Cell Layout Research Articles

A hybrid optimization algorithm with genetic and bacterial operators for the design of cellular manufacturing systems

We consider a design problem for cellular manufacturing systems. In order to improve the efficiency of the designed system, three optimization problems are considered jointly in the same optimization procedure: cell formation, workload balancing and cell layout. A hybrid metaheuristic algorithm with genetic and bacterial operators is developed to optimize the performances of the designed cellular manufacturing system. The results obtained on benchmark problems are discussed.

Assessment of shop floor layouts in the context of process plans with alternatives

Abstract Paper aims The paper seeks to compare the performance of three layouts in a make to order (MTO) production system with high product variability. Originality No previous work sought to compare job shop, cellular and virtual cell layouts in an MTO system with high product variability, with just 21 resources, a low amount. The analysis considered models with the same capacities and demand for the three layouts. Research method The complete factorial design and ANOVA were used with simulation. The main effects plots of the control factors for response variables were obtained (e.g. throughput, lead time, and resource utilization). Main findings The virtual cell layout had results similar to the job shop, but achieved better outcomes compared with the traditional cell. Implications for theory and practice The knowledge gap regarding virtual cells signals the importance of this topic, as well as the possibilities not yet investigated about it in manufacturing companies.

Automatic layout generation of robotic production cells in a 3D manufacturing simulation environment

Facing an increasing demand for flexible and reconfigurable production lines, the development and implementation of extensive simulation tools for faster planning of robot cells or entire production lines continue to gain importance. Simulation tools offer the opportunity to test robotic applications before the physical existence of the system, to ensure reachability and feasibility of the actual cell implementation and examine compliance with the desired cycle time during process execution. During simulation analysis, extracting data from the given layout and building the corresponding simulation model takes a considerable amount of time. To reduce the required time, one applicable approach is to automate the generation of the simulation model using data from tools used prior to the simulation analysis, such as layout planning tools. So far, data representation limits the straightforward data exchange between planning and simulation tools and constitutes a time-consuming task during simulative ramp up. This paper focuses on the automatic layout generation in a 3D simulation environment. To enable automatic layout generation, a suitable representation of the imported layout data is derived. For this purpose, available data exchange formats are compared and their suitability for automatic model generation is evaluated. As a result of the evaluation, AutomationML is identified to meet the requirements best. Using this format, the development of an interface is described, which makes it possible to import layout data into the simulation environment of Visual Components and automatically generate a simulation-model of the complete robotic cell layout.

SRAM Circuits for True Random Number Generation Using Intrinsic Bit Instability

This paper describes a novel approach to a true random number generator (TRNG) using SRAM circuits. The principles of operation are described in the context of past work on integrated circuit TRNGs. The required modifications to standard SRAM arrays are minor and have little impact on the area. Experimental results from large 1-Mbit SRAM arrays fabricated on a 55-nm process using the foundry supplied SRAM cell layouts show good results. Simple helper functions, suitable for very small hardware implementation, allow improvement, including the ability for the resulting binary strings to pass all of the National Institute of Standards randomness tests. We describe the circuits, their principle of operation and statistical behavior, as well as the underlying physical mechanisms providing the entropy.

A Map-like Micro-Organization of Grid Cells in the Medial Entorhinal Cortex

How the topography of neural circuits relates to their function remains unclear. Although topographic maps exist for sensory and motor variables, they are rarely observed for cognitive variables. Using calcium imaging during virtual navigation, we investigated the relationship between the anatomical organization and functional properties of grid cells, which represent a cognitive code for location during navigation. We found a substantial degree of grid cell micro-organization in mouse medial entorhinal cortex: grid cells and modules all clustered anatomically. Within a module, the layout of grid cells was a noisy two-dimensional lattice in which the anatomical distribution of grid cells largely matched their spatial tuning phases. This micro-arrangement of phases demonstrates the existence of a topographical map encoding a cognitive variable in rodents. It contributes to a foundation for evaluating circuit models of the grid cell network and is consistent with continuous attractor models as the mechanism of grid formation.

Analysis of the charge sharing effect in the SET sensitivity of bulk 45 nm standard cell layouts under heavy ions

For nanometer technologies, SET is increasingly growing in importance in circuit design. Accordingly, different hardening techniques were developed to reduce the Soft-Error Rate. Considering selective node hardening technique based on standard cells, this work evaluates the SET response of logic gates from a Standard-Cell library under heavy ions. Overall, it is observed that the usage of NOR and NAND gates coupled with an output inverter provides reduced SET cross-section and increased threshold LET compared with the standalone OR gate and AND gate, respectively. With the results gathered in this work, circuit designers can implement reliability-aware synthesis algorithms with selective hardening more efficiently to tackle the threat of SET in combinational circuits.

A photovoltaic window with sun-tracking shading elements towards maximum power generation and non-glare daylighting

Vertical space bears great potential of solar energy especially for congested urban areas, where photovoltaic (PV) windows in high-rise buildings can contribute to both power generation and daylight harvest. Previous studies on sun-tracking PV windows strayed into the trade-off between tracking performance and mutual shading, failing to achieve the maximum energy generation. Here we first build integrated models which couple the performance of sun-tracking PV windows to the rotation angles. Secondly, one-degree-of-freedom (DOF) and two-DOF sun tracking are mathematically proven to be not able to gain either maximum power generation or non-glare daylighting under reasonable assumptions. Then we derive the optimum rotation angles of the variable-pivot-three-degree-of-freedom (VP-3-DOF) sun-tracking elements and demonstrate that the optimum VP-3-DOF sun tracking can achieve the aforementioned goals. When the restriction of the proposed model is relaxed, the same performance can be achieved by the optimum one-DOF sun tracking with extended PV slats and particular design of cell layout, requiring less complicated mechanical structures. Simulation results of nine global cities show that the annual energy generation and average module efficiency are improved respectively by 27.40% and 19.17% via the optimum VP-3-DOF sun tracking over the conventional perpendicular sun tracking. The proposed optimum sun-tracking methods also reveal better protection against sun glare. The optimum VP-3-DOF sun tracking is also demonstrated to be applicable to horizontal PV windows, as those applied in the sun roof of a glass greenhouse.

A method for planning human robot shared tasks

A multi criteria method, in support of the planning of shared human robot assembly tasks is presented in this paper. CAD models are used for the extraction of a product's assembly sequence, whilst an algorithm is applied for the generation and examination of alternative assignment scenarios. The design algorithm performs the joint planning of task-to-resource assignment and cell layout at the same time. The evaluation of each planning scenario against a set of ergonomics, quality and productivity criteria is made for the identification of the most efficient ones. The method's implementation, in the form of a prototype planning tool (Task Planner), enables its application to a pilot case from the automotive industry. The results indicate that the method can provide high quality solutions with respect to the end users' criteria and has potential applicability as a decision making support tool in the planning stage.

Machine Reliability in a Dynamic Cellular Manufacturing System: A Comprehensive Approach to a Cell Layout Problem

Machine Reliability in a Dynamic Cellular Manufacturing System: A Comprehensive Approach to a Cell Layout Problem

Impact of Cell Layout and Device Structure on On-Voltage Reduction of 6.5-kV n-Channel SiC IGBTs

A box cell layout and a hole-barrier structure were used to realize low-on-voltage n-channel 4H-SiC IGBTs with 6.5-kV blocking capability. Box cell layout can increase the channel width, leading to reduction of the channel resistance and an enhancement of electron injection from an emitter. Hole-barrier structure, which is a potential barrier for holes to prevent them from flowing out of the emitter, can enhance conductivity modulation. An on-voltage of 3.98 V at a collector current of 100 A/cm2 was achieved from a fabricated SiC IGBTin this study. Since the on-voltage of a SiC IGBT with a conventional structure was 4.81 V at the same collector current, the effect of our new structure was successfully shown to reduce the on-voltage of SiC IGBTs. An estimation of each voltage component involved in the on-voltage was also carried out by utilizing a device simulation, and the estimation shows that a SiC IGBT incorporating a box layout and hole-barrier structure will thus have quite a low drift-layer voltage and an on-voltage close to the limit determined by the bipolar built-in voltage.

A queuing theory- based approach for designing cellular manufacturing systems

This paper presents a new cell formation and cell layout problem considering multiple process routings and subcontracting using the principles of queuing theory. It is assumed that each machine operates as an M/M/1 queuing system and a queuing network is used to obtain in-process inventories and machine utilization. The problem is formulated as a mixed-integer nonlinear program with the objective of minimizing the total costs, including the production, subcontracting, material handling, machine idleness, and holding costs. Due to the computational complexity of the problem, a heuristic method is suggested to effectively solve the problem. A numerical example is given to clarify the proposed approach, and finally, further instances are solved to verify the performance of the solution method and to accomplish comparisons. The computational results show that the proposed heuristic is both effective and efficient.

Sector and Site Switch-Off Regular Patterns for Energy Saving in Cellular Networks

Cell switch-off (CSO) is an important approach to reducing energy consumption in cellular networks during off-peak periods. CSO addresses the research question of which cells to switch off when. Whereas online CSO, based on immediate user demands and channel states, is problematic to implement and difficult to model, off-line CSO is more practical and tractable. Furthermore, it is known that regular cell layouts generally provide the best coverage and spectral efficiency, which leads us to prefer regular static (off-line) CSO. We introduce sector-based regular CSO patterns for the first time. We organize the existing and newly introduced patterns using a systematic nomenclature; studying 26 patterns in total. We compare these patterns in terms of energy efficiency and the average number of users supported, via a combination of analysis and simulation. We also compare the performance of CSO with two benchmark algorithms. We show that the average number of users can be captured by one parameter. Moreover, we find that the distribution of the number of users is close to Gaussian, with a tractable variance. Our results demonstrate that several patterns that activate only one out of three sectors are particularly beneficial; such CSO patterns have not been studied before.

Determination system for solar cell layout in traffic light network using dominating set

Graph Theory is one of the fields in Mathematics that solves discrete problems. In daily life, the applications of Graph Theory are used to solve various problems. One of the topics in the Graph Theory that is used to solve the problem is the dominating set. The concept of dominating set is used, for example, to locate some objects systematically. In this study, the dominating set are used to determine the dominating points for solar panels, where the vertex represents the traffic light point and the edge represents the connection between the points of the traffic light. To search the dominating points for solar panels using the greedy algorithm. This algorithm is used to determine the location of solar panel. This research produced applications that can determine the location of solar panels with optimal results, that is, the minimum dominating points.

Additive manufacturing functionally graded titanium structures with selective closed cell layout and controlled morphology

This article presents the results of deploying a new approach for additive manufacturing (AM) functionally graded titanium (Ti) cellular structures with selectively built closed cells, which tailor the mechanical behavior of structures to mimic the similar properties of bones. A hybrid AM system, which combines two methods of binder jetting and material extrusion, was applied. Ti parts were fabricated from powder-bed AM (binder jetting) with encapsulated sacrificial polymeric droplets within the layers and at designated locations to form a periodic pattern. After a heat treatment step, which resulted in the polymer decomposition, the measurement of porosity among the specimens demonstrated the range of 6 to 16% enhancement in these parameters in samples with periodic cells compared to others. Additionally, micro-computerized tomography was performed on the candidate samples to determine the pore morphology and layout within the specimens. The measurement of stiffness and yield stress suggested a range of 2.48 ± 0.37 to 3.55 ± 0.49 GPa and 107.65 ± 18.14 to 145.75 ± 13.85 MPa, respectively. These results suggested that the statistical significance occurred in the batches with periodic cells.

Concurrent cell formation and layout design based on hybrid approaches

Considering the interaction between the cell formation and cell layout problems when designing cellular manufacturing systems (CMSs), this paper investigates the integrated cell formation and layout problem (ICFLP). A comprehensive mixed-integer linear programming model is developed. This model features the simultaneous incorporation of some specific design attributes of CMSs, such as unequal machine dimensions, duplicate machines, alternative process routings, coexistence of alternative process routings, lot splitting, and production planning. Given the computational difficulty of the model, two hybrid approaches, one combining a genetic algorithm and linear programming (GALP) and the other combining simulated annealing and linear programming (SALP), are proposed to efficiently solve real-sized problems. The results of an illustrative example reveal that lower production cost and higher machine utilization rate can be generated by the concurrent cell formation and layout design, and the incorporation of relevant attributes. Comparison experiments show that the GALP and SALP outperform a previous metaheuristic and an existing heuristic for solving a simplified ICFLP model. They also excel pure GA, pure SA and CPLEX on solving the proposed model.

Efficient Layout Design of Junctionless Transistor Based 6-T SRAM Cell Using SOI Technology

In this work novel 6-T SRAM layout has been proposed using Junctionless SOI MOS transistor. The key idea of the proposed structure is to reduce the area consumed by the device with an aim to improve its performance. The junctionless SOI n- and p-MOS transistor exhibits lower off-state current and higher Ion to Ioff ratio when compared to double gate junctionless transistor available in the literature. In the proposed 6-T SRAM cell layout formation, an arrangement of latch circuit was done and later on two n-transistors back-to-back were cascaded to form a compact SRAM layout configuration. Thus, the proposed structure utilizes nearly half the area of conventional junctionless 6-T SRAM layout. The proposed design also shows improvement in delay time in read/write operations. The proposed structures were designed and simulated using Sentaurus and Cogenda device simulator.

Relaxation of Self-Heating-Effect for Stacked-Nanowire FET and p/n-Stacked 6T-SRAM Layout

In this paper, we investigated the source/drain recessed contact structure to mitigate the self-heating-effects in vertically stacked-nanowire FETs. As a result, lattice temperature of nanowire regions during device operation was considerably decreased by using the source/drain recessed contact structure. This is attributed to an increase in heat dissipation mainly from heat source to bulk wafer. Moreover, we proposed the p/n-stacked nanowire on bulk FinFET and its 6T-SRAM layout. Area of the proposed SRAM was reduced approximately 15%, as compared to the conventional cell layout.

Safe Layout Design and Evaluation of a Human-Robot Collaborative Application Cell through Risk Assessment – A Computer Aided Approach

Risk assessment is a sequential process which requires understanding the hazards and analyzing risks associated, to determine required safety measures, like safeguarding to mitigate the risks to an acceptable level. In this article a thorough task-based risk assessment process is conducted in the early stage of layout design and building of a collaborative cell for sealing application performed in aircraft industries using a medium sized industrial robot system integrated with safety control functions. This article will also discuss how simulation could contribute in eliminating the threats as required by the safety standards before investing in equipment for collaborative cell layout.

Layout optimization of a robotic cell for foundry application by CAD based point cloud modeling – a case study

PurposeIn an industrial robotic cell, the optimal layout planning problem needs critical analysis, as it indirectly affects the manufacturing time and cost involved in the production process. This paper aims to propose a generic three-step robotic cell layout planning method and aims to enhance the adaptability of robotic manufacturing cell in small-scale industries.Design/methodology/approachThe method uses the data generated from the point cloud modeling and simulation of the objects (machines and robot) to optimize their positions and orientations in the cell. The simulated annealing algorithm has been used to solve the optimization problem with minimum joint displacement criterion. This approach is critically analyzed and discussed against the data collected from an industrial robotic cell in a foundry shop of a pipe manufacturing industry.FindingsMore than 50 per cent reduction in the net joint movement of the robot has been achieved. Immediate feedback of the results by a three-dimensional view of the optimal cell layout without using any commercial robotic simulation package.Originality/valueThe layout optimization of an industrial robotic cell based on the point cloud modeling of its objects is the novelty of the method.

High-order three-scale method for mechanical behavior analysis of composite structures with multiple periodic configurations

A new high-order three-scale (HOTS) method for simulating the mechanical behaviors of composite material structures with multiple heterogeneities is developed. The heterogeneities of the structures are taken into account by periodic layouts of unit cells on the microscale and mesoscale. A novel unified micro-meso-macro multiscale formulation based on reiterated homogenization and multiscale asymptotic expansions is established successively. Two kinds of local cell functions defined on the mesoscale and microscale cells, including first- and second-order, are established. The equivalent material parameter is calculated by up-scaling procedure and homogenized problem is subsequently defined. Further, the displacement, strain and stress are constructed as multiscale asymptotic expansions by assembling the cell functions and homogenation solution. In the present method, both the mesoscopic and microscopic information are synthesized with homogenization solution to capture more local characteristics inside the composite material structures. Then, the finite element numerical algorithm based on the three-scale method is brought forward in details. Finally, numerical examples are given to demonstrate the usability of the HOTS analysis method to simulate the mechanical behavior. This study offers a unified multiscale framework that enables mechanical behavior analysis of composite structures with multiple spatial scales.