Line Scan Camera

Unlike area scan cameras that capture a full 2D frame at once, a line scan camera uses a single row of photosensitive pixels—typically 1,024 to 16,384 pixels wide. As the object or camera moves, the sensor captures sequential lines at high frequencies, assembling a theoretically infinite-length image. This architecture eliminates frame-boundary artifacts and provides geometric fidelity across the entire scan axis.

• Pixel widths: 1K, 2K, 4K, 8K, 16K
• Line rates: up to 200 kHz in modern CMOS sensors
• Ideal for: webs, rolls, rotating cylinders

The narrow, one-dimensional field of view demands high-intensity, focused illumination concentrated on a thin line. Standard diffuse lighting wastes energy outside the sensor's view. Common solutions include fiber-optic line lights, high-power LED bars, and laser line generators. The lighting geometry must be co-planar with the sensor to maximize photon collection at high line rates.

• Bright-field: direct reflection for surface defects
• Dark-field: angled illumination for scratches and texture
• Laser profilometry: triangulation for 3D height maps

A defining application is inspecting the full surface of rotating cylindrical parts—bearings, pistons, rollers, and pharmaceutical vials. The part spins on a fixture while the camera captures lines, effectively 'unwrapping' the 360-degree surface into a flat 2D image. This reveals defects like scratches, pits, and inclusions that would be hidden or distorted in a single area-scan snapshot.

• Rotation synchronized to line rate
• Produces seamless panoramic surface maps
• Enables 100% surface inspection at production speed

TDI line scan sensors contain multiple parallel rows of pixels that sequentially image the same line on the moving object. The charge from each row is summed in perfect synchronization with the object's motion, effectively multiplying the integration time without reducing speed. This provides dramatically higher signal-to-noise ratio in high-speed, low-light applications like web inspection of dark materials.

• Common stages: 16, 32, 64, 128, 256 rows
• SNR improvement: proportional to the number of TDI stages
• Critical for: PCB inspection, semiconductor wafer scanning

Color line scan cameras use tri-linear sensors with three separate pixel rows, each filtered for red, green, and blue. Alternatively, prism-based cameras split the incoming light onto three discrete monochrome sensors for superior color registration. Beyond visible light, line scan cameras operate in UV, NIR, and SWIR wavelengths to reveal subsurface defects, material composition differences, and contaminants invisible to the human eye.

• Tri-linear: cost-effective, requires spatial correction
• Prism: precise co-site sampling, no interpolation
• SWIR (900–1700 nm): sees through silicon, detects moisture

Line scan cameras are the standard for inspecting continuous materials like paper, textiles, and metal foil produced in rolls. As the web moves at high speed under the sensor, the camera captures a seamless, unbroken image without the frame overlap or gaps inherent to area scan cameras.

• Printing Industry: Detects streaks, color registration errors, and missing print at speeds exceeding 100 meters per minute.
• Non-Woven Textiles: Identifies holes, stains, and fiber density variations in real-time.
• Battery Electrode Coating: Monitors the uniformity of lithium slurry coatings on copper and aluminum foils, where pinhole defects cause catastrophic cell failure.

Inspecting the entire surface of cylindrical components—such as bearings, pharmaceutical vials, or ammunition casings—requires unwrapping the object into a flat 2D image. A line scan camera synchronized with a rotating stage captures the full circumference in a single, distortion-free image.

• Bearing Manufacturing: Detects surface pitting, scratches, and grinding burns on roller elements and raceways.
• Pharmaceutical Packaging: Inspects the sidewalls of glass vials and syringes for cracks, cosmetic defects, and particulate contamination.
• Ammunition & Aerospace: Verifies the integrity of casings and fasteners, where surface flaws can lead to catastrophic failure under extreme pressure.

The manufacture of flat panel displays and printed circuit boards demands pixel-level defect detection across meter-wide substrates. Line scan cameras with high-density sensors and telecentric lenses provide the necessary resolution and geometric accuracy.

• OLED/LCD Panels: Identifies dead pixels, mura (non-uniformity), and color filter defects on substrates exceeding Gen 10.5 dimensions.
• PCB & Semiconductor Wafers: Detects micro-cracks, solder bridging, and trace width violations with micron-level precision.
• Solar Cell Manufacturing: Inspects photovoltaic wafers for micro-cracks and finger interruptions that reduce energy conversion efficiency.

In free-fall optical sorting, products cascade past a line scan camera at high velocity. The camera captures a snapshot of each object's entire surface as it passes, and downstream air jets eject defective items based on real-time classification.

• Grain & Seed Sorting: Removes discolored, moldy, or foreign-material kernels from bulk food streams at throughputs measured in tons per hour.
• Recycling & Waste Management: Separates plastics by polymer type using near-infrared (NIR) hyperspectral line scan cameras.
• Frozen Food Processing: Detects foreign material and color defects in individually quick-frozen vegetables and fruits.

Line scan cameras mounted on track inspection vehicles capture continuous, high-resolution images of rail surfaces, overhead catenary wires, and tunnel linings at mainline speeds. The resulting image strips are analyzed for fatigue cracks, wear patterns, and geometric deviations.

• Rail Surface Inspection: Detects rolling contact fatigue cracks, corrugation, and squats that precede rail breaks.
• Overhead Wire Monitoring: Measures the stagger and wear of contact wires to prevent pantograph entanglement.
• Tunnel & Bridge Surveying: Creates high-resolution surface maps to detect concrete spalling and water ingress over time.

Unlike area scan cameras that capture discrete frames, line scan cameras require precise synchronization with the motion of the object. A rotary encoder mounted on the conveyor or web drive outputs pulses that trigger each line acquisition, ensuring the aspect ratio remains correct regardless of speed variations.

• Quadrature Encoders: Provide direction and speed data, allowing the camera to maintain spatial accuracy during acceleration and deceleration.
• Line Rate Calculation: The required line rate (in kHz) is determined by dividing the object speed (mm/s) by the desired pixel resolution (mm/pixel).
• Image Distortion: Without encoder synchronization, speed fluctuations cause compression or stretching artifacts, rendering dimensional measurements invalid.

The process of estimating intrinsic parameters (focal length, optical center) and extrinsic parameters (position, orientation) of the line scan sensor. Calibration corrects for lens distortion and perspective errors, ensuring that each pixel corresponds to a known, real-world coordinate. This is critical for metrology applications where dimensional accuracy is paramount.

A 3D imaging technique that projects a known pattern of light onto a surface and analyzes its deformation with a line scan camera. By triangulating the distortion of the projected pattern, the system calculates depth and surface topography. This reveals subtle physical defects like scratches, dents, and warpage that are invisible to standard 2D intensity imaging.

A hardware mechanism that triggers the line scan camera to capture a new row of pixels based on the actual distance traveled by the object, not a fixed time interval. A rotary encoder on the conveyor or web drive emits pulses proportional to movement. This ensures the aspect ratio of the final 2D image remains correct regardless of speed fluctuations, preventing image stretching or compression.

Post-processing steps often applied to line scan imagery. Binarization converts a grayscale image to pure black-and-white using a threshold, separating foreground defects from the background. Blob Analysis then identifies connected groups of pixels and extracts properties like:

• Area and perimeter
• Centroid location
• Circularity and elongation This quantifies the size and shape of detected anomalies.

The primary alternative to a line scan camera. An area scan sensor captures a full 2D frame in a single exposure using a matrix of pixels. While simpler to set up, it is limited to inspecting discrete, stationary objects or those within a fixed field of view. Line scan cameras are preferred for continuous webs, cylindrical parts, and applications requiring ultra-high resolution along one axis.

A statistical method used to validate the precision of the entire line scan inspection system. Repeatability measures variation when the same operator measures the same part multiple times. Reproducibility measures variation when different operators measure the same part. A successful GR&R study confirms that the camera system provides consistent, reliable measurements for quality assurance.