Walking Worker Research Articles

Modelling human performance within an automotive engine assembly line

In this paper, we first investigate a semi-automated automotive engine assembly line in which the traditional strategy of using fixed workers in each manual assembly section is replaced by a new strategy of using walking workers. With this approach, both worker and engine travel simultaneously down the line; each worker is previously trained to accomplish a series of assembly tasks independently from start to finish in each manual assembly section. The study has shown great improvement of the overall system performance in terms of flexibility, efficiency, responsiveness and re-configurability using dynamic, flexible and skilled walking workers. Nevertheless, the main problem of this design is that each worker needs to be cross-trained to acquire a satisfactory level of skills associated with the assignment of assembly tasks. This is crucial for achieving a relatively even working speed at which each worker assembles a product down the line without major interruption between two adjacent workstations. In theory, the familiar degree of completing assigned tasks by each worker through training can be measured and expressed as a learning curve. In this case, the learning curve has been used to determine a trade-off decision between the complexity of assigned tasks and the duration of completing these tasks by a walking worker at a stabilised level. It has also been used to investigate the impact of the system variation that may affect the performance of individual walking workers through a learning process. Thus, the paper also describes a framework to assess the human performance by modelling the learning curve for each walking worker based in an integrated model. This model was created using a simulation tool Witness with its key input/output data manipulated externally by a series of Microsoft Excel worksheets incorporating the effect of a number of human factors in terms of cognitive and physical elements. With this method, the possible and realistic assignment of selected assembly tasks for each walking worker can be quantified.

Impact of Walking Worker Assembly Line Configuration on Ergonomics Performance

Manual assembly lines with walking workers may be designed in many configurations. Different configurations have profound impact on the performance of the system. This paper analyses and evaluates the ergonomics performance measures for different system configurations. Based on developed mathematical model, different combinations of structural factors are compared to evaluate effects of these factors on the mentioned performance. The work demonstrates that various design factors should be considered jointly when designing or redesigning walking worker assembly line because setting different levels for factors can considerably affect the ergonomics performance of the system.

Mathematical modelling for process design of walking worker assembly line in productivity and ergonomics perspectives

High worker-hour productivity and improving ergonomics conditions are major concerns of industry, especially in human-centred production systems (e.g. manual assembly systems). From the view of some manufacturing managers, converting fixed worker assembly line to walking worker assembly line (WWAL) involves opportunities and pitfalls for both mentioned aspects. This view point is supported by the complaint, i.e. no modelling research that can help them to develop their own capacity in the design of WWAL considering both productivity and ergonomics. This paper proposes a mathematical model that can be used by designers, manufacturers and dealers for the effective design of WWAL that significantly affects the productivity and ergonomics performance measures. Different combinations of process design parameters are compared with several alternative scenarios of WWAL design using well-planned numerical experiments. Graphical analyses were carried out to examine the relationships between design parameters (factors) and performance measures. The model can support WWAL practices in two ways: firstly, it can improve the understanding of how such systems behave and what factors drive performance. Secondly, it can help to determine what types of policies for successful operation of this system can quickly and economically be selected in light of the different levels of production demand.

Impact of walking worker assembly line configuration on ergonomics performance

Impact of walking worker assembly line configuration on ergonomics performance

The Role of Randomness of a Manual Assembly Line with Walking Workers on Model Validation

Designing a dynamic system inherent with randomness requires predictable and dependable mathematical models that focused well on variability of the output. In addition, the model should provide an understanding for the impact of that randomness on the model validation as an abstraction for the real system. Lack of this fact causes inaccuracy in the results from the mathematical model, especially when modelling systems with high manual work content such as manual assembly lines with walking worker(s) (WWAL). This paper deals with validation of the mathematical model of WWAL and effect of sources of randomness in the system on worker operating times and in the end on the output of the system.

Analysis of Production Loss on a Linear Walking Worker Line

This paper mathematically analyses the varying magnitude of production loss, which may occur due to idle time (inprocess waiting time and traveling time) on a linear walking worker assembly line. Within this flexible and reconfigurable assembly system, each worker travels down the line carrying out each assembly task at each station; and each worker accomplishes the assembly of a unit from start to finish and then travels back to the first station to start the assembly of a new product. This strategy of system design attempts to combine the flexibility of the U-shaped moving worker assembly cell with the efficiency of the conventional fixed worker assembly line. The paper aims to evaluate the effect of idle time that may offset the labor efficiency of each walking worker providing an insight into the mechanism of such a flexible and reconfigurable assembly system.

Analysis of a linear walking worker line using a combination of computer simulation and mathematical modeling approaches

It has become increasingly important in the last few years to develop rapid, dynamic, responsive and reconfigurable manufacturing processes and systems. This is because manufacturing enterprises are now being forced to develop and constantly improve their production systems so that they can quickly and economically react to unpredictable conditions such as varying production volumes and product variants with small lot size, high quality and low costs. One effective method to achieve this is to create a more flexible, highly skilled and agile workforce capable to perform multiple or all the required tasks in a production area where the system can be reconfigured easily as needed to accommodate changes of production requirement on a daily or weekly basis. This paper presents a study of a so-called linear walking worker assembly line based on a combination of computer simulation and mathematical analysis. The linear walking worker assembly line is a flexible assembly system where each worker travels down the line carrying out each assembly task at each station; and each worker accomplishes the assembly of a unit from start to finish. This design attempts to combine the flexibility of the U-shaped moving worker assembly cell with the efficiency of the conventional fixed worker assembly line. The paper aims to evaluate one critical factor of in-progress waiting time that affects the overall system performance providing a dynamic simulation outlook as well as an insight into the mechanism of such a flexible and reconfigurable manufacturing system.

A study of in-process waiting time on a linear walking worker assembly line

This paper presents a study of in-process waiting times on a linear walking worker assembly line in a real buffer-constrained flowshop environment using the simulation method. The in-process waiting time can lead to production loss and in-process inventory; it can also affect the throughput time for completion of a product assembled in a sequential flowline-based manufacturing system. The aim of this research is to investigate the varying magnitude of the total in-process waiting time for individual walking workers who may have to wait to carry out operations at a station due to blocking on the line ahead. The results were obtained by varying a number of system parameters embedded in a simulation model created using Witness® with the key input/output data being manipulated by a series of MS Excel-spreadsheets. The main finding of this work is that the in-process waiting time (which affects the expected throughput time) can be determined and it is adjustable by the strategic application of walking workers on a linear assembly line, even if the system behaviour is random.

The Effect of Worker's Location, Orientation, and Activity on Exposure

The impact of a worker's location, orientation, and activity was studied in an experimental room (2.86 m × 2.35 m × 2.86 m) at known flow rates of 5.5 m 3 /min and 3.3 m 3 /min. A person in the room, wearing a full-facepiece, air-supplied respirator represented a worker. Propylene tracer gas was emitted at a constant rate from a 1-m pedestal at the center of the room and a continuous air sample was drawn from a point midway between the worker's mouth and nose. Breathing zone concentration (BZC) was monitored at 12 worker locations within the room for a stationary worker. At each location, BZCs were measured separately for four worker orientations: east, west, south, and north. BZCs of a walking worker were also monitored along the path defined by the 12 worker locations used in the stationary experiments. In a separate set of experiments, area concentration was monitored to see whether the worker's activity disturbed the contaminant concentrations at a fixed sampling point located behind the source looking from the direction of air inlet (location: 1.34 m, 1.20 m, 0.45 m). The following average differences in BZC over the 12 fixed locations were observed: 43% higher for near-field than for far-field locations; 20% higher when the worker was facing the source than when facing away (p-values for all four conditions: < 0.033), and 30% higher for a moving worker than for a stationary worker (p-values for all four conditions: < 0.01). When the worker was walking, the concentration at the fixed area sampling point was generally lower than the area concentration when the worker was absent or stationary in the room, possibly due to greater mixing of room air by the worker's movement. Because a worker's activities may be irregular and complicated, incorporating them as parameters in mathematical models is often not feasible. Instead, these findings may be used to assess uncertainty or adjust exposure estimates from simple models.

Modelling randomness of a manual assembly system with walking workers

Most proposed approaches for modelling and simulation of an assembly production line have focused on conventional assembly lines where one (or more) stationary worker stays at a given station to complete a repetitive assembly operation and when this operation is accomplished, the assembled part is transferred to another worker at the next station for the next assembly operation. This paper presents an investigation of a linear walking worker assembly line where one worker walks along the line to complete the assembly of a product from start to finish. The study was carried out based on a real job shop environment with a demand-pull production control system. The randomness of walking worker activities was modelled using a proprietary simulation package. The paper discusses several issues which may assist in the early stages of designing a linear walking worker line.

Determining numbers of workstations and operators for a linear walking-worker assembly line

This paper presents an investigation into a system of linear walking-worker (WW) assembly lines that have been implemented in a local small and medium enterprise (SME). The work aims to observe the relevant impact on logical interactions and interrelationships between the number of workstations and the number of walking workers against the system performance and to minimize these numbers providing a quick response in re-configuration of the system to meet a given output and cycle time. This has been achieved by developing a simulation model for a theoretical study into the linear WW system using a manufacturing-focused simulation tool. By examination of the results of a series of simulation experiments, a minimization of the numbers of workstations and walking workers for a linear WW line configuration can be quantified. The research concluded that this multiskilled linear WW assembly line is able to sustain a higher flexibility and efficiency as compared with a conventional linear fixed-worker (FW) assembly line under similar conditions.

女性の静止立位作業による血圧低下の実態調査

The "Just-in-Time system" improves productivity and efficiency through cost reduction while it makes workers work in a standing posture. The aim of this study was to investigate the prevalence of postural hypotension in females during prolonged standing work, and to discuss preventive methods. Twelve female static standing workers (mean age+/-standard deviation; 32+/-14 yr old), 6 male static standing workers (30+/-4 yr old), 10 female walking workers (27+/-7 yr old) and 9 female desk workers (31+/-5 yr old) in a certain telecommunications equipment manufacturing factory agreed to participate in this study. All participants received an interview with an occupational physician, and performed the standing up test before working and ambulatory blood pressure monitoring (ABPM) while working. Although the blood pressure of the standing up test did not differ among the groups, mean pulse rates on standing up significantly increased in every group. Hypotension rates in the female standing workers' group by ABPM were 9 persons of 12 participants (75%) for systolic blood pressure (SBP), and were 11 persons of 12 participants (92%) for diastolic blood pressure (DBP). There were significantly higher than those in the female desk workers' group, none of 9 participants (0%) for SBP and 2 of 9 participants (22%) for DBP. The hypotension rates both male standing and female walking worker groups did not differ. Because all 8 workers who were found to have postural hypotension by the standing up test had decreased SBP and/or DBP by ABPM, it is suggested that persons at high risk of postural hypotension during standing work could be screened by the standing up test. The mechanism of postural hypotension may be a decrease of venous return due to leg swelling, and neurocardiogenic or vasovagal response. Preventing the congestion of the lower limbs by walking, managing standing time and wearing elastic hose to keep the amount of the venous return could prevent postural hypotension during prolonged standing work.

Comparison between fixed- and walking-worker assembly lines

Linear walking-worker assembly lines are a novel form of flexible assembly system where fitters travel along the line carrying out each assembly task at each workstation. They attempt to combine the flexibility of the workbench system with the efficiency of the conventional fixed-worker assembly line. This concept has been implemented in a local manufacturing company where conventional assembly systems have been dominant for many years. This paper describes an investigation into this implemented walking-worker assembly line. The research work makes a comparison of the system's performance based on the same production line operated with fixed workers or with walking workers. The research approach was to develop simulation models for the alternative systems and to compare their simulation results. The results have shown that by using multiple-skilled walking workers this novel system has several advantages over the conventional fixed-worker assembly line under similar conditions.

The role of decouplers in JIT pull apparel cells

Various staff methodologies of a just‐in‐time (JIT) apparel assembly cell with various numbers of walking workers, and various levels of process time variation were discussed and evaluated by simulation models. Decouplers are placed between two workstations (or subcells) to improve capability and flexibility in an apparel cell. Decouplers enable JIT pull cells to operate with minimum stock‐on‐hand and allow parts and information to flow in opposite directions. Decouplers also provide the JIT pull cell with “make one, check one, and pass one on” capability. A manned assembly cell’s throughput rate depends on the number of workers in the cell and on the variation in each worker’s processing time. Normally, as the processing time variation increases, the throughput rate decreases. However, these simulation studies show that doubling the decoupler capacity increases the cell’s output, even as the processing time variation increases.

Simulation of an apparel assembly cell with walking workers and decouplers

Abstract In the apparel industry, cells for manufacturing and assembly are called modules. A simulation model has been developed to study the behavior of a unique module that employed five multifunctional, walking workers and 13 sewing stations with great variations in processing times. Cells are the major components in integrated pull manufacturing systems (IPMSs). IPMSs are the designs for the factories with a future.

Simulation of an apparel assembly cell with walking workers and decouplers

Simulation of an apparel assembly cell with walking workers and decouplers