Zhouping Yin

A connector-based hierarchical approach to assembly sequence planning for mechanical assemblies

This paper presents an approach to find feasible and practical plans for mechanical assemblies based on a connector-based structure (CBS) hierarchy. The basic idea of the approach is to construct plans for an assembly (i.e. the root node of the CBS hierarchy) by systematically merging plans for primitive structures in the CBS hierarchy, while the plans for primitive structures are built using one of three methods: by reusing the existing plans, by retrieving the stored plans, and by geometric reasoning. The input to the approach consists of the assembly solid model, the connector-based relational model (CBRM) graph, the spatial constraint graphs, and the selected base part for the assembly, all of which are assumed to be generated previously in an interactive and/or automated way. Then, a CBS hierarchy for the assembly is automatically derived from the input CBRM by firstly establishing its functional model, which is constructed from the CBRM by decomposing the assembly or resulted part sets with respect to their connectors. Based on the CBS hierarchy, a set of assembly precedence diagrams representing good plans for the assembly are generated by merging plans for primitive structures systematically in a bottom-up manner. It can be proved that the proposed approach is both correct and complete. To verify the validness and efficiency of the approach, a variety of assemblies including some complicated products from industry are tested in the experimental CBHAP planner.

Energy Harvesters for Wearable and Stretchable Electronics: From Flexibility to Stretchability

The rapid advancements of wearable electronics have caused a paradigm shift in consumer electronics, and the emerging development of stretchable electronics opens a new spectrum of applications for electronic systems. Playing a critical role as the power sources for independent electronic systems, energy harvesters with high flexibility or stretchability have been the focus of research efforts over the past decade. A large number of the flexible energy harvesters developed can only operate at very low strain level (≈0.1%), and their limited flexibility impedes their application in wearable or stretchable electronics. Here, the development of highly flexible and stretchable (stretchability >15% strain) energy harvesters is reviewed with emphasis on strategies of materials synthesis, device fabrication, and integration schemes for enhanced flexibility and stretchability. Due to their particular potential applications in wearable and stretchable electronics, energy-harvesting devices based on piezoelectricity, triboelectricity, thermoelectricity, and dielectric elastomers have been largely developed and the progress is summarized. The challenges and opportunities of assembly and integration of energy harvesters into stretchable systems are also discussed.

The Fast Multilevel Fuzzy Edge Detection of Blurry Images

To realize the fast and accurate detection of the edges from the blurry images, the fast multilevel fuzzy edge detection (FMFED) algorithm is proposed. The FMFED algorithm first enhances the image contrast by means of the fast multilevel fuzzy enhancement (FMFE) algorithm using the simple transformation function based on two image thresholds. Second, the edges are extracted from the enhanced image by the two-stage edge detection operator that identifies the edge candidates based on the local characteristics of the image and then determines the true edge pixels using the edge detection operator based on the extremum of the gradient values. Experimental results demonstrate that the FMFED algorithm can extract the thin edges and remove the false edges from the image, which leads to its better performance than the Sobel operator, Canny operator, traditional fuzzy edge detection algorithm, and other multilevel fuzzy edge detection algorithms

A Universal Denoising Framework With a New Impulse Detector and Nonlocal Means

Impulse noise detection is a critical issue when removing impulse noise and impulse/Gaussian mixed noise. In this paper, we propose a new detection mechanism for universal noise and a universal noise-filtering framework based on the nonlocal means (NL-means). The operation is carried out in two stages, i.e., detection followed by filtering. For detection, first, we propose the robust outlyingness ratio (ROR) for measuring how impulselike each pixel is, and then all the pixels are divided into four clusters according to the ROR values. Second, different decision rules are used to detect the impulse noise based on the absolute deviation to the median in each cluster. In order to make the detection results more accurate and more robust, the from-coarse-to-fine strategy and the iterative framework are used. In addition, the detection procedure consists of two stages, i.e., the coarse and fine detection stages. For filtering, the NL-means are extended to the impulse noise by introducing a reference image. Then, a universal denoising framework is proposed by combining the new detection mechanism with the NL-means (ROR-NLM). Finally, extensive simulation results show that the proposed noise detector is superior to most existing detectors, and the ROR-NLM produces excellent results and outperforms most existing filters for different noise models. Unlike most of the other impulse noise filters, the proposed ROR-NLM also achieves high peak signal-to-noise ratio and great image quality by efficiently removing impulse/Gaussian mixed noise.

Virtual prototyping of mold design: geometric mouldability analysis for near-net-shape manufactured parts by feature recognition and geometric reasoning

This paper presents a virtual prototyping (VP) approach for geometric mouldability analysis of near-net-shape manufactured parts. The geometric mouldability of a part depends on the geometry of the part and is affected by the number and types of undercut features. A virtual prototype (VP) of a mold, which is a realistic digital product model, is generated by combining automated and interactive approaches to evaluate the mouldability of a part in the early stages of the product development cycle. The automated approaches for generating a VP are proposed to construct the parting surface, cores and cavity of the mold based on the recognized undercut features. Interaction with the VP in the virtual reality environment allows the designers to evaluate the mouldability of a part in an intuitive way. A new volume-based feature recognition method and data structure using non-directional blocking graph (NDBG) have been developed to recognize both isolated and interacting undercut features in a uniform way. Firstly, a set of potential undercuts are generated by performing the regularized difference between the part and its convex hull. The optimal parting direction is then determined by minimizing the number of undercuts. Finally, undercut features are identified from a set of potential features with respect to the optimal parting direction. The potential features of an interacting feature are generated by two stages: volume decomposition, in which the volume to be recognized is decomposed into convex cells by intersecting it with half spaces of its faces having concave edges; and reconstruction of features, in which potential features are reconstructed through systematically connecting the small cells using NDBG of the cells and the part. Moreover, multiple interpretations of an interacting feature can be easily generated by simply subtracting potential external undercut features from each other in different orders. A system configuration for the proposed VP has been developed and implemented using available virtual reality technologies.

Highly sensitive, temperature-dependent gas sensor based on hierarchical ZnO nanorod arrays

The low-cost growth of patterned zinc oxide (ZnO) nanorod arrays (NAs) has attracted much attention with the rapid development of electronics and nanotechnology. A mechanoelectrospinning-assisted continuous hydrothermal synthesis method (MES-CHSM) is proposed to direct-write the precursor patterns for the growth of the ZnO-NAs, in a digital, low-cost, and mask-free manner. The morphology and distribution of the hierarchical ZnO nanorods, having a tremendous impact on the gas response, are determined by the process parameters of the MES-CHSM. It is highly desirable that the diameter, interval, orientation and distribution of the ZnO nanorods can be tuned proactively by changing the growth time, the solution concentration, the nature of the precursor layer, and the pattern by MES. The ZnO-NAs exert excellent Ohmic contact with interdigital electrodes when exposed to dry air, NO2 gas and then dry air again. The gas response of the ZnO sample is surface-reaction-determining. The gas sensing results show highly sensitive and repeatable response–recovery cycles following NO2 gas exposure and air purging, respectively. The dynamic response of the gas sensor shows a temperature-dependent response to NO2, even at low concentrations (1–50 ppm). The best gas response is located between 200 °C and 225 °C. Gas sensors, prepared by different process parameters, show two laws regarding the corresponding responses and the NO2 concentrations: approximately linear and saturation regions. The optimal process parameters are presented to postpone the occurrence of the saturation region, to enlarge the measuring range.

Versatile, kinetically controlled, high precision electrohydrodynamic writing of micro/nanofibers

Direct writing of hierarchical micro/nanofibers have recently gained popularity in flexible/stretchable electronics due to its low cost, simple process and high throughput. A kinetically controlled mechanoelectrospinning (MES) is developed to directly write diversified hierarchical micro/nanofibers in a continuous and programmable manner. Unlike conventional near-field electrospinning, our MES method introduces a mechanical drawing force, to simultaneously enhance the positioning accuracy and morphology controllability. The MES is predominantly controlled by the substrate speed, the nozzle-to-substrate distance, and the applied voltage. As a demonstration, smooth straight, serpentine, self-similar, and bead-on-string structures are direct-written on silicon/elastomer substrates with a resolution of 200 nm. It is believed that MES can promote the low-cost, high precision fabrication of flexible/stretchable electronics or enable the direct writing of the sacrificial structures for nanoscale lithography.

Continuously Tunable and Oriented Nanofiber Direct-Written by Mechano-Electrospinning

A mechano-electrospinning method is presented to direct-write oriented nanofiber with high deposition accuracy in continuously tunable manner. This method uses a large nozzle to deposit high-resolution fiber-arrays by near-field localization. Due to the existence of mechanical drawing force, a higher resolution pattern can be direct-written by a lower voltage, which just keeps the Taylor cone stable. Then the fiber is stretched through a moving substrate, by which the deposited fiber can be continuously tuned from 400 nm to 200 nm in a linear relationship. The effects of the speed on the diameter and morphology of fibers are studied, and the analysis of the mechanism of the fiber alignment is given. The positionability and controllability make mechano-electrospinning very different from the traditional electrospinning, which only collects the fibers in the form of nonwoven fabric. In addition, the fibers fabricated by this method can directly deposit over a large flat area in the form of arrays and complex patterns with high precision.

Controllable self-organization of colloid microarrays based on finite length effects of electrospun ribbons

This paper presents a mechanoelectrospinning (MES)-assisted surface-tension driven self-organization to provide a possible route towards inexpensive generation of large-scale ordered microarrays in a controllable manner. To control the self-organization driven by surface tension and Plateau–Rayleigh instability, finite length effects are utilized to manipulate the self-organizing processes and adjust the competition between nucleation and free surface instability. We introduce fine ribbon-lattices to determine the boundary conditions of ribbons to make use of the finite length effects. The ribbon-lattices are electrodeposited precisely by MES, borrowing ideas from the “Chinese kite”, by involving the mechanical drawing force and the electric field force. Then the samples are transferred to a moisture-rich environment in which the ribbons absorb water vapour and become liquid lines. Surface instability emerges and leads the liquid lines to controllable self-organization. We uncover the controllable area to manipulate the self-organization behavior. A uniform or hierarchical microarray with a specific position, gap and droplet-size can be generated in a continuously tunable manner. This bottom-up method provides a digital approach for the fabrication of large-scale ordered microarrays and micropatterns.

Visibility theory and algorithms with application to manufacturing processes

Visibility arising from computer vision, geometrical design and complexity analysis is widely used in manufacturing processes. According to the definition of the visibility cone of a point, two kinds of visibility of a feature, namely a complete visibility cone and a partial visibility cone, are defined, and the relation between visibility map and complete visibility cone is also discussed. To solve a kind of accessibility and setup problem in mold parting, NC-machining and CMMs inspection path planning, a procedure is proposed to perform visibility analysis with respect to the geometry of the part, the shape of the effector, and degrees of freedom between part/effector. A new method for computing visibility cones is formulated by identifying C-obstacles in Configuration Space (C-Space), in which a general and efficient algorithm is presented and implemented using visibility culling. Compared with previous methods, the proposed algorithm is efficient even in very complex scenes. Finally, the contributions and limits of our work are discussed.