Force oscillations in contact motion of industrial robots: An experimental investigation

This paper describes the results of research on the oscillatory behavior that has been systematically experienced in the force measured during contact motion of an industrial robot. Two phenomena have been found to bf mainly responsible for it, namely, the arm structural elasticity due to the torsional flexibility of the joints and the torque ripple of the brushless motors. The structural elasticity is characterized by a resonance frequency which varies with the arm configuration, while the torque ripple has harmonics of frequency proportional to thf motor velocity. Most severe oscillations, and even loss of the contact, arise when the resonance and ripple frequency values come closer or match, so that elasticity and ripple excite each other.