This method answers the key questions in the field of soft cell robotics by showing the fabrication method of soft pneumatic network actuators with oblique chambers that characterizes coupled bending and twisting motions. The main advantage of this technique is that it is fast, reliable, low-cost and suitable for the fabrication of soft pneumatic actuators with varied structures. Generally, individuals new to this method will struggle because the fabrication contains many steps, and one minor inappropriate operation can cause lethal failure of the actuators.
The fabrication process requires molds. Design and 3D print a set of molds for the actuator with a 30 degree oblique chamber. Two parts will form the chamber mold, with one part having a hole to create a tubing connection.
The third part will form a base. Next, place a mixing container on a scale. In separate syringes, have silicone elastomer component parts A and B.Use the syringes and scale to add the desired mass of each component to the mixing container.
Now, move the mixing container to a Planetary Centrifugal mixer and mix well. After mixing, the silicone elastomer is ready for the protocol. Work with the mold pieces for the chamber.
On each of the pieces, evenly spray mold release agent for silicone elastomer products. Orient the two pieces properly and bring them together to assemble the mold. Hold both ends of the mold with clips to prevent leakage.
Get five milliliters of silicone elastomer with a syringe. Inject the elastomer slowly into the hole of the mold to fabricate the connection end. Then, fill the whole mold with the silicone elastomer.
Use a low-flow rate and move the elastomer back and forth slowly. Once the mold is filled, use a needle to pierce any bubbles that form on the surface. Use a blade to scrape off excess elastomer on the upper surface of the mold.
Now, place the mold in a 70 degrees Celsius oven until it is cured. After curing, inspect the mold. Use a syringe to inject silicone elastomer into bubbles and holes on the surface of the actuator.
Scrape off any excess elastomer on the surface. Return the mold to the 70 degrees Celsius oven until it is cured. This is an example of a chamber produced by these steps after curing and demolding.
Get the mold piece for the base. Spray mold release agent for the silicone elastomer evenly on its surface. Pour the silicone elastomer into the mold to fill it completely.
Then, with a needle, pierce any bubbles that form on the surface. Scrape off any excess silicone elastomer along the upper surface with a blade. Place the mold in a 70 degree Celsius oven until the silicone elastomer is cured.
This is an example of the base produced by these steps after curing and demolding. At this point, the actuator components are ready. Work with both a chamber and a base.
Begin by pouring a one millimeter thick layer of silicone elastomer on one face of the base. Then, place the chamber part on the base. There will be a space between the two pieces.
Use a syringe to inject silicone elastomer into the space. Place the actuator in the oven at 70 degrees Celsius until the elastomer is cured. After curing the actuator, tap the actuator tubing connector.
It should accept the screw of a male stud push-in fit pneumatic fitting. With a needle, pierce the connection end of the actuator along the central line of the cylinder. Use a steel rod to increase the diameter of the hole to about two millimeters.
Get the actuator tubing connector and screw it into the actuator. Once it is in place, push a section of tubing into the pneumatic fitting. The final step is to check for leaks.
For this, use a container of water that can cover the actuator. Get the actuator and connect it to an air source. Place the entire actuator into the water and pressurize it.
Observe whether bubbles are formed due to a leak. After the test, remove the actuator from the water. In this video, a 30 degree actuator starts under zero applied air pressure.
As the pressure increases from zero kilopascals to 90 kilopascals, without interruption, the actuator both bends and twists. As the pressure is reduced, it returns to its original state. The bending angle for the actuator is defined as the angle between the body line in unactuated position and the body line in the actuated position.
The twisting angle is the angle between the tip line in the unactuated position and the actuated position. This plot shows the bending angle as a function of pressure for actuators with oblique angles of 30, 45 and 60 degrees. Here is a similar plot for the twisting angle as a function of pressure.
Note the difference in the vertical scales. While attempting this procedure, it is important to remember to pierce any bubbles that form on the top surface and scrape off excess elastomer on the upper surface of the mold before placing it into the oven. In this procedure, the silicone elastomer can be mixed manually and the elastomer can be cured at room temperature if the mixer and oven are not available.
After its development, this method has paved the way for researchers in the fabrication of soft pneumatic actuators to explore oblique chambers capable of bending and twisting motion in 3D space. Don't forget that working with needles and blades can be extremely hazardous and attention should be paid;avoiding any hurt. In addition, nitrile gloves should always be worn when working with silicone elastomers.
