Graftek Imaging, Inc.A National Instruments Alliance MemberA National Instruments Alliance Member

Providing Complete Solutions For Image Providing Complete Solutions For Image Acquisition and AnalysisAcquisition and Analysis

INTRODUCTION TO LINE SCAN CAMERAS

Graftek Imaging, Inc.

What is a Line Scan Camera?

• A line scan camera is similar to a fax machine, photocopier or scanner.

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

• Line scan cameras use a one dimensional array to create a two dimensional image.

Area Camera Sensor Line Scan Camera Sensor

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

Sensor

• 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.

PCB Example Image

Original Image = 2545 pixels x 1329 pixels

Actual Resolution

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

4000 x 2624$38000.00+

Area Cameras• Area cameras become dramatically more expensive as

their resolution increases.

640 x 480$700.00

1280 x 1024$3000.00+

1920 x 1024$4950.00+

2048 x 2048$9450.00+

3072 x 2048$7995.00+

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+

Area Cameras

640 x 480 (NTSC)

1000 x 1000

Line Scan Verse Area Scan

4096 x 1 = $3725.00

640 x 480 (NTSC) = $700.00

1000 x 1000 = $3000.00

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.

Types of Motion

• Linear Motion

• Rotating Objects

Linear Movement

Original Image 2200 x 11000

Rotating Objects

Original Image 2048 x 19459

System Components

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

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Host PC

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.

• 1) Line Scan Camera

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Choosing a Line Scan Camera

Choosing a Line Scan Camera

• Select Camera Resolution• Select Camera Line Rate• Select Camera Output

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).

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

20 KHz 10 KHz 5 KHz

Elongated

Line Rate

5 KHz

10 KHz

20 KHz

Tech Tip:

Over scanning an object can accentuate defects.

Available Line Rates

• As the number of pixels increases, the maximum line rate of a linear cameras decreases:

1024 x 1 pixel = 79 kHz2048 x 1 pixel = 36 kHz4096 x 1 pixel = 18 kHz6144 x 1 pixel = 12 kHz8196 x 1 pixel = 9 kHz

• Note: Maximum exposure time decreases as the line rate increases.

Choosing a Lens

• 1) Line Scan Camera• 2) Lens

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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

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.

Nikon 60mm f/2.8D AF Micro-Nikkor

Computar V1213

Determining Focal Length• Sensor Size (SS): Multiply Cell Size by the

number of cells (Example: 10m x 1024 = 10.24mm)

• Field of View (FOV: What is the viewable area?)

• Focal Length = SS*(Distance/FOV)Lens

Camera Sensor Size (SS)

Field of View (FOV)

Focal Length (FL) Minimum Focal Distance (D)

System Components

• 1) Line Scan Camera• 2) Lens• 3) Frame Grabber

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Host PC

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

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.

Encoder

• 1) Line Scan Camera• 2) Lens• 3) Frame Grabber• 4) Encoder 1

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Host PC

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.

Free Running

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

Encoded

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

Trigger

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

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Host PC

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.

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.

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.

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Images Acquired at Regular Intervals

Triggered Acquisition

Lighting

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

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Host PC

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

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.

Line Lights

• A typical line light system consists of two to four parts.

Light Source Line Light

Cylindrical or

Apertured Lens

Polarizer

And/Or

Bright Field• General (Single or Dual Line Lights) -

Non-Critical Applications

Non Polarized

Polarized

Direct On Axis• Direct on Axis - Flat, Specular

Surfaces

Dark Field

• Dark-Field - Flat, Diffuse Surfaces

Bright Field

Dark Field

Back Light

• Back-Light - Contour Analysis, Clear Substances

Lighting

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

Contacting Graftek Imaging, Inc.

• Phone: (512) 416-1099

• Email: eastlund@graftek.com

• URL: www.graftek.com