Leveraging Disturbance Observer Based Torque Control for Improved Impedance Rendering with Series Elastic Actuators

The fidelity with which series elastic actuators (SEAs) render desired impedances is important. Numerous approaches to SEA impedance control have been developed under the premise that high-precision actuator torque control is a prerequisite. Indeed, the design of an inner torque compensator has a significant impact on actuator impedance rendering. The disturbance observer (DOB) based torque control implemented in NASA's Valkyrie robot is considered here and a mathematical model of this torque control, cascaded with an outer impedance compensator, is constructed. While previous work has examined the impact a disturbance observer has on torque control performance, little has been done regarding DOBs and impedance rendering accuracy. Both simulation and a series of experiments are used to demonstrate the significant improvements possible in an SEA's ability to render desired dynamic behaviors when utilizing a DOB. Actuator transparency at low impedances is improved, closed loop hysteresis is reduced, and the actuator's dynamic response to both commands and interaction torques more faithfully matches that of the desired model. All of this is achieved by leveraging DOB based control rather than increasing compensator gains, thus making improved SEA impedance control easier to achieve in practice

Performance and manufacturing considerations for series elastic actuators

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 achievedMechanical Engineerin

Planning and Control Strategies for Motion and Interaction of the Humanoid Robot COMAN+

Despite the majority of robotic platforms are still confined in controlled environments such as factories, thanks to the ever-increasing level of autonomy and the progress on human-robot interaction, robots are starting to be employed for different operations, expanding their focus from uniquely industrial to more diversified scenarios. Humanoid research seeks to obtain the versatility and dexterity of robots capable of mimicking human motion in any environment. With the aim of operating side-to-side with humans, they should be able to carry out complex tasks without posing a threat during operations. In this regard, locomotion, physical interaction with the environment and safety are three essential skills to develop for a biped. Concerning the higher behavioural level of a humanoid, this thesis addresses both ad-hoc movements generated for specific physical interaction tasks and cyclic movements for locomotion. While belonging to the same category and sharing some of the theoretical obstacles, these actions require different approaches: a general high-level task is composed of specific movements that depend on the environment and the nature of the task itself, while regular locomotion involves the generation of periodic trajectories of the limbs. Separate planning and control architectures targeting these aspects of biped motion are designed and developed both from a theoretical and a practical standpoint, demonstrating their efficacy on the new humanoid robot COMAN+, built at Istituto Italiano di Tecnologia. The problem of interaction has been tackled by mimicking the intrinsic elasticity of human muscles, integrating active compliant controllers. However, while state-of-the-art robots may be endowed with compliant architectures, not many can withstand potential system failures that could compromise the safety of a human interacting with the robot. This thesis proposes an implementation of such low-level controller that guarantees a fail-safe behaviour, removing the threat that a humanoid robot could pose if a system failure occurred

Haptics: Science, Technology, Applications

This open access book constitutes the proceedings of the 13th International Conference on Human Haptic Sensing and Touch Enabled Computer Applications, EuroHaptics 2022, held in Hamburg, Germany, in May 2022. The 36 regular papers included in this book were carefully reviewed and selected from 129 submissions. They were organized in topical sections as follows: haptic science; haptic technology; and haptic applications