Soft Robotics - Week 4 (02/14/2025)

Silicone - Part 1

This week we watched as Kari demoed a silicone casting of the Bibenda actuator so that we could try our hand at casting for our homework. And boy was she not kidding about how messy it can become. I tried to do the assignment on Sunday (2 days after class) and we were completely out of nitrile gloves. 

Bibenda Actuator

The silicone casting process was pretty straightforward as we were given the exact instructions to follow. 
Since I worked alone over the weekend, I did not get documentation of my casting process, however, during the degassing periods, I had 5 minutes to document the delightful action of air bubbles surfacing and popping.

One challenge I did face, which I didn't think too much about was how much the PVC cement would affect the curing of the silicone. I don't think I let the cement completely dry before beginning the casting procedure so not only did I have trouble removing the cast from the mold, the bottom section of the actuator is still a little sticky, even after 4 days. 

Origami-Inspired Silicone Actuators

This week I read about new silicone actuator designs that are inspired by origami principals.
Here is a very VERY short and condensed summary of the paper
What makes this research different from other origami based soft robots is that these new actuators do not include any rigid frameworks or shells. Instead, the team incorporated the origami folds in the silicone casting to create a fully soft and flexible structure.

Feng and team developed two types of origami-inspired soft pneumatic actuators (O-SPAs) were developed:

• Flasher origami-inspired SPA (FO-SPA): Produces torsion and radial contraction
• Kresling origami-inspired SPA (KO-SPA): Generates torsion and height contraction

​Both of the actuators respond to minimal negative pressures and the team created three applications with the two actuator designs.

​The first is a circular soft gripper:
​
This gripper uses three FO-SPAs and can handle delicate fruits. When the vacuum is on, the actuators contract and create larger negative space to fit around the object. once the gripper is aligned with the object, the vacuum is turned off to expand and gently mold around the object, relying on the tension to grip around the object. 

This gripper can successfully handled fragile items like loquats and waxberries without damage

​The second is a bipedal walking soft robot:

When contracted, KO-SPAs can provide a combination of motions

1. Leg lifting (telescopic motion)
2. Stepping (twisting motion) 

Which makes them well suited for this type of action.
This robot consists of two KO-SPAs, two suckers, and 3D-printed connections.
When the air pressure in the KO-SPAs and suckers are adjusted in sequence, the researchers are able to achieve the desired walking motion (as seen in the chart to the right)

​Finally, the 3rd robot is a soft pipeline crawling robot:

This robot combines two FO-SPAs and one KO-SPA with adapter pieces. 

• FO-SPAs prevent sliding when unactuated and reduce friction when actuated
• the KO-SPA provides driving force through contraction

The travel distance of this robot is the height delta of the KO-SPA when it contracts. 

Y. Feng, W. Yan, J. Song, Z. Hong, H. Qiu, K. Cui, X. Song, J. Tan, Origami-Inspired Reconfigurable Soft Actuators for Soft Robotic Applications. Adv. Mater. Technol. 2024, 9, 2301924. https://doi.org/10.1002/admt.202301924