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REPORT as partial requirement
for the course on
KINEMATICS OF MECHANISMS
ME 3310, A’16
DESIGN PROJECT TITLED: DESIGN OF PEANUT BRITTLE FLIPPING LINKAGE SYSTEM
Submitted by:
Robert Boulanger [email protected]
Constantine Christelis [email protected]
Yuxin Gao [email protected]
Nathaniel O’Connor [email protected]
Submitted to:
Prof. Onal Cagdas
DEPARTMENT OF MECHANICAL ENGINEERING
WORCESTER POLYTECHNIC INSTITUTE WORCESTER, MA 016092280
09/19/2016
Project Score: TOTAL: _______ out of 100%
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Abstract
The goal of this project aims to design a linkage system to flip peanut brittle 180 degrees
along a moving conveyor belt. Using our understanding of mechanisms from our studies in ME
3310, and research on designs relevant to our purpose, we have developed a design that would
satisfy the necessary task specifications. Our final design consisted of a fourbar rocker with a
dwell mechanism to allow proper timing for the loading and unloading of the peanut brittle.
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Table of Contents Abstract p2 Table of Contents p3 Introduction p4 Background Research p5 Goal Statement p7 Task Specifications p7 Designs p8 Results p15 Conclusion p16 Appendix p17 Bibliography p23
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Introduction
A local company is one of the leading peanut brittle manufacturers in the world. They
want to continue to be the best, and so they have assessed that their production speed needs to be
increased. The peanut brittle is extruded onto a 1 ft. wide conveyor belt and travels at 1 ft/sec. It
moves through an oven which bakes the peanut brittle candy. After baking the peanut brittle is
still soft and begins cooling. In order to speed up this cooling process, the peanut brittle needs to
be flipped to cool both sides evenly. We need to design a flipping mechanism which will fit
around the conveyor belt. Our company already has patented a novel spatulalike device which
will be used to flip the peanut brittle with ease. Our goal is to design a mechanism which moves
the spatulalike piece.
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Background
The product that this project design surrounds is peanut brittle. Peanut brittle is a
confection consisting of flat broken pieces of hard sugar candy embedded with peanuts. Sugar
and water are mixed together and heated to approximately 300 degrees Fahrenheit (149 degrees
Celsius). The nuts, spices, and leavening agents are then mixed with the caramelized sugar. The
mixture is poured onto a flat surface to cool, usually granite or marble slabs. Once cooled, the
brittle is shattered. It is during the cooling process that this linkage mechanism will work to flip
the cooling brittle as it moves on the conveyor belt. (Citation: Wikipedia)
Before we began drafting our first designs, we performed preliminary calculations that
would help us later on in the design and analysis process. In the project description, we were
given constant values for the dimensions of the spatula, peanut brittle, displacement between the
peanut brittle, and the speed of the conveyor belt. The spatula is a 10 in. square, the peanut
brittle a 9 in. square, distance between each piece is 6 in., and the rate of conveyor movement is
1 ft/sec. With these specifications, we were able to calculate the time it would take to fully load
the peanut brittle onto the spatula and the time that the linkage would have to complete its
movement before returning to the origin position. Given the speed of the conveyor belt,
dimensions of the peanut brittle, and the distance between each piece, we were able to determine
that it would take 0.75 sec to fully load the peanut brittle onto the spatula and it would take 0.5
sec after loading before the spatula had to be ready for the next piece of peanut brittle. The
entire cycle would need to be completed in 1.25 sec.
One design on the market that performs a function similar to what we are looking for is
used for flipping pancakes made to be frozen. The cycle functions similarly to our project
problem in that the product is moving at a constant rate along the conveyor belt and needs to be
flipped 180 degrees and maintain constant distance between each piece of product before and
after flipping. While this design was useful for establishing a base for how our design could
work, portions were not applicable to our project. The flipping motion was performed by
torsional force acting on the spatula, not through a linkage mechanism as asked of us. (Citation:
YouTube Video)
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During our research, we found a video of an 8bar linkage mechanism that performed a
flipping motion. As with the pancake flipper design, the 8bar was useful in helping us establish
a base for what we could work with, though had its own drawbacks. While the flipping motion
was quick, the placement of the peanut brittle would be uncontrolled and the design would have
the peanut brittle launched into the air during flipping. Also, with the motion at a constant rate, a
dwell mechanism would have to be created to allow the proper amount of downtime for the
peanut brittle to be loaded on. (Citation: Vimeo)
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Goal Statement Design a means to flip peanut brittle 180 degrees such that previously downward facing side is now facing up. Task Specifications Motion of spatula will be achieved via linkage mechanism Input should be a motor rotating a single link. Full joints are prefered to half joints A spatula which can efficiently load peanut brittle (PB) has been designed and given to
us PB is 9” square PB must be flipped 180 degrees PB should not be placed on top of other pieces of PB PB should not be broken while being flipped PB should be centered on conveyor after flipping No damage or alterations should be done to the conveyor Spatula should remain stationary or in forward level motion to allow at least half of the
PB to be loaded onto the spatula Linkages must be strong enough to hold PB Linkages and joints must be strong enough to rotate at high speeds.over 3 rad/s PB loading time should be 0.5 seconds minimum, 0.75 seconds max Linkage “cycle” must keep up with the rate at which PB approaches the flipper, which
would give a mechanism 1.25 seconds to complete a flip cycle before a new PB must be loaded
PB must maintain a separation of 6 in between each piece both before and after flipping All designs and PB handling must be OSHA and FDA compliant
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Design and Innovation
Design #1 Parallel Motion into Similar Coupler Curves
The idea behind this design was initially to use parallel motion is some sort of way to flip
the coupler over. This evolved into using similar coupler curves in hopes of accomplishing this.
Unfortunately it is very difficult to find curves with perfect arcs, so the mechanism would always
lock up. The second iteration of this design used a simple slider instead of another fourbar to
cause the coupler to flip over and then return to the level position. The curves shown in the
photos were particularly chosen due to their flat bottoms which could have performed a
sweeping and scooping motion to hasten the loading of the peanut brittle onto the spatula.
Design #1 Illustrations
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Design #2 Dwell
Assuming peanut brittle had to be fully loaded onto the spatula, and given the rates at
which peanut brittle moves down the conveyor, we calculated our dwell period to correspond to
216 degrees of crank rotation a MASSIVE time ratio for a dwell mechanism. We struggled in
finding a coupler curve that would meet this requirement, and did not find a solution until we
began our second iteration. While the dwell itself was appealing, the “flipping” motion of the
rocker did not seem substantial enough to flip a piece of peanut brittle.
Design #2 Illustration
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Design #3 3Line Synthesis
For this design, we assumed we could use two spatulas that would form a V, with one
side being attached / colinear with the coupler. Assumed the “Vshape” peanut brittle holder
pass three positions as shown in the diagram. At the first position, the peanut brittle enters the
holder at B1 point. Then the mechanism starts rotating and sends the holder pass the second
position. The brittle will lean to the other side of holder during this process. At last position, the
holder will land and put the peanut brittle on the belt at point A3 . The quick return dyad will
pull the holder back to the first position to start next flip.
Design #3 Illustration
Final Design Selection
When it came to choosing a design, only Design #3 actually performed a motion that
would guarantee the peanut brittle to flip. The attachment of a dwell mechanism similar to
Design #2 to Design #3 seemed like an obvious design solution, as it combined a system with
perfect motion with a system that would allow for a dwell to let peanut brittle load.
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Final Design Process
Construction of the 3line synthesis DoubleRocker
After further consideration, we decided the most optimal way to return the peanut brittle
to the conveyor belt was to have the last position of the “spatula” be at an angle to the conveyor,
taking advantage of gravity so that we can minimize the distance (and proportionally the time)
the coupler would have to travel. Full construction can be viewed in the appendix (A2A3).
Final step for Construction of the DoubleRocker
Construction of the Dwell
By changing our assumption that the peanut brittle would have to be fully loaded onto the
spatula to be flipped properly, we realized we wouldn’t need as long a dwell period. By only
having 6” of the peanut brittle loaded on the spatula instead of the full 9”, we were able to save
an entire 0.25 seconds off of the dwell period, giving us a new time ratio of 1:2 meaning only
120 degrees of crank rotation would correspond to a dwell (as opposed to the 216 degrees
required previously).
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Time Ratio Math
For basic link proportions, we turned to the symmetrical coupler curve tables provided by
Norton. After reconstructing the coupler curve in LINKAGES, we constructed the link
properties of links A and B and found the location of the 3rd ground joint. Link lengths and joint
positions were measured via ruler and scaled in relation to the crank.
LINKAGES software
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Dwell Construction
Paper to CAD Issues and Developments
As construction for the dwell was done by hand and measured with a ruler, inaccuracies
quickly became apparent when the CAD model locked up. In this figure we see that the dwell
did not achieve the required 137.5 degree output the 3line synthesis directed we must have.
This was fixed inCAD by reconstructing link lengths to satisfy a rocker motion of 140 degrees
(chosen to accommodate changes in link sizes). Finalized link lengths in appendix (A4).
Measurement of rocker motion reveals mistake made in measurements
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Final Assembly : MultiDesign Connection
The dwell and 3line designs were physically combined by setting the dwell into its
“dwell” position, setting the 3line into its “loading” position, and then joining the rocker of the
dwell assembly and the top rocker of the 3line assembly and locking them together so that they
are effectively one link. A full render of the design can be seen in the appendix (A1).
Planer Representation of Completed Design
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Results
With the CAD model complete and all linkage lengths finalized, we have a working
model that we can perform analysis on and observe. A quick motion study by adding a motor
rotating at 75 rpm (the speed required to perform the cycle in time) has been constructed and
made available for viewing at the following url: https://www.youtube.com/watch?v=AwAHPSoeBk4.
Upon observation of the motion study, the spatula clearly reaches its main starting and
ending positions, making our linkage mechanism a success as far as pure geometry and position
analysis goes (see below figures). Unfortunately, there are some clear problems we can see with
the dwell and overall motion of the assembly; mainly the incredible speed at which the spatula
moves in its flipping motion. Additionally, there is a poor transmission angle within the dwell
assembly during the spatulas initial “lifting” period.
The Two Extreme Positions of the Spatula, shown in Blue
Position and velocity calculations were performed in MathCAD, and can be viewed in
full in the appendix (A5 A8). The green fourbar above was first taken and positions were
calculated for every 90 degrees of crank rotation. Then the dwell was taken as a 5 bar using the
known angles calculated in the first analysis to find the angle which the fixed rocker would be
positioned. Then using that known angle the positions of the spatula could be determined.
Velocity analysis was also done as it was deemed most important to know the velocity that the
peanut brittle would be moving at while it was released. We calculated the velocity that the
coupler point would be moving at would be 96.77cm/s in the x direction and 56.101 in the y
direction.
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Conclusion
While the linkage mechanisms satisfies the initial 3Line synthesis it was designed to
move with accordance to, the resulting motion is very fast and runs the risk of having peanut
brittle leave the spatula prematurely. Premature peanut brittle evacuation from the spatula could
result in the peanut brittle underflipping, overflipping, not land on the conveyor, and possibly
become damaged upon landing. All of these possibilities would clash with our original task
specifications, thus proving this design to be illsuited for the task at hand if no changes are
made.
However, in an industrial environment this can easily be solved by having an additional
flipping mechanism of the same design placed further down the conveyor line. With two
flipping mechanisms now flipping every other peanut brittle, mechanisms will have double the
time to complete a cycle before they must be in the loading position for the next peanut brittle.
Crank rotation speeds would be reduced from 75 rpm to 37.5 rpm. This can be easily visualized
by playing the motion study video at half speed: https://www.youtube.com/watch?v=AwAHPSoeBk4.
If such a solution is deemed undesirable by the customer, the original design may be
iterated again with a different 3line synthesis such that the 3 positions are closer together along
the xaxis, and thus having the coupler go through these positions at a slower speed. The
nonoptimal transition angle with the current dwell can be fixed by selecting a different coupler
curve.
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Appendix
A1: Total Mechanism in SolidWorks
A2 : 3line Construction
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A3 : 3line Construction 2
A4 : Final Lengths of Dwell Assembly
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A5 : Position Analysis
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A6 : Position Analysis 2
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A7 : Position Analysis 3
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A8 : Velocity Analysis
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Bibliography
Brittle (Food). (2016, June, 23). Retrieved from https://en.wikipedia.org/wiki/Brittle_(food) Norton, R. L. (2012). Design of Machinery – An Introduction to the Synthesis and Analysis of
Mechanisms and Machines. New York, NY: McGrawHill. [Sam King]. (2012, February, 16). Kinematics Food Flipping Machine. [Video File] Retrieved
from https://vimeo.com/36887419 [SoleFerry]. (2013, July, 1). How It’s Made – Frozen Pancakes. [Video File]. Retrieved from
https://www.youtube.com/watch?v=4043Htlxjg
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