Inverse and variable structure trajectory control of a flexible robotic manipulator

This thesis introduces two schemes that control the end effector trajectory and stabilize a two-link flexible robotic arm. They are (i) The Inverse Trajectory Control scheme and (ii) The Variable Structure System (VSS) scheme; The Inverse Trajectory Control scheme develops a control law based on the inversion of an input-output map. The stable maneuver of the arm depends on the stability of the zero dynamics of the system. A linear stabilizer is designed for the final capture of the terminal state and stabilization of the elastic modes; The second scheme incorporates a Variable Structure Control law which includes robustness in its design. A discontinuous output control law is derived which accomplishes the desired trajectory tracking of the output. This control scheme involves two phases, the \u27reaching phase\u27 and the \u27sliding phase\u27; Simulation results are presented to show that large maneuvers can be performed in the presence of payload uncertainty. (Abstract shortened with permission of author.)

Topics in Machining with Industrial Robot Manipulators and Optimal Motion Control

Two main topics are considered in this thesis: Machining with industrial robot manipulators and optimal motion control of robots and vehicles. The motivation for research on the first subject is the need for flexible and accurate production processes employing industrial robots as their main component. The challenge to overcome here is to achieve high-accuracy machining solutions, in spite of the strong process forces required for the task. Because of the process forces, the nonlinear dynamics of the manipulator, such as the joint compliance and backlash, may significantly degrade the achieved machining accuracy of the manufactured part. In this thesis, a macro/micro-manipulator configuration is considered to the purpose of increasing the milling accuracy. In particular, a model-based control architecture is developed for control of the macro/micro-manipulator setup. The considered approach is validated by experimental results from extensive milling experiments in aluminium and steel. Related to the problem of high-accuracy milling is the topic of robot modeling. To this purpose, two different approaches are considered; modeling of the quasi-static joint dynamics and dynamic compliance modeling. The first problem is approached by an identification method for determining the joint stiffness and backlash. The second problem is approached by using gray-box identification based on subspace-identification methods. Both identification algorithms are evaluated experimentally. Finally, online state estimation is considered as a means to determine the workspace position and orientation of the robot tool. Kalman Filters and Rao-Blackwellized Particle Filters are employed to the purpose of sensor fusion of internal robot measurements and measurements from an inertial measurement unit for estimation of the desired states. The approaches considered are fully implemented and evaluated on experimental data. The second part of the thesis discusses optimal motion control applied to robot manipulators and road vehicles. A control architecture for online control of a robot manipulator in high-performance path tracking is developed, and the architecture is evaluated in extensive simulations. The main characteristic of the control strategy is that it combines coordinated feedback control along both the tangential and transversal directions of the path; this separation is achieved in the framework of natural coordinates. One motivation for research on optimal control of road vehicles in time-critical maneuvers is the desire to develop improved vehicle-safety systems. In this thesis, a method for solving optimal maneuvering problems using nonlinear optimization is discussed. More specifically, vehicle and tire modeling and the optimization formulations required to get useful solutions to these problems are investigated. The considered method is evaluated on different combinations of chassis and tire models, in maneuvers under different road conditions, and for investigation of optimal maneuvers in systems for electronic stability control. The obtained optimization results in simulations are evaluated and compared

Space Exploration Robotic Systems - Orbital Manipulation Mechanisms

In the future, orbital space robots will assist humans in space by constructing and maintaining space modules and structures. Robotic manipulators will play essential roles in orbital operations. This work is devoted to the implemented designs of two different orbital manipulation mechanical grippers developed in collaboration with Thales Alenia Space Italy and NASA Jet Propulsion Laboratory – California Institute of Technology. The consensus to a study phase for an IXV (Intermediate eXperimental Vehicle) successor, a preoperational vehicle called SPACE RIDER (Space Rider Reusable Integrated Demonstrator for European Return), has been recently enlarged, as approved during last EU Ministerial Council. One of the main project task consists in developing SPACE RIDER to conduct on orbit servicing activity with no docking. SPACE RIDER would be provided with a robotic manipulator system (arm and gripper) able to transfer cargos, such as scientific payloads, from low Earth orbiting platforms to SPACE RIDER cargo bay. The platform is a part of a space tug designed to move small satellites and other payloads from Low Earth Orbit (LEO) to Geosynchronous Equatorial Orbit (GEO) and viceversa. The assumed housing cargo bay requirements in terms of volume (<100l) and mass (<50kg) combined with the required overall arm dimensions (4m length), and mass of the cargo (5-30kg) force to developing an innovative robotic manipulator with the task-oriented end effector. It results in a seven degree-of-freedom arm to ensure a high degree of dexterity and a dedicate end-effector designed to grasp the cargo interface. The gripper concept developed consists in a multi-finger hand able to lock both translational and rotational cargo degrees of freedom through an innovative underactuation strategy to limit its mass and volume. A configuration study on the cargo handle interface was performed together with some computer aided design models and multibody analysis of the whole system to prove its feasibility. Finally, the concept of system control architecture, the test report and the gripper structural analysis were defined. In order to be able to accurately analyze a sample of Martian soil and to determine if life was present on the red planet, a lot of mission concepts have been formulating to reach Mars and to bring back a terrain sample. NASA JPL has been studying such mission concepts for many years. This concept is made up of three intermediate mission accomplishments. Mars 2020 is the first mission envisioned to collect the terrain sample and to seal it in sample tubes. These sealed sample tubes could be inserted in a spherical envelope named Orbiting Sample (OS). A Mars Ascent Vehicle (MAV) is the notional rocket designed to bring this sample off Mars, and a Rendezvous Orbiting Capture System (ROCS) is the mission conceived to bring this sample back to Earth through the Earth Entry Vehicle (EEV). MOSTT is the technical work study to create new concepts able to capture and reorient an OS. This maneuver is particularly important because we do not know an OS incoming orientation and we need to be able to capture, to reorient it (2 rotational degrees of freedom), and to retain an OS (3 translational degrees of freedom and 2 rotational ones). Planetary protection requirements generate a need to enclose an OS in two shells and to seal it through a process called Break-The-Chain (BTC). Considering the EEV would return back to Earth, the tubes orientation and position have to be known in detail to prevent any possible damage during the Earth hard landing (acceleration of ∼1300g). Tests and analysis report that in order for the hermetic seals of the sample tubes to survive the impact, they should be located above an OS equator. Due to other system uncertainties an OS presents the potential requirement to be properly reoriented before being inserted inside the EEV. Planetary protection issues and landing safety are critical mission points and provide potential strict requirements to MOSTT system configuration. This task deals with the concept, design, and testbed realization of an innovative electro-mechanical system to reorient an OS consistent with all the necessary potential requirements. One of these electro-mechanical systems consists of a controlled-motorized wiper that explores all an OS surface until it engages with a pin on an OS surface and brings it to the final home location reorienting an OS. This mechanism is expected to be robust to the incoming OS orientation and to reorient it to the desired position using only one degree of freedom rotational actuator

Industrial Robotics

This book covers a wide range of topics relating to advanced industrial robotics, sensors and automation technologies. Although being highly technical and complex in nature, the papers presented in this book represent some of the latest cutting edge technologies and advancements in industrial robotics technology. This book covers topics such as networking, properties of manipulators, forward and inverse robot arm kinematics, motion path-planning, machine vision and many other practical topics too numerous to list here. The authors and editor of this book wish to inspire people, especially young ones, to get involved with robotic and mechatronic engineering technology and to develop new and exciting practical applications, perhaps using the ideas and concepts presented herein

Robotic manipulation with flexible link fingers

A robot manipulator is a spatial mechanism consisting essentially of a series of bodies, called "links", connected to each other at "joints". The joints can be of various types: revolute, rotary, planar, prismatic, telescopic or combinations of these. A serial connection of the links results in an open-chain manipulator. Closed-chain manipulators result from non-serial (or parallel) connections between links. Actuators at the joints of the manipulator provide power for motion. A robot is usually not designed for a very specific or repetitive task which can be done equally well by task-specific machines. Its strength lies in its ability to handle a range of tasks by virtue of being "re-programmable". Therefore, in addition to the mechanical hardware two other elements are integral to the description of a robot: sensors and control. With the advent of micro-electronics and digital computers the availability of sensors is ever increasing and the control is usually done by software executed by computers which also collect the sensory data. It is possible to model quite accurately, the dynamics of robot manipulators for purposes of control. However, for most practical robots the models are complex and numerically intensive to calculate in real-time. Traditional analyses of robot manipulators consider the whole mechanism to be rigid. Relaxation of the assumption of rigidity leads to further complication of the dynamics of the manipulator, leading to more difficulties in control. The overall motion of the manipulator is augmented by additional motion due to the dynamics of flexibility which must be considered. Sensing is also made more difficult. However, the ability to control robots with significant structural flexibilities, referred to as flexible robots in the rest of this thesis, influences robotics in many ways. It allows for consideration of new applications, observance of less conservative structural design and performance enhancements in certain classes of robotic tasks, which will be addressed in greater detail in the sections which follow

Motion Control of the Hybrid Wheeled-Legged Quadruped Robot Centauro

Emerging applications will demand robots to deal with a complex environment, which lacks the structure and predictability of the industrial workspace. Complex scenarios will require robot complexity to increase as well, as compared to classical topologies such as fixed-base manipulators, wheeled mobile platforms, tracked vehicles, and their combinations. Legged robots, such as humanoids and quadrupeds, promise to provide platforms which are flexible enough to handle real world scenarios; however, the improved flexibility comes at the cost of way higher control complexity. As a trade-off, hybrid wheeled-legged robots have been proposed, resulting in the mitigation of control complexity whenever the ground surface is suitable for driving. Following this idea, a new hybrid robot called Centauro has been developed inside the Humanoid and Human Centered Mechatronics lab at Istituto Italiano di Tecnologia (IIT). Centauro is a wheeled-legged quadruped with a humanoid bi-manual upper-body. Differently from other platform of similar concept, Centauro employs customized actuation units, which provide high torque outputs, moderately fast motions, and the possibility to control the exerted torque. Moreover, with more than forty motors moving its limbs, Centauro is a very redundant platform, with the potential to execute many different tasks at the same time. This thesis deals with the design and development of a software architecture, and a control system, tailored to such a robot; both wheeled and legged locomotion strategies have been studied, as well as prioritized, whole-body and interaction controllers exploiting the robot torque control capabilities, and capable to handle the system redundancy. A novel software architecture, made of (i) a real-time robotic middleware, and (ii) a framework for online, prioritized Cartesian controller, forms the basis of the entire work

Proceedings of the Fifth NASA/NSF/DOD Workshop on Aerospace Computational Control

The Fifth Annual Workshop on Aerospace Computational Control was one in a series of workshops sponsored by NASA, NSF, and the DOD. The purpose of these workshops is to address computational issues in the analysis, design, and testing of flexible multibody control systems for aerospace applications. The intention in holding these workshops is to bring together users, researchers, and developers of computational tools in aerospace systems (spacecraft, space robotics, aerospace transportation vehicles, etc.) for the purpose of exchanging ideas on the state of the art in computational tools and techniques