IMPROVEMENTS RELATING TO MOWING DEVICES

Abstract: A cutting head for a rotary mowing device incorporating a flat flail strip (7) which is wound onto a drum (20). The strip then leads past a reaction block (25) and is fed out through a pivotally mounted bush (26) which causes the strip to be twisted so that it lies substantially in the plane of rotation of the cutting head.

Description: "Improvements relating to mowing devices" This invention relates to mowing devices incorporat¬ ing a rotary head carrying projecting blades or flails. Such devices are used for conventional mowing or trimming for grass, weeds and other vegetation. Some such mowing devices are also called brush cutters. One type of rotary mowing device incorporates cord-like flails / made for example from round section nylon line. Cord-like flails have their limitations. A line of small cross-section has a low mass and therefore is easily deflected so that uneven cutting or severing often results giving a beaten down appearance to the vegetation. The flail ends also tend to wear or split away at a rapid rate requiring constant replacement. If a line of greater cross- section is used the increase in the cutting face presented to the vegetation requires a corresponding increase in the motive power to keep the cutting head revolving at the desired speed. Another type of mowing device incorporates mounted independent blades made from plastic (or possibly metal) . These blades have to be manufactured with a retaining portion to be fitted on a mounting member on the cutting head. The retaining portion has to be suitably robust and hence adds significantly to the weight of the blade. In addition as the blade wears away at its tip the optimum performance is diminishe both because of loss of mass and the resulting reduced diameter of the cutting swathe. Typically about two-third of the blade will be discarded when it comes to the end of its useful life and so the device has- a relatively expensive running cost. Furthermore the cutting head has to, be dismantled to enable the new blade to be fitted which is inconvenient. It is an_object of this ' invention to provide a cutting device which incorporates many of the advantages of the devices discussed above but avoids at least some of their disadvantages. Accordingly this invention provides a mowing device comprising a rotary cutting head within which is-stored a coiled length of a flat flail strip, a terminal portion of the strip passing through a bush so as to project beyond the circumference of the cutting ead, the passageway through the bush being formed to impart twist to the strip so that the edges of the projecting portion of the flat strip lie substantially in the plane of- rotation of the cutting head, and wherein the bush is pivotally mounted within the cutting head about an axis which is generally parallel to the axis of rotation of the cutting head. The rigidity achieved by using a flat flail strip results in a very acceptable cutting action whilst avoiding the provision of a substantial cutting face so that the resistance to movement of the strip is kept low. Further more since the strip is stored in a coil within the cutting head the strip can be pulled out continually to replace worn tip portions of the strip so that the amount of strip ultimately discarded is only a small proportion of the original length of strip. It is much preferred that the coiling axis of the strip should lie. parallel to or concentric with the axis of rotation of the cutting head and the strip is twisted through 90° by the body of the cutting head. In the preferred arrangement the bush will have rounded or flared bearing surfaces at the entry and exit ends for the strip, which will minimise the effects of wear on the strip. Ideally also the strip will project through a circu ferentially defined slot in the cutting head providing clearance for movement of the strip about the pivot point for the bush. A deflector portion can project from the bush outwardly of the cuttinghead along the trailing edge of the strip, which can direct cut grass into a collecting box. Another desirable feature is to provide that the weight of the bush is substantially balanced about its pivot point. In one preferred arrangement means will be included for releasably clamping the strip within the cutting head. The strip will ideally pass around a reaction block between the clamping means and the bush. In this construction the cutting head may comprise top and bottom sections secured together by releasable fixing members to grip the strip against movement between the two sections. In an alternative arrangement a clutch mechanism may be included for allowing the strip to be fed automatically or semi-automatically from the cutting head. The clutch mechanism could comprise complime tarily interlocking parts which can- be released from one another to allow rotation of a drum holding the strip with respect to the body of the cutting head. Thus the drum could be releasable by pressure against a spring or other biassing arrangement. The strip itself will ideally define a sharp cutting surface on at least the leading edge. Furthermore the strip may be formed with an aerofoil or other profile to cause it to adopt a predetermined attitude whilst it is being rotated by the cutting head. It is preferred that there should be two or more (preferably two) coiled strips stored within the cutting head and each having terminal portions projecting beyond the cutting head circumference. The invention may be performed in various ways and preferred embodiments thereof will now be described with reference to the accompanying drawings, in which:- Figure 1 is a perspective view of a cutting head for a mowing device of this invention; Figure 2 is an exploded perspective view of the cutting head of Figure 1 ; Figure 3 is an internal plan view of one of a pair of casing sections of the cutting heads; Figures 4 and 5 are partial sectional views in the direction of the arrows IV and V of Figure 3; Figures 6 and 7 are vertical sectional views through the upper and lower casing parts of the cutting head on lines VI-VI and VII-VII of Figure 3. Figure 8 is an overhead plan view of an alternative form of cutting head of the invention with a cover plate removed; and Figure 9 is a vertical sectional view on line IX-IX of Figure 8. The cuttinghead shown in the drawings is enclosed by two casing sections 1,2 held together. An adaptor 4 leading from the gearbox of the drive motor has a shaft 5 which passes through the two casing sections 1,2 to be fixed in place by a bolt 6, which, when tightened, clamps the casing sections 1 and 2 together. ithin the cutting head there are carried two coiled flat flail strips 7 each mounted within a -respective casing section 1,2 about a central boss 8 so that the strips 7 overlie one another. The free ends of the strip sEss around a respective reaction block 9 and are then le through bushes 10 mounted about pivots 11 within openings 3 and 12 in the casing sections 1,2 (it should be noted that Figure 3 is a diagrammatic illustration of the manne in which the two strips 7 are each held in their respective casing section 1 or 2 ) . The strip 7 passes between the reaction block 9 and a wall portion 13. When the bolt 6 passing through the sections 1 and 2 is tightened raised portions 14,15 (Figures 4 and 5) on the sections 1,2 will between them squeeze the strip 7 and thus clamp the strip against movement which would tend to draw the strip out from its coil. In Figure 3 one strip (7A) is shown in the rest condition wherein it naturally lies against the wall portion 13 and bows out around the reaction block 9. When the cutting head is rotated the strip 7 swings out and moves along a slot 16 defined between the two casing sections 1,2 until the rotating bush 10 butts up against a stop into the condition 7 (B) illustrated in Figure 3. As can be seen from Figure 3 the bush 10 causes the strip to be twisted so that the edges of the strip lie in the plane of rotation of the cutting head. Because of the pressures exerted on the strip 7- the entry mouth to the bush 10 will be flared and the rear edge at least of the exit mouth of the bush 10 will be rounded. If the rotating strip 7 should meet a rigid object it can collapse back within the circumference of the cutting head by movement along the slot 16. As the strip 7 wears away it can be replaced by a further length as necessary fed out from the cutting head by first freeing the bolt 6, so that the clamp is released. Alternative forms of clamping may be employed. For example, the strip could be clamped by a fixed spring- loaded clip or attached to a spool which itself may be fixed in a variety of ways. Another possibility is to provide a clutch mechanism which allows automatic or semi-automatic feed of the strip. A modified form of cutting head is illustrated in Figures 8 and 9. Only one flail strip 7 is illustrated but it will be appreciated that the unit could be modified to house two (or even more) flail strips. Two housing parts 17 and 18 are clamped together by screws 19 to enclose the strip 7 which is coiled onto a drum 20. A Boss 21 extends from a flange member 22 (integral with the drum 20) and through an opening in the casing section 17. A spring 23 biases the boss 21 outwardly of the casing section 17. Inter-engaging teeth are formed along thejunction 24 between the flange 22 and the casing section 17 which hold the drum 20 in a desired condition. However, if the boss 21 is pressed inwardly against the bias of the spring 23, the inter- engagement of the teeth is released and the drum 20 can be rotated to enable a further length of strip 7 to be drawn out of the cutting head. The strip 7 passes around a reaction block 25 and leaves the cutting head after passing through a pivotally mounted bush 26. The bush is so designed that its weight is balanced about the axis of its pivot pin 27 so that centrifugal force acts on the cutting strip 7 only. However, the weight could be positioned nearer to the outlet of the bush 26 which would aid in overcoming resistance to deflection of the strip 7 if the strip is formed from a particularly stiff material. Shifting the balance in an opposite direction naturally has an opposite effect. A deflect¬ ing plate 28 could be formed from the bush 26 along the trailing edge of the strip 7 to provide more support for the strip,and provide an outwardly deflecting portion 29 which could lead to a grass collecting box. This modification is shown in dashed outline. ■ Si - It is preferred that the strip should have a sharp leading edge thus reducing the motive power required to cut effectively. Furthermore desired cutting characteristics or attitudes can be achieved by choosing a. suitable profile for the strip and/or slightly modifying the angle or mannor in which the strip is held in the pivoting bush. For example the strip could be caused to project downwardly from the cutting head but have an aerofoil section which thus causes it to adopt an attitude during rotation so that it lies in the plane of rotation of the cutting head.

Claims: CLAIMS 1. A mowing device comprising a rotary cutting head within which is stored a coiled length of a flat fXail strip, a terminal portion of the strip passing thncαgh a bush so as to project beyond the circumference off tire cutting head, the passageway through the bush being formed to impart twist to the strip so that the edges of the projecting portion of the flat strip lie substantially in the plane of rotation of the cutting head, and wherein the bush is pivotall' mounted within the cutting head about an axis which is parallel to the axis of rotation of the cutting head. 2. A mowing device according to Claim 1, wherein the coiling axis of the strip lies parallel to or concentric with the axis of rotation of the cutting head and the strip is twisted through 90° by the body of the cutting head. 3. A mowing device according to Claim 1 or Claim 2, wherein the bush has rounded or flared bearing surfaces at the entry and exit ends for the strip. 4. A mowing device according to any one of Claims 1 to 3, wherein a deflector portion projects from the bush outwardly of the cutting head along the trailing edge of the strip. 5. A mowing device according to any one of Claims 1 to 4, wherein the weight of the bush is substantially balanced about its pivot point. 6. A mowing device according to any one of Claims 1 to 5, wherein the strip projects through a circumferentially defined slot in the cutting head providing clearance for movement of the strip about the pivot point for the bush. 7. A mowing device according to any one of Claims 1 to 6, including means for releasably clamping the strip within the cutting head. 8. A mowing device according to Claim 7, wherein the strip passes around a reaction block between the clamping means and the bush. 9. A mowing device according to Claim 7 or Claim 8 wherein the cutting head comprises top and bottom sections secured together by releasable fixing members to grip the strip against movement between the two sections. 10. A mowing device according to any one of Claims 1 to 8, including a clutch mechanism for allowing the strip to be fed automatically or semi-automatically from the cutting head. 11. A mowing device according to Claim 10, wherein the clutch mechanism comprises complimentarily interlocking parts which can be released from one another to allow rotation of a drum holding the strip with respect to the body of the cutting head. 12. A mowing device according to Claim 11 , wherein the drum can be released by pressure against a spring or other biassing arrangement. 13. A mowing device according to any one of Claims 1 to 12, wherein the strip defines a sharp cutting surface on at least the leading edge. 14. A mowing device according to any one of Claims 1 to 13, wherein the strip is formed with an aerofoil or other profile to cause it to adopt a predetermined attitude whilst it is being rotated by the cutting head. 15. A mowing device according to any one of Claims 1 to 14, wherein two or more coiled strips are stored within the cutting head and have terminal portions projecting beyond the cutting head circumference. 16. A mowing device substantially as herein described with reference to the accompanying drawings.

Inventors: BRAITHWAITE PHILIP WILSON, BRAITHWAITE, PHILIP, WILSON
Applicants: BRAITHWAITE PHILIP WILSON, BRAITHWAITE, PHILIP, WILSON
Application year: 1986
Main classification: A01D34
IPC codes: A01D34