What Is The Difference Between Incremental And Absolute Encoders?
Key Takeaway
The main difference between incremental and absolute encoders is how they track and retain position. Incremental encoders provide relative position information by generating pulses for each movement, but they lose track of position after a power loss, requiring recalibration. On the other hand, absolute encoders assign a unique value to each position, allowing them to retain position data even after power is turned off.
Absolute encoders are ideal for applications where continuous position tracking is critical, such as robotics and industrial automation, while incremental encoders are suitable for tasks that prioritize speed measurement and relative positioning at a lower cost. The choice depends on your need for accuracy, reliability, and whether position retention during power loss is essential.
Key Functional Differences Between Incremental and Absolute Encoders
The primary difference between incremental and absolute encoders is how they track position. Incremental encoders measure relative position by counting pulses from a reference point, while absolute encoders provide a unique position value for every location, ensuring continuous position tracking even after a power loss.
Incremental Encoders: These encoders track the position by generating pulses as the object moves. The system counts these pulses to determine the position and direction of movement. However, if the system is powered off, the encoder loses its position data and needs to reset or recalibrate to a reference point on power restoration.
Absolute Encoders: Unlike incremental encoders, absolute encoders provide a unique digital code for every position. Even if the system loses power, the encoder retains its exact position, eliminating the need for recalibration. Each position has its own specific value, allowing the control system to immediately know the current position upon startup.
These functional differences make absolute encoders ideal for applications requiring continuous, accurate position tracking, while incremental encoders are suitable for scenarios where relative movement tracking is sufficient.
Signal Generation in Incremental vs. Absolute Encoders
Signal generation is another key difference between the two encoder types. Incremental and absolute encoders generate position data in distinct ways, impacting their applications and performance.
Incremental Encoders: These encoders generate pulses as the encoder shaft or object moves. For each movement, the encoder produces a set number of pulses, which the control system counts to determine how far the object has traveled. Quadrature encoders use two pulse channels, A and B, which are 90 degrees out of phase, allowing the system to also detect the direction of movement. Additionally, some incremental encoders have a Z channel that sends a pulse once per revolution to mark a reference point.
Absolute Encoders: In contrast, absolute encoders output a unique digital value for each position. This value could be encoded in binary, gray code, or another format. The system reads this value directly to determine the exact position, with no need to count pulses. For multi-turn absolute encoders, additional electronics track the number of complete rotations, providing both position within a single turn and the total number of turns.
The choice between pulse-based and value-based signal generation is a significant factor when selecting an encoder, as it determines whether relative or absolute position tracking is required for a given application.
Applications Where Absolute Encoders Excel Over Incremental
Absolute encoders are better suited to certain applications due to their ability to provide continuous, exact position data. Some key areas where absolute encoders excel include:
Robotics: In robotic arms and systems, absolute encoders ensure that the exact position of joints and end-effectors is known at all times. This continuous feedback is essential for complex tasks like assembly, where high precision is required.
Aerospace and Aviation: Absolute encoders are used in flight control systems and navigation equipment, where position data must be maintained even after power interruptions. Safety and reliability are critical in this field, making absolute encoders a must.
Medical Devices: In medical applications like surgical robots or imaging equipment, where precision and reliability are vital, absolute encoders ensure that devices can return to their exact position after any interruption, reducing errors and improving patient outcomes.
CNC Machines: In CNC machining, absolute encoders provide precise control over the position of cutting tools, ensuring accurate machining operations. The ability to retain position data during power loss helps avoid the need for recalibration, improving efficiency.
In applications where position data retention and immediate accuracy are crucial, absolute encoders are the preferred choice.
When to Choose an Incremental Encoder Over an Absolute Encoder
While absolute encoders offer clear advantages in some applications, incremental encoders still hold significant value due to their simplicity and cost-effectiveness. Here are some scenarios where incremental encoders are preferred:
Cost-Sensitive Applications: Incremental encoders are generally more affordable than absolute encoders. In applications where cost is a primary concern, and continuous position tracking is not essential, incremental encoders are a better choice. For example, in simple conveyor systems, the relative movement is often sufficient to track position.
Speed and Frequency Monitoring: Incremental encoders are widely used in applications that require speed and frequency monitoring, such as motor control systems. These encoders provide pulse data that allows the system to measure speed accurately in real-time.
Applications with a Known Reference Point: In systems where the machine can easily return to a reference point at startup, such as in printing presses or basic industrial automation, incremental encoders provide reliable performance without the need for absolute position tracking.
Short Power Cycles or Non-Critical Positioning: For applications where short-term power cycles are not an issue, or exact position tracking is not critical after power loss, incremental encoders provide effective and simple solutions.
Choosing between incremental and absolute encoders depends on the specific precision and position retention requirements of the application.
Understanding the Cost and Performance Trade-offs
When selecting between incremental and absolute encoders, understanding the cost and performance trade-offs is essential:
Cost Considerations: Incremental encoders are typically less expensive than absolute encoders. This makes them ideal for applications where budget constraints are a key concern, and where recalibration after a power loss is acceptable.
Performance and Accuracy: Absolute encoders offer higher accuracy by providing continuous position feedback, even in the event of a power loss. This ensures that the system can restart from the exact position without recalibration, improving performance in high-precision environments.
Complexity and Maintenance: Absolute encoders can be more complex to install and maintain due to their multi-turn capabilities and the need for extra electronics to store rotational data. Incremental encoders, on the other hand, are simpler and easier to integrate but require periodic recalibration or homing procedures.
Long-Term Reliability: For applications that need long-term reliability and minimal downtime, the investment in absolute encoders may be worthwhile, as they reduce maintenance efforts and downtime due to recalibration after power cycles. Incremental encoders, while simpler, may require more frequent maintenance in applications with frequent power interruptions.
By weighing these trade-offs, businesses can select the encoder type that best meets their operational needs and budget constraints.
Conclusion
The primary distinction between incremental and absolute encoders lies in how they track position data. While incremental encoders rely on counting pulses from a reference point and lose position data after a power loss, absolute encoders provide continuous position tracking, retaining position data even during power outages. Each type has its specific advantages, with incremental encoders being more cost-effective and simpler, while absolute encoders excel in applications requiring high precision and reliability in position feedback. The decision to choose one over the other depends on the specific requirements of the application, such as the need for continuous position feedback, the operational environment, and budget considerations.