Figure 2

Principle of an active-caster (caster mechanism). It is a same mechanism as a passive caster. The rotational motions of the wheel and steering shafts, ω _w and ω _s , generate active velocities along the wheel rotation and perpendicular directions, V _w and V _s , respectively. By cooperative control of these velocities, the active-caster generates a velocity V _d on the steering shaft with the required direction and magnitude.