Lai Xinmin

A study of a reverse engineering system based on vision sensor for free-form surfaces

Reverse engineering can quickly create a CAD model of a new product, in which, the sensor, sampling planning and surface reconstruction are three crucial elements. In this paper, a reverse engineering system involving a new vision sensor, an improved sampling planning module and a fine surface reconstruction module is developed. A characteristic of the proposed sensor is strong linearity between output and input, obtained by the structure optimization when a simple lens replaces the asperic lens. Back propagation (BP) neural network error compensation heightens accuracy. To increase efficiency of digitization, an improved sampling planning approach is proposed; it is based on surface curvature and tangent line slope of a measured point. In surface reconstruction, a new adaptive extracting approach based on curvature of surface reconstructs the non-uniform rational B-spline (NURBS) surface for the scattered data. The accompanying reverse engineering experiment proves the proposed system to be reliable and efficient.

Theoretical and Experimental Study on Dynamic Coefficients and Stability for a Hydrostatic/Hydrodynamic Conical Bearing

This paper presents a theoretical study and experimental method to recognize the dynamic performance (stiffness and damping coefficients) of an externally pressurized deep/ shallow pockets hybrid conical bearing compensated by flat capillary restrictors. The equations governing the flow of fluid film in the conical bearing together with the pressure boundary condition and the restrictor flow equation are solved by using the finite element method. A delicate test rig is constructed and bearings having a big end diameter of 97 mm, a length of 90 mm, and a radial clearance of 0.02-0.025 mm are analyzed. It is assumed that the fluid film force of the hydrostaticlhydrodynamic conical bearing is characterized by a set of linear stiffness and damping coefficients. The experiment used the impulse excitation method to recognize these coefficients and established their characteristics under different operating conditions. Numerical results are compared with the experimental results. The stability parameters of hybrid conical, hydrodynamic, and hydrostatic bearings are compared. The results show that the hybrid conical bearing has the advantages of high load carrying capability and high stability under small eccentricity.

Robust fixture layout design for multi-station sheet metal assembly processes using a genetic algorithm

The optimal fixture layout is crucial to product quality assurance in the multi-station sheet metal assembly processes. Poor fixture layout may lead to product variation during the assembly processes. In this paper, a genetic algorithm (GA)-based optimisation approach has been presented for the robust fixture layout design in the multi-station assembly processes. The robust fixture layout is developed to minimise the sensitivity of product variation to fixture errors by selecting the appropriate coordinate locations of pins and slot orientations. In this paper, a modified state space model for variation propagation in the multi-station sheet metal assembly is developed for the first time, which is the mathematical foundation of optimal algorithm. An e-optimal is applied as the robust design criteria. Based on the state space model and design criteria, a genetic algorithm is used to find the optimal fixture layout design. The proposed method can greatly reduce the sensitivity level of product variation. A four-station assembly process of an inner-panel complete for a station wagon (estate car) is used to illustrate this method.

Performance of Flat Capillary Compensated Deep/Shallow Pockets Hydrostatic/Hydrodynamic Journal-Thrust Floating Ring Bearing

This article presents a theoretical study concerning the static and dynamic performance of an externally pressurized deep/shallow pockets hydrostatic/hydrodynamic journal-thrust floating ring bearing compensated by a flat capillary restrictor. A new fluid-lubricated hybrid bearing that can support a radial and an axial load at the same time is designed and manufactured that can satisfy modern rotary machinery at high speed. The equations governing the flow of the inner and the outer and the radial and the axial fluid film in the journal-thrust floating ring bearing together with the pressure boundary condition and the restrictor flow equation are solved by using the finite element method. The study describes the influence of the eccentricity ratio and journal rotational speed on the static and dynamic characteristics such as the load-carrying capacity, the friction moment, the friction power efficiency, the volume flow rate, the stiffness, the damping, the critical mass, etc. By analyzing the journal center motion, it is theoretically proved that the journal section plays a decisive effect on the stability and the thrust section makes the journal-thrust bearing more stable. This bearing has been applied to certain turbine expansion units and rotates stably at 45,000 rpm. The result shows that the bearing has the advantages of low friction, high stability, and can be easily controlled and applied in turbine machinery and other high-speed rotational machinery.

Recent progress in fabrication methods for micro structures on optical thin film

Optical thin film with micro structures on the surface is expected to be widely applied on large-area optical devices such as thin film solar cells and flexible display, due to the enchancement of the light extraction efficiency or light utilization. Geometric characteristics and physical properties of micro structures such as shape precision, structural defects and residual stress, have comprehensive influence on the quality of optical thin film. Ultraviolet (UV) curing and hot embossing are two major processes for the fabrication of micro structures on the optical thin film. This review surveys the recent progress of UV curing and micro hot embossing in terms of polymeric material behavior, filling mechanism and demolding process. For the UV curing process, filling process is firstly discussed and the bubble defects, residual layer and size effect are systematicall analyzed. Then, the curing mechanism is well summarized and the effect of UV dose on the physical properties of micro structure is futher explored. Finally, the challenges in the demolding process for micro structures with high aspect ratio are cataloged and some corresponding approaches are proposed. For hot embossing process, thermoplastic polymer flow behavior is investigated and single-peak and dual-peak deformation molds are discovered. Novel methods, such as ultrasonic assisted and gas assisted process are addoped to improve the filling height. Besides, demolding temperature and demolding force are two major factors for the micro structure defects. In addition, mold fabrication techniques are comprehensively summarized into direct machining method and indrect machining method. Some innovations are also introduced for the roller mold fabrication. Furthermore, the recent advancement of roll-to-roll apparatuses for the UV curing process and hot embossing process is systematically cataloged as well. The highest rolling speed reaches 5 and 3 m/min for R2R UV curing process and R2R hot embossing process, respectively. However, the current status is still far from the final destination of 60 m/min for the large-scale industrial application. Therefore, in order to meet the final destination, technical challenges and future trends are presented for fabrication methods of micro structrues on optical thin film, in terms of size effect modeling in micro or submicro scale, process control for the comprehensive performance of micro structures, large-area mold fabrication technologies with high-precision and high-consistency, and coordinate control technology for the multi rollers in roll-to-roll movement.

A Simplified Method for Optimal Sensor Distribution for Process Fault Diagnosis in Multistation Assembly Processes

The fault diagnosis plays an important role for product quality improvement in the multistation assembly processes (MAPs) and the efficiency of diagnosis significantly depends on the sensor distribution strategy, such as the number and location of the sensor. The diagnosis-oriented sensor distribution optimization in MAP has been studied for the purpose of a full diagnosis of the process faults with the minimum sensing stations number as well as the minimum sensor number. However, the existing studies are time consuming with the complex analysis and calculation processes, and no intuitive principles are given directly according to the process configuration. In this paper, a simplified method for the optimal sensor distribution is presented for a fully diagnosis of the process faults. First, two different types of assembly modes are defined and the variation trans-missibility ratios for these two assembly modes are discussed based on the process configuration. Then, the conditions for between-station diagnosability and within-station diagnosability are analyzed, respectively. Based on the results, the optimal sensor distribution method is derived finally. After comparing with the former methods, the optimal sensor distribution in this paper is based only on the process configuration without using for model-based matrix computation. Therefore, the proposed method greatly simplified the process.

Tolerance Optimization Considerations Applied to the Sheet Metal Compliant Assembly

ABSTRACTSheet metal parts are widespread used in the assembly of product such as automotive and airframes bodies. This paper presents how Dimensional Engineering (DE) process and the simulation-based tolerance analysis used in the development process of the assembly tolerance analysis. Focusing on the sheet metal component, which should be treated as non-rigid part, compliant assembly analyzing is adopted in the simulation process. Deviations of the components due to the tolerance between pin locator and hole and the locator layout scheme are defined as the key point characteristics (KPCs) during the optimization process. Inspection data incorporated close-loop optimizing approaches is applied to the final deviation estimation in simulation. Dimensional engineering software solution, 3DCS, is used as the analyzing tool in the case study