Jinoh Lee

Practical Nonsingular Terminal Sliding-Mode Control of Robot Manipulators for High-Accuracy Tracking Control

This paper presents a practical nonsingular terminal sliding-mode (TSM) tracking control design for robot manipulators using time-delay estimation (TDE). The proposed control assures fast convergence due to the nonlinear TSM, and requires no prior knowledge about the robot dynamics due to the TDE. Despite its model-free nature, the proposed control provides high-accuracy control and robustness against parameters variations. The simplicity, robustness, and fast convergence of the proposed control are verified through both 2-DOF planar robot simulations and 3-DOF PUMA-type robot experiments.

Continuous Nonsingular Terminal Sliding-Mode Control of Shape Memory Alloy Actuators Using Time Delay Estimation

We have developed a continuous nonsingular terminal sliding-mode control with time-delay estimation (TDE) for shape memory alloys (SMA) actuators. The proposed method does not need to describe a mathematical model of a hysteresis effect and other nonlinearities; thus, it is simple and model free. The proposed control consists of three elements that have clear meaning: a TDE element that cancels nonlinearities in the SMA dynamics, an injection element that specifies desired terminal sliding-mode (TSM) dynamics, and a reaching element using a fast terminal sliding manifold that is activated accordingly when the system trajectory is not confined in the TSM. The proposed control has been successfully implemented in an SMA actuated system and experimental results show the proposed control is easily implementable and highly accurate. Once the TSM and the reaching condition are suitably specified, the tracking performance of the proposed control is improved compared with a conventional time delay control with a linear error dynamics.

Relative Impedance Control for Dual-Arm Robots Performing Asymmetric Bimanual Tasks

This paper presents a method of implementing impedance control (with inertia, damping, and stiffness terms) on a dual-arm system by using the relative Jacobian technique. The proposed method significantly simplifies the control implementation because the dual arm is treated as a single manipulator, whose end-effector motion is defined by the relative motion between the two end effectors. As a result, task description becomes simpler and more intuitive when specifying the desired impedance and the desired trajectories. This is the basis for the relative impedance control. In addition, the use of time-delay estimation enhances ease of implementation of our proposed method to a physical system, which would have been otherwise a very tedious and complicated process.

WALK‐MAN: A High‐Performance Humanoid Platform for Realistic Environments

In this work, we present WALK-MAN, a humanoid platform that has been developed to operate in realistic unstructured environment, and demonstrate new skills including powerful manipulation, robust balanced locomotion, high-strength capabilities, and physical sturdiness. To enable these capabilities, WALK-MAN design and actuation are based on the most recent advancements of series elastic actuator drives with unique performance features that differentiate the robot from previous state-of-the-art compliant actuated robots. Physical interaction performance is benefited by both active and passive adaptation, thanks to WALK-MAN actuation that combines customized high-performance modules with tuned torque/velocity curves and transmission elasticity for high-speed adaptation response and motion reactions to disturbances. WALK-MAN design also includes innovative design optimization features that consider the selection of kinematic structure and the placement of the actuators with the body structure to maximize the robot performance. Physical robustness is ensured with the integration of elastic transmission, proprioceptive sensing, and control. The WALK-MAN hardware was designed and built in 11 months, and the prototype of the robot was ready four months before DARPA Robotics Challenge (DRC) Finals. The motion generation of WALK-MAN is based on the unified motion-generation framework of whole-body locomotion and manipulation (termed loco-manipulation). WALK-MAN is able to execute simple loco-manipulation behaviors synthesized by combining different primitives defining the behavior of the center of gravity, the motion of the hands, legs, and head, the body attitude and posture, and the constrained body parts such as joint limits and contacts. The motion-generation framework including the specific motion modules and software architecture is discussed in detail. A rich perception system allows the robot to perceive and generate 3D representations of the environment as well as detect contacts and sense physical interaction force and moments. The operator station that pilots use to control the robot provides a rich pilot interface with different control modes and a number of teleoperated or semiautonomous command features. The capability of the robot and the performance of the individual motion control and perception modules were validated during the DRC in which the robot was able to demonstrate exceptional physical resilience and execute some of the tasks during the competition.

Development and control of a series elastic actuator equipped with a semi active friction damper for human friendly robots

Compliance is increasingly being incorporated in the transmission of robotics actuation systems to cope with unpredictable interactions, improve the robustness of the robot and in some cases its efficiency. However, compliance also introduces some drawbacks as e.g.?reduced bandwidth of the controlled system and typically underdamped vibration modes which decrease the accuracy and stability margin of the controlled system. To tackle these issues, variable physical damping has recently been incorporated in such actuation systems. This paper presents the analysis, development, control, identification and experimental evaluation of a novel actuation system which embodies transmission characteristics such as passive compliance and variable physical damping. The first part of this paper introduces an analysis on how these two physical properties affect the performance of the actuation system with the second part analysing the mechatronic design and control in detail. Furthermore, a novel damping estimation method is presented. Results are presented to validate the results obtained in the analysis section advantages gained by employing such actuation approach and to show the effectiveness of the actuation unit in replicating and estimating desired mechanical impedance values. Whole realization process of a successful implementation of a variable impedance actuator.Comprehensive analysis on the effects of compliance and variable physical damping.Mechatronic implementation of the variable impedance actuator.Introduction of a novel mechanical impedance estimator for measuring physical damping.Experimental results validate the analysis and the whole mechatronic system.

Model-Free Robust Adaptive Control of Humanoid Robots With Flexible Joints

A model-free robust adaptive controller is proposed for control of humanoid robots with flexible joints. The proposed controller uses a time-delay estimation technique to estimate and cancel nonlinear terms in robot dynamics including disturbance torques due to the joint flexibility, and assigns desired dynamics specified by a sliding variable. A gain-adaptation law is developed to dynamically update the gain of the proposed controller using the magnitude of the sliding variable and the gain itself. The gain-adaptation law uses a leakage term to prevent overestimation of the gain value, and offers stable and chattering-free control action. The effectiveness of the proposed adaptive controller is experimentally verified on a humanoid robot equipped with flexible joints. Tracking performances of the autotuned adaptive gain are better than those of the manually tuned constant gains. The proposed control algorithm is model-free, adaptive, robust, and highly accurate.

A manipulation framework for compliant humanoid COMAN: Application to a valve turning task

With the purpose of achieving a desired interaction performance for our compliant humanoid robot (COMAN), in this paper we propose a semi-autonomous control framework and evaluate it experimentally in a valve turning setup. The control structure consists of various modules and interfaces to identify the valve, locate the robot in front of it and perform the manipulation. The manipulation module implements four motion primitives (Reach, Grasp, Rotate and Disengage) and realizes the corresponding desired impedance profile for each phase to accomplish the task. In this direction, to establish a stable and compliant contact between the valve and the robot hands, while being able to generate the sufficient rotational torques depending on the valves friction, Rotate incorporates a novel dual-arm impedance control technique to plan and realize a task-appropriate impedance profile. Results of the implementation of the proposed control framework are firstly evaluated in simulation studies using Gazebo. Subsequent experimental results highlight the efficiency of the proposed impedance planning and control in generation of the required interaction forces to accomplish the task.

Control Architecture Design for a Fire Searching Robot using Task Oriented Design Methodology

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

Upper-body impedance control with variable stiffness for a door opening task

The advent of humanoids has brought new challenges in the real-world application. As a part of ongoing efforts to foster functionality of the robot accommodating a real environment, this paper introduces a recent progress on a door opening task with our compliant humanoid, CoMan. We presents a task-prioritized impedance control framework for an upper body system that includes a dual-arm, a waist, two soft hands, and 3D camera. Aimed to create desired responses to open the door, a novel stiffness modulation method is proposed, incorporating a realtime optimization. As a preliminary experiment, a full door-opening scenario (approaching to the door and reaching, grasping, rotating and pulling the door handle) is demonstrated under a semi-autonomous operation with a pilot. The experimental result shows the effectiveness and efficacy of the proposed impedance control approach. Despite of uncertainties from sensory data, the door opening task is successfully achieved and safe and robust interaction is established without creating excessive forces.

Proxy-based position control of manipulators with passive compliant actuators

In this work we introduce a position control scheme which is targeted at the enhancement of the safety of compliant joint robots. In addition to the necessity for accuracy and robustness that both serve as prerequisites for the successful performance of various tasks, the ability to safely handle unexpected events, such as communication failures or unintended interactions which may endanger the robot/human safety, is a paramount requirement. To achieve a smooth motion behaviour of compliant systems under different circumstances, damping control actions are essential. To this end, a novel proxy-based approach for compliant joint robots, integrated into a passivity-guaranteed controller, is proposed. The stability analysis of the proposed scheme is presented and the global asymptotic convergence, as well as the passivity of the control scheme, are analytically proven. The performance of the proposed approach is practically evaluated by means of experiments on a spatial robotic arm with passive compliant actuators, and is compared with that of a classical PD approach. Experimental results validate the ability of the proposed approach to inject damping in order to provide smooth and damped recovery when an interruption in task execution occurs.