User:Medelen8/ENES100/Example Conceive Report

Idea
The AFSM100 (Automated Flats Sorting Machine) has been used for many years to sort the majority of mail delivered in the United States. In this system, each mail piece is injected vertically into a compartment in one of many plastic mail buckets. The mail buckets, joined by a chain, travel horizontally in a loop, periodically dropping the mail pieces down chutes and into carrier trays. The plastic mail buckets are prone to fatigue cracking, due to repeated impact loads from injected mail pieces. Additional information regarding the AFSM system can be found here. The operator of the AFSM machines would like to reduce the maintenance costs associated with replacing cracked mail buckets.

Problem Statement
The project is to redesign and/or replace the existing AFSM100 mail-injection shock-absorber assembly, which is not preventing bucket (see Figure 1) failure.

Market/Customer needs
The customer is a large company that owns and operates approximately 500 of the AFSM mail-sorting systems. These systems were designed by a engineering firm, but maintenance is the responsibility of the customer. The customer runs these systems for up to 20 hours a day, 360 days a year, so continuous maintenance is vital to system operation. There are daily maintenance periods, but these are very brief (1-2 hours). Any extended maintenance time causes down-time for the system, and could result in backlogs of unsorted mail. The customer is also very sensitive to the financial implications of regular maintenance. For these reasons, the customer seeks a solution to the problem of cracked mail buckets. Each AFSM system has 253 black plastic mail buckets (visible here), meaning that there are over 125,000 buckets in service nationally. After several years of operation, cracks have been noticed in many buckets, due to plastic embrittlement and fatigue resulting from millions of impacts from injected mail. Bucket failure has become a significant maintenance cost for the customer. The customer needs a redesigned shock-absorber assembly that will reduce the shock loading on the buckets. The solution must reduce bucket breakage enough to offset the cost of installing the new shock-absorber assemblies.

Enterprise goals and capabilities
The customer has contracted this work to the company that originally designed the AFSM system. The company is a large defensive contractor, with a division specializing in mail sorting automation. The company's primary goals are: The engineering company has extensive design, analysis, testing, and manufacturing capabilities. For this project, engineers will have access to drafting support, test equipment, a machine shop and raw materials for prototyping, and access to AFSM systems for preliminary testing and field testing.
 * providing quality life-cycle support for their product (the AFSM system)
 * maintaining a positive relationship with their primary customer

Competitors and benchmarking information
For this project, there is no competitor, as the customer has selected a sole-source for the redesign effort. The benchmark is the existing shock-absorber assembly, which was installed on each system as part of the original design. The existing design (see below) consists of a sheet metal support plate, mounting brackets, four fins that interleave with the bottom of the black buckets, rubber pads designed to absorb some impact, and stainless steel plates adhered to the rubber. The stainless steel plates are impacted from above by mail pieces injected into moving buckets. The existing design is simple, but ineffective in absorbing enough energy to prevent bucket damage. The impact surface is too rigid, causing mail damage and mail bounce (sometimes out of the bucket). Also, when not adjusted properly, the impact surface is too low, causing the bucket itself to experience large shock loads.

Ethical, social, environmental, legal and regulatory influences
The design must not present a safety or environmental hazard as it wears over time. Due to the high cycle rate, durable materials must be selected that will not create dust or debris in an area where employees are working. Also, the impact surface must not leave any material residue on mail pieces.

Initial target goals (based on needs, opportunities and other influences)
The photograph to the right shows a heavy magazine being injected into one compartment of a mail bucket. The red line highlights a typical crack location, due to impact loading. The following design goals have been established by the customer:
 * reduce shock load on buckets
 * limit mail bounce
 * must not damage mail (damage rate < 0.1%)
 * required maintenance with max frequency of once per year
 * durability to last 30 million injections (impacts) per year for 10 years (300 million total impacts)
 * retrofit installation time less than 2 hours
 * assembly cost and complexity similar to existing assembly
 * all of the above must be satisfied for all types of mail (TV Guide, newspapers, thin envelopes, heavy magazines, plastic-wrapped, etc)

System performance metrics
Some of the system goals described above are performance goals. These performance goals will be measured according to the following metrics:
 * peak impact force on bottom of bucket from heaviest (4.5 lb) mail piece injected at a downward speed of 5 m/s
 * mail bounce height, measured as the max height achieved by a mail piece rebounding from the initial impact on the bottom of the bucket
 * mail damage rate, measured as the percentage of mail pieces damaged by the injection

Necessary system functions
The shock-absorber assembly has two primary functional requirements.
 * To provide a shock-absorbing impact surface for injected mail, such that the bucket receives minimal shock loading.
 * To allow mail already in the buckets to move freely across the system. Failure to meet this function can result in damaged mail.

System concepts
At a high level, there are two approaches to solving this problem:


 * 1) Make a minor modification to the existing design by replacing the impact pads (part number 3 in Figure 2A) with a different material combination or different thicknesses.  The existing design employs 5 mm thick stainless steel bonded to 12 mm thick rubber.  The stainless steel is effective in preventing wear, but it is a very stiff material, resulting in mail damage and limited shock absorption.  The rubber material is not thick enough to allow for much compression.  In addition, rubber deforms elastically, contributing to mail bounce.  Using thinner steel and thicker rubber (or a different material) could improve performance.  Alternatively, the steel layer could be removed, if a sufficiently durable plastic material could be found.
 * 2) Redesign the entire assembly, using new methods to absorb shock.  Within this approach, there are many potential concepts:
 * 2A. Simple bumpers made of a compressible material, but with greater thickness or different geometry (e.g. cylindrical)
 * 2B. Pneumatic (air) shocks oriented vertically for direct impact
 * 2C. Pneumatic (air) shocks oriented horizontally, requiring a mechanism for redirecting the impact force
 * 2D. Same as the previous two concepts, but using hydraulic (oil-filled) shocks
 * 2E. Electromagnetic "eddy current dampers", using the principle of induction to resist motion
 * 2F. Inertia damper, using a mechanical arm and massive counterweight to dampen the effects of shock loads.

An overview of industrial solutions to shock-absorption can be found here. Note that some of the least expensive solutions (cushions, springs, etc) tend to behave elastically, instead of absorbing kinetic energy. In all of the system concepts, the existing mail guide fin (Figure 2, part number 2) design will be retained. The material and geometry of the leading edge of the fin, upon which mail pieces slide, will not be altered. In some of the concepts, it could be necessary to use springs to return the impact surface to its original position.

Trade-offs among concepts
There are a number of trade-offs among the concepts described above. The first approach (minor revision to existing design) is the simplest and least expensive, but it also has a lower likelihood of increased performance. Among the other concepts, there is a trade-off between energy absorption and reliability/maintenance. The concepts that would absorb energy most effectively (2B,2C,2D,2E) tend to be involve more mechanical complexity (excluding 2E). The addition of moving parts typically requires inspection, periodic maintenance, and reliability concerns over millions of cycles. Concepts 2E and 2F have some advantages, but could be the most expensive. Finally, there is the problem of the extended "landing zone" for injected mail pieces. Some concepts are better suited for this (e.g. 2C), while in others additional components are required (e.g. multiple shock absorbers or bumpers).

High level architectural form and structure
The design concepts are mostly simple mechanical assemblies, consisting of few parts. For this reason, the system architecture is very simple. The mail guide assembly will consist of something very similar to the existing mail guide fins, with associated fasteners. The mounting assembly consists of a base plate and two brackets, which support the entire shock absorber assembly and attach it to the AFSM100 frame via four M8 hex head bolts. The shock absorber assembly will include all components associated with mail impact and energy dissipation. This assembly will mount onto the base plate.

The decomposition of form into subsystems, assignment of functions to subsystems, and definition of interfaces
Not applicable. Due to the simplicity of this device, there are no major subsystems. The entire device will be one mechanical assembly, without any electrical or software components. The only interface is external, in which the assembly is mounted to the frame of the AFSM machine.

Appropriate models of technical performance
The system performance will not be modeled, since the physics of the mail injection process are highly complex and difficult to accurately model at a reasonable expense. For this reason, the importance of system durability, and the relatively low cost of prototyping, performance will be estimated based on testing instead of modeling.

The plan of implementation and operations
If the customer decides to move forward with implementation, they plan to: The customer will manage all aspects of operations, including annual maintenance, monthly inspection for wear, supplying spare parts, etc.
 * 1) Conduct an expanded field test for 12 additional months on 5 AFSM machines.
 * 2) Request a final drawing package from the engineering company and place a purchase order for 1000 units (two assemblies per AFSM).  The engineering company will manufacture the units and deliver them to the customer.
 * 3) Distribute the system across the country and manage the retrofit installation process.
 * 4) Train field technicians on maintenance and inspection procedures.

Trade-offs among various goals and functions
There are three important trade-offs between the system requirements:
 * Shock absorbing materials (e.g. soft plastics) tend to wear rapidly, which conflicts with the durability requirement. Conversely, hard materials exhibit less wear, but don't absorb energy.
 * The wide variety of mail types (material, size, weight) conflicts with the requirements regarding mail bounce and damage. Certain types of mail are prone bouncing or tearing, depending the material that they impact and/or slide across.
 * The requirement of minimal maintenance places constraints on the materials and off-the-shelf components used in the design. Certain types of shock absorbers would likely require maintenance and/or periodic adjustment, in spite of their suitability for absorbing shock.

Project cost and schedule
The budget for the design and field-testing phase of the project is $200,000. This amount includes engineering labor, management costs, prototyping, preliminary testing, manufacturing of test units, and field-testing expenses. The costs associated with full-scale implementation and operation are not included. The final design must be presented to the customer 18 months after the start of the project. Assuming that the field test will take approximately 12 months, the next 5 months are allotted for developing the design, creating prototype(s), doing preliminary testing, revising the design and manufacturing test units. Drafting and manufacturing is expected to take at least 3 weeks, which allows approximately 4 months for the design process.

Estimation and allocation of resources
This project will be conducted by one junior engineer (full-time), supervised by one senior engineer (5 hrs per week), and managed by one engineering manager (2 hrs per week). In addition, drafting support may be required in order to produce final drawings. One AFSM system, owned by the engineering company, will be used for preliminary testing. The customer will provide access to one in-service AFSM system for field-testing; one field engineer will support the installation and monitoring of the field test. Several standard "test decks" of mail will be used for testing purposes, as well as an oscilloscope and other test equipment. The in-house machine shop could be used for rough prototyping.

Risks and alternatives
The primary risk to the customer is that a new shock-absorber assembly is designed and installed, but it does not significantly reduce the rate of bucket failure (and replacement). Based on a 12-month field test on one system, there might be insufficient data to prove that this retrofit provides sufficient return-on-investment to be worthwhile. It is also possible that many buckets have already started to crack, but only the worst cases are visible. In this case, the damage is effectively done; even with reduced shock, the small cracks will propagate and continue to cause failures. An alternative solution for the customer is to inspect all buckets and replace any buckets showing any signs of cracking. The customer could also replace all buckets as a preventative measure, or modify existing buckets with a strengthening patch. These alternatives are unattractive to the customer, due to the large number of buckets in circulation.

Next Steps
Having established system requirements, based on customer needs, the design process can begin. Using the rough system concepts described above, engineers will refine these concepts, brainstorm additional ideas, and select one or more concepts for prototyping and preliminary testing. Based upon test results, a final design will be selected and manufactured for the field test.