Kinematic Analysis and Verification of a New 5-DOF Parallel Mechanism

This paper first designs a new 5-DOF parallel mechanism with 5PUS-UPU, and then analyses its DOF by traditional Grubler–Kutzbach and motion spiral theory. It theoretically shows that the mechanism meets the requirement of five dimensions of freedoms including three-dimensional movement and two-dimensional rotation. Based on this, the real mechanism is built, but unfortunately it is found unstable in some positions. Grassmann line geometry method is applied to analyze its unstable problem caused by singular posture, and then an improving method is put forward to solve it. With the improved mechanism, closed loop vector method is employed to establish the inverse position equation of the parallel mechanism, and kinematics analysis is carried out to get the mapping relationships between position, speed, and acceleration of moving and fixed platform. Monte Carlo method is used to analyze the workspace of the mechanism, to explore the influencing factors of workspace, and then to get the better workspace. Finally, an experiment is designed to verify the mechanism working performance.

Study of a New 5-DOF Parallel Mechanism for Multi-Directional 3D Printing

This paper first designs a new 5-DOF parallel mechanism with 5PUS-UPU for multi-directional 3D printing, and then analyses its DOF by traditional Grubler-Kutzbach and motion spiral theory. It theoretically shows that the mechanism meets the requirement of 5 dimensions of freedoms including three-dimensional movement and two-dimensional rotation. Basing on this, the real mechanism is built, but unfortunately it is found unstable in some positions. Grassmann line geometry method is applied to analyze its unstable problem caused by singular posture, and then an improving method is put forward to solve it. With the improved mechanism, closed loop vector method is employed to establish the inverse position equation of the parallel mechanism, and kinematics analysis is carried out to get the mapping relationships between position, speed and acceleration of moving and fixed platform, Monte Carlo method is used to analyze the workspace of the mechanism, to explore the influencing factors of workspace, and then to get the better workspace. Finally an experiment is designed to verify the mechanism working performance to satisfy the spatial motion requirements of multi-directional 3D printing.

A method to reduce harmonic distortion of MEMS accelerometer

This paper recommends a method to reduce harmonic distortion of MEMS accelerometer. The fifth-order MEMS accelerometer interface circuit designed in this work used the Cascade-of-Integrators, Feedforward modulation structure. This paper analyzes and calculates the main sources of HD, the unstable problem brought by the vacuum encapsulation sensitive structure. The use of front-phase compensation and the increase in loop forward gain helps ensure the system’s stability as well as reduce the system harmonic distortion. Simulink is used to get the simulation results. After harmonic optimization, the third harmonic reached −141.83 dB, the Signal-to-Noise-and-Distortion-Ratio rose to 118.1 dB, the noise density is under 200 ng/Hz[Formula: see text], the effective number of bits rose up to 19.33 bits.

On the correctness of numerical simulation of gravitational instability with the evolution of multiple gravitational collapses

Изучена корректность численных моделей на основе SPH-метода для нестационарных задач гравитационной газодинамики с развитием гравитационных неустойчивостей, в том числе с формированием множественных коллапсов газа в околозвездном диске. Исходные дифференциальные начально-краевые задачи некорректны из-за своей неустойчивости к изменению входных данных. Показано, что в численном методе на основе SPH для решения этих некорректных задач проводится следующая регуляризация: 1) если решение исходной неустойчивой задачи существует на всей временной оси, то ограниченность области изменения переменных в численном методе позволяет удовлетворить условию его устойчивости к малым изменениям входных данных; 2) если решения исходной неустойчивой задачи существуют только на ограниченном временном интервале, как в случае множественных коллапсов, то устойчивый численный метод строится на классе функций, ограниченных фиксированной постоянной, выбираемой из физических соображений. На этом классе функций исходная задача тоже становится корректной. Комбинация SPH-метода с сеточным методом расчета гравитационных сил позволяет обеспечить такую ограниченноcть численных решений. Для выяснении смысла приближенных численных решений, получаемых в вычислительных экспериментах, следует использовать интегральные функции, слабо чувствительные к деталям численного алгоритма. We study the correctness of numerical models based on the SPH-method for nonstationary problems of gravitational gas dynamics with the development of gravitational instability, including with the formation of multiple collapses of a gas in a circumstellar disk. The original differential initial boundary value problems are ill-posed because of their instability with respect to variations of input data. It is shown that the following regularization is performed in the SPH-based numerical method of solving such problems: (1) if the solution to the original unstable problem exists on the entire time axis, then the condition of the method's stability with respect to small variations of input data is satisfied due to a bounded range of the variables; (2) if the solution of the original unstable problem exists only on a bounded time interval, as in the case of multiple collapses, then a stable numerical method can be developed on a class of functions bounded by a fixed constant chosen from physical considerations. On this class of bounded functions, the original problem becomes well-posed. A combination of the SPH method with a grid-based method of calculating the gravitational forces allows one to ensure the boundedness of numerical solutions. In order to clarify a meaning of the approximate numerical solutions obtained by computer simulations, it is necessary to use the integral functions weakly sensitive to the details of the numerical algorithm in use.

Research on Applied Technology and Data Processing with Inversion Method Based on Bayesian Formula

Inversion problem is always represented as ill-posed and unstable problem, especially in the practical application problem such as geophysics, geodetics, ocean science and so on. Regularization item, subject to data misfit is used to stabilize the inversion problem. In this paper we test its validity .The result shows that In selection of the trade-off parameter is very important.Trade-off parameter brings convenience for data processing of inversion method.

Handling and Stability Study on Non-Rod Aircraft Tractor in Backward-Motion

The kinematic model of a tractor pushing an airplane without rod on the flat ground was established. Based on Lyapunov stability theory, backing up the system was proved to be an open-loop unstable problem by kinematic analysis. In this paper, we investigate the effects of different kinematic parameters on the manoeuvring stability of the system in backward-motion. The handling and stability of the reversing operation has been simulated with a steering wheel angle step input. A tractor drivers operation of correcting steering angle has been proposed according to the experiment results. Theoretical verification and experimental results indicates that it is referential to study the handling and stability of the non-rod tractor-aircraft system in backward-motion.