Weighing scales – With total register – Integrator of steadily flowing fluent material
Reexamination Certificate
2000-01-31
2001-11-06
Gibson, Randy W. (Department: 2859)
Weighing scales
With total register
Integrator of steadily flowing fluent material
C177S136000, C177S185000, C073S001130, C701S050000, C702S174000
Reexamination Certificate
active
06313414
ABSTRACT:
BACKGROUND OF THE INVENTION
1. The Field of the Invention
The present invention relates systems and methods for measuring and weighing a moving mass. More particularly, the present invention relates to measuring and weighing a mass that is on a moving and/or sloped platform and subject to external forces other than the gravitational force.
2. The Prior State of the Art
A primary business goal is to maximize output or production while minimizing costs. With regard to agricultural operations maximizing output potentially includes measuring the weight or volume of a crop, collecting weight data while harvesting the crop to develop a crop yield map, and using the crop yield map to identify problem areas of an agricultural field. Maximizing output also includes ensuring that the vehicles used to transport a harvested crop to a destination are fully loaded but not overloaded. In many harvest scenarios, trucks are loaded as the crop is being harvested and an overloaded truck not only may damage the truck but may also incur overload penalties. In the alternative, a less than fully loaded truck is inefficient because more loads are needed to transport the crop to market.
The act of weighing the crop as it is harvested has presented many challenges which are related to the manner in which crops are harvested. For example, many agricultural vehicles such as harvesters use conveyors to transport a crop from the harvesting vehicle to a transport truck. Many different types of conveyors have been developed including augers and continuous belt or chain link devices, and while conveyors provide an effective method for loading crops onto trucks, they present various problems when the weight of the crop being harvested is measured.
It is inconvenient and inefficient for a conveyor to deposit the crops onto a static scale before loading the crops in a truck, because the crop must then be removed from the scale and because additional time and equipment are required to harvest the crop. Another approach for weighing a crop involves positioning the entire conveyor assembly on a scale platform and subtracting the weight of an empty conveyor from the measured weight of the crop and the conveyor. In any case, weighing accuracy is compromised due to the slope and motion of the machine.
Another method for determining the weight of a crop while it is being harvested is to monitor the power required by a conveyor to transport the crop from the harvester to a truck. These systems have proved problematic, especially on variable pitch conveyors. The power consumption of a conveyor assembly does not uniquely correspond to the weight of the material due to the variable friction forces of the system. Thus, it has proven difficult to accurately measure the weight of material carried on a conveyor using this method.
Weighing crops as they are being harvested or weighing other materials that are carried by moving vehicles has been difficult, due to dynamic forces (i.e. acceleration) and the variable slope of the vehicles. For example, a harvester that traverses a field is subjected to dynamic forces and has a variable angular position with respect to the horizontal plane as it encounters and moves over uneven terrain. Weighing harvested crops using a simple load cell under these conditions leads to inaccurate results due to both the dynamic forces associated with movement and the variable angle of the load cell. These problems associated with weighing material have also been experienced in other agricultural and industrial settings. For example, accurate measurements of animal feed, gravel cement, and other bulk materials on moving platforms have been difficult to obtain.
In view of the foregoing, there is a need in the art for weighing systems that are capable of accurately measuring materials, such as crops, as the material is carried on a vehicle that is subjected to dynamic forces and variable inclination. It would also be desirable for such weighing systems to be capable of use with a variety of materials environments, and vehicles.
SUMMARY OF THE INVENTION
Accurate weight measurement, particularly on moving vehicles, is becoming increasingly important as information technology becomes more widespread in agriculture, industry, business, and research. Accurate weight measurement allows operations such as agricultural operations to improve production while lowering overhead by allowing crop yield maps to be developed which enable an agriculturist to identify areas of an agricultural field that are underproducing. Once this information is known, appropriate action can be taken to increase the crop yield of those plots. The overall effect of accurate weight measurement is to increase the productivity of the agricultural operation.
In an agricultural context, the present invention relates to a weighing system that allows accurate weight measurements of the crop to be made as the crop is being harvested. For example, many harvesters have a conveyor or other transport mechanism that transports the harvested crop to a truck. The weighing system of the present invention can be incorporated with the conveyor, another transport mechanism, or can otherwise be integrated into the harvesting process such that the weight of the crop may be continually monitored and measured.
In one implementation of the invention, at least one weighing load cell (i.e., load cells that weigh the material) and a reference load cell are included in the weighing system. The axis of measurement of the weighing load cell and the axis of measurement of the reference are in a specified relationship one to another (preferably parallel) and remain so as the weighing load cell experiences linear and angular motion. The reference load cell generates data representing the measured weight of a known reference mass. The weighing load cell generates data representing the measured weight of the material to be weighed. The weighing load cell often will generate weight data that does not represent the actual weight of the material, due to acceleration of the material in the direction of the axis of measurement of the weighing load cell and deviation of the axis of measurement from the vertical direction.
As the acceleration and variable inclination are experienced, the output of the reference load cell is used to compensate for inaccuracies introduced into the data generated by the weighing load cell. The reference load cell can compensate for these inaccuracies because it experiences the same variable inclination and acceleration as the weighing load cell. The compensation is improved when the reference load cell and reference mass are selected to have a similar dynamic response to motion as the weighing load cell. It has also been found that passing the output of the reference load cell and the weighing load cell through low pass filters can reduce or eliminate potential mismatch in the measured dynamic characteristics (e.g., system resonant frequency) of the “reference” and “weighing” systems.
The invention also extends to novel techniques of measuring the electronic zero offset of the reference load cell. In order to accurately compensate for motion using the output of the reference load cell, it is important to know the electronic zero offset of the reference load cell, which in turn allows the output of the reference load cell associated with the reference mass to be determined. Prior to the invention, known techniques for determining the zero offset of a load cell, such as a full bridge strain gage load cell, without removing a known mass from the load cell included taking a static measurement of the reference mass, then taking another static measurement after rotating the entire assembly 180° about a horizontal axis. An average of the two static measurements eliminated the contribution of the known mass, and yielded the zero offset of the load cell.
According to one implementation of the invention, the zero offset is determined by sealing the reference load cell and the reference mass in a substantially air-tight chamber, such that dust accumulation
Gibson Randy W.
HarvestMaster, Inc.
Workman & Nydegger & Seeley
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