Normal Vector Tracing Control for Ultra-Precision Shape Measurement
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Solution Overview
Problem
Current normal vector tracing methods for ultra-precision shape measurement are limited by steady-state deviations in the control system, preventing high-precision angle measurements and shape measurements below 1 nm PV due to semi-closed feedback control systems.
Innovation Solution
Implementing fully-closed feedback control for one pair of biaxial goniometers and the uniaxial straight-ahead stage, with direct input from the QPD into the axis drive motor, and semi-closed feedback control for the other pair of biaxial goniometers, allowing simultaneous reading of encoder and QPD outputs to correct measurement point coordinates and normal vectors, thereby avoiding steady-state deviation influences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If semi-closed feedback control is used for biaxial goniometers, then device complexity is reduced, but measurement precision deteriorates due to steady-state deviations
Solution Approach 1:
The patent segments the control system into two distinct modes: semi-closed feedback control for positioning the biaxial goniometers to measurement points, and full feedback control for tracing normal vectors. This segmentation allows each subsystem to operate with appropriate control precision, reducing overall system complexity while maintaining high measurement precision where needed.
Solution Approach 2:
The patent dynamically switches between semi-closed and full feedback control modes based on the operational phase. During positioning, semi-closed control is used; during normal vector tracing, full feedback control is activated. This dynamic adaptation resolves the contradiction by applying different control strategies at different times.
2Measurement precision
If full feedback control is used for normal vector tracing, then measurement precision improves, but measurement time increases due to continuous control adjustments
Solution Approach 1:
The patent applies full feedback control only partially - specifically during the normal vector tracing phase rather than throughout the entire measurement process. The semi-closed control handles positioning, and full feedback is activated only when needed for high-precision normal vector acquisition, thus reducing total measurement time while maintaining precision.
Solution Approach 2:
The patent maintains continuous useful action by seamlessly transitioning between semi-closed and full feedback control modes without interruption. The system continuously operates in the most efficient control mode for the current operational phase, eliminating idle time and maintaining measurement continuity.
3Measurement precision
If probe microscopes are used for ultra-precision measurement, then measurement precision reaches atomic-level resolution, but productivity decreases due to extremely limited measurement range and long measurement time
Solution Approach 1:
The patent merges the advantages of two different measurement approaches: the high precision of probe microscopes and the large measurement range of LTPs. By combining biaxial goniometer positioning with laser-based normal vector tracing, the system achieves both atomic-level precision and fast measurement speed across large surfaces.
Solution Approach 2:
The patent replaces the mechanical contact-based probe microscope system with an optical-based laser measurement system. This substitution eliminates the need for physical contact, enabling non-contact measurement of large surfaces at high speed while maintaining ultra-precision through optical detection of normal vectors.
4Productivity
If LTPs are used for shape measurement, then productivity improves with large measurement range, but measurement precision deteriorates for surfaces with space wavelength of 1 mm or less
Solution Approach 1:
The patent transitions from measuring surface height directly (one-dimensional approach of LTPs) to measuring normal vector directions (angular dimension). By measuring the orientation of surface normals rather than just height, the system achieves high precision for fine surface features while maintaining large measurement capability.
Solution Approach 2:
The patent changes the measurement parameter from direct height displacement (LTP method) to normal vector angle (optical method). This parameter transformation enables precise measurement of fine surface features with space wavelength of 1 mm or less, as angular measurements are more sensitive to small surface variations than direct height measurements.
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
This approach enables high-precision shape measurement of free-form surfaces with a precision of 1 nm PV or more, shortening measurement time, and allowing non-contact measurement of large objects without a reference surface, while maintaining high accuracy and speed.
Implementation Method 1
a light detector using a quartered photodiode (QPD)
Implementation Method 2
measure obtained displacements of reflected light to determine inclination angles on the surface of the object
Data Source
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AI summary
[Object] To provide a drive axis control method used by a normal vector tracing ultra-precision shape measurement device that derives a surface shape of an object to be measured from coordinates at measurement points and measurement values of normal vectors, and shortens measurement time at each of the measurement points by devising a method for controlling each axis, thereby realizing higher-speed and higher-precision measurement of the surface shape of the object to be measured. [Solution Means] Of two pairs of biaxial goniometers and a uniaxial straight-ahead stage, one pair of biaxial goniometers and the uniaxial straight-ahead stage are subjected to fully-closed feedback control (follow-up control) under which output from a QPD is directly input into an axis drive motor, and the remaining pair of biaxial goniometers are subjected to semi-closed feedback control (constant-value control), encoder outputs on all the axes and QPD output are acquired simultaneously, measurement point coordinates and normal vectors derived from the encoder outputs are corrected with the QPD output, thereby eliminating influence of steady-state deviation in a goniometer control system.