In robotics, scientists and engineers are constantly looking for the strongest, most efficient, lowest cost, and fastest ways to enable or allow robots to carry out the necessary movements for their intended functions. This quest is a prevalent trend in the robotics industry and any development in this area is always an interesting move in the right direction.
There is a constant search for new technologies based on biomimetics, which is where robotic machines are designed specifically to mimic human movement. This is done with the intention of producing robots that will outperform their human counterparts. As productive and efficient as hydraulic pistons and electric motors are, they are limited as they possess a rigid form.
Artificial muscle technologies
Artificial muscles, which are also referred to as muscle-like actuators, are devices or materials that copy the functions of human muscle and can expand, contract, vary their stiffness, or rotate due to an external force (current, voltage, temperature, or pressure). There are three basic responses to actuation, expansion, contraction, and rotation. These can then be combined by a single device and used to create further different types of motion. For example, a material may be bent by expanding one end of the material while contracting the other. A typical pneumatic rotary or linear actuator, or a motor is not classed as an artificial muscle, because there are multiple components required for actuation to be possible.
Artificial muscles are versatile, highly flexible, and have a great power to weight ratio when compared to regular rigid actuators, because of this they have the ability to become a very disruptive new technology. They are in limited capacity at the moment, but as they have many advantages over natural muscles, it is believed they will continue to grow in popularity.
There is no direct way to compare artificial muscles to natural muscles, but there are some categories called “power criteria” in which their performance can be compared. These criteria are:
- Cycle life
- Elastic modulus
- Strain
- Strain rate
- Stress
There have been some other criterial stated by some authors of research papers, such as strain resolution and actuator density. Researchers also record data for artificial muscles in the energy density, speed, efficiency, and power categories. In 2014, the strongest artificial muscle in the world provided power that was 100 times more than a comparable natural muscle with equivalent length of fibers.
Types of artificial muscles
There are three major groups that artificial muscles can be separated into: Electric field actuation, Pneumatic actuation, and Thermal actuation. Electric field actuation is carried out by polymers called Electro-Active Polymers (EAPs). As the name suggests is possible through the application of electric fields. These have a relatively low capacity for torque and lack an standard device material, which has hindered commercialization.
Pneumatic actuation is carried out by pneumatic artificial muscles (PAMs), and these function by filling up a special pneumatic bladder with air pressurized to a specific pressure. The bladder fills and translates this motion to a contraction along the actuator’s axis.
Fishing line is the best example of thermal actuation. Artificial muscles that have been made by sewing thread and fishing line have been reported to lift and produce power 100 times more that human muscles. While also being very cheap, it has poor efficiency, and when wound up into a coil, fishing line artificial muscles contract at very similar speeds to human muscles.
Cavatappi artificial muscles
There is a progression in robotics towards more biological forms and biomimetic prosthesis, and therefore these actuators must evolve. In light of this, a new, high-performance artificial muscle technology has been developed by engineers at Northern Arizona University’s mechanical engineering department. This new technology reportedly allows more adaptability and flexibility in robots, resulting in a much more human-like motion, and improved performance in many areas. These revolutionary linear actuators are being called “cavatappi artificial muscles”, as they closely resemble the Italian pasta!
Their name is derived from their helical, coiled structure, and this structure is what gives it the ability to generate more power that similar technologies. This makes it the ideal technology for robotics and bioengineering applications, and in the first batch of testing it was proved that in the categories of power and work, the new artificial muscle technology outperformed human skeletal muscle by five and 10 times! As the technology continues to improve and progress, the performance is expected to increase as well.
What are the cavatappi artificial muscles made of? They are based on Twisted Polymer Actuators (TPAs), which was widely known as a revolutionary technology when it was first conceived due to its lightweight, powerful, but cost-effective features. However, it was very slow and inefficient, and it had to be manually heated and cooled, it is stated that their efficiency was around two percent! This new version has overcome this hurdle by employing pressurized fluid that allows it to actuate, which makes it much more likely to be widely adopted. The speed at which it can actuate is pretty much determined by how fast this pressurized fluid can be pumped into it.
The use of this pressurized fluid has resulted in a major jump in the efficiency of the actuator, jumping from two percent all the way up to 45 percent, which is an impressive number in the soft actuation field. There are numerous applications for this technology, the main candidates would be soft robotics, conventional robotic actuators (walking robots), or even assistive technologies like prostheses or exoskeletons. It is expected that this new technology will be widely used due to its low-cost, flexible, simple, efficient properties, and its ability to recover strain energy.
What do you think about this new artificial muscle technology? Do you think it will be used as much as expected, or is there something else that might challenge it? Let Engineering360 know in the comments below!
