Non-contact width and length gauges are optical systems dedicated to the dimensional control of rolled products, webs, sheet metal, panels and profiles, whether moving or stationary. They mainly use laser technologies (triangulation or structured light) and machine vision to measure width and length continuously, with accuracies in the order of tenths of a millimeter on products several meters wide. They are indispensable in metal rolling lines, in calendering, in film extrusion and in the manufacture of precast panels and construction components.
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Measuring technologies
Width measuring systems use two or more laser triangulation sensors positioned at the edges of the web, or line-scan cameras synchronized with dedicated illuminators, or light curtains (photocell arrays). Length is measured with contact encoders on precision rollers (with slip compensation), with non-contact laser Doppler sensors, or with image cross-correlation systems. The most advanced systems combine width and length in a single measuring head, also providing the calculation of product area and production statistics.
Technical characteristics
Width gauges cover widths up to 6000 mm and beyond, with typical accuracy of ±0.1-0.5 mm. Non-contact laser length gauges reach uncertainties of 0.05% of the measured length. The acquisition rate reaches the kHz range, allowing products to be measured at high line speeds. Standard industrial digital interfaces (Profinet, EtherCAT, OPC UA) allow real-time integration with line control systems for managing cuts, calculating lengths and generating reel labels automatically.
Applications
They are widely used in rolling lines for steel, aluminum and copper; in extrusion lines for plastic films, sheets and foils; in the production of textile webs and nonwovens; in the manufacture of sandwich and precast panels; in the calendering of rubber and plastic; and in the production of metal foil for the automotive and packaging industries. Laser length measuring systems are essential in cut-to-length lines, in the production of reels of defined length and in the metrological verification of the length measuring machines used for trading continuous products.
Advantages and considerations
Non-contact systems eliminate the mechanical wear typical of measuring wheels, reduce maintenance times and guarantee consistent performance over time. They can operate on hot products (immediately after rolling or extrusion), and on wet or dusty ones, without compromising performance. Automatic calibration with built-in references ensures the stability of the measurement. Installation considerations concern the mechanical stability of the head, the cleanliness of the optical windows and initial and periodic calibration.
Standards and selection criteria
Industrial optical measuring systems comply with VDI/VDE 2617 and VDI/VDE 2634, while length measuring machines for commercial use comply with OIML R124. The choice depends on the maximum width of the product, on the accuracy required, on the line speed, on the temperature of the product, on the ambient conditions, on the interfaces for integration with the control system, on the need for automation and on the availability of staff for routine maintenance.
Integration with production management systems makes it possible to keep performance statistics for each production campaign, identifying trends of dimensional deviation that may indicate the need to calibrate the line or to service critical mechanical components.
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