US Patent 8156569 Protective helmet with movable outer shell relative to inner shell

A helmet is wearable on a user's head for mitigating neck injury. The helmet incorporates an outer member which defines a concavity; an inner member, at least a portion of which is located within the concavity; and a path-motion guide mechanism which couples the inner member to the outer member. The path-motion guide mechanism permits guided relative movement between the inner member and the outer member in response to an impact force. The guided relative movement is constrained to one or more predetermined paths and comprises, for each of the one or more predetermined paths, relative translation and/or rotation between the inner and outer members.