Difference between Resolvers, Encoders, Pulse Coders and other motor and axis feed back systems.

These are the basic types of ways positional feedback can be achieved. There are many different types and configurations today, all of which stem back from the resolver. Here is a general description and understanding of the technologies.

What is a Resolver?

This rotary positioning device is an analog sensor which has been used for many years in military applications. Resolvers were engineered to be reliable in the harshest conditions. Resistance to heat, dust, humidity, oil and extreme pounding and vibration makes this device outperform encoders and pulse coders. In typical applications the resolver transfers data to a PLC and is then interpreted to perform various functions.

What is an Encoder?

This is a digital device which contains a glass scale. This glass scale contains evenly spaced divisions in which a light passes through the glass .The encoder generally contains 3 sensing cells. One for home position (Z channel) and two for incremental position (A+B channel). Encoders also contain a higher resolution and greater accuracy then resolvers. However, they are much less tolerable to shock and higher temperatures above 100 degrees C.

What is a Pulse Coders?

A pulse coder is very similar to an encoder in that it detects positional feedback. Pulse coders, however; also track the velocity feedback or rotational speed of the encoder.

What is a Scale feedback system?

A typical scale contains a scanner head, a glass metal scale, or disc of some kind. Linear glass scales are probably the most common and widely used in the industry. Some horizontal machine tools also contain a rotary scale on the table rotation axis. The scale generally has to be kept clean and often times has an air purge attached to keep debris out. It has a reader moving on it linearly with a photocell and three receiving cells, exactly the same as the encoder. There are many home pulses throughout the scale. Many times a unit inside the scale can be moved to assign a home position to the axis, but is not always used.