Potato harvester
The invention relates to a potato harvester. 
     It is known to provide a potato harvester having a screening conveyor belt following a lifting device, an elevator disposed after the screening conveyor belt, a haulm separating device and a stone separating device. The elevator and the haulm separating device form separate units which are also known in various designs. Ring conveyors, conveying wheels or side elevators are used as elevators. A first known haulm separating device provides a haulm plucking roll which, in co-operation with the upper end of the screening conveyor belt, conveys the haulms away between such haulm separating device and the end of the belt while potatoes and any entrained stones run over it. These are then fed by an elevator to a stone separating device. A second known haulm separating device provides a haulm elevator formed by a bar-type conveyor belt with narrow openings. This is disposed after the upper end of a screening conveyor belt and conveys potato haulms brought up by the screening conveyor belt, while potatoes and any entrained stones fall down between the upper end of the screening conveyor belt and the lower end of the haulm elevator onto an elevator or an intermediate preceding elevator - which feeds the potatoes and stones to a stone separating device. A third known haulm separating device consists of a double conveyor which is disposed after the screening belt and which comprises a bar-type conveyor belt having narrow-openings and rotating on the inside as a potato conveyor and a bar-type conveyor belt operating as a haulm conveyor with wide openings rotating outside in the same direction and guided parallel to the inside conveyor at least in the region of the conveying run of the double conveyor. The double conveyor is constructed in the form of an inclined conveyor rising slightly in the conveying direction and the elevator, which feeds potatoes separated from the haulms and any entrained stones to the stone separating device, is disposed after the end of the potato conveyor, either directly or following an intermediate conveyor. 
     It is an object of the invention to provide a potato harvester, the elevator of which is constructed in the form of a haulm separating device at the same time. 
     To this end, the elevator is formed from a double conveyor with one bar-type conveyor belt having narrow openings and rotating internally and another bartype conveyor belt having wide openings which rotates externally in the same direction and which is guided parallel at least in the region of the conveying run of the elevator, and one of the bar-type conveyor belts is equipped with the transversely directed entrainment webs which divide the gap between the conveying runs into compartments. 
     In a potato harvester according to the invention, the elevator, which may be arranged immediately behind the upper end of the screening conveyor belt, takes over the function of the haulm separating device at the same time, leading to a considerable reduction in cost and in the structural size of the machine. 
     Specific embodiments of the invention will now be described by way of example and not by way of limitation with reference to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a simplified perspective general view of a potato harvester according to the invention; 
     FIG. 2 is a broken away detail of the double conveyor forming the elevator; and 
     FIG. 3 is a simplified illustration of a potato harvester with the plane of rotation of the double conveyor aligned transversely to the direction of travel. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The potato harvester illustrated in FIG. 1 comprises a lifting device 1 which is formed from lifting blades 2 and a mound drum 3 travelling in front of the blades 2. A screening conveyor belt 4 follows the lifting device 1 and is constructed in the form of a bar-type conveyor belt which rotates around guide rollers 5 and guide and drive rollers 6, the conveyor belt 4 being endlessly driven. An elevator 7 directly follows the upper or rear end of the screening conveyor belt 4 and forms a haulm separating device at the same time. A stone separating device 8 follows and transfers the potatoes, separated from stones, onto a conveyor belt 9 and is then transferred to a storage bin 10. The separated stones are deposited directly onto the ground or delivered to a conveyor 11 which conveys the stones to a non-illustrated collecting bin. 
     The machine may be attached, as a trailer, to an agricultural tractor or the like towing vehicle or it may be constructed in the form of a self-propelled machine. 
     Instead of the illustrated single-row model, a double-row model may also be provided. For the individual units of the machine, drives are provided as far as necessary, which are formed from individual drive motors, for example hydraulic motors, or from transmissions which are set in operation from the towing vehicle. 
     The elevator 7 is formed from a double conveyor which comprises a bar-type conveyor belt 12 with narrow openings, rotating internally as a potato conveyor and a bar-type conveyor belt 13 with wide openings, rotating externally in the same direction and guided parallel at least in the region of the conveying run of the elevator 7, and operating as a haulm conveyor. The bar-type conveyor belt 12 rotates around guide rollers 14, 15, 16 as well as guide and drive rollers 17. The bar-type conveyor belt 13 rotates around guide rollers 18, 19, 20, 21, 22, 23 and 24 of which the guide rollers 22, for example, may form drive rollers at the same time. The conveying strand run of the bar-type conveyor belt 13 extends between the guide rollers 19 and 22 and the conveying run of the bar-type conveyor belt 12 extends between the guide rollers 15 to 17. 
     In the region between the conveyor rollers 15 and 17, the bar-type conveyor belts 12, 13 are guided parallel to one another. The stone separating device 8 is disposed immediately after the upper end of the bar-type conveyor belt 12, and includes a transversely extending bristle belt 30. The device 8 receives potatoes and stones elevated by the conveying run of the elevator 7 in order to carry out a stone separating operation. The bristle belt 30 is situated inside a loop in the upper region of the bar-type conveyor belt 13 and its discharge extends outside the region of the loop. 
     One of the bar-type conveyor belts 12 or 13, preferably the bar-type conveyor belt 13 forming the haulm conveyor, is equipped at its side adjacent to the other bar-type conveyor belt with transversely directed entrainment webs 25 which divide the gap between the conveying runs of the two bar-type conveyor belts 12, 13 into bucket-like compartments. The entrainment webs 25 are formed by rubber flights which end, at their free marginal edges, each in a resilient lip 26 rolled inwards in the form of an eye. The conveying surface 27 of the entrainment webs 25 forms an angle slightly exceeding 90° with the conveying surface of the bar-type conveyor belt 12 defined by the bars 12&#39; in the region of its conveying run. The oblique decline of this conveying surface 27 towards the bar-type conveyor belt 12 is adjusted to an angle of inclination which imparts to the potatoes contained in the bucket compartments a tendency to move towards the conveying surface of the bar-type conveyor belt 12. As a result, the potatoes are prevented from falling out of the compartments and, in the event of a fixed difference, or a difference which is variable in stages or adjustably variable, in the speeds of rotation of the bar-type conveyor belts 12 and 13, which difference is possible according to the invention, rolling and therefore screening or cleaning effects are achieved, such as are desired according to the soil conditions. With light soils somewhat higher speed of rotation is preferred for the bar-type conveyor belt 12 such that a slight rolling motion in a clockwise direction, as viewed in FIG. 3, is imparted to the potatoes in the compartments and this may be sufficient for cleaning the potatoes. In the case of heavy soils, a somewhat higher speed of rotation of the bar-type conveyor belt 13 may be provided in order to obtain an intensified rolling process taking place in a counterclockwise direction, as viewed in FIG. 2, such that a more aggressive potato cleaning action is achieved. In the case of sandy soils, the screening effect through the screening conveyor belt 4 may be sufficient for cleaning so that the two bar-type conveyor belts 12, 13 may also have the same speed of rotation. The ratio of the speeds of rotation of the bar-type conveyor belts 12, 13 to one another should assume a value which lies in the range between 0.8 and 1.2. 
     Whereas the bars 12&#39; of the bar-type conveyor belt 12 have a mutual spacing of the order of magnitude of about 35 to 44 mm and are thus set with narrow openings, the bars 13&#39; of the bar-type conveyor belt 13 have a mutual spacing which may be in the range from 120 to 240 mm and is preferably about 160 mm. The entrainment webs 25 preferably have a mutual spacing which corresponds to the spacing of the bars 13&#39; of the bar-type conveyor belt 13. 
     In the embodiment shown in FIG. 1, the plane of rotation of the elevator extends parallel to the direction of travel of the machine, but it is also possible to align this plane of rotation transversely to the direction of travel as the diagrammatic illustration in FIG. 3 shows. Such an embodiment enables the potato haulms to be dumped in rows for example or to be dumped directly into a collecting bin travelling parallel with the machine. 
     With a steep setting of the elevator 7, in the interests of gaining height, the bar-type conveyor belts 12, 13 co-operate in the conveying of potatoes and stones if, as preferred, the entrainment webs 25 are secured to the bar-type conveyor belt 13 which alone participates in conveying the haulms. The main conveying work is done by the entrainment webs 25 with which the bar-type conveyor belt 12 is essentially associated only as a boundary, forming the bottoms of the bucket compartments.