Dynamic characterization of multi-axis dynamometers

In this paper, we present a comprehensive technique for accurate determination of three-dimensional (3D) dynamic force measurement characteristics of multi-axis dynamometers within a broad range of frequencies. Many research and development efforts in machining science and technology rely upon being able to make precise measurements of machining forces. In micromachining and high-speed machining, cutting forces include components at frequencies significantly higher than the bandwidth of force dynamometers. Further, the machining forces are three-dimensional in nature. This paper presents a new experimental technique to determine the three-dimensional force-measurement characteristics of multi-axis dynamometers. A custom-designed artifact is used to facilitate applying impulsive forces to the dynamometer at different positions in three dimensions. Repeatable and high-quality impulse excitations are provided from a novel impact excitation system with a bandwidth above 25 kHz. The force measurement characteristics are presented within 25 kHz bandwidth using 3 × 3 force-to-force frequency response functions (F2F-FRFs), which capture both direct and dynamic cross-talk components to enable fully three-dimensional characterization. The presented approach is used to characterize the dynamic behavior of a three-axis miniature dynamometer. The effects of force-application position, artifact geometry, and dynamometer-fixturing conditions are explored. Moreover, the relationship between the force-measurement characteristics and structural dynamics of the dynamometer assembly is analyzed. It is concluded that the presented technique is effective in determining the force-measurement characteristics of multi-axis dynamometers. The changes in dynamometer assembly that affect its structural dynamics, including artifact (workpiece) geometry and especially the fixturing conditions, were seen to have a significant effect on force-measurement characteristics. Furthermore, the force-measurement characteristics were seen to change substantially with the force-application position. The presented technique provides a foundation for future compensation efforts to enable measuring forces within a broad range of frequencies.