Artificial muscle

In this study, "pneumatic artificial muscle" is a core element.

Lei Feng learned that pneumatic artificial muscle is a kind of artificial muscle. Artificial muscle, namely electroactive polymer, is a new intelligent polymer material. It is composed of three amino acids, valine, proline and glycine, arranged in a certain order according to the biological principle. It can stretch, bend, tighten or expand through the change of internal structure under the applied electric field, which is very close to the biological muscle fiber.

Pneumatic artificial muscle, literally, is an artificial muscle driven by external compressed air for push-pull action, which has the advantages of flexibility, lightness, green and so on. This material is light (the minimum is only 10g), but it can provide great strength. It can be described as "four or two kilos".

In fact, due to the bionic weaving structure similar to biological muscle fiber and the characteristics similar to skeletal muscle, pneumatic artificial muscle has been widely used in the fields of soft bionic robot, variable stiffness hydrostatic bone and so on. In addition, these materials play an important role in medicine, robotics, military, aerospace, optics and other fields, and have great commercial potential.

As early as the 1940s, researchers began to study this field. In July 2019, MIT scientific research team also published a paper on science, introducing their new artificial muscle made of two polymer materials with different thermal expansion coefficients, high-density polyethylene and cycloolefin copolymer. Once heated, this artificial muscle can stretch freely and lift an object 650 times heavier than itself. This study also appeared on the cover of the current science.

[source of pneumatic artificial muscle Baidu Encyclopedia]

"Elephant trunk like" flexible robot

In recent years, many research teams have designed various forms of flexible robots inspired by petals, falcons, snakes, pigeons, fish, rabbits and so on. Inspired by the elephant trunk, the research team of Harbin Institute of technology designed a new type of flexible robot.

The research team pointed out that pneumatic artificial muscle movement is limited to uniaxial contraction and stretching to a certain extent, which also limits its development.

To this end, the team designed a new type of curved spiral extensible / contractile pneumatic artificial muscles (he PAMS / HC PAMs) on the basis of extensible / contractile pneumatic artificial muscles.

According to the paper, he PAMS / HC PAMS are mainly composed of end fittings, elastic tubes, braided tubes and embedded flexible frames (as shown in the figure below).

When he PAMS / HC PAMS expand, it will produce bending and rotation movement around the axis, causing spiral deformation of the actuator, similar to the bending and rotation process of elephant trunk we have seen in the zoo.

The distinction between extension and contraction mainly depends on the "weaving angle" - he PAMS when the weaving angle > 54.74 degrees (figure I below); HC PAMS when weaving angle < 54.74 degrees (Figure II below).

On this basis, the research team explored the potential application of he PAMS / HC PAMS in the field of flexible robots through an elephant trunk like high degree of freedom flexible arm. The researchers said that HC PAMS have strong output and load capacity, while he PAMS can produce more deformation.

It is worth mentioning that this study proposed a unified theoretical method, which will provide a reliable reference for other researchers - the team established a generalized bending behavior model of pneumatic artificial muscle through experiments and analysis, and studied the characteristics of axial, bending and spiral pneumatic artificial muscle under the same theoretical framework.

It is understood that axial, curved and helical pneumatic artificial muscles can be widely used in all directions, such as software classification robots, search robots, biological robots, motion assisted exoskeletons, force feedback wearable devices and so on.

Flexible robot for improving human-computer interaction

In fact, artificial muscle materials have become the frontier and hot research, which is inseparable from people's increasing attention in the field of flexible robots.

100 years ago, Karel chapek, a Czechoslovak writer, created the word "robot" in his science fiction novels based on Robota (Czech "labor, hard work") and Robotnik (polish "worker"). After 100 years, robots are no longer just rigid and cold machines. Flexible robots are entering our vision. Industrial flexible robots and biological flexible robots are its two main branches.

Lei Fengwang learned that the characteristics of flexible robots include the softness of materials, excellent environmental adaptability, strong safety and good human-computer interaction. As Wang Yu, Dean of Robotics Research Institute of Hong Kong University of science and technology and professor of mechanical and aerospace engineering, said at the 2018 World robotics conference:

Compared with rigid materials, soft materials have much better interaction. If soft materials are used to make new robots, it may open up new application fields.

However, there are still many technical problems to perfectly combine the above characteristics at the same time. At present, researchers are also looking for a breakthrough. For example, Liu Jing, a researcher at the Institute of physical and chemical technology of the Chinese Academy of Sciences and a professor at Tsinghua University, considered the application of room temperature liquid metal in the field of flexible robots; MIT researchers have used 3D printing and hydraulic drive to drive the robot.

Although the field of flexible robot is still "conceptualized" at this stage, it has a wide application prospect and will bring new changes in the future.