Fabrication: Laboratory

In this section, we will provide step-by-step instructions on how to fabricate Laminar Jamming Structures in a laboratory environment. Please refer to the Design section or the Design Tool for recommendations on design choices. We will additionally cover alternative methods of fabrication in the Classroom section, which illustrates accessible and fast methods of prototyping LJS.

The main goal in the fabrication of LJS is to obtain a component which is completely airtight - except for a small tube connection - and in which the enclosed material (here referred to as filling) is arranged in layers that are in contact with each other in all areas. The surface contact area  between layers should be maximized, ensuring that the entire structure gets jammed . 

An overview of the process is provided below:

  • Set-up: Cut acrylic frame and filling material
  • Step 1: Vacuum form TPE layer to the acrylic frame
  • Step 2a: Heat press TPE case with filling
  • Step 2b: Impulse seal TPE case with filling
  • Step 3: Look for leaks and adjust tube connection

Fabrication Steps

Bill of Materials

This section will give a list of items that are used in this project with selected links to suppliers. 

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. 

Structural Materials

    TPE Sheet                   Paper Sheets  Plastic sheets     

    Thermoplastic elastomer (TPE)                                  Filling material of your choice (list)

       Pneumatic Tube                                                        Tube Connectors

Tubing of your choice (here used 1/8'' TPU tubing)                  Optional: Tube connectors 

Assembly Materials

           Acrylic Sheet                                               Sealing Tape

                            Acrylic sheet                                                                 PTFE thread sealant tape 

                    Thermal resistant tape                                                                      PTFE sheet                   

             PTFE surface protection tape                                                                       PTFE sheet                        

                         Utility knife                                                                Step 3 - part 3

                       Cutting tools                                                                                 Butyl sealant tape

 Equipment

 Vacuum forming machine                           Heat Presser

            Vacuum forming machine                                                                   Heat press      

          Impulse Sealer                            Vacuum source Vacuum source

                 Impulse Sealer                                                       Vacuum source (laboratory or hand-operated)

Step 1: Vacuum Forming

Set up

Frame and PTFE tape

Before starting the fabrication of your Laminar Jamming Structure, you may need to assemble an acrylic frame. An acrylic frame will allow the forming of your TPE envelope to the geometry determined by your frame, therefore creating a pocket that will fit thick structures and will prevent the bag from exerting forces on the filling material. If you believe an acrylic frame is not necessary for your LJS, please proceed to Step 2b for a fabrication process without it.

If you wish to laser cut the acrylic frame (see Recommendations), you should create a vector file (e.g. .dxf, .ai, .svg) of the frame that will be used in the forming process. Regardless of the fabrication type, create a space in one of the sides of the acrylic frame for the air circulation tubing. In this documentation, we used tubes with 1/8'' diameter.

Tape acrylic frame After making the acrylic frame, cover one face using a PTFE surface protection tape, and cut the excess on the sides.

 

Vacuum Forming

step 1 - part 1 Turn on vacuum forming equipment, wait 20 min for the heating element to heat up. Make sure that the entire heating element has a uniform temperature.
Step 1 - part 2

Place the acrylic frame on the bed of the vacuum former and cover it with a single layer of TPE on top. The TPE sheet should be big enough to cover the entire frame a second time if folded.

Step 1 - part 3

Tightly clamp the TPE sheet to the equipment, trying to minimize the wrinkles in the material as the ones seen in the bottom left of the image.

 Lower the platform that contains the acrylic frame.

Step 1 - part 4 Bring heating element over TPE sheet. Wait 1-2 minutes or until the TPE layer is glossy and soft.
Step 1 - part 5 Check if the surface is completely smooth. Turn the vacuum on and immediately raise platform with the acrylic frame.
Step 1 - Part 6 Wait a few seconds until the TPE has covered the frame completely and there are no air bubbles. Turn the vacuum off and release the clamps. Carefully remove frame and TPE from the machine.

Recommendations

Forming FramesA great advantage of Laminar Jamming Structures is that you can create components with the shape and material of your choice, provided that they are layered and sealed in a plastic envelope.  

In order to achieve high precision even in more complicated geometries, the encapsulated material and the frame used to form the plastic bag in the special shape can be laser-cut. In this page, we list some recommendations when following this process.

1. Always check if the material can be used in a laser-cutter. Some materials may have the desired characteristics for the laminar jamming structure but at the same time can be extremely hazardous to humans or the machine itself when used in the laser cutter. Some of the websites that provide guidelines for materials that can be laser cut are the Fabrication Lab at Harvard and the companies Epilog Laser and Trotec Laser.

2. Round the edges of the encapsulated material as this will prevent punctuating the airtight bag.

3. If you plan to design LJS with openings or stripes, as the ones pictured below, make sure to give enough space for the bag to be sealed in the in between regions.

Structures with openings

.

Step 2a: Heat Press

In order to seal the TPE envelope, you might use a heat press or an impulse sealer. If your LJS is thick and/or has a complicated geometry, the use of an acrylic frame, vacuum form and heat press would be more appropriate to create the airtight structure. Below we present the process of using a heat press to create a seal in a TPE envelope: 

Sealing with a heat press machine

Step 2a- Part 1

Place the filling material for the LJS (e.g. paper sheets) on top of the TPE bottom layer formed to the acrylic frame.

Step 2a - Part 2 Adjust the placement of the tube within the opening in the acrylic frame. Make sure the tube is not above the frame height.

 

Step 2a - part 3 Fold the TPE sheet over the acrylic frame to create the top layer above the filling material.

 

Step 2a - part 4 Place a PTFE sheet on top of the materials to prevent the TPE sheet from sticking to the heat press.
Step 2a - Part 5 Use heat press for 1 minute (at 270°F for green TPE)
Step 2a - Part 6 To ensure that there are no openings in the connection, cut the extra material outside the seal. Be careful not to cut into the sealed area. 

Step 2b: Impulse Seal

An alternative to the heat press is the impulse sealer, which does not require an acrylic frame and is a fast way to produce prototypes. This method, however, is more susceptible to imperfections and requires the LJS to have a simple geometry.

Sealing with Impulse Sealer 

Cover internal material (e.g. paper sheets) with TPE in the bottom and top layers. Seal every side of the Laminar Jamming Structure.

Adjust the time of application according to the type of TPE used. In this tutorial, we applied the sealer for 3 seconds using the Strechlon 200 TPE with 0.0015" thickness. 

Do NOT include the tube inside the TPE container.

Step 2b - part 2 Carefully cut extra material outside the sealed area.
Step 2b - Part 3 Create a small cut to insert the plastic tube.
Step 2b - part 4 Seal it with PTFE thread seal tape.
Finished structure

Wrap the interface between the tube and the envelope thoroughly. You have now finished the fabrication process.

Step 3: Final Adjustments

In order to ensure that the Laminar Jamming Structure created presents the desired characteristics after being jammed, it is necessary that the TPE container is completely sealed and airtight. We present some strategies to identify leaks and correct them. 

Identifying leaks

Step 3 - Part 1

One method of identifying leaks in the LJS is to pump air in it and attach a one-way check valve (right) to the tube, preventing air from escaping. Large leaks would be obvious because the envelope will immediately deflate. For small leaks, you may submerge the structure in water and look for air bubbles. Another option is to search for air leaks by listening to the jammed structure with a stethoscope.

Simple fixes

Step 3 - part 2 One quick way to fix leaks is to use butyl sealant tape in previously identified leaks. Although the method is not ideal for a practical application in which the LJS will undergo multiple cycles of jamming/unjamming, it is sufficient for fixing prototypes.  

 

Step 3 - Part 3

The places that leaks are most frequently found are around the tube connection. In order to prevent these leaks, you may reinforce the connection with PTFE thread sealant tape.

Final Structure 

Step 3 - Part 4

After finishing the fabrication of your Laminar Jamming Structure, you may attach it to a laboratory vacuum source or to a hand operated vacuum pump and assess the difference in properties between the unjammed (vacuum off) and the jammed (vacuum on) structure.