Patent Publication Number: US-6035511-A

Title: String trimmer head with opposing centrifugal forces filament feed

Description:
BACKGROUND--FIELD OF INVENTION 
     This application is a continuation of application Ser. No. 08/937,696, filing date Sep. 29, 1997; now abandoned with identical title, and relates to string trimmer heads that use flexible filament to cut vegetation; and the use of opposing centrifugal forces on the filament and its flail to feed filament to the flail. Applicant specifically claims the filing date Sep. 29, 1997. 
    
    
     BACKGROUND--DESCRIPTION OF PRIOR ART 
     In the past twenty or so years, hand-held string trimmers using flexible and expendable filament have become very common. Many patents have been issued for devices that store and feed out filament, mainly the familiar bump feed heads, plus heads that automatically feed out cord with very limited operator influence. 
     Among the heads that automatically feed out filament almost independently of operator control, research has identified these: 
     
         ______________________________________                                    
4,561,180 (1985) to Pittinger                                             
                 Bump feed to incrementally feed                          
                 the flail                                                
4,236,312 (1980) to Lombard and                                           
                 Electric motor maintains                                 
Foster           constant flail length                                    
4,285,127 (1981) to Zerrer                                                
                 Speed actuates cams                                      
4,290,200 (1981) to Lombard                                               
                 Speed actuates a cam                                     
4,347,666 (1982) to Moore                                                 
                 Speed actuates a cam                                     
4,366,621 (1983) to Mitchell                                              
                 Speed actuates a cam                                     
4,366,622 (1983) to Lombard                                               
                 Speed actuates a cam                                     
4,483,069 (1984) to Moore                                                 
                 Speed actuates a cam                                     
4,835,867 (1989) to Foster,                                               
                 Speed actuates a cam                                     
Collings and Stuart                                                       
4,852,258 (1989) to Foster                                                
                 Speed actuates a cam                                     
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     Trimmer heads using the principles described in these patents have moving parts which collect grit and grime and very often fail to function acceptably or to function at all. These heads also have spools on which the cutting filament wraps over on top of itself, then refuses to feed, a very common problem with the bump feed heads too. 
     The market for heads with manually-installed flails will remain good until a trimmer head that feeds dependably--with few or no malfunctions--comes on the market. 
     OBJECTS AND ADVANTAGES 
     (a) This patent application describes a very simple device, a spool with closely-spaced walls that won&#39;t allow filament to wrap over on top of itself and then refuse to feed. 
     (b) The only moving part in the trimmer head is the filament. There are no springs, ratchets, pawls, cam or cup. Lack of moving parts means that dust, grime, dirt, etc. will not easily disable this device. 
     (c) An operator can easily reload the spool with filament without any disassembly of the trimmer head. All he has to do is to pull out the remainder of the used filament from the filament loading hole and then insert the end of a pre-cut length of filament into the loading hole, push it in until the end emerges from between spool walls, then draw it out until the other end stops at the loading hole, then lace the filament inside the flail anchors until it is all wound up. No tools are required. 
     (d) The spool can be so built that the filament will wind up on the spool in either direction, with the direction of rotation or against it. The preferred choice is to wind the filament with the direction of rotation. 
     (e) This device is simpler and cheaper to produce than all other types except those with manually installed flails. 
    
    
     REFERENCE NUMBERS IN THE DRAWING FIGURES 
     FIG. 1 Top plan view of the spool 
     FIG. 2 Elevation of the spool 
     10t Top Spool Wall 
     10b Bottom Spool Wall 
     12 Mounting Arbor 
     14 Flail Anchor 
     16 Flail 
     18 Inside Filament 
     18h Slanted Filament Loading Hole in the top Spool Wall 10t 
     20 Spacer Between Spool Walls 10b and 10t 
     22 Bottom of Trimmer Drive Train 
     -24 Centrifugal Force Vector on the Filament 
     -26 Centrifugal Force Vector on the Flail 
    
    
     SUMMARY 
     This invention comprises a spool with close spool walls mounted on an arbor; flail anchors connecting spool walls at their periphery; a elliptically shaped spacer of special shape between spool walls, on which spacer a filament is wound, a filament loading hole in at least one spool wall, and means of anchoring the filament onto the spool. 
     Description 
     A typical material for the spool walls 10t and 10b and the spacer 20 is polyvinyl chloride or a polycarbonate, or anything else suitable. The whole spool can be cast in two pieces, then machined as necessary. One of the spool walls, typically the top spool wall 10t, has a slanted filament loading hole 18h to allow insertion of a pre-cut length of filament which can be drawn from between spool walls 10t and 10b, then threaded inside the flail anchors 14, then wound up on the spacer 20. 
     Operation 
     When the trimmer head is in operation, it will not feed filament 18 to the flail 16 until the centrifugal force vector -24 on the filament 18 is greater than the centrifugal force vector -26 on the flail 16. When the flail 16 is short enough, filament 18 will &#34;suck in&#34; flail 16, which then slings out ahead of the flail anchor 14. The flail 16 is then longer because part of the filament 18 has joined it. The next in line flail anchor then anchors the newly-lengthened flail. The feeding process can be hastened by slapping the flail against a convenient object, thus reducing its radius of gyration, thus the force vector -26, but only when the flail is short enough. 
     Conclusions, Ramifications and Scope 
     This trimmer head is nothing more than a spool with close spool walls that won&#39;t let trimmer cord wrap over on top of itself and thus refuse to feed; that has a convenient way of loading the trimmer cord; that feeds filament to the flail only when the dynamics are correct; that has only one moving part--the filament; and can be readily used on practically any trimmer machine. The principle of operation can readily adapt to more powerful trimmers, to lawn mowers and brush hogs. 
     The larger machines can use &#34;stacked&#34; spools, i.e., a plurality of spool walls to accommodate more than one cutting cord. 
     Construction and operation are simple enough for practically anybody. And with only one moving part, the device will have few malfunctions, thus keeping downtime and repair costs to a minimum. The ordinary housewife, working in her yard, won&#39;t have to visit a repair shop very often because of this device.