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P.RANJITH. 141212601004.

M-TECH MFG. BSAU.

DATA ACQUISITION METHODS

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Process flow chart

• Data capture

• Pre processing

• Segmentation and surface fitting

• Cad model creation

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DATA ACQUISITION

NON CONTACT

OPTICAL

TRIANGULATION RANGING

INTERFEROMETRY STRUCTURED LIGHTING

IMAGE ANALYSIS

ACOUSTIC

MAGNETIC

CONTACT

ROBOTIC ARM CMM

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TRIANGULATION METHOD

• Triangulation is a method which uses location and angles between light sources and photo sensing devices to deduce position.• A high energy light source is focused and projected at a pre-specified

angle at the surface of interest.

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TRIANGULATION ARRANGEMENTS USING SINGLE AND DOUBLE CCD

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STRUCTURED LIGHTING

• Structured lighting involves projecting patterns of light upon a surface of interest and capturing an image of the resulting pattern as reflected by the surface.• The image must then be analyzed to determine coordinates of data

points on the surface.• To improve the capturing process, a light pattern containing multiple

strips is projected onto the surface of an object

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DIFFERENT LIGHT PATTERNS USED IN STRUCTURED-LIGHT TECHNIQUES

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IMAGE ANALYSIS

• Image analysis : This is similar to structured lighting methods in that frames are analyzed to determine coordinate data. The stereo pairs are used to provide enough information to determine height and coordinate position. • This method is often referred to as a passive method since no structured

lighting is used. Active methods are distinguished from passive methods in that artificial light is used in the acquisition of data. • Correlation of image pairs and landmarks within the images are big

difficulties with this method and this is why active methods are preferred

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Image analysis

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Tactile methods

• Tactile methods represent another popular approach to shape capture. • Tactile methods touch a surface using mechanical arms. Sensing

devices in the joints of the arm determine the relative coordinate locations. • These methods are mostly limited by the measuring device limitations.

For example, a 3-axis milling machine

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Tactile method

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CMM

• CMM: Probably the most popular method is the use of coordinate measuring machines (CMM). • These machines can be programmed to follow paths along a surface

and collect very accurate, nearly noise-free data.• A CMM with a touch-trigger probe can be programmed to follow

planned paths along a surface. • A CMM provides more accurate measurement data compared to the

articulated arm.

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Co ordinate measuring machine

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ACOUSTIC METHOD

• Acoustic: The final type of data acquisition methods we will examine are acoustic, where sound is reflected from a surface, and magnetic, where a magnetic field touches the surface.• The method is essentially the same as time-of-flight, where a sound

source is reflected of a surface and then distance between the source and surface is determined knowing the speed of sound.

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INTERFEROMETRY

• The interferometry technique is well known in dimensional inspection as well as in flatness and deformation measurements in which structured-light patterns are projected onto a surface to produce shadow.• The light contours produced by moiré effects are captured in an image

and analyzed to determine distances between the lines. • This distance is proportional to the height of the surface at the point of

interest, and so the surface Coordinates can be calculated.

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FORMATION OF MOIR・ FRINGES

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TIME OF FLIGHT METHOD

• The principle behind all time-of-flight implementations is to measure the amount of time (t) that a light pulse (i.e., Laser electromagnetic radiation) takes to travel to the object and return.• The speed of light (C) is known, it is possible to determine the

distance travelled. The distance (D) of the object from the laser would then be equal to approximately one half of the distance the laser pulse travelled: D= C × t/2• The high velocity of light allows TOF scanners to make hundreds, or

even thousands of measurements per second.

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PRINCIPLE OF TOF SCANNERS

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COMPUTERIZED TOMOGRAPHY

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Thank you…