17.1 - Initial Proposal
Introduction
Have you ever observed a busy bar counter where the bartenders not only need to interact with customers while preparing various cocktails, but also have to open a bunch of cans manually in a short time? Have you ever experienced the inconvenience of a hand or finger injury/trauma that made the can-opening task suddenly hard? Are you or your friends afraid to ruin the condition of your vulnerable nails when opening a can? The can-opening task can be bothersome or inconvenient in many cases.
Problem Statement
Due to the inconvenience that opening a can presents, the issue that our team is targeting focuses on eliminating the user input of the task. We plan to develop a can-opener mechanism that will autonomously locate the tab of a can and open it with adequate force. The complexity of our design stems from determining the correct link lengths, and force such that the end effector or tip of our mechanism will consistently pull the tab of the can open. Incorrect parameters may result in poor placement of the end effector and inadequate motion to complete the task. Furthermore, another complexity is that the mechanism must achieve an orientation at a certain angle to be under the tab. The use of simple joints is not suitable to accomplish this task because we need linkages that have enough compliance to achieve desired angles while maintaining structural integrity to lift the tab and open the can.
Mechanism
Our team has identified that an 8-bar mechanism, similar to a Jansen’s linkage, could be used to achieve the positional profile for this project. The Jansen mechanism is a planar combination of 4-bar linkages that involves the use of one motor to drive the position of the entire system. This mechanism creates complex motion from a circular input. These mechanisms are commonly used to generate walking motions. Pictured below is an example of a combination of 4-bars that we could use to generate the sliding mechanism to get under the tab of the can and then sequentially pull upward. We will edit the ratio of the linkages to generate the desired path profile. The end link will be pushed underneath the tab before moving in a semi-circular path that will generate a moment about the tab, pushing it upwards, before sliding back out from under it.
Example of a Jansen Mechanism used for walking.
Proposed Scope
The proposed solution to our unique problem statement will revolve around developing a motion pattern with an appropriate force to lift the tab of a canned beverage. The movement that the solution follows should orient the end effector to be under the tab of a 12 ounce can. Additionally, the end effector should have enough force to lift the tab and open the can. Our plan to create a solution for this unique problem will include the following steps:
- Perform position and force analysis on the 4-bar mechanism to position the end effector to be under the tab of the can and lift the tab
- Fabricate mechanism with appropriate hardware to interact with the tab of the can
- Program the software to control the end effector position and force to lift the tab of the can
Analysis will focus on determining the kinematics of the linkages and the joints needed to move to and under the tab, as well as the force to lift the tab. Since there will be multiple mechanisms connected in series, the workspace of the end effector and it's relation to the first grounded link will determine the dimensions of the fabrication for the solution. The force of the end effector should be able to only lift the tab and not add additional forces to disturb the system. In addition to the mechanical structure of the solution, the code for the electronics must account for both the position and the force applied. This will be determined once the relationship between the motor’s properties and the desired parameters for our system are clearly defined.
Currently, our team is eager to fabricate this solution with the goal of finding a certain fabrication technique that is best to maintain durability while performing this unique movement pattern. We hope to find a solution that best suits our needs for this project as well as the needs for using this solution in the real world. Additionally, many of our team members are interested in continuing this project as this solution is very helpful to them with their canned beverages. We strive to complete this solution and hope to improve on certain areas for future iterations.
Preliminary Design
We have utilized MotionGen to mock up a few potential 8-bar geometries that could generate the position profile that would scoop under the tab and push it upward. These linkages are shown below. The video shows the first mechanism in motion. In addition to this 8-bar, the end effector link would have a tip that can be pushed back when the link meets the top of the can, and as the link meets the tab the interaction locks the tip into place. This effective variation in compliance of the tip would allow for more flexibility for getting under the tab, but also ensures that the link is rigid enough to impart maximum torque. This mechanism is not able to fully push the tab upwards. This is to show that we are able to achieve the circular motion pattern and consider more design for improvement.
Geometry 2 Linkage Lengths:
L1: 1 in
L2: 5.15 in
L3: l24: 4.09 in, l45: 3.82 in, l25 4.32 in
L4: 4.26 in
L5: 3.81 in
L6: 4.74 in
L7: l48: 5.78 in, l45: 6.52 in, l58 8.23 in
L8: 3.88 in
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