Frictional memory in servo control

Frictional memory is a delay between a change in sliding velocity or normal force and the consequent change in friction. Previously, several sensitive studies of frictional dynamics have shown the presence of frictional memory in tribology experiments and servo controlled machines. In the present work, frictional memory is shown to be necessary to account for the extinction of stick slip at high stiffness. By showing that frictional memory is required to account for the gross behavior of common mechanical systems, the range of mechanisms known to exhibit frictional memory is greatly extended. Stiff (high gain) control has long been used to eliminate stick slip in precision, position-controlled mechanisms. Consideration of frictional memory will permit the systematic design of these controllers so that stick-slip free motion is achieved.