Mail Processing Research Articles

Weekly staff scheduling with workstation group restrictions

This paper addresses the weekly adjustment problem for staff scheduling when movement restrictions exist between workstation groups (WSGs). In practice, it is common for employees to be organized into physical or logical groups to match the layout of a facility or to facilitate managerial oversight. A complication in the problem arises when each employee is required to spend more time at his or her assigned home base during the week than at any other WSG. This conflicts with a common strategy of reassigning employees to different WSGs when idle time exists in their schedules. Ordinarily, the full problem is tackled with a two-phase approach, where optimal shifts and overtime allocations are first derived and then tasks are assigned. When movement restrictions exist in a facility, this approach is no longer practical or even possible for all but the smallest instances. Alternatively, a new model is proposed that integrates WSG restrictions with the shift scheduling and task assignment constraints. The model takes the form of a large-scale integer program and is solved with one of two decomposition heuristics. The first splits the movement restrictions network into manageable pieces; the second uses column generation to identify good individual schedules that are used to construct a set-covering-type master problem. A solution to the master problem provides a feasible solution to the original integer program. Extensive testing was done with data obtained from the U.S. Postal Service mail processing and distribution center in Dallas. The results show that good feasible solutions can be obtained in less than an hour.

Workforce planning at USPS mail processing and distribution centers using stochastic optimization

Service organizations that operate outside the normal 8-hour day and face wide fluctuations in demand constantly struggle to optimize the size and composition of their workforce. Recent research has shown that improved personnel scheduling methods that take demand uncertainty into account can lead to significant reductions in labor costs. This paper addresses a staff planning and scheduling problem that arises at United States Postal Service (USPS) mail processing & distribution centers (P&DCs) and develops a two-stage stochastic integer program with recourse for the analysis. In the first stage, before the demand is known, the number of full-time and part-time employees is determined for the permanent workforce. In the second stage, the demand is revealed and workers are assigned to specific shifts during the week. When necessary, overtime and casual labor are used to satisfy demand.

The task assignment problem for unrestricted movement between workstation groups

The purpose of this paper is to investigate the problem of assigning tasks to workers during their daily shifts. For a homogeneous workforce, a given set of workstation groups, and a corresponding demand for labor, the objective is to develop a disaggregated schedule for each worker that minimizes the weighted sum of transitions between workstation groups. In the formulation of the problem, each day is divided into 48 1/2-hour time periods and a multi-commodity network is constructed in which each worker corresponds to a unique commodity and each node represents a workstation group-time period combination. Lunch breaks and idle time are also included in the model. Initial attempts to solve large instances with a commercial code indicated a need for a more practical approach. This led to the development of a reduced network representation in which idle periods are treated implicitly, and a sequential methodology in which the week is decomposed into 7 daily problems and each solved in turn. To gain more computational efficiency, a tabu search procedure was also developed. All procedures were tested using data obtained from a U.S. Postal Service mail processing and distribution center. Depending on the labor category, anywhere from 3 to 28 workstation groups and up to 311 full-time and part-time workers had to be scheduled together. The results were mixed. While small problems could be solved to near-optimality with the integer programming approaches, tabu search was the best alternative for the very large instances. However, the excessive number of swaps needed to gain marginal improvements, undermined its effectiveness.Combining the two provided a good balance in most cases.

A multi-period machine assignment problem

In this paper, a multi-period assignment problem is studied that arises as part of a weekly planning problem at mail processing and distribution centers. These facilities contain a wide variety of automation equipment that is used to cancel, sort, and sequence the mail. The input to the problem is an equipment schedule that indicates the number of machines required for each job or operation during the day. This result is then post-processed by solving a multi-period assignment problem to determine the sequence of operations for each machine. Two criteria are used for this purpose. The first is to minimize the number of startups, and the second is to minimize the number of machines used per operation. The problem is modeled as a 0–1 integer program that can be solved in polynomial time when only the first criterion is considered. To find solutions in general, a two-stage heuristic is developed that always obtains the minimum number of startups, but not necessarily the minimum number of machines per operation. In a comparative study, high quality solutions were routinely provided by the heuristic in negligible time when compared to a commercial branch-and-bound code (Xpress). For most hard instances, the branch-and-bound code was not able to even find continuous solutions within acceptable time limits.

Generation of bioaerosols during manual mail unpacking and sorting

The dynamics of bioaerosol generation in specific occupational environments where mail is manually unpacked and sorted was investigated. Total number of airborne particles was determined in four different size classes (0.3-0.5, 0.5-1, 1-5 and >5 microm) by laser particle counting. Time dependent formation of bioaerosols was monitored by culturing methods and by specific staining followed by flow cytometry. Besides handling of regular mail, specially prepared letters ('spiked letters') were added to the mailbags to deliberately release powdered materials from letters and to simulate high impact loads. These letters contained various dry powdered biological and nonbiological materials such as milk powder, mushrooms, herbs and cat litter. Regarding the four size classes, particulate aerosol composition before mail handling was determined as 83.2 +/- 1.0, 15.2 +/- 0.7, 1.7 +/- 0.4 and 0.04 +/- 0.02%, respectively, whereas the composition changed during sorting to 66.8 +/- 7.9, 22.3 +/- 3.6, 10.4 +/- 4.0 and 0.57 +/- 0.27%, respectively. Mail processing resulted in an increase in culturable airborne bacteria and fungi. Maximum concentrations of bacteria reached 450 CFU m(-3), whereas 270 CFU of fungi were detected. Indoor particle concentrations steadily increased during mail handling mostly associated with particles of diameters >1 microm. However, it was not possible to distinguish spiked letters from nonspiked by simple particle counting and CFU determinations. The dynamics of bioaerosol generation have to be addressed when monitoring specific occupational environments (such as mail sorting facilities) regarding the occurrence of biological particles.

Lessons learned from the CDC's post‐exposure prophylaxis program following the anthrax attacks of 2001

The bioterrorism-related outbreak of anthrax in Fall 2001 was the result of unprecedented attacks on residents of the United States. Although addressees of anthrax spore-filled letters were most likely the targets of the attacks, thousands of U.S. postal employees and others were exposed through aerosolization of spores in mail processing facilities. 1 These attacks precipitated decisions to recommend post-exposure prophylaxis (PEP) to an estimated 10 000 individuals potentially exposed to Bacillus anthracis to prevent inhalational anthrax. 2 Initially, the Centers for Disease Control and Prevention (CDC) recommended 60 days of antimicrobial PEP (initial PEP program), mainly either doxycycline or ciprofloxacin. 2 The CDC eventually extended its recommendation to 40 additional days of antimicrobial prophylaxis with or without three doses of anthrax vaccine adsorbed (AVA) under an investigational new drug (IND) protocol (extended PEP program). 3 Overall, approximately 5420 individuals received education about the extended PEP program. Of these, 1727 individuals agreed to take antibiotics for a full 100 days, but only 199 also chose to be vaccinated with AVA. 4,5 Fifty-seven percent of those who took at least one dose of antimicrobial prophylaxis during the first 60 days of PEP sustained an adverse event (AE), of which less than 1% were considered serious. 6 No deaths were attributed to PEP. Of the thousands of exposed individuals who were advised to take PEP, none developed any form of anthrax, whether or not they

A generic method for determining up/down orientation of text in roman and non-roman scripts

This paper presents a method for determining the up/down orientation of text in a scanned document of unknown orientation, so that it can be appropriately rotated and processed by an optical character recognition (OCR) engine. The method analyzes the “open” portions of text blobs to determine the direction in which the open portions face. By determining the respective densities of blobs opening in a pair of opposite directions (e.g., right or left), the method can establish the direction in which the text as a whole is oriented. We first describe a method for determining the up/down orientation of roman text based on the asymmetry in the openness of most roman letters in the horizontal direction. For non-roman text such as Pashto and Hebrew, we provide a method that determines a direction that is the most asymmetric, and therefore the most useful for the determination of text orientation, given a training data set of documents of known orientation. This work can be adapted for use in automated mail processing or to determine the orientation of checks in automated teller machine envelopes, scanned or copied documents, documents sent via facsimile, and digital photographs that include text (e.g., road signs, business cards, driver's licenses), among other applications.

Generating labor requirements and rosters for mail handlers using simulation and optimization

In this research, we introduce a dual-purpose simulation model that integrates two decision support systems used by the US Postal Service to configure and staff their mail processing and distribution centers (P&DCs). The first system is designed to optimize the daily equipment schedules and the second to optimize the size and composition of the permanent workforce. Large-scale integer programs are solved in both cases. Because some compromise is needed in the time granularity, it is important to have an independent means of validating the results. This is the first purpose of our simulation model. The second involves the generation and validation of labor requirements for a category of workers known as mail handlers. While there is a one-to-one relationship between machine operators and the equipment schedule derived from the mail arrival profiles, no such relationship exists for those responsible for moving the mail between workstations. Neither productivity measures nor formal work rules exist. To resolve this shortcoming, we use simulation again, but this time to estimate mail handler requirements and then to determine whether the weekly schedules derived from the staff optimizer are adequate to meet the facility's service standards. Holistically speaking, the simulation serves as a bridge between the two optimization systems. The procedure is demonstrated with data provided by the Dallas P&DC.

Weekly scheduling in the service industry: an application to mail processing and distribution centers

This paper addresses the midterm planning problem that arises at various service facilities staffed by full-time and part-time employees. In response to updated demand forecasts, expected leave, training assignments, and other contingencies, weekly adjustments are often required to better match available personnel with demand over the planning horizon. Unlike manufacturing where uniform 8-hour shifts are the rule, service organizations may experience several busy periods during the day that do not fit a standard shift. In such cases, supervisors must adjust employee schedules by assigning overtime, increasing the number of part-time hours, and calling in temporary workers. The situation is complicated by union contracts, labor rules, and company policies. To find solutions that can be implemented in a real-world environment, a two-phase approach was developed. In the first phase, the adjustment problem is formulated as a large-scale integer program and solved with a commercial code for those cases in which demand increases are limited to no more than 10% above the baseline. For the more general case, a new target-based heuristic was designed with the goal of finding good feasible solutions. In the second phase, the shift schedules are post-processed to provide daily assignments for each worker. An analysis of the problem arising in the first phase is presented for an application involving weekly scheduling at a mail processing and distribution center. The results indicate that high quality solutions can be obtained within a matter of minutes.

Equipment scheduling at mail processing and distribution centers

Mail Processing and Distribution Centers (P&DCs) run 24 hours a day, 7 days a week and are staffed by a skilled complement of full-time, part-time, and temporary employees. A recurrent problem faced by facility managers involves the development of daily schedules for the automation equipment used to process the mail. The ultimate goal is to minimize the labor costs associated with running the facility while ensuring that all service standards are met. The focus of this paper is on the equipment scheduling aspect of the problem. In particular, we seek a weekly schedule that satisfies all operational, technological, and legal constraints of the system at a minimum cost. The problem is modeled as a large-scale mixed-integer linear program and solved sequentially using a three-stage methodology. In each stage, a separate criterion is optimized and the corresponding objective function value is used as a constraint in subsequent stages. To ease the computational burden, two major enhancements are developed. The first is a pre-processor designed to reduce the number of integer variables; the second is a heuristic that uses the linear programming solution as a target and attempts to find a feasible integer point as close to it as possible. The methodology is demonstrated with data obtained from the Dallas P&DC. The computations indicate that for letter operations alone the annual savings will be on the order of $1.6 million per facility when the system is implemented nationwide over the next 3 years.

Selecting the appropriate input data set when configuring a permanent workforce

This paper explores the issue of choosing the best data to use when running a scheduling model to select a permanent workforce for a service facility. Because demand is assumed to vary over the day and throughout the week, the choice of the input data is crucial. If a week of low volume is selected, the solution might call for an insufficient number of workers; if a week of high volume is chosen, excessive idle time might be the result. Staff scheduling at mail processing and distribution centers (P&DCs) in the United States provides the backdrop. In operating these facilities, a critical objective is to manage overtime, part-time workers, and temporaries so that when volumes are high, additional costs are kept to a minimum, and when volumes are low the permanent workforce is almost never idle. In quantitative terms, this means selecting the size and composition of the workforce so that over the year, no more than a total number of overtime hours, part-time hours and temporary worker hours are used when demand exceeds some baseline and absenteeism is taken into account. To solve the problem, an engineering approach is proposed in which estimates of productivity are made based on a single run of the optimization model and the final data set is chosen to satisfy a small error tolerance. The full methodology is illustrated with data provided by the Dallas P&DC.

Staff scheduling in high volume service facilities with downgrading

This paper discusses the problem of scheduling a multi-skilled workforce in service organizations where demand varies throughout the day, 7 days a week. The goal is to determine the optimal complement of workers so that demand is met without violating labor rules, union agreements, and company policies. It is assumed that each member of the workforce possesses a particular type of skill and can be categorized as either full-time, part-time, or temporary. Demand is specified by skill type, and in the downgrading analysis, a person in a higher skill category can be assigned a job in a lower skill category, but at the original rate of pay. We develop a mixed-integer linear programming model for this problem based on staffing requirements at US Postal Service mail Processing and Distribution Centers (P&DCs). The solution methodology involves the use of a commercial code to find daily shifts, and post-processing heuristics to construct 5-day a week schedules, allocate lunch breaks, and assign workers to jobs during the day. Results are presented for the Dallas P&DC where it is seen that considerable savings are possible when downgrading is implemented.

Comparative approaches to equipment scheduling in high volume factories

Mail processing and distribution centers (P&DCs) are large factories that accept, sort, and sequence mail in preparation for delivery. A central problem in these facilities is how to schedule the equipment over the day to ensure batch production under tight equipment and workforce constraints. The problem falls into the general category of multi-level lot sizing and is notoriously difficult to solve. No exact algorithms exist that are efficient and can consistently provide high-quality solutions. In the paper, we investigate two specialized approaches for solving this problem. The first is a piece-by-piece LP-based heuristic and the second is a Benders decomposition. The heuristic uses the LP fractional solution as a target and attempts to find an integer solution that is as close to it as possible by minimizing the L 1 -norm. The procedure consists of solving the LP relaxation of the original model and two reduced mixed-integer programs. The process is similar to what has been called ‘piece-by-piece decomposition’ in nonlinear programming. While the goal there is to find better initial starting points for the nonlinear code, our goal is to improve solution quality. Computational testing using data provided by the Dallas P&DC confirmed the superiority of the piece-by-piece LP-based heuristic with respect to branch and bound, which proved to be computational expensive, and the Benders algorithm which took several hours to find feasible solutions. In general, the LP-based heuristic was an order of magnitude faster than branch and bound and provided solutions that were able to process more than 99.75% of the daily volume.

Development of Evaluation Procedures for Local Exhaust Ventilation for United States Postal Service Mail-Processing Equipment

Researchers from the National Institute for Occupational Safety and Health (NIOSH) have conducted several evaluations of local exhaust ventilation (LEV) systems for the United States Postal Service (USPS) since autumn 2001 when (a) terrorist(s) employed the mail system for acts of bioterrorism. As a part of the USPS 2002 Emergency Preparedness Plan, the development and installation of LEV onto USPS mail-processing equipment can reduce future exposures to operators from potentially hazardous contaminants, such as anthrax, which might be emitted during the processing of mail. This article describes how NIOSH field testing led to the development of recommended testing procedures for evaluations of LEV capture efficiency for mail-processing equipment, including tracer gas measurements, smoke release observations, air velocity measurements, and decay-rate testing under access hoods.

Workforce planning in a lotsizing mail processing problem

The treatment of mail objects in a mail processing centre involves many operations, in particular sorting by destination. Out of the batching problem that we can identify in such a process, there are also staff planning concerns. In this paper, we analyse a treatment area (registered mail) belonging to a mail processing center, where mail objects are treated in a chain production process. The production quantities and the transfer amounts among machines are required to be determined along the daily work period. The objective is to minimize the costs with human resources needed in the process, linked with the lotsizing production plan, by matching staff to work requirements. This leads into a lotsizing and workforce problem, for which we propose an integer programming formulation. A case study of a particular treatment area is also discussed. The formulation is adjusted to the specific constraints of this case study and some computational results are included, considering average, small and high daily amounts of mail arrived to that particular treatment area.

Bacillus anthracis contamination and inhalational anthrax in a mail processing and distribution center.

Four inhalational anthrax cases occurred in a large mail processing and distribution center in Washington, DC, after envelopes containing Bacillus anthracis spores were processed. This report describes the results of sampling for B. anthracis spores during investigations conducted in October and December 2001. Wet swabs, wet wipes, vacuum sock, and air-filter samples were collected throughout the facility to characterize the extent of building contamination. The results showed widespread contamination of B. anthracis spores, particularly associated with one delivery bar code sorter (DBCS) machine that had sorted the spore-containing envelopes and an area where the envelopes were handled by postal workers. Spore concentrations decreased as distance from the DBCS machine increased, but spores were widely dispersed into surrounding areas. The spatial distribution of culture positive samples was closely related to the work areas of the inhalational anthrax cases and supported epidemiological evidence that the workers became ill from exposure to B. anthracis spores in areas where the contaminated envelopes had travelled. The results of this investigation were used to guide decontamination efforts and provided baseline spore concentrations for follow-up measurements after the building had been cleaned. Implementing methods to reduce aerosolization and dispersion of dust within the facility would reduce postal workers' potential exposures to bioterrorism agents.

Sequencing the processing of incoming mail to match an outbound truck delivery schedule

This paper considers the problem of sequencing the processing of incoming mail in a processing and distribution center (P&DC) to match a given outbound truck delivery schedule. Mail arrives at a P&DC from local associate offices or remote P&DCs following an incoming schedule. The mail from an origin has different proportions to different destinations. For each destination, there are trucks scheduled with limited capacities. The objective of the problem is to determine the sequence in which the incoming mail should be processed so that the total unused truck capacity is minimized. Since, we are not concerned with detailed scheduling/routing decisions inside the P&DC, we treat the P&DC system as a single machine. Dispatching rules and heuristics are proposed for this single machine problem and tested via computational experiments. Simulation experiments are performed to test the efficiency of these methods for the original multi-center multi-machine system.

The North Staffordshire Osteoarthritis Project--NorStOP: prospective, 3-year study of the epidemiology and management of clinical osteoarthritis in a general population of older adults.

BackgroundThe clinical syndrome of joint pain and stiffness in older people is the commonest cause of disability and health care consultation in this age group. Yet there have been few prospective studies of its course over time and its impact on personal and social life. We plan a cohort study in the general population aged 50 years and over to determine the course and prognosis of hand, hip, knee and foot pain, and the impact of these syndromes on participation levels and health care use.MethodsAll patients aged 50 years and over registered with 3 local general practices are to be recruited to a population-based cohort study through the use of a two-stage mailing process. Participants will initially complete a "Health Survey" questionnaire. This will collect information on several areas of life including socio-demographics, general health, physical function, participation, and bodily pain. Those who state that they have experienced any hand problem or any pain in their hands, hips, knees, or feet in the previous 12 months, and also give permission to be re-contacted, will be mailed a "Regional Pains Survey" questionnaire which collects detailed information on the four selected body regions (hand, hips, knees, feet). Follow-up data for the three-year period subsequent to cohort recruitment will be collected through two sources: i) general practice medical records and ii) repeat mailed survey.

Responding to a bioterrorist attack: environmental investigation of anthrax in New Jersey.

A bioterrorism attack using the United States postal system to deliver a hazardous biological agent to specific targets created multiple environmental and occupational exposure risks along the path of the anthrax-containing letters. On October 18, 2001, a suspected case of cutaneous anthrax was confirmed in a postal worker from the Trenton Processing and Distribution Center where at least four suspect letters were postmarked. Over the next three weeks, a team of investigators collected samples at 57 workplaces in New Jersey as part of a comprehensive environmental investigation to assess anthrax contamination as a result of this bioterrorist attack. A total of 1369 samples were collected with positive sample results found in two mail processing and distribution centers, six municipal post offices, and one private company. This large-scale epidemiological and public health investigation conducted by state and federal agencies included environmental evaluations utilizing general industrial hygiene principles. Issues of sampling strategy, methods, agency cooperation and communication, and site assessment coordination are discussed.

La mise en place d'une démarche d'assurance qualité : exemple des Services vétérinaires français

Due to the increasing complexity of food production systems and the concerns that these systems raise, there has been increasing demand from the general public for more State control of these processes. In France, it is the official Veterinary Services who are responsible for food safety and who must respond to these demands. The Veterinary Service is formulating a quality assurance procedure in accordance with standard EN 45004-ISO 17020, which determines the requirements that inspection bodies must follow to be recognised, at national, European and international level, as competent and reliable. As part of this procedure, the Veterinary Service will review requirements in terms of organisation, functions, qualifications and resources. The progress of inspection service orders, from their conception by the Central Administration, to their implementation by decentralised services, must be carefully managed. It is essential that service orders be implemented effectively and systematically by using recognised methods and issuing adequate inspection reports. The training and qualifications of inspectors are very important: their skills must remain up-to-date so that there is always a network of qualified staff, that is, staff who have an understanding of production processes and who have recognised competences in terms of initial training, continuous professional development and adequate experience. The quality systems implemented will only meet expectations if they are continuously monitored by means of regular evaluations. For this reason, both internal and external audits are performed. These new practices contribute to establishing a basis for the improvement of internal evaluation. In order to facilitate the implementation of a quality assurance procedure for inspection services, several tools, that are linked with the information system of the government department responsible for food, are, or will be, at the disposal of the decentralised Veterinary Services, i.e. a national database, mail and service order processing software, and inspection procedures.