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Visit to assisted living facility, explored arms mimicking chair motion and squishy handles preferences. CAD drawing, material selection, strength and stability analysis conducted for improved design. Safety factor calculations and tipping prevention methods utilized to enhance reliability.
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Assisted Living Facility Visit • Talked with elderly who are currently using walkers, a few who were using the same model as the one we have • Sitting down and standing up use same motion, they wanted something that would simulate the arms of a chair • They like squishy handles
Linkage Design • Geometry was used so that the lever would go exactly 90° and the handle would go exactly 80°
Materials Selection • All components analyzed using 1015 steel as the building material, which was found to have the one of the lowest yield stresses of most steels • May elect to change material selection pending cost-of-materials analysis • Aluminum Alloy 2014-T6 is relatively cheap, has a higher yield stress, lower weight, possible material for construction
Strength of Materials Shear stress 2 shear locations Stress related to bending moment 2nd moment of inertia circular cross section These values were then compared to the materials yield stress
Strength of Materials Other analysis done was using the stress caused by the compression of the beam, this was used to find the minimum radius of the support beam for the stopper; rmin=0.78 mm
Handle Analysis Handle Bending Stress Bolt Shear Stress
Stability During Operation • Most reliable solution is to fix the stopper/brace assembly in one position • In order to prevent tipping when a 200 lb force is applied to handles, the stoppers must extend 20 cm from the rear legs (in perpendicular direction)
Safety Factor • To enhance safety consideration, as many “worst-case” scenarios as possible were used in the analyses. • Force location • Materials choice • Component construction • Average weight of men and women, ages 20+ is 165 lbs • Factor of safety = 200 lbs/ 165 lbs • Factor of safety = 1.21 > 1
Tipping of Walker • Largest problem, required the center of mass and all forces involved during use • ΣM was taken about the front leg • If this moment was found to be less than or equal to 0, then the body did not tip
Tipping Centroid Assumed all members were equal weight Center of mass was found to be (24.50 cm, 51.76 cm) about the axis shown in the following slide
Centroid Because all components were assumed to be the same weight, the total weight of the walker was applied to the centroid of the body
