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MMAE 432
"The Hussars"
DISPENSSO BLOG
In 10 weeks, our team is asked to complete a significant product development task, from concept generation and inception, to Alpha prototype and marketing strategies. This blog chronicles some of the design, analysis and construction of the Beta and Alpha prototypes of DISPENSSO.
Week 1 (Class week 4): Needs and Concepts
For the first week, concept generation kicked off with a brainstorming session for consumer or commercial problems and some proposed solutions. Our team was to complete a series of engineering solutions to common needs by people or businesses. Each member created over 20 needs with two propsed design solutions for each. A total of 240 solutions were produced by the Hussars.
Later on, two needs and solutions were narrowed down: A liquid and spice dispenser. Due to numerous existing solutions on the market for a cheap, non-automated liquid dispenser, the spice dispenser has been chosen for lower apparent barrier to market.
Week 4 (Class week 7) Sketch Model
Our next few weeks consisted of generating solutions to an automated and fully programmable spice dispenser. A variety of of mechanisms have been proposed to move spices from a container source to a final collection cup, with any sort of grinder or mixer in between. A set of functional requirements were set as end design goals:
1. Should hold at least 6 spices.
2. Container capacity should be no less than 1/2 of a cup.
3. Should dispense 1/2 of a cup of spices in less than 15 seconds.
4. Dispensing container should have a capacity of at least 3/4 of a cup.
5. Smallest dispensing increment should be 1/2 of a teaspoon or less.
6. Should be powered by 120 VAC outlet.
The following designs were proposed for a delivery mechanism:
Auger/Corkscrew
This is a tried and proven design for a variety of dispensed goods and media. Though manufacturing costs are uncertain with the helical geometry, proper calibration and tolerancing can result in quite accurate relationships between angular displacement in the motor and dispensed spice volume.
Vertical Paddle Wheel
A simple design with few moving parts. For larger pieces or media, this solution has potential to effectively dispenser bay leaves, peppercorns and capers. For smaller dispensed matter such as powders and grains, sealing becomes cumbersome and contributes partially to friction and eventual binding of the entire machine, an issue that even may persist in single or two pouch designs. Perhaps, not the most efficient solution for our grain size range.
Carousel
A carousel eliminates some of the drawbacks of spices clumping and scaping against the vertical walls. This allows for better flexibility in the packaging geometry as well. Similar propensity of binding with the vertical paddle wheel due to friction can also be observed.
Open and Shut Dispenser
In this design, a linear motion accomplishes a similar task to the Paddle Wheel and Carousel. A cavity moves between opened and closed spaces to collect material, then deposit it elsewhere. Linear motion reduces design complexity in sealing and instead only demands tighter tolerances to work properly. This motion becomes the clear choice in the type of dispensing geometry to use.
At first, the rotary carousel was mocked up to spot potential operating problems and explore design solutions. The following image shows the inlet and outlet of the dispenser wheel, media path and four paddles. Clockwise from upper right shows metal scrapers, spice channel grooves, spira/helical flutes, and no geometric treatment.
Another image showing a possible enclosure of the mechanism.
Initial testing proved that the motor size needed to overcome friction from salt grains would be too large for a traditionally sized enclosure for a consumer.
Week 8 (Class Week 11)
Several lessons were learned from the sketch model week in the dispenser delivery design. The budget-minded HITEC servos we planned to use were far to weak to properly break the friction and binding from larger grains. We opted to go for a linear dispensing methods. The next design task called for finding a mechanism which would provide the linear motion needed. The first solution that came to mind was a linear actuator such as a solenoid. Precise solenoids were expensive while cheap and strong actuators had too short of a stroke distance (8mm) to accomodate a dispensing volume of 1/4 teaspoon. To keep high peak dispensing force and maximize displacement, our team settled for a simple rack and pinion design.
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