Enrico Mingo Hoffman

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.

OpenSoT: A whole-body control library for the compliant humanoid robot COMAN

A fundamental aspect of controlling humanoid robots lies in the capability to exploit the whole body to perform tasks. This work introduces a novel whole body control library called OpenSoT. OpenSoT is combined with joint impedance control to create a framework that can effectively generate complex whole body motion behaviors for humanoids according to the needs of the interaction level of the tasks. OpenSoT gives an easy way to implement tasks, constraints, bounds and solvers by providing common interfaces. We present the mathematical foundation of the library and validate it on the compliant humanoid robot COMAN to execute multiple motion tasks under a number of constraints. The framework is able to solve hierarchies of tasks of arbitrary complexity in a robust and reliable way.

Yarp Based Plugins for Gazebo Simulator

This paper presents a set of plugins for the Gazebo simulator that enables the interoperability between a robot, controlled using the YARP framework, and Gazebo itself. Gazebo is an open-source simulator that can handle different Dynamic Engines developed by the Open Source Robotics Foundation. Since our plugins conform with the YARP layer used on the real robot, applications written for our robots, COMAN and iCub, can be run on the simulator with no changes. Our plugins have two main components: a YARP interface with the same API as the real robot interface, and a Gazebo plugin which handles simulated joints, encoders, IMUs, force/torque sensors and synchronization. Different modules and tasks for COMAN and iCub have been developed using Gazebo and our plugins as a testbed before moving to the real robots.

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.

A Modular Approach for Remote Operation of Humanoid Robots in Search and Rescue Scenarios

In this work we present a modular, robust and user-friendly Pilot Interface meant to control humanoid robots in rescue scenarios during dangerous missions.

Efficient self-collision avoidance based on focus of interest for humanoid robots

This paper deals with the self-collision avoidance problem for humanoid robots in an efficient way. Self-collision avoidance is introduced as a constraint for each task in a hierarchical Inverse Kinematic (IK) problem. Since the number of link pairs which needs to be updated and checked for self-collision, in every control loop, is large, the novel concept of Self-Collision Avoidance Focus of Interest (SCAFoI) is proposed. SCAFoIs permits to predict and dynamically select the necessary link pairs to be checked online to improve the computation efficiency. For each of the several SCAFoIs, which corresponds to the related pairs of kinematic chains of the whole body, the status of the relative positional relationship is predicted. The prediction is done using a Support Vector Machine (SVM) which is a widely used classifier from the machine learning field. Moreover, techniques are proposed to guarantee and improve the prediction performance of the trained classifier. The effectiveness of the framework is verified using the whole-body motion control library OpenSoT by simulation on the model of the recently developed humanoid robot WALK-MAN.

XBotCore: A Real-Time Cross-Robot Software Platform

In this work we introduce XBotCore (Cross-Bot-Core), a light-weight, Real-Time (RT) software platform for EtherCAT-based robots. XBotCore is open-source and is designed to be both an RT robot control framework and a software middleware. It satisfies hard RT requirements, while ensuring 1 kHz control loop even in complex Multi-Degree-Of-Freedom systems. It provides a simple and easy-to-use middleware Application Programming Interface (API), for both RT and non-RT control frameworks. This API is completely flexible with respect to the framework a user wants to utilize. Moreover it is possible to reuse the code written using XBotCore API with different robots (cross-robot feature). In this paper, the XBotCore design and architecture will be described and experimental results on the humanoid robot WALK-MAN [17], developed at the Istituto Italiano di Tecnologia (IIT), will be presented.

Robot Dynamics Constraint for Inverse Kinematics

Inverse Kinematics is a fundamental tool in Cartesian/Operational Space control. Recent approaches make use of Quadratic Programming Optimization to obtain desired joint velocities or accelerations from Cartesian references. QP based IK also permits to specify constraints to affect the solution. Constraints are fundamental and necessary when working with real robotic hardware since they prevent possible damages: joint limits, self collision avoidance and joint velocity limits are examples of such constraints. In this work we present a constraint to take into account joint torque limits based on the robot dynamics and force/torque sensor measurements. Despite the robot dynamics can be naturally expressed at acceleration level, our main goal is to specify this constraint in a resolved motion rate control IK. For this reason we formulate it also at the velocity level to be used in any IK QP based scheme. Hence, this formulation allows to generate dynamically feasible motions of the robot even in simple IK velocity based schemes. We apply this constraint to our humanoid robot COMAN while performing a Cartesian task which requires high torques in some joints. The constraint is developed inside the OpenSoT library.

An affordance-based pilot interface for high-level control of humanoid robots in supervised autonomy

In this work we present the concept of a pilot interface to control a humanoid robot on an abstract level in unknown environments. The environment is perceived with a stereo camera system and then simplified into a set of environmental primitives. Based on these primitives the interface proposes affordances to the pilot. Affordances are represented as certainty functions over the space of end-effector poses. The pilot operates the robot by selecting among proposed affordances and related action primitives, i.e. Object-Action Complexes (OACs). Before initiating execution, the pilot can review and revise the parameterization of the scheduled action primitive in a 3D reconstruction of the environment. The pilot interface proposed in this work has been implemented and evaluated on the humanoid robot WALK-MAN. With this work we also demonstrate the transferability of the perceptual concept, as our previous experiments have been performed using the humanoid robot ARMAR-III.

Upper limb compliant strategy exploiting external physical constraints for humanoid fall avoidance

Ensuring humanoid balance stability to prevent falling is one of the most crucial control problems in humanoid robotics and has been extensively studied in the past, resulting in a diverse range of balance recovery schemes. These balancing control methods effectively perform body posture control using three main motion strategies, namely: ankle, ankle-hip and stepping strategies. In this work we present a novel balance strategy which fundamentally differs from the previous methods as its principle is to exploit contacts with the environment to prevent falling rather than only performing body posture control. An uncoupled impedance controller for the upper body of the humanoid robot is combined with a lower body stabilizer, and the balancing capabilities are enhanced by the establishment of additional physical contacts with the environment. The generation of the reactive arm motion and the impedance regulation are discussed in details. Experimental trials with the humanoid robot COMAN, provided with active and passive compliance, demonstrate the potential of the approach and the first step towards the development of more human-like balancing skills using an integrated approach where all body parts (not only legs but also arms and hands) can establish contacts with the surrounding environment so as to ensure a stable and balanced behavior.