If we have an exoskeleton with a frame we have a static structure, but if we want to be able to walk we need actuators. An actuator converts energy into movement or force. In an exoskeleton, these actuators are called the joints. The main goal of the joints is to move the bones of the exoskeleton relatively to each other.
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First of all, there are a lot of different types of joints that can be categorized in many different ways. As you can imagine, tiny drones or small robots need different actuators than large cranes in large cargo ports or in the automotive industry. Exoskeleton actuators should be able to deliver enough rotational force and speed but should also be small and lightweight. And even within these requirements, there are still quite some options. Not all possible actuators are explained in this reading, but the most common ones will be.
In exoskeletons, you can use passive and active joints. Active joints are actuated where passive joints are not. Passive joints are connection points between bones. With an axis, the bones can turn around, with optional non-actuated parts such as springs attached to them. You can't control the precise position of the joint within the outer limits. Active joints are more common in exoskeletons since you often want control over the position of limbs and therefore the joints. If a passive joint is used, it is often the ankle joint. You don't need to power this joint to be able to walk, although you lose some control over the exoskeleton position if you don't. Joints can move in different ways. In linear joints, two parts glide past one another without changing the angle between them and without rotation. The mobile part retracts and extends from its housing.
Joints can move in different ways. In linear joints, two parts glide past one another without changing the angle between them and without rotation. The mobile part retracts and extends from its housing.If a linear joint is placed around a passive rotating joint, it turns the passive joint into an active joint. By shortening and lengthening the linear joint, the bones start rotating around their connection point.
Figure: Motion of a linear joint
If a linear joint is placed around a passive rotating joint, it turns the passive joint into an active joint. By shortening and lengthening the linear joint, the bones start rotating around their connection point.
Figure: Motion of an actuated linear joint and passive rotational joint
As the name already suggests, rotary joints make the bones on both sides rotate respectively to each other.
Figure: Motion of a rotary joint
Although these rotary joints might look more similar to the joints in our body, our body actually uses the same mechanism as the combination of a linear joint and a passive rotary joint. The joints in our body are simply connections between bones that allow movement in certain directions. By contracting and releasing the muscles that are connected to the bones on either side you are able to move your limbs! In exoskeletons, rotary joints are used more often. They can deliver enough rotational force and speed, but with a larger range of motion and a more compact design compared to linear joints.
In the MARCH IV exoskeleton, both rotational and linear joints are used. As you can see in the picture below, the knees and hips are equipped with rotary joints. The hips also have linear joints for a sideways motion, and so do the ankles.
Figure: Render of the March IV exoskeleton
Actuators can be powered by electricity, but also by pressurized air or fluids. All these types have their advantages and disadvantages. At this moment, most exoskeletons use electric actuators.
Pneumatic actuators are powered by pressurized air. By moving compressed air to different compartments within a joint, the position of the joint can be determined. Pneumatic actuators are quite safe since they do not contain any hazardous materials, although high pressure itself can always lead to unsafe situations. On the other hand, they deliver little force to power the exoskeleton (it is possible though) and they have quite a low efficiency due to air leakage. If you want to accurately control the actuator, you need regulators and valves, which complicate the design and increase the weight, dimensions, and costs.
Figure: Pneumatic or hydraulic linear actuator
Hydraulic systems operate quite similar to pneumatic systems, but with the use of fluids instead of air. They can generate very high forces. Although there is a loss of efficiency over time due to leakage of fluid. Leakage of fluids can also cause damage to the surrounding systems. It requires reservoirs, pumps, valves, and more to be able to have precise control over the actuator and therefore greatly increase the complexity and weight of the exoskeleton.
Electric actuators offer very precise control and are quick and easy to use. They can generate quite some power and are more quiet compared to both hydraulic and pneumatic systems. They are relatively compact and lightweight, which makes them suitable for exoskeleton use.
When using electrical actuators, there is a difference between the motor and the transmission. The motor actually uses electricity and converts it into movement, or kinetic energy. Transmission converts it into the movements that you actually need. On the next page, there will be a video with some explanation on different types of transmission and how you can do some calculations on transmission. In exoskeletons, it is very common to use a drone motor or another small motor that has a high rotational frequency, combined with a transmission that slows down the speed and increases the rotational force.
You can also combine hydraulic, pneumatic, and electrical systems. You can, for example, use an electric motor and combine it with a hydraulic transmission system. The benefits of combinations like this are that you get to combine favorable properties of both systems and reduce the disadvantages.
Overall, there are many different types of actuators for a great range of applications. By being precise in establishing your list of requirements you should be able to pick the right joint for your exoskeleton.
Robotic exoskeletons are not a far-removed idea from our imagination, thanks to pop culture. Exoskeletons have been featured in films like Edge of Tomorrow [1], where Tom Cruise's strength is augmented using a combat jacket [2], Marvel's Iron Man [3], where Tony Stark's abilities are amplified using AI and mechanics, and Avatar [4] where the AMP suit [5] is used to navigate Pandora. And now, they are no longer just part of science fiction but are a part of our reality. In , Julian Pinto, who is completely paralyzed in his lower extremities, made history by kicking off the World Cup in Brazil with a robotic exoskeleton that was created by a team of more than 150 researchers. [6]
The robotic exoskeleton industry is experiencing a boom as more use cases are developed in new industries, and experts predict it will be worth $1.8 billion by . [7] This article will cover everything you need to know about exoskeletons, including interesting little-known facts about exoskeletons.
An exoskeleton is a wearable device or a suit that works alongside the user to enhance their strength and amplify their performance. It is usually worn on the body. Exoskeletons use a combination of robotics and biomechatronics to enable body independence and are designed to provide support rather than replace functionality. In physical rehabilitation, they help patients relearn skills. In construction, they reduce the amount of energy expended and make repetitive tasks easier. And in the military, they are used to help soldiers carry heavier loads over longer distances.
The first exoskeleton-like device was invented by a Russian inventor known as Nicholas Yagn in . It had a spring-operated design that was intended to be used by the military to run and jump, but it didn't make it to production. However, that was just the beginning of what would later become a growing industry. In General Electric created a 1,500-pound exoskeleton called the Hardiman (Human Augmentation Research and Development Investigation). Unfortunately, it was too heavy and large, so the project was shelved. [8]
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In , engineers at UC Berkeley, backed by The Defense Advanced Research Projects Agency (DARPA), created a pair of robotic legs that were meant to reduce the energy used in carrying heavy loads over long distances. [9] Finally, there was a successful break into functional exoskeleton designs.
Today, robotic exoskeletons are more diversified and have undergone multiple iterations to create complex and advanced designs with various features and applications. For instance, Ekso Bionics creates exoskeletons used for neurorehabilitation, military research, and industrial uses.
There are different types and classifications of exoskeletons which depend on the body part where they are worn and how they are powered.
Exoskeleton Classification
Types of Exoskeletons
These are exoskeletons that rely on batteries and electric cable connections to work. One great example of a powered exoskeleton is the EksoNR, which uses two sets of long-lasting, rechargeable lithium-ion batteries. Powered exoskeletons are divided into static and dynamic exoskeletons.
These exoskeletons do not require electrical power in order to run. They rely on other mechanisms in order to work and are good for:
These are exoskeletons that have all the features of a powered exoskeleton but do not provide actuation. E.g., the C-brace by Ottobock.
These exoskeletons typically have all the features of a powered exoskeleton but use the input of the muscles as actuators.
Exoskeletons simulate natural gait during rehabilitation which initiates powerful brain signals that thanks to brain plasticity, can help patients recover their ability to walk. Exoskeletons also simulate natural gait by using drives in the hip and knee joints which move the wearer's legs. Exoskeletons can be used by the patient independently or with the help of a therapist. They contain a predesigned program that helps therapists control the level of speed and power based on the patient's needs. Exoskeletons can also be customized to an individual by adjusting the size.
Patients who train with exoskeletons report improved moods, morale, and mental health after just a few sessions. This can come from the ability to have conversations at eye level with other people. Exoskeletons also give hope to patients who were completely immobilized as they are able to walk again during training.
Standing in vertical positions also has benefits like better blood circulation and lung volume, which contribute to better overall health. Exoskeletons make the training more exciting as they are a far more advanced way of rehabilitation and tend to give patients confidence which can reduce depression and other mental health issues.
This is not science fiction, we promise. You see, exoskeletons normally have different types of control systems like buttons, tablets, and smart crutches, which help the patient control the amount of support they receive from the exoskeleton. The most advanced control method in the world today is a brain activity interface that helps the patients actuate the exoskeleton using their thoughts. This allows for improved neural plasticity, which may contribute to the speed of recovery. 'Hybrid Assistive Limb (HAL) works by using small sensors on the skin that detect minor electrical signals in a patient's body,' explains Brooks Rehabilitation director of clinical technology Robert McIver, 'As those signals are detected by the robot, it responds with a movement at the joint. It is the only system that I have come across where the patient's nervous system acts on an external device.' [10]
Other exoskeletons like the EksoNR have touchscreen controls that help clinicians set goals and alter assistance levels for patients of all different functional levels. Physical therapists can also easily access the medical device's database to analyze complex movement patterns and record patient progress.
All exoskeletons use different materials in their build. The most common being carbon fiber and metal. Others are made from materials like steel alloys and aluminum which are heavy and rigid. All exoskeleton materials should be strong enough to support patients when in a vertical position.
Did you know that there are different types of exoskeletons? As highlighted above, exoskeletons are divided into full-body, upper-body, and lower-body exoskeletons. Exoskeletons can also cover a specific body part like the hip, knee, elbow, and even finger. Ekso Bionics is continually iterating exoskeleton designs to create more efficient and effective solutions.
There are two types of exoskeletons; medical exoskeletons and industrial exoskeletons. Medical exoskeletons are normally used in rehabilitation to help patients regain mobility, while industrial exoskeletons are used to augment human performance. Industrial exoskeletons are meant to make work easier for the wearer. You can read up on the use of exoskeletons in construction here.
Industrial exoskeletons were first developed in the s when they were used in the military. They have since then found applications in construction, automotive, and agriculture. They are very mainstream, so much so they are considered a part of personal protective equipment (PPE) for some automobile companies like Ford.
A lot of people tend to think that exoskeletons are a 21st-century idea, but in truth, it was existent even in the 20th century. Exoskeletons were first depicted in The Master Mystery, which is a American mystery silent film.
Apart from medical and industrial applications, exoskeletons have found a new, fun application in the world of sports. As crazy as that sounds, Jonathan Tippett is pioneering an exoskeleton racing sport where racers control a 14 feet tall prosthesis and compete against other players. [11] The prosthesis relies on the leg, arm, hand, and feet movements of the user to move. It is powered by a lithium-ion battery and can run up to 20 mph. This sport is referred to as mechanical racing.
Fancy having an exosuit that makes you ten times bigger than you already are? Now you can get one. Skeletonics create 10 feet tall exosuits that can turn you into a giant. Without the use of batteries or motors, all joints and limbs, including fingers, can move with precision mechanically. They utilize kinetic energy instead of electricity to power the exoskeletons. [12]
Just when you've learned everything there is to know about exoskeletons, a new exoskeleton is developed, or a new use case is created. That's the beauty of being in the middle of a developing and fast-growing industry. At Ekso Bionics, we aim not just to be the leaders in exoskeleton technology but also to make exoskeletons that help patients regain full mobility.
We always aim to develop disruptive wearable robotics in the medical arena, and so far, we've helped thousands of patients with lower extremity disabilities take over 200 million Ekso-aided steps. We are at the forefront of shaping new devices for neurorehabilitation with FDA-cleared exoskeletons for MS, stroke, SCI, and other brain injuries. To learn more about Ekso Bionics, click here.
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