Papers by Author: Shi Ming Ji

Abstract: A novel orthogonal 5-DOF parallel manipulator was proposed, and the statics equations of the 5-DOF parallel manipulator were derived in closed forms based on its layout feature, then the statics transmission indices wer defined, and discussed in detail. It can provide theoretical base for the applications of the 5-DOF parallel machine tool. The novel 5-DOF parallel manipulator can be used as the precision platform in which the requirements for high stiffness, high accuracy and good technological efficiency.

Abstract: Considering the demand of precision in mould structural surface polishing method, a new method based on soft abrasive flow machining(SAFM) was proposed, which was supposed to achieve polydirectional and multi-angle cutting acting on the surface of the workpiece by utilizing the irregular motion of both wear particles and the media in turbulence flow. Thus as the monodirectional marks on the machined surfaces was eliminated, the disadvantage in machining precision in conventional abrasive flow machining(AFM) method would be overcome. According to the particle distribution characteristics of SAFM, a two-phase dynamic model of abrasive flow oriented to SAFM combined with Discrete Phase Model(DPM) was built to analog simulation with the software Fluent. Sequently the mechanism of ultraprecision machining towards mould structural surface was analyzed briefly. Simulation results show that the abrasive efficiency along the flow passage can be influenced by the development of turbulence and the distribution of dispersed phase. Thus there a specific region can be obtained in the passage in which the abrasive efficiency is relatively stable.

Abstract: Gasbag polishing is an automatic, flexible, controllable and practical technique, which has wide application prospect. A pulse technique based on robotic gasbag polishing system is proposed. Its main principle is to use the Pulse Width Modulation (PWM) technique to control the switching time of High-speed Solenoid Valve (HSV). It can not only control the internal pressure of gasbag, but also make the rubber gasbag present pulsation with PWM technique. Moreover, the performance of pulse technique is presented and the effects of different frequency pulse pressure on the polished surface roughness are analyzed through a series of experiments. At last, experimental results show that the pulse technique can improve the polished surface roughness more rapidly in certain extent with appropriate pulse frequency and process parameters comparing with conventional gasbag polishing way.

Abstract: Combining the advantages of rheological behavior of magnetorheological fluid (MRF) and flexibility adjustability of rubber gasbag, a magnetorheological flexible gasbag polishing technique applied to free-form mould is proposed. With the development of robotic gasbag polishing technique, the flexibility of rubber gasbag can be adjusted by three methods of changing its internal pressure controlled through a pressure control unit, its own material property and structural parameter, and the rheological behavior of MRF inside of it in response to the application of an alterable magnetic field. Effect of rheological behavior to the flexibility of rubber gasbag and surface quality of mould is the single most important focus in this paper. The magnetorheological flexible gasbag polishing system is established and rheological behavior of MRF with magnetic field is described. Through polishing experiment focusing on the relationship between the surface roughness and current around electromagnetic coil, it can be obtained that magnetorheological flexible gasbag polishing technique is effective to improve surface quality when increasing current around coil in certain extent.

Abstract: The paper discusses the near wall region of soft abrasive particle flow in weak force finish machining method. Turbulent flow morphology in near wall region of rectangular channel with different viscosity is numerically simulated and compared. Through the analysis of kinetic equation of abrasive particle, the abrasive particle motion trace of different diameter in turbulent flow with different viscosity is simulated and compared. The result reveals the condition under which the fluids with different viscosity can form Turbulent flow is different. The greater the viscosity is, the greater the velocity needed is. Also the quantitative relation of velocity and flow volume is available to determine the pump parameter in abrasive particle flow machining. Fluid at wall has pressure and shear stress on work piece. The greater the viscosity and velocity is, the greater the wall pressure and shear stress is. So it is helpful to make material removal on work piece surface. But the greater the viscosity is, the greater the velocity attenuation of abrasive particle is. Abrasive particle mainly move along the flow direction with the movement of fluid. The velocity attenuation of larger diameter abrasive particle is much than the smaller particle but the latter can maintain greater velocity in a longer distance favorable for collision with the work piece surface salient.

Abstract: This paper studies mainly apples non-destructive selection technology, and presents the principle and implementation of non-destructive selection system for apple quality based on the theory of the fuzzy and neural network. Firstly, we can differentiate the kinds of apples by neural network theory. Then, the apple’s quality greatly depends on its size, shape, and color, which are considered as three input parameters in selection system. The pick-up of three character parameters is handled by computer image processing. Only one output parameter is apple rating, which is fall into three grades: A, B and C. Regarding three character parameters as input, we obtain the apple grade based on fuzzy arithmetic. Finally, we set forth the archetypal non-destructive selection system, which includes robot, AGV, conveyor, sensors and etc. Results of experiments show that this method can distinguish the apple’s quality as well as we set before the experiments, and the non-destructive system is feasible.

Abstract: The attenuation of structure vibration is very slow when flexible strucure is stirred external force. It seriously affected the life of flexible structure. Smart structures used piezoelectric ceramics as actuators are an effective manner to solve the problem. This paper uses Fiber Bragg Grating (FBG) as sensors and piezoelectric ceramics as actuators to study the active vibration control for the resonance of the smart beam. Two groups of piezoelectric ceramics will be used for vibration exciter and vibration abatement, respectively. The fiber smart beam is excited to a sharp vibration nearby the particular resonance frequency by controlling the frequency of the vibration excitation. The vibration signal is measured by the FBG sensors and the close loop feedback control is fulfilled by the vibration abatement group, and the vibration amplitude of the fiber smart beam is abated. The experiment results show that the resonance amplitude of the beam is obviously abated by adjusting the frequency, amplitude and phase of the vibration abatement circuit.

Abstract: A parallel micromanipulator (PmM) which can be applied into the precision machining is optimized in the paper. This paper adopts a methodology to determine a set of optimal design parameters of PmM whose workspace is as close as possible of being equal to a prescribed cuboid dexterous workspace (PCDW). The kinematic problem is analyzed in brief to determine the design parameters and their relation. Then, an optimal design procedure which adopts the generalized pattern search algorithm in the genetic algorithm and direct search toolbox of Matlab is proposed to solve these problems. As an applying example, the results of four cases PCDW to PmM are presented. And the design result is compared with a concept of the distance between the best state of the PmM and the requirement of the operation task. The method and result of this paper are very useful for the design of micromanipulator for the machining field which requires the high precision and accuracy.

Abstract: Static analysis plays an important role on the design and applications of manipulator. In this paper, The torque balance equations of the spherical 3-DOF manipulator was derived in closed forms by analyzing the relationship of its input and output torques, then the torque transmission evaluation index and the global torque transmission evaluation index were defined based on the torque balance equation and discussed in detail, at last, by using the physical model technique, the parameters of the spherical 3-DOF manipulator were optimized based upon the global torque transmission evaluation index. Moreover, an integrated design scheme of the spherical 3-DOF manipulator was confirmed when satisfied the assembly conditions, which can provide theoretical base for the applications of the spherical 3-DOF manipulator. The spherical 3-DOF manipulator can be used as the waist, wrist and the ultra-precision machine in which the requirements for high stiffness, high accuracy and good technological efficiency.

Abstract: A single-chip silicon condenser microphone with a sandwich diaphragm and an electroplating perforated copper backplate has been developed. The sandwich diaphragm is designed to have a slight tensile stress. The backplate is made using copper electroplating technology and perforated with circular holes. Perforated circular holes on backplate are laid out as hexagon to adjust air-gap damping between diaphragm and backplate to critical damping to enlarge frequency bandwidth of microphone. Fabrication is simple enough and only needs five photolithography marsks. Measurements show the open-circuit with 9V bias voltage reaches 5.45mv/Pa in 1KHz, pull-in voltage is 14V, and the flat frequency response within 3Db is from 100Hz to 20KHz. The performances of microphone meet the requirement of industrial use. Thereby, it has promising prospect for industrial and commercial field.