Fabrication

The steps for obtaining a multi-module manipulator are:

  1. Fabrication of the single modules;
  2. Fabrication of custom membranes for managing the granular jamming;
  3. Thermoforming of the sheath;
  4. Integration of all components.
Each step is in details described in the next sections.

The final result is the manipulator shown in the following movie:

 

Bill of Materials

This section will give a list of items that are used in this project. You can download a more detailed Bill of Materials sheet here.

Note: Many of the items listed are just examples and you can use your own discretion to substitute parts which are easier or cheaper to obtain. 

Molds

From Download Section you can download the .stl files for these molds. They can be printed with a  3D printer.

Materials

       Materials

Tools

                            Tools

Equipment

                           Equipment

Modules Fabrication

The multi-module manipulator is composed of three modules in-series connected. This section presents the details for the fabrication of the single modules. 

Fabrication of Module 3

1. Preparation of the Ecoflex 0050 Silicone
1.1. Weigh 12 g of part A and 12 g of part B in a mixing cup and mix them together with a plastic stirring rod.

1.2. Place the cup in a degasser machine at 1 bar vacuum pressure for about 10 min. When the air bubbles are completely removed, the silicone is ready to be used.

2. Fabrication of the silicon module

2.1 Assemble the mold (a), close the shells around it and pour the silicone up to the edge of the shells (b). 

2.2 Place the mold in the oven at 60 °C for about 30 min.

2.3 Remove shells and cap_A (c), reverse the module and insert cap_B (d), close the shells so that their edges are aligned with the stiffening cylinder (e). Pour the silicone inside the rearranged mold up to the edge of the shells (f).

2.4 Put the mold into an oven at 60 °C for about 30 min.
2.5 Remove the external shells, cap_B, the chambers and the stiffening cylinder (g).

3. Insertion of the actuation tubes
3.1 Cut 3 silicone tubes to the same desired length (300 mm for example).
3.2 Put silicone glue around one end of each tube for 10 mm, without obstructing the tubes.
3.3 Insert the tubes inside the dedicated channels into the module (h).
3.4 Put the module inside the oven at 50° - 60° for 10 minutes. 

After these steps, you have a module (Module 3 of the manipulator) able to move when the air is supplied by the yellow tubes. This module does not yet include granular jamming and external braided sheath. If you actuate the module, you have the typical "balloon effect" as shown in the following pictures and movie (please note that the central transparent piece is just a plastic support where the module is placed).

Balloon effect

Fabrication of Module 1 and Module 2

Other two modules have to be fabricated following steps 1 and 2. Do not insert the tubes (Step 3). These modules represent Module 1 and Module 2 of the manipulator.
Now you have three modules: only one module includes the tubes.

Granular Jamming Membranes

With this steps you can fabricate custom membranes, in particular the granular jamming membranes to be inserted in the central channels of the modules.    

1. Fabrication of the granular jamming membranes

The membranes fabrication is based on Latex material because it ensures good performance when the vacuum is applied. However, you can choose to fabricate the membranes with another material, for example the Ecoflex 0050 Silicone, if you do not need a strong vacuum level. 

1.1 Pour 5 g of liquid latex into a mixing cup.
1.2 Dip the mold (cylinder for the membrane) inside the liquid latex until the surface is completely covered (a).
1.3 Put the dipped mold in a support (a plastic piece with a hole) and let it dry under a hood for 20 min (b).
1.4 Repeat the dipping phase again. 

1.5 Remove the membrane from the mold (c). 

Remember to fabricate 3 membranes, one for each module of the manipulator (Membrane 1, 2, 3).

Membrane fabrication

2. In-series connection of three granular jamming membranes

2.1 Cut two plastic tubes to 12 mm length and one tube to a longer desired length (300 mm for example).

2.2 Cut three squared pieces of about 100 mm2 of nylon tissue. Close both the ends of the short tubes with this tissue using Parafilm or superglue, then close only one end of the longer tube.

2.3 Fill the Membrane 3 (that is the membrane of the Module 3) with 4 g of powder coffee, insert one short tube (the end with the filter) inside the filled membrane and fix it around the tube using Parafilm.

2.4 Insert the other end of the same short tube inside Membrane 2 holding its top side directly with the tube and fix it around the tube using Parafilm. Fill Membrane 2 with 4 g of powder coffee.

2.5 Repeat 2.4 for connecting Membrane 2 to Membrane 1.

In-series membranes

3. Insertion of granular jamming membranes into the manipulator

3.1 Apply the vacuum with the vacuum pump on the freeside of the long tube (the membranes become stiffer).

3.2 Insert Membrane 3 inside the empty central channel of Module 3. Slide Module 2 up to Membrane 2 passing the long tube through the central channel. Repeat for Module 1 up to Membrane 1.

Now you have three modules with granular jamming integrated in the central channels. 

Braided Sheath

The external sheath is fabricated starting from a commercial one.

1. Cut about 1.5 m of the expandable braided sheath (a).
2. Insert a metallic cylinder of 30 mm in diameter and 250 mm in length inside the sheath.
3. Push down and force the sheath by hand sliding over the cylinder, in order to create crimps (b).
4. Heat with a heating gun at 350 °C for 2-3 min until a permanent deformation is obtained (b).

5. Let the sheath cool down and remove the internal cylinder (c).

Crimped sheath fabrication

The sheath fabrication is based on a simple procedure. Remember that the development of the crimps has to ensure the necessary space to insert the module and the right distance between the crimps. These features ensure the right behavior of the module when the chambers are inflated. The sheath has the function to limit the radial expansion of the silicone when the chambers are inflated, avoiding  the “balloon effect” showed in Design Section. Close crimps improve the expansion of the silicone along the motion direction optimizing the bending and the elongation movements. In addition, particular care is needed when heating the sheath because an overheating could degrade the material. 

Manipulator Assembly

Now you have all elements for mounting the manipulator:

- 3 granular jamming membranes in-series connected and inserted inside three modules;

- One crimped braided sheath.

The mounting process for obtaining one manipulator consists of three main phases:

Phase 1. Connection by tubes. Climp the tubes of Module 3 with tweezers and insert (forcing) them inside the actuation chambers of Module 2. Fix the tubes on the top of Module 2 with silicone glue. Insert new tubes inside the base of Module 2 and fix together with the tubes coming out from the chambers of Module 2. Do the same for Module 1. It is very important that the tubes inside the chambers are longer than the chambers (see the figure), so that their function is guaranteed during the motion of the modules. 

Phase 1

Phase 2. Silicone junctions. In order to connect the modules, pour Dragon Skin 10 between modules using one semi ring mold with 25 mm diameter. Put the semi ring around the modules and pour the silicone from one side. Repeat from the opposite side. The distance between modules is 5 mm. The junction is not actuated and it does not include the granular jamming based stiffening channel. It has been designed in order to minimize its non-active effect on the system performance and not to prevail on that. For this reason we use a stiffer silicone and we tried to minimize the space between modules.

Phase 2

Phase 3. Integration of external braided sheath. Slide the crimped sheath around the manipulator. For fixing the sheath on the top side of the manipulator, close the rings around the top and push 2 crimps of the sheath inside. Pour 2 g of Ecoflex 0050 into the rings. Wait until the silicone is dried and repeat the same phase for the bottom side.

Phase 3

This integration strategy permits to have free space in the manipulator usable for the integration of other tools like sensors, camera or gripper. However, this technology is limited to the integration of 3 - 4 modules. This is due to the tubes that pass inside the actuation chambers. A future optimized solution could be based on a modular approach in which miniaturized valves are on-board integrated at the base of each module, limiting the number of the actuation tubes inside the manipulator.