functional, assembly, cost, and safety analysis of...
TRANSCRIPT
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FUNCTIONAL, ASSEMBLY, COST, AND SAFETY ANALYSIS OF THE TRASH KRUSHER (TK) 10,
A MANUAL TRASH COMPACTOR
L. Castro, S. Garcia, M. Herdon, C. Kunka, R. Morocoz Mechanical and Aerospace Engineering, University of Florida
14 MAR 2014
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TABLE OF CONTENTS
INTRODUCTION ……………………………………………………………………………………………… p. 4 HOW IT WORKS ……………………………………………………………………………………………… p. 5
1.1 Lifting the Lid ……………………………………………………………………………….......... p.
5 1.2 Compacting Trash ……………………………………………………………………………….. p.
7 1.3 Releasing Lid …………………………………………………………………………………..... p. 9 1.4 Reattaching Compactor …………………….………………………………………………….. p.
10 1.5 Locking Lid Open ……………………………………………………………………………….. p.
11 1.6 Securing Trash Bag …………………………………………………………………………….. p.
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PERFORMANCE ……..……………….…………………………………………………………………….. p. 12
2.1 Pedal Force ………………...…………………………………………………………………… p.
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2.2 Compactor Detachment Force ………………………………………………………………… p. 15
2.3 Compaction Ratio ………………………...…………………………………………………….. p.
16 2.4 Dampening Ratio .……………………………………………………………………………..... p.
17 2.5 Packaging ……………………………………………………………………………………….. p.
18 PARTS ………………………………………………………………………………………………………... p. 19
3.1 Naming Convention …………………………………………………………………………….. p. 19
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3.2 Material Identification ……………………………….………………………………………...... p. 20
3.3 Part Functions ......................................................…………………………………………... p. 23 3.4 Fatigue Analysis ………………………………………………………………………………… p. 33 MANUAL ASSEMBLY ………………………………………………………………………………………. p. 35 4.1 Manual Assembly Sequence...………….……………………………………………………... p. 35 4.2 Manual Assembly Time...……………………………………………………………………… p. 50 COST …………………………………………………………………………………………………………. p. 54 5.1 Landed Cost ……………...…………………………………………………………………….. p. 54 5.2 Facilities Costs ....……………...………………………………………………………………. p. 55 5.3 Labor Costs …......……………...………………………………………………………………. p. 56 5.4 Total Cost per Unit .…………....………………………………………………………….……. p. 57 SAFETY ………………………………………………………………………………………………………. p. 59
6.1 Fire Test …..…………………………………………………………………………………...... p. 59
6.2 Risk Assessment ……………………………………………………………………………….. p.
59 6.3 Safe Operation ……………………...…………………………………………………………... p. 60 DESIGN ANALYSIS …………………………………………………………………………………………. p. 61 7.1 Pros/Cons of Design ...…………………………………………………………………………. p. 61 7.2 Conclusion ………………………………………………………………………………………. p. 61
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APPENDIX ………………….………………………………………………………………………………... p. 62
A. Plastic Identification Flow Chart ……...…………………………………………………..……. p. 62
B. Assembly Handling and Insertion Time Tables ..…………………………………………...… p. 63
C. Safety Chart ……………………………………………………………………………………… p. 64
D. Example Non-Landed-Cost Calculations ……………………………………………………. p. 65 E. International Labor Cost ………………………………………………………………………... p. 68
REFERENCES …………………………………………………………………………………………...….. p.69
INTRODUCTION
The purpose of this report was to analyze a manual trash compactor, the Trash Krusher (TK) 10 (Fig. 1). The functional requirements section explains how the device functions and assigns performance specifications based on experimental and analytical models. The parts section reveals how each part works to satisfy the overall function and relates material selection to its function. Manual assembly includes the assembly sequence and time. The cost section includes landed costs, facility costs, and labor costs both in the United States and China. Safety includes risk assessment and instructions for safe operation. Finally, the design analysis evaluates the overall design and summarizes the findings of this report. Trash compactors are devices that reduce the volume of waste material. They are available for commercial and residential use and are powered electrically or mechanically. The TK10 Trash Krusher falls in the mechanical category of trash compactors because the user has to physically apply the force that will be transmitted to the waste.
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The compactor in the TK10 allows the user to vertically apply a force to the bulk of waste inside the trash receptacle and compress it up to half its original volume. Since this design allows packing twice the waste in the same size bag as a regular trash receptacle, amount of plastic waste as well as the time spent disposing trash are reduced. Also, to improve sanitation and safety, the design of the TK10 shields the user from contacting the trash.
Figure 1: Drawing of TK10, “The Ultimate Trash Krusher.” Important features include manual compaction, bag locking mechanism, damped hinge, and foot pedal. All dimensions are inches.
HOW IT WORKS This section provides an overall technical discussion of how the TK10 functions. Refer to the “Parts” section for naming conventions and a more detailed analysis on a part-by-part level. Refer to “Mechanical Model” for a mathematical evaluation of the function. Refer to the “Safe Operation” section for a more simple discussion of how to operate the device. 1.1 Lifting the Lid
To open the lid, force is transmitted through the foot pedal and several other parts (Fig. 2 -- 4). The
user applies a vertical force to the foot pedal with his foot. The foot pedal lever rotates around the lever
fulcrum rod to transfer the force from the user to the coupler rod and fork. The coupler rod and fork is
attached to the foot pedal assembly through the coupler rod revolute mount (lower) which allows slight
rotation in this interface. The coupler rod and fork is attached to the damper w/ traveler tab as well as to
the coupler rod revolute mount (upper). The coupler rod and fork goes through an orifice in the lip. This
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hole offers the ability to lock the lid in place if necessary. The coupler rod revolute mount (upper)
transfers the force and displacement from the coupler rod and fork to the lid. The lid rotates with
respect to the hinge rod. The hinge rod connects the hinge (external can side) to the hinge (lid side).
The hinge (external can side) is statically attached to the external can while the hinge (lid side) is
allowed to rotate. The hinge (lid side) is connected to the lid sub-assembly and the coupler rod revolute
mount (upper), allowing the lid to rotate whenever the coupler rod revolute mount (upper) is pushed by
the coupler rod and fork.
Figure 2: Parts and sub-assemblies involved in the process of opening the lid. The labels correspond to: 1) Foot
pedal sub-assembly, 2) Foot pedal lever, 3) Lever fulcrum rod, 4) Coupler rod revolute mount (lower), 5) Damper
w/ traveler tab, 6) Coupler rod and fork, 7) Lid locking sub- assembly (lib, lid lock), 8) Lid hinge sub-assembly
(coupler rod revolute mount, hinge (lid side), hinge (external can side), and hinge rod, 9) Lid sub-assembly
Figure 3: Applied force creates moment to extend damper w/ traveler tab to the force through the coupler rod/fork.
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Figure 4: Lid hinge sub-assembly. These figures show the reaction of the sub-assembly when the coupler rod and
fork displaces upward. The labels correspond to: 6) Coupler rod and fork, 7) Lid locking sub- assembly (lib, lid
lock), 8a) coupler rod revolute mount (upper), 8b) hinge (lid side), 8c) hinge rod, 8d) hinge (external can side), 9)
Lid sub-assembly
1.2 Compacting Trash
To compress the trash inside the internal can, the user must first detach the compactor from the lid.
The user holds the handle with the preferred hand and applies a vertical force downward to separate
the compactor assembly from the lid (Fig. 5). The force has to be high enough to overcome the force of
the hooks/clips and magnets in the interface between the compactor assembly and ring assembly (Fig.
6). Once the compactor has been separated from the lid, the user can apply the force to compress the
waste (Fig. 7). The compaction ratio depends on the type of trash that has to be compressed. See
“Compaction Ratio” section for a more detailed discussion.
8a
8c
8d 6
7 9
8b
8
Figure 5: These figures show the process of separating the compactor sub-assembly from the lid sub- assembly. Initially the compactor sub-assembly is secured in place with two hooks/clips and six magnets located on the ring sub-assembly. The red arrow is the applied force.
Figure 6: The compactor sub-assembly is secured to the ring sub-assembly. The two hooks/clips are located at the left and right interface of the lid and compactor sub-assembly. The six magnets and steel inserts are distributed to disperse the weight of the compactor sub-assembly. The steel inserts are housed within the compactor sub-assembly while the magnets reside in between the top and bottom ring.
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Figure 7: The vertical force applied to the compactor sub-assembly creaates a pressure that compresses the
waste. The reported compaction ratio is 2 to 1, which means that the waste can be compressed up to half its
original size. The labels correspond to the lid assembly (1), compactor (2), internal can (3), trash bag (4), and
waste (5).
1.3 Releasing Lid
Once the trash has been placed inside the bag within the internal can, the force applied to the foot
pedal can be released. The damper w/ traveler tab resists the displacement of the lid back to closing
position. The damper w/ traveler tab slows down the angular velocity of the lid which results in the
smooth closing of the lid. Figures 8 -- 9 show the process of closing the lid by releasing the force from
the foot pedal as well as the parts involved in the damping process.
1 2
3
4 5
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Figure 8: Reaction of the foot pedal sub-assembly once the force applied to the foot pedal is released. The weight
of the lid, coupler rod and fork, and the hinge sub-assmebly forces the foot pedal sub assembly back to its original
position.
Figure 9: The damper w/ traveler tab oposes the downward displacement (represented by arrows) of the coupler rod and fork. The damper slows the displacement so the lid closes slowly and smoothly. Upward displacement is slowed much less than the upward displacement.
1.4 Reattaching Compactor To lock the compactor assembly back to the lid once the trash has been compressed (Fig. 10), the user
will have to align and apply a vertical force upwards. The magnets will help aligning the compactor in
the right place. When the compactor has been aligned, a vertical upward force has to be applied to
attach the snap fits. The compactor will produce a locking sound once is safely secured.
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Figure 10: The red arrows show how to correctly align the compactor sub-assembly so the magnets can attract the steel inserts and the hooks can securely lock the compactor sub-assembly to the ring sub- assembly and the lid. The black arrow represents the force necessary to raise the compactor. The blue arrow shows the force required to overcome the initial hook/clip force, and the green arrow is the force that has to be applied to the lid or ring to prevent the lid from opening when the compactor is being locked in place. 1.5 Locking the Lid Open The user has the option to lock the lid open by locking the coupler rod and fork (Fig. 11). The lip
assembly is equipped with the lid lock which can be used by applying a horizontal force. The lid lock is
capable of sliding with the lid lock screw and washer.
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Figure 11: Process of operating the lid-locking mechanism. 1.6 Securing Trash Bag To prevent the trash bag from detaching from the internal can during compaction, pull excess bag through the bag locking mechanism (Fig. 12). This part allows easy insertion of the bag but prevents sliding out.
Figure 12: Secure trash bag by pulling excess bag through the bag locking mechanism (shown in blue).
PERFORMANCE
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The Trash Krusher has three main functions: (1) lifting the lid, (2) compressing trash, and (3) closing the lid. To evaluate these features, pedal force, compactor detachment force, compaction ratio, and damping ratio are evaluated. Additionally, the packaging is tested. 2.1 Pedal Force The trash can features a foot pedal that is used to raise the lid, allowing hands-free access. This feature is useful when disposing of bulky trash or if the operator has difficulty bending over to lift the lid manually. It is necessary to determine the minimum force required to depress the foot pedal and raise the lid. In terms of a mechanical model, the input is pedal force, and the output is lid angle. This force was evaluated experimentally and analytically. For the experimental analysis, a load cell was used to measure the forces required. A simple LabVIEW program was created to display the output voltages of the load cell which could converted to forces through calibration. The calibration curve for the load cell was created by placing known masses on the load cell and comparing the voltage given by the load cell to the values for the unloaded case. The load cell was placed onto the pedal and gradually pressed downward until the lid was fully open, which corresponds to 77° relative to the vertical. Once the lid was fully opened, the pedal was held down so
that the lid would stay open. This test was done three times and the average maximum force was determined to be 81 N (Fig. 13).
Figure 13: Pedal input force as a function of time for raising the lid using the pedal. The initial upward slope is
when the force is gradually being increased to a point where the lid begins to open. This point is a maximum
because the lid’s center of gravity is farthest from the axis of rotation (worst-case scenario). Between the first
peak at 1.5 seconds and the trough at 2.5 seconds, the lid is. The remaining curve represents the lid bouncing off
the hinge while pedal force is maintained.
For the analytical analysis, a mechanical model was established to relate the required input pedal force
to the output lid angle. The required input force varies because the lid’s center of gravity changes as a
function of lid angle. Figures 14 – 16 show the balance of forces to arrive at the mechanical model
plotted in Fig. 20. Note that this segment only represents the lid-opening portion of Fig. 16.
From the free body diagram of the pedal (Fig. 17), the moments were summed about the fulcrum. The
distances from points 1 to 2 and points 2 to 3 are 5.79 inches and 5.46 inches, respectively.
0
10
20
30
40
50
60
70
80
90
0 1 2 3 4 5
Fo
rce, F
(N
ew
ton
s)
Time, t (seconds)
14
Eq. 1
Figure 14: Free body diagram for the pedal with the arrows representing the forces. The input force, Fi is force 1. Force 2 is the reaction force at the hinge, Rh. Force 3 is the force being transmitted from the connecting rod to the pedal, Fcp.
For the connecting rod free body diagram (Fig. 18), the forces were summed and equated to zero.
Eqn. 2
Fd is the force from the damper and is equal to the damping constant for the damper multiplied by the
velocity at which the rod is moving. Since the rod is constrained to move in only one direction and the
offset of the damper is small, any bending moment created is neglected. Also, since the damping
provided by the damper while being extended is very small, this force can probably be neglected as
well. It is included here for sake of completeness. Any bending moment due to the curve at the end of
the connecting rod is also neglected.
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Figure 15: Free body diagram for the connecting rod. Force 4 is the reaction force from the pedal, Fpc. Force 5 is
the force from the damper, Fd. Force 6 is the force due to the weight of the rod, Fwc. Force 7 is the force being
applied to the connecting rod by the lid assembly, Flc. In this case, forces 3 and 4 are equal and opposite.
For the lid/compactor assembly, the free body diagram has three forces (Fig. 19). To find Fwl and Fcl,
the moments were summed about the hinge at point 8. The distance between points 8 and 10 is 5.71
inches and the distance between points 8 and 9 is 1 inch. For this analysis, θ will denote the angle
formed as the lid opens from the horizontal and ϕ is the angle formed by a line connecting points 8 and
9 and horizontal. Due to the fixed geometry, this angle is 21.16 degrees less than θ.
Eqn. 3
Figure 16: Shows the free body diagram for the lid assembly. Force 8 is the reaction force at the hinge, Rh.
Force 9 is the force being transmitted from the connecting rod to the lid assembly, Fcl. Force 10 is the force due
to the weight of the lid/compactor assembly, Fwl. Note that forces 7 and 9 are equal and opposite.
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Combining equations 1-3 yields the following mechanical model (the force required to raise the lid as a
function of angle θ) (Fig. 17).
Figure 17: Plot of input pedal force required to lift the lid as a function of the lid angle, θ. The force is largest when the lid is fully closed since that is when the moment arm through which the weight of the can is acting is longest. As the lid opens and θ increases, the moment arm gets shorter and the force required to open the lid decreases. Due to the geometry of the hinge, the moment arm for the connecting rod actually gets slightly longer initially and then starts to decrease, causing the linearity in the first part of the graph.
The mechanical model is valid because its slope matches the slope of the lid-opening region. The
difference in maximum required pedal force between the experimental value (81 N) and the analytical
value (50 N) is due to the fact that the experimentally applied pedal force is at an angle less than 90°
has frictional losses (ex: damper). By assuming all of the error originates from the application angle
difference, the actual angle would be 38° relative to the horizontal. Additionally some of the error could
arise experimentally.
2.2 Compactor Detachment Force For trash compaction, it is necessary to determine the force required to separate the compaction device from the lid. If too little force is required, the compaction device may become unattached if the lid closes too quickly. If too much force is required, it becomes difficult to remove. To measure the force required to separate the compaction device from the lid, the load cell was placed on top of the compactor handle and pressed down until the compactor (magnets and snaps) released from the lid. Three tests were conducted to obtain an average (Fig. 18). The average force required to disengage the compactor was found to be approximately 91 N.
0
10
20
30
40
50
60
0 20 40 60 80
Inp
ut
Fo
rce R
eq
uir
ed
, F
i (N
ew
ton
s)
Lid Angle, θ (degrees)
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Figure 18: Shows the force as a function of time when disengaging the compaction device from the lid. The force gradually increases until the snaps separate and the force quickly decreases. The upward slope at the beginning is when the force is being gradually increased, and the peak corresponds to the point right before the snaps release.
2.3 Compaction Ratio The Trash Krusher is equipped with a manual compaction device housed in the lid that enables the consumer to compact the trash in the can, allowing more trash to be stored in each trash bag. This feature reduces the number of trash bags used by the consumer, ultimately limiting the number of trash bags that end up in landfills. Since this feature is the main selling point of the trash can, determining the actual compaction ratio is important as it gives the consumer an idea of how many trash bags can be saved. Although this ratio is a function of trash stiffness, the goal is to assess the reported 2:1 relationship. Quantifying trash is challenging since it is non-uniform. Paper products, plastics, food scraps, glass or metal bottles and cans, and many other items inevitably find their way into the garbage can. Each of these items has radically different material properties, and this has an important effect on how much compaction the consumer will realistically see. One consumer might claim a reduction in volume of 30% while another may claim 80%, but it all depends on the type of trash being compressed. A trash can full of wadded-up newspapers will be much easier to compress than a can full of plastic bottles. It is also very likely that some of the items in the can might shift or reorient themselves while being subjected to compressive force. The amount of compaction will also be greatly affected due to the orientation of some objects, such as aluminum cans which are easy to compress in one dimension and difficult in others. There is also the possibility of some of the items rearranging in a way such that they cannot be compressed by hand. To determine the compaction ratio, representative samples of garbage was used. This meant filling the can with “normal” household waste, trying to simulate as closely as possible what a full household garbage can might contain, such as a random combination of items listed previously. Once the can was full, the initial level of garbage would be measured. The compaction device would then be removed and the trash compressed. The level of garbage after compaction would be measured and
0
10
20
30
40
50
60
70
80
90
100
0 0.2 0.4 0.6 0.8 1 1.2 1.4
Fo
rce, F
(N
ew
ton
s)
Time, t (seconds)
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compared to the measurement taken before compression. The experimental average compaction ratio of 0.46 was close to the reported 0.50.
Table 1: Data from the compaction tests. Depth of trash was measured with a yardstick before and after compaction. Tests were conducted by an average-size male, and the trash was compressed as much as possible without the aid of any machinery. Based three tests with standard deviation of 0.103, average compaction ratio was 46%. This ratio can vary dramatically depending on trash type.
Test Original Trash Height (in) Final Trash Height (in) Compaction Ratio
1 20 13 0.35
2 18 8 0.56
3 19 10 0.47
Average: 0.46
2.4 Damping Ratio The lid of the Trash Krusher is equipped with a damper to ensure that the lid does not slam closed. To quantify the damping, the damping constant was determined. The damper was removed from the can and clamped in a vice. A small length of pipe was placed over the end of the damper, and a small rod was inserted into the pipe so that it rested on the end of the damper. Weights of varying masses were then placed on the end of the rod, and the time it took for the damper to fully compress under each mass was measured. The total travel of the damper was measured to be 54.4 millimeters. Using the time it took for the weight to fall and the travel of the damper, the velocity for each case could be determined (Table 2). The damping constant could then be calculated assuming viscous damping (force is linearly related to velocity). The results shown in Fig. 19 confirm this linearity and give a damping coefficient of 1690 N*s/m when the intercept is assumed to be zero. Table 2: Damping test conditions and calculated damping.
Test Mass (g)
Rod Mass (g)
Total Mass (kg)
Force (N)
Time (s)
Velocity (m/s)
Damping Coefficient (N s/m)
204 100 0.304 2.98 64.3 0.00085 3523
524 100 0.624 6.12 18.9 0.00288 2125
895 100 0.995 9.76 10.2 0.00534 1829
1815 100 1.915 18.79 4.7 0.01158 1622
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Figure 19: The results of the damping experiment confirm the linear assumption. Damping coefficient is 1690 N*s/m. For the linear fit, the intercept was set to the origin because zero velocity should give zero damping.
2.5 Packaging To evaluate the impact resistance of the packaging, several impact tests were performed [8]. All tests were performed by dropping the boxed assembly from 8 feet high. The three tests comprised a corner impact, front side (flat) impact, and edge impact. Note that the compactor was not included in the drop test because it is packaged inside the can with significantly more padding than between the can and outer box. After all three tests (compounded failure), the can was inspected (Fig. 20). The front of the can was dented, and some of the plastic parts of the foot pedal assembly were broken. The front was dented because the foam was insufficiently wide. The plastic broke because there was insufficient thickness of foam and stiffness of packaging. Overall, the packaging failed but could be fixed with a slightly larger box and wider foam in front (refer to definition of stiffness).
Figure 20: Drop tests were performed on the corner, front face, and side [8]. The tests showed the design failed due to insufficient padding on the front face and corners.
F = 1690 N*s/m (v)
R² = 0.96
0
5
10
15
20
25
0 0.002 0.004 0.006 0.008 0.01 0.012 0.014
Fo
rce,
N (
New
ton
s)
Velocity, V (m/s)
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PARTS
This section contains the naming convention, function, material, and manufacturing method for all of the parts. Table 3 summarizes the naming convention and part quantities. Tables 4 -- 5 contain the material identification experimentation process, manufacturing method, and benefits for material selection. Table 6 describes the function of each part under ideal and adverse conditions (water and/or fire), if applicable. Finally, fatigue analyses is performed to check the 10-year warranty. 3.1 Part Naming Convention Table 3: Summary of parts according to part group: compactor, main body, foot pedal, and lid.
GROUP PART NO. PART NAME QUANTITY
Com
pacto
r
1 Bottom 1
2 Top 1
3 Handle 1
4 Screw for handle (1/2” No.7 #2 Drive) 4
5 Steel insert 6
6 Foam pad 1
7 Screw for top/bottom (5/16” No.6 #2 Drive) 4
8 Screw cover 4
Main
Body 9 External can 1
10 Lip 1
11 Lid lock 1
12 Lid lock screw (5/16” No.6 #2 Drive) 1
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13 Lid lock washer (No.10) 1
14 Bottom 1
25 Feet 4
26 Coupler rod and fork 1
27 Damper w/ traveler tab 1
28 Damper mount 1
29 Rivet 4
30 Damper cover 1
31 Internal can 1
32 Bag locking mechanism 1
39 Screw for mounting hinge to external can (3/4” No.7 #2 Drive) 4
38 Hinge rod 2
37 Hinge (external can side) 1
Foot
Ped
al
15 Foot pedal lever 1
16 Foot pedal front bottom part 1
17 Foot pedal front cover 1
18 Foot pedal front backwall 1
19 Screw for foot pedal front short (3/8” No.4 #1 Drive) 2
20 Screw for foot pedal front long (1/2” No.4 #1 Drive) 2
21 Lever fulcrum rod 1
22 Fulcrum rod screw (5/8” No.12 #3 Drive) 1
23 Screw for coupler rod mount (lower) (7/16” No.6 #2 Drive) 2
24 Coupler rod revolute mount (lower) 1
Lid
33 Lid cover 1
34 Coupler rod revolute mount (upper) 1
35 Screw for coupler rod revolute mount (7/16” No.4 #1 Drive) 4
36 Hinge (lid side) 1
40 Screw for ring (5/16” No.6 #2 Drive) 4
41 Bottom ring 1
42 Top ring 1
43 Magnet 6
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3.2 Material Identification Table 4: Material identification is based on float, solder-iron, flame, magnet, density, and scratch tests according to Table 5. Injection molding and cold drawing are inexpensive means of manufacturing plastic and cylindrical metal parts respectively. Asymmetrical manufacturing marks on the foam pad suggested press cutting with oval-shape patterns. Refer to Cost section for complete purchase information.
PART NO. PART NAME MATERIAL MANUFACTURING
1 Bottom ABS Injection Molding
2 Top ABS Injection Molding
3 Handle ABS Injection Molding
8 Screw cover ABS Injection Molding
10 Lip ABS Injection Molding
11 Lid lock ABS Injection Molding
14 Bottom Polypropylene (PP) Injection Molding
16 Foot pedal front bottom part Polypropylene (PP) Injection Molding
18 Foot pedal front backwall Polypropylene (PP) Injection Molding
24 Coupler rod revolute mount (lower) POM Injection Molding
28 Damper mount ABS Injection Molding
30 Damper cover POM Injection Molding
31 Internal can Polypropylene (PP) Injection Molding
32 Bag locking mechanism POM Injection Molding
34 Coupler rod revolute mount (upper) ABS Injection Molding
36 Hinge (lid side) ABS Injection Molding
37 Hinge (external can side) ABS Injection Molding
41 Bottom ring Polypropylene (PP) Injection Molding
42 Top ring ABS Injection Molding
25 Feet Rubber Cut from sheets
6 Foam pad Foam Cut from sheets
5 Steel insert Low Carbon Steel Cold Drawn
15 Foot pedal lever Low Carbon Steel Drilled from Sheets and Bent to Shape
21 Lever fulcrum rod Low Carbon Steel Cold Drawn, Bent and Soldered Together
26 Coupler rod & fork Low Carbon Steel Cold Drawn
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38 Hinge rod Aluminum Alloy Cold Drawn
9 External can Stainless Steel Bent and Cut
17 Foot pedal front cover Stainless Steel Bent and Cut
32 Lid cover Stainless Steel Bent and Cut
4 Screw for handle Zinc-Plated Steel Purchased
7 Screw for top/bottom 18-8 Stainless Steel Purchased
12 Lid lock screw 316 Stainless Steel Purchased
13 Lid lock washer 316 Stainless Steel Purchased
19 Screw for foot pedal front short 316 Stainless Steel Purchased
20 Screw for foot pedal front long 316 Stainless Steel Purchased
22 Fulcrum rod screw 316 Stainless Steel Purchased
23 Screw for coupler rod mount (lower) 18-8 Stainless Steel Purchased
27 Damper w/ traveller tab Steel and Plastic Purchased
29 Rivet Aluminum Alloy Purchased
35 Screw for coupler rod revolute mount 18-8 Stainless Steel Purchased
39 Screw for mounting hinge to external can 18-8 Stainless Steel Purchased
40 Screw for ring 18-8 Stainless Steel Purchased
41 Magnet Alnico (Al, Ni, Co) Purchased
Table 5: Summary of material identification methods. Plastics excluding the rubber and foam were identified according to the plastics identification flow chart (Appendix A). Metals were identified through relative density, magnet test, and appearance when scratched. Magnets were identified based on cost and required magnetic force (see Mechanical Model section).
MATERIAL IDENTIFYING CHARACTERISTICS
ABS
Softens under solder iron
Sinks in water
Does not self-extinguish a flame
Drips under flame
Burns with yellow flame
Burns slowly
Burns with black soot
Polypropylene
Softens under solder iron
Floats in water
Burns with blue flame with yellow tip
Does not scratch under finger nail
Polyoxymethylene (POM) Softened under solder iron
Sinks in water
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Does not self-extinguish a flame
Drips under flame
Burns with yellow flame
It burnt slowly
No smoke
Rubber Has high coefficient of friction and low density
Foam Is cheap, soft, and easily cut
Low-Carbon Steel Is strong, cheap, and ferrous (magnetic)
Stainless Steel Is strong, silver, shiny and ferrous (magnetic)
Aluminum Alloy Is strong, heavy and non-ferrous
3.3 Part Functions This section covers the function of each part. Parts are not shown to scale. For how groups of parts work in concert to accomplish the overall function, see “How it Works” section. Reason for material selection and possible functional issues under adverse conditions are also included. 2.3.1 Bottom The bottom interfaces with the waste material during the compaction. The convex surface produces shear and normal stress in the waste material during compaction. Six plastic extrusions hold the steel inserts in place. The bottom attaches to the top through screws. ABS plastic is used for its strength, impact resistance and surface roughness. The smooth surface prevents collection of waste. Adverse conditions like humidity and heat are not effective against ABS. 2.3.2 Top
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The top connects the handle to the bottom to transmit force from the user to the trash. Two holes in the handle are secured through screws. The surface that contacts the ring has six holes to ensure
transmission of the magnetic force. The hand recess contains the foam pad that that protects the hand when vertical force is applied. ABS plastic is used for its strength, impact resistance and surface roughness. The smooth surface prevents collection of waste. Adverse conditions like humidity and heat are not effective against ABS. 2.3.3 Handle
The handle is the ergonomic grip that directly receives the user’s compaction force. The extrusions on each side are inserted into the top. ABS plastic is used for the same reasons as the top and bottom. Adverse conditions like humidity and heat are not effective against ABS.
2.3.4 Screw for Handle
This screw connects the top to the handle. It is No.7 #2 Drive with a length of 1/2”. It is made out of Zinc-Plated Steel because of its low cost. The plating should prevent rust due to humidity but may wear out. 2.3.5 Steel Insert The steel inserts are embedded into the top and bottom and offer magnetic attraction between the compactor and
lid. This magnetism not only holds the compactor in place but also aids in alignment during reattachment of the compactor. The head of the steel inserts hold them in place during magnetic
attraction. Low-carbon steel is used for cost and stiffness but is susceptible to rust due to humidity. A buildup of rust may affect strength of magnetic attraction. Since these parts are enclosed by the top and bottom, moisture is an issue. 2.3.6 Foam Pad
The foam pad is in the recess of the top to protect the user’s hand during compaction. Foam is used for its impact resistance and low cost. Adverse conditions like high humidity and heat can negatively affect the adhesive that connects this part to the top.
2.3.7 Screw for Top/Bottom
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This screw connects the top to the bottom. The screw for handle is No.6 #2 Drive with a length of 5/16”. It is made out of 18-8 Stainless Steel because of its low cost and may be susceptible to rust under humidity.
2.3.8 Screw Cover The screw cover protects the screws from the trash. Adverse conditions like rust, moisture, and unsanitary buildup of trash would hurt performance. Additionally, the appearance of the surface hides the screws to improve aesthetics. The head of the screw cover prevents the cover from being inserted too far. ABS
plastic is used to imitate the surface of its surroundings. Adverse conditions are not an issue for ABS. 2.3.9 External Can The external can is the main attachment point for many of the parts, contains the internal can, and improves aesthetics. Four holes in the upper region secure the hinge. The large rectangular hole permits the connection and displacement of the coupler rod and fork and the damper w/ traveler tab. The four holes in the lower region around the rectangular hole are mounting points for the damper mount. The smaller rectangular holes allow a snap fit of the damper cover. Stainless steel is used for
is aesthetics, resistance to oil/finger marks, and resistance to rust. Humidity and heat will not affect the performance of this steel. 2.3.10 Lip The lip protects the upper edges of the external can, secures the hinge to the main body, and houses the lid locking mechanism. The lip connects to the external can through a press fit. Four holes are for attaching the hinge (external can side). The large hole contains the coupler rod and fork. Once the lid has been opened, the lid locking mechanism prevents the coupler rod and fork from closing. The lip has a smaller hole for the lever of
the lid locking mechanism. The triangular hole indicates when the lid locking mechanism is being used or not. The extruded cylinder is responsible for holding the lid lock in place while
permitting it to slide from close to open set up (lid-locking mechanism). The ABS plastic is malleable, impact resistant and smooth (aides cleaning). Adverse conditions like high humidity and heat will not affect it since it is made of ABS plastic. Dust and trash particles might affect the behavior of the lid lock mechanism. The friction in the interface between the lid lock, lid lock screw, lid lock washer, and the lip might increase do to rust and dust which would negatively affect the process of locking the lid. 2.3.11 Lid Lock The lid lock is responsible for locking the lid in the open position. The surface that contacts the coupler rod and fork when the lid lock prevents the lid from
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closing. The hole allows the cylindrical extrusion in the lip to go through. The size and shape of this hole allows the lid lock to slide from open to close position. The lever allows the user to lock and
unlock the lid. The triangular hole tells the user the direction to unlock the lid. ABS plastic is used for its strength and surface finish, which permits the lid lock to easily slide. Adverse conditions like high humidity and heat will not affect it since it is made of ABS plastic. Dust and trash particles might affect the behavior of the lid lock mechanism. 2.3.12 Lid Lock Screw This screw connects the lock to the lip. The lid lock screw is No.6 #2 Drive with a length of 5/16”. It is made out of 316 Stainless Steel because of its low cost.
2.3.13 Lid Lock Washer
The lid lock washer prevents the lid lock from falling out and allows sliding. The lid lock washer is No.10. It is made out of 316 Stainless Steel because of its low cost. 2.3.14 Bottom (Main Body)
The bottom (main body) supports the external can and increases stability. The two extrusions on the bottom hold the lever fulcrum rod. Four corner extrusions add more stability to the press fit between the external can and the bottom. The front hole allows the foot pedal sub-assembly to go through. A hole on the upper surface allows the coupler rod to go through freely.
Four cylindrical extrusions hold the feet. One cylindrical extrusion is used to screw the lever fulcrum rod in place. A rectangular extrusion that has a hole on the side secures the cylindrical side of the lever fulcrum rod. Polypropylene (PP) plastic is used because it is rigid, has high tensile strength, is easy to maintain and clean, and has a long life span. Adverse conditions like high humidity and heat will not
Polypropylene (PP). 2.3.15 Foot Pedal Lever The foot pedal lever transfers force from the foot pedal to
the coupler rod and fork. This part is strong, heavy, and resistant to bending stress. The weight increases rigidity. Four holes located in the front of the foot pedal lever secure the foot pedal sub-
assembly. Two transverse holes allow the lever fulcrum rod to go through. These holes let the foot pedal lever to rotate and transmit the force from the pedal to the coupler rod and fork. Three holes in the back of the foot pedal lever align the coupler rod revolute mount (lower) and secure it to the foot pedal lever. A low carbon steel
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is used because of its density (lowers center of mass) and low cost. Adverse conditions like high humidity will not rust the foot pedal lever unless the protective layer wears out.
2.3.16 Front Pedal Front Bottom Part This part receives the force from the user’s foot. The long extrusion that protrudes through the foot pedal front cover increases the friction between the smooth stainless steel surface and the foot of the user. Four threaded holes on the bottom surface allow the foot pedal assembly to be securely attached to the foot pedal lever. Polypropylene
(PP) plastic is used because it is rigid, has high tensile strength, is easy to maintain and clean, and has a long life span. Humidity and heat will not affect Polypropylene (PP).
2.3.17 Front Pedal Front Cover This part covers the previous part for protection and aesthetics. The thin hole allows the extrusion of the foot pedal front bottom to protrude. Stainless steel is used for aesthetics and scratch resistance. Adverse conditions will not affect it.
2.3.18 Front Pedal Front Backwall This part connects the foot pedal front bottom part and foot
pedal front cover. The rectangular hole that houses both the foot pedal front bottom and the foot pedal front cover. The back wall helps prevent dirt and waste from contacting the lever mechanism and foot pedal lever area. Polypropylene (PP) plastic is used because it is rigid, has high tensile strength, is
easy to maintain and clean, and has a long life span. Adverse conditions will not affect polypropylene (PP).
2.3.19 Screw for Foot Pedal Front Long This screw is part of the foot pedal subassembly and lid-opening mechanism. The screw for foot pedal front short is No.4 #1 Drive with a length of 3/8”. It is made out of Type 316 Stainless Steel because of its low cost. 2.3.20 Screw for Foot Pedal Front Short This screw is part of the foot pedal subassembly and lid-opening mechanism. It is No.4 #1 Drive with a length of
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1/2”. It is made out of Type 316 Stainless Steel because of its low cost.
2.3.21 Lever Fulcrum Rod This part allows the foot pedal lever to rotate. One side of the rod is flat in order to offer a secure surface for the fulcrum rod screw. Low carbon steel is used for its high density (lower the
center of mass of the TK10) and low cost. Adverse conditions like high humidity could rust the lever fulcrum rod. Rust would make inhibit the foot pedal lever from freely rotating around the lever fulcrum rod. The interface between both parts would be negatively affected by rust, dust, and dirt.
2.3.22 Fulcrum Rod Screw This part is from the lid-locking mechanism. It is No.12 #3 Drive with a length of 5/8” and made of 316 Stainless Steel because of its low cost.
2.3.23 Screw for Coupler Rod Mounter (Lower) This part is from the lid-locking mechanism. It is No.6 #2 Drive with a length of 7/16” and made of 18-8 Stainless Steel because of its low cost. 2.3.24 Coupler Rod Revolute Mount (Lower) This part is the interface between the foot pedal lever and the coupler rod and fork. It transfers force from the pedal subassembly vertically to the coupler rod and fork. Two
threaded holes allow the connection between the foot pedal lever and the coupler rod revolute mount (lower). The cylindrical extrusion helps aligns the coupler rod revolute mount (lower) to the foot pedal lever. Another hole interfaces the coupler rod revolute mount (lower) and the coupler rod and fork. This
hole allows slight movements in order to transfer the force and displacement vertically upwards. The coupler rod and fork go through the coupler rod revolute mount during assembly, but once the rod is positioned vertically, the shape of the coupler rod and fork turns and it is safely secured through the coupler rod revolute mount (lower) hole. POM plastic is used for its high strength and environmental resistance. This plastic is not susceptible to adverse conditions. 2.3.25 Feet The feet connect the TK10 to the floor and increase stability through friction. The feet are made out of rubber because of their environmental resistance and high coefficient of friction.
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2.3.26 Coupler Rod and Fork This part connects the lower and upper coupler rod revolute mounts. The fork is soldered to the fork and aligned with the damper w/ traveler tab. The coupler rod and fork transmits force from the damper to the lid. On the upper part of the
coupler rod and fork, the rod bends. The upper coupler rod revolute mount is hooked to this feature. The fork aligns with the damper w/ traveler ta and is
responsible from displacing the traveler tab upwards (opening the lid) and downwards (closing the lid). On the lower part of the coupler rod and fork,
the rod bends, and there are fins on each side of the rod. The lower coupler rod revolute mount is hooked to this feature. The fins help the rod to stay in place once the rod is inserted inside the hole in the coupler rod revolute mount (lower). A low-carbon steel is used for strength and price. Rust may inhibit performance if the protective layer were removed. 2.3.27 Damper w/ Traveler Tab The damper slows the closing of the lid. Its body is held to the external
can through the damper mount. The traveler tab transmits the force to the Coupler rod and fork. Important adverse conditions, including humidity and dirt, would negatively affect the sliding and damping performance. 2.3.28 Damper Mount
This part connects the damper to the external can through rivets and the four holes on the damper mount. The extrusions secure the damper with a press fit. ABS plastic is strong and malleable and not susceptible to adverse conditions.
2.3.29 Rivet
Four rivets connect the damper to the damper mount. They are made from an aluminum alloy for its tensile strength and cost. Aluminum does not rust but may scratch. 2.3.30 Damper Cover
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The damper cover protects the damper from the environment. Six extrusions hook it to the external can through snap fits. POM is used for its strength and resistance to adverse conditions. 2.3.31 Internal Can The internal can holds the trash bags and waste. A circular hole houses the bag-locking mechanism. Two handles allow easy removal of the internal can for cleaning. Polypropylene is used for its rigidity, tensile strength, surface roughness (good for cleaning), and life span.
2.3.32 Bag-Locking Mechanism This part secures the trash bag during compaction. The teeth allow the bag to be easily inserted from the hole but
bend to prevent the bag from coming back out during compaction. POM is used for its malleability and environmental resistance. Humidity and heat will not affect POM, but fatigue may.
2.3.33 Lid Cover The lid cover closes the upper orifice of the TK10 from the environment. The large hole contains the compactor. The four small holes allow the top ring, bottom ring, and lid cover to be secured together. Stainless steel is used for its aesthetics, resistance to corrosion, resistance to fingerprints/oil, and density.
Adverse conditions are not a problem.
2.3.34 Coupler Rod Revolute Mount (Upper) This part is the interface between the lid subassembly and the couple rod/fork. Four holes allow the connection between the hinge (lid side) and the coupler rod revolute mount (upper). The hole that behaves as the interface between the coupler rod revolute mount (upper) and the coupler rod and fork allows slight movements in order to transfer the force and displacement to the lid while it opens and closes. ABS plastic is used for its strength,
cost, and environmental resistance.
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2.3.35 Screw for Coupler Rod Revolute Mount It connects the top to the bottom and is No.4 #1 Drive
with a length of 7/16”. It is made out of 18-8 Stainless Steel because of its low cost.
2.3.36 Hinge (Lid Side) This helps connect the lid to the external can. Four threaded holes secure the coupler rod revolute mount (upper) to the lid cover. A rectangular extrusion prevents the lid from opening too wide. A hole allows the hinge rod to connect the hinge (external can side) to the hinge (lid side). The ABS plastic has high strength and environmental resistance. High humidity and heat will not affect ABS, but dust and dirt might affect the interface between the hinge on the lid side and the external can
side.
2.3.37 Hinge (External Can Side) This helps connect the lid to the external can. Four threaded holes to secure the lip, external can, and the hinge (external can side). A rectangular hole contains the rectangular extrusion from the hinge (lid side) which prevents opening too far. Two holes allow the hinge rod to connect the hinge (external can side) to the hinge (lid side). The hinge rods are press fit through these holes. High humidity and heat will not affect ABS, but dust and
dirt might affect the interface between the hinge on the lid side and the external can side. 2.3.38 Hinge Rod The hinge rod aligns and secures the two other hinge parts. The indentation on one side allows a press fit in the hinge (external can side). The aluminum alloy is easily machined, has high tensile strength, and is not affected by rust. However, foreign particles in the interface may reduce performance.
2.3.39 Screw for Mounting Hinge to External Can This screw connects the top to the bottom. Refer to assembly instructions for particular placement. It is No.7 #2 Drive with a length of 3/4”. It is made out of 18-8
Stainless Steel because of its low cost.
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2.3.40 Screw for Ring
This screw connects the ring. It is No.6 #2 Drive with a length of 5/16”. It is made out of 18-8 Stainless Steel because of its low cost.
2.3.41 Bottom Ring
The bottom ring contacts the top (compactor). It has six cylindrical structures that are responsible for housing the magnets. The locations of these structures allows for the equal distribution of the magnets. Four cylindrical holes are made for the screw for ring and the screw covers. The bottom ring is made of Polypropylene (PP) plastic because it is rigid, has high tensile strength, is easy to maintain and clean, and has a long life span Adverse conditions will not affect the Polypropylene (PP).
2.3.42 Top Ring
The top ring holds the compactor with two hooks and protects the perimeter of the lid cover’s inner hole. One bar at each side aids the initial placement of the parts when assembling. Six cylindrical extrusions push each magnet down and secure them against the bottom ring. Two clips attach to the hooks on the top of the compactor sub-assembly. ABS plastic has high strength and environmental resistance.
2.3.43 Magnet
The magnets are located within the top and bottom ring. They help align the compactor sub-assembly to the lid sub-assembly during the process of locking the compactor to the lid. Also, the magnets help distribute the weight of the compactor sub-assembly. The magnet type was likely selected through cost.
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3.4 Fatigue Analysis The two main functions, opening/closing lid and compacting, cause fatigue stress. The goal is to evaluate whether any of the parts will fail from fatigue within the Trash Krusher’s 10-year warranty. Assuming the lid is operated 20 times per day and that the compactor is operated 2 times per day, the parts will experience 73 000 and 7300 cycles per 10-year lifetime respectively. The parts most likely to fail from fatigue are the following: the coupler rod revolute mount (lower) (Fig. 24), the coupler rod revolute mount (upper) (Fig. 25), hinge (lid side) (Fig. 26), and the hook/clips in the interface between the compactor and lid sub-assembly (Fig. 27). Von Misses stresses were calculated through finite-element models and the forces described in the “Performance” section. Ideal conditions are assumed; refer to the “Part Function” section for information on adverse conditions.
Figure 24: FEA analysis of coupler rod revolute mount (lower). The material, resolved force, and resulting maximum stress are POM, 86.4 N, and 2.28 MPa respectively. Note: forces, not boundary conditions are shown.
Figure 25: FEA analysis of coupler rod revolute mount (upper). The material, resolved force, and resulting maximum stress are POM, 86.4 N, and 12.5 MPa respectively. Note: forces, not boundary conditions are shown.
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Figure 26: FEA analysis of hinge (lid side). The material, resolved force, and resulting maximum stress are POM, 86.4 N, and 1.35 MPa respectively. Note: forces, not boundary conditions are shown.
Figure 27: FEA analysis of top (compactor). The material, resolved force, and resulting maximum stress are POM, 91.0 N, and 19.5 MPa respectively. Note: forces, not boundary conditions are shown.
SN-curves for most plastics are not well-defined or sometimes even available, so assumptions must be made. Because ABS and PPO have similar material properties, SN-curve are assumed similar (Fig. 27). Also, POM is stronger than PP, so if PP parts survive based on the POM curves (Fig. 27), the PP succeed. Based on those assumptions, the parts most likely to fail in fatigue are the tabs on the compactor top. However, even these parts are safely under the SN curve for the entire 10-year lifetime. Assuming ideal conditions; it would take over 25 years to fail. Therefore, the Trash Krusher passes the fatigue criteria.
Figure 28: This graph [8] shows the relationship of the stress to cycle failures of different plastics. The colored dots represent the maximum stress at the assumed number of cycles over the ten-year lifetime. From top to bottom: top (compactor) (red dot), coupler rod revolute mount (upper) (blue dot), coupler rod revolute mount (lower) (green dot), hinge (lid side) (purple dot). Although all four dots are within failure criteria in ten years, the tabs of the compactor are closes to failure.
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MANUAL ASSEMBLY 4.1 Manual Assembly Sequence Step 1: Set external can on workspace table.
Step 2: Attach the damper mount to the back lower part of the external can. Note: Make sure to not have damper mount upside down. There is an opening on top where the damper must lie in
Step 3: Insert rivets (x4) into the locations highlighted in blue. They will secure the damper mount permanently to the external can.
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Step 4: Attach external can bottom part as shown in the image. The bottom part simply snaps on.
Step 5: Attach the foot parts (x4) to the appropriate spots on the external can bottom piece. All four locations are highlighted in blue in the image.
Step 6: Grab the foot pedal lever and place on the work station.
Step 7: Attach coupler rod revolute mount to the foot pedal lever. Note: Make sure to place it as shown in the image. The lifting mechanism will not work correctly otherwise.
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Step 8: Fasten 7/16” No.4 #1 Drive (2x) to the outer two holes that align the coupler rod revolute mount to the foot pedal lever.
Step 9: Insert coupler rod and fork into the coupler rod revolute (lower) as illustrated.
Step 10: Pass the pedal and rod assembly through the opening in the bottom of trash compressor.
Step 11:
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Insert lever fulcrum rod (left to right) so that it holds the correct location of the foot pedal lever so that there is no need to keep holding the foot pedal lever.
Step 12: Fasten single screw 5/8” No.12 #3 Drive into the end of the lever fulcrum rod.
Step 13: Graph foot pedal front bottom and set it on workspace.
Step 14: Snap on foot pedal front cover on top of the foot pedal front bottom part.
Step 15: Attach foot pedal backwall. This part snaps on the back side of the part from the previous step with little resistance.
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Step 16: Attach this sub assembly to the foot pedal lever.
Step 17: Fasten screws (3/8” No.4 #1 Drive x2) to secure part of the foot mini assembly.
Step 18: Fasten screws (1/4” No.4 #1 Drive x2) to finish securing the foot pedal lever subassembly.
Step 19: Place lid cover on workspace.
Step 20: Snap on the top ring part of the lid sub assembly.
Step 21: Place bottom ring on workspace as shown.
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Step 22: Insert magnets (x6) into designated locations. Reference image for locations.
Step 23: Attach bottom ring with the lid/top ring assembly. These parts snap together.
Step 24: Fasten the bottom ring to the top ring/lid cover with screws (5/16” No.6 #2 Drive x4).
Step 25: Insert screw covers (x4) into the same places where the previous 4 screws were fastened
Step 26: Insert coupler rod revolute mount (upper)
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into location shown in image.
Step 27: Insert hinge (lid side) into designated location; refer to image.
Step 28: While holding both of the previous two parts in place, fasten them together with the (7/16” No.4 #1 Drive x4) screws.
Step 29: Place lip on work station as shown.
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Step 30: Align the lid lock to the bottom of the lid part, and snap in the lid lock into place as shown in image.
Step 31: Get the screw that fastens the lid lock mechanism, and hold in hand (5/16” No.6 #2 Drive).
Step 32: Attach washer to the screw as illustrated in the image
Step 33: Fasten the lid lock with the lip by using the screw/washer: (5/16” No.6 #2 Drive)/ (No.10).
Step 34: Align the top of the lid with the opening made for the coupler rod and fork part to fit through, and insert it into the top of the external can.
Step 35: Align the hinge (external can side) with the screw holes on the inside of the external can. Continue to hold for next step.
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Step 36: Fasten the hinge (external can side) part with screws (3/4” No.7 #2 Drive x4).
Step 37: Position the lid assembly (making sure that the coupler rod and fork slides inside the couple rod revolute mount (upper) red circle) so that the hinge (lid side) lies inside the hinge (external side). See image for more details. For the second image the part highlighted in yellow is the hinge (lid side) within the inside of the hinge (external side).
Step 38: Insert hinge rod into the hinge rod hole on the hinge (external can side) part.
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Step 39: Repeat previous step with remaining hinge rod, and insert it into the other hinge rod hole that is opposite the hinge (external can side).
Step 40: Place internal can on work station.
Step 41: Insert bag locking mechanism into the internal can with a press fit.
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Step 42: Insert internal can into external can. Note: The external can is shown transparent for illustration purpose only.
Step 43: Insert damper with traveler tab into the damping mount on the back side of the trash compressor by a snap fit. Note: the tab must align with the fork (yellow) of the coupler rod and fork part
Step 44: Snap on the damping cover.
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Step 45: Grab the top of the compactor sub assembly.
Step 46: Stick the foam in the hand recess section of the top part of the compactor.
Step 47: Forcibly insert the handle into place with slight snap fit.
Step 48: Fasten the handle with screws (1/2” No.7 #2 Drive x4).
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Note: locations are highlighted in blue in the image.
Step 49: Drop the metal inserts (x6) into the highlighted locations in the image.
Step 50: Attach on the bottom of the compactor through a snap fit as shown in the image.
Step 51: Fasten the bottom and top of the compactor together with screws (5/16” No.6 #2 Drive x4). The locations of the four screws are highlighted in image.
Step 52: Press fit the screw covers (x4). The four screw locations are highlighted in image.
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Step 53: Place the internal cardboard box inside the crusher.
Step 54: Insert compactor assembly inside the internal cardboard box.
Step 55: Place outer cardboard packaging box on the workstation. Step 56: Fold the box into shape.
Step 57: Tape bottom of box shut according to the red paths in the figure.
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Step 58: Insert the bottom packaging foam into the large cardboard box.
Step 59: Insert the compressor inside the large box. Note: box is shown transparent to show how the crusher fits inside.
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Step 60: Insert front packaging foam (blue in image only).
Step 61: Insert top packaging foam (blue in image only).
Step 62: Close the top of the packaging box, and insert the cardboard locking mechanism.
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4.2 Manual Assembly Time The manual assembly time analysis is an approximation of how long it will take to make a Trask Krusher. This is estimated based on the Manual Handling and Manual Insertion – Estimated times (seconds) tables (Appendix B, [2]). Thickness usually the length of the shortest side of the smallest rectangular prism that encloses the part. However, if the part is cylindrical, or has a regular polygonal cross-section with five or more sides, and the diameter is less than the length, then thickness is defined as the radius of the smallest cylinder which can enclose the part. Size is the length of the longest side of the smallest rectangular prism that can enclose the part [9]. The total estimated manual assembly time is 518 s or 8 min 38 s. To compensate for slow-down this assembly time is estimated at 9 minutes. Table 7: Manual assembly time totals 518 s (8 min 38s). To compensate for slow-down, this estimate was increased to 9 min for cost estimates. Note that steps 56 and 57 (box handling) are experimentally evaluated.
Step (--)
α (°)
β (°)
α + β (°)
Handling Times (s), Source (#,#)
Insertion Times (s), Source (#,#)
1 360 360 720 1.95 (3,0) N/A
2 360 360 720 1.95 (3,0) 1.5 (0,0)
3a 360 0 360 2.25 (1,2) 7 (3,5)
3b 360 0 360 2.25 (1,2) 7 (3,5)
3c 360 0 360 2.25 (1,2) 7 (3,5)
3d 360 0 360 2.25 (1,2) 7 (3,5)
4 360 360 720 1.95 (3,0) 2.5 (0,1)
5a 360 0 360 1.8 (1,1) 1.5 (0,0)
5b 360 0 360 1.8 (1,1) 1.5 (0,0)
5c 360 0 360 1.8 (1,1) 1.5 (0,0)
5d 360 0 360 1.8 (1,1) 1.5 (0,0)
6 360 360 720 1.95 (3,0) N/A
7 360 360 720 1.95 (3,0) 5.5 (0,6)
8a 360 0 360 1.8 (1,1) 6 (3,8)
8b 360 0 360 1.8 (1,1) 6 (3,8)
9 360 360 720 1.95 (3,0) 1.5 (0,0)
10 360 360 720 1.95 (3,0) 5 (1,2)
11 360 180 540 1.8 (2,0) 2.5 (0,2)
12 360 0 360 1.5 (1,0) 6 (3,8)
13 360 360 720 1.95 (3,0) N/A
14 360 360 720 1.95 (3,0) 1.5 (0,0)
15 360 360 720 1.95 (3,0) 2.5 (0,1)
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16 360 360 720 1.95 (3,0) 1.5 (0,0)
17a 360 0 360 1.8 (1,1) 6 (3,8)
17b 360 0 360 1.8 (1,1) 6 (3,8)
18a 360 0 360 1.8 (1,1) 6 (3,8)
18b 360 0 360 1.8 (1,1) 6 (3,8)
19 360 360 720 1.95 (3,0) N/A
20 360 360 720 1.95 (3,0) 1.5 (0,0)
21 360 360 720 1.95 (3,0) N/A
22a 180 0 180 1.43 (0,1) 1.5 (0,0)
22b 180 0 180 1.43 (0,1) 1.5 (0,0)
22c 180 0 180 1.43 (0,1) 1.5 (0,0)
22d 180 0 180 1.43 (0,1) 1.5 (0,0)
22e 180 0 180 1.43 (0,1) 1.5 (0,0)
22f 180 0 180 1.43 (0,1) 1.5 (0,0)
23 360 360 720 1.95 (3,0) 2.5 (0,1)
24a 360 0 360 1.8 (1,1) 6 (3,8)
24b 360 0 360 1.8 (1,1) 6 (3,8)
24c 360 0 360 1.8 (1,1) 6 (3,8)
24d 360 0 360 1.8 (1,1) 6 (3,8)
25a 360 0 360 1.8 (1,1) 2.5 (0,1)
25b 360 0 360 1.8 (1,1) 2.5 (0,1)
25c 360 0 360 1.8 (1,1) 2.5 (0,1)
25d 360 0 360 1.8 (1,1) 2.5 (0,1)
26 360 360 720 1.95 (3,0) 5.5 (0,6)
27 360 360 720 1.95 (3,0) 5.5 (0,6)
28a 360 0 360 1.8 (1,1) 6 (3,8)
28b 360 0 360 1.8 (1,1) 6 (3,8)
28c 360 0 360 1.8 (1,1) 6 (3,8)
28d 360 0 360 1.8 (1,1) 6 (3,8)
29 360 360 720 1.95 (3,0) N/A
30 360 360 720 1.95 (3,0) 1.5 (0,0)
31 360 0 360 1.8 (1,1) N/A
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32 180 0 180 1.43 (0,1) 1.5 (0,0)
33 360 0 360 1.8 (1,1) 6 (3,8)
34 360 360 720 1.95 (3,0) 3.5 (0,3)
35 360 360 720 1.95 (3,0) 5.5 (0,6)
36a 360 0 360 1.8 (1,1) 6 (3,8)
36b 360 0 360 1.8 (1,1) 6 (3,8)
36c 360 0 360 1.8 (1,1) 6 (3,8)
36d 360 0 360 1.8 (1,1) 6 (3,8)
37 360 360 720 2.73 (3,5) 1.5 (0,0)
38 360 0 360 1.5 (1,0) 1.5 (0,0)
39 360 0 360 1.5 (1,0) 1.5 (0,0)
40 360 360 720 1.95 (3,0) N/A
41 180 0 180 1.13 (0,0) 2.5 (0,1)
42 360 360 720 1.95 (3,0) 1.5 (0,0)
43 360 0 360 1.5 (1,1) 2.5 (0,2)
44 360 360 720 1.95 (3,0) 1.5 (0,0)
45 360 360 720 1.95 (3,0) N/A
46 360 180 540 1.8 (2,0) 1.5 (0,0)
47 360 180 540 1.8 (2,0) 2.5 (0,1)
48a 360 0 360 1.8 (1,1) 6 (3,8)
48b 360 0 360 1.8 (1,1) 6 (3,8)
48c 360 0 360 1.8 (1,1) 6 (3,8)
48d 360 0 360 1.8 (1,1) 6 (3,8)
49a 360 0 360 1.8 (1,1) 1.5 (0,0)
49b 360 0 360 1.8 (1,1) 1.5 (0,0)
49c 360 0 360 1.8 (1,1) 1.5 (0,0)
49d 360 0 360 1.8 (1,1) 1.5 (0,0)
49e 360 0 360 1.8 (1,1) 1.5 (0,0)
49f 360 0 360 1.8 (1,1) 1.5 (0,0)
50 360 360 720 1.95 (3,0) 2.5 (0,1)
51a 360 0 360 1.8 (1,1) 6 (3,8)
51b 360 0 360 1.8 (1,1) 6 (3,8)
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51c 360 0 360 1.8 (1,1) 6 (3,8)
51d 360 0 360 1.8 (1,1) 6 (3,8)
52a 360 0 360 1.8 (1,1) 1.5 (0,0)
52b 360 0 360 1.8 (1,1) 1.5 (0,0)
52c 360 0 360 1.8 (1,1) 1.5 (0,0)
52d 360 0 360 1.8 (1,1) 1.5 (0,0)
53 180 180 360 1.5 (1,0) 1.5 (0,0)
54 360 360 720 1.95 (3,0) 1.5 (0,0)
55 360 360 720 1.95 (3,0) N/A
58 360 360 720 1.95 (3,0) 1.5 (0,0)
59 360 360 720 1.95 (3,0) 2.5 (0,2)
60 180 180 360 1.5 (1,0) 2.5 (0,1)
61 360 360 720 1.95 (3,0) 1.5 (0,0)
62 0 0 0 1.13 (0,0) 1.5 (0,0)
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COST 5.1. Landed Cost Table 8 contains the landed cost of the parts. Off-the-shelf parts were selected from McMaster-Carr, and the cost of the others were estimated with custompart.net.com. Note that this calculation accounts for attrition and die costs. Refer to Appendix D for a few examples of these calculations. Total landed cost is $200.51/Trash Krusher. The landed cost is assumed to be the same in China and the United States. Table 8: Landed cost of parts. Note that part multiciplicty is accounted for in the cost columns. All outsourced, off-the-shelf costs are from McMaster-Carr.
PLASTIC PARTS
COST/ CAN ($)
METAL PARTS COST/
CAN ($) OUTSOURCED
PARTS MCMASTER PRODUCT #
COST/ CAN ($)
Bottom 0.84 Steel insert (x6) 10.26 Screw for
handle (x4) (90190A170) 0.162
Top 1.352 Foot pedal lever 11.04 Screw for
top/bottom (x4) (92470A145) 0.248
Handle 0.65 Lever fulcrum
rod 1.85 Lid lock screw (92470A145) 0.041
Screw cover (x8)
0.328 Coupler rod &
fork 3.56 Lid lock washer (91950A027) 0.083
Lip 0.963 Hinge rod (x2) 3.4 Screw for foot
pedal front short
(90184A105) 0.113
Lid lock 0.278 External can 107.36 Screw for foot pedal front l.
(x2) (90184A108) 0.12
Bottom (external can)
2.782 Foot pedal front
cover 2.02
Fulcrum rod screw
(90184A450) 0.36
Foot pedal front bottom part
0.539 Lid cover 7.61 Screw for
coupler rod mount l. (x2)
(92470A147) 0.129
Foot pedal front backwall
0.35 Damper w/ traveler tab
(6521K61) 22.35
Coupler rod revolute mount
(l) 0.099 Rivet (x4) (93482A631) 0.742
Damper mount 0.147 Screw (coupler rod r. m.) (x4)
(92470A111) 0.198
Damper cover 0.322 Screw (hinge to
external can) (x4)
(92470A173) 0.297
Internal can 5.125 Screw for ring
(x4) (92470A145) 0.248
Bag locking mechanism
0.099 Magnet (x6) (57295K73) 11.22
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Coupler rod revolute mount
(u) 0.157
Hinge (lid side) 0.183
Hinge (external can side)
0.338
Bottom ring 0.332
Top ring 0.343
Foot (x4) 0.035
Foam Pad 1.84
Total ($) 17.10 147.10 36.31
Landed Cost $200.51
The projected units per month is selected as 10 000 based on the speed of assembly. At this rate, 9 worker stations working at 168 hours per month (21 8-hour days in US) or 6 workstations at 288 hours per month (24 12-hour days in China) are needed.
5.2. Facilities Costs Peter Ellman provided information on facility cost in China [11]. Mike Griffis provided information on facility costs in the United States [3]. Rent comprises cost of assembly space (US and China), office space (US and China), and housing (China only). Note that China’s cost are higher due to the on-site housing. This increase is justified by the gains in labor cost and efficiency.
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Electricity costs include air conditioning and assembly lines. Again, China’s cost are higher because of increased hours per month. The gain is efficiency.
Other utilities include phone/internet, water, waste, product liability, supplies, and licensing (US only).
Therefore, a total monthly facilities cost (F) follow. Despite accounting for on-site housing, China’s facility costs are around a third of US’s cost due to licensing costs in the US.
5.3. Labor Costs Appendix E contains information labor provided by Peter Ellman on cost in China [11]. Mike Griffis provided information on labor costs in the United States [3]. Direct labor (DL) cost in US comprises wage (W), tax (T), and fringe (ex: health insurance) (F). Taxes come from social security (employer’s contribution), Medicare, workman’s compensation, unemployment insurance, and other mandates. According to M. Griffis, the non-wage benefits can be estimated by multiplying hourly wage by 1.15. For direct labor in China, labor cost only comprises wage. The resulting wages far favor workers in US.
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Indirect labor (IDL) comprises all labor that does not fall under direct or burden labor. For both US and China, three people at an increased hourly wage compared to direct labor were assumed. Additionally, for China, shipping company costs and tariffs were included.
Burden labor (BL) consists of an engineer, manager, and salesman. The same cost is assumed in China and the United States.
5.4. Total Cost Use Rate is the cost to run a workstation per minute.
Direct Labor Rate is the
Overhead rate is the ratio of use rate to direct labor rate. The OR of China is high because of the low direct labor rate.
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Fully-burdened labor rate (FBLR) is the combination of direct labor and
Total cost per unit was dominated by the labor costs. This pricing scheme is not sustainable since it has no profit and costs more than the MSRP selling price of $159. Note that the cost of US and China are very similar because the landed cost was assumed the same. Likely, the landed cost was overestimated. Also, the projected quantity is quite low (only 6 or 9 workstations required). By increasing output, China’s cost would show a bigger advantage.
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SAFETY 6.1 Fire Test To simulate a fire that could start by placing smoldering contents into the can, a fire test was done [8]. Although the TK10 instructions prohibit putting smoldering contents in the can, the safety of the can should be evaluated in case of accident. For the test, 6-feet of standard-sized paper towels were placed into a trash bag inside the can. The recommended heavy-duty trash bag had thick plastic to compensate for pinching in the compaction process but was unimportant for this test. After lighting the paper towels on fire and closing the lid for ten minutes, the lid was opened to inspect the contents. The only permanent damage was some slight burn marks on the inner plastic liner and completely burned bag/contents. Therefore, the can successfully smothered a fire when the lid was closed. Note that this test was performed after the drop tests, so the results are an underestimate of the can’s ability to extinguish a fire. Therefore, the can’s design successfully handles this hazard. 6.2 Risk Assessment / Safety Features The probable hazards for a manual trash compactor and their risk assessments are included in Table 8. The risk estimation is based on safety instructions for industrial robots [4]. Risk estimation is evaluated before and after the included safety features (safeguards). A risk of category R3 or R4 is acceptable Table 8: Evaluation of TK 10 safety before and after safeguards. Safety of R3 or R4 is acceptable.
Hazard Severity Exposure Avoidance Old Safety Safeguards New
Safety
Burns / fire from smoldering contents
Serious (S2)
Infrequent (E1)
Likely (A1)
R2B Self-
extinguishing with closed lid
R3
Compacting sharp objects
Serious (S2)
Infrequent (E1)
Likely (A1)
R2B Safety
Instructions R3
Animal/infant caught in compactor opening
Serious (S2)
Infrequent (E1)
Not Likely (A2)
R2B Isolate can in
enclosed space R4
Animal/infant trapped or crushed under can
Slight (S2)
Infrequent (E1)
Not Likely (A2)
R2B Isolate can in
enclosed space R4
Sanitation Slight (S1)
Frequent (E2)
Likely (A1)
R3 Clean Can Regularly
R4
Pinching fingers in compactor
Slight (S1)
Infrequent (E1)
Likely (A1)
R4 N/A R4
Pinching fingers in lid/hinge
Slight (S1)
Infrequent (E1)
Likely (A1)
R4 N/A R4
Trapped Gas Slight (S1)
Infrequent (E1)
Likely (A1)
R4 N/A R4
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6.3 Safe Operation Safe operation of the Trash Krusher comprises three categories: opening the lid, closing the lid, compacting trash, and storing the can. Other operations, like using the bag locking mechanism do not require detailed safety instructions. Refer to the How it Works section for instructions on these processes. 6.3.1 Opening Lid To open the lid, ensure the foot pedal is free of obstruction. Depressing an obstructed pedal may break the plastic parts of the foot pedal subassembly or cause the lid to open suddenly if the obstruction suddenly breaks. Before opening the lid, ensure nothing smoldering is inside the can by feeling the can surface. Note: according to the smoldering test, the can will extinguish a fire if given sufficient time. Slowly open the can while keeping face away from opening in case of heat from smoldering or trapped gas. 6.3.2 Closing Lid To close the lid, remove hands/arms from opening, and release foot pedal. The damper will allow the lid to slowly close, so slowly removing foot pedal force is not necessary. See section 2.3 Damping Ratio for a more detailed description. 6.3.3 Compacting Before compacting, ensure no sharp objects, like glass fragments, are in the can. Sharp objects may damage the trash can’s interior and may cut the user during compaction. Slowly detach the compactor from the lid. The compactor is attached through snap fits and magnets so that the required force should be relatively low. Carefully detach perpendicular to lid surface so that the snap fits do not break. To compact, continue the perpendicular force while preventing interference of hand/arm with the compactor’s opening. Touching the sides of the can may be unsanitary or dangerous if sharp contents were not removed). 6.3.4 Storage If an infant or small animal could access the can, store the Trash Krusher in an isolated area like an enclosed cabinet or room to improve safety (see Table 3). Additionally, clean the can monthly to improve sanitation. The inner liner and area between the compactor and the lid need the most cleaning.
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DESIGN ANALYSIS 7.1 Pros and Cons of Design The Trash Krusher patent [5], website [6], and press release [7] enumerate the pros of the product. The analysis included in this report shows the cons of the design (Table 9). Overall, the product is well-built and includes many safety features but has a high price. A regular trash costs $5 to $20, but there are few competing manual compactors (ex: Stomp-It). Table 9: Pros and Cons of TK 10. Positive aspects are offset by the large cost.
Pros Cons
Eco-friendly manual compaction Huge cost (MSRP $159)
Easily cleaned inner liner Many moving parts compared to traditional can
Flexibility to use bags of 10 or 13 gallons Must clean compactor after several uses
Aesthetics (stainless steel)
Finger-print-proof (stainless steel)
Stay-open lid
Silent, slow-close lid
Soft-touch and wide foot pedal
Bag-locking mechanism
Medium size (40 L)
10-year warranty
Patented
Extinguishes fires when lid is closed 7.2 Conclusion This report has unveiled the product’s function, performance specifications, assembly sequence/time, cost, safety, and pros/cons. The maximum compaction ratio of 0.46, required pedal force of 81 N, and detachment force of 91 N were sufficient for everyday use. The damping ratio of 1690 N*s/m supported the claim of a silent, slow-close lid, which is an important benefit of the design. However, the drop-test showed the packaging was sub-par. The assembly time per part was 9 min. Total cost in USA and China were $209 and $205 respectively. The costs are similar because landed costs were assumed the same. Also, the projected quantity is quite low (only 6 or 9 workstations required). By increasing output, China’s cost would show a bigger advantage. As mentioned in the pros/cons section, this cost is prohibitively high. Finally, the risk of hazards was relatively low. The trash can could even extinguish a fire when the lid was closed.
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APPENDIX A. Plastic Identification Chart [1]
B. Assembly Time Tables [2]
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66
C. Safety Charts [4]
67
68
D. Example Non-Landed-Cost Calculations Example for substitute for POM (price per pound - $1.41/lb, density – 0.0509 lb/in3)
PET, 20% glass reinforced is closest to POM in terms of price per pound and density (price per pound -
$1.42/lb, density – 0.0535 lb/in3)
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70
Example for ABS screw cover
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Metals - External Can example
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E. International Labor Cost [11]
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REFERENCES
1. “Plastics Identification Flow Chart,” http://www.partec.qld.edu.au <accessed JAN 2014>. 2. Boothroyd, Dewhurst, Knight. Product Design for Manufacture and Assembly, 2nd Edition, CRC
Press, 2002. 3. M. Griffis. Lectures on assembly, labor, and facilities costing, JAN 2014. 4. “Risk Estimation” and “Safeguard Selection,” ANSI/RIA R15.06-1999. 5. P. Ellman, “Garbage container with detachable manual compaction device,” US 8584886 B1,
MAY 2012. 6. P. Ellman. “The TK 10 Trash Krusher,” http://trashkrusher.com/?page_id=2 <accessed MAR
2014>. 7. E. Birkhead “TK Products Awarded U.S. Patent for TK 10 Trash Krusher” (press release), 25
NOV 13. 8. M. Griffis. Lecture on drop and fire tests, FEB 2014. 9. “Product design for manual assembly,” Sakai, accessed FEB 2014. 10. S. Lampman. “Characterization and Failure Analysis of Plastics.” p. 250, ASM Internation,
2003. 11. P. Ellman. Powerpoint from Skype Interview. 10 FEB 2014.