Apparatus and method for sensing angular displacement

An apparatus for measuring angular motion of an object, comprising:

• a reference object that independently maintains an angular position despite rotational motion of the object;
• a reference device coupled to the object, the reference device including an angular compensator having an output providing a control signal that controls rotation of the reference device with respect to the object so that the reference device maintains an angular relationship with the reference object;
• and
• a position unit having an input that receives the control signal and an output that provides an indication of the rotational motion of the object based upon the control signal.

A method for measuring angular motion of an object, comprising the steps of:

• arranging a reference object so that the reference object is coupled to the object but maintains an independent angular reference despite the angular motion of the object;
• controlling a reference device to move in relation to the reference object so that the reference device substantially maintains an angular relationship with the reference object;
• and
• measuring the motion of a platform based upon an amount that the reference device is controlled in the step of controlling.

A system for measuring a displacement angle of an object, the system including an apparatus comprising:

• a container having fluid;
• a rotating object having weight, the rotating object being allowed to rotate freely within the container and is positioned within the container, wherein the weight of the rotating object is substantially suspended by the fluid;
• and
• a sensing element configured to sense an angular displacement of the rotating object.