The Glass Engraver
2.5 Axis Motion System
The 2.5 Axis Motion System was an extremely large task, and was the most challenging of them all. This assignment was not only the largest, but the most challenging as my team and I had to build a 2.5-axis motion system within a constrained work volume limited to a cube of 2.5 in x 2.5 in x 2.5 in. On top of the work constrain, the system had to be lightweight and small enough to fit into a backpack, and we were given a limited supply of mechanical parts that included 25mm x 25mm or 12.5mm x 25mm 8020 aluminum extrusion, two stepper motors, and the requires belts and pulleys for 2 linear stages.
The main learning objectives to this was firstly to enable us to ponder on different ways to embody ideal joints such as revolute, prismatic, spherical and/or universal joints. Secondly, it challenged us to design mechanical components with rotational shapes by taking into account their function, mechanical loading, its required accuracy, method of fabrication and assembly. Lastly, it aims to give insight into the integration and testing of a product prototype with mechanical and electrical components.
The most crucial aspect of this design was understanding the design and functionality of a linear drive. Thus, we began this project not by going head-on into designing our product, but to build and design a linear drive system. This gave us a better understanding, and also aided in stimulating ideas for our own prototype to build later on.
Diagram 2: Linear Drive
Diagram 1: Linear Drive
Video 1: Linear Drive
After contemplating and brain-storming over various ideas, we decided to build and design a glass cup engraver, with the engraver being the end-effector. The cup engraver will utilize a rotating plate to rotate the cup and pulleys that move in the y-axis to control the end-effector. The main function of the system will be controlled via an Arduino. Furthermore, the end-effector could be adjusted in the x-axis in accordance with various cup sizes.
We started off by building the foundation and the mechanical aspect, and ensure it was perfect before adding in the electronic component. We started off by creating a rough sketch and an outline of the system from various viewpoints, with exact measurements. These measurements were able to be set in place as we constantly focused on the constraints of its compactness. This sketch allowed us to cut the required dimensions of 8020 aluminum extrusion, and to create holes at specific points. This gave us the foundation of the entire project, giving us a physical foundation to work off.
Diagram 3: Prototype structure
Diagram 4: Prototype Structure
Majority of all the joints were designed using Creo and 3D printed, while the rest utilized other bolts and pins. The joints used included two motor holders for the pulley systems, one rotating plate, one pin holder/slider that prevents the glass cup from falling over when the end-effector works on it, two sliders for the pulley system in the y-axis and one motor holder for the end-effector. Tolerance was extremely important to keep in mind while designing these parts, and we also had to consider the functionality of the joints in order to if a high or low tolerance is more important. For instance, the rotating plate was to utilize two bearings that would be press-fitted into the specific holes. With this knowledge, we ensured to design the rotating plate to the exact size of the bearing in order for the bearing to stay in place. Additionally, to fit the bearing snuggly into the holes, we placed them in the freezer to allow it to contract which permits us to squeeze it in and thereafter expanding and fitting in well.
Diagram 5: Completed Prototype (i)
Diagram 7: Completed Prototype (iii)
Diagram 6: Completed Prototype (ii)
With the mechanical aspect and foundation laid out and working perfectly, the electronic aspect was implemented. The glass engraver is controlled by an Arduino UNO, whereby a code to engrave the desired outcome will be programmed that will alternate between the end effector and the rotating plate. The motors controlling both the rotating plate and the end effector was connected to the Arduino via a breadboard. Before starting the device, we had to ensure it was calibrated to the right position before starting the engraving process (Diagram 9). Once this was done, it could be programmed to design anything. In this case, we programmed it to engrave the letters BU onto the glass cup (Diagram 8). Snippets of the code are shown below. Lastly, the end-effector was controlled by batteries as having it permanently on and off is suitable.
Diagram 8: Arduino Code Example
Diagram 9: Calibration Example
Diagram 10: 'BU' engraved onto glass cup
All in all, our product prototype worked perfectly with both the end effector and rotating plate working smoothly. However with all prototypes, we stumbled upon a number of obstacles. The main obstacle in the mechanical part of the prototype was designing the 3D joints. We failed to take into account the various functions required out of the parts. For instance, the holder holding the motor of the end effector was first designed to primarily hold the motor, with a spring allowing the engraver to quickly move in and out (hence, the engraver). However, after designing it and fixing the physical joint in we realized that the spring we had used was too strong and could not move the engraver as desired. To overcome this hurdle, we decided not to use a spring and realized that the servo had enough power to push on the end-effector. Thus, we re-designed the motor holder to include a hole whereby the servo could fit part of its rotating head into the holder, allowing it to push back and forth. Another prominent hurdle included iterating a specific joint from using just a bolt to designing a 3D part, specifically for the pin holder/slider. This pin is a crucial aspect of the prototype as it creates a counter-force to prevent the cup from tilting over when the end-effector pushes against it. With this part manually adjusted by the user, we decided to have it be adjusted using a simple screw. However, moving further with the prototype, we recognized that it would be more appropriate to create an easier and more manageable adjusting system for the user to handle, and hence we decided to design a holder that combined both uses we had previously implemented for the motor holders and sliders. As a result, we designed a pin holder that could slide back and forth within the 8020 aluminum extrusion. Despite the obstacles and challenges faced, we managed to overcome them as a team within the given timeframe and deadline given.
Video 2: Overview of Prototype
Video 3: Prototype Demonstration
I thoroughly enjoyed designing and building the glass engraver and I have gained several valuable lessons from this project that would allow me to better handle future, more advanced projects. Team-work inevitably emerges from this assignment, but more so in dividing and conquering the workload to meet deliverable deadlines within a tight timeframe. Each one of us worked on our strengths and contributed to the team equally.
Working within constraints is another pivotal role present in this assignment. Like the real world, prototype parts and components cost money, and taking into account these limitations and well as implementing them significantly effects how an engineer approaches any design. Working hands on and building a prototype on a small scale has showed me how important every step is, from envisioning the final product as well as being able to manipulate and modify the plans as pieces of the product come together. Theoretical results and strategies do not always transcribe and signify that the actual outcome may work as planned. This assignment has emphasized the importance of understanding the various phases required for a specific project, in this case the mechanical and electrical phases, and being able to work around any stumbling block one may stumble onto. Hence, to be able to re-design and figure out a solution to overcome the problem.
Another critical element to digest is the significance of tolerance when designing a part. In this case, understanding that the 3D printer prints parts slightly smaller than outlined, and also taking into account the desired outcome of the part was important in helping us attain the best dimensions. Furthermore, examining and being aware of where the part is being placed and its function alleviates the need to re-design and re-parts, and assists in developing an efficient design without having to modify thereafter.
Finally, with this only being a product prototype, there certainly is plenty of room for improvement for both the mechanical and electrical aspects. However, it is apparent that the prototype can be improved aesthetically as well as ergonomically, to enhance its physical appearance and make it enticing to customers.
** The video below summarizes the entirety of the glass engraver. Enjoy!
Video 4: Kickstarter Video Summary
CAD parts
Slider
End Effector Holder
Rotating Plate
Motor Holder
Pin Slider and Holder
