Line Scan Camera

Fundamentals and Working Principle

A line scan camera contains a one-dimensional photosensitive array that integrates light along a single line of the object for a defined exposure interval. The array may be implemented as a linear CCD, a linear CMOS sensor, or a TDI (time delay and integration) architecture that effectively stacks multiple exposures of the same moving line to increase sensitivity without increasing illumination. According to the Sogou Baike entry on 线阵相机, line scan cameras historically use linear CCD sensors as the dominant technology, with linear CMOS sensors appearing on the market by 2012 but not yet displacing CCD as the mainstream architecture in that reference text.

Image formation in a line scan system requires motion. Either the object moves on a conveyor, web, or rotating drum while the camera and illumination remain stationary, or the camera is translated or rotated past a stationary object. The encoder that drives the motion, or an external shaft encoder, is typically the trigger source for line acquisition. The S5 document on line scan systems describes two principal synchronization modes available on these cameras, free run mode (also called internal synchronization, in which the camera free-runs at a programmed line rate set by the manufacturer) and external synchronization modes driven by external triggers. Selecting the synchronization source is one of the first integration decisions because line rate must match the object velocity divided by the desired pixel size in the scan direction.

Illumination is integral to the principle rather than an accessory. Because each line is exposed in isolation, any change in reflectance, LED output, web flutter, or encoder jitter appears as a streak or banding artefact in the assembled image. Continuous LED line lights, fiber optic line lights, and structured laser lines are the conventional sources, chosen so that the illuminated region matches the sensor line length and so that the light is stable from scan to scan. The S6 reference explicitly states that the typical application domain of line scan cameras is the inspection of continuous materials such as metal, plastic, paper, and fiber, where the object is normally moved at a uniform velocity and one or more cameras perform line-by-line scanning of the entire surface, with the resulting image processed either line by line or as a composed area image assembled from many lines.

Specifications and Key Parameters

The parameter set that defines a line scan camera differs from an area scan camera because resolution is expressed in pixels per line rather than in pixels per frame. The S4 Basler source states that the company offers line scan cameras with resolutions from 2K to 16K, and the same source gives a maximum line rate of 500 kHz for the high speed line scan family. Camera interface is a second headline parameter. The S4 source enumerates CoaXPress-over-Fiber, CXP-12, 5GigE, GigE, and Camera Link as the supported interface options for the Basler line scan product family, while the Keyence S3 page documents the existence of the Line Scan series as part of the vision system product family. The S5 document on line scan systems adds a third group of parameters, those governing output channelization, with single tap, dual tap, triple tap, quad tap, and octal tap configurations as the standard output options found on the market.

Pixel pitch and line length together set the field of view at a given working distance. Smaller pitch supports higher resolution per unit of web width but demands more demanding optics and higher illumination because each pixel collects less light. Line rate sets the maximum producible throughput; for a constant web speed, halving the line rate halves the number of pixels per millimetre in the scan direction. The S5 document notes that one tap corresponds to a 40 MHz output as a baseline value, and that with octal output the aggregate output can reach 320 MHz, while the same document records that a single tap output has in practice risen to 60, 80, and 85 MHz as the per channel data rate has increased, which in turn tightens the practical cable length limit because higher per channel rates shorten the cable length at which signal attenuation causes noise on the image.

Synchronization, exposure control, and pixel format are equally part of the specification. The S5 document names free run mode (internal synchronization) as the factory default for line scan cameras and lists it as one of the available modes, with additional external synchronization modes also available on the same camera family. Bit depth, monochrome versus trilinear or prism color, and the availability of TDI stages are documented per model. Because the supplied sources do not enumerate every value for every vendor, individual cells of the comparison table below are written as varies by model where the source set does not provide a verbatim number, and every row is attributed to a specific vendor or standard so that the table is read as a representative lineup rather than a category-wide claim.

Types and Configurations

Line scan cameras divide first by sensor technology. The Sogou Baike entry on 线阵相机 states that the dominant sensor is the line scan CCD, with line scan CMOS sensors appearing in the market by 2012 but not displacing CCD as the mainstream architecture in that reference. A second division is by color. The S6 reference lists the two classifications as single color (monochrome) and color, and Basler's product page (S4) confirms monochrome and color line scan cameras as the two color branches supplied. Color line scan cameras are typically implemented as trilinear sensors with three parallel lines covered by red, green, and blue filters, or as prism cameras that split the incoming light into three separate sensors through a dichroic prism assembly; the supplied sources do not quantify the share of each implementation.

A third division is by number of output taps. The S5 document lists single tap, dual tap, triple tap, quad tap, and octal tap as the standard output options, with the rationale that multiple taps accelerate the readout of the line. The same document explains that one tap corresponds to a 40 MHz baseline and that octal output can reach 320 MHz, with single tap data rates in practice rising to 60, 80, and 85 MHz as the camera data rate has increased. Higher tap counts shorten the maximum usable cable length because attenuation and noise grow with both frequency and conductor length. The S5 document specifically records that at single tap 85 MHz, general cable stock begins to introduce visible noise in the output image, and that a 7 metre cable length is a practical operating point without observable noise at that rate.

A fourth division is by synchronization mode. The S5 document names free run mode (internal synchronization, in which the manufacturer presets the line rate) as one of the available modes, with additional external synchronization modes available on the same camera family for integration with an external trigger or encoder. A fifth division is by the application pattern: single camera over a single line, multiple cameras arrayed across a wide web, or multiple cameras viewing the same line from different angles to inspect different features. The S6 reference states that the inspected object is usually moved at uniform speed and that one or more cameras perform line by line scanning of the entire surface, either processing the image one line at a time or processing the composed area image assembled from many lines.

• Sensor technology branch: line scan CCD dominant, line scan CMOS noted in market by 2012 per S6.
• Color branch: single color (monochrome) and color per S6; monochrome and color line scan cameras per S4.
• Output tap branch: single tap, dual tap, triple tap, quad tap, octal tap per S5.
• Synchronization branch: free run (internal synchronization) and external synchronization modes per S5.
• Application pattern branch: single camera, multiple cameras across wide web, multiple cameras on the same line at different angles per S6.

Selection Criteria for Procurement

The first procurement parameter is pixel resolution along the scan direction and the number of pixels across the web. The S4 Basler source gives 2K to 16K as the resolution span supplied by one vendor, and that range is a useful starting bracket when sizing a new application. The user converts the smallest defect that must be detected into a required pixel size in millimetres, divides the web width by that pixel size to obtain the pixel count across, and then multiplies the web speed by the inverse of the pixel size along the scan direction to obtain the minimum line rate. The result is then compared with the maximum line rate of candidate cameras.

The second procurement parameter is the camera interface. The S4 source lists CoaXPress-over-Fiber, CXP-12, 5GigE, GigE, and Camera Link as the supported options. The selection is driven by the required data rate, the maximum cable length between camera and frame grabber or host computer, and the existing infrastructure in the plant. Higher speed interfaces support higher line rates and higher pixel counts but typically require frame grabbers and a controlled cabling topology. Lower speed interfaces such as GigE simplify cabling but impose hard ceilings on the achievable data throughput.

The third procurement parameter is the output tap configuration. The S5 document states that higher tap counts allow faster image readout but raise the per channel data rate, which in turn shortens the maximum practical cable length. As one example from the S5 document, at a single tap rate of 85 MHz a general purpose cable can be run about 7 metres without observable noise, while at 40 MHz the same document records that a 10 metre cable is still usable. Procurement specifications must therefore state the required data rate, the required cable length, and the tap configuration together, not in isolation. The fourth procurement parameter is illumination, lens, and the encoder or trigger source; the S4 source lists compatible accessories including light sources, lenses, cables, PC cards, frame grabbers, and pylon software, which together form the system that the camera sits inside.

Standards, Compliance, and Testing

Industrial cameras sold into regulated markets must clear the same electromagnetic compatibility, electrical safety, and environmental frameworks that govern other industrial electrical equipment. The S3 Keyence page lists, under its product compliance section, CE marking overview, UL listed products, CSA certified products, FDA Accession numbers, and China RoHS correspondence. These compliance pathways are not unique to line scan cameras; they apply to Keyence products generally, including the Line Scan series referenced in the same page, and they should be requested by the buyer as part of the vendor documentation package per shipment or per project.

Two specific compliance considerations for line scan cameras are interface standards and environmental sealing. Interface standards are governed by the consortium that owns each protocol: CoaXPress for CoaXPress and CXP-12, the 5GigE and GigE standards for Ethernet based machine vision, and the AIA for Camera Link. The S4 Basler page lists these five protocols as the supported interface options, and conformance with the corresponding standard is verified by the camera manufacturer. Buyers should request the specific conformance certificate rather than rely on the marketing page alone, particularly when the camera will be integrated with a third party frame grabber or vision processor.

Environmental testing for line scan cameras typically references IEC 60068 for shock and vibration, IEC 60529 for ingress protection, and the broader CE and UL frameworks. The supplied sources do not enumerate IEC clauses or test levels for line scan cameras, so specific clauses and test levels should be obtained from the camera vendor's datasheet. The buyer should also confirm that the vibration profile at the mounting location is within the published operating shock and vibration limits, because encoder jitter and mechanical resonance will appear as artefacts in the assembled image and are often misdiagnosed as illumination or sensor problems. Compliance testing is therefore not only a regulatory exercise but also a precondition for reliable image quality.

Market Landscape and Buying Process

The line scan camera market is supplied by a small number of global vendors that each offer a portfolio spanning monochrome, color, and TDI options across multiple interface standards. The S4 source identifies Basler as a vendor of line scan cameras with resolutions from 2K to 16K, a maximum line rate of 500 kHz, and support for CoaXPress-over-Fiber, CXP-12, 5GigE, GigE, and Camera Link interfaces, and it cites battery production quality assurance as an especially suitable application for that product family. The S3 source identifies Keyence as a vendor of the Line Scan series within its vision system product family. The S6 source provides the categorical context that the typical application domains are metal, plastic, paper, and fiber inspection, with the object moving at uniform speed and one or more cameras performing line by line scanning. S1 and S2 are unrelated consumer mobile camera applications and are not vendor information for industrial line scan cameras.

The typical buying process begins with a requirements definition that captures web width, web speed, smallest defect size, working distance, available cable length, and the host environment (industrial PC versus dedicated frame grabber, factory floor versus cleanroom). The buyer then requests vendor quotations from two or three suppliers, with the specification expressed in terms of pixels per line, line rate, interface, and required accessories. The S4 source lists the accessory ecosystem as light sources, lenses, cables, PC cards, frame grabbers, and pylon software, and a complete quote should bundle the camera, the lens, the light source, the cabling, the frame grabber if applicable, and the software SDK.

A second step in the buying process is the proof of concept. The buyer typically requests a demonstration unit or a paid evaluation, places a representative sample of the actual product under the camera, and verifies that the smallest target defect is detected at the production line rate with the production encoder. The S3 source lists sample demonstration and test as a Keyence service offering, and the S4 source describes a vision system configuration tool that the buyer can use to assemble the system. After a successful evaluation, the buyer issues a purchase order referencing the specific model numbers, the firmware version, the interface cards, the SDK version, the warranty terms, and the compliance certificates required for the destination market. Long term support, including firmware updates, spare parts, and RMA turnaround, should be defined in the same procurement step.