Anti-drift Sensor Alignment via Feedback Control

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Solution Overview

Problem

Precision displacement measurement systems are susceptible to environmental changes such as temperature and humidity fluctuations, leading to signal drift and reduced measurement precision, especially in micrometer and nanometer scale measurements.

Innovation Solution

A system comprising a displacement sensor, an actuator, and a feedback unit that controls the actuator based on signals from the displacement sensor to maintain relative position or orientation, using a low-frequency feedback loop with an integrator, amplifier, and noise minimization unit to reduce signal drift, and employing damping materials to reduce resonance and noise in the actuator.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If a fine linear translation stage is used to adjust the object surface height within the linear region of the ADS, then the measurement range is improved, but signal drift problems still arise and can cause the object surface to drift out of the detection region

Engineering Contradiction:

Improvemeasurement rangeVSAvoidsignal stability

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The patent implements a feedback control system that continuously monitors the position of the object surface relative to the displacement sensor and automatically adjusts the position to maintain it within the linear detection region. This closed-loop feedback mechanism prevents signal drift from causing the object surface to drift out of the detection region, thereby maintaining both measurement range and signal stability simultaneously.

Inventive Principle:

Principle #23Feedback

2Reliability

If materials with low thermal expansion coefficients such as granite, Invar, or Zerodur are used, then thermal drift is reduced, but the cost increases and machining difficulty increases

Engineering Contradiction:

Improvesignal stabilityVSAvoidmanufacturing cost and machining difficulty

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The patent replaces passive mechanical solutions (using special low-expansion materials) with an active control system. Instead of relying on material properties to prevent thermal drift, the system uses sensors to detect drift and actuators to compensate for it, achieving signal stability without the need for expensive, difficult-to-machine materials like Zerodur or Invar.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent changes the approach from static parameter selection (material thermal expansion coefficient) to dynamic parameter adjustment. The system actively adjusts the relative position between sensor and object in real-time to compensate for thermal effects, transforming a material property problem into a controllable process parameter problem.

Inventive Principle:

Principle #35Parameter changes

3Reliability

If the environment is carefully controlled by air conditioning or ambient control systems, then temperature and humidity variations are reduced, but local time-varying temperature gradients from actuators and sensors are not easily mitigated

Engineering Contradiction:

Improvesignal stabilityVSAvoidenvironmental control system complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent uses feedback control to directly compensate for local temperature gradients and other environmental effects at the measurement location. Rather than attempting to control the entire environment, the system monitors the actual displacement signal and adjusts the relative position to maintain measurement accuracy, effectively bypassing the need for complex ambient control systems.

Inventive Principle:

Principle #23Feedback

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 alignment and anti-drift mechanism significantly reduces slowly varying signal drift, enabling high-resolution measurements of microscale and nanoscale features for extended periods, such as over a day, while minimizing vibrational noise and maintaining alignment between the displacement sensor and target object.

Implementation Method 1

The actuator includes a stack of piezoelectric ceramics

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 2

The actuator includes a voice coil motor

Methodology Applied

Scientific EffectElectromagnetic induction: Electromagnetic Induction

Implementation Method 3

The actuator includes a damping material. The damping material is selected to reduce at least one of a resonance amplitude and a quality factor of the actuator

Methodology Applied

Scientific EffectDamping: Damping

Implementation Method 4

The displacement sensor includes a photo detector and an objective lens positioned between the target object and the photo detector

Methodology Applied

Scientific EffectOptical detection:

Data Source

PatentUS8606426B2Alignment and anti-drift mechanism

Publication Date: 2013.12.10 ACAD SINICA

AI summary

A system includes a displacement sensor, an actuator connected to the displacement sensor, and a feedback unit. The displacement sensor is configured to measure at least one of a relative position and a relative orientation between the displacement sensor and the target object. The feedback unit receives a signal from the displacement sensor related to the measured relative position or relative orientation and controls the actuator to move the displacement sensor on the basis of variations in the received signal arising due to a change in environmental conditions.