Development of a floating element photoelastic force balance

We present a floating element force balance design that uses an optical measurement of the force using photoelastic stress analysis. The force sensing element consists of pins embedded in photoelastic polyurethane pads, which generate an internal stress when the floating element is loaded that is observed via a transmission polariscope. A series of known loads and their corresponding fringe patterns allow a calibration matrix to be derived using a polynomial model solved by least squares regression. Finite element analysis (FEA) simulation is carried out to validate the proposed method. The balance then measured a lift curve of the NACA0015 wing at low speed. A comparison of the photoelastic balance and a commercial, 6-axis strain-gauge load cell showed typical differences of less than 6 % . This optical approach enables accurate measurements with inexpensive and simple components inside the sensor. This work demonstrates that a photoelastic balance is a simple, inexpensive, and sensitive force transducer.