26.09.2022
Modeling, observer design, and control of continuous casting processes

  26.09.2022
Modeling, observer design, and control of material properties in strip processing lines

  26.09.2022
Modeling, observer design, and control of the coating weight and surface quality in hot-dip galvanizing lines for steel strips

  29.08.2022
Optimization of start times and product sequences in a multi-line hot rolling mill

Project focus

• Modelling of the processing times of products
• Computation of optimal product start times with deterministic and stochastic processing times
• Optimization of the sequence of products

Description

In a multi-line rolling mill for stainless steel, sectional and flat bars as well as wire are produced. The products have different production parameters (steel grades, cross-sections, rolling temperatures, rolling speeds, etc.). Figure 1 shows an outline of the considered plant. In the first processing step, the products are reheated to specific rolling temperatures. Most of them are heated in a walking beam furnace and only a few are heated in induction furnaces. In the next step, the hot products are rolled out to an intermediate square cross-section by a reversing roughing mill. Afterwards, the intermediate products are processed to steel bars or wire in the profile rolling line or to flat steel in the flat rolling line.

At the profile rolling line, see Fig. 2, tool changes are required when the dimensions of the product cross section change. During these tool changes, products are manufactured at the flat rolling line. The following points are important for the throughput and efficiency of the plant:

1. Considering all safety-relevant time buffers, the start times of the products should be chosen to minimize the time intervals between successive products. This strategy maximizes the product throughput.
2. The product sequence has to be chosen so that retooling times entailed by different product parameters of successive products are minimized.
3. During tool changes at the profile rolling line, the products processed at the flat rolling line should be chosen so that their total production time optimally fills the time span of the tool changes. This total production time depends also on the rolling sequence of the chosen products at the flat rolling line.

 

As a basis for optimizing the start times, models of the processing times of products are developed for all relevant sections of the plant. These models can predict the processing of all products in the form of discrete-event times at which products pass defined points along the line. The optimal start time of a product is then determined based on the event times of the previous product and displayed to the operators on a terminal.

The optimization problem of selecting and sequencing the products is known to be NP-hard. To approximately solve this problem, various heuristic algorithms (local search, simulated annealing, tabu search) are implemented and analyzed. Furthermore, the application of methods to determine exact solutions (branch and bound, constraint programming optimization) is studied, at least to find optimal sequences for subsets of products. The optimized selection and sequence of products minimize unproductive retooling and setup times and thus maximize the product throughput of the plant.

Selected publications

• M. Kowalski, A. Steinboeck, A. Aschauer, and A. Kugi, Optimal Start Times for a Flow Shop with Blocking Constraints, No-Wait Constraints, and Stochastic Processing Times, in Proceedings of the 17th IFAC Symposium on Information Control Problems in Manufacturing INCOM 2021, Budapest, Hungary, 2021, pp. 659-664.
  [BibTex]

  @InProceedings{Kowalski2021,
  author = {M. Kowalski and A. Steinboeck and A. Aschauer and A. Kugi},
  booktitle = {Proceedings of the 17th IFAC Symposium on Information Control Problems in Manufacturing INCOM 2021},
  title = {Optimal Start Times for a Flow Shop with Blocking Constraints, No-Wait Constraints, and Stochastic Processing Times},
  doi = {10.1016/j.ifacol.2021.08.176},
  note = {17th IFAC Symposium on Information Control Problems in Manufacturing INCOM 2021},
  number = {1},
  pages = {659-664},
  url = {https://www.sciencedirect.com/science/article/pii/S2405896321009460},
  volume = {54},
  address = {Budapest, Hungary},
  issn = {2405-8963},
  journal = {IFAC-PapersOnLine},
  year = {2021},
  }

• M. Kowalski, A. Steinboeck, and A. Kugi, Scheduling Multiple Groups of Jobs for a Multi-Line Steel Hot Rolling Mill, in Proceedings of the 19th IFAC Symposium on Control, Optimization and Automation in Mining, Mineral and Metal Processing MMM, Montreal, Canada, 2022, p. 168–173.
  [BibTex]

  @InProceedings{Kowalski2022,
  author = {M. Kowalski and A. Steinboeck and A. Kugi},
  booktitle = {Proceedings of the 19th IFAC Symposium on Control, Optimization and Automation in Mining, Mineral and Metal Processing MMM},
  title = {Scheduling Multiple Groups of Jobs for a Multi-Line Steel Hot Rolling Mill},
  doi = {10.1016/j.ifacol.2022.09.262},
  note = {IFAC-PapersOnLine},
  number = {21},
  pages = {168--173},
  volume = {55},
  address = {Montreal, Canada},
  month = {08},
  year = {2022},
  }

Applications

• Automation of rolling mills
• Optimization of processing times and product sequences in production processes

  22.03.2022
MobileSpectro

Development of a high precision handheld FTIR spectrometer for the mobile chemical analysis of fluids

Project goals

• Development of a handheld Fourier-transform infrared (FTIR) spectrometer
• Measurement  and mobile analysis of samples in the condensed phase
• Miniaturization and ruggedization to bring high-performance spectroscopy to the field

Description

Infrared spectroscopy is considered to be a fundamental technique for the characterization and analysis of chemical compounds. As illustrated in Figure 1, measurement of the sample’s wavelength-dependent absorption, which is directly related to its molecular structure, enables the application of multivariate chemometric techniques for the elucidation of the contained chemical compounds.

Figure 1: Polychromatic light, emitted by a black-body radiator (Ir) is transmitted through a specimen and recorded by the spectrometer (Is). Knowledge of both quantities allows for the calculation of the sample’s absorptivity (As), which is indicative of its molecular structure.

In contrast to dispersive instruments, FTIR spectrometers typically use a scanning interferometer, such as shown in Figure 2, to record the transmitted intensity as a function of optical path difference (OPD). This offers not only the advantage of significantly increased signal-to-noise ratio and reduced measurement time, but also enables a broad spectral region (typically 650 cm^-1 to 4000 cm^-1) to be observed simultaneously and provides high wavenumber accuracy by using a reference laser for position measurement. Owing to the interferometric measurement principle, existing systems offer limited applicability to field usage scenarios due to their temperature and vibration sensitivity, as well as their limited signal-to-noise ratio. Currently available devices focus on attenuated total reflection (ATR) sampling methods, making them unsuitable for the analysis of liquid samples, especially for spectral resolutions better than 4 cm^-1.

Figure 2: Typical FTIR spectrometer arrangement. Radiation from a source is collimated, passed through a Michelson interferometer and through the specimen, and focused on a detector (PD1). By scanning the position of one mirror, the intensity signal as a function of optical path difference is recorded. The Fourier transform of the spatially sampled interferogram corresponds to the source spectrum.

MobileSpectro aims to design a miniaturized FTIR spectrometer that enables handheld operation, is sufficiently robust for field use, offers a spectral resolution of better than 2cm^-1, and has a signal-to-noise ratio that allows the application of advanced chemometric techniques. Based on highly-integrated mechatronic system components, novel opto-mechatronic assebmlies, advanced data processing and control algorithms, a highly robust device, tailored to the needs of future in-field spectroscopy, is developed.

Applications

• Predictive maintenance of heavy machinery
• Quality control in petrochemical, pharmaceutical, and cosmetical industries
• Detection and identification of unknown chemical agents
• Environmental pollution and contamination monitoring

Project partner

• Grabner Instruments Messtechnik GmbH

Funding

• FFG – Die Österreichische Forschungsförderungsgesellschaft

 

  07.01.2022
Fast trajectory planning for robotic systems in the presence of obstacles and dynamically moving targets

Project focus

• Fast planning and replanning of trajectories
• Obstacle avoidance, moving targets
• MPC-based trajectory tracking control

Description

This research work addresses the development of new methods for fast path planning in presence of obstacles and moving targets.This is an important topic for various applications in the field of robotics, handling systems and construction machines such as cranes or collaborative robots. Fig. 1 shows the lab-sized experimental setup of the 3D gantry crane. The task is to implement a fast algorithm to re-plan the trajectories for a payload to reach the moving truck while avoiding obstacles.

Fig. 1: System overview and experimental setup of the 3D gantry crane

Description

In this research, fast optimization-based trajectory planning algorithms are investigated and implemented in both simulation and experiment. Since optimization of trajectory planning usually takes a long time, it is reasonable to use the suboptimal solutions as the initial guess trajectory then refine the overall solution through iterations. In addition, the proposed algorithm should be able to generate a new trajectory when the target configuration changes by using previously computed suboptimal solutions from a database.  In addition, fast trajectory planning must be executed at any time, i.e., the algorithms can be interrupted at any time, but will always lead to reasonable, albeit suboptimal, results. This is an important requirement for the real-time capability of the proposed algorithms.

The focus of this project lies on the efficient trajectory (re)planning, which consists of two steps:

• First, an offline trajectory planner is implemented to setup a time-optimal, collision-free, and dynamically feasible trajectory database that connects all the starting points from a predefined starting subspace to all target points in a target subspace.
• Second, based on linear constrained quadratic programming, the online trajectory replanner utilizes the offline trajectory database to generate an optimal trajectory in real time that accounts for all changes in the target state.

Additionally, a trajectory tracking controller is developed to take into account the dynamic constraints for the gantry crane and to compensate for the possible influence of model inaccuracies, disturbances, and other non-modeled effects.

Video

Selected publications

• M. N. Vu, P. Zips, A. Lobe, F. Beck, W. Kemmetmüller, and A. Kugi, Fast motion planning for a laboratory 3D gantry crane in the presence of obstacles, in Proceedings of the 21st IFAC World Congress, Berlin, Germany, 2020, p. 9508–9514.
  [BibTex]

  @InProceedings{Vu2020,
  author = {Vu, M.N. and Zips, P. and Lobe, A. and Beck, F. and Kemmetmüller, W. and Kugi, A.},
  booktitle = {Proceedings of the 21st IFAC World Congress},
  title = {Fast motion planning for a laboratory 3D gantry crane in the presence of obstacles},
  doi = {10.1016/j.ifacol.2020.12.2427},
  note = {IFAC-PapersOnLine},
  number = {2},
  pages = {9508--9514},
  volume = {53},
  address = {Berlin, Germany},
  issn = {2405-8963},
  month = {06},
  year = {2020},
  }

  03.11.2021
ConvoyFence

  Title

Active vibration isolation platform for mobile drone identification systems for the protection of vehicle convoys

Project goals

• Design and implementation of a scalable multi-degree-of-freedom vibration isolation platform for mobile drone detection and identification
• Integration and control of the platform and the optical drone tracking and identification system developed in OptoFence II

Description

In recent years, drones and other types of unmanned aerial vehicles (UAVs) have gained massive importance in both the private and professional sectors. Correct identification of UAVs is essential for public safety, especially during major events. Due to technological advances, the detection, tracking, identification and defense of UAVs poses enormous challenges to modern drone interception systems. Optical drone reconnaissance systems are susceptible to vibrations and unstable surfaces, especially in mobile environments, due to the high magnifications as well as the high tracking speeds required to identify approaching objects.
Nevertheless, they are the backbone of a modern, multispectral drone detection system, as only the timely provision of high-resolution imagery enables appropriate and rapid decision-making to protect a troop transport or convoy. Thus, a universally applicable technical solution is needed to make optical drone reconnaissance systems, as well as other directed detection systems, “mobile” and to ensure the protection of people and vehicles even when they are on the move.

This project aims to develop a modular vibration isolation platform that enables the mobile deployment of optical drone reconnaissance systems. Mechatronic system design and state-of-the-art control technology ensure the required decoupling and stabilization of the sensor systems even while the vehicle is in motion (Fig. 1).

As shown in Fig. 2, a rigidly mounted system in mobile use leads to a considerable angular error of the optical detection system and correct UAV identification is thus made impossible. Although vibration amplitudes can be attenuated by additional passive isolation, telescope tracking and image stability are still limited.

Only through active vibration suppression by means of an actuated platform detection of vibrations by suitable sensors as well as advanced control strategy the necessary tracking accuracy as well as image smoothness can be achieved. A block diagram of the planned control structure for vibration isolation is shown in Figure 3. Only the combination of feedback and feedforward control enables a low-vibration environment in mobile use for the operation of the drone identification system from Optofence II.

By closely coordinating the platform with the development of a high-performance telescope system for drone identification from the complementary project “OptoFenceII”, a direct link is established to the project results and an overall more powerful, flexible and, above all, mobile drone reconnaissance system is created (Fig.4).

 

 

Applications

• Vibration isolation platform for mobile applications
• Drone tracking and identification
• Optical communication

Project partners

• ASA Astrosysteme GmbH
• Austrian Federal Ministry of Defence

Funding

This project is funded by the Austrian defense research programme FORTE of the Federal Ministry of Agriculture, Regions and Tourism (BMLRT).

 

 

  28.10.2021
Optimal TCP and Robot Base Placement for Complex Continuous Paths

Project focus

• Computation of the optimal TCP (tool center point) for an industrial robot
• Formulation of an objective function and optimization problem
• Development of a fast underlying path planning algorithm

Description

The robot base placement of an industrial robot w.r.t. to the workpiece is crucial for the execution of a predefined robot motion. This placement is chosen once in the course of planning and constructing the robot work cell. However, in a flexible production environment, the robot trajectories change frequently, and in some cases an expensive and time-consuming repositioning of the robot becomes necessary. This project shows that with small adaptions of the robotic tool, a repositioning of the robot can be avoided.

To this end, an underlying path planning algorithm is developed. This path planner considers wide turning ranges of the robot axes and is capable to plan through kinematic singularities. Based on the path planner, an optimization problem is formulated,  with which the optimal TCP for multiple end-effector paths is determined. The objective function of this optimization problem considers the total number of inverse kinematic solutions, the total number of accomplished solutions, the joint movements and the reserves to the mechanical joint limits. Further, by rephrasing the problem, the proposed optimization algorithm is also capable to derive the optimal robot base position. This work is demonstrated for a trim application in a production line, where an optimal TCP and the optimal robot base position is derived.

Video

Selected Publications

• T. Weingartshofer, C. Hartl-Nesic, and A. Kugi, Optimal TCP and Robot Base Placement for a Set of Complex Continuous Paths, in Proceedings of the International Conference on Robotics and Automation (ICRA), Xi’an, China, 2021, pp. 9659-9665.
  [BibTex]

  @InProceedings{Weingartshofer2021,
  author = {Weingartshofer, T. and Hartl-Nesic, C. and Kugi, A.},
  booktitle = {Proceedings of the International Conference on Robotics and Automation (ICRA)},
  title = {Optimal TCP and Robot Base Placement for a Set of Complex Continuous Paths},
  doi = {10.1109/ICRA48506.2021.9561900},
  pages = {9659 - 9665},
  address = {Xi'an, China},
  issn = {2577-087X},
  month = {5},
  year = {2021},
  }

  22.10.2021
Observer-based Iterative Learning Control to Improve Path Accuracy of Industrial Robots

Project Focus

• Modeling of nonlinear effects within the drive train of robots
• Design of precise model-based state observers
• Iterative learning control to improve path accuracy at the end-effector

Description

For machining tasks with robots, path accuracy is an essential performance criterion. In many applications, accuracies in the range of tenths of a millimeter and below are required. Examples include the seam sealing of car bodies with robots and laser welding. In these applications, it is not only high static accuracy that is important, but also overall accuracy, which includes tracking errors of the control system, as well as dynamic effects of the mechanical structure. Figure 1 shows the tracking error in laser marking.

A major cause for the deviation from the ideal behavior shown above lies in the drive trains. Here, the gearboxes have the most significant influence. Compared to the ideal behavior, gearboxes exhibit the following behavior:

• Non-uniform friction: due to the varying engagement of the gear teeth, the friction is position-dependent and load-dependent.
• Non-constant gear ratio: due to imperfect tooth flanks, small deviations occur in the endeffector position. For robots 1-3 meters arm length, this can give rise for TCP (Tool Center Point) errors in the range of a few tenths of a millimeter.
• Finite and variable stiffness: due to the compliance of the gearbox, vibrations are excited in interaction with friction and imperfect transmission behavior. If the frequency of the variable stiffness coincides with the resonant frequency of the robot axes, this can lead to very high dynamic errors.

The gear effects are complex, especially in their dynamic interaction. Measurement methods usually require high-priced measuring equipment. Each robot for which compensation is to be used must be measured individually.

The aim of the project is to develop suitable robot models and state observers that incorporate the gear effects described above. Based on this, new control strategies are to be designed with which the growing accuracy requirements can be achieved. The main goal is to combine mechatronic, physical models in an optimal way with the processing of unstructured data in order to achieve the highest possible efficiency and ease of use. Furthermore, to address the availability of highly accurate measurement systems in practice, inexpensive available sensors will be used to guarantee a broad applicability of the developed methods. The measurement data obtained in this way will be used in the course of an iterative learning control to ultimately achieve the desired accuracy, not only in positioning tasks, but also while traversing paths.

Selected Publications

• B. Bischof, T. Glück, M. Böck, and A. Kugi, Path Following Control for Elastic Joint Robots, in Proceedings of the 20th IFAC World Congress, Toulouse, France, 2017, p. 4806–4811.
  [BibTex]

  @InProceedings{Bischof17,
  author = {Bischof, B. and Gl\"uck, T. and B\"ock, M. and Kugi, A.},
  title = {Path Following Control for Elastic Joint Robots},
  booktitle = {Proceedings of the 20th IFAC World Congress},
  year = {2017},
  volume = {50},
  number = {1},
  month = {7},
  pages = {4806--4811},
  doi = {10.1016/j.ifacol.2017.08.965},
  address = {Toulouse, France},
  issn = {2405-8963},
  }

• B. Bischof, Path and Surface Following Control for Industrial Robotic Applications, A. Kugi and K. Schlacher, Eds., Aachen: Shaker Verlag, 2020, vol. 47.
  [BibTex]

  @Book{Bischof2020,
  author = {Bischof, Bernhard},
  title = {{Path and Surface Following Control for Industrial Robotic Applications}},
  year = {2020},
  editor = {A. Kugi and K. Schlacher},
  volume = {47},
  series = {Modellierung und Regelung komplexer dynamischer Systeme},
  publisher = {Shaker Verlag},
  isbn = {978-3-8440-7200-6},
  address = {Aachen},
  organization = {Institute f{\"u}r Automatisierungs- und Regelungstechnik (TU Wien) und Regelungstechnik und Prozessautomatisierung (JKU Linz)},
  }

  13.10.2021
Control strategies for high-energy pulsed laser sources

Project focus

• mathematical modelling and theoretic investigation of involved laser dynamics
• development of adaptive model-based pulse shaping strategies
• suppression of dynamic and stochastic instabilities by means of feedback control
• explore the potential of systematic hardware/software codesign for pulsed laser sources

Description

Short high-energy pulses of laser light have become a valuable and flexible tool with applications in basic research (i.e., in strong field physics, for pumping of optical parametric amplifiers and free electron lasers, or for coherent stimulation of atomic of molecular processes) as well as applications such as ablation-based material processing and laser-based eye surgery. The generation of particularly short pulses can be achieved by injecting seed pulses from a pulse source such as a mode-locked laser into resonator cavity with a pumped gain medium inside – a socalled master oscillator power amplifier (MOPA) concept. A more economic approach in case the required pulse durations allow it  is to self-seed the cavity from spontaneous emission – a traditional Q-switched laser.

Many current and future applications of pulsed laser light require increasingly extreme operating parameters that entail specific issues depending on the chosen concept. For example, high repetition rates typically favoured in scanning or spectroscopic applications operate pumped resonator cavities close or within their dynamically unstable regime. This is particularly relevant if multiple amplification stages are economically or spatially unfeasible for the intended application. Additionally, the intrinsic stochastic fluctuations in self-seeded cavities often results in large energy fluctuations within the obtained pulse sequences that are highly detrimental for sensing applications. Another problem arises from the broad spectral bandwidth required for ultra-short pulsed operation, which leads to severely distorted and temporally broadened pulse shapes.

The timing requirements of modern pulse sources already largely relies on computerized control methods and the availability of programmable optical actuators such as acousto-optic modulators (AOMs) or spatial light modulators (SLMs). As a result, the application of advanced automatic control schemes can be used to mitigate or eliminate current limitations. Specifically, including the possibility of algorithmic solutions expands the range of strategies during the laser engineering process which in turn leads to more effective, more economic, and more flexible laser systems.

Selected publications

• L. Tarra, A. Deutschmann-Olek, and A. Kugi, Nonlinear feedback stabilisation and stochastic disturbance suppression of actively Q-switched lasers, in Proceedings of the 22nd IFAC World Congress, Yokohama, Japan, 2023 2023, pp. 77-82.
  [BibTex]

  @InProceedings{Tarra2023,
  author = {Tarra, L. and Deutschmann-Olek, A. and Kugi, A.},
  booktitle = {Proceedings of the 22nd IFAC World Congress},
  date = {2023},
  title = {Nonlinear feedback stabilisation and stochastic disturbance suppression of actively Q-switched lasers},
  doi = {10.1016/j.ifacol.2023.10.1550},
  number = {2},
  pages = {77-82},
  volume = {56},
  address = {Yokohama, Japan},
  issue = {2},
  journaltitle = {IFAC-PapersOnLine},
  month = {7},
  year = {2023},
  }

• L. Tarra, A. Deutschmann-Olek, V. Stummer, T. Flöry, A. Baltuska, and A. Kugi, Stochastic nonlinear model of the dynamics of actively Q-switched lasers, Optics Express, vol. 30, iss. 18, p. 32411–32427, 2022.
  [BibTex]

  @Article{Tarra2022,
  author = {Lukas Tarra and Andreas Deutschmann-Olek and Vinzenz Stummer and Tobias Fl\"{o}ry and Anrius Baltuska and Andreas Kugi},
  title = {Stochastic nonlinear model of the dynamics of actively Q-switched lasers},
  doi = {10.1364/OE.464508},
  number = {18},
  pages = {32411--32427},
  url = {http://opg.optica.org/oe/abstract.cfm?URI=oe-30-18-32411},
  volume = {30},
  journal = {Optics Express},
  keywords = {Amplified spontaneous emission; Fiber lasers; Q switched lasers; Random lasers; Spontaneous emission; Stimulated Brillouin scattering},
  month = {Aug},
  publisher = {Optica Publishing Group},
  year = {2022},
  }

• A. Deutschmann, W. Kemmetmüller, and A. Kugi, On the global feedback stabilization of regenerative optical amplifiers, in Proceedings of the 21st IFAC World Congress, Berlin, Germany, 2020, p. 5447–5452.
  [BibTex]

  @InProceedings{Deutschmann2020a,
  author = {A. Deutschmann and W. Kemmetmüller and A. Kugi},
  booktitle = {Proceedings of the 21st IFAC World Congress},
  title = {On the global feedback stabilization of regenerative optical amplifiers},
  doi = {10.1016/j.ifacol.2020.12.1547},
  note = {IFAC-PapersOnLine},
  number = {2},
  pages = {5447--5452},
  volume = {53},
  address = {Berlin, Germany},
  issn = {2405-8963},
  month = {06},
  year = {2020},
  }

• A. Deutschmann, T. Flöry, K. Schrom, V. Stummer, A. Baltuška, and A. Kugi, Bifurcation suppression in regenerative amplifiers by active feedback methods, Optics Express, vol. 28, iss. 2, pp. 1722-1737, 2020.
  [BibTex] [Download]

  @Article{Deutschmann2020,
  author = {Deutschmann, A. and Fl\"ory, T. and Schrom, K. and Stummer, V. and Baltu\v{s}ka, A. and Kugi, A.},
  title = {Bifurcation suppression in regenerative amplifiers by active feedback methods},
  journal = {Optics Express},
  year = {2020},
  volume = {28},
  number = {2},
  pages = {1722-1737},
  doi = {10.1364/OE.380404},
  }

• A. Deutschmann, P. Malevich, A. Baltuska, and A. Kugi, Modeling and iterative pulse-shape control of optical chirped pulse amplifiers, Automatica, vol. 98, p. 150–158, 2018.
  [BibTex] [Download]

  @Article{Deutschmann2018a,
  author = {Deutschmann, A. and Malevich, P. and Baltuska, A. and Kugi, A.},
  title = {Modeling and iterative pulse-shape control of optical chirped pulse amplifiers},
  journal = {Automatica},
  year = {2018},
  volume = {98},
  pages = {150--158},
  issn = {0005-1098},
  doi = {10.1016/j.automatica.2018.09.002},
  }

Partners

Ultrafast Laser Group, Photonics Institute at TU Wien

EKSPLA