ArtsAutosBooksBusinessEducationEntertainmentFamilyFashionFoodGamesGenderHealthHolidaysHomeHubPagesPersonal FinancePetsPoliticsReligionSportsTechnologyTravel

Reading Motor Speed Using Optical Encoder - Electrical Engineering

Updated on February 14, 2013

________________________________________________________________

Navigation

This is Stage 5 of the design for a 50 V, 10 A DC motor drive. You can follow the link(s) below to the previous article(s) that this hub builds up on. Alternatively, you can navigate to hubs for the stages ahead.

________________________________________________________________

For both position and speed control, we require a medium that translates the speed of the motor or its revolutions into digital signals that the microcontroller can read. The device for our purpose is the optical encoder.

Optical encoders are devices that convert mechanical position into a representative electrical signal by means of patterned disk or scale, a light source and photo-sensitive elements. The output(s) and layout of its disk of one such incremental encoder is show in the figure below:

An incremental encoder disk and its output(s).
An incremental encoder disk and its output(s).

Notice how the encoder delivers not one but two output signals. One of the outputs is a simple delayed version of the first output. This is quite interesting and helpful for our purposes. For example, if our encoder gives 10 pulses per revolution, we can double the counts by a simple XOR gate whose inputs would be the two signals from the encoder. Hence we shall get 20 pulses per revolution and can gain more resolution in the control of motor and precision reading of the motor speed.

The encoder of our concern delivers 500 pulses per revolution of the motor. In our code, the XOR function has not been implemented and counts for 1500 rpm are 40.

It should be made clear that the microcontroller deals only in counts received and does not calculate the speed of the motor using the counts. It merely compares the counts received to the reference value and increases or decreases the duty-cycle accordingly. This is why we are interested in increasing the counts of the encoder as they give us a higher resolution of speed control.

________________________________________________________________

Navigation

You can follow the link(s) below to the previous article(s) that this hub builds up on. Alternatively, you can navigate to hubs for the stages ahead.

________________________________________________________________

If you have any queries or want help on your project / design, fire away and I shall get back to you as soon as possible with as much help as I can provide.

Your comments are most appreciated and would be an enlightening beacon for my hubs to come.

Comments

    0 of 8192 characters used
    Post Comment

    • profile image

      zahid 3 years ago

      sir i want to know how we calculate poles of motor when we get an ampty stator pitch no. of turn and no.of wire thanks my email zanjum97@yahoo.com