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To cope with the mounting sophistication, many designers and manufacturers have turned to the "Systems Approach" for designing new hardware. Described below is an overview of one notion to the systems approach to design and how human factors engineering fits into it. We have taken the approach from previous work done on maintainability design for underground mining equipment. (1) Designing a system is a fluid process. That is, the procedure itself has to be adapted to the situation in which it is being applied. The emphasis placed on each step in the design process presented below may change. However, you should include all of the steps discussed as part of the overall design process. The chart below illustrates one method of the Systems Approach to Design.
Conceptual Design PhaseDuring Conceptual Design, the initial concept for the new machine or system is defined. User needs and performance requirements are identified, preliminary research and development efforts initiated, and the system is specified. The product of this phase is a set of preliminary system specifications. Needs DefinitionUnder the Systems Approach to Design, efforts are made to identify all user needs and requirements, equipment performance specifications, regulatory constraints, market conditions, and other factors impacting the system's performance before the formal design process is initiated. These factors may include:
The needs defined during this period provide the foundation for the conceptual design of the new machine. Early Research And DevelopmentDuring the Conceptual Design Phase, designers may initiate focused research efforts to identify ways to reduce costs, improve the design, or enhance productivity. This research may address the use of new materials, better fabrication techniques or design innovations, use of emerging technologies, analysis of competitor products, and similar topics. Often, market research is conducted to quantify the potential market for the new products or features. Outputs from this phase include updated engineering practices and technologies to be incorporated into the new product. Conceptual DesignWhen needs have been defined and initial research completed, an early conceptual design of the machine is developed. This process permits the engineers to integrate user requirements with available technology. It also allows development of an overview of what the system may look like prior to hard tradeoffs that must be made later. The conceptual design step output may take the form of a series of functional specifications along with a description of the machine. The conceptual design and related supporting materials will often serve as the basis for project go/no-go decisions. Questions To Ask During the Conceptual Design PhaseThe following are some questions you may want to consider as the design engineer during the Conceptual
Design Phase of the equipment development process: (2)
Preliminary Design PhaseThe design team next moves into the Preliminary Design Phase. During this phase, overall system requirements are integrated with available technology to produce detailed specifications for the new system. The output is a set of working system specifications. The following tasks are generally completed at this time. System AnalysisA system functional analysis is completed to develop detailed specifications for all subsystems and major components on the machine. These specifications may include flow rates, power requirements, speeds, capacities, life cycles, weight, size, and other design shaping factors. For a simplified hypothetical continuous miner, the functions so specified may cover:
Preliminary IntegrationUser and other requirements are integrated with the preliminary system specifications to produce the preliminary system design. This design will identify subsystems and components to be developed during the detailed design phase of the project. It will also serve to identify potential problem areas that must be addressed prior to finalizing the design. Reliability, Availability, Maintainability (RAM) TradeoffsRAM design tradeoffs are conducted at this point in the design. The objective is to increase the mean-time-between-failure for all performance critical components on the machine. Component reliability is researched and the higher performance components specified. This is followed by a maintainability requirement assessment for the selected components. Little improvement in maintenance performance is gained by selecting a high reliability component that requires higher-than-normal servicing. Reliability-maintenance requirements tradeoffs are then made. Other design tradeoffs must be made to permit expeditious management of maintenance requirements. Parts with high frequency of repair, for example, should be located in readily accessible locations on the machine. The component-machine interface must be improved to permit rapid installation. Low probability of failure parts may be located in less accessible points on the machine. A second analysis is then completed to ensure compliance with all buyer RAM specifications. System OptimizationSystem Optimization consists of a series of higher order design tradeoffs intended to optimize overall system performance, cost, delivery schedules, and other factors. These tradeoffs are conducted to finalize the preliminary design of the machine so that detailed specifications can be developed. System optimization is typically conducted just prior to the "Design Freeze." Detailed SpecificationsThe last step in the Preliminary Design Phase is the preparation of detailed system design and performance specifications. The specifications may include:
Completion of Computer-Aided Design (CAD) and other support systems may be required to be completed prior to proceeding to the next phase. Questions To Ask During the Preliminary Design PhaseThe following are some questions you may want to consider as the design engineer during the Preliminary
Design Phase of the equipment development process: (2)
Detail Design PhaseThe Detail Design Phase includes completion of system or product design, production planning, prototype development, and final testing and evaluation. The output from this phase is a set of production-ready plans and specifications and usually a prototype system. The following functions are performed during this phase. System or Product DesignProduct design includes preparation of engineering drawings for the new system hardware, software, and supportware. Personnel may have to be familiarized with new technologies, such as Computer-Aided Design Systems, to complete this step. Production Planning and SchedulingProduction planning is generally completed at this time. Availability of production resources, customer delivery requirements, scheduling of vendor-supplied components, and related actions are included. The output is the final project timeline and delivery schedule. Prototype DevelopmentWhen a new or redesigned machine is being developed, fabrication of an engineering prototype or preproduction model may be warranted. This prototype, or mockup, can be used for final testing and preproduction evaluation. Prototypes are also useful in identifying operator or maintainer interface problems and in assessing proposed manufacturing techniques. Prototype Testing and EvaluationA carefully planned series of prototype tests and evaluations may be initiated at this point. These tests are designed to:
Questions To Ask During the Detail Design PhaseThe following are some questions you may want to consider as the design engineer during the Detail Design Phase of the equipment development process: (2)
Production PhaseWhen the engineering evaluation is completed, the new system is turned over to manufacturing for production. Important Things To ConsiderFor human factors design to be most effective, you should consider it to be an essential part of a good design, not as something separate. Human factors has the greatest impact when it is integrated into the total design process from start to finish (3). Other important points to consider about human factors design are:
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