This paper proposes an optimization method for dual-arm robots, inspired by a study on human asymmetric bimanual action called Guiard's principle which states that when humans perform asymmetric bimanual tasks, the right hand (as the lateral preference) performs a fine motion (and force) resolution, while the left hand performs a coarse resolution. To effectively transfer the human bimanual-task knowledge to dual-arm robots, we proposed a cost function, based on task-compatibility index, which is used to set the desired motion and force resolution for each end-effector of the dual-arm according to its role in the bimanual action. Thus the right-arm posture is optimized such that the tool attached to its end-effector can exert fine motion and force. And the left-arm posture is optimized to assume a strong and dynamic structural support for the right arm action. We experimentally compare the proposed cost function against previous methods for dual-arm robots using two six degrees-of-freedom torque-controlled manipulators. The control performance, when mimicking Guiard's principle shows considerably better results.

This paper presents new formulations in task-prioritization for dual-arms with multiple, conflicting tasks and experimental validations. An essential part of the proposed method is the use of relative Jacobian that treats the dual-arm as an equivalent single arm. As a result, three formulations are derived. The first formulation, called relative task prioritization, expresses a task prioritization at the acceleration level for a dual-arm, with multiple tasks, that is controlled as a single manipulator. The second formulation is an impedance control equation that allows direct control of the relative motion and impedance between two end-effectors. Our third formulation is a control law that combines relative task prioritization, impedance control, and time-delay estimation, which contributes to the ease of implementation of our proposed method. In the physical implementation, one arm draws a circle on a plate attached to the other arm in parallel with three subtasks. Then, intentional conflict among subtasks is induced. The experimental results show that when such conflict occurs, the higher priority task is guaranteed an immediate execution without influence from the lower priority task.

This paper focuses on a kinematic redundancy resolution of bimanual robotic system for a machining task as a part of factory automation. Inspired by a study of human bimanual action, called Guiard's principles, a cost function is proposed by using task-compatibility indices. An acceleration-level redundancy resolution is provided via optimization of the cost function in order to reflect the role of human arm movement: one arm performs coarse motion, and the other fine motion. A dynamic simulation with two 6 degrees-of-freedom robots shows the effectiveness of the proposed idea.

The operational space formulation (OSF) has been enhanced from a practical viewpoint through the application of the time-delay estimation (TDE). In principle, the OSF enables an excellent decentralized control owing to its ability to achieve dynamic consistency. In reality, however, it can suffer from modeling errors and relatively large computational demands. As a remedy for these problems, the OSF has been combined with the TDE, which is known for its accurate estimation of robot dynamics with high computational efficiency. By virtue of the TDE, the OSF with the TDE (OSFTDE) shows enhanced accuracy in terms of dynamic consistency and control performance along with enhanced computational efficiency. Through simple but obvious simulations and experiments, the OSFTDE shows much better accuracy than the OSF with modeling error of 5% or higher, although accuracy is slightly worse than the OSF with a perfect model, thereby demonstrating its practical advantages.

This paper proposes a performance index called telepresence index for bilateral teleoperation, which can be used both for the performance evaluation of bilateral control architectures and for design purposes. This index is intended to represent a comprehensive performance objective consisting of transparency and kinematic correspondence, which are two major performance objectives of bilateral teleoperation. In order to quantify the performance objective, telepresence index has employed the error vector magnitude, which enables a seamless combination of magnitude and phase errors and the accommodation of time delay. In comparison with existing performance indices, it was observed that telepresence index possesses the comprehensiveness of performance objectives, magnitude/phase integrity, and the capacity to include time delay, which the others lack in one way or another. The index was applied to evaluate the performances of two widely known control architectures: PD-type bilateral control and Ueda's ideal control. In all cases, telepresence index has been compared favorably with the other indices in terms of clarity, convenience, and accuracy, thereby demonstrating its superiority.

In this paper, the practical problems of the Operational Space Formulation (OSF) are considered. The OSF provides decentralized control of the tasks by virtue of the ‘dynamic decoupling property’. In the practical view point, however, the OSF can be unfavorable due to the inevitable modeling error and large computational effort. As a remedy for this problem, the OSF is enhanced with Time-Delay Estimation (TDE) scheme. The robustness and efficiency of the proposed control have been analyzed and demonstrated to be effective against the practical problems while preserving the dynamic decoupling property.

A task-priority based framework for multiple tasks of highly redundant robots was derived using the Lagrangian multiplier method. The framework was proved to prioritize a generic number of tasks without algorithmic problems - so called an algorithmic singularity and an algorithmic error. The computational efficiency of the framework excels other conventional task-priority strategies. The efficiency and efficacy of the framework was demonstrated theoretically and experimentally through comparative study.

An accurate and robust impedance control technique is developed based on internal model control structure and time-delay estimation: the former injects desired impedance and corrects dynamics estimation error; the latter estimates and compensates the nonlinear dynamics of robot manipulators. Owing to the simple structure, the proposed control is designed without requiring entire dynamics computation or complex algorithms. The accuracy and robustness of the proposed control are verified using a two degrees of freedom robot with stiff wall simulation. The proposed control realizes desired impedance accurately compared with other competent controllers throughout the task, i.e., free motion, constrained motion, and transition between these motions. Further, proposed control realizes four sets of desired impedance accurately. Thus, accuracy and robustness of proposed control is confirmed.

In bilateral teleoperation, the performance measure has significant considerations: control objective, quantitativeness, time delay and human haptic perception, but no suitable performance measure exist. Therefore this paper investigates extended transparency as a performance measure in bilateral teleoperation. First, through an analysis based on control objective, extended transparency has two independent control objectives: trackability and immersivity. Second, we develop the performance measure for each control objective of extended transparency by using both the transmission delay constant and the error vector magnitude for the effect of time delay, and both the meaningful perception bandwidth and the compliance just-noticeable-difference for human haptic perception. Finally, extended transparency is applied to two kinds of control architecture in a one-DOF LTI teleoperation system. The case study and simulations demonstrate the ease of application and the validity of the proposed method.

This paper presents stability analysis and experimental results of the nonlinear bang-bang impact controller for robotic manipulators. A stability condition has been derived based on the analysis in Ln ∞ space and its physical interpretation has been given. The analysis shows that the stability of nonlinear bang-bang impact control depends on sampling time and the accuracy of inertia estimation. Stability is enhanced with the decrease of changes in the Coriolis, centrifugal, and disturbance forces. The stability condition is verified by simulations and experiments. Experiments show that overall performance is comparable to or better than existing impact control techniques which employ more complicated control strategies.

This paper presents significance of causality analysis in attaining transparency of bilateral teleoperation. The causality analysis enabled novel understanding of teleoperation systems, thereby providing methods for finding transparency-attainable control architectures with proper control parameters. Furthermore, when combined with the causality-based stability, stability could still be guaranteed while attaining transparency. Experimental verification is given for simple 1-DOF teleoperation tasks.

This paper investigates transparent teleoperation using two-channel control architectures. First, we show the transparency attainability using hybrid parameters and present transparency conditions according to each class of two-channel control architectures. In addition, for real implementation, the following practical solutions are introduced: design guidelines for control parameters to reduce the effect of impedance estimation error, and a hybrid control law based upon time delay control for unknown impedance. Finally, the proposed scheme is applied to a haptic simulation using a 1-DOF master and a teleoperation task using a 2-DOF master-slave system. The experimental results show the validity of the theoretical works.

For stabilization of a robot manipulator upon collision with a stiff environment, a nonlinear bang-bang impact controller is developed. Under this control, a robot can successfully achieve contact tasks without changing control algorithm or controller gains throughout all three modes: free space, transition and constrained motion. It uses a robust hybrid impedance/time-delay control algorithm to absorb impact forces and stabilize the system. This control input alternates with zero when no environment force is sensed due to loss of contact. This alternation of control action repeats until the impact transient subsides and steady state is established. After impact transient, the hybrid impedance/time-delay control algorithm is utilized. This bang-bang control method provides stable interaction between a robot with severe nonlinear joint friction and a stiff environment and achieves rapid response while minimizing force overshoots. During contact transition, we employ one simple control algorithm with same gains that switches only to zero, while other controllers use more than one control algorithms or different control gains. It is shown via experiments that overall controlled performance is superior or comparable to existing impact force control techniques.

Reports the discovery of a new type of singularity that is as significant as other singularities like kinematic singularity, algorithmic singularity, and semi-singularity. This singularity, named semi algorithmic singularity (SAS), occurs when a redundant manipulator, faced with inequality constraints arising from kinematic limits such as joint angle limits and obstacles, proceeds to conduct optimization of a performance measure. Through mathematical analysis, we have proved its existence and proposed an analytic matrix function to identify its presence. In conjunction, we have exposed its relationship with the other singularities above. More specifically, SAS is similar to the algorithmic singularity in that it is an artificial singularity coming from an endeavor for performance optimization. They are different in that the former occurs in one direction in the C-space, whereas the latter occurs bidirectionally. Besides, we have also found an analogy in the real singularities that while the semi-singularity is unidirectional in the workspace, the kinematic singularity is bi-directional. Through a simulation for a three DOF planar manipulator we have visualized the existence of SAS and its relationship with the other singularities.

In this paper, causality of teleoperation is described. By using bond-graph modeling, the causality of ideal operation is derived and desirable architectures for the causality are suggested. The importance of causality consideration is demonstrated by that inconsistent causality gives rise to instability, and is confirmed through experiments.

The control of a robotic excavator is difficult from the standpoint of the following problems: parameter variations in mechanical structures, various nonlinearities in hydraulic actuators and disturbance due to the contact with the ground. The more the size of robotic excavators increase, the more the length and mass of excavator's links; the more the parameters of a robotic excavator vary. A time-delay control with switching action (TDCSA) using an integral sliding surface is proposed for the control of a heavy-duty robotic excavator. The proposed controller is applied to straight-line motions of a robotic excavator with a speed level at which skilful operators work. Experiments, which were designed for surfaces with various inclinations and over broad ranges of joint motions, show that the proposed controller exhibits good performance.

It is widely and frequently observed that industrial robots conducting fast motion involve serious residual vibration, the period of which varies with time. To this problem, this paper presents a practical solution by providing a practical design and application of time-varying input shaping technique (TVIST) for an industrial robot. To suppress the time-varying vibration, at first, a guideline for designing practical TVIST is presented. Following the guideline, then, we design TVIST for a large size 6 degrees of freedom industrial robot. In doing so, a simple yet effective equation is derived from robot dynamic equations to estimate the time-varying period. Furthermore, a simple payload adaptation scheme is also included. The TVIST thus designed is experimented on the industrial robot under spatial motion and payload variation conditions. The experimental results show that the residual vibration is reduced to less than 10% of original one in magnitude, demonstrating that the efficiency of the TVIST does not compromise its effectiveness.

Presents our finding of a critical point that has not been reported thus far in the inverse kinematics of redundant manipulators under inequality constraints. The critical point, named algorithmic barrier was first encountered in the form of peculiar phenomena in our experiment with an 8-DOF robot, which we believe to have significance in the order of so-called algorithmic singularity. In addition, the paper deals with the characteristics of optimal solutions (COS) in resolving manipulator redundancy under inequality constraints. In order to analyze the COS, analytic functions of sufficient conditions and critical point conditions are derived. As a result, we find that COS is drastically affected by the introduction of inequality constraints. That is, COS under no inequality constraints is known to change only at algorithmic singularity while COS under inequality constraints turns out to change at semi-singularity and algorithmic barrier as well as algorithmic singularity. We prove the existence the critical points and present their analytical properties by using a planar 3-DOF manipulator.

For resolving the manipulator redundancy under inequality constraints, the compact QP method (including the improved Compact QP method) is very effective and efficient. From a viewpoint of practical applications, however, it turns out, we found, to have some performance limitations such as unrealistically high torque due to joint angle limit constraints and tracking errors due to joint torque limit constraints under parameter variation and disturbance. Remedying the limitations, the enhanced compact QP method is developed by using the practical inequality constraints with p-step-ahead predictor and time delay estimation. Through dynamic simulation results, it is verified that the enhanced compact QP method significantly improves the compact QP method in terms of efficiency and effectiveness for the real-time control of redundant manipulators under physical limits.

In this paper, a closed-form formulation for inverse kinematics for redundant manipulators with inequality constraints has been proposed. This formulation has been derived by using the Kuhn-Tucker condition, the Lagrange multiplier method, and the active/working set method, so that its solution may satisfy the necessary and sufficient condition for optimization subject to equality and inequality constraints. From the formulation, computationally efficient kinematic control methods have been derived using differential kinematics and gradient projection method. The effectiveness of the proposed methods has been demonstrated with a 4-DOF planar manipulator, and then a 7-DOF spatial manipulator as a practical application to a nozzle dam task of a nuclear power plant.

Robot hybrid control has been noted for its difficulty due to so called dynamic stability problem, and consequently demands robust control algorithms that can overcome this difficulty, yet with accuracy. In this paper, a control law based on time delay control has been derived for hybrid control, with a condition for closed-loop stability. Throughout simulations and experiments, this control law was observed to outperform PD or PID control, thereby proposing itself as a promising one for the hybrid control purpose.>

A closed-form solution formula for inverse kinematics of manipulators with redundancy is derived using the Lagrangian multiplier method. The proposed method is proved to provide the exact equilibrium state for the resolved-motion method. The repeatability problem in the resolved-motion method does not exist in the proposed method. The method is demonstrated to give more accurate trajectories than the resolved-motion method.