Seung-kook Yun

Momentum-based reactive stepping controller on level and non-level ground for humanoid robot push recovery

This paper presents a momentum-based reactive stepping controller for humanoid robot push recovery. By properly regulating combinations of linear and angular momenta, the controller can selectively encourage the robot to recover its balance with or without taking a step. A reference stepping location is computed by modeling the humanoid as a passive rimless wheel with two spokes such that stepping on the location leads to a complete stop of the wheel at the vertically upright position. In contrast to most reference points for stepping based on pendulum models such as the capture point, our reference point exists on both level and non-level grounds. Moreover, in contrast with continuously evolving step locations, our step location is stationary. The computation of the location of the reference point also generates the duration of step which can be used for designing a stepping trajectory. Momentum-based stepping for push recovery is implemented in simulations of a full size humanoid on 3D non-level ground.

Safe fall: Humanoid robot fall direction change through intelligent stepping and inertia shaping

Although fall is a rare event in the life of a humanoid robot, we must be prepared for it because its consequences are serious. In this paper we present a fall strategy which rapidly modifies the robots fall direction in order to avoid hitting a person or an object in the vicinity. Our approach is based on the key observation that during “toppling” the rotational motion of a robot necessarily occurs at the leading edge or the leading corner of its support base polygon. To modify the fall direction the robot needs to change the position and orientation of this edge or corner vis-a-vis the prohibited direction. We achieve it through intelligent stepping as soon as a fall is detected. We compute the optimal stepping location which results in the safest fall. Additional improvement to the fall controller is achieved through inertia shaping techniques aimed at controlling the centroidal inertia of the robot. We demonstrate our results through the simulation of an Asimo-like humanoid robot. To our knowledge, this is the first implementation of a controller that attempts to change the fall direction of a humanoid robot.

Adaptive Coordinating Construction of Truss Structures Using Distributed Equal-Mass Partitioning

This paper presents a decentralized algorithm for the coordinated assembly of 3-D objects that consist of multiple types of parts, using a networked team of robots. We describe the algorithm and analyze its convergence and adaptation properties. We partition construction in two tasks: tool delivery and assembly. Each task is performed by a networked team of specialized robots. We analyze the performance of the algorithms using the balls into bins problem and show their adaptation to failure of robots, dynamic constraints, multiple types of elements, and reconfiguration. We instantiate the algorithm to building truss-like objects using rods and connectors. We implement the algorithm in simulation and show results to construct 2-D and 3-D parts. Finally, we describe hardware implementation of the algorithms, where mobile manipulators assemble smart parts with IR beacons.

Compliant manipulation for peg-in-hole: Is passive compliance a key to learn contact motion?

We examine the usefulness of passive compliance in a manipulator that learns contact motion. Based on the notice that humans outperforms robots with the contact motion, we follow two aspects of human manipulation: passive compliance and learning. As imitation of humans arm and learning, we use a robot arm with passive compliant joints and it learns a policy for peg in hole by the proposed gradient descending method. We present that the passive compliance provides with quick and stable learning as well as a slow control sampling time.

Self-assembling mobile linkages

Self-reconfiguring robots are modular robot systems that are physically connected and capable of making different geometric structures. Most current research in this field is focused on homogeneous systems in which all the modules are identical. This article explores the concept of self-assembling robot systems consisting of passive structural modules plus active robotic modules.

Adaptation to robot failures and shape change in decentralized construction

Our prior work [1] presented a decentralized algorithm for coordinating the construction of a truss structure out of multiple components. In this paper, we discuss adaptation in decentralized construction. We partition construction in two tasks, tool delivery and assembly. Each task is performed by a networked team of specialized robots. We analyze the performance of the algorithms using the balls into bins problem, and show their adaptation to failure of robots, dynamic constraints, multiple types of elements and reconfiguration. The algorithms can be used for general types of source elements.

Experiments in decentralized robot construction with tool delivery and assembly robots

Our prior work [1] presented a decentralized algorithm for coordinating the construction of truss shaped objects out of multiple components (rods and connectors). In this paper, we consider how to transfer the theory to practice, implementing the algorithm to create a decentralized multi robot construction system. The system is composed of mobile manipulators and smarts parts with an embedded communication device. We discuss the delivery and assembly algorithms that comprise this system and the assumptions behind them. We present data from extensive hardware experiments with 4 robots coordinating an assembly task.

Safe Arm Design with MR - based Passive Compliant Joints and Visco - elastic Covering for Service Robot Applications

In this paper a safe arm with passive compliant joints and visco—elastic covering is designed for human-friendly service robots. The passive compliant joint (PCJ) is composed of a magnetorheological (MR) damper and a rotary spring. In addition to a spring component, a damper is introduced for damping effect and works as a rotary viscous damper by controlling the electric current according to the angular velocity of spring displacement. When a manipulator interacts with human or environment, the joints and cover passively operate and attenuate the applied collision force. The force attenuation property is verified through collision experiments showing that the proposed passive arm is safe in view of some evaluation measures.

Planning the reconfiguration of grounded truss structures with truss climbing robots that carry truss elements

In this paper we describe an optimal reconfiguration planning algorithm that morphs a grounded truss structure of known geometry into a new geometry. The plan consists of a sequence of paths to move truss elements to their new locations that generate the new truss geometry. The trusses are grounded and remain connected at all time. Intuitively, the algorithm grows gradually the new truss structure from the old one. The truss elements are rigid bars joined with 18-way connectors. The paper also introduces the design of a truss-climbing robot that can execute the plan.

Self assembly of modular manipulators with active and passive modules

We describe self-assembling robot arm systems composed of active modular robots and passive bars. We present a case study where the robotic module is the Shady3D robot and the passive component is a rigid bar with embedded IR LEDs. We propose algorithms that demonstrate the cooperative aggregation of modular robotic manipulators with greater capability and workspace out of these two types of elements. We present results from physical experiments in which two 3DOF Shady3D robots and one rigid bar coordinate to self-assemble into a 6DOF manipulator. We then demonstrate cooperative algorithms for forward and inverse kinematics, grasping, and mobility with this arm.