A vibration mode-based adhesion impulse characterization technique

In this paper a technique for the characterization of small impulses produced by adhesion force is described. The need to address this topic arose in the frame of the ground testing of a space mechanism dedicated to the precise injection of a body into a geodesic trajectory, both as a reference for the spacecraft navigation and for a scientific measurement. The experimental facility consists of a proof mass suspended by a simple pendulum, and a second actuated body which can be moved and quickly retracted from the adhesive contact. At the retraction, the motion of the proof mass is measured to estimate the impulse (and its time duration) produced by the adhesive bonds arose between the two bodies, up to separation. In the current set-up, systematic effects (elastic energy stored in the system), structural vibration modes and measurement noise affect the displacement signal of the proof mass, dominating the adhesion contribution under study. However, the information on the force impulse and time duration – even if with a low signal to noise ratio – is available in the different response of the vibration modes to the same input. An innovative technique is developed to estimate the adhesion impulse and time duration from the amplitudes of oscillation of the vibration modes of the proof mass in a relevant point of the modal shapes. Since no modification nor installation of additional sensors on the sensing body are required, the method can be applied also to systems with limited access and/or possibility of interaction. The vibration modes of the proof mass are calculated by means of FEA allowing for an accurate modal decomposition of the measured signal, focusing on the bottom end of the relevant bandwidth. The amplitudes of oscillation of each mode, even if affected by systematic effects and strong disturbances, are estimated by means of optimal filtering of the dynamic response. By means of the vibration mode-based mathematical model the adhesion impulse and its time duration are calculated from the estimated oscillation amplitudes.