Model predictive control of magnetically actuated mass spring dampers for automotive applications

Mechatronic systems such as those arising in automotive applications are characterized by significant non-linearities, tight performance specifications as well as by state and input constraints which need to be enforced during system operation. This paper takes a view that model predictive control (MPC) and hybrid models can be an attractive and systematic methodology to handle these challenging control problems, even when the underlying process is not hybrid. In addition, the piecewise affine (PWA) explicit form of MPC solutions avoids on-line optimization and can make this approach computationally viable even in situations with rather constrained computational resources. To illustrate the MPC design procedure and the underlying issues, we focus on a specific non-linear process example of a mass spring damper system actuated by an electromagnet. Such a system is one of the most common elements of mechatronic systems in automotive systems, with fuel injectors representing a concrete example. We first consider a linear MPC design for the mechanical part of the system. The approach accounts for all the constraints in the system but one, which is subsequently enforced via a state-dependent saturation element. Second, a hybrid MPC approach for the mechanical subsystem is analysed that can handle all the constraints by design and achieves better performance, at the price of a higher complexity of the controller. Finally, a hybrid MPC design that also takes into account the electrical dynamics of the system is considered.     

Optical and mechanical performance of a novel magnetically actuated MEMS-based optical switch

A novel magnetically actuated 8/spl times/8-port MEMS-based fiber-optic switch is described. Fiber-to-fiber insertion loss measurements of six 8/spl times/8 switch units show average and worst-case insertion loss of 1.3 dB and 2 dB, respectively. Low insertion loss is achieved through a unique MEMS design that uses anisotropically etched single-crystal silicon sidewalls to provide a global mechanical alignment stop for an array of MEMS mirrors. This alignment surface produces a uniform and repeatable mirror angle across the mirror array. Mirror misalignment is attributed to the surface roughness of the silicon sidewalls. Repeated interferometric measurements of the mirrors of 24 8/spl times/8 switch units show repeatability of the mirror angle of 3/spl times/10/sup -3/ degrees, while the uniformity of the mirror angle across the MEMS array is 2/spl times/10/sup -2/ degrees, in agreement with the angular error predicted from measurements of sidewall surface roughness. In turn, the average repeatability and uniformity of the insertion loss are 0.01 dB and 1 dB, respectively, in agreement with predictions based on the interferometric measurements. Finally, the unique dynamics of the magnetic actuation and electrostatic addressing scheme are described. Measurements show that fast switching can be achieved by driving the mirrors with a magnetic pulse that is faster than the mechanical resonant frequency of the mirror, relying on an electrostatic clamping force to capture the mirror as it overshoots the magnetic field angle. This actuation scheme is shown to result in switching times of 8.5 ms to 13.5 ms, but requires accurate control of the kinetic energy of the mirror.     

Tracking and disturbance rejection for fully actuated mechanical systems

In this paper, we solve the tracking and disturbance rejection problem for fully actuated passive mechanical systems. We assume that the reference signal r and its first two derivatives are available to the controller and the disturbance signal d can be decomposed into a finite superposition of sine waves of arbitrary but known frequencies and an arbitrary L² signal. We combine the internal model principle with the ideas behind the Slotine-Li adaptive controller. The internal model-based adaptive controller that we propose causes the closed-loop state trajectories to be bounded, and the tracking error and its derivative to converge to zero, without any prior knowledge of the plant parameters. An important part of our results is that we prove the existence and uniqueness of the state trajectories of the closed-loop system.     

Controllability of nonlinear time-varying systems: applications to spacecraft attitude control using magnetic actuation

Nonlinear controllability theory is applied to the time-varying attitude dynamics of a magnetically actuated spacecraft in a Keplerian orbit in the geomagnetic field. First, sufficient conditions for accessibility, strong accessibility and controllability of a general time-varying system are presented. These conditions involve application of Lie-algebraic rank conditions to the autonomous extended system obtained by augmenting the state of the original time-varying system by the time variable, and require the rank conditions to be checked only on the complement of a finite union of level sets of a finite number of smooth functions. At each point of each level set, it is sufficient to verify escape conditions involving Lie derivatives of the functions defining the level sets along linear combinations over smooth functions of vector fields in the accessibility algebra. These sufficient conditions are used to show that the attitude dynamics of a spacecraft actuated by three magnetic actuators and subjected to a general time-varying magnetic field are strongly accessible if the magnetic field and its time derivative are linearly independent at every instant. In addition, if the magnetic field is periodic in time, then the attitude dynamics of the spacecraft are controllable. These results are used to show that the attitude dynamics of a spacecraft actuated by three magnetic actuators in a closed Keplerian orbit in a nonrotating dipole approximation of the geomagnetic field are strongly accessible and controllable if the orbital plane does not coincide with the geomagnetic equatorial plane.     

A fault tolerant single sided matrix converter for flight control actuation systems

We describe a single sided matrix converter (SSMC) designed for safety critical applications like flight control actuation systems. Dynamic simulations of multi-phase SSMC using Matlab Simulink are carried out to evaluate the fault tolerance capabilities. Investigation into different numbers of phases and power converter topologies under single phase open circuit, single switch open circuit, and single switch short circuit has been executed. The simulation results confirm 5-phase SSMC design as a compromise between fault tolerance and converter size/volume. A 5-phase SSMC prototype was built. Experimental results verify the effectiveness of our design.     

Kinematics and deformation of ferrofluid droplets under magnetic actuation

This paper reports the experimental results on kinematics and deformation of ferrofluid droplets driven by planar coils. Ferrofluid droplets act as liquid magnets, which can be controlled and manipulated by an external magnetic field. In our experiments, the magnetic field was generated by two pairs of planar coils, which were fabricated on a double-sided printed circuit board. The first pair of coils constrains the ferrofluid droplet to a one-dimensional motion. The second pair generates the magnetic gradient needed for the droplet motion. The direction of the motion can be controlled by changing the sign of the gradient or of the driving current. Kinematic characteristics of the droplet such as the velocity–position diagram and the aspect ratio of the droplet are investigated. The analysis and discussion are based on the different parameters such as the droplet size, the viscosity of the surrounding medium, and the driving current. This simple actuation concept would allow the implementation of lab-on-a-chip platforms based on ferrofluid droplets.     

Concurrent design of controller and passive elements for robots with impulsive actuation systems

There are some biological evidences showing that the actuation system in legged animals is impulsive; it is not continuous. As opposed to continuous control/actuation, the control actions occur in specific intervals, and from the instant of one actuation until the start of the next one, passive elements guarantee the stability of the robotic system and govern its natural dynamics. In this paper, we present an analytical method for concurrent design of impulsive controller and passive elements (compliance and damper) for robotic systems; e.g., manipulators and legged-robots. To optimize the force profiles of passive elements, three different cost functions are presented which optimize the natural dynamics and energy consumption of the robot. The presented method can be applied to both cyclic and non-cyclic (explosive) tasks so as to attain energy efficient and bio-inspired motions. The method is applied to three biological models: a simulated human arm for throwing an object, a swing leg for drawing an oval, and a 3D quadruped robot for performing walking gait. Our findings in the simulation studies are in line with the hypothesis of impulsive actuation in nature and show the applicability of our method in robotics.     

A realistic elastic rod model for real-time simulation of minimally invasive vascular interventions

Simulating intrinsic deformation behaviors of guidewire and catheters for interventional radiology (IR) procedures, such as minimally invasive vascular interventions is a challenging task. Especially real-time simulations for interactive training systems require not only the accuracy of guidewire manipulations, but also the efficiency of computations. The insertion of guidewires and catheters is an essential task for IR procedures and the success of these procedures depends on the accurate navigation of guidewires in complex 3D blood vessel structures to a clinical target, whilst avoiding complications or mistakes of damaging vital tissues and blood vessel walls. In this paper, a novel elastic model for modeling guidewires is presented and evaluated. Our interactive guidewire simulator models the medical instrument as thin flexible elastic rods with arbitrary cross sections, treating the centerline as dynamic and the deformation as quasi-static. Constraints are used to enforce inextensibility of guidewires, providing an efficient computation for bending and twisting modes of the physically-based simulation model. We demonstrate the effectiveness of the new model with a number of simulation examples.     

Design and testing of track-following controllers for dual-stage servo systems with PZT actuated suspensions

 This paper discusses the design and testing of two track-following controllers for dual-stage servo systems in hard disk drives. The first controller is designed using the μ-synthesis multivariable robust optimal controller design methodology. The second is designed using classical single-input-single-output (SISO) frequency shaping design techniques, based on sensitivity transfer functions decoupling of the dual-stage actuator. The controllers were implemented and tested on a disk drive with a PZT actuated suspension based dual-stage servo system. The position error signal (PES) for the servo system was obtained by measuring the slider displacement using an LDV and injecting simulated track runout. In the experiment, both designs achieved a track-mis-registration (TMR) less than 10 nm. Received: 25 July 2001/Accepted: 1 November 2001     

Digital self-control interventions for distracting media multitasking - A systematic review

Digital distractions can interfere with goal attainment and lead to undesirable habits that are hard to get red rid of. Various digital self-control interventions promise support to alleviate the negative impact of digital distractions. These interventions use different approaches, such as the blocking of apps and websites, goal setting, or visualizations of device usage statistics. While many apps and browser extensions make use of these features, little is known about their effectiveness. This systematic review synthesizes the current research to provide insights into the effectiveness of the different kinds of interventions. From a search of the ‘ACM’, ‘Springer Link’, ‘Web of Science’, ’IEEE Xplore’ and ‘Pubmed’ databases, we identified 28 digital self-control interventions. We categorized these interventions according to their features and their outcomes. The interventions showed varying degrees of effectiveness, and especially interventions that relied purely on increasing the participants' awareness were barely effective. For those interventions that sanctioned the use of distractions, the current literature indicates that the sanctions have to be sufficiently difficult to overcome, as they will otherwise be quickly dismissed. The overall confidence in the results is low, with small sample sizes, short study duration, and unclear study contexts. From these insights, we highlight research gaps and close with suggestions for future research.     

A biomechanical assessment of hand/arm force with pneumatic nail gun actuation systems

A biomechanical model is presented to estimate user hand/arm force exertion with two pneumatic nail gun trigger systems. The sequential actuation trigger (SAT) is safer than the contact actuation trigger (CAT) but increases the user's exertion of force because the trigger must be actuated after the safety tip is held pressed against the workpiece. Time integrated hand force was calculated for a single user based on direct measurement of nail gun tip force against the workpiece (tip contact) and from estimated force to support the tool weight during transfer between nails and during idle holding. The model shows that hand/arm force increases when nailing with the SAT (relative to CAT) and with a vertically-oriented workpiece (relative to horizontal). Expressed per nail fired, the user exerted 0.13 Ns (horizontal orientation) and 2.88 Ns (vertical orientation) integrated hand force during tip contact with CAT compared to 26.15 Ns (horizontal) and 46.08 Ns (vertical) with SAT. Depending upon idle holding duration, integrated hand force during tip contact was estimated to have been 1–3% of 48–132 Ns total hand force with CAT and 21–44% of 83–167 Ns total hand force with SAT (average of horizontal and vertical orientations). Based on standard time allowances from work measurement systems it is proposed that efficient application of hand force during tip contact with SAT can reduce this contribution to 6–15% of 55–139 Ns total hand force. The model is useful for considering differences in hand/arm force exertion between the SAT and CAT systems     

Comparing double-step and penalty-based semirecursive formulations for hydraulically actuated multibody systems in a monolithic approach

The simulation of mechanical systems often requires modeling of systems of other physical nature, such as hydraulics. In such systems, the numerical stiffness introduced by the hydraulics can become a significant aspect to consider in the modeling, as it can negatively effect to the computational efficiency. The hydraulic system can be described by using the lumped fluid theory. In this approach, a pressure can be integrated from a differential equation in which effective bulk modulus is divided by a volume size. This representation can lead to numerical stiffness as a consequence of which time integration of a hydraulically driven system becomes cumbersome. In this regard, the used multibody formulation plays an important role, as there are many different procedures for the constraint enforcement and different sets of coordinates to choose from. This paper introduces the double-step semirecursive approach and compares it with a penalty-based semirecursive approach in case of coupled multibody and hydraulic dynamics within the monolithic framework. To this end, hydraulically actuated four-bar and quick-return mechanisms are analyzed as case studies. The two approaches are compared in terms of the work cycle, energy balance, constraint violation, and numerical efficiency of the mechanisms. It is concluded that the penalty-based semirecursive approach has a number of advantages compared with the double-step semirecursive approach, which is in accordance with the literature.

     

A review of atlas-based segmentation for magnetic resonance brain images

Normal and abnormal brains can be segmented by registering the target image with an atlas. Here, an atlas is defined as the combination of an intensity image (template) and its segmented image (the atlas labels). After registering the atlas template and the target image, the atlas labels are propagated to the target image. We define this process as atlas-based segmentation. In recent years, researchers have investigated registration algorithms to match atlases to query subjects and also strategies for atlas construction. In this paper we present a review of the automated approaches for atlas-based segmentation of magnetic resonance brain images. We aim to point out the strengths and weaknesses of atlas-based methods and suggest new research directions. We use two different criteria to present the methods. First, we refer to the algorithms according to their atlas-based strategy: label propagation, multi-atlas methods, and probabilistic techniques. Subsequently, we classify the methods according to their medical target: the brain and its internal structures, tissue segmentation in healthy subjects, tissue segmentation in fetus, neonates and elderly subjects, and segmentation of damaged brains. A quantitative comparison of the results reported in the literature is also presented.     

A review of vision-based systems for soccer video analysis

This paper presents a survey of soccer video analysis systems for different applications: video summarization, provision of augmented information, high-level analysis. Computer vision techniques have been adapted to be applicable in the challenging soccer context. Different semantic levels of interpretation are required according to the complexity of the corresponding applications. For each application area we analyze the computer vision methodologies, their strengths and weaknesses and we investigate whether these approaches can be applied to extensive and real time soccer video analysis.     

A review on architecture and models for autonomic software systems

The Journal of Supercomputing - Autonomic computing was the term coined by IBM in 2001. The term autonomic computing was used to define the self-adaptable nature of the human body. According to...     

Control of mechanical motion systems with non-collocation of actuation and friction: A Popov criterion approach for input-to-state stability and set-valued nonlinearities

The presence of friction in mechanical motion systems is a performance limiting factor as it induces stick-slip vibrations. To appropriately describe the stiction effect of friction, we adopt set-valued force laws. Then, the complete motion control system can be described by a Lur’e system with set-valued nonlinearities. In order to eliminate stick-slip vibrations for mechanical motion systems, a state-feedback control design is presented to stabilize the equilibrium. The proposed control design is based on an extension of a Popov-like criterion to systems with set-valued nonlinearities that guarantees input-to-state stability (ISS). The advantages of the presented controller is that it is robust to uncertainties in the friction and it is applicable to systems with non-collocation of actuation and friction where common control strategies such as direct friction compensation fail. Moreover, an observer-based output-feedback design is proposed for the case that not all the state variables are measured. The effectiveness of the proposed output-feedback control design is shown both in simulations and experiments for a typical motion control system.     

Stabilization of linear systems with simultaneous state,actuation, and measurement delays

This paper considers the problem of stabilizing continuous-time linear systems with time delays. Specifically, a fixedorder (i.e. full- and reduced-order) dynamic compensation problem is addressed for systems with simultaneous state, input, and output delays. The principal result involves sufficient conditions for characterizing fixed-order dynamic controllers for delay systems via a system of modified coupled Riccati equations. The controllers obtained are delay independent and hence apply to systems with arbitrary unknown delay.     

基于知识的推荐系统综述

基于知识的推荐算法在弥补过滤式传统推荐算法冷启动、数据缺失、"信息茧房"等问题上发挥着重要的作用.对基于知识的推荐算法相关研究进行评述,探讨其研究现状及研究进展.通过梳理CNKI相关文献和WOS中2017-2020的论文,采用内容分析法对国内外学术界基于知识的推荐算法的研究进展进行分析,对实际进展包括会话过程的优化、领...     

A systematic review of provenance systems

Provenance refers to the entire amount of information, comprising all the elements and their relationships, that contribute to the existence of a piece of data. The knowledge of provenance data allows a great number of benefits such as verifying a product, result reproductivity, sharing and reuse of knowledge, or assessing data quality and validity. With such tangible benefits, it is no wonder that in recent years, research on provenance has grown exponentially, and has been applied to a wide range of different scientific disciplines. Some years ago, managing and recording provenance information were performed manually. Given the huge volume of information available nowadays, the manual performance of such tasks is no longer an option. The problem of systematically performing tasks such as the understanding, capture and management of provenance has gained significant attention by the research community and industry over the past decades. As a consequence, there has been a huge amount of contributions and proposed provenance systems as solutions for performing such kinds of tasks. The overall objective of this paper is to plot the landscape of published systems in the field of provenance, with two main purposes. First, we seek to evaluate the desired characteristics that provenance systems are expected to have. Second, we aim at identifying a set of representative systems (both early and recent use) to be exhaustively analyzed according to such characteristics. In particular, we have performed a systematic literature review of studies, identifying a comprehensive set of 105 relevant resources in all. The results show that there are common aspects or characteristics of provenance systems thoroughly renowned throughout the literature on the topic. Based on these results, we have defined a six-dimensional taxonomy of provenance characteristics attending to: general aspects, data capture, data access, subject, storage, and non-functional aspects. Additionally, the study has found that there are 25 most referenced provenance systems within the provenance context. This study exhaustively analyzes and compares such systems attending to our taxonomy and pinpoints future directions.