Safety knife

BACKGROUND OF THE INVENTION

The invention relates to knives and particularly to safety knives of the kind where a part of a blade projects from a handle and there is provided a guard to shield the point and/or cutting edge of the blade so as to prevent or minimise the risk of accidental injury to a user of the knife.

In existing knives of this type, however, the guard for the blade is usually fixed and spaced from the blade so that the cutting edge of the blade is exposed. The object is to allow the exposed cutting edge to be applied to the material to be cut, while the fixed guard is intended to reduce the risk of a part of a person's body, or other surface or object, accidentally coming into contact with the exposed cutting edge when the knife is handled. Although such arrangements may reduce the risk of accidental injury or damage there is still some possibility of such injury or damage occurring since the exposed blade is still accessible, even though access to it is limited to a certain extent by the guard.

The present invention sets out to provide an improved form of safety knife where these disadvantages may be overcome.

SUMMARY OF THE INVENTION

According to the invention there is provided a safety knife comprising a handle, a blade mounted on the handle so that at least a portion of the blade projects from the handle, and at least one guard which is mounted on the handle for movement between an extended position where it overlies at least a part of the cutting edge of the blade, and a retracted position wherein said part of the cutting edge is exposed, resilient biasing means being provided to bias the guard towards the extended position.

Thus, during normal handling of the knife, the protective guard may be sufficient to prevent or reduce the risk of the projecting part of the blade accidentally cutting a person or damaging surfaces or materials, provided that the guard is not engaged with a force sufficient to overcome the resilient biasing means. At the same time, the more positive force which is likely to be applied in deliberate use of the knife for cutting will overcome the resilient bias acting on the guard, causing the guard to be displaced so that the cutting edge of the blade contacts the material being cut. The guard may thus be of any desired size or shape and, since it is retractable it may completely overlie the whole of the projecting part of the blade so that none of the blade is exposed when the knife is not in use.

Preferably the guard is at least partly retractable into a recess in the handle as it moves from the extended position towards the retracted position.

Said resilient bias means may comprise a spring, such as a helical compression spring, mounted on the handle and engaging a part movable with the guard.

The guard may move from its extended position to its retracted position with translatory linear movement. Alternatively, the guard may move from its extended position to its retracted position by angular pivotal movement.

As previously mentioned, the guard, when in the extended position, may overlie substantially the whole of at least one side face of the portion of the blade which projects from the handle.

There may be provided on the handle adjustable stop means movable between a locking position, in which it prevents the guard from moving from its extended position, and a release position in which it permits movement of the guard from its extended position to its retracted position. The stop means may comprise an element which is movable, by operation of a manipulating member, from a locking position in which it obstructs movement of a part movable with the guard, to a release position in which it does not obstruct movement of said part. Said movable element may be rotatable from its locking position to its release position. Said manipulating member may comprise an operating lever connected to the rotatable element so that angular movement of the lever effects rotation of the rotatable element between its locking and releasing positions.

In one embodiment, the rotatable element may comprise a disc having a peripheral edge, a portion of which lies in the path of movement of a part movable with the guard when the disc is in its locking position, said peripheral edge being formed with a recess which lies in the path of movement of said part movable with the guard when the disc is rotated to its release position, so that said part may enter the recess and permit movement of the guard from its extended position to its retracted position.

Alternatively or additionally, the rotatable element may be formed with an abutment which lies in the path of movement of a part movable with the guard when the element is in its locking position and is moved out of said path of movement when the element is rotated to its release position.

In any of the above arrangements said movable element is preferably biased into its locking position by spring means.

In the case where the movable element is rotatable, said operating lever may be directly connected to the rotatable element. Alternatively, the operating lever may be mounted on the handle for pivotal movement separately from the rotatable element, and may have a part which is engageable with the rotatable element in a manner to rotate the element to its release position upon pivotal movement of the lever.

In any of the arrangements previously described, there are preferably provided two of said guards mounted on the handle on opposite sides of the portion of the blade which projects from the handle. In this case the two guards are preferably both controlled by a single movable element and manipulating member. The two guards may be connected together so as to move in unison.

Means may be provided for adjusting the position of each guard independently of the other. For example, means may be provided for locking one guard in a retracted position while the other guard remains movable from its extended position to its retracted position against the action of said resilient balancing means.

In any of the above arrangements there may be further mounted on the handle manually adjustable stop means for adjusting the distance which the guard may move from its extended position towards its retracted position. For example, the adjustable stop means may comprise a movable stop element mounted on the handle and formed with a plurality of recesses of different depths which may be selectively moved into the path of movement of a part movable with the guard, whereby the extent of permitted movement of the guard is determined by the depth of the recess which is brought into said path of movement. The part movable with the guard may comprise a pin extending laterally from the guard. In this case, the laterally extending pin may pass through a slot in the handle, so as to project to the exterior of the handle, said movable stop element being mounted on the exterior of the handle.

The movable stop element may be in the form of a rotatable disc, said recesses of different depths being spaced apart around the periphery of the disc.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1

shows a safety knife according to the present invention, shown in an open position,

FIG. 2

is a similar view showing the knife in the closed position and ready for use,

FIG. 3

is a view from below of the knife in the closed position,

FIG. 4

is a section on the Line

4

—

4

of

FIG. 2

showing the catch for securing the two halves of the knife together,

FIG. 5

is an end view of the catch shown in

FIG. 4

,

FIG. 6

is a similar view to

FIG. 1

of an alternative form of safety knife according to the invention,

FIG. 7

is a part-view showing a possible modification to the knives- of

FIGS. 1 and 6

,

FIG. 8

is an enlarged view of an alternative form of control mechanism for the knife of

FIG. 7

,

FIG. 9

is an enlarged view of the guard and blade of a further form of safety knife according to the invention, and

FIG. 10

is a similar view to

FIGS. 1 and 6

, showing a further embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to

FIGS. 1

to

4

, the knife comprises a handle

10

, formed from two overlying parts: a left part

11

and a right part

12

. Each part is essentially a mirror image of the other, the two parts being pivotally connected together by a pivot pin

13

so that they may be swung from the open position shown in

FIG. 1

, where the parts are arranged at an angle to one another, to the closed position shown in

FIGS. 2 and 3

where the two parts of the handle overlie one another.

In the closed position shown in

FIGS. 2 and 3

the shaped outer surfaces of the two parts of the handle provide a handgrip portion

14

and a head portion

15

. The underside of the handgrip portion is shaped, as indicated at

16

, to receive the user's fingers as the hand grips the knife, and an upper portion

17

is formed with transverse ribs against which the user's thumb may rest.

The knife comprises two operative blades: a trapezium shaped main blade

18

and a double-ended hooked blade

19

which acts as a fixed guard. Each blade is received in a shallow recess in the inner surface of the right handle part

12

, so that the blades are clamped between the two halves of the knife handle when these are brought into overlying relationship.

As best seen in

FIG. 1

, the main trapezium shaped blade

18

is so located within the knife handle that a pointed end

20

of the blade projects beyond an inclined edge surface

21

of the handle so that the exposed portion

22

of the cutting edge

23

of the main blade extends at an obtuse angle to the edge

21

of the handle.

The hooked guard blade

19

is of the kind having a central portion

24

having two parallel unsharpened edges, opposite ends of the blade being formed with transverse tangs

25

extending approximately at right angles to the main axis of the blade. Concavely curved sharpened cutting edges

26

are formed between the tangs

25

and the main central portion of the blade

19

. The two blades

18

and

19

are so located in relation to one another that one unsharpened main side edge of the blade

19

lies alongside an inclined end edge of the blade

18

. One of the tangs

25

of the blade

19

is disposed outwardly beyond the exposed pointed extremity

20

of the main blade

18

so that the curved cutting edge

26

adjacent that tang extends around the point

20

of the main blade

18

. As will be seen from

FIG. 1

, the inclined unsharpened edge of the main blade

18

extends at approximately a right angle to the edge surface

21

of the handle, and the adjacent tang

25

on the guard blade

19

extends generally parallel to the surface

21

.

The two blades may be located in the shallow recesses in the right part

12

of the handle, being closely embraced by those recesses. Alternatively or additionally, however, the right part

12

of the handle may be provided with projecting bosses, such as indicated at

27

, which locate within one or more of the slots

28

conventionally provided in such blades, so as to assist in locating them.

Spare blades, indicated at

29

, are stored within a suitably shaped recess within the handgrip part of the knife handle. This recess is deep enough to hold two or more blades stacked one-upon-the-other and a spring arm

30

is mounted to one side of the recess, as indicated at

3

1

, and bears on the topmost spare blade so as to prevent the spare blades rattling when the handle is closed, or falling out of the recess when the handle is open. The mounting

31

is such as to allow the spring arm

30

to be swung to one side, and received in a recess

32

, thus enabling a spare blade to be removed when required.

A quick release fastener

33

is provided to lock the two parts

11

and

12

of the handle together when they are in a overlying relationship. The construction of the fastener is shown in greater detail in

FIGS. 4 and 5

.

Referring to those figures, the fastener comprises a circular shaft

34

which is received in a hole in the left handle part

11

and is formed with a circular manipulating head

35

. The lower end of the shaft

34

is formed with two diametrically opposed lugs

36

which cooperate with a shaped slot

37

in the right handle part

12

. In one rotational position of the shaft

34

the lugs

36

may pass through the slot

37

. The shaft is then turned clockwise through 90° bringing the lugs

36

into a position where they lie at right angles beneath the slot

37

thus locking the two halves of the handle together. When it is required to separate the two halves of the handle, the shaft

34

is rotated anticlockwise through 90°, bringing the lugs

36

into register with the slot

37

. The shaft

34

may then be withdrawn axially out of the slot

37

so as to be disengaged from the slot allowing the two halves of the handle to be swung apart. The shaft

34

may be lifted by manually pulling on the manipulating head

35

, or the shaft may be automatically biased upwardly by a spring, for example by a helical compression spring (not shown) which encircles the shaft

34

between the underside of the manipulating head

35

and an annular abutment on the upper handle part

11

.

The knife, when closed, may be used to cut sheet material, for example thick cardboard, by pulling the exposed portions of the blades

18

and

19

over the edge of the sheet material and drawing the knife towards the user so that the cutting edge of the exposed point

20

cuts into the material as it enters the slot between the tang

25

and the adjacent surface

21

of the knife handle. As the material passes the pointed part

20

of the main blade

18

it meets the concavely curved cutting edge

26

of the guard blade

19

. The curved cutting edge

26

cuts any part of the thickness of the material which passes beyond the pointed tip

20

of the main blade

18

and which does not therefore become fully severed by the main blade.

Instead of drawing the exposed blades over an exposed edge of a material to be severed, the tang

25

may also be forced through the material at a location away from its edges, by using sufficient force, the knife being drawn towards the user once the tang has been plunged through the material. The knife is therefore particularly suitable for ripping open cardboard boxes, self-adhesive wrapping tape, paper sacks and the like, where it may not be possible to apply the knife to an exposed edge of the material to be cut. The knife may also be used for cutting other materials such as strapping, string or other similar packaging materials.

The arrangement of the two blades ensures that there is little risk of fibres or other particles from the material becoming jammed in the blade, as can often happen with other safety knife blade arrangements. Although, as explained above, it is desirable for the concave edge of the guard blade to be sharpened, so as to provide an auxiliary cutting action, the invention does not exclude arrangements where the guard blade is not sharpened, but simply comprises a blade-like element of substantially constant thickness and having an unsharpened edge around the pointed tip of the main blade.

As may be seen from

FIGS. 1 and 2

, the unsharpened outer edges of the blade

19

and tang

25

provide a safety guard around the pointed tip

20

of the main blade

18

thus preventing, or reducing the risk of, the user's finger, or other part of the body, coming into contact with the point

20

of the blade or the exposed portion

22

of its cutting edge. The knife can therefore be safely left lying around, or kept in a pocket, with little risk of accident, while at the same time always being ready for use.

According to the invention, the knife is also provided with spring-loaded guards

39

located on each side of the exposed portions of the blades

18

and

19

.

Each guard

39

is slidable within a recess

40

formed in one of the parts

11

,

12

of the knife handle. A rod

41

extends rearwardly from each guard

39

and extends through a narrow gap leading from the slot

40

to a smaller auxiliary recess

42

. The extremity of the rod

41

within the recess

42

has an enlarged head

43

to limit the extent to which the guard

39

can project from the recess

40

. During assembly the rod

41

is placed laterally into the gap so that the enlarged head

43

is received in the recess

42

. The rod

41

and enlarged head

43

may be integrally moulded with the guard

39

. Alternatively, the rod

41

may be screw-threaded, the enlarged head

43

comprising a nut in screw-threaded engagement with the end of the threaded rod, so that the extent to which the guard

39

projects from the recess

40

may be adjusted. Alternatively or additionally, the extent of movement of each guard

39

may be controlled by a laterally extending pin

44

on the guard which slides along a slot

45

in the associated handle part. A helical compression spring

46

encircles the rod

41

between the rear surface of the guard

39

and the end of the recess

40

so as to bias the guard

39

outwardly. Alternatively, a compression spring may be provided between the enlarged end

43

of the rod

41

and the end surface of the recess

42

.

As may be seen from

FIGS. 1 and 2

, each guard

39

, when in the fully extended position, overlies the exposed portions of the cutting edges of both the main blade

18

and the guard blade

19

. As the blades are drawn over the cardboard or other material being cut, the material passing into the slot between the tang

25

and the surface

21

engages the inclined edges

47

of the two guards

39

and forces the guards back into their respective recesses

40

, against the action of the springs

46

, so that the material engages the cutting edges of the blades.

The force necessary to retract the guards

39

may be increased or decreased by varying the angle of inclination of the edges

47

, and/or varying the strength or compression of the springs

46

.

The guards

39

increase the safety of the knife and reduce the risk of a user's finger or other body part engaging the cutting edges of the blades, since they prevent the user's finger or other body part from contacting the side faces of the exposed part of the blades, which might otherwise result in the user being cut, particularly if the pointed end

20

of the main blade does not happen to be exactly co-planar with the tang

25

on the guard blade

19

. The guards also reduce the risk of clothing becoming snagged on the blades.

The shape of the guards

39

is so chosen in relation to their direction of sliding movement that it is unlikely that a user's finger will press against the guards

39

in such a manner as to cause them to be pushed into their recesses

40

sufficiently to enable the finger to come into contact with the cutting edge of either blade. At the same time, the shape of the guards is such that they readily retract when the knife is used to cut cardboard or other sheet material since the guards are pushed directly into their slots as a result of their bearing directly on the surface of the sheet material being cut on either side of the cut.

In some cases it may be desirable for the width of the effective slot into which the sheet material passes to be matched to the thickness of the sheet material. In the arrangement shown in the drawings the effective width of the slot is the distance between the inner surface of the tang

25

and the adjacent edge surface

21

of the knife handle. While this distance as shown may be necessary for cutting thick card, it might improve the cutting of thinner card if the effective width of this slot were smaller. This effect could be achieved by permitting adjustment of the extent to which the guards

39

may be retracted into their recesses

40

. In the arrangements shown the guards may retract fully into the slots so that they become flush with the edge surface

21

exposing the full width of the slot between the tang

25

and the surface

21

. However, adjustment means may be provided so that, at the inward limit of their retracting movement, the guards

39

still project beyond the surface

21

but to a lesser extent. The effective width of the slot leading to the cutting edges of the blades is then effectively reduced to the distance between the inner edge of the tang

25

and the outer parts of the guards

39

. Any convenient means may be employed for limiting the inward movement of the guards

39

. For example, an adjustable abutment may be provided for engagement by the pin

44

to limit the distance which the pin

44

can move along the slot

45

. Such an arrangement will be described below in relation to FIG.

7

.

Alternatively, the rod

41

connected to each guard

39

may be extended rearwardly through the handle so as to be engageable with a sliding element within the handle which may be slid, by movement of an external manipulating button, into and out of a position where it lies in the path of movement of the end of the rod

41

. Thus, when the element is in one position it may allow the guards

39

to be retracted fully, and when in an alternative position it may be engaged by the ends of the rods

41

so as to prevent retraction of the guards beyond a certain point. The surface of the element which is engaged by the ends of the rods

41

may be stepped or otherwise shaped so as to permit different amounts of movement of the rods, depending on the position of the element. By this means the arrangement may provide for a number of alternative degrees of retraction of the guards

39

. Preferably, the arrangement is such that in a safety position of the sliding element it prevents any retraction of the guards

39

, and locks the guards in a fully extended position.

Means may also be provided for fixedly locating the sliding guards

39

in alternative positions relative to the surface

21

and the tang

25

. In this case the outer extremities of the guards

39

will be spaced inwardly of the inner edge of the tang

25

, thus reducing the effective width of the gap into which the sheet material can be passed. A small region of the cutting edges of the two blades will therefore be exposed and the guards

39

will not be allowed to retract. Accordingly, they will be less effective than when they are retractable, but will still provide some reduction in the risk of a user being accidentally cut by the blades.

The present invention is not restricted to safety knives having the two blade arrangement shown in

FIGS. 1-3

, and is equally applicable to knives having only a single blade with a part of its cutting edge exposed. Thus in the arrangement of

FIGS. 1-3

the second blade

19

could be omitted. In this case the cutting action will be effected solely by the exposed cutting edge of the blade

18

, the exposed point

20

of the blade still being protected by the spring-loaded guard assemblies

38

.

In the two-blade arrangement of

FIGS. 1-3

, the exposed tang

25

of the second blade

19

reduces the likelihood of a user's finger, or other part of the body, being pressed against the guard assemblies

38

in such a manner as to cause them to be retracted so that the finger can come into contact with the cutting edge of either blade. If the second blade

19

is omitted, there may a greater risk of this occurring and it is therefore preferable for means to be provided for locking the guard assemblies

38

fixedly in position on the knife, when the knife is not in use.

FIG. 6

shows such an arrangement. Components which are common between

FIGS. 1 and 6

bear the same reference numerals.

Referring to FIG.

6

: as in the previous arrangement each guard

39

is slidable within a respective recess

40

formed in one part

11

,

12

of the knife handle. A rod

41

extends rearwardly from each guard

39

and extends through a hole in an annular abutment

50

at the end of a reduced width portion of the recess

40

. Each guard

39

is biased outwardly by a compression spring

51

which encircles the rod

41

between the guard

39

and abutment

50

. In the fully extended position of each guard

39

, as shown in

FIG. 6

, the end of the rod

41

on the guard which is mounted in the knife part

12

bears against the periphery of a circular disc

52

which is rotatably received in a part-circular recess

53

in the knife part

12

. Alternatively or additionally the disc may have a central shaft, or journals, which are rotatable in small bearing recesses in the two halves of the knife blade. The disc

52

can be rotated through an angle by means of a lever

54

which is integral with the disc

52

and projects through a slot in the upper edge of the part

12

and carries at its extremity a manipulating button

55

. The lever

54

is angularly slidable across a triangular recess

56

anti-clockwise from the locked position shown in

FIG. 6

to an unlocked position where the lever

54

lies at the left hand side of the slot.

A generally triangular abutment

57

is formed on the surface of the disc

52

and is engaged by one arm of a spring

58

which is mounted on a circular boss

59

on the part

12

adjacent the disc

52

. The spring

59

biases the disc

52

clockwise to the position shown in

FIG. 6

where the lever arm

54

lies at the right hand end of the slot through which it passes.

When the disc

52

is in the rest position shown in

FIG. 6

the abutment

57

on the outer surface of the disc is engaged by the end of the rod

41

which is connected to the guard

39

on the handle part

11

. Accordingly, in this rest position both guards

39

are prevented from retracting into their respective recesses

40

and exposing the point

20

of the blade

18

.

However, if the disc

52

is rotated anti-clockwise, against the action of the spring

58

, by moving the lever

54

to the left, a recess

60

within the body of the disc

52

(as shown in dotted lines in

FIG. 6

) is brought into register with the end of the rod

41

on the part

12

and the abutment

57

is rotated out of engagement with the rod

41

on the guard

39

mounted on the part

11

. Since the ends of the rods

41

are then no longer obstructed, both guards

39

are then free to be retracted into their respective recesses

40

in the blade handle by outside pressure.

Thus, when the knife is not in use, the guards

39

are held rigidly in their extended positions, as shown in

FIG. 6

, by the disc

52

and abutment

57

. When the knife is to be used, the user pushes the lever

54

,

55

along its slot so as to rotate the disc

52

anti-clockwise as seen in FIG.

6

. This renders the guards

39

free to retract, but they remain extended, protecting the blade point

20

, until the tip of the blade and the guards are drawn over the cardboard or other material to be cut. The pressure of the cardboard on the curved surfaces of the guards

39

causes the guards to retract, against the action of the springs

51

, so that the point

20

of the blade

18

can enter and cut the cardboard or other material. When the knife is removed from the material, the springs

51

automatically extend the guards

39

to cover the blade tip

20

and the user releases the lever

54

,

55

so that the spring

58

returns the lever and the disc

52

to the original rest position so as to prevent the guards

39

being retracted once more. In practice, the user can release the lever

54

,

55

at any time while cutting is still taking place since the disc

52

will be prevented from rotating back to its rest position so long as the rod

41

lies within the recess

60

in the disc

52

and also by virtue of the abutment

57

bearing against the side of the rod

41

of the guard on the part

11

of the knife. It is only after the knife is removed from the material that the springs

51

will extend the guards

39

automatically so that the rods

41

withdraw from the disc

52

, thus allowing the disc to snap back to its original rest position under the action of the spring

58

.

In the arrangement of

FIG. 6

the disc

52

is rotated from the locked position by the user pushing head

55

of the lever

54

forwards with his thumb. It will be appreciated, however, that by suitably modifying the disc

52

the device could be arranged to operate in the opposite sense so that the mechanism is moved from the locked position to the operative positive by drawing the lever back with the thumb.

Other mechanisms may be employed for locking or unlocking the guards

39

. For example, as previously mentioned, the guards may be controlled by a sliding element within the handle which may be slid into and out of the path of movement of the rods

41

.

The knife of

FIG. 6

could also be modified to incorporate a hooked blade of the kind indicated at

19

in

FIG. 1

, where the sharpened tang at one end of the blade co-operates with the pointed end

20

of the blade

18

. The hooked blade may be formed with cut-outs to accommodate the projection

57

on the disc

52

. The arrangement may be such that when hooked blade is used engagement between the blade and the projection

57

holds the disc

52

in the position where the guards

39

can retract, so that the knife operates in a similar fashion to the version shown in FIG.

1

. Then if the hooked blade is removed the disc

52

can revert to the position shown in

FIG. 6

so that the guards

39

can be locked and the knife can operate in the manner described with respect to the form of the knife shown in

FIG. 6

, without a hooked blade.

As previously mentioned, in some uses of the knife it may be desirable for a smaller area of the tip

20

of the blade

18

to be exposed, when the guards are retracted, and this may be achieved by limiting the extent to which the guards

39

can be retracted to expose the tip of the blade.

FIG. 7

shows an arrangement whereby the extent of retraction of the guards may be adjusted.

FIG. 7

shows a modified portion of the outer surface of the knife part

11

. As in the arrangements of

FIGS. 1 and 6

, each guard

39

has an integral lateral pin

44

which slides along a slot

45

as the guard

39

is retracted and extended. In the modification of

FIG. 7

, which may be applied to both the FIG.

1

and the

FIG. 6

arrangements, a disc

61

is rotatably mounted within a circular recess in the outer surface of the part

11

. The disc

61

is integrally formed with an upstanding manipulating knob

62

and three slots

63

,

64

and

65

which extend inwardly from the periphery of the disc

61

by different distances. The disc may be rotated to bring any of the three slots

63

,

64

,

65

into line with the slot

45

along which the pin

44

slides. A detent device may be provided on the disc

61

and/or the surrounding part

11

of the handle, so that the disc

61

can snap into each of the three positions where one of the slots is in line with the pin

44

. For example, the periphery of the disc

61

may be formed with a “sprung pip” which can snap into any of three spaced recesses in the periphery of the circular recess in which the disc

61

rotates.

When the shortest slot

63

is in line with slot

45

the guard

39

on the part

11

can only be retracted by a short distance by virtue of the pin

44

striking the inner end of the slot

63

. When the disc

61

is rotated to bring the longest slot

65

into line with the slot

45

, then the guard

39

may be retracted to its full extent. The slot

64

provides an intermediate extent of retraction. It is only necessary to control the retraction of the guard

39

on one of the two parts

11

,

12

of the knife, since if the distance by which one of the two guards can be retracted by pressure from the surface being cut is limited, then the surface will automatically push the other guard inwards by the same amount.

As previously described, when using the knife of

FIG. 6

, the user may release the lever

54

,

55

at any time while cutting is still taking place so that after the knife is removed from the material the springs

51

extend the guards

39

automatically, allowing the disc and lever to snap back to their original rest position, under the action of the spring

58

, so as once more to lock the guards

39

in their extended position.

Although this works well in practice, it is theoretically possible for the user to hold the lever

54

,

55

in its forward position during the cut and even after the cut has been finished. If the user does this, it is possible for the knife to leave the material being cut with the guards

39

extended over the point of the blade, but still able to retract into the handle. If the guards were to strike against a part of the user's body in this condition, it is possible that they could retract under pressure so that the user is cut by the blade.

Although in practice this is a remote possibility,

FIG. 8

shows diagrammatically an alternative arrangement whereby the guards

39

are automatically locked against retraction when the knife leaves the material being cut, regardless of the position of the operating lever. Parts in

FIG. 8

which correspond to parts in

FIG. 6

bear the same reference numerals.

Referring to FIG.

8

: the disc

52

having the internal recess

60

is in this case rotatable in a slightly oval recess

66

in the body of the knife part

12

.

Instead of an operating lever being connected directly to the disc

52

, as in the

FIG. 6

arrangement, the disc is formed with an anchor

67

for a helical tension spring

68

which is connected to a separate operating lever

69

which is pivotally mounted at

70

on the knife part

12

. The upper end of the lever

69

extends through a slot

71

in the knife part

12

and is formed with a manipulating head

72

. The lower end

73

of the pivoted lever

69

is engageable with a lobe

74

formed between two recesses

75

and

76

on the periphery of the disc

52

.

FIG. 8

shows the rest position of the mechanism where the rods

41

on the guards

39

engage the periphery of the disc

52

and the underside of the abutment

57

respectively so that the guards are locked in the extended position where they protect the point of the blade

18

.

When the user wishes to use the knife to perform a cut, he presses the guards

39

against the surface to be cut and draws the head

72

of the lever

69

back towards the rear of the slot

71

, as indicated by the arrow

77

. The consequent upward movement of the lower end

73

of the lever, in engagement with the lobe

74

, rotates the disc

52

anti-clockwise so as to bring the recess

60

into register with the rod

41

on the guard

39

on the part

12

, and to move the abutment

57

out of engagement with the end of the rod

41

on the knife part

11

. The guards

39

are thus retracted into the knife body under the pressure exerted on the material to be cut. As the upper end of the lever

69

comes to the rear end of the slot

71

its lower end

73

snaps upwardly over the lobe

74

into the recess

76

, with an audible snap, indicating to the user that the knife is ready to cut.

Should the user continue to hold the head

72

of the lever in its rearward position during the cut and after the knife has left the material, the disc

52

will still rotate clockwise, after the guards

39

have been automatically extended by the springs

52

, back to the position shown in

FIG. 8

so as to lock the guards

39

in the extended protective position. When the user wishes to use the knife again, it is necessary to release the head

72

of the lever

69

so that it moves forwards again under the action of the spring

68

. The lower end

73

of the lever then snaps downwards over the lobe

74

back to the position shown in

FIG. 8

, this being permitted by the slight lateral movement of the disc

52

allowed by the slightly enlarged recess

66

.

The arrangement therefore ensures automatic locking of the guards in the extended position, when the blade leaves the material being cut, even if the user retains the lever in its “ready to cut” position during and after making the cut.

If the user instead pushes the head

72

of the lever

69

forwards while making the cut, the lower end

73

of the lever will again snap downwardly over the lobe

74

, this being permitted by the slight floating of the disc

52

and in this case, again, when the guards

39

are automatically extended when the blade leaves the material being cut the disc

52

will be rotated clockwise to the locking position under the action of the spring

68

.

In the arrangement of

FIG. 8

stop means are preferably provided to limit the extent of rotation of the disc

52

. For example, the exposed surface of the disc

52

may be formed with a slot or recess which is engaged by a raised pip on the interior of the handle part

11

, or vice versa. Alternatively, the anchor

67

on the disc

52

may be arranged to abut the surface on the handle part

12

when the disc

52

has reached the required clockwise limit of its rotation.

In another alternative arrangement, the periphery of the disc

52

may be integrally formed with an outwardly extending lever which passes through a slot through the peripheral wall on the handle part

12

. Engagement of the lever with the ends of the slot then provide limits to the clockwise and anti-clockwise rotation of the disc

52

under the action of the lever

69

and the spring

68

. An advantage of this latter arrangement is that the lever can act as a manual override to the automatic operation described in relation to

FIG. 8

, since the disc

52

may then be manually rotated anti-clockwise, by use of the lever, to the position where the guards

39

may retract.

As in the arrangement of

FIG. 6

, the disc

52

of

FIG. 8

could also be mounted on a central axle rotatable in bearing recesses in the handle parts. In this case, however, an appropriate clearance is required between the axle and the recesses to enable the disc

52

to move laterally, as previously described.

As an alternative to the disc

52

being displaceable laterally in the arrangement of

FIG. 6

, in order to allow the lower end

73

of the lever

69

to snap downwards over the lobe

74

, the lever

69

could be formed in two hinged parts so that the lower end

73

could deflect inwardly towards the main part of the lever

69

, against the action of a spring, to enable the part

73

to snap over the lobe

74

without lateral movement of the disc

52

.

FIG. 9

shows an enlarged view of a blade and associated guard or guards on a different form of knife.

In this case the cutting edge

80

of the blade

81

is generally parallel to one side edge

82

of a retractable guard

83

. The guard

83

is retractable into the blade handle

84

in a direction, indicated at

85

which is generally parallel to the cutting edge of the blade. When part of the body of a person, or other object or material, accidentally strikes the guard

83

, there is a high probability that the guard will be struck on the edge

82

which is parallel to the cutting edge of the blade or the inclined edge

86

which is adjacent an unsharpened edge of the blade. Impact on the edge

82

is unlikely to cause the guard

83

to retract since it will be generally at right angles to the direction of retraction. The guard will therefore remain in position to prevent the object striking the cutting edge

80

of the blade. If the object strikes the inclined edge

86

of the blade there is a greater possibility that the guard will be displaced since the striking force will have a greater component in the displacement direction. However, since the edge

86

is only, protecting an unsharpened edge of the blade this is less significant.

The object is therefore only likely to displace the guard and engage a sharpened part of the blade if it impacts on the apex

87

of the guard, and then only if it impacts with sufficient force to overcome the resistance provided by the biasing spring

88

. This small risk can be further reduced by slightly rounding-off the point of the blade, as indicated at

89

, if this is acceptable for the type of cutting which the blade is designed to do.

Although the guard

83

thus provides significant protection against accidental damage, when the knife is applied to a surface with a firm cutting action and in an appropriate orientation, the surface to be cut being indicated for example at

90

, the guard or guards

83

will be forced back by the greater pressure exerted on the material so that the point and cutting edge of the blade can enter and cut the material.

In the arrangements described above the two guards are independently slidable and each guard has its own return spring. However, the invention includes within its scope arrangements where the guards are linked together, within or outside the handle, so that they move in unison. For example the two guards may be integral parts of a single movable guard member.

In the above-described arrangements, the guards which shield the blade are retracted into the handle with translatory linear movement, i.e. they slide into the handle without any change of orientation. However, this is not essential and the invention also includes within its scope arrangements where the orientation of the guards changes as they are retracted. In particular the guards may be pivotally mounted on the handle so that they swing into and out of the handle as they are retracted and extended.

Such an arrangement is shown in FIG.

10

. This is a modified version of the knife shown in FIG.

6

and corresponding parts have the same references in the two figures. In

FIG. 10

, however, the sliding guards

39

of

FIG. 6

are replaced by two pivotally mounted guards

91

.

Each guard is formed on one end of a lever arm

92

which is pivotally mounted at

93

on the respective half of the blade handle. At the same end of the lever arm as the guard

91

there is formed a projection

94

which co-operates with the disc

52

in similar manner to the rods

41

on the sliding guards of FIG.

6

.

Each lever arm

92

is biased outwardly by means of a two-armed spring

95

so that each guard

91

is normally in the extended position shown in FIG.

10

. As in the previously described arrangements, the guard

91

on the handle part

12

is locked in the extended position by engagement of the projection

94

with the periphery of the disc

52

, while the guard

91

on the other handle part

11

is locked in the extended position by engagement of its corresponding projection

94

with the abutment

57

on the surface of the disc

52

.

When the disc

52

is rotated anti-clockwise by means of the lever

54

,

55

, the projection

94

on the lever arm on the part

12

can enter the recess

60

within the disc

52

and the corresponding projection on the lever arm on the handle part

11

can pass the abutment

57

, so that both guards

91

can be retracted by pressure on them. The two guards

91

rotate about the pivots

93

against the action of the springs

95

.

It will be appreciated that pivoted rather than sliding guards can be used in any safety knife according to the present invention. For example, the knife of

FIG. 1

, and particularly the knife of

FIG. 8

, could be modified to have pivoting rather than sliding guards.

For some purposes it may be desirable to have a fixed guard on one side of the projecting portion of the knife blade and a retracting guard on the other side. For example, when it is required to remove the top surface from a cardboard box, this may be done by holding the knife with the blade horizontal and resting the uppermost guard on the top edge of the box. The blade may then be pushed into the sidewall of the box, just below the top edge, the lower guard retracting under the pressure applied to the knife. The knife is then run around the periphery of the box so as to remove the top surface of the box as a flat panel or “lid”. While the cut is being made the fixed upper guard bears against the upper surface of the box and serves as a guide so that the cut made by the blade is a small fixed distance below the upper surface. The upper guard can, if desired, be larger than the lower guard so that it extends over a greater area of the top surface of the box as it is run around its periphery.

In a knife of this kind, the upper guard can be permanently fixed and only the lower guard retractable according to the invention. However, in this case it may be necessary to manufacture a different form of the knife for use by a left-hander who will normally hold the knife in such a w ay that the other guard is uppermost. In order to avoid the necessity of manufacturing two forms of knife, therefore, both guards may be constructed so that they are retractable, according to the invention, but means may be provided to lock either guard in the extended position so that the knife can be used to cut the top surface from a box as described above.

Such an arrangement is shown in the knife of

FIG. 10

where each lever arm

92

is formed with a hole

96

which may be engaged by a screw or other form of detent mounted on the handle part on which the lever arm is mounted.

FIG. 10

shows a screw

97

on the handle part

11

which can be screwed into engagement with a hole

96

in the lever arm (not shown) mounted on the handle part

11

so as to lock that lever arm, and hence the corresponding guard

91

in the extended position. A similar screw (not shown) is provided on the outside of the handle part

12

to co-operate with the hole

96

in the lever arm

92

which is visible in FIG.

10

.

The user of the knife may thus select which guard

91

is to be fixed in the extended position and which is to retract, depending on whether the user is left-handed or right-handed. When the knife is to be used for other purposes where it is desirable that both guards

91

should retract, then both screws

97

may be disengaged from the respective lever arms

92

. It will be appreciated that, if desired, when the knife is not in use both screws

97

may be tightened to lock both guards

91

in the extended position. This renders the knife entirely safe for someone, such as a child, to pick up and handle even if the lever

54

,

55

is accidentally operated.

The present invention relates only to the safety guards and other features of the handle in which the cutting blade or blades are mounted, and does not relate to the configuration of the cutting blades themselves. Although a two blade configuration is shown in

FIGS. 1-3

, by way of example, this is only an example of the many possible types of cutting blade, and cutting blade configurations, with which the features of the present invention may be used. The invention is not therefore intended to be limited to the use of any particular blade type or configuration, and the particular blade types and configurations shown in the drawings do not form a part of the present invention.

Number	Name	Date	Kind
2376887	Walters	May 1945	A
2730800	Bailey	Jan 1956	A
3943627	Stanley, Jr.	Mar 1976	A
4012836	Baer et al.	Mar 1977	A
4086698	Sparks	May 1978	A
4091537	Stevenson, Jr.	May 1978	A
4241500	Iten	Dec 1980	A
4473076	Williams et al.	Sep 1984	A
4503612	Davis	Mar 1985	A
4569133	Schmidt	Feb 1986	A
4757612	Peyrot	Jul 1988	A
5010648	Takigawa	Apr 1991	A
5241750	Chomiak	Sep 1993	A
5620454	Pierce et al.	Apr 1997	A
5878501	Owens et al.	Mar 1999	A
6195896	Ireland	Mar 2001	B1
6233832	Berns	May 2001	B1

Number	Date	Country
3116354	Nov 1982	DE
0963820	Dec 1999	EP
2338444	Dec 1999	GB
WO9907525	Feb 1999	WO

Safety knife

Information

Patent Number

Date Filed

Date Issued

Inventors

Examiners

Agents

CPC

US Classifications

Field of Search

US

International Classifications

Abstract

Description

Claims

Priority Claims (1)

US Referenced Citations (17)

Foreign Referenced Citations (4)