Characteristics of job rotation in the Midwest US manufacturing sector

Job rotation has been advocated as a suitable intervention to control work-related musculoskeletal disorders. However, little is known regarding the prevalence of job rotation, methods used to identify jobs for rotation or the benefits or limitations of job rotation. A web-based questionnaire was developed to survey job rotation practices from Midwest US manufacturing companies. Results indicated that 42.7% of the companies contacted used job rotation, where the median time for which they had used job rotation was 5 years. Job rotation was used mainly to reduce exposure to risk factors for work-related injuries and to reduce work related injuries, whereas supervisor decisions and ergonomic analyses were used to select jobs for the rotation scheme. Major limitations to successful implementation of job rotation included rotation of individuals with medical restrictions, decreased product quality and lack of jobs to rotate to. These findings suggest that further study is needed to determine if exposure to risk factors is reduced through current efforts.     

Characteristics of job rotation in the Midwest US manufacturing sector

Job rotation has been advocated as a suitable intervention to control work-related musculoskeletal disorders. However, little is known regarding the prevalence of job rotation, methods used to identify jobs for rotation or the benefits or limitations of job rotation. A web-based questionnaire was developed to survey job rotation practices from Midwest US manufacturing companies. Results indicated that 42.7% of the companies contacted used job rotation, where the median time for which they had used job rotation was 5 years. Job rotation was used mainly to reduce exposure to risk factors for work-related injuries and to reduce work related injuries, whereas supervisor decisions and ergonomic analyses were used to select jobs for the rotation scheme. Major limitations to successful implementation of job rotation included rotation of individuals with medical restrictions, decreased product quality and lack of jobs to rotate to. These findings suggest that further study is needed to determine if exposure to risk factors is reduced through current efforts.     

The effects of job rotation on the risk of reporting low back pain

Job rotation has been widely recommended as an administrative control to reduce the risk of developing work-related musculoskeletal disorders. However, evidence of its benefits are hard to find in the literature. The effect of job rotation on predictions for the risk of reporting low back pain was estimated using Low Back Pain Reporting (LBPR) and Time Weighted Average (TWA) approaches. Index scores calculated using the peak hand force, the peak L4/L5 shear force and the L4/L5 moment cumulated over the entire shift were used to estimate the effects of job rotation on the probability of reporting low back pain. Simulations of realistic rotations between two jobs showed that workers in low demand jobs who rotate into higher demand jobs experience a linear increase in reporting probability using the TWA approach. With the LBPR approach a step increase in reporting probability occurred because of the immediate exposure to the peak loading parameters associated with the more demanding job. With a 50-50 rotation the TWA and LBPR index scores increased by 39% and 57%, respectively. With the LBPR approach the redistribution of risk was not uniform with job rotation. The increase was greater for those who rotated into the demanding job compared to the reduction experienced by those who rotated out of the demanding job. The effects of job rotation are not easily estimated because of the complex effect that mixing jobs has on peak and cumulative tissue loading.     

An ergonomic expert system for risk assessment of work-related musculo-skeletal disorders

A computer-based expert system (SONEX) was developed to identify ergonomic risks for work-related musculoskeletal disorders (WRMSDs) in a wide variety of jobs and provide expert prevention advice. SONEX uses a rule base and 6 knowledge base modules: WRMSD risk factors are grouped into two main knowledge base modules (symptoms, engaged body part) with four supplementary knowledge base modules (work environment, work chair, work tools, organization factors). SONEX uses a menu-based interface and a series of simple questions that lead a user through each of the two main modules. Based on user responses it then recommends other knowledge base modules that are relevant for a detailed analysis of work risks. The SONEX rule base has over 140 questions, the knowledge base includes over 200 risk factors, and around 500 possible answers can be generated. SONEX relates ergonomic shortcomings in the job with worker's subjective symptoms; it predicts possible WRMSDs; and it offers preventive suggestions for ergonomic improvements to the job to prevent WRMSDs. It has been tested in a variety of work places with known ergonomic problems and with known employee WRMSDs by comparing its performance with conventional analytical methods and results show that it accurately predicts possible WRMSD risks and identifies ergonomic shortcomings. The advantages of SONEX are that it is much faster than other ergonomic analysis methods and it can be used by ergonomists and other professionals and also by workers themselves.     

The effects of job rotation on the risk of reporting low back pain

Job rotation has been widely recommended as an administrative control to reduce the risk of developing work-related musculoskeletal disorders. However, evidence of its benefits are hard to find in the literature. The effect of job rotation on predictions for the risk of reporting low back pain was estimated using Low Back Pain Reporting (LBPR) and Time Weighted Average (TWA) approaches. Index scores calculated using the peak hand force, the peak L4/L5 shear force and the L4/L5 moment cumulated over the entire shift were used to estimate the effects of job rotation on the probability of reporting low back pain. Simulations of realistic rotations between two jobs showed that workers in low demand jobs who rotate into higher demand jobs experience a linear increase in reporting probability using the TWA approach. With the LBPR approach a step increase in reporting probability occurred because of the immediate exposure to the peak loading parameters associated with the more demanding job. With a 50-50 rotation the TWA and LBPR index scores increased by 39% and 57%, respectively. With the LBPR approach the redistribution of risk was not uniform with job rotation. The increase was greater for those who rotated into the demanding job compared to the reduction experienced by those who rotated out of the demanding job. The effects of job rotation are not easily estimated because of the complex effect that mixing jobs has on peak and cumulative tissue loading.     

Effect of job rotation on work demands, workload, and recovery of refuse truck drivers and collectors

Job rotation is often advocated to reduce workload, but its efficacy has seldom been investigated. The aim of this study is to compare the work demands, workload, and recovery among truck driving, refuse collecting, and rotating between these two jobs, between days and during the day. Three teams of 3 employees each participated in this study. Work demands were assessed by systematic observation of tasks and activities. Workload was quantified by means of heart rate, oxygen uptake, subjective ratings, and urinary excretion rates of catecholamines. Recovery was quantified by excretion rates of catecholamines after work. Job rotation between driving and collecting is an effective measure to reduce physical workload as compared with collecting only and to decrease mental workload as compared with driving only. However, job rotation resulted in increased physical workload as compared with driving only. Job rotation did not increase mental workload as compared with collecting only. No effects were seen on recovery. No differences were found between rotating between days and during the day. Actual or potential applications of this research include the recommendation that before job rotation is introduced, its efficacy be determined in terms of well-chosen workload measures because a reduction in work demands does not directly imply a reduction in workload. Therefore, job rotation might be less effective than expected.     

Optimal control laws for lot-sizing and timing of jobs on a single production facility

The optimal control of a single machine processing a certain number of jobs and modeled as a discrete-event dynamic system is considered. The number of jobs and their sequence are fixed, whereas their timing and sizes represent the control variables of the system. The objective function to be optimized is a weighted sum of the quadratic earliness and tardiness of each job, and of the quadratic deviations of job lot sizes and actual machine service speeds from those specified by the production demand and by the regular machine speeds. An optimization problem with quadratic cost function and nonlinear constraints is stated and formalized as a multistage optimal control problem. Necessary conditions to be satisfied by an optimal control sequence are derived. A simpler model is also considered in which the machine speeds are fixed; in this case, the control problem is solved by a procedure making use of dynamic programming techniques. The optimal control laws at each stage are thus obtained.     

Job rotation as a factor in reducing physical workload at a refuse collecting department

The effect of job rotation on the physical workload was investigated for male employees working at a refuse collecting department. Before the introduction of job rotation, an employee worked as a street sweeper, as a refuse collector or as a driver. After the introduction of job rotation, every employee was allowed to alternate between two of the three possible jobs during the day, i.e. refuse collecting/street sweeping, refuse collecting/driving or street sweeping/driving. Two non-rotation groups (i.e. refuse collectors and street sweepers) and two rotation groups (i.e. refuse collectors/street sweepers and street sweepers/drivers) were mutually compared. The physical workload was determined by measuring the perceived load, energetic load and postural load during a full working day. Job rotation resulted in a significant decrease of the perceived load and energetic load and a slight decrease of the postural load. The results indicate that the total amount of work performed by means of job rotation resulted in an overall reduced physical workload of the employees of the refuse collecting department.     

Job rotation as a factor in reducing physical workload at a refuse collecting department.

The effect of job rotation on the physical workload was investigated for male employees working at a refuse collecting department. Before the introduction of job rotation, an employee worked as a street sweeper, as a refuse collector or as a driver. After the introduction of job rotation, every employee was allowed to alternate between two of the three possible jobs during the day, i.e. refuse collecting/street sweeping, refuse collecting/driving or street sweeping/driving. Two non-rotation groups (i.e. refuse collectors and street sweepers) and two rotation groups (i.e. refuse collectors/street sweepers and street sweepers/drivers) were mutually compared. The physical workload was determined by measuring the perceived load, energetic load and postural load during a full working day. Job rotation resulted in a significant decrease of the perceived load and energetic load and a slight decrease of the postural load. The results indicate that the total amount of work performed by means of job rotation resulted in an overall reduced physical workload of the employees of the refuse collecting department.     

Optimal constant due-date assignment and sequencing

This paper considers the sequencing of n jobs in a single-machine shop in which each job is assigned a constant flow allowance. The objective is to determine the optimal value of the flow allowance and the optimal job sequence to minimize a cost function based on the flow allowance and the job earliness and tardiness values. We first propose a linear programming (LP) formulation of the problem. We then derive the optimal constant flow allowance via considering the LP dual problem and show that it is independent of the job sequence. After the theoretical treatment, a numerical example is presented for discussion.     

A goal programming approach to job evaluation

Job evaluatio refers to a systematic determination of the relative values of jobs in an organization. Often, jobs are evaluated based upon subjective judgement. By considering each job to consist of certain levels of different job factors, this paper develops a goal programming model to evaluate various levels of job factors. The main constraints in such a formation are obtained by using some existing benchmark jobs. The model development and application in evaluating new jobs are illustrated by solving an example problem consisting of four factors and six levels of each factor.     

The use of turnover rate as a passive surveillance indicator for potential low back disorders

Passive surveillance techniques which rely only on injury reporting to locate ergonomic problems within a facility may not be sensitive enough to identify all jobs that place a worker at risk of low back disorder. The current study examines whether turnover rate data provide useful input to a passive surveillance approach. It is hypothesized that the turnover of employees through individual jobs, when not attributable to differential pay scales within a facility, is likely to indicate the presence of ergonomic hazards associated with low back cumulative trauma disorders. This study used the database and multiple logistic regression model developed by Marras et al. (1993) to evaluate this hypothesis. Two data sets were evaluated with the model to determine whether jobs with turnover resemble those with a high historical risk of LB-CTD. The first data set contained trunk motion and workplace data from jobs in which there had been turnover but there were no incidents of LB-CTD. When comparing these data to truly low risk jobs (no LB-CTD incidents or turnover), the model yielded an odds ratio of 5·2. This moderate odds ratio indicates that many of the jobs with turnover have characteristics similar to those found in high LB-CTD risk jobs. The second data set included jobs with turnover and moderate LB-CTD incident rates. The model's resulting odds ratio of 11·0 indicates that jobs with moderate incident rates and turnover are very similar to jobs with a high LB-CTD risk. These results suggest that passive surveillance programs would be more sensitive if turnover rates were determined for each job within a facility and were used to supplement incident rate data.     

Evaluation of ergonomic working conditions among standing sewing machine operators in Sri Lanka

BackgroundStanding Sewing Machine Operators (SSMOs) are engaged in highly repetitive operations, and work while standing during their entire working hours. This leads to discomforts and Musculoskeletal Disorders (MSDs). However, there is a dearth of research in SSMOs’ working conditions.Objective: Aim of the study is to evaluate the prevalence of MSDs and related ergonomic risk factors among SSMOs in the Sri Lankan textile industry.Methods: The sample included 552 female sewing machine operators. Data were collected through self-reported questionnaires which included demographic, job-related factors and Cornell Musculoskeletal Discomfort Questionnaire [CMDQ], along with the application of validated ergonomic tools (Rapid Entire Body Assessment [REBA] and Strain Index [SI]) to assess the ergonomic risks amongst them. The inter-rater reliability test ensured the reliability among observers. An individual regression model was developed for each body parts to assess the associated risk factors.Results: The highest occurrence of musculoskeletal symptoms were in knee, foot, thigh, lower leg and lower back of SSMOs. REBA grand score (4–11) indicated that workers’ postures were at medium, high and very high risk levels necessitating evaluation to change. Moreover, SI indicated medium and high risk of upper extremity disorders. Finally, regression models revealed associated risk factors with musculoskeletal symptoms among various body parts including age, Body Mass Index (BMI), marital status, SSMO experience, job satisfaction, job stress, daily walking distance to the boarding place/factory, interest in job rotation and satisfaction with the design of sewing machine.Conclusion: The findings highlighted that the prevalence of discomfort and MSDs in the lower limbs were higher than in the upper limbs among SSMOs. The findings revealed the working conditions of SSMO and emphasised the need for ergonomic interventions to minimise the MSDs among them.Relevance to industryThe findings highlighted ergonomic risks among SSMOs and associated risk factors which will help managers and researchers better understand the working conditions of SSMOs. The identified risk factors could be considered during the implementation of standing sewing operation layouts and during the selection and allocation of new employees.     

The influence of task design on upper limb muscles fatigue during low-load repetitive work: A systematic review

Ergonomic interventions such as increased scheduled breaks or job rotation have been proposed to reduce upper limb muscle fatigue in repetitive low-load work. This review was performed to summarize and analyze the studies investigating the effect of job rotation and work-rest schemes, as well as, work pace, cycle time and duty cycle, on upper limb muscle fatigue. The effects of these work organization factors on subjective fatigue or discomfort were also analyzed. This review was based on relevant articles published in PubMed, Scopus and Web of Science. The studies included in this review were performed in humans and assessed muscle fatigue in upper limbs. 14 articles were included in the systematic review. Few studies were performed in a real work environment and the most common methods used to assess muscle fatigue were surface electromyography (EMG). No consistent results were found related to the effects of job rotation on muscle activity and subjective measurements of fatigue. Rest breaks had some positive effects, particularly in perceived discomfort. The increase in work pace reveals a higher muscular load in specific muscles. The duration of experiments and characteristics of participants appear to be the factors that most have influenced the results. Future research should be focused on the improvement of the experimental protocols and instrumentation, in order to the outcomes represent adequately the actual working conditions.Relevance to industryIntroducing more physical workload variation in low-load repetitive work is considered an effective ergonomic intervention against muscle fatigue and musculoskeletal disorders in industry. Results will be useful to identify the need of future research, which will eventually lead to the adoption of best industrial work practices according to the workers capabilities.     

A dynamic programming formulation of a production sequencing problem

A dynamic programming algorithm is presented for determining an optimal solution to a problem where n jobs are to be sequenced in a two-stage production environment. Conditions are that the job sequence is the same in both stages; each job requires setups at each stage; setup times are sequence dependent; the second stage setups may overlap first stage production; and the optimal solutions is that with minimum overall duration. The recursion relation is developed, and computational schemes are described for obtaining the optimal solution or solutions. Computational experience is reported. The recursion relation is also extended to the case of any number of stages.     

Decomposition heuristics for minimizing earliness–tardiness on parallel burn-in ovens with a common due date

This paper considers a scheduling problem for parallel burn-in ovens in the semiconductor manufacturing industry. An oven is a batch processing machine with restricted capacity. The batch processing time is set by the longest processing time among those of all the jobs contained in the batch. All jobs are assumed to have the same due date. The objective is to minimize the sum of the absolute deviations of completion times from the due date (earliness–tardiness) of all jobs. We suggest three decomposition heuristics. The first heuristic applies the exact algorithm due to Emmons and Hall (for the nonbatching problem) in order to assign the jobs to separate early and tardy job sets for each of the parallel burn-in ovens. Then, we use job sequencing rules and dynamic programming in order to form batches for the early and tardy job sets and sequence them optimally. The second proposed heuristic is based on genetic algorithms. We use a genetic algorithm in order to assign jobs to each single burn-in oven. Then, after forming early and tardy job sets for each oven we apply again sequencing rules and dynamic programming techniques to the early and tardy jobs sets on each single machine in order to form batches. The third heuristic assigns jobs to the m early job sets and m tardy jobs sets in case of m burn-in ovens in parallel via a genetic algorithm and applies again dynamic programming and sequencing rules. We report on computational experiments based on generated test data and compare the results of the heuristics with known exact solution for small size test instances obtained from a branch and bound scheme.     

基于Petri网的JSP动态优化调度

提出一种在柔性制造系统动态优化调度中处理紧急定单的方法。以带有控制器的 Petri 网为建模工具对柔性生产调度中的离散事件建模,对系统的设备维护、各种优先级等特性进行描述,利用遗传算法和模拟退火算法获得调度结果,用于解决作业车间的加工受到机床、操作工人等双资源制约条件下的动态优化调度。当有紧急定单需要加工时,该方法把剩余任务和紧急任务作为两个独立的任务分别处理,然后进行集成,在紧急任务为最优调度的基础上选取剩余任务的最优调度,找到兼顾整体和局部的最优解。仿真结果说明了算法的有效性和鲁棒性。     

Inter-rater reliability of PATH observations for assessment of ergonomic risk factors in hospital work

This study examined the inter-rater reliability of expert observations of ergonomic risk factors by four analysts. Ten jobs were observed at a hospital using a newly expanded version of the PATH method (Buchholz et al. 1996), to which selected upper extremity exposures had been added. Two of the four raters simultaneously observed each worker onsite for a total of 443 observation pairs containing 18 categorical exposure items each. For most exposure items, kappa coefficients were 0.4 or higher. For some items, agreement was higher both for the jobs with less rapid hand activity and for the analysts with a higher level of ergonomic job analysis experience. These upper extremity exposures could be characterised reliably with real-time observation, given adequate experience and training of the observers. The revised version of PATH is applicable to the analysis of jobs where upper extremity musculoskeletal strain is of concern.     

Parallel machine scheduling problem to minimize the earliness/tardiness costs with learning effect and deteriorating jobs

The focus of this work is to analyze parallel machine earliness/tardiness (ET) scheduling problem with simultaneous effects of learning and linear deterioration, sequence-dependent setups, and a common due-date for all jobs. By the effects of learning and linear deterioration, we mean that the processing time of a job is defined by an increasing function of its starting time and a decreasing function of the position in the sequence. We develop a mixed integer programming formulation for the problem and show that the optimal sequence is V-shaped: all jobs scheduled before the shortest jobs and all jobs scheduled after the shortest job are in a non-increasing and non-decreasing order of processing times, respectively. The developed model allows sequence-dependent setups and sequence-dependent early/tardy penalties. The illustrative example with 11 jobs for 2 machines and 3 machines shows that the model can easily provide the optimal solution, which is V-shaped, for problem.     

Parallel machine scheduling problem with preemptive jobs and transportation delay

In this research the parallel machine scheduling problem with preemption by considering a constant transportation delay for migrated jobs and minimization of makespan as the criterion i.e., P_m|pmtn(delay)|C_max is investigated. It is assumed that when a preempted job resumes on another machine, it is required a delay between the processing time of the job on these two machines. This delay is called transportation delay. We criticize an existing mathematical model for the research problem in the literature [Boudhar M, Haned A. Preemptive scheduling in the presence of transportation times. Computers & Operations Research 2009; 36(8):2387–93]. Then, we prove that there exists an optimal schedule with at most (m−1) preemptions with transportation among machines for the problem. We also propose a linear programming formulation and an exact algorithm for the research problem in case of equal transportation delay. The experiments show that the proposed exact algorithm performs better than the proposed mathematical model.