module 7

System Phase-Out and Retirement

. System functions are terminated and the system is disassembled to the level of its components; the system is disposed of. The natural resources from which the system is built are limited, so it is unlikely that the system will be completely discarded and wasted; it is desirable to retrieve materials from retired systems as far as possible, to save the cost of the materials,, and more importantly, to reduce the amount of waste to the environment.

Knowing the difference between the lower limit and upper limit enables the designers to specify the appropriate levels of design features to meet user needs. A typical design that includes anthropometry data usually involves the following steps (Wickens et al. 2003):

1.Determine the intended user population. Based on the design require-ments, find out who will be using the system and their workplace, identify the variability factors involved for the target user groups, including the gender, age, race, and occupational characteristics. 2.Determine the relative body dimensions that are involved in the design. Find out the main body dimensions for the intended use of the systems. For example, a chair design primarily is concerned with height while seated, hip breadth, and leg length, while a control panel primarily involves arm reach and finger size. 3.Determine the appropriate percentile value for the selected body dimensions to account for the variability involved. A general rule of thumb for consideration is to use the "design for extreme" approach first, that is, considering the data for the individuals at the extremes such as the lower or upper limits mentioned above; if considering these individuals will not meet the requirements, then the next step is to "design for adjustable range," in which the design can be adjusted within a range so that different users will be accommodated; of course, this would require more sophistication in the design. If there are some constraints to or a lack of feasibility in making the design adjustable, a third approach would use the "design for the average," which uses the 50th percentile value to accommodate a majority of the users involved. For example, many big department store designs use this percentile to plan the checkout counter to accommodate a large group of customers, since the variability of the customers is very large and, also, it is impossible to make the counter adjustable. Once the tar-get value has been determined, the percentile value will be calculated using the appropriate data sources and equations above. 4.Make the necessary modifications for the calculated percentile value. Much of the anthropometry data is measured in a very ideal situation, with standard posture and minimum clothing involved, which is not realistic for most systems designs. A nec-essary adjustment for the percentile value is necessary to account for clothing, protection devices, and dynamic body movement for user tasks. 5.Evaluate the design by testing it using a prototype or simulation. Before finalizing the design using the calculated anthropometry data, the design needs to be verified by using the prototype or simu-lation to make sure it truly meets the requirements. Many design software packages, such as CATIA, allow designers to visualize and simulate the physical fit of the users in the system configuration and workplace, inspecting the interaction from different perspectives, simulating various scenarios to identify any potential difficulties and problems with the design. Any problems found can then be addressed before the design is finalized.

Nielsen (1993) gave ten general heuristic evaluation criteria:

1.Visibility of system status: The system interface should always keep users informed about what is going on, providing a visible status for the system functions through an appropriate feedback format within a reasonable time frame. 2.Match between system and the real world: The system should speak the users' language, with terms, words, phrases, and con-cepts familiar to the user, matching users' mental models and expectations with system functions. It should follow real-world conventions, presenting information in a natural and logical order and format. 3.User control and freedom: When encountering problems and difficulties, there should be little difficulty for users to leave the current, unde-sired state easily with a clearly marked "exit", without having to go through an extended number of tedious steps; the system should support the undoing and redoing of the most recent user actions and functions. 4.Consistency and standards: The style of the interaction through-out the system interface levels should be consistent to minimize unnecessary learning and confusion between different levels of interactions. 5.Error prevention: A good usable interface is always designed in a way that prevents a problem from occurring in the first place; this should include eliminating error-prone conditions or checking for those con-ditions and present users with options before they make an error. This feature is important for all levels of user groups, especially when the system complexity increases. 6.Recognition rather than recall: A good design should minimize the user's memory load by making objects and actions visible and easily understandable. The user should be presented with ample informa-tion for them to choose from, not have to remember lots of infor-mation and retrieve them from memory. A good analogy for this principle is multiple-choice questions versus essay questions in a test; a multiple-choice question provides more recognition while an essay question primarily relies on one's recall ability. 7.Flexibility and efficiency of use: A good interface should provide flexibility for different users to suit their needs for efficiency. For example, while a novice user might need lots of detailed tutorials for them to learn to use the system efficiently, an experienced user might want to skip those tutorials and get straight to the tasks, even using some accelerators/shortcuts to speed up the tasks. A good system interface should have this flexibility to cater for both inex-perienced and experienced users and allow users to tailor their actions. 8.Aesthetic and minimalist design: A good usability interface should be attractive. This requires that every piece of information in the design should be relevant, minimizing clutter, maximizing visibil-ity, and complying with the psychological principles of user visual comfort. 9.Help users recognize, diagnose, and recover from errors: Error messages are inevitable in every system. When an error occurs, the system should provide the error message in plain language (no codes), indi-cate precisely the nature of the problem, and constructively suggest a solution or directions for solving the problem. 10.Help and documentation: A good system should provide help and doc-umentation. Such information should be easy to search and written from users' perspectives. This documentation should be available at all times and not be too large in size.

With regard to the sources of the components, the selection approach has to be based on system specification and driven by requirements, but generally speaking, the following sequence is usually followed:

1. Use a standard COTS item. COTS items are usually easy to obtain from a number of suppliers. The benefits of using a standardized part is because most suppliers specialize in manufacturing those parts, which usually conform with established government and industrial regulations and specifications, such as FAA or ISO9000/ISO9001. These parts are often produced in large volumes at a relatively low unit price. Using standard parts can significantly reduce the cost and increase the efficiency of system development, and even system maintenance/ support. The objective of selecting the right components from COTS is to derive detailed requirements for these components through system design analysis, to pick the appropriate supplier for the parts. 2. Modify an existing COTS item to meet the system requirements. If a COTS item cannot meet the configuration requirements completely, a close form of the item obtained from COTS can be modified. These modifications may include adding a mounting device, adding an adapter cable, or providing a software module. The rule for the modification is that it should be kept to a minimum and be simple and inexpensive, to ensure that no new problems or new requirements are introduced to the system design. 3. Design and develop a unique component for the system. If there is no standard component available and it is not possible to modify a standard part to meet our needs, designing a special unique part is our only option. The manufacturing process and materials used for the part, defined in the Type C, D, and E specifications, need to be based on the systems requirements, and it is desirable to use standard tooling/equipment and assembly parts for ease and economy of the installation, operation, and maintenance.

System Operations and Maintenance

After the system has been produced, assembled, and delivered to the customer, it will be in fully operational mode for the period of time designed, providing functions to users and operators. Users and operators are usually the same group of people; the difference between these two lies in the complexity of the system itself. If the system is fairly simple in nature, the term users, that is, the user-equipment combination, is employed; if the system is very large and complex, the term operators is used instead. System users and operators essentially represent the same type of user class; namely, the end customer of the system. There are also other classes of systems user; systems maintainer is one of the classes. Although highly reliable systems are desired, systems do fail sometimes, requiringmaintenance activities to be carried out. At this stage of the system life cycle, the emphasis is on customer service and support of the system; since the design of the system has been finalized, no further design changes are possible. However, follow-up tests and evaluations of systems are still necessary to identify any problems within operations and maintenance; these test results, together with feedback from customers, serve as a guide for any engineering changes that may be made for the subsequent version or next generation of the system. Emerging problems are addressed and fixed immediately, especially those pertaining to user safety and hazards. Faulty systems are fixed, recalled, or replaced to minimize the impact from these issues. At this stage of the system life cycle, operation, maintenance, and evaluation efforts are carried out continuously, until the system is ready to be retired.

CAD Tools and Prototypes in Detailed Design

At the detailed design stage, all the design components have been specified and integrated together. The level of detail and information involved is vast and overwhelming. It is imperative to use computer-aided tools and system project management software to control the design activities and manage all the data involved. The system has evolved to the final form of its physical model; this model needs to be built, verified against the system requirements, and traced against other forms of the system models, including functional and operational models. CAD/CAM tools provide great benefits for detailed design integration and verification; these benefits are similar to those mentioned in Section 2.3.2 (preliminary design phase), providing a well-structured and controlled database and project for implementing the design more effectively. These tools, sometimes combined with system simulation software, enable the design team to create a robust design more efficiently, through quick iterations with different configuration alternatives.

The main activities in the detailed design stage are to further meet the topdown system requirements with bottom-up system component selections; sometimes this is called the middle-out approach.

Based on the system functional structure and its allocation baseline, components are sought and the system is built. The designer's job is to select the best way to obtain the components (hardware and software) and integrate them into the system as a whole.

The Importance of Early Concept & Product Architecture Decisions

By the time a product has been designed, only 8% of the total product budget has been spent. By that time, the design has determined 80% of the cost of the product! See graph from the book, Design for Manufacturability. The design determines the manufacturability which determines a significant part of the introduction and production cost (the 80%) of the product. Once this cost is locked in, it is difficult for manufacturing to remove it. Note that the concept or architecture alone determines 60% of the cost!

Some Key Design for Manufacturability Guidelines

DFM Guideline A1) Understand manufacturing problems/issues of current/past products In order to learn from the past and not repeat old mistakes, it is important to understand all problems and issues with current and past products with respect to manufacturability, introduction into production, quality, repairability, serviceability, regulatory test performance, and so forth. This is especially true if previous engineering is being "leveraged" into new designs. DFM Guideline A3) Eliminate overconstraints to minimize tolerance demands. An overconstraint happens whenever there are more constraints than the minimum necessary, for instance guiding a rigid platform on four rigidly mounted bearings or trying to precisely align two parts with multiple round pins inserted into round holes (the solutions for both are shown below). • For critical alignment of parts use round/diamond pins. Use pairs of inexpensive but tight-tolerance dowel pins to locate critical parts. Matching tight-tolerance hole diameters can be made with reamers. To eliminate the tolerance match problem between holes, use one round pin to locate in "x" and "y" dimensions and a diamond pin to locate the angle from the round pin. The diamond is precision ground to locate in the angle direction, but is relieved in the direction of the hole spacing. Aligned parts are held together with bolts, with ample clearance holes so the bolts do not try to align the parts. This technique was developed to locate tooling, but it can also be useful for aligning parts for assembly. DFM Guideline P1) Adhere to specific process design guidelines. It is very important to use specific design guidelines for parts to be produced by specific processes such as welding, casting, forging, extruding, forming, stamping, turning, milling, grinding, powdered metallurgy (sintering), plastic molding, etc. Some reference books are available that give a summary of design guidelines for many specific processes. Many specialized books are available devoted to single processes. DFM Guideline P2) Avoid right/left hand parts. Avoid designing mirror image (right or left hand) parts. Design the product so the same part can function in both right or left hand modes. If identical parts can not perform both functions, add features to both right and left hand parts to make them the same. Another way of saying this is to use "paired" parts instead of right and left hand parts. Purchasing of paired parts (plus all the internal material supply functions) is for twice the quantity and half the number of types of parts. This can have a significant impact with many paired parts at high volume. At one time or another, everyone has opened a brief case or suit case upside down because the top looks like the bottom. The reason for this is that top and bottom are identical parts used in pairs. DFM Guideline P3) Design parts with symmetry. Design each part to be symmetrical from every "view" (in a drafting sense) so that the part does not have to be oriented for assembly. In manual assembly, symmetrical parts can not be installed backwards, a major potential quality problem associated with manual assembly. In automatic assembly, symmetrical parts do not require special sensors or mechanisms to orient them correctly. The extra cost of making the part symmetrical (the extra holes or whatever other feature is necessary) will probably be saved many times over by not having to develop complex orienting mechanisms and by avoiding quality problems. It is a little know fact that in felt-tipped pens, the felt is pointed on both ends so that automatic assembly machines do not have to orient the felt. DFM Guideline P4) If part symmetry is not possible, make parts very asymmetrical. The best part for assembly is one that is symmetrical in all views. The worst part is one that is slightly asymmetrical which may be installed wrong because the worker or robot could not notice the asymmetry. Or worse, the part may be forced in the wrong orientation by a worker (that thinks the tolerance is wrong) or by a robot (that does not know any better). So, if symmetry can not be achieved, make the parts very asymmetrical. Then workers will less likely install the part backward because it will not fit backward. Automation machinery may be able to orient the part with less expensive sensors and intelligence. In fact, very asymmetrical parts may even be able to be oriented by simple stationary guides over conveyor belts. DFM Guideline P5) Design for fixturing. Understand the manufacturing process well enough to be able to design parts and dimension them for fixturing. Parts designed for automation or mechanization need registration features for fixturing. Machine tools, assembly stations, automatic transfers and automatic assembly equipment need to be able to grip or fixture the part in a known position for subsequent operations. This requires registration locations on which the part will be gripped or fixtured while part is being transferred, machined, processed or assembled. DFM Guideline P6) Minimize tooling complexity by concurrently designing tooling. Use concurrent engineering of parts and tooling to minimize tooling complexity, cost, delivery leadtime and maximize throughput, quality and flexibility. DFM Guideline P7) Make part differences very obvious for different parts. Different materials or internal features may not be obvious to workers. Make sure that part differences are obvious. This is especially important in rapid assembly situations where workers handle many different parts. To distinguish different parts, use markings, labels, color, or different packaging if they come individually packaged. One company uses different (but functionally equivalent) coatings to distinguish metric from English fasteners. DFM Guideline P8) Specify optimal tolerances for a Robust Design. Design of Experiments can be used to determine the effect of variations in all tolerances on part or system quality. The result is that all tolerances can be optimized to provide a robust design to provide high quality at low cost. DFM Guideline P9) Specify quality parts from reliable sources. The "rule of ten" specifies that it costs 10 times more to find and repair a defect at the next stage of assembly. Thus, it costs 10 times more cost to find a part defect at a sub-assembly; 10 times more to find a sub-assembly defect at final assembly; 10 times more in the distribution channel; and so forth. All parts must have reliable sources that can deliver consistent quality over time in the volumes required.

The Importance of Good Product Development

C Good product development is a potent competitive advantage. C Product design establishes the feature set, how well the features work, and, hence, the marketability of the product. C The design determines 80% of the cost and has significant influence on quality, reliability and serviceability. C The product development process determines how quickly a new product can be introduced into the market place. C The product design determines how easily the product is manufactured and how easy it will be to introduce manufacturing improvements like just-in-time and flexible manufacturing. C The immense cost saving potential of good product design is even becoming a viable alternative to automation and off-shore manufacturing. C True concurrent engineering of versatile product families and flexible processes determines how well companies will handle product variety and benefit from Build-to-Order and Mass Customization.

Before DFM, the motto was "I designed it; you build it!" Design engineers worked alone or only in the company of other design engineers in "The Engineering Department." Bad old days

Designs were then thrown over the wall leaving manufacturing people with the dilemma of either objecting (but its to late to change the design!) or struggling to launch a product that was not designed for manufacturability. Often this delayed the both the product launch and the time to ramp up to full production, which is the only meaningful measure of time-to-market.

Design for Manufacturability and Concurrent Engineering are proven design methodologies that work for any size company.

Early consideration of manufacturing issues shortens product development time, minimizes development cost, and ensures a smooth transition into production for quick time to market. These techniques can be used to commercialize prototypes and research.

According to Nielsen (1994), usability is a quality issue of a system interface; it carries two separate but related meanings

First, usability is the assessment how friendly an interface is, and second, it also refers to the methods and models to improve the ease of use during the design process. In addition to usability testing, other testing methods that have been used in usability evaluation are heuristic evaluation, cognitive walk-through, and competitive evaluation. The idea of "heuristics" came from the fact that inter-face design principles are fairly broad and would apply to many types of user interfaces (Nielsen 1993)

In anthropometry, the following terms are used for a unified and standard theme for measurements of human body dimensions (Wickens et al. 2003).

Height: A straight-line, point-to-point vertical measurement Breadth: A straight-line, point-to-point horizontal measurement across the body Depth: A straight-line, point-to-point horizontal measurement running fore-aft through the body Distance: A straight-line, point-to-point measurement between body landmarks Circumference: A closed measurement following a body contour (not circular) Curvature: A point-to-point measurement following body contours (neither circular nor closed)

The idea of "heuristics" came from the fact that inter-face design principles are fairly broad and would apply to many types of user interfaces (Nielsen 1993). Implementing usability testing could be costly and time consuming; heuristic evaluation and testing could be a faster and more economical way of obtaining initial results.

Heuristic evaluation is done by having experts evaluate an interface and form an opinion about what is good and bad about it. After years of experience, heuristic evaluation has become a systematic inspection of a user interface design. Evaluation is usually performed by a small set of expert evaluators using recognized usability principles.

Prototypes play a vital role in almost all kinds of design projects; it is hard to imagine a design being completed without any kind of prototype being developed during the design process.

In software engineering, there are designs that evolve primarily with the prototypes, as this is straightforward for the users and easy to demonstrate. For example, the rapid prototyping approach utilized in software development is an iterative and evolutionary design process that primarily uses prototypes as the main tools to convey the design ideas and get users involved in the early stages of the design.

With the functional baseline (Type A specification) developed at the conceptual design stage and the allocation baseline (Type B specification) developed at the preliminary design stage, the system configuration is derived in terms of hardware and software components. It is now time to proceed to integrate all the components into a final form of the system; this is the main goal for system detailed design.

In the detailed design phase, system engineers will (1) develop design specifications for all the lower-level components and items; (2) develop, procure, and integrate the system components into the final system configuration; (3) conduct a critical system review, identify any possible problems with the system configuration with regard to systems requirements, and control/incorporate changes to the system configuration.

Another area in which human factors engineering is applied extensively in the context of systems engineering is design for usability. Usability plays an important role in our daily lives.

It makes our interactions with any inter-face easier to understand and to operate. For a human-system interface, it is similar to "user-friendliness," but it is not a single, one-dimensional prop-erty of a user interface.

Manufacturability and producibility is an engineering specialty. The machines and processes used to build a system must be architected and designed. A systems engineering approach to manufacturing and production is necessary because manufacturing equipment and processes can sometimes cost more than the system being built (Maier and Rechtin 2002). (Seebok)

Manufacturability and producibility can be a discriminator between competing system solution concepts and therefore must be considered early in the study period, as well as during the maturing of the final design solution.

a general rule of thumb of applying percentile values in the design is to use the 5-95 range. For example,

NASA's 1995 design of space system guidelines chose a range from a 5th-percentile Japanese woman to a 95th-percentile American man as the data for inclusion. Whether to use the 5th or 95th percentile depends on the nature of the design, or in other words, the lower or upper limit for the design.

In detailed design, high-fidelity prototypes are to be developed to serve as the test bed for validating the system components configuration

Prototypes enable designers from different disciplines to come together to communicate in a very cost-effective and time-efficient way.

Here we present a simple example of the work-time measurement models that can be used in work system design to develop a time standard (Stevenson 2009). The time standard involves three time components, the observed time (OT), the normal time (NT), and the standard time (ST). Imagine that, for a particular task, we observe a sample of task times, xi, i=1, 2, ..., N, where N is the number of observations.

The OT is simply the average of the time samples collected, as shown in Equation 5.39

After the physical system model has been built, tested, and finalized, the system will move to the next life cycle phase, which is full-scale production, distribution, and deployment. what happens

The system is in its final format, and is transferred to the production assembly line to start formal mass production. At this stage, the system is produced, possibly in multiple copies. All the components are specified, either produced separately if they are specially designed for the system, or procured if using standard commercial offthe-shelf (COTS) items. These components are delivered to the production site, assembled, and then distributed via retail outlets to customers. A final production of the system may involve hundreds or thousands of suppliers, depending on the level of complexity of the system. The supply chain plays an important role at this stage, as greater cost may be incurred in distribution and deployment than in the production/assembly itself. Much of the system's assembly work may be outsourced internationally; for example, to take advantage of cheap labor and materials locally. For instance, the cost of labor and materials of many U.S.-designed systems in third-world countries, such as China, is less than 10% of the total cost of the system. As a matter of fact, the majority of the cost is incurred in system distribution and deployment, in addition to the cost of research and development. The system has now evolved from its models to the final realization of its designed format, together with its supplemental materials including manuals and training services; it is delivered to customers and installed for operations.

Unfortunately, disposability has a lower priority compared to other activities associated with product development. This is due to the fact that typically, the disposal process is viewed as an external activity to the entity that is in custody of the system at the time. Reasons behind this view include:(seebok)

There is no direct revenue associated with the disposal process and the majority of the cost associated with the disposal process is initially hidden. Typically, someone outside of SE performs the disposal activities. For example, neither a car manufacturer nor the car's first buyer may be concerned about a car's disposal since the car will usually be sold before disposal.

Some disposal of a system's components occurs during the system's operational life. This happens when the components fail and are replaced. As a result, the tasks and resources needed to remove them from the system need to be planned well before a demand for disposal exists. (seebok)

Transportation of failed items, handling equipment, special training requirements for personnel, facilities, technical procedures, technical documentation updates, hazardous material (HAZMAT) remediation, all associated costs, and reclamation or salvage value for precious metals and recyclable components are important considerations during system planning. Phase-out and disposal planning addresses when disposal should take place, the economic feasibility of the disposal methods used, and what the effects on the inventory and support infrastructure, safety, environmental requirements, and impact to the environment will be (Blanchard 2010). Disposal is the least efficient and least desirable alternative for the processing of waste material (Finlayson and Herdlick 2008). The EPA collects information regarding the generation, management and final disposition of hazardous wastes regulated under the Resource Conservation and Recovery Act of 1976 (RCRA). EPA waste management regulations are codified at 40 C.F.R., parts 239-282. Regulations regarding management of hazardous wastes begin at 40 C.F.R. part 260. Most states have enacted laws and promulgated regulations that are at least as stringent as federal regulations. Due to the extensive tracking of the life of hazardous waste, the overall process has become known as the "cradle-to-grave system". Stringent bookkeeping and reporting requirements have been levied on generators, transporters, and operators of treatment, storage, and disposal facilities that handle hazardous waste.

Let us give a simple example here. Assume we are interested to know the 75th percentile value for a body dimension x. We have measured a sample of x and estimated that x has a mean value of 25.5 in. and a standard deviation of 3.6 in. From the standard normal table, we know the Z-value for a 75th percentile value is approximately 0.674 (for readers who are not familiar with the standard normal table, please refer to Appendices I and II of this book for a brief review of the normal distribution and a quick reference standard normal table).

Using Equation 5.43, we can derive the percentile value for xas x=μ+Zσ=25.5+(0.674)(3.6)=27.93 in.

In addition to usability testing, other testing methods that have been used in usability evaluation

are heuristic evaluation, cognitive walk-through, and competitive evaluation.

Concurrent Engineering is

is the practice of concurrently developing products and their manufacturing processes.If existing processes are to be utilized, then the product must be design for these processes.If new processes are to be utilized, then the product and the process must be developed concurrently.

Design for manufacturability (DFM)

is the process of proactively designing products to (1) optimize all the manufacturing functions: fabrication, assembly, test, procurement, shipping, delivery, service, and repair, and (2) assure the best cost, quality, reliability, regulatory compliance, safety, time-to-market, and customer satisfaction.

Regarding the measurement of usability, it is typically measured by hav-ing a number of representative users interact with the system to perform a specified and predetermined task. Nielsen (1993) proposed a detailed meth-odology for interface testing; his methodology includes

testing goals and plan development, obtaining testing users, choosing experimenters, the ethical aspects of the study of human subjects, developing testing tasks, per-forming tests, and measurement.

A large amount of anthropometry data has been compiled since the 1980s by a group of researchers and organizations. For example,

, a survey of personnel under the age of 40 was completed by the U.S. Army in 1989, looking at several body measurements of men and women; NASA compiled anthropometry data and guidelines for the design of space systems in the 1990s. Some private organizations also conducted their own studies and surveys for their own system design; this data is also available for purchase.

Generally speaking, human factors studies the following subjects:

1. Human visual sensory system: Over 90% of information is perceived by the visual system. Human factors studies the human eyeball system and optic nerves, including the lens and the visual receptor system, and investigates the effects of visual stimulus (light) on human visual reception, such as the location of the stimulus, acuity, sensitivity, color, adaption, and differential wavelength sensitivities. From the study of the human visual system, we can obtain the advantages and disadvantages or limitations of human vision, such as contrast sensitivity, color sensation, and night vision. These understandings have significant impact on designing for human visual information processing; for example, designs to facilitate visual search and detection, and provide comfort and signal discrimination. 2. Auditory, tactile, and vestibular system: As the second most used sensory channel, the human auditory system responds to sound stimuli. Human factors studies the physical properties of the sound, understanding the nature of the sound, its measurements (amplitude and frequency), envelope information, and sound location. The human receptor of the sound stimulus is the ear and vestibular system. The experience of human hearing is investigated to understand the relationship between loudness and pitch, and masking effects of different sound sources. This provides implications for designing sound systems for human users, including alarms, speech communication and recognition, managing and controlling noises, and providing hearing protection if the noise is above certain danger thresholds. Other senses, including the tactile and haptic senses, and the proprioception and kinesthesis channels, are also important for certain types of user interaction with systems. . Cognition: The basic mechanisms by which humans perceive, think, and remember things are the focus of the study of cognitive psychology. The core mechanism describing human cognition is a topdown, linearly ordered process: the information processing model, as shown in Figure 5.18. From the information processing model, human factors study the selective attention pertaining to different sensory channels, the three perceptual processes (bottom-up feature analysis, utilization, and top-down processing), and investigate the effects of association of stimuli and contextual information, short-term memory capacity limitation (e.g., Miller's 7±2 chunks models) and long-term memory mechanisms (forgetting and retrieving information). This information is essential for the design of better systems to aid human situational awareness and easy learning and recalling of knowledge and procedures. 4. Human decision making: Decision making is at the latter stages of the information processing model. After perceiving what is present and understanding what it means, humans need to decide on a course of action to respond to the information perceived. Human decision making and problem solving is a highest-level human cognitive behavior; it involves information processing from multiple sensory channels and complex processes involving short-term and long-term memory. Human factors is concerned with different decision-making models that can capture human decision-making activities, such as normative decision-making models, descriptive decision-making models, and, sometimes, heuristics and biases to simplify decision-making problems, as our information processing models pose significant limits to decision-making capabilities concerning complex problems. Human factors focuses on task design, decision support system (DSS), visual aids, and displays to facilitate a more rational decision-making process. 5. Motor skills and control: Human control is the last stage of the information processing model to execute a response based on the results of decision making. The primary psychological measures of the effectiveness of human control is the accuracy of that control and the response time. One factor impacting the response time is the complexity involved in the decision; there are many empirical models, such as the Hick-Hyman model to address the relationship between the response time and the number of alternatives. Design features to facilitate user control and motor skills include the visibility of the stimulus, the physical feel of the control and feedback, size, and labeling. There are many empirical models to address different types of control mechanism. For example, a well-known model for positioning control devices is Fitts's model, or Fitts's law, which explains the relationships between movement time and difficulty of the movement (A = amplitude of the movement and W = size of the target), or MT=a+b log2(2A/W). The device characteristics, such as direct/indirect control, control gain, control order, time delay, closed loop/open loop, and stability all play a role in determining the human control performance. 6. Anthropometry: Anthropometry is the study of human body dimensions, to match the physical dimensions of the system and workplaces to human users. Humans have a large degree of variability, in terms of age, gender, race, and occupation. The most useful tool for addressing such variability is the use of statistics. Readers should review the materials in Appendix I to familiarize themselves with statistical concepts, to understand the models involved in this book, particularly within the human factors field. A typical application of the statistics applied in anthropometry is to derive a percentile value for a particular body dimension. By using the normal (Gaussian) distribution, especially the normalized standard normal table (Appendix II), we can obtain a percentile value by X=μ+Zασ, where Z𝛼 is the Z-value for a certain α-level, μ is the mean, and σ is the standard error for the body dimension. Most anthropometry data is static, but when movement is involved, necessary adjustments are needed. When using anthropometry data, we need to (1) first determine the user population for the system and then (2) determine the relevant body dimensions; (3) determine the percentile value used for this design based on the design requirements, and calculate the value based on the data; and finally (4) make the necessary adjustments to accommodate for the dynamic work environment. Areas of application of anthropometry may involve upper and lower limits for special user groups, adjustability design, posture and normal line of sight, components arrangement, and workplace design (work surface height and inclination, etc.) with environmental conditions in mind. 7. Biomechanics: Awkward body posture is not the only factor to cause injury to the human body; sometimes, forces resulting from improper exertion may also cause severe body damage. Biomechanics studies the physics involved in the physical work of humans, trying to understand the impact of external forces on different body components. First, we need to understand the human musculoskeletal system, the muscles and bones of the human body, and the biomechanical models of humans performing physical tasks, such as the application of Newton's law on human joints and muscles. This helps designers to understand different ways that the body may be injured by external forces, such as lower back pain problems. There are many standards and regulations for man material handling jobs, such as those of the National Institute for Occupational Safety and Health (NOISH), which published a lifting guide for recommended weight limits (RWL) in 1991, based on three kinds of criteria: biomechanical, physiological, and psychophysical. RWL are a product of several multipliers, including the horizontal, vertical, distance, asymmetric, coupling, and frequency multipliers. Many guidelines were published based on this limit, such as manual material handling guidelines, seated work and chair design, and proper handtool design to prevent cumulative trauma disorders (CTDs). 8. Work physiology: For humans to perform a physical task, they need enough energy to support muscular activities. Physiology studies how human physiological systems work together to meet the energy requirements for human activities, both physical and mental. The central topic of work physiology is the study of muscle structure and metabolism involved in muscular activities, including aerobic and anaerobic metabolism, and the circulatory and respiratory systems (i.e., heart, blood vessels, and lungs), including blood function/flow and lung structure/capacity. A fundamental measure of work physiology is to calculate the energy cost for the work, measured in calories per minute. The workload of activities can be measured in terms of oxygen consumption, heart rate, blood pressure and minute ventilation, and sometimes through subjective surveys and questionnaires. The main goal of the study of work physiology is to avoid body fatigue, in both the short and long term, as such fatigue, if not properly controlled, will lead to stress and long-term permanent body damage.

Detailed Design Requirements and Specifications The analysis of the detailed design will lead to a comprehensive description of the system configuration in terms of system components and operations. With these descriptions, it should be easy to build or install the system with minimum confusion. The detailed design configuration usually consist of the following design baselines:

1. Product baseline (Type C specification): This, according to Blanchard and Fabrycky (2006), describes the technical requirements for any items below the system level, either in inventory internally or that can be procured commercially off the shelf. Type C specifications cover the configuration of the system at the system elements and components level; it comprises the approved system configuration documentation, including the component/part lists, component technical specifications (TPMs), engineering drawings, system prototype models, and integrated design data, which also includes the changes made and the trade-off studies/models for the decisions made for the components. 2. Process baseline (Type D specification): This, according to Blanchard and Fabrycky (2006), describes the technical requirements for the manufacturing or service process performed on any system elements or components to achieve the system functions. It includes the manufacturing processes necessary for system components, such as welding, molding, cutting, bending, and so on, or the service/logistics processes such as material handling, transportation, packaging, and so forth; and any related information processing procedures, including any management information systems and database infrastructure for the design. 3. Material baseline (Type E specification): This describes the technical requirements pertaining to the materials of the system elements/ components, including the raw materials, supporting materials (such as paints, glues, and compounds), and any commercially available materials (such as cables and PVC pipes, etc.) that are necessary for the construction of the system components. These baselines are built on one another, and are derived from the system technical requirements and system analysis, taking into consideration economic factors from the global supply chain, and gradually lead to the realization of the system.

Some of the values and benefits for the detailed design, according to Blanchard and Fabrycky (2006), include:

1. Provide the designers with opportunities to experiment with different detailed design configuration ideas, including (not limited to) facility layout, interface style, packaging schemes, controls and displays, cables and wires, and so on. 2. Provide different engineers with a test bed to accomplish a more comprehensive review of the system configuration, including system functions and operations, reliability and maintainability, human factors and ergonomics, and support and logistics. Reviews are more open and straightforward, with the possibility of interactions between different problem domains. 3. Provide design engineers with a test bed for conducting user task analysis, including the task sequence, time constraints, and skills requirements, which in turn specify the training requirements for system operators and maintainers. 4. Provide a vehicle for designers to demonstrate their ideas and design approaches during the design review. 5. Provide a good tool for training purposes. 6. Provide a good reference for tools and facility design. 7. Serve as a tool in the later stages for the verification of a modification kit design prior to the finalization of data preparation.

The quality of the workplace determines the efficiency of the work performed in that place. Human are not machines, and it is true that most humans work to earn a living; however, other aspects beyond that basic purpose are also important for humans' work performance and sometimes their safety and well-being in the workplace; these factors include emotions, motivations, self-esteem, and the need for socialization. The quality of work life can be measured by several factors; these factors include the physical working conditions and work compensation (Stevenson 2009).

1. Working conditions. Physical working conditions play a significant role in humans' safety and thus have a great impact on their productivity and work performance. These factors include temperature, humidity, ventilation, illumination, noise, and vibration. There are well-defined condition limits for these factors, usually specified in government regulations and standards; for example, OSHA standards. Besides these factors, there are other regulating factors such as work time and work breaks, which also have a significant impact on humans' health. Appropriate shift length and break frequency will not only provide human operators with time to rest from fatigue and boredom, but also give a sense of freedom and control over one's work. Occupational safety measures are mandatory to ensure workers' safety and prevent accidents from happening, primarily through job design and workplace housekeeping, to make the job safer, to make humans aware of unsafe actions, and, most importantly, to eliminate potential hazards that may cause injuries. 2. Work compensation. Work compensation is an important factor in motivating human workers to be productive and efficient. Appropriate compensation attracts the best people to work for the employer and the best compensation keeps competent employees. Different organizations use different ways to compensate employees. The most commonly used approaches are time-based, output-based, and knowledge-based systems. Time-based systems compensate employees based on the hours they spend on the job. It is the most widely used compensation system overall; the method is straightforward and easy to manage. It is suitable for work that is difficult to put an incentive on, such as office work and administration. When incentives are desirable, output-based systems should be used to compensate work based on the amount of output produced; this ties the compensation directly to the efforts, making it possible to earn more if one is performing well. However, incentive compensation makes it difficult for management to predict the cost of the production, is difficult to implement together with the time-based system, and, sometimes, since it is more flexible than the time-based system, it also increases scheduling problems. The knowledge-based compensation system is used to reward employees who have higher skills. With more systems becoming complex and more advanced technology being involved, skillful employees who are capable of multiple tasks are more valuable. Knowledge-based compensation systems reward people with more skills, encouraging them to undergo training and education to acquire more skills to be more competitive.

Practical Considerations disposal and retirement

A prime objective of systems engineering is to design a product or service such that its components can be recycled after the system has been retired. The recycling process should not cause any detrimental effects to the environment. One of the latest movements in the industry is green engineering. According to the EPA, green engineering is the design, commercialization, and use of processes and products that are technically and economically feasible while minimizing: the generation of pollutants at the source; and the risks to human health and the environment.

In the detailed design, prototype-based simulation is of importance for validating the design.

A prototype is a simulated representation of the system that enables designers and users to visualize, conceptualize, touch and feel, and interact with it to validate the design effectively and efficiently. Prototypes come with different kinds of forms and levels of detail. They range from concept cards, cardboard, hand-sketched flow charts, and storyboards, to near complete complex versions of the system interface or hardware mock-ups. Prototypes are used at all stages of the system design, with different levels of information and different aspects of the system for different purposes. In software interface design, fidelity is used to measure the level of detail included in the prototypes. Fidelity of the prototype refers to the degree of closeness of the prototypes to the system counterparts they represent; the closer to the real system, the higher the fidelity. Fidelity is also used in the aviation training and simulation community to measure the quality of the training devices; it has a similar meaning here as with prototypes, as the training devices are often replicas of the real system; for example, the personal training devices (PTD) to train novice pilots. In the early design stages, such as in the conceptual design stages, since the design is focused on the high-level system operational concepts, the prototypes developed at these stages are often of low fidelity. In other words, they do not look like or feel like the final system, but are in a more abstract format, to capture the most important logical relationships of the system functional structure, as they are cheaper and easier to build, and thus provide advantages for exploring different conceptual design alternatives. In the later design stages, especially when approaching the end of the preliminary design stage and detailed design stage, with all the components configured, the prototypes are closer to the final forms of the systems. At this stage, the focus is on investigating the more detailed low-level aspects of the design, such as the physical dimensions, look and feel, and interaction with users.

Ecological considerations associated with system disposal or retirement are of prime importance. The most concerning problems associated with waste management include: (seeboK)

Air Pollution and Control, Water Pollution and Control, Noise Pollution and Control, Radiation, and Solid Waste. In the US, the Environmental Protection Agency (EPA) and the Occupational Safety and Health Administration (OSHA) govern disposal and retirement of commercial systems. Similar organizations perform this function in other countries. OSHA addresses hazardous materials under the 1910-119A List of Highly Hazardous Chemicals, Toxics, and Reactives (OSHA 2010). System disposal and retirement spans both commercial and government developed products and services. While both the commercial and government sectors have common goals, methods differ during the disposition of materials associated with military systems. US DoD Directive 4160.21-M, Defense Material Disposition Manual (1997) outlines the requirements of the Federal Property Management Regulation (FPMR) and other laws and regulations as appropriate regarding the disposition of excess, surplus, and foreign excess personal property (FEPP). Military system disposal activities must be compliant with EPA and OSHA requirements.

The European Union's Registration, Evaluation, Authorization, and Restriction of Chemicals (REACH) regulation requires manufacturers and importers of chemicals and products to register and disclose substances in products when specific thresholds and criteria are met (European Parliament 2007). The European Chemicals Agency (ECHA) manages REACH processes. Numerous substances will be added to the list of substances already restricted under European legislation; a new regulation emerged when the Restriction on Hazardous Substances (RoHS) in electrical and electronic equipment was adopted in 2003. Requirements for substance use and availability are changing across the globe. Identifying the use of materials in the supply chain that may face restriction is an important part of system life management. System disposal and retirement requires upfront planning and the development of a disposal plan to manage the activities.

An important consideration during system retirement is the proper planning required to update the facilities needed to support the system during retirement, as explained in the California Department of Transportation Systems Engineering Guidebook (2005). Disposal needs to account for environmental and personal risks associated with the decommissioning of a system and all hazardous materials involved. The decommissioning of a nuclear power plant is a prime example of hazardous material control and exemplifies the need for properly handling and transporting residual materials resulting from the retirement of certain systems. The US Defense Logistics Agency (DLA) is the lead military agency responsible for providing guidance for worldwide reuse, recycling, and disposal of military products. A critical responsibility of the military services and defense agencies is demilitarization prior to disposal.

Detailed Design Review

At the end of the detailed design stage, with all the components selected, it is time to review the final configuration before going into production. The detailed design review is a critical checking point, since it is the final review for the system design phase; sometimes it is also called the critical design review (CDR) The purpose of the critical design review is to formally review all the system components, hardware, and software with the real users, for compliance with all the system specifications. The majority of the design data is expected to be fixed, and the system is evaluated in terms of its functionality, producibility, usability (human factors), reliability, and maintainability.. The critical design review usually involves all the stakeholders and the complete set of data, including all the baselines, design drawings, applicable analysis reports and trade studies results, detailed plans on the production, operation, and distribution of the system, and system retirement plans. Human factors professionals need to assess the interaction between the system with the users, in terms of its control and display, dimensions, look and feel, safety features, environment factors, space layouts, training requirements, staffing models, and other human-related factors, under the real operating conditions. The iterative review, once successful, leads to the approval of the final system configuration, and the system is released to the next phase, full-scale production and distribution.

In order to design for manufacturability, everyone in product development team needs to:

C In general, understand how products are manufactured through experience in manufacturing, training, rules/guidelines, and/or multi-functional design teams with manufacturing participation. C Specifically, design for the processes to be used to build the product you are designing: If products will be built by standard processes, design teams must understand them and design for them. If processes are new, then design teams must concurrently design the new processes as they design the product.

Application of Anthropometric Data

One of the most important applications of human factors engineering in systems engineering is to design proper tools, equipment, and workplaces, to fit the physical dimensions of the design to the physical requirements and constraints of human users. A good source for the design comes from quantitative anthropometric data. Anthropometry, originating from the Greek words "anthropos" (meaning "man") and "metron" (meaning "measure"), is a scientific discipline that studies and measures human body dimensions. As mentioned earlier, humans have a large number of variabilities; these arise from different sources, such as age, gender, race, occupation, and generational variability. To account for these variabilities, statistics have to be applied to anthropometry data.

An important consideration during service system retirement or disposal is the proper continuation of services for the consumers of the system. As an existing service system is decommissioned, a plan should be adopted to bring new systems online that operate in parallel with the existing system so that service interruption is kept to a minimum. This parallel operation needs to be carefully scheduled and can occur over a significant period of time.

Examples of parallel operation include phasing in new Air Traffic Control (ATC) systems (FAA 2006), the migration from analog television to new digital television modulation (FCC 2009), the transition to Internet protocol version 6 (IPv6), maintaining water handling systems, and maintaining large commercial transportation systems, such as rail and shipping vessels. The Systems Engineering Guidebook for Intelligent Transportation Systems (ITS) provides planning guidance for the retirement and replacement of large transportation systems. Chapter 4.7 identifies several factors which can shorten the useful life of a transportation system and lead to early retirement, such as the lack of proper documentation, the lack of effective configuration management processes, and the lack of an adequate operations and maintenance budget (Caltrans, and USDOT 2005).

Component selection decisions should be systems requirements driven. The decision-making process usually involves vigorous modeling, simulation, and prototype testing, using systems TPMs as the decision-making criteria.

For example, the impact of the selection of components on system functionality performance, economic merits, systems reliability, maintainability, supportability, usability, and even ease of system retirement are all part of the considerations. Just as mentioned above, the selection process is a combined approach, both from the top down and the bottom up; it is systems requirements driven and, meanwhile, involves familiarizing oneself with the available technology and suppliers. Both are essential for the detailed design of the system components.

Since the 1940s, human factors engineering has demonstrated its value in systems design processes. Traditionally, human factors engineers and professionals are not involved in systems design until some types of system prototypes are developed, as the role of human factors professionals is primarily thought of as back-end verification and evaluation. When systems become large and complex, and many problems are found in the later stages that are extremely difficult and costly to be implemented, there is a need for concurrent integration of human factors engineering into the design process.

Instead of only involving human factors professionals in the later stages of the design, the design team should include all the relevant stakeholders and players from the very beginning, incorporating all requirements at the conceptual stage to avoid the difficulties of unnecessary late changes. Almost every system needs some human factors support; as mentioned above, a system has be used, operated, and maintained by human users. Human factors professionals do not work in an isolated way, but rather team up with other designers and engineers, bridging the gap between the system technical specifications and the intuitive and straightforward user interaction with the system. For many decades, many successful stories have shown the value that human factors has offered to system design. Human factors is consulted at almost every stage of the design. There are many great texts presenting various techniques that human factors professionals apply in systems engineering; by no means do we intend to repeat these techniques in great detail here. Since this book is primarily about systems engineering, we just give readers a brief overview of the subject and present the three most commonly used human factors models in systems engineering application; that is to say, work system design, anthropometry and ergonomics design, and usability engineering in user-centered interaction.

The Good New Days of Product Development Teams

One way that manufacturability can be assured is by developing products in multi-functional teams with early and active participation from Manufacturing, Marketing (and even customers), Finance, Industrial Designers, Quality, Service, Purchasing, Vendors, Regulation Compliance specialists, Lawyers, and factory works. The team works together to not only design for functionality, but also to optimize cost, delivery, quality, reliability, ease of assembly, testability, ease of service, shipping, human factors, styling, safety, customization, expandability, and various regulatory and environmental compliance.

There are many studies have shown that both user testing and heuristic analysis are needed in systems design. These two methods have different strengths; the best evaluation of a user interface comes from applying mul-tiple evaluations.

It is believed that the difference in nature of these two techniques would make them appropriate for different testing purposes. Most of the time, heuristic analysis finds more problems than user testing because it provides more freedom to explore the interface, while user testing needs a well-developed test bed and a more controlled environment (Rogers et al. 2011). Typically, in the earlier design stages, the interface is often not fully developed. Heuristic analysis would be able to project potential usability problems, a quality that user testing lacks. Feedback from heuristic analysis can be used to create a design standard for the rest of the interface. After design improvements are made following the initial heuristic analysis, thor-ough user testing is required, as user testing and heuristic analysis find very different types of problems. User testing is able to assess the usability issues most pertinent to users much more directly, without bothering with basic problems. Feedback from user testing can be used to fine-tune the interface, which is typically done in the later stages of the design process. User testing may also detect potential new usability problems that are the direct result of the design improvement. In other words, both user testing and heuristic analysis are needed for usability in system design. To reap the optimal benefits, it is believed that both user testing and heuristic analysis should be used in different stages of the user interface design process. We believe that heuristic analysis should be implemented in the early stages of the development process, while user testing should be conducted at a later stage.

The system being built might be intended to be one-of-a-kind, or to be reproduced multiple times. The manufacturing system differs for each of these situations and is tied to the type of system being built. For example, the manufacture of a single-board computer would be vastly different from the manufacture of an automobile. Production involves the repeated building of the designed system. Multiple production cycles require the consideration of production machine maintenance and downtime.(seebok)

Manufacturing and production engineering involve similar systems engineering processes specifically tailored to the building of the system. Manufacturability and producibility are the key attributes of a system that determine the ease of manufacturing and production. While manufacturability is simply the ease of manufacture, producibility also encompasses other dimensions of the production task, including packaging and shipping. Both these attributes can be improved by incorporating proper design decisions that take into account the entire system life cycle (Blanchard and Fabrycky 2005).

In many cases, the architecture may have to literally be designed around the off-the-shelf components, but this can provide substantial benefits to the product and the product development process:

Off-the-shelf parts are less expensive to design considering the cost of design, documentation, prototyping, testing, the overhead cost of purchasing all the constituent parts, and the cost of non-core-competency manufacturing. Off-the-shelf parts save time considering the time to design, document, administer, and build, test, and fix prototype parts. Suppliers of off-the-shelf parts are more efficient at their specialty, because they are more experienced on their products, continuously improve quality, have proven track records on reliability, design parts better for DFM, dedicate production facilities, produce parts at lower cost, offer standardized parts, and sometimes pick up warrantee/service costs. Finally, off-the-shelf part utilization helps internal resources focus on their real missions: designing products and building products

Another important aspect in detailed design is the implementation of the team effort.

Systems engineering requires that all the parties are involved at the early stages of the design, to facilitate communication and stay "on the same page." It is at the detailed design stage that the integration of all the different disciplines reaches the highest level of complexity. With a tremendous amount of data and information, and many personnel involved (even in different parts of the world), the coordination and management of the design team members are very critical for the efficiency of the design activities. With the proper design aids and computer-aided systems management tools, it is now easier to synchronize all the design activities and data within a central database structure. Another important aspect of teamwork is to deal with the design changes. It is inevitable that some changes will occur at the different stages of the design process, due to changes of customer requirements, changes in technology/resources, and so forth. As mentioned above, systems engineering design has traceability incorporated within the design structure; in other words, every design outcome and decision made is not random, but rational, primarily based on the evolvement of the system requirements through the design process. At the later stages of the design, such as the detailed design stage, a small change in the system specification could cause a significant impact on the whole system. As systems engineers, we always try to identify the causes for changes as early as possible, since the further downstream the changes occur, the more costly they will become. Regarding the required changes, a responsible design engineer or staff member cannot just simply implement the change; a proper procedure has to be followed to minimize the impact on the whole system that has been developed. When incorporating changes, the control process or protocol has to ensure proper traceability from the originating baseline to another, through a formally prepared engineering change proposal (ECP), reviewed by the control change board (CCB). Each change proposal is carefully reviewed in terms of its importance, priority, and impact on the system, TPMs, and life cycle costs. Once approved, the responsible teams then prepare the necessary document, models, tools, and equipment, incorporating the changes into the system configuration. All the data, models, and reports are documented, as well as the communication logs and memos. This procedure is illustrated by Figure 2.7.

Application to Enterprises disposal and retirement

The disposal and retirement of large enterprise systems requires a phased approach, with capital planning being implemented in stages. As in the case of service systems, an enterprise system's disposal and retirement require parallel operation of the replacement system along with the existing (older) system to prevent loss of functionality for the user. See the OSHA standard (1996) and EPA (2010) website for references that provide listings of hazardous materials. See the DLA Disposal Services website for disposal services sites and additional information on hazardous materials.

The detailed design starts with the two baselines developed from the previous design stages, the functional baseline (Type A specification) from the conceptual design stage and the allocation baseline (Type B specification).

These two baselines are normally at system level, and describe the overall system structure/configuration. At the detailed design stage, all the system components must be finalized, including hardware, software, users, assemblies/packages, system requirements, and specifications, which all need to be further evolved to the lowest level. On the one hand, the analysis process is similar to that of the conceptual design and preliminary design stages; system designers need to iteratively perform the allocation and decomposition analysis, to derive the requirements and related TPMs for the lowest level of components. This is, again, a top-down process; however, since all the components need to be specified and procured or developed in the detailed design stage—and depending on the complexity of the system, the majority of the components most likely need to be procured from external suppliers or using COTS items—it is imperative to understand what is available "out there" before a selection decision can be reached. At the detailed design stage, the top-down process is usually combined with a bottom-up process, to get a complete picture of what is needed and what is available, to obtain the most efficient design solutions.

Human factors engineering, according to Chapanis (1996),

is not the same as human factors. Human factors is a "body of information about human abilities, human limitations, and human characteristics that is relevant to design," while human factors engineering is the "application of human factors information to the design of the tools, machines, systems, tasks, jobs and environments for safe, comfortable and effective human use." Based on these definitions, human factors is an applied science discipline while human factors engineering refers to engineering. As the foundation of human factors engineering, human factors study humans, utilize knowledge discovered from biology, physiology, psychology, and life sciences, and derive the information that is relevant to the interaction between human and engineered systems. This section is not intended to give a comprehensive review of the human factors body of knowledge, as human factors cover a wide range of topics that exceeds the scope of this book. There are many excellent references available for a more in-depth review, such as Wickens et al.'s (2003) text on human factors engineering

Sustainable development or green engineering is

one of the most important types of development, depending on the different kinds of components. There may be different end uses for the components: reuse, remanufacturing, or recycling. Reuse is the highest level at which a system is preserved—usually a nonfaulty system—to keep it at a degraded function level to prolong its life cycle (one can think of this as a semiretirement phase). For example, older computer systems may not be fast enough for laboratory scientific computation purposes, but since they are still functional, they may be donated to charity for educational purposes in schools and offices. Remanufacturing (also known as closed-loop recycling, or sometimes called refurbishing) implies a series of activities to put a retired system back into use in its complete form, by repairing or replacing faulty parts, to become operational again. Recycling is a process that retrieves useful raw materials, to reduce waste and the cost of procuring similar fresh new materials. It is believed to benefit the environment by reducing pollution and saving the energy consumption of obtaining new materials. Although a common practice for a long time, it did not catch people's attention until the twentieth century; as an outcome of the industrial revolution, productivity has increased tremendously, as has demand for materials. With more humanmade systems, the by-products, waste, and pollution from the production process has influenced our natural environment, which has caused many problems for human health and quality of life. Sustainable development and green engineering of systems have become more and more important for assessing their effectiveness. With more customer awareness and globalization of system development, green engineering has become an essential part of system competitiveness. The life cycle consideration of system design enables designers to take systems retirement into account in the early phases of the design process—assembling it in a way which will simplify its disassembly—to facilitate the system being phased out and retired, to impact the environment at a minimum level, and meanwhile save internal costs and energy. Where the system is retired only partially, its materials will be recycled or reused for the next generation of the system and some of the concepts will be carried over to the next generation, as part of the requirements for the new system; at that time another life cycle will begin.

There are many reasons for system retirement

the majority of these are incompatibility with emerging technology, discontinuation of supply of materials, changes to legislation and regulations, new trends in customer demand, and so on. At the system retirement stage, the system is often characterized by a reduction in the number of customers, increasing numbers of system problems, high costs, and difficulty of maintenance.

Upper limit, on the other hand, refers to

the maximum value that system cannot exceed, otherwise a small user would have difficulties using the sys-tem. An example of the upper limit is the weight of a tool to be carried by a human, which has to be below a certain level (the upper limit) so that the smallest user is able to carry it. Usually a low percentile value (i.e., the 5th percentile) is used to set the upper limit.

The Rule of 10

the part itself X at sub-assembly 10 X at final assembly 100 X at the dealer/distributor 1,000 X at the customer 10,000 X level of completion-c-> cost to repair and detect FM Guideline P10) Minimize Setups. For machined parts, ensure accuracy by designing parts and fixturing so all key dimensions are all cut in the same setup (chucking). Removing the part to re-position for subsequent cutting lowers accuracy relative to cuts made in the original position. Single setup machining is less expensive too. DFM Guideline P11) Minimize Cutting Tools. For machined parts, minimize cost by designing parts to be machined with the minimum number of cutting tools. For CNC "hog out" material removal, specify radii that match the preferred cutting tools (avoid arbitrary decisions). Keep tool variety within the capability of the tool changer. DFM Guideline P12) Understand tolerance step functions and specify tolerances wisely. The type of process depends on the tolerance. Each process has its practical "limit" to how close a tolerance could be held for a given skill level on the production line. If the tolerance is tighter than the limit, the next most precise (and expensive) process must be used. Designers must understand these "step functions" and know the tolerance limit for each process.

Lower limit refers to

the physical size of the system, not the human user per se. The lower limit implies that the system cannot be smaller, otherwise it would be unusable by a larger person. An example of the lower limit would be the height of a doorway, or the sitting weight capacity strength of a chair. In the case of the lower limit, the high percentile value (i.e., the 95th percen-tile) is used to determine this limit.

In a typical user test, the experiment includes three phases in a session:

the planning phase, the testing phase, and the reporting phase. During the planning phase the testing procedure will be explained to the subjects using a set of training scenarios. The post evaluation questionnaires to which they are supposed to respond are also explained, if there are any after the test. The post evaluation questionnaire deals with users' general impression of the system, usage of terminology, information content, and information structure. During the testing, problems and feedback from the users will be recorded. In the post testing session, users are given the opportunity to provide feedback and opinions regarding the problems that they have faced during the test. This session also serves as an opportunity for the observer to clarify any doubts that they might have had during the test with regard to the observations made. In the reporting stage, inherent problems and inconsistencies, according to post evaluation questionnaires, interviews, and expert discussions, are identified. Problems are usually identified using standard statistical methods, such as descriptive statistics (mean or standard deviation, for example) or analysis of variance (ANOVA) if multiple designs are being compared.

According to the INCOSE Systems Engineering Handbook (2012), "The purpose of the disposal process is (seebok)

to remove a system element from the operation environment with the intent of permanently terminating its use; and to deal with any hazardous or toxic materials or waste products in accordance with the applicable guidance, policy, regulation, and statutes." In addition to technological and economical factors, the system-of-interest (SoI) must be compatible, acceptable, and ultimately address the design of a system for the environment in terms of ecological, political, and social considerations.

Product or service disposal and retirement is an important part of system life management. At some point, any deployed system will become one of the following: (seebok)

uneconomical to maintain; obsolete; or unrepairable. A comprehensive systems engineering process includes an anticipated equipment phase-out period and takes disposal into account in the design and life cycle cost assessment. A public focus on sustaining a clean environment encourages contemporary systems engineering (SE) design to consider recycling, reuse, and responsible disposal techniques. (See Environmental Engineering for additional discussion.)

For the design to improve usability, there is no set template to follow as every system has its unique design features; one needs to tailor usability principles to accommodate different types of systems. Nielsen (1993) summarized five main elements or principles for usability design:

• Learnability: Learnability refers to how easy the system is for users to learn the functionality and how easy it is to accomplish basic tasks for the first time. Learnability implies a good match between users' expectations and experience to facilitate learning to use the system. • Efficiency: Efficiency means that once users have learned the system, how efficiently can they perform tasks in terms of time and errors? • Memorability: Memorability aspects of usability refers to the level of retention of learned tasks performance, especially when users come back to use the system after a period of not using it; how easily can they recall what they learned about their interaction with the system to reestablish proficiency? • Errors: A system with good usability should enable the users to min-imize the possibilities of making errors, in terms of how many errors users make, how severe those errors are, and how easily users can recover from those errors. • Satisfaction: Satisfaction refers to the look and feel of the interface to the user; in other words, how pleasant and attractive is it to use the design? Satisfaction is usually measured subjectively, using methods such as surveys, questionnaires, interviews, and focus groups. As part of the system requirements, requirements concerning system usability are collected in the early stages of the design, as, following the top-down process, these requirements are gradually translated into design specifications, similar to other types of systems requirements, as mentioned in Chapter 3. The functionalities of user interaction, such as menus and con-trols, are determined through an iterative process, from concepts to compo-nents, by using the various levels of prototyping and evaluation, just as for the rest of the system requirements.

Usability engineering contributes to system engineering mainly in the area of the testing phases. Design requirements concerning usability vary a great deal among different groups of users; this makes an empirical approach more appropriate when specifying usability issues. Ever since the concept of "usability" was introduced into interface design, many researchers have completed particular research and experimentation on usability evaluation. Typically, user testing is driven by scenario-based tasks that users need to perform. For example, the following list illustrates a sample usability testing scenario list for an online voting system interface design:

• Scenario 1: Vote registration • Scenario 2: Reading and understanding a specific item on a ballot • Scenario 3: Use of tools and navigation through different levels of the system • Scenario 4: Review and modify voting choices • Scenario 5: Exit the system and confirm the vote