Vibrotactile sensor generating impulsive signals for distinguishing only slipping states

This paper mainly concerns a vibrotactile sensor capable of generating impulsive high-frequency signals by which only slipping states of an object can be distinguished. Slip information is so indispensable to guaranteeing the grasp of an object and detecting static friction coefficient that various kinds of slip sensors have been proposed. However, there has been no report on such a slip sensor that slip signals supply real-time critical information to extract only a slipping state from various contact states. We propose a sensor structure with surface ridges in the concavity of which strip-shaped sensor elements are vertically fixed. We analyzed the slip signals of the sensor and showed that the output signal in slipping states was originated in the free vibration mode of the sensor elements. Then, we verified, by using a two-fingered robot hand that the slip signals of the sensor could distinguish the slipping state from other contact, release, or rolling state. Finally, we demonstrate that the slip signal of the sensor output guarantees a slipping state to increase the grasping force of the two opposing robot fingers not to drop the object, by making full use of the impulsiveness of the slip signals.