| 1. |
- Hedberg, Erik, 1986-
(författare)
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Control, Models and Industrial Manipulators
- 2020
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The two topics at the heart of this thesis are how to improve control of industrial manipulators and how to reason about the role of models in automatic control.On industrial manipulators, two case studies are presented. The first investigates estimation with inertial sensors, and the second compares control by feedback linearization to control based on gain-scheduling.The contributions on the second topic illustrate the close connection between control and estimation in different ways. A conceptual model of control is introduced, which can be used to emphasize the role of models as well as the human aspect of control engineering. Some observations are made regarding block-diagram reformulations that illustrate the relation between models, control and inversion. Finally, a suggestion for how the internal model principle, internal model control, disturbance observers and Youla-Kucera parametrization can be introduced in a unified way is presented.
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| 2. |
- Ighani Arani, Perna, 1989-, et al.
(författare)
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Bariatric surgery prior to total knee arthroplasty is not associated with lower risk of revision : a register-based study of 441 patients
- 2021
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Ingår i: Acta Orthopaedica. - : Taylor & Francis. - 1745-3674 .- 1745-3682. ; 92:1, s. 97-101
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Tidskriftsartikel (refereegranskat)abstract
- Background and purpose: Obesity is a considerable medical challenge in society. We investigated the risk of revision for any reasons and for infection in patients having total knee arthroplasty (TKA) for osteoarthritis (OA) within 2 years after bariatric surgery (BS) and compared them with TKAs without BS.Patients and methods: We used the Scandinavian Obesity Surgery Registry (SOReg) and the Swedish Knee Arthroplasty Register (SKAR) to identify patients operated on in 2009-2019 with BS who had had primary TKA for OA within 2 years after the BS (BS group) and compared them with TKAs without prior BS (noBS group). We determined adjusted hazard ratio (HR) for the BS group and noBS group using Cox proportional hazard regression for revision due to any reasons and for infection. Adjustments were made for sex, age groups, and BMI categories preoperatively.Results: 441 patients were included in the BS group. The risk of revision for infection was higher for the BS group with HR 2.2 (95% CI 1.1-4.7) adjusting for BMI before the TKA, while the risk of revision for any reasons was not statistically significant different for the BS group with HR 1.3 (CI 0.9-2.1). Corresponding figures when adjusting for BMI before the BS were HR 0.9 (CI 0.4-2) and HR 1.2 (CI 0.7-2).Interpretation: Our findings did not indicate that BS prior to TKA was associated with lower risk of revision.
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| 3. |
- Robertsson, Kristofer, et al.
(författare)
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A continuum damage model for creasing and folding of paperboard
- 2023
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Ingår i: Packaging Technology and Science. - 0894-3214. ; 36:12, s. 1037-1050
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Tidskriftsartikel (refereegranskat)abstract
- A continuum damage framework is proposed for modelling the delamination process occurring in paperboard during mechanical loading. The main application of interest is line creasing and subsequent line folding used in package forming. To adequately capture creasing and folding, a continuum damage framework that uses a single isotropic damage variable that evolves with the plastic strains associated with out-of-plane shearing is used. The damage evolution is calibrated against folding experiments for a specific reference mesh, and a simple scaling strategy is proposed to reduce the inherent mesh dependency. To highlight the potential of the proposed model, an illustrative 3D example is considered where a paperboard sheet is creased by two plates and folded to resemble the corner of a package.
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| 4. |
- Robertsson, Kristofer, et al.
(författare)
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A rate-dependent continuum model for rapid converting of paperboard
- 2021
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Ingår i: Applied Mathematical Modelling. - : Elsevier BV. - 0307-904X. ; 99, s. 497-513
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Tidskriftsartikel (refereegranskat)abstract
- A rate-dependent continuum model for paperboard is developed within a framework for finite strains and finite deformations. A multiplicative split of the deformation gradient into an elastic and an inelastic part is assumed. For the in-plane modes of deformation, viscoelasticity is introduced via a thermodynamically consistent generalization of the Maxwell formulation. The elastic transition between out-of-plane compression and out-of-plane tension is smooth, excluding the need for a switch function which is present in a number of existing paperboard models. The evolution of the inelastic part is modeled using two potential functions separating compression from shear and tension. To calibrate the material model, a set of experiments at different loading rates have been performed on single ply paperboard together with creep and relaxation tests for in-plane uniaxial tension. The model is validated by simulating two loading cases related to package forming, line-folding followed by subsequent force-relaxation and line-creasing during different operating velocities in conjunction with a creep study.
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| 5. |
- Robertsson, Kristofer, et al.
(författare)
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Out-of-plane uniaxial loading of paperboard: experimental procedure and evaluation
- 2023
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Ingår i: Nordic Pulp and Paper Research Journal. - 0283-2631. ; 38:3, s. 389-398
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Tidskriftsartikel (refereegranskat)abstract
- Development of three-dimensional continuum models for paperboard is an active field and the need for reliable measurements to calibrate and validate such models is evident. An experimental device and protocol for cyclic out-of-plane loading is developed. This loading sequence is present during converting operations of paperboard. The experimental tests reveals that the commonly observed soft initial non-linear response during out-of-plane compression is a structural effect that stems from the surface roughness rather than being an inherent material behavior. A gluing procedure, used to perform cyclic out-of-plane loading, is mitigating the effect of the surface roughness. Several novel cyclic loading experiments are performed, alternating between compression and tension which indicates that fiber bonds are not recovered in compression after they have been broken through delamination. Measurements also show that the transition in compression and tension is continuous, hence the use of a switch function present in a number of constitutive continuum models for paperboard is deemed questionable.
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| 6. |
- Savasci, Mehmet, et al.
(författare)
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DDPC: Automated Data-Driven Power-Performance Controller Design on-the-fly for Latency-sensitive Web Services
- 2023
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Ingår i: ACM Web Conference 2023 - Proceedings of the World Wide Web Conference, WWW 2023. - 9781450394161 ; , s. 3067-3076
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Konferensbidrag (refereegranskat)abstract
- Traditional power reduction techniques such as DVFS or RAPL are challenging to use with web services because they significantly affect the services' latency and throughput. Previous work suggested the use of controllers based on control theory or machine learning to reduce performance degradation under constrained power. However, generating these controllers is challenging as every web service applications running in a data center requires a power-performance model and a fine-tuned controller. In this paper, we present DDPC, a system for autonomic data-driven controller generation for power-latency management. DDPC automates the process of designing and deploying controllers for dynamic power allocation to manage the power-performance trade-offs for latency-sensitive web applications such as a social network. For each application, DDPC uses system identification techniques to learn an adaptive power-performance model that captures the application's power-latency trade-offs which is then used to generate and deploy a Proportional-Integral (PI) power controller with gain-scheduling to dynamically manage the power allocation to the server running application using RAPL. We evaluate DDPC with two realistic latency-sensitive web applications under varying load scenarios. Our results show that DDPC is capable of autonomically generating and deploying controllers within a few minutes reducing the active power allocation of a web-server by more than 50% compared to state-of-the-art techniques while maintaining the latency well below the target of the application.
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| 7. |
- Wittsten, Jens, et al.
(författare)
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Removing numerical dispersion from linear evolution equations
- 2021
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Ingår i: Pure and Applied Analysis. - Berkeley : Mathematical Sciences Publishers. - 2578-5893 .- 2578-5885. ; 3:2, s. 253-293
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Tidskriftsartikel (refereegranskat)abstract
- We describe a method for removing the numerical errors in the modeling of linear evolution equations that are caused by approximating the time derivative by a finite difference operator. The method is based on integral transforms realized as certain Fourier integral operators, called time dispersion transforms, and we prove that, under an assumption about the frequency content, it yields a solution with correct evolution throughout the entire lifespan. We demonstrate the method on a model equation as well as on the simulation of elastic and viscoelastic wave propagation.
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