Voice of the Engineer (VOE) Function Trees Fall 2012-1

Functions (VERB NOUN pairs) Start with ranked groups of needs Create a list of functions that need to be accomplished to meet those needs VERB NOUN pair (support load, apply torque, store data, etc.) Does it need: Power Information User interface Supports Enclosures

Step 1: Formulate – Identify Core Functions Shopping carts That leaves us with… Function 1: Handle Products Function 2: Transport Products

Step 2: Assume – Identify the subfunctions which Each Primary function must achieve Next, identify the further details or subfunctions that the shopping cart needs to provide. Focus on WHAT the shopping cart needs to do, in order to provide the functionality of each primary function.

Step 2: Assume – Identify the subfunctions which Each Primary function must achieve Function 1: Handle Products Support Products Contain Products Protect Products Function 2: Transport Products Translate products Stop moving Rotate products

Transport the Products Step 3: Chart - Function Tree in Graphical Form Describe HOW you plan to meet your shopper’s need: Design a device to enable a customer to collect products and easily move them through the store. Handle Products. Support Products Contain Products Protect Products Transport the Products Translate products Stop moving Rotate products

Step 4: Execute – Fill in the details of the function tree, (and articulate the interface specifications) Performance Specifications will define what each of the top level subsystems must do for the customer. Design Specifications will define how each of the top level subsystems will connect, or interface, with one another. Typically, the customer worries, and cares, more about the performance specifications. As engineers, we tend to focus, worry, and care more about the design specifications. It’s important to make sure we always insure that our natural attention to the design interfaces does not detract our attention away from the customer’s needs, which are more accurately represented by the performance specifications. We will look at interfaces next week in class. Needs Assessment

Step 4: Execute – Fill in the details of the function tree, and articulate the interface specifications Design a shopping cart. Handle Products. Support Products Mass of product (kg) Contain Products Max volume of product (m3) Min volume of product (m3) Max surface area of product (m2) Min surface area of product (m2) Protect Products Transport products without damage? (Y/N) Transport the Products Translate products Force to initiate motion to # speed (N) Stop moving Force to stop moving from # speed in # sec (N) Rotate products Turning radius (rad) Force to change direction (N)

Constraints There might be other things that have to be met that are not functions -cost limits -production methods These constraints can be listed alongside the functions

Step 5: Test Engineering Judgment – Ask your mentor to punch some holes in your function tree, interface specifications, and complete understanding of the customer need. Invite them to be critical now – before you spend a lot of time solving the wrong problem! Quality Review – Seek buy-in from Your mentor and professor, your clients, the students, instructors, robot users, etc. The shop staff and others who will help you design & build Insure that this function tree addresses all aspects of the mission statement and objective tree, and will result in a satisfied customer! Concept Development

Functions interrelate Flow of power (mechanical, electrical) Flow of information (signals, sensors, actuators) Flow of material (water, widgets)

Example

Functions (focus of brainstorming) Brainstorming focuses on ways to achieve the functions

Brainstorm on Shopping cart handle

Brainstorm on Obtain direction information from user

Specifications Objective Can be measured Practical (test costing $10,000 won’t work) Need to be measured Complete - Relate to the customer needs

Needs vs. Metrics Metrics translate needs into objective things that can be measured. “I need it to be light” Product and battery but not charger must have a mass <= 1.5kg This allows you to objectively see if a design meets the customer needs One metric may meet more than a single need House of Quality

Specifications cover all needs “House of Quality” Some needs are covered by more than one metric Some metrics cover more than one need

House of Quality bicycle shock From Ulrich and Eppinger

Metrics also can protect you What if the customer is unhappy with the thing you produce which meets all the specifications (list of metrics)

Non-standard metrics “The system needs 3 different diameter wheels” Yes/no Spread in diameters “The product must instill pride in the user” Subjective Focus groups/ surveys

Caution! Try not to spec. your project so that: It is impossible (no solutions) It requires costly exotic materials (unless needed) There is only a single solution It requires too much time to analyze or build It requires fabrication processes that we don’t have access to It is exceedingly dangerous or risky It is not challenge at all It’s ok to have 1 or 2 “reach” specs but not all of them Specifications can drastically change the outcome

Simple initial hand calculations It’s very easy to set up an “impossible” set of metrics to be met Weight: < 0.01 g Volume: > 10 m^3 Load carrying capacity: > 10 kN Engineering analysis will help you determine a reasonable set of specifications

Exercise Mass of shopping cart: < 2 kg Is this a reasonable spec?

Shopping cart initial analysis Load bearing capacity Mass of cart Frictional losses Power consumption Refueling times Cost Can you come up with a design that you can show will meet the specifications you list?

Negotiation What if you agree to meet an impossible specification? How do you deal with creeping elegance? What is creeping elegance? Types of customers that you may have to manage.

Next week Continue specifications