How to Choose the Right model
Choose QualiPP™ V300 Series when your parts fit a Ø300 mm class viewing range and you want a smaller footprint for routine inspection. Choose QualiPP™ V400 Series when you need a larger screen class, larger travel options, or more comfortable coverage for bigger parts and fixtures.
Why choose QualiPP™ V-Series
- Stable vertical motion supports consistent focus and repeatable inspection work.
- Adjustable contour and surface illumination helps tune contrast across different materials and finishes.
- High-resolution optics support clear projected edges with low magnification error (as specified in the brochures).
- QualiDigi™ Readout 400 supports fast 2D measurement and practical documentation.
Vertical Profile Projector (Optical Comparator): Non-Contact 2D Inspection for Production QC
A vertical profile projector gives quality control teams a fast, reliable way to inspect part dimensions without touching the workpiece. By projecting a magnified silhouette onto a screen, the operator measures profiles, radii, angles, and feature locations in seconds rather than minutes. For machined, stamped, and molded parts that require repeatable dimensional checks, the vertical profile projector (also called an optical comparator) remains one of the most practical tools on the shop floor.
This category page explains the working principle behind vertical profile projectors, the key specifications that affect measurement performance, and how to evaluate the right system for your inspection workflow.
How a Vertical Profile Projector Works
A vertical profile projector measures parts by projecting a magnified shadow of the workpiece onto a ground-glass screen. A collimated light source (the contour illumination) sends parallel rays upward through the part, a telecentric projection lens captures the shadow without perspective distortion, and a mirror directs the enlarged image onto the screen for measurement against crosshairs or an overlay.
The Underlying Principle: Telecentric Shadow Projection
The core of every profile projector is shadow projection, a technique rooted in geometric optics. A condenser lens collects light from an LED source and reshapes it into a parallel (collimated) beam. This beam passes the workpiece and creates a shadow that carries the exact outline of the part's cross-section.
A standard lens would introduce perspective error: features closer to the lens would appear larger than features farther away. Profile projectors solve this by using a telecentric optical system. In a telecentric lens, the chief rays travel parallel to the optical axis, so the magnification stays constant regardless of how far the feature sits from the focal plane. This property allows the operator to trust that every edge on the screen represents the true dimension of the part, scaled only by the stated magnification factor.
The Japanese standard JIS B 7184 defines the metrological characteristics and default accuracy specifications for profile projectors. No equivalent international (ISO) or American national standard currently exists, so JIS B 7184 serves as the primary reference for evaluating stage accuracy, magnification accuracy, and screen rotation accuracy across manufacturers.
Contour Illumination vs. Surface Illumination
A vertical profile projector typically offers two lighting modes, each revealing different part features.
Contour illumination (also called transmitted or profile lighting) sends collimated light upward through the part from below the stage. The projector captures the resulting shadow to display the part's outline. This mode measures external profiles, edges, radii, chamfers, and through-holes with sharp edge visibility.
Surface illumination (also called reflected or episcopic lighting) directs light downward onto the top surface of the part. The reflected image projects onto the screen and reveals surface features such as scribe lines, engravings, surface defects, and blind holes that do not pass through the part. Adjusting the angle and intensity of the surface light helps the operator tune contrast on different materials and finishes.
Key Features That Affect Measurement Performance
When comparing vertical profile projectors, focus on the specifications that directly influence whether the system can handle your parts and tolerances.
- Screen diameter: A larger screen (for example, 400 mm vs. 300 mm class) provides a wider viewing area at the same magnification, which reduces the need to reposition the part during inspection.
- Stage travel (X x Y): Determines how large a part or how many features the operator can reach without remounting. Larger travel accommodates bigger fixtures and multi-feature parts.
- Linear resolution: The smallest increment the stage encoders report. A resolution of 0.0005 mm (0.5 micrometer) supports fine-dimension work and tight-tolerance checks.
- Accuracy specification: Typically expressed as a formula such as (3 + L/200) micrometers, where L is the measured length in millimeters. This formula accounts for both the fixed error component and the length-dependent component, following JIS B 7184 conventions.
- Objective lens options: Different magnifications serve different part sizes. A 10X lens covers larger fields of view for general inspection. A 50X lens resolves finer detail on small features. The ability to swap lenses (bayonet or screw mount) adds flexibility across part families.
- Screen rotation accuracy: Specified in arc-minutes (for example, 6 arc-minutes). This parameter matters when measuring angles, tapers, or aligning projected features to a reference line.
- Load capacity: The maximum weight the stage can support without degrading accuracy. A 10 kg capacity covers most small-to-medium machined and stamped parts.
How to Evaluate a Vertical Profile Projector for Your Workflow
Selecting the right vertical profile projector starts with matching the system to your parts, tolerances, and throughput requirements. Consider these factors before specifying a unit.
Part size vs. screen class and magnification. Calculate the field of view you need. At 10X magnification, a 300 mm screen covers roughly a 30 mm field; a 400 mm screen covers roughly a 40 mm field. If your largest feature exceeds the field, you need either a lower magnification lens or a larger screen class.
Stage travel vs. part coverage. Ensure the X and Y travel can reach all features you need to inspect in a single setup. Larger travel reduces part handling time and improves throughput on multi-feature parts.
Tolerance vs. accuracy. A common rule of thumb in dimensional metrology is that the measuring instrument should resolve at least one-tenth of the part tolerance. Compare the projector's stated accuracy formula against your tightest tolerance to confirm it qualifies.
Illumination needs. If you only measure external profiles and through-features, contour illumination alone may suffice. If you also need to inspect surface marks, blind features, or engraved details, confirm the system includes adjustable surface illumination.
Digital readout capability. Evaluate whether the DRO supports the measurement functions your workflow requires: point-to-point distance, angle measurement, circle fitting, data output to SPC software, or connection to a printer for immediate documentation.
Frequently Asked Questions
What Is the Difference Between a Profile Projector and an Optical Comparator?
A profile projector and an optical comparator refer to the same type of instrument. Both names describe a device that projects a magnified shadow of a part onto a screen for dimensional inspection. The term "optical comparator" emphasizes comparing the projected image against a reference overlay or standard, while "profile projector" emphasizes the projection function. Manufacturers and buyers use both names interchangeably.
How Accurate Is a Vertical Profile Projector?
Accuracy depends on the model and is typically stated as a formula such as (3 + L/200) micrometers, where L is the measured length in millimeters. For a 50 mm measurement, this formula yields approximately 3.25 micrometers of allowable error. The JIS B 7184 standard defines the default accuracy classes for stage travel, magnification, and screen rotation that most manufacturers reference.
What Is Telecentric Illumination and Why Does It Matter?
Telecentric illumination produces a collimated beam of parallel light rays. Because the rays do not converge or diverge, the shadow cast by the workpiece maintains a constant magnification regardless of the part's position along the optical axis. Without telecentricity, features at different heights would project at slightly different scales, introducing measurement error that is difficult to quantify or correct.
Can a Profile Projector Measure Surface Features, Not Just Profiles?
Yes. By switching from contour illumination (transmitted light from below) to surface illumination (reflected light from above), the operator can view surface details such as scribe lines, engravings, blind holes, and surface defects. Surface illumination does not provide the same edge sharpness as contour illumination, so it is typically used for qualitative inspection rather than precise edge measurement.
How Often Should a Profile Projector Be Calibrated?
Calibration intervals depend on usage intensity and your quality management system requirements. Typical intervals range from six months to three years. Calibration checks verify stage accuracy, magnification accuracy, and screen rotation accuracy using certified reference standards such as glass scales and angle blocks.
What Magnification Should I Choose for My Parts?
Start with 10X for general inspection of parts in the 5 mm to 40 mm range. Move to 20X or 50X when you need to resolve finer features or tighter tolerances on smaller components. Lower magnifications such as 5X cover larger fields of view for bigger workpieces. Many systems accept interchangeable objective lenses, so you can switch magnification to match different part families without replacing the projector.
