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

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hook allows the customer to operate in the full strength position only when necessary. Customer interaction has confirmed that this full strength setting offers more grip force than his currently modified prosthetic. Additionally, the customer can use half of the grip force and, therefore, have only half of the input force by a simple adjustment of a lever. Immediate effects of the upgrade to springs are that the user will be able to perform a wider variety of tasks with the increased grip force and also use the hook at half power, similar to a standard existing one-load hook. Long term effects could include fatigue and increased stress on the user’s body if the hook is used at full load fairly often and possibly an increase in the stresses in the entire prosthetic resulting in shorter product life due to fatigue. The mechanical advantage system offers relief for this. The ideal case for this system would give the user a 2:1 advantage in the input force required to open the spring hook. For example: Assume the original spring at the high setting required 35 lbs. Now, with the mechanical advantage pulley, it should ideally only require 17.5 lbs to open the hook at full load. The impact of this system to the user would be a drastic reduction of the input force required for both settings on the two-load hook. Our design reduces the input force required by the user by 47% from 18 lbs to 9.5 lbs or about a 1.9:1 advantage. The negative impacts discussed for the move to the Otto Bock hook and its stiffer springs would be reduced significantly, because even with an increase in grip force, the user would be able to exert less force than in an unmodified system. With respect to the mechanical advantage system, the user would theoretically have to pull their cable twice as far as was previously required to fully open the hook in order to balance the energy and forces for a 2:1 mechanical advantage. It currently takes about 1.75 inches of cable travel to fully open the customer’s hook. The Otto Bock hook, however, does not open as wide as the customer’s hook. This reduces functionality somewhat, but is beneficial in that he will only have to pull the cable ~2.75” inches, instead of the 3.5 inches it would take to fully open his current hook. Short term effects of a mechanical advantage system upgrade would be an increase in user comfort due to the ease in which he or she can use their prosthesis. It would allow for the immediate implementation of an increased-strength two-load hook without increasing the force needed to operate such a device. Long term effects are an increased life for the cable operating the pulley, and an increase in the workload the user could accomplish. Some possible negative long term effects could include shorter lifespan of the cable post and the cable connecting it to the pulley since they would be experiencing an increase in tension from the springs. Also, there is a possibility of eventual back and shoulder injuries from prolonged use, though this fact exists with all current prosthetic hook designs. The overall impact of the production of this system on the environment or society would not be very significant. As currently designed, this upgrade kit uses mostly pre-produced parts that need little machining. Most of the work required is in assembly and can be done by a few trained operators. The greatest impact or effect of the combined upgrade system would be to the life of the customer who would be using this system on a daily basis, allowing him or her wider range of tasks that they can complete and decreasing the wear on his or her body. 30
7.0.3 Professional/Ethical Standards Our team’s main goal is to help our customer, Tim Lang. We believe that our decisions should benefit him, first and foremost, and also stay within our parameters with respect to safety of our team and customer, budget, and design specifications. Our team conducts our meetings in a professional and productive manner, and pays close attention to our schedule to maximize efficiency and overall benefit to Tim. This attitude is reflected in our decision making process, customer and team interaction, and devotion that each team member has to our goals and successful completion of our project. Also, working together as a cohesive unit is far more productive than acting as individual with disjointed priorities. 7.0.4 Function In order to add mechanical advantage to our system, a movable pulley was mounted in the forearm of the prosthetic. A movable pulley allows the user to input only half of the force required to open the hook. This is due to the fact that the forces on the pulley have to balance when the pulley is at equilibrium. Since two ends of the input cable are supporting the pulley in one direction, they will equally share the load pulling on the axle of the pulley. In our case, the load on the pulley will be the force required to open the prosthetic hook. Therefore, our customer will be able to pull on the free end of the input cable with half of the force required to open the hook. In the ideal case this will be a 2:1 advantage. A small disadvantage to the system is that it requires twice the input cable travel in order to obtain the mechanical advantage. This has been talked over with the customer and has been deemed an acceptable trade-off for gaining a 2:1 advantage. 7.0.5 FMEA & Safety Figure 7.0.1 <strong>–</strong> Mechanical Advantage Schematic For the hook, initial consideration was given to minimize ways in which the Otto Bock design may fail in the agricultural setting where it would be used. This was approached by completing FMEA of the hook design, and the results of this analysis are presented in table 7.0.1. 31
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: Once the design of the system was u
Page 33 and 34: Table 7.0.2 - Risk Priority Number
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……

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