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Design Principles of Load Cell Elastic Element

Within the strain area of ideal normal stress and shearing stress elements, the strain degree should form a strict linear relationship with the externally-imposed load, which is also at the core of designing all load cell elastic elements. Difficulties to finish this process are mainly caused by limitations of structural design, computing and economic budget. Only when the load cell R&D and production rules and elastic element structural design and boundary selection principles are adhered to can the above limitations be resolved and the comprehensive influence of various factors be overcome to turn out the load cell with the minimum fluctuation.
To sum up, below are major design principles for the structure and boundary of load cell elastic elements:
  1. Elastic elements should be designed into an integrated structure instead of the assembled or welded structure, for the friction and displacement between connecting pieces of any assembly structure might cause nonlinearity and dispersiveness.
  2. Elastic element strain area (namely the resistance strain gauge pasting area) receives even stress distribution, and the cylindric and columnar elastic elements should adhere to the Saint-Venant force diffusion principle.
  3. The strain degree of the elastic element strain area should not be too high. Outside the strain area, there should not be the highest strain distribution area and strain concentrated points, since nonlinearity, lag, creep error and fatigue life of elastic elements change with the strain degree of the strain area. When the stress and strain of the strain area are low, the deviation of the ideal linear elastic performance is the smallest. It also means that elastic elements have a large stiffness and a high fixed frequency.
  4. Boundary conditions of elastic elements are major factors affecting measurement performance. The supporting part should be stiff and fixed, and the installation force should be far away from the strain area.
  5. The load introduction mode of elastic elements is an important factor influencing measurement performance. The loading and bearing pressure head and pressure pad design should ensure overlapping between the loading line and the center line of elastic elements, and that the stability of loading points should remain unchanged.
  6. The elastic element structural and shell design should eliminate or alleviate the influence of mechanical disturbing factors (such as horizontal load, bending moment, and torque), and minimize the performance fluctuations. Since the elastic elements are subject to influence of any load, certain degree of nonlinear error will appear.
  7. Convenient and economical pasting of the resistance strain gauge should be taken into full consideration. The pasting surface of the elastic element strain area should be as flat as possible, and precision of lineation (when the high-definition LCD video and image technology is used for positioning, the precision of positioning fork filament should be ensured) and convenience of installing compression clamps should be ensured.
  8. The elastic element pasting resistance strain gauge should be convenient for maintenance and sealing. When elastic elements adopt sealing and welding, the structure and stiffness of the welding membrane as well as the welding groove design are reasonable, avoiding or alleviating the influence on sensitivity and ensuring the welding and sealing quality.
  9. The elastic element strain utilization coefficient can be given by C = εCp/εmax. (The ratio of the average strain actually measured by the resistance strain gauge to the maximum strain). The larger the value is, the better.
  10. In the electronic scale and electronic weighing system, overloading is the most commonly-seen cause of the elastic element failure. If the elastic element structures and accessories allow, overload protection measures should be adopted to improve the safety and reliability of the load cell.

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