Faculty members of Case Western Reserve University conduct extensive research in various aspects of Biomedical Engineering. The Orthopedic Engineering Laboratory is involved in the design and development of implanted orthopedic devices. They routinely perform experiments to measure the mechanical properties of soft and hard tissue, i.e., ligaments and bone, as part of their research in orthopedic device design. We have designed and produced a variety of very delicate load cells like those displayed in figure A, using foil and semiconductor strain gages and traditional load cell configurations. We have also developed new load cell configurations, many of which are unique to the particular application. These load cells are used as part of a research project to measure the creep and stress rupture properties of soft tissue.
That same basic configuration is used by one of our long-term clients as a strain transducer to measure the deformation of large civil engineering structures. We have produced over 10,000 of these devices over a 12 year period and enjoy an enviable record for reliability and repeatability of this product. Figure B shows the deformation element of this strain device with the terminal strip and mounting tabs.
We believe the keys to this product quality success are based on the selection and rigorous application of the gage installation steps on a well designed and machined straining element. Working with a premier gage manufacturer, we developed a four element strain rosette that includes the Wheatstone Bridge circuit requiring only four solder connections to attach the leads.