A new type of touch sensor for detecting contact pressure at human fingertips is presented. Fingernails are instrumented with micro LEDs and photodetectors in order to measure changes in the nail color when the fingers are pressed against a surface. Unlike traditional electronic gloves, in which sensor pads are placed between the fingers and the environment surface, this new sensor allows the fingers to directly contact the environment without being impeded by any object between the finger and the environment. The finger force is detected by measuring changes in the nail color; hence the sensor is mounted on the nail side rather than the finger pad. The technique termed “photoplethysmography” is used for measuring the nail color. A prototype sensor is built and tested, and is used to create a new “free-fingered” electronic glove. The new sensor system is applied to the interface of a cooperative human-robot control system. The information acquired from the finger touch sensors is interpreted within the context of a given task description, and the robot motion is coordinated with the human motion based on the interpreted human behavior. This method is applied to a collaborative task in which a robot equipped with a powered screwdriver assists the human by observing the human hand assembling cable connectors.

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