III. B. Parts and Systems Management
III. A. 12. Reliability Apportionment or Allocation Techniques
III. Reliability in Design and Development
A. Reliability design techniques
12. Reliability apportionment (allocation) techniques (Analyze)
Use these techniques to specify subsystem and component reliability requirements.
Breaking down system reliability requirements provides necessary guidance across the team.
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Additional References
Reliability Allocations (article)
Reliability Apportionment (article)
Quick Quiz
1-46. A system made up of four series components has a design reliability set to .97. If three of the
components have reliabilities apportioned to them of 0.992, 0.994, and 0.991, what should the
reliability apportionment for the fourth component be?
(A) 0.970
(B) 0.990
(C) 0.993
(D) 0.997
(C) 0.993
The formula for a series system and a little algebra is all that is needed here. The formula to determine system reliability given a series system is
$$ {{R}_{sys}}={{R}_{1}}\times {{R}_{2}}\times {{R}_{3}}\times {{R}_{4}}$$
Since we’re given Rsys and three of the four other reliability values, solve for the missing value, say R4
$$ {{R}_{4}}=\frac{{{R}_{1}}\times {{R}_{2}}\times {{R}_{3}}}{{{R}_{sys}}}$$
Plugin the values for the three component reliability values and divide the system reliability to find the minimum reliability value of the last component.
$$ {{R}_{4}}=\frac{0.992\times 0.994\times 0.991}{0.97}=0.993$$
III. A. 11. Design for X – DFX
III. Reliability in Design and Development
A. Reliability design techniques
11. Design of X (DFX)Â (Apply)
Apply DFZ techniques such as design for assembly, testability, maintainability environment (recycling and disposal), etc., to enhance a product’s producibility and serviceability.
There are many factors influencing the design, many enhance reliability.
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Additional References
Design for Assembly (article)
SOR 041 Design for Reliability and Testing (podcast)
8 Factors of Design for Maintainability (article)
Descriptive Models of the Design Process (article)
Understanding the Design Process (article)
Quick Quiz
1-82. Which of the following statements is true about techniques of design control?
(A) Design control techniques are applicable generally throughout industry.
(B) Design control techniques are unique to military applications.
(C) Design control techniques are limited to hardware-manufacturing enterprises.
(D) Design control techniques are too expensive for general application.
(A) Design control techniques are applicable generally throughout industry.
Even when not documented or a formal process, the product generation process generally starts with an idea, then proceeds into design and development, assembly or manufacturing, then distribution. The product lifecycle and specifically the control of the design process generally uses a phase gate approach with reviews at the end of each phase assessing readiness to proceed to the next phase.
Your organization may have different names for the process or phases of the process, yet the design control techniques apply across industries and types of products.
III. A. 10. Human Factors
III. Reliability in Design and Development
A. Reliability design techniques
10. Human factors (Understand)
Describe the relationship between human factors and reliability engineering.
Does your system play well with humans?
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Additional References
General Human Factors Design Principles (article)
Comparing Human and Machine Capability (article)
Human Factor Considerations (article)
Quick Quiz
1-98. In an automobile factory in with a highly repetitive operations, how should this operation be assigned?
(A) A machine should perform all the operations.
(B) A human operator should perform all the operations.
(C) A machine and a human operator should perform the operations alternately.
(D) A human operator should be assisted by a computer for the operations.
(A) A machine should perform all the operations.
Machines are very good at repetitive, precise, and fast operations. Humans are not. If done by a person a good practice is to rotate the people though the position regular within a shift of prevent boredom and errors, plus to minimize the risk of repetitive motion injures.
- For critical functions, what is the human line-of-sight angle specified by MIL-STD-1472?
(A) 7.5 degrees
(B) 15 degrees
(C) 30 degrees
(D) 45 degrees
(B) 15 degrees
This is tough if you do not know the standard or have experience working with human factor considerations. You can quickly narrow done the options by assuming the requirements expect the person to not have to strain their eyes or turn their head (I do not know if this true or now… just guessing). Either you have the standard available – which for similar problems that dive into very specific details you will not have those documents available (most likely) is to make an educated guess.
1-104. Why are human factors important when designing for reliability?
I. Â because habits can sometimes be difficult to change
II. Â because weak components must be easily replaceable
III. because environmental conditions can influence performance
IV. Â because age and skill can limit one’s ability to use equipment
(A) I and IV only
(B) II and III only
(C) II, III, and IV only
(D) I, II, III, and IV
(D) I, II, III, and IV
Human factors including any interaction of a human with the equipment, thus includes installation, operation, and maintenance.
III. A. 9. Reliability Optimization
III. Reliability in Design and Development
A. Reliability design techniques
9. Reliability optimization (Apply)
Use various approaches, including redundancy, derating, trade studies, etc., to optimize reliability within the constraints of cost, schedule, weight, design requirements, etc.
Reminds me of the Oliver Wendall Holmes poem, The Wonderful One Hoss Shay – perfect reliability for 100 years and a day. We can make a system better such that every part is as strong as every other part.
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Additional References
What is Reliability Optimization? (article)
Solving a Reliability Optimization Example (article)
Product Reliability Design Guidelines: The Design for Reliability Manual (article)
The Derating & Safety Margin Manual (article)
Derating Value (article)
Product Reliability Design Guidelines: The Design for Reliability Manual (article)
Standby Redundancy, Equal Failure Rates, Imperfect Switching (article)
Standby Redundancy with Equal Failure Rates and Perfect Switching (article)
Quick Quiz
1-13. Which of the following would not enhance software reliability?
(A) structured programming
(B) redundant code programming
(C) programming for fault tolerance
(D) modular programming
(B) redundant code programming
Replicating the same code would replicate any faults within the code. Instead use redundancy with program diversity, where the elements in parallel are different sets of code, the employ a voting routine to determine the correct result if the alternative sets of code do not agree.
Structured programing constrains the programmers to use specific clear, well-defined design practices. Fault tolerance programming attempts to identify and mitigate, or if possible avoid, software failures. Modular programs breaks down complex software projects into smaller, easier to define portions of code, making debugging less complex.
O’Connor and Kleyner, Practical Reliability Engineering section 10.5 page 268 – 270 5th ed.
III. A. more Reliability Design Techniques
III. A. 8. Fault Tolerance
III. Reliability in Design and Development
A. Reliability design techniques
8. Fault Tolerance (Understand)
Define and describe fault tolerance and the reliability methods used to maintain system functionality.
When something bad happens how does your system respond?
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Additional References
Deciding What Should Have Fault Tolerance (article)
Fault Tolerance Basics (article)
The Downside of a Fault Tolerant System (article)
Quick Quiz
III. A. 7. l. Robust Design
III. Reliability in Design and Development
A. Reliability design techniques
7. Design of Experiments (Analyze)
Plan and conduct standard design of experiments (DOE) (e.g., full-factorial, fractional factorial, Latin square design). Implement robust-design approaches (e.g., Taguchi design, parametric design, DOE incorporating noise factors) to improve or optimize design.
Robust means the design will work over a large and sometimes unexpected range of stresses.
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Additional References
Quick Quiz
1-38. Identify which of the following statements is not true about the Taguchi DOE approach.
(A) It includes the concept of loss function in factorial experiments.
(B) The loss function is assumed to be a step function relative to the specification limits.
(C) Losses are assumed to occur when a process fails to meet a target value.
(D) Losses are assumed to be due to variability within the process.
(B) The loss function is assumed to be a step function relative to the specification limits.
There are two tenets emphasis by Taguchi’s approach. 1. Reducing product variation reduces the loss to society. 2. A proper development strategy includes intentionally reducing variation.
The Taguchi design of experiments approach uses orthogonal arrays to optimize performance or minimize cost with equivalent performance. The concept of the loss function is the squared deviation of the objective characteristic form it’s target value, it is a continuous parabolic function and does not include the tolerances or specification limits.
All of the other statements are true about the Taguchi DOE approach.
III. A. 7. k. A Simple Taguchi Example
III. Reliability in Design and Development
A. Reliability design techniques
7. Design of Experiments (Analyze)
Plan and conduct standard design of experiments (DOE) (e.g., full-factorial, fractional factorial, Latin square design). Implement robust-design approaches (e.g., Taguchi design, parametric design, DOE incorporating noise factors) to improve or optimize design.
Sometimes working through an example helps to get the concepts.
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Additional References
Quick Quiz
III. A. 7. j. Various Designs
III. Reliability in Design and Development
A. Reliability design techniques
7. Design of Experiments (Analyze)
Plan and conduct standard design of experiments (DOE) (e.g., full-factorial, fractional factorial, Latin square design). Implement robust-design approaches (e.g., Taguchi design, parametric design, DOE incorporating noise factors) to improve or optimize design.
Classical DOEÂ includes a vast range of approaches such that you will find a design to meet your experimental needs.
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Additional References
Quick Quiz
III. A. 7. i. Classical DOE
III. Reliability in Design and Development
A. Reliability design techniques
7. Design of Experiments (Analyze)
Plan and conduct standard design of experiments (DOE) (e.g., full-factorial, fractional factorial, Latin square design). Implement robust-design approaches (e.g., Taguchi design, parametric design, DOE incorporating noise factors) to improve or optimize design.
Classical DOE, best described by Box, Hunter, and Hunter are very powerful tools.
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Additional References
Quick Quiz
III. A. 7. h. Adjusting the Design
III. Reliability in Design and Development
A. Reliability design techniques
7. Design of Experiments (Analyze)
Plan and conduct standard design of experiments (DOE) (e.g., full-factorial, fractional factorial, Latin square design). Implement robust-design approaches (e.g., Taguchi design, parametric design, DOE incorporating noise factors) to improve or optimize design.
There are ways to alter the array to customize the design for your particular situation.
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Additional References
Quick Quiz
III. A. 7. g. Interactions and Confounding
III. Reliability in Design and Development
A. Reliability design techniques
7. Design of Experiments (Analyze)
Plan and conduct standard design of experiments (DOE) (e.g., full-factorial, fractional factorial, Latin square design). Implement robust-design approaches (e.g., Taguchi design, parametric design, DOE incorporating noise factors) to improve or optimize design.
Designing your experiment should include considerations of how the variables may create results due to interactions or be difficult to isolate due to confounding.
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Additional References
Confounded DOEÂ (article)
Quick Quiz
III. A. 7. f. Dealing with Measurements
III. Reliability in Design and Development
A. Reliability design techniques
7. Design of Experiments (Analyze)
Plan and conduct standard design of experiments (DOE) (e.g., full-factorial, fractional factorial, Latin square design). Implement robust-design approaches (e.g., Taguchi design, parametric design, DOE incorporating noise factors) to improve or optimize design.
The process of running a set of experiments creates data via measurements.
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Additional References
Quick Quiz
