# High-Speed Cell Assembly with Piezo-Driven Two-Finger Microhand
## 4 Automated Assembly Strategy for Cells and Experimental Results
### Operational Path Planning  
After successfully recognizing the target and end-effector, it is necessary to plan the operation path, including the grasping path and assembly path. Grasping path planning determines the operation sequence for targets and the movement of the end-effector approaching the targets. Assembly path planning includes the sequence of target array positions when forming a specific shape.  
Due to the limited imaging range of the microscope, when the number of targets in a single microscopic field of view is insufficient to meet the assembly requirements, it is necessary to supplement targets from adjacent views. We hope to have as abundant targets as possible in the initial field of view, so our first step is the selection of the operational field of view. To avoid complications in target recognition and manipulation caused by an excessive number of cells in the field of view, we controlled the cell density to approximately five cells per average microscopic field. However, precise control of cell density in different microscopic fields is challenging, so this may result in insufficient target numbers in the current field of view during the arraying process.  
To address the aforementioned issue, as illustrated in Figure 5a, we assigned numbers to the surrounding operational fields of view. Following the numerical sequence, we added the number of detected targets in the current field of view to the total number of targets detected in all previous fields of view. If the sum was greater than or equal to the required number of targets, we selected the current field of view as the operational field. After completing the manipulation in the current field of view, we sequentially returned to the previous field of view to grasp additional targets for supplementation.  
For example, the target number required for assembling the letter 'T', as shown in Figure 5b, is six. As shown in Figure 5a, the number of targets in view 1 is four, which is insufficient, so the microscope moves to view 2. The number of targets detected in view 2 is 5, adding the 4 from view 1, for a total of 9 targets, which is sufficient for the array of the letter 'T.' Therefore, view 2 is selected to start the array operation, and the assembly order is shown in Figure 5b.  
Due to the target array located in the upper right corner of the field of view, to avoid collisions with the targets, the grasping path planning of the end-effector is horizontal first and then vertical. For each array position, find the target with the minimum horizontal and vertical distances from it, as shown in Equation (5). This ensures the shortest path under  
Figure 5: (a) Illustration of operational field selection. (b) Array strategy illustration.  
the premise of the collision-free operation, which is defined as the scanning obstacle-free path planning algorithm.  
\[\min\left(\left.\left|\left.Tx-Ex\right|\right.+\left.\left|Ty-Ey\right|\right.\right)\right. \tag{5}\]  
As shown in Figure 5b, after completing the operations on all targets in the current view 2, we return to view 1 to grasp the additional targets, and then return to view 2 to continue the unfinished assembly. The red circles represent the desired array positions, where (\(Ex\), \(Ey\)) is the coordinate of the desired array position and the numbers on them represent the order of assembly. The assembly order is from top to bottom and from right to left. The gray-black circles represent the actual positions of the current targets, where (\(Tx\), \(Ty\)) denote the actual position coordinate of the target yet to be operated and the numbers on them represent the order of operations. Target 6 is a candidate target from the previous view. Since its horizontal and vertical distance to the sixth desired position is the smallest, it is chosen as the target for supplementation.