POSITION SENSOR :optical encoder

IN ROBOTICS THERE ARE TWO TYPES OF SENSOR

1.Internal state sensor

2.external state  sensor

Internal state sensor

 

internal state sensors are the sensors (optical encoder) which tells  us about the basic movement of the robots.basic movement like velocity, acceleration, position  etc. if their is a controller. first i want to tell you about the controller. what is controller ?.

controller is the cpu(central processing unit) on chip which make the system useful for a specific task .in the controller basically the desired signal is compared with the actual signal(measured).this difference between the desired and actual signal will give us the error. the controller mainly works on the  error.

this error is then amplified by an amplifier which can actually drive the motor or any robot.after the actual response of the robot we measure it with the help of sensor.sensor give us the actual or measured signal which is again feed to the controller.
this make a close loop which is known as closed loop system.

External state sensor

External state sensors are the sensors  which can communicate or interact  with the environment. they are likely touch sensor,  vision , smell, slip ,feel, forces etc.these sensors are more important to make the robot more intelligent.

 

ABSOLUTE OPTICAL ENCODER
Optical encoders are the sensors which converts the posotion and rotation motion into the electrical pulse.optical encoder are useful and reliable because they have no any physical contact.in potentiometer there is contact between wiper and resistive element which may produce unnecessary noise or vibration .optical encoder are used to detect the position of  shaft .

in optical encoder we have a disk and over the disk  their are some diodes which will emit light  and also putting some sensor(photodetectors). over that disk , sensors(photodetectors ) are provided which receive light form the light source.we have a kind of coding disk .the disk have opaque holes and also have some clear sections.

There are two types of optical encoder
1.Rotary Optical  Encoder
2.Linear Optical  Encoder

images POSITION SENSOR :optical encoder

WORKING OF  ABSOLUTE OPTICAL ENCODER
From the above schematic we can easily understand  that the there is disk whose angle has to be measured. the potodetectors( that are situated in the left side of the disk) are used to detect the photons of light whch is comming from the led light source(light source is situated in the right side of the disk).this whole assembly(photodetector and light source means they are not rotates with disk only disk  rotates) is fixed .AS you can easily see that disk consist of some alternating pattern (opaque or non -opaque)   on it .this is also known as coding  .

now as the disk  starts to rotate then the pattern or coding  track also flow with it. the light source continuously emits the photon of light and these  photon of light falls on the disk and due to the coding track some of the photon  pass through the disk and received by the photodetector.but some of  the photo of light does not   pass through the disk and get reflected back.the photon that received by the photodetector generates a electrical signalsor electrical pulses.
these electrical signals then converted into the digital signals and according to these signals the binary and gray
code is generated which tells us the actual position of the shaft.

LINEAR  ABSOLUTE OPTICAL ENCODER
The linear type of optical encoder are similar as the rotary type of optical encoders.
instead  of rotary track code they have linear track code.working principle  is similar as the rotary type.

 

 

 

 

 

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