Robot tactile sensation can enhance human–robot communication in terms of safety, reliability and accuracy. The final goal of our project is to widely cover a robot body with a large number of tactile sensors, which has significant advantages such as accurate object recognition, high sensitivity and high redundancy. In this study, we developed a multi-sensor system with dedicated Complementary Metal-Oxide-Semiconductor (CMOS) Large-Scale Integration (LSI) circuit chips (referred to as “sensor platform LSI”) as a framework of a serial bus-based tactile sensor network system. The sensor platform LSI supports three types of sensors: an on-chip temperature sensor, off-chip capacitive and resistive tactile sensors, and communicates with a relay node via a bus line. The multi-sensor system was first constructed on a printed circuit board to evaluate basic functions of the sensor platform LSI, such as capacitance-to-digital and resistance-to-digital conversion. Then, two kinds of external sensors, nine sensors in total, were connected to two sensor platform LSIs, and temperature, capacitive and resistive sensing data were acquired simultaneously. Moreover, we fabricated flexible printed circuit cables to demonstrate the multi-sensor system with 15 sensor platform LSIs operating simultaneously, which showed a more realistic implementation in robots. In conclusion, the multi-sensor system with up to 15 sensor platform LSIs on a bus line supporting temperature, capacitive and resistive sensing was successfully demonstrated.

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.

For installing many sensors in a limited space with a limited computing resource, the digitization of the sensor output at the site of sensation has advantages such as a small amount of wiring, low signal interference and high scalability. For this purpose, we have developed a dedicated Complementary Metal-Oxide-Semiconductor (CMOS) Large-Scale Integration (LSI) (referred to as “sensor platform LSI”) for bus-networked Micro-Electro-Mechanical-Systems (MEMS)-LSI integrated sensors. In this LSI, collision avoidance, adaptation and event-driven functions are simply implemented to relieve data collision and congestion in asynchronous serial bus communication. In this study, we developed a network system with 48 sensor platform LSIs based on Printed Circuit Board (PCB) in a backbone bus topology with the bus length being 2.4 m. We evaluated the serial communication performance when 48 LSIs operated simultaneously with the adaptation function. The number of data packets received from each LSI was almost identical, and the average sampling frequency of 384 capacitance channels (eight for each LSI) was 73.66 Hz.