09. Konferenssit, seminaarit ja kokoomateokset / Conferences, Seminars and Compiled works

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Yliopiston järjestämien konferenssien kokoomateoksia / Conference proceedings of the university's events

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Active control of radial rotor vibrations in electric machines : identification, modeling and control design
(Helsinki University of Technology, 2008) Orivuori, Juha; Laiho, Antti; Sinervo, Anssi; Department of Automation and Systems Technology; Automaatio- ja systeemitekniikan laitos; Faculty of Electronics, Communications and Automation; Elektroniikan, tietoliikenteen ja automaation tiedekunta
This paper presents results related to modeling, identification, control design and simulation of an electric motor equipped with a new force actuator. The model consists of several partial models, thus separating certain physical phenomena into independent processes. The inputs and outputs of the models to be identified are strongly correlated. This makes the identification process significantly more complicated. Three different control algorithms are designed for the process. The performance of the control algorithms are tested against finite element models in extensive simulations. The paper concludes in description of preliminary test results with an actual test machine.
Dynamic Obstacle Overcoming Capability of Pendulum-driven Ball-Shaped Robots
(IASTED, 2014) Ylikorpi, Tomi; Forsman, Pekka; Halme, Aarne; Automaatio- ja systeemitekniikan laitos; Department of Automation and Systems Technology; Sähkötekniikan korkeakoulu; School of Electrical Engineering
This paper discusses dynamic step-crossing capability of pendulum-driven ball-shaped robots. We introduce an extended dynamic model that allows modeling of ballrobot rolling, bouncing and slipping. Based on the new model, our simulations predict the maximum over-passable step-height for the robot. The simulation results agree well with the result from a parallel simulation in Adamssoftware as well as with practical experiments. The new dynamic model can be applied for mobility analysis of robot-ball designs as well as for path planning.
Feature Based Modeling and Mapping of Tree Trunks and Natural Terrain Using 3D Laser Scanner Measurement System
(IFAC, 2013) Hyyti, Heikki; Visala, Arto; Automaatio- ja systeemitekniikan laitos; Department of Automation and Systems Technology; Autonomous systems; Autonomiset järjestelmät; Sähkötekniikan korkeakoulu; School of Electrical Engineering
This paper presents a novel approach to measure tree trunks and to model the ground using a 3D laser scanner. The 3D scanner, self-build using two 2D Sick scanners on a rotating base, measures each scan line approximately at 45° angle towards the ground and the trees. Single scan lines are segmented to find ground and tree returns. 3D point clouds from the surrounding forest are recorded while the measuring vehicle is moving. Sequential scan lines are joined together as the pose changes are reduced from the older buffered measurements. Laser odometry and inertial measurements are used to measure the pose changes. The ground is modeled by fitting a 1m grid to 3D point cloud extracted using a ground return detector. Tree trunks are searched from the 3D point cloud using a histogram approach to segment measurements into separate point clouds for each tree trunk. Tree trunks are modeled using ten circle features one on the other using the extracted point cloud. Instead of using the whole point cloud, mapping is done only for the extracted features and the travelled path to save computation time. Our method can detect nearly all tree trunks and measure them on short ranges of less than 8m with errors less than 4cm in diameter.
Gyroscopic Precession In Motion Modelling Of Ball-Shaped Robots
(ECMS, 2014) Ylikorpi, Tomi; Forsman, Pekka; Halme, Aarne; Automaatio- ja systeemitekniikan laitos; Department of Automation and Systems Technology; Sähkötekniikan korkeakoulu; School of Electrical Engineering
This study discusses kinematic and dynamic precession models for a rolling ball with a finite contact area and a point contact respectively. In literature, both conventions have been applied. In this paper, we discuss in detail the kinematic and dynamic models to describe the ball precession and the radius of a circular rolling path. The kinematic model can be used if the contact area and friction coefficient are sufficient to prevent slippage. The dynamic precession model has significance in multi-body simulation environments handling rolling balls with ideal point contacts. We have applied both the kinematic and dynamic precession model to evaluate the no-slip condition of the existing GimBall-robot. According to the result, the necessity of an external precession torque may cause slipping at lower velocities than expected if ignoring this torque.
ISO 11783 Compliant Forest Crane As a Platform for Automatic Control
(Aalto University, 2013) Kalmari, Jouko; Pihlajamäki, Tuomas; Hyyti, Heikki; Luomaranta, Markku; Visala, Arto; Automaatio- ja systeemitekniikan laitos; Department of Automation and Systems Technology; Sähkötekniikan korkeakoulu; School of Electrical Engineering
ISO 11783 is a communication standard for agricultural and forest machines. This standard allows an implement to command specific functions of a tractor. Agricultural tractors can be equipped for silvicultural work forming small scale forest machine. It could cost-efficiently compete against common forest machines in some tasks. We have developed an ISO 11783 compliant forest crane connected to an agricultural tractor. The combination is designed to work as a test platform for an autonomous forest machine. The dynamics of the system have been studied using first and second-order models. Based on identification tests with no load on the crane, first-order model is sufficient for describing the motion of most of the cylinders. According to the identification results, small controls do not cause motion on the crane, and a non-linear model is required. Currently used hydraulics of agricultural tractors is not entirely adequate for controlling forest cranes. With more intelligent tractor hydraulics, the crane could be more controllable and energy-efficient.
Real-time Detection of Young Spruce Using Color and Texture Features on an Autonomous Forest Machine
(Aalto University, 2013) Hyyti, Heikki; Kalmari, Jouko; Visala, Arto; Department of Automation and Systems Technology; Automaatio- ja systeemitekniikan laitos; Autonomous systems; Autonomiset järjestelmät; Sähkötekniikan korkeakoulu; School of Electrical Engineering
Forest machines are manually operated machines that are efficient when operated by a professional. Point cleaning is a silvicultural task in which weeds are removed around a young spruce tree. To automate point cleaning, machine vision methods are used for identifying spruce trees. A texture analysis method based on the Radon and wavelet transforms is implemented for the task. Real-time GPU implementation of algorithms is programmed using CUDA framework. Compared to a single thread CPU implementation, our GPU implementation is between 18 to 80 times faster depending on the size of image blocks used. Color information is used in addition of texture and a location estimate of the tree is extracted from the detection result. The developed spruce detection system is used as a part of an autonomous point cleaning machine. To control the system, an integrated user interface is presented. It allows the operator to control, monitor and train the system online.
Sway Estimation Using Inertial Measurement Units for Cranes with a Rotating Tool
(Aalto University, 2013) Kalmari, Jouko; Hyyti, Heikki; Visala, Arto; Automaatio- ja systeemitekniikan laitos; Department of Automation and Systems Technology; Sähkötekniikan korkeakoulu; School of Electrical Engineering
Cranes have often a freely hanging load or tool that starts easily swaying. Anti-sway control requires that the angles and angular velocities of the swinging object are measured. Some cranes can also rotate the tool with a hydraulic motor, and in many cases this rotator angle should also be known. Instrumenting all three axes, two swaying and one rotating axis, with traditional rotary encoders can be challenging. We propose an extended Kalman filter based system using two inertial measurement units. This system can measure the swaying in both directions and estimate the rotator angle. Computer vision system is used as reference. The initial results show that the error is approximately 5 degrees in the rotator angle and 2 degrees in the sway angles. The observer runs at 100 Hz on an embedded microcontroller.
Unified Representation Of Decoupled Dynamic Models For Pendulum-Driven Ball-Shaped Robots
(ECMS, 2014) Ylikorpi, Tomi; Forsman, Pekka; Halme, Aarne; Saarinen, Jari; Automaatio- ja systeemitekniikan laitos; Department of Automation and Systems Technology; Sähkötekniikan korkeakoulu; School of Electrical Engineering
Dynamic models describing the ball-robot motion form the basis for developments in ball-robot mechanics and motion control systems. For this paper, we have conducted a literature review of decoupled forward-motion models for pendulum-driven ball-shaped robots. The existing models in the literature apply several different conventions in system definition and parameter notation. Even if describing the same mechanical system, the diversity in conventions leads into dynamic models with different forms. As a result, it is difficult to compare, reproduce and apply the models available in the literature. Based on the literature review, we reformulate all common variations of decoupled dynamic forward-motion models using a unified notation and formulation. We have verified all reformulated models through simulations, and present the simulation results for a selected model. In addition, we demonstrate the different system behavior resulting from different ways to apply the pendulum reaction torque, a variation that can be found in the literature. For anyone working with the ball-robots, the unified compilation of the reformulated dynamic models provides an easy access to the models, as well as to the related work.

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Browsing 09. Konferenssit, seminaarit ja kokoomateokset / Conferences, Seminars and Compiled works by Department "Automaatio- ja systeemitekniikan laitos"

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