Load cell

Claim 1

An improved load cell for measuring with strain gages the magnitude of forces aligned with a preselected axis, while being insensitive to all other forces and moments, which comprises: a first system of four substantially coplanar beams arranged as the four sides of a parallelogram; a second system of four substantially coplanar beams arranged as the four sides of a parallelogram; the planes of said first and second beam systems each being perpendicular to the preselected axis representing the line of action of the forces to be measured, said beam systems being spaced from each other along said preselected axis and so oriented as to place the individual beams in one of said systems in substantial alIgnment and superposition in relation to the respective beams of the other of said systems when viewed along said preselected axis; one pair of opposite vertices of said first system being rigidly connected to each other and to the corresponding pair of opposite vertices of said second beam system by a first auxiliary structure, and the remaining pair of opposite vertices of said first beam system being connected to each other and to the corresponding pair of opposite vertices of said second beam system by a second auxiliary structure, said first and second auxiliary structures being spaced from each other and free of any interconnection except that provided by said eight beams, and said beams being free of any contact with any surface or body whatsoever along substantially their entire length intermediate their ends; each of said auxiliary sructures being provided with a connecting means or force application surface through which they can be subjected to equal and opposite external forces along the preselected axis, and each of said auxiliary structures being of sufficient strength to be essentially rigid when subjected to forces below a predetermined limit; each of said beams being so dimensioned as to be resiliently yieldable when subjected to bending forces parallel to and induced by the externally applied force to be measure, which externally applied force is transmitted to the respective ends of each of said beams by said auxiliary structures, and said beams being relatively nonyieldable when subjected to linear forces acting along any other axis; whereby appropriately connected strain gages applied to said beams can be calibrated to measure the magnitude of the unknown external force by their indication of the induced bending strains in said beams, all externally applied forces or moments other than forces along the preselected axis inducing compressive or tensile stresses rather than bending stresses in said beams.