A laser profilometer is a non-contact sensor that projects a laser line onto a surface and uses a camera viewing from an angle to measure the line’s shape, producing a height profile of the surface. Moving the part or the sensor stacks those profiles into a full 3D map. Laser profilometers, also called laser profile scanners or laser line profilers, measure heights, widths, steps, gaps, flatness and warp, and reveal defects that a flat 2D image can miss.
Laser profiling is one of the main 3D methods in machine vision. This article explains how laser triangulation works, how to work out resolution and scan time, what affects accuracy, and when a laser profilometer is the right tool compared with other 3D methods.
How laser triangulation works
Inside a laser profilometer, a laser diode and a lens spread a beam into a thin line. A camera sits beside the laser and looks at the line from a known angle, called the triangulation angle. On a flat surface the line appears straight. Where the surface rises or falls, the line moves along the laser beam, and because the camera sees it from the side, the line appears shifted in the camera image. The sensor converts each point’s shift into a height using the known geometry, so one camera frame gives one complete height profile across the line.
Why the angle matters
If the camera views at an angle θ from the laser beam, a height change Δz moves the spot by about Δz × sin θ perpendicular to the camera’s line of sight. At 30°, sin θ = 0.5, so a 0.1 mm step looks like a 0.05 mm shift. At 45°, sin θ ≈ 0.71, so the same step looks like about 0.07 mm. A larger angle gives more height sensitivity, but also more occlusion, where a raised feature hides the line from the camera. Sensor designers balance the two.
| Triangulation angle | sin θ | Apparent shift for a 0.1 mm step | Trade-off |
|---|---|---|---|
| 30° | 0.50 | 0.050 mm | Less occlusion, lower sensitivity |
| 45° | 0.71 | 0.071 mm | Higher sensitivity, more shadowing behind steps |
Resolution and scan time: a worked example
A profilometer has two resolutions. Across the line (X), resolution is set by the camera pixels spread over the line width. Along the direction of travel (Y), resolution is set by how far the part moves between profiles. Height (Z) resolution depends on the optics and the triangulation angle.
Take a benchtop scanner where a linear stage moves the part at 15 mm/s and you want a profile every 0.1 mm. The sensor must capture 15 ÷ 0.1 = 150 profiles per second. A 200 mm long part then takes 200 ÷ 15 ≈ 13.3 seconds to scan and produces 200 ÷ 0.1 = 2,000 profiles. These are the settings used on the Sciotex benchtop 3D laser scanning system, where an encoder triggers each line scan so profiles stay evenly spaced even if the speed varies slightly.
| Setting | Value | Result |
|---|---|---|
| Travel speed | 15 mm/s | |
| Profile spacing (Y resolution) | 0.1 mm | 150 profiles per second |
| Part length | 200 mm | ≈ 13.3 s scan, 2,000 profiles |
What a laser profilometer measures
- Height and step: the difference between two surfaces, such as a shoulder, a bead or a seal.
- Width and gap: the distance between edges across the line, such as a slot, a weld or a gap between panels.
- Profile shape: radius, angle and contour compared with a nominal profile, common on extrusions and seals.
- Flatness and warp: how far a surface deviates from a plane across the whole scan.
- Volume: material added or missing, such as adhesive beads or dents.
- 3D surface defects: dents, bumps, chips and scratches with depth, which 2D images can confuse with stains.
For the bigger picture of measuring parts, see automated dimensional inspection.
What affects laser profilometer accuracy
| Factor | Effect | What to do |
|---|---|---|
| Shiny or mirror-like surfaces | Light reflects away or creates false reflections | Adjust angle and exposure; use sensors built for specular surfaces |
| Dark or absorbent materials | Weak signal and noisy points | Longer exposure or a higher-power laser within safety limits |
| Translucent materials | The laser scatters below the surface and blurs the line | Blue lasers often penetrate less than red |
| Occlusion | Steep walls hide the line from the camera | Change angle, scan from two sides, or use two sensors |
| Vibration and motion | Distorts the profile stack | Rigid mounting and encoder-triggered scanning |
| Temperature | Sensor and part expansion | Warm up the sensor; measure in stable conditions |
Laser profilometer vs other 3D methods
| Method | Best for | Limitation |
|---|---|---|
| Laser profilometer | Parts moving past the sensor, profiles, long parts, inline scanning | Needs motion to build 3D; occlusion on steep features |
| Structured light | Complete 3D snapshot of a stationary part | Slower for moving parts; sensitive to ambient light |
| Stereo vision | Large scenes and robot guidance | Lower accuracy on featureless surfaces |
| Time-of-flight | Large objects such as pallets and bins | Millimetre-level, not micron-level, accuracy |
For a broader comparison of these technologies, read 3D machine vision systems for automated inspection. A laser line can also be part of a larger inline system, as in the extrusion inspection system example.
Need 3D profiles of your parts?
The Sciotex benchtop 3D laser scanning and profilometer system scans parts on a linear stage at 0.1 mm resolution and saves the full 3D data for review. Free testing of your sample parts is available.
Frequently asked questions
A laser profilometer is a non-contact sensor that projects a laser line onto a surface and uses an angled camera to measure the line’s shape, producing a height profile. Scanning the part builds a full 3D map.
A camera views the laser line from a known angle. When the surface height changes, the line shifts in the camera image, and the sensor converts that shift into height using the known geometry.
The terms overlap. A laser profilometer or line profiler measures one profile per frame; a 3D laser scanner usually means a system that moves the part or sensor to stack those profiles into a full 3D model.
It depends on the sensor’s field of view and optics. Benchtop systems commonly work at about 0.1 mm spacing; small-field sensors resolve heights in the micron range. Surface finish, angle and vibration all affect real accuracy.
Yes, with care. Mirror-like surfaces reflect the laser away from the camera, so the angle, exposure and sensor type have to suit the surface.
