HASSLE-FREE CRAFT COCKTAILS
Market Need
High-Quality Juice
Save
Money
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Eliminate food waste: Bars will no longer have to pre-juice before opening because this machine allows them to juice constantly throughout the night, allowing them to juice only what they need that day
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Save on wages: Prepping fresh juice can save 7 man-hours each week, equal to $364/mo in San Francisco
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Comparable mechanical juicers can cost around $9,000
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Avoid Workplace Injury
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Tendonitis and overuse injuries have resulted from the repetitive motion of hand-juicing, which involves applying 50lbs to the lever arm, several hundred times a day, every workday
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Fingers are safely out of the way of the juicing mechanisms
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Peer-reviewed study:
https://www.ncbi.nlm.nih.gov/pubmed/25324489
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Home juicers only pulp the flesh of the fruit, failing to extract the essential oils in the peel. These are key for quality craft cocktails; bars currently opt for hand-juicing for this reason
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65,000 bars in the US, we can estimate the top 1/5th are interested in these high quality cocktail juices: target market size of 13,000 businesses
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Potential home enthusiast and restaurant market as well
Product
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Description of operation: This iteration is based on draft 3 below. This design focused on the lemon crushing in order to create a working prototype, but left out the more trivial lemon indexing mechanism due to time constraints. In this prototype, a user loads a cut lemon, face down, into cup (5), Controlled by arduino, linear actuator (6) extends its piston, pushing a hemisphere (9) into the lemon, inverting it. The juice drips into a user-provided cup below. A barbed harpoon at the tip of the piston skewers the lemon, and two dowels pass through two holes in the piston to push the lemon off the barbs. It falls and is pushed to the side by the indexer, which deposits a new lemon into the cup (schematics below). The wooden housing serves to provide support for the linear actuator, but in the mass-produced design this would be stainless steel.
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Material Considerations: Housing material needs to be strong enough to endure loads up to 50 lbs and should be food-safe and easy to clean with a diluted bleach solution or dish soap. Surfaces on which the fruit slides need to be relatively smooth. For production, stainless steel has the strength, easy sterilization, and water-stain-resistance needed to house this machine and make up most of its components. For prototyping, we are considering .5 to 1 inch thick plywood. Actuator and cup will be affixed to the frame with dowels for added support.
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Tolerances: We want the fit between (5) and (9) to be a clearance fit, because there needs to be room for the crushed lemon even when fully extended. We need a clearance fit between the bottom of the machine and a user-provided cup. The linear actuator we bought, so it already has perfect fits between its housing and other components. Aside from that, the other fits are not critical to the design. The actuator piston is the only moving part. The large variation in part sizing that could occur for the machine to still work, means that mass production can be accomplished more cheaply. This is good for our large market size.
Components
& Production
Harpoon (for removing lemons/limes): 316 stainless steel
We wanted to make the harpoon out of a metal because it can be easily and cost-effectively machined into the desired geometry. The most common food-safe metals are cast iron, aluminum, and stainless steel [1]. Cast iron is not ideal because it has significant surface roughness without post-processing and therefore will not look aesthetically pleasing. Aluminum is not ideal because it dissolves into highly acidic foods (such as the limes and lemons that will be squeezed). Therefore, stainless steel was chosen. Of the readily accessible stainless steel alloys, 316 stainless steel has a comparatively high corrosion resistance due to its high molybdenum content.
Process selection:
Material: Metal
Shape: 3D solid
Diameter: 0.2 in. or 5.08 mm
Mass: 4x10-3 kg (assuming a density of 8000 kg/m3 and a length of 1 in.) [2]
Tolerance: 0.01 in. or 0.25 mm (This was arrived at somewhat arbitrarily. An RC 9 fit specifies a tolerance range of 0.003 in. and this was rounded up to the nearest tenth inch. There will be a large clearance between the harpoon and its receiver because they will be glued. )
Roughness: 5 µm (The component must be smoother than a part obtained through sand casting, but not so smooth that it affects the ability of the harpoon to extract the citrus.)
Economic Batch Size: 13000
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Conventional machining is the best process after screening, although it should be noted that this process is not ideal for the batch size being considered. Electro-machining, the next best choice, is generally used in applications requiring complicated geometries and extremely fine tolerances and implies increased cost and time of manufacturing. In view of this and the fact that it is not ideal for the batch size being considered, conventional machining was chosen.
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Tray (for holding lemons/limes that need to be juiced): polyethylene terephthalate
The tray does not have any significant mechanical forces on it; it simply needs to stay rigid. The most important feature of the tray design is that it be transparent as this is visually pleasing and may be helpful to the operator if a jam occurs so that the problem may be visualized.
Some common transparent materials are glass, polycarbonate (PC), polyethylene terephthalate (PET) and polyvinyl chloride (PVC). Glass can be eliminated because they are brittle and dangerous if shattered. All of the remaining three choices are suitable mechanically. PET is notable for being particularly clear and rigid and avoids the food safety concerns associated with PVC and PC. It also generally less expensive [2].
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Process Selection:
Shape: Prismatic/Circular
Material: Polymer
Thickness: 1/8 in. or 3.2 mm
Mass: 0.22 kg (assuming a density of 1320 kg/m3, a height of 15 in., an outer radius of 3.5 in., and an inner radius of 3.375 in.) [4]
Tolerance: 1 mm (There are no significant fits and clearances associated with this component. A difference of 1 mm would not significantly affect the capacity of the tube to hold lemons because its dimensions have been chosen to exceed the diameter of a large lemon by a ½ in. This tolerance was chosen because it can be accomplished by nearly all processes.)
Roughness: 2 µm or less (This is a standard value for noncritical components. The component needs to be smooth enough not to prevent significant catching on the sides of the lemons which might cause them to rotate as they are loaded into the tube.)
Economic Batch Size: 13000
Based on screening, injection molding is the preferred choice.
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[1] https://www.katom.com/learning-center/food-grade-metals.html
[2] http://www.azom.com/properties.aspx?ArticleID=863
[3] http://plasticker.de/preise/pms_en.php?show=ok&make=ok&aog=A&kat=Mahlgu
[4] Record of Polyethylenterephthalat in the GESTIS Substance Database of the Institute for Occupational Safety and Health, accessed on 7 November 2007
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Housing: 316 stainless steel
This material decision was made by developing a merit index and maximizing it graphically with the help of an Ashby Chart. The physical situation was modeled as a thin square plate with forces applied at the ends (See Figure 1 below.)
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Figure 1: Wall with forces applied at the ends by linear actuator.
The objective is to minimize cost, c:
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where CV is the cost per unit volume of the material, V is the volume, is the side length of the plate, and is the plate thickness. The constraint is that the stress on the walls be less than the fracture strength of the material, . The stress is related to the material dimensions as follows:
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where is the applied force and is the area over which that force is applied. Simplifying, substituting, and regrouping, we arrive at the following:
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The quantity represents a merit index that we want to minimize in order to minimize cost. This is performed using the Ashby Chart as follows:
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Three materials were shortlisted: grain wood, cast iron, and carbon steel. Grain wood was eliminated because it cannot sustain prolonged exposure to a wet environment and cast iron was eliminated for aesthetic reasons as it does not provide a smooth finish without significant post-processing. Thus, carbon steel was chosen. Due to the need for food-safe, corrosive-resistant steel, 316 stainless steel was selected.
An analogous analysis was used to establish that 316 stainless steel was also an ideal choice for the lime/lemon receiver and press, and other interior structure within the housing.
Process Selection:
Shape: Sheet/flat
Material: Metal
thickness: 1/8 in. or 3.2 mm
Mass: 4 g (assuming a density of 8000 kg/m3 and a side length of 20 in.)
Tolerance: 0.5 mm (Although there are no significant fits and clearances associated with the size of housing plates, if two housing plates are significantly different than each other, the final device may appear lopsided. A tolerance of 0.5 mm makes all plates vary by less than a mm in length dimensions.)
Roughness: 0.01 µm (mirror-like)
Economic Batch Size: 13000
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Based on screening alone, sheet forming is the best candidate. As indicated by the chart, sheet forming does not achieve the desired roughness. Thus, surface-finishing processes such as lapping and polishing will be necessary in order to complete the component.
Description of Operation: The frame (6) consists of two matching stainless steel panels that sandwich the machine and hold it 7 inches above the table surface. The top panel can flip up on a hinge (as pictured) for easy cleaning and to see the workings of the machine.
First, a human loads sliced citrus fruits, cut side down, into the tube (3). This tube can be as tall as space will allow, so the machine can run without human interaction for longer. The block (1), actuated by a small motor, pulls back, allowing one lemon half to fall onto the platform. Then (1) moves forward, pushing the cut lemon into the cup of (2) while sealing off the tube so no more lemons fall. Block (2) has slits in the bottom for the juice to drain out into user-provided cup (8). The linear actuator (4) then pushes the crusher (5) into the lemon, squeezing all juice out and inverting its peel for a spritz of essential oils. The crusher (5) has a small barbed spear on the tip, which punctures the lemon peel as it presses. When the actuator withdraws the crusher, the speared lemon is now stuck to the barb and is pulled out of the cup. When the actuator has withdrawn far enough, it encounters a stationary fork (9) that is made to pass through the two grooves in the crusher without interference. However the lemon, lacking these two cutouts, is blocked and pushed off by the fork, and falls into compost bucket (7). While the actuator is withdrawing, block (1) is loading a new lemon into the cup. The whole process happens in around 6 seconds, comparable to a human.
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Description of Operation: A rotor attached to a piston will push the fruit into a cup supported by the device housing. A linear actuator attached to a round piston will provide the necessary pressure to squeeze the juice out of the fruit. Slits in the bottom of the cup will allow the juice to pass to a container provided by the operator, such as a cup. Finally a motor will actuate a hinge to discard the squeezed fruit into a compost container. This operation will repeat until all the fruit in the loading chamber has been squeezed. This draft is nice for its simplicity, but only juices half as fast as a human can. We needed more speed, and professional bartenders said that size is less of a concern than speed because during prep the space isn't needed to make drinks.
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Material Considerations: Housing material needs to be strong enough to endure loads up to 50 lbs and should be food-safe and easy to sterilize. Surfaces on which the fruit slides needs to be relatively smooth.
The first draft of this product would have worked on a rotational system, where a laterally-fixed crusher pivots on a fulcrum to descend and press each fruit in a rotating wheel of cups. We moved away from this design due to its larger size, which is less convenient behind a bar, and the fact that linear actuators are a more simple and easily accomplished motion than pivoting on a fulcrum with 50lbs of force. Additionally, we wanted to take the human hand out of the equation as much as possible to save on labor costs. Other than that, the material considerations are the same as above.
Second Draft
Iteration Process
Third Draft
First Draft
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We have created and tested a small prototype of the juicing mechanism to make sure that the crusher and barb work. They do! As visible in the image at left, Nearly all of the juice was extracted from this lime. It also became lodged on the barb and was withdrawn from the cup as the actuator pulled back, as planned. However, it's clear that the peel did not invert, which is one of our goals. This seems to be because we used an excessively small and hard lime, and because the white cup was too large for the curvature to flip the fruit. We will iterate with different cup and crusher shapes and sizes until we achieve inversion of the peel. This is easy because both parts are 3D printed, and the barb is just a screw.
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The Bougie Juicer was intended as a fully-automated juicer for limes and lemons that would invert the peel and juice as fast as a human equipped with a hand juicer. The juicing operation comprises three functions: squeezing, extraction, and indexing. In this reflection, we consider the success of our design by evaluating (1) its ability to accomplish these functions, (2) its degree of automation, and (3) its speed.
Squeezing
In our design, squeezing is performed by a 12 V linear actuator initiated by a button. When the button is pressed, the linear actuator begins its downstroke, pressing a cup-shaped piston into a receiver containing the lime or lemon. When the downstroke is complete, the upstroke begins and the piston ascends to its initial position where it stays until the button is pressed again. The cup is capable of pressing as much juice as a hand juicer. Moreover, it inverts the peel, allowing oils from the peel to be mixed into the final product. This is a prerequisite for producing the high quality juice demanded by craft cocktail bars.
The prototype design was not fully automated as it was necessary to push the button to initiate each cycle of linear actuator. In the next iteration, the power circuit will be designed so that the button initiates a continuous cyclic movement of the piston until the button is pressed again. This will allow squeezing to occur without human involvement.
The current design can squeeze a citrus once every 16 seconds. An average barback juices a citrus every 5 seconds. Thus, the current design is roughly 3 times slower than a human equipped with a hand juicer. In order to rectify this, future iterations will likely squeeze multiple citrus at the same time. A quick survey of linear actuators available for less than $200 indicates that it would be possible to purchase an actuator the provides over 400 lbs of force at a rate of 0.45 in./s. (It is worth noting that more expensive actuators are generally not faster, just stronger, so future iterations will involve squeezing more citrus, not squeezing them faster.) This would make our design about equally as fast as a human barback. It would also be interesting to consider using the upstroke to squeeze by designing an assemblage of gears that directs the force of the upstroke into pressing other citrus. If this were designed appropriately, it would be possible to juice faster than a human barback.
Extraction & Indexing
In our design, extraction and indexing represents a coupled operation. A harpoon affixed to the piston raises the squeezed citrus peel out of the receiver. Next, a pair of dowels that are fixed with respect to the piston pushes the squeezed peel off of the harpoon and the indexer block moves in simultaneously to push out the squeezed peel and index an unsqueezed citrus. Our prototype indicates that this method is a reliable way of accomplishing extraction and indexing.
While extraction itself is fully automated, indexing requires regular refilling of a ramp that contains a row of unsqueezed citrus. This is not necessarily a disadvantage. Normally a barback spends 10 minutes cutting citrus and dumping them into a sink prior to juicing. If the rate of juicing is increased as discussed above, it would be possible for the barback to cut fruit while juicing; instead of dumping the citrus into a sink, the barback would feed them into the ramp to provide new citrus to be indexed. Thus, the total time spent by the human operator is the same if the indexing is fully automated and if it is not, and future iterations are not expected to make any changes to this system.
The time duration of extraction and indexing in the current design is 8 seconds, which is equivalent to the amount of time the juicer takes to complete its upstroke. Therefore extraction and indexing adds no additional time to the juicing. Moreover, the limiting factor on the rate of juicing is the speed of the linear actuator in the squeezing operation and not the motor driving the indexer. For this reason, it is not expected that extraction and indexing will have to be redesigned for speed in future iterations.
In summary, the current design of the Bougie Juicer provides reliable squeezing, extraction, and indexing, but does not do it fast enough to be competitive with a hand juicer. Future designs will implement a stronger actuator to enable pressing of multiple citrus simultaneously, better automation in the squeezing step, and possibly squeezing on the upstroke using an assemblage of gears. Beyond this, the design intent could be expanded to include automated cutting. This would probably require the development of a completely separate system, actuated by another motor, and would likely be sold and priced as a separate model. The current design has been designed in such a way that the vast majority of its components can be manufactured from 316 stainless steel, using a combination of conventional machining and sheet forming. With the modifications listed above, the Bougie Juicer represents a possible candidate for automated juicing at a reasonable price point.