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Gra f tek Imaging, Inc.

Gra f tek Imaging, Inc. A National Instruments Alliance Member Providing Complete Solutions For Image Acquisition and Analysis. INTRODUCTION TO LINE SCAN CAMERAS. Gra f tek Imaging, Inc. What is a Line Scan Camera?. A line scan camera is similar to a fax machine, photocopier or scanner.

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Gra f tek Imaging, Inc.

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  1. Graftek Imaging, Inc. A National Instruments Alliance Member Providing Complete Solutions For Image Acquisition and Analysis

  2. INTRODUCTION TO LINE SCAN CAMERAS Graftek Imaging, Inc.

  3. What is a Line Scan Camera? • A line scan camera is similar to a fax machine, photocopier or scanner.

  4. Unlike a photocopier or a scanner, a line scan camera is able to image very large and 3D objects.

  5. Line scan cameras use a one dimensional array to create a two dimensional image. Area Camera Sensor Line Scan Camera Sensor

  6. A two dimensional image results from the movement of the camera or object. Sensor

  7. The image is acquired line by line as the object moves perpendicularly relative to the sensor. • Single lines or complete two dimensional images can be transferred to the host PC for display, processing or archiving.

  8. PCB Example Image Actual Resolution Original Image = 2545 pixels x 1329 pixels

  9. Benefits of Line Scan Cameras • Very high spatial resolution at low cost • Continuous Image/100% Inspection of moving objects • Reduced Distortion • Even illumination of large areas/objects

  10. Area Cameras • Area cameras become dramatically more expensive as their resolution increases. 2048 x 2048 $9450.00+ 640 x 480 $700.00 4000 x 2624 $38000.00+ 1280 x 1024 $3000.00+ 3072 x 2048 $7995.00+ 1920 x 1024 $4950.00+

  11. Line Scan Cameras • By comparison, the price tag to achieve high resolution with a line scan camera is small. 1024 x 1 $1895.00+ 2048 x 1 $1975.00+ 4096 x 1 $3725.00+ 6144 x 1 $4325.00+ 8192 x 1 $4600.00+

  12. Area Cameras 640 x 480 (NTSC) 1000 x 1000

  13. Line Scan Verse Area Scan 640 x 480 (NTSC) = $700.00 1000 x 1000 = $3000.00 4096 x 1 = $3725.00

  14. Line Scan Camera Applications • Most line scan camera applications involve either moving the object or moving the camera. • When the object is moving, the line scan camera behaves like a fax machine. The object is fed past the sensor. • When the camera is moving, the line scan camera is like a photocopier or scanner. The sensor of the line scan camera sweeps across the object.

  15. Types of Motion • Linear Motion • Rotating Objects

  16. Linear Movement Original Image 2200 x 11000

  17. Rotating Objects Original Image 2048 x 19459

  18. System Components Host PC • 1) Line Scan Camera • 2) Lens • 3) Frame Grabber • 4) Encoder • 5) Trigger Source • 6) Lighting 3 1 2 6 5 4

  19. Motion and Vision • A line scan camera can be used to create an image of a normally stationary object by mounting either the camera or the object on a linear or rotary stage. Image Courtesy of Design and Assembly Concepts, Inc.

  20. Choosing a Line Scan Camera • 1) Line Scan Camera 1

  21. Choosing a Line Scan Camera • Select Camera Resolution • Select Camera Line Rate • Select Camera Output

  22. Camera resolution • Select the camera’s resolution based on the application’s requirements. • Resolution is determined by dividing the available number of pixels into the field of view (FOV). • Line scan cameras are available with the following resolutions: 512, 1024, 2048, 4096, 6144 and 8192 • A 1024 pixel linear camera viewing a 1m FOV would have a resolution of approximately 1mm per pixel (0.9765625mm).

  23. Line Rate • Divide the rate of motion by the per pixel resolution to determine the minimum line rate, for example 10 meters per second / 1mm resolution = 10 KHz line rate • A line rate that is too slow or too fast will result in geometric distortion of the object Elongated 10 KHz 5 KHz 20 KHz

  24. Line Rate 5 KHz Tech Tip: Over scanning an object can accentuate defects. 10 KHz 20 KHz

  25. Available Line Rates • As the number of pixels increases, the maximum line rate of a linear cameras decreases: 1024 x 1 pixel = 79 kHz 2048 x 1 pixel = 36 kHz 4096 x 1 pixel = 18 kHz 6144 x 1 pixel = 12 kHz 8196 x 1 pixel = 9 kHz • Note: Maximum exposure time decreases as the line rate increases.

  26. Choosing a Lens • 1) Line Scan Camera • 2) Lens 1 2

  27. Choosing a Lens • Line scan camera sensors are typically larger than area camera sensors, resulting in the need for large format lenses. • Typical area camera sensors range from 3.6mm x 2.4mm in size to 12.8 mm x 8.8 mm. • Line scan camera sensors range from 5.12 mm to 57.37 mm wide. Image of a Line Scan Camera Sensor

  28. Types of Lenses • Line Scan cameras with 1024 or fewer use C-mount or F-mount lenses. • Line Scan cameras with 2048 or more pixels use F-mount (photography) or specialty lenses. Computar V1213 Nikon 60mm f/2.8D AF Micro-Nikkor

  29. Lens Camera Sensor Size (SS) Field of View (FOV) Focal Length (FL) Minimum Focal Distance (D) Determining Focal Length • Sensor Size (SS): Multiply Cell Size by the number of cells (Example: 10mm x 1024 = 10.24mm) • Field of View (FOV: What is the viewable area?) • Focal Length = SS*(Distance/FOV)

  30. System Components Host PC • 1) Line Scan Camera • 2) Lens • 3) Frame Grabber 3 1 2

  31. Interfacing Line Scan Cameras With NI Products • PCI/PXI-1422 + specific camera cable + D2504 I/O cable • PCI-1424 + specific camera cable + D2504 I/O cable + memory upgrade (32 or 64MB) • PCI-1428 + camera link cable + D6804 I/O cable • NI-IMAQ for IEEE-1394 + PCI, PCMCIA, PXI or CVS-1454 + firewire cable and trigger cable

  32. Image Acquisition Forms • Individual lines can be acquired and sent to the host for processing. • Individual lines can be built into 2D images in host PC memory. • Individual lines can be buffered in frame grabber memory and sent as complete images to the host PC for processing.

  33. Encoder Host PC • 1) Line Scan Camera • 2) Lens • 3) Frame Grabber • 4) Encoder 3 1 2 4

  34. Acquisition Modes • Free running- the camera acquires lines at a predetermined rate, if the rate of movement changes the image will elongate or contract proportionally. • Encoded- the line rate of the camera is determined by an encoder. A single line is generated each time the camera receives a pulse from an encoder.

  35. Free Running • Objects contract and elongate as the rate of motion changes.

  36. Encoded • The image’s geometry remains constant as the rate of motion changes.

  37. Trigger Host PC • 1) Line Scan Camera • 2) Lens • 3) Frame Grabber • 4) Encoder • 5) Trigger Source 3 1 2 5 4

  38. Triggered Acquisition • Like area scan cameras, the start of each image can be triggered via an external TTL signal. • Line scan cameras can also take advantage of Variable Height Acquisition. Here, the beginning and end of the image is determined by a TTL signal, varying the size of the image to match changes in the length of the object.

  39. Continuous Image Acquisition • When the inspection is of a continuous object (for example a moving web or cable), it is not necessary to provide a trigger signal. • The image is transferred to the host for processing based on frame grabber and application requirements.

  40. Triggered Image Acquisition • When the inspection is of discreet objects, it is necessary to synchronize the start of image acquisition with the arrival of the component/object. Images Acquired at Regular Intervals 5 Triggered Acquisition

  41. Lighting Host PC • 1) Line Scan Camera • 2) Lens • 3) Frame Grabber • 4) Encoder • 5) Trigger Source • 6) Lighting 3 1 2 6 5 4

  42. Light Guides • The most common form of illumination for line scan cameras is the line light. Line lights are available off the shelf in widths ranging from 1 inch to 40 inches. 6” Line Light 40” Line Light

  43. Light Guides • A line lights can be used as a bright field, diffuse on axis, dark field or backlight. • Pairs of line lights can be used to achieve different lighting geometries or to increase the amount of available light. • Custom line lights are available with multiple light inputs for increased light output.

  44. Line Lights • A typical line light system consists of two to four parts. Cylindrical or Apertured Lens And/Or Light Source Line Light Polarizer

  45. Bright Field • General (Single or Dual Line Lights) - Non-Critical Applications Non Polarized Polarized

  46. Direct On Axis • Direct on Axis - Flat, Specular Surfaces

  47. Dark Field • Dark-Field - Flat, Diffuse Surfaces Bright Field Dark Field

  48. Back Light • Back-Light - Contour Analysis, Clear Substances

  49. Lighting • For even illumination of the object, the light guide should be wider than the object.

  50. Contacting Graftek Imaging, Inc. • Phone: (512) 416-1099 • Email: eastlund@graftek.com • URL: www.graftek.com

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