Soft Robotic Wearable Actuator: Fluidic Fabric Muscle Sheets

This is a detailed instruction for making Fluidic Fabric Muscles Sheets (FFMS) soft actuator. FFMS are composite fabric structures that integrate fluidic transmissions based on arrays of elastic tubes. These sheet-like actuators can strain, squeeze, bend, and conform to hard or soft objects of arbitrary shapes or sizes, including the human body.

Please refer to the following publication for other details about this research:

Zhu, M., Do, T. N., Hawkes, E., & Visell, Y. (2020). Fluidic fabric muscle sheets for wearable and soft robotics. Soft robotics, 7(2), 179-197.

https://doi.org/10.1089/soro.2019.0033

Materials and tools needed:

Soft latex tubing: ID 1/8 in, OD 3/16 in. https://www.mcmaster.com/5234K24/

Fabrics (non-stretch cotton plain weave)

Sewing threads (non-stretch embroidery threads)

Super glue and disposable gloves for handling super glue

Wood or other rigid thin rod

Syringes slip tip

Rigid tubing: ID 1/16 in, OD 1/8 in. https://www.mcmaster.com/6546T33/

Barbed tube fitting reducer: https://www.mcmaster.com/5463K46/

Barbed tube fitting cap: https://www.mcmaster.com/5463K74/

Push-to-connect tube fitting: 5/32 OD - 1/8 OD: https://www.mcmaster.com/5779K351/

Eyelets and tools to install eyelets

String and cord lock

Scissors

Ruler

Sewing machine or embroidery machine (used in this instruction) or needles for hand sewing

Serger (optional but highly recommended)

'Pfaff creative sensation pro' allows you to program the stitching design on the interface. If you do not have access to the embroidery machine, you can also draw the pattern on the fabrics, then using standard sewing machine or manual sewing to sew straight stitches on the patterns you draw. The parameter of this pattern is shown in the first image in step 2.

Use the embroidery hoop that has a size of 240X150. Stack two layers of non-stretch fabrics together and put the stacked fabrics on the embroidery hoop bottom part. Put the embroidery hoop top part on top and tighten the hoop by pressing the spring switch. Then install the hoop on the sewing machine.

The stitching pattern is two straight stitching lines separated by 7.5 mm. The length of the straight stitches is 177 mm. Two to three reinforcing stitches at the ends of the lines are used to lock the stitching in place (first image). I have programed a pattern consists of 6 of the 'two line' pattern in the embroidery machine 'Pfaff creative sensation pro'. Here are the steps to load the pattern and execute the embroidery pattern.

1. Click the loading pattern as shown in image 2.
2. In the pattern list, select the file 'L177mmCW7.5INT2.vp3'. Here L stands for length (177mm), CW stands for channel width (separation between the two lines, 7.5 mm), INT stands for interval (2cm).
3. Click check mark on the top right corner, then the stitching will be loaded to the screen (image 3). Make sure the hoop size is correct on the top right corner of the screen (240X150).
4. Click go to embroidery interface as shown in image 4.
5. Change the thread color to one color as shown in image 5.
6. Change the thread metering setting to 65 as shown in image 6.
7. Change the speed setting as shown in image 7 (I would always do a slow speed for the first try but feel free to go faster once you have tested the speed out).
8. Then press start on the embroidery machine and the machine should be stitching out the patterns you loaded (image 8)! Follow the instructions if anything prompts on the screen.

The machine will stop once it finishes all the pattern (image 1).

1. Remove the stitched fabrics from the hoop.
2. Cut the jumping threads between lines.
3. Cut the fabrics as shown in image 2, leaving 1 cm on the long side and 3 cm on the short side.
4. Cut each unit (6 unit total) out following the pattern shown in image 1 in step 2, leaving 1 cm on the long side and 3 cm on the short side (image 3).
5. Serge each side of the individual layer of fabrics (image 4-6). Do not serge both layers together because that will block the way to insert the soft tubing. You can fold the underneath fabrics to the left side when you serge on the top layer. There are two layers of fabrics so the total number of sides need to be serged is 8.

1. Attach the soft latex tubing with a rigid thin rod for guidance (image 1).
2. Insert the rigid tubing into the fabric channels formed by stitching and two layers of the fabrics (image 2).
3. Pull the tubing through the channel so that the end of the latex tubing is close to the end of the fabrics (image 3).

1. Gloves are recommended when using super glue. Put a little bit super glue around the groove of the barbed tube fitting (cap) as shown in image 1.
2. Insert the cap into one end of the latex tubing as shown in image 2. The other end of the latex tubing is still attached to the rigid rod.
3. Put a little bit super glue on the latex tubing, around the groove of the barbed tube fitting (image 3).
4. Wrap thread around the groove tightly to lock latex tubing onto the groove securely and then use super glue on the thread to lock the thread in place (image 4).
5. Carefully pull the fabric up until the barb of the cap is fully inserted into the stitched channel (image 5).
6. Put super glue at the end of the stitching on both layers of the fabrics (image 6 and 7).
7. Wait for the super glue to dry out.

1. After the other end dries out completely, hold the dried end, and pull the soft latex tubing. The fabrics will wrinkle naturally (image 1, 2).
2. Repeat step 1 until the wrinkled stitching channel has a length of about 70 mm (that corresponds to a wrinkling ratio of 2.5) (image 3).
3. Mark this position on the latex tubing (image 4).
4. Pull the latex tubing a little bit more out (image 5) and cut the latex tubing at the marked location (image 6).

1. Put a little bit super glue on the groove on the larger side of the barbed tube fitting (reducer) as shown in image 1.
2. Insert the larger side of the barbed tube fitting into the latex tubing (image 2).
3. Put a little bit super glue on the latex tubing, around the groove of the barbed tube fitting.
4. Wrap thread around the groove tightly to lock latex tubing onto the groove securely (image 3) and then use super glue on the thread to lock the thread in place (image 4).
5. Carefully pull the fabric up until the barb of the cap is fully inserted into the stitched channel (image 5, 6).
6. Put super glue at the end of the stitching on both layers of the fabrics (image 7, 8).
7. Wait for the super glue to dry out.
8. A complete FFMS unit is shown in image 9.

After the super glue dries completely, hold both ends of the actuator and stretch a few times to adjust the wrinkles to be more uniform.

1. Attach rigid tubing to the smaller side of the barbed tube fitting (reducer) as shown in image 1.
2. Attach the push-to-connect tube fitting to the syringe tip (already filled with water) and the rigid tubing.
3. Now the actuator can be actuated! Press the syringe and see your actuator elongate and contract! Hold both ends when the actuator is pressurized, when withdrawing the fluid out, you will feel a force. This force can be used to lift weights. It can also be used as compression force when wrapped around an object.

1. Install eyelets following the instructions of your eyelet installing tools (image 1- 3).
2. Thread a string into the eyelets and use a cord lock to lock the string (image 4).
3. Pressurize the actuator and wrap it around your arm. Tighten the string using the cord lock (image 5, 6).
4. Release the syringe and you are turning the FFMS actuator to a compression bracelet (gif)!