Cutlery – Cutting tools – With blade moving means
Patent
1996-12-12
1998-09-22
Watts, Douglas D.
Cutlery
Cutting tools
With blade moving means
30347, A01D 3467
Patent
active
058096558
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to an apparatus for cutting of plants and, more particularly, to an apparatus for cutting of plants having at least one free end of a cutting filament which rotates about a rotational axis and protrudes radially outward from it, defining a cutting plane, and which forms a winding in a winding chamber of a spool, which chamber is defined by axially spaced-apart disks disposed on a central hub; a cup nonrotatably mounted on a drive shaft in which the spool is rotatably mounted and which is provided with at least one throughgoing opening through which the cutting filament passes radially, the cutting filament being readjustable to a certain predetermined length, especially when wear has shortened it.
An apparatus for cutting plants, in which a spool that carries a cutting filament has a flexible strip, on its circumference, that is embodied as a closed ring, is described in German Utility Model DE-GM 69 38 265. The closed ring loosely surrounds the cutting filament winding and is spaced apart radially from it. The ring has a continuous radial opening whose edge closely surrounds the cutting filament passed through it. The task of the ring is to prevent independent unwinding of the cutting filament, and especially of its free end, from the spool and to prevent slipping radially back into the winding chamber, so that a length of cutting filament always protrudes radially out of the spool and is accessible to manual or automatic length adjustment.
The closed ring can be slipped on the spool only axially, but not radially, and the cutting filament must be threaded relatively inconveniently through the central opening of the ring. The ring does not rest directly on the winding and under tension, but instead is braced on the spool body.
U.S. Pat. No. 4,104,796 discloses another apparatus for cutting plants, in which the length of the free end of the cutting filament is automatically regulated by centrifugal force.
When the cutting filament rotates, that is, when the engine is running, the centrifugal force regulation begins whenever a portion of the free end of the cutting filament is torn off because of wear. The shortening of the cutting filament changes the airflow resistance and the mass moment of inertia of the spool, and correspondingly its rpm, as well. The increased centrifugal force then acts on the free end of the filament, pulls the cutting filament radially outward and seeks to rotate the spool relative to the housing. This trips centrifugal force-actuated locking means, which release the spool from its surrounding housing, so that the spool can rotate relative to the housing by a certain angular amount. This rotation lengthens the free end of the cutting filament radially outward. These steps of automatic readjustment of the cutting filament are repeated as often as needed until the free end of the cutting filament reaches a certain specified minimum length. At this minimum length, the mass inertia and air flow resistance are so great that the rpm drops, and consequently the centrifugal force is too slight to release the locking means.
In the automatic readjustment of the filament, unintended changes in the moment of mass inertia of the filament spool can impede readjustment of the cutting filament. This can happen for instance if, because of the change in rpm, the spool winding shifts in the winding chamber, in other words shifts radially or axially, during the filament readjustment. As a result, the mass distribution on the spool changes. Moreover, under some circumstances, some layers of the spool winding can become jammed, so that the cutting filament cannot be readjusted at all or only with insufficient length. This makes the cutting performance of the apparatus unsatisfactory.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an apparatus for cutting plants of the above-described type, which does not have the above-described disadvantages.
According to the invention the apparatus for cutting plants comprises a spool
REFERENCES:
patent: 4202094 (1980-05-01), Kalmar
patent: 4490910 (1985-01-01), Mattson et al.
patent: 4640084 (1987-02-01), Baba
patent: 4866846 (1989-09-01), Hoffmann et al.
patent: 5020223 (1991-06-01), Desent et al.
patent: 5461787 (1995-10-01), Araki et al.
Houben Jan P.
Jung Bob
Robert & Bosch GmbH
Striker Michael J.
Watts Douglas D.
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