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

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

The rings are the most expensive part of the mechanical advantage system because they will be made out of a 2-1/2” diam. stainless steel pipe. The minimum length of stock for this pipe size is 12’’ and as such a large amount of extra material had to be purchased. The high cost (approximately $73) is hard to justify for the construction of a single system, however this stock would be fine if multiple systems were to be constructed. A nylon pulley with a stainless steel housing was selected. This item cost around $20 and will require no additional modifications. The bearings were selected due to the flexibility of sizes available and the low cost. Ball bearings are approximately one-third the cost of rubberized wheels. The 1/4” diameter stock for the axles and spacers was very inexpensive at around $6 per 12” length. All materials, with the exception of the nylon pulley, of the mechanical advantage system are stainless steel which makes any necessary welding possible and is good for corrosion 7.0.7 Design Analysis For mechanical advantage system, yielding of the tracks is the most pertinent failure mode for formal analysis. This failure mode involves potential yielding of the track’s sidewalls due to the forces inherent to having the pulley travel centrally through the forearm. The central translation of the pulley requires the cable leading to the hook’s cable post to be at an angle at all times. This is illustrated below in a top-down view. Figure 7.0.2 – Pulley Vector Analysis The concern here is that the side-wall force “Fw” could torque the walls of track, and make them yield. There is also a possibility of a shearing failure where the tracks are welded to the retaining rings. Fortunately, theta decreases as the pulley is moved away from the front of the forearm during operation. Therefore, when the hook is fully open, the pulley is at its farthest point from the wrist, which results in the smallest value of theta to be encountered. This is desirable because at this condition, the largest forces are applied, but the effect of Fw is (geometrically) at its smallest. With these considerations in mind, this failure mode was analyzed at the point of highest user input with FEA software. FEA was chosen because of the unusual loading condition, and because it can simultaneously display the stresses at the sidewalls of the tracks, and the welded area. 34
The actual FEA testing involved utilizing a drawing of our current track. By using our hook simulation spreadsheet, a user input force of 70 lbs was needed, and a side-load of 13.4 lbs (determined by the triangular relationship pictured above) was distributed among nodes in the inner wall of one track to simulate the effect of the bearing force “Fw/2” (only one track). The material chosen was annealed 302 stainless steel, because it was similar to the 304 stainless steel in which our actual tracks are made of. The following pictures give a visual summary of our FEA results. Figure 7.0.3 – Algor track model 1 Figure 7.0.4 – Algor track model 2 Figure 7.0.5 – Algor track model 3 35
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 and 32: 7.0.3 Professional/Ethical Standard
Page 33: Table 7.0.2 - Risk Priority Number
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……

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