This study proposes a novel approach for low-impedance rendering in robots to ensure safe human-robot interaction. Low-impedance control enhances safety by enabling robots to respond flexibly to physical contact with humans. However, real-world disturbances such as friction often necessitate high impedance, creating a trade-off between safety and task precision. To address this challenge, a modified disturbance observer (DOB)-based control framework is introduced, designed to prevent external contact forces from being treated as disturbances. Experimental results demonstrate significant improvements in impedance rendering performance under various conditions, ensuring precise and safe robot operations in dynamic shared environments.

This paper presents a robust control algorithm for precise orientation control of robot manipulators using a disturbance observer (DOB) specifically designed for orientation dynamics. Our approach addresses the challenges of 3D orientation control by incorporating various orientation representations, such as Euler angles, quaternions, and exponential coordinates, and analyzing their impact on DOB performance. Through theoretical analysis and experimental validation, we demonstrate the effectiveness of our method in achieving high-precision orientation control under uncertainties and disturbances. This work offers a comprehensive framework for robust orientation control, advancing the application of DOB in complex robotic tasks.

This paper presents a novel, nonlinearity robust identification method for deriving the inertia matrix of multi-DOF Flexible Joint Robots (FJR), utilizing resonance and anti-resonance frequencies in the Frequency Response Functions (FRF). Our proposed method overcomes the limitations of conventional approaches, which are susceptible to mechanical nonlinearities, leading to inaccurate models. By leveraging frequency domain techniques, our approach effectively mitigates the influence of nonlinear characteristics, providing a more accurate and reliable means of robot control. Furturmore, the paper highlights the benefits of frequency domain system identification, including nonlinear robustness and the ability to decompose the flexible joint into motor and load components. Finally, a novel sequential excitation algorithm is proposed to obtain the inertia matrix of a multi-DOF robot manipulator without relying on complex theories or optimizations. The effectiveness of the proposed algorithm is verified through simulation and experiment.

The use of impedance control has become widespread in applications requiring simultaneous position tracking and compliance in contact. However, disturbances such as friction and model uncertainties can adversely affect the performance of impedance-based motion control. The disturbance observer (DOB) has been proposed to address this issue, which is a widely-utilized robust controller that eliminates observed disturbances with the nominal model. However, current DOB applications fail to consider the aspect of interactive force control properly. This study proposes a novel Workspace Force/Acceleration Disturbance Observer (WFADOB) controller, which utilizes both interaction force and acceleration to design a disturbance observer loop, enabling precise motion tracking even with low-impedance gain settings. Additionally, the proposed controller offers fine impedance rendering performance, offering safe contact while maintaining low impedance. This paper discusses the problem of motion tracking performance due to friction and the interaction force that arises during contact. The proposed controller is theoretically analyzed and experimentally verified, demonstrating its performance compared to conventional methods.

Upper limb exoskeleton robots have been widely used to assist humans in industry and rehabilitation. Human-robot interaction control consists of two modes. A compliant mode and an assistive mode. The compliant mode is manipulating the robot compliantly according to the movement of the human. At this time, the human must not receive impedance from the robot. Therefore, in this paper, a novel external force control which makes the robot follow human movement without causing resistance is proposed. The assistive mode is to generate assistive power according to human intention. In this paper, the algorithm for recognizing the human intention for primitive movement and generating assistive forces adaptive to real-time work environments is proposed. The proposed two modes are also integrated into a novel human-robot interaction control framework. The performance of the proposed methods is verified through experiments.