What Is an Incremental Encoder? How Motors Track Position and Movement.

What Is an Incremental Encoder?

An incremental encoder is a sensor that produces electrical signals representing changes in position as a shaft rotates or a component moves.

Unlike an absolute encoder, which reports a position value directly, an incremental encoder typically requires a controller to count movement from a known reference.

Incremental encoders are widely used in motors, conveyors, industrial equipment, and robotic systems.

For example, a mobile robot can use incremental encoders on its wheels to estimate how far it has traveled.

Key Takeaways

• Incremental encoders generate pulses or signals representing changes in position.
• Controllers can use these signals to estimate movement, direction, and speed.
• Conventional incremental systems usually need a known reference or a suitable retained count to recover position after losing power.

How Does an Incremental Encoder Work?

Imagine an encoder attached to a rotating motor shaft.

As the shaft turns, the encoder generates electrical pulses.

The number of pulses corresponds to the amount of rotation.

A controller counts these pulses to estimate how far the shaft has moved.

For example, an encoder producing 1,000 pulses per revolution generates 500 pulse cycles during half a revolution.

Depending on the decoding method, the controller may count additional transitions within those cycles.

By examining how quickly pulses arrive, the controller can also estimate rotational speed.

What Are Channels A, B, and Z?

Many incremental rotary encoders provide three signal channels.

Channel A: Produces pulses associated with shaft movement.

Channel B: Produces pulses shifted relative to channel A, allowing the controller to determine rotation direction.

Channel Z: Provides an index pulse, commonly once per revolution, that can help establish a reference position.

The relationship between channels A and B is called quadrature encoding.

The controller determines direction by observing which signal leads the other.

Not every incremental encoder uses the same interface or channel arrangement.

Incremental vs. Absolute Encoder

An incremental encoder reports changes in position.

An absolute encoder reports a position value within its supported measurement range.

Consider a robot joint that loses power while positioned halfway through its travel.

An absolute encoder may allow the controller to identify the joint's position immediately after startup.

A conventional incremental encoder does not automatically retain the accumulated position count.

The robot may therefore need a homing procedure or another reference.

Some incremental systems use external memory, battery backup, or other mechanisms to preserve position information.

What Is Encoder Resolution?

Encoder resolution describes how finely movement can be represented.

A rotary encoder may be specified in pulses per revolution, or PPR.

The effective count resolution can differ depending on how the controller interprets signal transitions.

For example, quadrature decoding can count multiple transitions per pulse cycle.

Higher resolution provides more detailed movement information, but it does not automatically guarantee higher measurement accuracy.

Frequently Asked Questions

Can incremental encoders measure speed?

Yes. Controllers can calculate speed from pulse frequency or changes in position over time.

Are incremental encoders cheaper than absolute encoders?

They are often simpler and can be less expensive, but actual prices depend on performance, interface, and environmental requirements.

The Bottom Line

Incremental encoders provide movement feedback by generating signals that controllers count. They are useful for motor control and odometry, although reliable position tracking depends on maintaining or establishing a reference.