A humanoid robot is a robot with its body shape built to resemble the human body. The design may be for functional purposes, such as interacting with human tools and environments, for experimental purposes, such as the study of bipedal locomotion, or for other purposes. In general, humanoid robots have a torso, a head, two arms, and two legs, though some forms of humanoid robots may model only part of the body, for example, from the waist up. Some humanoid robots also have heads designed to replicate human facial features such as eyes and mouths. Androids are humanoid robots built to aesthetically resemble humans. The main purpose of having humanoid robots: The humanoid robots are not designed for working; instead they have been designated to behave safely amongst human beings and extent the human capability to a range of environments and tasks. Humanoid robotics is not yet a well-known field today, but it is a fundamental instinct driving collective effort that cut across various regulations. Computer, mechanical and electrical engineers, biologists, psychologists, physicists, cognitive scientists, philosophers, linguists and artificial intelligence are all combined for the contribution and claiming for the diversification of different humanoid projects all through the world. Inexorably, there are quite a few projects that choose to put emphasis on the mechanical function and form of the body of the humanoid robot while there may be other projects that choose to emphasize the software for the animation of these humanoid robotic bodies. The Features of a Humanoid Robots: Features are basically much concerned for the development of useful applications that are made use of commercially in the entertainment and service industry. Many a times, there may be deeply methodological and ideological differences. There is basically no easy way to describe a humanoid robot, just as it is to define a human being. One will only understand what the robot is on seeing it but will still have difficulties in penning it down on a piece of paper. The body is physically constituted to be very crucial. And it is not astonishing, that most of the times people opt for humanoid robots as a robot with two arms, two legs and a head like that of humans. Inopportunely, this definition does not completely explain the functionality and capability of these robots to receive process and respond to information. In addition, there are several human robotic projects that spend almost all their bulk efforts on one portion of the body, which can be the legs, arms or head. Instead of differentiating these humanoid robots by their physical appearances, we must identify them with the complementary researches that have taken place and have managed to stand out as distinctive emphasis. Sensors For a humanoid robot to safely walk in unknown environments, various sensors are used to identify the surface condition and recognize any obstacles. The humanoid robot is not fixed on the surface and the base/orientation of the kinematics change while it is walking. Therefore, if the foot contact changes from the estimated due to the unknown surface condition, the kinematics results are not correct.
The robot may not be able to perform the motion commands based on the incorrect surface condition. Some robots have built-in range sensors but it’s difficult to accurately model the surface from the sensor readings because the movement of the robot should be considered, and the robot localization should have zero error for correct interpretation of the sensor readings. In this paper, three infrared range sensors are used to perceive the floor state. Covariance analysis is incorporated to consider the uncertainties.
The accelerometer and gyro sensor are also used to detect the moment a foot hits the surface. This information provides correction to the motion planner and robot kinematics when the environment is not modeled correctly. Proprioceptive sensors Proprioceptive sensors sense the position, the orientation and the speed of the humanoid’s body and joints. In human beings the otoliths and semi-circular canals (in the inner ear) are used to maintain balance and orientation. In addition, humans use their own proprioceptive sensors (e.g. touch, muscle extension, limb position) to help with their orientation. Humanoid robots use accelerometers to measure the acceleration, from which velocity can be calculated by integration; tilt sensors to measure inclination; force sensors placed in robot’s hands and feet to measure contact force with environment; position sensors, that indicate the actual position of the robot (from which the velocity can be calculated by derivation) or even speed sensors. Exteroceptive sensors An artificial hand holding a lightbulb Arrays of tactless can be used to provide data on what has been touched. The Shadow Hand uses an array of 34 tactless arranged beneath its polyurethane skin on each fingertip. Tactile sensors also provide information about forces and torques transferred between the robot and other objects.
Vision refers to processing data from any modality which uses the electromagnetic spectrum to produce an image. In humanoid robots it is used to recognize objects and determine their properties. Vision sensors work most similarly to the eyes of human beings. Most humanoid robots use CCD cameras as vision sensors.
Sound sensors allow humanoid robots to hear speech and environmental sounds and perform as the ears of the human being. Microphones are usually used for this task.
Actuators
Actuators are the motors responsible for motion in the robot.
Humanoid robots are constructed in such a way that they mimic the human body, so they use actuators that perform like muscles and joints, though with a different structure. To achieve the same effect as human motion, humanoid robots use mainly rotary actuators. They can be either electric, pneumatic, hydraulic, piezoelectric or ultrasonic.
Hydraulic and electric actuators have a very rigid behavior and can only be made to act in a compliant manner using relatively complex feedback control strategies. While electric coreless motor actuators are better suited for high speed and low load applications, hydraulic ones operate well at low speed and high load applications.
Humanoid robots do not yet have some features of the human body. They include structures with variable flexibility, which provide safety (to the robot itself and to the people), and redundancy of movements, i.e. more degrees of freedom and therefore wide task availability. Although these characteristics are desirable to humanoid robots, they will bring more complexity and new problems to planning and control. The field of whole-body control deals with these issues and addresses the proper coordination of numerous degrees of freedom, e.g. to realize several control tasks simultaneously while following a given order of priority.
