# High-Speed Cell Assembly with Piezo-Driven Two-Finger Microhand
## 2 System Setup
### Construction of Micromanipulation Robot System  
Figure 2 illustrates the configuration diagram of the micromanipulation robot system, mainly divided into the motion control part and the image processing part. The motion control part is utilized to position the cells into an array. The image processing part can send real-time image information to provide visual feedback for automated cell assembly. The two parts are controlled through a PC (Windows).  
The motion control part is mainly conducted by a piezo-driven two-finger microhand mounted on a 3-DoF motorized positioning stage, and a 3-DoF stage for cell transportation, as shown in Figure 2. The two-finger microhand is used to grasp the cells and release them at the desired position. The whole microhand is held by an X-Y-Z stage and can be moved in a large 3-D workspace, which enables a substantial travel distance in the cell assembly while maintaining high precision. The 3D stage for cell transportation (sample holder) is utilized to switch between different fields of view to search for cells.  
The three piezoelectric actuators of the microhand are driven by a voltage amplifier (Matsusada Precision Inc., PZJ-0.15P, Shiga, Japan). The voltage range outputted to the microhand ranges from 0 to 150 V, and this voltage value will be initialized to 75 V before each use to calibrate the end-effector to the center of the workspace. Two strain gauges are orthogonally attached to the piezoelectric actuator for close-loop control and hysteresis avoidance. The maximum error caused by hysteresis in the piezo actuator is approximately around 0.16 \(\upmu\)m. The feedback signal is conditioned by the strain gauge bridge box and amplified by the amplifier (KYOWA, MCD-8A, Tokyo, Japan). The signal is then input into the microhand controller (AD chip ADC78H90, DA chip DAC-AD5363, MCU STM32 F767 ZI, STMicroelectronics, Plan-les-Ouates, Switzerland) for AD conversion. The onboard motion control algorithm of both the microhand and stages is executed on this controller. The feedback program in the control board continuously measures the differences between the actual output and the target values and then adjusts the output in real-time based on these differences. This adjustment is facilitated by a proportional-integral (PI) controller, which compares the current and historical errors to calculate both the proportional and integral terms. The X-Y-Z stage (OptoSigma, TAM 655, Tokyo, Japan) is motorized by three linear motors (OptoSigma, SGSP-13 ACT-B0) with a maximum travel distance of 13 mm and a maximum speed of 2 mm/s.  
The image processing part includes an inverted microscope (OLYMPUS DX73, Tokyo, Japan) for observing the microhand and obtaining the position and status information  
Figure 2: Micromanipulation robot system composition diagram.  
of the cells. The inverted microscope features a six-slot objective turret that can achieve various magnifications, including 4\(\times\), 10\(\times\), 20\(\times\), 40\(\times\), and more. All the experimental processes were recorded using a CCD camera (HIKROBOT, MV-CA050-11 UM, Hangzhou, China) that offered a framerate of up to 35 fps under a maximum resolution of 2448 \(\times\) 2048. The real-time images were processed by computer vision (OpenCV 3.0), providing position and posture feedback to the microhand controller.