# Design and Research of Intelligent Assembly and Welding Equipment for Three-Dimensional Circuit
## 3 Overall Equipment Scheme Design
### System Coordinate Unity  
The realization of three-dimensional circuit intelligent assembly welding equipment processing tasks, are based on the conversion relationship between the system-related coordinate system. Before the coordinate system calibration, it is necessary to return all axes of motion to zero. The system-related coordinate system schematic is shown in Figure 13 (The coordinate system is represented by pink, blue, and green arrows), where Base represents the machine base coordinate system, TCP1, TCP2, and TCP3, respectively, represent the solder paste spraying end coordinate system, the surface mount resistor end coordinate system, and the laser welding end coordinate system, Tool1 and Tool2, respectively, represent the feeder coordinate system and the solder paste cleaning device coordinate system, Turntable represents the two-dimensional rotary motion module coordinate system, and Sensor represents the point cloud camera coordinate system of the three-dimensional reconstruction mechanism. This equipment adopts the laser tracker for the overall coordinate system calibration, which has the advantages of easy installation, high precision, and real-time tracking, suitable for the coordinate system calibration of this kind of equipment [33]. \begin{table}
\begin{tabular}{c c} \hline \hline
**Process Name** & **Process Parameters** \\ \hline \multirow{4}{*}{Solder paste} & Model number: YB-B63; \\  & Type 5 powder \\  & Particle size range: 15-25 \(\upmu\)m \\  & Solder paste viscosity: 60-200 Pa/s \\ \hline \multirow{2}{*}{Solder paste viscosity} & Left: 4 mg; right: 4 mg \\ \hline Air pressure/Dwell time during soldering & 4 mg–0.2 Mpa/370 ms \\ \hline \multirow{2}{*}{Type of dispensing needle} & Dispensing needle: 22 g \\  & Inner diameter: 0.25 mm \\ \hline \multirow{2}{*}{Laser welding machine power} & 60 W \\ \hline Spot diameter & 1.83 mm \\ \hline Laser focal length & 75 mm \\ \hline \multirow{2}{*}{Laser temperature mode} & Power upper limit: 40\% \(\pm\) 2; temperature \\  & setting: 120 \({}^{\circ}\)C/1 s; 165 \({}^{\circ}\)C/0.5 s; 230 \({}^{\circ}\)C/1 s \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Solder paste coating and surface mount welding test parameters. Figure 12: Soldering and welding effect images. For each relevant coordinate system, the end coordinate system, tool coordinate system, and rotary table coordinate system can all be calibrated through the translation and rotation movement of the machine tool, but the calibration of point cloud camera coordinate system is the most complex and important. Point cloud camera coordinate system [Sensor] is the image coordinate system of point cloud camera of the three-dimensional reconstruction mechanism, and the obtained processing point coordinates are expressed in this coordinate system. After obtaining the pose of the processing point in the coordinate system of the point cloud camera [Sensor], hand-eye calibration of the point cloud camera is also required. After calibration, the machining point coordinates and normal vectors can be converted to the reference coordinate system [Base]. As shown in Figure 6, the point cloud camera is fixed on the 3D reconstruction mechanism; therefore, an auxiliary coordinate system [Temp] is established on the end of visual detection; then, in the actual work process, the conversion relationship between the auxiliary coordinate system and the coordinate system of the point cloud camera is fixed, and the coordinates of the measured point in the base coordinate system can be obtained from Equation (1):  
\[{}^{Base}P= \begin{matrix}{}^{Base}P\\ {}^{Temp}\end{matrix} ^{Temp}T^{Sensor}P \tag{1}\]  
The calibration process of the point cloud camera is as follows:  
(1) First, each movement axis of the machine tool is returned to zero, and the target ball is fixed at any position convenient for measurement at the end of visual detection.