Innovative Rocking ChairDesign with Electro-

Magnetically Induced Rocking Motion

Jorge Alvarado-Colón Yocli Comas-TorresAndrés Cruz-VélezTamarys Heredia-Arroyo

Mayagüez, PR

May 14, 2005

University of Puerto Rico-Mayagüez CampusMechanical Engineering Department

• Project Description• Materials Selection• Assembly and Dynamic Analysis• Stress Analysis• Failure Analysis• Cost Analysis

Areas of Focus

Electro-Magnetic Rocking Chair

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

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 ChairinD

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4.0

9.0

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

FailureTo 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)

100 118.3875

103 106.5488

106 18.15

108 18.15

Electro-Magnetic Rocking Chair

MaterialCost

(dollars)Solenoids (two) and base 100

UHS Steel supports 12

Massage system 50

Seat and components 100

Other electronic and miscellaneous components

20

Total cost 282

Manufacturing cost 1,000

Engineering services 6,000

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