Smart Stiction

Abstract

Stiction (sometimes referred to as “stick-slip”) is a word construction derived from friction and sticking. It represents the forces due to static friction which manifests itself as a cohesion force threshold which must be overcome to enable relative motion between otherwise stationary objects in contact [1]. Following the onset of movement, resistance to motion is provided exclusively by dynamic friction. In engineering, stiction is usually considered to be a problem [2]. However, in certain applications, stiction can be deliberately implemented to advantage, as in the case of soft robotics where movement is to be achieved through controlled sliding rather than rolling or crawling. It is not easy to make a clear distinction between adhesion and stiction. Both are related to inter molecular viscoelastic effects and both are influenced by surface roughness. Adhesion (for example magneto adhesion and electro adhesion) concerns the application of an astrictive force which causes prehension whereas magnetostriction and electrostriction pertain to the control of friction though a magnetic or electric field respectively. Should it not be possible to sustain post contact retention on lifting, then adhesion properties are absent. If, despite this, the frictional coefficient is still controllable by means of some external influence, then stiction is present.