The Hbot : A Holonomic Spherical Haptic Interface Driven by Non-Holonomic Wheels

We present the Hbot, a holonomic, singularity-free spherical robot designed for haptic simulations. The Hbot is made up of a caged sphere actuated by steered and driven nonholonomic wheels to produce continuous and unlimited spherical motions. We analyse the kinematic interface between a sphere and n arbitrarily positioned, steered and driven non-holonomic wheels in the general case. We also present a detailed singularity analysis and show that workspace-boundary and workspaceinterior singularities can both be avoided at the design stage. We implement a prototype using two steered and driven nonholonomic wheels and show experimental results for trajectory tracking and rendering of various rotational stiffness levels.