Qualitative Motion Control Optimization of the Pad Dressing Process for Bonnet Tool

The surface quality of polyurethane pad attached to the polishing tool is of great importance to the polishing performance, and it is usually maintained by a dressing process. In this study, in order to improve the pad dressing quality, optimization of motion control during the dressing process is presented, from the aspects of the uniformity of the particle trajectories on the pad and the consistency of the relative velocity of each point on the dressed surface. First, kinematic modeling of the particles on the dressing tool based on multibody theory was proposed, which expresses the particle trajectories as a function of the key motion parameters n
_g
and n
_b
. Subsequently, with the above model, simulations were conducted to find the optimized range of rig and rib. The results have shown that the particle trajectories do not distribute uniformly while n
_g
= n
_b
, and along with the increase in the difference between rig and rib, the uniformity of the particle trajectories would improve. After that, to further optimize these motions, the relative velocity of each point on the dressed surface that involves rig and rib was calculated and compared. The results indicated that only if n
_g
>n
_b
are the consistencies of the relative velocity of various points on the dressed surface preferred. Consequently, n
_g
> n
_b
is the premise to satisfy both the particle trajectories and the relative velocity. Furthermore, by considering the limitation of the dressing machine and dressing efficiency, the optimized ranges for rig and rib are 500-1000 and 100-200 r/min, respectively. Finally, experimental validation was conducted and the result agreed well with the above conclusion, which proved the optimization of the motions.