Tony Stark’s J.A.R.V.I.S. (Just A Rather Very Intelligent System) brings home the possibility of designing an intelligent exoskeleton. The latest advances in virtual reality, artificial intelligence, neurosensing technologies have shown promises of achieving this in the near future. Most existing exoskeletons are designed to serve two broad ranges of use, human strength augmentation and human gait rehabilitation.
Passive exoskeletons can’t adapt to the fluctuations in the actuation demands during various activities. It’s because each activity requires different amounts of joint moments at the knee, hip and ankle. For example, the torque requirement at the hip varies during level walking and stair ascent. An active exoskeleton has a feedback mechanism that enables the actuators to provide the desired torque. The actuators can be electric, pneumatic, hydraulic or hybrid. Active exoskeletons that can be brain-controlled are still to be a great success, although minor success with Mindwalker has been observed.  These neuro-orthotic devices have enormous potential in restoring the ability of the patients with strokes and paraplegia.
According to FDA, “A powered exoskeleton is a prescription device that is composed of an external, powered, motorized orthosis that is placed over a person’s paralyzed or weakened lower extremity limb(s) for medical purposes.”  Although several exoskeletons have been designed by various research groups across the globe, very few of them are commercially available or being used in clinical trials and approved for use by FDA, CE and ISO. For example, exoskeletons like ARKE are currently in clinical development phase. The list excludes treadmill-based active robotic devices such as Lokomat and G-EO as these are static at a particular location. In fact, Lokomat is categorized by FDA as an isokinetic evaluation and testing system used in rehabilitation, which is a different category than other approved exoskeletons. The list presents commercially available and clinically approved or ISO certified lower extremity powered exoskeletons for the purpose of overground ambulation.
Hybrid Assistive Limb (HAL) is an exoskeleton designed for both strength augmentation and medical use. This suit was used by relief workers after Fukushima nuclear plant meltdown. CYBERDYNE Inc., the Japanese manufacturer has obtained clearance from FDA in 2015 for an iteration of the exoskeleton named ‘Medical HAL’.  The actuation is controlled using EMG signals received from the various muscles.
By October 2012, HAL suits were in use by 130 medical institutions across Japan. In 2013, HAL received CE certification for clinical use in Europe. In fact, HAL is the first powered exoskeleton to receive global safety certificate in 2013. Although the initial versions were quite heavy, HAL-5 model weighs only 10 kg and has its battery and control computer strapped around the waist of the wearer. The subsequent iterations are expected to be sophisticated in terms of engineering and design.
It is a commercially available and FDA approved assistive device. At the time of initial release, it was available in two versions-the ReWalk I and the ReWalk P. ReWalk P system is designed for use at home and the community, while ReWalk I is used for medical institutions. ReWalk is a hope for the differently abled and rightly termed ‘exoskeleton for disabled’. There are motor actuators at the hip and knee joints. The exoskeleton controls its movements using subtle changes in center of gravity of the user, unlike HAL that uses EMG sensors. It has enabled paraplegics to stand upright, walk and climb stairs. The ReWalk robotic leg attachments weigh around 21 kg, while the backpack containing the battery weighs around 2.3 kg. ReWalk featured in an episode of the American TV series ‘Glee’.  The weight and bulk of the exoskeleton, in addition to the pricing in the ranges of US$69000 to US$85000 have received critical reviews from various spheres.
It is one of the few extant exoskeletons that have received clearance from the US Food and Drug Administration (FDA) after successful clinical trials. It weighs around 26 pounds and has been extensively tested for safe use in indoors as well as outdoors. INDEGO is based on the exoskeleton design of the engineers at Vanderbilt University and is a result of intensive 10 years of effort.  It allows people paralyzed below the waist to stand up and walk. INDEGO’s selling point is its low weight, lower than most FDA approved exoskeletons. In fact, it is 20 pounds lighter than ReWalk. In 2012, Parker, a global leader in motion and control technology, purchased an exclusive license to market the device and currently, it is available for both clinical and personal use. The exoskeleton straps tightly around the torso and the hip and knee joints are controlled by a microcontroller.
The latest design also incorporates Functional Electric Stimulation (FES) that applies small electric current to paralyzed muscles and thus, helps in improving strength in the legs of patients with paraplegia. It is available in the European market after receiving the clearance with CE mark, the European equivalent of FDA. It is currently priced at $80,000.
4. EKSO GT
It is the first FDA cleared exoskeleton for stroke and spinal cord injury rehabilitation although HAL and some other exoskeletons happen to be clinically approved for use in Europe and Japan before this.  FDA has granted the use of Ekso GT in rehabilitation institutions under the supervision of a trained physical therapist. However, CE certification allows its usage in the non-clinical setting as well. Ekso Bionics, headquartered in Northern California, claims that the exoskeleton can help patients get back on their feet supporting re-learning of correct step patterns, weight shifting from one leg to another during walking and thus helping to correct posture.
It consists of battery-powered motors to move the limbs in a reciprocating manner. The controller allows the patient to change settings to respond to the changing needs. The ‘SmartAssist’ software can be reconfigured during rehabilitation and thus, promote personalized therapy. One can easily measure the progress in different rehab sessions. One of the salient features of Ekso is its ergonomic design allowing a user to adjust hip width and optimal hip and knee angles.
5. PheoniX and MAX Exoskeleton
The PheoniX exoskeleton is one of the world’s lightest exoskeleton designed to assist people with mobility disorders. PheoniX has only two actuators at the hip and the knee joints provide support and not any real actuation. It weighs 12.25kg and boasts of a modular design, which means you have the choice to power a particular joint.  Nevertheless, SuitX has come up with LegX and ShoulderX. However, PheoniX is limited to investigational use in the US. You can get this exosuit for around US$40,000.
MAX is another exoskeleton by the creator of PheoniX, SuitX. Both these exoskeletons have received ISO 13485 and ISO 9001 certifications. MAX targets industrial workers to reduce work-related injuries.  The technology behind SuitX’s industrial and medical exoskeletons originated at the Robotics and Human Engineering Laboratory at the University of California, Berkeley.
The REX by Rex Bionics is the first commercial powered exoskeleton that can move individuals with complete spinal cord paralysis. The exoskeleton can independently support itself and the weight of the user. It can shift weight from one leg to the other like a reciprocating gait cycle.
It is available in two versions: REX for clinical use and REX P for personal use. It has a different technology compared to most other commercially available designs. REX takes complete control of the wearer during the gait cycle. Thus, REX can be used as a starting point in a medical program for users with severe mobility impairments. In fact, it is the only available exoskeleton that can prove effective for people lacking the necessary upper body strength, which happens to be a key design assumption for several other exoskeletons. You can buy it at US$110,000. However, it has been approved for personal use and clinical trials in Australia only by the Therapeutic Goods Administration (TGA). TGA is Australia’s regulatory authority for therapeutic goods.
It is also a mobility assistance exoskeleton, specifically for people with spinal cord injury and meant for clinical use. It has been certified for sale in the Russian market. However, it weighs around 100 kg. Further iterations of the model are being developed focusing on personal use and are expected to be lighter.  This exoskeleton is not much different in technology from most of the extant exoskeletons. However, it focuses on better actuation strategies and enabling patients who are totally disabled stand. Thus, the exoskeleton usage eliminates the use of crutches during use unlike PheoniX and Ekso.
8. RB3D Hercule
It is a strength augmenting exoskeleton that can help people walk with heavy loads. ‘Hercules’ is an exoskeleton developed by the French robotics company RB3D. The latest version of the design can fit a wide range of body sizes and specifically targets the industrial workers. Currently, it costs over 30000 Euro. ‘Hercule’ has been exhibited in several occasions: at MILIPOL Fair in October 2011 and EUROSATORY in June 2012. It can operate for 4 hours in the standard mode. 
RB3D also manufactures several COBOTS or ‘collaborative robots’ that can be used for handling heavy loads. These robots are not wearable and hence, can’t be classified as exoskeletons.
KEEOGO is a sophisticated commercially available exoskeleton for purchase or rental (in Canada only) that has enabled people to do away with their walking sticks. It is a powered assistance device integrating B-TEMIA’s Dermatoskeleton technology. The Canadian company claims that the Dermatoskeleton technology is a pure human-machine interface technology that eliminates musculoskeletal stresses on the body of the wearer. At any given time, Keeogo reads your body position and movements, in order to interpret your intentions and help you along the way. It also adapts to your pace as well as the terrain, whether you are walking on flat ground, up a hill or a set of stairs.
Keeogo is useful for people who can demonstrate basic mobility without assistance and can maintain their balance. The device has been proven to work with patients who suffered from stroke, osteoarthritis and Parkinson’s disease, leading to partial mobility impairment. It is available for investigational use only in the United States.
EXO-H2 by Techniad S.L. is an outcome of several years of research by National Research Council of Spain’s Bioengineering Group. It consists of joint position and torque sensors and 6 motors at the knee, hip and ankle for actuation. It weighs around 11kg and can support a maximum user weight of 100 kg. A person with cerebral palsy or with minor gait impairment can use the exoskeleton with success. However, he may need a crutch for maintaining the balance. You can easily customize its control which is otherwise fixed for most exoskeletons and this gives Exo-H2 an edge over its competitors.