Yonghwan Oh

Posture/Walking Control for Humanoid Robot Based on Kinematic Resolution of CoM Jacobian With Embedded Motion

This paper proposes the walking pattern generation method, the kinematic resolution method of center of mass (CoM) Jacobian with embedded motions, and the design method of posture/walking controller for humanoid robots. First, the walking pattern is generated using the simplified model for bipedal robot. Second, the kinematic resolution of CoM Jacobian with embedded motions makes a humanoid robot balanced automatically during movement of all other limbs. Actually, it offers an ability of whole body coordination to humanoid robot. Third, the posture/walking controller is completed by adding the CoM controller minus the zero moment point controller to the suggested kinematic resolution method. We prove that the proposed posture/walking controller brings the disturbance input-to-state stability for the simplified bipedal walking robot model. Finally, the effectiveness of the suggested posture/walking control method is shown through experiments with regard to the arm dancing and walking of humanoid robot.

Disturbance-observer-based motion control of redundant manipulators using inertially decoupled dynamics

In this paper, a robust motion control method for kinematically redundant manipulators is addressed to control the motion of the end-effector, as well as the null-space motion. To reduce the disturbance effects on the system performance, a new disturbance observer is proposed to improve the performance of the conventional structure. A minimal parametrization of the null space is performed to visualize the null-space motion explicitly using the weighted decomposition of joint space. Augmenting this null motion with conventional velocity relations, an extended task space formulation is obtained. The proposed disturbance observer is adopted in the extended task space formulation and a motion control method is devised based on the passivity concept. The performance of the proposed controller is verified through experiments with a three-link planar direct-drive manipulator.

CPG based self-adapting multi-DOF robotic arm control

Recently, biologically inspired control approaches for robotic systems that involve the use of central pattern generators (CPGs) have been attracting considerable attention owing to the fact that most humans or animals move and walk easily without explicitly controlling their movements. Furthermore, they exhibit natural adaptive motions against unexpected disturbances or environmental changes without considering their kinematic configurations. Inspired by such novel phenomena, this paper endeavors to achieve self-adapting robotic arm motion. For this, biologically inspired CPG based control is proposed. In particular, this approach deals with crucial problems such as motion generation and repeatability of the joints emerged remarkably in most of redundant DOF systems. These problems can be overcome by employing a control based on artificial neural oscillators, virtual force and virtual muscle damping instead of trajectories planning and inverse kinematics. Biologically inspired motions can be attained if the joints of a robotic arm are coupled to neural oscillators and virtual muscles. We experimentally demonstrate self-adaptation motions that that enables a 7-DOF robotic arm to make adaptive changes from the given motion to a compliant motion. In addition, it is verified with real a real robotic arm that human-like movements and motion repeatability are satisfied under kinematic redundancy of joints.

Real-Time Walking Pattern Generation Method for Humanoid Robots by Combining Feedback and Feedforward Controller

This paper focuses on real-time walking pattern generation for humanoid robots with linear inverted pendulum model (LIPM). In general, there are many issues in generating proper walking patterns of center of mass and zero moment point (ZMP) with the LIPM since the LIPM has two drawbacks such as instability and non-minimum phase property. For resolving these difficulties, the paper proposes a new real-time approach by combining a feedback and a feedforward controller. The feedback controller employs a pole placement method which shifts the poles of the LIPM in order to improve system stability. The feedforward controller utilizes advanced pole-zero cancelation by series approximation method (APZCSA) for reducing non-minimum phase property which occurs by an unstable zero and is not able to be dealt with by the feedback controller. In addition, the APZCSA improves the tracking error induced by finite series approximation. Using the two controllers, the proposed method makes the transfer function of overall walking pattern generation system approximately unity and consequently generates a stable walking pattern which follows a desired ZMP according to walking path. The efficiency of the proposed method is verified by walking pattern planning examples and experiments with the humanoid robot MAHRU-R.

Dependable Humanoid Navigation System Based on Bipedal Locomotion

In this paper, a dependable humanoid navigation system is proposed by considering many difficulties in humanoid navigation based on bipedal locomotion in an uncertain environment. In particular, we propose a layered architecture to resolve complicated problems through a hierarchical manner. Within the proposed software architecture, a walking path planner, a walking footstep planner, and a walking pattern generator are integrated in a hierarchy to create a reliable motion that overcomes foot slippage and localization sensor noise. Each layer is designed to overcome difficulties originating from bipedal locomotion such as unstable dynamics, inclusion of a sinusoidal noise component in the localization sensor measurement, and disturbance regarding discrete footstepping. The designed navigation system is implemented on a human-sized experimental humanoid platform and is tested for the evaluation of its reliability and robustness in various tasks.

Extended impedance control of redundant manipulators using joint space decomposition

An impedance control approach based on extended task space formulation is addressed to control the kinematically redundant manipulators. Defining a weighted inner product in joint space, a minimal parametrization of the null space can be achieved. Based on this formulation, we propose a control law called inertially decoupled impedance controller by expanding the conventional impedance control approach to control the motion of the end-effector as well as the internal motion. Some numerical simulations are given to demonstrate the performance of the proposed control methods.

An Analytical Method to Generate Walking Pattern of Humanoid Robot

An analytic method to generate the real-time trajectory of the center of mass (CoM) is proposed for given zero moment point (ZMP) pattern. The whole walking process is divided into transient and periodic walking phases. For each phase of walking, we compute the analytic solution of the center of mass for given ZMP based on the inverted pendulum model. Specially, for the transient walking phase, we actively utilize the non-minimum phase solution to extract the center of mass trajectory. The proposed pattern generation method were implemented to a real humanoid robot system called by MAHRUII. Those are verified by the experiments.

Motion/force decomposition of redundant manipulator and its application to hybrid impedance control

An approach to resolve the kinematic redundancy and to control the motion/force of redundant manipulators is presented. By defining a proper metric in joint space, minimal parametrization of motion and force controlled subspaces as well as the null motion component is realized. With this formulation, control of both motion/force and internal motion of redundant manipulator can be achieved via a new hybrid impedance control method with inertial decoupling of each space. Some numerical examples are given to demonstrate the performance of the proposed control method.

Walking Control of a Humanoid Robot via Explicit and Stable CoM Manipulation with the Angular Momentum Resolution

This paper presents a walking algorithm for bipedal humanoid robots in the motion-embedded CoM Jacobian framework with angular momentum resolution. Walking constraints in the previous resolved momentum control framework are reformulated to utilize motion-embedded CoM Jacobian and reduce computational complexity. In this method, the conventional linear momentum control is replaced by the explicit CoM manipulation and the angular momentum equation only is used for upper body motion resolution without any other subject variables; whole body cooperative motions are completed with the walking constraints expressed by motion-embedded CoM Jacobian. The conventional resolved momentum control is able to play a more unified framework role owing to this method and lose computational weight while making compatibility with the motion-embedded CoM Jacobian framework. Validity and walking stability are demonstrated by the experiment on the real robot, MAHRU-II

Balance control in whole body coordination framework for biped humanoid robot MAHRU-R

This paper presents balance and vibration control algorithm for bipedal humanoid robots in the motion embedded CoM Jacobian framework. The vibration control is employed during a single supporting phase, which can suppress residual vibration of the un-modelled flexibility. Because the previously proposed walking control method in the resolved momentum control framework is based on the rigid body motion, vibration control algorithm which compensates for residual vibration can make the humanoid motion into rigid body motion. The vibration control consists of the modified global planning CoM trajectory and modified ankle joint controller in the motion embedded CoM Jacobian framework. The parameters of the controller are acquired easily using Matlab system identification tool box. Also, balance control algorithm which controls body orientation is applied to the whole body coordination framework. By dynamic walking experiments using a humanoid robot MAHRU-R, the validity of the proposed control methods is verified.