Sang-Rok Oh

Disturbance observer based force control of robot manipulator without force sensor

In this paper, a force estimation method is proposed for force control without force sensor. A disturbance observer is applied to each joint of an n degrees of freedom manipulator to obtain a simple equivalent robot dynamics being represented as an n independent double integrator system. To estimate the output of disturbance observer due to internal torque, the disturbance observer output estimator (DOOE) is designed, where uncertain parameters of the robot manipulator are adjusted by the gradient method to minimize the performance index which is defined as the quadratic form of the error signal between the output of disturbance observer and that of DOOE. When the external force is exerted, the external force is estimated by the difference between the output of disturbance observer and DOOE. A force controller is designed for force feedback control employing the estimated force signal. Several numerical examples and experimental results are illustrated for a 2-axis direct drive robot manipulator.

A stable target-tracking control for unicycle mobile robots

This paper deals with target tracking control of unicycle type mobile robots. Target tracking function is essential for autonomous robots such as guide robots, security guard robots, etc. In the field of mobile robot control, many control schemes for posture stabilization and trajectory tracking problem have been proposed. Target tracking control, however, cannot be achieved using these kinds of control laws. Therefore, a new global asymptotic stable controller for this problem is designed using the backstepping method. The stability of the system is proved using the Lyapunov function. Various simulation results validate the performance and theoretical analysis.

On the stability of indirect ZMP controller for biped robot systems

This paper proposes the indirect zero momentum position (ZMP) controller for biped robot systems and proves its disturbance input-to-state stability (ISS). The ZMP control has been used as a standard method for stable walking control of biped robot systems. Since the ZMP information consists of position and acceleration of the center of gravity (COG) for a biped robot system, the ZMP can be indirectly controlled by the motion of COG. In this paper, the reference COG planner is developed by solving the reference ZMP differential equation. The indirect ZMP controller is proposed to derive the desired motion of COG from the reference ZMP trajectory and the COG error (the difference between the reference and real COG). The ISS of the proposed indirect ZMP controller is proved for the simplified biped robot model. The robustness of the proposed indirect ZMP controller is shown in simulation.

Stable whole-body motion generation for humanoid robots to imitate human motions

This work presents a methodology to generate dynamically stable whole-body motions for a humanoid robot, which are converted from human motion capture data. The methodology consists of the kinematic and dynamical mappings for human-likeness and stability, respectively. The kinematic mapping includes the scaling of human foot and Zero Moment Point (ZMP) trajectories considering the geometric differences between a humanoid robot and a human. It also provides the conversion of human upper body motions using the method in [1]. The dynamic mapping modifies the humanoid pelvis motion to ensure the movement stability of humanoid whole-body motions, which are converted from the kinematic mapping. In addition, we propose a simplified human model to obtain a human ZMP trajectory, which is used as a reference ZMP trajectory for the humanoid robot to imitate during the kinematic mapping. A human whole-body dancing motion is converted by the methodology and performed by a humanoid robot with online balancing controllers.

A framework for Internet-based interaction of humans, robots, and responsive environments using agent technology

In this paper, a systematic framework for Internet-based interaction of humans, robots, and environments is proposed by using agent technology. The framework is validated by proposing the concept of slave agents, a virtual directory facilitator (VDF) to control the slave agents, and a responsive multiagent environment. It creates a robot control system in which humans, robots, and environments can interact without much prior knowledge. Finally, a number of experiments have been conducted successfully by adopting JadeLeap middleware and Foundation for Intelligent Physical Agents (FIPA) standard under the environment composed of a personal digital assistant (PDA), a home service robot-intelligent, sweeping security assistant companion (ISSAC), and a video camera network. Experimental results show that the proposed framework increases the availability of whole system, decreases the time for Internet connection of robots and user devices such as PDAs, and provides the responsiveness of environments.

Non-dimensionalized performance indices based optimal grasping for multi-fingered hands

Abstract When a multi-fingered hand grasps an object, the ways to grasp it stably are infinite, and thus an optimal grasp planning is necessary to find the relatively optimized grasp points on object for achieving the objective of the given grasping and manipulating task. For this, we first define several grasp indices to evaluate the quality of each feasible grasp. Since the physical meanings of the defined grasp indices are different from each other, it is not easy to combine those indices to identify the optimal grasping. Thus, we propose a new generalized grasping performance index to represent all of the grasp indices as one measure based on a non-dimensionalizing technique. Next, by using the proposed grasping performance index, we try to determine the optimal grasp points for multi-fingered hands performing contact tasks. Through task-based simulation studies, we discuss the feasibility of each grasp index as the grasp polygons and then, we show that the trend of the proposed optimal grasp planning is coincident to the physical sense of human grasping. Furthermore, some experimental results showing the task specific performances are incorporated to corroborate the effectiveness of the proposed optimal grasp planning algorithms.

Optimal grasping based on non-dimensionalized performance indices

For a multi-fingered hand to grasp an object, there are numerous ways to grasp it stably, and thus an optimal grasp planning is necessary to find the optimal grasp point for achieving the objective of the given task. First, we define several grasp indices to evaluate the quality of each feasible grasp. Since the physical meanings of the defined grasp induces are different from each other, it is not easy to combine those indices to identify the optimal grasping. In this paper, we propose a new generalized grasping performance index to represent all of the grasp indices as one measure based on a non-dimensional technique. Through simulations, we show that the proposed optimal grasp planning is resemblant to the physical sense of human grasping.

A five-bar finger mechanism involving redundant actuators: analysis and its applications

A five-bar finger mechanism driven by redundant actuators is given as an illustrative example. It is shown that judicial choice of the location of one redundant actuator greatly enhances the load handling capacity of the system, when compared to those of minimum actuation and more than two redundant actuators. Also, methodologies for stiffness and motion frequency modulations via redundant actuation are investigated. Internal load distribution associated with the stiffness and motion frequency modulations is further discussed. Specifically, the motion frequency of the system is modulated by employing inertial and spring-like impedance properties created by internal loading. The motion frequency as well as the amplitude of oscillation can be actively adjusted during the motion, and the equilibrium position about which the vibration occurs can also be arbitrarily changed during the motion. Furthermore, using the stiffness modulation capability, a point-to-point motion can be accomplished by a progressive movement of equilibrium posture, which is called a virtual trajectory. To show the effectiveness of the proposed algorithms, several simulation results are illustrated.

Optimal design and development of a five-bar finger with redundant actuation

In order to develop a human hand mechanism, a five-bar finger with redundant actuation is designed and implemented. Each joint of the finger is driven by a compact actuator mechanism having an ultrasonic motor and a gear set with a potentiometer, and controlled by a VME bus-based control system. Optimal sets of actuator locations and link lengths for cases of a minimum actuator, one-, two-, and three-redundant actuators are obtained by employing a composite design index which simultaneously considers several performance indices, such as workspace, isotropic index, and force transmission ratio. According to the optimization result, several finger-configurations optimized for a special performance index are illustrated, and it is concluded that the case of one redundant actuator is the most effective in comparison to the cases of more redundant actuators, and that the case of two redundant actuators is the most effective in multi-fingered operation in which the force characteristic is relatively important, as compared to the kinematic isotropy and the workspace of the system.

Optimal design of a five-bar finger with redundant actuation

In order to develop a human hand mechanism, a 5-bar finger with redundant actuation is suggested. Optimal sets of actuator locations and link lengths for the cases of minimum actuator, one, two and three redundant actuators are obtained by employing composite design index which simultaneously consider several performance indices such as workspace, isotropic index, and force transmission ratio. Finally, several finger-configurations optimized for special performance indices are illustrated.