Field of the invention

The present disclosure relates to an electrically powered vegetation cutter, compris- ing a shaft tube, a cutting implement at a bottom end of the shaft tube, a top housing at a top end of the shaft tube, and a handle arrangement. The handle arrangement is connected to the shaft tube at a location in between the cutting implement and the top housing, and the vegetation cutter comprises an electric motor configured to drive the cutting implement and a battery configured to supply power to the electric motor. Technical background

Such a vegetation cutter is disclosed for instance in WO-201 1/005156-A1 . One problem associated with such cutters is how to make them more suitable for professional use.

Summary of the invention One object of the present disclosure is therefore to provide a vegetation cutter which is more suitable for use professionally. This object is achieved with a vegetation cutter as defined in claim 1. More specifically, in a vegetation cutter of the initially mentioned kind, the top housing comprises at least one of the electric motor and the battery. The handle arrangement comprises a connector link, which at a first end is connected at the top housing via a pivotal connection and at second end is

connected to the shaft tube, at a distance from the top housing and via a resilient element. The vegetation cutter further comprises a handle bar comprising a first and a second handle, which are attached to the connector link.

In such a vegetation cutter, vibrations originating from the cutting implement must propagate through the shaft tube, via the upper housing and the connector link to reach the handles. With the well-defined mass determined by the electric motor and/or the battery and the elastic suspension of the handles in relation to the upper housing, there is provided a very effective dampening effect on the vibrations, particularly for higher frequencies that do not easily influence the motor/battery mass. This reduces vibrations experienced when holding the vegetation cutter in the handles and makes the vegetation cutter more suitable for long-term professional use. The connector link may be configured to surround the shaft tube which provides for a both strong and compact structure.

Both the electric motor and the battery may be located in the top housing, which provides for a both considerable and well-defined mass providing substantial dampening of vibrations.

The connector link may be connected by means of a resilient element in the form of at least one spring to a shaft collar which is firmly attached to the shaft tube. This provides a reliable connection point at the shaft tube.

The connector link may be connected to the top housing by means of a pivotal connection in the form of one or more bushings.

The rotating mass of the vegetation cutter may be higher below the point of the shaft tube where the resilient element is connected than above the same.

Brief description of the drawings

Fig 1 shows a vegetation cutter according to the present disclosure.

Fig 2 illustrates schematically the operation of a vibration reducing arrangement according to the present disclosure.

Fig 3 shows an exploded view of the handle arrangement of the vegetation cutter in fig .

Detailed description

One example of a vegetation cutter 1 according to the present disclosure is shown in fig 1 . The vegetation cutter 1 comprises a cutting implement 3 attached to a bottom end of a shaft tube 7. In the illustrated case, the cutting implement 3 is a cutting wire intended to cut for instance grass. It is however possible to replace the cutting wire with a clearing saw blade or similar, and the vegetation cutter may be devised as a trimmer, a brush cutter or a clearing saw depending on the cutting implement used as well as the desired use of the vegetation cutter. A screen 9 may be provided at the cutting implement 3 to protect a user from debris.

A top housing 5 is located at a top end of the shaft tube 7 and may comprise either or both of an electric motor 1 1 and a battery 13 supplying electric power to the electric motor 1 1 . A handle arrangement 15 is provided comprising first and second handles 17, 19, either of which may as shown be provided with control devices, such as a throttle controlling the motor, and the like.

In the present disclosure, the handle arrangement 15 is devised to reduce vibrations induced in the device by the cutting implement's 3 operation. While there exist anti- vibration solutions for non-electric vegetation cutters, such solutions have been adapted to minimize the transfer of vibrations from a combustion engine to the handles held by the user. Electric motors on the other hand produce comparatively negligible vibrations. In the present disclosure, the motor and/or battery 1 1 , 13 in the top housing 5 is instead used as a dampening mass that serves to reduce vibrations travelling from the cutting implement at the bottom end of the shaft tube 7 to the handles 17, 19 held by the user.

Although the most significant top housing mass is provided when both the battery 13 and the motor 1 1 are located in the top housing 5, also including only one of those items in the top housing would provide a dampening effect. This may be the case if for instance a large backpack battery is used and only the motor is located in the top housing, or if the motor is located at the cutting implement and only the battery is placed in the top housing.

A vibration reducing arrangement is schematically illustrated in fig 2. The handle arrangement 15 comprises a connector link 21 , which at one end is connected to or at the top housing 5 via a pivotal connection 23 and at or close to another end is connected to the shaft tube 7, at a distance D from the top housing 5, via a resilient element 25. The connector link 21 may be made in one piece, for instance in a magnesium alloy, which may be cast and is both light and strong.

Typically, as will be shown in greater detail, the pivotal connection 23 may be a rubber bushing connected to the top housing 5 or to the shaft tub 7 next to the top housing. The resilient element 25 may be a spring connected to a shaft collar attached to the shaft tube 7. The distance D may typically be in the range between 35 and 50 cm although not limited to this range. The handle bar comprising the first and second handles 17, 19 may be attached to the connector link 21 . With this arrangement, the mass located in the top housing will function as a vibration isolator, dampening vibrations that propagate from the cutting implement 3 towards the handles 17, 19. Thanks to the use of an electric motor 1 1 and/or a battery 13 in the housing, this mass will be more or less constant during use, which means that the connector link 21 length and the dynamic properties of the resilient element 25 may be adapted to carry out vibration dampening in a desired way with respect to predicted vibration frequencies produced by the working cutting implement. This is in contrast to for instance a combustion engine where the weight of a petrol tank will fall during use as petrol is consumed. Further a liquid fuel will function in an unpredictable way as it can move in the tank.

With the presently disclosed arrangement it is even possible to devise the mass of the top housing as a frequency adapted spring mass system that cancels specific frequency vibrations by resonating out of phase therewith as is known per se.

Fig 3 shows an exploded view of the handle arrangement 15 of the vegetation cutter in fig 1 . As shown, the connector link 21 may be a hollow element through which the shaft tube 7 runs, although other configurations are possible such as locating the connector link on the upper side of the shaft tube 7. The shown configuration how- ever, is compact, provides a significant second area of moment, i.e. is strong, and still allows the connector link 21 to move in relation to the shaft tube 7 and vice versa. There is thus provided a play between the shaft tube 7 and the connector link 21 .

In the illustrated case, the connector link 21 at one end is attached to the top housing 5 by means of two bushings providing the above-mentioned pivotal connection 23. It would of course be possible to use a different number of bushings. It would also be possible to attach the connector link to the shaft tube 7 or an intermediate member connected to the shaft tube 7 at a location close to the top housing 5. Typically, the pivotal connections 23 are attached to a motor bracket 29, which is also used as a base for the electric motor. The motor bracket 29 in turn may be firmly attached to the shaft tube 7.

At the other end, the connector link is attached, via two springs forming the above- mentioned resilient member 25, to a shaft collar 27 which in turn is firmly attached to the shaft tube 7. Needless to say, one or more than two springs may be used to this end, and other forms of resilient members would be possible. The handles 17, 19 are attached to the connector link 21 by means of an intermediate bar 31 which is firmly connected to the connector link 21 at the lower end thereof. Other handle configurations may be possible as well. With this general configuration, vibrations originating from the cutting implement can to a great extent be prevented from propagating to the handles 17, 19 which improves the working conditions for the user who is subjected to less vibrations. This particularly advantageous in professionally used vegetation cutters that are used long hours for instance maintaining parks or recreational areas.

If a dominant vibration frequency can be predicted, the mass-spring system can be tuned to dampening this frequency in particular. For instance, a three-teeth brush cutter rotating at 700 rpm will produce a dominant 2100 Hz vibration, and the spring- mass system can be tuned to dampening this frequency in particular, as is well known per se. The rotating mass of the vegetation cutter may be higher below the point 33 (cf. fig 2), where the resilient element 25 is connected to the shaft tube 7, than above this point and still provide a useful dampening of vibrations.

The terms 'top' and 'bottom' as well as 'upper' and 'lower' as used herein refer to the normal use of the vegetation cutter where cutting implement 3 at the bottom end of the shaft tube 7 is close to the ground and the top housing 5 is not.

The present disclosure is not limited to the above described examples, and may be varied and altered in different ways within the scope of the appended claims.