| 1. |
- Axelsson, Patrik, 1985-, et al.
(författare)
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Lego Segway Project Report
- 2011
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This project was a part of the course Applied Control and Sensor Fusion (http://www.control.isy.liu.se/student/graduate/AppliedControl/index.html) during summer and fall 2010. The goal of the course was to be a practical study of implementation issues, not always encountered in the life of a PhD student.A segway was constructed using a LEGO Mindstorms NXT kit and a gyro, and the goal was to construct a self balancing segway. To do this the motor angles and the gyro measurements were available, and a working Simulink program. The main focus in this project has been to construct an observer.The segway can be used for demos in basic control courses, and a manual can be found at the end of the report
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| 2. |
- Carvalho Bittencourt, André, et al.
(författare)
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Modeling and Identification of Wear in a Robot Joint under Temperature Uncertainties
- 2010
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This paper considers the problem of wear estimation in a standard industrial robot joint. The effects of wear to the static friction of a robot joint are analyzed from experiments. An extended static friction model is proposed that explains changes related to joint speed, load, temperature and wear. Based on this model and static friction observations, a model-based wear estimator is proposed. The performance of the estimator under temperature uncertainties is found both by means of simulations and experiments in an industrial robot. Special attention is given to the analyses of the best speed region for wear estimation. As it is shown, the method can distinguish the effects of wear even under large temperature variations, opening up for the use of robust joint diagnosis for industrial robots.
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| 3. |
- Jung, Ylva, 1984-
(författare)
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Inverse system identification with applications in predistortion
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Models are commonly used to simulate events and processes, and can be constructed from measured data using system identification. The common way is to model the system from input to output, but in this thesis we want to obtain the inverse of the system.Power amplifiers (PAs) used in communication devices can be nonlinear, and this causes interference in adjacent transmitting channels. A prefilter, called predistorter, can be used to invert the effects of the PA, such that the combination of predistorter and PA reconstructs an amplified version of the input signal. In this thesis, the predistortion problem has been investigated for outphasing power amplifiers, where the input signal is decomposed into two branches that are amplified separately by highly efficient nonlinear amplifiers and then recombined. We have formulated a model structure describing the imperfections in an outphasing \abbrPA and the matching ideal predistorter. The predistorter can be estimated from measured data in different ways. Here, the initially nonconvex optimization problem has been developed into a convex problem. The predistorters have been evaluated in measurements.The goal with the inverse models in this thesis is to use them in cascade with the systems to reconstruct the original input. It is shown that the problems of identifying a model of a preinverse and a postinverse are fundamentally different. It turns out that the true inverse is not necessarily the best one when noise is present, and that other models and structures can lead to better inversion results.To construct a predistorter (for a PA, for example), a model of the inverse is used, and different methods can be used for the estimation. One common method is to estimate a postinverse, and then using it as a preinverse, making it straightforward to try out different model structures. Another is to construct a model of the system and then use it to estimate a preinverse in a second step. This method identifies the inverse in the setup it will be used, but leads to a complicated optimization problem. A third option is to model the forward system and then invert it. This method can be understood using standard identification theory in contrast to the ones above, but the model is tuned for the forward system, not the inverse. Models obtained using the various methods capture different properties of the system, and a more detailed analysis of the methods is presented for linear time-invariant systems and linear approximations of block-oriented systems. The theory is also illustrated in examples.When a preinverse is used, the input to the system will be changed, and typically the input data will be different than the original input. This is why the estimation of preinverses is more complicated than for postinverses, and one set of experimental data is not enough. Here, we have shown that identifying a preinverse in series with the system in repeated experiments can improve the inversion performance.
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| 4. |
- Jung, Ylva, 1984-
(författare)
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Predistortion of a Radio Frequency Power Amplifier
- 2010
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- A linearized digital radio frequency (RF) power amplifier (PA), a switched RF PA, is more power efficient than an analog amplifier, but may cause interference in adjacent transmitting channels similar to analog amplifiers. This interference is due to the inherent nonlinearities, and this project investigated the possibility of reducing this interference by using a prefilter, a predistorter, to improve the linearity of the linearized digital amplifiers. Two models, a forward model and an inverse model, the predistorter, have been estimated from measured data. The model addresses the gain and phase errors of the power amplifier. The first experiments show promising results, like improved Adjacent Channel Leakage Ratio (ACLR) for WCDMA and improved margins to the spectral mask for EDGE 8PSK measured at 2 GHz.
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