Dual Axis Microscanners for Infrared Camera
Flex-pivot mirror design for improving infrared focal plane array resolution
C. L. Lee — Chartered Electro-Optics Pte Ltd
Overview
This paper presents dual-axis microscanners developed to capture image data lost in the gaps between cells of infrared focal plane array (FPA) detectors. The microscanner assembly uses flex-pivot-mounted mirrors actuated by low voltage piezo translators (LVPZ) to displace the image in both X and Y axes, covering the ineffective inter-pixel area and improving overall image resolution. The design was implemented in a closed-loop PID controller with an optical angular position sensor.
Key Highlights
Flex-Pivot Mirror
Flexural pivots serve as the shaft bearing and torsional spring for the mirror unit
Dual-Axis Coverage
X and Y displacement fills inter-pixel gaps in the FPA detector
LVPZ Actuation
Low voltage piezo translators in differential mode for temperature stability
0.292 mRad Displacement
Sub-milliRadian angular precision with closed-loop PID control
2.5 ms Rise Time
Fast settling for high frame-rate infrared camera operation
-20°C to +70°C Range
Full operational temperature range with ±5% accuracy at ±10°C
Problem and Approach
Conventional infrared cameras using focal plane array (FPA) technology suffer loss of image information due to the ineffective area between detector cells — a fundamental limitation of semiconductor fabrication. Two microscanners displace the image on the thermal detector plane in both X and Y axes so that the inter-pixel gaps are covered, improving overall image resolution and extending the detection range of the camera.
Flexural Pivot Mirror Unit
The mirror unit consists of the mirror, actuator arm, and flexural pivots. The actuator arm transforms the linear movement of the LVPZ actuator into angular movement of the mirror. Flexural pivots are chosen to support the mirror shaft because they combine the functions of a shaft bearing and a torsional spring — providing frictionless angular motion with a well-defined spring return force. The preload force is determined by the flex pivot radial stiffness, mirror shaft stiffness, and actuator geometry.
Actuation and Sensing
Two LVPZ actuators applied in differential mode provide better temperature stability than single-actuator designs. The angular position sensor uses an infrared LED and bi-cell detector with an arm and optical window clamped to the mirror shaft. A closed-loop PID controller with integrator and second-order low-pass filter networks maintains positioning accuracy of ±5% at ±10°C and ±10% over the full -20°C to +70°C operating range.
Performance Results
The microscanners achieved the required angular displacements (0.178 and 0.292 mRad), 2.5 ms rise and settling time, and a maximum jitter of 20 µRad. Vibration and temperature testing were conducted alongside functional tests. The design demonstrates that flex-pivot-mounted microscanner assemblies can improve infrared camera resolution in a compact, controlable package suitable for advanced FPA-based thermal imaging systems.
Dual Axis Microscanners for Infrared Camera — PDF
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