# Enhanced Calibration Method for Robotic Flexible 3D Scanning System

## TL;DR

This paper introduces a new calibration method to improve the accuracy of a robotic 3D scanning system for manufacturing large components.

## Contribution

The novel method simultaneously calibrates hand-eye transformation and robot kinematic parameters using a multidimensional ball-based calibrator.

## Key findings

- The proposed method reduced maximum measurement error from 1.053 mm to 0.421 mm.
- Average measurement error decreased from 0.814 mm to 0.373 mm after calibration.
- Experiments confirmed the effectiveness of the enhanced calibration method.

## Abstract

Large-sized components with numerous small key local features are essential in advanced manufacturing. Achieving high-precision quality control necessitates accurate and highly efficient three-dimensional (3D) measurement techniques. A flexible measurement system integrating a fringe-projection-based 3D scanner with an industrial robot is developed to enable the rapid measurement of large object surfaces. To enhance overall measurement accuracy, we propose an enhanced calibration method utilizing a multidimensional ball-based calibrator to simultaneously calibrate for hand-eye transformation and robot kinematic parameters. Firstly, a preliminary hand-eye calibration method is introduced to compensate for measurement errors at observation points, leveraging geometric-constraint-based optimization and a virtual single point derived via the barycentric calculation method. Subsequently, a distance-constrained calibration method is proposed to jointly estimate the hand-eye transformation and robot kinematic parameters, wherein a distance error model is constructed to link parameter errors with the measured deviations of a virtual single point. Finally, calibration and validation experiments were carried out, and the results indicate that the maximum and average measurement errors were reduced from 1.053 mm and 0.814 mm to 0.421 mm and 0.373 mm, respectively, thereby confirming the effectiveness of the proposed method.