Jeremy S. Smith

Morphological Lifting Scheme for Current Transformer Saturation Detection and Compensation

Current transformer (CT) saturation can cause protective relay mal-operation or even prevent tripping. The wave shape of the secondary current is severely distorted as the CT is forced into deep saturation when the residual flux in the core adds to the flux change caused by faults. In this paper, a morphological lifting scheme is proposed to extract features contained in the waveform of the signal. The detection of the CT saturation is accurately achieved and the points of the inflection, where the saturation begins and ends, are found with the scheme used. This paper also presents a compensation algorithm, based upon the detection results, to reconstruct healthy secondary currents. The proposed morphological lifting scheme and compensation algorithm are demonstrated on a sample power system. The simulation results clearly indicate that they can successfully detect and compensate the distorted secondary current of a saturated CT with residual flux.

Infrared sensor for top face monitoring of weld pools

The development of a novel sensor for the measurement of bead size in tungsten inert gas (TIG) welds is described. A passive vision-based sensor combines infrared imaging of the weld pool and selective optical filtering, both to reduce excessive arc glare and improve contrast between weld pool and heat affected zone (HAZ). The arc interruption and external illumination techniques, used by others, are not required. Image quality is shown to be comparable to that obtained with external illumination and superior to that of arc interruption methods. The technique has been successfully applied to both pulsed and continuous TIG welding of stainless steel in order to maintain the bead size during a welding run.

Morphological undecimated wavelet decomposition for fault location on power transmission lines

This paper presents a novel morphological undecimated wavelet (MUDW) decomposition scheme for fault location on power transmission lines. The MUDW scheme is developed based on the morphological wavelet (MW) theory for both the extraction of transient features and noise reduction in signal processing. The analysis operators and the synthesis operator of MUDW strictly satisfy the pyramid condition. In this paper, the MUDW scheme is used to extract features from noise imposed fault-generated transient voltage and/or current signals of power transmission lines. The efficiency of the MUDW scheme used for noise reduction and the extraction of sudden changes in the transient signals are evaluated in simulation studies. The simulation results show that the fault location can be accurately detected in noisy environments

Real‐time top‐face vision based control of weld pool size

Purpose – Top‐face control of weld penetration in TIG welding is required for fully automated systems to overcome variations in the welding process and fixturing systems.Design/methodology/approach – This paper presents a system based upon based on the real‐time vision measurement and control of the upper surface or “topface” weld pool size. The primary objective has been to demonstrate the feasibility of using vision‐based image processing to provide measurements and the subsequent control of upper bead weld geometrical properties during the weld formation or molten phase and correlate this to the backface weld bead size.Findings – Vision based measurement of the upper surface of the weld pool can be used, in real‐time, to control the weld pool size. This allows more uniform weld penetration to be achieved in the presence of disturbances.Research limitations/implications – The system requires that the pool edges can be accurately identified using a correlation method. This requires images with good contr...

Empirical Mode Decomposition For Power Quality Monitoring

This paper presents an empirical mode decomposition (EMD) technique as a powerful tool for monitoring power quality in electric power systems. As a multi-resolution signal decomposition technique, EMD has the ability to detect and localize transient features of power disturbances. In this paper, firstly, the theoretical background of EMD is briefly introduced and discussed. Then the technique is presented in detail and used to extract the features of power disturbances. Finally the practicality and advantages of the EMD is discussed based on the simulation results obtained from several scenarios of power disturbances. The results demonstrate the potential of the proposed methodology for power quality monitoring and assessment

A vision-based seam tracker for butt-plate TIG welding

In the automation of the TIG (tungsten inert gas) welding process, robots and dedicated machines have been used to place the welding torch at the correct orientation above the seam to be welded. Sensors are required to determine whether the workpiece is located correctly with respect to the welding torch, or whether distortion of the workpiece takes place due to thermal expansion during welding. The authors describe a seam tracker for following the small gap between closed butt plates. The system uses a CCD monochrome video camera with a coherent fibre-optic bundle to view the workpiece. Illumination is provided by an infrared laser diode mounted on the tracker head. The use of these components enables the tracker head to be kept extremely compact. The video signal from the camera is digitised and stored in a microcomputer which analyses the image to obtain the position and width of the gap. This information is then transferred, via a serial line, to the robot controller which then modifies the torch path to keep the welding torch over the seam throughout the welding process.

A visual servoing system for edge trimming of fabric embroideries by laser

Abstract This paper describes a position-based visual servoing system for edge trimming of fabric embroideries by laser. The high-speed vision system, based on a 220 Hz digital camera and the TMS320C40 parallel DSP processor is presented, and the novel image processing algorithm developed for seam tracking applications is briefly explained. Two methods for seam trajectory generation are discussed. In the first method the tracking trajectory is determined only by using the vision data; in the second method, which is suitable for periodic patterns, the predetermined path data is modified by the vision data. A tracking controller using a feedforward controller in the tangential direction of the seam and a feedback controller in the normal direction is described. The custom built manipulator is a four-axis velocity controlled gantry robot with independent PID controllers for each axis. The axes’ reference speeds are commanded and updated by the top-level tracking controller in equal time intervals. The gantry controller program runs on a Pentium PC. The experimental results in edge trimming of different seam patterns are presented.

Multi-fibre calibration of incoherent optical fibre bundles for image transmission

This paper presents a multi-fibre illumination technique for automatically calibrating incoherent optical fibre bundles to enable the transmission of optical images. The calibration system consists of a host computer, a T414 Transputer board, a dedicated calibration board, a CCD camera, two TV monitors, and an incoherent optical fibre bundle. Multiple light spots produced on the screen of a TV monitor are used as a light source to illuminate simultaneously many input fibres in the bundle. The position of the corresponding output fibres can be found by capturing and analysing the image recorded by a CCD camera. Three incoherent optical fibre bundles with different resolutions have been calibrated using this technique and verified by transmitting several different types of picture. The reconstructed image is achieved by means of a dedicated calibration board operating in nearly real time mode, i e within a delay time of one field period of 20 ms from the capture of the image. From the experimental results, the adequate transmission of images by an incoherent optical fibre bundle is clearly shown to be possible. The disadvantage of the long calibration time required by the single-fibre calibration method has been overcome by using this new technique.

Real-time detection via homography mapping of foreground polygons from multiple cameras

A real-time object detection algorithm by using multiple cameras is proposed. The information fusion is based on homographic transformation of the foreground information from multiple cameras to a reference image. Unlike the most recent algorithms which transmit and project foreground bitmap images, we approximate the contour of each foreground region with a polygon and only transmit and project the polygon vertices. These polygons are rebuilt and fused in the reference image. This greatly reduces the requirement on network bandwidth and avoids homographic transformations at image levels. The results on an open video dataset are demonstrated.

Sensor for automated weld bead penetration control

A backface penetration control system has been developed for DC pulsed tungsten inert gas (TIG) welding. The system is based on a binary vision system built around the BBC microcomputer. The system utilizes a coherent optical bundle to transmit the images of the backface bead to a b/w vidicon camera. The penetration control system regulates the bead size by controlling the pulse duration of the TIG process. Comparisons are made between the required and actual bead sizes in real time, the arc current being returned to the background level when the required penetration is reached. The system has been tested extensively on type 304 stainless steel, using various plate thicknesses for both bead on plate and butt weld tests. The system has also been tested on tapered plates from 0.5 mm to 4 mm. The backface penetration control system performs well over the complete range of tested plate thicknesses, in addition to the tapered plate tests. The image of the weld bead does not necessarily have to be in the centre of the screen to produce good welds; as long as the whole bead appears within the field of view of the lens, the bead size may be controlled. This allows the system to be easily set up and operated.