Applied Mechanics and Materials Vols. 336-338

Abstract: Low frequency oscillations due to the lack of damping may occur in power systems under normal operation and will cause system instability. These oscillations are essentially nonlinear power responses which are difficult to extract the inherent characteristics by the time domain method. This paper aims to analyze nonlinear power responses by using the Hilbert-Huang transform (HHT) which is a time-frequency signal processing method which comprises steps of the empirical mode decomposition and the Hilbert transform. Dynamic power system responses, including generator output power and line power are to be processed by the HHT and a set of intrinsic mode functions and the associated Hilbert spectrum are obtained. The generator with most effects on the system will be accordingly found out through the time-frequency analysis and the power system stabilizer will be placed at the generator. Numerical results from a sample power system are demonstrated to show the validity of the time-frequency approach in the study of power system low frequency oscillations.

Abstract: A novel flux switching external rotor doubly salient permanent magnet (DSPM) motor was researched. The two-dimensional model of the motor was established by Ansoft motor design software and the effects of air gap length and rotor pole arc on motor performance were discussed. The simulation results show that larger or smaller air gap length and rotor pole arc improve the torque ripple rate, but the increase of air gap length is helpful to enhance the overload capacity. The conclusions of this article have positive significance for improving the motor performance.

Abstract: This paper presents one kind of digital closed loop control system of MEMS (Micro Electro-Mechanical Systems) vibratory gyroscope, particularly concentrating on the sense mode of MEMS gyroscope. The controller consists of a sine wave source realized by CORDIC algorithm, multiplication demodulators, some low-pass filters and force feedback rebalance module. Compared with the open loop sense system of gyroscope, the closed loop sense system has larger measurement range and wider bandwidth. Besides, the sine wave source realized with CORDIC algorithm can save hardware resources. The digital system is demonstrated on a PCB with a FPGA on it. The test results show that the measurement range of the closed loop system can be increased to 3 times by the open loop, and the bandwidth can be extended to 262Hz from 27Hz of the open loop system.

Abstract: Based on the electrostatic comb drive structure, the comb will do relative motion when it is driven up, and the space between them will be less than 1μm. Considering the micro-scale effect, the Van der Waals force and the Casimir force is used to analyze the influence on the micro-structure, compared with the electrostatic force. The van der Waals force and the Casimir force is almost equivalent to the electrostatic force when the initial gap of the micro-structure and the relative displacement between the micro-structure is relatively small. Therefore the van der Waals force and the Casimir force play an important role in the micro-structure and cannot be ignored.

Abstract: Port of wheel cranes are popularly applied in the logistics, and their lifting, luffing and slewing mechanisms generally adopt DC motors. Traditional method with stepwise resistors to start motors was very complex in calculation and control, but poor performance. Considering specific conditions of wheel cranes, a composited excited system and a new approach with dynamic resistors based on IGBT to start DC motors are presented. By expounding the principle, selection and control method, it illustrates the dynamic resistors could be simple in calculation and control, and could make motors linearly start and smoothly run. Examples prove that the dynamic resistors are perfectly practicable in port of wheel cranes for their small size, simple control method, excellent property and suitability for different DC motors.

Abstract: In this paper, novel configurations of a compact and high damping force engine mount featuring magnetorheological fluid (MRF) is proposed and analyzed. In the mount, a MR valve structure with both annular and radial flows is employed to generate a high damping force. Firstly, several configurations of the MR mount are proposed. The MRF flows in the mount are then analyzed and the governing equations of the MR mount are then derived based on Bingham plastic behaviour of the MRF. Optimal design of the proposed MR mount is then considered. In the optimization, the objective is to find out the optimal structure of the MR mount that can generate a maximum damping force while the off-state force of the mount is constrained in such a manner that the force ratio of the mount is greater than a required value. Performance of the optimized MR mount is then evaluated based on finite element analysis and validated by experimental results.

Abstract: The transfer learning paradigm promises to improve the adaptability of mobile robots which apply machine learning (ML) algorithms for perception and localization. An system framework based on transfer learning paradigm for mobile robots was proposed. The keys of the framework are 1) how to arrange the knowledge database, 2) how to select the source data, source model and priori knowledge, 3) the method to achieve the target model and 4) the method to gain new samples. An experimental platform was built up in order to gain data to verify the framework, whose underpan is the same as the Freescale Cup, MCUs core is ARM Cortex-M4, raw data is stored in a SD card and model is trained offline by a more powerful computer using ML algorithms. The MCU communicates with the powerful computer by Zigbee or WiFi. The experimental platform is cheap and feasible, which is validated by data collection and model training experiments.

Abstract: In this study, a novel class of swarm robots with fuzzy logic based attractive/repulsive force function is presented. This kind of attractive/repulsive function seems to be more general and natural than other explicit mathematical formulations. It shows that the members of swarm robot will asymptotically form a cohesive cluster in predicted bounded region. Simulation example is demonstrated to validate the theoretical results.

Abstract: Applying the global path planning to traditional A* algorithm in a complex environment and a lot of obstacles will result in an infinite loop because there are too many search data. To resolve this problem, this paper provides a new divide-and-rule path planning method which is based on improved A* algorithm. It uses several transition points to divide the entire grid map areas into several sub-regions. We set different speeds in each sub-region for local path planning. Thus the complex global path planning is turned into some simple local path planning. It reduces the search data of A* algorithm and avoids falling into the infinite loop. By this method, this paper designs the path planning of heading the ball, and smoothes the orbit. The simulation results show that the improved A* algorithm is better and more effective than the traditional one.

Abstract: Aircraft anti-skid braking system providing protection for the safety of the aircraft landed by controlling the brake pressure to be maintained slip ratio in best condition. The aircraft anti-skid braking system is hard to control as the nonlinear model of the aircraft dynamics, the uncertainty of friction between the tires and the ground of braking process. With the study of slip ratio and research of aircraft anti-skid braking system dynamics model, the sliding mode variable structure controller is designed. Then index reaching law is adopted to eliminate the system chattering and the performance is analyzed, further more the robustness is strengthen. Simulation results indicate that: the slip ratio follows the optimum slip ratio, the input signal is smooth, achieve the purpose.