Biped Robots are a new version of mobile robots in comparison with conventional wheeled ones. They have more mobility than wheeled robots which enables them to walk stably in various environments: such as on rough terrain, up and down slopes, even in regions containing obstacles.
Humanoids are special types of biped robots which have more capabilities than simple bipeds. They could have more degrees of freedom which may be used in arms, head or in any other limb. The most distinguished advantage of humanoid is the Intelligence that allows him to control himself, plan his future tasks, and also have more abilities like learning, vision, speaking, hearing and touching.
Nowadays, many researches about humanoid robots are carried out which contribute as an important branch of Advanced Robotics.
In the Dynamics and Robotics Center at Isfahan Science and Technology Town, a project was defined about humanoid robots in the begging of 2003 by a Team composed of 4 undergraduate Students that in this year they could complete the project by design, manufacture and controlling a fully autonomous humanoid robot named “Persia Robot".
Here is a brief overview of the process of this project.
Simulation and Control
In this part, we first focus our study on Human Walking Pattern obtained from experiments, researches and recommended theories and by considering the important features in these patterns, extract the principle concepts of a human-like walking model, such as Inverted Pendulum Upper Body Motion , Swinging Leg Motion, Foot Landing Phenomenon, Lateral Motion and so on.
After these elementary studies, we selected one of the most human-like planar approaches and developed it to a spatial model. In this way, we simplified a humanoid trajectory to some key points and by interpolating between these key points using some smooth functions, the final trajectory was gained.
But having a walking pattern is not enough for controlling a robot and specially in this case, a Humanoid Robot. Indeed, the following specifications of biped robots remember us a forgotten subject about this pattern:
1) Naturally unstable dynamics
2) Limited foot-ground interaction
3) Discretely changing dynamics
Stability is the lost point in this pattern. Maybe, we have the most human-like trajectory but who can satisfy the robot's stability if we try to control it on this trajectory. In fact, the human trajectory which is different from man to man because of the difference in their physical parameters should be also different for a humanoid robot with a quite different body in sizes, shapes and other physical features.
For this case, we considered all stability criteria, and from two main ones: COG (Center of Gravity) and ZMP (Zero Moment Point), we selected the ZMP criterion, which includes the first one in static situations more than dynamic states and it is more usable specially for dynamically stability requirements, then by changing the parameters of the gained walking pattern, the best stable trajectories was obtained.
Now, it was the time to simulate this trajectory on a visual physical model. Modeling the robot in software and controlling the joints' trajectories on the specified paths, we could observe the stability and force analysis. Fortunately, we gained the best possible results which can be seen in the Photos & Videos Section.
Design and Manufacture
After Force Analysis it was the time to design the robot to manufacture it. At first, the actuators were selected from some small size advanced servo motors with required specifications like torque, power and speed. By designing the Articulation of the joints, adding the actuators to them, and considering the spaces for control and vision systems and batteries, the structure of the robot was complete.
After preparing the parts and assembling the robot, the platform was ready to experiment; now software was required to control the robot which was written in the parallel period of time to the designing and manufacturing of robot.
This software is written in a Visual C++ platform based application and is composed from several packages. Control, Communication, Vision, Monitoring and Intelligence are the main packages. Here you can see an illustration of some units of this software.