06.1 Project Proposal
Introduction:
Juicing oranges to make one glass of orange juice is a long, labor intensive task. To make a single glass, four oranges, eight halves, must be squeezed on a juice press. Current automatic juicers found in grocery stores, as shown below, are large and not conducive to a typical house kitchen. We propose creating a more compact juicer with fewer mechanisms to complete the tasks found in an automatic juicer: cutting, loading, pressing, and ejecting the oranges.
Problem Description:
Completing these four identified tasks within in the semester is a very large undertaking so for the purpose of this project we will focus on the pressing and ejecting parts of this problem to solve. We will create a juicer that can press and eject the orange peel using one mechanism with one controlled motor in order to reduce the space it takes to complete these two tasks that are a part of an automatic juicer.
In order to complete this problem, we will need to calculate the mechanical advantage of the press in order to squeeze the orange. We will also need to calculate the mechanical advantage of the link that pushes the peel off of the press. Additionally, we will need to design a mechanism that combine these to tasks into one actuation without creating any links that can bind in the motion profile.
Proposed Mechanism:
We propose using a combined four bar mechanism and simple hinge motion to accomplish these tasks. The four bar will produce the movement force needed to squeeze the fruit, while the hinge will be used for disposal.
Several factors need to be considered:
Fruit Size: the mechanism must be able to juice differently sized oranges, and preferably also other fruits in order to increase its versatility, without significantly affecting juice return efficacy.
Seed Clogging: given that many fruits come with the seeds, the base of the press must be designed so that it both prevents the seeds from getting into the juice and avoids the mechanism clogging from the seeds - for example, many hand-held citrus presses accomplish this by having small holes that allow for juice flow but not seeds passing through; seeds may still get stuck in these holes and accumulate if not removed properly.
Mechanization: to avoid increasing the cost of the system, the amount of motors and the like must be reduced as much as possible.
These factors complicate the problem; a simple 4-bar slider crank would achieve the desired juice pressing motion and could be adjusted for any fruit size, but it would not accomplish the peel and seed removal. As such, the mechanism must be modified to also power a disposal method, which then would need to be controlled in such a way that minimized the amount of motors used, thus introducing the need for careful mechanical advantage analysis.
Proposed Scope:
As was mentioned earlier, for this semester we will only be focusing on the pressing and ejecting sections of this problem in order to produce strong results in these areas in the time frame. Key tasks will include:
Mechanical Advantage Analysis: how much force can the mechanism exert on the fruit to be juiced with one motor on the input link and with the links reasonably sized (i.e. whole mechanism can fit on a kitchen counter)?
Disposal Design: how does the mechanism handle the leftover peel and seeds without clogging the mechanism? Does it need a second motor, or can that motion be tied to the juicing motor?
Combination: do both parts of the mechanism successfully move together?
Testing: does the full prototype successfully accomplish both juicing and disposal?
Additionally, we will not be using real oranges this semester. Instead, we plan to use small clementines for this scale of our project. Given our links will likely be made out of plywood or acrylic, we do not see using the press on a full size orange as realistic, however, we believe we can achieve the same motion and force profile that can be later scaled up as we design for a clementine. Additionally, a clementine has a thick enough peel, that the proposed ejection mechanism as shown above should still work on the same principles and be able to scale up as well. Another portion of this project we will not focus entirely on is juice return, as for an actual juicer this would be an important factor in the design. However, due to us reducing the overall scope of our project, the stated point will not be a focus, rather the examination and implementation of our mechanisms.
Preliminary Design Ideas:
For the design of this mechanism, we need two linkages powered by one source, with one of the linkage being timed to move only after the first one has. This will be accomplished by setting up the motor to directly output to a link and a gear, the link will control the juicer linkage directly, while the gear will have a pulley or chain connecting it to another gear with intermittent teeth, this gear will apply power to another gear at a specified angle range (determined by the placement of the teeth) that will activate the disposal linkage.
For Grashof’s Law of a slider crank, we assume that the lengths of L1 and L4 are infinite and cancel out in the equation, leaving us with S < P → L2 < L3 , this means that as long as our L2 is shorter than our L3, our mechanism will be a Grashof Class I, allowing our L2 to make a full rotation.
Our juicer linkage is a four-bar vertical slider crank mechanism with a DOF of 1 as determined by Gruebler’s equation: