This project shall be completed in a time span of two ...
Improvements to Juice Work Cell
May 2004
Final Report
Technical Data Package
Project Sponsor: Kraft Foods, Avon, New York
Team Members:
Jessica Vastola - ISE
James Hildick - ME
Molly Kearns - ISE
Michael Leiston - ME
Laura Pleten - ME
Michael Russell - ME
Nicole Verley - ME
Table of Contents
Chapter 1: Project Overview 5
1.1 Introduction 5
1.2 Background 5
1.3 Ergonomic Risk Factor Assessment – Juice Supply 6
1.4 Ergonomic Risk Factor Assessment – Juice Placing 7
Chapter 2: Needs Assessment 8
2.1 Project Mission Statement 8
2.2 Product Description 8
2.3 Scope Limitations 8
2.4 Stakeholders 9
2.5 Key Business Goals 9
2.6 Financial Parameters 9
2.7 Critical Performance Parameters (Order Qualifiers) 9
2.8 Critical Performance Parameters (Order Winners) 10
2.9 Describe the Need 11
2.10 Constraints 11
2.11 Project Management 11
Chapter 3: Concept Development 11
3.1 Brainstorming Technique 11
3.2 Concept Alternatives 12
3.3 Handheld Device 13
3.4 Group Drawing Method 14
3.5 Empathy Method 14
3.6 Concept Selection 15
3.6.1 Pugh’s Method 15
3.6.2 Weighted Comparison 15
3.6.3 Radar Chart 16
3.6.4 Qualitative Evaluation 17
3.6.5 Decision 18
Chapter 4: Feasibility Assessment 18
4.1 Feasibility Introduction 18
4.2 Design Feasibility 19
4.3 Functional Feasibility 19
4.4 Materials Feasibility 20
4.5 Fabrication Feasibility 21
4.6 Cost Feasibility 22
4.7 Ergonomic Feasibility 23
4.8 Design Structure Matrix 24
Chapter 5: Design Objectives and Performance Specifications 24
5.1 House of Quality 25
5.2 Design Objectives 26
5.3 Performance Specifications 27
Chapter 6: Analysis of Problems and Synthesis of the Design 28
6.1 Analysis Introduction 28
6.2 Compressed Air Cylinder 28
6.3 The Main Frame and Mounting the Cylinder 29
6.4 Rod mounting plate 30
6.5 Guide Plate and Box Guide Plates and Rods 31
6.6 Toggle Rods 32
6.7 Mounting the Directional Valve 32
6.8 Formulae and Calculations (Reference Appendix H) 33
6.8.1 Cylinder Calculations 33
6.8.2 Free Body Diagram Calculations 34
6.9 Fatigue Analysis 35
6.10 Purchased Items 38
6.10.1 Toggles 39
6.10.1.1 Fatigue analysis for spring 40
6.10.2 Cylinder 41
6.10.3 Control Valve 42
6.11 Failure Modes and Effects Analysis -Design FMEA 42
6.12 Ergonomic Risk Factor Assessment 44
Chapter 7: Preliminary Design Documents 44
Chapter 8: Fabrication and Assembly 52
8.1 Mounting plate 52
8.2 Handle Fabrication 52
8.3 Rod Fabrication 53
8.4 Directional Valves and Mounting Plates 53
8.5 Outside Fabrication 56
8.6 Assembly 58
Chapter 9: Final Design Documents 59
Chapter 10: Testing and Design Adjustments 70
Chapter 11: Conclusion and Recommendations 71
Chapter 12: Contingency Plan Manual Handheld Tool 73
12.1 Needs Assessment 73
12.2 Concept Development 74
12.3 Concept Selection 75
12.4 Feasibility 76
12.5 Design Documents 77
12.6 Fabrication 79
12.7 Testing 80
12.8 Conclusion 80
References 82
Appendix A 86
Appendix B 87
Appendix C 88
Appendix D 91
Appendix E 92
Appendix F 93
Appendix G 94
Appendix H 96
Appendix I 98
Appendix J 100
Appendix K 101
Appendix L 102
Appendix M 103
Appendix N 104
Chapter 1: Project Overview
1.1 Introduction
Currently, a technique and tool are used to accomplish the task of opening pre-packaged juice cases at Kraft Foods in Avon, New York. Both result in excessive workload and physical strain on the workers. After opening, the juice pouches are fed to several placing stations using a conveyor. The scope of this project is to design and create a prototype device to improve the box-opening process. Since the introduction of the current tool, the juice supply process has not been further addressed by Kraft Foods.
1.2 Background
Kraft Foods, located in Avon, New York receives corrugated cases of juice pouches in two quantities, 10-packs and 60-packs. These cases must be opened manually at a rapid pace. The 10-pack cases are of highest concern.
Up to four pallets of juice are staged in the supply area at a time. The 10-pack cases are shrink-wrapped in bundles of four and the shrink-wrap must first be scored and removed by hand. After the shrink wrap is removed, the current tool is used to aid in breaking the glue sealed flaps. This tool only opens one flap and a worker must break the opposite flap by hand to fully open each case. The cases of juice pouches are then manually lifted and dumped onto an auxiliary conveyor that moves them to the juice-placing position at the main conveyor. Once the cases are dumped, the empty boxes are placed in tipper carts. The pace of this operation is set by juice placing at a speed of 130-240 pouches per minute and can create congestion in the area because of full tipper carts and exchanging them with empty ones.
1.3 Ergonomic Risk Factor Assessment – Juice Supply
An Ergonomic Risk Factor (ERF) Assessment of the juice supply process was performed by Kraft personnel prior to involvement by the Rochester Institute of Technology Senior Design Team. The study resulted in a total score of 29 out of 82 on the Kraft scale, the highest of all processes evaluated at the Kraft site. According to the rating scale, a total score of 0 to 2 is classified as Green, “within established criteria”; 3 to 11 is Yellow indicating “opportunity for continuous improvement”; greater than 11 is Red, noting “high priority action item requiring intervention.” At 29, this task is clearly in the red zone for requiring intervention.
Appendix G is the evaluation sheet and the results of this assessment. Based on the ERF evaluation sheet, the Juice Supply process scored a three, for “occurs more than one time per cycle” in the following areas:
• F1: Two handed lift greater than 20lbs
• F8: Trunk rotation with a weight greater than 10lbs
• F9: Wrist rotation while manipulating greater than 6lbs
• P1: Trunk forward flexion greater than 45°
• P4: Trunk or next side-bent plus twisted
• P8: Elbow flexion greater than 135°
• P9: Wrist flexion or extension greater than 65°
• P11: Forced pronation or supination of hand and wrist
The following scored a 1 for occurs “occasionally, not every cycle”:
• F4: Two handed carry greater than 30 lbs
The following “Other Risk Factor” scored a “Yes” which is equivalent to 2 points:
• O5: Squat or kneel for greater than 50% of the cycle
The number of passes and the speed, at which the opening must occur, creates extensive ergonomic strain on the worker. Three passes are required over each box before emptying: shrink-wrap removal, open first flap with tool, and open second flap by hand. This process requires bending, rapid hand movement, twisting, kneeling, squatting, and lifting. The tool aids in the process, but causes additional strain to the hand due to the shape of the handle, as well as the second pass without the tool.
1.4 Ergonomic Risk Factor Assessment – Juice Placing
The juice-placing position is where the juice pouches are manually placed in a slot provided on the pin-line. Employees rapidly place these pouches by hand at a rate in the range of 130-240 per minute. The high level of hand activity poses ergonomics concern. This is a standing position and the juice pouches must be correctly oriented to ensure visibility in the product packaging. The study of this area resulted in a score of 7 out of 82 on the Kraft scale.
Appendix G is the evaluation sheet and the results of this assessment. Based on the ERF evaluation sheet, the Juice Placing process scored a three, for “occurs more than one time per cycle” in the following areas:
• P10: Wrist ulnar or radial deviation greater than 25°
• P11: Forced pronation or supination of hand and wrist
The following scored a one, for “Occasional, not every cycle”
• P4: Trunk or neck side-bent plus twisted
Chapter 2: Needs Assessment
2.1 Project Mission Statement
The mission of this design project team is to design a process and/or device to replace or improve the existing box opening and unloading process currently in place at Kraft Foods. The final design should address ergonomic and manpower concerns.
2.2 Product Description
Currently, a technique and tool are used to accomplish the task of opening pre-packaged juice cases before placing them into Lunchables trays. Both the technique and the tool currently used result in excessive workload and physical strain on the workers.
2.3 Scope Limitations
A team comprised of mechanical and industrial engineers shall design a new process and/or device, with any electrical engineering concerns alleviated by consultation.
This project shall be completed in a time span of two academic quarters ending in late February and late May, respectively. Formal proposals and drawings for the team’s designs must be presented by the end of the first quarter. A working prototype shall be the final deliverable for the second academic quarter.
With respect to the team’s time constraints, the scope of this project is to design and create a prototype device to improve the box-opening process. In addition, the team will conduct a feasibility assessment to offer suggestions to address ergonomic concerns of the current workstation.
2.4 Stakeholders
Primary Stakeholders:
• Fifth year mechanical and industrial engineering students
• Kraft Foods, Avon, New York and their employees
Secondary Stakeholders:
• Rochester Institute of Technology
• Additional Kraft Food plants and their employees
2.5 Key Business Goals
• Produce a prototype, which will facilitate process efficiency and reduce ergonomic risk
• Improve cost effectiveness by eliminating non-value adding steps
• Create a safer working environment
2.6 Financial Parameters
In absence of an actual budget, the team must produce a low-cost tool and other process improvements using Kraft site funds. Any spending must be justified and approved by Kraft, based on return on investment.
2.7 Critical Performance Parameters (Order Qualifiers, Minimum Required Performance)
• The process shall reduce ergonomic risk factor of 29 out of 82
• The improved tool shall be able to open the pallet of boxes in the amount of time necessary to keep up with the packaging line, running at 130 to 240 pouches per minute (six bundles of four 10-packs per minute)
• The tool shall reduce the number of passes necessary to open the box flaps
• The design shall meet all Kraft required regulations and standards for plant machinery
• The design concept shall meet Kraft safety requirements
• The tool shall be able to be used by all workers
• The tool shall be an acceptable weight of less than 10 pounds.
• The tool shall not be larger than 16 inches by 10 inches by 12 inches to allow for convenient use and storage
2.8 Critical Performance Parameters (Order Winners, Desired Performance)
• The tool should open four 10-packs at one time
• The tool should be easily cleaned and sanitized
• The tool should be constructed of primarily off-the-shelf or easily-made parts allowing for easier replacement parts
• The tool should not puncture or destroy any juice pouches when opening the boxes
• The tool should require only one employee to perform the job without assistance of another worker
• The tool should improve ease of box opening by using pneumatic cylinders to assist with the force needed to open the boxes
• An ergonomic assessment should be performed, resulting in suggestions for further workstation improvements
2.9 Describe the Need
The objective of this project is to design a process and/or device to replace or improve the existing box opening and unloading process currently in place at Kraft Foods. The final design should address ergonomic and manpower concerns.
2.10 Constraints
• Limited Time (6 months)
• Limited Funds (Avon site funds only)
2.11 Project Management
The team is comprised of a team leader, a lead engineer, one staff industrial and systems engineer and four mechanical engineers. One faculty member serves as a mentor and advisor. The Industrial and Systems Engineering Department Head serves as the Project Coordinator. An organizational chart illustrates these relationships, located in Appendix A. Appendix B is a high level Work Breakdown Structure to show resource allocation. The timeline and Gantt chart in Appendix C has been created to keep track of tasks and assignments.
Chapter 3: Concept Development
Techniques for concept development were used to determine the best tool design. Outlined below is the process and criteria used to compare the three different concepts.
3.1 Brainstorming Technique
The first brainstorming technique was used to generate numerous ideas. All ideas, no matter how unrealistic, were accepted for this part of the process. In this step of the concept development process there is no specific criteria to be followed. The ideas were listed on the form provided in the EDGE™. After a significant list had been generated each team member was allowed to cast five votes which included multiple votes for one item if the individual felt it was necessary. Due to the changing scope of the project, the team used this technique two separate times. This first attempt at this method was to solve the problems with the entire juice placing process. It was then used a second time to brainstorm ideas for a way to open the boxes. After all votes had been cast, they were counted and the three concepts with the highest number of votes were pursued in more depth.
3.2 Concept Alternatives
At this point three possible design ideas still remained: the wedge tool, a handheld tool using toggles, and a stationary tool to be mounted to the tabletop also utilizing toggles. The team discussed the feasibility of each concept.
The wedge tool involves a wedge shaped device to open the boxes by introducing the wedge’s tip where the major flaps meet on the ends of the Kool-aid boxes. The operator would drive the wedge down the flaps opening an eight-high column of four 10-packs at once. This operation could be done by hand but the team looked into a pulley system to divert some of the force needed to open the boxes.
The stationary tool would have the same performance operations as the handheld tool, but instead it would be mounted on a table that is currently located at the top of the feeding line. The operators’ only function with the device would be to introduce the four 10-packs into the tool. A foot pedal or switch would be used to open the boxes and then the operator would empty the boxes onto the feeding line.
The third and final concept is hand-held and capable of opening one shrink-wrapped bundle of four 10-packs at a time, after the shrink wrap is removed.
3.3 Handheld Device
This device consists of spring-loaded toggles that are pushed into the box through the slit between the major flaps. The toggles’ default position is spread open so that the toggles are approximately two inches wide. When they are pushed into the box, the toggles are pushed down to a closed position. Once inside, the toggles spring open again and are pulled back out. The spread toggles grab the flaps and rip them open as they are pulled back.
Initial brainstorming envisioned a device that was purely manual, where the operator would push and pull the device by arm power alone. This idea was quickly dismissed after measurements were made as to the force necessary to rip the box flaps open using a spread toggle. Using a push/pull measurement scale, it was found that a force in excess of sixty pounds was needed in order to recover the toggle. This force is far greater than what would be considered acceptable for repetitive work on the part of the operators. Furthermore, this is only the force needed to open one box.
These initial thoughts led the team to decide that the only way to make the handheld device practical is to make it powered in some way. The cheapest, safest and most accessible form of power available to the plant floor is compressed air. Compressed air lines containing 110 psi are present throughout the plant, thus pneumatics was the primary choice for power on the handheld device. A compressed air cylinder of appropriate size was chosen to handle the load necessary to open four 10-pack boxes at once. Through a system that includes a control valve and the cylinder, the operator will be able to place the device against the boxes and simply push a button while the toggles are pushed into the boxes and then retracted as the boxes are opened. The specifics of the design process, as well as drawings and finite element analysis results, are presented and discussed in chapters six and seven.
3.4 Group Drawing Method
The three concepts: a wedge tool, a stationary tool, and a handheld tool were developed in greater detail using the group drawing method. Each team member was assigned a concept to draw. Since the team members are from different engineering disciplines the perspectives from each member was unique. During this process, the design of the box and the orientation of the pallet were taken into account. After thirty seconds of drawing the designs were passed to the person on the right for further detail to be added. This was repeated until each team member had worked on every drawing.
3.5 Empathy Method
In order to identify system interactions and coupling between subsystems, the team conducted an empathy method exercise to help understand the problem. Each team member represented a component involved in the system, and after ten minutes of role-playing, a greater insight was revealed concerning what is involved in the situation and also what other elements may be needed to address the problem.
3.6 Concept Selection
In order to proceed with a single design, it is important to objectively evaluate design concepts. By applying Pugh’s Method of Direct Comparison of Alternatives, a Weighted Comparison Method, and a Radar Chart, an evaluation of the chance that the project will be successful is accomplished. By comparing alternatives against a baseline concept, the concept among the alternatives that best meets the feasibility criteria can be chosen. In this case, the baseline concept refers to the current tool used at Kraft.
3.6.1 Pugh’s Method
In Pugh’s Method, each attribute used to evaluate the feasibility is scored against the baseline with either -, 0, or +. The minus suggests a concept inferior to the baseline, the zero suggests that the attributes match up evenly, and the plus suggests that the alternative concept is superior to the baseline.
3.6.2 Weighted Comparison
The Weighted Comparison Method, like Pugh’s Method, compares alternatives against a baseline concept. However, this technique yields comparisons having greater resolution than Pugh’s Method. This weighted approach takes into consideration the magnitude of the differences of the levels of attainment of each concept. Each attribute is scored in a range of 1 to 5 where: 1 = much worse than the baseline, 2 = worse than the baseline, 3 = same as the baseline, 4 = better than the baseline, and 5 = much better than the baseline.
3.6.3 Radar Chart
The purpose of a radar chart is to display the level of achievement among alternatives to evaluate concepts and concept feasibility. The alternative that covers the most area on the diagram is the best alternative. Each Concept is evaluated compared to the baseline of the currently used hand tool. Attributes evaluated are Resource Feasibility, Economic Feasibility, Schedule Feasibility, and Technological Feasibility.
|Resource Feasibility |
|R1: |Sufficient Skills |
|R2: |Sufficient Equipment |
|R3: |Sufficient Number of People |
|R4: |Sufficient Space |
|R5: |Safety |
|Economic Feasibility |
|E1: |% of Total Required Funds |
|Schedule Feasibility |
|S1: |Chances of meeting the intermediate mileposts |
|S2: |Chances of meeting the PDR Requirements |
|S3: |Chances of meeting the CDR Requirements |
|Technologically Feasible |
|T1: |Feasibility Level (L0, L1, L2, L3, L4) |
|T2: |Keep up with Packaging Line (130-240 pouches/min) |
Table 1: Feasibility Attributes
[pic]
Figure 1: Radar Chart
In evaluating juice supply, Concept 2, the Handheld device covers the most area. Concept 1, the Wedge, covered the least area, proving to be a worse option than the baseline tool. The Stationary device, Concept 3, was little better than the baseline and in some cases worse.
After completing these evaluation processes, it was determined that the handheld device rated best, compared to the baseline and to the other concept alternatives. Other factors were also considered in addition to the Pugh’s and weighted methods for concept selection.
3.6.4 Qualitative Evaluation
The Wedge concept was rejected because this type of opening device would require too much space in order to attach a pulley system. Also, without the pulley system, the force needed to drive the wedges down a column of juice boxes would be unreasonable for the operators, hence increasing the ergonomic risk factor.
The stationary device was rejected due to reduced productivity and an increase in ergonomic risk. The tabletop is currently used as a staging area for 10-pack boxes that will be emptied onto the conveyor. If this design were to be pursued, the operator would have to put the boxes in the opener, which is where the boxes are usually started, wait for them to be opened, and then dump them onto the conveyor. This process would be entirely too slow, and may compromise the ability to achieve high productivity. The motions associated with this method also require the workers to lift and put down boxes with greater frequency, which results in an increase in ergonomic risk.
3.6.5 Decision
In respect to the quantitative methods and qualitative evaluation, the concept of a handheld device to open four bundled 10-packs at once was the best alternative. The handheld device is shown in Figure 2.
Figure 2: Design Concept
Chapter 4: Feasibility Assessment
4.1 Feasibility Introduction
The question to be answered through the feasibility evaluation of this project is whether the team’s goals and design requirements can be met within the allotted amount of time and with the given budget constraints. These feasibility constraints were responsible for the team’s decisions as far as setting the scope of the project. The early stages of the brainstorming process saw the team trying to solve a problem that would have been far too time consuming and expensive to complete in twenty weeks and on a reasonable budget. The requirements for the project dictated the extent of the project and the final design goal is one that was feasible given time and budget constraints.
4.2 Design Feasibility
The design of the handheld device will have to be completed within the given time and budget constraints, as mentioned above, as well as within the limits of the team’s design and fabrication capabilities. To achieve this, the design was kept relatively simple, without unnecessary components or other gadgetry that would increase the complexity, cost and weight of the design. As stated, the device will work on compressed air and does not include any electrical or robotic components. The design is purely mechanical in nature and was designed to be as robust as possible without adding excess weight.
4.3 Functional Feasibility
Functional Analysis Systems Technique (FAST) is a creative stimulus to explore innovative avenues for performing functions. FAST describes the system and causes the team to think through the functions that the system performs. The FAST model has a horizontal directional orientation described as the How-Why dimension. From left to right, the question “How that function is performed”, and from right to left the question “Why that function is performed” is asked. Appendix D illustrates a FAST diagram for the currently used tool and procedure as well as Brainstorming FAST to illustrate possibilities for design development. These FAST diagrams help insure the feasibility of the concept design.
The purpose of a functional flow block diagram (FFBD) is to show the functions that a system is to perform and the order in which they are to be enabled (Vitech). A FFBD for the process is illustrated in Appendix E.
4.4 Materials Feasibility
All materials that will be used in the fabrication of this design are standard materials that can be purchased from any number of distributors. The design is a compromise between an effort to reduce weight, provide adequate strength and to make the design compatible with the working environment.
There are four main load-bearing components in the design that will bear the brunt of the 240 pounds of force needed to open four boxes of juice at once. These components were designed to be made of stainless steel and provide adequate strength in a robust design. Finite element analysis (FEA) of the part helped the team to strengthen specific areas of high stress and then cut off unnecessary material from low stress areas to reduce overall weight of the design. The final design will incorporate stainless steel in order for the device to be compatible with the food-grade working environment at Kraft (Reference Appendix H).
All tools are periodically cleaned to maintain a sanitary working environment and must be able to cope with both acidic and basic cleaning solvents. The stainless steel will not corrode and can be easily cleaned in the sanitary conditions. Other components on the design may be comprised of materials other than steel. None of the components will be made of any type of metal other than stainless steel because of corrosion characteristics. Aluminum, for instance, would be advantageous because of its low density, but will corrode in the acidic and basic cleaning solutions and is very difficult to weld effectively. Polymers may be used for some components in an effort to reduce weight. The polymers must be able to withstand sanitation measures and must not be too expensive to purchase.
4.5 Fabrication Feasibility
This device was designed with fabrication in mind. Every component of the device was added amid questions of “how will it be assembled and attached?” The skills and resources available to the team members were established during the beginning stages of the design of this concept and were kept in mind throughout the design process.
The major mode of fabrication to be used is the welding of the steel components. Welding offers a very strong bond and requires fewer parts. The device consists of a main steel tubing frame that will have the other necessary components of the device welded onto it. Mounting brackets needed for the pneumatic cylinder, and control valve will be welded onto the main frame. The guide plate will also be welded onto this main frame. Further descriptions of these parts will be provided in proceeding chapters.
Apart from welding, fabrication will also include fastening devices such as typical nuts, bolts and washers. Any part of the device that is considered a permanent component, that does not have to move, will be welded to the main frame, while other objects that may need to be replaced periodically will be attached to these permanent components via fasteners. For example, mounting brackets for the pneumatics will be welded to the main frame, while the pneumatic components themselves will be attached to these brackets using nuts, bolts and washers. Aside from the pneumatic components, the rods and the toggles will also be attached with fasteners to the mounting plate, while the mounting plate will be bolted onto the pneumatic cylinder’s shaft.
Laser cutting, using nitrogen gas, will be used during the fabrication process, and will be used mainly to help in the reduction of unnecessary material in order to reduce the weight of the device and its tolerance to cut to a +/- 0.005 inches of the specified part dimensions. Finite element analysis determined how much material was needed in order to achieve the proper strength for the device to maintain reliability. A satisfactory factor of safety was achieved while using the smallest amount of material possible. Where possible, holes were cut in steel parts to reduce weight. Laser cutting of steel is available to a member of the team and this resource will be utilized to achieve optimum performance of the final device (Reference Appendix I).
4.6 Cost Feasibility
As was the case with fabrication, this device was designed with cost in mind. Where possible, the team used off-the-shelf components to keep the price as low as possible. There are components on this design that require parts to be custom made, but those parts are made from raw materials that are easily accessible and not very expensive. For example, the steel tube main frame needs to be custom bent, but the steel tubing needed for the component uses standard sizes and is easily purchased. All of the smaller components, such as the nuts and bolts, are used in standard sizes and are also easily purchased from any distributor (Reference Figure 18).
There is one area in which the team opted for higher price in order to achieve greater performance. The need for stainless steel in the sanitary food-processing environment led the team to make the decision to construct all of the steel components with stainless steel. Other than the need for stainless steel, the team was able to design the device with economy in mind.
4.7 Ergonomic Feasibility
The tool is designed with ergonomics in mind. The handle position is of a pistol-grip in nature, allowing for power grip, the strongest of all grips. This is the best orientation for vertical, powered operations (Niebel 1999). In addition, the shoulders are in a relaxed position, hanging down naturally, while the elbows are flexed at 90 degrees, parallel to the ground (Niebel 1999). Optimal tool weight for one-handed tools is less than five pounds, as this concept is two-handed, weight shall be reduced to less than ten pounds.
Size constraints are based on box size. However, 50th Percentile elbow-elbow breadth is 15.1 inches and 16.4 inches for females and males, respectively. The width of the tool is 15.375 inches with the handles being mounted approximately 2.5 inches from the outside. Handle location provides a suitable width for the 50th percentile and should not pose undue strain on 5th or 95th percentiles.
The toggle switches use to activate the pneumatics will have a minimum diameter of 19 millimeters and maximum displacement of 120 degrees. The force needed to operate the pneumatics shall be less than 16 pounds. The handle diameter shall be between 1.5 and 2 inches (Niebel 1999).
4.8 Design Structure Matrix
“Complex projects require a series of activities, some of which must be performed sequentially and others than can be performed in parallel with other activities. This collection of series and parallel tasks can be modeled as a network. The Program Evaluation and Review Technique (PERT) is a network model that allows for randomness in activity completion times” (Netmba 2004). The PERT chart illustrates the tasks necessary to build the concept design.
Stemming from the PERT charts is a Design Structure Matrix (DSM), in Appendix F. The purpose of this technique is to decide the order of tasks by sequencing the specification of design parameters. The DSM iterates a list of tasks to make dependent tasks sequential.
Chapter 5: Design Objectives and Performance Specifications
The purpose of this facet is to clearly define the project’s design objectives and performance specifications. The design objectives are based on the customer’s requirements for the project. The team based on the project definition, determined design objectives. These are discussed in detail in the following sections.
5.1 House of Quality
Figure 3: House of Quality
The House of Quality (Figure 3) combines the design objectives and customer needs to ensure all requirements are met. It is a means of quantifying the voice of the customer. The objective is “the overall goal of the project.” The Engineering Characteristics include “measurable quantities that relate to customer requirements and desired direction of improvement.” The customer requirements section lists “what is important to the customer.” This section includes items such as “cost, availability, packaging, performance, ease of use, assurances, life cycle costs, and social standards.” The Customer Important ratings scale the Customer Requirements from 1-10 on a scale of importance in producing the product or process. The Target Values section specifies the “nominal specification for the new product or process. It utilized benchmarking data and results from value analysis.” The “roof” or correlation matrix shows interaction between engineering characteristics. The interactions are denoted by (+) for a strong relationship, (-) for a negative relationship, and circles for very strong or very negative and no symbol if the interaction between the two is not significant. A strong relationship indicates that the two characteristics aid in achieving the respective target values. The relationship matrix creates a link between engineering characteristics and customer requirements. The scale is 1 to 9, with 9 being the strongest relationship (Stiebitz, 2003).
To analyze, thus calculating absolute and relative importance, for each engineering characteristic, the rating is multiplied by the relationship for each customer requirement, then summed. The total becomes absolute importance. Relative importance is calculated by dividing absolute importance by the sum of all absolute importances.
According to the House, the most heavily weighted factors are addressing 10-packs (0.25) and using available resources (0.23). As indicated by the House, decreasing the number of passes (0.19), reducing ergonomic risk (0.16) and line speed (0.10) are the next highest group of importances. Least important is utilizing the number of workers assigned at 0.08.
5.2 Design Objectives
Kraft approached Rochester Institute of Technology’s Occupational Safety and Ergonomic Excellence Department for assistance in addressing ergonomic concerns with their provisional box-opening tool. The scope of the initial opportunity was expanded to include overall ergonomic issues of the juice supply process. The main objective is to design, build, and demonstrate the functionality of a single tool to replace or improve the existing box opening and unloading process currently in place at Kraft Foods.
5.3 Performance Specifications
The entire tool should be as small as possible while still maintaining overall effectiveness and should weigh no more than ten pounds.
In terms of performance, the improvement shall reduce the ergonomic risk factor of 29/82 on the Kraft scale and the number of passes per box. The improvement shall open the pallet of boxes in the amount of time necessary to keep up with the packaging line, running at 130 to 240 pouches per minute (six bundles of four 10-packs per minute).
Environmental Requirements focus on safety and regulations required at Kraft. All materials used shall be resistant to the required daily acid and base wash down. The Federal Food and Drug Administration (FDA) shall approve all materials and assembly methods.
Functional Specifications state that all workers shall be able to operate the tool.
The team shall complete a final design package, which includes a concept design report, a technical paper, and a working prototype. In addition each team member shall submit a personal logbook which details design progress.
Chapter 6: Analysis of Problems and Synthesis of the Design
6.1 Analysis Introduction
The initial analysis that was performed was done with the performance specifications of the device in mind. Toggle testing with a push/pull scale was done to establish the amount of force needed to tear open a box of juice pouches. A force of approximately 60 pounds was needed to accomplish this task. The team planned to open four boxes at once, as the boxes are shrink-wrapped together into bundles of four; therefore, a total force of approximately 240 pounds would be necessary to open all four boxes at the same time. In the interest of creating a robust design, the team proceeded with analysis with a force of 300 pounds in mind, which results in a factor of safety of 1.25.
With the experimentation that yielded the necessary amount of force to open the boxes, the decision had been made to use some form of power to open the boxes. Applying a force of 60 pounds repetitively at a rapid pace would be far too strenuous on even the strongest workers. Furthermore, the team insisted that opening one box at a time was not enough. The device needed to be able to open several boxes at once.
6.2 Compressed Air Cylinder
Power used to operate the device will be compressed air, and a compressed air cylinder is the simplest and most economical way of applying the necessary force to the boxes. The type of cylinder to be used is known as a double acting compressed air cylinder. The term ‘double acting’ means that there are two air ports in the cylinder. In other words, compressed air can be introduced to either side of the piston inside the cylinder. By alternating the side on which the force is applied, the piston can be pushed back and forth with the full force of the compressed air. This will allow the box opening device to have enough force available to get the toggles into the boxes and to pull them out.
In order to calculate the size of the cylinder that would be needed to achieve the necessary 300 lbs. of force, the team worked backwards from the established information to arrive at the size of the bore necessary in the cylinder. The given facts are that 300 lbs. of force is needed and that there is 110 psi available in the plant’s airlines. Force divided by air pressure will yield the amount of surface area needed for the application of the air pressure. Once this surface area is known, the equation for the area of a circle is used to calculate the necessary diameter of a circular bore inside of a cylinder (see section 6.8). The final diameter was calculated at 1.863 inches. The compressed air cylinder to be purchased will have a bore size of two inches.
6.3 The Main Frame and Mounting the Cylinder
The design of the device begins with a basic rectangular frame made from steel tubing. Everything on the device is based on and attached to this frame. As time progresses and the specifics of the design are more clearly defined, the exact dimensions of the frame and the size of the tubing are modified to achieve optimal performance.
The cylinder is to be mounted directly in the center of the rectangle that is formed by the frame. If the cylinder will be opening several boxes at once, it should be placed in the center so that the force application is equally distributed and no unnecessary moments are created. In order to mount the cylinder to the frame, a plate is attached across the frame, with each end of the plate being welded to the tubing. A hole is cut in the center of the plate where the cylinder is to be placed. There are threads built in to the cylinder so that a nut can be used on the bottom side of this plate to hold the cylinder in place (reference Figures 1-16). Finite element analysis (FEA) is performed on this plate to ensure that it could handle the necessary loads. Each end is fixed with a load of 300 pounds applied at the hole. The 12-gage sheet steel originally used failed and, as a result, the thickness was increased to 0.179 inches, or 7-gage sheet steel. In an attempt to compromise between added strength and added weight, material is removed from low stress areas on the plate, resulting in the present shape (Reference Appendices H and I).
6.4 Rod mounting plate
The rod mounting plate is the plate that attaches the cylinder shaft to the toggle rods that will be used to open the boxes. One cylinder is used to operate eight toggles, while two toggles are assigned to opening each box. A rectangular plate, similar in size to the frame is designed so the cylinder shaft can be mounted to the center and the eight rods can be mounted to the opposite side in the same manner. The rods are attached to the plate in such an orientation as to allow two toggles to open each box (Reference Figure 7).
Finite element analysis is applied on this plate, as it would be bearing the force necessary to open the boxes. The center mount is held in a fixed position, while the load of 300 pounds is evenly distributed among the eight rod mounting locations. Upon examination of the results and in order to optimize the design, holes are cut in the center to eliminate extra weight, while the outer edges on the long side of the rectangle are bent up to act as a channel to increase the stiffness of the plate. The result of this optimization is the present form of the part (Reference Appendices H and I).
6.5 Guide Plate and Box Guide Plates and Rods
The guide plate is a device that serves two separate purposes. First, the fixed guide plate with holes for the toggle rods is needed to ensure that the rods travel straight and do not bend or twist. Secondly, as stated previously, the cylinder is placed in the center of the frame to avoid any undesirable moments or uneven application of power. Thus, the guide plate serves the same purpose, allowing the rods to travel in a straight line. This plate is welded to the main frame to provide a stable platform for guiding the rods. The box guide plates and rods are attached to this fixed platform and serves to push against the boxes as they are opened. A fixture is needed to provide a reaction force against the boxes as the cylinder pulled at the flaps with 300 pounds of force. In the absence of this force, the flaps on the boxes might hold and pull the boxes off the pallet. These box guide plates are positioned between the boxes where they will not interfere with opening the flaps. A rod will be welded to the bottom of each of these guide plates to act as a buffer so the plate will not cut into the cardboard of the boxes (Reference Figures 8, 9, 10).
As with the case of the rod mounting plate, FEA is performed on the guide plate. There are five box guide plates attached to the large guide plate and the 300 pounds of force will be transferred through them to the guide plate. The guide plate will be fixed on its edges where it will be welded to the frame. The FEA produced results that confirmed that the 12-gage steel originally used would be sufficient. Again, as with the box guide plates, some of the material can be removed in order to save on unneeded weight. The ability of these parts to perform under the applied loads is not compromised (Reference Appendices H and I).
6.6 Toggle Rods
The design of the toggle rods is relatively simple, in that the only loads they would need to endure are simply tensile and compressive loads, applied longitudinally. Both ends of the rods are threaded for fastening purposes. One end will be attached to the toggle bolt mounting plate, and will be fastened with a washer and a nut on each side of the plate. The other end will have the toggle threaded onto it and Loc-tite to hold the toggle in place. The ends of the toggle rods have been filed to provide a smooth rounded tip to the rod so as to cause minimal damage to anything the rod may touch once inside the flaps. ¼-inch diameter rod is used, in order to be easily handled and formed, while remaining lightweight. The strength of the rods is not a concern, as the steel tested can easily handle the applied loads in tension and compression.
6.7 Mounting the Directional Valve
The directional control valve needs to be mounted to the main frame so the air can easily be supplied to the cylinder and controlled by the operator. The control valve needs to be mounted next to the handle, so the worker can easily reach the finger-operated lever used to operate the device. This dictates the orientation in which the control valve should be placed. With this in mind, a simple bracket is welded to the main frame. This bracket also includes holes that line up with the mounting holes on the particular valve chosen for this application. The bracket, made from 14-gage steel, is slightly thinner than the 12 or 7 gage sheet steel that will be used elsewhere on the design. The reason for this is the bracket is not subjected to any significant load, other than the weight of the valve (approximately 0.14 lb.), and so a lighter sheet steel can be used to minimize weight.
6.8 Formulae and Calculations (Reference Appendix H)
Variables
Asw = Effective area of ¼ inch stainless steel washer
Alw’ = Effective area of ½ inch stainless steel washer with 2 inch outer
diameter
Alw = Effective area of ½ inch stainless steel washer with 0.6250 inch
outer diameter
Agp = Effective area of guide plate
Acyl = Area required for cylinder
Dcyl = Diameter required for cylinder
Fgp = Force due to box guide plates reaction force
Fc = Force due to cylinder push/pull force
Fmf = Force on main frame due to cylinder mount reaction force
FR = Force applied through each rod from juice boxes
Pgp = Pressure due to box guide plates reaction force
Pc = Pressure due to cylinder push/pull force
Pmf = Pressure on main frame due to cylinder mount reaction force
PR = Pressure force applied through each rod from juice boxes
Area
Circle: [pic]
Rectangle: [pic]
Force [pic]
Pressure [pic]
6.8.1 Cylinder Calculations
Area [pic] (where 110psi is plant pressure)
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Diameter [pic]
6.8.2 Free Body Diagram Calculations
Area
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Force
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Pressure
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6.9 Fatigue Analysis
In order to ensure that each part will not fail during use, 1,000,000 cycle fatigue analysis was performed. General practice indicates that 1,000,000 cycles for steel components is an adequate limit to ensure material integrity.
Variables: CL = Load Factor
CG = Gradient Factor
CS = Surface Factor
Su = Ultimate Strength
Sy = Yield Strength
Sn = Endurance Limit
Sn’ = R. R. Moore Endurance Limit
N = Number of Cycles to Achieve
S = Stress to Achieve N Cycles
Equations:
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Check…
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Figure 4: Goodman Diagram
When steel is being used for a given application, it is generally accepted that if the part does not fail in 106 cycles, it will last indefinitely. The purpose of the first series of calculations is to find the endurance limit Sn. This value of the endurance limit indicates the amount of stress that the part can withstand in order to survive 106 cycles without failure. The first step in these calculations is to find Sn’, also known as the R. R. Moore endurance limit, which is approximated at half of the ultimate strength for steel. This value is then multiplied by several factors: CL, CG, CS. These factors take into account such issues as geometry, loading conditions and surface finish. Once the R. R. Moore endurance limit has been multiplied by the several factors, the result is the 106 endurance limit. The previous calculations show an endurance limit stress of roughly 28 ksi. That is, the steel parts on the design can be subjected to cyclic loading of 28 ksi and they should never fail.
A second method of calculation was done for the purpose of acting as a check for the first method. The equation [pic] is used to find the stress that will allow a part to undergo a specific number of cycles that the designer may be interested in. S is this allowable stress, while N is the number of cycles desired by the designer. In the case of this project, the desired number of cycles is one million, for reasons stated earlier. The constants m and b had to be calculated using the formulas that are shown above. This method yielded an allowable stress for one million cycles of roughly 28 ksi again, which supports the findings of the first series of calculations. All of these calculations were previously shown, and the exact values are there for comparison.
Following the calculations is a Goodman diagram (Fig. 4) that has been produced in order to show where the design stress of 28 ksi lies in relation to the endurance limit and the yield strength of the material. On this graph, the mean stress of the cyclic loading is plotted on the horizontal axis versus the stress amplitude on the vertical axis. The blue line indicates the stress that would fail before 106 cycles. In order for a part to survive for this many cycles, the design stress must be plotted below and to the left of this line. The green line indicates the yield stress limit. That is, if the design stress goes over this line at all, the part will deform plastically, which is also considered a failure. The mean stress and stress amplitude for which this part is designed, when plotted on the Goodman diagram, must fall below both of these lines to be a success. The stress placed on this part will alternate between the calculated 28 ksi and 0 ksi. This yields a mean stress of 14 ksi and also an amplitude of 14 ksi. These values are then plotted from the horizontal and vertical axes on the Goodman diagram. The stress for which this part was designed is indicated by the yellow point and does fall under both lines.
6.10 Purchased Items
Any items that were to be purchased off the shelf and not manufactured by the team were chosen with the same thoughts in mind that dictated the design of the other parts. First to be considered was performance. Could the part do its job? Once options were found, the products that were the lightest were preferred. It is the goal of this team to create a product that any employee can use in a repetitive and rapid manner, and so creating a device of minimal weight was a top priority. Such items included the toggles, cylinder, control valve, and all nuts, screws and washers.
6.10.1 Toggles
The toggles are the most important elements of the design. Each toggle is composed of two wings, a spring, and a nut. Due to the number of individual parts of the toggle, it is a part, which is likely to malfunction. As such, no special design was created, for ease of replacement. However, it is necessary to determine the expected life of the spring, to prepare for replacement and maintenance. Rather than design a device to mechanically test the toggles, mathematical calculations were performed to determine the life of a spring. In order to ensure that each part will not fail during use, 1,000,000 cycle fatigue analysis was performed. General practice indicates that 1,000,000 cycles for steel components is an adequate limit to ensure material integrity. According to the formulas and calculations in section 6.9.1.1, the springs are expected to last for more than one million cycles. As shown by the calculations, the applied stress is a small fraction of the endurance limit stress for this part. The applied stress is approximately 250 psi, while the endurance limit stress is approximately 28,000 psi. The endurance limit stress is the stress to which the part can be loaded cyclically and survive one million cycles. When the applied stress of 250 psi is used to calculate the allowable number of cycles that can take place before failure occurs, calculations yield an answer of [pic] cycles. This number is so large that it serves merely as an illustration to the fact that this torsion spring will never fail due to fatigue under these operating conditions.
Failure of the toggle will not be due to the spring, rather to another failure of the functionality of the toggles. To extend the life of the moving parts, and to protect the toggle from becoming jammed from possible juice contamination, a food grade lubricant will be used.
Tests were performed to determine the value of adding a second spring. It was hypothesized that a second spring would aid the toggle in opening should the device become sticky or encounter resistance, such as from a juice pouch or other obstacle.
During testing it was found that the addition of a second spring did improve the performance of the toggles. However, as the addition of a spring requires approximately 5 minutes of labor, per toggle, the cost of modifying a purchased part does not outweigh the cost in more frequently replacing a toggle end due to failure to open. As a result, the final design will consist of toggles with single springs.
6.10.1.1 Fatigue analysis for spring
Variables: CL = Load Factor
CG = Gradient Factor
CS = Surface Factor
Su = Ultimate Strength
Sy = Yield Strength
Sn = Endurance Limit
Sn’ = R. R. Moore Endurance Limit
N = Number of Cycles to Achieve
S = Stress to Achieve N Cycles
Equations:
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Number of cycles to failure for 250 psi cyclic loading:
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6.10.2 Cylinder
The cylinder is the second most important single item on the design. It was no problem finding a cylinder that could produce the 300 lb. of force needed to get the job done. Furthermore, cylinders are relatively cheap, and thus economy was not a problem. Weight, however, was an important issue. The first cylinder considered weighed 8 lbs. This ended up being a very significant portion of the final weight of the entire device, and so a lighter model was sought. A model was found that uses polymers as well as steel, rather than making the entire cylinder out of steel. This resulted in a cylinder that weighs approximately 1.5 lbs. and was still able to deliver the necessary force.
6.10.3 Control Valve
The purpose of the control valve is to regulate when the cylinder’s shaft is retracted and extended. The type of control valve that was needed for this application is a 5 port, 2-position valve. The compressed air comes in one end and the valve sends it in one of two possible directions. One output direction corresponds with extending the shaft, the other with retracting the shaft. The default position is for the cylinder shaft to be retracted. When the operator pushes on the trigger, it changes the direction of the airflow and causes the cylinder shaft to extend. The valve is spring loaded, so that when the operator lets up on the trigger, the valve returns to its default position.
6.11 Failure Modes and Effects Analysis -Design FMEA
FMEA - Failure Mode and Effects Analysis is a pro-active, structured engineering quality method that helps to identify and counter weak points in the early conception phase of products and processes(FMEA Infocentre 2003). FMEA is used to identify potential failures in a system, product, or process operation. Causes are then identified either as design or process; Recommended Actions are then identified to eliminate potential failures or reduce their rate of occurrence. FMEA also identifies design or process characteristics that require special controls to prevent or detect failure modes (FMEA Failure Modes 2003). The Food and Drug Administration (FDA) has recognized FMEA as a design verification method for Drugs and Medical Devices (Quality 2004).
To perform an FMEA, all functions of the device are listed. Next, potential failures are listed for each function. The effect of each failure is determined and noted, followed by a rating of severity. The effect is what a user would experience from the failure. The severity rating is “the seriousness of the potential failure on a scale of 1 to 10” (Stiebitz 2003). Potential causes of failure are determined as well as an occurrence estimate. The Potential cause is the mechanical means of failure or “a list of conceivable causes of the failure” (Stiebitz 2003). The occurrence estimate is “a scaled estimate of the likelihood that a specific cause will occur during the design life of the product” (Stiebitz 2003). Current design controls are noted for each failure. These are activities or devices already in place to prevent a failure, such as a guide. Failure detection and risk priority are noted next. Recommended actions as well as responsibility for actions are noted for each mode of failure. The final section is a record of correction, what actions were taken, and a resulting estimate of corrective actions (Stiebitz 2003).
The FMEA in Appendix J is the analysis of the handheld tool concept. Four failure modes are noted, with six potential failure effects for the function of Opening Boxes. Five failures have controls in the design and place the burden of correction on the operator. These forms of failure would be noted during prototype testing. Addressing tool comfort is a responsibility of the design team.
6.12 Ergonomic Risk Factor Assessment
A preliminary ergonomic risk factor assessment was completed to estimate the process improvement with the new tool. The new process scored a 7. This significantly reduces the risk associated with this process. A table of the results can be referenced in Appendix K.
Chapter 7: Preliminary Design Documents
The following design documents are representations of the scaled drawings. Actual documents, can be found in the EDGE™ (These drawings are for the original tool that was presented at the preliminary design review. Several of these parts were updated during the second quarter of senior design and will be described in chapters 8 and 9).
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Figure 5: Main Frame Tube
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Figure 6: Handle Mount Tube
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Figure 7: Toggle Bolt Mounting Plate
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Figure 8: ¼-20 x 4” Rod
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Figure 9: Guide Plate
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Figure 10: Box Guide Plate
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Figure 11: Box Guide Rod
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Figure 12: Pneumatic Cylinder Mount
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Figure 13: Threaded Handle Mount
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Figure 14: Removable Handle
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Figure 15: Control Valve Mount
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Figure 16: Control Valve Mount Gusset
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Figure 17: 10-Pack Box Opener
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Figure 18: Welded Frame Assembly
Figure 19: Bill of Materials
Chapter 8: Fabrication and Assembly
The design team fabricated most of the parts for the tool. Those pieces not made by the design team were produced either by CNC machine or at OXBO International Corporation. The following section details main fabrication procedures used to create a prototype of the design.
8.1 Mounting plate
The cylinder mounting plate is welded to the frame and is used to mount the compressed air cylinder to provide the force needed to open the boxes. The mounting plate is made out of 7-gage sheet steel. The shape of the plate was designed to reduce overall weight while maintaining strength. The cylinder mounting plate was fabricated by programming the drawing onto the CNC mill. Due to the difficult curves in the part, it was decided by the team that it would be best to use the CNC machine available to the RIT machine shop, in the RIT Brinkman lab.
8.2 Handle Fabrication
The two stainless steel handles are connected to the mainframe at a distance of 12 inches apart. This distance is the widest possible elbow-to-elbow breath that could be allowed for this tool since the total width is 15 3/8”. In addition, the diameter of these features is 1 ½”, which falls in the range of the anthropometric guideline of 1 ½” – 2” for handle diameter.
To achieve the handle lengths of 7 inches, the 1 ½” tubing was cut to length with a lathe in the RIT machine shop. It was also on this machine that 3 ¼” was knurled for each handle. Since only food-grade material can be used, the handles are knurled instead of left smooth to hold rubber grips. As the employees wear gloves in the 42-degree plant environment, the knurled feature actually serves more purpose than added rubber grips would.
8.3 Rod Fabrication
The toggles are threaded onto stainless-steel rods to be connected to the rod mounting plate. As the rods must be made of food-grade material, each of the eight ¼ inch rods must be stainless steel and are 4 3/4 inches in length. This fabrication was completed in the RIT Machine shop. The parts were cut to length on a band saw, and faced off to the correct length on a high-speed lathe. Thread was then put on both ends of the rods with a ¼-20 UNC die. The end of the threaded rod was then rounded using the speed lathe in conjunction with a standard file to give it a smooth and rounded finish.
Attached to the end of the guide plates are 3” stainless steel rods. The rods are in place to keep the guide plates from becoming wedged between the boxes when the toggles are actuated. Five rods were cut to length from ¼” stainless steel rod and then welded to the 5 guide plates, previously laser cut from 12-gauge stainless steel.
8.4 Directional Valves and Mounting Plates
The original design of the handheld tool called for a single L-shaped bracket that would hold the directional control valve in place. This directional control valve is a finger operated device, which controls whether air is extending or retracting the piston shaft. At the Preliminary Design Review, representatives from Kraft expressed interest in making the tool necessitate both hands for operation. The reasoning behind this request is based on safety concerns. It is desirable for the workers to always have both hands on the machine so that there is never a free hand that could get in the way of moving parts. In order to accomplish this, the design was modified to incorporate a second directional control valve. These valves are arranged in series with respect to each other along the air lines. The valves are arranged in such a way as to require both be operated at the same time for the machine to work. Figure 20 below illustrates the valve and hose configuration.
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Figure 20: Valve and hose configuration schematic
The first thought was to simply install a second L-shaped bracket to hold the second directional control valve. Unfortunately, this caused conflicts between the placement of tube fittings and the optimal position for finger operation. To solve this problem, the brackets were changed from the L shape to a trapezoidal shape, with the bottom corners being welded to the tube frame. The new bracket is parallel to the handles and stretches across the entire frame. It is made of the same 14-gauge sheet steel to reduce the weight of the tool.
In order to reduce the weight of the tool, the suggestion was made that these brackets should be made of a polymer material. Determining whether this was a feasible concept required the investigation of two topics. First, how much weight could be saved by switching to a polymer for this part? Second, how easily could a polymer bracket be attached to a steel tube frame?
The original steel brackets have a weight of 0.193 lb. each. Using the volume of this part and the density of the proposed polymer, it was possible to find the weight of the part if it was made out of a polymer. The volume of the part is 0.681 in3. Delrin was chosen as the polymer of choice because it is strong, easy to machine into the desired shape and acceptable in the food grade environment. This material has a density of 0.05 lb/in3. This yields a weight of 0.034 lb for the polymer bracket, which results in a weight savings of 0.159 lb per bracket. The entire design would be just under one third of a pound lighter with the polymer bracket.
The problem of how to mount the polymer bracket on the steel tube frame is not easy to solve. In order to mount the polymer to the steel tubing, it would be necessary to change the geometry in such a way as to allow the bracket to be attached using fasteners. This would add a large amount of complexity to the design and fabrication of the polymer bracket. Also, the added material needed for these geometry changes, as well as the material needed for the fasteners would add weight as well as increase the time and effort put into this design. A steel bracket could be cut out of sheet steel and welded in place in a fraction of the time.
For the amount of weight saved by switching to a polymer bracket, the amount of effort needed to accomplish this task is far greater than is acceptable. This task would carry with it a large price tag in terms of time and effort and would not yield much benefit. Therefore, this idea was abandoned.
The 14-gauge stainless steel brackets were milled to shape in the machine shop. After the final configuration of the directional control valves was determined, the design for notches and holes was determined. These were then cut out of the part.
8.5 Outside Fabrication
Several of the parts that go into our final assembly are constructed of sheet metal and the machine shop at RIT does not have the tools to manufacture and form the blanks that would become our finished part. This caused us to go to a local machine shop that a team member works at, OXBO International Corporation, which deals with sheet metal on a daily basis. By making these parts at this shop, we were able to hold tolerances between ±0.001” and ±0.005” on the parts, which would not have been the case if the parts were made at RIT.
The first part that we made outside of RIT was the handle end plug (KRAFT013). The shop at RIT would have been able to make this part, but it would have been very difficult to make because there is no easy way in the shop to cut out a circle and save the center part. If this was made at RIT, it would have been made on a mill and would require the blank that the part was made from to be fixtured several times in order to make one part. After the mill, it would have to be sanded down at the belt sander to finish making it round. This was very labor intensive and for this reason, it was brought to OXBO international and the circles were punched out using a 1-3/8” die. The punch that was used is capable of producing 40 tons of force, and the force required to punch a 1-3/8” hole through 14-gauge stainless steel is 12.38 tons, so this punch was able to make the parts. Using the punch, the four circles were made in just a few seconds to an outside diameter of 1.375”. Once the burr was removed from the edge of the parts with a file, this outside diameter moved to 1.370”, which was the dimension specified on our drawing.
The most complex part to manufacture on the tool is the rod guide plate (KRAFT007) because it has several areas where material was removed from low stress areas to reduce the weight of the part. There was no easy way to design the part with simple circular or rectangular cutouts in it that would have reduced the weight of the part as much as the shapes that are currently used. With these complex shapes, the only way to manufacture this part is with a CNC laser. For this reason, this part was also brought to OXBO International to be made on their Bystronic laser, which is capable of producing 2500 Watts of power and has the capability of cutting through ¾” thick steel. To manufacture this part on the laser, a .dxf file of the unfolded part was required, which was done by exporting the file out of the Solidworks CAD software in which it was designed. This file contains the outlines of all the shapes that need to be cut out and when this file is inputed into the laser, the laser cuts on the lines that were in the .dxf file and the end result is the finished unformed part with all of the holes cut out. To finish making this part, four flanges needed to be bent up at 90° each. To accomplish this, the parts were bent on the CNC Amada press brake, which has the capability of producing 242 tons of force. By inputting the required flange lengths into the press brake’s computer, the machine automatically determined how far back the backstop that the part is pressed up against needed to be and how far down the punch on the press brake needed to travel in order to form the 90° angle. Once these settings were entered into the computer, the part was put into the machine and the four flanges were formed.
Since the sheet of 12-gauge stainless steel was going to be in the laser to make the rod guide plate, the box guide plates (KRAFT008) were also lasered out at the same time. These parts could have been made at RIT, but because the material was going to be in the laser at OXBO International it was logical to have all 12-gauge parts made up at one time. Once these parts were lasered out, they were finished because they do not require any further machining other than being welded onto the final assembly.
8.6 Assembly
After all parts were fabricated, the tool was assembled using stainless-steel screws, nuts and washers, or by welding, according to the fishbone diagram in figure 21. Loc-tite will not be used on the assembly until all testing is completed.
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Figure 21: Fishbone Assembly Diagram
Chapter 9: Final Design Documents
The following design documents are representations of the scaled drawings. Actual documents can be found in the EDGE™. These documents reflect any changes made to the design during fabrication.
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Figure 22: Knurled handle
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Figure 23: Toggle bolt mounting plate
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Figure 24: ¼”-20 x 4” rods
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Figure 25: Guide Plate
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Figure 26: Box guide plate
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Figure 27: Box guide rod
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Figure 28: Pneumatic cylinder mount
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Figure 29: Handle end plug
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Figure 30: MV-50 mounting brackets
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Figure 31: LTV-50 Mounting bracket
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Figure 32: Long frame tube
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Figure 33: Short frame tube
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Figure 34: Vertical handle tube
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Figure 35: Horizontal handle tube
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Figure 36: Welded Frame
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Figure 37: 10-pack box opener with cut tubing
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Figure 38: Bill of Materials for Welded Frame (Kraft 105)
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Figure 39: Bill of Materials for Assembled Tool (Kraft 106)
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|ITEM NUMBER |PART NUMBER |DESCRIPTION |QUANTITY |
|1 |KRAFT105 |WELDED FRAME |1 |
|2 |KRAFT005 |TOGGLE BOLT MOUNTING PLATE |1 |
|3 |KRAFT006 |1/4-20 X 4-3/4" ROD |8 |
|4 |KRAFT201 |VALVE, LTV-50 |1 |
|5 |KRAFT205 |1/4" STAINLESS WASHER |16 |
|6 |KRAFT207 |1/2 STAINLESS FENDER WASHER |2 |
|7 |KRAFT204 |1/4-20 STAINLESS NUT |16 |
|8 |KRAFT206 |1/2-20 STAINLESS NUT |2 |
|9 |KRAFT209 |TOGGLE |8 |
|10 |KRAFT210 |1/8 NPT X 2" STAINLESS NIPPLE |1 |
|11 |KRAFT211 |10-32 X 1" STAINLESS SCREW |2 |
|12 |KRAFT212 |10-32 STAINLESS NUT |2 |
|13 |KRAFT213 |1/4" DU BUSHING |8 |
|14 |KRAFT228 |BIMBA PC CYLINDER, 2" STROKE |1 |
|15 |KRAFT214 |QUICK DISCONNECT AIR FITTING |1 |
|16 |KRAFT223 |1/4" TUBING TO 1/4" NPT, 90° FITTING |2 |
|17 |KRAFT217 |1/4" TUBING TO 1/8" NPT, STRAIGHT FITTING |1 |
|18 |KRAFT224 |VALVE, MV-50 |1 |
|19 |KRAFT226 |6-32 X 1" STAINLESS SCREW |2 |
|20 |KRAFT227 |6-32 STAINLESS NUT |2 |
|21 |KRAFT222 |1/4" NPT TO 1/8" NPT BUSHING |1 |
|22 |KRAFT225 |1/4" TUBING TO 1/8" NPT, 90° FITTING |3 |
Figure 40: Exploded View of Tool with Bill of Materials
Chapter 10: Testing and Design Adjustments
After assembling the tool, the team performed initial testing at the Kraft plant. This allowed the team to operate the tool while using the plant’s air pressure of 110 psi. The first attempt was made at opening the boxes horizontally, as will be the practice when the boxes are stacked on the pallet. However, due to the lack of backpressure on the boxes, the boxes were able to slide and the rods pushed them away from the tool. In order to provide the proper amount of force to get the rods into the boxes, testing continued as the bundle was placed on its short end, requiring the prototype to be operated vertically downward.
Results from this test proved unsuccessful. The rods and toggles deflected the box flaps inward, restricting full toggle engagement. In addition, when the cylinder retracted, those toggles, which successfully entered the box flaps and sprung open, did not return far enough to fully open the flaps.
One suggestion to address this toggle concern was to use a convex disc, a washer, or other large device to break the glue seal or cardboard upon entry rather than exit. Also, it seems a different tip does not require the extra depth that a toggle does. However, the team concluded that the first priority was to increase the stroke length of the cylinder from 1.5 inches to 2 inches. This extra half inch would cause the rods to be inserted slightly farther into the box and retracted slightly farther out of the box, allowing the toggles, or chosen tip, to enter inside the box completely, past the deflected flaps, and retract enough to fully open both flaps.
In response to these initial tests, alterations were made to the tool. The 1.5 inch cylinder was replaced with a cylinder with a stroke of 2 inches. The threading on each rod was increased as well, so that the toggles could start and end farther away from the box flaps. The distance would be made just long enough for the toggles to enter the box.
The team then performed additional testing, incorporating the adjustments and suggestions. However, they yielded the same results. Even when the team attempted to open the flaps with the washers on the tip of the rods instead of the toggles, the tool was not successful. The intention with this change of tips was to allow for an entry with a shorter extension length, due to the fact that the toggles span wider than a washer. However, the washer tip with no flexibility causes greater deflection of the box flaps and even more difficulty with insertion.
Based on all observations and tests, the consistent problem of not retracting the toggle tips far enough was the major concern.
Chapter 11: Conclusion and Recommendations
Although senior design spanned over two consecutive quarters, twenty weeks was not enough time to successfully complete the final tool for Kraft. Testing of the working prototype was conducted in the final weeks, leaving little time to calculate adjustments, and no time to implement them. Despite these shortcomings, the tool does perform in the manner in which it was designed and built. Appendix L details the Ergonomic Risk Factor Assessment (ERF) for use of the new tool, as currently fabricated. The ERF Assessment score is 8, which is a 74% reduction from the current practice.
To address the current tool deficiencies, calculations were completed to determine what changes are required to allow the toggles to travel enough in both directions to open the flaps. These calculations included measurements of the current tool, maximum deflection of the box flaps, thickness of the cardboard box, and the distance needed to open the flaps. The 2 inch cylinder provided enough extension to fully insert the toggles into the box, therefore focus was placed primarily on opening the flaps. To accomplish this task, the results from previous measurements and calculations determined that the toggles need to be pulled out a minimum of 1-1/2 inches from the box. To accomplish this, the box guide plates need to be increased an extra quarter of an inch to provide enough clearance for the toggles to completely retract. However, as a result of lengthening the guide plates, the cylinder stroke that pressed the toggles into the boxes was shortened so the toggles will not travel completely into the box. To compensate for this change, a new cylinder with a 3 inch stroke is necessary for operation. This length was chosen because the toggles require 1-1/2 inches to press the toggles into the boxes and 1-1/2 inches to pull the flaps open. Since the current tool only provides enough space for a cylinder with a maximum stroke length of 2 inches, the height of the rod guide plate needs to increase 1 inch to allow enough clearance for the larger cylinder stroke.
The final element of the tool that needs to be updated is the length of the threaded rods. The resulting increase in rod length is from 4-3/4 inches to 5 inches. This will allow the cylinder to press and pull the toggles completely into and out of the boxes.
In summary, the following steps are required for successful operation of the tool:
1. Box guide plates need to increase ¼” in length
2. Rod guide plate needs to increase from 3” tall to 4”
3. Cylinder stroke needs to increase from 2” to 3”
4. Rods need to increase from 4-3/4” long to 5” long
Appendix M contains the Detailed Process Sheet for operation of the pneumatic box opening tool.
Chapter 12: Contingency Plan Manual Handheld Tool
The objective is to design a manual device to replace the existing box opener currently in place at Kraft foods with a box opener that addresses some of the ergonomic concerns. This tool is an improvement to the current handheld tool. The device will be more comfortable than the current tool and lighter than the pneumatic tool, but less efficient than the pneumatic device.
12.1 Needs Assessment
Currently, the device being used by Kraft Foods consists of a rectangular block handle with a threaded rod attached in the center of the handle. On the end of the rod is a washer and stainless steel nylon lock nut, which is used to open one of the major flaps. The main reason for replacing this device is comfort. When being used the threaded rod is located between the operators fingers and the block handle puts more stress on the operators hand than is necessary.
This tool needs to be made of food grade materials that meet standards currently in place at Kraft Foods. This device also needs to be comfortable for the operator, open both major flaps at once, weigh less than three pounds, have a replaceable tip (if any) and be usable by all employees.
12.2 Concept Development
Through brainstorming, several different concepts were developed for redesigning the current manual tool in use at Kraft.
The first redesign consists of an inline D handle with the current tip. This is a delrin D shaped handle with a threaded rod, washer and stainless steel nylon lock nut at the tip, centered on the front face of the handle. Another redesign idea consisted of the same style handle with either a single toggle tip instead of the washer or a pair of toggles centered vertically on the front face of the handle.
Another set of redesign ideas consisted of a delrin pistol grip D handle, with one of the three tips previously mentioned. This handle shape takes into account the natural hand position of 70 degrees when grasping an item.
Another solution developed through brainstorming is to round the handle edges of the current tool in use at Kraft. This will change the shape of the rectangle block handle to a handle with an oval shape, taking out the sharp corners of the current handle. Also, adding a rubber coating to the face of the opening tip that makes contact with the major flaps of the box while opening was suggested as a way to add more friction between the device tip and the box to assist with the opening.
12.3 Concept Selection
The replacement tool will consist of a delrin pistol grip D-shaped handle for comfort. A pair of spring-loaded toggles will be mounted to this handle with 2.8 inch threaded rods, centered on the front face of the handle. Using a pair of toggles tips may prove to be more advantageous than using just one. It will distribute the force from the tool over a larger surface area of the major flaps. This will increase the chances of major flaps being separated from the minor flaps, rather than ripping the flaps in the mid-section of the box without opening the box. Also, the reactant force from the box on the toggle will be distributed between the pair, which will increase the life of the toggles tips and require less maintenance from the operators. These toggles are pushed into the box through the slit between the major flaps. The toggles’ default position is spread open so that the toggles are approximately 1.75 inches wide. When they are pushed into the box, the toggles are pushed down to a closed position forming around the threaded rods in which they are mounted. Once inside, the toggles spring open again. The spread toggles grab the flaps and pull them open as the operator pulls the device back towards them.
12.4 Feasibility
The current tool in use at Kraft is fabricated out of a delrin and stainless steel. The redesigned tool will also be made out of these food grade materials.
Using a delrin D-shaped handle provides the operator with a lightweight, comfortable handle. More importantly, it removes the threaded rod from being located in between the operators’ fingers while in use. The pistol grip feature takes into account the natural 70-degree position of the hand when grasping an item, which increases the comfort level while using this tool.
Using a toggle tip for opening the boxes allows for easy insertion into the boxes, as well as ensuring contact with both major flaps of the box. Using a pair of toggles tips may prove to be more advantageous than using just one. It will distribute the force from the tool over a larger surface area of the major flaps.
Customizing the toggle shape, as well as adding a rubbing coating to the toggle tip will not be addressed due to time constraints. Moreover, the current toggle shape available does not have enough substantial surface area needed to effectively use a rubber coating.
12.5 Design Documents
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Figure 41: Handle for Manual Tool
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Figure 42: Threaded Rod for Manual Tool
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Figure 43: Manual Tool
12.6 Fabrication
The threaded rods were built from a ¼ inch stainless steel rod. This was achieved by first using a hacksaw to cut the rod down to two, 3-inch pieces. Then using the speed lathe to face and cut the pieces to a length of 2.80 inches. Once the rods were cut to the correct the length ¼-20 (UNC) threads were added using a die. The end of the threaded rod was then rounded using the speed lathe in conjunction with a standard file to give it a smooth and rounded finish.
Two tapped holes for the threaded rods are centered on the front face of the handle at a distance of 1.6 inches apart. This dimension was chosen to ensure the toggles would only pull on the major flaps of the box when opening, as long as it is centered with the box. If the handle is not centered when opening the box, the toggles are set at this dimension to ensure that the operators will not have to pull through both major and minor flap ends at once. Rather, one of the toggles will pull through the major flaps alone, while the other toggle may pull through the major and minor flaps at one end only. The grip portion dimensions are derived from the hand anthropometrical guidelines using the 95th percentile dimensions so everyone can use the tool comfortably. Due to the contours of the handle, it was machined using a Computerized Numeric Controller (CNC) Mill in the RIT Brinkman Lab.
The standard ¼-20 toggles were used on the ends of the threaded rods to open the boxes. The wings of the toggle are cut to a length of 0.9375 inches. This is so the toggles will have enough clearance to open when entering the box and enough material to grab and pull the flaps open.
When assembling the manual tool the two rods should be threaded into the tapped holes located on the front of the handle by mating the shorter threaded end of the rod with the handle, and securing with Loc-tite. The toggles should be threaded onto the opposite end using Loc-tite to secure the toggles into a horizontal position on the rod, in relation to handle.
12.7 Testing
The manual tool was successful in opening the boxes in one pass during testing. Although it is easier to open the flaps when the tool is centered before force is applied, the box flaps did open when the tool was not perfectly centered. The standard toggle also held up through testing without failure, making replacement toggles for the tool easily accessible for the customer (Kraft).
12.8 Conclusion
The manual tool has met the design goals proposed. It will open the juice boxes in one pass, after the shrink wrap has been scored, removes the threaded rod on the current tool from being located between the operators fingers when in use and is much more comfortable to use then the current tool at Kraft. Unfortunately, the operators will still have to use manpower to open the boxes, pushing and pulling the tool by hand to separate the flaps.
A Detailed Process Sheet for operation and maintenance of the manual tool is located in Appendix N.
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Appendix A
Organization Chart
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Appendix B
Appendix C
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Appendix D
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Appendix E
Appendix F
Un-partitioned Design Structure Matrix
Partitioned Design Structure Matrix
Appendix G
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Appendix G cont.
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Appendix H
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[pic]
Appendix H cont.
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Appendix I
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[pic]
Appendix I cont.
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Appendix J
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Appendix K
| |Kraft Foods, Inc. | |
| |Ergonomic Risk Factor Assessment | |
| | | |
|Job Name: |Anticipated Juice Supply Procedure | |
| | | |
|FORCE: | | |
|# |Risk Factor |RV |
|F1 |Two handed lift greater than 20lbs |2 |
|F2 |Vertical travel distance of lift, greater than 60" |0 |
|F3 |Horizontal lifting reach greater than 20" from the body |0 |
|F4 |Two handed carry greater than 30 lbs |0 |
|F5 |Horizontal carry distance of greater than 20 ft |0 |
|F6 |Two handed horizontal push / pull greater 40 lbs |0 |
|F7 |Two handed vertical push / pull greater than 25 lbs |1 |
|F8 |Trunk rotation with a weight greater than 10 lbs |2 |
|F9 |Wrist rotation while manipulating greater than 6 lbs |0 |
|F10 |One hand horizontal palmer push greater than 15 lbs |0 |
|F11 |Use of hand tool greater than 7 lbs |2 |
| |FORCE RF TOTAL= |7 |
| | | |
|POSTURE: | |
|# |Risk Factor |RV |
|P1 |Trunk forward flexion greater than 45o |0 |
|P2 |Trunk extension greater than 20o |0 |
|P3 |Neck flexion or extension greater than 45o |0 |
|P4 |Trunk or next side-bent plus twisted |0 |
|P5 |Shoulder abduction greater than 90o |0 |
|P6 |Working with hands or arms behind the body |0 |
|P7 |Full elbow extension with shoulder elevation |0 |
|P8 |Elbow flexion greater then 135o |0 |
|P9 |Wrist flexion or extension greater than 65o |0 |
|P10 |Wrist ulnar or radial deviation greater than 25o |0 |
|P11 |Forced pronation or supination of hand & wrist |0 |
| |POSTURE RF TOTAL= |0 |
| | | |
|OTHER RISK FACTORS: |(Note: Each "Y"=RV Value of 2) |
|# |Risk Factor |YES |
|O1 |Unusually high tool or floor vibration |N |
|O2 |Frequent ladder or stair climbing |N |
|O3 |High exposure to direct pressure or mechanical stress |N |
|O4 |Work with hands over shoulder level for greater than 50% of cycle |N |
|O5 |Squat or kneel for greater than 50% of cycle |N |
|O6 |Stand on one leg for greater than 50% of cycle |N |
|O7 |Awkward / immobile body position for greater than 50% of cycle |N |
|O8 |Greater than 6 thumb and or finger exertions with one hand |N |
| |OTHER RF TOTAL= |0 |
| |ERF Total= |7 |
Appendix L
[pic]
Appendix M
[pic] DETAILED PROCESS SHEET
HOW TO OPERATE THE PNEUMATIC BOX OPENER
CREATED BY: MOLLY B. KEARNS, RIT SENIOR DESIGN TEAM DATE: 5/3/2004
PAGE: 1 OF 1
Appendix N
[pic] DETAILED PROCESS SHEET
HOW TO OPERATE THE MANUAL TOOGLE TOOL BOX OPENER
CREATED BY: MOLLY B. KEARNS, RIT SENIOR DESIGN TEAM DATE: 5/3/2004
PAGE: 1 OF 1
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James Hildick
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