System safety approach for automated mobile work-machines

In industrial sectors such as mining, construction, civil engineering, container handling and material handling, which are using mobile work machines, a new growing trend is to automate mobile work machine operations. The shift from manually operated mobile work machines toward automated mobile work-machine systems takes machinery-safety considerations also to a new, system safety, level. The biggest concern is the new automation-related threats and possible unexpected hazardous events. Regardless of the extensive international standardisation efforts, there are not yet safety-engineering or risk-assessment guidelines specific to overall complex automated mobile work-machine applications. The research gap is in the lack of knowledge and experience of a system-safety approach and practical methodology applicable for integration into the general systems-engineering approach to risk-assessment for automated mobile work-machine systems. The author’s work to construct the approach and methodology for system-level hazard identification and risk assessment in automated mobile work-machine systems was based on knowledge of machinery-safety and machine-control-system safety-design methodology, international safety requirements, standards, and regulations. Author’s knowledge of these topics has increased and been updated over the years as part of research and development activities in several research projects in VTT within VTT’s ‘Reliability management and system safety’ research team. The theoretical basis for the approach including system theory, system modelling, the system-safety approach to safety engineering, and safety-related factors in complex human–technology interaction was studied and integrated into the risk-assessment approach. Reaching the system-safety objectives of safety-engineering work The aim of the work has been to provide new information on how the risk-analysis methods in current use should be utilised for reaching the system-safety objectives and to increase the quality and effectiveness of safety-engineering work. The main result of the study is the three-level risk-assessment approach which integrates selected risk-analysis methods into a continuous process. The risk-assessment approach and selected risk analysis methods have been applied in several industrial projects in 2000–2013 and experiences of risk-analysis work and feedback on the usefulness of the approach and methodology have been received from industrial partners and utilised for the development of the approach. Evaluation of the overall three-level approach and risk analysis methods has been done following the qualitative case-study research approach. Author’s doctoral thesis on this subject was published last year. In the author’s thesis four case studies were used to evaluate the applicability and usefulness of the three-level risk-assessment approach and selected risk-analysis methods: Safety evaluation of a semi-automatic mobile work machine system in use in an underground mine in Kiruna, Sweden. Conceptual design of an automated ore-transportation system at Sandvik Mining and Construction in Finland. System design of an underground ore-transportation system using automated dump trucks to be implemented in the De Beers Finsch mine in South Africa. System design of an automatic stacking crane system at Cargotec in Finland and its application at a container harbour in Germany. The research results show that the three-level approach to risk assessment is applicable for automated mobile work-machine applications and the selected methods: Preliminary hazard analysis (PHA), Operating hazard analysis (OHA), and Hazard and operability study (HAZOP) are applicable for system-level hazard identification and hazard analysis. The results also show that the risk estimation methods and risk-evaluation practices need to be developed to be more appropriate for the specific needs of risk assessment activities at the various levels of systems engineering and in the individual phases in the system life cycle. The three-level approach to risk assessment The three-level approach to risk assessment brings key elements from system safety, machinery safety and industrial safety engineering practices. The three main perspectives – human, technology, and environment – are considered in all risk assessment activities. The overall system thinking clarifies that safety of complex mobile machine application cannot be solved by machine level safety solutions. System safety solution integrates risk reduction measures from all system levels considering all available types of safety measures. The benefits of the approach have been confirmed by the industry and the methods have been adopted in case companies. In general the results can be utilised among mobile work-machine manufacturers, system suppliers, end users of automated mobile work-machinery systems, and safety experts. The scientific contribution of this study can be considered from two perspectives. Firstly the study contributes to the development of the approach to risk assessment and its integration with the work of the academic communities in the machinery-safety, functional safety, and system-safety sectors. Secondly the case-study research results provide new valuable information and experiences in how the risk-analysis and risk-estimation methods were utilised, how practicable and useful they were, and what kinds of problems were faced in the case projects in various phases of the system life cycle. Simulator assisted safety engineering approach The research on the three-level risk-assessment approach and, specifically, on the new supporting methods and techniques has continued since 2011 in a research project that is part of the Finnish Metals and Engineering Competence Cluster’s (FIMECC) programme ‘Energy and life cycle cost efficient machines’ (EFFIMA). The focus in the research has been on the use of a simulator-assisted design approach utilising 3D models and work-site-level simulator environments in automated mobile work-machine systems. The main goal of the research on simulator assisted safety engineering practice was to describe and outline an overall safety engineering process that utilises the latest virtual environment and HIL simulator environments. The practice follows the standardised safe lifecycle model and integrates analysis, modelling, simulation, HIL testing and full scale testing. The simulator assisted safety engineering practice combines multidisciplinary competences and technologies: systems engineering approach and process, system safety engineering methods and tools modern simulator based design, engineering and verification environments, functional safety evaluations and calculation tools. In a long run the aim is to develop practice to support the integration of risk management process to companies R&D processes and system life cycle management processes from the early system requirement specification through system design and verification up to the requirement validation phase. The research and development work on the simulator assisted safety engineering practice utilised the virtual environment laboratory in VTT in Tampere, mobile machine simulator developed for this purpose in Creanex Oy in Tampere, and HIL simulator in Tampere University of Technology were utilised. Virtual environments and simulator assisted engineering methods Analysis of complex automated machinery applications, different operating scenarios and innovative safety solutions is made possible today with virtual environments and simulator assisted engineering methods. In the research project new virtual supporting tools were developed and a new process model evaluated to see the effect of agile design principles when designing demanding safety features. The safety function development platform was a HIL (hardware-in-the-loop) simulator with the actual machine control system hardware and a sophisticated dynamic modelling of an open pit mine environment. Among the new simulation features were the capability to execute experimental safety logic code alongside the dynamic simulation and the graphic visualisation of the safety control system states. The benefits of the agile engineering process and virtual tools were demonstrated in a multi-machine application were safety functions intelligently and efficiently adapts to changing work site conditions. Different approaches to safety mechanisms were tried in quick cycles, their capabilities evaluated and lessons learned from the intermediate results. The final result is ready to be evaluated by the machine end user audience. Experiences and results of the experiments conducting risk analysis with the simulator assisted methodology confirm its benefits to hazard identification and risk estimation in overall work site level and complex machinery applications. In practice the methodology enables to visualize and study operational situations that cannot be tested without damaging equipment or putting test persons in danger. The simulator assisted approach supports the systems engineering work and improves the current safety engineering practices for system analysis in conceptual design and system definition phases and also in the functional analysis and comparison of various concept and design alternatives. Observed decrease in development time for advanced safety functions help to compensate the increasing costs of complex mobile machinery automation development. Modelling and simulation seems to be promising tool for the conceptual safety engineering. It provides possibilities to simulate and demonstrate various concepts and compare their effects on productivity and risk mitigation. The use of a simulator environment and visualization improved the conceptualization of the new work site environment, machine system operation and system functionalities. Simulator and virtual reality environments offer good possibilities to develop test and demonstrate different machinery automation concepts with different machine functionalities and in different work site situations. They also helped sharing of system information and improved the common understanding of the overall system and interactions between subsystems among the analysis team that consists of expert from different technological background. The simulator assisted approach seems to be able to provide new verifiable and traceable evidence for the possible certification of adaptive safety functionalities and safety systems in automated mobile work machine applications. The results in this context are in line with the general systems engineering principles and objectives for modelling and simulation technologies. About the Author: Risto Tiusanen, Dsc (Tech), is a senior scientist at VTT’s Lifetime management Research area. He has over 25 years of experience in system safety and risk conscious development of complex machinery applications, and risk assessment. His research interests include risk assessment concepts, processes to support machinery life cycle management, development of risk analysis and risk evaluation methods in complex machinery systems. This article is an edited excerpt of his currently published doctoral thesis on the risk assessment approach and methodology for complex automated machinery applications. Sources: http://www.vtt.fi/inf/pdf/science/2014/S69.pdf http://link.springer.com/chapter/10.1007%2F978-3-319-09507-3_151

System safety approach for automated mobile work-machines

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