Browsing by Subject "Impedance control"

Now showing 1 - 6 of 6

A comparative analysis of cable conduit series elastic actuators for realistic haptic rendering
(2020-08-18) Times, Matthew William; Deshpande, Ashish D.
Optimally designed wearable haptic devices have the potential to improve the quality of teleoperation and simulation systems through the creation of immersive experiences of touch. Though several metrics of haptic performance have been developed for assessing and improving these devices, there is yet to be one that captures the nuances of haptic realism and targets the assessment of highly nonlinear haptic devices. This thesis presents a novel metric for the assessment of haptic performance, intuitive tools for the optimization and comparison of haptic designs, and general design principles for two types of haptic device. Using the developed metric, novel Cable-Conduit Series Elastic Actuator (CC-SEA) type haptic devices and impedance type haptic devices are assessed and compared in terms of their ability to render a variety of virtual environments, under a variety of operator interaction conditions. It is shown that, assuming a stable system, the average CC-SEA type haptic device has comparable or better performance than that of the average impedance type device under relatively rough handling by the operator and when rendering high impedance virtual environments
A planning and control framework for humanoid systems : robust, optimal, and real-time performance
(2016-12) Zhao, Ye, active 2013; Sentis, Luis; Fernandez, Benito R; Stone, Peter; Bakolas, Efstathios; Topcu, Ufuk; Fahrenthold, Eric P
Humanoid robots are increasingly demanded to operate in interactive and human-surrounded environments while achieving sophisticated locomotion and manipulation tasks. To accomplish these tasks, roboticists unremittingly seek for advanced methods that generate whole-body coordination behaviors and meanwhile fulfill various planning and control objectives. Undoubtedly, these goals pose fundamental challenges to the robotics and control community. To take an incremental step towards reducing the performance gap between theoretical foundations and real implementations, we present a planning and control framework for the humanoid, especially legged robots, for achieving high performance and generating agile motions. A particular concentration is on the robust, optimal and real-time performance. This framework constitutes three hierarchical layers, which are presented from the following perspectives. First, we present a robust optimal phase-space planning framework for dynamic legged locomotion over rough terrain. This framework is a hybrid motion planner incorporating a series of pivotal components. Via centroidal momentum dynamics, we define a new class of locomotion phase-space manifolds, as a Riemannian distance metric, and propose a robust optimal controller to recover from external disturbances at runtime. The agility and robustness capabilities of our proposed framework are illustrated in (i) simulations of dynamic maneuvers over diverse challenging terrains and under external disturbances; (ii) experimental implementations on our point-feet bipedal robot. Second, we take a step toward formally synthesizing high-level reactive planners for whole-body locomotion in constrained environments. We formulate a two-player temporal logic game between the contact planner and its possibly-adversarial environment. The resulting discrete planner satisfies the given task specifications expressed as a fragment of temporal logic. The provable correctness of the low-level execution of the synthesized discrete planner is guaranteed through the so-called simulation relations. We conjecture that this theoretical advance has the potential to act as an entry point for the humanoid community to employ formal methods for the planner verification and synthesis. Third, we propose a distributed control architecture for the latency-prone humanoid robotic systems. A central experimental phenomenon is observed that the stability of high impedance distributed controllers is highly sensitive to damping feedback delay but much less to stiffness feedback delay. We pursue a detailed analysis of the distributed controllers where damping feedback effort is executed in proximity to the control plant, and stiffness feedback effort is implemented in a latency-prone centralized control process. Critically-damped gain selection criteria are designed for not only rigid but also series elastic actuators (SEAs). In particular, we devise a novel impedance performance metric, defined as “Z-region”, simultaneously quantifying the achievable SEA impedance magnitude and frequency ranges. Finally, this distributed control strategy is generalized to the time-delayed Whole-Body Operational Space Control with SEA dynamics. To ensure passivity, we separate the overall closed-loop system into two subsystems interconnected in a feedback configuration. By designing Lyapunov-Krasovskii functionals, we propose a delay-dependent passivity criterion of the closed-loop system in the form of linear matrix inequalities (LMIs), and solve for the allowable maximum time delays via the passivity criterion. The proposed distributed control strategy is validated through extensive experimental implementations on UT rigid and series elastic actuators, an omnidirectional mobile base Trikey and a SEA-equipped bipedal robot Hume.
Control strategies for series elastic, multi-contact robots
(2019-09-16) Thomas, Gray Cortright; Sentis, Luis; Djurdjanovic, Dragan; Bakolas, Efstathios; Chen, Dongmei
As robots designed for physical interaction with humans---humanoids, exoskeletons and beyond---make their entrance into society, understanding the limitations of their interaction behavior will be key to their effective use. The state of the art method for allowing such systems to be both compliant and force sensitive is to introduce mechanical springs into the joints of these robots, making them "series elastic". But this complicates the control of these robots, making it hard to separate truth from optimism in what they will be able to accomplish using feedback control. Robots are programmed in hierarchical layers, and each layer makes assumptions about the layer below it. The planning layer assumes the plan will be followed. The whole body controller layer assumes the actuators will supply whatever torque it specifies. And the actuator control layer assumes the actuator behaves like a linear system. This dissertation studies the interfaces between these layers as they are influenced by the choice to include series elastic actuation, hoping to resolve the mismatch between assumptions and guarantees that arise from this choice. These questions lead it naturally to the lowest of the layers, where a new system identification system allows the actuator to assume a bounded uncertainty model. The dissertation then refines the insights from studying uncertain SEA models into a simpler model that explains the most important factors. It uses this to design SEA controllers that go beyond the traditional limits of passivity. These insights also apply to the problem of strength augmentation exoskeleton control. Factor of 3 amplification results are reported on a tethered, 12 degree of freedom, powered, lower body exoskeleton with four passive joints using a simplified version of the controller and a far more advanced whole body control framework. These ideas are introduced in the context of the authors's work with various testbeds and state of the art robots including a point foot biped, the DARPA virtual robotics challenge simulator, the NASA R5 Valkyrie Humanoid, and the Apptronik Sagittarius Lower Body Exoskeleton.
Development of an elastic and compliant manipulator to perform contact tasks in hazardous and uncertain environments
(2019-05) Pettinger, Adam Lawrence; Landsberger, Sheldon; Pryor, Mitchell Wayne
This thesis details the creation of a robotic manipulator to perform complex tasks in a harsh and uncontrolled environment. The manipulator was built from its base level actuator and link components. A wide range of topics were required to bring the manipulator to its final form, and they are discussed in detail in this work. These topics span from low level robotic concepts to high level control theory and include the consideration of the hardware layout, joint-level control loops, filtering sensor data, Cartesian end effector jogging, impedance control, and user interfaces. After the implementation specifics and software design are discussed, demonstrations completed with the manipulator are presented. Included is the design and testing of a passive tool changer created for the motivating project, which is used to validate the overall system
Development of an upper-body robotic rehabilitation platform that furthers motor recovery after neuromuscular injuries
(2016-05) Kim, Bongsu; Deshpande, Ashish D.; Longoria, Raul G.; Dingwell, Jonathan B.; Chen, Dongmei; Sulzer, James S.
This dissertation presents the development of an upper-body exoskeleton and its control framework for robotic rehabilitation of the arm and shoulder after a neurological disorder such as a stroke. The first step is designing an exoskeleton hardware that supports natural mobility of the human upper body with a wide range of motion for enabling most rehabilitation exercises. The exoskeleton is equipped with torque-controllable actuation units for implementing various robotic rehabilitation protocols based on force and impedance behaviors. The control framework is designed to exhibit a highly backdrivable behavior with a gravity compensation for the robot's weight and optional gravity support for user's arm weight to promote voluntary movements of patients with motor impairments. The control framework also serves as a `substrate' of other robotic control behaviors for rehabilitation exercises by superimposing desired force or impedance profiles. A stability analysis is performed to examine the coupled stability between the robot and human. After designing the hardware and control, several experiments are carried out to test the mobility and dynamic behavior of the robot. Lastly, a human subject study evaluates the effectiveness of the robot's shoulder mechanism and control algorithm in assisting the coordination around the shoulder. The results show that the robot induces desirable coordination in the presence of abnormalities at the shoulder.
Performance and manufacturing considerations for series elastic actuators
(2017-05-05) Isik, Kenan, Ph. D.; Sentis, Luis; Fernandez, Benito R; Chen, Dongmei; Barr, Ronald; Mok, Aloysius K
Robots are becoming an integral part of our lives. We are already physically connected with them through many robotic applications such as exoskeletons in military, orthosis devices in health care, collaborative robots in industry, etc. While the integration of robots improves the quality of human life, it still poses a safety concern during the physical human-robot interaction. Series Elastic Actuators (SEAs) play an important role in improving the safety of human-robot interaction and collaboration. Considering the fast expansion of robotic applications in our lives and the safety benefits of SEAs, it is conceivable that SEAs are going to play an important role in robotic applications in every aspect of human life. This dissertation focuses on reducing the cost, simplifying the use and improving the performance of SEAs. The first research focus in this dissertation is to reduce the cost of SEAs. Robots are successful in reducing production and service costs when used but the capital cost of robot installations are very high. As robotics research shifts to safe robotic applications, reducing the cost of SEAs will greatly help to deploy this technology in more robotic applications and to increase their accessibility to a broader range of researchers and educators. With this motivation, I present a case study on reducing the cost of a SEA while maintaining high force and position control performance and industrial grade service life. The second research focus in this dissertation is to simplify the laborious gain selection process of the cascaded controllers of SEAs. In order to simplify the gain selection process of the impedance controllers of SEAs, an optimal feedback gain selection methodology was developed. Using this method, the feedback gains of the cascaded PD-type impedance controllers of SEAs can easily be calibrated. The developed method allows the users to find the highest feedback gains for a desired phase-margin. Beyond the low-cost realization and simple controller tuning of SEAs, performance improvements on SEAs are possible utilizing the series elasticity in these actuators. As the third research focus in this dissertation, a sequential convex optimization-based motion planning technique is developed in order to improve the joint velocity capabilities of SEAs with nonlinearities. By using this method, higher joint velocities, that are not achievable with the rigid counterparts of SEAs can be achieved