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Abstract
The junior design project of my Mechanical Engineering degree was to design, produce, and test a pill bottle filling machine. The idea of this machine was that empty bottles would be loaded into the machine, a specified number of pills would be added to each bottle, a child-safety cap would be screwed on the neck, then filled and sealed bottles would leave the machine. From the loading of bottles to their departure from the machine, no hands-on interaction would be necessary. The project sponsors, Norwalt Design and Omega Design, provided guidance and industry insight to each team.
This project lasted two semesters, beginning on September 1st and lasting until the Junior Design Showcase on May 24th. The first semester was focused on producing a low-fidelity and manually powered proof of concept, with the second semester focused on electronics and fabrication in final materials. Rather than a dedicated project course, this project was a part of the machine design courses taught at the the University of Delaware.
Figure 1. Industry standard, square-based pill bottle used in this project.
Figure 2. Child-safety cap used with the bottles for this project.
Figure 3. 6 mm diameter airsoft pellets used as proxies for pills.
Background
The project started with the construction of our machine frame, in which all components had to be mounted. The frame was made from 80/20, and measured 20 inches square by 40 inches long.
Figure 4. Partially assembled frame. Each square face is 20" x 20", 40" apart from one another.
Figure 5. Fully assembled frame with handles.
Figure 6. Overhead view of assembled frame.
We then constructed prototypes to explore various methods of transporting bottles about our frame: lead screws, rotary tables, and conveyor belts. These prototypes helped us begin brainstorming different concepts for our three main tasks: transporting, filling, and capping.
We then constructed prototypes to explore various methods of transporting bottles about our frame: lead screws, rotary tables, and conveyor belts. These prototypes helped us begin brainstorming different concepts for our three main tasks: transporting, filling, and capping.
Figure 7. Lead screw motion prototype. The wooden carriage travels linearly along the screw.
Figure 8. Conveyor belt motion prototype. The aluminum tubes at each end rotate to drive the blue belt over the wooden guide plate.
Concept Generation and Selection
Our team of ten students generated a plethora of both system-level and task-level concepts. Some of mine can be seen in the image below.
Figure 9. Some of the concepts and ideas created in concept generation. These are just the ones by me, one tenth of the team!
These concepts were judged against others within their scope using weighted decision matrices based on six criteria: Cost, Size, Reliability, Simplicity, Bulk Processing, and Output Speed.
Cost was among the lowest weighted criteria, with its inclusion due to an assigned budget we needed to keep our orders below or face penalties.Â
Size had the greatest weight, since it was a stated requirement in the project definition and space inside the frame was capped at roughly 9.25 ft3. With the need to fit systems to handle many different tasks into this small volume, no one concept could be allowed to take up excessive amounts.
Reliability came next. We wanted our machine to not require constant supervision, so concepts that we expected to be more consistent in their performance were more desirable than those with potential for frequent error.
Simplicity was related to reliability, but we considered it in the sense of how complex the parts and their assemblies were. Fragile, intricate, and integral parts would be difficult to replace and could halt operation of the entire machine.
Bulk Processing was the other lowest weighted criterion, with it being favorable but not necessary. Concepts that could accommodate multiple bottles or caps at once would be less liable to become backed up during operation.
Output Speed was given a moderate weight since the purpose of the machine was to exceed the ability of trained human workers. Otherwise, there would be little reason to rely on the machine in their place. We considered it different from bulk processing in that Output Speed was intended to gauge how long a bottle spent at each station.
Table 1. Weighted decision matrix to compare various concepts related to placing caps in place on the neck of bottles and tightening them down. Scores were assigned for each concept's expected performance in each category with 1 and 5 being the worst and best possible, respectively. The highest performing delivery concept was the Cap Chute, highlighted in yellow. Similar tables were used to determine the concepts selected for Conveyance/Bottle Manipulation, Pill Filling, and overall system layout.
The top performing selections are covered in the following sections.
Bottle Loading
The top performing bottle loading concept was called the Bottle Chute. It stored reserves of upright bottles on an inclined plane, which used gravity to feed them into a vertical chute. This chute had an opening in one wall tall enough for a single bottle to pass through, controlling the flow of bottles into the machine.
Figure 10. Angled portion of Bottle Chute, where reserve bottles would be stored.
Figure 11. Vertical portion of Bottle Chute, where upright stacked bottles would await entry to the filling station.
Conveyance/Bottle Manipulation
It was decided that bottles would travel between stations via conveyor belts (dubbed Bottle Belts), and would pass through each station via rotary table. The concepts were very similar to their respective motion prototypes. Bottles would leave the frame by a ramp, called the Bottle Slide. Concepts with and without guiding rails were considered.
Figure 12. Sketch of Bottle Belt concept carrying bottles.
Figure 13. Bottle Slide concepts to remove bottles from the frame.
Pill Filling
Filling of each bottle with pills was to be accomplished through a concept referred to as the Carousel. Like a carousel that rotates with rider aligned to vertical poles connecting the floor to the ceiling, this concept would have multiple tubes through which pills would funnel to bottles below. A hopper above each spout would supply pills, with the length of each tube sized to accommodate the desired quantity of pills per bottle. Tubes would follow a dead plate to keep pills inside until above an empty bottle.
Figure 14. Carousel pill-filling concept. A series of tubes direct pills from a hopper (not shown) into empty bottles below. The hopper would be placed in the semicircular portion above the dead plate.
Cap Conveyance
Caps would be placed on the necks of bottles as they passed to the tightening station by a system called the Cap Chute. Similar to the Bottle Chute, the Cap Chute would have reserve caps stored on an inclined plane until needed. A mechanism (at first rollers, but later changed to a pair of servo motors) would halt one cap hanging over the edge at angle, so that a passing bottle could tug it off to settle onto the neck.
Figure 15. Cap Chute cap conveyance concept. Overhanging caps are tugged off the chute by the necks of passing bottles, where they would ideally settle flat as the bottle continues to move.
Cap Tightening
Initially, a concept using cams called the Cam Cap Spinner was selected, but complexity and difficulties in its implementation led us to pivot to a different concept. The Cam Cap Spinner would have used a series of motors and cams to screw caps on, but was replaced by the Cap Tightener, a simpler version that relied only on friction and the motion of the rotary table itself. The Cap Tightener rigidly holds a bottle as the cap makes contact with a stationary wedge, inducing a relative motion which screws the cap onto the bottle.
Figure 16. Cam Cap Spinner cap tightening concept. A rotary table would drive bottles with resting caps through a spinning motor and spring cam. Concerns over the cost and implementation of so many motors and cams led us to our Cap Tightener concept shown in Figure 15.
Figure 17. Cap Tightener concept. A stationary, textured wedge makes contact with the cap resting on a bottle neck. A guide rail (not pictured) would follow the perimeter of the rotary table and provide the force to push the bottles into the wedge.
Prototyping
The prototyping stage of this project lasted many months, with the creation of low-fidelity wood and foam board parts to confirm functionality before time was invested in final parts.
Low Fidelity Proofs of Concept
Figure 18. Early prototype of the entry belt directing bottles from the Bottle Chute into the Carousel.
Figure 19. Foam core dead plate for Carousel.
Figure 20. Carousel prototype made from cardboard, plastic straws, clay, and hot glue.
Figure 21. Carousel hopper made from foam core scored with a knife and hot glue.
Figure 22. Foam core Bottle Slide prototype.
Figure 23. Front view of some early prototype systems in the machine frame.
Figure 24. Rotary table spinning freely.
Figure 25. Bottle being directed by a rotary table.
Figure 26. Bottle transferring from rotary table to Bottle Slide.
Figure 27. Second generation 3D print of Cap Chute curved connector.
Figure 28. Early prototype Cap Chute. Foam core rails guide the caps down a pair of ramps, where magnetic stoppers hold them above a Bottle Belt.
Figure 29. Wooden Bottle Slide with rails.
Figure 30. Entry belt with added metal guide rails.
Figure 31. Labeled wooden prototype of the Carousel.
Figure 32. Labeled front view of the frame at the end of the first semester.
Figure 33. Rear view of the frame at the end of the first semester.
High Fidelity Parts and CAD
From the beginning of the spring semester, our team began replacing the low-fidelity wood and foam parts with ones made from 3D printed plastic, laser cut acrylic, and powered by electronics.
Figure 34. CAD assembly of the final design.
Figure 35. Animated collapse and explode of the CAD assembly for the driven shafts used in the Bottle Belts.
Figure 36. Animated collapse and explode of the CAD assembly for the short ramp support used in the Cap Chute.
Servo and stepper motors, break beam sensors, buttons, and LEDs were controlled using the Arduino coding language, an Ardunio UNO board, and a pair of motor shields. Break beam sensors were used to track when bottles entered or left stations, and controlled logic dictating which belts or tables ought to be in motion. For systems like the Bottle and Cap Chutes where the weight of reserve items was a factor, a pair of servo motors functioning like an airlock allowed for controlled release.
Figure 37. Bottle dropping from the Bottle Chute, entering the Carousel, and receiving its payload of pills.
Figure 38. Bottle leaving the Carousel to receive a cap.
Figure 39. Servo motor "airlock" releasing a single cap onto the filled bottle.
Figure 40. Organized wiring of the project electronics.
Figure 41. Closeup of the electronics breadboard. The colored buttons controlled the start of the machine, as well as emergency stops for the two rotary tables. Red and yellow signal LEDs would indicate whether the emergency stops were in effect.
Figure 42. Bottles with loose caps being pressed into the Cap Tightener as they move around the rotary table.
Figure 43. Bottle leaving the machine via Bottle Slide.
Design Validation and Conclusions
With our single Arduino UNO, we were unable to run more than one table or belt at once, but through testing we found that each system functioned in isolation. Though not faster than benchmarking tests we did to determine the human pace for filling bottles, we were confident the speeds and handoffs between systems could be significantly reduced with an additional month or so.
Additional steps in our path forward included:
Seeking ways to stabilize the Carousel's pill storage
Replacing belt stepper motors with DC counterparts for smooth motion
Replacing fabric belts with textured alternatives
Replacing plug and tube rollers with a more secure version
A point of pride for our team was achievement of the Best Overall Design award not once, but twice! At the end of each semester, a panel of professors, machinists, and industry professionals judged the projects of the junior class and found ours to be the best each time.
Figure 44. Our team's recognition for Best Overall Design in both Fall (top) and Spring (bottom).
Figure 45. Half of our team posing next to our machine after being awarded Best Overall Design, with a celebratory bottle of champagne and bottle trophy resting on the machine. Pictured from left to right: David Harkins, Sebastian Graper (me), John Papadopoulos, Jordan Tatis, Sarah Bartlett.
Members not pictured: Rocky Li, Ethan Chappell, Harrison Silverston, Dominic d.Agostino, and Riley O'Connor.
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