A Treatise on the Analytical Dynamics of Particles and Rigid Bodies: THE GENERAL THEORY OF ORBITS

This survey presents the state of the art of basic compliant control algorithms in a unified view of past and present literature. Compliant control is fundamental when dealing with unstructured environments, as in the case of human–robot interaction. This is because it implicitly controls the energy transfer to the environment, providing a safe interaction. In this review, we analyze solutions from traditional robotics, usually involving stiff joints, and recent literature to find common control concepts and differences. To this aim, we bring back every schemas and relative mathematics formulation to a common and simplified scenario. Then, for each schema, we explain its intuitive meaning and report issues raised in the literature. We also propose an expansion of taxonomy to account for recent research.

A Review of Algorithms for Compliant Control of Stiff and Fixed-Compliance Robots

This paper presents implementation of a highly dynamic running gait with a hierarchical controller on the MIT Cheetah. The developed controller enables high-speed running of up to 6 m/s (Froude number of Fr â 7.34) incorporating proprioceptive feedback and programmable virtual leg compliance of the MIT Cheetah. To achieve a stable and fast trot gait, we applied three control strategies: (a) programmable virtual leg compliance that provides instantaneous reflexes to external disturbance and facilitates the self-stabilizing shown in the passive dynamics of locomotion; (b) tunable stance-trajectory design, intended to adjust impulse at each foot-end in the stance phase in a high speed trot-running according to the equilibrium-point hypothesis; and (c) a gait-pattern modulation that imposes a desired cyclic gait-pattern taking cues from proprioceptive TD feedback. Based on three strategies, the controller is hierarchically structured. The control parameters for forward speeds, a specific gait-pattern, and desired leg trajectories are managed by a high-level controller. It consists of both a gait-pattern modulator with proprioceptive leg TD detection and a leg-trajectory generator using a BA¨zier curve and a tunable amplitude sinusoidal wave. Instead of employing physical spring/dampers in the robot's leg, the programmable virtual leg compliance is realized using proprioceptive impedance control in individual low-level leg controllers.

To verify the developed controller, a robot dynamic simulator is constructed based on the model parameters of the MIT Cheetah. The controller parameters are tuned with the simulator to achieve self-stability, and then applied to the MIT Cheetah in an experimental environment. Using leg kinematics and applied motor current feedbacks, the MIT Cheetah achieved a stable trot-running gait in the sagittal plane.

High speed trot-running: Implementation of a hierarchical controller using proprioceptive impedance control on the MIT Cheetah

ATRIAS is a human-scale 3D-capable bipedal robot designed to mechanically embody the spring-mass model for dynamic walking and running. To help bring the extensive work on this theoretical model fu...

ATRIAS: Design and validation of a tether-free 3D-capable spring-mass bipedal robot:

This paper presents a human-inspired control approach to bipedal robotic walking: utilizing human data and output functions that appear to be intrinsic to human walking in order to formally design controllers that provably result in stable robotic walking. Beginning with human walking data, outputs-or functions of the kinematics-are determined that result in a low-dimensional representation of human locomotion. These same outputs can be considered on a robot, and human-inspired control is used to drive the outputs of the robot to the outputs of the human. The main results of this paper are that, in the case of both under and full actuation, the parameters of this controller can be determined through a human-inspired optimization problem that provides the best fit of the human data while simultaneously provably guaranteeing stable robotic walking for which the initial condition can be computed in closed form. These formal results are demonstrated in simulation by considering two bipedal robots-an underactuated 2-D bipedal robot, AMBER, and fully actuated 3-D bipedal robot, NAO-for which stable robotic walking is automatically obtained using only human data. Moreover, in both cases, these simulated walking gaits are realized experimentally to obtain human-inspired bipedal walking on the actual robots.

/pdf/human-inspired-control-of-bipedal-walking-robots-29pq1qynca.pdf

Human-Inspired Control of Bipedal Walking Robots

In this paper, we present a novel control strategy for running which is robust to disturbances, and makes excellent use of passive dynamics for energy economy. Our strategy combines two ideas: an existing flight phase policy, and a novel stance phase impulse control policy. The state-of-the-art flight phase policy commands a leg angle trajectory that results in a consistent horizontal center-of-mass velocity from hop to hop when running over uneven terrain, thus maintaining a steady gait and avoiding falls. Our novel stance phase control policy rejects ground disturbances by matching the actuated model's toe impulse profile to that of a passive spring-mass system hopping on flat rigid ground. This combined strategy is self-stable for changes in ground impedance or ground height, and thus does not require a ground model. Our strategy is promising for robotics applications, because there is a clear distinction between the passive dynamic behavior of the model and the active controller, it does not require sensing of the environment, and it is based on a sound theoretical background that is compatible with existing high-level controllers for ideal spring-mass models.

Impulse Control for Planar Spring-Mass Running

In this paper, we present a novel control strategy for spring-mass running gaits which is robust to disturbances, while still utilizing the passive dynamic behavior of the mechanical model for energy economy. Our strategy combines two ideas: a flight phase strategy, which commands a hip angle trajectory prior to touchdown, and a stance phase strategy, which treats the spring-mass system as a force-controlled actuator and commands forces according to an ideal model of the passive dynamics. This combined strategy is self-stable for changes in ground height or ground impedance, and thus does not require an accurate ground model. Our strategy is promising for robotics applications, because there is a clear distinction between the passive dynamic behavior and the active controller, it does not require sensing of the environment, and it is based on a sound theoretical background that is compatible with existing high-level controllers.

Force control for planar spring-mass running

We demonstrate in simulation that active force control applied to a passive spring-mass model for walking and running attenuates disturbances, while maintaining the energy economy of a completely passive system during steady-state operation. It is well known that spring-mass models approximate steady-state animal running, but these passive dynamic models are sensitive to disturbances that animals are able to accommodate. Active control can be used to add robustness to spring-mass walking and running, and most existing controllers add a fixed amount of energy to the system based on information from previous strides. Because spring-mass models are schematically similar to force control actuators, it is convenient to combine the two concepts in a single system. We show, in simulation, that the resulting system can attenuate sudden disturbances during a single stance phase by matching its toe force profile to that of the undisturbed spring-mass model.

Force control for spring-mass walking and running

For robotic manipulation tasks in uncertain environments, good force control can provide significant benefits. The design of force or torque controlled actuators typically revolves around developing the best possible software control strategy. However, the passive dynamics of the mechanical system, including inertia, stiffness, damping and torque limits, often impose performance limitations that cannot be overcome with software control. Discussions about the passive dynamics are often imprecise, lacking comprehensive details about the physical limitations. In this paper, we develop relationships between an actuator's passive dynamics and the resulting performance, for the purpose of better understanding how to tune the passive dynamics for a force control task. We present two distinct scenarios for the actuator system and calculate the required input to produce a desired output. These exact solutions provide a basis for understanding how the parameters of the mechanical system affect the overall system's bandwidth limit. Our model does not include active control; we computed the optimal input to the system to produce the required torque at the load with zero error. This is important so that our results only reflect the physical system's performance.

Optimal passive dynamics for torque/force control

A robot for legged locomotion incorporating passive dynamics with active force control and method are provided.

Apparatus and method for legged locomotion integrating passive dynamics with active force control

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