Papers by Author: Da Wei Zhang

Abstract: In this paper, a systematic algorithm for the dynamic analysis of 4R 3-DOF wrists is presented. Based on the theory of graph, kinematics is completed. Links are divided into primary links and secondary links. The generalized inertia force of the system results from the motions of primary links and secondary links. The concept of virtual 3R 3-DOF open-loop chain and additional link are introduced to describe the primary links. The generalized inertia forces of 3R 3-DOF open-loop chain, additional link and secondary links are derived by Lagrangian formulation, respectively, based on their location in the wrist. Then the dynamic equation of 4R 3-DOF wrists is got by making a combining. A simulation is performed to illustrate the efficiency of the algorithm.

Abstract: This study has developed a model in order to show the relationship between deflection of the low-rigidity processing system such like thin-walled component and the flexible milling force. The new model takes the deflection of cutter-workpiece system into account. The cutting force is analyzed simulatively by utilizing modified Newton–Raphson iterative algorithm. The simulative results show that the total normal deflection of workpiece–cutter system is the main factor affecting the change of cutting force.

Abstract: This paper presents relationships between some vital parameters and the natural frequency of the ball screw feed drive system. A finite element model (FEM) of a machine tool feed drive system is established with joint parameters added in based on the SAMCEF software. Using the finite element model, the influences of the material properties of the worktable, the diameter of the ball screw and joint parameters on the natural frequency of axial vibration are derived. These results provide a reliable basis for the optimization design of the ball screw feed drive system.

Abstract: In order to meet the requirements of high-precision machine tool, it has been an important factor to select an appropriate way to support the bed. By building a multidisciplinary optimization (MDO) process based on iSIGHT, this article select the deformation difference of the guides and the deformation difference of the joint surface between column and bed of the machine tool as the objective functions, and then conduct a multi-objective optimization (MOO) of the positional parameters of the three-point support. Eventually the optimization result is given and the optimal position of the three-point support is determined.

Abstract: Hydrostatic guideway is widely used in heavy and ultra-precision machine tools due to their high bearing capacity, low coefficient of friction and high capacity of precision-remaining. So it is necessary to carry on theoretical research on its dynamic characteristics. Firstly, the oil-film damping coefficient of closed hydrostatic guideway throttled by capillary is derived. Secondly, a new dynamic mathematical model, considering the oil damping effect, the extrusion effect and the volume effect, of the closed hydrostatic guideway is proposed. Thirdly, the frequency characteristics and step characteristics of it are simulated in Matlab Simulink through the transfer function. Finally, the paper investigates the influence of damping coefficient, the oil pressure, volume effect and the initial oil-film thickness on the dynamic characteristics of closed hydrostatic guideway throttled by capillary.

Abstract: The motorized spindle is a primate part of the machine tool and its thermal characteristics have great influence on the accuracy of the machine tools. The thermal errors of the spindle of a certain type of precision horizontal machining center were measured with PLC acquisition system. By multivariate linear regression method, the axial thermal error model was built. Online real-time error compensation was implemented by applying the FANUC 18i CNC system external machine coordinate system shift function. A verification method was proposed which include three steps: model validation, compensation validation and experimental machining verification. The accuracy of the model was 84.1%, 64.9% and 49.4% respectively. The quantitative analysis results showed the precision was effectively improved and the compensation method was reliable.

Abstract: The text takes Z-Axis of precision machine tool as study object, and proceed the thermal character's experiment of Z-Axis feed system in different working condition (different Cooling strategy, different Feeding speed, load or not). The data of experiment shows the higher of the feed speed, the more heat is generated. Position accuracy can be increase by apply the right load and load is nearly none business with temperature rise. Cooling strategy is nearly none business with temperature rise and may cause the discretization of position accuracy.

Abstract: Model built for the bicycle, road and the driver and contact established between them is the core technological issue for the study of frame’s deformation and driver’s injury on the electric bike accidents. A rigid model of bicycle, road and obstacle is built by using ADAMS software, and the driver is as Hybrid Ⅲ body collision model by LifeMOD software. Contact between them is established, especially on the driver’s chest to handlebar. Base on the rigid-body collision theory, the collision point of head and the speed of the chest were compared with different speed in the range of 15-35km/h. The simulation results shows that the impact between the rider’s chest and handlebar is the main reason to the difference of rider’s dynamic behave. Simulation results verify the validity of this model and lays fundamentals for the study of driver injury in electric bicycle accidents.

Abstract: A complete system of vibration excitation with force feedback control for piezoelectric inertial exciter is presented. The vibration exciter is constructed and its dynamic model is established composed by piezoelectric stack, inertial mass and pretension institutions based on principle of inertia and reaction. The control system takes software program as the core part. The workflow of the digital step sine sweep control software for exciting force limit is recounted. Variety techniques are utilized to ensure real time and stability in the control process, including synchronization output and acquisition, extracting single tone information from waveform, model reference adaptive scaling control for amplitude of the output waveform. Some tests on a micro driving platform with high stiffness are carried out to verify the actual performance of the system. The results show that the piezoelectric inertial exciter and control system designed are very suitable for step sine sweep vibration excitation and exciting force control in high frequency range.

Abstract: Positioning systems with higher speed and accuracy are required in semiconductor package manufacturing, and the product quality and production efficiency can be further improved. So this paper presents a new 2-DOF precision positioning platform with high speed. The platform is directly driven by linear motors, and a novel elastic decoupling mechanism is put forward. High positioning accuracy and good stability in a short stroke, high precision and high speed movement can be achieved using linear motors. The X axis and Y axis kinematic decoupling is realized through the novel elastic decoupling mechanism based on a preloaded spring and flexure hinges, and the dynamic characteristics of the system are improved. The dynamic characteristics of the positioning platform in free state are investigated based on finite element analysis, and the natural frequencies and vibration modes of the positioning platform are obtained, which provides theoretical basis for the further dynamic control of the positioning platform.