Robotic sensors

Types of robot sensors (Light and Sound sensors)

Robotic sensors are used to estimate robot condition, its environment and passes that signal to robot controller in order to control robot functionality.^[1]^[2]

Sensors in robots are based on the function of human sensory organs. For example, sensors are often intended to mimic the sensory functions of the eyes or skin. As such, terms like vision, tactile, and similar terms for other sensory functions are commonly used in discussion of robotic sensors. Robots, like humans, must gather extensive information about their environment in order to function effectively.

Part-Picking

In a special parts feeder, an alignment pallet is not necessarily required since an automatic system can be constructed at low cost for alignment operations such as vision sensors that perform inspection, pick bins, etc. Insertion robots can perform fitting and insertion operation of machine parts precisely with the help of different kind of sensors. Different phases' parts are attached by the robot after matching. Such a robotic system can perform tasks that are beyond a human approach.^[3]

Robot Sensation

Robot Sensation is a term that refers to sensory input allowing robots to measure the distance between objects, the presence of light, the frequency of sound, etc., depending on the type of sensors embedded in the robot.^[4] Robots can measure:

Object Proximity: Presence/absence of an object, bearing, color, distance between objects.
Physical orientation. co-ordinates of object in space.
Heat: Wavelength of infrared or ultra violet rays, temperature, magnitude, direction.
Chemicals: Robot can measure presence, identity, concentration of chemicals or reactants.
Light: Presence of light, different color, intensity of light.
Sound: Presence, frequency, intensity.^[5]

Sensor Classification

Sensors in robots are like our eyes, nose, ears, mouth, and skin. The major capabilities required by a robot are as follows:

Simple Touch: The presence or absence of an object.
Taction or Complex Touch: The presence of an object plus some information on its size and shape.
Simple Force: Measured force along a single axis.
Comples Force: Measured force along two or more axes.
Proximity: Non-contact detection of an object.
Simple Vision: Detection of edges, holes, corners, and so on.
Complex Vision: Recognition of shapes.

For motion control, potentiometers, tacho-generators, encoder, etc. are used as joint sensors, whereas strain-gauge based sensing etc., are used at the end-effector location for contact force control.

Internal sensor

Internal sensors as the name suggests are used to measure the internal state of a robot, i.e. its position, velocity, acceleration, etc. at particular instant.

Position sensors measure the position of each joint i.e., the joint angle of a robot. Different position sensors are explained next.

Encoder: Encoder is a digital optical device that converts motion into a sequence of digital pulses.
Potentiometer:Potentiometer, also referred to as simply ‘pot’，is a variable resistance device that expresses linear or angular displacements in terms of voltage.
LVDT: The linear variable differential transformer (LVDT) is one of the most used displacement transducers, particularly when high accuracy is needed. It generates an AC signal whose magnitude is related to the displacement of a moving core.
Synchros and Resolvers.

Velocity Sensors or speed sensors measure try taking consecutive position measurements at known time intervals and computing the time rate of change of the position values or directly finding it based on different principles.

References