Industrial & Medical Technology

Bipedal robots are not even close

28 September 2020
Source: AlienCat/Adobe

Industrial automation has made major strides, but not quite to the level of science fiction technology in "Star Wars" or "I, Robot," where robots helping their humans with both mundane and superhuman tasks alike.

This is in part because most buildings, facilities and infrastructure have been custom designed for human anatomy, and bipedal robots are difficult to develop, expensive and limited in use – so far.

Walking with two legs is not a natural process for mammals. Even for humans, it developed because of evolutionary need to be able to see great distances in search of prey or to be aware of predators in the massive grassland some four to seven million years ago. And since then humans have been making changes to walking patterns (gait) to suit current needs.

Nonetheless, walking is still a complex process – something akin to long-distance, controlled, forward falling. Human stance is an example of an inverted pendulum model which makes it harder to stabilize in upright position. Walking can be typically divided in two phases: single support phase (open kinematic chain) and double support phase (closed loop kinematic chain) alternating between swinging and supporting leg. The number of articulations in the lower leg such as hip motion, knee motion, ankle motion as well as support from the toes is absolutely critical to walking. Perhaps it is one of the reasons why human babies take so much time to learn to walk as compared to all the other mammals.

To expect robots to learn what we have achieved because of millions of years of evolution is impossible, but since the turn of last century there have been huge strides (figuratively) in every possible direction.

Self-driving cars evolved from concept to reality, but there is not a single robot that has done the same. Current bipedal robots are far advanced from the passive dynamic walkers developed by McGeer in the late 1980s and early 1990s, which used slope and gravity for motion without a power source, but effectively reduce its operation to laboratory settings only. Then we had articulated robots with actuation at joints and huge battery pack as the power source, and one of the very first that we saw was Honda ASIMO (Advanced Step in Innovation Mobility) in the early 2000s. It was a small 4 ft tall humanoid robot capable of slow walking without any external support. Since then it had several upgrades making it possible for ASIMO to climb stairs, run, hop and even dance, but it is still far from being useful to humans for everyday tasks.

Today, more complex and advanced robots like Boston Dynamics Atlas can run on uneven surfaces and even can get themselves up after falling, while carrying a payload of 25 lb. And now, newer versions of Atlas can even do a gymnastics routine. So what is stopping robots from becoming ubiquitous?

For starters, the complexity of a walking motion combined with different terrains that it would encounter means that a robot should modify its gait accordingly to achieve stability, be it on gravel, a hillside or staircase. The need of active actuation at each articulating joint (hip, knee, ankle and toes) means the choice of placing a servo motor at each joint, making it bulky, or to complex control systems using pneumatic articulated muscles or serial elastic actuators. Also, the actuation requires power, which must be provided by a dense battery that supplies good power yet is low in weights. And on top of it all so far, consider the cameras, sensors and computers, which would be even more complex than self-driving cars, so as the robot can safely navigate through areas that include humans.

In a nutshell, to make bipedal robots a reality, two key technologies have not matured enough yet. Bipedal robots need advances in battery technology and development of intelligent algorithms to accurately predict and respond to foot positioning and changes. Once these have successfully been achieved, it at least makes the legs of the robot mobile – then it needs all the above-the-waist sensing technologies. And then it needs to be affordable.

An interactive artificially intelligent system on top of biped would be a great virtual assistant, receptionist or guide for tours, while suitable actuators with significant weight-lifting capacity would be useful in construction, mining or at hazardous places. Looking at the advances made in last 20 years it would be possible for us to see a robot in critical applications, but it would take a long time for robots to be our household companions.

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