Table 1.1 in Chapter 1 described major events in the development of system health management (SHM). Another way to look at the history of SHM development is to consider the evolution of the drivers for SHM research and development. New motivations or fields of application can spur the development of new technologies and applications to meet emerging demands and requirements. In the military, the emergence of new requirements often results in the availability of funding to researchers and contractors which in turn leads to spending on new research and development. The evolution of SHM technology development in military applications, from a funding and programmatic point of view, is shown in Table 23.1. Within the defense industry, much of the early motivation for the development of SHM technology can be traced back to concerns for improving safety. In particular, safety concerns associated with helicopters led to the development of health and usage monitoring systems (HUMS). Early HUMS were essentially data recorders which captured flight hours to ensure that usage-based maintenance was carried out in accordance with established procedures. The early HUMS also provided basic capability to monitor the health of certain aircraft subsystems and components. Of particular concern to the helicopter community was the drive train. The ability to field monitoring systems with basic condition monitoring capability led to a push to transition from traditional time and usage-based maintenance strategies to condition-based maintenance (CBM) strategies (Moubray, 1997). There was a strong push toward the adoption of CBM as the primary maintenance philosophy across the military services for ships and aircraft, which drove much of the investment in new SHM technology through the 1990s. With the push to transition to a CBM approach to maintenance also came the realization that in applications such as ships, where a significant portion of the personnel required to operate the platform is dedicated to performing periodic maintenance, the adoption of CBM could lead to reduced manning requirements. Since a significant portion of the defense budget goes to covering the costs associated with personnel, reducing their number can result in significant cost savings. Consequently, the desire to decrease maintenance-associated personnel requirements became a driver for the development and adoption of new SHM technologies, particularly in the US Navy where several new classes of ships such as the DDG-51 and CVN-21 were under development. As the cost to develop and procure new military systems continued, and continues, to increase, the military began to consider the total lifecycle cost of platforms and look for ways to reduce those costs incurred above and beyond the procurement cost as a way of saving money. If the development and procurement costs could not be reduced, then maybe the long-term cost of ownership could be reduced through the adoption of new technologies, such as CBM and increased machinery automation, and new practices, such as CBM and reduced manning. One example is the use of SHM technology to accurately measure the health of major components on a platform which would normally require periodic overhaul and replacement. With the proper application of SHM technology, major overhauls can be delayed and, over the lifecycle of the platform, it may be possible to eliminate one or more major overhauls and save significant costs (Banks et al., 2003). One of the most recent drivers for the development and adoption of SHM technologies in the military has been logistics modernization. Webster's Dictionary defines logistics as "the aspect of military science dealing with the procurement, maintenance, and transportation of military matériel, facilities, and personnel." More generally, logistics is defined as the management of the flow of goods, information, and other resources, including energy and people, between the point of origin and the point of consumption in order to meet the requirements of consumers. Military logisticians are responsible for planning and carrying out the movement and maintenance of military equipment. Chapter 1 defined SHM as the capabilities of a system that preserve the system's ability to function as intended. Since logisticians are responsible for providing the necessary support to ensure that equipment is capable of operating as intended, SHM is clearly an enabling technology for the logistics community. One reason for the focus on the application of SHM in logistics in both the military and commercial industry is the desire to leverage cost savings resulting from the adoption of SHM-enabled process and practice improvements on single platforms to the management of fleets of vehicles or equipment. Personnel and support requirements across a fleet can be driven by the requirements of the most personnel and support-intensive platforms. Fleet managers are often faced with the choice of replacing or upgrading all platforms within the fleet to improve overall fleet dependability, or adopting technologies that can be retrofitted to legacy platforms to bring them up to the levels achieved by newer platforms. Given the age and lifetimes of military platforms (e.g., the B-52 bomber has been in service since 1952), technologies which can be retrofit to legacy platforms are attractive. More recently, high-level guidance within the US Department of Defense has directed the managers of acquisition programs and the designers of new systems to implement a CBM+ strategy. The US Army's CBM+ Roadmap (US Army, 2007) provides the following definition of CBM+: CBM+ is a proactive equipment maintenance capability enabled by using system health indications to predict functional failure ahead of the event and take appropriate action. The capability marks an evolution from the earliest applications of embedded health management. While the CBM+ guidance differs little from the definition of a CBM approach that would be found in traditional reliability-centered maintenance approaches, it does identify a goal of predicting functional failure, not just monitoring for failures after their occurrence. The final driver for SHM development listed in Table 23.1 is increased autonomy. As automated and autonomous unmanned systems become more widely fielded, the ability of the platform to detect and respond to failures without intervention by a human operator becomes a key enabler for increased levels of autonomy (Huang et al., 2003). Autonomy and increased automation - of the maintenance planning process, of systems operations, of logistics - have been a common theme throughout the history of SHM development. The primary change in the implementation of SHM in unmanned autonomous systems is the removal of the human operator from the critical role of data fusion and decision-making. The focus of this chapter is the role of SHM in enabling autonomic logistics (AL). The goal of AL is to transition traditional logistics support systems from a report-request-respond model, where the logistics system responds to requests for support based on manual reporting of usage and supply levels, to an autonomic response model, where the logistics system responds to user needs without the user specifically requesting resupply or support. The model for AL is the human body's autonomic nervous system, which monitors, controls, and adjusts the body's response to external stimuli. SHM represents an enabling technology for the implementation of AL in both the military and commercial industry. SHM enables CBM, CBM+, and the automation of parts ordering and maintenance scheduling. The resulting reducing in support costs provides part of the return on investment for AL. Examples are provided from recent deployment of SHM as part of US Marine Corps (USMC) AL capability.
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