| 摘要 |
The spool impeller is a fully automatic cutting head for whirling filament vegetation trimmers, simpler, less expensive, and more reliable than the predecessors. Unlike the predecessors, the spool impeller does not waste filament. It consists of a single part, a small diameter spool attached to the drive shaft. The free end of filament coiled on the spool extends tangentially so that the tip traces a circle about the axis of rotation. In use, the coiled filament gradually unwinds to compensate for filament wear, maintaining a cutting swath of precisely constant size. There is no need for the operator to monitor the filament. Feeding new filament is controlled by the aerodynamic drag and centrifugal force acting directly on the extended filament. If the length of the extended filament is correct, drag and centrifugal force balance, and no unwinding or rewinding occurs. Too long, drag dominates over centrifugal force, rewinding the extended filament onto the spool just enough to restore the proper length. If the extended filament is shortened by wear, centrifugal force dominates over drag, unwinding the extended filament just enough to restore the proper length. A mechanism to index the spool or to release a spool brake to feed more filament is unnecessary: the spool impeller is fixed onto the drive shaft and does not rotate with respect to the drive shaft. Reloading is fast and easy. No disassembly is required.Other systems, devices and methods are disclosed.
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