Cutlery – Blades – Rotary
Reexamination Certificate
2001-09-14
2002-10-01
Watts, Douglas D. (Department: 3724)
Cutlery
Blades
Rotary
C030S276000
Reexamination Certificate
active
06457242
ABSTRACT:
BACKGROUND
Weed and grass trimmers have been developed which employ a rotatable hub with a short length of flexible nylon or other plastic line extending from the hub. When the hub is rotated (typically at speeds from 6,000 RPM to 12,000 RPM), the tip of the line extending from the hub provides the cutting or trimming action. Grass and weed trimmers using this principle of operation have become popular for their versatility of use, and because the flexible trim line is safer to use than rigid rotating steel blades.
Various types of devices have been developed for using such trim lines. Typically, rotating line trimmers or rotating string trimmers employ a trimmer line which generally has a circular cross section. The line, in many trimmers, is wound on a storage reel in the hub of the device, and is fed out of a hole or a plurality of holes in the hub in discrete amounts, as the end breaks off or wears off. Trimmers of this type sometimes are referred to as “bump-and-feed” trimmers. When the line breaks off, the bottom of the storage reel is bumped on the ground while the hub continues rotating to cause a spring release of the line within the trimmer. A short length of line then plays out through a hole in the hub by means of centrifugal force. Typically, the smaller (2½ inch diameter to 3½ inch diameter) head bump-and-feed string trimmers use relatively small diameter line, normally in the rang of 0.65″ to 0.080″ diameter, since the smaller diameter flexible line functions better for the centrifugal feeding of such smaller diameter bump-and-feed heads.
The reason that small diameter line is used in bump-and-feed string trimmers is that heavier diameter line (for example, 0.115″ to 0.160″ diameter) typically is too stiff for winding and for the centrifugal feeding used in bump-and-feed heads. Commercial bump-and-feed heads use a larger diameter head than those designed for home use, and operate with somewhat larger diameter flexible line, generally from 0.95″ to 0.105″ diameter. These commercial heads normally have a larger capacity for such line, so that less frequent reloading of the line is required.
A problem exists with all bump-and-feed trimmers, however, in that frequently the line which is wound on the storage reel in the hub tends to become stuck, either due to partial fusion of the line in the hub, caused by high frequency vibration, or by successive turns of the line wound on the hub becoming somewhat entangled. As a result, feeding of the line from the hub, when desired, does not always take place. When this occurs, it is necessary to remove the hub from the string trimmer device and manually extract the desired length of line prior to re-attaching the hub of the device. This is a time consuming and frustrating experience for many users of flexible line string trimmers. It is particularly frustrating for professional landscapers because of the relatively significant amount of lost time required to remove the hub, extract the line, and re-attach the hub before operation can resume.
For commercial use employing relatively large diameter lines, for example 0.115″ to 0.160″ diameter, fixed line or fixed length line trimmer heads usually are employed. Large diameter monofilament nylon lines are particularly useful where weed and grass growth is dense. The large diameter lines also provide longer length of service before the line needs to be replaced. Due to the hole design and pattern, smaller standard sized lines (under about 0.095″ diameter) have a tendency to slip out of commercial fixed heads during operation.
One type of fixed line trimmer head for commercial use is the Echo® heavy duty fixed line trimmer head, stock No. 999442-0020. This trimmer head is designed to replace a saw blade trimmer/brush cutter, or other types of flexible line trimmer heads. The Echo® trimmer head is open on its underside, and provides serpentine paths for the insertion of two fixed lengths of 0.130″ diameter monofilament line. The line is inserted between closely spaced, offset guide surfaces to hold it in place during operation. When a new length of line needs to be inserted, the old line must be removed; and the new line then is guided into place around the guide surfaces. Because the guide surfaces are close together and because 0.130″ diameter line is relatively stiff, it is difficult to install and remove sections of nylon line from the Echo® trimmer head. This difficulty results in excessive time being consumed for the removal and replacement of line segments.
Another fixed-line trimmer head is known as the Grass Terminator® replacement head, designed for replacing the bump-and-feed spool cartridges of a variety of line trimmer machines designed for home use. The Grass Terminator® fixed head also employs guide paths for feeding two segments of line into and out of the head. The guide paths used with this head, in some cases, tend to allow the line to be pulled out of the head when it strikes an obstruction, such as a chain link fence or the like, particularly when the small diameter trim lines for which the head is designed are used.
The United States patent to Rouse U.S. Pat. No. 4,756,146 discloses a head for a string trimmer machine in which a pair of enclosed guide tunnels are formed in the head to guide a segment of string trimmer line from an entry hole to an exit hole. These tunnels are located with one end of each tunnel located near a corresponding one of a pair of relatively closely spaced entry holes, and the exit ends of the tunnels are located at a greater distance around the periphery of the trimmer head to allow exiting of the inserted line from the head. A problem which exists with this construction, however, is that the tunnels are configured to accommodate the particular size of line which is to be used with the trimmer, and because of the relatively low clearance provided by the inside diameter of the tunnel, it is possible for the tunnels to become clogged, or for difficulty to be encountered with the insertion of the line into the head.
The United States patent to Fogle U.S. Pat. No. 6,035,618 is a fixed-line trimmer head which overcomes the disadvantages of the prior art devices discussed above. The fixed line trimmer head of Fogle employs a pattern of pairs of entry and exit holes for inserting a fixed length of trimmer line through a pair of relatively closely spaced entry holes, and then extending each end of the line out through exit holes located in the head. The entry holes and exit holes are offset from one another in different planes perpendicular to the axis of the trimmer head, and securely hold the line in place during use of the trimmer. It is relatively easy to remove an expended section of line and replace it with a new section of line when necessary. The fixed line trimmer head of the Fogle '618 patent, however, does require the user to manually to insert the opposite lengths of the line through the two entry holes, and then again manually insert each of the line segments into the exit holes in the head whenever a line replacement is required. The Fogle patent also discloses utilization of sets of entry holes of different diameters to allow the use of segments of trimmer line having different diameters, as desired, in the same head. Even though the device of the Fogle patent is a significant improvement over the bump-and-feed trimmers and over the fixed line trimmers discussed above, it still is necessary to manually insert the ends of a line through separate entry and exit holes for each length of the line. This requires the user to have access to the bottom of the hollow trimmer head in order to extend the ends of the line into the exit holes for use.
Accordingly, it is an object of this invention to provide an improved fixed line trimmer head for string trimmer machines, which overcomes the disadvantages of the prior art, which may be used as an alternative to bump-and-feed trimmer cartridges, which is easier to load than the devices of the prior art, and
Phillips Robert L.
Ptak LaValle D.
Watts Douglas D.
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