12.3 Design Process
Top Plate: Slider-Crank Cutting System
The design of the top pinching slider begins by measuring the force needed to insert the can opener blade into the side of a can. Testing shows that this insertion force is about 200 N. Therefore, the goal is to design a slider-crank mechanism that can deliver at least 200 N of output force.
To achieve this, we focused on selecting linkage lengths that provide a high mechanical advantage during the blade insertion, while also ensuring the blade penetrates deep enough to make an effective cut. Measurements indicate that the blade must insert about 6 mm into the can to create a cut roughly 5 mm wide. Cuts smaller than 5 mm are generally not effective for opening a can.
In slider-crank systems, a higher mechanical advantage is typically achieved by using a shorter input link (link 2) and a longer connecting link (link 3). Since link 2 connects to the servo arm and a 12 mm bearing (used for durability), its minimum length is set to 40 mm to allow a stable and functional attachment. After testing various lengths for link 3, we found that the mechanical advantage increases with length but plateaus beyond 100 mm. Therefore, link 3 is set to 100 mm.
Next, we determined the range of motion that provides the best mechanical advantage while ensuring the blade moves at least 6 mm. A full 360° analysis shows the highest mechanical advantage occurs at θ2=180°. However, setting the starting position at 180° would place the blade fully retracted against the can, leaving no space to rotate it. To address this, we chose a starting angle of 160° and positioned the slider-crank system so that it is 3 mm away from the can. This setup ensures that when θ₂ = 180°, the blade is retracted and sits exactly 3 mm away from the can surface, providing enough clearance for safe positioning before insertion begins. As the servo rotates from 160° to 125°, the blade moves forward by 6 mm, penetrating the can sufficiently to make an effective cut.. The ending angle is set to 135°, which results in a 6 mm insertion of the blade.
Within this motion range (160° to 135°), the mechanical advantage ranges from 4.7 to 2.1. At the starting angle of 160°, with a mechanical advantage of 4.7, a 45 N input force at link 2 is enough to generate the required 200 N cutting force. Given that link 2 is 40 mm long, the required input torque is approximately 1.8 Nm. To provide a safety margin and ensure reliable performance, we selected a servo motor capable of delivering up to 4.5 Nm of torque.
Bottom Plate: Clamping
One of the components needed for our can opener is a clamp to hold the can while we pierce into it. Through brainstorming, we first came to two solutions. One contains two screw rods that would extend into the can, and the other would be reverse engineering the drum brake in a homework problem to clamp on the inside instead of the outside.
We decided to settle on Option B, the Brake Drum as it would contain more surface area to create friction against the drum and utilizes linkages to create a higher mechanical advantage. After this discussion, an initial CAD design was made to wrap around a 3in can.
This initial CAD design worked, however, as can be pictured here, it did not align perfectly with the 3in diameter circle and had no way of being powered. This proved to be a problem as we would then need a motor attached to this base while the base would be moving to rotate the can. We eventually settled on a manual style of clamping the can by designing a lever arm that can have a screw go through it to essentially lock the can in place. After these 2 fixes, we landed on our second CAD design iteration.
After some testing, only two more changes needed to be made. One was to include more holes as the can we were testing with was slightly smaller than 3 inches and the assembly was a bit loose with how it was designed so more holes were made at 2.5, 2.67, and 2.83 to accommodate. Our second change was to add sandpaper strips along the clamp edges to prevent the cutting device on top from applying torque and wedging the can out of the clamp.
Bottom Plate: Rotation System
The final component of our design is the rotation system. This part was relatively simple yet still went through some design changes. The goal of this system is to rotate the can at set intervals so there are many ways to do it. Originally, we were going to have a problem with the amount of force we would need for this system if the blade were to be constantly inserted into the can as this system rotates, but we decided very early on that that would be impossible with how much torque would be required. To start off with, we wanted to be fancy and use parallel arms, but found that gears would work just as well.
Only problem with gears is that it can be hard to get them to mesh, so we went through 2 different iterations with many equations set in SolidWorks to finally land in a design that made them mesh well.
The main problem with the first set of gears is that there wasn’t enough space for the gear teeth to mesh, the beveled gears also didn’t distribute the forces as well, and more teeth were needed to make the movement smoother which ended us up with the second iteration of gears. With the gears being done, you can also see that we created a D-shaped hole in the driver gear to fit a stepper motor into it to finalize the design!