Soft high precision contact positioning control

Abstract

The problem of approaching with high precision contact two generally actuated objects or work-pieces in industrial environment is discussed in a large parameter range. It is first noticed that main three actuation systems, electrical, pneumatic and hydraulic, obey the same type of equations which are coupled to object dynamics including its specific material reaction. For complete safety, especially for avoiding excitation of long lasting and potentially damaging vibrations, a controller is researched which guarantees that at contact the two object are at full rest with respect to each other in the sense that both relative velocity and acceleration are strictly zero. This is not always the case with usual position and force controls. Present controller is an explicit family of extended PDA-type one including on top a new part the role of which is to exactly fulfill contact conditions. It is shown that minimum time control is not possible and that minimum energy control is not easily realizable, owing to natural system constraints. A workable control, allowing to achieve extremely high precision in micron range, is analytically displayed.