Transcript
Inventors and researchers have been developing robots for almost 70 years. To date, all the machines they have built — whether for factories or elsewhere — have had one thing in common: they are powered by electric motors, a technology that is already 200 years old. Even walking robots feature arms and legs that are powered by motors, not by muscles as in humans and animals.
This in part suggests why they lack the mobility and adaptability of living creatures. But now, a new muscle-powered robotic leg has been shown to be more energy efficient than a conventional one, but it can also perform high jumps and fast movements as well as detect and react to obstacles all without the need for complex sensors.
The new animal-inspired musculoskeletal robotic leg, explained recently in Nature Communications, was developed by researchers at ETH Zurich and the Max Planck Institute for Intelligent Systems. As in humans and animals, an extensor and a flexor muscle ensure that the robotic leg can move in both directions. These electro-hydraulic actuators, which the researchers call HASELs, are attached to the skeleton by tendons.
The actuators are oil-filled plastic bags, similar to those used to make ice cubes. About half of each bag is coated on either side with a black electrode made of a conductive material. As soon as a voltage is applied to the electrodes, they are attracted to each other. As one increases the voltage, the electrodes come closer and push the oil in the bag to one side, making the bag overall shorter.
Pairs of these actuators attached to a skeleton result in the same paired muscle movements as in living creatures; that is, as one muscle shortens, its counterpart lengthens. The researchers use computer code which communicates with high-voltage amplifiers to control which actuators contract, and which extend.
The researchers compared the energy efficiency of their robotic leg with that of a conventional robotic leg powered by an electric motor. Among other things, they analyzed how much energy is unnecessarily converted into heat. Typically, electric motor driven robots need heat management which requires additional heat sinks or fans for diffusing the heat to the air. The new system doesn’t require heat sinks or fans.
The new robotic leg’s ability to jump is based on its ability to lift its own weight explosively. In contrast to electric motors requiring sensors to constantly determine the angle of the robotic leg, the artificial muscle adapts to suitable position through its interaction with the environment. This is driven just by two input signals: one to bend the joint and one to extend it. Adapting to the terrain is a key aspect.
When a person lands after jumping into the air, they don’t have to think in advance about whether they should bend their knees at a 90-degree or a 70-degree angle. The same principle applies to the robotic leg’s musculoskeletal system; upon landing, the leg joint adaptively moves into a suitable angle depending on whether the surface is hard or soft. The field of robotics is making rapid progress with advanced controls and machine learning; in contrast, there has been much less progress with robotic hardware, which is equally important.
The research field of electrohydraulic actuators is still young, having emerged only around six years ago and it’s likely just getting started. Simplicity, energy efficiency, and responsiveness imply great potential. However, electro-hydraulic actuators are unlikely to be used in heavy machinery on construction sites, even though they offer specific advantages over standard electric motors. This is particularly evident in applications such as grippers, where the movements have to be highly customized depending on whether the object being gripped is, for example, a ball, an egg or a tomato.
|
