Cycle Time Model Research Articles

Analytical examination of shuttle-based storage and retrieval systems with multiple-capacity lifts

The unbroken trend towards e-commerce and the ever-increasing demands on storage technology present the providers of storage systems with ever greater challenges. One way to meet these requirements is to significantly enhance warehouses’ handling systems. Multiple capacity lifts in tier-captive single-aisle shuttle-based storage and retrieval systems (SBS/RS) are a method to raise the throughput performance of such systems. Therefore, a straightforward calculation approach is presented based on a cycle time model combined with a time-continuous single open Markovian queue with limited capacity. A comparison of the invented approach to a discrete-event simulation (DES) is made to validate it. Finally, a numerical example of the influences of the different handling capacities and their usage in the design process of SBS/RS is depicted. The result is that with double the handling capacity, the throughput increases by about 50%\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$50\\%$$\\end{document}. Another result is sorting the stops within one handling cycle, which leads to a significantly higher throughput.

Remaining cycle time prediction: Temporal loss functions and prediction consistency

The usefulness of remaining cycle time models for predictive and prescriptive process monitoring depends not only on the overall accuracy of the predictions but also on their earliness: predictions should be as accurate as possible, as early as possible. To give this criterion more weight in model fitting, the paper evaluates three L1 loss functions with temporal decay. All have the property of increasing the weight of residuals from the early stages of a process relative to residuals from later stages but do so to different degrees. The loss functions are used in LSTM networks for training remaining throughout time models of four different business processes based on publicly available event log data sets. Compared to models trained with unweighted L1 loss, the suggested modifications yield small but significant improvements in earliness on out-of-sample data. Neither the unweighted L1 loss nor the modifications led to models with strictly monotonically decreasing predictions of the remaining time.

Investigation of cycle time behavior in the robotic grinding process

The production of power transmission components such as gears and bearing rings involves precision finishing of highly specialized and dedicated precision grinding machine tools. Six degree-of-freedom (6-dof) articulated arm industrial robots are less expensive and more versatile than precision grinding machines because they can be readily reconfigured for a variety of production tasks including precision grinding of free-form surfaces. However, the high compliance of such robots poses a challenge in high-precision operations, particularly as it relates to the overall cycle time of the process. The paper presents an analysis of the effects of robot compliance and grinding parameters on the cycle time of a precision grinding process. Specifically, a process model for robot-workpiece interaction and grinding process cycle time is developed. This model is used to analyze the behavior of a face grinding process cycle. The results show that for a given robot stiffness, minimizing the face grinding cycle time requires the process to be operated at the highest achievable wheel speed and infeed rate with a wheel of higher hardness. The paper also shows that a 6-dof robot offers the flexibility of modifying the Cartesian stiffness at the end effector by varying the robot pose, which is difficult to achieve in conventional grinding machines. This capability, along with the process cycle time model, permits optimization of process cycle times for precision grinding of surfaces, including free-form surfaces, using 6-dof robots.

Task Scheduling Problem of Double-Deep Multi-Tier Shuttle Warehousing Systems

Double-deep multi-tier shuttle warehousing systems (DMSWS) have been increasingly applied for store-and-retrieval stock-keeping unit tasks, with the advantage of a reduced number of aisles and improved space utilization. Scheduling different devices for retrieval tasks to increase system efficiency is an important concern. In this paper, a Pareto optimization model of task operations based on the cycle time and carbon emissions is presented. The impact of the rearrangement operation is considered in this model. The cycle time model is converted into a flow-shop scheduling model with parallel machines by analyzing the retrieval operation process. Moreover, the carbon emissions of the shuttle in the waiting process, the carbon emissions of the lift during the free process, and the carbon emissions of the retrieval operation are considered in the carbon emissions model, which can help us to evaluate the carbon emissions of the equipment more comprehensively during the entire retrieval task process. The elitist non-dominated sorting genetic algorithm II (NSGA-II) is adopted to solve the non-linear multi-objective optimization function. Finally, a real case is adopted to illustrate the findings of this study. The results show that this method can reduce carbon emissions and improve system efficiency. In addition, it also help managers to reduce operational costs and improve the utilization of shuttles.

Balancing a multistage vehicle number plate production line using effective cycle time model

Shortest product cycle time is a key criterion for job sequencing and measuring competitiveness among entrepreneurial-based firms. Now, the long waiting time of job orders constitutes a deterministic production line problem in vehicle number plate production plants in Nigeria. Case studies were conducted on those plants, confidentially identified in this paper as A, B, C, and D. Delays caused by non-value-adding work processes are major culprits among other contributors to the long queues at these plants. The value stream mapping technique was applied to identify non-value adding activities before the production line was balanced using an effective cycle time model. The index cases to a balanced line, as shown in the results, are increases in process rate by 41 %, 59 %, 42 %, and 71 % for A, B, C, and D, respectively, and overall line efficiency. Next, the system capacities correspondingly increased with the elimination of wastages. These increments imply that bottleneck activities have been minimized, and we have a balanced production line. The devised solution procedure is reliable and recommended to other line manufacturing concerns that experience delays and bottleneck problems.

Patent prospects and trends in post-harvest management technology of fresh agricultural products

To predict the best direction for post-harvest management technology of fresh agricultural products, the growth potential of patents was evaluated using 1,517 valid patents from 1998 to 2017 for four countries (Korea, China, Japan, and United States) and the European Union. A patent portfolio (PP) index was used to evaluate the technological growth of the collected patents. Patent increase (PI) and patent sharing (PS) indices were used to evaluate the emerging trends in technology. A technology cycle time (TCT) model based on the PI, PS, and market power (MP) indices was used to compare the growth potential of each category. The PP index indicated that post-harvest management technology is in a growth stage; both the PI and PS indices showed that storage technology has high development potential, whereas packaging technology has low development potential owing to a low rate of increase. A multi-layer TCT model predicted that post-harvest management technology has high growth potential because the PI was 168.8%, the ratio of PS was 36.6%, and the MP increased 111.3%. Our results indicate that post-harvest management technologies have high growth potential, although patent applications decreased in some countries early in the study period. This study is important to establish the future strategy for extending the exportation of fresh agricultural products in Korea.

Planning and design of a chassis container terminal

Chassis or wheeled container terminals are common inland intermodal terminals; however, research efforts related to this kind of terminals are very scarce. In this work we want to expand the current literature basis relating chassis terminals and propose a mathematical model that aids the design process of the terminal. We develop cycle time models for gantry cranes and tractor units which allow computing the expected equipment cycle time in a single command cycle. Next, we integrate the cycle time models into an optimization framework that seeks to minimize the investment and operation costs of the terminal. The results show that container dwell time has a substantial impact on total cost, especially for a large terminal. We also found that optimal configuration uses only a small number of gantry cranes due to high investment costs.

Factors affecting forwarder productivity

Modern forwarders are an effective extraction option for timber harvesting operations that provide the opportunity for higher levels of mechanization. With their ability to carry logs from the forest to the roadside or processing areas, they have an established lower environmental impact in comparison to tree-length skidding options. However, little is published regarding their productivity potential or the factors that influence productivity. Three case studies were carried out; (1) a selective harvest in Calabria, Italy, with a smaller 12 t capacity John Deere 1110E, (2) a clear-cut on the West Coast of New Zealand, with a larger 19 t capacity John Deere 1910E and (3) a larger clear-cut operation in Canterbury, New Zealand, with two John Deere 1910E forwarders. An elemental time and motion study was used resulting in 73.4 h of detailed data, with 159 cycles extracting 2241 m3 of timber. Productivity models were created for all three sites as well as one combined model. Average cycle time was 33.2, 24.2 and 22.8 min, and average productivity 24.6, 37.1 and 42.7 t per productive machine hour, respectively. Cycle time was the fastest, and consequently productivity the highest, at the Canterbury site where the terrain roughness was low, overcoming any effect of the average small piece size (0.59 m3). Travel speed was slowest at the West Coast site showing the effect of wet and difficult terrain, with travel empty speed being just 3.8 km/h, compared to 6.7 and 6.9 km/h at the other two sites. Productivity at the two clear-cut operations was significantly higher than the selective cut, compounded by the use of the larger capacity forwarders. Distance and payload were significant factors for each cycle time model; in the combined model the sites were also significant. The calculated unit cost of forwarder extraction in the sites ranged from €2.55 to €4.70/m3. For regions such as southern Italy that have relatively low levels of forest mechanization, this information can be used to help design and improve more traditional labor-intensive harvesting systems.

Modeling the mixed storage strategy for quay crane double cycling in container terminals

A mixed storage strategy was proposed to improve the efficiency of yard operations and horizontal transportation to corporate with quay crane double cycling. The effects of the mixed storage strategy on terminal operations, including truck travel distance, yard crane operations and the number of required trucks, were analyzed. An approach based on cycle-time models, the queuing theory was proposed to evaluate the performances from long-term run. Results show using the mixed storage strategy, the truck travel distance can be decreased and the number of required trucks and yard crane’s operation time can be reduced by 16% and 26% respectively.

An adaptive BPSO algorithm for multi-skilled workers assignment problem in aircraft assembly lines

Purpose – The purpose of this paper is to investigate the multi-skilled workers assignment problem in complex assembly systems such as aircraft assembly lines. An adaptive binary particle swarm optimization (A-BPSO) algorithm is proposed, which is used to balance the workload of both assembly stations and processes and to minimize the human cost. Design/methodology/approach – Firstly, a cycle time model considering the cooperation of multi-skilled workers is constructed. This model provides a quantitative description of the relationship between the cycle time and multi-skilled workers by means of revising the standard learning curve with the “Partition-And-Accumulate” method. Then, to improve the accuracy and stability of the current heuristic algorithms, an A-BPSO algorithm that suits for the discrete optimization problems is proposed to assign multi-skilled workers to assembly stations and processes based on modified sigmoid limiting function. Findings – The proposed method has been successfully applied to a practical case, and the result justifies its advantage as well as adaptability to both theory and engineering application. Originality/value – A novel cycle time model considering cooperation of multi-skilled workers is constructed so that the calculation results of cycle time are more accurate and closer to reality. An A-BPSO algorithm is proposed to improve the stability and convergence in dealing with the problems with higher dimensional search space. This research can be used by the project managers and dispatchers on assembly field.

Optimal Payment time for a Retailer with exponential demand under permitted credit period by the Wholesaler

In paper Jamal et al.[32] developed a retailer’s model for optimal cycle time and payment times for a retailer’ in a deteriorating item inventory situation where a wholesaler allows a specified credit period to the retailer for payment without any charge. This paper is the extension of Jamal et al. [32] paper. In competitive business environment the most important objectives for companies is to reduce replenishment cost. This paper considers the inventory policy for non deteriorating items with exponential demand rate. The demand rate is assumed to be increasing function of time .In this study a retailer’s model for optimal cycle time and optimal payment times for a retailer have been developed, where a supplier allows a particular credit period to the buyer for payment without any extra charge. The supplier and buyer system is modeled as a optimal profit problem to determine the optimal payment time under different parameters under the same condition. The numerical technique method is used to solve the problem for finding optimal payment time and optimal inventory cycle time. The results are discussed with the help of sensitivity analysis of the optimal solution with respect to the different parameters of the system is given.

A case productivity model for automatic climbing system

Purpose – Tight schedules in high-rise building construction force project managers to use the formwork even in a bad weather condition. Insufficient craning, which is typically the bottleneck in construction activities, and lack of space in confined sites make it hard to install the formwork on the ground. The Automatic Climbing System (ACS), a type of jump forms, solves these problems enabling the formwork to climb in various weather and height conditions. The aim of this paper is to discuss these issues. Design/methodology/approach – Current research focusses on the ACS, its application, and productivity assessment. Productivity and construction data are collected from a specialized company in such type of forms. A bracket productivity model has been developed to estimate floor construction cycle time and productivity. Findings – Results show that average productivity is four days/floor. The developed model is validated, which shows robust results 97.80 percent. Research limitations/implications – The implementation of the developed models are limited to only two projects. However, the developed models and framework is sound for future improvement. Practical implications – The developed methodology and model play essential roles in decision-making process. Originality/value – The developed methodology and model are beneficial to researchers, practitioners, and planners of construction projects. It provides practitioners with charts that assist in scheduling and managing resources for jump form application. In addition, it provides researchers with a floor cycle time model and framework of implementing jump forms to high-rise buildings.

A multi-stem feller-buncher cycle-time model for partial harvest of small-diameter wood stands

Due to the increased partial harvest of small-diameter stems and the lack of feller-buncher time-consumption information in Maine, it was necessary to develop new cycle-time equations. Data were collected from seven different sites in Maine with six different operators to capture the variability in site and stand conditions as well as operator experience and proficiency. The results showed that over 55% of the trees harvested were cut in accumulations of two or more trees. Significant variables in the final model included sum of dbh and stem count per accumulation. An approach to simulate a list of accumulations with the required variables is described based on a tree list with dbh classes. Treating the combination of operator, machine, and site conditions as a random effect in a linear mixed-effects model resulted in an adjusted R 2 of 0.40 for fixed and random effects. The combination of operator, machine, and site conditions explained 32% of the variance caused by random effects. The results of this study can be incorporated into existing harvest cost prediction programs to improve estimates for this region.

Retailer's optimal policy under inflation in fuzzy environment with trade credit

Trade credit plays an important role in financing many industries. In the classical inventory model it is assumed that the buyer must pay for the items as soon as the items are received. In this problem, it is considered that the retailer can pay the supplier either at the end of the credit period or later pay interest on the unpaid amount for the overdue period. Here, the retailer's inventory model for the optimal cycle time and payment time for a retailer is developed. The effects of the inflation rate, deterioration rate and delay in payment have been discussed. The whole study is performed in a fuzzy environment by taking the opportunity cost, interest earned and interest paid rate as a triangular fuzzy number. Fuzzy profit functions, which involve fuzzy arithmetic operation, are defined using the function principle. We use the signed distance method to defuzzify the fuzzy profit function. Moreover, numerical and sensitivity analysis is performed to validate the proposed model.

A cycle time model for analysing the efficiency of working capital management in a value chain

When technology already enables just-in-time operations and immediate financial transactions, financial supply chain management has emphasised the importance of financial flows and working capital management, which consist of the management of inventories, accounts receivable and accounts payable. However, the literature lacks concrete models and practices to control working capital, especially in the inter-organisational context. This paper introduces a working capital management (WCM) model for analysing the efficiency of working capital management at corporation level and for observing the financing cost caused by tied-up working capital in an inter-organisational value chain. The model emphasises the benefits of a new cycle time measure, the adjusted cash conversion cycle, when observing the inter-organisational context, and when calculating the financing cost. The WCM model was applied to a value chain of four companies in the automotive industry, a raw material supplier, a component supplier, a system supplier and a car manufacturer. A numerical example of the model with the data of financial statements is shown.

The impact of batch retrievals on throughput performance of a carousel system serviced by a storage and retrieval machine

Abstract A carousel system is an example of an automated storage and retrieval system that is used in distribution centers and manufacturing facilities. We analyze the impact batch retrieval processing has on throughput performance for horizontal carousel systems that use automated storage and retrieval machines as robotic pickers. By developing an analytical cycle-time model we provide the theoretical base necessary to support the management decision of whether to batch or not. We conduct a computational experiment to test the accuracy of our analytical model, to demonstrate how our approach can guide management decisions, and to illustrate the throughput improvements that can be realized through the use of a batch policy. Testing indicates that batch processing increases carousel throughput performance over sequential processing. For the instances tested, batch processing resulted in an average decrease in cycle time over sequential sequencing of 20%. Our results indicate that with batch retrievals, adding to the carousel's length increases storage capacity with a negligible impact on the carousel's throughput performance.

A mathematical model for process cycle time - theory and case study

The article focuses on derivation of a regression model which describes dependence of process cycle time on relevant factors entering the process. The analyzed processes are typical in that the coefficient of variation of times corresponding to a given level of influential factors remains stable if the level of the factors change. The derived model is subsequently applied to real industrial data which show that such a model is suitable for the description of relations. The paper has been published with support of Slovak Ministry of Education project KEGA 3/6411/08 „Transformation of the already existing study programme Management of production quality to an university-wide bilingual study programme“.

Comparison and evaluation of various cycle-time models for yard cranes in container terminals

Yard cranes are important pieces of handling equipment in container yards. This study analyzes cycle times of various handling operations of yard cranes, including receiving, loading, discharging, and delivery operations. An operation cycle is divided into elementary movements, and formulas for expected time and variance of each elementary movement are derived analytically. Cycle times of various types of yard crane are compared with each other analytically and numerically. The accuracy of the formulas is evaluated through a simulation study.

The effects of force and exertion duration on duty cycle time: Implications for productivity

Ergonomics has positive effects on both physical health and productivity, but estimating productivity benefits is difficult at the task design/redesign stage. Rest-allowance prediction models are not suitable for repetitive, short-cycle dynamic tasks, and methods–time measurement (MTM) techniques are limited in their suitability for considering ergonomics risk factors such as posture and force. The purpose of this study was to investigate the relationship between force and exertion duration on self-selected duty cycle time and discomfort. Twenty-one participants completed repetitive, upper-limb exertion treatments, each of a 10-minute duration. Five levels of force (10, 20, 40, 65, and 80% maximum voluntary contraction [MVC]) and exertion period (1, 2, 4, 6.5, and 8 seconds) were investigated. The psychophysical adjustment method was used whereby participants self-selected a work pace for the second half of each treatment. Duty cycle, derived from the self-paced cycle time, was the measure of productivity effects in the experiment. Analysis of variance revealed a significant effect on duty cycle time for force, exertion period, and their interaction (each p < 0.0001). Friedman's test indicated a significant effect of force (p < 0.0001) and exertion period (p < 0.0001) on discomfort. Spearman's correlation analysis showed a strong correlation between discomfort and duty cycle time (p < 0.05). Multiple regression analysis was used to develop a predictive model for duty cycle time based on force and exertion period, and this was a good fit to the data (R2 = 0.98, p < 0.05). Profiles were generated presenting zones of acceptable self-selected duty cycle times based on force and exertion duration. © 2010 Wiley Periodicals, Inc.

A capacity analysis framework for the IEEE 802.11e contention-based infrastructure basic service set

We propose a multimedia capacity analysis framework for the Enhanced Distributed Channel Access (EDCA) function of the IEEE 802.11e standard. Our analysis shows that the multimedia capacity of the EDCA function for each Access Category (AC) can accurately be estimated by appropriately weighing the service time predictions of a saturation model over different number of active stations. We propose a simple and generic cycle time model to derive the service time in saturation which we employ in the calculation of an accurate station- and AC-specific queue utilization ratio. Based on the estimated queue utilization ratio, we design a simple model-based admission control scheme. We show that the proposed call admission control algorithm maintains satisfactory user-perceived quality for coexisting voice and video connections in an infrastructure Basic Service Set (BSS) and does not present over-or under-admission problems of previously proposed models in the literature.