Kenneth N. McKay

Executing production schedules in the face of uncertainties: A review and some future directions

We review the literature on executing production schedules in the presence of unforeseen disruptions on the shop floor. We discuss a number of issues related to problem formulation, and discuss the functions of the production schedule in the organization and provide a taxonomy of the different types of uncertainty faced by scheduling algorithms. We then review previous research relative to these issues, and suggest a number of directions for future work in this area. � 2003 Elsevier B.V. All rights reserved.

Predictable scheduling of a single machine with breakdowns and sensitive jobs

Production schedules released to the shop floor have two important functions: allocating shop resources to different jobs to optimize some measure of shop performance and serving as a basis for planning external activities such as material procurement, preventive maintenance and delivery of orders to customers. Schedule modification may delay or render infeasible the execution of external activities planned on the basis of the predictive schedule. Thus it is of interest to develop predictive schedules that can absorb disruptions without affecting planned external activities while maintaining high shop performance. We present a predictable scheduling approach, that inserts additional idle time into the schedule to absorb the impacts of breakdowns. The effects of disruptions on planned support activities are measured by the deviations of job completion times in the realized schedule from those in the predictive schedule. We apply our approach to minimizing total tardiness on a single machine with stochastic...

Unifying the theory and practice of production scheduling

Abstract The theory and practice of what has traditionally been called scheduling have been relatively close in some domains, while remaining worlds apart in others. Success at higher levels of production control has often been seen where the execution issues can be glossed over, especially in industries where there are prolonged periods of stability and maturity. Scheduling theory at the detailed level has been particularly successful in process industries or in situations where there are relatively few machines with significant setup issues. Unfortunately, the theory and practice have not been close in intermittent job shops or industries where there is inherent uncertainty or human judgment is necessary. This paper discusses the traditional scheduling problem and develops a framework based on the practice of scheduling that assists in understanding the requirements for an extended definition of scheduling that goes beyond the sequencing problem.

Integrated decision support for planning, scheduling, and dispatching tasks in a focused factory

Standard software for decision support in production control tasks is commonly structured according to the hierarchical production planning (HPP) concept. However, in a focused factory one planner may carry out planning, scheduling and dispatching. This paper presents a case study where one integrated planner is responsible for planning, scheduling and dispatching. Hence, the integrated planner needs a seamless system from the generation from the daily level through the generation of the 5-year-plan. This paper presents a design of a decision support system for the integrated planner.

'Common sense' realities of planning and scheduling in printed circuit board production

The researchers conducted an indepth field project to study the planning and scheduling process in the printed circuit board industry. The formal versus informal scheduling practices are compared, and several aspects of the scheduling situation discussed. Heuristics and techniques used to address instability in the manufacturing system are presented. Instability refers to the manufacturing state when expected or unexpected changes are encountered—e.g. changes in policies, procedures, or a machine fails. The ability to encode the heuristics as a formal model or computer program and have the heuristics mechanically applied is also discussed. The study also provides insights regarding the existence and nature of scheduler expertise.

A review of hierarchical production planning and its applicability for modern manufacturing

Abstract The hierarchical production planning (HPP) paradigm has become an accepted planning and control strategy for many medium-to-large manufacturing situations. While the paradigm appears intuitively obvious and appropriate for many factories, there are a number of modern manufacturing situations where the application of the HPP approach may not be appropriate. By understanding the fundamental principles and concepts inherent in the HPP approach, it is possible to identify situations suitable for HPP with little or no adaptation, and situations where HPP must be extensively modified before use. A poor understanding of HPP

The application of computerized production control systems in job shop environments

Abstract Job shops are the most perplexing and challenging of environments for computerized scheduling systems. Some vendors call them problematic and avoid them whenever possible. The development of a generic scheduling tool that can be widely installed has eluded the many vendors who have tried. Installations in job shops are still painfully slow and are heavily customized. The wide variety of types of industry and processes found in the job shop category explains part of the problem. However, there is an additional challenge facing a scheduling tool after it has been installed: will it be used and does it really help the scheduler do the task of scheduling? Is the tool used for rough planning in the next few days or is it really used for dispatching on the fly by the people sequencing work? Few studies have looked at these issues and vendors are not willing to share this information. Furthermore, few customers who have invested significantly in the purchase and installation of a scheduling tool perform an unbiased postmortem or will share the results. In this study, we will present two field studies where computer scheduling aids were considered and discuss the requirements that will support the scheduler in the daily dispatch task. We have found that while analytical and algorithmic aids have limited benefits to a typical job shop, the appropriate use of computer technology can address information overload, cue filtering, and assist the scheduler in problem solving. We describe seven steps of the job shop scheduling task and the implications of each.

‘Aversion dynamics’ scheduling when the system changes

Real schedulers are observed to avoid scheduling rare and expensive jobs immediately after preventative maintenance or a machine repair. The repairs or similar events produce ‘aversion’ in these jobs. The authors create a class of heuristics called aversion dynamics (AD) which focus on similar ideas of attraction and aversion in production planning. A preliminary heuristic (Averse-1) introducing the topic and related issues is formulated and the computational analysis is presented. AD is specially designed to piggy-back on a traditional heuristic and functions for a limited time after which the traditional heuristic regains control. The study shows that when impact results from an event such as a repair, Averse-1 significantly out-performs other dispatching heuristics for a wide range of scheduling problems. Since there is uncertainty about the expected impact, the heuristic is also analysed for the situations when the schedule is adjusted but the impact does not occur. In these cases, the heuristic takes a conservative posture (in hindsight) and sub-optimizes for a limited time. The study shows that while there is an added cost, the cost is relatively small. We conclude that (i) it is possible to reasonably extend traditional heuristics to include dynamic phenomena from the real world, and (ii) modelling the secondary impact of events is a significant factor in schedule generation. Copyright

Historical survey of manufacturing control practices from a production research perspective

Manufacturing control is concerned with what is done where, when and why in manufacturing. Over time, methods and practices have developed for efficient and effective inventory control, resource utilization and ensuring customer delivery. A limited review of the production research literature from the past two centuries was undertaken to determine the prior existence and awareness of a number of present practices. Rather than focus on one particular practice and explore it exhaustively, 22 practices were researched, five of which are described at greater depth. It is clear from this limited review of the historical literature that many of the same or similar manufacturing problems have been consciously recognized and dealt with in the past, often with the same concepts and philosophies. The elegant and sophisticated mathematical modelling and justification of the present might have been absent in the past, but the common sense basis of the solutions can be observed.

Schedulers & Planners: What and How Can We Learn From Them

As part of a larger project investigating the nature of planning and scheduling, we conducted an interdisciplinary research agenda focusing on the scheduler and the scheduling task. Preliminary field research resulted in a paradigm being derived for planning and scheduling in industries that are under a state of development or that have a degree of inherent uncertainty (e.g., electronics, ceramics, biotech, and custom job shops). Methods from the social sciences (e.g., Organizational Behavior and Cognitive Science) were then used to gather and analyse information from the field to validate and support the concepts. This paper describes the approach taken for the field research and discusses the benefits that can be obtained when a social science perspective is taken to studying the management of operations.