Operator performance and subjective response in control of flexible manufacturing systems

In this study, allocation of functions and system size (number of machines) were manipulated to test their effects on operator performance and subjective response in a flexible manufacturing system (FMS). An experiment was conducted using a cross-over design with three independent variables: number of machines, task allocation, and sequence of task presentation. Operator performance was measured by response time, and subjective response assessed using two questionnaires. Physiological measures were also taken (EKG and respiratory rate). The results revealed that the number of machines in the system did not affect performance or subjective or physiological response while the effect of allocation level was significant for both performance and subjective response.     

Performance analysis of re-entrant flow shop with single-job and batch machines using mean value analysis

We propose an approximate method based on the mean value analysis for estimating the average performance of re-entrant flow shop with single-job machines and batch machines. The main focus is on the steady-state averages of the cycle time and the throughput of the system. Characteristics of the re-entrant flow and inclusion of the batch machines complicate the exact analysis of the system. Thus, we propose an approximate analytic method for obtaining the mean waiting time at each buffer of the workstation and a heuristic method to improve the result of the analytic method. We compare the results of the proposed approach with a simulation study using some numerical examples.     

A proposed methodology for the prediction of mental workload, based on engineering system parameters

In the design of engineering systems, mental workload is one of the most important factors in the allocation of cognitive tasks. Current methods of task allocation have criteria that are defined in only general terms and are thus not very useful in aiding detailed decision-making in system design. Whilst there are many quantitative criteria available to determine the physical space in human-machine interaction, system designers really require an explicit model and specific criteria for the following identification of the mental workload imposed by the system; prediction of both human and system performance; evaluation of the alternatives of system design; and the design of system components. It is argued that the available methods of workload or performance are either too domain-dependent to apply to the design of other systems, or subject-dependent and thus do not reflect the objective workload imposed by the system. The presented research adopts a new approach to cognitive task analysis in dynamic decision-making systems. Based on the characteristics derived from task analysis, a general conceptual model of the prediction of mental workload in system design is proposed. In the new model, workload is represented by a set of system parameters—task arrival rate, task complexity, task uncertainty, and performance requirements—which are considered to be the main sources of workload. In this context, workload becomes an objective demand of engineering systems, independent of any subjective factors. Whether an individual or population is overloaded depends upon their workload threshold with respect to the specified task and environment. It is hoped that this new model, after both laboratory and industrial validation, could be used by system designers to predict the workload imposed on people by systems.     

Determination of the optimal number of kanbans and kanban allocation in a FMS: A simulationbased study

A simulation-based study is presented to compare the performance of a set of kanban allocation rules in a flexible manufacturing system (FMS) operating in a pull mode. This paper also presents a simulation-based direct search approach to determine the optimal number of kanbans and their simultaneous allocation to different part types. This paper presents a realistic cost function that includes a penalty for failing to meet the demand on time, and a penalty for rescheduling delivery of materials from vendors. The model captures limited flexibility in the form of operational flexibility in a FMS. Future extensions to this study are discussed.     

The Effects of Individual Monetary Incentives With and Without Feedback

Abstract

This study examined the effects of an individual monetary incentive system with and without feedback to determine if feedback would supplement the effects of incentives. Participants were seven college students who performed a computerized task called SYNWORK. SYNWORK presented four sub-tasks concurrently: memory, arithmetic, visual monitoring and auditory monitoring. Participants earned points for correct responses. The dependent variable was the number of points earned. An ABAC design was used with A = individual monetary incentives without feedback, B = individual monetary incentives with feedback, and C = hourly pay with feedback. Sessions were 90 minutes, and there were 5 to 10 sessions per phase. The point scores of six of the seven participants increased when feedback was added to the incentive system but stabilized or continued to increase when feedback was removed. The feedback intervention was staggered in time across participants, and performance increased when feedback was added, hence the data suggest that feedback enhanced the effects of the incentives. One possible reason for the reversal failure is that feedback evoked higher levels of performance that were then maintained by the additional incentives. Because performance did not reverse, however, the results must be viewed cautiously.     

After-effects of working at visual display units

Abstract

Two experiments were carried out to examine the acute and chronic after-effects of working with VDUs on subsequent subjective mood and performance efficiency. Both showed that working at a VDU has a negative after-effect on the user's subjective well-being but only if that person has a high level of cognitive failure. There was no evidence of any such effect on measures of performance efficiency.     

When Knowing You Are Doing Well Hinders Performance

Summary

The effect of two types of verbal consequences, rule-following feedback and task performance feedback, on rule-induced insensitivity to programmed schedules of reinforcement were examined. Rule-following feedback could be either accurate or non-contingently positive. The task involved moving a sign through a grid using telegraph keys operating on a multiple DRL 6/FR 18 schedule of reinforcement in the presence of an initially accurate rule. After acquisition, the multiple schedule was changed without notice to a FR 1/FI Yoked schedule. Accurate rule-following feedback plus feedback on task performance produced striking insensitivity to the DRL 6 to FR 1 schedule change, the opposite of what might be expected by a common sense analysis of task performance feedback, even after controlling for contact with the changed contingency. It is argued that findings such as these can only be understood by considering the mutual verbal relations evoked by the combinations of rules and feedback, rather than treating feedback as a simple consequential event or as a verbal consequence whose effects do not depend on the relations sustained with other events.     

Keeping an Uphill Edge

Abstract

Several behaviors in a ski shop were identified as being deficient using Austin's Performance Diagnostic Checklist (2000) and Daniels and Daniels' PIC/NIC Analysis (2004). During a 4-week baseline, 7 cleaning behaviors were monitored and 5 were subsequently targeted in an intervention package using an ABC design. The intervention included: a task clarification session, a posted behavioral checklist, graphic feedback of the group's performance for the previous week, and daily task-specific feedback. Immediately after the checklist was posted, the frequency of employee cleaning behaviors increased 52%. Cleaning behaviors increased an additional 12% after the implementation of daily task-specific feedback. Results suggest the interventions generalized to the 2 cleaning behaviors not mentioned in the task-clarification session.     

The Relative Effects of Different Frequencies of Feedback on Work Performance

Abstract

This laboratory simulation examined the relative effects of two frequencies of feedback on work performance under hourly pay and incentive pay. The study had four experimental conditions: feedback delivered after every session under hourly pay and under incentive pay, and feedback delivered after every fourth session under hourly pay and under incentive pay. Thirty-five college students were randomly assigned to one of the four conditions. Each participant attended 24 thirty-minute sessions. Participants performed a simulated work task on the computer that consisted of computer-related activities such as dragging, clicking, and typing. The dependent variable was the number of correctly completed units of work. An analysis of covariance was conducted to analyze the data using pretest scores as a covariate. Participants who received feedback every session completed significantly more work units than participants who received feedback every fourth session. In addition, an interaction between feedback frequency and pay systems was found: Feedback delivered every session was more effective than feedback delivered every fourth session under the incentive pay system, but not under the hourly pay system. The results suggest that the relative effects of feedback frequency may depend upon the extent to which feedback is correlated with differential consequences for performance.     

A simulated annealing algorithm for designing cellular manufacturing systems with productivity consideration

In this paper, we propose a productivity model for solving the machine-part grouping problem in cellular manufacturing (CM) systems. First, a non-linear 0-1 integer programming model is developed to identify machine groups and part families simultaneously. This model aims to maximize the system productivity defined as the ratio of total output to the total material handling cost. Second, an efficient simulated annealing (SA) algorithm is developed to solve large-scale problems. This algorithm provides several advantages over the existing algorithms. It forms part families and machine cells simultaneously. It also considers production volume, sales price, and maximum number of machines in each cell and total material handling cost. The proposed SA also has the ability to determine the optimum number of manufacturing cells. The performance of the developed models is tested on eight problems of different size and complexity selected from the literature. The results show the superiority of the SA algorithm over the mathematical programming model in both productivity and computational time.     

Improved algorithmic results for unsplittable stable allocation problems

The stable allocation problem is a many-to-many generalization of the well-known stable marriage problem, where we seek a bipartite assignment between, say, jobs (of varying sizes) and machines (of varying capacities) that is “stable” based on a set of underlying preference lists submitted by the jobs and machines. Building on the initial work of Dean et al. (The unsplittable stable marriage problem, 2006), we study a natural “unsplittable” variant of this problem, where each assigned job must be fully assigned to a single machine. Such unsplittable bipartite assignment problems generally tend to be NP-hard, including previously-proposed variants of the unsplittable stable allocation problem (McDermid and Manlove in J Comb Optim 19(3): 279–303, 2010). Our main result is to show that under an alternative model of stability, the unsplittable stable allocation problem becomes solvable in polynomial time; although this model is less likely to admit feasible solutions than the model proposed in McDermid and Manlove (J Comb Optim 19(3): 279–303, McDermid and Manlove 2010), we show that in the event there is no feasible solution, our approach computes a solution of minimal total congestion (overfilling of all machines collectively beyond their capacities). We also describe a technique for rounding the solution of a stable allocation problem to produce “relaxed” unsplit solutions that are only mildly infeasible, where each machine is overcongested by at most a single job.     

Just-in-time scheduling with controllable processing times on parallel machines

We study scheduling problems with controllable processing times on parallel machines. Our objectives are to maximize the weighted number of jobs that are completed exactly at their due date and to minimize the total resource allocation cost. We consider four different models for treating the two criteria. We prove that three of these problems are NP\mathcal{NP} -hard even on a single machine, but somewhat surprisingly, the problem of maximizing an integrated objective function can be solved in polynomial time even for the general case of a fixed number of unrelated parallel machines. For the three NP\mathcal{NP} -hard versions of the problem, with a fixed number of machines and a discrete resource type, we provide a pseudo-polynomial time optimization algorithm, which is converted to a fully polynomial time approximation scheme.     

Helping people to sort it out: The role of social support in the Job Strain Model

This paper reports three studies of occupational stress investigating the role of social support as an intervening variable in the Job Strain Model (Karasek, 1979). A computer simulated mail-sorting work environment was used to assess the effect of demands, control and social support on measures of strain, satisfaction, and perceived and actual task performance. The first experiment ( N =60) tests the basic Job Strain Model by manipulating levels of task demand and control. The second experiment ( N =120) compares high and low levels of two types of social support (informational support and emotional support) to determine whether and how they interact with extreme conditions of the Job Strain Model (high strain and low strain). The final experiment ( N =90) investigates positive and negative forms of social support (praise and criticism) in relation to extreme job strain conditions. Results show that the job strain model is consistent with the stress and performance data, although stress showed no Demand 2 Control interaction. Social supports increased arousal, satisfaction and perceived performance, but did not affect stress or task performance. Moreover, contrary to buffer theories, social supports did not interact with the job strain variables. Congruence between preferred and experienced emotional support levels also predicted performance.     

An asymptotically optimal algorithm for large-scale mixed job shop scheduling to minimize the makespan

This paper considers the large-scale mixed job shop scheduling problem with general number of jobs on each route. The problem includes ordinary machines, batch machines (with bounded or unbounded capacity), parallel machines, and machines with breakdowns. The objective is to find a schedule to minimize the makespan. For the problem, we define a virtual problem and a corresponding virtual schedule, based on which our algorithm TVSA is proposed. The performance analysis of the algorithm shows the gap between the obtained solution and the optimal solution is O(1), which indicates the algorithm is asymptotically optimal.     

Effects of Process and Human Performance Improvement Strategies

Abstract

Organizational performance is a function of many variables, two of which are work process factors and human performance factors. Our study compared the effects of changing a work process versus human performance improvement techniques and the combined effects of combing both techniques. A 2 (manual vs. electronic process) X 2 (with vs. without behavioral intervention) between-subjects design with stratified random assignment was employed. Forty-eight participants performed a word processing task where their minutes-in-possession and error rate were recorded. Results revealed a main effect for process type and a main effect for behavioral intervention. The largest effects were observed with the context of a combined intervention. The implications of using a combined approach and topics for future researchers are discussed.     

A 14-h night-shift in the control room of a fire brigade

Abstract

All 29 operators in the control room of a fire brigade performed test sessions during work and leisure time at 2-h intervals on a day with a 14-h night-shift, a day off and a day with a 10-h morning shift. The test sessions consisted of a visual search choice reaction time test and two Sternberg memory search tests (1 or 5 letters had to be memorized). Furthermore, the operators recorded their oral temperature and their subjective alertness before each test session. The subject also kept a diary of work and sleep times for 14 days. The circadian rhythm of body temperature was hardly changed by a single night-shift. Parallel to the body temperature, the subjective alertness fell significantly during the night-shift reaching a minimum value at 06:00 h. The mean reaction times increased non-significantly at the end of the night-shift and the results of the two Sternberg memory search tests showed no significant trends. The sleep of the operators after the night-shift was on average reduced to 5 hs 34 min. The results of subjective rating of alertness and reaction time test are interpreted as effects of the combined influences of circadian rhythmicity, sleep loss and time on professional task. Most results support the conclusion that a 14-h night-shift without extensive breaks is not acceptable.     

The Effects of a Combined Task Clarification,Goal Setting,Feedback, and Performance Contingent Consequence Intervention Package on Telephone Customer Service in a Medical Clinic Environment

Abstract

Appointment coordinators at a mid-western medical clinic were to provide exceptional telephone customer service. This included using a standard greeting, speaking in an appropriate tone of voice during the conversation, and using a standard closing to end the call. An analysis suggested performance deficiencies resulted from weak antecedents, poor knowledge and skills, and weak performance contingencies. An intervention package consisting of task clarification, goal setting, feedback, and performance contingent consequences was designed to improve customer service behaviors of four participating appointment coordinators. An ABAB reversal design was used, and overall performances of all four participants increased during intervention phases. This study indicates that a multi-component intervention may be an effective strategy to increase telephone customer service behavior in medical clinic settings.     

Effects of sleep inertia on cognitive performance following a 1-hour nap

Abstract

This study investigated the effects of a 1-h nap on subsequent performance in spatial memory (SM) and logical reasoning (LR) tasks. The objective was to evaluate the duration of the effects of sleep inertia (SI). The performance was measured in two independent groups of subjects. The 1-h nap took place at 00:00 h in group 1 and at 03:00 h in group 2. In each task, the experimental design comprised one no-nap condition in which subjects had no sleep before the night tests, and a nap condition that comprised the 1-h nap followed by the test sessions. To measure the duration of SI effects, the subjects were tested in two 30-min sessions and the data in each session were analysed in sub-units of time of 3 min each. In each task the results showed no effects on accuracy, and no circadian effects of napping were found. In each task, analyses of pooled data of the two groups showed that the performance in the 1-h nap condition exhibited significant reductions of speed immediately following awakening, when compared with no-nap, reflecting SI effects. In SM, the slowing lasted 24 min, and 27 min in LR. Practical implications of the results are discussed.     

Effects of Accurate and Inaccurate Feedback on Work Performance: The Role of the Awareness of Inaccuracy

ABSTRACT

This study compared the effects of accurate (i.e., contingent) and inaccurate (i.e., non-contingent) feedback on work performance under two different work conditions. Under one work condition, participants could clearly see the outcome of their performance (i.e., visible condition). Under the other condition, they could not clearly see the outcome of their performance (i.e., non-visible condition). One hundred and twenty participants were randomly assigned to four experimental conditions (i.e., accurate/visible, inaccurate/visible, accurate/non-visible, and inaccurate/non-visible) and asked to perform a simulated work task. The results indicated that inaccurate feedback was as effective as accurate feedback under the non-visible condition, but inaccurate feedback was less effective than accurate feedback under the visible condition.     

Dynamic scheduling of manufacturing job shops using extreme value theory

Most job shop scheduling approaches reported in the literature assume that the scheduling problem is static (i.e. job arrivals and the breakdowns of machines are neglected) and in addition, these scheduling approaches may not address multiple criteria scheduling or accommodate alternate resources to process a job operation. In this paper, a scheduling method based on extreme value theory (SEVAT) is developed and addresses all the shortcomings mentioned above. The SEVAT approach creates a statistical profile of schedules through random sampling, and predicts the quality or 'potential' of a feasible schedule. A dynamic scheduling problem was designed to reflect a real job shop scheduling environment closely. Two performance measures, viz. mean job tardiness and mean job cost, were used to demonstrate multiple criteria scheduling. Three factors were identified, and varied between two levels each, thereby spanning a varied job shop environment. The results of this extensive simulation study show that the SEVAT scheduling approach produces a better performance compared to several common dispatching rules.