3D Optical Focus Measurement for AM Laser Focal Drift Control
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Solution Overview
Problem
Additive manufacturing machines face challenges in maintaining precise focal length of the laser, leading to build failures, part weakness, and instability due to thermal lensing and other factors, which are not detected until service intervals.
Innovation Solution
Implementing a closed-loop feedback system that uses a measurement laser to capture backreflected signals, which are then analyzed by a sensor to measure focal distance errors, allowing for real-time adjustments to maintain optimal focal length.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If focal length calibration is performed only at service intervals, then device complexity is reduced, but manufacturing precision deteriorates due to thermal lensing and focal drift
Solution Approach 1:
The patent implements a feedback mechanism where a sensor continuously monitors the focal position by detecting the reflected laser signal from the powder bed. The system compares the actual focal position with the desired focal position and automatically adjusts the laser focus through a voice coil actuator, creating a closed-loop control system that maintains manufacturing precision without complex periodic calibration procedures
Solution Approach 2:
The system performs self-calibration and self-correction by using the laser signal itself to detect focal drift caused by thermal lensing. The voice coil actuator automatically compensates for focal position changes in real-time, allowing the system to maintain precision through self-service without external intervention or complex calibration mechanisms
2Manufacturing precision
If real-time focal length monitoring is implemented, then manufacturing precision is improved, but device complexity increases due to additional sensors and feedback systems
Solution Approach 1:
The sensor system serves multiple functions: it detects the focal position of the laser, monitors the powder bed surface, and provides feedback for focus control. The voice coil actuator both positions the laser initially and continuously compensates for thermal drift. This multi-functionality reduces the need for separate dedicated components, thereby limiting the increase in device complexity while maintaining high manufacturing precision
3Loss of time
If periodic calibration is used instead of continuous monitoring, then loss of time is reduced, but reliability deteriorates due to undetected focal drift
Solution Approach 1:
The patent implements continuous focal monitoring and adjustment during the entire additive manufacturing process. The sensor continuously detects focal position, and the voice coil actuator continuously compensates for drift, ensuring the laser remains properly focused throughout the build. This continuous action eliminates undetected focal drift that would occur with periodic calibration, significantly improving reliability without requiring excessive calibration time
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 solution enables continuous monitoring and adjustment of the focal distance, reducing the likelihood of build failures and part weaknesses, thereby improving the reliability and stability of additive manufacturing processes.
Implementation Method 1
A measurement laser beam is sent through a focus unit of an additive manufacturing (AM) machine and is reflected off of a powder surface
Implementation Method 2
A cylindrical lens focuses the backreflected signal into a line and the one-dimensional (1D) complementary metal-oxide-semiconductor (CMOS) sensor determines an intensity location of the line
Data Source
AI summary
Methods, apparatus, systems, and articles of manufacture are disclosed to implement and operate an additive manufacturing machine with focal length error determination and correction. An example apparatus includes a main laser to create a main laser beam of the AM machine, the main laser beam used to fuse particle powder together in an AM process; a focus unit to focus the main laser beam at a specified distance, the focus unit also including a measurement beam; a semi-transparent mirror to split a backreflected signal, created from a reflection of the measurement beam from a powder surface, from the measurement beam; and a sensor element to measure a focal distance error from the backreflected signal. The example apparatus can also include a measurement laser to generate a measurement laser beam with the main laser beam.