GB2048751A - Pruning Device - Google Patents

Abstract

A pruning device for pruning trees comprising a spring loaded telescopic arm (1) terminating in a fixed cutter (7) and a power transmission linkage (16, 14, 19) for transmitting a multiple of the pulling force applied to the arm (1) to a movable cutter (11). The movable cutter (11) is supported and guided in a slide assembly (13) to slide substantially axially along a body (8) of the fixed cutter (7) moving towards the cutting edge of a fixed jaw (9) so as to provide an equal force over its entire width. <IMAGE>

Description

SPECIFICATION Delimber The present invention relates to a manually operated delimber, comprising a cutting means, telescopic arm and power transmission linkage.

The device is mainly intended for delimbing of standing trees.

In the present wood production pruning of growing trees is an important step which guarantees that quality wood will be available even after thickly grown and self-pruned natural woods are finished. Major trees are pruned at as early stage as possible to a level that corresponds to the length of a future root log. To make delimbing serve its purpose providing quick healing limb cuts without rot infections, it is necessary according to scientific studies that the tools employed permit delimbing exactly along the trunk without, however, damaging the bark.

The tools should further be easy to operate and effective.

Prior art delimbers and scissors, fitted with a telescopic arm and power transmission linkage (e.g. Finnish patent application 781340 and Finnish patent 47246), differ in principle from the present invention in the sense that the prior art devices have a cutter, driven by a power transmission means, pivotably journalled to the body of a fixed cutter.This solution is above all impaired by'the following drawbacks: (a) Small twigs, which during the pruning step are forced near the fulcrum of the cutters, i.e. to the bottom of the gap, receive more cutting force than the thick limbs which stay further away from the fulcrum of the cutters, i.e. at the mouth of the gap, and (b) The power transmission linkage, which should move freely during delimbing, is disposed at such a high level that it often gets entangled in neighbouring branches, since tree branches usually growing in layers, in so-called "limb circles".

According to the present invention there is provided a delimber, comprising a spring-loaded telescopic arm terminating in a fixed cutter at its top end, and a power transmission linkage for transmitting a multiple of a pulling force applied to the telescopic arm to a movable cutter which is supported and guided by a slide assembly so as to slide substantially axially along a body of the fixed cutter, and, during the working stroke, moves towards a cutting edge of a fixed jaw so as to provide an equal force over the entire width thereof.

Thus, the present invention is characterized in a movable cutter, supported and guided by a slide assembly, is adapted to slide substantially axially along the body of a fixed cutter in such a manner that, during the working stroke, it pushes its way towards the cutting edge of a fixed jaw with equal strength over its entire width.

In a preferred embodiment of the invention, the short, and thus powerful, moment of a lever arm develops continuously increasing force as the working stroke progresses. The lever arm and a connecting bar journalled thereto are preferably completely disposed below the working level of the delimber.

In addition, this design permits the use of thin, one-sidedly sharpened cutters which cut in alignment with each other with cutting edges opposite to each other and in the lateral plane of the device, so the present delimber meets all the demands on quality for the delimbing work but, above all, the present invention eliminates theefficiency drawbacks of the prior art equipment.

Embodiments of the present invention will be described by way of example with reference to the accompanying drawings, in which: Figure 1 shows a side view of an embodiment of the present invention, and Figure 2 illustrates the operation of the embodiment shown in Figure 1.

A telescopic arm 1 comprises an outer sleeve 2 slide-fitted with an inner pipe 3. Within the telescopic arm 1 is located a spiral spring 4 secured to the inner pipe 3 by means of a pin 5 and to the outer sleeve 2 by means of a pin 6. The top end of the inner pipe 3 comprises a fixed cutter 7 consisting of a body 8 and a jaw 9 which is bevelled or sharpened on one side so that its cutting edge 10 lies in the lateral plane of the device. A movable cutter 11, which is correspondingly sharpened so that its cutting edge 12 lies in alignment with that of the fixed jaw, is mounted on the body of the fixed cutter by -means of a slide member 13.Power transmission linkage comprises a lever arm 14 pivotably journalled to the body of the fixed cutter by means of a link 15, an intermediate arm 16 journalled to the lower end of the lever arm 14 (as close to point 1 5 as possible) by means of a link 17 and to the movable cutter 11 by means of a link 18, as well as a connecting bar 19 journalled to the upper end of the lever arm 14 by means of a link 20 and to the outer sleeve 2 of the telescopic arm 1 by means of a link 21. The cutting edges of the cutters cannot touch each other the downward movement of the lever arm 14 being stopped by abutment of the rear of the lever arm against an adjustable limiter 22.

The operation ofthe delimber is shown in Figure 2. The fixed jaw 9 is positioned on a limb so that the cutting plane of the cutters lie against the trunk. Pulling the telescopic arm 1, produces a pulling motion force which is multiplied and transmitted through the linkage to the movable cutter 11 which simultaneously both squeezes and severs the limb against the cutting edge of the fixed jaw 9 which, thus, also participates in the actual cutting operation Since the delimbing is effected simultaneously from two opposite sides, a falling limb cannot tear the bark of the trunk.

When the working stroke is finished, the limiter 22 prevents the cutting edges from touching each other and the spring 4 in the telescopic arm 1 returns the moving parts to their initial positions.

Since the design permits the use of a very effective transmission ratio which, in addition, gains in strength as the working stroke progresses and since the push force is the same over the entire width of the movable cutter, even thicklimbs can be severed easily. In addition operation of the delimber is trouble-free since, by virtue of its low position, the power transmission linkage will not be entangled in neighbouring branches.

By fitting the delimber with an extension delimbing at even a higher level can be effected just as easily.

The delimber can also be used for clearing minor trees and for thinning of plants up to the thickness that fits in the gap of the delimben

Claims (4)

Claims

1. A delimber, comprising a spring-loaded telescopic arm terminating in a fixed cutter at its top end, and a power transmission linkage for transmitting a multiple of a pulling force applied to the telescopic arm to a movable cutter which is supported and guided by a slide assembly so as to slide substantially axially along a body of the fixed cutter, and, during the working stroke moves towards a cutting edge of a fixed jaw so as to provide an equal force over the entire width thereof.

2. A delimber as claimed in claim 1, wherein the short, and thus powerful moment of a lever arm produces a continuously increasing force as the working stroke progresses.

3. A delimber as claimed in claim 1 or 2, wherein the lever arm and a connecting bar journalled thereto are located -entirely below the work level of the delimber.

4. A delimber substantially as herein described and as illustrated in the accompanying drawings.