A quadruped robot appears on the cover of the latest issue of science robotics. No, it's wrong. It should be the one below. It's said that the inspiration of this robot's research and development is from the tortoise in nature. It's really a bit like that!
On February 17, 2021, the related research results were officially published in science robotics with the title of Electronics free pneumatic circuits for controlling soft legged robots, and appeared on the current cover. The author is from the Department of mechanical engineering and materials science and engineering, University of California, San Diego, USA.
Research background of robot without electronic components
Pneumatically activated soft robots have good adaptability to the environment.
At the ICRA 2017 International Conference on Robotics and automation, the Robotics Laboratory of the University of California, San Diego announced a 3D printing software quadruped robot, which the research team claims can conquer all terrain.
The robot is driven by gas, and each leg is made of three retractable inflatable rubber tubes. The four legs are connected in an X-shape, and can walk through the design of inflation or leakage.
As shown in the figure below, many robots are controlled by electromechanical components (such as valves and pumps), which are usually bulky and expensive.
Based on this, the research team designed an oscillators using soft valve.
Oscillator can be used to generate repetitive electronic signals. It is an energy conversion device that can convert DC power into AC power of a certain frequency.
Through such a ring oscillator, oscillation signals can be generated, and then the oscillation signal is generated by the pneumatic logic element in response to the input of the sensor.
The process of generating oscillatory signals is similar to that of natural organisms including quadrupeds, which use central pattern generators (CPGs) to achieve repetitive movements of limbs such as walking, flying and swimming.
Generally, this process is mediated by sensory feedback, but the structure of CPG is basically a repetitive circuit, which drives muscles to produce stable and continuous gait in order. In this case, the pneumatic muscles are driven into opposite pairs to form a diagonal (line) gait, with the diagonal legs rotating forward and backward at the same time.
This paper introduces that each leg of the robot has three degrees of freedom and needs a constant compressed air source to support the control system and drive system.
Specifically, the researchers succeeded in directing a pressure source (either a rope or a built-in carbon dioxide cartridge) to four legs through an oscillating three-way valve circuit made entirely of soft material, with three different chambers on each leg.
So, how about the principle of oscillating three-way valve circuit?
It is understood that the circuit itself is composed of three bistable pneumatic valves, which are connected by pipes to provide resistance to the flow of gas through pipes (which can be adjusted by changing the length and inner diameter of the pipe).
In one experiment, the researchers found that:
Three pneumatic memory elements (valves) are used to control the basic gait;
Through two oscillator circuits (seven valves), the movement speed can be increased by 270%.
Researchers designed a pneumatic memory element to simulate a double pole double throw switch (DPDT switch). DPDT switch has two inputs and four outputs, and each input has two corresponding outputs.
In addition, they demonstrated a control circuit that allows the robot to move in all directions between gait and respond to sensor inputs.
It is worth mentioning that although the Venus probe being developed by NASA's Jet Propulsion Laboratory is not a soft robot, it can operate in a similar way because it can not rely on traditional electronic systems for autonomous navigation or control. IEEE spectrum reports:
It has been proved that there are many smart ways to make robots complete relatively complex autonomous behaviors.
How to develop soft robots?
Generally speaking, the so-called soft robots are not made of soft materials as we think. This is because it is always a big difficulty to develop flexible energy supply and control components (such as flexible batteries and circuit boards).
And the coolest part of the robot is that it has a new way to achieve gait control.
The team said:
This research is a step towards the application of fully autonomous robot without electronic components, which has played a role in promoting the development of low-cost entertainment robots and the application of robots in extreme environments.
Even so, the development of soft robots is still relatively slow
In essence, soft robots should be safe, flexible and very cheap. These characteristics make it possible to be widely used. However, compared with robots in other fields, the development of soft robots is relatively slow. One of the reasons is that soft robots can not directly benefit from the remarkable development of computing force, sensors and actuators in the past few decades.
Undoubtedly, the development of soft robots is inseparable from multi-disciplinary progress, including materials science, robotics, biomechanics, sensing and control. With the rapid development of related disciplines in recent years, soft robots with different driving modes begin to emerge.