Hybrid robotic platform for wall profile tracking

Cable-Driven Parallel Robots (CDPRs) offer large workspaces and favorable payload-to-weight ratios, but their accuracy is limited by cable elasticity, posture-dependent stiffness, and sensitivity to orientation errors. This paper presents a 5-DOF hybrid robotic platform for wall-profile tracking that combines a CDPR, a deployable Sarrus mechanism, a Pan–Tilt unit, and Time-of-Flight (ToF) sensing. The novelty of the work lies in coupling configuration-dependent stiffness modulation with real-time distance feedback to improve trajectory accuracy and orientation stability during surface-following tasks. A complete kinematic model of the hybrid platform is developed, including the CDPR planar motion, Sarrus axial deployment, and Pan–Tilt orientation. An energy-based stiffness analysis is introduced to explain how the Sarrus configuration affects deformation amplification. Experimental validation is performed through wall-profile tracking tests comparing extended and contracted Sarrus configurations, as well as different link-material conditions. Results show that the contracted Sarrus configuration reduces the RMS trajectory error from 20.99 mm to 9.73 mm, corresponding to an improvement of approximately 53%. Roll deviations are reduced from 1.2° to approximately 0.6°, while yaw remains within ±0.4°. Additional material tests confirm that increased structural stiffness improves tracking accuracy and reduces oscillatory behavior. These results demonstrate that combining adaptive mechanical stiffness with ToF-based feedback improves wall-profile tracking performance in hybrid CDPR systems.