|MSD I & II||MSD I||MSD II|
Phase 4: Detailed Design
Phase IV Overview
Phase IV of the project was an extension of the systems design process that the team conducted in Phase II and Phase III. In the week following the Phase III review, the team met again with the staff of St. Joseph's to review the new concepts for aerial storage of the sleeping materials. The Pugh's Matrix created in Phase III was used as the basis for the discussion, ensuring that the selection of a concept was based upon engineering requirements. The "platform lift" storage method was selected as the concept which best met the needs of St. Joseph's.
Benchmarking of technologies for aerial storage was conducted, and several commerically available storage lifts were discovered. Some of the commercially available lifts were considered as potential solutions for St. Joseph's. However, feasibility investigations into each of these concepts revealed that the off-the-shelf systems would require extensive modification in order to meet St. Joseph's needs. Based on these investigations, the team determined that the best approach was to design a complete system from the ground up (or rather, from the ceiling down).
The team conducted preliminary design studies of several aspects of the system design. The design aspects studied included a layout of potential locations for the storage lifts, the time required to set up and remove the mattresses, and the weight capacity of the lift. Inputs to each of these preliminary analyses were derived from the engineering requirements to ensure the analysis reflected the needs of St. Joseph's. Design factors related to human interaction with the lift were studied.
To aid in planning for MSD II, a preliminary bill of materials (BOM) for the platform lift was created. The BOM was driven by the system architecture and the feasibility analyses to ensure that all required components for the system were included in the BOM. In addition, the test plans created in Phase III were revised to include more detail relevant to the platform lift concept. More test plans were completed, covering the engineering requirements that were not addressed with a test plan in Phase III.
Documents Relevant to Phase IVBelow is a list of links to the "live" documents created or updated during Phase III of the project. Screenshots of these documents are shown throughout this page.
- The Phase IV planning documents, created at the end of Phase III:
- The Phase IV task completion status (Microsoft Excel .xlsx format)
- The mid-phase progress report (Microsoft Excel .xlsx format).
- The updated customer requirements and engineering requirements (Microsoft Excel .xlsx file)
- The aerial storage benchmarking (Microsoft Word .docx file)
- The feasibility analysis documents (link to folder)
- The visual appeal feasibility document
- The financial allocations document (Microsoft Word .docx format)
- The test plans (link to folder)
- The risks assessment, updated through Phase IV
The following links are to "live" documents that establish the team's project plan for MSD II:
- Plan for completing the detailed design (Microsoft Word .docx format)
- MSD II team vision (Microsoft Word .docx format)
Team Vision for Detailed Design PhaseBelow is the team task list for Phase IV, showing the completion status of each task planned for this phase. The live document can be found here (Microsoft Excel .xlsx format).
The team vision for Phase IV, created at the end of Phase III. The completion status of each task is shown.
As the table above shows, there are a few tasks remaining from Phase IV to be completed before the team is ready for MSD II. The planning document for MSD II (found lower on this page in the Plans for Next Phase section) addresses these tasks and includes a plan for their completion during winter break and in the first two weeks of MSD II.
Progress ReportA summary of the team's progress towards the Phase IV objectives as of Thanksgiving break can be found by clicking the link below. The live document can be found here (Microsoft Excel .xlsx format).
Final MSD I Customer RequirementsThe customer requirements were updated to reflect all the needs of the project that were in our scope. One major change was that the lunch requirements were removed because the system changes did not relate to this aspect. The only connection between lunch and shelter was the safety issue with having the beds in the kitchen room. This is covered by Customer Requirement SA8 as an overall requirement.
Previously, we had removed engineering requirements for the bed bugs. This document also reflects that change that SA9 and SA10 do not have any engineering requirements associated with them. The team felt that this could not be tested and was also partially covered by the new purchase of mattresses (see St. Joseph's meeting notes 10/31 for the link). Also, there were two new customer requirements that were added: Our system will be safe to use and our system will maximize floor space. This was added due to the customer responses from our previous and current concept ideas.
The updated customer requirements are shown below. The live document (which includes removed customer requirements) can be found here.
The final customer requirements. Many requirements were added over the course of MSD I, and several requirements were removed. The removed requirements are not shown here but can be found in the live document.
Engineering RequirementsThe engineering requirements were updated to reflect the changes of the system as well as the changes of the customer requirements. As the lift concept was selected, there was more of a need to look at the safety aspect of the system. Therefore, there was a new engineering requirement of safety factor (ER #20) that was added. For the other engineering requirements, they all stayed the same except for a few changes to the marginal and/or ideal values to reflect a more realistic value. The reasoning of these changes can be seen in the comments section. The direction of improvement was also completed to show which direction the requirements should aim for an improvement in the system. The updated engineering requirements are shown below. The live documents can be found here. (This document includes the removed engineering requirements.)
The final engineering requirements. Nearly all requirements underwent substantial revisions over the course of MSD I, and several requirements were removed. The removed requirements are not shown here but can be found in the live document.
Lift benchmarkingIn order to focus on exactly how the lift concept will be implemented, a benchmarking was completed to compare current existing lift. The table shows the differences between the implementations of each lift concept.
Overall, we can see that the costs for modifying a current lift will cost about $300. Creating a new lift will cost a bit more (projected to be around $350). However, creating a lift that will fit our exact needs would be more beneficial for the team to implement. To further determine which concept to go with, another Pugh's Method was completed.
Looking at the Pugh's Method results, we can conclude that making the lift from scratch will be the best lift option to implement the platform concept. The Racor Platform lift did come in second, however as the lift does not fit our requirements, there would be a lot of modifications to make, driving the cost up. Making the lift from scratch does have a higher cost for creating it, but it can be modified to fit the exact needs of the mattress dimensions, weight, and adjustable distance. The 3D CAD drawings for this in detail over the break and reviewed in the first week of MSD II.
The live document containing the benchmark concepts and Pugh's method can be found here (Microsoft Word .docx format). This document contains links to supplier webpages for each of the concepts.
The sketches above show a lift system that can be controlled by a brake winch attached to the wall. A user would be able to lower the platform of the lift by using a hand drill to activate the winch. Once lowered the user can load the platform with 10 mattresses per lift. The user would then return to the winch and use the drill to raise the mattresses up near the ceiling.
Concept for a safety latch which prevents the platform from lowering in the event that the winch brake releases.
The sketches above show a safety mechanism that would need to be included in any potential lift system. Brake winches and motors are not rated for overhead hanging and require a permanent stopper when not in use. This metal ring included in the cable of the lift would allow the cable to be fixed to a wall mount when not in use. One option for a connection between the metal ring and the wall mount could be a heavy duty load-rated carabiner clip.
Feasibility StudiesThree feasibility studies related to critical aspects of the system design were conducted in order to demonstrate the viability of the platform lift concept.
Space FeasibilityThe purpose of the space feasibility study was to determine whether there is a feasible arrangement of the storage platforms. In a feasible arrangement, the storage platforms will not impinge upon ceiling fans, exit routes, lights, or protrusions from the walls. Additionally, in a feasible arrangement, the platforms when suspended will meet the minimum ceiling height requirements set forth in the New York State buildling code.
The live space feasibility document can be found here.
- Can the sleeping materials be suspended from the ceiling of the hospitality room without blocking the lights, hitting the fans, or striking protrusions on the walls?
- Can the sleeping materials be suspended from the ceiling using a lift system while still allowing adequate overhead clearance?
- The ceiling layout is given by the dimensions shown in Figure 1 of the space feasibility document.
- The height of the ceiling is 137in.
- The height of the step running along the walls of the hospitality room is 5 inches.
- The width of each mattress is 36 inches.
- Two mattress lifts are used.
- The only sleeping materials that need to be stored are 20 mattresses.
- The lift apparatus will require 5in of vertical space below the ceiling.
- The mattress platform will be 4in thick.
AnalysisTo demonstrate that the platform lifts would meet the requirements of Question 1, a simple 2D layout of the hospitality room ceiling was created. The size of the platform lifts was estimated at 4ft by 7ft, which gives ample room to store ten twin-size mattresses. As the image below shows, there are numerous possible locations (shown in blue outline) where a platform lift could be mounted. The room can easily accommodate two lifts. The answer to Question 1 is a resounding YES!
To demonstrate that the platform lifts would meet the requirements of Question 2, another 2D sketch of the lift system was created. The height of the room was sketched, an allowance was left for any apparatus of the system that would be mounted to the ceiling, ten mattresses were arranged below that, and then another allowance was left for the thickenss of the platform itself. This arrangement was duplicated, with one positioned above the step in the hospitality room and another positioned above the regular floor level. This sketch is shown below.
This analysis revealed that the clearance above the regular portion of the floor was 7ft 8in. This meets the New York State requirement of at least 7ft 6in. The clearance above the step, however, was only 7ft 3in. With judicious design decisions, the thickness of the platform and the allowance needed for apparatus at the ceiling might be reduced, which might allow the platforms to be installed above the step. Question 2 may be answered in the affirmative, as there are indeed possible locations for the lifts which would give the requisite overhead clearance.
Time Efficiency Simulation FeasibilityThe live document for the time efficiency feasibility study can be found here.
- In the selected concept, how efficient are staff members in setting-up / cleaning-up the shelter?
- Assume repetitive processes are all of equal processing distributions.
- Assume processes meet the distribution fitted to the data.
- Assume there are no variances between the staff member's performance.
- Assume the walking speed/distances between each tasks are realistic.
- Assume all staff members can complete all tasks.
This spaghetti diagram shows the current layout and system followed by the St. Joe's staff. The red lines represent paths that the St. Joe's staff member or volunteer would need to take to complete the system tasks. This diagram helps us to have a better idea of the amount of effort the system requires.
The Simio Simulation of the current state of the shelter operations is still in progress. Simio Models are to be completed over winter break, with data collection to happen in the first week of MSD II. The feasibility document is expected to be complete by end of week 2. The image below shows the current Simio model, which will be modified after data has been collected.
This spaghetti diagram shows one of the possible proposed layouts with the lift systems. Again the red lines represent the paths taking by the St. Joe's staff or volunteers. Compared to the first spaghetti diagram above, we have not eliminated the total number of trips the worker would need to take but we have drastically reduced the total distance they would need to travel.
The Simio simulation of the platform lift design will not be completed until the actual design of the lift has reached a more solid state.
Weight FeasibilityThe purpose of the weight feasibility study was to address a very important aspect of the platform lift concept: the weight capacity of the system. The weight capacity of the system is dependent upon many factors: (factors listed in bold have been addressed, other factors have not been satisfactorily answered)
- Strength of the cables
- Ability of the platform structure to withstand mattress weight without yielding
- Ability of the ceiling to support the weight of suspended mattresses
- Ability of the winch or actuation mechanism to support the tension in the cable
- Ability of the pulleys to remain attached to the ceiling when under load
- Can the lift system support the weight of the platform plus ten mattresses?
AssumptionsTo determine if our lift system will be able to support the weight of the platform with 10 mattresses on it, we assume the following properties of the proposed system:
- The platform is supported by four cables.
- The weight of one mattress is 17.5 pounds.
- The platform is assumed to be built of square
aluminum tubing, 1" X 1" with 0.125" wall thickness.
- Approximate platform dimensions: 8 ft long, 4 ft wide
- Platform construction: three long members, and two cross members (see Figure 1).
- Density = 0.098 lb/in^3 (from http://matweb.com/search/DataSheet.aspx?MatGUID=0cd1edf33ac145ee93a0aa6fc666c0e0&ckck=1)
- A multiplier of 4 is used in computing the weight of the platform, to account for walls, hooks, etc that will be part of the final design.
- Ultimate tensile strength of aluminum is 18ksi (from http://matweb.com/search/DataSheet.aspx?MatGUID=626ec8cdca604f1994be4fc2bc6f7f63 for aluminum 6061-T0, which is a low-strength aluminum temper)
- Platform must support ten mattresses.
- The overall weight of the platform and mattresses is assumed to be evenly distributed along two of the long members of the platform.
AnalysisFor details of the calculations performed in this analysis, please view the live document (Microsoft Word .docx format). The calculations were performed in this Microsoft Excel spreadsheet.
The weight supported per cable was found to be 60.21 pounds, causing an average stress of 1227psi in the cable. This gives the cable a factor of safety of 28.5 against failure.
The loading of the platform structure was assumed to be as shown in the image above. For this loading, the peak bending moment is 276.6 pound-inches, causing a maximum bending stress of 2427psi. This gives the beam a factor of safety of 7.4 against failure. The bending moment as a function of position in the beam and the deflection of the beam as a function of position are shown below.
Plot of the deflection of the beam as a function of position. Note that the y-axis scale makes the deflection appear much larger than it actually is.
After calculating the total weight of the system and imparting a weight multiplier to account for any error or weight of hardware, the maximum bending moment, factor of safety, and maximum deflection were calculated over the length of the platform. The graph of the bending moment and deflection distribution can be seen in the figure above. As can be seen, our design specifications create a maximum deflection of 0.055 in (less than 1.5 mm) and a stress factor of safety over 7, which validates our design as feasible from a weight standpoint. Deflection graph needs axis labels with units.
Human Factors/ErgonomicsTo assess the human-related design factors and ergonomic concerns related to the platform lift system, a survey to be conducted among the guests of St. Joseph's was created. The survey questions are shown below and are included in the visual appeal feasibility document.
Bill of Materials
The bill of materials is combined with the team budget here to create a more efficient means of tracking materials and finances. The items which are marked with an asterisk are materials which are tentative purchases, recorded as ideas and will be validated for their usefulness. The bill will be updated as items are purchased and decisions regarding the best option are made.
The live BOM can be found here (Microsoft Word .xlsx format).
Test PlansA number of test plans were written in Phase IV to complete the set of test plans. Each engineering requirement now has an associated test plan.
One of the most critical tests is the test of the system's weight capacity. This test will be conducted in two steps. First, the system will be tested on a test rig, in a test which will take place at RIT. After confidence in the system's performance has been established, the system will be installed at St. Joseph's. To verify that the installation was performed correctly, the system will be tested again in a "live" test at St. Joseph's.
The weight capacity test will consist of loading the platform with a specified amount of weight, raising the platform, checking for signs of failure, and lowering the platform. The weight on the platform will then be incremented by a fixed amount, and the test will be repeated. This procedure will continue until the weight on the platform is equal to a specified weight times a specified factor of safety. Both the specified weight and specified factor of safety are determined by the engineering requirements.
Risk AssessmentThere were three new risks added to risk assessment documented related to the concept selection and all the updated information.
- The first new risk was that the wiring of the system is infeasible or strenuous. This risk can cause the entire lift system to fall and hurt someone which has a high severity, but a low likelihood as our feasibility analysis should ensure that the wiring will be the optimal solution.
- The second new risk was a safety risk relating to the sleeping material platform falling. This will have a low likelihood but a high severity as people can get hurt. Therefore, a new engineering requirement of safety factor (ER #20) was created to ensure that the system will be able to safely support the weight and be secured properly.
- The third new risk is that the guest or staff will tamper with the platform. This also has a low likelihood but high severity as a danger to people. In order to mitigate this risk, the team decided to create a cover that is attached to the ceiling that will cover the area. That way, the lift will be enclosed and the guests cannot touch it.
The updated risk assessment is shown below, and the live document can be found here (Microsoft Excel .xlsx format).
Remaining Phase IV Plan and MSD II PlanMany tasks for MSD I are currently incomplete. A plan has been developed to allow the team to complete the detailed design by Week 2 of the spring semester.
The team vision for MSD II has been laid out and can be found here