Capacitive Laser Head Distance Sensing With Noise-Tolerant Gap Measurement
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Solution Overview
Problem
Capacitive distance sensors used in laser processing are limited by the need for customization for specific processing heads and nozzles, and they suffer from noise-related issues that reduce temporal resolution and dynamic range, making them ineffective for real-time, precise distance measurement across a broad range of applications.
Innovation Solution
A capacitive distance-measuring apparatus that uses a conductive housing and a constant-current source to measure voltage changes between the housing and a reference node, allowing for precise gap distance determination, and includes a null capacitor to nullify background capacitance, enabling robust, noise-tolerant, and high-resolution distance measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a capacitance sensor with RC circuit is used for distance measurement, then measurement precision can be improved by operating on spectral edge of bandpass filter, but noise increases and temporal resolution decreases
Solution Approach 1:
The patent extracts the distance measurement function from the traditional RC circuit with bandpass filter and implements it using a time-to-digital converter (TDC) that directly measures the time for a voltage threshold to be reached during capacitive charging. This extraction removes the noise-prone spectral filtering stage while preserving measurement precision through direct time-domain measurement.
Solution Approach 2:
The patent replaces the electrical RC circuit measurement system with a time-domain measurement system using a TDC. Instead of measuring voltage changes through noisy electrical filters, the system converts the capacitive charging process into a time measurement that is inherently more resistant to electrical noise while maintaining precision.
2Measurement precision
If RC circuit is customized for specific processing head and nozzle, then measurement precision is optimized for that configuration, but device complexity and customization requirements increase
Solution Approach 1:
The patent implements a universal distance measurement system where the TDC-based capacitive sensor can accommodate different processing heads and nozzles without customization. The system measures the actual capacitance value during operation and automatically adjusts, allowing the same hardware to work with various configurations of processing heads, nozzles, and workpiece materials.
Solution Approach 2:
The patent allows the measurement system to dynamically adapt to different configurations by detecting changes in capacitance parameters. When a different processing head or nozzle is used, the system measures the new capacitance value and adjusts its operation accordingly, eliminating the need for physical circuit customization while maintaining measurement precision.
3Adaptability or versatility
If capacitance sensor is used with processing head exchange, then adaptability is reduced as sensor becomes impotent, but device complexity decreases
Solution Approach 1:
The patent implements a dynamic measurement system where the TDC continuously adapts to changing capacitance values when processing heads or nozzles are exchanged. The system measures the actual capacitance in real-time and adjusts its timing measurements accordingly, maintaining effectiveness and reliability regardless of configuration changes.
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 apparatus provides a broad dynamic range and rapid distance measurement, accommodating various processing heads and nozzles, while minimizing noise and complexity, enabling real-time control of laser processes with improved precision and flexibility.
Implementation Method 1
A favored method is to treat the processing head and the workpiece as two conductors of a capacitance sensor. The capacitance is proportional to the surface areas of the conductors, the dielectric constant of any medium between them, and inversely proportional to the distance between them.
Implementation Method 2
When the capacitance sensor is charged, a change in distance will be proportional to the change in electric potential difference (hereafter referred to as 'voltage') between the two conductors, which is easily measured.
Data Source
AI summary
Apparatus for distance gauging in laser material processing includes a source of laser-radiation, an electrically-conductive focusing assembly, a constant-current source, and a voltmeter. The focusing assembly focuses laser-radiation towards an electrically conductive workpiece being processed. The focusing assembly and the workpiece form a capacitive sensor. The constant current source provides a constant electrical current to the focusing assembly for a constant time. The focusing assembly and the workpiece are separated by a distance that is proportional to a change in voltage measured on the focusing assembly during the constant time.