Applied Mechanics and Materials Vols. 29-32

Abstract: Strong EMI (Electro-Magnetic Interference) brings the problem of packet error and following retransmission. Especially in motion control area, the widely used Real-Time Ethernet SERCOS III will be seriously affected by EMI from the motor and other power electronic devices. This paper focus on the behaviors of synchronization mechanism of SERCOS III in a strong EMI environment. Strong EMI affect the precondition of SERCOS III’s synchronization mechanism, and the precision of synchronization is highly affected. A Timed Petri Net model of the former mechanism in packet error environment is created and simulated in the Timed Petri Net simulation software CPN TOOLS. The simulation results indicate that the synchronization error is up to about 0.5 to 45 times of retransmission cycle time. This error is unacceptable in motion control area. Then, the paper provides an improved synchronization mechanism, and similar simulation is run. Simulation results indicate that synchronization error is eliminated by the improved mechanism.

Abstract: In order to accurately simulate the process of laser deep penetration welding, a mathematical model to describe laser deep penetration welding was developed by using the heat source derived from the ray-tracing model, and taking account into the effect of keyhole on welding pool. With all the governing equations including continuity, momentum and energy equation, the VOF method is adopted to trace the free surface of the molten pool. Numerical simulation was conducted by FLUENT 6.3 software package. The simulation results show that the formation of keyhole in the weld is caused by recoil pressure.

Abstract: During fault diagnostics of mechanical systems, information fusion methods were widely used to improve the reliability. However, diagnostic information comes from all life cycle of a mechanical device and they are always heterogeneous. Whereas heterogeneous information is difficult to be interconnecting, intercommunicating and inter-operating, so how to represent heterogeneous information is a key problem in integrated diagnostics. In this paper, a novel ontology-based representation method of heterogeneous diagnostic information is presented in detail. Firstly it introduces basic principles of ontology-based modeling. Then three methods of ontology-based information modeling are studied respectively. In the end an example of ontology-based modeling for a diesel engine is given.

Abstract: Vibration signal analysis is one of the most effective ways for condition monitoring of gearboxes. Traditional way is often to mount additional accelerometer sensors on their cases, which has two unavoidable defects: signal-to-noise ratio is often low due to long signal travel paths and it may be not allowable due to space limitations. While embedded diagnostics (ED) can solve these two problems well by embedding sensors close to fault sources. However, embedded sensing design is a great challenge of ED because embedded sensors must have effects on the structure integrity of a gearbox. So it is necessary to determine how to embed sensors in order to ensure normal functions of a gearbox. In this paper, a finite element-based structure analysis method was proposed to perform embedded sensing design of bearings and gears to determine the optimal modified structure size.

Abstract: In view of the fact that dehulled rapeseed cake formed under cold pressing condition is a fractal structure, the relation between the permeability and the pore fractal dimension of dehulled rapeseed cake has been investigated using fractal geometry. The microstructures of dehulled rapeseed cake under six pressing pressures are measured by using scanning electronic microscope and Image-pro image analyzer. The fractal dimensions of pore size distributions are measured by the box-counting method. Combining Hagen-Poiseulle equation with Darcy’s law for flow of fluid through porous media, the relational expression of fractal dimension and permeability has been developed to predicate the permeability of compressed dehulled rapeseed cake under cold condition. The permeability experiments of dehulled rapeseed cake are also carried out in order to validate the predication model proposed in this study. The value of mean relative error is 15.5%. A fairly good agreement is obtained in the case of high pressing pressures.

Abstract: The pretension of the central gear floating NGW planetary gear reducer tumbler bearing is studied. The relative displacements of the inner and outer rings of the tumbler bearing are analyzed according to the light, medium and heavy pretension loads. The tumbler bearing is tested in the different pretension loads. In some operating conditions such as constant power, constant rotating speed and constant torque, etc., the transmission efficiency, vibration and temperature of the reducer are tested and analyzed and the dynamic characteristic curve is obtained. According to the test curve, the principles of choosing the pretension loads of the tumbler bearing are presented. The experiment of this paper is also of reference value for studying the pretension of the other types of reducer bearings.

Abstract: The experimental table of the innovative design of the machine driving plan is introduced. The experimental table mainly consists of CAD system and machine structure assembly platform. Based on the experimental table, CAD, dimensional design and motion analysis of the machine driving plan can be carried out. The basic mechanisms and parts provided by the experimental table are used to assemble the machine driving plan and inspect the design plan. The experimental table has the novel structure, complete types of basic mechanisms and parts, big scale of adjustment of the motion dimensions of the members and simple assembly and jointing. The teaching exploration of the learning model of the innovative design of machine driving based on the experiment is made. Practice proves that the new learning model plays the role of promoting the students’ innovative thinking, cultivation of the students’ practice capability and improving the cultivation quality of talents.

Abstract: Chaotic motion of symmetric laminated composite arch with two hinge supports under transverse periodic excitation was investigated. The nonlinear dynamic equations of the arch are changed into the square-order and cubic nonlinear differential dynamic system by Galerkin method, and its homoclinic orbit parameter equations are also acquired. The critical conditions of horseshoe-type chaos are obtained by using Melnikov function. The influence of loading frequency on chaotic region are analysed by numerical calculation. The motion behaviors of system are described through the bifurcation diagrams, the time-history curve, phase portrait and Poincaré map. The results are given as follows. The influence of loading frequency on chaotic region are significant. When the height of arch reach some value, the system can occur horseshoe-type chaos. The system of symmetric laminated composite arch under transverse periodic excitation may occur steady motion and chaotic motion.

Abstract: A novel 5-DOF upper limb rehabilitation robot, which can implement single joint and multi-joint complex motions and provide activities of daily living (ADL) training for hemiplegic patients, was presented. The solutions of the robot’s kinematics equation were set up by the method of D-H according to the 5-DOF rehabilitation robot for upper limb. Based on the software of ADAMS, the mechanism was simulated and analyzed. Thus the movement of robot is determinate in a certain condition of importation. It offered important data for the trajectory planning and the actual intellective control of rehabilitating robot.

Abstract: Building is a complex and opening system, and settlement plays an important role in its safety. Settlement components of building are analyzed and their calculating methods are introduced. Based on growth of building settlement, three aspects of building safety risks induced by excessive settlement are analyzed, namely excessive differential settlement, total incline and disharmony with living environment. Four methods are proposed to reduce and prevent the risks caused by settlement, which include improving calculating method, determining soil mechanical parameter reasonably, predicting time-dependent settlement and optimizing design of the building foundation.