GB2280632A

GB2280632A - Reciprocating cutter blades of power driven tools

Info

Publication number: GB2280632A
Application number: GB9315087A
Authority: GB
Inventors: Geoffrey Denis Hayday; Vanessa Mary Hayday
Original assignee: Individual
Current assignee: Individual
Priority date: 1993-07-21
Filing date: 1993-07-21
Publication date: 1995-02-08
Also published as: GB9315087D0

Abstract

A cutter arm of a power tool comprises two reciprocatable cutter blades A, B having cooperating teeth which are not uniformly aligned allowing the cutting load to be distributed over the cutting cycle. A spacer tooth d on one of the blades ensures that groups of teeth 1, 2 are simultaneously at different parts of the cutting cycle thus evening out the cutting load. Consecutive teeth may be offset by increasing amounts along the length of the cutter arm (figs 4 - 6). The power source to drive the cutters may be an electric motor, compressed gases or an internal combustion engine. This cutter arrangement may be utilised on hedge trimmers, agricultural combine harvesters, river weed cutters, grass cutters, power carving knives, power saws and hair or wool clippers. <IMAGE>

Description

IMPROVEMENTS IN AND RELATING TO THE CUTTING BLADES OF POWER DRIVEN CUTTING TOOLS Description This invention relates to the cutting blades used in power-driven cutting tools having two relatively reciprocatable blades. In particular the invention relates to hedge trimmers, agricultural combine harvesters, river weed cutters, grass cutters, power carving knives, power saws and hair or wool clippers.

Throughout this specification and claims a toothed blade is referred to as the cutting blade; The pair of cutting blades which reciprocate against each other are referred to as the cutting arm and the total movement of the cutting blades relative to each other from a start position back to the same position is referred to as the cutting cycle. That part of the cutting cycle at which the cutting or sheering of the subject matter takes place is referred to as the cutting or sheering element of the cycle. For the purpose of this description, the fixed spikes or tines through which the cutting teeth on an agricultural combine harvester or river weed cutter pass in order to achieve a cutting action are also referred to as teeth. On any blade1 where the cutting action results from the intervention of the teeth of one blade against the teeth of the other blade, both sets of teeth are described as cutting teeth. This is notwithstanding the fact that the teeth of one or both blades may have no sharp cutting edge.

Reciprocating cutting blades are well known features of power driven cutting tools. A power driven cutting tool comprises a power source, cutting blades (as described above) and drive means for connecting the power source to the cutting blades such that they reciprocate relative to each other.

The power source may be an electric motor, compressed gases or an internal combustion engine.

The cutting teeth of such tools are regularly spaced along the cutting blades, such that the cutting or sheering action of all or the majority of the teeth on the cutting side of the cutting blade takes places simultaneously.

It is an object of the present invention to reduce the power needed to drive the cutting blades in a power driven cutting tool such as a hedge trimmer or appliance as described above. This is achieved by positioning the teeth in such a way that the cutting or shearing load is spread over the cutting cycle (Claim 1). This reduction in power requirement is in comparison to existing designs, in which the teeth are so positioned that all or the majority of the teeth reach that part of the cutting cycle where the cutting or shearing load is greatest at the same point in the cutting cycle.

The cutting arm comprises two blades each having cutting teeth and mounted for relative reciprocating movement to produce a cutting action from the interaction of the teeth of each blade.

Each blade may be mounted for driving movement relative to the other. Alternatively. one blade may be fixed in which case the other blade is mounted for driving movement relative to the fixed blade. The blades may be elongate with teeth disposed along one or each of the lateral edges.

Alternatively, the blades may be formed as sectors of a circle (Claims 2 to 4).

Various embodiments of cutting blades in accordance with the invention will now be described, by way of example, with reference to the accompanying drawings.

Figures 1 to 3 show different views of the same cutting blades suitable for use in a hedge trimmer, at various stages of the cutting cycle. The blades are elongate and relatively reciprocatable, having in this instance, teeth on both sides.

The following annotation has been used throughout drawings 1 to 9 (where applicable):- Tooth "d" represents a spacer tooth, "A" and "B" refer to the cutter blades arrowed and "1" and "2" refer to the respective groups of teeth bracketed. Labels "a", "b" and "c" refer to the specific teeth arrowed.

Cutter blade "B" is moving from left to right relative to cutter blade "A".

Figure 1 shows the blades at the commencement of the cutting cycle and in accordance with this invention demonstrate two groups of the cutting teeth, each group separated by a spacer tooth, "d". Those teeth to the left of the spacer tooth are about to commence the cutting or sheering element of the cutting cycle whilst those to the right of the spacer tooth (and the spacer tooth itself) are just completing that part of the cutting cycle (Claim 5).

Figure 2 shows the same pair of blades in which tooth "b" has moved from a position corresponding to that of tooth "a", and now lies between tooth "a" and tooth "c", 1/4 through the cutting cycle. The teeth to the left of the spacer tooth "d" in group 1 are shown completing the cutting or sheering part of the cutting cycle, whilst those to the right are about to commence that element of the cycle.

Figure 3 shows the same pair of cuffing blades in which tooth "b" has moved on to a position corresponding to that of tooth "c" (as defined in figure 2), % through the cutting cycle. The blades are about to reverse direction relative to each other. The teeth to the left of the spacer tooth (and the spacer tooth) are about to commence the cutting or sheering element of the cutting cycle in the reverse direction, whilst the teeth to the right of the spacer tooth have just completed that element of the cycle.

It may be observed from these illustrations that in this example the teeth to the left and right of the spacer tooth are positioned such that they commence and complete the cutting or sheering element of the cutting cycle at opposite points of the cutting cycle. The numbers of teeth completing and commencing the cutting element of the cutting cycle at any one stage are approximately equal (Claim 5).

The following features of the invention in this embodiment are not explicitly illustrated in figures 1 to 3: a) The drawings illustrate a design in which two sets of culling teeth are positioned at diametrically opposite ends of the cutting cycle. Depending on the number of teeth on the cutting blades, further spacer teeth may be incorporated so as to position any number of sections of blade at different positions in the cutting cycle, the objective at all times being to apportion the load evenly over the cutting cycle (Claim 6). Altematively, where a power source is used such that torque is not produced equally over all points of the cutting cycle, the design may be used to allocate the peak cutting or sheering load to correspond with the peak torque of the power source (Claim 8).

b) The teeth which at the extremities of their travel fall to be positioned between (as opposed to on top of, when viewed from the perspective used in figures 1 to 3) the teeth of the other blade may be designed so that the interval between the teeth is a distance less than the width of the teeth at that point. In figures 1 to 3, this description would apply to the teeth to the right of the spacer tooth in group 2 (Claim 9). This would be desirable in instances where the principal purpose of the tool is to cut relatively thin or flexible strands such as hair or wool, and it is essential to ensure that the teeth so described overlap the teeth of the opposite blade at the extremity of their travel sufficiently to ensure all strands are cut.

c) An alternative or complimentary method of cutting thin or flexible strands from that described in (b) above is to extend the length of travel of the cutting blades relative to each other, such that adequate overlap (of the teeth of each cutting blade) to complete the cutting or sheering action is achieved by all teeth (Claim 10).

d) Where it is found that the cutting action of teeth at one section of the cutting arm is more efficient than at another section (for example, due to a greater overlap of teeth at the extremities of the cutting cycle), then that section of the cutting arm should be utilised where the travel of the cutting arm through the subject matter to be cut (and hence volume of subject matter to be cut) is the greatest. In the example of a hand held hedge trimmer, this distance of greatest movement is likely to be that part of the cutting arm furthest from the operator (Claim 11).

Figures 4 to 6 show an alternative method of positioning the teeth to achieve the objective, but avoiding the need for a spacer tooth. In these drawings the teeth of one cutting blade have been progressively adjusted in position relative to the teeth of the other blade. The teeth to the right of the blades in figure 4 are at the opposite end of the cutting cycle to those on the left of the blades.

The drawings illustrate how the cutting element of the cutting cycle moves progressively along the blades as the blades move through the cutting cycle in drawings 4 to 6 (Claim 7).

The relative position of cutter blade "A" to cutter blade "B" in figures 4, 5 and 6 correspond to the relative positions of the blades in figures 1, 2 and 3 respectively.

The following features of this design are not explicitly illustrated in figures 4 to 6: e) Depending on the number of teeth on the cutting blades, further sections of the blades repeat the relative positions of teeth. This would be desirable on blades having many teeth (Claim 7).

f) Where a power source is used such that torque is not produced equally over all points of the cutting cycle, the design may be used to allocate the peak cutting or sheering load to correspond with the peak torque of the power source. This would be achieved by variably adjusting the progressive position adjustment of the teeth along the blade. The effect of making this adjustment should be to arrange the teeth such that a greater proportion of them approach the element of the cutting cycle where the maximum load occurs at a point to correspond with maximum torque of the power source (Claim 8).

Figures 7 to 9 show an alternative method of positioning the teeth, where the teeth in group 1 are at one point in the cutting cycle and the remaining few teeth are at another point in the cutting cycle. The object in this arrangement is to provide a facility to the right of the spacer tooth whereby larger strands of the subject matter to be cut will fit between the cutting teeth of cutter blades A and B. In the case of a hedge trimmer, these larger strands would be represented by larger branches of the hedge. By positioning the teeth as shown, it may be seen that all of the power of the power tool is directed solely to cutting these larger branches at that part of the cutting cycle. By concentrating the power of the power tool in this way, it will be possible for the power tool to cut larger branches than would be the case if a greater quantity of branches were attempted to be cut at the same point of the cutting cycle (Claim 12).

The relative position of cutter blade "A" to cutter blade "B" in figures 7, 8 and 9 correspond to the relative positions of the blades in figures 1, 2 and 3 respectively.

Claims

1. A cutting arm comprising a pair of toothed cutting blades. in which a relatively reciprocating action is induced by a power source and drive means for connecting the power source to the cutting blades. The teeth are arranged on the cutting blades such that the cutting or sheering load is spread over the cutting cycle. The power source may be an electric motor, compressed gases or intemal combustion engine.

2. A cutting arm according to claim 1 where each cutting blade is independently driven.

3. A cutting arm according to claim 1 where one blade is fixed and the other blade is mounted for relative reciprocating movement.

4. A cutting arm according to Claim I comprising two blades each having cutting teeth and means for creating relative reciprocating movement of the blades to produce a cutting action resulting from the intervention of the teeth of each blade.

5. A culling arm according to claim 1 where the cutting teeth are arranged in groups, with each group of teeth being positioned relative to the teeth on the opposing cutting blade such that they are at a different position in the cutting cycle from other groups of teeth at any point in time.

6. A cutting arm according to any preceding claim where two or more groups of teeth may be positioned at the same point in the cutting cycle at any one time, where one or more further groups of teeth are positioned at an alternative point in the cutting cycle at that moment in time.

7. A cutting arm according to claims 1, 2, 3 and 4 where the relative position of the teeth on the cutting arm is adjusted progressively, such that a cutting or sheering action is caused at more than two points in a cutting cycle.

8. A cutting arm according to any preceding claim where the maximum cutting or sheering load(s) correspond with the peak torque point(s) of the power source.

9. A cutting arm according to any preceding claim where the width of the cutting teeth on one blade exceed the width of the interval between the teeth of the opposite blade at that point.

10. A cutting arm according to any preceding claim where the length of travel of a tooth in a complete cutting cycle exceeds the distance between the centre points of two adjacent teeth on the opposite cutting blade.

11. A cutting arm according to any preceding claim where the teeth having the most efficient cutting action are situated on that part of the cutting arm where the travel of the cutting arm through the subject matter to be cut is the greatest.

12. A cutting arm according to any preceding claim where a small number of teeth are positioned to approach the cutting element of the cutting cycle at a given point in time; the objective in this instance being to concentrate the power of the power tool on these teeth and enable largeritougher strands of the subject matter to be cut than would be the case where many teeth approach the cutting element of the cutting cycle at the same point in time.

13. A cutting arm as substantially described herein with reference to figures 1 - 9 of the accompanying drawings.