GE 121 – Engineering Design Engineering Design GE121 Functions & Specifications Lecture 6B

GE 121 – Engineering Design Functions and Specifications  Moving from the language of the client to the language of the engineer  Functions  Tell us what the designed object must do to realize the stated objectives  Have to establish which functions have to be performed before we can specify how well they must be performed  Performance Specifications  Tell us how well the designed object must do something  Will look at various tools and techniques for deriving them

GE 121 – Engineering Design Identifying Functions to Realize Objectives  Bookcase example  A child may say that a bookcase doesn’t ‘do’ anything – it just sits there  Engineer would see: Resists weight of books Dividers may be used to organize May be visually appealing  An engineer looking at designed objects is educated to see that artifacts do things even when they just sit there  There are consequences for engineers that fail to understand / design for ALL functions in a design  Forensic Engineering (study of failure) has many examples!

GE 121 – Engineering Design What are Functions?  Engineering Functions  Like mathematical or business functions Specify how some set of inputs is transformed into a set of outputs  Usually a verb (action word) – noun pair Lift a weight Light a fireplace  Several important types of functions to consider Basic Functions Secondary Functions – Required Secondary Functions – Unwanted Secondary Functions  Avoid tying a function to a particular solution

GE 121 – Engineering Design What are Functions? (continued)  Example – Overhead Projector  Basic Functions  Specific work that designed artifact is intended to accomplish  Example - Project Images  Secondary Functions  Any other function OR  Those that result from the basic function  Required Secondary Functions Those secondary functions that are needed for the basic function to be accomplished Example - Convert energy, generate light, focus image  Unwanted Secondary Functions Functions related to undesired byproducts of either basic or secondary functions Example - Generate Heat, Generate Noise Unwanted secondary may require new Basic (quiet, dissipate heat)

GE 121 – Engineering Design How Do We Identify/Specify Functions?  Several techniques commonly used to identify and specify functions  Enumeration  Simply making a list of the functions  Works well if we’re already familiar with artifact/problem  Some tricks to help extend an enumerated list (see next slide)

GE 121 – Engineering Design How Do We Identify/Specify Functions? (cont’d) Imagine if it suddenly vanished – Example: A Bridge –Cars would fall into river  Function = Support loads –If no abutments, deck / superstructure would collapse  Function = Support own weight (1907 Quebec Bridge – 75 fatalities - our iron rings) –If no on/off ramps – no traffic  Function = Connect to roadways –If opposing traffic in same lane – accidents  Function = Separate traffic by direction Consider how an object might be used and maintained over its lifetime –May require bridge to be painted  Function = Provide maintenance workers access to all part of structure (design ladders, catwalks, elevators etc.)

GE 121 – Engineering Design How Do We Identify/Specify Functions? (cont’d)  Beverage container design example (Functions) Contain liquid Get liquid into container (fill the container) Get liquid out of the container (empty the container) Close the container after opening (if it is to be used more than once) Resist forces induced by temperature extremes Resist forces induced by handling in transit Identify the product  Getting liquid into and out are distinct functions – may be identified by examining life cycle  Designer needs a verb-noun pair for each function

GE 121 – Engineering Design How Do We Identify/Specify Functions? (cont’d)  Black Boxes/Transparent Boxes  Two methods of associating inputs and outputs  Black Boxes After indicating the system boundary, all the inputs are shown going into (left) and outputs coming out of (right) the system Include ALL inputs/outputs including undesirable byproducts from secondary functions Fig. 4.1(a) p82

GE 121 – Engineering Design How Do We Identify/Specify Functions? (cont’d)  Transparent Boxes Cover of the box is then “removed”, and the designer can focus attention on how the various inputs are transformed Process can be repeated iteratively (black boxes shown inside transparent boxes) until designer is satisfied that a suitable means of realizing functions can be developed Fig. 4.1(b) p83

GE 121 – Engineering Design How Do We Identify/Specify Functions? (cont’d)  Must be careful with setting boundaries or limits with both black boxes and transparent boxes  Requires tradeoffs  Too wide – may specify functions that are beyond our control (include AC power?)  Too narrow – may limit scope of the design (speakers included?)

GE 121 – Engineering Design  Functions, Means and your Project  Means are methods of achieving functions, and they imply solutions  Don’t propose solutions to your Project at this point in the process  Only examine means that have been used in other designs when looking at current State-of-the-Art or Reverse Engineering, at this point in your project  Means will be examined AFTER the Midterm Report has been submitted How Do We Identify/Specify Functions? (cont’d)

GE 121 – Engineering Design How Do We Identify/Specify Functions? (cont’d)  Function-Means Trees  A graphical representation of a design’s basic and secondary functions  Top level specifies functions to be met For each function, several means of accomplishing the function are listed Subsidiary functions that result from that are listed below the means Continues until the designer is satisfied that all the functions have been developed  Can list functions that are common to most (or all) means, and which functions are related to specific means  Begins the process of associating what we must do with how we might do it

GE 121 – Engineering Design How Do We Identify/Specify Functions? (cont’d)  Function-Means Tree for cigarette lighter Fig. 4.2 p85

GE 121 – Engineering Design How Do We Identify/Specify Functions? (cont’d)  Some cautions – Function-Means trees NOT a substitute for either formulating the problem or for generating solutions Should not be used without using some of the other tools listed earlier. Don’t adopt a tool because it fits with your preconceived idea of a solution

GE 121 – Engineering Design How Do We Identify/Specify Functions? (cont’d)  Dissection and Reverse Engineering  Designer can often find an existing artifact that performs some or all aspects of the basic function  Artifact can then be examined with the question, “what does this do?” being asked of all the components of the artifact  Dissecting, deconstructing or disassembling it to find out how and why it works is called Reverse Engineering

GE 121 – Engineering Design How Do We Identify/Specify Functions? (cont’d)  May not be able to use the design May not do all things that we require May not do them well May be too expensive May be patented May be our competitor’s design  But may allow us insight into our problem by looking at how others have solved the same, or similar, problems  Look at Means, and try to determine function May press buttons, or test, and try to determine as many functions as possible

GE 121 – Engineering Design How Do We Identify/Specify Functions? (cont’d)  Cautions for Reverse Engineering Client / Users for dissected artifact may be quite different from yours Temptation to limit new means once existing means have been identified Reverse Engineering goes beyond Dissection, in that we are trying to determine why and how the artifact was made to do what it does Need to define functions in the broadest terms – only focus down when it is necessary. To mimic an existing design may violate intellectual property (patent) laws, and you could be sued!

GE 121 – Engineering Design A Repeated Caution About Functions and Objectives  While young or inexperienced designers confuse the two, a useful distinction is:  Functions describe what artifacts DO  Objectives tend to characterize what artifacts ARE

GE 121 – Engineering Design Activity  Xela-Aid chicken coop  For the list of functions shown (developed by one student group) Clarify / focus with verb-noun pairs –Example: Allow for removal of waste  Remove Waste Look for any that imply solutions –Example: Keep Water Fresh implies changing water frequently. Other options could be to continuously stream water, removing old water, detoxifying water  A Better statement might be: Supply chickens with potable water

GE 121 – Engineering Design Xela-Aid chicken coop p93