Difference Between Absolute and Incremental Encoders

The encoding principle is a common method of categorizing encoders. The detection of angular and linear motion is a critical function in the electronics factory’s machine control. The microcomputers in these devices often require the position, direction, and rotation speed of the shaft or shaft and must convert this information into digital form. 

Absolute vs Incremental Encoders

The main difference between Absolute and Incremental Encoders is comparable to that between a stopwatch and a clock. Because a stopwatch measures the amount of time that passes between its start and stop, you can read the time by adding the value of the elapsed time to the current time. A clock, on the other hand, displays the current time within a 24-hour period.

Absolute and Incremental Encoders

At each point of rotation, an absolute encoder delivers a unique position value or data word that represents the encoder’s absolute position. The absolute encoder can provide you with the exact position of the rotating axis that it monitors from the moment it is turned on. It accomplishes this by reading a unique code from an optical disc that uses an optical, magnetic or capacitive sensor to rotate with an axis.

An incremental encoder is a type of encoder that translates rotational movement or rotor position into an analogue or digital code in order to determine position or motion. One of the most common types of rotary encoders is an incremental encoder. Because there are few sensors involved, incremental encoders provide great speed and distance feedback, and the systems are both simple and inexpensive. Because an incremental encoder can only provide change information, it needs a reference device to calculate motion.

Comparison Table Between Absolute and Incremental Encoders

Parameters of Comparison Absolute Encoders Incremental Encoders
BasicsAn absolute encoder has a special identifier for each turbine shaft that specifies the encoder’s absolute position.An incremental encoder produces an output signal every time the shaft turns a specific angle, with the number of generated pulses corresponding to the shaft’s angular position.
Operating PrincipleAn absolute encoder is made out of a data type disc that is positioned on the axis and spins with it. An incremental encoder produces an output signal for each increase of angular position of the shaft, which is calculated by measuring the output strokes recognize.
Cost EfficiencyMore complex, more costly. Less Complex, less expensive.
Works as a Stopwatch Clock
StabilityAbsolute encoders have the potential to provide higher performance, more precise output, and reduced total costs.An incremental encoder must be switched on at all times during the device’s operation.

What are Absolute Encoders?

Each axis position in an absolute encoder is assigned a different code that specifies the encoder’s absolute position. It immediately generates a digital output representing the absolute displacement. When the system is turned on, the value of the actual position is calculated right away. Since the measured value is obtained directly from the graduation pattern, an absolute encoder does not need a counter.

It directly outputs a digital signal that corresponds to the current position. A dedicated LED pair encodes each bit point separately. Each code denotes the shaft’s absolute angular location as it rotates. An absolute encoder’s disc employs a Gray code, in which one bit is changed at a time, reducing encoder communication mistakes. The resolution is expressed in bits, which correspond to the number of distinct data words for each revolution.

Absolute encoders can be used in single-turn and multi-turn configurations. The output of the single-turn encoder repeats every rotation and provides position data for a complete 360° rotation of the shaft. Multi-turn encoders, like only one encoders, offer position data for numerous turns, but they also have a turn counter that counts the number of rotations.

What are Incremental Encoders?

The angular position of the shaft is converted into digital or pulse signals via an incremental encoder, which is an electro-mechanical device. It produces a fixed number of cycles every revolution, one for each step of the rebellion. It can only measure relative position changes, not absolute position changes. Consequently, it is unable to identify the position of a known reference.

The shaft’s angular location determines how many pulses are generated. When a velocity or a velocity and direction combination is required, incremental encoders are utilized. When the device is turned on or reset, it starts counting from zero and creates an output signal for each movement of the shaft. The incremental encoder generates a pulse for each incremental step in the rotation.

Despite the fact that incremental encoders do not produce absolute positions, they could provide a good degree of precision at a low cost. The tachometer encoder generates a short pulse whose frequency determines the speed of movement. This pulse uses an incremental encoder with a single code track. The single-channel encoder’s output, on the other hand, does not indicate the direction.

Main Differences Absolute and Incremental Encoders

  1. An absolute encoder has a special identifier for each turbine shaft that specifies the encoder’s absolute position, whereas an incremental encoder produces an output signal every time the shaft turns a specific angle, with the number of generated pulses corresponding to the shaft’s angular position. Only the change in position, not the absolute position, can be measured using an incremental encoder.
  2. An absolute encoder is made out of a data type disc that is positioned on the axis and spins with it. As the desired resolution rises, so does the number of channels. In contrast, an incremental encoder produces an output signal for each increase of angular position of the shaft, which is calculated by measuring the output strokes recognized.
  3. Because the encoder disk’s code matrix is more complex and more light sensors are required, absolute encoders are often twice as expensive as incremental encoders. Incremental encoders, on the other hand, are less sophisticated than absolute encoders and, as a result, are usually less expensive.
  4. An absolute encoder acts as a stopwatch, and an Incremental encoder acts as a clock.
  5. Absolute encoders have the potential to provide higher performance, more precise output, and reduced total costs. An incremental encoder, on the other hand, must be switched on at all times during the device’s operation.

Conclusion

In short, an incremental encoder must always be provided throughout the performance process. In the event of a power outage, the measurement must be re-initialized, or the system will generate an error.

On the other hand, the absolute encoder only needs power when sampling, and because it can provide absolute angle readings, each measurement is independent of the accuracy of the previous measurement. However, because an absolute encoder’s disc code matrix is more complex, it often costs half more than an incremental encoder, which is less complicated and hence less costly.

References

  1. https://www.osapublishing.org/abstract.cfm?uri=ao-35-1-201
  2. https://ieeexplore.ieee.org/abstract/document/4913270/
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