1) Initial Proposal

Group 6 Project Proposal

Introduction

The ability to flip an egg without a spatula is a skill many develop through experience in the kitchen. Without achieving the correct, nuanced motion and velocity of the pan, an egg may not complete exactly one rotation or land in the pan following the flip. We plan to construct a mechanism that will be able to repeatedly flip an egg, a task that many struggle with. Furthermore, we will complete the motion with only one input motor spinning at a constant velocity.

Problem/Complexity

The complexity of flipping an egg can be attributed to the translational and angular velocity required to launch, flip, and catch an egg. To create a mechanism that can accomplish this, we first must understand and analyze the required velocity and motion profile. Then, we will develop and refine a mechanism that can mimic this velocity profile to successfully flip an egg.

By hand alone, flipping an egg is no simple task. Studying the flipping motion of many chefs, we find that most incorporate a translational movement forward to move the egg to the front edge of the pan, a rotation upwards to give the egg vertical motion, and a sudden stop in motion to allow the egg to continue its trajectory upwards while flipping. However, some are able to complete the flipping motion using pure rotation. Then of course, comes the issue of catching the egg, which if the stopping motion is not properly timed, can move not only in the z direction but also x and y. Because we need such a specific motion and velocity profile, simple mechanisms including four-bar linkages would require a motor and motor controller to adjust the speed properly, and even then may have some inaccuracies that could build up and lead to failure in achieving the proper profile. Furthermore, a four-bar linkage alone may not give us enough control of the tilt of the pan needed to give the egg rotation for the flip.

Proposed Mechanism

Due to the complex velocity profile of varying speeds we believe is necessary to successfully flip an egg, we plan to use a variation of the six-bar mechanism shown below in the “Preliminary design ideas” section. This linkage would serve to generate the velocity profile we are looking for, where the pan accelerates down and back up to simulate the rotary flipping motion and pauses at the top of the motion profile to allow the egg to flip and fall back into the pan. It is important to note that while this mechanism effectively creates a complex velocity profile, the motion of the output is completely rotational. We believe an egg could still be flipped with pure rotation of the pan given the right pan geometry (proper radius of wall curvature, including larger walls), friction (or lack thereof) between the egg and the pan such that the eggs will slip and translate forwards in the pan, angular velocity of the pan, etc. However, in order to truly tell whether or not pure angular rotation will be sufficient, we will need to perform analysis on the velocity and motion profiles of the system. If the velocity profile created by the proposed six-bar linkage below is not enough to successfully flip the egg on a consistent basis, we will look into adding another linkage to the mechanism, such as a four-bar or a crank and slider. This would give us translatory motion to force the eggs to translate forward in the pan towards the front edge, allowing us to combine the velocity profile of the six-bar with a slightly more complex motion profile to produce the desired result. 

Scope

We plan to complete a fully working linkage that will be able to flip eggs as our final project. Our final project on demo day should include the following: a working linkage, a connection point to a pan, and simulated eggs with similar consistency to what is expected of an egg being cooked in a pan. 

We must perform a good bit analysis before fabrication, as mentioned before. While we have a good idea of the velocity profile needed, our position profile is not as determined. During our research, we found multiple ways of flipping objects in pans, some including a combination of translation and rotation, with others relying on pure rotation, which requires the objects in the pan to have minimal friction against the pan. We plan on testing this by attaching a pan to a simple rotary joint or hinge, then attaching our phones with an accelerometer app to the pan to track the velocity profile. Furthermore, we plan on testing the optimal stopping angle such that the egg’s trajectory does not vary wildly when in freefall, as well as if placement of the egg in the pan has additional effects to its trajectory that we must take into account. 

If this analysis results in the conclusion that pure rotation alone is not sufficient, additional analysis will be required to determine what manner of linkage might be added to the mechanism to combine the six-bar’s velocity profile with a slightly more complex position profile.

From our preliminary research, the most exciting part of building this robot will be the analysis. Not often do you get to play with food and pans and get to call it “research for a project.” It seems that once our analysis is finished, the most challenging part of the process will be adjusting our linkages to get the exact position and velocity profile to match our optimized profiles from analysis. This may take multiple iterations and fine tuning.

Preliminary Design Ideas

Our preliminary designs have been multiple versions of this 6-bar linkage, found in a YouTube video at 6:50. For analysis purposes, the linkage can be split in half, with the left side including a large link which the pan can be connected to, which connects to a coupler and input crank. The right side consists of the velocity control system, which allows for the pan to stop movement at a specific angle. If pure rotation is not enough, we have a handful of possible solutions, such as adding a crank and slider on the edge of the large link, where the crank speed can be connected to the input motor. We also have ideas to add a non-driven slider at the end of the large link that the pan will sit on, which will slide when tilted downwards due to gravity.