What is mean by incremental encoder, absolute encoder, singleturn encoder and multiturn encoder?

Answer 1

By definition, a 'resolver' is a device that separates a position signal into its coordinate 'vectorial' components.

An 'encoder' translates a rotational motion (or position) into an electronic pulse.

Typically, if the absolute position of the shaft needs to be known while the shaft is AT REST, a resolver is the correct choice. It is also a better fit for reversing applications, due to the +/- nature of vector definition. It can be used for speed sensing, but is not normally employed as such.

If the relative position of the shaft needs to be known AT SOME POINT DURING ROTATION an encoder can be used (and probably be more cost-effective). What actually happens for the encoder is that there is a 'marker pulse', which denotes a certain shaft position relative to a 'zero' point. As the speed of rotation is computed (by counting the number of pulses generated), a rotational displacement is defined. However, there is (usually) no directional sensitivity ...

For example: a motor shaft has both an encoder and a resolver attached to it (serially - encoder to motor shaft, resolver to encoder). From a 'zero' point (i.e. the marker pulse on the encoder registers), the motor shaft is rotated through 90 degrees. The encoder will give two points - 90 clockwise or 90 counterclockwise (the smarts to figure out which is correct have to be elsewhere). The resolver will correctly define a turn of 90 in the CORRECT direction.

In today's manufacturing environments, encoders are used primarily as speed sensors and resolvers are the (normal) choice for position control. What each device manufacturer is capable of may require a choice between one and the other - for example, there are few truly digital resolvers! On the other hand, a highly accurate speed reference (several thousand pulse per rev) may require going to an encoder, regardless of the original intent.

INCREMENTAL ENCODER: will translate rotational motion into a specific electronic pulse ... which is NOT direction-specific. It is simply a value relative to another point (at which the counter was 'zeroed').
ABSOLUTE ENCODER: will translate rotational motion into an electronic pulse ... with reference to a 'zero' mark. This is not direction-specific either ... a 90 degree turn in either direction will give the same encoder value.
SINGLE-TURN ENCODER: counts everything relative to a 'zero' mark, returning its value to zero when it passes the mark. Thus every position that is exactly 360 mechanical degrees apart will have the same encoder output.
MULTI-TURN ENCODER: counts everything relative to the 'zero' mark, but has additional capacity to account for the number of times it passes the zero ... thus it can indicate a certain amount of multiples of 360 mechanical degrees as well.

Answer 2

Encoder Meaning

Answer 3

It is common to use the encoders in pairs, a low resolution encoder to provide absolute position geared to a high resolution encoder. For example a rotating antenna would have the low resolution encoder diriectly coupled to the antenna mast and have a 32:1 gearing to the high resolution encoder, making the high resolution encoder turn 32 times for every one turn of the low resolution encoder.