| 1. |
- Hosseini Yazdi, Morteza, et al.
(author)
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Experimental Study of Rolling Element Bearing Failure Pattern Based on Vibration Growth Process
- 2019
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In: Proceedings of the 29th European Safety and Reliability Conference (ESREL). - Singapore : Research Publishing Services. ; , s. 1179-1186
-
Conference paper (peer-reviewed)abstract
- Rolling-element bearing (REB) Failure is one of the most common failure in rotary machines in industry. Therefore, this concern draws attention to the concept of diagnostic and the prediction of REB failure. The efficacy of vibration analysis in this area has led many researchers to focus on this topic in recent decades. Defective bearings such as fatigue, surface roughness, and corrosion can lead to disastrous accidents. Therefore, providing an algorithm for the detection and classification of bearing defects is valuable and useful. The prediction of the bearing's lifetime is important to ensure the planned production in an industrial unit. In this paper, different models for performance degradation of mechanical parts and signal processing techniques are presented for fault detection in ball bearings. Then, the failure modes of bearings and their relations to the final fault using the vibration signals are discussed. Thereafter, by examining the experimental data of the PRONOSTIA test and using the root mean square of signals, the degradation performance of the bearings and the corresponding failure patterns are obtained. In addition, using the results of frequency analysis via Envelope method, the initiated/existed defects on the bearings of each test are detected. In the application of this method, selection of appropriate frequency band for filtering the vibration signal is important. By analyzing the results, it can be concluded that any ball bearing failure pattern does not necessarily refer to a specific defect. Also, the proper area for filtering a signal in envelope analysis is not necessarily a resonance region, but it should also check several areas to select the best area.
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| 2. |
- Hosseini Yazdi, Morteza, et al.
(author)
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Prognostic of rolling element bearings based on early-stage developing faults
- 2020
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In: International Journal of COMADEM. - England : COMADEM International. - 1363-7681. ; 23:1, s. 55-60
-
Journal article (peer-reviewed)abstract
- Rolling-element bearing (REB) failure is one of the general damages in rotating machinery. In this manner, the correct prediction of remaining useful life (RUL) of REB is a crucial challenge to move forward the unwavering quality of the machines. One of the main difficulties in implementing data-driven methods for RUL prediction is to choose proper features that represent real damage progression. In this article, by using the outcomes of frequency analysis through the Envelope method, the initiated/existed defects on the ball bearings are identified. Also, new features based on developing faults of ball bearings is recommended to estimate RUL. Early-stage faults in ball bearings usually include inner race, outer race, ball and cage failing. These features represent the sharing of each failure mode in failure. By calculating the severity of any failure mode, the contribution of each mode can be considered as the input to an artificial neural network. Also, the wavelet transform is used to choose an appropriate frequency band for filtering the vibration signal. The laboratory data of the ball bearing accelerated life (PROGNOSTIA) are used to confirm the method. To random changes reduction in recorded vibration data, which is primary in real-life experiments, a pre-processing calculation is connected to the raw data. The results obtained by using new features shows a more accurate estimation of the bearings' RUL and enhanced prediction capability of the proposed method. Also, results indicate that if the contribution of each failure mode is considered as the input of the neural network, then RUL is predicted more precisely.
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| 3. |
- Ahmadi, Alireza, et al.
(author)
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Estimation of economic consequences of aircraft system failures
- 2012
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In: Communications in Dependability and Quality Management. - 1450-7196. ; 15:1, s. 39-49
-
Journal article (peer-reviewed)abstract
- A large portion of the direct and indirect aircraft operational costs stems from the consequences of decisions made during the maintenance program development. Decision on maintenance task selection for non-safety category of failures, is based on the cost effectiveness, in which the cost of preventive maintenance should be less than the costs associated with the corrective action and failure consequence. Although the assessment of the direct cost for preventive and corrective maintenance is quiet straightforward, however quantification and estimation of the cost associated with the consequence of failure is a great challenge. This is due to a long list of contributory factors and lack of adequate data regarding the cost headings. This study attempts to estimate the economic consequences of aircraft system failures which lead to a technical delay. The paper considers financial losses, mostly due to the additional unexpected costs related to the flight crew, passengers, aircraft itself, ramp and airport, when one of the cost headings, e.g. the pre-fixed crew cost is known. The experience of the field experts has been used following a pairwise comparison technique to compare the cost headings, and to estimate the contribution of each one to the total cost of a delay. The study shows that the proposed model can be a tool to assess the cost of failure consequences in aircraft operation, when there is a limited data and information regarding the cost headings.
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| 4. |
- Ahmadi, Alireza, et al.
(author)
-
Optimum Failure Finding Inspection During Extended Operation Life
- 2013
-
Conference paper (peer-reviewed)abstract
- In a complex system such as railway and aviation equipment’s, it may be necessary to employ a combination of Failure Finding Inspection (FFI) and a scheduled discard task, as suggested by Reliability-Centered Maintenance (RCM). This strategy ensures an adequate level of availability of hidden functions, as well as the reduction of the risk of multiple failures to an acceptable level. However, in some situations, operators prefer to extend the discard life of components beyond their recommended life limit, due to the operational restrictions. This necessitates the definition of an optimal Failure Finding Inspection interval for the extended life period. This paper aims to provide a mathematical model for defining optimal FFI interval, during the extended period of the replacement life. A cost function (CF) is developed to identify the cost per unit of time associated with different FFI intervals, for the proposed extended period of life, i.e. postponement period. The proposed method concerns as-bad-as-old (ABAO) inspection and repairs (due to failures found by inspection). It considers inspection and repair times, and takes into account the costs associated with inspection and repair, the opportunity cost of lost production due to maintenance downtime created by inspection and repair actions, and also the cost of accidents due to the occurrence of multiple failure
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| 5. |
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| 6. |
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| 7. |
- Ahmadi, Alireza, et al.
(author)
-
Risk based maintenance decision for periodically tested repairable components subject to hidden failure
- 2011
-
In: Proceedings of 2nd International Conference on Reliability, Safety and Hazard - ICRESH 2010. - Piscataway, NJ : IEEE Communications Society. - 9781424483440 - 9781424483433 ; , s. 197-204
-
Conference paper (peer-reviewed)abstract
- This paper aims to develop a graphical method to facilitate the identification of risk and cost of postponement of restoration for repairable components which are periodically tested and whose failures are hidden, i.e, are detectable by inspection or upon demand. The paper focuses on the items which are under aging, however, the methodology is flexible to implement for any aging pattern. The paper considers Failure Finding Inspection (FFI) with restoration actions (FFI+Res), for the “safety effect” categories of hidden failures. As-bad-as-old (ABAO) inspection effectiveness and as-good-as-new (AGAN) restoration effectiveness are considered. In case of repair due to findings by inspection, as-bad-as-old repair effectiveness is considered. The graphical methodology proposed in this paper considers inspection and repair times, as well as the costs associated with accident, inspection, repair, and restoration, and takes into account the opportunity losses due to the maintenance downtime. The analytical approach is based on the Mean Fractional Dead Time. In the case of an operational limit, when it is not possible to remove the unit for restoration, or one needs to use the unit longer than the expected operating time, the paper introduces an approach to analyzing the possibility of and conditions for providing an extension to the restoration interval that satisfies the risk constraints and the business requirements at the same time.
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| 8. |
- Ahmadzadeh, Farzaneh, et al.
(author)
-
Mean Residual Life Estimation Considering Operating Environment
- 2012
-
Conference paper (peer-reviewed)abstract
- The cost of maintenance of mechanized and automated mining systems is too high necessitating efforts to enhance the effectiveness of maintenance systems and organization. For effective maintenance planning, it is important to have a good understanding of the reliability and availability characteristics of the systems. This is essential for determining the Mean Residual Life (MRL) of systems so that maintenance tasks could be planned effectively. In this paper we used the statistical approach to estimate MRL. A Weibull proportional hazard model (PHM) with time-independent covariates was considered for modelling of the hazard function so that operating environment could be integrated in the reliability analysis. Methods are presented for calculating the conditional reliability function and computing the MRL as a function of the current conditions to guarantee the desired output. The model is verified and validated using data from the Hydraulic system of an LHD fleet from a Swedish mine. The results obtained from the analysis is useful to estimate the remaining useful life of such system which can be subsequently used for effective maintenance planning and help controlling unplanned stoppages of highly mechanized and automated systems.
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| 9. |
- Al-Chalabi, Hussan S., et al.
(author)
-
Downtime analysis of drilling machines and suggestions for improvements
- 2014
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In: Journal of Quality in Maintenance Engineering. - 1355-2511 .- 1758-7832. ; 20:4, s. 306-332
-
Journal article (peer-reviewed)abstract
- Purpose– The purpose of this paper is to analyse and compare the downtime of four drilling machines used in two underground mines in Sweden. The downtime of these machines was compared to show what problems affect downtime and which strategies should be applied to reduce it.Design/methodology/approach– The study collects failure data from a two-year period for four drilling machines and performs reliability analysis. It also performs downtime analysis utilising a log-log diagram with a confidence interval.Findings– There are notable differences in the downtime of most of the studied components for all machines. The hoses and feeder have relatively high downtime. Depending on their downtime, the significant components can be ranked in three groups. The downtime of the studied components is due to reliability problems. The study suggests the need to improve the reliability of critical components to reduce the downtime of drilling machines.Originality/value– The method of analysing the downtime, identifying dominant factors and the interval estimation for the downtime, has never been studied on drilling machines. The research proposed in this paper provides a general method to link downtime analysis with potential component improvement. To increase the statistical accuracy; four case studies was performed in two different mines with completely different working environment and ore properties. Using the above method showed which components need to be improved and suggestions for improvement was proposed and will be implemented accordingly.
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| 10. |
- Allahkarami, Zeynab, et al.
(author)
-
Identifying the mixed effects of unobserved and observed risk factors on the reliability of mining hauling system
- 2021
-
In: International Journal of Systems Assurance Engineering and Management. - : Springer. - 0975-6809 .- 0976-4348. ; 12:2, s. 281-289
-
Journal article (peer-reviewed)abstract
- Reliability is widely used as a performance indicator of mining equipment to achieve a cost-effective maintenance plan. Reliability is a function of time as well as environmental and operational factors. Applying an adequate model by taking into account the mentioned factors is vital to ensure an accurate estimation of reliability characteristics. The aim of this study is to investigate the application of mixed frailty model to describe both observed and unobserved heterogeneity in reliability analysis of mining equipment. The capability of the model is assessed using field data from a fleet of dump trucks in an open-pit mine. The results indicate that the proposed model is superior to the traditional Cox model when data are heterogeneous. The results also show that the operator's skill and road conditions have a significant effect on the reliability of dump trucks.
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| 11. |
- Allahkarami, Zeynab, et al.
(author)
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Mixed-effects model for reliability assessment of dump trucks in heterogeneous operating environment: A case study
- 2022
-
In: Quality and Reliability Engineering International. - : John Wiley & Sons. - 0748-8017 .- 1099-1638. ; 38:5, s. 2881-2898
-
Journal article (peer-reviewed)abstract
- Reliability of mining equipment is influenced by different operational and environmental risk factors. However, in practice, including all relevant factors in reliability analysis is not possible. Ignoring the risk factors leads to unobserved heterogeneity and biased estimation of reliability characteristics. This research proposes a semi-parametric mixed-effects model to assess the simultaneous effects of observed and unobserved risk factors on reliability. Furthermore, the model can be used for investigating inter-cluster dependency and variability. To illustrate the model, a comprehensive case study is presented using data from three mines in Iran. The results show that the model can address the effect of unobserved risk factors. Moreover, it is found that the hazard of dump trucks is significantly associated with operator skill, season and the elevation difference between dumping and loading points.
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| 12. |
- Amini, Hasel, et al.
(author)
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RAM analysis of earth pressure balance tunnel boring machines: A case study
- 2015
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In: International Journal of Mining and Geo-Engineering. - Iran : University of Tehran. - 2345-6930 .- 2345-6949. ; 49:2, s. 173-185
-
Journal article (peer-reviewed)abstract
- Earth pressure balance tunnel boring machines (EPB-TBMs) are favorably applied in urban tunneling projects. Despite their numerous advantages, considerable delays and high maintenance cost are the main disadvantages these machines suffer from. Reliability, availability, and maintainability (RAM) analysis is a practical technique that uses failure and repair dataset obtained over a reasonable time for dealing with proper machine operation, maintenance scheduling, cost control, and improving the availability and performance of such machines. In the present study, a database of failures and repairs of an EBP-TBM was collected in line 1 of Tabriz subway project over a 26-month interval of machine operation. In order to model the reliability of the TBM, this machine was divided into five distinct subsystems including mechanical, electrical, hydraulic, pneumatic, and water systems in a series configuration. According to trend and serial correlation tests, the renewal processes were applied, for analysis of all subsystems. After calculating the reliability and maintainability functions for all subsystems, it was revealed that the mechanical subsystem with the highest failure frequency has the lowest reliability and maintainability. Similarly, estimating the availability of all subsystems indicated that the mechanical subsystem has a relatively low availability level of 52.6%, while other subsystems have acceptable availability level of 97%. Finally, the overall availability of studied machine was calculated as 48.3%.
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| 13. |
- Barabadi, Abbas, et al.
(author)
-
Reliability and spare parts estimation considering operational environments : a case study
- 2012
-
Conference paper (peer-reviewed)abstract
- Spare parts provision is a complex problem andrequires an accurate model to analysis all factors that mayaffect the required number of spare parts. The number ofspare parts required can be effectively estimated based onthe reliability performance of the item. The reliabilitycharacteristics of an item are influenced not only by theoperating time, but also by factors such as the operationalenvironment. Therefore, for spare parts provisioning to beeffective, the impact of these influence factors on thereliability performance of the item should be quantified.Hence, the statistical approach selected for reliabilityperformance analysis must be able to handle the effect ofthese factors. One of the important models for reliabilityperformance analysis that takes influence factors intoaccount is the proportional hazard model (PHM), which hasreceived less attention in the field of spare partsprovisioning. In this paper the application of PHM to spareparts provision is discussed and demonstrated by a casestudy.
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| 14. |
- Bonnet, Benjamin, et al.
(author)
-
Optimization of maintenance policy based on operational reliability analysis : application to railway switches & crossings
- 2011
-
Conference paper (peer-reviewed)abstract
- The present communication reports on a collaboration between ALSTOM Transport and Luleå Technology University, under the sponsorship of Trafikverket, the Swedish Infrastructure Manager.For 2020, the European Rail Research Advisory Council (ERRAC) has set among other the following objectives [2] : doubling passenger traffic and tripling freight traffic and reducing the life-cycle cost of infrastructure by 30%.This need applies to rail infrastructure in general. Clearly, the highest leverage will be obtained by concentrating the efforts on key cost and availability drivers. For instance, it is reported that switches and crossings (S&C) are one of the subsystems that cause the most delays on Swedish Railways while accounting for at least 13% of maintenance costs. (It is the main reason why we chose to base our study on this subsystem).Intelligent data processing allows to understand the real reliability characteristics of the assets to be maintained. Furthermore simulation and optimisation techniques are applied in order to adapt the maintenance strategy so as to achieve minimum cost while guaranteeing target availability.The first step has been to determine the S&C reliability characteristics based on field data collection. Because field failure data are typically strongly censored, we have developed our own statistics software package to process field failure data, as commercial packages have not been found satisfactory in that respect. The resulting software, named RDAT® (Reliability Data Analysis Tool) has been relied upon for this study: it is especially adapted to statistical failure data analysis. The next step will be to customize the maintenance interval by adapting it to individual switches and crossings behaviour characteristics. In order to predict and optimize life-cycle cost (LCC) and availability, Monte Carlo simulations will be performed with stochastic Petri nets. The failure rates estimated with RDAT® will be used as inputs to the Petri net. Such a model lends itself to maintenance optimization. Indeed, designs of experiments can be used in conjunction with simulations in order to express both LCC and availability as functions of various maintenance-related decision variables (such as preventive maintenance frequency, maintenance efficiency, etc, see [7]).Further improvement could result from applying condition-based maintenance, where preventive maintenance times would no longer be predetermined but rather based on the observed S&C condition, as measured by : number of displacement cycles, current absorbed, vibration intensity during train passage, traffic intensity etc. It is planned to resort to the Watchdog Agent ® software, of Intelligent Maintenance System, to that end [4].
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| 15. |
- Dandotiya, Rajiv, et al.
(author)
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Optimal pricing and terminal location for a rail-truck intermodal service : a case study
- 2011
-
In: International Journal of Logistics. - : Informa UK Limited. - 1367-5567 .- 1469-848X. ; 14:5, s. 335-359
-
Journal article (peer-reviewed)abstract
- To be competitive with other modes of transport, the railway needs to be cost-effective. In order to become more competitive in the logistics industry, Indian Railways has taken new initiative to improve their operations in recent years. A rail-truck intermodal transportation service for Indian Railways is described in this paper. The main focus of the present research is to optimize the freight rate and terminal location together, in order to minimize the total shipping cost of truckers while ensuring the targeted profit of the railway. A model has been developed for the determination of the optimal freight rate and the corresponding intermodal terminal location. The key regulators of this model are the price sensitivity of the trucker and profit guarantee for railways. A case study was developed on the Delhi - Mumbai freight corridor. An analysis was performed to gain insight into the trade-offs among shipment cost and terminal locations.
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| 16. |
- Galar, Diego, et al.
(author)
-
Fusion of CMMS data and CM data : a real need for maintenance (part I)
- 2012
-
In: Maintworld. - 1798-7024 .- 1799-8670. ; :2, s. 42-45
-
Journal article (other academic/artistic)abstract
- Maintenance can be considered as an information processing system. Therefore, thedevelopment of future maintenance information systems is one of the most importantcurrent research problems to model the effects of automatic condition monitoringsystems enabled by embedded electronics and software.
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| 17. |
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| 18. |
- Gharahasanlou, A. Nouri, et al.
(author)
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Maintainability measure based on operating environment, a case study: Sungun copper mine
- 2017
-
In: Journal of Mining and Environment. - : Shahrood University of Technology. - 2251-8592 .- 2251-8606. ; 8:3, s. 511-521
-
Journal article (peer-reviewed)abstract
- The life cycle cost of a system is influenced by its maintainability. Maintainability is a design parameter, whose operational conditions can affect it significantly. Hence, the effects of these operational conditions should be quantified early in the design phase. The proportional repair model (PRM), which is developed based on the proportional hazard model (PHM), can be used to analyze maintainability considering the effects of the operational conditions. In PRM, the effects of the operational conditions are considered to be time-independent. However, this assumption may not be valid for some cases. The aim of this paper is to present an approach for prediction of the maintainability performance of the mining facilities considering the time-dependent influencing factors. The stratified Cox regression method (SCRM) is used to determine maintainability in the presence of time-dependent covariates for fleet vehicles operating in Sungun Copper Mine, Iran.
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| 19. |
- Ghodrati, Behzad, et al.
(author)
-
Consideration of operating environment when optimizing spare parts inventories
- 2009
-
In: 2009 proceedings. - Piscaaway, NJ : International Society of Science and Applied Technologies. - 9780976348658 ; , s. 315-319
-
Conference paper (peer-reviewed)abstract
- Spare parts estimation, consumption and management are greatly influenced by the reliability characteristics of system or components under consideration. Any maintenance policies and spare parts planning without considering the reliability characteristics are not optimum. Therefore it is important to study and analyse the reliability characteristics before making decision concerning spare parts planning. It is known that the operating environmental conditions in which the system is to be operated, such as temperature, humidity, dust, load, voltage stress, etc. often have considerable influence on its reliability characteristics. These factors, in fact affect the failure rate of a repairable system and non-repairable component, but are usually ignored in the reliability analysis. In general, new products are often used under conditions that are not anticipated. It is common to modify the predicted life length and reliability characteristics of product by considering the environmental and other factors. In this paper a general approach of integrating the system operating environment in dimensioning of spare parts planning is briefly studied. Two approaches, Poisson and renewal process are considered in the analyses of system/component failure behaviour. Eventually, two case studies that are used the mentioned methods are presented. The main purpose of the paper is to highlight the effect of system operating environment in system behaviour and consequently spare parts needs.
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| 20. |
- Ghodrati, Behzad, et al.
(author)
-
Context-driven mean residual life estimation of mining machinery
- 2018
-
In: International Journal of Mining, Reclamation and Environment. - : Taylor & Francis. - 1748-0930 .- 1748-0949. ; , s. 486-494
-
Journal article (peer-reviewed)abstract
- Maintenance is crucial to ensure production/output and customer satisfaction in the mining sector. The cost of maintenance of mechanised and automated mining systems is very high, necessitating efforts to enhance the effectiveness of maintenance systems and organisation. For effective maintenance planning, it is important to have a good understanding of the reliability and availability characteristics of the systems. Determining the Mean Residual Life (MRL) of systems allows organisations to more effectively plan maintenance tasks. In this paper, we use a statistical approach to estimate MRL and consider a Weibull proportional hazard model (PHM) with time-independent covariates to model the hazard function so that the operating environment could be integrated into the reliability analysis. The paper explains our methods for calculating the conditional reliability function and computing the MRL as a function of the current conditions. The model is verified and validated using data from the hydraulic system of LHD equipment in a Swedish mine. The results are useful to estimate the remaining useful life of such systems; the method can be used for maintenance planning, helping to control unplanned stoppages of highly mechanised and automated systems.
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| 21. |
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| 22. |
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| 23. |
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| 24. |
- Ghodrati, Behzad, et al.
(author)
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Enhancement of mining machineries performance through supportability
- 2011
-
In: International Journal of COMADEM. - 1363-7681. ; 14:2, s. 35-43
-
Journal article (peer-reviewed)abstract
- Cost analysis of mining operations in general shows that 30 to 50 percent of direct mining costs are related to maintenance and losses related to lost production during equipment downtime. To reduce these losses one first needs to improve the equipment reliability and thereafter to reduce the downtime losses through improved maintainability and supportability. The mining operational environment is often harsh and may severely impact all three of these abilities. In this paper we focus on how to improve the estimation of spare parts by taking into account the operating environment in the estimation models. By having better models to predict spare parts needs, one can avoid logistics delays and thereby reduce downtime. In this study we develop an improved statistical-reliability (S-R) analysis approach that take into account the system/ machine operating environment. The analysis approach is multiple regressions based on Cox’s proportional hazards modeling (PHM). Subsequently, in a case study, the management of the spare parts inventory based on the economic order quantity and required performance of the product is addressed.
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| 25. |
- Ghodrati, Behzad, et al.
(author)
-
Environmental friendly manufacturing and support : Issues and challenges
- 2015
-
Conference paper (peer-reviewed)abstract
- Environmentally Conscious Manufacturing and Product Support (ECMPS) is animportant issue driven by concern for the escalating deterioration of the environment.ECMPS involves integrating environmental thinking into the design of a product, theselection of materials, manufacturing processes, delivery and support to consumers, andend-of-life management of the product after its useful life has ended. Both academia andindustry are interested in finding solutions in this newly emerging research area. Relatedresearch is on pollution prevention, remanufacturing, disassembly, life cycle of products,after sale support and material recovery. The aim of this study is emphasizing the productdesign, operation, maintenance and disassembly effects on environment, and how theseissues can be considered in manufacturing phase to minimize the negative environmentalimpact.
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| 26. |
- Ghodrati, Behzad, et al.
(author)
-
Fuzzy Risk Prioritization of the Failure Modes in Rolling Stocks
- 2018
-
Conference paper (peer-reviewed)abstract
- Failure Mode and Effects Analysis (FMEA) is extensively used to identify and eliminate the potential failures in products, processes, designs, and services. In this approach, the detectability, occurrence and the severity of each identified failure mode need to be determined usually by a FMEA team. This paper aims to prioritize the failure modes of rolling stocks by integrating Analytical Hierarchy Process (AHP) and Risk Priority Number (RPN). To reduce the uncertainties and ambiguities, all calculations are done in the fuzzy environment instead of the crisp values. The importance degree of each failure mode is determined and then the overall fuzzy RPN is calculated. In this way, the critical failure modes are defined to make an efficient maintenance decision.
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| 27. |
- Ghodrati, Behzad, et al.
(author)
-
Lean mining
- 2016
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In: The Routledge companion to lean management. - New York : Routledge. - 9781317416517 - 9781138920590 ; , s. 302-310
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Book chapter (peer-reviewed)
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| 28. |
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| 29. |
- Ghodrati, Behzad, et al.
(author)
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Monitoring the condition of rolling element and plain bearings
- 2007
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In: 4th International conference on maintenance.
-
Conference paper (peer-reviewed)abstract
- Experience has proved that maintenance cost of rotating equipments is a huge expense of different industries. The need for reducing these kinds of expenditures reveals the importance of condition monitoring day by day. Applying different methods of condition monitoring allows maintenance departments to perform their activities based on the current condition of machineries not on the basis of approximated machineries life length arising from statistics. Due to the Prognosis and diagnosis of failures as duty of condition monitoring units and with proper maintenance planning of the plants, maintenance activities could result in reduction of repair and maintenance costs. In this report we study the methods, tools and effectiveness of condition monitoring of rolling-element (anti-friction) and plain (journal) bearings and their fault diagnosis using vibration analyzing.
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| 30. |
- Ghodrati, Behzad, et al.
(author)
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Operating environment based maintenance and spare parts planning : a case study
- 2004
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In: Advanced Reliability Modeling. - : World Scientific and Engineering Academy and Society. - 9812388710 ; , s. 125-132
-
Conference paper (peer-reviewed)abstract
- Maintenance strategies and spare parts consumption is greatly influenced by the reliability characteristics of system or components under consideration. Any maintenance policies or spare parts planning without considering the reliability characteristics are not optimum. Therefore it is important to study and analyse the reliability characteristics before making decision concerning spare parts and maintenance planning. It is known that the operating environmental conditions in which system is to be operated, such as temperature, humidity, dust, load, voltage stress, etc. often have considerable influence on its reliability characteristics. These factors, in fact affect the failure rate of a repairable system and non-repairable components, but are usually ignored in the reliability analysis. Thus operating environment should be considered as an important factor while making decision about maintenance, spare parts planning, product support, and service delivery strategies. In general, new products are often used under conditions that are not anticipated. It is common to modify predicted life length and reliability characteristics of product by considering the environmental and other factors. The purpose is to incorporate the effect of the environmental factors such as temperature, humidity, dust, voltage stress, etc in reliability analysis.
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| 31. |
- Ghodrati, Behzad, et al.
(author)
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Operating environment-based spare parts forecasting and logistics : a case study
- 2005
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In: International Journal of Logistics. - : Informa UK Limited. - 1367-5567 .- 1469-848X. ; 8:2, s. 95-105
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Journal article (peer-reviewed)abstract
- In today's highly dynamic and constantly changing industrial environment, issues relating to product support are becoming increasingly important. However, the extent of attention given to these issues varies considerably depending on the perspective of the interested person or profession. These are likely to vary from design engineers at the conceptual stages of product development to manufacturers and users in the latter stages. Additionally, the make up a particular product support package varies according to type of system/mission, application and stages of machine/system life. The lack of timely or incomplete support is likely to cause unexpected downtimes, which in turn will lead to losses for which one is unable to compensate. Falling within the definition of product support items are spare parts. The lack of a critical spare part can cause untimely stoppage of machine/system. Forecasting of product support and spare parts requirements based on reliability and maintainability (R&M) characteristics of system/components together with system operating environment(s) is one of the most effective strategies for prevention of unplanned stoppages. In this paper the effects of environmental factors on hydraulic brake pump used in mine loaders are presented and analysed. The reliability of this non-repairable part and its operational impact are assessed for both when the environmental factors are considered and when they are ignored. From the study, it is found that the forecasting for brake pump inventory is more accurate when environmental factors are included in the calculations. These results demonstrate the value of the inclusion of environmental factors data in the product support logistics' optimisation process.
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| 32. |
- Ghodrati, Behzad, et al.
(author)
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Optimizing product support (spare parts procurement) strategy by considering system operating environment : A case study
- 2009
-
In: 13th IFAC Symposium on Information Control Problems in Manufacturing 2009. - Red Hook : Curran Associates, Inc.. - 9781617380211
-
Conference paper (peer-reviewed)abstract
- Existing industrial system / machinery availability depends highly on the form and the level of product support. Product support, which is also referred to as after sale service to the product, is important for the customer as well, because it assures the expected function of the product in its operational phase. Product support is affected by different factors, such as reliability and maintainability characteristics and the operating environment of the product. The forecasting of required product support and spare parts based on these factors is one approach for product life cycle cost optimization along with system availability maximization. This paper describes a method to estimate the spare part requirements based on an estimation of reliability of the existing product under the influence of the product-operating environment. Subsequently, in a case study, the management of the spare parts inventory based on the geographical location and required performance of the product will be addressed.
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| 33. |
- Ghodrati, Behzad
(author)
-
Product support and spare parts considering system reliability and operating environment
- 2003
-
Licentiate thesis (other academic/artistic)abstract
- The required spare parts planning for a system/machine is an integral part of the product support strategy. The number of required spare parts can be effectively estimated on the basis of the product reliability characteristics. The reliability characteristics of an existing machine/system are influenced not only by the operating time, but also by factors such as the environmental parameters (e.g. dust, humidity, temperature, moisture, etc.), which can degrade or improve the reliability. In the product life cycle, for determining the accurate spare parts needs and for minimizing the machine life cycle cost, consideration of these factors is useful. Identification of the effects of operating environment factors (as covariates) on the reliability may help in the prediction and calculation of the required spare parts for a system under given operating conditions, which constitutes the research problem studied in this thesis. The Proportional Hazard Model (PHM) method is used for estimation of the hazard (failure) rate of components under the effect of covariates. In this research an approach has been developed to forecast and estimate accurately the spare parts requirements and to create rational part ordering strategies. Subsequently, a model considering environmental factors is developed to forecast and estimate the required number of spare parts within a specific period of the product life cycle. This thesis only discusses non- repairable components (changeable/service parts), which must be replaced after failure. In addition, the existing method for calculating the number of spare parts on the basis of the reliability characteristics, without consideration of covariates, is modified to arrive at the optimum spare parts requirement. To test the model, case studies concerning spare parts planning based on the reliability characteristics of parts and with/without considering the operating environment have been carried out. The results show clearly the differences between the consumption patterns for spare parts with and without taking into account the effects of covariates in the estimation. The final discussion treats spare parts logistics and inventory management. In this work an attempt is made to minimize the inventory cost and consequently the product life cycle cost. Two models for ordering, purchasing and storing spare parts are discussed in connection with the inventory management.
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| 34. |
- Ghodrati, Behzad, et al.
(author)
-
Product support improvement by considering system operating environment : a case study on spare parts procurement
- 2012
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In: International Journal of Quality & Reliability Management. - : Emerald. - 0265-671X .- 1758-6682. ; 29:4, s. 436-450
-
Journal article (peer-reviewed)abstract
- The ongoing availability of existing industrial systems/machines depends to a great extent on the form and level of product support. Product support, or the after sale service of a product, is important because it assures the expected function of the product in its operational phase. Product support is affected by a number of factors, including system reliability and maintainability characteristics and the operating environment. The purpose of this paper is to analyze the influence of time independent external factors of industrial systems on product support requirements and spare parts need.
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| 35. |
- Ghodrati, Behzad, et al.
(author)
-
Product support logistics based on product design characteristics and operating environment
- 2003
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In: Proceedings of the 38th annual International Logistics Conference and Exhibition. - : Society of Logistics Engineers.
-
Conference paper (peer-reviewed)abstract
- To improve the reliability, maintainability, and supportability (RMS) of a product, it is necessary to understand the factors influencing the product performance. This factors can be user environment, human (operator) aspects like training, and technical characteristics of the product. The environmental conditions in which the equipment is to be operated, such as temperature, humidity, dust, road conditions, maintenance facilities, maintenance crew training, operators' skill, etc, often have considerable influence directly on the product reliability and indirectly on the product supportability characteristics. Thus operating environment should be seriously considered while dimensioning product support and service delivery performance strategies, since it will have an impact on operational and maintenance cost and service quality to provide product support plan in an optimal condition. Spare parts are classified, as a product support items whose availability is important when planned or unplanned maintenance is to be carried out. Forecasting the required support/spare parts based on technical characteristics and operating environmental conditions of a system, is the one of the best ways for optimizing unplanned stoppages. This paper discusses about product support (required spare part) logistics based on product design characteristics and operating environment both for conventional and functional products.
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| 36. |
- Ghodrati, Behzad, et al.
(author)
-
Product Support Logistics Based on System Reliability Characteristics and Operating Environment
- 2014
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In: IEEE International Conference on Industrial Engineering and Engineering Management. - Piscataway, NJ : IEEE Communications Society. - 9781479909865 ; , s. 457-461
-
Conference paper (peer-reviewed)abstract
- The environmental conditions in which the equipment is to be operated, such as temperature, humidity, dust, operators’ skill, etc, often have considerable influence directly on the product reliability and indirectly on the product supportability characteristics. This paper, after discussing the factors influencing product reliability, describes a method to estimate spare part requirements based on estimation of the actual reliability of a product under the influence of the product-operating environment using a proportional hazard model. In this research only non-repairable components/parts in repairable systems are studied. Results express a considerable difference between considering and ignoring the operating environmental factor on system performance. So, this factor should be seriously considered while dimensioning product support and service delivery performance strategies, since it will have an impact on operation, maintenance and service quality.
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| 37. |
- Ghodrati, Behzad
(author)
-
Product support optimization through monitoring of system operating condition
- 2007
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In: Proceedings of Condition Monitoring and Fault Diagnosis. - : Sharif University of Technology.
-
Conference paper (peer-reviewed)abstract
- Product support, which is also referred to after sale service to the product is important for customer because it increases the availability of the product and it assures the expected function of the product in its operational phase. It gets influence by many factors such as - reliability and maintainability characteristics, operating environment of the product. By highlighting these influencing factors in design and manufacturing phases, the product life cycle cost (LCC) can be minimized. One of the important steps in product design is the decision making for design out maintenance (DOM) or designs for maintenance (DFM). The DOM alternative leads to produce high reliable, and vice versa, whereas the DFM assure the similar performance with lower reliability beside support. The forecasting of required product support and spare parts based on both reliability-maintainability characteristics and working condition is one approach for the product LCC minimization. This article describes a method to forecast the spare part requirements based on reliability estimation of the existing product under the influence of the product-operating environment.
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| 38. |
- Ghodrati, Behzad, et al.
(author)
-
Product support (spare parts procurement) strategy based on reliability characteristics and geographical location
- 2003
-
In: International Conference on Industrial Logistics. - Vaasa : University of Vaasa. - 952476010X ; , s. 222-235
-
Conference paper (peer-reviewed)abstract
- Product support, which is also referred to after sale service to the product is important for customer because it increases the availability of the product and it assures the expected function of the product in its operational phase. It gets affected by many factors such as - reliability and maintainability characteristics and geographical location of the product. By highlighting the reliability issues and geographical distribution of product in design and manufacturing phases, the product life cycle cost (LCC) can be optimized. One of the important steps in product design is the decision making for design out maintenance (DOM) and/or designs for maintenance (DFM). The DOM alternative leads to produce high reliable, and vice versa, whereas the DFM assure the similar performance with lower reliability. However, the need for product support and spare parts must be considered in both alternatives. The forecasting of required product support and spare parts based on reliability-maintainability characteristics is one approach for the product LCC optimization. Consequently, spare parts inventory management based on geographical distribution and reliability characteristics of the product can be also used as an alternative. This article describes a method to forecast the spare part requirements based on reliability estimation of the existing product under the influence of the product-operating environment. Subsequently the management of the spare parts inventory will be discussed based on the geographical location and required performance of the product.
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| 39. |
- Ghodrati, Behzad, et al.
(author)
-
Project: CAMM - Lean mining
- 2012
-
Other publication (pop. science, debate, etc.)abstract
- The current status of Scandinavian mining industry is characterized by semi-autonomous to autonomous and intelligent production machines. Since many of these autonomous machines are expected to perform round the clock, the importance of system characteristics such as reliability, availability, flexibility and controllability are of prime importance. Other area is focused on seamless integration of information to realize the vision of autonomous mining system and been actively developing and implementing the concept of collaborative and intelligent operation and maintenance for operating systems. Therefore, the vision of a Digital Mine with autonomous mining systems seems a possibility especially with the advent of new and emerging technologies together with willingness of mining industry to make investment towards semi autonomous and autonomous mining systems.For achieving lean production, all the processes and systems need to communicate in real time so as to eliminate uncertainty and address the critical issues and challenges often arising at short notices in a continuously changing environment as found in mining operations.The plan for research development intends to take the mining industry several steps forward in creating a reliable robust and productive autonomous mining system. Our goal is to build a state of the art research capability in the area of mine production system by working on the following subproject addressing the critical issues to realise the vision of lean mining system.Work plan A: Improvement of production availability and delivery assuranceWork plan B:Rock and machine interfaceWork plan C:Remaining useful life of mining systemsWork plan D:Integration of mine work environment into production systems
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| 40. |
- Ghodrati, Behzad, et al.
(author)
-
Project: Cost effective availability enhancement of switches and crossings using reliability analysis
- 2012
-
Other publication (pop. science, debate, etc.)abstract
- The main reason for the complexity of the railway system is that it is often a mixture of components of different age and status that have to work together in a system.Replacement of components is also a continuous and ongoing process. Today the railway infrastructure is therefore like a patchwork that has to perform to higher demands. For this reason changes have to be carefully executed.Infrastructure managers must keep infrastructure highly available so that railway undertakings (train operating companies) can deliver a high quality service at affordable price to end users. Expected increases in traffic volume will impose higher utilization of existing capacity and reduce the time available for maintenance and unplanned interruptions.Maintenance must therefore be performed near capacity limits, time between asset renewals should be long enough to balance maintenance cost and acquisition cost and components replaced by deferred or planned maintenance.In summary, the key goal is to achieve availability target cost effectively, or to minimize life-cycle cost subject to availability constraints. Availability itself is a function of reliability and maintainability of a system as well as the maintenance support. It implies that for achieving high availability we need to go through reliability, maintainability, product support and service delivery approaches. It is proposed to apply RAMS (reliability, availability, maintainability and safety) analysis along with advanced statistics and decision support techniques in order to address this need. Intelligent data processing will allow understanding the real reliability characteristics of the assets to be maintained. Furthermore simulation and optimization techniques will be applied in order to adapt the maintenancestrategy so as to achieve minimum cost while guaranteeing target availability. If maintenance is organized in such a way as to minimize equipment downtime, availability will be maximized and it will be possible to extract as much capacity as possible out of existing assets. In this way, asset renewal can be postponed as much as possible, so as to minimize total life cycle cost without detriment to service quality.Therefore, the goal of proposed study is summarized as: developing a method to improve switches and crossings availability cost effectively through maintenance optimization using reliability analysis.
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| 41. |
- Ghodrati, Behzad, et al.
(author)
-
Railway switches and crossings reliability analysis
- 2016
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In: 2016 IEEE International Conference on Industrial Engineering and Engineering Management. - 9781509036653 ; , s. 1412-1416
-
Conference paper (peer-reviewed)abstract
- Switches and crossings (S&Cs) connect the rail network, guiding trains from one track to another and supporting path crossing. They are critical systems given the frequency of their functional failure and the consequences on the operation, cost and safety of railway transportation. Reliability studies are required to support the transport objective of providing dependable, sustainable and cost effective transportation. The main objective of this study is to assess the reliability characteristics of S&Cs based on field data collection. As field failure data have censored nature, commercial packages have not been satisfactory for processing them; therefore, the study uses a special statistical software package RDAT® (Reliability Data Analysis Tool). The availability of the studied switches and crossings is estimated based on the estimated reliability characteristics. The results show the availability of the S&Cs varies between x and y. This is useful information, as it helps the contractor plan and schedule maintenance. It also helps the asset owner to identify units whose performance is below the desired target and to make replacement decisions.
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| 42. |
- Ghodrati, Behzad, et al.
(author)
-
Reliability Analysis of Switches and Crossings : A Case Study in Swedish Railway
- 2017
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In: International Journal of Railway Research. - Iran : Iran University of Science & Technology. - 2423-3838 .- 2423-382X. ; 4:1, s. 1-12
-
Journal article (peer-reviewed)abstract
- It is reported that switches and crossings (S&C) are one of the subsystems that cause the most delays on Swedish Railways while accounting for at least 13% of maintenance costs [6]. It is the main reason why we chose to base our study on this subsystem.Intelligent data processing allows understanding the real reliability characteristics of the assets to be maintained. The first objective of this research is to determine the S&C reliability characteristics based on field data collection. Because field failure data are typically strongly censored, an especial statistics software package was developed to process field failure data, as commercial packages have not been found satisfactory in that respect. The resulting software, named RDAT® (Reliability Data Analysis Tool) has been relied upon for this study: it is especially adapted to statistical failure data analysis.In the next step the availability of studied switches and crossings is estimated based on the reliability characteristics founded in the first step.
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| 43. |
- Ghodrati, Behzad, et al.
(author)
-
Reliability analysis of switches and crossings : a case study in Swedish railway
- 2013
-
Conference paper (peer-reviewed)abstract
- It is reported that switches and crossings (S&C) are one of the subsystems that cause the most delays on Swedish Railways while accounting for at least 13% of maintenance costs [6]. It is the main reason why we chose to base our study on this subsystem.Intelligent data processing allows understanding the real reliability characteristics of the assets to be maintained. The first objective of this research is to determine the S&C reliability characteristics based on field data collection. Because field failure data are typically strongly censored, an especial statistics software package was developed to process field failure data, as commercial packages have not been found satisfactory in that respect. The resulting software, named RDAT® (Reliability Data Analysis Tool) has been relied upon for this study: it is especially adapted to statistical failure data analysis.In the next step the availability of studied switches and crossings is estimated based on the reliability characteristics founded in the first step.
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| 44. |
- Ghodrati, Behzad, et al.
(author)
-
Reliability and operating environment-based spare parts estimation approach : a case study in Kiruna Mine, Sweden
- 2005
-
In: Journal of Quality in Maintenance Engineering. - : Emerald. - 1355-2511 .- 1758-7832. ; 11:2, s. 169-184
-
Journal article (peer-reviewed)abstract
- A case study was conducted to examine system reliability and operating environment, which are two important parameters, in spare parts estimation approach. It was found that required number of spare parts could be obtained based on technical and life parameters. It was also studied that forecasting the required number of spare parts, based on technical characteristics and operating environmental conditions of a system, is one of the best ways to optimize unplanned stoppages. It is suggested that to avoid downtime regarding the unavailability of spare parts, the company should take the operating environmental factors into consideration while estimating the spare parts need.
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| 45. |
- Ghodrati, Behzad
(author)
-
Reliability and operating environment based spare parts planning
- 2005
-
Doctoral thesis (other academic/artistic)abstract
- The required spare parts planning for a system/machine is an integral part of the product support strategy. The number of required spare parts can be effectively estimated on the basis of the product reliability characteristics. The reliability characteristics of an existing machine/system are influenced not only by the operating time, but also by factors such as the environmental parameters (e.g. dust, humidity, temperature, moisture, etc.), which can degrade or improve the reliability. In the product life cycle, for determining the accurate spare parts needs and for minimizing the machine life cycle cost, consideration of these factors is useful. Identification of the effects of operating environment factors (as covariates) on the reliability may facilitate more accurate prediction and calculation of the required spare parts for a system under given operating conditions. The Proportional Hazard Model (PHM) method is used for estimation of the hazard (failure) rate of components under the effect of covariates. The existing method for calculating the number of spare parts on the basis of the reliability characteristics, without consideration of covariates, is modified and improved to arrive at the optimum spare parts requirement. In this research an approach has been developed to forecast and estimate accurately the spare parts requirements considering operating environment and to create rational part ordering strategies. Subsequently, two models (exponential and Weibull reliability based) considering environmental factors are developed to forecast and estimate the required number of spare parts within a specific period of the product life cycle. This study only discusses non-repairable components (changeable/service parts), which must be replaced upon failure. To test the models, the data collection and classification was carried out from two mining company in Iran and Sweden and then the case studies concerning spare parts planning based on the reliability characteristics of parts, with/without considering the operating environment were done. The results show clearly the differences between the consumption patterns for spare parts with and without taking into account the effects of covariates (operating environment) in the estimation. The final discussion treats a risk analysis of not considering the system’s working conditions through a non-standard (new) event tree approach in which the organizational states and decisions were included and taken into consideration in the risk analysis. In other words, we used the undesired states instead of barriers in combination with events and consequent changes as a safety function in event tree analysis. The results of this analysis confirm the conclusion of this research that the system’s operating environment should be considered when estimating the required spare parts.
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| 46. |
- Ghodrati, Behzad, et al.
(author)
-
Reliability considerations in automated mining systems
- 2015
-
In: International Journal of Mining, Reclamation and Environment. - 1748-0930 .- 1748-0949. ; 29:5, s. 404-418
-
Journal article (peer-reviewed)abstract
- Automation is the operation of machinery or processes by devices, such as robots and machines, able to make and execute decisions without human intervention. Automation is one of the most attractive research and development areas in mining, as it aims to solve many technical, production and safety problems in current and future mining. This paper studies the structure of automated mining systems from a reliability and failure occurrence perspective. It reviews the main subsystems and related failure modes. Based on field investigation and a literature review, it highlights some critical issues and technical difficulties. Finally, it presents some challenges for future automated mines and offers some related solutions
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| 47. |
- Ghodrati, Behzad, et al.
(author)
-
Remaining useful life estimation of mining equipment : A case study
- 2012
-
In: Proceedings of MPES 2012.
-
Conference paper (peer-reviewed)abstract
- To ensure the production/output and customer satisfaction in mining sector the estimation of Remaining Useful Life of mining machineries is a prime. In this paper we used the reliability analysis in order to estimate an optimal mining equipment repair/replacement policy by estimating their remaining useful life. The proportional hazard model was used in reliability analysis to be realistic and take the operational influencing factors in calculation. Methods are presented for calculating the conditional reliability function and computing the remaining useful life (RUL) as a function of the current conditions to guarantee the desired output. The model is applied in the hydraulic jack unit of LHD machine in an underground mine in Sweden. A Weibull proportional hazard model (PHM) with time-independent covariates was considered for the hazard function in an illustration of the proposed model. Presented results can be used, e.g. for developing of preventive maintenance plan or replacement intervals based on the conditional probability of failure or RUL.
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| 48. |
- Ghodrati, Behzad
(author)
-
Rock engineering
- 1999
-
Reports (other academic/artistic)
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| 49. |
- Ghodrati, Behzad, et al.
(author)
-
Spare parts estimation and risk assessment conducted at Choghart Iron Ore Mine: A case study
- 2007
-
In: Journal of Quality in Maintenance Engineering. - : Emerald Group Publishing Limited. - 1355-2511 .- 1758-7832. ; 13:4, s. 353-363
-
Journal article (peer-reviewed)abstract
- Purpose – Spare parts needs are dependent on the characteristics of the product in question, e.g. its reliability and maintainability, and the characteristics of the environment in which the product is going to be used (e.g. the temperature, humidity, and the user/operator's skills and capabilities), which constitute covariates. The covariates have a significant influence on the system reliability characteristics and consequently on the number of required spare parts. The main objective of this research study is to evaluate the associated risks (i.e. risk of shortage of spare parts) in estimation of the required number of spare parts due to not considering the characteristics of system operating environment. Design/methodology/approach – An event tree is a graphical logic model that identifies and quantifies possible outcomes following an initiating event (non-considering system operating environment in this case) in spare parts planning. In the present research a risk analysis is performed through a new and non-standard event tree analysis. It used an event tree analysis in which the states of organization and managerial decisions took place in risk analysis. Findings – In the present study a modified form of event tree analysis was introduced and implemented. In the new version the undesired states were used instead of barriers in combination with events and consequents changes as a safety function in event tree analysis. The output of the event tree analysis shows that there is a considerable operational risk due to losses (production and economical) associated with the non-consideration of the machine working environment. Practical implications – In the estimation of the accurate amount of support and spare parts needed for any industrial system/machine, it is strongly recommended to take the product operating environment into account. This can be proved by the event tree risk analysis method used in a modified and non-standard form in the present research. The results of risk analysis can help managers in making accurate decisions for product support and spare part needs in the future. Originality/value – Modified event tree analysis is a new approach suggested for visualizing the risk associated with non-considering of system operating environment in required support/spare parts estimation. Visualization of risk in graphics can facilitate correct decision making in spare parts planning.
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| 50. |
- Ghodrati, Behzad, et al.
(author)
-
Spare parts estimation for machine availability improvement addressing its reliability and operating environment : case study
- 2013
-
In: International Journal of Reliability, Quality and Safety Engineering (IJRQSE). - 0218-5393. ; 20:3
-
Journal article (peer-reviewed)abstract
- Industrial operation cost analysis shows that, in general, maintenance represents a significant proportion of the overall operating costs. Therefore, the improvement of maintenance follows the final goal of any company, namely, to maximize profit. This paper studies spare parts availability, an issue of the maintenance process, which is an important way to improve production through increased availability of functional machinery and subsequent minimization of the total production cost. Spare parts estimation based on machine reliability characteristics and operating environment is performed. The study uses an improved statistical-reliability (S-R) approach which incorporates the system/machine operating environment information in systems reliability analysis. For this purpose, two methods of Poisson process and renewal process are introduced and discussed. The renewal process model uses a multiple regression type of analysis based on Cox’s proportional hazards modeling (PHM). The parametric approaches with baseline Weibull hazard functions and time independent covariates are considered, and the influence of operating environment factors on this model is analyzed. The outputs represent a significant difference in the required spare parts estimation when considering or ignoring the influence of the relevant system operating environment. The difference is significant in the sense of spare parts forecasting and inventory management which can enhance the parts and consequently machine availability, leading to economical operation and savings.
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