Stig Moberg

Modeling and Control of Flexible Manipulators, PhD Thesis No 1349, Linköping University, Linköping, Sweden, 2010

Stig Moberg’s thesis, Modeling and Control of Flexible Manipulators, deals with different aspects of modeling and control of flexible, i.e., elastic, manipulators. For an accurate description of a modern industrial manipulator, it is shown that the traditional flexible joint model, described in literature, is not sufficient. An improved model where the elasticity is described by a number of localized multidimensional spring-damper pairs is therefore proposed. The main contributions of the work are the design and analysis of identification methods, and of inverse dynamics control methods, for the extended flexible joint model. A methodology to solve for the inverse dynamics based on the solution of a differential algebraic equation (DAE) is introduced. The inverse dynamics solution is then used for feedforward control of both a simulated manipulator and of a real robot manipulator. The last part of the work concerns feedback control. First, a model-based nonlinear feedback control (feedback linearization) is evaluated and compared to a model-based feedforward control algorithm. Finally, two benchmark problems for robust feedback control of a flexible manipulator are presented and some proposed solutions are analyzed.

Johanna Wallén

Estimation-based iterative learning control, PhD Thesis No 1358, Linköping University, Linköping, Sweden, 2011.

Johanna Wallén’s thesis, Estimation-based iterative learning control, defended in February 2011, describes a method for self-learning with the aim to substantially improve the precision of robots. The main contribution of the thesis is to consider ILC algorithms applied to a flexible dynamic system where the controlled variable cannot be measured directly. The idea is to use indirect measurements, a model of the system, and estimation techniques to get a calculated value of the controlled variable. In the thesis Wallén also introduces estimation based Iterative learning control (ILC), a framework where it is possible to analyze stability and performance in the combination of estimation and ILC. Experimental results are also included to show the usefulness of the concept and the framework for analysis and design.

Patrik Axelsson

Sensor Fusion and Control Applied to Industrial Manipulators. PhD thesis, No. 1585, Linköping University, Linköping, Sweden, 2014.

Patrik Axelsson’s PhD thesis considers the fundamental question, how to control a flexible mechanical system when limited measurement are available from the controlled variable. Axelsson considers the general control problem in two parts. The first part is the estimation of the controlled variable based on measurements of the actuator position and the acceleration of the end-effector. Bayesian estimation methods for state estimation, represented by the extended Kalman filter (EKF) and the particle filter (PF), are evaluated and the methods are assessed in simulation as well as in experiments using an industrial manipulator and an industrial control platform. The second part of the work considers the control problem including the estimated values of the controlled variables in the controller. One approach which is proposed is the estimation-based norm-optimal ILC algorithm where the objective is extended to include not only the mean value of the estimated variable but also information about the uncertainty of the estimate. A second approach considered in the thesis is H-infinity control where a method for control of a flexible joint, with non-linear spring characteristics is proposed and evaluated in simulation.

André Carvalho Bittencourt

Modeling and Diagnosis of Friction and Wear in Industrial Robots, PhD thesis, No. 1617, Linköping University, Linköping, Sweden, 2014.

André Carvalho Bittencourt’s PhD thesis deals with robot fault diagnosis and monitoring of industrial robots. The main focus is on the design of methods for the detection of excessive degradations due to wear in a robot joint. A mathematical model of friction is developed, including dependence on temperature and load, in addition to the velocity dependence normally present in friction models. Based on a proposed friction model and friction data collected from dedicated experiments, a method is suggested to estimate wear-related effects to friction. A part of the work is also devoted to the development and evaluation of methods to estimate the wear directly. Finally a part of the work focuses on developing a method that can be applied without modifying the production cycles, i.e. to use data from normal use of the robot. A key feature is that the majority of the robots used in industry carry out their operation repeatedly. This has resulted in a method that is based on monitoring of the torque distribution. The key element is to compare the distribution from different repetitions of a cycle, using different statistical distance measures related to the distribution, and to diagnose wear changes based on the distance measure.

Graduates Aerial Vehicles and Marine Vessels:

Roger Larsson

System Identification of Flight Mechanical Characteristics, Licentiate’s thesis No. 1599, Linköping University, Linköping, Sweden, 2013.

Roger Larsson is an industrial PhD student from Saab and his licentiate’s thesis concerns aircraft system identification. It covers two different areas that are highly relevant for the industrial application. The first topic concerns a sequential system identification method for online aircraft modeling. The idea is to use this method in Saab’s flight test monitoring system in order to provide the engineers with more reliable measures of the information content in the collected data. This method has a significant cost-saving potential and the process of implementing it in the real flight monitoring system has already been started. The second topic of the licentiate’s thesis concerns identification of unstable nonlinear systems operating under closed-loop conditions, like the Gripen aircraft produced by Saab. The project has focused on the development and evaluation of a number of candidate approaches to this challenging problem and benchmarked the different methods using both simulated and real flight test scenarios.

Zoran Sjanic

Navigation and Mapping for Aerial Vehicles Based on Inertial and Imaging Sensors. PhD thesis No 1533, Linköping University, Linköping, Sweden, 2013.

Zoran Sjanic’s PhD thesis concerns navigation and mapping for aerial vehicles based on inertial and imaging sensors. The main idea is to use sensor fusion of signals from relatively cheap sensors for navigation and surveillance purposes in UAVs. For example, by combining Synthetic Aperture Radar (SAR) data and data from inertial sensors, more accurate and focused SAR images as well as better estimates of the motion of the vehicle can be obtained. Furthermore, camera images and inertial sensors can be used to support the navigation system and simultaneously build a three-dimensional map of the observed environment. This is an example of inertial-visual Simultaneous Localization and Mapping (SLAM).

Martin Skoglund

Inertial Navigation and Mapping for Autonomous Vehicles. PhD thesis No 1623, Linköping University, Linköping, Sweden, 2014.

Martin Skoglund´s PhD thesis deals with inertial navigation and mapping for autonomous vehicles. One SLAM application in this thesis concerns determination of sensor and vessel positions in a scenario where a vessel with a known magnetic signature moves in a region covered by a network of magnetometer sensors. Another application concerns remotely operated underwater vehicles and the proposed method can be used to improve the navigation performance using a hydrodynamic model and data from the vessel’s sensors. The third problem addressed is SLAM with inertial sensors, accelerometers and gyroscopes, and an optical camera contained in a single sensor unit. It is shown how a SLAM estimate can be improved by solving a nonlinear least-squares problem initialized using EKF-SLAM or by the use of an expectation maximization approach. Some benefits are the scalability of the approach as well as the accuracy of the results.

Jonas Linder

Graybox Modelling of Ships Using Indirect Input Measurements, Licentiate’s thesis No. 1681, Linköping University, Linköping, Sweden, 2014.

The licentiate’s thesis written by Jonas Linder concerns graybox modeling of ships using an approach where not all inputs affecting the ship are measured directly. Here, a subsystem that can be used to describe some safety-critical properties of the ship is identified based on IMU and rudder angle measurements. The measured acceleration is treated as an indirect input measurement and it is shown that this solves the problem of missing input measurements. The resulting estimation problem is similar to closed-loop system identification and an iterative joint closed-loop instrumental variable approach based on a graybox formulation and using multiple datasets simultaneously is introduced to estimate the parameters. Finally, experiments with a scale ship model are described. The joint identification method is applied to the collected data and gives promising results.

Graduates Automotive Systems:

Johan Wahlström

Control of EGR and VGT for Emission Control and Pumping Work Minimization in Diesel Engines. PhD thesis No. 1256, Linköping University, Linköping, Sweden, 2009

In Johan Wahlström´s PhD thesis, control structures are proposed and investigated for coordinated control of Exhaust Gas Recirculation (EGR) Valve and Variable Geometry Turbochargers (VGT) position in heavy duty diesel engines. Main control goals are to fulfill the legislated emission levels, to reduce the fuel consumption, and to fulfill safe operation of the turbocharger. In the research a freely available and open Diesel Engine model has been implemented and made available. Scania has adopted the diesel engine model implementation and is using it in many research and development projects providing significant value for Scania. The model family provides a basis for industrial concept investigation and product development, and as such enables a shortening of the time to market.

Oskar Leufven

Modeling for control of centrifugal compressors. PhD thesis, No. 1556, Linköping University, Linköping, Sweden, 2013.

Oskar Leufven´s PhD thesis contributes with new knowledge about how a compressor operates in advanced turbocharger installations like, for example, a two stage turbocharger and most importantly how the extended compressor operation can be modeled using compact control oriented models. These results build on previous year’s data acquisition of turbocharger data, provided through the LINK-SIC collaboration with Scania and SAAB Automobile Powertrain. The dataset is acquired for a wide range of conditions and contains information of high importance for improving the modeling of turbocharger systems. The focus of the analysis and modeling work has been on compressor modeling and it has led to a further refinement of control oriented compressor models. This has strengthened the general area a model structures for gas flows in engines that has been built up over several years at LiU. Based on the structure, and data from the gas stand, a family of models for turbocharged engines has been developed in LINK-SIC. Results from the turbocharger further strengthens the capabilities of the previously developed models and thereby widens the possible applications and investigations that further strengthens the product development process.

Andreas Thomasson

Modeling and control of actuators and co-surge in turbocharged engines. PhD thesis, No. 1590, Linköping University, Linköping, Sweden, 2014.

The research focus of Andreas Thomasson’s PhD thesis lies within the area of control oriented modeling and control of turbocharged engines and actuators. The actuator research direction of the research contributed with the best performing controller in the IFP throttle control benchmark. The thesis further contributes with new knowledge about how a compressor operates in advanced turbocharger installations like, for example, a bi-turbo charged V-engine and most importantly how the extended compressor operation can be modeled using compact control oriented models.

Andreas Myklebust

Dry Clutch Modeling, Estimation, and Control. PhD thesis, No. 1612, Linköping University, Linköping, Sweden, 2014.

Andreas Myklebust’s PhD thesis concerns clutch modeling and control, more specifically focusing on analysis of clutch friction and estimation of the state of the clutch as well as an evaluation of the potential for micro slip control. The analysis is based on data from several measurements performed during several years on trucks at the Scania test site, aiming at improving the knowledge about the torque transferred in the clutch under various conditions. The measurement campaign and analyses have been used for clutch modeling and the results from the LINK-SIC research are new models for the clutch system where the temperature effect in the clutch has been identified as an important contributor to variations in the transmitted clutch torque. Andreas Myklebust finished his PhD thesis in September 2014.

Graduates Industrial Robotics: