Event-Driven Tactile Sensing System Including 100 CMOS-MEMS Integrated 3-Axis Force Sensors Based on Asynchronous Serial Bus Communication

This paper describes an event-driven tactile sensing system including 100 CMOS-MEMS integrated 3-axis force sensors of 2.7 mm square footprint for providing robot tactile sensation. The system has the following features: (1) the event-driven function of the CMOS LSI integrated in the sensor can reduce the number of stimulated sensors, (2) the stimulated sensors send data packets on a shared differential bus line of 90 cm by asynchronous serial communication, and (3) the data collision avoidance and adaptation functions of the sensor enable multiple sensors to be stimulated simultaneously. According to the event-driven function, the sensor sends data packets only when the digital sensing value is over a set threshold. The collision avoidance function detects data collisions, stops sending data, and avoids further collisions. The adaptation function varies the time interval between data packets and reduces the bus occupation by a specific sensor. These functions make the sensor autonomous to some extent that can judge whether and when to send data packets. The sensor in the system can operate at a data sending rate of 1 Mbps, 2 Mbps, 4 Mbps, or 8 Mbps by configurations. When 100 sensors with the same function settings are stimulated, almost the same amount of data packets are received from each sensor. As the data rate changing from 1 Mbps to 8 Mbps, the average sampling frequency of the 100 sensors is about 36.87 Hz, 73.00 Hz, 142.99 Hz, and 274.28 Hz with the data packet format of 244 bits.