AVR200 and AVR300 User Guide
Understanding Measurement Strategy
7.
AVR systems are available with either 6.5:1 zoom optics with adjustable magnification from 0.47X to 3.0X, with 12:1 zoom optics with adjustable magnification from 0.4X to 4.7X, or with numerous telecentric lens options with a fixed magnification of 0.14X, 0.3X, 0.5X, 0.8X, 1.0X, 2.0X or 4.0X. Magnification is the image size at the camera CCD detector place divided by the object size. Since the CCD size is fixed, each magnification has a corresponding field of view (FOV), which is the CCD size divided by magnification. The higher the magnification, the higher the resolution, but also the smaller the field of view. AVR optical assemblies are matched to a specific camera. They are not user changeable, but require installation, alignment, calibration, and optimization of substage illumination by a factory trained technician.
The following information discusses the measurement strategy for the available optics.
7.1 Zoom Optics Measurement Strategy
While zoom optics can provide the same field of view (FOV) as four of the telecentric lenses, they do not offer the ultra-low optical distortion that is required for purely optical measurements across the entire FOV. However, they can be more accurate than telecentric lenses when used at high magnification in combination with stage motion, where reading accuracy is based on the system’s calibrated linear encoders.
Select zoom optics to measure the following:
• Large parts that would not fit into a single FOV
• Smaller parts where extremely high magnification is required.
The lowest zoom magnification setting accommodates parts up to 11.2 x 9.4 millimeters (0.44 × 0.37 inches) in the FOV. To measure large parts, locate the edge of interest at minimum magnification, then take the actual measurement at maximum magnification using the system's crosshairs. The zoom optics’ parcentricity feature ensures that a feature will remain at the optical center of the video image throughout the magnification range. In general, higher magnification provides greater resolution and accuracy; however, not all features should be inspected at the highest available magnification. Too high a magnification can make it difficult to discern edges by exaggerating edge defects such as burrs or chips. Try decreasing the magnification until the edge is more clearly identifiable. Also consider factors such as tolerance requirements, manufacturing processes, functional requirements and optical characteristics of the part. Features with loose tolerances might not need to be inspected at high magnification. Select the magnification best suited for the requirements.
7.2 Telecentric Lens Measurement Strategy
Select telecentric optics to perform high accuracy, high throughput field-of-view (FOV) measurements. If all measurements are to be in the FOV, select the highest magnification lens whose FOV encompasses the entire part. The 0.14X lens enables field-of-view measurements which can encompass an entire small part up to 60 × 51 millimeters (2.36 × 2.00 inches) or a feature of a larger part. If the entire part cannot fit into the FOV, the stage can be moved--up to 200 millimeters (4 inches) for the AVR200 or 300 millimeters (12 inches) for the AVR300. The M3 software will seamlessly integrate FOV measurements with encoder readings from stage motion.
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