Harvesters – Motorized harvester – Including cutter yieldably mounted on its drive means
Reexamination Certificate
1999-12-07
2002-03-05
Pezzuto, Robert E. (Department: 3671)
Harvesters
Motorized harvester
Including cutter yieldably mounted on its drive means
C172S017000
Reexamination Certificate
active
06351930
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to flexible flail trimmers for trimming and edging and cutting grass and weeds and other vegetation. More particularly, the invention is directed to a flexible flail apparatus which can be used both for general trimming and for producing a straight, consistent edge in, for example, a lawn adjacent a sidewalk, drive, or other pavement.
BACKGROUND OF THE INVENTION
Flexible flail or “string” trimmers have become very popular tools for trimming grass and weed areas that cannot be reached by a lawn mower. Owners of trimmers also use them to edge vertically, or at some lesser angle than vertical, the edges of curbs, sidewalks and driveways and even mulched beds. They do this because it saves the considerable cost and hassle of having to purchase and use a separate edger, which is usually in the form of a powered metal blade. The cost alone of the least expensive powered edger on the market is as much or more than the initial cost of the usual flexible flail trimmer. In addition, the least expensive powered edger is electrically powered, requiring the use of an extension cord that then has to be dragged about a lawn to be edged. The least expensive gasoline-powered edger on the market is almost twice the price of the initial cost of a flexible flail trimmer even though the same engines can be used by the string trimmer which also power these edgers.
These alone are significant reasons attempting to use a string trimmer to edge. In addition, all powered blade type edgers also use metal blades that are not sharpened. Just like a lawn mower with a very dull blade, the aesthetic result is a chewed appearance of the grass blade tips at the lawns edge rather than a clean crisp cut. Even if one sharpened the metal blade it would not stay sharp long because it comes into contact with the soil, the edge of the pavement and most especially corners of pavement. Often the operators of the blade edgers will edge too far at this junction and literally contact the pavement at the corner.
This is especially detrimental to concrete walks, curbs and driveways because the metal blade actually chips away at the concrete corner. Over time, significant aesthetic and even structural damage occurs to said paved areas.
In contrast, a string trimmer can cut a much crisper edge while not damaging the pavement. In addition, due to the natural tendency of the string to wobble out of its ideal or theoretical inertial path or plane, trimmer operators find that the edge they cut with a vertically held trimmer creates a wider edge than with a blade. This does two things: first a groove is created adjacent to a paved edge that is as much as a half inch or more in width. This looks much more distinctive, doing a better job of outlining the lawn, which most people find pleasing to the eye. Metal blades, on the other hand, are only an eighth of an inch wide, resulting in a narrow, almost imperceptible edge or groove.
Second, since the edge created by the trimmer is wider, the edged appearance lasts longer between edgings. All of these are intuitive reasons people may choose to attempt to use their trimmers to edge rather than purchase a separate edger.
However, there are several significant problems experienced when using string trimmers to edge. The trimmers are usually held freehand while edging, which makes creating a straight, vertical edge a slow, tedious task. And if the operator tries to edge in this manner at walking speeds, the results are usually not straight, sometimes not vertical and almost always wavy and unattractive. There is little physical feedback between the edge of the pavement and the operator trying to hold the free-spinning string in a vertical plane and in the exact lateral position at the edge of the pavement while moving.
The first time a lawn is edged each season is particularly difficult because the lawn has grown all the way over to the pavement edge necessitating removal, not just of the grass stems, but also plant crowns, which are significantly more difficult to cut all the way to the soil. In addition, every time the operator takes a step, the result is the spinning string plane wandering in all directions from that perfect position or hold that could create the perfect edge.
This results in edges being several inches wide in places as well as too deep in some areas, or not all the grass being cut and the operator having to stop and back up to redo a section of edge. This results in crooked, unattractive edges and tedious work for the operator. If he tries to take advantage of the groove he has established this first edging by edging again every week, the result can be a continual widening and deepening of the edge after repeated freehand edgings.
Thus, cutting a straight edge requires a very slow pace for all those except the most accomplished professional trimmer operators. Because of this arduous task, homeowners often will not edge as often as they would if the task were fast and easy.
After a month or two, the edge looks so bad they have to edge again, but essentially have to start from scratch to create a new groove each time. Accordingly, lawns are not edged very often because of the difficulty using a string trimmer to edge, or not at all because of the cost of the blade edgers. And, if a string trimmer is used to edge, it is done ineffectively.
Accordingly, it is desirable to provide a flexible line trimmer capable of consistently edging in terms of depth and straightness. In this regard, there are several edging guides currently on the market. One is described by U.S. Pat. No. 5,107,665 wherein a guide is mounted on the trimmer shaft via a two piece mounting block, an arm and a guide wheel. This guide will index the trimmer's spinning string in a set vertical position. This restricts the depth of cut as an operator proceeds down an edge. However, bigger problems are the lateral orientation of the vertical string plane and the lack of a physical reference of the string end in its cutting area. The guide wheel is nowhere near the plane of the string, and the operator still must try to hold the spinning string, which he cannot see, in the narrow groove. This is still quite hard to do at any reasonable walking rate of speed. A second device on the market manufactured by Homelite is similar to the patented device, except that it does not have a wheel, forcing the operator to walk backward in order to proceed down an edge.
Another aspect of the problem of edging with a flexible flail is the “wobble” of the flail string as it rotates in a plane, the thickness of which is affected by numerous influences. A wide or thick or variable plane is undesirable.
What can be called the natural wobble of the flail would be that wobble amplitude brought about by aerodynamic instabilities of the string itself as it spins. Natural wobble is also brought about by forces stored in the molecular structure of the string, such as where the string has been wound about a spool after manufacture, then is wound in a different way around a storage spool in the trimmer's head. This causes the string's tip to point off in some other direction other than its natural path (with no inertial mass beyond this point to hold it straight, said forces take over even at high RPMs). Another wobble causing influence are those forces that act on the string as a result of the string tip contacting objects in the cutting exercise. These force the string from its theoretical path or plane perpendicular to the axis of rotation and having an amplitude about equal to the thickness of the flail.
Because this natural wobble exists to some degree most of the time and almost constantly during the edging process, not just any string stabilizer surface can be brought into this working path of the string or even adjacent to it. Anything that would offer an obtuse surface to the direction of travel of the string as it spins brings about the kind of disruptive wobble, if not catastrophic wobble, described above. However, if one brings a non-obtuse surface into the working plan
Pezzuto Robert E.
Wood Herron & Evans LLP
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