A new type of a wearable robot is becoming more popular: soft exoskeletons or exosuits! Soft exoskeletons address one of the main problems of exoskeletons: an exoskeleton is a hard, rigid structure that has to be worn over a soft, flexible body. Soft exoskeletons and exosuits do away with ALL of the hard, rigid frames that make up a classical exoskeleton. This new wearable robot is made entirely out of soft materials. Some components, such as battery packs and controllers have to remain rigid, but are usually stashed away in a backpack behind the user. Power is transmitted by flexible materials only, for example bowden cables (the same thing used on a bicycle’s brakes), air muscles (soft tubes that can shrink or expand using compressed gas) or filaments that shrink due to heat or electrical current.
Advantages of Soft Exoskeletons:
When the external metal frame is removed, soft exoskeletons hold some tremendous advantages over their regular counterparts:
- Soft exoskeletons are compliant (they bend with the body).
- Custom fitting a soft exoskeleton to an individual user becomes simpler. Rather than having to scan the user and create a custom metal suit for each person, soft exoskeletons should only come in as many sizes as clothing.
- Soft exoskeletons are smaller and much lighter and require less energy to use.
- Exosuits are easier to wear: they provide fewer limitations to the user’s joints.
- Exosuits can be worn underneath clothing. This is a very big deal because in general, current exoskeletons are viewed as ugly and unattractive. If an augmenting exoskeleton can be completely hidden while in use, it would make its adoption by the general population significantly easier (note that there are some passive exoskeletons that can already do this, example Ski-Mojo). Exosuits will most likely be adapted by the general public before any other type of exoskeletons.
- Soft exoskeletons could be significantly less expensive than rigid frame wearable robots.
Disadvantages of Soft Exoskeletons:
Soft exoskeleton’s main drawback is the same as their main strength: they have no external rigid frame. This means that the wearable device will have difficulty transferring power from any area of the body to the ground. Motors and sensors will be more difficult to mount. In addition, torque and force generated by actuators will enter the user’s body. Imagine for example an elderly person that uses an exoskeleton to go the store and back, the exoskeleton will have to provide assistance with balance, stairs, entering and exiting a vehicle (currently no product on the market can do this but the technology is getting close). A soft exoskeleton can provide the additional force to supplement the user’s muscles, but most if not all of that energy will go into the user’s body. Elderly and disabled people already have weakened bones and muscles, so adding more strain to their body will be counterproductive.
The above described drawbacks can be solved if a soft exoskeleton is able to act like a solid frame exoskeleton just for the duration of time needed to transmit forces and energy away from the user, and then become soft again. There is also a possibility for a middle ground, where part of an exoskeleton product remains rigid but some of the design techniques developed by making soft exosuits are integrated into the final design.
Examples of Soft Exoskeletons:
Power Jacket – REALIVE™
Panasonic – Matsushita Electric Industrial
The Power Jacket is one of the first soft exoskeletons. Developed by Mathushita Electric Industrial, the parent company of Panasonic, for use by stroke patients that have lost the motor control ability in one arm. The Power Jacket is soft and extremely compliant, making it easy to wear. One sleeve is filled with non-contact sensors that monitor the position of the healthy arm. The other sleeve is equipped with 8 air muscles that contract when filled with compressed air. The suit is connected to a mobile air compressor that also houses a control display. The Power Jacket is its own master-slave system: one arm is a tele-operator, while the other arm executes the motions. It is not clear what became of this project as all newer Panasonic exoskeletons are a standard rigid frame.
For more information on the REALIVE™ Power Jacket refer to the Panasonic Headquarters News.
Australia’s Defence Science and Technology Organisation Operations Exoskeleton
Australia’s Defense Science and Technology Organization Operations Exoskeleton is a passive, soft exoskeleton designed to decrease the burden to dismounted infantry. According to the original article by Gizmodo.UK, the average Australian soldier needs to carry equipment, weapons and supplies that weigh as much as 85kg. To put 85kg in perspective, that is equivalent to carrying 280 cans of Coke to a party or 3 suits of plate mail armor with nothing underneath. The Operations Exoskeleton uses two bowden cables (similar to the ones for bicycle breaks) to re-direct the weight of the soldier’s backpack directly into the ground. The entire exosuit weighs in at 3kg, which is many times lighter than previous prototypes for the military such as the HULC or XOS 2. Regardless of how soft the bowden cables are, they will still provide resistance to movement in the legs. For more information, refer to the original article at Gizmodo.UK.
DARPA Warrior Web Program – Harvard Soft Robotic Exosuit (Sep, 2014)
The Harvard School of Engineering, Wyss Institute and Boston University have created a tight-fitting exosuit and a lab to put it through rapid testing. The project is funded by the Defense Advanced Research Projects Agency (DARPA) under the Warrior Web project. This soft exoskeleton is powered, with the mechanical force being transferred from a waist harness or backpack down the user’s body. Interestingly, the project also emphasizes the need for rapid prototyping and testing, as the proper integration of man and machine in the human body is still mostly a guessing game. The above video is very well made and provides a fantastic overview of the project.
The California company Ekso Bionics is also working with soft exoskeletons, and is expected to complete their next prototype at the end of 2015.
Soft exoskeletons and exosuits are quite new compared to rigid frame exoskeletons, and the technology appears to be very promising. Have you worked with soft exoskeletons? If so, please contact us with additional information for this article!