An electric wheelchair is the device to support the self-movement of the elderly and people with physical disabilities. In this paper, a prototype design of an electric wheelchair with a high level of mobility and safety is presented. The electric wheelchair has a high level of mobility by employing an omnidirectional mechanism. Large numbers of mechanisms have been developed to realize omnidirectional motion. However, they have various drawbacks such as a complicated mechanism and difficulty of employment for practical use. Although the ball wheel drive mechanism is simple, it realizes stable motion when negotiating a step, gap, or slope. The high level of mobility enhances the freedom of users while increasing the risk of collision with obstacles or walls. To prevent collisions with obstacles, some electric wheelchairs are equipped with infrared sensors, ultrasonic sensors, laser range finders, or machine vision. However, since these devices are expensive, it will be difficult for them to be widely used with electric wheelchairs. We have developed a prototype design of collision-detecting device with inexpensive sensors. This device detects the occurrence of collisions and can calculate the direction of the colliding object. A prototype has been developed to perform motion experiments and verify the accuracy of the device. The results of experiments are also presented in this paper. 1. Introduction The reduced physical functions associated with aging or disability make independent living more difficult. Lower extremity function ability limits the scope to take part in vocational and educational opportunities and many also negatively affect self-esteem. If people with reduced physical functions cannot receive support, they may become bedridden. A wheelchair can compensate for a lower extremity function, by allowing users to move freely by themselves. An electric wheelchair is the device to support the self-movement of the elderly and people with physical disabilities. Previous research topics based on electric wheelchairs can be classified into projects to develop increasing a high level of mobility and projects to add intelligent functions to wheelchairs. The conventional wheel-type mechanism needs to switch the drive when negotiating narrow spaces. An omnidirectional vehicle has no limits to its direction of motion and is expected to have a wide range of applications. Omnidirectional vehicles are an active area of research in robotics and a numerous mechanisms have been developed. To realize omnidirectional motion, vehicles so far have been equipped
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