Design and Variable-stiffness Control of a High-load Cable-driven Robot for Transfer Care Operations

To address the shortage of nursing staff and the practical need for transferring bedridden patients in the context of an aging population, a new type of high-load nursing robot driven by ropes is designed and developed for assisting in transfer care operations. Firstly, this nursing robot simulates the antagonistic drive principle of human arm muscles through flexible rope drive. By placing the motor, reducer and other drive components at the rear, the inertia and mass of the movable parts of the entire arm are significantly reduced. Not only the kinematic parameters but also the dynamic parameters are similar to those of the human arm, thereby enhancing the flexibility and safety during human-robot interaction. Secondly, a unique dual-motor direct-drive differential mechanism at the shoulder is designed for transfer care operations, effectively enhancing the load capacity of the shoulder joint and achieving an excellent load ratio. A variable-stiffness structure is innovatively integrated in the elbow joint, which makes the compliant interaction characteristics of the manipulator adjustable at different stages of care tasks through stiffness modeling and active variable-stiffness control. Experimental results show that the manipulator demonstrates outstanding load performance, with a single arm mass of only 5 kg; its end effector can carry a load of 15 kg, and the elbow joint can bear a load of 30 kg, achieving a repeat positioning accuracy of less than 0.4 mm. Finally, the care task of assisting in lifting and transferring is successfully completed in physical experiments, and the basic performance and variable-stiffness compliant control ability of the cable-driven nursing robot are verified, fully demonstrating its safety and efficiency in nursing application scenarios.