Enhanced closed loop performance using non-dimensional analysis

This paper investigates the benefits of using non-dimension analysis to develop a control law for a flexible electro-mechanical system. The system that is analyzed consists of a DC motor connected to a load inertia through a set of gears. A state space system model is derived using LaGrange\u27s equation and then non-dimensionalized using a linear transformation. The resulting system model reveals the system character more clearly through the resulting dimensionless parameters. The parameters highlight the interaction between system properties and motor constants and demonstrate the benefits of a concurrent mechatronics design process. Open-loop behavior is analyzed and an optimal value for these paramaters can be found by varying the gear ratio. Once the best possible gear ratio is determined, a PID control law is developed and the closed loop performance is analyzed. With the optimal gear ratio, the power required to control the system is minimized. Also, dynamic inversion is applied to control the system. Dynamic inversion requires a square B matrix in the state space model. A new method to apply dynamic inversion to a system with a non-square B matrix is demonstrated. To make the matrix invertible, a linear transform is applied to the state space model. A Linear-Quadratic Regulator (LQR) design method is applied to find the transformation matrix values that will make the B matrix invertible. The power consumption of this control law is also minimized when the system contains the optimal gear ratio

Modeling, Analysis, Force Sensing and Control of Continuum Robots for Minimally Invasive Surgery

This dissertation describes design, modeling and application of continuum robotics for surgical applications, specifically parallel continuum robots (PCRs) and concentric tube manipulators (CTMs). The introduction of robotics into surgical applications has allowed for a greater degree of precision, less invasive access to more remote surgical sites, and user-intuitive interfaces with enhanced vision systems. The most recent developments have been in the space of continuum robots, whose exible structure create an inherent safety factor when in contact with fragile tissues. The design challenges that exist involve balancing size and strength of the manipulators, controlling the manipulators over long transmission pathways, and incorporating force sensing and feedback from the manipulators to the user. Contributions presented in this work include: (1) prototyping, design, force sensing, and force control investigations of PCRs, and (2) prototyping of a concentric tube manipulator for use in a standard colonoscope. A general kinetostatic model is presented for PCRs along with identification of multiple physical constraints encountered in design and construction. Design considerations and manipulator capabilities are examined in the form of matrix metrics and ellipsoid representations. Finally, force sensing and control are explored and experimental results are provided showing the accuracy of force estimates based on actuation force measurements and control capabilities. An overview of the design requirements, manipulator construction, analysis and experimental results are provided for a CTM used as a tool manipulator in a traditional colonoscope. Currently, tools used in colonoscopic procedures are straight and exit the front of the scope with 1 DOF of operation (jaws of a grasper, tightening of a loop, etc.). This research shows that with a CTM deployed, the dexterity of these tools can be increased dramatically, increasing accuracy of tool operation, ease of use and safety of the overall procedure. The prototype investigated in this work allows for multiple tools to be used during a single procedure. Experimental results show the feasibility and advantages of the newly-designed manipulators

Cooperative Object Manipulation with Force Tracking on the da Vinci Research Kit

The da Vinci Surgical System is one of the most established robot-assisted surgery device commended for its dexterity and ergonomics in minimally invasive surgery. Conversely, it inherits disadvantages which are lack of autonomy and haptic feedback. In order to address these issues, this work proposes an industry-inspired solution to the field of force control in medical robotics. This approach contributes to shared autonomy by developing a controller for cooperative object manipulation with force tracking utilizing available manipulators and force feedback. To achieve simultaneous position and force tracking of the object, master and slave manipulators were assigned then controlled with Cartesian position control and impedance control respectively. Because impedance control requires a model-based feedforward compensation, we identified the lumped base parameters of mass, inertias, and frictions of a three degree-of-freedom double four-bar linkage mechanism with least squares and weighted least squares regression methods. Additionally, semidefinite programming was used to constrain the parameters to a feasible physical solution in standard parameter space. Robust stick-slip static friction compensation was applied where linear Viscous and Coulomb friction was inadequate in modeling the prismatic third joint. The Robot Operating System based controller was tested in RViz to check the cooperative kinematics of up to three manipulators. Additionally, simulation with the dynamic engine Gazebo verified the cooperative controller applying a constant tension force on a massless spring-damper virtual object. With adequate model feedback linearization, the cooperative impedance controller tested on the da Vinci Research Kit yielded stable tension force tracking while simultaneously moving in Cartesian space. The maximum force tracking error was +/- 0.5 N for both a compliant and stiff manipulated object

Optimal Control of the Cheetah During Rapid Manoeuvres

Cheetahs are incredibly fast, manoeuvrable and highly dynamic, but relatively little is understood about how this is achieved. Thus, understanding their abilities is a subject of research for roboticists and biologists. Trajectory optimisation is a tool often used to increase our understanding of cheetahs, but current approaches which handle the full complexity of poorly understood manoeuvres are slow. The lack of data means that there are no simulated models of cheetahs known to be representative of dynamic movements such as acceleration and turning. In this project, a modelling change is investigated that decreases the time to find trajectories for models involving long serial chains of rigid bodies. Leveraging this development, a software library is created which facilitates the process of finding trajectories of models of legged robots and animals. Using this library, a complex model of a cheetah is developed, based on real data and some experimentation. Finally, the model is used to generate high speed dynamic manoeuvres which present progress towards understanding the incredible abilities of cheetahs

Potential flows about airfoils/hydrofoils with one- and two-way coupled boundary layer models

The main objectives of this thesis are to implement the one- and two-way couplings of an inviscid flow formulation with an appropriate boundary layer model and to verify and benchmark the implementations against experimental results. The coupling between the boundary layer and the inviscid formulation allows a quick calculation of the most important aerodynamic/hydrodynamic coefficients, i.e., lift and drag coefficients. There are two possibilities when coupling inviscid formulations with boundary layer models: one- and two-way couplings. One-way coupling model neglects the effect of the boundary layer thickness on the body itself, i.e., the modification of the shape that the flow sees. In one-way coupling, the initial tangential velocity distribution along the body coming from the inviscid model is used for the computation of the boundary layer and subsequently the calculation of drag. In two-way coupling, the boundary layer thickness, which is computed in the boundary layer model, modifies the shape of the airfoil used in the inviscid model and a second computation of the tangential velocities around the modified body is performed. The procedure is repeated till we achieve the required convergence. Obviously, two-way coupling is generally expected to produce more accurate results

Pilot and control system modelling for handling qualities analysis of large transport aircraft

The notion of airplane stability and control being a balancing act between stability and control has been around as long as aeronautics. The Wright brothers’ first successful flights were born of the debate, and were successful at least in part because they spent considerable time teaching themselves how to control their otherwise unstable airplane. This thesis covers four aspects of handling for large transport aircraft: large size and the accompanying low frequency dynamics, the way in which lifting surfaces and control system elements are modelled in flight dynamics analyses, the cockpit feel characteristics and details of how pilots interact with them, and the dynamic instability associated with Pilot Induced Oscillations. The dynamics associated with large transport aircraft are reviewed from the perspective of pilot-in-the-loop handling qualities, including the effects of relaxing static stability in pursuit of performance. Areas in which current design requirements are incomplete are highlighted. Issues with modelling of dynamic elements which are between the pilot’s fingers and the airplane response are illuminated and recommendations are made. Cockpit feel characteristics are examined in detail, in particular, the nonlinear elements of friction and breakout forces. Three piloted simulation experiments are described and the results reviewed. Each was very different in nature, and all were designed to evaluate linear and nonlinear elements of the cockpit feel characteristics from the pilot’s point of view. These included understanding the pilot’s ability to precisely control the manipulator itself, the pilot’s ability to command the flight path, and neuro-muscular modelling to gain a deeper understanding of the range of characteristics pilots can adapt to and why. Based on the data collected and analyzed, conclusions are drawn and recommendations are made. Finally, a novel and unique PIO prediction criterion is developed, which is based on control-theoretic constructs. This criterion identifies unique signatures in the dynamic response of the airplane to predict the onset of instability

Proceedings of the 3rd Annual Conference on Aerospace Computational Control, volume 1

Conference topics included definition of tool requirements, advanced multibody component representation descriptions, model reduction, parallel computation, real time simulation, control design and analysis software, user interface issues, testing and verification, and applications to spacecraft, robotics, and aircraft

Proceedings of the ECCOMAS Thematic Conference on Multibody Dynamics 2015

This volume contains the full papers accepted for presentation at the ECCOMAS Thematic Conference on Multibody Dynamics 2015 held in the Barcelona School of Industrial Engineering, Universitat Politècnica de Catalunya, on June 29 - July 2, 2015. The ECCOMAS Thematic Conference on Multibody Dynamics is an international meeting held once every two years in a European country. Continuing the very successful series of past conferences that have been organized in Lisbon (2003), Madrid (2005), Milan (2007), Warsaw (2009), Brussels (2011) and Zagreb (2013); this edition will once again serve as a meeting point for the international researchers, scientists and experts from academia, research laboratories and industry working in the area of multibody dynamics. Applications are related to many fields of contemporary engineering, such as vehicle and railway systems, aeronautical and space vehicles, robotic manipulators, mechatronic and autonomous systems, smart structures, biomechanical systems and nanotechnologies. The topics of the conference include, but are not restricted to: ● Formulations and Numerical Methods ● Efficient Methods and Real-Time Applications ● Flexible Multibody Dynamics ● Contact Dynamics and Constraints ● Multiphysics and Coupled Problems ● Control and Optimization ● Software Development and Computer Technology ● Aerospace and Maritime Applications ● Biomechanics ● Railroad Vehicle Dynamics ● Road Vehicle Dynamics ● Robotics ● Benchmark ProblemsPostprint (published version