An agricultural harvesting machine such as a combine tractor generally includes a harvesting front attachment mounted onto a feeder or crop elevator. The front attachment gathers the crop material from the field while the feeder directs it to a threshing separating and cleaning mechanism located in the combine to produce grains. The process further completes when those grains are sent from the combine to the next step of the production chain selected for this type grain.
For low growing, thin stemmed crops such as soybeans, barley, wheat, bean, etc., the header driven by the combine has a reciprocating knife at the leading edge called cutterbar. The crop is severed by the cutterbar and falls onto a laterally extending conveyor that carry the crop to a central section of the header. Nowadays, this laterally extending conveyor is preferably a draper conveyor, usually comprising multiple draper belts.
The header is mounted to the combine tractor at open end. The crop material travels laterally by means of the draper conveyor and passes then through this open end to the feeder of the combine.
The draper conveyor generally consist of two side belt conveyors, one on each side of the platforms open end. Each side belt conveyor normally comprises a closed loop belt wrapped around two rollers. Generally, one of this inner rollers is set to work as a driver and the other as an idler.
To grant the friction that allows the belts to be driven by the roller, each belt has to be tensioned to create the proper pressure against the corresponding idler and drive rollers. Most generally, belt tension is achieved by separating corresponding driver and idler roller from each other. Tension load to belts is such to permit the belt to carry the crop without driver roller slipages.
In modern design flexible draper platforms, the cutterbar assembly is forced to go up and down and curl to assimilate the contour of the ground to minimize crop picking losses; in most draper headers the draper conveyor behind the cutterbar is forced to flex therewith.
While in operation, the draper belts of the draper conveyor tend to curl and shape more aggressively at its leading edge close to the cutterbar than at its rear end close to the pivot point of the arms. As the belts are made of a non-resilient material, the draper belts tend to shape to a “V-form”, forcing the supporting rollers to violently twist inwardly at their front margin.
Accommodating the flexing and twisting of the conveyor belts is difficult using traditional belt tensioners. The rollers must be able to push outward against the belt and also pivot side to side to distribute the tension across the belt. Tension on the belts may result inconstant and widely varying, thus resulting into belt breakages, slippages, or belts that may suffer premature wear.
Belt working tension for agricultural harvesting headers is usually within the range of 15 N/cm to 40 N/cm—tension per centimeter width of the belt. Most widely used belts are about 1000 mm width, thus requiring a tension equivalent to 407 kg. A male human operator shall output, on average, 345 N pulling force in a comfortable position. The rollers commonly used so support the draper conveyor of agricultural draper headers are about 60 mm diameter.
Under patent application publication number US20050045452 Hansrudolf discloses a mechanism to release draper belt from tension involving a crack-lever mechanism. Patent describes two belt tensioning devices arranged laterally offset of the roller mount, thus requiring the operator to execute two de-tensioning steps per belt each time service is required. Hansrudolf does not describe how to tolerate the roller twisting that occur in flexible draper headers; moreover, Hansrudolf presumes the displacement of the deflection roller should occur evenly. Moreover, considering the height of traditional draper header rollers, the crank lever as per Hansrudolf construction must be less than 63 mm, and also considering also the operators average output force and flexible drapers common belt width, the operating lever as per Hansrudolf will only permit a short motion of retraction of the roller thus not providing a comfortable looseness of the draper to quickly perform cleaning and service operations.
Under U.S. Pat. No. 8,495,855 Conrad and Dow disclose a method to tolerate belt uneven tension across its width. Method proposed is having both, idler and driver rollers featuring a twisting pivot axle in such manner that these rollers must pivot in the same direction about their roller pivot axes. Conrad and Dow do not specify how this mechanism tolerate the belt shringkage difference between belts rear and front margins when operating in a flexible draper header, that tend to twist rollers in opposite directions instead. Moreover, the method disclosed do not propose any mechanism to give constant tension to the belts that also can adapt to belt shape changes.
Beltman et al disclose under US20130284567 a construction to guarantee a correct belt tracking. Actuating elements to give proper tension to the belt as per Beltman disclosure require a bulky construction not applicable to traveling harvesting headers due to size requirements. Moreover, method is not applicable to flexible draper header where severe variating conical shape of the belt occur during operation because of different shrinkages from the rear to the front.
Tippery et al disclose under U.S. Pat. No. 7,448,491 a belt tensioning apparatus for a harvesting header. The first drawback of this mechanism is that it shall be applied to rigid draper conveyor structures, where no flexible cutterbar is needed and thus no severe belt shape change is required. Tippery et al disclose a mechanism with roller supported by a support bracket with said bracket being held by a pair of bracket extensions laterally offset of the roller; each bracket extension is slidingly engaged to a longitudinal support member, thus roller twist is accepted by different extensions of the bracket extensions. However, having the telescopic functionality of the bracket extensions with respect to the longitudinal support members do not permit the configuration to be used with pivoting transverse support members, because it would be necessary for the longitudinal support members to be flexible, and consequently the configuration cannot be used in flexible draper headers. Furthermore, Tippery et al disclose method to apply a uniform force to a roller, not a constant, which is not helpful when rollers twist to accommodate belt flexing. Moreover, Tippery et al mentions the actuator could be a hydraulic cylinder serviceable and configurable with an external hand pump. Hydraulic fluid is substantially non-compressible and do not permit easy actuator's extension and retraction during operation to accommodate belt shrinkages. Also, hydraulic cylinder power source is external and requires operators intervention to achieve belt tension.
It is an object of this invention to provide a compact belt tensioner to be installed in draper harvesting headers that accommodates the flexing and twisting of the conveyor belts and generates a constant tension evenly distributed across the width of the conveyor belts. Furthermore, the disclosed tensioner performs an automatic belt tension without the operators intervention.