Multipart Measurement in Laser Triangulation: Capturing Multiple Zones in a Single Scan

A laser profile sensor operating in single-zone mode evaluates one continuous measurement window across the full sensor array. Complex workpieces with 2 or more geometrically distinct surface levels — such as stepped shafts, grooved profiles, and multi-tier connector housings — produce undefined data points at surface discontinuities within a single window. The transition region between a raised plateau and a recessed channel generates reflected laser light at 2 different Z-heights simultaneously. A single-window evaluation assigns one peak per sensor column, producing ambiguous or corrupted height values at the transition boundary. Multipart measurement resolves this by assigning each surface level to a dedicated evaluation window with its own independent peak detection logic.

Single-zone scanning captures one continuous surface region per scan pass. Multipart scanning captures 2 or more geometrically distinct surface regions per scan pass. The 3 primary differences between the 2 modes are measurement consistency, cycle time, and configuration complexity.

A zone in Multipart measurement is a defined pixel range on the sensor array corresponding to a specific depth interval and lateral position on the workpiece surface. The sensor operator defines each zone by specifying 3 parameters: the pixel start position, the pixel end position, and the working distance range within which that zone’s surface is expected to lie.

The sensor’s internal processing assigns the peak detection algorithm — identifying the centroid of the reflected laser peak — independently to each zone’s pixel range. Zone boundaries do not overlap: each column of sensor pixels belongs to exactly one zone. This exclusivity ensures that reflected laser light from one surface level does not interfere with the peak detection of an adjacent zone.

The total number of zones supported by a laser profile sensor in Multipart mode depends on the sensor’s processing architecture and FPGA throughput capacity. Industrial laser profile sensors support 2 or more simultaneous Multipart zones, with zone count scaling inversely with the sensor’s output frame rate as processing load increases with each additional zone.

Each Multipart zone generates an independent height profile — a sequence of Z-values (height measurements) distributed along the X-axis of the laser line, covering the pixel columns assigned to that zone. The output format per zone is a 1D profile array with Z-coordinate values per column, identical in structure to the output of a full single-zone scan but spatially limited to the zone’s column range.

Downstream software receives these zone profiles either as separate data streams or as a merged composite profile, depending on the sensor’s interface configuration. Independent zone outputs enable zone-specific quality decisions: a workpiece with 3 measured zones can pass or fail on a per-zone basis without invalidating the entire measurement result.

Industrial laser profile sensors operating in Multipart mode support between 2 and 8 zones per scan, with the specific maximum determined by the sensor model’s signal processing architecture. Zone arrangement follows 2 spatial rules: zones are non-overlapping in the sensor’s column domain, and zones are ordered sequentially from the leftmost to the rightmost column position on the sensor array.

Zone count directly affects the sensor’s output frame rate. Each additional zone increases the sensor’s per-frame processing time by the computational cost of one additional peak detection pass. A laser profile sensor operating at 4,000 Hz in single-zone mode reduces its frame rate when configured for 4 Multipart zones, with the reduction factor dependent on the sensor’s internal processing pipeline.

Zone width — the number of columns assigned to each zone — is configurable and does not need to be equal across all zones. A narrow zone of 50 columns and a wide zone of 300 columnsoperate simultaneously in the same Multipart configuration.

Each Multipart zone requires individual calibration when the surfaces assigned to different zones are not coplanar or lie at different working distances from the sensor. A workpiece with a raised plateau at 80 mm working distance and a recessed channel at 95 mm working distance presents each zone’s target surface at a different point in the sensor’s depth-of-field curve.

Calibrating each zone independently — using a reference surface positioned at that zone’s expected working distance — ensures that the Z-values produced by each zone carry the correct dimensional scaling. Zones operating on coplanar surfaces at the same working distance share a single calibration. The relationship between per-zone calibration and overall measurement accuracy connects to the broader metrological framework of measurement system analysis.

Stepped workpieces are the primary application target of Multipart measurement in industrial inspection. A stepped workpiece contains 2 or more surface levels with defined vertical offsets — such as precision-machined flanges with raised sealing faces, injection-molded connector housings with multiple contact surface planes, and layered semiconductor lead frames with bonding pad elevations above the substrate.

Each surface level in a stepped workpiece occupies a distinct depth range in the sensor’s field of view. Multipart measurement assigns one zone per surface level, enabling simultaneous height profiling of all levels in a single scan pass. This enables the sensor to verify step height — the vertical distance between two surface levels — as a derived measurement combining the Z-output of two adjacent zones, without requiring a second scan at a different sensor height.

Gap measurement is a Multipart application that characterizes the spatial relationship between 2 adjacent surfaces separated by a physical gap, such as the gap between a door panel and a body frame in automotive assembly, the clearance between a PCB and a housing wall, and the spacing between 2 assembled mating surfaces in precision mechanical joints.

A laser profile sensor operating in single-zone mode across a gap region produces undefined or interpolated data points within the gap interval, because no surface reflects the laser line at that position. Multipart measurement assigns one zone to each surface flanking the gap, excluding the gap interval from any zone’s evaluation range. This configuration captures the height profile of both flanking surfaces cleanly, and the gap width is derived from the known zone boundary positions combined with the absence of valid Z-values between them.

Multi-component assembly verification uses Multipart measurement to simultaneously characterize the spatial relationship between 2 or more assembled components fixed in a defined spatial configuration. Examples of this application include verifying the coplanarity of 3 solder joints on a PCB relative to a reference pad, checking the relative height and tilt of 2 press-fit pin rows in an electrical connector, and confirming the Z-position of 4 locating pins on a stamped metal bracket relative to a reference surface.

Each component or feature group is assigned to one Multipart zone. The sensor captures the height profile of all assigned features in a single scan, enabling the downstream software to compute relative height deviations, tilt angles, and assembly offsets across all zones simultaneously.

Multipart measurement and Multipeak detection operate at different levels of the sensor’s evaluation hierarchy: Multipart divides the sensor array into column segments, while Multipeak resolves ambiguous peak data within each column of any given zone. A Multipart configuration with Multipeak enabled in one or more zones captures both the surface profile of each zone and the sub-surface or layer information at each measurement point within that zone simultaneously.

In a Multipart configuration, HDR parameters are assignable per zone, enabling the sensor to apply a high-exposure setting to a low-reflectivity zone and a low-exposure setting to a high-reflectivity zone within the same frame. This per-zone HDR assignment eliminates the need for a global exposure compromise that would underexpose one surface or saturate the other. A typical application is a matte black rubber seal adjacent to a polished stainless steel flange — 2 surfaces requiring different exposure levels, each assigned to its own Multipart zone with an individual HDR configuration.

In a Multipart configuration, Multiple Slope is activatable per zone, enabling zones covering edge features or steeply inclined surfaces to use adapted slope evaluation while adjacent zones covering flat surfaces use standard peak detection. This is relevant for workpieces that combine flat reference surfaces with steeply inclined flanks or undercut geometries, such as dovetail profiles, V-groove channels, and chamfered assembly edges.