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Backlight Optical Sand Screen Inspection Process Disclosure Number: IPCOM000220065D
Publication Date: 2012-Jul-19
Document File: 6 page(s) / 603K

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Introduction. The invention is a method of optical sand screen inspection which uses backlight to measure slot width or pore openings created during a screen manufacturing process. This invention targets the manufacturing inspection process of sand screens which uses a wrapping process to mount a wire wrap onto a perforated or solid base pipe. The method also applies to screen jackets made as a wire wrapped jacket or a mesh jacket. Summary. The invention is centered on the illumination of a surface under the sand screen after wrapping onto a pipe or forming into a jacket or cartridge. This provides the reflective properties needed to accurately disperse light upwards into the slot or mesh area. The development eliminates photographic noise and measurement inaccuracy which are common distractions in more traditional methods of optical inspection and measurement, whereby the outer screen, mesh or jacket surface is illuminated. A common principle for the different embodiments is the use of a light source placed on the outside of the screen surface, either it being a screen wrapped on a pipe, a screen jacket or a filter cartridge. The invention utilizes the principle of illuminating a surface or an element on the inside of the screen surface which again reflects light back into a camera. The light source is oriented in such a way that the screen surface seen by the camera is only minimally illuminated directly by the light source. This is achieved by orienting the light source at a given angle relative to the camera and at a distance from the camera. The light source and camera are typically pointing towards the same reflective and or opaque surface being below the screen surface. The opaque element will also typically be illuminated over a larger area than what is directly being illuminated by the light source. This means a perfect orientation of light source versus camera is not needed. As the light source is not significantly illuminating the screen surface seen by the camera, a variation in intensity of the light being reflected by the surface or element below the screen is acceptable. Consequently, the system becomes very robust with respect to an accurate identification of the edge of the pore or slot. With the given exact identification of the edge of a pore or slot of the screen, dimensions like slot opening, pore opening and wire width can be measured. This measurement process can also be automated to make it possible to measure a large part or the whole surface of a screen Detailed Description Including Examples and Drawings. Traditional slot verification procedures encompass a measurement process with a camera unit which photographs the screen section, whilst simultaneously reflecting light on the outer screen surface. Inherently, this light reflection creates a high level of photographic noise during the measurement process. The algorithm which determines the slot width, based on the position of the wire edge, has difficulty selecting the true outer edge. This leads to a high amount of measurement uncertainty and error throughout the process. The invention seeks to improve the known art by providing greater optical accuracy through the use of light from below the slot surface to illuminate the slot width requiring measurement. This is outlined by the various embodiments below. The key element of the concept is to place the light source under the filter media. This light source emits light through the pore or slot openings of the filter media in the sand screen. As the light comes from below, the pore opening or the slot opening will appear as a bright area, while the wires appear much darker. Figure 1 highlights a graphical illustration of the light source illuminating the outer screen surface, whilst a camera simultaneously captures an image of the slot and the adjacent wrap wires. This system can make relative measurements with high accuracy, but it is based on light being reflected off the screen surface. This means that it is challenging to measure absolute accuracy, as the reflected light varies, depending on the wire surface and light intensity. Figure 2 clearly highlights this problem showing the varying light levels across the wire surface. Figure 4.illustrates the reduced levels of noise seen during a backlight image capture. Only the actual slot is illuminated; all other areas are black. This allows the processing software to accurately select the correct wire edge to begin the measurement procedure. Embodiment 1. Figures 5 and 6 highlight the screen jacket attached to a base pipe, with light being reflected off the inner surface, populating upwards and illuminating the slot directly beneath the camera from below. This embodiment requires a base pipe with sufficient reflective properties. This can be achieved through the use of suitable coating, or alternatively by applying a reflective surface to the base pipe. This method is preferable for a screen without perforations in the base pipe of the area being examined. The light is supplied via a fixed source, typically in a plane perpendicular to the base pipe and parallel to the slots of the screen, and oriented at an angle different from the viewing angle of the camera. The light source can be connected to the camera carriage. One or more light sources are orientated to emit light at an optimal angle into the annulus which in turn reflects off the base pipe, into the slot (Figure 5). Embodiment 2. As shown in Figures 7 and 8, an opaque element which can be a piece of plastic or metal with desired optical properties, has been placed in the annulus between the wire wrap and perforated base pipe, along the entire length of screen. The opaque element gives an even and uniform surface to reflect light off. Furthermore, the amount of light needed to illuminate the slot is decreased. Similar to embodiment 1, the light is again illuminated into the annulus at a specific angle, whilst avoiding obstruction of the camera's field of view on entry. Embodiment 3. This embodiment utilizes a slot illumination identical to that of embodiment 2. The transfer of light is provided using a smaller opaque piece, which is positioned directly beneath the slot being measured. It is held in place and travels along the screen through the use of a magnetic force which is transferred downwards from the camera carriage. An alternative method of moving the opaque piece can be by the use of a wire or similar which is pulling the piece as the camera is moving.

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