Abstract
Walking aid is a kind of vehicle that can be designed only by intensive use of
automotive engineering. Walking aids for outdoor use must run over rough surface, while
giving small vibration and sure support to their users. The aids must turn in small space and
stop in a desired manner. Such functions are the fundamentals of motor vehicles. This report
describes an advanced dynamical design for outdoor walking aid that can go over rough roads.
The first step of this study was identifying the people who can stand on their feet but have to
rely on some aids in walking as the assumed users. They need to walk outdoors to train their
walking ability and to meet their daily needs at post offices, convenience stores, etc.
The second step was setting human factor design criteria. Firstly, survey of the barriers in a
typical suburban residential area was conducted. Statistical data such as the curb stone height
were obtained. Secondly, permissible vibration level at the handle grips was identified.
Simulating the grip vibration with an electro-magnetic shaker, desirable and permissible
vibration amplitude thresholds were identified. Thirdly, design specifications of the walking
aid dynamics were set. The design parameters corresponding relevant performances were
found to be 1) The center of gravity height, 2) Front wheel suspension compliance in
longitudinal and vertical directions, and 3) Stiffness of the space frame in the frequency range
below 63 Hz 1/3 octave band.
In the third step, a new type front wheel suspension system was invented based on a design
principle that realizes a virtual large radius wheel by enveloping multi small wheels. This
front wheel system uses a leading small wheel and a main load-carrying wheel attached at the
two ends of a swinging V-shaped link. The leading wheel rides on a step and supports a part
of the front load and helps the main wheel climb up. The V link rotation is suspended by a
torsion spring and can absorb shock when the main wheel hit a step. The suspension geometry
and spring stiffness were optimized by applying multi-body-dynamics simulation.
In the fourth step, a lightweight space frame was designed to avoid heavy resonances in low
frequency to meet the vibration level criteria. The shape and geometry were created through
topological and parametrical optimization process. Finally, a prototype was built. This
prototype has a power train consisting of a servo-motor, a planetary gear set, and a cogged
belt for each rear wheel. The speed is controlled manually by a grip lever.
In the final step, the running performances were evaluated on a model rough surface course
objectively and subjectively. Most of the design specifications were achieved successfully.
Keywords - Dynamics, Ride, Vibration, Structure optimization, Walking aid