The validation and development of an inline piezoelectric force transducer
University of New Brunswick
The inertial effects present in a commercial dynamometer signal were diagnosed using experimental modal analysis (EMA) and a Timoshenko beam (TB) model. The model accurately predicted the tool tip’s flexural vibration in both directions. The EMA results provided evidence that the tool tip’s transverse vibration had a direct effect on the dynamometer’s measured force signal. Model predictions described this effect as well, however had limited accuracy at higher frequencies and near system resonances, such as the tool arm’s flexural mode and the natural frequency of the dynamometer’s cover plate. Using this model, the effect of system dynamics were identified in orthogonal cutting experiments. The model was able to estimate the response of the tool tip during turning, and was able to predict the response as the tool length changed. The tool arm’s vibration would resonate near the model’s predicted natural frequencies. Similar to the model and EMA results, the dynamometer’s response was affected by tool arm length changes. However, the experimental modal results showed a stronger correlation. The predicted results from the impact hammer tests and TB model were then used to reduce the inertial effect present through the direct inversion approach, which had limited success near the system’s resonances. Predicted correction functions from the Timoshenko model were tested, but deemed inferior to experimentally calculated functions. Lastly, the concept of an inline piezoelectric transducer (IPT) to provide accurate force measurements was assessed. The IPTs, which were mounted on the insert’s bottom and back side, were calibrated through a set of hammer impulses. These results showed that the IPTs were less sensitive to inertial effects compared to the dynamometer. After successfully calibrating the IPTs, they were used in orthogonal cutting experiments. Collected results from the IPTs were compared to the dynamometer’s readings and showed accurate results with a limited bandwidth of 500 to 2000 Hz. Results from the Timoshenko model and prototype IPT design were deemed a success and with future improvements could be applied to machining practices. These improvements are listed in the Closing Remarks, Chapter 7.