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Overview of Status of Analysis, Design, Fabrication, Tests, etc.
Analysis:
Currently in the process of analysis on the following subcomponents:
Feeder mechanism:
Conducted coefficient of friction and FBD analysis of feeder mechanism.
Tension (monitoring)
Providing upper and lower bounds on tension to ensure the Nafion tubing is not in too much slack, but not enough tension to damage the material.
Length Tracking
Began development of algorithm to track length at feeder mechanism assuming no slip
Design:
Finished preliminary design of feeder mechanism.
Finalizing design decisions for take-up spool.
Working on finalizing the design for the spooling guide and horizontal mounts for each spool.
Fabrication
Laser cutting / machining of parts for feeder mechanism sub component
Machining larger and better scaled rollers for the feeder mechanism.
Tests
Experimental tests for length tracking are under better development.
Setting up and designing tests for length tracking, tension monitoring, and spooling rate
Accomplishments from Previous Week
During last week, the primary focus was to redevelop the feeder mechanism using some form of friction based surface coated around the polypropylene rollers. Upon further consideration and analysis, it has been determined that polypropylene alone may be efficient and meet the contamination requirement much easier. Other materials for friction that were considered were vinyl, nitrile, or cleanroom grade rubber. However, the sponsor recommended that if these materials are considered, they would have to be sent out and tested independently for cleanroom grade requirements. Therefore, we have decided to pursue the roller mechanism using just polypropylene.
After further research, the correct terminology for what we aim to accomplish with this system is web tension control.
With this information, we were able to better understand how to control the tension.
First: There needs to exist what we call a "feeder mechanism" which allows for separate tension zones within the spooling process.
Looking at the FBD below there exists two separate tensions:
Tension (unwind): This is the tension we need to peel the Nafion and unwind from the supply spool.
Tension (rewind): This is the tension that we will wrap the take-up spool with.
Second: Tension can be monitored and put in closed-loop control with load cell to determine tension in the rewind section.
Cartridge style cantilevered tension transducers are common in web tension control applications, and will allow for accurate tension monitoring.
Third: The take-up spool can be controlled in closed-loop with the load cell to maintain rewind tension.
We are currently exploring different control implementations:
Velocity: Using a determined rewind tension zone, the rotational velocity of the take-up spool can be increased/decreased to control the tension.
Position: Using a few assumptions, the tension in the rope can be connected to the rotational position of the take-up spool, which can be controlled to achieve proper tension.
Translation of idler pulley: Additional control can be had using a translating idler pulley to increase/decrease tension in the rewind section. This allows for constant velocity at the take-up spool.
Polypropylene only feeder mechanism accomplishments:
Redesigned the feeder mechanism to have horizontal axes, and determined that if proper force is applied, the feeding mechanism works very well, and understanding the forces acting on the Nafion tubing would have to be conducted.
FBD of tubing at roller mechanism interface:
During previous risk reduction efforts, T(unwind), the peeling force, has been determined to be on the order of 100 mN. In order to determine the normal force needed, the coefficient of friction needed to be determined between the nafion and PP.
Using a surfaced piece of PP and Nafion tubing, an experiment was conducted to determine the coefficient of friction.
Five different masses were applied to the Nafion, and with the use of a load cell, three tests were done per mass.
This resulted in a coefficient of friction between 0.1644, and 0.1938 with a confidence of 95 %.
Using the lower bound of the coefficient of friction (which requires more force to be applied), and with the unwind tension known, the normal force needed to ensure no-slip was 0.1367 lbf. With a factor of safety of 2, we used 0.3 lbf as a sufficient minimum applied normal force.
The feeder mechanism, as seen in the risk reduction presentation, applies force via springs mounted on the shafts.
Springs were ordered that applied a minimum of at least 0.3 lbf from McMaster.
Model Number: 9432K26
k = 2.5 lbf/ in
minimum force = 0.3 lbf
maximum force = 3.29 lbf
Unstretched length: 1 "
Maximum stretched length: 2.2 "
With this information in mind, new mounts were made, and another motor was ordered to drive the feeding mechanism.
Additionally, this is a lower bound on the applied normal force to ensure no-slip condition is met, however, there is need to determine an upper bound in terms of damaging the material.
Damage by compression:
Will discuss with sponsor and with adviser on best way to approach this if necessary.
May need to send test samples to Colleen to make sure not compressing the material too much.
Damage by tension:
Will need to conduct a better stress-strain plot to determine yielding and plastic failure criterion.
New CAD developed for feeder mechanism based on these preliminary findings, and is currently being prototyped.
Began looking into tension control mechanisms based of web tension control.
As noted above, there exist load cells designed for this kind of tension monitoring.
Goals for Next Week (list names after each item). Use specific and measurable objectives.
Our current goals for this week are split into two separate categories:
Deliverables:
Report: The first draft of the report is due by Week 5 Friday at midnight. The team will work together to ensure 50% completion by this due date.
Webpage:
Patrick: Develop front page of website
Patrick/Jhon: Develop final design page.
Proof of concept presentation: Team development.
To the end of the presentation, certain individual deliverables have been assigned:
Jhon: Finish CAD of total system currently under consideration
Iman: Assist Jhon with CAD, and in charge of machining all parts for prototype further discussed below.
Patrick: FBD of system, and analytical methods used to determine parameters of the system.
Anthony: Development of control algorithm to be implemented in closed-loop setup for tension control.
Prototype development: To ensure that hard deliverables and deadlines are met, certain prototype goals are set for the current week.
Iman/Jhon: Machine 4" long PP spools to be mounted to motor driven feeder mechanism.
Iman/Jhon: Machine or lasercut mounting brackets for motor and feeder mechanism.
Anthony: Setup electronics for prototype including:
New motor driver
Both motors for both the take-up spool, and the feeder mechanism
Servo driven spooling guide
Patrick: Mounting of the entire system currently including base board, and L brackets.
Prototype setup:
The prototype this week will be setup as outlined in the CAD development above for the feeder mechanism.
A new take-up spool will be mounted with a rigid shaft coupler.
Prototype outcomes:
Proof of concept of feeder mechanism design using only PP as the contact material with roller axis vertical and proper normal force applied.
Length tracking using encoders and assuming no-slip condition at feeder mechanism.
Additional low priority goals:
Patrick/Anthony: Get quote for load cell used in this application.
Patrick/Anthony: Develop preliminary control algorithm for decided direction on best control implementation.
Patrick/Anthony: Spooling guide incorporation, and any necessary purchases in terms of servo/material.
Jhon: Finalize take-up spool design, and order necessary PP.
Iman: Finalize take-up spool design, and order necessary PP.
Sponsor Comments from Last Meeting and Actions Taken to Address these Comments (indicate date of comments and if via email or in person)
Sponsor was okay with using Nitrile glove material, but informed that any material not mentioned to us previously (ie Vinyl, nitrile, rubber...) will have to be independently tested.
Needs access to website (emailed Ian Richardson again to follow up).
Was confirmed by Ian Richardson (4/29/19) that this action had been taken, and sponsor should have access.
Sponsor was also okay with sacrificial Nitrile being used, but cautioned against the long term use since Nafion becomes harder and discolored under halogen lights over time.
Instructor Comments from Last Meeting and Actions Taken to Address these Comments (indicate date of comments and if via email or in person)
Drive to precision:
To this regard, the team should focus on driving to precision in terms of length tracking, and not accuracy.
For example, be able to repeat 40 ft consistently, even if test is setup to spool 50 ft.
Was not confident in length tracking on secondary spool.
Recommended idler pulley with at least one wrap around it as an intermediate tensioner to replace feeder/slapper.
Comments from Other Students in the Class (indicate date of comments and if via email or in person)
N/A
Risks and Areas of Concern
Current high risk area of concern is the damaging of the tubing at the contact interface of the Nafion and feeder mechanism. Further tests and prototyped developed this week will address these concerns.
Tension control in rewind tension zone
Explained in more detail in goals for next week and will discuss further to better understand control implementation.
Resources or Information Required but not Available
N/A
Schedule
Describe upcoming milestone
Update Gantt chart.
Budget (list amount spent and amount remaining)
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