17.3 - Design Process

Iterative Documentation

The goal of the first three protypes was to figure out how to configure our links to achieve out calculated motion profile. The following prototypes test our development of the end effector link in accomplishing our goal to open the tab of the can. 

Prototype 0: MotionGen

When starting this project, our team had two ideas that could answer the problem of opening a tab of a can. Our first idea was to simplify a Janson walking linkage to am open four-bar linkage mechanism that can replicate a horizontal motion at the bottom of the loop and immediately transitions into a lifting motion.

                          Figure 1: Open Four-Bar Mechanism

Our next idea was to develop a crossed four-bar linkage configuration that was found to mimic the curved motion of a human finger. We based our model off of a finger mechanism patent described in the kinematics section and developed a curved pattern that is similar to a curved motion of a finger.

                        Figure 2: Crossed Four-Bar Mechanism

After our kinematic analysis, we found that the open four-bar linkage mechanism reproduces the motion and force output that was what desired to complete the project.

Prototype 1: Cardboard

When starting our prototype, we began creating the mechanism with cardboard to map out the movement with physical pieces. We measured the the link lengths to approximately the desired lengths that were defined in Motion Gen. The goal for this prototype is to observe and understand the motion of the mechanism using physical components. However, cardboard is very flimsy and susceptible to breaking down.

Figure 3: Cardboard prototype of the open 4-bar mechanism

Prototype 2: Laser cut

For this prototype, we tried recreating the same prototype with the desired link lengths using laser cut wood and rods. We found that the motion is not as smooth as we desired and future iterations will have rods and bearings. 

Figure 4: Laser cur prototype of our open 4-bar mechanism.

Prototype 2.1: Laser cut and Manual Motion

This prototype is similar to the previous in that we laser cut linkages; however, we replaced the rods with M6 screws and mounted it to a board to produce smooth motion. In the gif below you can see that the position profile of the end-effector models the position profile we determined in our kinematic analysis. 

Figure 5: Moving laser cut prototype of our open 4-bar mechanism.

Prototype 3: Acrylic and Automation

After iterating through laser cut prototypes, we were confident in our open 4 bar mechanism's ability to achieve our desired position profile. We decided to switch to acrylic links because of the added strength and stiffness that we needed to hold our end effector so that it could open the tab of a can. In addition, the automation aspect of mechanism must be added using a 12V DC motor to create the desired cyclical pattern.

                                 Figure 6: Acrylic automated prototype of our open 4-bar mechanism.

Prototype 3.1: End Effector

We also iterated through the potential end effectors that we could use to lift the tab of the can. We needed something that is able to fit the opening between the tab and the lip of the can. Additionally, the end effector needs to be thin enough to slide under the tab. From these parameters, we created an end effector that is able to cup under the tab and lift the entire tab up.

End Effector Prototype 1:

Prototype 1 uses a bracket with a screw to lift the tab. This was the first material we thought of trying as it is thin and sturdy on the links.

Figure 7: Initial design of the end effector

End Effector Prototype 2:

After testing prototype 1 for the end effector, we found that the bracket is not strong enough to withstand the force needed at the tab. We saw that the bracket started to warp and much of the force from the links is being transferred into the deflection of the bracket instead of onto the tab. We switched out our bracket system and machined a steel piece that is both thin enough to get under the tab and strong enough to pull the tab.

Figure 8: Laser cut linkages with custom end effector 

End Effector Prototype 3:

The last prototype was to fix the new end effector to the acrylic links. Below is the final iteration of the end effector piece.

Figure 9: Final end effector with acrylic linkages

Prototype 4: Final Iteration 

With the previous iteration, we found that the torque output from motor does not supply enough force to open the can. Additionally, we currently don't have linkage system at the correct height to reach the top of the can. We addressed the torque issue by created a 49:1 gear systems from the motor shaft to the rotating link to overcome the lack of torque output. Because of the size of the gears, we elevated the system using two acrylic sheets, which addressed the height problem we were also having.

Figure 10: Final Iteration