Houman Dallali

WALK‐MAN: A High‐Performance Humanoid Platform for Realistic Environments

In this work, we present WALK-MAN, a humanoid platform that has been developed to operate in realistic unstructured environment, and demonstrate new skills including powerful manipulation, robust balanced locomotion, high-strength capabilities, and physical sturdiness. To enable these capabilities, WALK-MAN design and actuation are based on the most recent advancements of series elastic actuator drives with unique performance features that differentiate the robot from previous state-of-the-art compliant actuated robots. Physical interaction performance is benefited by both active and passive adaptation, thanks to WALK-MAN actuation that combines customized high-performance modules with tuned torque/velocity curves and transmission elasticity for high-speed adaptation response and motion reactions to disturbances. WALK-MAN design also includes innovative design optimization features that consider the selection of kinematic structure and the placement of the actuators with the body structure to maximize the robot performance. Physical robustness is ensured with the integration of elastic transmission, proprioceptive sensing, and control. The WALK-MAN hardware was designed and built in 11 months, and the prototype of the robot was ready four months before DARPA Robotics Challenge (DRC) Finals. The motion generation of WALK-MAN is based on the unified motion-generation framework of whole-body locomotion and manipulation (termed loco-manipulation). WALK-MAN is able to execute simple loco-manipulation behaviors synthesized by combining different primitives defining the behavior of the center of gravity, the motion of the hands, legs, and head, the body attitude and posture, and the constrained body parts such as joint limits and contacts. The motion-generation framework including the specific motion modules and software architecture is discussed in detail. A rich perception system allows the robot to perceive and generate 3D representations of the environment as well as detect contacts and sense physical interaction force and moments. The operator station that pilots use to control the robot provides a rich pilot interface with different control modes and a number of teleoperated or semiautonomous command features. The capability of the robot and the performance of the individual motion control and perception modules were validated during the DRC in which the robot was able to demonstrate exceptional physical resilience and execute some of the tasks during the competition.

Development of a dynamic simulator for a compliant humanoid robot based on a symbolic multibody approach

This paper reports on development of an open source dynamic simulator for the Compliant huMANoid robot, COMAN. The key advantages of this simulator are: it generates efficient symbolic dynamical equations of the robot with high degrees of freedom, it includes a user-defined model of the actuator dynamics (the passive elasticity and the DC motor equations), user defined ground models and fall detection. Users have the freedom to choose the proposed features or include their own models. The models are generated in Matlab and C languages, where the user can leverage the power of Matlab and Simulink to carry out analysis to parameter variations or optimization and also have the flexibility of C language for realtime experiments on a DSP or FPGA chip. The simulation and experimental results of the robot as well as an optimization example to tune the ground model coefficients are presented. This simulator can be downloaded from the IIT website [1].

Modelling human balance using switched systems with linear feedback control

We are interested in understanding the mechanisms behind and the character of the sway motion of healthy human subjects during quiet standing. We assume that a human body can be modelled as a single-link inverted pendulum, and the balance is achieved using linear feedback control. Using these assumptions, we derive a switched model which we then investigate. Stable periodic motions (limit cycles) about an upright position are found. The existence of these limit cycles is studied as a function of system parameters. The exploration of the parameter space leads to the detection of multi-stability and homoclinic bifurcations.

An asymmetric compliant antagonistic joint design for high performance mobility

This paper presents the design of a novel compliant joint for high performance mobility. The design principle of the joint is based on an asymmetric compliant antagonistic scheme which is actuated by two motors of different power capability and efficiency. Torques from the two motors are transmitted to the joint through two elastic elements of different stiffness and energy storage capacity. The proposed compliant joint design combines high power performance, large energy storage capacity and physical resilience all necessary features for performing high performance mobility such as agile locomotion. The paper introduces the principle of operation, the design and mechanical implementation of the joint. Preliminary experimental trials demonstrate the joint performance in a single degree of freedom leg prototype system.

Compliant antagonistic joint tuning for gravitational load cancellation and improved efficient mobility

This paper introduces the design tuning of a recently introduced compliant actuation scheme that was developed to provide large energy storage capacity and demonstrate energetic efficient operation. The joint is based on an asymmetric compliant antagonistic actuation scheme where torques from two motors are transmitted to the joint through two elastic elements of different stiffness level and energy storage capacity. The paper presents the method used to tune the joint compliance and shows how this can be used to select the passive elasticity of a single degree of freedom (DOF) hopping leg for improving its energetic efficiency. The design and modeling of the hopping leg are discussed and experimental results are presented to verify the improved efficiency of the leg, particularly the power and torque reduction benefits obtained under static postures or cyclic motions.

Designing a High Performance Humanoid Robot Based on Dynamic Simulation

In this paper, we present a study on dynamic simulation to assist designing a high performance compliant humanoid robot. An open source dynamic simulator is introduced which includes the rigid body and actuator dynamics of the full humanoid robot. A set of representative tasks for humanoid robot in rescue operations are chosen and simulated. The data from these tasks are used in sizing the motor and transmission gear for each joint of the robot. It is shown that in the representative tasks, the most critical joint of the robot (in terms of power consumption) is the knee joint. Furthermore, a recently proposed optimization method is used to obtain the value of passive compliance for each joint. The data obtained from simulation studies are used for designing the new humanoid robot.

On Global Optimization of Walking Gaits for the Compliant Humanoid Robot COMAN Using Reinforcement Learning

Abstract In ZMP trajectory generation using simple models, often a considerable amount of trials and errors are involved to obtain locally stable gaits by manually tuning the gait parameters. In this paper a 15 degrees of Freedom dynamic model of a compliant humanoid robot is used, combined with reinforcement learning to perform global search in the parameter space to produce stable gaits. It is shown that for a given speed, multiple sets of parameters, namely step sizes and lateral sways, are obtained by the learning algorithm which can lead to stable walking. The resulting set of gaits can be further studied in terms of parameter sensitivity and also to include additional optimization criteria to narrow down the chosen walking trajectories for the humanoid robot.

Robust and adaptive whole-body controller for humanoids with multiple tasks under uncertain disturbances

This paper focuses on the development of a dynamic model-free whole-body controller for a humanoid robot with high kinematic redundancy. The proposed controller is based on force-level operational-space control framework, which computes joint torques for the required forces of prioritized multiple tasks. While typical approaches based on this framework require to obtain an accurate robot dynamics model, which has been generally recognized as a major hurdle to overcome for implementation in real humanoid robots, the proposed controller incorporates adaptive sliding-mode and online dynamics estimation schemes; thus, it can be easily realized on a humanoid without identifying complex robot dynamic parameters. As a result, the gains of the proposed controller are adaptively adjusted to assure the control accuracy, when the humanoid robot changes its posture and undergoes uncertain disturbances. Experiments with a 23-DoFs humanoid under uncertain disturbances verify that the proposed controller can robustly perform multiple tasks with high accuracy.

A passivity based compliance stabilizer for humanoid robots

This paper presents a passivity based compliance stabilizer for humanoid robots. The proposed stabilizer is an admittance controller that uses the force/torque sensing in feet to actively regulate the compliance for the position controlled system. The low stiffness provided by the stabilizer permits compliant interaction with external forces, and the active damping control guarantees the passivity by dissipating the excessive energy delivered by disturbances. Both the theoretical work and simulation validations are presented. The effectiveness of the stabilizer is demonstrated by the simulations of a simplified cart-table model and the multi-body model of a humanoid under impulsive/periodic force perturbations during standing and walking in place. Simulation data show the quantitative evaluation of the stabilization effect by comparing the responses of body attitude, center of mass, center of pressure without and with the stabilizer.

Can active impedance protect robots from landing impact

This paper studies the effect of passive and active impedance for protecting jumping robots from landing impacts. The theory of force transmissibility is used for selecting the passive impedance of the system to minimize the shock propagation. The active impedance is regulated online by a joint-level controller. On top of this controller, a reflex-based leg retraction scheme is implemented which is optimized using direct policy search reinforcement learning based on particle filtering. Experiments are conducted both in simulation and on a real-world hopping leg. We show that although the impact dynamics is fast, the addition of passive impedance provides enough time for the active impedance controller to react to the impact and protect the robot from damage.