanism for assisting the user in the folding and unfolding of the blade from the pocket of the liner. The spring-assisted articulation mechanism also helps retain the blade in the folded position to prevent the blade from becoming unintentionally unfolded. The knife includes a pocketed liner and a blade attached to liner at one end of the liner by a pivot pin. The blade has a pointed end and a base end, the base end pivotally secured to the second end of the liner by the pivot pin such that the blade is capable of pivoting between a folded “closed” position and an unfolded “open” position. A guide pin is also attached to the blade of the knife at the base.

[0014] A spring arm is attached the liner and is used to supply a spring force to the guide pin. The spring arm is secured to the liner at its base, and has a free-moving tip and an apex near the tip. A cutout is provided in one side of the liner to permit movement of the spring arm. An arcuate slot is also provided in the side of the liner to permit the guide pin to project from the blade through the liner and travel radially about the pivot screw when the blade is articulated.

[0025]

10	folding knife
12	blade
14	liner
16	pocket
18	bolster
20	spring arm
22	apex
24	arm tip
26	pivot pin
28	guide pin
30	arm base
32	contact point
34	contact tangency line
36	contact-pivot line
38	arm cutout
40	arcuate slot
42	blade lock
44	pivot
46	lock base
48	lock tongue
50	blade cam
52	blade notch
54	spacer
56	spring arm slot
58	bore
60	toe

[0026] The present invention, folding knife 10 is illustrated in FIG. 1. Folding knife 10 includes blade 12 which articulates into and out of pocket 16 of liner 14. Blade 12 is pivotally attached to one end of liner 14 so that the cutting surface of blade 12 is contained within liner 14 when folding knife 10 is in the closed position. In the present illustration, folding knife 10 is shown in the partially open position. Folding knife 10 includes a locking mechanism which locks blade 12 in position when the user articulates the blade to the completely open position. Bolsters 18 are sandwiched around both sides of liner 14. Bolsters 18 facilitate gripping and hide moving parts of folding knife 10 which would otherwise be exposed through liner 14.

[0027] An exploded view of folding knife 10 is provided in FIG. 2. The exploded view illustrates the various parts of folding knife 10. Liner 14 is actually composed of three separate pieces—one corresponding to each side of liner 14, and spacer 54 positioned therebetween. When folding knife 10 is assembled spacer 54, blade 12, spring arm 20, and blade lock 42 are held in place by the side pieces of liner 14. In the assembled state, the base of spring arm 20 is captured thin spring arm slot 20 in spacer 54. Blade lock 42 is held in position by a pin placed through pivot 44. Blade 12 is held in position by pivot pin 26 which extends through both sides of the liner and bore 58 provided near the base of blade 12. Bolsters 18 are then attached around liner 14.

[0028] FIG. 3A shows folding knife 10 with blade 12 in the closed position and bolsters 18 removed. Blade 12 includes guide pin 28 positioned near the base of blade 12. Guide pin 28 is radially offset from pivot pin 26 so that guide pin 28 travels in a substantially circular path around pivot pin 26 when blade 12 is articulated. Spring arm 20 extends outside of liner 14 through a cutout in liner 14 and is shaped so that spring arm 20 bears against guide pin 28 near the tip of spring arm 20.

[0029] As shown in FIG. 3B, spring arm 20 includes “U” shaped arm base 30 and apex 22 near arm tip 24. Apex 22 denotes the highest point along the curved surface of spring arm 20 when blade 12 is in the closed position in the perspective shown in the present view. The reader will note that the two sides of arm base 30 are compressed together slightly by when blade 12 is in the closed position. Spring arm 20 extends through arm cutout 38 in liner 14. Arm cutout 38 allows spring arm 20 to travel up and down during articulation of blade 12. Arcuate slot 40 is also provided in liner 14 so that guide pin 28 can extend through the liner and travel in a substantially circular path around pivot pin 26 during articulation of blade 12.

[0030] As illustrated in by the arrow in FIG. 3C, spring arm 20 exerts a spring force on guide pin 28 at contact point 32. When blade 12 is in the closed position the spring force acts as a “closing force” or “closing torque” that tends to keep the blade in the closed position. Spring arm 20 has a curved surface facing guide pin 28. At contact point 32, the spring force exerted by spring arm 20 is normal to contact tangency line 34. Contact tangency line 32 is a line tangent to the surface of spring arm 20 at contact point 32. In order for spring arm 20 to provide a closing force when the blade is in the closed position, guide pin 28 is positioned at a location where spring arm 20 will interact with guide pin 28 in such a way that the spring force will counteract the articulation of the blade. Contact-pivot line 36 illustrates the relationship between contact point 32 and the center of rotation or pivot pin 26. The component of the spring force acting perpendicular to contact-pivot line 36 supplies the closing force.

[0031] FIG. 4A illustrates folding knife 10 with blade 12 in a partially open position. In this perspective, the reader will observe that blade lock 42 is in its normal position. Lock base 46 is positioned under arm base 30. Lock tongue 48 protrudes from blade lock 42 in the direction of the base of blade 12. When the blade is at this stage of articulation, lock tongue 48 is positioned near the base of blade 12 but is not actually touching the blade.

[0032] FIG. 4B is a detailed view of folding knife 10 in the stage of articulation shown in FIG. 4A. The reader will note that guide pin 28 has traveled a small distance across the surface of spring arm 20 so that the contact point between guide pin 28 and spring arm 20 is near apex 22. At this stage of articulation contact tangency line 34 is perpendicular to contact-pivot line 36. As before, the arrow illustrates the spring force exerted by spring arm 20 on guide pin 28. At this stage of articulation, folding knife 10 has reached a balance or equilibrium point. Because the spring force is in the direction of contact-pivot line 36, there is no component of the spring force acting perpendicular to contact-pivot line 36. Accordingly, spring arm 20 exerts a neutral force since there is neither any closing force nor any opening force at this stage.

[0033] FIG. 5 shows folding knife 10 when blade 12 is articulated past the equilibrium point shown in FIGS. 4A and 4B. Guide pin 28 has traveled further along the surface of spring arm 20 so that it passes over apex 22. Contact tangency line 34 and contact-pivot line 36 are also illustrated. The reader will note that the spring force (force exerted by the spring perpendicular to contact tangency line 34) supplies an opening force on blade 12 when folding knife 10 is in the present stage of articulation. Like the closing force, opening force is proportional to the component of the spring force acting perpendicular to contact-pivot line 36.

[0034] Blade cam 50 is provided at the base of blade 12. Because blade cam 50 has an increasing radius, blade cam 50 approaches lock tongue 48 as blade 12 is articulated and blade cam 50 rotates around pivot pin 26. In the present view, blade cam 50 is in contact with lock tongue 48 of blade lock 42. When folding knife 10 reaches this stage of articulation, blade lock 42 begins to provide frictional resistance to the articulation of blade 12.

[0035] FIG. 6 illustrates folding knife 10 when folding knife 10 reaches its second equilibrium stage during articulation of blade 12. Spring arm 20 continues to supply an opening force on blade 12, but the opening force supplied at this stage or articulation is less than the opening force supplied in the previous stage. The opening force is less than the previous stage because a greater portion of the spring force is exerted in the direction of contact-pivot line 36. Likewise, a smaller portion of the spring force is exerted in a direction perpendicular to contact-pivot line 36.

[0036] The second equilibrium stage is achieved when the force exerted by lock tongue 48 on blade cam 50 matches the opening force supplied by spring arm 20. As shown in FIG. 6, the increasing radius of blade cam 50 pushes lock tongue 48 out of the bottom of liner 14. This pushing force is illustrated by the arrow beneath lock tongue 48 in FIG. 6. Blade lock 42 is a lever and pivots around pivot 44. When blade lock 42 rotates around pivot 44 lock base 46 makes contact with toe 60 of arm base 30. Toe 60 supplies a force that acts to resist the rotation of blade lock 42 around pivot 44. Accordingly, the second equilibrium stage is achieved when the force supplied to toe 60 of the spring is sufficient to counteract the opening force supplied by spring arm 20.

[0037] Folding knife 10 is shown in its completely open stage in FIG. 7. The reader will note that to articulate folding knife from its second equilibrium stage to the present stage, the user must provide additional opening force on the knife. This can be accomplished in a couple of ways. First, the user may simply grab the non cutting edge side of blade 12 and rotate blade 12 around pivot pin 26 until it locks. Alternatively, the user may press lock base 46 against toe 60, so that the opening force supplied by spring arm 20 causes blade 12 to rotate around pivot pin 26 until it locks. The blade locks in place as lock tongue 48 inserts into blade notch 52 at the base of blade 12. Because the user must supply the opening force to completely open the blade, the proposed invention cannot be classified as a switchblade and avoids the prohibitions and restrictions placed on such knives.

[0038] The preceding description contains significant detail regarding the novel aspects of the present invention. It should not be construed, however, as limiting the scope of the invention but rather as providing illustrations of the preferred embodiments of the invention. As an example, it is not necessary that the same spring be used to supply spring force to guide pin 28 and blade lock 42. Instead, a separate spring may also be provided to engage the base of blade lock 42. Such variations would not alter the function of the invention. Thus, the scope of the invention should be fixed by the following claims, rather than by the examples given.