The elastic element of the center shear beam weighing sensor is formed on the basis of the center beam structure. In order to improve the ability of the parallel beam weighing sensor to resist bending and torsional loads and meet the needs of assembling a single weighing sensor on a larger electronic platform scale, the elastic element of the parallel beam structure is pasted on the upper and lower parallel beams of the resistance strain gauge to become a flexible beam, and a parallel center strain beam is added. At this time, the upper and lower parallel beams only play the role of increasing the longitudinal and transverse stiffness. They are very soft in the direction of load introduction and do not affect the output sensitivity, but they are very rigid in the transverse and longitudinal directions to ensure the stability of the center strain beam under external loads. In order to meet the needs of assembling a larger electronic scale table size for a single weighing sensor, the width of the upper and lower parallel flexible beams of the elastic element of the center parallel beam structure is increased to improve the ability to resist torsional and bending. In order to ensure the measurement accuracy and working stability of a single electronic platform scale, the anti-torsion and anti-bending stiffness of the center shear beam weighing sensor should be improved as much as possible, and the natural frequency should be increased. To this end, the force mode of the central parallel beam must be changed, that is, the bending stress of the central beam is changed to shear stress, which forms a new type of central shear beam weighing sensor. When the central shear beam weighing sensor is assembled into an electronic platform scale, it is connected to the support and load-bearing table bracket on the base respectively. When the object to be weighed is placed on the table of the platform scale, the central beam generates shear stress. As we all know, shear stress cannot be measured, but the principal stress and principal strain generated by it, which are perpendicular to the axis of the central beam and compressed at 45°, can be measured, which is exactly what is needed to form a Wheatstone bridge circuit. The central shear beam weighing sensor has the following characteristics: (1) Since the resistance strain gauge is attached to the central shear beam with greater rigidity, the cross section of the central shear beam does not change after loading, and the shear force is evenly distributed along the length of the beam. Therefore, the four working arms of the bridge produce basically the same resistance change, resulting in the central shear beam weighing sensor having good inherent linearity and small hysteresis, and it is easy to achieve a high level of accuracy. Moreover, it has fast dynamic response, with a rise time of one thousandth of a second.
(2) Because the width of the upper and lower parallel beams is increased, the central shear beam is protected to the maximum extent. The bending and torsion loads from any direction on the electronic scale platform are borne by the upper and lower parallel flexible beams instead of being transmitted to the central shear beam, ensuring that the central shear beam only senses the vertical load on the electronic scale table, ensuring the accuracy of the measurement.
(3) Compared with the same range of bending type weighing sensors, since it does not use the bending stress of the central beam but the shear stress of the central beam, it is easy to adjust the error caused by the additional stress of bending and torsion. Using a relatively small central shear beam weighing sensor, a larger size electronic platform scale can be assembled, making it simple, compact, low-cost, and greatly improved in accuracy and reliability.
(4) The internal space of the central shear beam weighing sensor is large, which is convenient for installing printed circuit boards, and is conducive to wiring, welding bridges, circuit compensation, and adjusting four-corner errors. (5) A new process of directly coating the protective sealing coating on the central shear beam can be used to effectively seal the resistance strain gauge attached to it, without the need to design a special protective shell. This protective sealing measure not only simplifies the protective sealing process and reduces the manufacturing cost, but also makes the expansion or contraction rate of the central shear beam elastic element caused by temperature changes consistent, reducing the temperature gradient error. When the central shear beam weighing sensor is assembled with the scale frame and table of the electronic platform scale, first, the installation force at both ends cannot be transmitted to the central shear beam, and secondly, the weighing sensor must have an overload protection measure, that is, one or more overload protectors must be set to effectively protect the impact load borne by any position of the electronic scale. The appropriate overload protection gap is adjusted through test to achieve the purpose of overload protection.