Continuous steering-function control of robot carts

Three alternative approaches for eliminating steering discontinuities are presented: changing the steering mechanism, changing the guide-point on the cart, or changing the curves on the path. The first approach requires a steering mechanism that allows the cart to move in any direction without changing its heading. The most common configurations in an automatically guided vehicle are the steered-wheel and differential-drive types. The second approach may be a reasonable choice for differential-drive carts but less so for steered-wheel carts because of their limited maneuverability. For applications where the third approach is preferred, two types of curves providing continuous steering functions for both steered-wheel and differential-drive carts are proposed: Cartesian quintics for lane changes and polar splines for symmetric turns of arbitrary angle. These curves have computationally simple, closed-form expressions that provide continuous curvature and precise matching of the boundary conditions at the line-curve junctions on the paths.>