What is a horizontal digital profile projector?
Profile projectors are also called shadowgraphs or optical comparators. Horizontal models use a horizontal light orientation and is best suited for 3D parts.
On conventional horizontal optical comparators, a projected shadow of a component is projected from an LED light source onto a frosted screen and is then compared against a Mylar overlay chart, or, using stage movements, physical dimensions are measured using cross hairs on the projected image to align the features. This method, with the use of a mechanical overlay on the projection screen, works effectively. Lateral measurements are made using a Digital Read Out (DRO) providing a resolution of up to 0.5µm, however comparisons against overlays are subjective and can lead to inaccuracies due to human error and/or change of operator.
An example of a standard overlay based horizontal projector is the Starrett HB400. While excellent for direct visual inspection of profiles, the image quality can be affected by ambient light. If this could be a potential issue, a video system which has higher digital clarity and colour capabilities may be beneficial.
What are the advantages of a digital optical comparator?
A more accurate comparison can be made using a digital video system that uses a 5MP high-resolution colour digital camera with advanced software capabilities where overlays are replaced by imported data files providing improved accuracy. These instruments can also double up as a vision system making a cost-effective acquisition and rapid ROI.
As these systems are PC driven there are many additional capabilities not available on overlay systems, these include: –
DXF CAD files can be imported and 2D Go-No-Go gauges created, this is like using a Mylar overlay chart on a comparator screen but with far with greater accuracy.
Video edge detection (VED) allows real-time interaction of the imported file with the video image of the part being inspected. As a result, productivity, speed, and accuracy are all improved.
Comprehensive 2D Geometry: Full software allows precise 2D geometric measurements (points, lines, circles, arcs, angles, distances) directly on the digital image) again removing human subjectivity.
Data Management and Reporting allows data to be easily saved and exported to spreadsheets or SPC software.
An example of this type of system is the HDV 300/400 Horizontal Digital Video comparator from Starrett, this horizontal digital optical comparator model combines the best features of a horizontal optical comparator and a vision metrology system.
It is available with 3 stage travel options of 300mm, 400mm or 500mm in “X” by 150mm “Y” built onto a rigid steel frame design, configured like a traditional horizontal comparator. It includes a powerful 64-bit PC and Touchscreen monitor, which runs MetLogix M3 Metrology software.
Steel construction with nickel plated stage tooling plate, 540 x 130mm workstage top plate, CNC controls, 150kg maximum load capacity, 75mm of focus travel, Helix angle adjustment with ±15° Vernier scale, X-Y and focus positioning via joystick and trackball positioning, Heidenhain glass scales for 0.5μm X and Y resolution, LED illumination for surface and profile lighting, 5 mega-pixel black and white digital video camera (2448 x 2058 pixels)
The instrument is available either as bench top models or as a floor standing model, the bench top model is more compact, making it a better fit for small workshops, laboratories, or environments where space is limited
Starrett Profile Projectors are available in the UK from Optimax Imaging and Inspection.
