Predictive maintenance approach

The degradation mechanisms affecting industrial systems, structures and components (SSCs) can be modeled as discrete-state transport processes (e.g., Baraldi et al., 2013 a and b Moghaddas Zuo, 2011). The stochastic transitions between the states obey known models (e.g., WeibuU distribution, exponential distribution, etc.), whose parameters (e.g., the scale and shape factors for the WeibuU distribution, the failure rate for the exponential distribution, etc.) need to be estimated. Degradation models are used in support to maintenance decision making, for example to optimize the inspection period in a preventive maintenance approach or to estimate the remaining useful life of a SSC in a predictive maintenance approach (Zio Compare, 2013). 

For routine monitoring of machine vibration, however, this approach is not cost effective. The time required to manually isolate each of the frequency components and transient events contained in the waveform is prohibitive. However, time-domain data has a definite use in a total plant predictive maintenance or reliability improvement program. 

Another method used by some plants to acquire data is hand-held transducers. This approach is not recommended if it is possible to use any other method. Hand-held transducers do not provide the accuracy and repeatability required to gain maximum benefit from a predictive maintenance program. If this technique must be used, extreme care should be exercised to ensure that the same location, orientation, and compressive load are used for every measurement. Illustrates a hand-held device. 

The only useful function of broadband analysis is longterm trending of the gross overall condition of machinery. Typically, sets of alert/alarm limits are established to monitor the overall condition of the machine-trains in a predictive maintenance program. However, this approach has limited value and, when used exclusively, severely limits the ability to achieve the full benefit of a comprehensive program. 

A listing of visual observations. Most of the microprocessor-based systems support visual observations as part of their approach to predictive maintenance. This report provides hard copies of the visual observations as well as maintaining the information in the computer s database. 

Since 2006 a research unit at the Universitaet Stuttgart has been working to develop new approaches, methods and models to improve the predictive maintenance of machine tools. Members of the research unit are the Institute for Machine Tools (IfW), the Institute for Control Engineering of Machine Tools and Manufacturing Units (ISW) and the Institute of Machine Components (IMA). Each institute contributes with its specific core competence, its models and methods. 

Duchowski JK, Mannebach H (2006) A novel approach to predictive maintenance a portable, multi-component MEMS sensor for on-line monitoring of fluid condition in hydraulic and lubricating systems. Tribol Trans 49 545-553. doi 10.1080/ 10402000600885183... 

The approach should include the assessment of the eqnipment as it relates to the business or personnel safety, prioritizing the equipment, and targeting the critical equipment. For predictive maintenance, one other criterion must be utilized in the assessment process the monetary value of the equipment. Even if the equipment is not critical, its value may warrant the use of predictive maintenance to reduce potential catastrophic failure of expensive equipment. 

One of the key approaches to a good predictive maintenance program is consistency or standardization. 

The purpose of reliability-centered maintenance is to reduce defects, downtime, and accidents to as close to zero as possible to maximize production capacity and product quality and to keep maintenance cost per unit to a minimum. But, the main purpose of RCM is to create a systematic approach to maintenance that introduces controlled preventive maintenance while properly applying predictive maintenance technologies. 

New approaches in the field of machine safety also cause changes in the conditions for their maintenance. The ISO/TS 16949 Standard for the automobile industry and its suppliers mainly requires the implementation of predictive maintenance to increase the quality level. The directive on machine safety states a requirement to be followed at the stage of construction and design in case of automated devices, and if deemed necessary, other devices, a connecting device must be provided for mounting [a] failure diagnostics device. ... 

To meet the above challenges, two ftmdamental initiatives are under way, namely, shifts to reliability-centered maintenance and predictive maintenance. Broadly speaking, prior to the maintenance revolution, the utilities maintenance approach had essentially been one of preventive maintenance on all components after fixed time intervals, irrespective of the components criticality and actual condition. The shortcomings of this approach included the following (1) overly conservative maintenance requirements, (2) limited gains in reliability from investments in maintenance, (3) inadequate preventive maintenance on key components, and (4) added risk of worker exposure to radiation through unnecessary maintenance. Anticipated benefits of the revised approach are related not only to reduced maintenance costs but also to improved overall operational reliability. 

The selection of materials to be used in design dictates a basic understanding of the behavior of materials and the principles that govern such behavior. If proper design of suitable materials of construction is incorporated, the eqiiipment should deteriorate at a uniform and anticipated gradual rate, which will allow scheduled maintenance or replacement at regular inteivals. If localized forms of corrosion are characteristic of the combination of materials and environment, the materials engineer should still be able to predict the probable life of equipment, or devise an appropriate inspection schedule to preclude unexpected failures. The concepts of predictive, or at least preventive, maintenance are minimum requirements to proper materials selection. This approach to maintenance is certainly intended to minimize the possibility of unscheduled production shutdowns because of corrosion failures, with their attendant possible financial losses, hazard to personnel and equipment, and resultant environmental pollution. 

Too little maintenance results in unexpected failures and consequential major losses of production and/or customers (Figure 7-1). This impractical approach is termed reactive strategy and should be avoided on all important machinery. Optimum maintenance strategy balances reasonable costs with maximum possible availability and reliability. The two main maintenance strategies employed by companies today are labelled predictive strategy and preventive strategy. These are part of a balanced approach as shown in Figure 7-2. 

Roozen HG, Kerhof AJ, van den Brink W Experiences with an outpatient relapse program (community reinforcement approach) combined with naltrexone in the treatment of opioid-dependence effect on addictive behaviors and the predictive value of psychiatric comorbidity. Eur Addict Res 9 53—58, 2003 Rosen TS, Johnson HL Long-term effects of prenatal methadone maintenance. NIDA Res Monogr 59 73-83, 1985... 

We re doing away with our traditional maintenance mindset of using heroic measures to fix something.. . our approach is to take ownership, to use predictive tools to get ahead of problems.. .. [7]... 

In many cases, the approach used has been mechanistically or empirically qualitative, with the primary purpose of developing immediate solutions to pressing environmental problems, or of improving plant maintenance and operating schedules and procedures. However, the need to preempt costly outages, extend plant lifetimes, or perform environmental assessments is leading to efforts to develop predictive models. The primary emphasis in this chapter is the development of such models and how electrochemical methods can be used in the process. 

---