Introduction
Robot mechanisms are often used to tackle complex problems in industry from manufacturing to transportation. However, complex mechanisms are seldom seen in the household despite their great potential to automate everyday tasks. Our project will focus on automating the process of eating. For example, when eating Oreos, it is difficult to get the perfect amount of sogginess without the Oreo breaking apart and getting messy hands. Our objective is to create a mechanism that automates the act of dipping Oreos while maximizing the use of mechanical components and minimizing our reliance on software.
Problem
When eating Oreo cookies, a few problems can arise and be rather annoying. For one, it is difficult to dip the cookie for the right amount of time to get a consistent sogginess. Also, if soggier Oreos are the preference, it is difficult to get to that point without having the cookie break off into the milk. Eating Oreos is also difficult when your hand is too big to fit in the glass and the cookie can't reach the milk. To get a mechanism to alleviate all these problems is going to bring up many complexities due to the intermittent motion, complex position profiles, mechanical timing components, and the grabbing mechanism.
One complexity that will arise is loading the cookies into the arm which is an intermittent motion problem. Indeed, when a person eats cookies, they pick cookies from the container when they are ready to eat. Accordingly, we need to have a part of the mechanism load cookies at a set interval to mimic a normal eating pace. Another component that we foresee being difficult is the complex position profile. The proposed robot is meant to be able to grab the cookie, displace it some amount in the x, y, and z directions, dip it, retract, and then rotate the cookie to feed the operator. This brings a lot of complexity to our mechanism design. Certainly, to minimize the number of motors and controllers we use, we will have to get creative with the linkage design which probably limits a simple four-bar linkage. We may also see issues in bearing the weight of multiple motors if we choose to go that route. Implementing mechanical timing with gears, cams, or another mechanism will also prove to be a challenge as we need to match the frequency of the loading mechanism to the movement of the arm. This will require a lot of testing and validation. Finally, the robot needs a gripper to grab the cookies which may be difficult to design to both be functional and food safe.
Proposed Mechanism
A mechanism we believe could achieve our desired path of motion for the consumption of a cookie is primarily composed of a modified slider crank and a Geneva mechanism. In our design, the Geneva mechanism acts as a cookie supply. The Geneva mechanism will be spring-loaded with Oreos and its intermittent motion will allow for the Oreos to be re-loaded and picked by the end effector. The slider crank and Geneva mechanism will share the same input crank, which will allow for the time synchronization of the end effector and the Geneva mechanism throughout our desired output motion. In our mechanism the slider is a ternary link; this configuration allows us to connect our end effector whose angular position depends on the position of the input crank. The motion of the end effector is restricted by a belt that wraps around a gear that shares a pin joint with the ternary link. As of now, there is still more development needed in the mechanism design that would allow the end effector to temporarily uncouple with the motion of the input crank and actuate in the clockwise direction to a position that benefits the consumption of the user. This motion is in orange in Figure 3 found under the Preliminary design section. Inspiration for this design came primarily from the semiconductor industry which also deals with transporting circular objects. In their case, the objects are silicon wafers, and examples of their mechanisms are shown below. In this mechanism, the arm slides underneath a wafer picks it up, and places it elsewhere. We also took inspiration from the industrial manufacturing industry for more ideas on how to implement a gripper mechanism onto our arm. That example is also shown below.
Figure 1: Example from the semiconductor industry
Figure 2: Example from industrial manufacturing
Scope of work
Our project's scope of work will be limited to picking and placing small lightweight items. As of now, we are limiting the amount of time that the Oreo is dipped to be fixed, however, in future iterations the amount of time dipped and therefore the sogginess of the cookie could be subject to variability depending on user preference. The core goal of this project is to build a pick-and-place mechanism that relies on intermittent motion to achieve the correct timing of the outputs. We plan to realize this goal with the following plan:
- Brainstorm additional mechanism configurations as well as problems that we may encounter with their respective solutions.
- CAD the Geneva and slider crank mechanism and plot the associated position, velocity, force, and motion profiles.
- Conduct a critical review of mechanical design and consider the strength of links, joint integrity, motor power, etc.
- Create a simple prototype with cardboard to validate that the design roughly maps the intended trajectory.
- Plan out Arduino pin connections and skeleton of code to obtain desired motion for end effector if necessary. (Redo 3 if necessary)
- Laser cut/3D print the parts and configure Arduino to construct a functional prototype.
- Review the functionality and integrity of the prototype and reinforce/iterate if necessary.
- Final product manufacturing.
Preliminary Design
Figure 3: Proposed cookie dipper mechanism
Figure 3 depicts a preliminary design of our cookie dipper mechanism. The left configuration shows the mechanism in the desired position to grab the cookie from the Geneva mechanism. The middle configuration shows the first desired output of placing the cookie in milk. The right configuration reveals that more development is needed on the preliminary design. To get the end effector from position 1 where it is being dipped in milk to position 2 where it is actuated away from the mechanism to a position convenient for the user, the mechanism may need to include another intermittent motion component or additional gears to aid in the timing of the movement. This challenge may involve intermittently reversing the direction on the belt so that the end effector rotates around a temporarily fixed point on the ternary link. This preliminary design showcases are thought process and how we are navigating through the challenges of obtaining our desired motion profile.