A 4WD omnidirectional wheelchair with a chair tilting mechanism for enhancing step climbing capability

This paper presents the development of 4WD omnidirectional wheelchair with a chair tilting mechanism and experimental verification using a wheelchair prototype. For enhancing the mobility of standard wheelchairs, a new type of omnidirectional mobile platform with four-wheel drive (4WD) mechanism is introduced. The mobile platform includes a pair of normal wheels on the rear side of the platform and a pair of omni-wheels on the front side. The normal wheel in rear and the omni-wheel in front, mounted on the same side of the base, are interconnected by a chain or a belt transmission to rotate in unison with a drive motor, i.e. a synchro-drive transmission. To rotate a chair at the center of the mobile base about vertical axis, the third motor is installed on the platform. The prototype wheelchair with the proposed 4WD system is capable of climbing over a 9 cm single step. The 4WD system provides enhanced step climb capability however, chair inclination becomes large when either front or rear wheels are on a step because wheelbase of the developed wheelchair is almost same as a standard one. This large inclination not only gives a high risk for falling but also brakes a load distribution condition between front and rear wheels which is required for climbing the step. To solve these problems relating to the chair inclination, we develop a chair tilting mechanism for the 4WD wheelchair including lift up mechanism controlled by a stability algorithm using an inclination sensor. To verify the proposed system, experimental results are also presented in which successful climbing of a 9 cm step is realized.