Distributed tactile sensing is crucial to perform stable, subtle, and precise manipulation so that a robot can recognize and handle objects properly. However, currently existing skin sensors still have common problems such as complex and expensive production or are difficult to integrate into robot hands. In particular, a practical distributed soft skin sensor system that can cover various parts of the robot hand, measure force in 3axis, with a subcentimeter spatial density, and digital output at the same time does not exist yet. This paper discusses uSkin, a soft, distributed, 3-axis force sensor for robot hands and presents its implementation for multi-curved fingertips. The sensor is lowcost, easy to manufacture, and can measure normal and shear forces. The experimental results revealed that this sensor has 10% hysteresis for perpendicular force with a maximum range of 6 N. The Signal to Noise Ratio (SNR) value of 54 dB for 0.4 N load was achieved, which constitutes the state of the art for this kind of sensors. Evaluation experiments also showed that the distributed 3-axis load cells could produce vectors that represent the shape of objects. This opens the possibility that the sensor can be used for classifying different shapes. Furthermore, the fingertip sensor was installed on the Allegro hand and the changing force measurements when the robot is grasping an object are presented.

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