Presented by
Pradeeshkumar P. D

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Abstract
In order to perform the task in a satisfactory way the robot must have certain humanlike senses and capabilities. These include vision and hand-eye coordination, touch and hearing. This is achieved by using sensors. The types of sensors used in robotics include vision, voice, tactile, proximity etc. proximity sensors measure the relative distance between the sensors and objects in the robot's environment. This sense keeps a robot from running into things. This paper describes the various proximity sensors employed in robots.
Introduction
Robot, once a creature of science fiction, is today a reality. It is the off-shoot of the second industrial revolution.
An industrial robot is a general purpose, programmable machine which possesses certain human like characteristics. The robot’s most functional element, its arm, together with its capability to be programmed makes it ideally suited to a variety of tasks in the field of industry, military, medicine etc. The robot can be programmed to a sequence of mechanical motions and it can repeat that motion sequence over and over until reprogrammed to perform some other job.
To carry out its task, a robot must have access to information on predetermined parameters of the environment. Sensors are used to provide this information. It must be remembered that best sensory power has been bestowed by nature in the homomorphic creatures. It is the aim of engineers to attain similar perfection for robots. In order to enable the robot to perform its tasks by understanding the environment around it, sensors provide the information like
(a) recognition data – to understand the shape, size and features of the object.
(b) orientation data – the position of the object in relation to the robot arm
co-ordinates.
© physical interaction data- to understand the intensity interaction between the
end effectors and the object.
The various types of sensors used for this purpose are
1. Vision sensors – to sense the presence of an object and its position and orientation.
2. Voice sensors - to sense the sound in environment and for programming.
3. Tactile sensors - to respond to contact forces between itself and other objects within the environment.
4. Proximity sensors- to sense when one object is close to another object.
What is a sensor?
The basic function of an electronic sensor is to measure some feature of the world, such as light, sound, or pressure and convert that measurement into an electrical signal, usually a voltage or current. Typical sensors respond to stimuli by changing their resistance, changing their current flow, or changing their voltage output. The electrical output of a given sensor can easily be converted into other electrical representations.
There are two basic types of sensors: analog and digital. The two are quite different in function, in application, and in how they are used with the Robots. An analog sensor produces a continuously varying output value over its range of measurement. For example, a particular photocell might have a resistance of 1k ohm in bright light and a resistance of 300k ohm in complete darkness. Any value between these two is possible depending on the particular light level present. Digital sensors, on the other hand, have only two states, often called "on" and "off." Perhaps the simplest example of a digital sensor is the touch switch. A typical touch switch is an open circuit (infinite resistance) when it is not pressed, and a short circuit (zero resistance) when it is depressed.
Proximity sensors
Proximity sensing is the ability of a robot to tell when it is near an object, or when something is near it. This sense keeps a robot from running into things. It can also be used to measure the distance from a robot to some object. This sensing capability can be engineered by means of optical-proximity devices, eddy current proximity detectors, acoustic sensors or other devices.
Proximity sensors currently come in four flavors:
1. inductive
operates by detecting the eddy current losses when a material enters to an electromagnetic field
2. capacitive
operates by generating an electrostatic field and detecting changes in this . . . field caused when a target approaches the sensing face.
3. ultrasonic
Ultrasonic sensors detect objects by emitting bursts of high-frequency sound . waves which reflect or “echo” from a target.
4. optical
designed to be sensitive to different wavelengths of light