Hello everyone, I am Yiyue Luo from MIT and I would like to present our work on digital
fabrication of pneumatic actuators with integrated sensing by digital machine knitting.
Pneumatic actuators have shown enormous promise in applications such as soft robotics,
assistive wearables, and interactive devices, due to their low response time
and relatively large output power density. Over the last decade, researchers demonstrated
diverse soft, silicone-based pneumatic actuators designs by molding, which is
one of the most common technique for pneumatic actuators. Recently, textiles and
fabrics have been devoted as candidates for soft actuators thanks to their ubiquitous utilization
in everyday life, high strength to weight ratio, and compliance with the human body. Researchers
have demonstrated textile-based pneumatic actuators through intrinsic modifications
or extrinsic reinforcement of the textiles. These strategies, while effective and now in
widespread use, are both manual and require trial and error cycles to optimize designs.
Further, incorporating sensorization into such workflows is rarely considered, and simple,
established recipes for doing so are lacking. To overcome the shortcomings of current workflows,
we propose a method for rapidly fabricating machine-knitted,
customizable pneumatic actuators with integrated sensing, and offer a predictive simulation and
interactive graphical user interface for users to design and preview actuator behavior easily.
Here shows an overview of our typical machine knitted sensorized actuator, with one actuation
region, three resistive pressure sensors, and two swept-frequency capacitive sensors.
Our actuator is composed of two parts: an off-the-shelf thin-wall silicone tube,
which serves as the base pneumatic channel and the knitted sheath with programmed stitches,
which wraps over the silicone tube and confines the shape of the inflated actuator.
The deformation of the actuators is mainly defined by the knitted sheath with locally
variable extensibility. As an example, here the front of the
tubular knits is constructed with normal acrylic knitting yarn and the back of the
tubular knits is constructed with the mixture of normal knitting yarn and elastic yarn,
which is about 100 times more extensible than normal knitting yarn. We then wrap the knitted
sheath over the silicone tube and anchor both ends of the wrapped tube by clamps.
When the silicone tube is inflated, the elastic stitches at the back side of the tube tend to
extend more than the non-elastic stitches, which forces the tube to bend forward.
We also integrated two different types of sensors into our acutators.
The integration was done automatically through one single knitting machine run.
We leverage the plating technique to insert conductive yarns at specific locations,
where the conductive yarns are blended with normal knitting yarn.
The knitted conductive yarn loops interlock loosely when there is no external pressure.
When applying a load, the conductive loops collapse, resulting in more electrical path;
and therefore, the resistance drops. It is worth mentioning that we apply a few
knitting tricks to prevent the pressure sensors from being stretched when the actuator infates
and ensures the reliability of pressure sensor performance. Details can be found in our paper.
We also integrate capacitive sensors. Swept frequency capacitive sensing leverages the
fact that alternating current (AC) signals of different frequencies flow through different
paths at the capacitive interface between the electrode and body-contacted object.
We integrated conductive yarns at specific location on the knitted actuators as the
capacitive sensing electrode, and by collecting amplitude responses over a range of frequencies,
we retrieve information on the existence of a human touch or human-contacted objects.
To allow users to design and preview inflated actuators quickly, we provide an interactive
design system and a predictive model, by which users are free to specify the actuation regions
and sensor locations, preview the actuators shape, and export low-level knitting machine
instructions for immediate fabrication. We incorporate a predictive simulation model in
our user interface, which allow users to preview the inflated shape of the designed actuator.
To obtain a realistic simulation result, we use a data-driven strategy to capture the shape of
individual normal and elastic stitch faces under pressure. Details can be our paper.
Here shows the qualitative results of our predictive simulation
on a J and S shape actuator. We further conducted an user study to
evaluate the usability and effectiveness of our computational design interface.
During the study, we asked the participants to perform two
tasks without and with the simulator feedback. The first task asked users to design an actuator
such that the endpoint of the actuator would make contact with a specified location when inflated.
The second task asked users to design an actuator that can circumnavigate a specified
cylinder while hitting the target when inflated. Here are some simulated and fabricated example
designs, which users designed using our user interface.
In general, participants achieved higher accuracy in both tasks, considered the tasks easier,
and obtained more confidence in their designs when our predictive simulation tool was provided.
Such results indicate the usability and effectiveness of our design pipeline.
Finally, we demonstrate diverse application scenarios of our
machine-knitted pneumatic actuators. Our actuators have outsized potential as
assistive wearable solutions because they are low-cost, lightweight, breathable,
conformal to the human body, and compatible with the current garment manufacturing process.
Here, we seamlessly integrate our actuator into knitted garments
such as gloves and sleeves. They are fabricated in one machine run as a whole piece of garments.
Minimal muscle activities are observed while completing tasks and motions when using the
assistive glove and assistive sleeve We design and fabricate a soft hand with
six individual machine-knitted actuators by activating different sets of actuators,
we can perform diverse grasps on objects of various sizes,
geometries, and weights, from a tennis ball to a wooden block, in a reliable manner
We demonstrate a two-finger gripper with integrated pressure sensors and
swept frequency capacitive sensing. The amplitude response from swept frequency capacitive sensing
offers real-time feedback on the presence of objects along with the finger interior
while the integrated pressure sensors provide real-time feedback on the quality of the grasp.
Our machine-knitted actuator with integrated swept frequency capacitive sensing
can be used as an interactive robot. We assemble four separate actuators,
each integrated with an electrode for the swept frequency capacitive sensing.
Real-time sensing feedback allows the robot to respond interactively:
when a human's touch is detected, they either activate or deactivate.
Our actuators can further be arranged as legs for a soft quadrupedal robot. Each
of the four legs consists of three actuators, two of which bend forward and backward while
the third bends the leg upward vertically. We pre-define the motion pattern of each leg,
combine to form a rowing-like motion. the quadrupedal robot can locomote forward and
backward by actuating all legs with the same sequence. The robot can further achieve a
turning motion by actuating the legs on one side forward and the other side backward.
Thanks for listening. More details can be found in our paper.