In this paper, the robustness problem in time-delay control (TDC) is considered in the presence of the nonlinear friction dynamics of robot manipulators. As a remedy for this problem, the TDC is enhanced with a compensator based on internal model control (IMC). The robustness and stability of the proposed method have been analyzed to be effective against friction while preserving the positive attributes of the TDC: It is simple, efficient, and easily applicable because it does not require a complete plant model. Through experiments, the proposed method achieves accuracy levels that are 10-20 times better than that of the TDC, thereby confirming its effectiveness under friction.

Impedance control is capable of further flexibly adjusting the driving-point impedance of series elastic actuators (SEAs) in conjunction with impedance reduction by the elastic element. This feature enhances safety and compliance during interaction between humans and robots, in comparison with rigid robots under impedance control or SEAs under position control. In this article, we propose an impedance controller for SEA systems that are developed based on the singular perturbation (SP) theory and time-delay estimation (TDE) technique. The SP theory allows for alleviating the burden of the requirement for states to be measured. The TDE technique is effective in compensating for system dynamics and uncertainties involved in system behaviors with minute computation loads. Employing both a simulation study and experimental study, we demonstrate the efficacy of the proposed control created from the combination of the SP theory and TDE technique. The effect of the proposed impedance control on broadening operational bandwidth while providing lower driving-point impedance is investigated.

In this paper, we propose a trajectory tracking controller with experimental verification for torpedo-like autonomous underwater vehicles (AUVs) with underactuation characteristics. The proposed controller overcomes the underactuation problem by designing the desired error dynamics in a coupled form using state variables in body-fixed and world coordinates. Unlike the back-stepping control requiring high-order derivatives of state variables, the proposed controller only requires the first derivatives of the states, which can alleviate noise magnification issues due to differentiation. We adopt time delay estimation to estimate the dynamics indirectly using control inputs and vehicle outputs, making the proposed controller relatively easy to apply without requiring the all of the vehicle dynamics. We also address some practical issues that commonly arise in experimental environments: handling measurement noises and actuation limits. To mitigate the effects of noise on the controller, a filtering technique using a moving window average is employed. Additionally, to account for the actuation limits, we design an anti-windup structure that takes into consideration the nonlinearity between the thrusting force and rotating speed of the thruster. We verify the tracking performance of the proposed controller through experimentation using an AUV. The experimental results show that the 3D motion control of the proposed controller exhibits an RMS error of 0.3216 m and demonstrate that the proposed controller achieves accurate tracking performance, making it suitable for survey missions that require tracking errors of less than one meter.

Recently, there has been an increase in the development of fire searching robots for indoor spaces such as the basements of buildings. This paper presents the control architecture for a fire searching robot using task oriented design (TOD) methodology. TOD is the systematic methodology used to design a system which follows a purpose closely by specifying a target clearly. As indoor spaces are blocked by walls, dangerous fires with smoke, high temperatures, and the possibility of explosions make it difficult for fire fighters to gain access to the fire. For this reason, a fire searching robot is developed in this study. It takes the place of fire fighters by means of an analysis of the properties of the environment of a fire, as well as the tasks demanded by the situation. For a stable operation, the fire searching robot is controlled by remote control. The control system is divided into three parts. The first is the robot controller, the second is a controller for the remote operating device, and the third is a wireless communication system. The appropriate hardware and software was developed for each part of the control system, and the fire search robot was tested in a test environment. The tests validated the performance and usefulness of the proposed control architecture

This study presents a mission management technique that is a key component of underwater docking system used to expand the operating range of autonomous underwater vehicle (AUV). We analyzed the docking scenario and AUV operating environment, defining the feasible initial area (FIA) level, event level, and global path (GP) command to improve the rate of docking success and AUV safety. Non-holonomic constraints, mounted sensor characteristic, AUV and mission state, and AUV behavior were considered. Using AUV and docking station, we conducted experiments on land and at sea. The first test was conducted on land to prevent loss and damage of the AUV and verify stability and interconnection with other algorithms; it performed well in normal and abnormal situations. Subsequently, we attempted to dock under the sea and verified its performance; it also worked well in a sea environment. In this study, we presented the mission management technique and showed its performance. We demonstrated AUV docking with this algorithm and verified that the rate of docking success was higher compared to those obtained in other studies.