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1

Friction compensation in the inverted pendulum controller by means of a neural network

Balcerzak M.

Mechanics and Mechanical Engineering

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2018

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Vol. 22, nr 4

875--883

EN

This paper presents an experimental confirmation of the novel method of friction modelling and compensation. The method has been applied to an inverted pendulum control system. The practical procedure of data acquisition and processing has been described. Training of the neural network friction model has been covered. Application of the obtained model has been presented. The main asset of the presented model is its correctness in a wide range of relative velocities. Moreover, the model is relatively easy to build.

2

Preprocessing danych uczących w neuronowych zagadnieniach regresyjnych

Kowalik M., Trzepieciński T.

Logistyka

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2015

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nr 4

4201--4207, CD2

PL

W pracy przedstawiono metody optymalizacji liczby zmiennych wejściowych sieci neuronowej na podstawie wyników badania tarcia metodą przeciągania pasa blachy ze zginaniem, która służy do modelowania zjawiska tarcia na progu ciągowym podczas wytłaczania blach. Badaniom poddano po trzy gatunki blach mosiężnych, stalowych oraz ze stopu aluminium. Optymalizację liczby zmiennych wejściowych dokonano za pomocą metod selekcji krokowej wstecznej oraz postępującej a także za pomocą algorytmów genetycznych. Na podstawie określonej w każdej z zastosowanych technik optymalizacyjnych liczby zmiennych zbudowano modele regresyjne sieci wielowarstwowej. W zakresie wprowadzanych wartości kary jednostkowej dla każdego z testowanych algorytmów zaobserwowano lokalne minimum wartości błędu sieci dla zbioru uczącego. Wysoką wartość błędu sieci przy dużej liczbie zmiennych można wytłumaczyć szumem wprowadzanym przez zmienne, które mogą być w pewnych zakresach ich wartości ze sobą skorelowane. Wysoka wartość miernika korelacji przy niskiej wartości S. D. Ratio dla zbioru uczącego świadczy o dobrych własnościach aproksymacyjnych zbudowanych sieci neuronowych.

EN

The paper presents a method to optimize the number of input variables of the neural network on the basis of the results of draw bead simulator test. This test is used to model the friction phenomenon on the draw bead in sheet metal forming. The study involved three kinds of brass, steel and aluminum alloy sheets. Optimization of the number of input variables was performed using three methods: backward stepwise selection, forward stepwise selection and genetic algorithms. On the basis of each number of input variables determined using optimization techniques the multilayer regression models of multilayer networks were built. In the range of unit penalty value input for all tested algorithms the local minima of network error for training set were observed. The high network error value including the big number of variables can be explained by noise caused by the variables which can be correlated in the certain ranges of their values. The high value of correlation coefficient at low value of S.D. ratio for training set denote the good approximate properties of built neural networks.

3

The Joint Vibration Analysis of a Multi-Link Surgical Manipulator

Leniowska L., Leniowski R.

Archives of Acoustics

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2012

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Vol. 37, No. 4

475-482

EN

This paper presents a vibration analysis of a multi-link surgical micromanipulator joint, based on its detailed mathematical model. The manipulator’s prototype contains 6 links with the diameter of 8–10 [mm] and with the length of the modules of about 130 [mm]. It is driven by brushless servomotors with worm and planetary gears, for which the total transmission ratio is above 1/10000. Regarding the low efficiency of micro-robot drive systems and its vibrations, a reliable joint model and its performance is crucial for the development of a high-precision control system. To achieve the required accuracy, modelling framework has been enriched with an advanced model of friction. Simulation results are presented and discussed.

4

Probabilistic Model of Dynamic Forces in Thread in the Knitting Zone of Weft Knitting Machines, Allowing for the Heterogeneity of Visco-Elasticity Yarn Properties

Kowalski K., Włodarczyk B., Kowalski T. M.

Fibres & Textiles in Eastern Europe

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2010

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Vol. 18, no. 4 (81)

61--67

EN

This study presents an explanation of the stochastic character of dynamic thread loads in the knitting zone of weft-knitting machines based on a probabilistic model of the knitting process in which thread has been treated as a body of heterogeneous viscoelastic proper- ties. Computer simulations were carried out according to the model presented, proving the influence of the randomly changing rheological parameters of thread on the force dispersion in thread in the knitting zone. Besides this it was established that the size of this dispersion also depends on the profile of the cam in the knitting zone.

PL

Wyjaśnienie stochastycznego charakteru dynamicznych obciążeń nitek w strefie dziania na szydełkarkach dokonano na podstawie probabilistycznego modelu procesu dziania, w którym nitkę potraktowano, jako ciało o niejednorodnych właściwościach lepko-sprężystych. Przeprowadzone symulacje komputerowe wg opracowanego modelu udokumentowały wpływ losowo zmiennych parametrów reologicznych nitki na wielkość rozrzutu sił w nitkach w strefie dziania. Stwierdzono ponadto, iż wielkość tego rozrzutu sił zależna jest także od profilu kształtki w strefie dziania.

5

Effect of temperature and strain rate on friction factor during hot deformation of Al-Mn and Al-Cu-Mg Al-alloys

Petrov P., Gnevashev D., Dubinchin A., Petrov M., Solotych V., Eiesland J. W.

Computer Methods in Materials Science

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2009

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Vol. 9, No. 1

55-60

EN

Massive hot forging of any aluminium alloy can be performed with the help of several types of metal-forming machines, namely hydraulic press, mechanical press, screw press etc. Applying one of these machines allows production of either typical forgings or near net shape forgings. Anyway, there is a technological parameter which has a strong influence the quality of a forging made of Al-alloy. This is the composition of lubricant. The choice of a lubricant for forging is major task, especially in case of aluminium alloys deformation. The efficiency of any lubricant can be estimated by at least three criteria: 1) the lubricant should have good tribological properties; 2) the lubricant should have good heat-shielding properties; 3) the lubricant should produce little or no smoke. The paper is linked to the investigation of the effect of temperature as well as strain rate on lubricants for massive hot forging. Friction factor was chosen as one of the criteria for the estimation of the effects mentioned. Wide range of temperatures was observed. The research on friction has been done for Al-Mn and Al-Cu-Mg aluminium alloys. In this connection, physical and numerical investigation of friction performed. The condition of experimental investigation corresponded to the forging process of Al-alloys with the help of the hydraulic and screw press as well. The ring upsetting technique with combination of FE-simulation was chosen for investigation of the effect of temperature and strain rate on friction factor value. The regressions for the relationship between friction factor and temperature as well as strain rate for all lubricant under study have been obtained. Some practical recommendations were given.

PL

Tematem artykułu są badania wpływu temperatury oraz prędkości odkształcenia na własności smarów w procesie kucia matrycowego na gorąco. Wspólczynnik tarcia został wybrany jako jedno z kryteriów estymacji analizowanego efektu. Badania tarcia wykonano dla stopów aluminium Al-Mg oraz Al-Cu-Mg w podwyższonej temperaturze. Zachowanie się smarów analizowano w zakresie temperatur 200-470°C. Przeprowadzono fizyczne oraz numeryczne symulacje. Badania doświadczalne wykonane zostały dla procesu kucia stopów aluminium na prasach hydraulicznej i śrubowej. Natomiast do analizy numerycznej wpływu temperatury i prędkości odkształcenia na współczynnik tarcia wybrano proces spęczania pierścieni symulowany przy użyciu metody elementów skończonych. Ostatecznie otrzymano zależności regresyjne pomiędzy analizowanymi parametrami, które zostały przedstawione w artykule wraz z pewnymi praktycznymi wskazówkami.

6

Robot cotroller with a self-measurement capability enabling the identification of friction

Woźniak A., Szynkiewicz W., Zieliński C.

Archives of Control Sciences

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2003

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Vol. 13, no. 4

391-414

EN

This paper proposes an open controller structure which beside realising the diverse control tasks enables gathering of the idetification data which in turn can be utilised for improving servo control algorithms. The authors are convinced that in case of research-oriented controller archtectrures self-identification and self-measurement components should be included. Moreover the paper shows how the gathered data has been utilised in the modelling of friction. This problem has been investigated to increase the precision of motions of a robot equipped with a machinning head.

7

Non-constant coefficient friction models in 3d simulation of drawing processes

Rońda J., Colville K. W., Mahrenholtz O.

Computer Assisted Mechanics and Engineering Sciences

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2001

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Vol. 8, No. 4

609-628

EN

Different friction models: the classic one proposed by Amontons-Coulomb (AC) with a constant friction coefficient, a three-parameter model proposed by Wriggers et al. [1], and a model based on the concept of `work-hardening' proposed by de Souza Neto et al. [2], are applied to the 3-D square-cup drawing and S-rail stamping FE simulations. The benchmark problems used during NUMISHEET'93 for a cup drawing and NUMISHEET'96 for S-rail stamping were simulated here. The results obtained for these three models are presented to illustrate the influence of the friction model on the drawing process. [1] P. Wriggers, T. vu Van, E. Stein. Finite element formulation of large deformation impact-contact problems with friction. Computers and Structures, 37: 319-331, 1990. [2] E.A. de Souza Neto, K. Hashimoto, D. Peric, D.R.J. Owen. A phenomenological model for frictional contact accounting for wear effects. Phil. Trans. R. Soc. London, A354: 819-843, 1996.

8

Almost periodic vibration excited by dry friction

Bogacz R., Ryczek B.

Mechanics and Mechanical Engineering

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2000

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Vol. 4, nr 2

197--212

EN

This paper attends to the problem of a self-excited system with dry friction. The system is composed of mass that interact viscoelasticly with the drive, and by means of dry friction with a foundation The objective of the experimental research on the system was to formulate a dry friction model that would describe the case of stick-slip vibration as well as almost-periodic vibration of steel-polyester pair The model allows for the impact of the following parameters: velocity of motion, acceleration sign, time of adhesion and force rate. The paper includes computer simulation of the vibration of the considered system and comparison between the results of experimental and theoretical analysis.