Dithering Scan Path for Polygon Mirror Wobble in Additive Manufacturing

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Solution Overview

Problem

Additive manufacturing processes face inaccuracies and inconsistent energy distribution due to bearing wobble in rotating polygon mirror scanners, which affect the surface quality and spot-size control of the light beam during energy delivery.

Innovation Solution

An auxiliary polygon mirror scanner is introduced to generate dithering in the scan path of the light beam, either parallel or perpendicular to the primary scan path, to reduce bearing wobble and enhance spot-size control by oscillating the light beam along the scan path, thereby improving energy distribution and surface quality.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If a rotating polygon mirror scanner is used to deliver energy in additive manufacturing, then productivity is improved through rapid scanning, but manufacturing precision deteriorates due to bearing wobble causing inconsistent spot size and energy distribution

Engineering Contradiction:

Improvescanning speedVSAvoidspot size control

Core Design Contradiction:

ProductivityVSManufacturing precision

Solution Approach 1:

The patent applies mechanical vibration by introducing a dithering motion to the polygon mirror scanner. A voice coil actuator generates controlled vibrations that oscillate the mirror around its nominal position, creating a dithering effect that prevents bearing wobble from degrading spot size control while maintaining high scanning speeds for productivity.

Inventive Principle:

Principle #18Mechanical vibration

Solution Approach 2:

The patent changes the operational parameters of the polygon mirror scanner by superimposing a high-frequency low-amplitude oscillation on top of the primary scanning motion. This parameter modification allows the system to maintain rapid scanning for productivity while the dithering compensation corrects precision losses from bearing wobble.

Inventive Principle:

Principle #35Parameter changes

2Productivity

Engineering Contradiction:

Improvescanning speedVSAvoidenergy distribution uniformity

Core Design Contradiction:

ProductivityVSManufacturing precision

Solution Approach 1:

The voice coil actuator generates controlled vibrations that create a dithering motion of the polygon mirror. This mechanical vibration compensates for bearing wobble effects, ensuring uniform energy distribution across the scanned surface while maintaining high scanning speeds for productivity.

Inventive Principle:

Principle #18Mechanical vibration

Solution Approach 2:

The system employs feedback control where the voice coil actuator continuously adjusts the mirror position to compensate for deviations caused by bearing wobble. This feedback mechanism ensures consistent energy distribution uniformity while maintaining the high scanning speeds required for productivity.

Inventive Principle:

Principle #23Feedback

3Device complexity

If bearing wobble in polygon mirror scanners is present, then device complexity is reduced through simpler scanner design, but manufacturing precision deteriorates due to scan path inaccuracies

Engineering Contradiction:

Improvescanner designVSAvoidscan path accuracy

Core Design Contradiction:

Device complexityVSManufacturing precision

Solution Approach 1:

Instead of using complex active compensation mechanisms, the patent employs a relatively simple voice coil actuator to generate dithering vibrations. This approach maintains scan path accuracy by preventing bearing wobble effects while adding minimal complexity to the overall scanner design.

Inventive Principle:

Principle #18Mechanical vibration

Solution Approach 2:

The patent modifies the operational parameters of the scanner by introducing controlled dithering motion through the voice coil actuator. This parameter change compensates for scan path inaccuracies caused by bearing wobble without requiring significant redesign of the scanner architecture.

Inventive Principle:

Principle #35Parameter 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 dithering mechanism reduces errors caused by bearing wobble and increases the effective spot size of the light beam, leading to improved surface quality and uniform energy distribution in additive manufacturing processes.

Implementation Method 1

an auxiliary polygon mirror scanner configured to receive the light beam from the light source and reflect the light beam

Methodology Applied

Scientific EffectReflection: Reflection

Implementation Method 2

The dither may be parallel and in-line with the scan path across the surface. The dither may be perpendicular to the scan path across the surface.

Methodology Applied

Scientific EffectMechanical vibration: Vibration

Implementation Method 3

a primary mirror scanner to receive the light beam reflected by the auxiliary polygon mirror scanner and direct the light beam to impinge on an exposed layer of feed material

Methodology Applied

Scientific EffectLight absorption and energy conversion: Absorption (EM radiation)

Data Source

PatentUS11331855B2Additive manufacturing with dithering scan path

Publication Date: 2022.05.17 APPLIED MATERIALS INC

AI summary

An additive manufacturing apparatus includes a platform, a dispenser configured to deliver a plurality of successive layers of feed material on a platform, a light source configured to generate a light beam, an auxiliary polygon mirror scanner configured to receive the light beam from the light source and reflect the light beam, and a primary mirror scanner to receive the light beam reflected by the auxiliary polygon mirror scanner and direct the light beam to impinge on an exposed layer of feed material.