Engineering Design – Functional Decomposition


I am working with an engineering team right now to develop a machine. We are at the Functional Decomposition phase where we are systematically examining the needed workstation functionality. I will have to relate the specific experiences some time but for now, I would like to share, for new followers, an example story of this phase. Please enjoy this short short story.

“Aaron, I can’t wait to show you what I’ve done.”

“Who is this?” Aaron spoke into the phone.

“It’s Ray. I can’t wait to show you the Functional Decomposition.”

“The what?”

“The Functional Decomposition, you know, for the machine. I was so excited about the project I did it over the weekend. I hope you don’t mind.”

“Sounds great.” Aaron said. “Gee, thanks. Let’s have you go first on the agenda at our meeting tomorrow morning.”

“Okay, I’ll see you then. Eight o’clock sharp.” Aaron said.

“Was that really Ray?” Aaron thought. “That will be a first if he’s on time.”

Aaron arrived early to get the room ready but Ray beat him to it. All four team members were on time ready to go. Ray was bouncing with excitement so Aaron made no delay.

Ray began, “I started by thinking through the sequence our machine will need to go through. Then I wrote the sequence steps from the perspective of the machine.”

“The machine doesn’t have a perspective,” Bryce said.

The door opened and in walked Wesley, the chief engineer. “Hey, could you use an extra team member today?”

Ray made a fist with his right hand, thrust it forward a little and under his breath cheered, “Yes!”

“You bet,” Aaron said. “We appreciate any ideas you have. It seems that Ray was doing some deep thinking over the weekend.”

“Great,” Wesley responded. “Please keep going.”

Bryce repeated to Ray, “You make the machine sound like it can think.”

“Well, it will have a computer or programmable controller, so I guess you could say it can think. Look at it this way, the controller doesn’t know anything except what it senses by way of inputs like sensors and switches.”

“That’s right,” Kate said. “We learned all about that in my automation class. Controllers have inputs and outputs, or I/O for short.”

Ray continued, “The inputs will allow the controller to know the state of the machine so it can take action steps and perform functions or outputs. Here are the actions, and then I will show you what I recommend for functions.”

“Boy I’m glad he’s on our team,” Aaron thought. “I hope Kate doesn’t mind Ray working in her territory.”

Ray moved to the whiteboard. “First the machine needs to ‘Receive and Retain two cutters.”

“Wait a minute,” Bryce interrupted. “The specification says ‘one or more cutters.”

“I know, but for discussion purposes, let’s suppose the number of cutters is two. I noticed the other day that many of their batches are done in twos. This assumption will let us move forward in Functional Decomposition. Next, the machine needs to wait for and ‘Receive a Start indication’ from the operator.”

“Two start indications.” Kate reminded.

Ray continued step by step writing the generic machine sequence on the left side of the board, explaining his thoughts whenever a question was asked. Wesley added a little here and there, but generally sat in his chair nodding his head with a proud smile.

“Here are the steps of a machine cycle from beginning to end.”

  1. Receive and Retain two cutters
  2. Receive Start indications
  3. Detect operator safety clearance
  4. Move first cutter into position for blasting
  5. Seal enclosure
  6. Start blasting and blasting timer
  7. Wait for timer to expire
  8. Stop blasting
  9. Move second cutter into position for blasting
  10. (Repeat 6-8)
  11. Open enclosure
  12. Move cutters to pickup position
  13. Release cutters
  14. Reset all elements of the machine

“I’ve looked over this list several times and have decomposed the basic machine functions as follows.” Ray looked hopeful toward his bright-eyed team mates as he began writing on the right side of the board. “Essentially, we need to design a machine that will do these things.”

  1. Receive and Retain Two Cutters
  2. Move Cutters to Multiple Positions
  3. Provide a Containment Environment that can be opened
  4. Perform directed SiC (Silicon Carbide) Blasting and SiC recovery
  5. Provide operator Interface with Start, Stop, and Options Selection
  6. Provide Control System with Controller, Electrical, and Software
  7. Provide Machine Structure, Cabinet, misc

“Well,” Aaron said, “I think this looks pretty great. Thanks Ray. What made you think of this anyway?”

“Oh,” Ray looked over at Wesley who remained silent. “I was working on my motorcycle Saturday and I got to thinking about it’s different parts, and I started thinking about the functions each part or assembly performs. Like, the brake handles, cables, and calipers perform the stopping function, the motor and throttle perform the acceleration function, the wheels, bearings and tires perform the rolling and steering function, the bike frame…”

“We get the idea,” Aaron said.

“Anyway,” Ray continued, “When designing something new, you just reverse the process by determining the functions that are needed, and then you can figure out what parts you need to accomplish those functions. I did it for the AutoBlaster by starting with the sequence, then figuring out the functions needed for that sequence.”

“I’m gonna start doing more of that kind of thinking when I look at things.” Aaron said.

“Don’t do it at the dinner table,” Kate said. “Your wife might not be interested in what function the tables and chairs perform.”

“Good job Ray,” Bryce added.

“Yes, great job everyone.” Wesley leaned forward looking one by one at each team member in the eye. “You are making great progress and I can tell you are each being proactive.

(Excerpt from, “The Cutting Edge.” Read the full story at https://stemstories.wordpress.com )

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