This protocol describes a rod-based approach, combining 3D-printing and soft lithography techniques for fabricating the soft gripper devices. This approach eliminates the need for an external air source by incorporating a chamber component and reduces the chance of occlusion during the sealing process, particularly for miniaturized pneumatic channels.
The overall goal of this procedure is to fabricate soft gripper devices using a rod-based approach. Combined with 3-D printing and soft lithography techniques. This method can help answer key issues faced in the fabrication of soft pneumatic grippers such as channel occlusion during the setting process and the incorporation of an air chamber.
The main advantage of this technique is that it allows us to build miniaturized pneumatic channels within the soft gripper structures to ensure consistent actuation. The implication of this technique extends to what's nerve anastomosis surgery because the soft robotic gripper permits delicate nerve manipulation without over-gripping damage. We first had the idea for this method when we faced difficulty developing functional soft gripper using conventional casting sealing process and started experimenting with thin rods in the casting phase.
Begin with weighing out an equal mass of the two component materials for the elastomer in a mixing vessel. Then, cover the container and load it into a centrifugal mixer along with a balancing mass. Now, run a 30 second mixing cycle with the mixing phase at 2000 RPM and the deaeration phase at 2200 RPM.
Expect that the thoroughly mixed components will now cure uniformly when molded. Note that the design and production of the molds is covered in the text protocol and the next section deals with their use. This process begins with molding the gripper-arm components.
First, insert the two 3-D printed chamber blocks into the left and right side of the chamber component to generate a sealed chamber with pneumatic channels connected to it. Next, insert one or two 1.5 millimeter diameter titanium wire rods through the chamber, depending on if this is a single-or double-channel model. Leave a distance of two millimeters between the gripper tip and the rod to create the pneumatic channels.
Now, fully load the mold with the elastomeric mixture, ensuring no air bubbles are trapped within. Then, cure the mold at 60 degrees Celsius for 10 minutes. The next step is to pull the wire rods and the two chamber blocks out from the mold.
Make certain that the connection between the pneumatic channels and the chamber is well-established, as this allows the compression of the chamber to actuate the gripper arms. Now, proceed with placing the 3-D printed gripper-block on top of the gripper component in order to create the chamber. First, insert the wire rods to block the holes in the wall of the mold.
Then, fill the mold with the elastomeric mixture and ensure there are no visible air bubbles trapped in the mold. Cure this mold for 10 minutes at 60 degrees Celsius as well. Next, de-mold the cured components to assemble the gripper chamber structure.
The final step is to fill the sealed chamber component with air. To do this, make the 2.5 millimeter sealing-layer that completes the assembly. Fill the mold with the elastomeric mixture and cure it at 60 degrees Celsius for 10 minutes.
Once cured, brush a layer of elastomeric material on the cured 2.5 millimeter sealing-layer. Then, place the gripper chamber structure on the sealing-layer and let the bond form, making certain the seal is perfect, thus an air-filled chamber is made. Now, cure the entire structure for another 15 minutes at 60 degrees Celsius.
Then remove the remaining mold to complete the device. The handling tool is also made from a mold and details are in the text protocol. Insert the gripper into the handling tool and cover the opening area with a removable rectangular cap.
Then, insert a movable piston to facilitate chamber compression which completes a manual tool. Alternatively, insert the gripper and a linear actuator into a robotic handling tool. In this case, cover the opening area with a movable rectangular cap.
To evaluate the functionality of the soft gripper, test it with a jumper wire. Adjust the gripper so that the wire is in between the two arms. Then, move the piston to compress the chamber which actuates the gripper arms to hold the wire.
Hold and move the wire at least 20 centimeters away from the wire's original location. The proposed technique demonstrates how to quickly fabricate low-cost soft pneumatic grippers. Simply changing the mold design and using the same elastomer can make grippers for different applications.
The design presented here is capable of picking up objects with dimensions of up to 1.2 millimeters in diameter. In a simulated surgery, the maximum compressive force generated by the single actuatable arm grip was around 0.27 Newtons. The double actuatable arm devices measured around 0.8 Newtons.
Comparatively, forceps with and without elastomer had grip forces of about 1.7 and 2.6 Newtons respectively. Once mastered, this technique can be done in an hour if it is performed properly. While attempting this procedure, it's as important to remember to align the rods firmly before casting and perform the final sealing carefully.
Following this procedure, the completed soft gripper can be attached onto a piston base or linear actuator base handling tool to allow intuitive control of the gripping. After it's development, this technique paved the way for researchers in the field of soft robotics to explore the design of chamber-gripper devices for delicate object manipulation. Don't forget that silicone-rubber can be an ingestion hazard and precautions such as wearing gloves should always be taken while performing this procedure.
