Innovative Rocking Chair Design with Electro-Magnetically Induced Rocking Motion Jorge Alvarado-Colón Yocli Comas-Torres Andrés Cruz-Vélez Tamarys Heredia-Arroyo Mayagüez, PR May 14, 2005 University of Puerto Rico-Mayagüez Campus Mechanical Engineering Department

Project Description Materials Selection Assembly and Dynamic Analysis Stress Analysis Failure Analysis Cost Analysis Areas of Focus Electro-Magnetic Rocking Chair

Project Description The design aims for a rocking motion similar to that of a pendulum. The model that will be used for the design is that of Waltenhofen's electromagnetic pendulum. For the chair’s support mechanism, two bars containing pin and slot configurations at each end will be attached to each side of the rocking chair. Electro-Magnetic Rocking Chair

Top 3 Material Candidates AISI 4043 Ti-6A-4V Aluminum Material Selection

Assembly Electro-Magnetic Rocking Chair

Dynamic analysis Angular velocities and accelerations were determined for the centrifugal motion of the rocking chair to estimate a rocking cycle period of 4 seconds by setting the length of the slot at the base, through which the support link bearings roll. Electro-Magnetic Rocking Chair

Stress Analysis The loads assumed take into account the distributed weight of the rocking chair and triangularly distributed weight of the user seating in the chair. A safety factor was empirically calculated using Collin’s method. Electro-Magnetic Rocking Chair

Stress Analysis After calculating axial forces and bending moments, the Von Misses stresses were calculated at the most critical point in order to calculate the cross sectional area of the support links, and a suitable inner diameter. The inner and outer diameters of the support structure were calculated. Electro-Magnetic Rocking Chair

Static Theories of Failure Since the material chosen is ductile, the Maximum Shear Stress Theory, which is the most conservative, was used to confirm that the structure would not fail by yielding. Using this theory, our safety factor assumption was also confirmed.

Electro-Magnetic Rocking Chair Assuming a possible crack on the on the rod, we calculated that our chair will not fail by fracture. Fracture

Electro-Magnetic Rocking Chair Buckling For a fixed free condition, the structure proved not to fail by buckling given an axial loading condition of 2500 lb (worst case scenario).

Electro-Magnetic Rocking Chair Failure To asses if the support structure would fail by fatigue, an S-N diagram for UHS steel was plotted, and appropriate failure theories for ductile materials were applied. For a fully reversed condition, the life cycle of the structure was 1.44 days. N (No. cycles) S (ksi)

Electro-Magnetic Rocking Chair Material Cost (dollars) Solenoids (two) and base100 UHS Steel supports12 Massage system50 Seat and components100 Other electronic and miscellaneous components 20 Total cost282 Manufacturing cost1,000 Engineering services6,000 Material Cost

Massage System Electro-magnetic Rocking System Audio System Why would anyone buy a traditional rocking chair? PEOPLE LOOK FOR COMFORT, RELIABILITY AND INNOVATION