A humanoid can be defined as something that resembles a human being and having the characteristics like opposable thump, ability to walk in upright position etc. In this century the concept of humanoids is being implemented widely in robotics and these robots are called Humanoid robots or simply HUMANOIDS.A humanoid robot is fully automated as it can adapt to its surroundings and continue with its goals.In general, humanoids have a torso with a head, two arms and two legs, that is exactly like a human. But, some of them may have only a part of body, for example from the waist up. Some of them may also have a face with eyes and mouth. Humanoids can be built to resemble male and female. Male humanoids are Androids and female are Gynoids.


      Technically speaking, the most important components of humanoids which support the working are sensors and actuators. Sensors are the devices which sense something like environmental, physical or psychological parameters like sound, temperature, light, movement etc. Actuators are just motors which help in the motion and movement of the robots.

1. SENSORS     
      Sensors can be again divided into Proprioceptive and Extroceptive.The Proprioceptive sensors are used to sense the position, orientation and speed of humanoids body, and they consists of accelerometers, tilt sensors etc.The Extroceptive sensors consist of arrays of touch receptors (tactels). They are used to provide data on what is being touched.CCD cameras are there for capturing image information and microphones and speakers are used for sound reception and production respectively.

      Actuators will perform like joints and muscles and helps to acheive effective human motion. They may be pneumatic, hydraulic, electric or ultrasonic.

      The workings of humanoids are mainly based on a concept called ZERO MOMENT POINT.
It explains the dynamic balance of humanoids during walking which requires information about the contact forces and the current and desired direction of motion. As per this theory, the pressure under supporting foot can be replaced by the appropriate reaction force acting at a certain point of the mechanism’s foot. Since the sum of all moments of active forces with respect to this point is equal to zero, it is termed as Zero Moment Point (ZMP). ZMP is a point on the walking ground surface at which the horizontal components of the resultant moment generated by active forces and moments acting on humanoid links are equal to zero. In addition to this, there are several other planning and control mechanisms which are used for self-collision detection, path planning and obstacle avoidance to allow humanoids to move in complex environments.
       Developmental psychology is employed in robotics research as a source of inspiration. Models from developmental psychology often offer behavioural decomposition and observations about task performance which may provide an outline for software architecture.This developmental approach to robot construction provides some practical benefits too. Main development exploits a gradual increase in both internal complexities to optimize the acquisition of new skills. From an external perspective, the robot’s behavior is quite rudimentary. For example, given a visual stimulus, typically by waiving an object in front of its cameras, robot is subjected to an instruction to take it and then reaches out its arms towards the target. Early reaches may be inaccurate, and often in the wrong direction, but after a few hours of practice, the accuracy improves drastically, – this is the effect of developmental psychology on humanoid.
       The main challenges before humanoid research are the following facts, imitation, behavioural responses, self correction of errors etc.An intelligent robot should be able to use imitation for the variety of purposes that humans do. Through an effective imitation mechanism social attachment, expanding the range of possible actions, establishing personal identity and discovering distinctions between self and other can be achieved. According to the data sensored by the sensors, the robot must be able to take a number of decisions to determine what actions are appropriate to imitate. The robot must determine which of these objects and events are necessary to the task at hand, which events and actions are important to the instructional process but not to the task itself and which are inconsequential. The robot must also determine to what extent each action must be imitated. The robot must also recognize the important aspects of the objects being manipulated so that the learned action will be applied to only appropriate objects of the same class.
      In future we require small, light and cheap robots that exhibit complex behaviours.Recent researches are a promise to that. But, even though technology has advanced much in the field of Humanoid robotics, there are several problems are remaining which need attention. The technological brilliance of the humanoids is required to be sharpened more and the shortcomings in the results must be considered properly. The field of Humanoid Robotics is a very promising one and there are a lot of changes needed to be brought into this technology.


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