Dynamic contact sensing by flexible beam

This paper discusses a new dynamic sensing system capable of detecting the contact point between a flexible beam and an object. The proposed sensing system, named dynamic antenna, is simply composed of an insensitive flexible beam, a torque sensor, a joint position sensor, an actuator, and a payload at the tip end of the beam. The contact point can be detected through estimation of the oscillation frequencies of the beam in contact with the object. At first, a dynamic model of the sensor is derived. It is proved that the contact position is uniquely determined if every mode of the natural frequencies of the beam is taken into consideration. Next, it is shown that information of the fundamental and the second natural frequencies is sufficient for unique determining of the contact point if the beam has uniform mass and stiffness distribution. In practical realization, the fundamental and the second natural frequencies of the beam in contact with the object are extracted from the torque sensor measurements with the use of the maximum entropy method. Then, the frequencies are mapped into the contact-point coordinate. Extraction of the frequencies and mapping them into the contact point constitute a sensing strategy which is tested under experiment. The experimental results show the feasibility of the dynamic antenna sensing scheme.