GB2380154A - Safety knife - Google Patents

Abstract

A safety knife comprises a blade 12 mounted upon a handle 10. The blade 12 has a cutting edge 14. The knife is provided with cutting depth control means 20, 40 to control the length of the cutting edge 14 which is exposed, in use. Further features include the presence of retractable guards disposed about the said blades.

Description

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"Safety Knife" The invention relates to a safety knife, for example to a knife intended for use in the opening of cardboard boxes.

In one known form of cardboard cutting knife, a blade is rigidly mounted upon a handle. A hook shaped second blade may also be mounted upon the handle and arranged to extend around a point of the blade to serve as a guard reducing the risk of injury to an operator. A pair of sideguards are also provided restricting access to the sides and cutting edge of the blade. Each sideguard is moveable between an extended position and a retracted position in which the cutting edge is exposed to allow use of the knife. The sideguards are springbiased towards their extended positions, and a control arrangement is provided to restrict movement of the sideguards and hence restrict access to the cutting edge of the blade, thereby reducing the risk of accidental injury to an operator.

Where the material to be cut using the knife is relatively thin compared to the length of the cutting edge of the blade, a relatively long part of the blade is exposed, in use, for example protruding from the rear face of the material being cut. Obviously, with such an exposed, unprotected cutting edge, there is an increased risk of injury, particularly if the hook-shaped blade is not present. It is an object of the invention to provide a safety knife in which the risk of injury in this manner can be reduced.

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According to the present invention there is provided a safety knife comprising a blade mounted upon a handle, the blade having a cutting edge, and cutting depth control means to control the length of the cutting edge that is exposed, in use The cutting depth control means preferably comprises a plurality of moveable members each being moveable between an operative position in which it can serve to limit the cutting depth and a rest position.

The blade may be moveable relative to the handle, the moveable members being engageable with the blade or a member moveable therewith to limit the range of movement of the blade relative to the housing to control the cutting depth. Alternatively, where the knife is of the type including one or more retractable guards for the blade, the moveable members may be c-operable with the guards to limit the degree by which the guards are retractable.

It will be appreciated that by controlling the length of the exposed part of the cutting edge of the blade in this manner, the length of the exposed part of the blade extending through a workpiece and forming a hazard to an operator is reduced, thus reducing the risk of injury.

The moveable members conveniently comprise blocks slidable relative to the handle between the operative and inoperative positions. Several such blocks are preferably provided to provide a range of alternative cutting depths. A detent

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mechanism may be provided to retain each block in its chosen position.

The invention will further be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a side view of a safety knife in accordance with an embodiment of the invention; Figure 2 is a diagrammatic view illustrating operation of the knife of Figure 1 ; Figure 3 is a diagrammatic view of the cutting depth control means of the knife ; Figure 4 is another view of the cutting depth control means; and Figure 5 is a perspective view of one of the components of the cutting depth control means.

The safety knife illustrated in the accompanying drawings comprises a multi-part plastics moulded housing 10 which supports a blade 12 having a cutting edge 14 in such a manner that the cutting edge 14 protrudes from a part of the housing 10. A second, hook-shaped blade 16 is also carried by the housing 10 the second blade 16 being arranged such that the hooked part thereof extends around a point 18 of the blade 14 reducing the risk of puncture injuries to an operator. A pair of sideguards 20 are mounted to the handle 10 in such a manner as to be moveable between an extended position as illustrated in the

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drawings in which the sideguards 20 overlie the sides of the blade 12 and retracted position in which the guards 20 are housed, at least in part, within the handle 10 exposing parts of the blade 12, and in particular the cutting edge 14 thereof so as to allow the knife to be used in, for example, the opening of a cardboard box.

As shown in Figure 2, each sideguard 20 is biased by means of a spring 22 towards its extended position, and a mechanism 24 is provided to lock each sideguard in its extended position. The mechanism 24 comprises a lock member 26 located within the handle 10 and moveable by a trigger 28 having an actuator part 30 which protrudes from the handle 10. The trigger 28 and member 26 are biased by means of a spring 32 towards a rest position as shown in Figure 2 in which the guards 20 are locked in their extended positions. Movement of the trigger 28 from the position illustrated in the direction of the arrow 34 causes the member 26 to move to a position in which a projection 36 thereof moves out of co-operation with a plunger 38 associated with each sideguard 20 to permit the sideguards 20 to move to their retracted positions upon the application of a suitable loading to the sideguards 20. The nature of the mechanism 24 is such that regardless as to whether or not the trigger 28 is returned to the position shown in Figure 2, upon the sideguards 20 returning to their extended positions, the member 26 will return to the position shown thereby locking the sideguards

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20 in their extended positions.

As described hereinbefore, where the knife is used to cut through a material which is relatively thin, an unnecessarily large length of the cutting edge 14 is exposed, and this part of the cutting edge 14 may pose an unnecessary risk of injury to an operator. The risk of injury is particularly acute if the hookshaped blade 16 is omitted or removed. In accordance with the invention, a mechanism is provided to permit control over the length of the cutting edge 14 of the blade 12 which becomes exposed, in use. This is achieved by providing the handle 10 with a plurality of moveable blocks 40, each block 40 being slidable between an operative position and a rest position such that, whilst in their rest positions, the blocks 40 do not interfere with the movement of the sideguards 20, but when moved to their operative positions they serve to limit the distance through which the sideguards 20 can be moved. As shown in Figure 5, each of the blocks 40 is provided with a projection 42 which, in use, extends or protrudes through an opening 44 provided in the handle 10 to permit an operator to move each of the blocks 40, individually, between its operative and inoperative positions.

In each of the accompanying drawings, two of the blocks 40 are shown in their inoperative positions, the remaining blocks 40 being shown in their operative positions. Each block 40 is, in this embodiment, of 2mm thickness,

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and the location of the blocks is such that, if the lowermost of the blocks 40 were in its operative position, each sideguard 20 would be locked in its extended position. It will be appreciated, therefore, that in the arrangement illustrated, the maximum distance through which the sideguards 20 can be lifted away from their extended position, in the position shown, is 4mm. If the next one of the blocks 40 were moved from its operative position to its inoperative position, then each sideguard 20 could be moved through a further 2mm giving a total lift of 6mm for the sideguard 20. Although in the arrangement illustrated, each block 40 is of 2mm thickness, and five such blocks are provided, it will be appreciated that this need not be the case, and that a greater or fewer number of blocks could be provided and that the blocks could be of different thicknesses depending upon the application with which the knife is to be used. By way of example, in one envisaged embodiment three blocks are provided of thicknesses 4mm, 3mm and 4. 5mm, respectively. Further, the location of the blocks could be altered to suit the knife design, for example the blocks could be located at the position denoted by dashed line 44a in Figure 1. A knife of this type is shown, in part, in Figure 6. The provision of the blocks 40 allows independent control of the distance through which each sideguard 20 may be moved thus if desired the knife could be arranged such that only one of the sideguards 20 can be retracted.

Under such conditions, the knife could be used, for example, to remove the top

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of a box. Obviously the manner in which movement of the sideguards 20 is controlled will depend upon the application in which the knife is to be used.

As shown in Figure 4, in order to ensure that the blocks 40 are free to move without impinging upon the blade 12, a cover 46 is provided between the blocks 40 and the blade. In order to reduce the risk of the blocks 40 moving between their operative and inoperative positions other than under the control of the operator, each block 40 is conveniently provided with a pair of ridges 48 which are positioned so that one of the ridges 48 is exposed in the window 44 when the block 40 is in one of its operative positions. Each block is conveniently of polypropylene form and includes a passage 50 associated with each ridge 48 to increase the flexibility or compressibility of the ridges 48.

Although described hereinbefore in relation to controlling the permitted range of movement of the sideguards of a knife, the invention may be used with a knife of the type having a retractable blade to control the maximum distance by which the blade is permitted to extend from the handle, thereby controlling the depth of cut. It will further be appreciated that other modifications may be made to the design within the scope of the invention.

Claims (11)

1. A safety knife comprising a blade mounted upon a handle, the blade having a cutting edge, and cutting depth control means to control the length of the cutting edge that is exposed, in use.

2. A knife according to Claim 1, wherein the cutting depth control means comprises a plurality of moveable members each being moveable between an operative position in which it can serve to limit the cutting depth and a rest position.

3. A knife according to Claim 2, wherein the blade is moveable relative to the handle, and the moveable members are engageable with the blade or a member moveable therewith to limit the range of movement of the blade relative to the housing to control the cutting depth.

4. A knife according to Claim 2, wherein, the knife is of the type including one or more retractable guards for the blade, the moveable members being cooperable with the guards to limit the degree by which the guards are retractable

5. A knife according to any of Claims 2 to 4, wherein the moveable members comprise blocks slidable relative to the handle between the operative and inoperative positions.

6. A knife according to Claim 5, wherein several such blocks are provided to provide a range of alternative cutting depths.

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7. A knife according to Claim 6, further comprising a detent arrangement to hold each block in its desired position.

8. A knife according to Claim 7, wherein the detent arrangement includes a pair of deformable ridges provided upon each block.

9. A knife according to any of Claims 5 to 8, wherein the blocks are of a varying thickness.

10. A knife according to any of Claims 5 to 9 when Claim 5 is dependent upon Claim 4, wherein two guards are provided, one being located at each side of the blade, and wherein separate sets of blocks are associated with each guard to allow individual control over the movement of each guard.

11. A knife substantially as hereinbefore described with reference to any one of the accompanying drawings.