# Online Measurement of Melt-Pool Width in Direct Laser Deposition Process Based on Binocular Vision and Perspective Transformation

## TL;DR

This paper introduces a binocular vision system to accurately measure melt-pool width during laser deposition, improving the quality of deposited layers.

## Contribution

A novel binocular vision method with perspective transformation and fuzzy entropy thresholding for online melt-pool width measurement in DLD.

## Key findings

- The binocular vision system achieved an average error of 0.056 mm and <3% error in measuring melt-pool width.
- The method effectively captures melt-pool width across various deposition angles (30°–60°).
- The proposed system improves the detectable range and accuracy of melt-pool measurements.

## Abstract

Direct laser deposition (DLD) requires high-energy input and causes poor stability and portability. To improve the deposited layer quality, conducting online measurements and feedback control of the dimensions, temperature, and other melt-pool parameters during deposition is essential. Currently, melt-pool dimension measurement is mainly based on machine vision methods, which can mostly detect only the deposition direction of a single melt pool, limiting their measurement range and applicability. We propose a binocular-vision-based online measurement method to detect the melt-pool width during DLD. The method uses a perspective transformation algorithm to align multicamera measurements into a single-coordinate system and a fuzzy entropy threshold segmentation algorithm to extract the melt-pool true contour. This effectively captures melt-pool width information in various deposition directions. A DLD measurement system was constructed, establishing an online model that maps the melt-pool width to the offline deposited layer width, validating the accuracy of the binocular vision system in measuring melt-pool width at different deposition angles. The method achieved high accuracy for melt-pool measurements within certain deposition angle ranges. Within the 30°–60° measurement range, the average error is 0.056 mm, with <3% error. The proposed method enhances the detectable range of melt-pool widths, improving cladding layers and parts.