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REHRIG PACIFIC MILK CRATE STACKER

Team Tebow

Peter Ligeiro, Matthew Mason

Cameron Cole, Sagar Raut

Tuan Huynh, Hu Lin

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Table of Contents

Executive summary ........................................................3

Introduction ....................................................................4

Design specification .......................................................4

Customer Specifications ......................................................................................................... 4

Design concepts..............................................................6

Receive crates from Cartesian robot ....................................................................................... 7

Re-orient the crates ................................................................................................................. 8

Stacking the crates .................................................................................................................. 8

Move crates for pick up by forklift ......................................................................................... 9

Concept selection and justification.................................9

Existing products and application patents ....................12

Patent Claim .................................................................16

Schedule .......................................................................17

Conclusion....................................................................17

References and citation.................................................18

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EXECUTIVE SUMMARY

The problem that is the subject of this report is the stacking of milk crates for the Rehrig

Pacific Company. The company is a leading manufacturer of reusable plastic pallets and crates

and has a largely automated production and handling system. However, the case of milk crates

has presented a formidable challenge in creating a sufficient automated solution. Significant cost

savings on the order of at least $30,000 annually can be realized by eliminating the need for

manual processing. This cost savings offers a design constraint in the complexity and

affordability of the final solution that will be proposed.

The crates are produced on a molding machine and delivered by Cartesian robot 4 at a

time, in a 2x2 formation, to a handling area. After receiving the crates, they are stacked into a

4x4x10 crate high stack. There is a cycle time of 30 seconds in between crate deliveries. The

essential design problem is to devise a consistent stacking mechanism that can receive the crates

in the handling area and form the stack of the desired size, thereby removing the need for human

interaction. This entails not only the stacking of the crates, but making the stack available for

transportation by forklift to the warehouse for storage.

The aspect of milk crates that has made automated stacking difficult up to this point is the

difficulty ensuring the milk crates fit within each other, termed nesting. If the crates are

misaligned just a few inches, they will not sit within other, making stacking impossible as the

crates will not be stable and topple over. Moreover, when the crates are received from the

Cartesian robot, they are received upside-down, which means they must be properly oriented

before final processing and storage in the warehouse. The design must also be able to function on

two separate, albeit similar machines, that produce the crates, requiring it to be readily moved

from one machine to the other.

Several preliminary designs have been postulated to solve the problem: the Flipping

Funnel, the CartWheel Machine, and the Rotational Plate. The Flipping funnel utilizes gravity to

both orient and stack the crates, whereas both the Cartwheel Machine and Rotational Plate clamp

onto the box and rotate it to produce the desired rotation and stack the crates. Stack formation is

achieved through the use of pushers in the Flipping Funnel and CartWheel Machine, whereas a

rotating baseplate forms the basis of the Rotational Plate design. Another possibility that requires

further review is an improved “upstacker” design, a stacking mechanism that has been

implemented in other Rehrig Pacific facilities with limited success.

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INTRODUCTION

The Rehrig Pacific Company is seeking an automated solution for stacking of their milk

crate products. The milk crates are produced on a molding machine, where they are then dropped

upside-down in a handling area for stacking via Cartesian robot and transportation to storage in

the warehouse via forklift. Stacking is down with the crates right-side-up in a 4x4 formation to a

height of 10 crates. The crates are currently stacked manually as attempts to automate the process

in other facilities have only been met with limited success. This presents a significant cost

savings opportunity if the manual labor can be otherwise utilized for other tasks. This cost

savings is currently estimated to be around $30,000, presenting a constraint on the complexity

and affordability of the chosen design. The chief technical challenge causing this difficulty is the

precision of the stacker that is necessary to ensure that the crates nest within each other properly.

Moreover, issues of crate orientation, 4x4 pattern formation and stack availability for forklift

transport present further challenges in devising a suitable solution. Lastly, the solution must be

adaptable and readily moved between the two machines, which both operate in the manner

described above, used to produce milk crates.

DESIGN SPECIFICATION

This project has numerous specifications supplied by the client. They require that the

design be consistent, movable, and cost efficient. The design that is required must be able to

receive, orient, and stack plastic milk crates as they come out of an injection molding machine.

The crates are currently being stacked manually, and the client would like a machine to automate

the process. There are 6 major specifications that need to be met.

Customer Specifications:

1. The crates must be received from the injection mold. The crates are removed

from the mold by a Cartesian robot 4 at a time. They can be dropped in a 2x2

pattern, which is the current mode of operation, or possibly in a 1x4 row. The

time in between delivery of each set of 4 crates is 30 seconds. The automated

system that is designed must be able to receive and process all 4 crates before the

next batch arrives.

2. The crates must be oriented. They are currently delivered face down. The client

requires that the crates are stacked face up for storing in a warehouse. The

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process designed needs to flip the crates 180° before stacking them. The crates

are delivered hot and are still somewhat deformable. Excessive handling or

clamping forces can cause permanent deformation of the product. If compressive

forces are used, the bottom of the crate is the optimal place for applying pressure.

3. Following the receiving and orienting of the crates, the crates must be stacked.

The crates are to be stacked 10 high, which is a height of 110 inches, and arranged

in a 4 crate by 4 crate block, totaling 160 crates and a weight of approximately

440 lbs. The crates can be stacked and then flipped or flipped before they are

stacked. All designs should be made to stack 10 crates on top of each other;

however, if stacks of 5 are more cost effective they can be worked with. The

crates must nest within each other, requiring a high level of precision in the

stacking mechanism as the tolerances for the crates to fit within each other are

small. Moreover, as the crates are stacked to large heights, the small variations in

nesting as well as the create deformability cause the stacks to lean slightly.

Following the formation of a 4x4x10 stack, the crates must be transported to an

area outside of the work cell for forklift handling.

4. The design needs to be interchangeable between two different molding machines.

Crate production can be moved from one machine to the other in the middle of the

workday which means the stacking machine would also need to be moved in a

timely manner. The stacking device also needs to be able to be stored when milk

crates are not in production. The work cell area available for the stacking

mechanism is similar at the two machines, but the Cartesian robots that deliver the

crates have some differences. The two robots can release the crates at different

heights, and one work area has a lift table that can be retracted back down to floor

level. The floor area encompassing the machines, however, is quite different

between the two machines of interest. This complication makes the delivering of

the crates to the forklift more difficult. One machine is surrounded by a large

amount of open area, making it a simple matter, whereas the other machine offers

very limited space and has several barriers in place further constricting the

available area.

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5. The cost of the device is an important limiting factor of the design. There have

been some machines already designed and in limited use to perform the crate

stacking function. However, many of the machines cost between $60,000 and

$80,000. This cost exceeds the monetary value that would be gained by replacing

manual labor, therefore making it an unprofitable solution. The specified target

given by the Rehrig Pacific was in the $30,000 range. Our specification is to have

our design come in at a lower price than these other machines.

6. In devising a solution, cost-effectiveness is the overriding factor that will

determine the feasibility in pursuing a particular design. Beyond that

specification, the capability of the stacking mechanism to produce a repeatable

well-nested 10 crate stack is the root problem and thusly the next most important

specification. The compactness and interchangeability of the design follows as if

the solution impedes the production of other items, it cannot be feasibly

implemented. The problem of orientation and the conveying of the stacks to an

area to be handled by forklift are the last two specifications in order of

importance.

DESIGN CONCEPTS

Functional

Requirements Strategy Physics Risks Counter-Measures

Drop crates onto a

conveyor belt

Gravity, Deformable

Body

Mis-alignment of

crates Sorting Plates, Guide

Receives crates from

the Cartesian Robot Funnel the crates into

device

Gravity, Deformable

Body

Crates getting stuck at

opening to funnel

Wide mouth with slant

down to the opening

Rotate using gravity Gravity, Def Bods,

Dynamics

Incomplete rotation of

crates

guides, rotating arm

added

Grasp and flip the

crates in ferris wheel

design

Def Bods, Robotics Deformation of crates pressure sensors

Conveyer that recieves

on top and releases on

bottom

Gravity, Def Bods,

Robotics

Deformation of crates,

Alignment of crates

into receiving graspers

Tune grasping force to

minimal value to hold

crates, guides

Flip crates 180o

Use forklift/ secondary

machine to flip crates

after they are stacked

Def Bods additional time and

cost

Last resort,

discouraged by client

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Use vertical funnel to

align the crates

Gravity, Statics, Def

Bods

Crates not properly

nesting, height

effecting mobility

Add vibrations plate,

make it in pieces

Drop crates onto a

inclined plate that

rotates to a vertical

position

Gravity, Dynamics,

Statics

Crates falling off the

plate Side rails added

Drop crates onto guide

rails/ posts to align 10

high

Gravity, Statics Where do posts go

after stacked?

Outside guide rails

instead, telescoping

capabilities

Stack Crates 10 high

Move crates into a

rotating box with one

open side

Dynamics, Gavity,

Statics

How to get the crates

out of the box?

Hinges on side of the

box

Conveyor belts Dynamics

can only move crates

as far as conveyor belt

goes

Make conveyor long

enough for multiple

4x4 blocks

Pneumatic Pistons Dynamics, Fluids Expensive, could

knock over stacks

metal rollers, extension

rate

Move crates for pick

up forklift

Rotating Turntable Dynamics

cannot get off the

turntable without

forklift assistance

add conveyor belt on

top of turn table

The FARDAPARC breaks this problem into four smaller problems: receiving the crates,

rotating them 180 degrees, stacking them in the proper arrangement, and moving them out of the

stacker to be picked up by the forklift. The chart suggests several strategies for each problem,

describes the physics associated with the strategy, as well as risks and associated

countermeasures.

Receive crates from Cartesian robot

The first strategy for this is merely dropping the crates onto a conveyor belt. However, if

the crates are dropped any distance more then a few inches, they will bounce and become mis-

oriented. This problem can be countered with sorting plates or guiding the crates while they fall.

A second idea was to funnel the crates into the stacking device. A problem would be the crates

not entering the funnel in the proper orientation and becoming stuck. Using a mouth that is wider

then the crates and tapers down to the opening would alleviate this problem.

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Re-orient the crates

Crates arrive from the robot with the top side down and must be stacked top side up, thus

requiring a rotation of 180 degrees. This could be done using gravity and having the crates fall

into an edge and then rotate around it. Due to the possibility of incomplete rotation, guides or a

rotating arm would be needed. The Ferris Wheel design could be used to grasp and flip the

crates, however deformation is a problem in this design. Use of pressure sensors as well as

experimenting and tweaking the exact applied force would alleviate this problem. A third

solution would be a conveyor that grips each crate while on top, holds it while the crate travels

about the end of the belt, and then releases it onto a lower platform. Associated problems are

again deformation, as well as aligning the crates onto the graspers. Once again the graspers could

be tuned to the minimal necessary grasping force; guides could be used to align the crates.

Finally, a secondary machine or perhaps the forklift could flip a completed stack. This would

cost additional time and money and is a last resort that has been discouraged by the client.

Stacking the crates

The crates must be stacked four by four by ten high. This could be done with vertical

guides that the crates would fall through into position. However, this is risky because the crates

might not nest properly, as well as the height of the apparatus decreasing its mobility. The

addition of a bottom vibration plate would allow the crates to be shook into position, while

making the guiding apparatus modular would allow it to be moved with some assembly required.

A second solution would be dropping the crates onto an inclined plate which would rotate to a

vertical position when a stack was completed. A major problem would be crates falling off the

plate, which is easily fixed with the addition of side rails. A third idea is to drop the crates onto

posts, which would come up through the weave pattern of the crates. Telescoping posts would

allow the crates to be move upon stack completion. Finally, the crates could be dropped in a two

by two grouping onto a plate, which would then rotate 90 degrees. This would be repeated four

times to achieve a four by four group and repeated until ten high. The crates would then be

pushed out of the box, with hinges allowing one side to guide the crates down by not block their

movement.

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Move crates for pick up by forklift

The forklift will not always arrive instantly to pick up a completed stack, thus the stack

must be moved out of the way to allow a new stack to be formed. This can be done with

conveyor belts, however they would have a limited range of movement, but this can be fixed by

making the conveyor long enough for over one four by four block. A second solution is

pneumatic pistons; however these are large, expensive, and could knock over stacks. The

expense and size could be lessened by having the crates on metal rollers to decrease friction,

while a slow extension rate would allow the crate stack to act as a rigid body and remain upright.

CONCEPT SELECTION AND JUSTIFICATION

1 2 3 4

Crate Orientation (right side up) 10 Θ ∆ O O x

Stack 10 Crates 8 Θ O O ∆ O x

4x4 pattern of the stacks 8 Θ O ∆ x

Cost Effective 8 Θ O Θ ∆ x x

Forklift's accessibility to receive the stacks 5 O O Θ x

Safety 10 ∆ Θ ∆ x

Able to fit into another production line 6 Θ ∆ ∆ ∆ O ∆ x27 18 21 21 27 18 15 15

234 132 156 150 228 111 126 120 Total 1257

0.186 0.105 0.124 0.119 0.181 0.088 0.100 0.095

Sum of Importance*Relationship

Importance Rating

Ease o

f dis

assem

ble

and a

ssem

bly

Meet O

HS

A requirem

ents

Deliver S

tacks to d

esig

nate

d a

rea

Min

imum

Main

tenance

Arr

ange S

tack to 4

x4 p

attern

Sta

ck w

ithin

30 s

econds c

ycle

Rating of Current

Product:

Crates Up-stacker

Cu

sto

mer

Pre

fere

nce

Total Value

Receiv

ing c

rate

s fro

m c

artesia

n robots

Ability to flip c

rate

rig

ht sid

e u

p

Imp

ort

an

ce

Engineering Requirements

Θ = 9 - Strong Relationship

O = 6 - Moderate Relationship

∆ = 3 - Weak Relationship

□

●

□

■

□

■

□

■

●

●

●

Correlations ■ Strong Neg. □Negative ● Strong Pos. ○Positive

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As shown on the House of Quality, the customer has highest requirements about the

orientation of the final stacked and safety. The crates need to be finally stacked right side up to

avoid bulk transportation from causing scratches on the top face of the crate. The cost effective is

another biggest concern from the customer. Current crate up-stacker can finish the task

effectively, while the cost of the machine is too high. To increase the efficiency of the

transportation and utilize the space of the warehouse, 10 crates per column are highly preferred

to be stacked, and the columns are expected to be arranged in 4x4 pattern. The compatibility of

the machine with another production line was scored 6 based on the customer’s requirements.

The forklift’s accessibility to receive the stacks is least important among all the customer’s

preferences.

On the middle part of the QOF, the relationships between engineering requirements and

customer preference are classified to three different levels with values of 3, 6 and 9. Each

engineering requirements are scored by summing the multiplication of the values of importance

and relationship. The ranking of the engineering requirement was derived and shown on the

bottom of the QOF. The rating of the current product is also shown on the right part of the QOF.

The current existing product meets the most of the customer’s requirements, while it is not cost

effective. It is not capable to stack 10 crates either.

After brainstorming through customer needs and design concepts, an evaluation matrix,

Figure 3, is produced to make comparison between alternative designs and standard design.

CONCEPT Funnel Flipper CartWheel Machine Rotational Plate Robotic Stacker

Criteria

Crate Orientation (right side up) 2 4 4 4

Stack 10 Crates 3 4 4 4

4x4 pattern of the stacks 3 3 4 4

Cost Effective 4 3 2 0

Forklift's accessibility to receive the stacks 3 4 2 3

Safety 4 4 3 3

Able to fit into another production line 2 3 3 2

Total 21 25 22 20

Relative Total 0.75 0.89 0.79 0.71

4=Very Good, 3=Good, 2= Satisfactory, 1=Just Tolerable, 0 = Unacceptable

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Figure 3. Evaluation Matrix

The Funnel Flipper, CartWheel Machine, Rotational Plate, and Robotic Stacker are all capable of

receiving the crates, flipping the crates right side up, stacking ten crates high, and assembling

4x4 pattern of the stacks. For each of the concepts, there are some advantage and disadvantage

on its functional ability.

1. The Flipping Funnel is a big funnel shape cylinder that stands underneath the robot arms

to catch the four crates dropping down from the Cartesian robotic arm. Once the crates

fall into the funnel, it will catch onto the middle edges inside the funnel and automatically

flip right side up. As it continues downward the tunnel, it starts to stack the crates one

after another by path sliding tool. After the stacks have ten crates, the side piston pushes

the stacks to designate area for the forklift to carry into storage. The design receives a

relative total of 0.75 because there are several set backs for this design. The flipping

mechanism is not always flipping 180o to be right side up. There is possibility that the

crate catches on the edges and flips sporadically. Consequently, this causes disorder in

the stacks and prevents the next crate to stack correctly. It doesn’t fit to other production

well due to the size of this design. However, the design scores good rating on cost and

safety because it has less automation parts and no moving parts in the forklift designate

area respectively.

2. The function steps of the CartWheel Machine are receiving from Cartesian robotic on

conveyor belt. The belt moves the crates toward the cart wheel like arm where the four

crates grabs by the cart wheel arm gripper. Then, the arm rotates 180o to flip it right side

up and drops onto the small incremental plate. The plate moves downward for the next

crates to have the same position as previous crates. Consequently, the technique stacks

the crates on top of each other in 2x2 pattern stacks. Once the stacks have ten crates, the

side piston pushes and arranges the stacks to 4x4 pattern on designate forklift area. The

drawbacks for this design are cost due to increase in automation and unable to fit well

into another production line due to many parts in the design decrease the mobility of this

machine. Since the piston pushes the stacks on the floor to align it in 4x4 pattern, it has a

chance to misalign the crate due to the uncontrollable friction on the floor which can

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cause the stacks misalign from the positions. Overall, the design has score very good for

safety, crate orientation, stacks, and forklift accessibilities.

3. The Rotational Plate is similar to CartWheel Machine. Instead of the crates drops onto

small incremental plate, it has big plate to accommodate 4x4 pattern of the stacks. The

big plate divides into four quadrants, and each quadrant holds 2x2 pattern of the stacks.

When the quadrant’s stacks have ten crates, the plate rotates and set at the exact position

for the cartwheel arm to stack the crate onto the new quadrant. This technique eliminates

the stacks misalign problem in the CartWheel Machine design. However, the scores

decrease for safety, cost, and forklift accessibility because of the moving plate.

4. Lastly, the Robotic Stacker has four of six axis robotic arms. Each arm grabs the crates

from a conveyor belt where the crates are being dropped by Cartesian robotic arm. Then,

the robotic arms flip the crate right side up and stack the crate on a plate and top of each

other. Next, the arms push and align stacks to 4x4 pattern. Lastly, the plate is moved by

conveyer belt to forklift designate area. The major problem with this design is

exceedingly expensive to obtain four robotic arms. Therefore, the design score zero,

unacceptable, for the cost of customer requirements. Since it scores zero on the cost of

customer requirements, the design will consider as last alternative solution.

Comparing all the alternative designs, the CartWheel Machine scores highest among other three

conceptual designs. This design will be discussed with Rehrig Pacific Company to further the

design process.

EXISTING PRODUCTS AND APPLICATION PATENTS

A similar design to the CartWheel concept is seen in Figure 1.

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Figure 1: Device for stacking and unstacking (Patent 6960058)

This machine receives the object from a conveyor on the right. This object is then picked up by

a ferris wheel type mechanism which drops the object on a lift table. As each object arrives, the

table moves progressively downwards, so that the drop from the ferris wheel to the stack is the

same each time. When the stack reaches the appropriate height, they are moved out via a

conveyor marked by “2” in Figure 1. This device differs from the CartWheel however, in that it

does not flip the objects when it receives them. Additionally, the CartWheel builds four stacks at

a time, whereas this device only produces one. Lastly, the CartWheel concept utilizes a turntable

in order to have room to produce the remaining stacks needed before moving them out.

A possible marketplace solution for stacking milk crates is a downstacker, shown in

Figure 2.

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Figure 2: Downstacker (Patent 4865515)

This machine receives containers from a conveyor above and then pulls them downwards. When

the next container arrives, it is allowed to rest atop the previous one to form a stack of two.

Then, the downstacker lowers the stack. Once the stack is formed, it is moved out of the work

cell on a conveyor below. One interesting aspect of this design are the vertical guides used to

ensure that the containers remained properly aligned. In this way, it is similar to the concepts we

have developed for the project. Both the CartWheel and the Flipping Funnel receive crates from

above and have vertical guides to ensure that the alignment is correct. However, as with the

stacking device, the downstacker does not have a mechanism for flipping the crates.

The machine used by Rehrig Pacific to stack milk crates is an upstacker, shown in Figure

3.

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Figure 3: Upstacker (Patent 3410046)

The upstacker, similar to the downstacker, receives a crate from a conveyor; then as shown in the

lower drawing of Figure 3, it is lifted upwards. When the next crate arrives, the previous crate is

dropped on top of it, creating a stack of two. This stack is then lifted upwards. This is repeated

until a stack of ten milk crates is created. The crates are lowered onto the conveyor which

transports the stack out of the work cell where a forklift may pick them up. The upstacker has

been implemented successfully in other Rehrig Pacific plants. However, it has numerous issues

that necessitated finding an alternative solution.

Firstly, the upstacker has numerous growing pains. It must be precisely programmed;

else the stack will not be properly formed. So, an alternative solution which is easier to

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implement—both in terms of programming and operator training—is needed. Secondly, the

upstacker struggles to create stacks of ten. A stack of ten made by the upstacker will lean

considerably because the milk crates nest very poorly. Therefore, the plants which use the

upstacker are limited to creating stacks of five, and using the forklift to place one stack of five on

top of the other. This is far from ideal, as it creates more work for the forklift operator. Lastly,

the upstacker is expensive, with prices exceeding $60,000. The Lawrenceville plant would like

to have their stacking problem solved for a much lower price.

PATENT CLAIM

We claim:

1. Device for orienting and aligning milk crates to create multiple stacks of milk crates using

gravitational forces.

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SCHEDULE

WBS Tasks

Task

Lead Start End % C

om

ple

te

1 Team/Project 1/11/10 1/13/10 100%

1.1 Design Process Lecture 1/12/10 1/12/10 100%

1.2 Team/Project Selection 1/13/10 1/13/10 100%

2 Project Selection Peter 1/14/10 1/20/10 100%

2.1 Team Meeting 1/15/10 1/15/10 100%

2.2 Ideas Brainstorming 1/18/10 1/18/10 100%

2.3 Intellectual Lecture 1/19/10 1/19/10 100%

2.4 Final Project Selection 1/20/10 1/20/10 100%

3

Preliminary Project

Process 1/21/10 1/27/10 100%

3.1

Milk Crate Stack

Dicussion 1/22/10 1/22/10 100%

3.2

Schedule Meeting With

Rehrig Pacific 1/22/10 1/22/10 100%

3.3 Tour Rehrig Pacific 1/25/10 1/25/10 100%

3.4

Present Problem

Description 1/26/10 1/27/10 100%

4 Design Partition 1/28/10 2/03/10 100%

4.1

Brainstorming Ideas/Patent

Search 1/29/10 2/01/10 100%

4.2 FRDPARRC Chart 2/02/10 2/02/10 100%

4.3 Ideas Presentation 2/03/10 2/03/10 100%

5 Presentation 1/Report 1 2/04/10 2/10/10 100%

5.1

DiscussRehrig

Pacific/Ideas 2/05/10 2/08/10 100%

5.2 Presentation 1 2/09/10 2/10/10 100%

6 CAD Drawings 2/11/10 2/17/10 100%

6.1 Draw ings Partition 2/11/10 2/17/10 0%

6.2 Finalize Report 1 2/15/10 2/15/10 0%

7 Engineering Analysis 2/18/10 3/03/10 0%

8 Design Prototype 3/04/10 3/10/10 0%

9 Presentation 2/ Report 2 3/11/10 3/17/10 0%

10 Finalize Prototype 3/18/10 3/31/10 0%

11 Ethic Analyzing 4/01/10 4/07/10 0%

12 Finalize/Company 4/08/10 4/21/10 0%

13

Spring 2010 Capstone

Expo 4/22/10 4/28/10 0%

21 -

Feb -

10

04 -

Apr

- 10

11 -

Apr

- 10

18 -

Apr

- 10

28 -

Feb -

10

07 -

Mar

- 10

14 -

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- 10

21 -

Mar

- 10

28 -

Mar

- 10

25 -

Apr

- 10

02 -

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10

07 -

Feb -

10

14 -

Feb -

10

10 -

Jan -

10

17 -

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24 -

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31 -

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10

CONCLUSION

Thus far we have formulated several project designs and narrowed them down to two

main choices. First, the Flipping Funnel uses gravity to re-orient the crates as well as stack them.

Pistons are then used to move the stacked crates out for pickup. Second, the Wheel-based

designs grasp and flip the crates, then release them to the stacking point. In the Cartwheel

Concept, a similar piston pushing mechanism as used in the flipping funnel is implemented for

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stack formation and transportation. In the Rotational Plate, the 4x4 stack is formed by rotating

the base plate, which consists of 4 2x2 quadrants, eventually producing a 4x4 stack after a 360

degree rotation. Our future action steps are to select a design and analyze it thoroughly. This

will followed by a detailed theoretical design and a prototype. However, we are open to the

possibility of devising different designs as we interact more with the actual machines. Moreover,

we may revisit some preexisting concepts such as the upstacking concept, where crates are

stacked, which Rehrig Pacific has attempted to implement in other mills with a limited degree of

success.

REFERENCES AND CITATION

Dorner, W.C., Patent 4865515, 1989.

Johnson, J.A., Patent 3410046, 1968.

Schwetz , A. et al., Patent 6960058, 2005.