## 2 Design of Soft Gripper
### The Design of the Soft Actuator  
The design of the soft gripper actuator includes the mold design, 3D printing mold, configuration of silica gel, preparation of limit layer, and casting molding. 1. Actuator molding process: The mold of the soft actuator consists of the upper mold, the lower mold, the plug, and the bottom mold. The molding are designed by 3D software UG and 3D printing. The type of 3D printing equipment is model SP600 with a wavelength of 355 nm and accuracy of 0.1 mm. The printing material was 9400 resin, milky white, 320 cps (30\({}^{\circ}\)), density 1.14 g/cm, curing depth 0.12 mm (Dp). Since the upper and lower mold surfaces of the soft gripper are closely bonded during the assembly of the mold, the upper and lower mold surfaces are equipped with an exhaust groove to avoid bubbles affecting the quality of the molded products. For the sake of facilitating the connection with the air source, a 3 mm round hole is arranged at the end of the mold, and the inlet pipe connects the actuator and fixture through the round hole. The whole soft actuator is cast by the casting molding method with the main process flow shown in the diagram. 2. Preparation of silica gel: Firstly, the silica gel Ecoflex-30 A and B were weighed by electronic weighing and then poured into a small beaker at a mass ratio of 1:1. The bubbles were removed by the vacuum pump for further use. 3. Molding of actuator cavity part: Vaseline was smeared on the upper and lower molding surfaces with a small brush to rapidly separate the actuator body from the mold after molding. The deformed silica gel was injected into the lower mold, and the mold should be slightly vibrated during the injection process to ensure the uniformity of the colloid in the cavity. Then, a 3 mm plug was inserted into the fixed position to make the upper and lower mold fully closed. After that, these molds were kept at room temperature for more than 4 h until they were fully cured. Finally, the molds were opened to take out the soft actuator cavity. 4. Preparation of the sealing layer: The prepared mixed colloid was injected into the bottom mold to make it evenly spread. On top of it, the nylon cloth limiting layer with a certain size was placed horizontally and smoothly. Besides, a layer of colloid was evenly coated on the nylon cloth. Finally, the actuator cavity was buckled on it. After being kept at room temperature for 4 h, the molds were removed after complete curing. The soft gripper actuator part was thus finished. Pruning molding actuators are mostly silicone rubber, and the actuators that are damaged or bubbled as unqualified parts were discarded. 5. Connecting the trachea: A 3 mm diameter trachea was matched with the actuator stomatal channel, and the trachea was inserted into the reserved channel by tweezers. Then, the adhesive at the connection between the trachea and the actuator cavity was evenly smeared. They were kept until firmly sealed. Finally, the air tightness of the actuator was tested by pressurizing air in the actuator. Figure 1: Casting molding process diagram. The same method was adopted to connect three or four tracheas to the soft actuator, and the fixture and the clamp were fixed on the test bench by bolts. At last, the pneumatic soft gripper production was completed, which is shown in Figure 2.  
The manufacture of the soft gripper adopted the \"split injection molding bonding\" method. The soft actuator was completed by two types of silicone injection molds. The outer wall of the cavity in the top strain layer was made of Ecoflex-0030 silica gel with high elasticity, which ensures the greater elongation of the soft gripper. To improve the stiffness of the limiting layer, nylon cloth and E610 silica gel with good stiffness were used for pouring and sealing. Among them, the nylon cloth ensures that the lower layer of the actuator does not have ductility and combines the cavity layer with the outer wall silica gel, thus making the structure of the soft gripper stable and not easily damaged.