Operating Principle and Optical Configuration
A profile projector, also known as an optical comparator, uses non-contact optical magnification to project an enlarged 2D silhouette or surface image of a workpiece onto a ground-glass screen for linear and angular measurement.
Telecentric Objective Lens Principle
Standard lenses introduce perspective distortion where features closer to the lens appear larger. Qualitest profile projectors eliminate this dimensional error using telecentric objectives with pupils positioned at infinity. Light travels in parallel optical paths across the stage glass, keeping magnification factors (10×, 20×, 50×, 100×) constant even if the workpiece shifts slightly along the optical axis. Advanced models like the QualiPP™ H412 combine telecentric objectives with coated reflector optics to maximize image sharpness and edge contrast.
Illumination Methods
- Contour (Transmitted) Illumination: Light passes straight through from beneath the stage glass, projecting a sharp silhouette with high-contrast edges onto the viewing screen. This method measures outer profiles, thread forms, radius curves, and chamfers.
- Surface (Reflected) LED Illumination: Adjustable surface LEDs project light directly onto the top face of the component, reflecting surface details into the optical lens. This method inspects stamped surface markings, shallow grooves, blind holes, and surface textures.
Coordinate Measurement and Edge Detection Method
Qualitest systems combine high-precision linear glass scales with multifunction readouts like the QualiDigi™ Readout 400. Working alongside optoelectronic edge detection sensors, the readout detects light-to-dark transitions across the profile, logging X/Y coordinates and angular values down to 1' resolution automatically without operator alignment bias.
Optical Layout Configurations: Vertical vs. Horizontal Axis
- Vertical Optical Axis (QualiPP™ V300 & QualiPP™ V400 / QVP400 Series): Featuring Ø300 mm and Ø400 mm projection screens, light travels vertically through a horizontal glass stage. This configuration fits flat metal stampings, rubber gaskets, small gears, watch parts, and thin medical components.
- Horizontal Optical Axis (QualiPP™ H300, QualiPP™ H400, QualiPP™ H3015 & QualiPP™ H412 Series): Utilizing Ø300 mm to Ø412 mm screens, light travels horizontally across the worktable. This configuration fits heavy turned shafts, long threaded fasteners, forming dies, and cutting tool inserts held between centers or in V-blocks.
Calibration and Measurement Uncertainty Method
Profile projector verification follows the measurement uncertainty evaluation framework established under ISO/IEC Guide 98-3:2008.
| Calibration Parameter | Measurement Range / Magnification | Expanded Uncertainty (U) | Coverage Factor (k) | Confidence Level |
|---|
| Magnification Deviation | 10× Magnification | 0.0096% | 2.04 | ~95% |
| Stage Positioning Deviation | 0 to 100 mm Travel | 0.005 mm | 2.01 | ~95% |
Uncertainty evaluation accounts for stage glass thermal expansion, scale encoder resolution, and lens distortion. Built-in cooling systems inside QualiPP™ mainframes prevent heat buildup during continuous operation, ensuring stable calibration performance on the shop floor.
Practical Measurement Applications and Method Limitations
Recommended Application Methods
- Flexible & Soft Components: Measuring rubber O-rings, elastomeric gaskets, and thin plastic connectors without physical touch probe deformation.
- Transparent Optics: Measuring clear components like intraocular medical lenses, where optical projection evaluates outer diameters without scratching delicate surfaces.
- Toolroom Inspection: Verifying thread pitch angles, gear tooth profiles, taps, dies, and cutting tool inserts on QualiPP™ inspection stages.
Method Boundaries
- 2D Planar Constraint: Profile projection is limited to two-dimensional planar measurements. The 2D shadow image cannot measure 3D spatial alignment or multi-axis rotational tilt.
- Internal Cavity Limitations: Deep blind cavities or internal features that block light paths cannot cast an unblocked shadow silhouette.
