In this paper, an assemblysystem is considered to assemble a given product. The demand in finished product is known and fixed, i.e., we know how many finished products it is necessary to assemble by the end of each period (fixed demand). To assemble one product, n different components are necessary. The components are ordered from external independent suppliers. The lead times (the time between order release and component delivery to assemblysystem) of suppliers are independent random discrete variables with known distributions of probabilities. There is no assumption about the form of distributions of probabilities. Any discrete distributions can be used, but these distributions are known before optimization. They are obtained from statistics on the past deliveries of similar components from the same suppliers. The assembly capacity is considered as infinite. We know the unit holding cost per component and per period and the unit backlogging cost per period for the finished product. The orders for components are given at the beginning of each period. The ordered components are delivered at the end of a period. We also know the unit purchasing cost of each component from the selected supplier. The purchasing cost can be increased if the supplier agrees to reduce the randomness of its lead time. The objective is to find the planned lead time and unit purchasing cost, minimizing the total cost.
Research limitations/implications – The collision detection performance is the bottleneck in any virtual assemblysystem. New methods of collision shape representation and collision detection algorithms must be considered.
Originality/value – HAMS introduces the use of dynamic assembly constraints to enhance the virtual assembly performance. HAMS also uses features not yet reported by similar systems in the literature. These features include: automatic or manual definition of assembly constraints within the virtual assemblysystem; the implementation of control panels and widgets to modify simulation parameters during running time to evaluate its influence on simulation performance; assembly data logging such as trajectories, forces and update rates for post-processing, further analysis or its presentation in the form of chronocyclegraphs to graphically analyse the assembly process.
able to execute different functions subject to individual sets of operations within the jobs (Weyer et al. 2015, Ivanov et al. 2016, Nayak et al. 2016, Zhong et al. 2017).
Practical environments for applications of scheduling and sequencing models and algorithms to customized assembly systems are multi-facet. With the help of smart sensors and plug-and-produce cyber-physical systems, the stations in the assemblysystem are capable to change the operation processing and setup sequences according to actual order incoming flows and capacity utilization (Otto et al. 2014, Theorin et al. 2017). In the front opening unified pods technology in semiconductor industry, robots are used in real-time operation sequencing. Robots read the information about the products from sensors and tags and decide flexibly where to forward a wafer batch next (Mönch et al. 2012).
Keywords: disassembly-assemblysystem; remanufactured components; stochastic lead times; machine failures; maintenance plan
Manufacturing companies aim to transform raw materials or components received from their suppliers and to assemble them into finished products to be delivered to their customers. As well as market volatility and the competitive context, the management of this concept differs from one company to another. Supply chain management draws the attention of several researchers in the field of industrial engineering. A growing body of recent books has been published whose researchers present supply chain management with different concepts and techniques in diverse entities related to the logistics chain [1–3]. Stadtler  also investigated the essence of supply chain management and advanced planning. He presented the latest research results for the resolution described in his paper. Management approaches in the field of industrial engineering are diverse. On the other side, with the rise of consumption, concepts of supply chain management are extended. Indeed, more and more of production waste, resources reduction, and even environmental degradation
The choice of an adapted production system is essential in today’s volatile market environment. For this choice the identification of common and distinct assemblies in between the product variants is of high importance. This paper presents four new similarity indices which are aggregated to categorize products. The categorization will support the choice of an assemblysystem type (dedicated, reconfigurable or hybrid) for a selection of product subassemblies when designing a new production facility. On this way, operational areas for a reconfigurable system can be defined. The novel approach is applied to an industrial case study in automotive industry.
ABSTRACT: To face the variable demand of the market, modular and mobile equipment are integrated on production lines. Previous works proposed design and evaluation methodologies to build reconfigurable production systems. However, taking the right decision concerning investments and the choice of equipment may be complex. In this paper, we present RAS design from a risk and decision analysis perspective to support decision making. Market demand scenarios are associated with occurrence probabilities. A decision tree represents consecutive scenarios, for which the decision maker is proposed to make a choice regarding investments for the assembly line. The utility function is computed based on the decision makerˆ as attitude to risk. The objective function computing the final score of a scenario and a decision covers investments, reconfigurability rate and performance of the system. Implications of early investments towards reconfigurability can be identified. The approach is applied on a real use case from the automotive industry.
However, the previous optimization approaches often fail to represent product designer’s and assembly planner’s preferences, so that the resulting assembly sequences are not fully satisfactory from their point of view.
Few authors have mentioned the interest of strategic constraints [Henrioud 89] [Homem 91] [Delchambre 92] [Gottipolu 03] [Perrard 12] that come from either technical or industrial concerns. These constraints are added to other design data that describe the product structure (product model). They are issued from an analysis that is performed by a team made of product designers and assembly planners [Demoly 11]. Assembly planners need assembly plans (or sequences) to define the flows of components throughout the assemblysystem. Surprisingly, few ASP algorithms based on strategic constraints have been developed whereas they make it possible to significantly reduce the research space of assembly sequence generation algorithms (decrease in the number of sequences) and to better satisfy the assemblysystem designers [Martinez 09].
In this study, we wanted to explore surface-patterning eﬀects of a functional lipid amphiphile bearing pH-responsive car- boxylic acid group and show that surface patterning can be induced by both pH and chemical nature of the surface. Small lipids have the advantage of rapid self-assembly without the requirement of additional annealing processes. We have shown in the present investigation that surface patterning can be obtained in water using dip-coating as a simple and fast deposition technique as it allows to control the physico- chemical parameters such as temperature and relative humid- ity, compared to spin-coating. The experiments have been performed using sophorolipids, 39,40 a class of microbial glyco- lipids obtained from yeasts. 41–45 They have been studied for the last 20 years because of their low carbon footprint and their extensive applications as antibacterial and antifungal agents, 46,47 activity against cancer cells, 48,49 cosmetic products 50,51 and biosurfactants. 52–54 The solution properties of non-acetylated, monounsaturated, acidic sophorolipids (SL, see Fig. 1), and in particular their pH-responsive self-assembly have been shown earlier. 55–57 It has also been established that the structure of the molecules greatly influenced the self-assembly. 58 Acidic mono- unsaturated sophorolipids form ellipsoidal micelles in water in a very broad pH range (from pH 11 to pH 3), 59 although at basic pH, formation of nanoplatelets is also observed. 60 We also reported the micellar structure and their surface charge induced by pH. 61,62 The same molecules were also reported to form giant ribbons. 55,58 We have recently shown that the micelle-ribbon duality depends on purity; a standard non-acetylated, monoun- saturated, acidic sophorolipid batch forms micelles, unless it is
Vibration criteria for assembly occupancies
Allen, D. E.; Rainer, J. H.; Pernica, G.
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Evaluating the effectiveness of the systems for the retrieval of 3D assembly models is not trivial. CAD assembly models can be considered similar according to different criteria and at different levels (i.e. globally or partially). Indeed, besides the shape criterion, CAD assembly models have further characteristic elements, such as the mutual position of parts, or the type of connecting joint. Thus, when retrieving 3D models, these characteristics can match in the entire model (globally) or just in local subparts (partially). The available 3D model repositories do not include complex CAD assembly models and, generally, they are suitable to evaluate one characteristic at a time and neglecting important properties in the evaluation of assembly sim- ilarity. In this paper, we present a benchmark for the evaluation of content-retrieval systems of 3D assembly models. A crucial feature of this benchmark regards its ability to consider the various aspects characterizing the models of mechanical assemblies. CCS Concepts
Figure 1 A current view of HIV assembly in macrophages. The viral genomic RNA transcribed in the nucleus is exported to the cytoplasm. The transmembrane envelope (Env) protein is produced in the endoplasmic reticulum and transits through the Golgi apparatus while Gag is synthesized on free cytosolic ribosomes. Both Env and the Gag precursors are targeted to the assembly site through unidentified pathways. The sites of Gag/Env interaction, Gag multimerization and binding to viral genomic RNA remain elusive as well. The main cellular factors suspected to play a role in these trafficking events are indicated; nevertheless most of the time their roles have still to be established in macrophages. The assembly process requires the hijacking of the cellular ESCRT machinery and occurs on cholesterol- and tetraspanin-enriched membrane microdomains. The assembly compart- ment can be connected at least transiently to the plasma membrane through thin microchannels that do not allow virion passage. The limiting mem- brane of the viral assembly compartment as well as the microchannels often exhibit thick molecular coats of which the composition remains obscure. See text for details.
The greatest benefit of on-orbit assembly is the ability to tailor propulsion capability, battery power, and on-the-ground vibration testing. One reason to prefer a modular, assembled-on-orbit approach is that it defeats/hampers an adversary’s ability to know what is coming. A configurable system that can take on a multitude of forms and capabilities as needs arise, confers a significant advantage – an adversary can not effectively respond to an unknown and dynamic capability. The “overhead” associated with SWAP allocated to the assembly process is offset by the ability to reload with specific modules (either to replenish those depleted by use, or to update to newer capabilities), and adapt to unforeseen needs, e.g. not limited to the few configurations provided by pre-integrated CubeSats. In addition to rapid-response single- or multi-U CubeSat form factors, this approach would be extensible to larger, higher performance space assets, such as apertures, through incremental on-orbit assembly advancements with the goal of being as simple as snapping together LEGO bricks. Sample mission capabilities include different spacecraft configurations to address a wide spectrum of use cases. For example, the deployment of RF diagnostic sensors, VIS sensors, IR sensors, and propulsion units.
and d MAX-IV Laboratory, Lund University, SE-22100 Lund, Sweden
Water evaporation concerns all land-living organisms, as ambient air is dryer than their corresponding equilibrium humidity. Con- trarily to plants, mammals are covered with a skin that not only hinders evaporation but also maintains its rate at a nearly constant value, independently of air humidity. Here, we show that simple amphiphiles/water systems reproduce this behavior, which sug- gests a common underlying mechanism originating from respond- ing self-assembly structures. The composition and structure gradients arising from the evaporation process were character- ized using optical microscopy, infrared microscopy, and small- angle X-ray scattering. We observed a thin and dry outer phase that responds to changes in air humidity by increasing its thickness as the air becomes dryer, which decreases its permeability to water, thus counterbalancing the increase in the evaporation driving force. This thin and dry outer phase therefore shields the systems from humidity variations. Such a feedback loop achieves a homeostatic regulation of water evaporation.