Information about integrity of pipelines and pressure vessels is vital to the oil and gas industry. This emphasizes the need for fast and cost effective non-destructive testing solutions for monitoring and inspection of these components. However, due to reasons such as corrosion protection and temperature maintenance, pipelines and pressure vessels are usually coated throughout the oil and gas industry. These coatings also present a barrier to inspections and typically need to be removed prior to inspection with nondestructive evaluation (NDE) methods. This article presents a pulsed eddy current (PEC) system suitable for nondestructive evaluation of steel pipelines and pressure vessels without the need for removing the coating layers. A PEC probe was fabricated and a custom computer code with built in signal processing and data analysis functions was developed to collect the measurement signals and calculate thickness variations in the test objects. From a lift-off distance of 12mm, experiments were performed on eight SS304 stainless steel samples with thicknesses ranging from 1mm to 8mm. The SS304 steel was chosen as the test material to represent the steel type commonly used in the pipeline industry. A calibration curve based on the zero crossing time of initial measurements was obtained and implemented into the measurement software. Using the calibrated system, 25 measurements where performed on each sample. Statistical analysis of results showed that the proposed system can accurately detect thickness variations in the test samples with maximum measurement error of 3.3 percent.

Effective maintenance practices improve safety of the operating unit, enhance safety during maintenance periods, increase operating up-time and decrease the overall maintenance costs. This paper outlines the application of Hatch’s furnace condition monitoring program. Emphasis is placed on Acousto Ultrasonic-Echo (AU-E), a manually operated, non-destructive testing and evaluation (NDT & E) measurement system, which determines the thickness and physical properties of the installed refractory components. The system is used to identify the refractory wear profile and to determine the positions of cracking, metal infiltrations and other anomalies, such as gaps and discontinuities within the linings. When the AU-E system is used after the rebuild and at regular time intervals, the results can be used to determine the degree and extent of the refractory deterioration. Moreover, data analysis and interpretation algorithms have been developed in order to identify areas of hydration, based on the AU-E results. Throughout the campaign, this information is applied to schedule the shutdowns, and to determine the extent of the repair. In this article, we are discussing the main principles of the AU-E technique and its application, particularly for determination of hearth, sidewall, taphole and roof refractory conditions. In addition, two case studies are presented to demonstrate application of the AU-E technique in an electric furnace and a flash furnace.

Recently, magnetic telemanipulation devices have shown a great deal of promise in such areas as semi-conductor manufacturing, wind tunnels, drug delivery, and many more. However, these devices are generally associated with problems caused by payload variation and uncertainties in the parameters of the system which in turn, have limited the development and application of magnetic telemanipulation technology to its full capacity. This paper addresses and deals with these is sues by implementation of a precise position control method for a magnetic telemanipulation system with high level of uncertainties in its parameters. The levitation system used in this study is p rimarily designed for performing remote pick and place operations. The levitated object is a 28 gr microrobot capable of grasping and releasing payloads as heavy as 8 gr. To cope with the uncertainties in the modeling and payload variation, a model reference adaptive feedback linearization (MRAFL) controller is designed and its performance compared with an ordinary feedback linearization (FL) controller. Through experimental results it is shown that the MRAFL controller enables the microrobot to grasp and transport a payload as heavy as 30% of its own weight without a considerable effect on its positioning accuracy. In the presence of the payload, the MRAFL controller resulted in a RMS positioning error of 8 µm compared with 27.9 µm of the FL controller. The approach presented in this work is versatile as it leads to the modeling and control of a highly nonlinear system through a modular approach that can be applied to a variety of magnetic levitation and telemanipulation systems.

Operation of pyrometallurgical and iron making furnaces is greatly affected by the integrity and thickness of their refractory lining. Hatch NDT Group uses three (3) innovative techniques to evaluate refractory lining integrity and thickness in operating furnaces: Acousto Ultrasonic-Echo (AU-E), Taphole Acoustic Monitoring (TAM), and Infrared (IR) thermography. Acousto Ultrasonic-Echo (AU-E) was developed based on the stress wave reflection principles [1]. The system corrects for effect of temperature on the refractory wave speeds to compute accurate refractory thickness. The AU-E technique could also be applied to determine position of lining delamination, cracks and other anomalies within the refractory structure [2, 3]. The Taphole Acoustic Monitoring (TAM) system was developed based on the acoustic emission (AE) principles [4]. The receiving transducers are installed on the inlet and outlet cooling circuits of water cooled tapping blocks. Using the sound generated from flow of molten metal in the taphole, the system is capable of continuously determining refractory wear within the tapping channel. This 24/7 continuous monitoring system is also capable of assisting the operators for better lancing/tapping/drilling practice as it could illustrate the intensity of the hits on the inner refractory lining in the tapping block. The infrared (IR) thermographic cameras are commonly used to determine “hot spots” on the vessels where the refractory wear could be worse than the surrounding areas. In our approach, the data from IR camera is used to accurately determine refractory thickness in one layer refractory lined cylindrical vessels such as converters and reactors [5]. In this paper, we introduce the principal concepts of the above three (3) NDT techniques and present case studies and examples to illustrate the accuracy and repeatability of the measurements.

This paper presents an adaptive controller design for a telemanipulation system with a varying mass. The telemanipulation system levitates a microrobot with weight of 28(gr). The levitated robot is equipped with a micro gripper and is designed for precise pick and place operations, and carrying payloads as heavy as 8(gr). In this paper, a model reference adaptive feedback linearization (MRAFL) controller is designed so as to reject the effects of variations in the mass of the levitated robot. Through experimental results it is shown that the proposed MRAFL controller is capable of rejecting mass variations as big as 30% of the robot's initial mass without any considerable effect on the positioning accuracy of the system.

Magnetic levitation is an emerging technology in applications such as MEMS production, high speed transportation and biomechanics. Due to the lack of mechanical contact, magnetically levitated devices are unimpeded by problems caused by friction, lubrication and sealing. This paper presents a dynamic model of a magnetic levitation device through the frequency response identification technique. Experimental results verify that the proposed model reasonably matches the actual system's behavior. The magnetic levitator consists of a set of modules comprising the electromagnets, an iron yoke, a power amplifier, laser position sensors, and a controller. In order to obtain the total transfer function of the system, the dynamic model of each of these modules was obtained individually. The routine presented in this work is remarkable as it leads to the model of a highly nonlinear system through a modular approach that can be applied to a variety of systems.

This paper presents an approximation method to simplify the magnetic field calculation for real-time control in a magnetic levitation device. Conventional field modeling methods generally involve the numerical solution of highly nonlinear differential equations of the field. The solution of these equations will take enormous computational time and disqualifies these methods for real-time control applications. In this paper, a fast and reliable mathematical model, called pivot point, is developed for the prediction of the magnetic field distribution and verified experimentally. This model is developed based on the geometry of a magnetic stator and its magnetization pattern. The model is then used in a magnetic levitation experiment to prove its real-time capabilities in position control operations. Experiments showed that application of the pivot point method improved the positioning accuracy of the levitation system in step response and trajectory tracking and reduced the settling time.

A single electromagnet can be used for one-dimensional (vertical) magnetic levitation, but cannot control the distribution of the magnetic field on a horizontal plane. For three-dimensional (3-D) levitated movement of objects, an arrangement of multiple electromagnets is required. A pole piece can connect the individual poles of the electromagnets in order to eliminate the appearance of multiple poles and produce a focal point of maximum magnetic field in the horizontal plane. This paper presents the results of an investigation of the effect on different pole pieces on the regulation and control of a large gap magnetic field for 3-D micromanipulation. In a large and wide magnetic gap, a levitated object tends to stay at the maximum point of magnetic field, Bmax, in order to minimize the system energy. By producing a unique Bmax point and controlling its position, 3-D levitated movement of a small permanent magnet (single magnetic dipole moment) can be realized. If the Bmax point is converted into an area with a uniform field that is stronger than any nearby point (Bmax area), complex objects, such as microrobots affixed with several permanent magnets, can be levitated and moved. By selecting a proper pole piece and tuning the electric currents in the electromagnets, the required field distribution will be obtained. The paper proposes a number of pole pieces and discusses their effect on magnetic field distribution. Through simulation results and experimental measurements, it shows that a number of proposed pole piece profiles can generate a magnetic field for 3-D levitated motion. Finally, it reports a demonstration of 3-D levitated motion of a single magnet (using the B max point) and a microrobot (using the Bmax area) to show the feasibility of the proposed method for micromanipulation

Various applications of micro-robotic technology suggest the use of new actuator systems which allow motions to be realized with micrometer accuracy. Conventional actuation techniques such as hydraulic or pneumatic systems are no longer capable of fulfilling the demands of hi-tech micro-scale areas such as miniaturized biomedical devices and MEMS production equipment. These applications pose significantly different problems from actuation on a large scale. In particular, large scale manipulation systems typically deal with sizable friction, whereas micro manipulation systems must minimize friction to achieve submicron precision and avoid generation of static electric fields. Recently, the magnetic levitation technique has been shown to be a feasible actuation method for micro-scale applications. In this paper, a magnetic levitation device is recalled from the authors’ previous work and a control approach is presented to achieve precise motion control of a magnetically levitated object with sub-micron positioning accuracy. The stability of the controller is discussed through the Lyapunov method. Experiments are conducted and showed that the proposed control technique is capable of performing a positioning operation with rms accuracy of 16 μm over a travel range of 30 mm. The nonlinear control strategy proposed in this paper showed a significant improvement in comparison with the conventional control strategies for large gap magnetic levitation systems.

This paper presents modeling and analysis of eddy-current damping that is formed by a conductive plate placed below the levitating object in order to suppress vibrations and ensure stability. It is demonstrated that vibrations should be damped to preserve stability and precision especially for stepwise motion. The levitated object is a small permanent magnet in our experiments. A magnetic drive unit is used for vertical motion of the magnet. Eddy-current distribution in the plate is calculated by solving diffusion equation for vector magnetic potential. The eddy force applied to the object is derived by a coil model representation. It is shown that if a 20 mm radius, 9 mm thick aluminum circular plate is used for eddy-current damping, the levitated object can closely follow a step input with a steady-state precision varying between 0.04 and 0.07 mm depending on the plate object distance. Eddy-current damping is a key technique that improves levitation performance to increase the diversity of applications of magnetic levitation systems in micromanipulation and microelectronic fabrication

Micromanipulation is an emerging technology in such diverse areas as precision engineering, microfabrication, and microsurgery. Each of these areas impose certain technological constraints and requirements in fabrication, actuation, and control. This paper performs a review on the latest technologies of microrobotic actuation techniques and suggests a suitable technique for the actuation of a magnetically levitated microrobot. The microrobot, suspended in an externally produced magnetic field, consists of a gripper attached to a series of permanent magnets and is capable of simple pick and place tasks. A number of electromagnets produce the external magnetic field and three laser sensors feedback the position of the levitated microrobot. Through finite element analysis, performance of the levitation system was investigated, and simulations and experiments were carried out to demonstrate the practical capabilities of the proposed system. (C) 2006 American Institute of Physics.

Magnetic levitation is a good choice for high precision micromanipulation. Several magnetic levitation systems have been proposed and shown to be effective for precision positioning. Most of these systems work with small air gaps and have a small movement range for levitated objects. Increasing the air gap will introduce uncertainty into the modeling and control of the system but is required for specific applications, such as micromanipulation. This paper investigates regulation methods and the control of a large gap magnetic field for non-contact manipulation. A two dimensional magnetic field analysis is performed on a system consists of two electromagnets. In order to increase the uniformity of the magnetic field and have control over the distribution of the field, the electromagnet poles are connected together through a soft magnetic iron called pole piece. The effect of pole piece is investigated through both finite element analysis and mathematical modeling. Definition of a working envelop through magnetic filed distribution is discussed. The results of 2D modeling are discussed and are extended into the 3D case. A number of pole piece profiles are proposed and their effect on the magnetic field investigated. An experimental setup is used for 3D levitated movement of a small permanent magnet. It is shown that manipulation of objects can be performed using an appropriate configuration of electromagnets, a special pole piece, and a yoke.

This paper presents a new approach for controlling SMA actuators with hysteresis compensation by using two energy based semi active controllers. SMA actuators exhibit severe hysteresis that is often responsible for position inaccuracy in a regulation or tracking system. In this paper, a SMA actuator model is recalled from [Alasty A, Shameli E. Dynamic modeling of a new varying stress SMA actuator for precise applications. In: Proceedings of 2004 IEEE international conference on mechatronics (ICM’04). Istanbul, Turkey, June 3–5, 2004]. Then, a PID and a novel PID-P3 controllers have been suggested to perform a position control. To investigate the stability of controlled system the dissipativity triplets of both controllers are obtained. At the end, simulation results show that in precision tracking control of the proposed SMA actuator, PID-P3 controllers are more efficient than ordinary PID controllers.

Shape memory alloys (SMA's) are inherently non-linear devices exhibiting significant hysteresis in their stress strain-temperature characteristic. We have used the variable sub-layer SMA model of Ikuta (1991) to extract the advanced dynamic model of our proposed varying stress SMA actuator. A nonlinear finite element analysis was used to model the proposed bending spring in the actuator and the extended variable sub-laver model of Ikuta was considered to extract stress-displacement relations. Finally, these two models are combined with thermo dynamic model of SMA and a schematic flowchart is proposed to calculate SMA resultant strain under an arbitrary current input. At the end, we applied this model to extract open loop harmonic and step responses of our proposed SMA actuator.