Biped Robot Design Actuated by Pneumatic Artificial Muscles

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Biped robots are becoming increasingly popular these days for their ability to jump, walk, and run. These robot designs have also become a fascinating research-hotspot for their striking similarity to human beings.

Bipedal locomotion is quite a simple task for any healthy human being but biped robots face numerous challenges. Researchers are continually experimenting with them to study and simulate human-like walking.

Today, we will take a closer look at the design and properties of biped robots. Read on to get a comprehensive overview of such robots.

#1 Zero Moment Point

Zeromoment point or ZMP is one of the most conventional approaches to achieve biped walking. Here, joint trajectories of any simplified robotic model are predetermined on the basis of zero-moment criteria to maintain a dynamic balance during locomotion. Then a position based controller, generally used for industrial robots is applied to track the trajectories.

The errors caused by environmental disturbances and model design are then eliminated by using a posture balance algorithm. Many humanoid robot designs are capable to walk and run steadily due to this high-performance trajectory tracking of the electric actuators.

However, these robots are energetically inefficient and extremely delicate against any terrain disturbance. In order to solve this problem of stilted gait and high energy consumption, McGeer proposed an alternative approach of passive dynamic walking. This is a major advancement toward natural and efficient walking.

#2 Passive Dynamic Walking

One of the most remarkable characteristics of passive dynamic walking robots is its ability to settle into a natural manner on a downhill slope through a passive interaction between inertia and gravity.However, the problem is that the walking behavior cannot be controlled since it is dominated by the fixed body dynamics.

In order to achieve this controllability, minimal actuation and control are added to these passive dynamic walking robots and thereby the quasi-passive dynamic walker robots are created.

Various quasi-passive dynamic robots can walk on any flat terrain as well as climb on small slopes and also adopt electric motors for generating precise torque. Thus they sacrifice the passiveness and compliance of joints.

#3 Pneumatic Artificial Muscle

The McKibben pneumatic artificial muscle is so far the best actuator to build a robot powered with a passive dynamic walking feature. It performs akin to a natural or biological muscle. It has a high compliance range and may provide a large force with comparatively a lightweight mechanism.

Several biped robots like Denise, Max, and Mike are developed with McKibben muscle actuators to exhibit a brisk walk on a flat floor.

In spite of some complicated characteristics of artificial muscles like time delay, hysteresis, and nonlinearity, these robot designs can walk steadily by employing a simple controller without really dealing with any complex dynamics.

Roboticists are researching on biped robots actuated by pneumatic artificial muscle depending on the musculo-skeletal architecture of human’s lower limbs. One of the significant traits of this type of biped robot is that it can incorporate both biarticular muscles that span two joints and monoarticular muscles in a flex-extensor configuration. The joint compliance of such a robot can be operated by using pressure inside the muscles that can also help in increasing energy efficiency in the robot and simulate natural motions.

Further, any collision between the ground and robotic foot also affects walking stability and thereby reduces energy efficiency during walking. Biarticular muscles ensure that work is transferred between joints by conjoining joint motions together. Walkingsimulations are also carried out for verifying any shock absorbency of various robot models.

Properties of Biped Robots

1. Distribution of DoFs

The lower limb of human beings consists of thigh, pelvis, shank, and foot, interconnected by knee, hip, and ankle joint. While simulating this in a robot design,the hip joint can be modeled with three DoFs (degrees of freedom). The knee joint possesses only one DoF around its pitch axis. And the ankle joint has two DoFs for greater flexibility. These play great roles in helping the robots maintain balance during movement.

 2. Muscle Arrangement

The muscle structure of the human legs has both biarticular and monoarticular muscles. While the former can only pool, the latter can ensure a dynamic movement. The biped robots are designed based on this architecture principle. Each leg includes eight monoarticular muscles and three biarticular ones.


As you can see, biped robot designs exhibit great flexibility and perfectly simulate the human body system. Roboticists are still working to improve their functionality and soon we can witness more efficient and versatile locomotion in the robots. From the medical field to entertainment – every domain can be benefitted from such advanced robotic models.

To learn more about biped robots, feel free to reach the experts at Custom Entertainment Solutions. Call 01.801.410.4869 today!  

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