GB2405308A - Rotary vegetation cutter with a static blade - Google Patents

Abstract

A rotary vegetation cutter comprising a rotary head cutter 16, rotatably mounted upon a stationary gear housing 12, and powered by an electric motor or internal combustion engine. A static cutter 24 is mounted on a flange 28 which is part of the gear housing. It is fastened to the flange by a through screw 30. The cutter cuts vegetation entrained by the cutter head and so prevents the long grass wrapping and binding around the drive shaft. Alternatively, the static blade may be arranged alongside and fastened to the cutter head guard.

Description

1 2405308

DESCRIPTION

VEGETA'I'ION CUTTER The present invention relates to rotary vegetation cutters.

A number of different types of rotary vegetation cutters are currently available. l wo examples are line trimmers and brush cutters. Although such cutters take various coinriguratior;s, they all rely upon a cutting head rotating at high speed about an axis whicl1 is typically generally vertical in use.

Rotary line trimmers can be powered by an internal combustion (I.C.) engine or an electric motor and usually comprise an elongate handle tenninating at its lower end in a rotary head which carries a protruding flexible line of a durable plastics material. In operation, the head rotates at a high speed and as it does so the line is thrown radially outwards by centrifugal force. The moving dine can sever certain types of vegetation such as grass or stems of weeds etc. Over time, the line may become damaged and shortened and the line is then extended out of a reel which is located in the head.

Rotary disc trimmers may also be either I.C. or electrically powered and usually comprise an elongate handle which terminates in a cutter head formed as a rotary disc, typically of metal. The rotary disc usually has profiled teeth around its circumference and allows stems of larger weeds to be cut. Rotary disc trimmers can cut more substantial material than line trimmers and are sometimes referred to as "brush cutters". Other types of brush cutter have rigid blades to perform the cutting, the blades sometimes being pivoted so that they are thrown outwards in use by centrifugal force but can pivot in the event that they strike an object which cannot be cut.

On electrical machines, the motor is usually mounted directly above the cutter head and is a direct drive. The elongate handle enables the operator to stand upright while presenting the cuber head to the vegetation at ground level. I.C.

engines are usually heavier and for reasons of balance and operator comfort these are usually mounted on the opposite end of a drive shat't tube from the cutter head.

I'here is usually a guard above the rotating cutter head that is designed to protect the operator from the head and also from any flying debris. The shape of the guard varies with different models and some are adjustable.

ivVhen using a vegetation cutter such as a rotary dine trimmer or rotary disc trimmer, the main restriction on the cutting rate, apart From the inherent power of the machine, is the maximum rate at which the weeds can be severed without the stalks or stems becoming wrapped around the rotating parts or trapped against the guard. This problem is inherent in both petrol and electric devices despite their slightly different configuration. The trapping of unwanted material results in the effective rate of cutting being significantly lower than the rate dictated by the maclline's power and cutting capacity.

Stalks carried up to the top of the cutter head should fall away but frequently they wrap around the top of the cutter head and/or around adjacent stationary components. Such a build up of material inevitably leads to interference with the rotation of the cutter head and the machine eventually stalls or its clutch disengages. The machine then has to be stopped so that the offending material can be removed. This procedure can be not only time consuming but also dangerous as there is the risk that the machine may be inadvertently re-started while the operator's hand is in the vicinity of the cutter head.

Tile cut vegetation can also accumulate against the guard and cause problems in use. Again., the device has to be stopped so that the offending material can be removed.

The faster the device is traversed, the more likely it is that one or both of these problems will occur. louse problems thus limit the speed at which the vegetation can be cut.

l IS 5,4] 4,934 discloses a vegetation cutter apparatus having a drive motor which drives a cutter head via a drive shaft within a guide tube. As with most prior art vegetation cutters, although part of the shaft is covered with a collar, vegetation can still be wrapped around the static part of z drive shaft housing leading to a rotatable part of the cutting head and the drive shaft.

US 4,817,738 discloses a portable hand-held motor-driven tool in the form of a rotary line trimmer with a conical housing and shaft cover. It is believed that this arrangement would reduce accumulation of the cut vegetation but would not altogether prevent it.

It is an object of the present invention to provide a rotary vegetation cutter which is capable of preventing or reducing the accumulation of cut vegetation in the vicinity of the cutter head.

In accordance with the present invention, there is a vegetation cutter comprising a rotary cutter head rotatably mounted upon a housing and having means for cutting vegetation and a power drive arranged to rotationally drive the cutter head, wherein at least one static coder is provided for cutting vegetation entrained by the cutter head and so preventing or reducing accumulation of vegetation in the vicinity of the cutter head.

A specific embodiment ofthe present invention will now be described, by way of example only, with reference to the accompanying figures, in which: Figure I is a perspective viewer of the cutter head and adjacent parts of a rotary vegetation cutter embodying the present invention; Figure 2 is a perspective view of a static cutter part used in the rotary vegetation cutter of Figure 1; and [Figure 3 is a perspective view of the cutter head and adjacent parts of a second v egetation cutter embodying the present invention.

The general construction of a rotary line trimmer is very well nOWi1 arid only selected components are illustrated. Certain components are common to the embodiments shown in Figures 1 and 3 and these are given the same rel'erence numerals in both drawings. The ii]ustrated machines use a petrol engine (not show/e) carried at an upper end of a tube whose lower end is seen at 10 in Figure 3 and which serves to house a drive shaft (concealed within the tube 10 and so not shown) driven by the engine. Bevel gearing (not shown) in a gear housing 12 transmits drive to a rotary cutter head 16 journalled upon the gear housing 12. The tube 10 leads, in an upper region, to an elongate handle portion which allows the user to present the cutter head to vegetation at ground level without stooping. The cutter head 16 contains a reel (not shown) on which is wound a flexible plastics line whose ends 18,20 protrude from the head and carry out the actua] cueing of vegetation. Such general constructional aspects of line cutters are very well lcnown and need not be described in more detail herein.

In Figure 1 it can be seen that this particular cutter head is shaped to form a discoidal portion] 4 at its upper extremity. Immediately above this is an exposed flange portion 22 of the gear housing 12. In use of conventional machines cut vegetation, particularly long pieces such as stems, tends to collect in this region.

The action of the rotating cutting head can cause them to be tightly wound around the stationary flange portion 22. Material accumulated in this region presses against the cutter head and the friction created can slow or even stop the cuber head, forcing the user to break off work periodically' to clear the accumulated material.

This problem is addressed by provision of a static cutter 24 mounted alongside the rotary cutter head 16 and serving to reduce the accumulation of cut material. The static cutter is disposed adjacent to and radially outward of tile rotary cutter head so that cut material is passed over the static cutter by the action of the rotating head and is thereby severed. In the illustrated arrangement the static cutter 24 can be seen to be adjacent the region where the rotary cutter head meets ille stationary gear housing i2 on which ii is journailed, since it is in this region that material tends to acc,-nulate. Clearance between the static cutter and the adjacent circumferential surface of the rotary cutter head 16 is kept to a Inini,llum to prevent cut material from getting between the static cutter and the rotary cutter head. 'J'l1e static cutter 24 has a sharp, static cutting edge 26 which extends along a direction generally parallel to the rotational axis of the rotary cutter head, so that it is roughly perpendicular to the direction of travel of material such as stems caught up with the rotary cutter head 16. 'I'he fact that the cutting edge is perpendicular to the steins means that they present the smallest possible cross section to the blade to facilitate cutting.

It will be observed in Figure I that the static cutting edge 26 is in this embodiment directed radially outwardly. That is, the edge 26 faces away from the axis of the rotary cutter head. The inventor has established that this provides particularly effective cutting of stems and other material caught up with the cutter head. Experiment suggests that the cutting edge need not face precisely along a radius but that it should face away from the axis, in the sense that it is inclined outwardly from the tangential direction. 'I'he angle of inclination may be user adjustable, e.g. to maxi,nise effectiveness for different types of vegetation, and could even be indexed so that selected angles only are available.

The shape of the static cutter is best seen in Figure 2. In the present crnbodin1ent it is of triangular section, one edge (or vertex) being sharpened to serve as the cutting edge 26. In the present embodiment the other two edges are rounded although in production versions it would be possible to sharpen these edges as well so that by rotating the static cutter through 120 degrees a new cutting edge would be brought into use. 'Pine static cutter could in practice take other forms. It could for example be of square section, a sharpened vertex again forming the cutting edge.

In the iiirstraied embodiment the static cutter 24 is metal and is conveniently;nounted on a flaIlge 28 of the gear housing by mealas of a through going screw 30.

Turning now to Figure 3, it can be seen that the rotary cutter head 16, gear housing 12 and related parts are formed as in the Figure 1 embodiment. The static cutter 24 is also provided. Figure 3 shows a shaped guard 31 of a type which is in itself conveilticonal, forming a shroud which in use comes between the user and the rotary cutter head 16. Such guards are typically part circular and are shaped to provide a depending lower flange. Elongate pieces of vegetation such as stems can collect on the guard, particularly upon its leading edge (witll respect to the rotating cutter head). This problem arises particularly with stalks long enough that part of the stalk goes over the guard while the rest goes underneath it.

I'he machine has been modified to avoid or at least alleviate this problem by provision of a static blade 32 arranged to sever material above the cutter head.

Tile static blade 32 is arranged at the level of the guard's leading edge 34, so that long stems dragged around by the rotary cutter head whicl1 could othe,^wise be; trapped on or under the guard are instead severed by the blade 32 allowing the stalks' bottom sections to pass beneath the guard and their top sections to pass over it and be shed. The blade 32 has a sharpened edge 34 which lies in or at some small angle to a plane which is radial with respect to the axis of tile rotary cutter 16 It extends along a direction which is generally radial to the axis, although again some deviation from a true radial direction need not impair the blade's function and it can be appreciated from the drawing that the line of the edge 34 does not precisely intersect the axis. Since most cutter heads rotate anti-clockwise, the blade 32 is on the left hand side of the guard, as viewed from above. In the illustrated embodiment the blade 32 is simply bolted at 36 to the guard, so that it is easily removable for sharpening, but other modes of attachment may be appropriate to a lrouuc;iion version.

The static cutter 94 and/or the blade 32 may be retrofitted to fun existing vegetation cutter, and may he sold as a retro-fit kit. Either one of these parts may he used in combination with the other or on its own. Design differences from one vegetation cutter to another may result in the design and mounting of the cutter and blade being adapted from that of the examples illustrated herein. While the above examples show the invention implemented in connection with a line trimmer, it will be apparent that the invention is equally well suited to implementation in brush cutters or other types of disc trimmer.

Claims (11)

1. vegetation cutter comprising a rotary cutter head rotatably mounted upon a housing and having means for cutting vegetation and a power drive arranged tc'roiationaily drive the cutter need, wherein at icast one static cutter is provided for cutting vegetation entrained lay the cutter head arid so preveiltiilg or reducing accumulation of vegetation in the vicinity of the cutter head.

2. A vegetation cutter as claimed in claim I which is a line trimmer or brush cutter.

3. A vegetation cutter as claimed in claim I or claim 2 wherein the static cutter is disposed adjacent to and radially outward of the cutter head.

4. A vegetation cutter as claimed in any preceding claim wherein the static cutter has a clotting edge which extends in a direction substantially parallel to the rotary cutter head's axis.

5. A vegetation cutter as claimed in any preceding claim wherein the static cutter has a cutting edge which faces away from the rotary cutter head's axis.

6. A vegetation cutter as claimed in any preceding claim wherein the static cutter is arranged to overlap a region where the cutter head adjoins a stationary housing part.

7. A vegetation cutter as claimed in any preceding claim wherein the static cutter is disposed immediately adjacent a radially outer surface of the cutter head.

8. A vegetation cutter as claimed in any preceding claim wherein the static cutter is mounted upon the housing.

9. A vegetation cutter as claimed in any preceding claim which comprises a guard in the vicinity of the cutter head and a further static cutter lying substantially in a radial plane and serving to cut vegetation entrained by the cutter head and so prevent or reduce accumulation of vegetation within the guard.

10. A vegetation cutter as claimed in claim 9 wherein the further static cutter lies substantially in a common radial lane with a leading edge of the guard.

11. A vegetation cutter substantially as herein described with reference to, -; and as illustrated in, the accompanying drawings.