ME360: PRODUCT DESIGN
ME360 Product Design is a project-based course completed during my third-year while in undergrad. The following menu presents the sections taught throughout the course, intended to aid in the development of various practical skills. Under each section, you will find a series of design exercises, completed projects, and design analyses.
THE FINAL DESIGN PROJECT
9
T
E
A
M
Assignment #4: 2.5-Axis Motion System
Written by Isabella R. Reyes designed and constructed alongside additional team members
April 29, 2021
-
MAIN GOAL: Design and build a 2.5-axis mechanical sub-system.
CONSTRAINTS:
-
Project Timeframe: 3.5 weeks total
-
The work volume (not the size of the system, but where the end effector will move) is limited to a cube of 2.5 in x 2.5 in x 2.5 in.
-
The system must be built such that it is small and light enough to be easily carried in a backpack.
-
The device can be totally or partially disassembled for transport, as long as it can be assembled by one person in no more than 10 minutes.
-
-
Except for the standard components (which are provided), design all parts to be 3D printed or laser cut.
-
Standard fasteners such as screws, pins, and others may be used, as well as additional supplies from the class kit.
-
DELIVERABLES:
1. Simulation Model
A complete simulation model including CAD components, joints, and motion elements must also be created. Belts are not anticipated to rotate, but the simulation model should demonstrate that the system performs the required motions.
2. Physical Prototype
All teams are provided the following structure and motion elements:
-
Actuators: the end effectors will depend on the application chosen by each team; provided options include a solenoid or a servomotor
-
Belts & Pulleys: timing and idler
-
Linear guides: 25 mm x 25 mm or 12.5mm x 25 mm 8020 aluminum extrusion
-
Additional electronic components
-
Additional components from your class kit.
TEAM MEMBERS:
Each team is composed of 4 to 5 members. Since this class is taken during a hybrid learning format during the COVID-19 pandemic, some members are able to work in person while others denoted their learning status as remote work only.
Assigned to Team 9, I proudly worked alongside Jett Curley, Dagny Read, and Panagiotis "Peter" Varsamis for the entire duration of this project.
The Covid-19 test sample mover
Due to the global pandemic, Boston University has adapted a hybrid learning format for all students during the 2020-2021 academic year. This format allows students to safely come back to campus, live amongst their peers, practice social distancing, attend classes in-person, and test for the virus frequently. The hybrid portion enables all in-person students to continue to connect with remote students who may be attending the same classes from anywhere in the world.
A component that is integral for maintaining the safety of students and all members of the BU community is to test for the virus. In order to do this, BU has established COVID testing sites throughout the campus where members schedule their test, swab their samples, have said samples processed, and then receive their results in a timely matter.
The following video is a shortened version taken from Boston University's Back2BU campaign highlighting the COVID-19 testing process.
Due to the extremely high risk of spreading the virus and the uncertainty of who is carrying it, the entire process must remain contact-free. One flaw in this seamless and efficient process is the handling of the completed samples. Up until the tradeoff, the entire process has been contact-free; only the test-taker handles their own sample, that is until the end. All completed samples get dropped off into a cup that is then transferred to a test tube rack by one of the test site volunteers. Since maintaining a contact-free system is a key factor in upholding the safety of the BU (and greater) community, we’ve decided to create a device that does just that!
CONCEPT DESIGN
Our mechanical subsystem is designed to serve as a contact-free, COVID-19, completed test sample mover.
The task of our end effector is to transfer a test tube from an initial holder (which holds a singular sample) to a final holder (which can have multiple possible entries). The actuator of our choice is a 12v solenoid, which allows the end effector to move in 0.5 degrees of freedom. All mechanical movement will take place at the top of the structure and is laid out in an H-like shape.
The sketch to the left shows the skeletal structure of our entire subsystem, while the sketch to the right shows the anticipated movement of the end effector (as indicated by the red arrows).
Simulation model
All CAD parts and assemblies are constructed using SolidWorks.
The following components have been modeled in SolidWorks, converted to .stl files, then sliced in Repetier Host to be prepped for 3D printing:
-
pulley mounts (3x)
-
motor mounts (3x)
-
the initial test tube holder (1x)
-
end effector (due to its design similarity, we've called it a vial forklift) (1x)
-
carriages (3x)
-
This component is the piece that slides along the middle groove of the 8020 bar. It has two slots, one with teeth that fixes the belt to the piece such that the motor is able to move it.
-
-
connection piece for carriage to end effector (1x)
The video below displays the motion study of our completed assembly. Note that the pulley belts serve as placeholders and are not anticipated to rotate. The simulation model demonstrates the anticipated motion of the system moves in the X-Y plane. The series of images below display the parts for printing described above.
physical prototype
THE ELECTRONICS
solenoid control
A solenoid is an electromagnet that extends and retracts a plunger when the current is passed through the device. This allows our end effector to pick up and place down our test tube. The photos above show the 12v solenoid retracted (its natural state) and extracted. The LED light of our breadboard circuit lights up when the plunger is retracted and turns off when the plunger is extracted. Current is passed through the solenoid at the push of a switch button while another switch button is used to cut off the current. The switch buttons are connected to two digital pins of one Arduino; these pins act as inputs that send information to another digital pin that serves as an output for the solenoid.
ARDUINO CODE for the SOLENOID:
The following PDF to the right contains code that
enables the solenoid. The file is password protected,
but uses the same password as our class's Zoom meeting.
motor control
We used three stepper motors to control the motion of our system. The motors are controlled by a joystick. The video above shows the control of the motors with the joystick. All motors are connected to an Arduino CNC shield. The motors are not automated, therefore user input is required to activate the motion of the system.
ARDUINO CODE for the MOTORS:
The following PDF to the right contains code that
controls the motors. The file is password protected,
but uses the same password as our class's Zoom meeting.
THE final WORKING STRUCTURE
Our structure is comprised of 8020 aluminum bars cut to size, 3D printed parts, as well as foam constructed holders.
The video to the left shows our completed structure and device in motion. The movement of the end effector is entirely controlled via a joystick and is plopped down and up via the solenoid. The forklift is positioned behind the initial test tube holder, drops down and picks up the tube, carries it over to the final holders, and drops down to slide it into its final position.
The gallery of images below showcases our physical prototype and highlights the component when in use.
Future improvements
Due to time constraints, our design was simplified throughout the project timeline. Additionally, our device only shows the placement of only one test tube; dimensionally we allotted enough room for many and can expand the final holder to fit multiple test tubes, but we were limited by our available materials.
If we had more time to further work on this project some ideas we collectively brainstormed to improve this project would include:
-
Sensing empty slots: utilizing a sensor with the Arduino to detect where the test tube is placed and where the device can reposition the tube.
-
Potentially utilizing a color sensor to do this since the cap of the test tube is of a vibrant color and if multiple are resting in the final holder, the device could then sense which slots are available.
-
-
Automating the process: using GCode to position the test tube from its initial placement to one of the final placements.
This subsystem has the potential of becoming part of a greater assembly line that ensures contact-free placement and transactions of completed COVID-19 test samples. From our constructed demo and based on realistic improvements our subsystem will contribute in the safe handling of potentially dangerous specimens.