Friction-Driven Multi-Disk Omni-Directional Spherical Wheel

Omnidirectional drive mechanisms enable mobile robots to move in any direction without changing their orientation, allowing holonomic motion and smooth directional transitions. Among these mechanisms, spherical drives provide continuous ground contact and rapid directional response, making them attractive for mobile robotic platforms. However, many existing spherical friction-driven mechanisms typically apply non-uniform and unregulated contact forces to the spherical wheel, resulting in uneven torque transmission, increased slippage, and accelerated mechanical wear. In addition, some designs suffer from kinematic limitations that restrict stable and continuous motion control. To address these issues, this paper proposes a friction-driven spherical omnidirectional mechanism based on a multi-disk configuration. The system employs sliding screws attached to the disks to regulate the normal force applied by each disk to the spherical wheel, enabling controllable friction-based torque transmission. A prototype is developed and experimentally evaluated using a force measurement setup. The results demonstrate that the transmitted torque can be effectively controlled by adjusting the disk–sphere contact conditions, and an optimal contact position for maximum torque transmission is identified. Furthermore, directional motion can be achieved by coordinating the force distribution among multiple disks, leading to reduced slippage and improved overall system efficiency.