12.2 Project Prototype
Kinematic Analysis
Top can opener gripping mechanism
Description of the ideal motion/force profiles
By actuating Link 2 with a servo motor from 43° to 130° in the local coordinate frame, we are able to rotate Link 4—directly connected to the upper arm of the can opener—by approximately 30°. This motion effectively closes the can opener and performs the blade-pinching action needed to initiate cutting.
Mobility calculation
L=4
J_1=4
J_2=0
M=3(L-1)-2J_2-J_1=1 L=1
Kinematic analysis
We are interested in the motion of link 4, which provides the force to close the can opener. The following graphs plot the angular position, velocity and acceleration of link 4 corresponded to a constant angular velocity from link 2 range from 43deg to 130 deg on a local coordinate.
Force analysis
For this system, we are interested in the amount of torque on joint 4 where the blade of can opener is located. Thus, a torque ratio relating the input torque from link 2 and output torque to link 4 is important.
As shown in the graph, the torque ratio remains relatively high throughout the range of motion, particularly at the start of the process when the blade first contacts the top of the can, which provides a high cutting force.
Animation
Bottom can spin mechanism
Description of the ideal motion/force profiles
By actuating Link 2, Link 4, designed with a circular profile matching the 3-inch diameter of the can, is pressed inward. This mechanism functions like a hand, securely clamping the can while the can opener performs the cutting operation. Clamping occurs when Link 2 is positioned at 241.56° relative to its local coordinate frame.
Mobility calculation
L=4
J_1=4
J_2=0
M=3(L-1)-2J_2-J_1=1 L=1
Kinematic analysis
We are interested in the motion of link 4, which provides the clamping force to the can. The following graphs plot the angular position, velocity and acceleration of link 4 corresponded to a constant angular velocity from link 2 range from 287.75 deg (starting position) to 241.56 deg on a local coordinate.
Force analysis
We are interested in evaluating the clamping force this system can provide when Link 4 contacts the can. Using a standard low-cost servo motor capable of delivering 2 N·m of torque, the mechanism generates approximately 270 N of clamping force—sufficient for securely gripping the can during operation.
Animation
Physical Prototype
Top can opener gripping mechanism
Iteration Documentation
Our iteration mainly stays on brainstorming and improving our system to achieve easier cutting processes.
First prototype
At the bottom of the first prototype, we implemented a can-clamping mechanism as previously described. This clamping mechanism is mounted to Link 4 of a secondary four-bar linkage, which provides a 180° range of rotational motion. At the top, we designed two in-line slider-crank mechanisms, each equipped with a can opener blade. These slider-cranks drive the blades inward to penetrate and cut into the lateral surface of the can. Once the initial cut is made, the bottom linkage rotates the can 180°, allowing for a complete opening.
Second prototype
After discussing with the TA, it was recommended that we replace the top slider-crank mechanism with a design that incorporates a real can opener. In this updated approach, the pulling motion of the can opener will be driven by a mechanism with high mechanical advantage. The main concern with the original design was that rotating the can during cutting would generate significant shear forces between the blade and the can’s surface. These forces could introduce substantial additional loads on the system, potentially compromising performance and durability. So, we replace the original design with this top can opener gripping mechanism which is discussed above.
Third prototype
However, it was found that attempting to cut the can by rotating it from the bottom required an excessive amount of torque. In practice, the can deform before a cut could even be made. To address this issue, we developed a new design, shown below, which builds on our original prototype with a few key modifications.
In this revised version, the bottom can-clamping mechanism is mounted onto a large gear, which is driven by a smaller pinion gear to provide a higher torque output through mechanical advantage. The top portion of the system still features a slider-crank mechanism with an attached blade, but the cutting process has been restructured to reduce the load on the system. The new operational principle is based on an incremental cutting strategy. Instead of trying to rotate the can while cutting in a single continuous motion, the blade is first inserted into the can’s surface at a fixed position using the slider-crank. Once the initial puncture is made, the blade is retracted. Then, the bottom gear-driven clamping system rotates the can by a small, predefined angle. This allows the blade to be reinserted at a new location along the can’s circumference to make another cut. This cycle; insert, cut, retract, rotate; repeats multiple times. After enough repetitions, the system completes a total rotation of 180°, effectively opening one side of the can through a series of small cuts rather than one continuous motion.
This approach significantly reduces the torque demand during cutting by distributing the required force across multiple low-load cycles. It also allows the system to maintain control over the cutting process without causing deformation of the can, making it both mechanically efficient and more robust.
Preliminary Bill of Materials
* Note: prices not included due to expected changes in design
Commercial Can Openers blade pack
Servo motors 6V to 12V (planned 3)
Rubber cover
TIW Plywood/Acrylic
Miscellaneous screws and fasteners
4 steel rods