GB2270489A

GB2270489A - Scissor action tools

Info

Publication number: GB2270489A
Application number: GB9318843A
Authority: GB
Inventors: Stephen Wensley; Alan Stanley Merrick; Andrew P Brian
Original assignee: Fiskars Oyj; Fiskars UK Ltd
Current assignee: Fiskars Oyj; Fiskars UK Ltd
Priority date: 1992-09-11
Filing date: 1993-09-10
Publication date: 1994-03-16
Anticipated expiration: 2013-09-10
Also published as: GB9219269D0; GB2270489B; GB9318843D0

Abstract

A scissor action tool, such as a pair of loppers, comprises two lever arms 10, 11 pivoted together at a point between the ends to provide two operating arms 17, 18 to one side of the pivot 12 and two co-operating jaws 13, 14 at the other side of the pivot 12. One operating arm 18 includes a mechanism which, in a first arc of movement, between an extreme open position of the arms and an intermediate open position of the arms, provides a force multiplying effect between the arm and the jaws by providing a 2:1 movement between the arm and the jaw. In the remainder of the closing movement, the ratio is 1:1. Lever arm 18 is pivotally connected to jaw 14 at 22 and has a crank 20. The mechanism comprises a cam 24, connected to crank 20, which cooperates with sides 28 of a guide slot 26 in arm 10. In addition a circular member around the cam cooperates with the sides 27 of slot 25 in a plate member 21 as part of jaw 14. <IMAGE>

Description

SCISSOR ACTION TOOLS The invention relates to scissor action tools.

Scissor action tools comprise two lever arms pivoted together at a point between the ends of the arms to provide two operating arms to one side of the pivot and two co-operating jaws to the other side of the pivot.

Examples of such tools are pliers, scissors, pruners, loppers and shears.

The jaws of such tools can act on objects of widely varying dimensions from very small articles with the jaws very close together to very large articles with the jaws widely angled apart. It is generally the case that, the larger the object, the greater the force required from the jaws. For example, in the case of loppers, the force required to sever a small diameter branch is much less than the force required to sever a large diameter branch.

This problem has often been overcome by providing tools of varying sizes with different lengths of operating arm long operating arms for providing large forces to large sized objects, and shorter arms for applying smaller forces to smaller sized objects.

According to the invention, there is provided a scissor action tool comprising first and second lever arms connected together at a first pivot point between the ends thereof to provide first and second- operating arms to one side of the pivot point and respective first and second co-operating jaws to the other side of the pivot, the second jaw being connected to a member projecting to the opposite side of the first pivot to the second jaw, the second operating arm being connected to said member by a second pivot which is parallel to said first pivot and which is spaced from an end of the second operating arm adjacent said second pivot, said second operating arm having a portion beyond said second pivot towards said end, said portion so co-operating with the member and the first operating arm that, as the first and second operating arms are closed together in a first arc of movement from a fully separated position, a point on said portion adjacent said end is held against translational movement relative to the first operating arm so that the second operating arm pivots about said point and said second pivot to pivot the second jaw about said first pivot to close said first and second jaws, the closing of the arms in a second arc of movement from said fully separated position and beyond said first arc locking the arm portion to the member against relative rotation so that the second arm portion and the member pivot together about said first pivot to close further the first and second jaws.

The following is a more detailed description of an embodiment of the invention, by way of example, reference being made to the accompanying drawings in which:- Figure 1 is a plan view of a lopper showing blades of the lopper and short portions only of operating arms of the loppers, and showing also a mechanical advantage mechanism acting on one operating arm, with the arm being shown in a disposition between first and second arcs of movement of the one operating arm, and Figure 2 is a similar view to Figure 1 but showing the operating arm at the commencement of a first arc of movement.

Referring first to Figure 1, the loppers comprise first and second lever arms 10,11 pivoted together at a pivot point 12. To one side of the pivot point 12 the first and second lever arms 10,11 form a pair of co-operating jaws 13,14, one jaw 14 being provided with a cutting edge 15 and the other jaw 13 being provided with a co-operating shearing edge 16. The lever arms 10,11 also form, on the opposite side of the pivot point 12, respective first and second operating arms 17,18. The first operating arm 17 is associated with the shearing edge jaw 16 and is formed in one piece with that jaw 16. The second operating arm 18 is associated with the cutting edge jaw 15 but a mechanical advantage mechanism is incorporated between the second arm 18 and the jaw 14. This mechanism will now be described in detail.

As seen in Figure 1, the second operating arm 18 is, at the end adjacent the pivot 12, provided with a short crank 20. The jaw 14 is formed in one piece with a plate member 21 which is disposed on the opposite side of the pivot point 12 from the jaw 14.

The crank 20 and the plate 21 are connected together in the following way.

A screw and nut 22 interconnect the crank 20 and the plate 21 at the knee of the crank 20. This provides a pivot point between the second operating arm 18 and the plate 21. The pivot axis of this pivot point is parallel to the axis of the pivot point 12.

The end of the crank 20 carries a pin 23 whose axis is parallel both to the axis of the pivot point 12 and to the axis of the crank pivot 22. The pin 23 carries a cam 24 which is locked to the pin 23 (and thus to the crank 20) and whose action will be described below.

The pin 23 projects through a slot 25 in the plate 21 and into a guide slot 26 in a flat section of the first operating arm 17 adjacent the pivot point 12. The plate slot 25 has curved sides 27 whose centre is the pivot point 12. The ends of the plate slot 25 extending between the curved sides 27 are rounded.

The operating arm guide slot 26 has sides 28 which form a narrower end and a wider end. At the narrower end, the sides are arcuate, the centre of the arcs being the pivot point 12. At the wider end, the sides and the associated end form a hole whose diameter is greater than the width of the narrower end, the axis of the hole being co-axial with the axes of the pivots, 12,22. The narrower end is the inner end of the slot 26 i.e. the closer of the ends to a line extending along the length of the first operating arm 17. The cam 24 is located in this guide slot 26.

The cam 24 is an elongate curved block which projects to diametrically opposite sides of the pin 23 and which is fixed on the pin 23. The ends of the cam 24 are provided with respective curved surfaces.

In explaining the relationship between the slots 25,26 and the operation of the loppers, the movement of the jaws 13,14 and the first and second operating arms 17,18 can be considered to be composed of two arcs of movement. The first arc of movement extends from the position in which the first and second operating arms 17,18 are fully separated apart (the position shown in Figure 2) to the partly open position shown in Figure 1. The second arc of movement is between the position shown in Figure 1 and the position in which the operating arms 17,18 are fully closed together.

In the position shown in Figure 1, between the first and second arcs of movement, the two slots 25,26 are in register. As will be seen, the plate slot 25 is wider than the guide slot 26 and of greater length.

The loppers operate as follows.

When the first and second operating arms 17,18 are closed together, the cam 24 lies in the narrower portion of the guide slot 26 as seen in Figure 1. The pin 23 engages by the end of the plate slot 25.

As the first and second operating arms 17,18 are opened, the second operating arm 18 and the plate 21 move together since relative rotation about the axis 22 is prevented by engagement of the cam 24 with the arcuate sides of the narrower end of the guide slot 26. This continues throughout the first arc of movement. The jaws 13,14 can be closed at any point during this arc of movement by the closing of the operating arms 17,18 with relative rotation between the second operating arm 18 and the plate 21 again being prevented by engagement of the cam 24 with the arcuate sides of the narrower end of the guide slot 26.

If the first and second operating arms 17,18 are opened through the second arc of movement, beyond the position shown in Figure 1, the cam 24 initially engages the wider end of the guide slot 26. Since the diameter of this wider end is generally equal to the length of the cam 24, the cam 24 and the hole of the guide slot 26 co-operate to provide a pivot with the curved ends of the cam 24 engaging the hole. This locks the end of the crank 20 to the first operating arm 17 so that the end of the crank 20 cannot perform translational movement relative to the first operating arm 17. As a result, continued opening movement of the first and second operating arms 17,18 causes the end of the crank 20 to pivot about the pivot formed by the hole and the cam 24 and the second operating arm 18 pivots around the pivot 22 to open further the jaw 13.The relative lost motion between the second operating arm 18 and the plate 21 is accommodated by the plate slot 25. The leverage effect is arranged such that during the second arc of movement, the second operating arm 18 moves approximately two degrees for every one degree moved by the jaw 14.

A similar lever effect takes place as the first and second operating arms 17,18 are closed together from a fully separated position. The end of the crank 20 is locked against translation relative to the first operating arm 17 and a lever force is applied to the plate 21 via the pivot 22. This effectively doubles the force which is applied by the jaws 13,14 to an object such as a branch between the jaws 13,14.

At the end of the second arc of movement, the cam 24 has rotated relative to the hole of the guide slot 26 until the cam 24 is aligned with the narrower end of the guide slot 26. At this moment, the end of the plate slot 25 engages the cam 24 and this prevents further relative rotation between the second operating arm 18 and the plate 25 (and hence the associated jaw 14). Continued movement of the first and second operating arms 17,18 towards one another results in the cam 24 entering the narrower end of the guide slot 26. The second operating arm 18 and the plate 21 and asscoiated jaw 14 are locked together for 1:1 movement during the second arc of movement.

It will be appreciated that the lever effect of the mechanism depends on the spacings between the pivots 12 and 22 and the pin 23. These may be adjusted as required to give lever effects other than 2:1.

It will also be appreciated that, while the mechanism as has been described above as applied to loppers, it could be applied to any other scissor action tool such as shears, pruners, pliers, scissors. In addition, although the jaws 13,14 are shown with co-operating cutting and shearing edges 15,16, one jaw could include an anvil and the other a cutting edge co-operating with the anvil.

Claims

1. A scissor action tool comprising first and second lever arms connected together at a first pivot point between the ends thereof to provide first and second operating arms to one side of the pivot point and respective first and second co-operating jaws to the other side of the pivot, the second jaw being connected to a member projecting to the opposite side of the first pivot to the second jaw, the second operating arm being connected to said member by a second pivot which is parallel to said first pivot and which is spaced from an end of the second operating arm adjacent said second pivot, said second operating arm having a portion beyond said second pivot towards said end, said portion so co-operating with the member and the first operating arm that, as the first and second operating arms are closed together in a first arc of movement from a fully separated position, a point on said portion adjacent said end is held against translational movement relative to the first operating arm so that the second operating arm pivots about said point and said second pivot to pivot the second jaw about said first pivot to close said first and second jaws, the closing of the arms in a second arc of movement from said fully separated position and beyond said first arc locking the arm portion to the member against relative rotation so that the second arm portion and the member pivot together about said first pivot to close the first and second jaws.

2. A tool according to claim 1 in which cam means and guide means are provided, one of said means being on the portion of the second operating arm and the other means being provided on the first operating arm, the cam means and the guide means co-operating to form said pivot in said first arc of movement from said fully separated position.

3. A tool according to claim 2 wherein said guide means includes a hole having an axis co-axial with the axes of the first and second pivots, the cam comprising an elongate block whose length is generally equal to the diameter of the hole, the cam lying in said hole during said first arc of movement so that the cam and the hole together form said pivot.

4. A tool according to any one of claims 1 to 3 wherein lost motion means are provided between said portion and said member to allow said rotation of said second operating arm about said second pivot during said first arc of movement from said fully closed position, said lost motion means locking the member to the portion during said second arc of movement from the fully separated position.

5. A tool according to claim 4 when dependent on claim 3 wherein said cam means are carried on the portion and project through a slot in said member to engage in said hole in the first operating arm, said slot forming said lost motion means and, at the end of said first arc of movement from the fully separated position, an end of said slot engaging said cam means to lock the member to the portion.

6. A tool according to claim 2 or claim 3 and comprising further guide means in said first operating arm, said further guide means receiving said cam means in said second arc of movement and, when said first and second operating arms are in said second arc of movement moving towards said fully separated position, engagement between said cam means and said further guide means preventing rotation of said second operating arm about said second pivot so that the second operating arm and the associated jaw pivot together about said first pivot.

7. A tool according to claim 6 when dependent on claim 3 wherein said further guide means comprise an arcuate slot whose axis is co-axial with the first pivot, the slot leading from the periphery of said hole, the elongate block rotating with the portion and in said hole during said first arc of movement and, at the end of the first arc of movement from said fully separated position, being aligned with the arcuate slot for entry into said arcuate slot in said second arc of movement.

8. A tool according to any one of claims 1 to 7 wherein said portion comprises a crank at said end of the second operating arm, said second pivot being provided at a knee of said crank, said member being a plate formed with said associated jaw and arranged between said cranked portion and said first operating arm, the crank carrying a cam projecting through a slot in the plate that permits relative motion between the second operating arm and said plate during said second arc of movement, the first operating arm including a hole having an axis parallel to the axes of said first and second pivots and an arcuate guide slot whose axis is co-axial with the axis of the first pivot, the cam engaging said hole in said second arc of movement to provide said point about which said second operating arm pivots in said second arc of movement, the cam being guided in said guide slot in said first arc of movement and the cam engaging the plate slot at the end of the second arc of movement from the fully separated position to prevent further relative rotation between the second operating arm and the plate.

9. A scissor action tool substantially as hereinbefore described with reference to the accompanying drawings.