Friction-based tactile sensor for measuring grip security

A method for assessing grip security, the method comprising detecting slip at a contact surface, wherein the contact surface has at least a first contact surface region and a second contact surface region, the first contact surface region being configured to resist slip less than the second contact surface region,

• wherein the contact surface comprises a plurality of protrusions extending from a base surface, the protrusions in the first contact region extending away from the base surface a distance less than the protrusions in the second contact region.

A method of estimating friction at a contact surface, the method comprising providing a plurality of protrusions extending from a base surface to a tip, measuring displacement of the tip in three dimensions using a sensor detecting light emanating from the base surface within a cavity of a given protrusion, reflecting from a reflector located at or near a distal end of the cavity, estimating forces applied to the tip in three dimensions at a moment of slip based on the displacement.