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Robot interaction control with fixed impedance parameters usually fails to achieve the desired interaction behavior, motivating the introduction of variable impedance or admittance control. A gradient-descent (GD) impedance learning approach with a limited iteration number can make robots more compliant by minimizing an objective function. However, due to the nature of GD optimization, impedance parameters can not be adjusted in time by this approach, resulting in degraded robot compliance. This paper combines GD optimization with sparse online Gaussian process (SOGP) to develop a GD-based SOGP (GD-SOGP) impedance learning approach for variable admittance control. A high-fidelity mathematical model of a 7-DoF collaborative robot called Panda is applied for simulation studies. It is shown that the proposed GD-SOGP impedance learning can make the robot more compliant and outperforms the GD impedance learning in terms of impedance convergence.

ByteDance offers several massively popular products such as TikTok, Jinri Toutiao and Douyin for creating, sharing and discovering a variety of content, in which recommendation plays an indispensable role for helping billions of users to interact with highly personalized content. The personalized experience in products largely comes from the ability of sophisticated machine learning models to make accurate predictions based on users’ interests and one key component in such systems is the user profile service.In this paper, we introduce Instance Profile Service (IPS), a large scale distributed system for managing unstructured profile data as well as serving various feature computations at ByteDance. Different products leverage IPS in many different ways and place various demands on the system, in terms of complex computation logic and latency requirements. One major challenge in the design of a large scale user profile system is how to strike the right balance among efficiency, scalability, reliability and versatility. With deliberated choices made on its design and implementation, we demonstrate IPS can provide a simple yet flexible solution to all these products while meeting the targeted high availability and performance goals. At ByteDance, IPS has successfully replaced many legacy profile systems and runs on thousands of machines. One of our largest production instances can process a hundred million feature queries and tens of millions writes per second.

Package delamination after reflow is a critical failure attribute for power electronic devices. Delamination reduces the path for removing the heat generated by the device and severely affects its functionality. Major factors affecting delamination in clip bonded devices include the moisture absorption of epoxy molding compound (EMC) and induced thermomechanical stresses in the package. In this study, four advanced formulation EMCs developed to improve delamination resistance of a clip bond power package were evaluated. These EMCs were formulated to the have low moisture absorption as well as low modulus. This was achieved using multi-aromatic resins, low moisture absorption hardeners and increased filler content (>80wt%). To determine the moisture absorption characteristic of the materials, these were subjected to moisture sensitivity level 1 (MSL1) conditions and 3x reflow at 260°C. Preconditioning was performed to simulate the stress that the package would experience during PCB assembly. The amount of moisture absorbed and moisture diffusion coefficient of the EMC after saturation were determined using weight gain experiments. Thermal analysis was done to determine coefficients of thermal expansion, glass transition temperature and elastic modulus of the EMCs. The stress induced by the EMC on die and leadframe interfaces were calculated based on the material property characterization results. Amount of delamination before and after reflow simulation was measured and analyzed using Scanning Acoustic Microscopy. Overall results showed that low moisture absorbing (

Surface mount technology (SMT) is widely used and being the major component assembly technology, it offers more reliable assembly with less package weight, less printing circuit board (PCB) area and much faster assembly speed, when compared to conventional through-hole (TH) technology. The surface mount device (SMD) packages structure, materials, processes, and assembly process are quite different from through-hole packages, as well as quality requirements. The SMD package are mounted on board by soldering process, it can be sensitive to moisture when exposing to environment, the moisture content of the SMD packages must be well controlled in order to prevent the delamination occurring during board solder reflow process. To understanding the moisture sensitivity performance of SMD packages, moisture sensitivity level (MSL) classification is introduced to identify the SMD packages performance from MSL 1 to MSL 6 at a reflow temperature of 260°C. Package achieved the most robust level MSL 1 can be interpreted as not sensitive to moisture, the floor life is unlimited under typical room temperature and humidity, also do not need dry packing as special control. As the continuous tightening of automotive requirements, package delamination level after MSL 1 become more and more concerned as a semiconductor packaging focusing point, zero delamination after MSL 1 is being pushed to be a solid requirement by semiconductor customers. The delamination between epoxy molding compound (EMC) and leadframe (LF), as well as die attach adhesive (DA) and LF are well known and understood, and with quite mature solutions e.g. enhancing the interfacial adhesion etc. In this study, a unique MSL 1 delamination symptom in the area around DA fillet is reviewed and discussed, root cause is identified by surface analysis techniques, and links to the die attach effect. The potential optimization in terms of packaging materials and process is proposed and validated by assembled packages, which subject to MSL 1 conditions and 3 times reflow at 260°C. Material characterization on the optimized packaging material is conducted to understand and verify the material impact, delamination levels are checked by C-Mode Scanning Acoustic Microscope (C-SAM) to assess the package interfaces after MSL 1 and reflow. Result shows zero delamination after MSL 1 can be achieved by the proposed optimization, a packaging solution can be concluded to enable MSL 1 zero delamination for leaded SMD package.

Enabling zero delamination in automotive power electronics is a key factor to meet environmentally demanding applications and stringent standards set by the automotive industry as delamination impacts overall package quality and device reliability. This study aims to evaluate potential electronic packaging solutions that will enable delamination-free packages for automotive power applications. Fractional factorial experimental design was used to investigate the effect and interaction of surface roughening, epoxy molding compound optimization and alternative deflash method in package interfacial delamination after assembly manufacturing and MSLI preconditioning. Extended environmental stress tests were performed to further validate the robustness of the proposed solutions. Overall results showed that EMC optimization has the highest impact to reduce delamination on package interfaces. Combination of the proposed packaging solutions successfully enabled an MSLI delamination-free robust clip bond power package that is highly capable of surviving harsh environments furthermore meeting the highest automotive quality standards.

Clip bonding technology is widely and increasingly used in microelectronic packages because of the increasing demand for high power and low loss automotive grade power package. Compared to wire bonding, clip bonding have much wider interconnection contact area which apply high lead solder with high thermal conductivity, exhibits lower electrical resistance and lower inductance. Meanwhile, large interface between different BOMs brings the stress management challenge during thermal cycling (TCT), especially under the increasingly higher automotive qualification requirements, solder crack including package level and board level solder crack during TCT is one of the key concerns of clip bond power package reliability.As most common encapsulation material, epoxy molding compound (EMC) provides strong mechanical protection and electrical insulation to electrical circuits, coefficient of thermal expansion (CTE) difference of EMC is one of the key factors contributing the overall package stress level. In most recent developments, EMC with high filler loading is preferred because of excellent moisture sensitivity level (MSL) performance and less CTE mismatch between EMC and silicon die. On the other hand, the CTE mismatch of EMC to Leadframe (LF) and package to printed circuit board (PCB) will be higher, resulting higher stress level to package internal bonding solder and external PCB solder. In this study, the consideration of EMC grades with different resin types, different mechanical properties, different CTE ranges and their impact to package integrity and reliability are discussed, optimization direction of EMC is proposed. The TCT performance of solder joint with different EMC materials are evaluated and investigated, advantages and disadvantages of different options are examined and discussed. Result shows that solder crack issue can be improved by preferred EMC types in suitable CTE range without negative effect, solder joint can survive under the thermal cycling longer than 4000 cycles. The TCT robust clip bond power package can be realized by the optimization of epoxy molding compound.

We demonstrate a novel way to control the coupling rate in coupled ring resonators by controlling the relative position of the nanowires between the two cavities to modulate the resonance frequencies. A new system is presented and experimental results show that by tuning the coupling rate, the coupled ring resonators can be stimulated at the same time due to the same resonance frequency. This study will provide new ways to manipulate coupled photonic cavities in silicon photonic circuits and benefit the development of coupled optical cavities to achieve advanced functions. Ministry of Education (MOE) National Research Foundation (NRF) Accepted version

An integrated volatile organic compounds (VOC) sensor based on silicon photonic ring resonator system is presented in this paper. A thin absorption layer is coated on the silicon surface required to selectively trap the target gas and response as refractive index change. This acts as the main sensing unit, which subsequently affect the resonance peak position. The relative high sensitivity (1.7 pm/ 1000 ppm for acetone), high stability (

Flying robots have many applications in constrained environments. But they are facing difficulties when they cannot take off again without human intervention if they are not in upright position after a fall. This paper presents a method to design a self-recovery mechanism for the quadrotor to protect itself and recover autonomously after accidental falls. The presented quadrotor with a self-recovery mechanism is 29.5 cm × 29.5 cm × 21 cm in size, and 340 g in weight. The self-recovery mechanism is consisted of two 27.5 cm long arms symmetric with respect to the body of the quadrotor and two cambered carbon fiber protecting-sticks forming a protective cage over the fuselage. The proposed self-recovery mechanism is simple and well-structured. With the self-recovery mechanism, the quadrotor can easily take off after a fall irrespective of the initial landing posture.

This paper presents algorithms for role assignment and formation control in multi-robot systems. Two circumstances have been discussed. One is with fixed target formation positions, and the other is without fixed target formation positions. For the former circumstance, a modified Hungarian algorithm has been proposed to assign a role for each robot with the purpose of consuming less time to form the target configuration. For the latter circumstance, the appropriate target formation location has been determined firstly. The algorithm based on both total distance and consuming time has been proposed. In the end, the desired configuration has been formed based on the distance-angle method with a virtual leader. Simulation results are presented to validate the proposed algorithms.