Investigation of optical force sensor using the concept of adaptable calibration

Despite the advancement in force sensor technology, conventional force sensors such as load cells are still used in majority of applications. Load cells have strict manufacturing tolerances and are expensive. Other sensing principles (optical and magnetic) are attractive for use in low-cost force sensing application, but are intrinsically nonlinear and are difficult to mass produce with consistent response characteristics. This thesis is based on the concept of adaptable calibration technique developed by George V. Kondraske (US patent number 4873655). The objective is to make the output of an unconditioned sensor to conform to a desired transfer function. For this purpose, a microprocessor based adaptive signal conditioning prototype using a minimum number of components is developed. The prototype uses a reference sensor whose transfer function is known and an unconditioned sensor with an unknown, but repeatable transfer characteristic.; The adaptable calibration concept is employed to make the unconditioned sensor follow the reference sensor over the entire input range. Optically and magnetically based force sensors were used as unconditioned sensors and a load cell was used as the reference sensor in the experimental evaluation of the prototype. The experimental results showed a high degree of correlation between the conditioned output of the optically and magnetically based force sensors and the reference load cell. The generic adaptive signal conditioning system can be a low cost, high performance alternative to conventional signal conditioners.