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- Karlsson, Johan, et al.
(författare)
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Shape Modeling by Optimising Description Length Using Gradients and Parameterisation Invariance
- 2012
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Ingår i: Analysis for Science, Engineering and Beyond, The Tribute Workshop in Honour of Gunnar Sparr held in Lund, May 8-9, 2008. - Berlin, Heidelberg : Springer Berlin Heidelberg. - 9783642202353 - 9783642202360 ; 6, s. 51-91
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- In Statistical Shape Modeling, a dense correspondence between the shapes in the training set must be established. Traditionally this has been done by hand, a process that commonly requires a lot of work and is difficult, especially in 3D. In recent years there has been a lot of work on automatic construction of Shape Models. In recent papers (Davies et al., Medical Image Computing and Computer-Assisted Intervention MICCAI’2001, pp. 57–65, 2001; Davies et al., IEEE Trans. Med. Imaging. 21(5):525–537 2002; Kotcheff and Taylor, Med. Image Anal. 2:303–314 1998) Minimum Description Length, (MDL), is used to locate a dense correspondence between shapes. In this paper the gradient of the description length is derived. Using the gradient, MDL is optimised using steepest descent. The optimisation is therefore faster and experiments show that the resulting models are better. To characterise shape properties that are invariant to similarity transformations, it is first necessary to normalise with respect to the similarity transformations. This is normally done using Procrustes analysis. In this paper we propose to align shapes using the MDL criterion. The MDL based algorithm is compared to Procrustes on a number of data sets. It is concluded that there is improvement in generalisation when using MDL to align the shapes. In this paper novel theory to prevent the commonly occurring problem of clustering under correspondence optimisation is also presented. The problem is solved by calculating the covariance matrix of the shapes using a scalar product that is invariant to mutual reparameterisations. An algorithm for implementing the ideas is proposed and compared to Thodberg’s state of the art algorithm for automatic shape modeling. The suggested algorithm is more stable and the resulting models are of higher quality according to the generalisation measure and according to visual inspection of the specificity.
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| 4. |
- Eker, Johan, et al.
(författare)
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A Nonlinear Observer for the Inverted Pendulum
- 1996
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Konferensbidrag (refereegranskat)abstract
- This paper deals with the design of a nonlinear observer for the inverted pendulum. The observer uses the standard structure of the linear observer with the linear model replaced by a nonlinear model. Nominal observer gains are determined from a linearised model. This model is also used to find a compromise between robustness and performance. The stability of the observer is then discussed and conditions for the stability of the observer are given. The results are illustrated by simulation and experiments on a real pendulum
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| 5. |
- Iwase, Masami, et al.
(författare)
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Analysis of safe manual control by using Furuta pendulum
- 2006
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Ingår i: 2006 IEEE Conference on Computer Aided Control System Design.
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Konferensbidrag (refereegranskat)abstract
- This paper focuses on the interaction of manual and automatic control in a demanding task where the process is unstable and has actuator limitation. The problem is inspired by control of high performance aircrafts but which is similar to controlling the arm of a Furuta pendulum while maintaining the stability of the pendulum. The task is to control the position of the pendulum arm manually while maintaining the pendulum in the upright position. The analysis of regions for safe maneuvers is important to realize the desired control system.
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| 10. |
- Johansson, Karl Henrik, et al.
(författare)
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Limit cycles with chattering in relay feedback systems
- 2002
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Ingår i: IEEE Transactions on Automatic Control. - 0018-9286. ; 47:9, s. 1414-1423
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Tidskriftsartikel (refereegranskat)abstract
- Relay feedback has a large variety of applications in control engineering. Several interesting phenomena occur in simple relay systems. In the paper, scalar linear systems with relay feedback are analyzed. It is shown that a limit cycle where part of the limit cycle consists of fast relay switchings can occur. This chattering is analyzed in detail and conditions for approximating it by a sliding mode are derived. A result on existence of limit cycles with chattering is given, and it is shown that the limit cycles can have arbitrarily many relay switchings each period. Limit cycles with regular sliding modes are also discussed. Examples illustrate the results.
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