Prosthetic Arm Force Reducer Team 1 – Halliday's ... - Ohio University

More documents

Recommendations

Info

$Introduction to Numerical Math and Matlab ... - Ohio University$

Failure Mode Table 7.0.1 - Risk Priority Number Analysis for Split Hook (Environmental) Potential Severity Likelihood of Occurrence Probability of Detecting Cable Break (at fitting) 7 3 8 168 Corrosion Over Time 2 10 5 100 Threading of <strong>Prosthetic</strong> Connection RPN 6 2 6 72 Environmental Deposits 2 10 1 20 Loss of Movement of Vector Hook 3 5 1 15 These failure modes were listed in order of importance according to the risk priority number (RPN) calculated in the far right column. The RPN is the product of potential severity, likelihood of occurrence, and detect-ability of the particular failure mode, as ranked on a scale from one to ten. Since the Otto Bock hook has been left in stock, OEM condition, failures relating to the stresses present in the hook itself were not included. The mechanical advantage, however, does allow the user to hypothetically pull twice as hard on the hook at full opening. Although this situation is not practical, it could lead to failures in the hook, which is not designed to experience twice as much force as is needed to open it to its maximum width. Corrosion over time and the hook accumulating environmental deposits are completely unavoidable considering the working conditions that it will be used under. As such, a stainless steel hook has been selected and all fabricated parts shall be made of stainless steel. Additionally, any mud or other element that fills some part of the hook should be able to be easily removed by our user. The only other failure mode of the hook of much concern was if the threading of the hook could be stripped in some way. The prosthetic arm provides the biggest guard against anything happening to the threading as the hook threads into a bushing that is then inserted into the prosthetic arm. This ensures that the threading is not constantly under torque but instead the arm will bear this force. FMEA was also completed for the mechanical advantage portion of the design in the same manner as conducted for the environmental effects on the system. The FMEA results are presented below in table 7.0.2. 32
Table 7.0.2 - Risk Priority Number Analysis for Mechanical Advantage Potential Severity Likelihood of Occurance Probability of Detecting RPN Threading of Rings Strips Resulting in System Pulling Away From <strong>Prosthetic</strong> Walls 7 (Inoperable) 3 6 168 Pulley Torques in Track and Locks 5 (Temp. Inoperable) 4 8 160 Rope Slips From Pulley Wheel 5 (Temp. Inoperable) 4 8 160 Bearings Seize in Track 5 (Temp. Inoperable) 4 4 80 Tracks Break Attachment With Rings 7 (Inoperable) 1 6 42 By comparing the RPN’s of the mechanical advantage system to the RPN’s of the environmental effects, the numbers are similar. At very worst, the user loses the ability to open or close the hook. At minimum, the faulty system would pose significant to the user. The worst failure with regard to mechanical advantage is if the rings that attach to the prosthetic were to strip and the bolts pull away. This would result in the system becoming completely inoperable and could cause damage to the prosthetic arm as well. This failure possibility is minimized by the fact that correct design of the threads can nearly eliminate that possibility. In addition, there would be the possibility of detecting the failure as the system should develop some amount of “slop” or looseness before it became completely separated from the prosthetic wall. The possibility of the pulley seizing in the track or the rope slipping off the pulley wheel is legitimate; however, such a failure would only leave the system temporarily inoperable. It would be a significant inconvenience for the user, but would not leave them in any real danger. If the bearings were to lock in the track it would leave the system inoperable but there should be only a very small chance of this occurring. Additionally this would more than likely occur due to build-up of some type of deposit in the track that could be removed to allow the system to operate once again. If the tracks were to break at the ring it would leave the system totally inoperable, but as with the bearings, once again there is a very small chance of occurring. 7.0.6 Economics/Value The decision to fabricate the tracks for the mechanical advantage system out of square tubing was economical. Both the manufacturing time and price are significantly less for this design than it would be to fabricate the tracks out of solid stock. The options for buying tracks were around the same base cost as the square tubing we chose ($7.82 per 12” length), but the quality and material were not acceptable. The most common track was made out of extruded aluminum which could bend and deflect relatively easily and is not compatible for welding with stainless steel. 33
Page 1 and 2: Prosthetic Arm Force Reducer Team 1
Page 3 and 4: 1.0 Introduction Limb loss generall
Page 5 and 6: 2.1 Weighting of Customer Needs Wei
Page 7 and 8: which could limit the use of rubber
Page 9 and 10: design of the two load hook allows
Page 11 and 12: Fig. 4.1.6 - Utah Arm 3 MAGNUM Para
Page 13 and 14: Feature Hosmer Model 7 Work Hook Ot
Page 15 and 16: hook is closed. The harness idea is
Page 17 and 18: purchase it. Safety is another exte
Page 19 and 20: Figure 5.1.2 - Solid Edge Model of
Page 21 and 22: 5.1.4 Concept D - Upgraded Springs
Page 23 and 24: 6.0 Concept Selection 6.1 Data and
Page 25 and 26: Figure 6.1.4 - Input Force FBD The
Page 27 and 28: Since the torques of the both the r
Page 29 and 30: Once the design of the system was u
Page 31: 7.0.3 Professional/Ethical Standard
Page 35 and 36: The actual FEA testing involved uti
Page 37 and 38: Another sector that has aided in ou
Page 39 and 40: Figure 7.0.10 Cable Path for Mechan
Page 41 and 42: 7.2.1 Rings (Part #’s THH-001 [El
Page 43 and 44: 7.2.4 Collars 1) Using lathe turn o
Page 45 and 46: 7.3 Cost Analysis & Bill of Materia
Page 47 and 48: manufacturing costs are $525.00. Th
Page 49 and 50: operation necessary. This convertib
Page 51 and 52: Appendix A - Split Hook Sample Calc
Page 53 and 54: George Platounaris - Interview (12:
Page 55 and 56: Appendix C - Tim Lang’s Forearm D
Page 57 and 58: Health Progress, “Disables Enteri
Page 59: Drawing Package 1. THH‐001……

Prosthetic Arm Force Reducer Team 1 – Halliday's ... - Ohio University

Create successful ePaper yourself

Delete template?

Save as template?