Engineering Design GE121 The Design Process

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Engineering DesignGE121The Design Process

• Lecture 3C

2
How A Design Process Unfolds

• We often begin with many questions about the
  clients needs and requirements, and about the
  process itselfExample Developing a new safe
  ladder project
• How is the ladder to be used?
• How much should it cost?
• What does safe mean?
• What is the market for this ladder?

3
How A Design Process Unfolds (continued)

• We can organize most of these questions and
  concerns into certain areas
• 1 . Clarifying objectives
• How is the ladder to be used?
• How much should it cost?
• 2. Establishing user requirements
• Should the ladder be portable?
• How much can it cost?
• 3 . Identifying constraints
• How is safety defined?
• What is the most the client is willing to spend?

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How A Design Process Unfolds (continued)

• 4. Establishing functions
• Can ladder lean against a support surface?
• Must ladder support someone carrying something?
• 5. Establishing specifications
• How much weight should a safe ladder support?
• What is allowable load on each step?
• How high should user of ladder be able to reach?
• 6. Generating alternatives
• Could ladder be an extension ladder or step
  ladder?
• Could material be wood/aluminum/fiberglass?

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How A Design Process Unfolds (continued)

• 7. Modeling and analyzing alternatives
• What is maximum stress in step under design
  load?
• How does loaded step bending vary with material?
• 8. Testing and evaluating
• Can someone on ladder reach specified height?
• Does ladder meet Occupational Health and Safety
  specs?
• 9. Refining or optimizing the design
• Is there a more economic design option?
• Is there a more efficient (material consumption)
  design?

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How A Design Process Unfolds (continued)

• 10. Documenting the design
• Setting fabrication specifications
• Justification for design specifications
• It is the organizing of these activities that is
  at the heart of models of the design process.

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Discussion about Questions

• Project typically begins with verbal description
  stating desired features of
• Function
• Form
• Intent, or
• Legal requirement
• Designers job to translate these into more
  concrete objectives or the right language.
  This is an essential element of design

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Case Study

• Familiarization with Case Study (Text 2.5 p38)
• Design of a microlaryngeal surgical stabilizer
  (device to stabilize instruments to assist
  surgeons operating on vocal cords)
• Laryngeal (vocal cord) surgery often required to
  remove polyps or cancerous tumors
• Important to accurately and completely remove
  lead cells, yet not damage vocal cords
• Surgeons now access the vocal cords through the
  mouth, rather than cutting open throat (longer
  distance) so hand tremors must be controlled to
  make accurate/precise cuts
• Tremors (natural, small scale shaking of hands)
  in surgeons hands are amplified by foot-long
  instruments

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Case Study (continued)

• Initial Problem Statement
• Provided by Dr. Brian Wong, Beckman Laser
  Institute of the University of California Irvine
• Surgeons who perform vocal cord surgery currently
  use microlaryngeal instruments, which must be
  used at a distance of some 12-14 in. to operate
  on surfaces with very small structure (1-2 mm).
  The tremor in the surgeons hand can become quite
  problematic at this scale. A mechanical system
  to stabilize the surgical instruments is
  required. The stabilization system must not
  compromise the visualization of the vocal cords
• Following interviews with surgeons, and basic
  research on laryngeal surgery, one of the design
  groups developed a Refined Problem Statement

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Case Study (continued)

• Revised Problem Statement
• Microlaryngeal surgery seeks to correct
  abnormalities in the vocal cords. The
  abnormalities, such as tumors and cysts, are
  often 1-2 mm in size and are typically removed
  from the vocal cords, which are only 0.15 mm in
  size. During the operation, the surgeon must
  control his or her surgical instruments from a
  distance of 300-360 mm (12-14 in) due to the
  difficulties in accessing the vocal cords. At
  this small scale, the physiological tremor in the
  surgeons hand can be problematic. Design a
  solution that minimizes the effects of hand
  tremors in order to reduce unintentional
  movements at the distal end of the instrument to
  an amplitude of no more than 1/10 of a
  millimeter. The solution must not compromise
  visualization of the vocal cords

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Case Study (continued)

• Notes on the Revised Problem Statement
• More detail (that is relevant to the design)
• Identifies size of vocal cords
• Defines acceptable amplitude of unintentional
  movement of instruments to 0.1 mm
• Includes all dimensions in common units (mm)
• Removes the implied mechanical solution

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Case Study (continued)

• Moving toward developing Objectives
• Start with list of attributes that client hopes
  for in the design. Work with client to arrange
  attributes in some order of priority
• Use Attributes to create a list of objectives
  that can be organized into an objective tree

Fig. 2.6 p41
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Case Study (continued)

• Refining Objectives into Constraints
• A Constraint list for the device
• It must be made of non-toxic materials
• It must be made of materials that do not corrode
• It must be sterilizable
• Its cost must not exceed 5,000
• It must not have sharp edges
• It must not pinch or gouge the patient
• It must be unbreakable during normal surgical
  procedures
• Some that stand out cost limit, no sharp edges,
  many are material related

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Case Study (continued)

• Creating Metrics for Objectives
• Rate how each design meets Objective
• Metrics for two of the Objectives, with Units
• Objective Minimize viewing obstruction
• Units Rating percentage of view blocked, on a
  scale of 1(worst) to 10 (best)
• Metric Measure the percentage of view blocked
  by the instrument. On a linear scale from
  1(100) to 10 (0), assign ratings to the of
  view blocked
• Objective Minimize the cost
• Units Rating on a scale of 1 (worst) to 5
  (best)
• Metric Determine a bill of materials, Estimate
  labor, calculate total cost 4,000-5,000
  receives 1 1-1,000 receives a 5

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Activity

• Continue developing your sketching ability
• Over the next week, when you need a break from
  your thinking homework, take some time to
  sketch objects.
• You will need to do sketching when you start your
  real projects next week
• Obtain a log book for next class
• Each student must obtain a Log Book to use
  beginning Monday of next week, when you start
  your Project. Use a Physics Note Book (Black or
  Blue) that can be obtained from the bookstore.
  We will post rules and examples for Log Book
  standards in an upcoming lecture