Controllable Degrees Of Freedom Research Articles

An investigation of variable power collective pitch control for load mitigation of floating offshore wind turbines

ABSTRACTThis paper investigates the loads on offshore floating wind turbines and a new control method that can be used to reduce these loads. In this variable power collective pitch control method, the rated generator speed, which is the set point that the collective pitch control attempts to drive the actual generator speed towards, is no longer a constant value but instead is a variable that depends on the platform pitch velocity. At a basic physical level, this controller achieves the following: as the rotor of a floating turbine pitches upwind, the controller adjusts so as to extract more energy from the wind by increasing the rated generator speed and thus damps the motion; as the rotor pitches downwind, less energy is extracted because the controller reduces the rated generator speed and again damps the motion. This method is applied to the NREL 5 MW wind turbine model, in above rated conditions where the platform motion is most problematic. The results indicate significant load reductions on key structural components, at the expense of minor increases in power and speed variability. The loads on the blades and tower are investigated more generally, and simple dynamic models are used to gain insight into the behavior of floating wind turbine systems. It is clear that for this particular design, aerodynamic methods for reducing platform motion and tower loads are likely inadequate to allow for a viable design, so new designs or possibly new control degrees of freedom are needed. Copyright © 2012 John Wiley & Sons, Ltd.

Singularity-Invariant Families of Line-Plane 5-S$\underline{\rm P}$ U Platforms

A 5-SPU robot with collinear universal joints is well suited to handle an axisymmetric tool, since it has five controllable degrees of freedom, and the remaining one is a free rotation around the tool. The kinematics of such a robot also having coplanar spherical joints has previously been studied as a rigid subassembly of a Stewart-Gough platform, which has been denoted a line-plane component. Here, we investigate how to move the leg attachments in the base and the platform without altering the robot's singularity locus. By introducing the so-called 3-D space of leg attachments, we prove that there are only three general topologies for the singularity locus corresponding to the families of quartically, cubically, and quadratically solvable 5-SPU robots. The members of the last family have only four assembly modes, which are obtained by solving two quadratic equations. Two practical features of these quadratically solvable robots are the large manipulability within each connected component and the fact that, for a fixed orientation of the tool, the singularity locus reduces to a plane.

A Novel PCCM Boost PFC Converter With Fast Dynamic Response

A novel pseudo-continuous conduction mode (PCCM) boost power-factor-correction (PFC) converter and its corresponding control strategy are proposed in this paper. Connecting a power switch in parallel with the inductor makes the boost converter operate in PCCM, which provides an additional degree of control freedom to realize PFC control. Therefore, a simple and fast voltage control loop of the PCCM boost PFC converter can be designed to realize output-voltage regulation. The additional degree of control freedom introduced by inductor current freewheeling operation of the PCCM boost PFC converter has been exploited through the dead-zone control technique, which can be dynamically adjusted in accordance with the output-voltage ripple. Compared with continuous conduction mode (CCM) boost PFC converter, the controller of the proposed PCCM boost PFC converter is much simpler. Moreover, the PCCM boost PFC converter benefits with reduced inductor-current ripple and improved power factor compared with boost PFC converter operating in discontinuous conduction mode (DCM). Analysis, simulation, and a 400-W prototype of the PCCM boost PFC converter have been presented and compared with those of boost PFC converters operating in conventional CCM and DCM. The results show that the dynamic response of the PCCM boost PFC converter is significantly faster than the existing boost PFC converter.

Radio frequency identification--an innovative solution to guide dexterous prosthetic hands.

Dexterous manipulation of a multi-fingered prosthetic hand requires far more cognitive effort compared to typical 1 degree of freedom hands, which hinders their acceptance clinically. This paper presents a Myoelectrically-Operated Radio Frequency Identification (RFID) Prosthetic Hand (MORPH); an implementation of RFID with a myoelectric prosthetic hand as a means to amplify the controllable degrees of freedom. Contextual information from an object equipped with an RFID tag allows automatic preshaping along with dexterous control in an attempt to reduce the cognitive effort required to operate the terminal device. The myoelectric-RFID hybrid has been demonstrated in a proof-of-concept case study where an amputee was fitted with the device and subjected to activities adapted from the Jebsen Hand Function Test and the Smith Hand Function Evaluation with RFID-tagged and untagged items. Evaluation tests revealed that the MORPH system performed significantly better in 4 of the 8 tasks, and comparable to the control in the remainder.

Effect of flapping kinematics on the mean lift of an insect-like flapping wing

An experimental investigation of the effects of varying flapping kinematics on the mean lift produced by an insect-like flapping wing in hover is presented. This was performed with application to flapping-wing micro-air vehicles (FMAVs) in mind. Experiments were accomplished with a first-of-its-kind mechanical flapping-wing apparatus capable of reproducing a wide range of insect-like wing motions in air on the FMAV scale (~150 mm wingspan). This apparatus gives an insect-like wing the three controllable degrees of freedom required to produce the three separate motions necessary for mimicking an insect-like flapping-wing trajectory: sweeping (side to side), plunging (up and down), and pitching (angle of attack variation). Lift was measured via a force balance while the following kinematic parameters were varied: flapping frequency ( f ), angle of attack at mid-stroke (αmid), timing of pitch reversal with stroke reversal (rotation phase), stroke amplitude (Φ), and plunge amplitude (Θ). Results revealed that mean lift scaled with f 1.5 and varied proportionally with Φ. A pitch reversal advanced by up to 5 per cent of the flapping period relative to stroke reversal was found to maximize mean lift, and delayed pitch reversals were detrimental to mean lift. Of the parameters tested, mean lift was also maximized for αmid = 45° and Θ = 8.6°.

Comparative Study on Carrier Overlapping PWM Strategies for Five Level Diode Clamped Inverter

This paper presents the comparison of Carrier Overlapping Pulse Width Modulation (COPWM) techniques for the Diode clamped Multi Level Inverter (DCMLI). Due to switch combination redundancies, there are certain degrees of freedom to generate the five level AC output voltage. This paper presents the use of Control Freedom Degree (CFD) combination. The effectiveness of the Pulse Width Modulation (PWM) strategies developed using CFD are demonstrated by simulation and experimentation. The results indicate that the multilevel inverter triggered by the developed COPWM-A strategy exhibits reduced harmonics. PWM strategies developed are implemented in real time using dSPACE/Real Time Interface (RTI). The simulation and experimental results closely match with each other validating the strategies presented.

Myoelectric Control Techniques for a Rehabilitation Robot

This work examines two different types of myoelectric control schemes for the purpose of rehabilitation robot applications. The first is a commonly used technique based on a Gaussian classifier. It is implemented in real time for healthy subjects in addition to a subject with Central Cord Syndrome (CCS). The myoelectric control scheme is used to control three degrees of freedom (DOF) on a robot manipulator which corresponded to the robot's elbow joint, wrist joint, and gripper. The classes of motion controlled include elbow flexion and extension, wrist pronation and supination, hand grasping and releasing, and rest. Healthy subjects were able to achieve 90% accuracy. Single DOF controllers were first tested on the subject with CCS and he achieved 100%, 96%, and 85% accuracy for the elbow, gripper, and wrist controllers respectively. Secondly, he was able to control the three DOF controller at 68% accuracy. The potential applications for this scheme are rehabilitation and teleoperation. To overcome limitations in the pattern recognition based scheme, a second myoelectric control scheme is also presented which is trained using electromyographic (EMG) data derived from natural reaching motions in the sagittal plane. This second scheme is based on a time delayed neural network (TDNN) which has the ability to control multiple DOF at once. The controller tracked a subject's elbow and shoulder joints in the sagittal plane. Results showed an average error of 19° for the two joints. This myoelectric control scheme has the potential of being used in the development of exoskeleton and orthotic rehabilitation applications.

The Challenge of Fuel Path Control at High Load Conditions

AbstractIncreasing emissions standards and fuel economy have forced engine designers to incorporate increasing numbers of degrees of control freedom into the engine. Consequently, calibration is becoming progressively more complex where the issue is most acute with diesel engines. This paper presents a project in which a closed loop controller is used in diesel engine fuel path, where no new calibration is required if any variation occurs. This is an initial investigation into diesel engine fuel path control. In order to prove that such a control technology could be developed over the whole speed and torque operating range, a high speed (2050 rpm) and the high torque (357Nm) point are chosen for investigations into control. This represents a challenging engine conditions for the application of control systems because of the limited time available for air supply and the need to complete combustion quickly. At these conditions the control authority is limited and the ability to detect for example small variations in torque and speed are quite limited owing to the high torque conditions. This paper demonstrates a closed-loop control at a high load condition and presents an architecture of controllable injection for a Caterpillar C6.6 engine using predictive control that includes exhaust temperature, of nitrogen oxides (NOx) and particulate matters (PM) without changing the fuel quantity.

Laboratory Platforms for Dynamic Positioning — Modeling and Identification

Abstract Dynamic positioning is a challenging task in control of marine vessels, with the primary objective of maintaining a desired, predefined position of the vessel. This paper describes an overactuated laboratory platform developed at the Laboratory for Underwater Systems and Technologies with the purpose of testing control algorithms. This paper focuses on the identification of the laboratory platform. The identification method which is used is based on recording open loop step responses. Preliminary experimental results for controllable degrees of freedom are presented. The paper also describes a MOOS (mission oriented operating system) based communication structure used to control the platform.

Simultaneous and Proportional Force Estimation for Multifunction Myoelectric Prostheses Using Mirrored Bilateral Training

This study presents a novel method for associating features of the surface electromyogram (EMG) recorded from one upper limb to the force produced by the contralateral limb. Bilateral-mirrored contractions from ten able-bodied subjects were recorded along with isometric forces in multiple degrees of freedom (DOF) from the right wrist. An artificial neural network was trained to provide force estimation. Combinations of processing parameters were evaluated and an estimation algorithm allowing high accuracy from relatively short signal epochs (100 ms) was proposed. The estimation performance when using surface EMG from the contralateral limb was 0.90 ± 0.02 for the able-bodied subjects. In comparison, the estimation performance for one subject with congenital malformation of the left forearm was 0.72 which, albeit lower than for able-bodied subjects, is still comparable to or better than previously reported results. The proposed method requires only the measured forces from one limb, such as in the case of unilateral amputees and has thus the potential to be used in clinical settings for intuitive, simultaneous control of multiple DOFs in myoelectric prostheses.

Modeling and Control of the MARES Autonomous Underwater Vehicle

AbstractIn this work, we address the modeling and control problems in the domain of underwater vehicles. We focus on a prototype of an autonomous underwater vehicle. Although the work presented here is applied to a particular vehicle with four controllable degrees of freedom, the method may be easily extended to several submerged bodies. In the engineering area, modeling of systems is done frequently, as it yields a mathematical translation of their behavior. Since models can become an important tool to solve problems related to its motion or even to the design of controllers, we obtain a model with six degrees of freedom for such a vehicle.Robust control of underwater vehicles is an area in which many efforts were applied over the last two decades. However, due to nonlinear dynamics, it may be hard to design robust controllers that yield the expected behavior, and there is no general procedure to develop them. Here, we propose an approach that combines nonlinear controllers based on the deduced model and on the Lyapunov theory to control the velocities of the vehicle with linear controllers that control the vehicle’s position. We derive control laws to perform several maneuvers, both in the vertical and the horizontal planes, in a decoupled way, which is made possible through the configuration of thrusters. Finally, we present realistic simulations and experimental results that validate the proposed approach in the definition of the control laws.

Tracking performance control of a cable communicated underwater vehicle using adaptive neural network controllers

In this paper, design, dynamic modeling and control of the fabricated underwater remotely operated vehicle have been considered. Dynamic model of the vehicle is presented for four degrees of freedom and an accurate representation of the dynamic effects of the towed cable is used for dynamic simulation and control design. A nonlinear adaptive neural network controller is developed and simulated. Multi-layer and radial basis function neural networks are used for designing the adaptive controllers. Finally, the performance of the vehicle with neural network controllers is compared with a PD controller. The significant improvement is observed for tracking performance of the vehicle in all controllable degrees of freedom. Also, the simulation illustrated the robustness of controllers for the relative large distributions of the communication cable.

Method for Evaluating Single-End Control of Distillation Columns

Distillation columns are, in an ideal situation, controlled using a dual-composition structure in which the light-key impurity in the bottoms and heavy-key impurity in the distillate are both maintained at the specified values. This structure minimizes energy consumption. However, it is often almost as efficient to use one-end control of either a composition or a temperature. This single-end distillation control structure is widely used in industry because of its simplicity and because it avoids dynamic interaction between the two competing loops. Because distillation columns have two control degrees of freedom, another variable besides the single temperature or composition must be selected among several alternatives. Usually these choices involve a ratio so that feed rate changes can be effectively handled. However, different ratio schemes handle feed composition changes with different degrees of effectiveness. The two most commonly used are either a reflux-to-feed ratio (R/F) or a reflux ratio (RR). The...

Dynamic simulation for internally heat-integrated distillation columns (HIDiC) for propylene–propane system

This paper reports a dynamic simulation study of the internally heat-integrated distillation column (HIDiC) using equilibrium-based models. First, three different HIDiC structures, i.e. an ideal HIDiC, a HIDiC with a pre-heater, and a HIDiC with a reboiler, are analyzed by control degrees of freedom (DOF). The reboiler is considered to be a necessary part of the HIDiC from DOF analysis, thermodynamic analysis, and engineering judgment. Then, a heuristic HIDiC control configuration including a bottoms reboiler control is proposed. A modular structured simulator for dynamic distillation columns using MESH equations is developed. The simulator also considers: (1) variable column pressure on each tray of the rectifying section, (2) dynamic vapor holdup, and (3) dynamic energy balance. In addition, the SRK equation of state is employed for estimating thermodynamic properties. A typical medium-pressure HIDiC for separation of propylene and propane explored by Olujic et al. [Olujic, Z., Sun, L., de Rijke, A., & Jansens, P. J. (2006). Conceptual design of an internally heat-integrated propylene–propane splitter. Energy, 31, 3083] is adopted as numerical examples for dynamic simulation studies.

Vehicle-following guidance for unmanned marine vehicles

Abstract The problem of an unmanned surface vehicle following another vessel, both underwater or on the surface, without having any a priori information about its path is addressed in this paper. Theoretically the problem is solved extending nonlinear Lyapunov-based control techniques to the case of a master-slave vehicle formation, introducing a virtual controlled degree of freedom for the target to be followed on the path. In order to validate the proposed approach for different classes of vehicles, two typical operational cases are considered: i ) a slave USV, acting as a communication relay, is required to remain over the vertical of a master AUV; ii ) a slave USV is required to follow the path of a master USV at a desired range, for instance, for collecting bathymetric profiles with two different sensors. Experiments on the AUV-USV case study are performed in the multi-vehicle simulation environment Thetis, developed by CNRS-LIRMM considering a joined mission of the Taipan AUV and Charlie USV. The effectiveness of the proposed approach in the USV-USV case has been demonstrated by at sea trials carried out with the Charlie and ALANIS USVs.

CO_2 laser writing of long-period fiber gratings in optical fibers under tension

We demonstrate experimentally that the efficiency of writing a long-period fiber grating in a single-mode fiber by CO(2) laser pulses increases significantly with the axial stress applied along the fiber. We attribute the enhancement in writing efficiency to the generation of nonuniform inelastic frozen-in strains across the fiber under tension by CO(2) laser heating. Controlling the axial stress distribution along a fiber during the CO(2) laser writing process thus provides an additional degree of freedom for control of the grating characteristics.

Control degrees of freedom using the restraining number: further evaluation

AbstractA simple and effective procedure for the computation of control degrees of freedom (CDOF) using the concept of restraining number has been recently proposed by our group. The goal of the present contribution is to further evaluate and enhance this procedure. The restraining number is applied to a few more important units. In particular, a detailed analysis has been done for determining the restraining number of membrane separators, given their increasing importance in the industry today. The restraining number procedure is then successfully applied to compute the CDOF of several industrial‐scale processes with distinctly unique characteristics. The simplicity, reliability, general applicability and effectiveness of the procedure are thus further demonstrated. To sum up, the present contribution improves upon and details the CDOF procedure clearly, discusses further issues like the restraining number for variable speed pumps and membrane separators, redundancies for absorbers and strippers and finally, the applicability of this procedure to three‐phase distillation columns and complex industrial processes. Copyright © 2008 Curtin University of Technology and John Wiley & Sons, Ltd.

Robust feedforward design for a two-degrees of freedom controller

In this paper we address the problem of designing the feedforward block of a two degrees of freedom controller in the case of single input single output (SISO) discrete-time linear systems with model uncertainty. In this work the design of the feedforward filter is formulated as a robust model matching problem. First, a closed form solution of the optimal noncausal filter, which minimizes the worst-case model matching error for each ω ∈ [ 0 , 2 π ] , is obtained. Then, suitable rational stable approximations of the optimal solution are derived either by means of causal filters or, when a preview of the reference signal is available, by means of noncausal FIR filters. The efficiency of the proposed method is tested on a simulated example.

Tracking and balance control of ball and plate system

An extension of the traditional ball and beam system into a ball and plate system is constructed using two magnetic suspension actuators for two degree of freedom control. System characteristics of the mathematical model with control configuration are developed. For control performance, a single‐chip microprocessor, serving as control kernel with basic electronic components, is designed and implemented. According to the backstepping control design procedure, the proposed controller is fabricated and tested. Several scenarios of dynamic operation, including oscillatory stabilization and circular trajectory tracking are tested to verify the system performance and capability.

BAYESIAN APPROACH FOR CONSTRAINT ANALYSIS OF MPC AND INDUSTRIAL APPLICATION

Profit margins from plant operations may be improved by changing the constraints so as to increase the degrees of freedom for control. Due to the presence of disturbances the chances of operating the plant outside the set limits cannot be ruled out. Thus, the expected return should be estimated by taking into account the variability. Bayesian Statistics can be used to estimate these probabilities subject to changes in operating constraint limits. The maximum a posteriori estimate of the process state due to the change in the operating conditions can be inferred using Bayesian methods and the profits or return thus obtained can be estimated. Also the decisions to obtain target value of the return can be made using the Bayesian methods.