To improve biped locomotion’s robustness to internal and external disturbances, this study proposes a hierarchical structure with three control levels. At the high level, a foothold sequence is ...generated so that the Center of Mass (CoM) trajectory tracks a planned path. The planning procedure is simplified by selecting the midpoint between two consecutive Center of Pressure (CoP) points as the feature point. At the middle level, a novel robust hybrid controller is devised to drive perturbed system states back to the nominal trajectory within finite cycles without chattering. The novelty lies in that the hybrid controller is not subject to linear CoM dynamic constraints. The hybrid controller consists of two sub-controllers: an oscillation controller and a smoothing controller. For the oscillation controller, the desired CoM height is specified as a sine-shaped function, avoiding a new attractive limit cycle. However, this controller results in the inevitable chattering because of discontinuities. A smoothing controller provides continuous properties and thus can inhibit the chattering problem, but has a smaller region of attraction compared with the oscillation controller. A hybrid controller merges the two controllers for a smooth transition. At the low level, the desired CoM motion is defined as tasks and embedded in a whole body operational space (WBOS) controller to compute the joint torques analytically. The novelty of the low-level controller lies in that within the WBOS framework, CoM motion is not subject to fixed CoM dynamics and thus can be generalized.
This paper proposes an online gain adaptation approach to enhance the robustness of whole-body control (WBC) framework for legged robots under unknown external force disturbances. Without properly ...accounting for external forces, the closed-loop control system incorporating WBC may become unstable, and therefore the desired task goals may not be achievable. To study the effects of external disturbances, we analyze the behavior of our current WBC framework
the use of both full-body and centroidal dynamics. In turn, we propose a way to adapt feedback gains for stabilizing the controlled system automatically. Based on model approximations and stability theory, we propose three conditions to ensure that the adjusted gains are suitable for stabilizing a robot under WBC. The proposed approach has four contributions. We make it possible to estimate the unknown disturbances without force/torque sensors. We then compute adaptive gains based on theoretic stability analysis incorporating the unknown forces at the joint actuation level. We demonstrate that the proposed method reduces task tracking errors under the effect of external forces on the robot. In addition, the proposed method is easy-to-use without further modifications of the controllers and task specifications. The resulting gain adaptation process is able to run in real-time. Finally, we verify the effectiveness of our method both in simulations and experiments using the bipedal robot
and the humanoid robot
.
Exoskeletons can help humans in a variety of ways in performing tasks. In particular, during the lifting operation, a human places a great burden on the knee or waist joint, and the exoskeleton can ...reduce the risks of this task. However, due to the weight of the exoskeleton itself and the movement of the overall center of gravity, balance ability and efficiency may decrease. Therefore, an appropriate assistance torque distribution strategy is required to achieve high performance with the exoskeleton. In order to solve the aforementioned problem, we propose an assistance method based on whole-body control. The proposed algorithm is meaningful because it is different from other simple model-based controllers. The controller fully utilize the dynamics to achieve a high performance. In addition, by adding a straight leg cost term, the singularity problem in the fully extended configuration was solved. This method finds the optimal solution that satisfies various constraints and minimizes the objective functions. Each objective is composed of a balancing-related term that minimizes the variation in the center of gravity, a term that supports the weight of the human and exoskeleton, a term that solves the singularity problem and a term related to efficiency. In this paper, first, a motion capture experiment is performed to analyze a human’s lifting motion. Through this experiment, the trajectory of each joint angle is obtained. With PD (proportional-derivative) feedback from the joint trajectories, the exoskeleton generates human torque in the simulation and implements a lifting operation. Second, a simulation is performed with the proposed controller. As a result, it is confirmed that the proposed method reduces the amount of human joint torque and increases stability and efficiency.
Balancing control of humanoid robots is of great importance since it is a necessary functionality not only for maintaining a certain position without falling, but also for walking and running. For ...position controlled robots, the for-ce/torque sensors at each foot are utilized to measure the contact forces and moments, and these values are used to compute the joint angles to be commanded for balancing. The proposed approach in this paper is to maintain balance of torque-controlled robots by controlling contact force and moment using whole-body control framework with hierarchical structure. The control of contact force and moment is achieved by exploiting the full dynamics of the robot and the null-space motion in this control framework. This control approach enables compliant balancing behavior. In addition, in the case of double support phase, required contact force and moment are controlled using the redundancy in the contact force and moment space. These algorithms are implemented on a humanoid legged robot and the experimental results demonstrate the effectiveness of them.
To realize an ultra-low-power and low-noise instrumentation amplifier (IA) for neural and biopotential signal sensing, we investigate two design techniques. The first technique uses a noise-efficient ...DC servo loop (DSL), which has been shown to be a high noise contributor. The proposed approach offers several advantages: (i) both the electrode offset and the input offset are rejected, (ii) a large capacitor is not needed in the DSL, (iii) by removing the charge dividing effect, the input-referred noise (IRN) is reduced, (iv) the noise from the DSL is further reduced by the gain of the first stage and by the transconductance ratio, and (v) the proposed DSL allows interfacing with a squeezed-inverter (SQI) stage. The proposed technique reduces the noise from the DSL to 12.5% of the overall noise. The second technique is to optimize noise performance using an SQI stage. Because the SQI stage is biased at a saturation limit of 2
, the bias current can be increased to reduce noise while maintaining low power consumption. The challenge of handling the mismatch in the SQI stage is addressed using a shared common-mode feedback (CMFB) loop, which achieves a common-mode rejection ratio (CMRR) of 105 dB. Using the proposed technique, a capacitively-coupled chopper instrumentation amplifier (CCIA) was fabricated using a 0.18-µm CMOS process. The measured result of the CCIA shows a relatively low noise density of 88 nV/rtHz and an integrated noise of 1.5 µV
. These results correspond to a favorable noise efficiency factor (NEF) of 5.9 and a power efficiency factor (PEF) of 11.4.
Traditional skid or wheeled landing gears fall short in meeting the rigorous requirements of challenging surfaces, such as rugged terrain and swaying deck, which restraints the application in extreme ...tasks including disaster rescue, cargo transportation as well as ship-relevant operations. This letter proposes a novel legged landing gear scheme for the unmanned helicopter in dealing with terrain irregularity by fully leveraging the antagonistic mechanism of cables to effectively reduce the power demand of indispensable actuators. The tailored control framework combining the whole body control (WBC) and the contact force optimization is developed for the legged landing gear to ameliorate internal force conflicts amongst individual legs at the landing stage. Experiments on an unmanned helicopter prototype are conducted to demonstrate the effectiveness of the legged landing gear in achieving stable slope landing and fuselage posture adjusting, enhancing the adaptation of the unmanned helicopter in unstructured environments.
This paper focuses on the development of the pneumatic CRONE suspension consisting of two different suspension architectures and a switching between them. The so called stiff architecture is oriented ...to the road behaviour. It enables the use of the levelling system, allowing, amongst others, the body control under driver inputs Bouvin J-L, Moreau X, Benine-Neto A, et al. CRONE body control under driver inputs through heave velocity regulation, 2017 IEEE Vehicle Power and Propulsion Conference (VPPC), Belfort, France; 2017. The second one, called CRONE architecture, isolates the vibrations from irregularities in the road surface. It provides outstanding performances in terms of body control under road inputs, robustness of body control to sprung mass variations and vibration isolation. It also enables to resolve the dilemma between mass and damping coefficient, inherent to classic suspensions.
Firm foot contact is the top priority of climbing robots to avoid catastrophic events, especially when working at height. This study proposes a robust planning and control framework for climbing ...robots that provides robustness to slippage in unknown environments. The framework includes 1) a center of mass (CoM) trajectory optimization under the estimated contact condition, 2) Kalman filter–like approach for uncertain environment parameter estimation and subsequent CoM trajectory re-planing, and 3) an online weight adaptation approach for whole-body control (WBC) framework that can adjust the ground reaction force (GRF) distribution in real time. Though the friction and adhesion characteristics are often assumed to be known, the presence of several factors that lead to a reduction in adhesion may cause critical problems for climbing robots. To address this issue safely and effectively, this study suggests estimating unknown contact parameters in real time and using the evaluated contact information to optimize climbing motion. Since slippage is a crucial behavior and requires instant recovery, the computation time for motion re-planning is also critical. The proposed CoM trajectory optimization algorithm achieved state-of-art fast computation
via
trajectory parameterization with several reasonable assumptions and linear algebra tricks. Last, an online weight adaptation approach is presented in the study to stabilize slippery motions within the WBC framework. This can help a robot to manage the slippage at the very last control step by redistributing the desired GRF. In order to verify the effectiveness of our method, we have tested our algorithm and provided benchmarks in simulation using a magnetic-legged climbing robot Manegto.
In this paper, we introduce a new teen-sized humanoid platform dubbed DRACO 3, custom-built by Apptronik and altered for practical use by the Human Centered Robotics Laboratory at The University of ...Texas at Austin. The form factor of DRACO 3 is such that it can operate safely in human environments while reaching objects at human heights. To approximate the range of motion of humans, this robot features proximal actuation and mechanical artifacts to provide a high range of hip, knee, and ankle motions. In particular, rolling contact mechanisms on the lower body are incorporated using a proximal actuation principle to provide an extensive vertical pose workspace. To enable DRACO 3 to perform dexterous tasks while dealing with these complex transmissions, we introduce a novel whole-body controller (WBC) incorporating internal constraints to model the rolling motion behavior. In addition, details of our WBC for DRACO 3 are presented with an emphasis on practical points for hardware implementation. We perform a design analysis of DRACO 3, as well as empirical evaluations under the lens of the Centroidal Inertia Isotropy (CII) design metric. Lastly, we experimentally validate our design and controller by testing center of mass (CoM) balancing, one-leg balancing, and stepping-in-place behaviors.
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