Dynamic active antenna - a principle of dynamic sensing

This paper discusses a dynamic active sensing system, capable of detecting the contact point between a flexible beam and an object. The proposed sensing system is simply composed of an insensitive flexible beam, a torque sensor, a joint position sensor, and an actuator. The dynamics (such as moment of inertia and stiffness) of the sensing system changes when the motion phase switches from non-contact to contact. We show that the natural frequency during contact is generally a multi-valued function of the contact location, which is not desirable from the viewpoint of determining the contact location uniquely. It is also shown that by adding a proper mass at the free end of the beam, we can make the function close to a single-valued one. The additional mass also contributes to reducing the oscillation frequency, which releases us from treating high frequency signals. We design the hardware model based on this idea, and verify the basic principle experimentally