Capacitive Sensor for Mirror Pivot Position Measurement
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Solution Overview
Problem
Existing mirror array systems for projection exposure apparatuses face challenges in accurately capturing the pivot position of mirror elements with two degrees of freedom, often requiring complex guide mechanisms and being sensitive to parasitic motions and thermal drift.
Innovation Solution
A sensor device with a differential capacitive comb structure that includes a transmitter electrode and a receiver electrode with a comb structure, capable of directly capturing the pivot position of a mirror element, and an actuator device with comb electrodes arranged in a single plane to provide a direct drive mechanism for pivoting the mirror element with two degrees of freedom, minimizing interaction with the actuator device and reducing sensitivity to parasitic motions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If complex guide mechanisms are used to capture pivot position, then measurement precision may be improved, but device complexity increases
Solution Approach 1:
The patent replaces complex mechanical guide mechanisms with a capacitive sensor system that directly measures pivot position. The sensor device includes a stator electrode structure and a rotor electrode structure that directly capture the pivot position of the mirror element without requiring intermediate mechanical guides, thereby reducing device complexity while maintaining measurement precision.
Solution Approach 2:
The rotor electrode structure serves multiple functions: it acts as both the moving element of the capacitive sensor and the pivot point for the mirror element. This multi-functionality eliminates the need for separate guide mechanisms, reducing device complexity while enabling direct measurement of pivot position.
2Object-affected harmful factors
If traditional sensor arrangements are used, then parasitic motions can be detected, but sensitivity to thermal drift increases
Solution Approach 1:
The differential evaluation of capacitance values from multiple sensor pairs provides feedback that automatically compensates for thermal drift. By comparing measurements from opposing sensor pairs and evaluating the differential signal, the system can distinguish between actual pivot position changes and thermal expansion effects, reducing sensitivity to temperature variations.
Solution Approach 2:
The patent employs an asymmetric arrangement of sensor pairs with different orientations relative to the pivot point. This asymmetric configuration allows the system to detect parasitic motions while being less sensitive to uniform thermal expansion, as thermal drift affects all sensor pairs equally and cancels out in the differential evaluation.
3Reliability
If comb electrode structures are used for actuation, then actuator characteristics improve, but sensitivity to parasitic motions increases
Solution Approach 1:
The actuator is divided into multiple independent comb electrode pairs, each responsible for actuation in a specific direction. This segmentation allows for precise control of the mirror element while reducing coupling effects and sensitivity to parasitic motions, as each electrode pair operates independently with well-defined actuation characteristics.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution enables precise and stable measurement of the mirror element's pivot position and tilt angle over a large range, improving the actuator characteristic and dynamic properties, while simplifying the bearing and production of the mirror array, and reducing sensitivity to thermal expansion and parasitic motions.
Implementation Method 1
The sensor device includes a sensor unit which includes a transmitter electrode with a comb structure, a receiver electrode with a comb structure
Implementation Method 2
a voltage source for applying an AC voltage to the transmitter electrode
Data Source
AI summary
A displacement device for pivoting a mirror element with two degrees of freedom of pivoting includes an electrode structure including actuator electrodes. The actuator electrodes are comb electrodes. All actuator electrodes are arranged in a single plane. The actuator electrodes form a direct drive for pivoting the mirror element.