Acousto-Optic Laser Focus Control for Uniform Micro Sweep Printing
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Solution Overview
Problem
Existing pattern generators using acousto-optic deflectors suffer from focus variations of a laser beam in a direction parallel with the micro sweep, leading to errors in printed patterns, especially as the length of the micro sweep increases.
Innovation Solution
Adapting the frequency of acoustic waves over time to vary the deflection angle of the laser beam, ensuring that differences in frequencies across the width of the beam in the direction parallel to the micro sweep achieve a desired focus, using a control unit to calibrate the frequency variation based on a function that compensates for focus errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the length of the micro sweep is increased to cover a larger area, then the coverage area is improved, but the focus variation in the direction parallel with the micro sweep direction worsens
Solution Approach 1:
The patent applies dynamics by making the acoustic wave frequency time-dependent rather than constant. The frequency is dynamically adjusted during the micro sweep to compensate for focus variations, allowing the system to maintain uniform focus across extended sweep lengths while covering larger areas.
Solution Approach 2:
The patent changes the frequency parameter of the acoustic waves over time to control and maintain the focus of the laser beam. By varying the frequency according to a specific function, the system compensates for focus drift that would otherwise occur with longer micro sweep lengths.
2Ease of operation
If the frequency of acoustic waves is varied linearly over time to achieve micro sweep, then the deflection angle control is simplified, but the focus in the direction parallel with micro sweep direction deteriorates
Solution Approach 1:
The patent modifies the frequency parameter of acoustic waves from a linear time dependence to a non-linear time dependence. This parameter change allows the system to maintain both ease of operation through programmable control and high focus accuracy by compensating for the natural focus drift that occurs with linear frequency sweeping.
Solution Approach 2:
The patent implements a feedback mechanism where the frequency variation is controlled based on a predetermined function designed to compensate for focus variations. This feedback loop ensures that the focus remains accurate throughout the micro sweep while maintaining simple deflection angle control.
3Device complexity
If a constant frequency sweep rate is used for micro sweep, then the system complexity is reduced, but the position linearity and focus uniformity worsen
Solution Approach 1:
The patent changes the sweep rate parameter from constant to variable over time. This allows the system to maintain position linearity and focus uniformity by adjusting the instantaneous frequency according to a predetermined function, while the overall system complexity remains manageable through software control.
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
Achieves a consistent focus of the laser beam in the direction parallel with the micro sweep, reducing pattern errors and ensuring accurate printing by compensating for focus and position nonlinearities.
Implementation Method 1
acousto-optic deflectors include a transparent material, such as a crystal material, which is subjected to acoustic waves at a frequency causing compressions and depressions in the material. Provided that acoustic waves with a wavelength sufficiently shorter than the wavelength of light of an optical beam passing through the material at angle that depends on the frequency of the acoustic waves, this in turn causes the material to act as a grating that deflects the optical beam.
Data Source
AI summary
A device, a computer program, a computer readable medium and a method for controlling focus of a laser beam during a micro sweep are disclosed. The laser beam is received to an acousto-optic deflector, and acoustic waves are provided to the acousto-optic deflector. The acoustic waves are varied in frequency over time to vary a deflection angle of the laser beam over time thereby achieving the micro sweep of the laser beam. Furthermore, a rate of variation in frequency of the acoustic waves is adapted over a time of the micro sweep in such a way that differences in frequencies over the time of the micro sweep of the acoustic waves are caused in the acousto-optic deflector over a width of the laser beam in a direction parallel to the micro sweep when passing through the acousto-optic deflector, where the differences in frequencies over the time of the micro sweep are such that they cause a desired focus of the laser beam in a direction parallel with the micro sweep over the micro sweep.