Right. So we have purchased our brand new servo motor. We know from our vast text books that the one key feature which separates servo motors and induction motors is that the former one has the capability to perform complex positional movements.

You want the cut to take place only for a length of 6 micron? Done.

You want to stop the motor when the ball screw has moved only 0.2 mm linearly? Done.

One who has tasted the power and precision of a servo motor would never ever again think about using an induction motor with time controls (of course if he has the budget). But what makes a servo motor so capable? How is the precision movements happening? How is the information fed back?

The one answer to all these questions is: Encoder.

This simple device has made the servo motors capable of rotating to accurate points, just how the user wants it to. And what’s an encoder?

To be brief, an encoder is just a scale. But the readings in the scale are kept subtle and is constantly fed back electronically to the controller. In rotary devices, the scale is a disc, whereas in linear system, the scale has a familiar “scaley” structure.

Let’s see how a rotary encoder looks X-rayed.

What you’re looking at, is a circular disc which we would place inside a rotary encoder. You can see that there are certain patterns printed into it. It may look like an old Mayan painting, but in fact, these are very useful in determining accurate positions. Move your finger through the circumference of that disc and stop somewhere. Now draw a line, from the place where your finger touched the disc to the centre of the disc. Now move your finger elsewhere on the circumference. Once again, draw a line to the centre. If you notice these two lines, both of them went through different patterns of dark and white areas.

Getting any ideas?

The black and white portions in the line which you drew can be said as the positional address of the point you touched, isn’t it? And as you can see, each point has a different positional address in this setting. So, the entire 360 degrees can be split into points with a different positional address. When this encoder is coupled with a motor, the black and white portions are configured to give out specific electronic signals, according to the current position of the motor shaft. Thus for every point the motor shaft turns, the encoder is capable of giving out a unique electronic feedback. This electronic feedback is in turn read by the servo motor to analyse the current position of the shaft, to which degree it has turned, and give commands to the motor to stop or move.

Simple isn’t it?

Now lets talk about linear encoders.

You see a reader head and a scale. Just like the rotary encoder, the scale which is used in a linear encoder is capable of giving out unique electronic signal for every single point in it. Thus enabling the user to understand at which point is his equipment currently at.

The only difference between a rotary encoder and a linear encoder is that in rotary system, the measurements of a rotating system is considered and in a linear system, its all straight line measurements.

If you want to make the measurement in an encoder more accurate, just invest in a higher resolution encoder. That’s just the capability of how small a measurement can be made in an encoder.

In a world where systems with precisions are the ruling factor, encoders are the best tools for a definitude measurement.

And as always,

Thanks for reading.