Material or article handling – Vertically swinging load support – Shovel or fork type
Patent
1981-07-13
1983-04-12
Spar, Robert J.
Material or article handling
Vertically swinging load support
Shovel or fork type
414733, 414917, 294 88, B66C 132
Patent
active
043796745
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Technical Field
This invention relates to load skidding vehicles having a chassis and a load grasping grapple, and, more particularly, to an apparatus for biasing the grapple to an optimum skidding position relative to the chassis during a load skidding operation.
2. Background Art
In certain classes of hauling operation such as moving harvested trees from their felling point to a collection point, there is often no feasible means of transporting a load other than by dragging it behind a vehicle. This is generally accomplished either by attaching the load to a load skidding vehicle (skidder) with a cable or by grasping the load with a grapple suspended from an elevated support boom carried by the vehicle chassis. Typical skidders have a front and rear axle each of which is supported on at least two wheels. Basic examples of grapple assemblies for use in load skidding applications are set forth in U.S. Pat. No. 3,620,394 which issued to Symons, et al. on Nov. 16, 1971, and U.S. Pat. No. 3,513,998 which issued to Stone, et al. on May 26, 1970.
Previously, grapple equipped skidders had a relatively smaller load capacity as compared to otherwise equivalent cable skidders. Such relatively smaller grapple skidder capacity resulted from the skidding load being born by the skidding vehicle at a comparatively high pivot point from which the grapple was suspended. Exertion of the skidding load at the elevated pivot point caused a substantial overturning moment to exist about the rearmost ground contacting point (rear tires' contacting points) of the loaded skidding vehicle. Such overturning moment tended to lift the front of the grapple skidder from the ground and thus reduce the traction of the grapple skidder's front wheels.
U.S. Pat. No. 4,140,233 which issued to Muntjanoff, et al. on Feb. 20, 1979, illustrates a force application arm attached to the vehicle for applying a downward force on the load at a point located rearwardly from the grapple. Activating the arm provided a reactive force tending to equalize the load distribution on the front and rear axles of the skidding vehicle. A copending U.S. patent application Ser. No. 258,504, filed Apr. 29, 1981, by Meisel, et al. illustrates a mechanism for pivoting the grapple relative to a supporting boom and vehicle chassis and locking the grapple in a desired relationship with the chassis. Such grapple pivoting is provided by an equalizing cylinder (hydraulic) and cooperating linkage joined between the cylinder and grapple. For most skidding applications the optimum position for the grapple is one in which the grapple is pivoted forwardly toward the vehicle chassis so as to push the distal (dragged) end of the load against the ground with a predetermined force. The load element (often logs) of Meisel, et al. tends to act as a structural compression member of the skidding vehicle by extending rearwardly from the chassis and into ground contact behind the rear wheels to resist the overturning moment exerted on the vehicle chassis. The load element must then be pushed into the ground to permit the front axle of the skidder to raise. Field tests of such equalizer cylinder and cooperating linkage exhibited drawbar capability improvements of skidder vehicles of between 50 and 70% as compared with equivalent skidders conventionally equipped.
While skidders having such pivotable, locking grapples perform admirably on flat ground, significant difficulties would be encountered when the skidders utilizing the aforementioned pivotable grapple either crested a ridge or forded the low point in a valley. In the former case with the grapple locked in the close-to-vehicle skidding position, the skidder would tend to raise the entire load from the ground and thus caused the skidder's front axle to rise from the ground. In the latter case as the skidder's front axle traversed the valley's low point and started climbing the adjacent slope, the skidded load would be forced against and into the ground so as to increase the skidding load as the dragged object increasingl
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ASN 270,533 Filed Dec. 4, 1980--Muntjanoff et al., .-+.Dampened Fully Pivotal Hanger for a Grapple".
ASN 250,742 Filed Aug. 20, 1980--Meisel, et al. for "Load Skidding Vehicle".
Meisel, Jr. Thomas C.
Price Robert J.
Caterpillar Tractor Co.
Keen Joseph W.
Siemens Terrance L.
Spar Robert J.
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