Conceptual design of the SH-soft pneumatic actuator
Most SPAs, like the BSPA, consist of more cells, containing air chambers. To evaluate the potential of creating a SH-SPA, a single soft pneumatic cell (SPC), built entirely out of theDPBM-FGE-Jx material, is designed. The SPC is a cubic cell with a side length of 15mm. It is assumed that starting from this single-cell prototype, it is straightforward to build a multi-cell prototype, a (Bending) SPA. The cubic cell was developed out of the most flexible, -J4000 material (storage modulus: 7.85 MPa). -J4000 is less soft in comparison with Ecoflex 00–30 (tensile modulus: 69 kPa) usually used. However, due to the high fracture strain of 450%, the SPC can be used to create relative large deformations before a failure occurs. If multiple self-healing soft pneumatic cells (SH-SPCs) would be put in series, a BSPA could be constructed.
The -J2000 (storage modulus: 28 MPa) material is less flexible than the -J4000 material and is therefore suitable to be used to create the anisotropy needed in the SPC design. Based on the design of the BSPA, the bottom sheet was produced out of the less flexible material, -J2000, in order to create an anisotropic movement response.
The dimensions of the SH-SPC are presented in the figure below. Because the -J4000 and -J2000 sheets were synthesized through solvent casting, the sheet thicknesses have a small variation. Combining the different mechanical properties of -J2000 and -J4000, a fully SH-SPC is developed, in which the air chamber as well as the less-stretchable sheet have the SH-property. In the bottom of the SPC, a small hole is made in which a narrow metal tube is inserted through which the over-pressured air can enter the cell.