ACCELERATION BASED INDIRECT FORCE MEASUREMENT IN METAL-CUTTING PROCESSES

A milling cutter instrumented with a three-component accelerometer is investigated as a sensor of dynamic cutting forces. Two major causes o f measurement errors are considered. These causes are: (1) the flexibl e mode vibrations, and (2) inertial and viscous forces associated with the ''rigid body'' motion of the spindle. A self-tuning filter consis ting of two subsystems is applied to attenuate these errors. The first subsystem converts accelerations from the rotating spindle into stati onary coordinates. It also analyses the corrupted signal and calculate s an optimal filter structure and the settings for the actual operatin g conditions. This information is utilized by the second subsystem, a digitally programmable filter, which performs signal correction in rea l time. Two examples are presented to illustrate performance of the pr oposed ''natural'' sensor. In the first example, a periodical force ap plied from an exciter is reconstructed from the accelerations measured during spindle rotation. The second example deals with estimation of a force impulse generated by means of an impact hammer.