Induction motor versus permanent magnet synchronous motor in motion control applications: a comparative study

High dynamic performance of an electric motor is a fundamental prerequisite in motion control applications, also known as servo drives. Recent developments in the field of microprocessors and power electronics have enabled faster and faster movements with an electric motor. In such a dynamically demanding application, the dimensioning of the motor differs substantially from the industrial motor design, where feasible characteristics of the motor are for example high efficiency, a high power factor, and a low price. In motion control instead, such characteristics as high overloading capability, high-speed operation, high torque density and low inertia are required. The thesis investigates how the dimensioning of a high-performance servomotor differs from the dimensioning of industrial motors. The two most common servomotor types are examined; an induction motor and apermanent magnet synchronous motor. The suitability of these two motor types indynamically demanding servo applications is assessed, and the design aspects that optimize the servo characteristics of the motors are analyzed. Operating characteristics of a high performance motor are studied, and some methods for improvements are suggested. The main focus is on the induction machine, which is frequently compared to the permanent magnet synchronous motor. A 4 kW prototype induction motor was designed and manufactured for the verification of the simulation results in the laboratory conditions. Also a dynamic simulation model for estimating the thermal behaviour of the induction motor in servo applications was constructed. The accuracy of the model was improved by coupling it with the electromagnetic motor model in order to take into account the variations in the motor electromagnetic characteristics due to the temperature rise.

Market Study of Electric Drive Motion Control Business

Tämän diplomityön tavoitteena oli tutkia älykkäiden paikoituskäyttöjen markkinoita ja liiketoimintamalleja. Työn pääongelmina oli määritellä alalla käytössä olevaa terminologiaa, määrittää markkinoiden koko paikoitusominaisuudet omaaville kolmivaihetaajuusmuuttajille, tutkia viiden alalla toimivan paikoituskäyttötoimittajan liiketoimintarakenteita ja tuotteita teknisestä näkökulmasta sekä esitellä kaksi teollisuuden käyttökohdetta paikoituskäytölle. Työn sisältö voidaan jakaa neljään eri osioon. Terminologian määrittely- ja markkinatutkimusosiot perustuvat pääasiassa kirjallisuustutkimukseen. Paikoituskäyttöjen toimittajia sekä niiden tuotteita käsittelevä osuus perustuu kirjallisuustutkimukseen sekä teknisiin esitteisiin ja manuaaleihin. Paikoituskäyttöjen sovellusesimerkit on selvitetty haastatteluin. Työ painottuu paikoituskäyttötoimittajien tuotteiden, tuoteominaisuuksien ja tuotetarjonnan tarkasteluun. Työn tuloksena on määritelty paikoituskäyttöjen liiketoiminnan tärkeimmät termit, paikoituskäyttöjen markkinoiden koko sekä markkinoiden koko paikoitusominaisuudet omaavalle kolmivaihetaajuusmuuttajalle. Alalla toimivien paikoituskäyttötoimittajien liiketoimintarakenne on selvitetty, jonka mukaan toimittajat on profiloitu komponentti-, komponenttipaketti-, toimialakeskeisiksi tai automaatiotoimittajiksi. Toimittajien paikoituskäyttötuotteet on luokiteltu viiteen eri luokkaan niiden teknisten ominaisuuksien perusteella. Lisäksi paikoituskäyttöjen suorituskyvyt on selvitetty säätimien momentti-, nopeus-, ja paikoituslaskenta-aikatasojen sekä kenttäväyläliityntöjen suhteen. Työssä kuvatut vanerinsorvausprosessi sekä FMS -materiaalinkäsittelyprosessi esittävät paikoituskäyttöjen potentiaalisia sovelluskohteita.

The effects of some variables on CO2 laser-MAG hybrid welding

The CO2-laser-MAG hybrid welding process has been shown to be a productive choice for the welding industry, being used in e.g. the shipbuilding, pipe and beam manufacturing, and automotive industries. It provides an opportunity to increase the productivity of welding of joints containing air gaps compared with autogenous laser beam welding, with associated reductions in distortion and marked increases in welding speeds and penetration in comparison with both arc and autogenous laser welding. The literature study indicated that the phenomena of laser hybrid welding are mostly being studied using bead-on-plate welding or zero air gap configurations. This study shows it very clearly that the CO2 laser-MAG hybrid welding process is completely different, when there is a groove with an air gap. As in case of industrial use it is excepted that welding is performed for non-zero grooves, this study is of great importance for industrial applications. The results of this study indicate that by using a 6 kW CO2 laser-MAG hybrid welding process, the welding speed may also be increased if an air gap is present in the joint. Experimental trials indicated that the welding speed may be increased by 30-82% when compared with bead-on-plate welding, or welding of a joint with no air gap i.e. a joint prepared as optimum for autogenous laser welding. This study demonstrates very clearly, that the separation of the different processes, as well as the relative configurations of the processes (arc leading or trailing) affect welding performance significantly. These matters influence the droplet size and therefore the metal transfer mode, which in turn determined the resulting weld quality and the ability to bridge air gaps. Welding in bead-onplate mode, or of an I butt joint containing no air gap joint is facilitated by using a leading torch. This is due to the preheating effect of the arc, which increases the absorptivity of the work piece to the laser beam, enabling greater penetration and the use of higher welding speeds. With an air gap present, air gap bridging is more effectively achieved by using a trailing torch because of the lower arc power needed, the wider arc, and the movement of droplets predominantly towards the joint edges. The experiments showed, that the mode of metal transfer has a marked effect on gap bridgeability. Transfer of a single droplet per arc pulse may not be desirable if an air gap is present, because most of the droplets are directed towards the middle of the joint where no base material is present. In such cases, undercut is observed. Pulsed globular and rotational metal transfer modes enable molten metal to also be transferred to the joint edges, and are therefore superior metal transfer modes when bridging air gaps. It was also found very obvious, that process separation is an important factor in gap bridgeability. If process separation is too large, the resulting weld often exhibits sagging, or no weld may be formed at all as a result of the reduced interaction between the component processes. In contrast, if the processes are too close to one another, the processing region contains excess molten metal that may create difficulties for the keyhole to remain open. When the distance is optimised - i.e. a separation of 0-4 mm in this study, depending on the welding speed and beam-arc configuration - the processes act together, creating beneficial synergistic effects. The optimum process separation when using a trailing torch was found to be shorter (0-2 mm) than when a leading torch is used (2-4 mm); a result of the facilitation of weld pool motion when the latter configuration is adopted. This study demonstrates, that the MAG process used has a strong effect on the CO2-laser-MAG hybrid welding process. The laser beam welding component is relatively stable and easy to manage, with only two principal processing parameters (power and welding speed) needing to be adjusted. In contrast, the MAG process has a large number of processing parameters to optimise, all of which play an important role in the interaction between the laser beam and the arc. The parameters used for traditional MAG welding are often not optimal in achieving the most appropriate mode of metal transfer, and weld quality in laser hybrid welding, and must be optimised if the full range of benefits provided by hybrid welding are to be realised.

Control of permanent magnet linear synchronous motor in motion control applications

The aim of the thesis is to study the principles of the permanent magnet linear synchronous motor (PMLSM) and to develop a simulator model of direct force controlled PMLSM. The basic motor model is described by the traditional two-axis equations. The end effects, cogging force and friction model are also included into the final motor model. Direct thrust force control of PMLSM is described and modelled. The full system model is proven by comparison with the data provided by the motor manufacturer.

Integration of Real-Time Simulator, Motion Platform and Haptics

This thesis describes the process of the integration of a real-time simulator environment with a motion platform and a haptic device as a part of the Kvalive project. Several programs running on two computers were made to control the different devices of the environment. User tests were made to obtain information of needed improvements to make the simulator more realistic. Also new ideas for improving the simulator and directions of further research were obtained with the help of this research.

Centralized Motion Control of a Linear Tooth Belt Drive: Analysis of the Performance and Limitations

A centralized robust position control for an electrical driven tooth belt drive is designed in this doctoral thesis. Both a cascaded control structure and a PID based position controller are discussed. The performance and the limitations of the system are analyzed and design principles for the mechanical structure and the control design are given. These design principles are also suitable for most of the motion control applications, where mechanical resonance frequencies and control loop delays are present. One of the major challenges in the design of a controller for machinery applications is that the values of the parameters in the system model (parameter uncertainty) or the system model it self (non-parametric uncertainty) are seldom known accurately in advance. In this thesis a systematic analysis of the parameter uncertainty of the linear tooth beltdrive model is presented and the effect of the variation of a single parameter on the performance of the total system is shown. The total variation of the model parameters is taken into account in the control design phase using a Quantitative Feedback Theory (QFT). The thesis also introduces a new method to analyze reference feedforward controllers applying the QFT. The performance of the designed controllers is verified by experimentalmeasurements. The measurements confirm the control design principles that are given in this thesis.

The Use of Radiostereometric Analysis in Fractures of the Distal Radius: From Phantom Models to Clinical Application

Radiostereometric analysis (RSA) is a highly accurate method for the measurement of in vivo micromotion of orthopaedic implants. Validation of the RSA method is a prerequisite for performing clinical RSA studies. Only a limited number of studies have utilised the RSA method in the evaluation of migration and inducible micromotion during fracture healing. Volar plate fixation of distal radial fractures has increased in popularity. There is still very little prospective randomised evidence supporting the use of these implants over other treatments. The aim of this study was to investigate the precision, accuracy, and feasibility of using RSA in the evaluation of healing in distal radius fractures treated with a volar fixed-angle plate. A physical phantom model was used to validate the RSA method for simple distal radius fractures. A computer simulation model was then used to validate the RSA method for more complex interfragmentary motion in intra-articular fractures. A separate pre-clinical investigation was performed in order to evaluate the possibility of using novel resorbable markers for RSA. Based on the validation studies, a prospective RSA cohort study of fifteen patients with plated AO type-C distal radius fractures with a 1-year follow-up was performed. RSA was shown to be highly accurate and precise in the measurement of fracture micromotion using both physical and computer simulated models of distal radius fractures. Resorbable RSA markers demonstrated potential for use in RSA. The RSA method was found to have a high clinical precision. The fractures underwent significant translational and rotational migration during the first two weeks after surgery, but not thereafter. Maximal grip caused significant translational and rotational interfragmentary micromotion. This inducible micromotion was detectable up to eighteen weeks, even after the achievement of radiographic union. The application of RSA in the measurement of fracture fragment migration and inducible interfragmentary micromotion in AO type-C distal radius fractures is feasible but technically demanding. RSA may be a unique tool in defining the progress of fracture union.

Non-Markovian Dynamics and the Quantum-To-Classical Transition for Quantum Brownian Motion

In this Thesis I discuss the dynamics of the quantum Brownian motion model in harmonic potential. This paradigmatic model has an exact solution, making it possible to consider also analytically the non-Markovian dynamics. The issues covered in this Thesis are themed around decoherence. First, I consider decoherence as the mediator of quantum-to-classical transition. I examine five different definitions for nonclassicality of quantum states, and show how each definition gives qualitatively different times for the onset of classicality. In particular I have found that all characterizations of nonclassicality, apart from one based on the interference term in the Wigner function, result in a finite, rather than asymptotic, time for the emergence of classicality. Second, I examine the diverse effects which coupling to a non-Markovian, structured reservoir, has on our system. By comparing different types of Ohmic reservoirs, I derive some general conclusions on the role of the reservoir spectrum in both the short-time and the thermalization dynamics. Finally, I apply these results to two schemes for decoherence control. Both of the methods are based on the non-Markovian properties of the dynamics.

Design of Instrument for Knee Joint Kinematics Measurement

This thesis describes the process of design and modeling of instrument for knee joint kinematics measurement that can work for both in-vivo and in-vitro subjects. It is designed to be compatible with imaging machine in a sagittal plane. Due to the invasiveness of the imaging machine, the instrument is designed to be able to function independently. The flexibility of this instrument allows to measure anthropometrically different subject. Among the sixth degree of freedom of a knee, three rotational and one translational degree of freedom can be measured for both type of subject. The translational, proximal-distal, motion is stimulated by external force directly applied along its axis. These angular and linear displacements are measured by magnetic sensors and high precision potentiometers respectively

Real-time Image-based RGB-D Camera Motion Tracking and Environment Mapping

In this work, image based estimation methods, also known as direct methods, are studied which avoid feature extraction and matching completely. Cost functions use raw pixels as measurements and the goal is to produce precise 3D pose and structure estimates. The cost functions presented minimize the sensor error, because measurements are not transformed or modified. In photometric camera pose estimation, 3D rotation and translation parameters are estimated by minimizing a sequence of image based cost functions, which are non-linear due to perspective projection and lens distortion. In image based structure refinement, on the other hand, 3D structure is refined using a number of additional views and an image based cost metric. Image based estimation methods are particularly useful in conditions where the Lambertian assumption holds, and the 3D points have constant color despite viewing angle. The goal is to improve image based estimation methods, and to produce computationally efficient methods which can be accomodated into real-time applications. The developed image-based 3D pose and structure estimation methods are finally demonstrated in practise in indoor 3D reconstruction use, and in a live augmented reality application.

Multibody models for examination of touchdown bearing systems

Increased rotational speed brings many advantages to an electric motor. One of the benefits is that when the desired power is generated at increased rotational speed, the torque demanded from the rotor decreases linearly, and as a consequence, a motor of smaller size can be used. Using a rotor with high rotational speed in a system with mechanical bearings can, however, create undesirable vibrations, and therefore active magnetic bearings (AMBs) are often considered a good option for the main bearings, as the rotor then has no mechanical contact with other parts of the system but levitates on the magnetic forces. On the other hand, such systems can experience overloading or a sudden shutdown of the electrical system, whereupon the magnetic field becomes extinct, and as a result of rotor delevitation, mechanical contact occurs. To manage such nonstandard operations, AMB-systems require mechanical touchdown bearings with an oversized bore diameter. The need for touchdown bearings seems to be one of the barriers preventing greater adoption of AMB technology, because in the event of an uncontrolled touchdown, failure may occur, for example, in the bearing’s cage or balls, or in the rotor. This dissertation consists of two parts: First, touchdown bearing misalignment in the contact event is studied. It is found that misalignment increases the likelihood of a potentially damaging whirling motion of the rotor. A model for analysis of the stresses occurring in the rotor is proposed. In the studies of misalignment and stresses, a flexible rotor using a finite element approach is applied. Simplified models of cageless and caged bearings are used for the description of touchdown bearings. The results indicate that an increase in misalignment can have a direct influence on the bending and shear stresses occurring in the rotor during the contact event. Thus, it was concluded that analysis of stresses arising in the contact event is essential to guarantee appropriate system dimensioning for possible contact events with misaligned touchdown bearings. One of the conclusions drawn from the first part of the study is that knowledge of the forces affecting the balls and cage of the touchdown bearings can enable a more reliable estimation of the service life of the bearing. Therefore, the second part of the dissertation investigates the forces occurring in the cage and balls of touchdown bearings and introduces two detailed models of touchdown bearings in which all bearing parts are modelled as independent bodies. Two multibody-based two-dimensional models of touchdown bearings are introduced for dynamic analysis of the contact event. All parts of the bearings are modelled with geometrical surfaces, and the bodies interact with each other through elastic contact forces. To assist in identification of the forces affecting the balls and cage in the contact event, the first model describes a touchdown bearing without a cage, and the second model describes a touchdown bearing with a cage. The introduced models are compared with the simplified models used in the first part of the dissertation through parametric study. Damages to the rotor, cage and balls are some of the main reasons for failures of AMB-systems. The stresses in the rotor in the contact event are defined in this work. Furthermore, the forces affecting key bodies of the bearings, cage and balls can be studied using the models of touchdown bearings introduced in this dissertation. Knowledge obtained from the introduced models is valuable since it can enable an optimum structure for a rotor and touchdown bearings to be designed.