François Keith

Dynamic Whole-Body Motion Generation Under Rigid Contacts and Other Unilateral Constraints

The most widely used technique for generating whole-body motions on a humanoid robot accounting for various tasks and constraints is inverse kinematics. Based on the task-function approach, this class of methods enables the coordination of robot movements to execute several tasks in parallel and account for the sensor feedback in real time, thanks to the low computation cost. To some extent, it also enables us to deal with some of the robot constraints (e.g., joint limits or visibility) and manage the quasi-static balance of the robot. In order to fully use the whole range of possible motions, this paper proposes extending the task-function approach to handle the full dynamics of the robot multibody along with any constraint written as equality or inequality of the state and control variables. The definition of multiple objectives is made possible by ordering them inside a strict hierarchy. Several models of contact with the environment can be implemented in the framework. We propose a reduced formulation of the multiple rigid planar contact that keeps a low computation cost. The efficiency of this approach is illustrated by presenting several multicontact dynamic motions in simulation and on the real HRP-2 robot.

Exploring humanoid robots locomotion capabilities in virtual disaster response scenarios

We study the feasibility of having various humanoid robots undertake some tasks from those challenged by the DARPAs call on disaster operations. Hence, we focus on locomotion tasks that apparently require human-like motor skills to be achieved. We use virtual scenes under the fully-3D-modeled-environment assumption. The robot autonomously plans and executes the motion with a high-level goal specification, such as reaching a global position or a particular contact state. We assess the feasibility according not only to the robot kinematics, but also to whole-body dynamics, non-desired collision avoidance, friction limits, and actuation limits. The results -the controlled motions- are demonstrated in the accompanying video.

Generation of dynamic motion for anthropomorphic systems under prioritized equality and inequality constraints

In this paper, we propose a solution to compute full-dynamic motions for a humanoid robot, accounting for various kinds of constraints such as dynamic balance or joint limits. As a first step, we propose a unification of task-based control schemes, in inverse kinematics or inverse dynamics. Based on this unification, we generalize the cascade of quadratic programs that were developed for inverse kinematics only. Then, we apply the solution to generate, in simulation, whole-body motions for a humanoid robot in unilateral contact with the ground, while ensuring the dynamic balance on a non horizontal surface.

Proactive behavior of a humanoid robot in a haptic transportation task with a human partner

In this paper, we propose a control scheme that allows a humanoid robot to perform a complex transportation scenario jointly with a human partner. At first, the robot guesses the human partners intentions to proactively participate to the task. In a second phase, the human-robot dyad switches roles: the robot takes over the leadership of the task to complete the scenario. During this last phase, the robot is remotely controlled with a joystick. The scenario is realized on a real HRP-2 humanoid robot to assess the overall approach.

Human-humanoid haptic joint object transportation case study

In this paper, we propose a control scheme that allows a humanoid robot to perform a transportation task jointly with a human partner. From the study of how human dyads achieve such a task, we have developed a control law for physical interaction that unifies standalone and collaborative (leader and follower) modes for trajectory-based tasks. We present it in the case of a linear impedance controller but it can be generalized to more complex impedances. Desired trajectories are decomposed into sequences of elementary motion primitives. We implemented this model with a Finite State Machine associated with a reactive pattern generator. First experiments conducted on a real HRP-2 humanoid robot assess the overall approach.

Multi-contact vertical ladder climbing with an HRP-2 humanoid

We describe the research and the integration methods we developed to make the HRP-2 humanoid robot climb vertical industrial-norm ladders. We use our multi-contact planner and multi-objective closed-loop control formulated as a QP (quadratic program). First, a set of contacts to climb the ladder is planned off-line (automatically or by the user). These contacts are provided as an input for a finite state machine. The latter builds supplementary tasks that account for geometric uncertainties and specific grasps procedures to be added to the QP controller. The latter provides instant desired states in terms of joint accelerations and contact forces to be tracked by the embedded low-level motor controllers. Our trials revealed that hardware changes are necessary, and parts of software must be made more robust. Yet, we confirmed that HRP-2 has the kinematic and power capabilities to climb real industrial ladders, such as those found in nuclear power plants and large scale manufacturing factories (e.g. aircraft, shipyard) and construction sites.

Framework for haptic interaction with virtual avatars

In this paper we present an integrative frame work centered on haptic interaction with virtual avatars. This framework is devised for general prototyping and collaborative scenario studies with haptic feedback. First we present the software architecture of the framework and give details on some of its components. Then we show how this framework can be used to derive in a short time a virtual reality simulation. In this simulation, a user directly interacts with a virtual avatar to collaboratively manipulate a virtual object, with haptic feedback and using fast dynamics computation and constraint based methods with friction.

Vertical ladder climbing by the HRP-2 humanoid robot

We report the results obtained from our trials in making the HRP-2 humanoid robot climb vertical industrial-norm ladders. We integrated our multi-contact planner and multi-objective QP control as basic components. First, a set of contacts to climb the ladder is planned off-line and provided as an input for a finite state machine that sequences tasks to be realized by our multi-objective model-based QP in closed-loop control. The trials we made revealed that hardware changes are to be made on the HRP-2, and the software has to be made more robust. Yet, we confirmed that HRP-2 has power capability to climb real industrial ladders, such as those found in nuclear power plants and large scale manufacturings (e.g. airliners, shipyards and buildings).

Optimization of tasks warping and scheduling for smooth sequencing of robotic actions

This paper presents a method for sequencing a set of robotic tasks in an optimal way. Tasks description and execution are based on the task-function approach, which enables to build complex whole-body behaviors from local control laws. A naive solution to this problem would be to schedule the execution of the tasks sequentially, avoiding concurrency. This solution does not exploit full robot capabilities such as redundancy and have poor performance in terms of execution time or energy. However, reasoning on concurrent tasks is difficult while accounting for all the physical constraints of the robot. Our contribution is to determine the time-optimal realization of the mission taking into account robotic constraints that may be as complex as collision avoidance. Our approach achieves more than a simple scheduling; its originality lies in maintaining the task approach in the formulated optimization of the task sequencing problem. This theory is exemplified through a complete experiment on the real HRP-2 robot.

Compliant control of a humanoid robot helping a person stand up from a seated position

Supporting somebody while standing up from a seated position is one of the most frequent tasks envisaged for a humanoid assistant used in order to help somebody with reduced mobility around the house. The safest way to do this for a human carer has been clearly defined in patient handling guides for hospitals where a policy of never lifting the patient is strongly recommended. Based on these guidelines, this paper proposes a stable initial posture for a humanoid robot supporting a person from sitting to standing, as well as a control law to make the robot keep a contact force and follow the motion of the person compliantly. This initial position and compliant control of the robot was implemented and tested on the humanoid HRP-4 interacting with a healthy subject.