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					                            Engineering Design
Microlaryngeal Stabilizer




                                       GE121



                             Case Study – Microlaryngeal
                                     Stabilizer



                                    GE 121 – Engineering Design - 2010
                                                 Case Study
                            Familiarization with Case Study (Text 2.5               p38)
Microlaryngeal Stabilizer




                              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


                                                GE 121 – Engineering Design - 2010
                                         Case Study (continued)
                            Initial Problem Statement
                               Provided by Dr. Brian Wong, Beckman Laser Institute
Microlaryngeal Stabilizer




                                 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
                                 surgeon’s 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

                                               GE 121 – Engineering Design - 2010
                                        Case Study (continued)
                            Revised Problem Statement
                              Microlaryngeal surgery seeks to correct abnormalities
Microlaryngeal Stabilizer




                               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 surgeon’s 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

                                              GE 121 – Engineering Design - 2010
                                       Case Study (continued)
                            Notes on the Revised Problem Statement
                              More detail (that is relevant to the design)
Microlaryngeal Stabilizer




                                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




                                            GE 121 – Engineering Design - 2010
                                             Case Study (continued)
                            Moving toward developing Objectives
                              Start with list of attributes that client hopes for
Microlaryngeal Stabilizer




                               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

                                                GE 121 – Engineering Design - 2010
                                        Case Study (continued)
                            Refining Objectives into Constraints
Microlaryngeal Stabilizer




                              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
                                             GE 121 – Engineering Design - 2010
                                         Case Study (continued)
                            Creating Metrics for Objectives
                              Rate how each design meets Objective
                              Metrics for two of the Objectives, with Units:
Microlaryngeal Stabilizer




                                 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

                                               GE 121 – Engineering Design - 2010
                                                 Case Study
                             Familiarization with Case Study (cont’d) (Text 2.5)
                               Have previously determined metrics for indicating the
Microlaryngeal Stabilizer




                                degree to which potential designs, or schemes, satisfy
                                the objectives
                               Other Tools allow us to determine the relative
                                importance of objectives, and required functions, which
                                are also important when it’s time to select the Final
                                Design
                               These tools will be discussed in detail later, but we will
                                examine them quickly now because they may be
                                helpful in determining the relative importance of
                                objectives, as well as any necessary functions for your
                                Project Proposal
                                                GE 121 – Engineering Design - 2010
                                        Case Study (cont’d)
                             Pairwise Comparison Charts
                              Allows Rank Ordering of Objectives in terms of
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                               their relative importance
                              Result from one design group is shown




                              Shows most important is reduction in surgeon’s
                               tremor, while least important is cost
                              Helps focus design attention and also, to see if
                               our intuition is correct
                                            GE 121 – Engineering Design - 2010
                                         Case Study (cont’d)
                             Functions and Performance Specifications
Microlaryngeal Stabilizer




                              Required functions can be determined by
                               using one or more of the related tools, which
                               are discussed in more detail in section 4.1,
                               some of which include:
                                Black Box (looks at functional Inputs/Outputs, but
                                 obscures process details)
                                Glass Box (similar to black box, but also allows
                                 observation of some relevant internal details)
                                Functions-Means Tree


                                             GE 121 – Engineering Design - 2010
                                        Case Study (cont’d)
                            Functions and Performance Specifications
Microlaryngeal Stabilizer




                            One sample list of functions for the
                             microlaryngeal stabilizer states that it must:
                              Stabilize the instrument
                              Move the instrument
                              Stabilize the distal end of the instrument
                              Reduce muscle tension of the surgeon during
                               surgery (or reduce shaking tremors)
                              Stabilize itself

                                           GE 121 – Engineering Design - 2010
                                         Case Study (cont’d)
                            Functions and Performance Specifications
Microlaryngeal Stabilizer




                            Performance Specifications (written for the
                             first function)
                              Function: Stabilize the Instrument
                              Performance Specification: This function is not
                               achieved if the design cannot reduce the
                               amplitude of a trembling hand to less than 0.5
                               mm. It is optimally achieved if it controls the
                               amplitude of a trembling hand to make it less
                               than 0.05mm. It is overly restrictive if it inhibits
                               or disallows any instrument or hand use.

                                             GE 121 – Engineering Design - 2010
                                        Case Study (cont’d)
                             Functions / Means – Morphological Chart
                              A Morphological Chart requires you to select
Microlaryngeal Stabilizer




                               one item from each row to produce a potential
                               instance, allowing a methodical search through
                               all of the possible changes/options (morphs)
                              Chart shown has Functions on one axis, and
                               the Means to achieve that Function on the
                               other axis
                              Effectively tells us how large a design space
                               we are working in


                                           GE 121 – Engineering Design - 2010
                                       Case Study (cont’d)
                             Functions / Means – Morphological Chart
Microlaryngeal Stabilizer




                                         GE 121 – Engineering Design - 2010
                                       Case Study (cont’d)
                             Functions / Means – Morphological Chart
                              One candidate design has the instrument held in
Microlaryngeal Stabilizer




                               and moved by the surgeon’s hands, with distal
                               support provided by crosswires, which are attached
                               directly to the laryngoscope. The surgeon uses a
                               forearm rest to reduce tremor-inducing muscle
                               tension
                              A second design alternative has the instrument
                               supported on a stand, moved by a system of pulleys,
                               and supported by the stand itself. The instrument
                               stand removes the need for the surgeon to operate
                               in a fixed position, which thus reduces tremor-
                               inducing muscle tension

                                          GE 121 – Engineering Design - 2010
                                         Case Study (cont’d)
                             Decision (Selection) Matrix
Microlaryngeal Stabilizer




                              These 3 potential designs satisfy all constraints
                                            GE 121 – Engineering Design - 2010
                                       Case Study (cont’d)
                             Decision or Selection Matrix – Find BEST !
Microlaryngeal Stabilizer




                                          GE 121 – Engineering Design - 2010
                                        Case Study (cont’d)
                             Testing of Design Concepts – an input to
                             the Decision Matrix
Microlaryngeal Stabilizer




                              Tracing a square with and without an
                               instrument stand

                                           GE 121 – Engineering Design - 2010