Abstract:
A top soil screening device comprising a plurality of screening racks, each rack comprising a plurality of interdigitated moveable and stationary bars is described. Drive means moves the moveable rack up and down such that there is a fixed phase relationship between the moveable racks which evenly distributes the weight of any load of soil to be screened across all of the screening racks.

Description:
REFERENCE TO PRIORITY DOCUMENT  
       [0001]     Applicant hereby claims priority of U.S. Provisional Application Ser. No. 60/716,009 filed Sep. 10, 2005. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     This invention relates to solid separation devices and particularly to screening devices useful to separate soil into useful topsoil and oversize materials such as rocks, wooden materials and other oversize items.  
         [0003]     Such devices have been used for over one hundred years and are known by such names as screeners, grizzlies and sorters. As is common in other areas of technologies, a large number of different solutions to a particular technical problem is an indication of the seriousness of the problem. When known efficient solutions to a problem are known, few variations will be found. However, when known solutions are inadequate, many variations and solutions have been proposed.  
         [0004]     In the technology of soil separators, there is a multitude of solutions; as there is no easy or best known implementation known.  
         [0005]     Known soil separators include those in which relatively large quantities of unscreened earth onto a large receiver including one or more sets of screens or parallel bars which allow soil to pass through spaces in the screen or bars while the remainder of material too large to pass through is discarded. In many proposals the screen or bars are moved or vibrated to assist in separation.  
         [0006]     In an effort to obtain more efficiency, improvements have included more and more complicated devices and features.  
         [0007]     A typical separator or grizzly consists of a screen, usually comprising a screen of perforated material or parallel bars mounted at an angle to the ground on a frame such that material to be separated is dumped by a bucket loader or other delivering means, such as a conveyor belt. The screen may be vibrated causing some of the deposited material to pass through the screen while the remainder of material too large to pass through the screen falls off of the inclined screen to the ground or other receiving device.  
         [0008]     Elaborate systems have been developed to increase the efficiency of the screening devices but at the risk of increasing the complexity and sensitivity of the screening devices to breakdown and failure.  
       SUMMARY OF THE INVENTION  
       [0009]     It is an object of the instant invention to provide an improved soil screener which has few components and reduced likelihood of failure.  
         [0010]     Another object of the invention is to provide a screener that is self-cleaning and not subject to clogging.  
         [0011]     The subject invention provides efficient soil separation with a minimum number of moveable parts and is capable of operating in the presence of oversize items without jamming. The separator if the invention is capable of handling large loads of mixed materials. The present invention provides these benefits by using a plurality of vertically oscillating screening decks have a predetermined relationship to each other so as to distribute the load to the driving mechanism such that very low torque is required to operate the screener. By providing adequate vertical movement between moveable and fixed racks of interdigitated horizontally extending bars, it becomes impossible to create jams as the moveable bars separate from the stationary bars to all but eliminate jamming. Moving multiple moveable racks in a phased relation to each other allows even distribution of the weight of the input load, reducing the strain and torque on the drive motor.  
         [0012]     These and other objects are achieved by the instant invention as further described in the accompanying description and drawings. 
     
    
     DESCRIPTION OF THE DRAWINGS  
       [0013]      FIG. 1  is an elevation view of the front of the soil screener of the invention.  
         [0014]      FIG. 2  is an elevation view of the back of the screener of the invention showing the plurality of moveable racks at different vertical positions.  
         [0015]      FIG. 3  is an oblique view of the top of one of the sections of racks, showing their attachment to the front of the screener.  
         [0016]      FIG. 4  is a partial sectional view of one of the journal means used to provide vertical movement of the moveable racks. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0017]     Referring to  FIG. 1  there is shown the front of the screener and the large receiving region for screened top soil or other material. The screener includes a frame comprising four corner posts  10 , horizontal cross bars  12  and lower bars  14 . On top of the frame are four separately operable screening units  16 A,  16 B.  16 C and  16 D. Each screening unit comprises a plurality of interdigitated vertically moveable and stationary steel bars. Solid sides and rear panels may be provided to maintain separation between screened material and unscreened material.  
         [0018]     The bars of the moveable racks are interdigitated with the stationary rack as has been practiced in the past. However, the moveable racks are cammed together in a fixed phase relationship, as described below.  
         [0019]      FIG. 2  shows the rear of the screener including the moveable ends of the racks  15 , each of which is fixed to a horizontal shaft  18  turned by a hydraulic motor  20  mounted at the far end of the shaft  18 . In order to move the free ends of the moveable racks each rack is attached to the shaft  18  by a journal means  22 . The journal means  22  is illustrated in greater detail in  FIG. 3 . Although a crank shaft could be used to drive the moveable racks, this embodiment achieves the same result by cutting the shaft  18  and welding a short piece of shaft to the cut ends of the shaft. The welded section of shaft is positioned at a phase angle of 90 degrees with respect to it&#39;s adjacent neighbor. This positions the racks such that as the shaft  18  turns, counter clockwise as shown in  FIG. 2 , rack  16 A will be in its highest position, rack  16 B will be moving downward at a point halfway between its top and bottom position, rack  16 C will be in its lowest position and rack  16 D will be moving upward halfway between top and bottom.  
         [0020]     It is this phased positioning of the moveable racks that allows the even distribution of the work load across the screener, assuming that the work load is relatively evenly distributed across the top of the screener. One half of the work load is always moving upward and one half is moving downward. To the extent that the work load is evenly distributed, the torque required by the drive motor  20  is minimal and, in fact, the shaft can be turned easily by hand.  
         [0021]     The drive shaft  18  is mounted to the frame of the screener on a beam  24  by a plurality of fixed journal bearings  26 .  
         [0022]     Referring now to  FIG. 3 , there is shown the detail in the method of forming a crank shaft out of a single piece of round stack. The stock is cut, forming a first piece of shaft  18  and a second piece  18 ′. A stub section  28  of round stock is welded to the main part of the drive shaft  18 . The stub section includes a bearing housing  30  to which is mounted a rack supporting member  32 . As indicated above, each stub section is welded in a phased relation to the remaining sections.  
         [0023]     While four phased rack sections  16  are shown, additional sections could be used in which the phasing would be adjusted such that the work load is evenly distributed to the drive shaft.  
         [0024]      FIG. 4  shows the upper end of the screener bars  16  which are welded to a round tube  34  which allows the moveable racks to pivot about the tube  34 . A short piece of stock  36  is welded to the frame to prevent horizontal movement of the top of the bars.  
         [0025]     In operation, the work load can be placed on the top of the racks  16  by a front end or bucket loader. The shaft can be driven by a hydraulic motor operated via a power take-off on a tractor, not shown. Because the work load is balanced, the drive shaft can be stopped or turning when the work load is deposited. The shaft is preferred to operate at about 300 rpm for best operation. The screener of the preferred embodiment has a deck six by 12 feet and can screen about three cubic yards of top soil at a time. This will allow adequate time for the screener to clean itself before the bucket loader can return with another load. If a conveyor is used to feed work load and remove screened soil, the rate of rotation can be adjusted for continuous operation.  
         [0026]     While the invention has been shown in terms of a single preferred embodiment, those skilled in the art will realize that various modifications can be made without altering the spirit of the invention.