Impact-Aware Online Motion Planning for Fully-Actuated Bipedal Robot Walking

The ability to track a general walking path with specific timing is crucial to the operational safety and reliability of bipedal robots for avoiding dynamic obstacles, such as pedestrians, in complex environments. This paper introduces an online, full-body motion planner that generates the desired impact-aware motion for fully-actuated bipedal robotic walking. The main novelty of the proposed planner lies in its capability of producing desired motions in real-time that respect the discrete impact dynamics and the desired impact timing. To derive the proposed planner, a full-order hybrid dynamic model of fully-actuated bipedal robotic walking is presented, including both continuous dynamics and discrete lading impacts. Next, the proposed impact-aware online motion planner is introduced. Finally, simulation results of a 3-D bipedal robot are provided to confirm the effectiveness of the proposed online impact-aware planner. The online planner is capable of generating full-body motion of one walking step within 0.6 second, which is shorter than a typical bipedal walking step

Design And Development of A Powered Pediatric Lower-limb Orthosis

Gait impairments from disorders such as cerebral palsy are important to address early in life. A powered lower-limb orthosis can offer therapists a rehabilitation option using robot-assisted gait training. Although there are many devices already available for the adult population, there are few powered orthoses for the pediatric population. The aim of this dissertation is to embark on the first stages of development of a powered lower-limb orthosis for gait rehabilitation and assistance of children ages 6 to 11 years with walking impairments from cerebral palsy. This dissertation presents the design requirements of the orthosis, the design and fabrication of the joint actuators, and the design and manufacturing of a provisional version of the pediatric orthosis. Preliminary results demonstrate the capabilities of the joint actuators, confirm gait tracking capabilities of the actuators in the provisional orthosis, and evaluate a standing balance control strategy on the under-actuated provisional orthosis in simulation and experiment. In addition, this dissertation presents the design methodology for an anthropometrically parametrized orthosis, the fabrication of the prototype powered orthosis using this design methodology, and experimental application of orthosis hardware in providing walking assistance with a healthy adult. The presented results suggest the developed orthosis hardware is satisfactorily capable of operation and functional with a human subject. The first stages of development in this dissertation show encouraging results and will act as a foundation for further iv development of the device for rehabilitation and assistance of children with walking impairments

Robust Spline Path Following for Redundant Mechanical Systems

Path following controllers make the output of a control system approach and traverse a pre-specified path with no a priori time-parametrization. The first part of the thesis implements a path following controller for a simple class of paths, based on transverse feedback linearization (TFL), which guarantees invariance of the path to be followed. The coordinate and feedback transformation employed allows one to easily design control laws to generate arbitrary desired motions on the path for the closed-loop system. The approach is applied to an uncertain and simplified model of a fully actuated robot manipulator for which none of the dynamic parameters are measured. The controller is made robust to modelling uncertainties using Lyapunov redesign. The experimental results show a substantial improvement when using the robust controller for path following versus standard state feedback. In the second part of the thesis, the class of paths and systems considered are extended. We present a method for path following control design applicable to framed curves generated by spline interpolating waypoints in the workspace of kinematically redundant mechanical systems. The class of admissible paths include self-intersecting curves. Kinematic redundancies of the system are resolved by designing controllers that solve a suitably defined constrained quadratic optimization problem that can be easily tuned by the designer to achieve various desired poses. The class of redundant systems considered include mobile manipulators for a large class of wheeled ground vehicles. The result is a path following controller that simultaneously controls the manipulator and mobile base, without any trajectory planning performed on the mobile base. The approach is experimentally verified using the robust controller developed in the first part of the thesis on a 4-degree-of-freedom (4DOF) redundant manipulator and a mobile manipulator system with a differential drive base

Path Following for Mechanical Systems Applied to Robotic Manipulators

Many applications in robotics require faithfully following a prescribed path. Tracking controllers may not be appropriate for such a task, as there is no guarantee that the robot will stay on the path. The objective of this thesis is to develop a control design method which makes the “output” of a robot get to, and move along the prescribed path without leaving the path. We consider the class of mechanical systems, which encompasses robotics. Various techniques exist for designing pah following controllers. We base our approach on a technique called “transverse feedback linearization”. Using this technique, if feasible, we decompose the dynamics of a mechanical system into a transversal subsystem and a tangential subsystem using a coordinate and feedback transformation. The transversal subsystem is linear, time-invariant and decoupled from the tangential subsystem. Stabilizing the origin of the transversal subsystem is equivalent to stabilizing a set corresponding to the output of the mechanical system being on the desired path, thereby partly achieving the control objective. Given a mechanical system and a path, we provide conditions under which this is possible. The tangential subsystem describes all of the motions of the mechanical system, when the output is on the path. Some tangential dynamics may move the output along the path, and thereby meet the design objective. In order to move the output of the mechanical system along the path, we further decompose the tangential subsystem into a subsystem which moves the output along the path, and a subsystem which does not, if feasible, using partial feedback linearization. The subsystem which governs output motions along the path is linear, time-invariant and decoupled. The remaining tangential dynamics have no special structure. We provide conditions under which such a decomposition of the tangential dynamics is possible. We show that a five-bar robotic manipulator has dynamics which may be transversely feedback linearized, and the tangential dynamics may be partially linearized. Given a circular path, we experimentally implement our path following design, and observe that our control objective is indeed met. Inherent advantages of path following over trajectory tracking are illustrated. Standard feedback linearization of a five-bar robotic manipulator with a flexible link has been shown to fail. We show that this system is transversely feedback linearizable, and its tangential dynamics may be partially linearized, under mild restrictions. Simulations illustrate path following applied to this complex system