Yutaka Nonomura

This paper reports on detection of raised cloths characteristics by a miniaturized warmth and force sensor. In our previous study, it was demonstrated that a warmth and force sensor discriminates block materials by a heat‐flow peak in a heat‐flow transitional phenomenon. In this study, heat‐flow‐peak characteristics of the raised cloths with different raising‐part lengths were measured, and capability of discrimination of raised cloths was investigated. The experimental results showed that the heat‐flow‐peak value decreases with increase of the raising‐part length when the raising‐part length is under 12 to 15 mm. The raising‐part lengths of the raised clothes were discriminated by the warmth and force sensor.

Accurate multi-axis inertial sensing is required for self-positioning estimation in automatic driving and robot posture control. In particular, a small bias drift is an important requirement for these applications. The bias drift is primarily caused by the external stress from the package. To reduce the bias drift in micro electro-mechanical systems (MEMS) sensors, a stress isolation suspension (SIS) structure inside the sensor chip is considered promising for miniaturization and cost reduction. To easily design an effective SIS, we propose a new design procedure based on the topology optimization method (TOM). The number of elements for the TOM in MEMS devices is often large owing to narrow lines and gaps such as release holes and comb-shaped electrodes, which increasing the computational cost of a TOM using an iterative algorithm. Before the TOM iterative calculation, we first identify the dominant external force mode affecting the bias drift using a single finite element analysis (FEA) with precise detailed geometry. Based on this, the TOM model is simplified. This combination of FEA and TOM allows a biasreducing topology-optimized SIS (T-SIS) structure to be designed with reduced computational cost. For validation, we applied the T-SIS design procedure to a capacitive accelerometer for z-axis bias drift reduction and compared its performance to accelerometers without T-SIS. The experimental results indicate that the T-SIS reduces the z-axis bias drift from ±811 mG to ±9.9 mG (temperature range: -30 °C to +70 °C), which is 1/80 of the bias drift of the sensor without T-SIS.

Silicon-on-insulator (SOI) wafers are used in many micro-electromechanical system (MEMS) devices because of their stable mechanical properties. However, one of the disadvantages of using the SOI configuration is residual stress deformation; strong residual stresses in the buried-oxide layer deform the device and deteriorate its performance. This could prevent the development of high-precision sensors and actuators. In recent years, a new deformation mode caused by this residual stress has been reported, involving tilting of the suspended MEMS structure owing to local deformation of the anchor. However, methods to solve this problem have not yet been proposed. In this study, we propose a simple T-shaped support as a solution to the tilt deformation. We verified its effects by finite element analysis and experiments; the proposed structure was observed to successfully reduce the tip displacement of a SOI-based cantilever by one-fourth. In addition, we applied the proposed method to a parallel-plate accelerometer as a demonstration to confirm that the sensitivity variations of the device reduced from 10.8% to 6.8% using the proposed support structure. Thus, we believe that the proposed design can contribute to the development of extremely accurate MEMS sensors and optical devices.

Assistant robots need a tactile sensing system. We propose a tactile sensor head with a nerve-net sensing system which measures force, temperature and heat flow with a heater simultaneously on a robot finger. For accurate heat flow measurements, it is necessary to stabilize the contact conditions between the sensor head and an object. A sensor stick which consists of the sensor head and an actuator was fabricated to control applied force. Heat flow measurements in three materials of different thermal conductivities such as polyethylene, glass and Aluminum were made with the sensor stick. As a result, three materials were discriminated clearly by heat flow peak values, saturations values and time constants. The tactile sensor stick with temperature measurement and force control is useful to discriminate materials of objects.

This paper reports a 3-axis fully integrated differential capacitive tactile sensor surface-mountable on a bus line. The sensor integrates a flip-bonded complementary metal-oxide semiconductor (CMOS) with capacitive sensing circuits on a low temperature cofired ceramic (LTCC) interposer with Au through vias by Au-Au thermo-compression bonding. The CMOS circuit and bonding pads on the sensor backside were electrically connected through Au bumps and the LTCC interposer, and the differential capacitive gap was formed by an Au sealing frame. A diaphragm for sensing 3-axis force was formed in the CMOS substrate. The dimensions of the completed sensor are 2.5 mm in width, 2.5 mm in length, and 0.66 mm in thickness. The fabricated sensor output coded 3-axis capacitive sensing data according to applied 3-axis force by three-dimensional (3D)-printed pins. The measured sensitivity was as high as over 34 Count/mN for normal force and 14 to 15 Count/mN for shear force with small noise, which corresponds to less than 1 mN. The hysteresis and the average cross-sensitivity were also found to be less than 2% full scale and 11%, respectively.

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.

Tactile sensing is required for assistant robots. A new stacked sensor head was proposed which detects forces and thermal sensations with a nerve-net LSI chip. To measure temperatures and heat flows, the sensor head required a thin and small heater to heat up the sensor head. The features of the polyimide heater are compact, low heat capacity, low power consumption and ease of attaching it to the LSI chip. The polyimide heater consisted of Au 10 nm/Cu 200 nm/Cr 20 nm thickness layers on a polyimide film. The surface of the sensor head heated up to 60 °C by the polyimide heater with 0.3 W. By the Cu thin film polyimide heater, the small stacked sensor head with the nerve-net LSI chip is enable to detect forces, temperatures, and heat flows, simultaneously.

This paper reports a 3-axis MEMS-CMOS integrated tactile sensor for surface-mounting on a flexible bus line. This 3-axis sensor uses a bran-new CMOS LSI with capacitive sensing circuit and other extended functionalities (e.g. configurability and a robust clock data recovery algorithm). The sensor is composed of a flip-bonded CMOS substrate with a sensing diaphragm and a special low temperature co-fired ceramics (LTCC) substrate with vias. These substrates are electrically and mechanically connected by Au-Au bonding, forming sealed differential capacitive gaps. The completed sensor outputs coded 3-axis digital signals according to applied 3-axis force with small cross-sensitivity and hysteresis.

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