Saligrama R. Agnihothri

Leveraging technology to improve field service

The primary objective of this paper is to propose a theoretical framework for assessing the role and influence of technology in creating an effective field service organization. We examine the role of technology in the context of managing relationships among the company, its employees and customers. Using the analogy of a country managing its foreign affairs, we suggest that consistent and concurrent attention to carrying out Diplomacy, Preparedness and Engagement responsibilities with the aid of Technology (DPEAT) would result in superior service outcomes. We illustrate implementing our framework in a field service organization and use a published case study to demonstrate the application of our model.

The impact of defects on a process with rework

In this paper, we attempt to quantify the impact of defects on various system performance measures for a production process with 100% inspection followed by rework. In the literature, the number of defects (feedback loops) is assumed to be a random variable having a geometric distribution. We model the number of defects as a random variable having any general discrete distribution, and investigate the impact of the defect distribution on system performance measures such as yield, production lead time, and work-in-process inventory. We provide management guidelines for short term control decisions such as identifying potential bottlenecks under increased workloads and allocating additional resources to release bottlenecks. In order to meet the long term goal of continuously decreasing defect levels, we propose a budget allocation method for process improvement projects.

Cross-training Decisions in Field Services with Three Job Types and Server–Job Mismatch*

To be cost-effective, field service managers must balance the high cost of machine downtime with the high cost of cross-training technicians in multiple skills. We study a field service system with three job types requiring three different skills. Each server has a primary skill, the cost of which is considered sunk, and up to two secondary skills, which is a managerial decision. We model two important characteristics that distinguish field services: server–job mismatch and the ratio of travel time to service time. We use a queueing framework and simulation to study three cross-training decisions: the number of servers cross-trained in secondary skills, the number of secondary skills each server should have, and the efficiency in each secondary skill. We find that complete cross-training is cost-effective in some field service situations. Typically, efficiency in secondary skills must be close to 100%, but when the probability of mismatch is high and the ratio of travel time to service time is high, efficiency in secondary skills must be less than 100%.

Performance evaluation of service territories

Field service support is important for certain products, such as computer systems and copiers, for which service performance has a significant impact on market share. In this paper, the problem of field service operations and its important characteristics are described. Models are developed to assist the field service manager in the evaluation of performance of a given service territory with heterogeneous machines scattered typically, nonuniformly over a region, repaired by a traveling serviceman. Given the probability distributions of machine uptimes and repair times, and travel times between machine locations, models are developed to approximate the overall travel time distribution. This is used in existing queueing models to determine the performance measures, such as mean downtime per machine and server utilization. The results of the models are tested by simulation and observed to provide good estimates for the measures of interest. These models are eventually intended to help in making decisions on territory design and staffing levels.

Interrelationships between performance measures for the machine-repairman problem

The machine-repairman problem with heterogeneous machines and multiple repairmen is considered. It is assumed that machine up times and repair times have general distributions, and a work-conserving service discipline is employed. Under these general assumptions, steady-state relationships between performance measures are examined for the individual machines. Also, various performance measures are defined for the aggregate system and interrelationships between these measures are established.

A mean value analysis of the travelling repairman problem

Abstract We consider the machine repairman problem where the machines are spatially distributed and repaired by a travelling serviceman. We assume identical machines with exponential up times and general repair times. We also assume that the travel times between pairs of locations have identical, but arbitrary distributions. Assuming a work-conserving, non-preemptive service discipline, a semi-Markov model is developed and various performance measures are evaluated. Some applications of the model are discussed. The model developed here, is used elsewhere to develop approximations for a more realistic situation where machines are non-identical and travel time distributions between pairs of locations are also non-identical.

Stochastic Allocation Rules

This paper considers the allocation of a fixed amount of resource across competing activities, where the rate of use of the allocated amounts is stochastic. The allocated amounts are said to have run out when the first of the allocations is used up and another distribution must then be considered. This problem arises in the allocation of stocks of a commodity to branch warehouses and in the allocation of production time to items that are jointly produced. It also occurs in the allocation of spares to subsystems when the total number of spares is constrained by volume or cost and when failure of one subsystem causes a failure of the whole system. Two alternative formulations are presented: the Maximization of Expected Time to Runout and the Minimization of Expected Discounted Time to Runout. Bounds are developed on the problems by using deterministic and exponential models for the time to runout. The case of two competing processes is investigated numerically, and it appears that the solutions to the bounding problems provide effective heuristics at least for such small problems.

Lot sizing with random yields and tardiness costs

Abstract We consider a single-stage manufacturing problem with random yields, and investigate the impact of yield uncertainty on lot sizing decisions when there is a tardiness cost for not meeting the customer specified due date. We assume that the demand, as well as the customer-specified due date for the product, is known. Due to the limited production capacity, the manufacturer has to produce the product in a single production run and deliver the product in a single shipment. We derive the optimal lot size for some specific yield-rate distributions. We also obtain some distribution free results by assuming that only the mean and variance of the yield-rate distribution are known. Sensitivity of the optimal solution to these parameters is investigated through some numerical examples. Scope and purpose Lot sizing problems deal with determining production and procurement quantities and their timing. Significant amount of research has been done on solving lot sizing problems when demand is known, as well as demand is uncertain. Although considerable research has been done when production yield-rate is known, few researchers have dealt with situations where yield rate is uncertain. Yano and Lee [1] present many variations of lot sizing problem with random yield and review the corresponding literature. Production yield-rate uncertainty can lead to delays in delivery, which may result in penalty costs. When yield-rate is constant, several researchers evaluated the impact of imposing tardiness cost for late delivery on lot sizing decisions. However, no research has been done to date to evaluate the impact of yield uncertainty on lot sizing decisions when there is a tardiness cost associated with delayed delivery. The main emphasis of this paper is to address this issue.

An assignment problem with queueing time cost

One studies the problem of assigning customers to service facilities with the objective of minimizing the total expected cost of accessing facilities and waiting for service at these facilities. One provides an integer programming formulation of the problem with a nonlinear objective function. A Lagrangian relaxation of the problem is described and a heuristic solution procedure is developed which utilizes the solution generated from the relaxed problem. Experimental results over a range of problems indicate that the solution method is both efficient and effective

Mobile Health Monitoring: Development and Implementation of an App in a Diabetes and Hypertension Clinic

Significant effort is being spent on providing better control of health in patients suffering from chronic diseases such as diabetes and hypertension in United States. About 1 in 5 adults are suffering from diabetes or hypertension and more than