Measurement Science and Technology · 2001 · 102 citations · 9 references
EngineeringMeasurementOptic DesignOptical TestingOptical MetrologyEducationProfile MeasurementLaser FabricationCalibrationOptical DiagnosticsComputational ImagingSurface ProfileLaser-based SensorInstrumentationOptical SystemsPickup HeadOphthalmologyOptical System AlignmentOptical TolerancingOptical ComponentsOptical SensorsSensor CalibrationProbe SystemBiomedical ImagingOptical System AnalysisMeasurement System
The study develops a low‑cost, precision autofocus laser probe system. The probe, adapted from a DVD pickup head, uses a four‑quadrant photodiode to detect focus error, feeds the signal to a controller that drives a voice‑coil motor, achieving a linear one‑to‑one relationship between current and lens displacement over several hundred micrometres. Calibration demonstrates a 200 µm linearity range, 0.2 µm accuracy, 0.1 µm resolution, and ~0.2 µm standard deviation, enabling accurate surface profile and roughness measurement.
In this research, a low-cost and precision autofocus laser probe system was developed. Modified from the pickup head of a commercially available DVD as a basis, it can detect the focus error signal (FES) of the object with a built-in four-quadrant photodiode. The FES will feed back to the developed controller, through which the objective lens can be adjusted in position automatically to remain in focus, driven by a voice coil motor (VCM). The driving current (converted from servo-FES) of the VCM and the objective lens displacement are one to one linearly related within several hundred micrometres. Because of this relationship, the surface profile and the surface roughness of the tested object can be realized. Calibrated results showed that the designed probe has 200 µm linearity range, 0.2 µm accuracy, 0.1 µm resolution and standard deviation of 0.2 µm on average. Some examples are given to show the applicability of this probe system.
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