1. Field of the Invention
The present invention relates to a vegetation cutting tool. In particular, the present invention relates to a powered vegetation cutting tool and more particularly to a linkage mechanism for a powered vegetation cutting tool.
2. Description of the Prior Art
Vegetation cutting tools such as pruning tools and secateurs are well known for use in cutting plant stems and trees and shrub branches There are three basic types of secateur: “anvil”, which comprise a single blade that can be moved against a fiat surface to cut a stem; “bypass”, which usually comprise a pair of blades (often just one of the blades has a cutting surface) that are operated like a pair of scissors, and which provide a shearing force to cut the stem as the blades are moved passed each other; and “parrot-beak”, which are also operable like a pair of scissors and which comprise a pair of concave blades, between which a stem can be trapped and cut.
Pruning tools may be manually operated or driven, usually by an electrical motor. Powered pruning tools operate to move at least one blade of a pair of blades between an open configuration, in which cutting edges of the moveable blade and a fixed blade are apart, and a closed configuration, in which the cutting edges of the blades abut or just pass one another. If powered cutting action is conducted in response to the actuation of an external user-control in the form of a button or trigger. When the user-control is released, the blades return to the open configuration. Typically, this is achieved by a reduction gearbox driving a partial gear segment on the moving blade.
For example, EP 803187 A2 describes a set of pruning shears which have two relatively adjustable cutting blades, one of which is secured to the housing of the shears, the other operated by an electric motor. The fixed blade is secured with a threaded spindle, a spindle nut and a displacement rod. The operation of the electric motor is controlled via a control switch with a pair of switch elements inserted in the electric motor current circuit. The spindle nut has a cam guide for control cams associated with the switch elements.
Electric scissors are also known. However, these devices operate by reciprocating the blades repeatedly to perform a sequence of cutting and opening movements. Unlike pruning tools, the scissor blades operate in a continuous manner without the need for a stop/reverse function. For example, US 2005/0160606 A1 describes a pair of electric scissors comprised of a casing, a motor, a driving disk, a crank, and a cutting unit with a pair of blades. The driving disk, crank and blades of the cutting unit are connected pivotally and eccentrically. The motor is installed with a speed change device so that the rotation speed of the motor, and thus the rotary shaft, can be reduced to provide a higher torsion force for cutting tougher objects.
Whilst the construction described in US 2005/0160606 A1 is appropriate for light duty use, its overhung loads and continuous operation make it unsuitable for pruning tools which utilise a single cutting operation that requires a far greater torsion force for the cutting operation.
The present invention seeks to overcome at least some of these disadvantages.
Accordingly, the present invention provides a vegetation cutting tool comprising a cutting head, a motor and transmission means drivable by the motor, wherein the cutting head comprises first and second cutter members having respective cutting surfaces, wherein the first cutter member is pivotably mounted with respect to the second cutter member, and wherein at least the first cutter member is drivable by the transmission means between a first angular position with respect to the second cutter member, in which a space is formed between the respective cutting surfaces, and a second angular position with respect to the second cutter member, in which the space between the respective cutting surfaces is closed, and wherein the transmission includes an engagement element associated with the first cutter member, and a crank drivable between defined first and second angular crank positions corresponding to the first and second angular positions, in which the crank is operatively coupled to the engagement means by a link.
Preferably, the transmission includes a reduction gear assembly, including an output bearing, which is drivable by the motor, and in which the crank is drivable by the gear assembly.
Preferably, the first cutter member comprises a cutting surface having a sharpened leading edge.
In one embodiment, the first cutter member is moveable in a plane parallel and adjacent to the plane in which the second cutter member lies, and is arranged to be slidably drivable over a surface of the second cutter member.
In an alternative embodiment, the first and second cutter members are arranged such that the cutting surface of the first cutter member is drivable against a cutting surface of the second cutter member.
Preferably, the engagement element has a tab formed on the first cutter member. Preferably, the link has a slot which is operatively engageable with the tab.
Suitably, the vegetation cutting tool comprises a user-control for activating the motor. Preferably, the user-control provides a non-continuous activation of the motor, in use. Preferably, the user-control is moveable between first and second positions to effect movement of the first moveable member between the first and second angular positions, and wherein release of the user-control, in use, causes the first cutter member to move to the first angular position.
Preferably, the user-control comprises a trigger. Preferably, the release of the trigger, in use, causes the first cutter member to return to the first angular position.
Suitably, the crank comprises a crank body and crank arm. Preferably, the crank body is operatively coupled to an output shaft of the motor or reduction gearbox. Preferably, the crank is operatively connected to the link such that the connection is substantially in-line with the gear assembly output bearing.
Preferably, the motor is a direct current motor.
Preferably, the vegetation cutting tool is battery-powered. Preferably, the battery is rechargeable; more preferably, the battery is a lithium-ion battery.
Suitably, the vegetation cutting tool further comprises one or more limit switches. At least one limit switch breaks the supply of power to the motor when the at least one of the cutter members has moved from the first angular position to the second angular position, in operation. Preferably, the one or more limit switches enable a short circuit across the motor terminals when the at least one of the cutter members has moved from the first angular position to the second angular position, in use. Preferably, the one or more limit switches activate relays to make or break the motor electrical connections, in use. Preferably, two relays are activated, in use. Preferably, the two relays are formed as a single twin-relay component.
Preferably, the gearbox is an epicyclic unit mounted coaxially to the motor. Suitably, the gearbox has a reduction ratio of between 300:1 and 700:1; preferably, between 400:1 and 600:1; more preferably about 516:1. Preferably, the reduction is carried out by means of a four stage assembly.
Suitably, the first cutter member is pivotably mounted with respect to the second cutter member by a pin and pivot bush. Preferably, the first cutter member is demountable. Suitably, the first cutter member is demountable by means of disengagement of the engagement means from the link, and by removal of the pin and pivot bush.
Preferably, the link is retained in position when the first cutter member is removed. Preferably, the cutting head comprises a linkage mounting moulding having a channel, and the link is moveable within the channel, to retain its position relatively with the linkage mounting moulding. Suitably, the link further comprises an integral link tab, formed therewith, and the link tab is moveable within the channel in the linkage mounting moulding.
Preferably, the link comprises a link aperture at an operatively upper end which is rotatably engaged with the crank to provide a mechanical engagement between the link and crank.
Preferably, the cutting head and transmission is formed as a single working unit.
Suitably, the pin is a screw or threaded fixing, such as a bolt.
The above and other aspects of the present invention will now be illustrated in further detail, by way of example only, with reference to the accompanying drawings in which:
Referring to
Moveable cutter member 15 includes a sharpened leading or cutting edge 23 and is pivotally drivable, in use, between retracted and extended positions by a motor (24 in
In use, the action of driving moveable cutter member 15 towards the fixed cutter member 20 and particularly its unsharpened leading edge 54 of the fixed cutter member (
In the illustrated embodiment, the fixed cutter member 20 is not moveable. However, in alternative embodiments (not shown) second cutter member 20 is reciprocally drivable relative to the moveable cutter member 15.
As can be seen most clearly in
As best shown in
In
The gear assembly, incorporating the output shaft end bearing 55 is housed within the linkage mounting moulding 60 to provide the ‘self-contained’ unit. Furthermore, the linkage mounting moulding 60 includes a groove or channel 37 in which a portion of the link 34 is moveable, and which restricts the range of movement of the link 34, during normal operation. In preferred embodiments, link 34 comprises a protrusion or link tab 36 which is moveable within channel 37 of the linkage mounting moulding 60.
Accordingly, in use, rotation of crank 30 by means of motor 24 causes link 34 to move in an upwards direction (in terms of the orientation shown in the Figures). As a result, the link 34 acts on the moveable cutter member 15, through the slot-tab engagement, to cause moveable cutter member 15 to rotate about the pivot point.
The offset formed between crank body 31 and crank arm 32 has the effect that its engagement with the link 34 is substantially in-line with the gearbox output shaft end bearing 55. This arrangement reduces the occurrence of bending loads on the gearbox output shaft and removes the need for additional load-carrying bearings.
Moveable cutter member 15 also includes profiles 44, 44′ which, in use, sequentially actuate a pair of electrical limit switches 45, 50 located on or adjacent plate 16, in response to the moveable cutter member being moved between retracted and extended positions. In particular, when the moveable cutter member is moved between the two positions, the profiles act upon electrical limit switches 45, 50 to indicate to the pruner control electronics (omitted for clarity) that the cutter member has reached the respective fully retracted or extended position. This causes the power supplied to the motor to be switched off, suitably, by means of electrical relays (not shown). Preferably, when the power to the motor is switched off a short-circuit is also applied to the motor terminals to provide a rapid braking effect upon the cutter member.
A limit to the angular movement of crank 30 is provided by mechanical means, in this case by contact between the crank and a linkage mounting moulding of the pruner (not shown). In preferred embodiments, movement of the link 34, and thus the crank 30 and moveable cutter member 15, is restricted due to the constraints imposed by the operative engagement of the integral link tab 36 of link 34 within channel 37 provided in the linkage mounting moulding (
Referring now to
The angular movement of crank 30 is also restricted by further mechanical means, such as by contact between the moving blade and the linkage mounting moulding of the pruner adjacent to the tab 40 (not shown). Alternative assemblies such as engagement of a portion of link 34 and the linkage mounting moulding surface around the gearbox output shaft end bearing 55 can be used.
As illustrated in
A further advantage of the described linkage mechanism is that the moveable cutter member 15 is easily demountable for sharpening or replacement. As shown in
The linkage mechanism provides a low cost, compact and mechanically efficient design. It is especially suitable for application in portable battery-powered tools, such as pruners, in which the mechanism forms a self-contained working element formed around and located to a linkage mounting moulding within the moulding of the case in which the pruner is housed.
The pruner is ideally powered by one or more lithium-ion cells 51, due to their relative lightness in weight. The high efficiency of the mechanism means that the pruner tool can even be used with a single battery cell for cutting material up to 14 mm in diameter. For example, a suitable battery cell of 3.6 Volt, 1.3 Ah could achieve around 400 cuts of 12 mm diameter vegetation before recharging was required. In preferred embodiments, control electronics for the motor and or limit switch operations are also utilised to provide lithium-ion battery monitoring and controlling functions. For example, it may be desired to disable operation of the motor in the event that the battery becomes discharged below a pre-selected voltage or its temperature exceeds a predefined limit.
The foregoing relates to the preferred exemplary embodiments of the invention, it being understood that other variants and embodiments thereof are possible within the spirit and scope of the invention, the latter being defined by the appended claims.
Number | Date | Country | Kind |
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08105135.1 | Aug 2008 | EP | regional |
This application is based on EP Application No. 08105135.1 filed Aug. 26, 2008.