Cup Vending Machine
Designing and building a machine capable of dispensing a plastic cup and then opening a door to allow the user access
A group project completed during 1st year of University
Teammates: Azim Zafran, Byron Houpis, Jerryl Lee, Miranda Gardiner, Razaullah Muhamammad, Regina Jefree, Rithik Sheen, Zixuan Xu
The Brief
The machine built is the cup dispensing system for an automatic coffee machine. The machine must, after user input, separate a standard plastic cup from a stack, an hold it in an upright position where it could theoretically be filled and where the user doesn't have access. Then, after ten seconds, open a door or move the cup so that the user can retrieve it.
One restriction for the task was that computer-aided design software was disallowed. This meant all design concepts had to be sketched by hand, the final designs had to be drawn using engineering drawing techniques, and design documents were hand-written. Though, for laser cutting, a DXF file could be made that mirrored a physical drawing.
Subsystems
Since the project involved a large team, the design was split into multiple subsystems: the cup separation mechanism, the user access mechanism, the user input mechanism, and the machine electronics. The machine ran on an Arduino board, though, as I was personally uninvolved in the electronics and programming, they won't be covered.
Initial Prototyping
Cup Separation
Conceptually, reliably separating only a single cup from the stack was the most challenging problem to solve. Therefore when brainstorming and roughly prototyping ideas, that was the focus.
Screw Threads
The stack of cups is suspended on large three screw threads. As the screws are turned, the stack of cups is pushed down and the bottom-most cup is released.
Wedge 1
The cups are suspended on a two-pronged surface that can move linearly back and forth. In this prototype, the cups moved and the wedge stayed still. As the cups move in one direction they drop down, then as they move back all but one of the cups are raised back up. The bottom cup falls.
Rolling Bars (not pictured)
The cups are suspended by two bars that are capable of rotating. As a cup needs to be dispensed, a motor rotates the two bars in opposite directions for long enough to push a single cup down while holding the rest of the stack up.
Wedge 2
Similiar to the initial wedge concept. However, the design is more compact and doesn't require pushing the stack of cups upwards at any point. This is a crucial benefit as the weight of a full stack of forty cups is significant.
3D Printed Version of the Wedge 2 Concept
The "Wedge 2" Concept was chosen for the final design as it performed best as a prototype and could be manufactured and assembled relatively easily. The initial plan to provide the reversible linear motion required was a linear actuator, though it was changed to a rotary motor and a rack and pinion mechanism.
User Access
There were two general options for controlling the user's access to the released cup: a door that opens and closes, or a mechanism that moves the cup into or out of reach. It was quickly decided that a door would be simpler to design and more effective.
The concepts for the door subsystem were drawn up by hand.
Chosen Final Door Concept
The roller with paper was chosen for the final design. It didn't require linear or angle-specific rotary motion, was simple to assemble, and, since it was only closed with gravity, couldn't cause any finger-trapping issues.
In the final design, a sheet of rubber was used instead of paper as it proved more durable and reliable.
User Input
The mechanism for user input was determined by the thematic design of the machine: a TNT box. Therefore a plunger design was chosen, mimicking cartoon explosion-triggering devices. Springs were used to improve the tactile feel and to reset the plunger, and a regular push-button sensor was fixed under the plunger mechanism to transform the motion into an electronic signal.
Final Design Documents
Interior Layout of the Cup Vending Machine
All the subsystems are housed in a cuboid outer casing made of 12mm thick MDF sheets. Inside that casing is another, smaller cuboid MDF casing that houses the cupholder and prevents the user from accessing the electronics.
Interior Layout of the Cup Vending Machine (Section A-A)
The wedge, guide rails, wedge motor, and door motor can all be seen.
Interior Layout of the Cup Vending Machine (Section C-C)
The door mechanism, door motor, cup holder, and cup tube can all be seen.
Interior Layout of the Cup Vending Machine (Section B-B)
The wedge motor, cup tube and interior box can all be seen.
Interior of the Machine During Manual Operation
The interior box, cupholders, wedge guide rails, and plunger mechanism can all be seen. The wedge functioned as expected.
The left and right outer wall panels are required to hold the guide rails, whereas the front and back panels can be left open for ease-of-assembly and testing.
Final Product
Fully Assembled Cup Vending Machine
A Full Cycle of the Machine's Operation.
The design as a whole was semi-succesful. The door was reliable, and the concept and appearence was novel, but the actual cup separating action wasn't perfect, functioning as intended approximately 90% of the time. The design was relatively easy to assemble but that compromised the machine's compactness considerably.
Given the opportunity to do something similiar again, creating a robust separating mechanism would be the first priority, and the case and layout would be designed around that, rather than creating a case first then filling it as needed.
For more details, get in touch at Michaelsvanidze0@gmail.com.