Modal Space Control of Bilateral System with Elasticity for Stable Contact Motion

Bilateral control realizes position synchronization and the “law of action and reaction” between two points. To advance applications of bilateral control, it is necessary to emphasize environmental adaptability, safety, and task execution. Accordingly, the bilateral system is required to consider contact with unknown environments and realize stable contact to avoid harm to the operator or the object. Thus, a bilateral control system using elastic manipulators is proposed in this paper. Moreover, the integration of mechanical and control designs for stable interaction with the operator and the environment is discussed. The proposed bilateral system with elasticity is modeled as a pair of two-mass resonant systems. Accordingly, a modal space control (MSC) is introduced with the aim of realizing the control goals, vibration suppression, and good operationality. Modal transformation independently configures the force and position controllers of each other in virtual common and differential spaces. MSC comprises reaction torque feedback loops in the modal space and modal space load-side disturbance observer (MLOB). MLOB compensates for load-side disturbance, including the interference between the common and the differential modes. It realizes disturbance suppression, decoupling control, and nominalization of parameters in the form suitable for each force and position control system.