When designing or upgrading a system that requires precise position feedback, you might come across the terms absolute rotary encoders and incremental rotary encoders. Both of these are essential components used in many industries, including robotics, automation, and machinery, to provide feedback on rotational position. But which one is the best for your system? Understanding their differences will help you choose the right one for your needs.
In this article, we’ll break down both types of rotary encoders, compare their features, and help you decide which one suits your project.
What Are Rotary Encoders?
Before we dive into the details, let’s first understand what rotary encoders are. A rotary encoder is a device that converts the rotational position of a shaft or axle into an electrical signal. This signal is then used by machines and controllers to determine the exact position of a part or motor. These encoders can either give you information about the position of the motor shaft (incremental) or provide the actual position in a continuous manner (absolute).
There are two main types of rotary encoders: absolute rotary encoders and incremental rotary encoders. Both have their strengths and weaknesses, so it’s important to choose the right one for your system.
1. Absolute Rotary Encoders: An Overview
What is an Absolute Rotary Encoder?
An absolute rotary encoder provides a unique position value for each distinct angle of the shaft. This means that when the system is powered off and back on, it will still know its exact position. In simpler terms, it gives you a “memory” of the position even after a power failure.
How Does It Work?
Absolute encoders work by using a code disk (or code ring) with a series of patterns, often binary or gray code, to represent different shaft positions. Each position on the disk has a unique code, which the encoder reads and sends to the system. This is how absolute encoders provide an exact position, regardless of whether the system has been turned off or not.
Advantages of Absolute Rotary Encoders
- No Need for Homing: With absolute encoders, the system always knows its exact position, even after a power outage. There’s no need to reinitialize or perform a “homing” operation, which saves time and ensures smooth operation.
- High Precision: Absolute encoders offer very precise position feedback. This makes them ideal for applications that require exact positioning, such as robotics, CNC machines, and aerospace.
- Error Reduction: Since the encoder gives a unique value for each position, there’s less chance of errors during operation, especially in complex systems.
Disadvantages of Absolute Rotary Encoders
- Higher Cost: Absolute encoders are generally more expensive than incremental encoders because of the complex technology involved in reading unique position codes.
- Complexity: The internal workings of absolute encoders are more complicated, which might make them harder to maintain or repair.
2. Incremental Rotary Encoders: An Overview
What is an Incremental Rotary Encoder?
An incremental rotary encoder works differently. Instead of providing an exact position, it gives feedback based on changes in the position from a reference point. This means it counts the number of steps or increments the shaft has moved from a starting point. When you turn on the system, the encoder only knows the number of rotations or changes in position since the last reset.
How Does It Work?
Incremental encoders use a code disk with evenly spaced patterns or marks, typically optical or magnetic, to detect movement. Each time the encoder passes one of these marks, it sends a signal to the controller, which counts the increments. The system only knows the relative position from the last known reference.
Advantages of Incremental Rotary Encoders
- Cost-Effective: Incremental encoders are generally cheaper than absolute encoders, making them a popular choice for many basic applications.
- Simplicity: Incremental encoders are simpler to design, maintain, and repair due to their basic functionality.
- High Speed: They work well in high-speed applications, as they can quickly send pulses to the system to indicate movement.
Disadvantages of Incremental Rotary Encoders
- Power Loss Issues: One of the main drawbacks of incremental encoders is that they lose their position when power is lost. After a power cycle, the system will need to perform a homing routine to reset the position.
- Less Precision: While incremental encoders provide good feedback on movement, they don’t offer the same level of absolute position accuracy as absolute encoders.
3. Key Differences Between Absolute and Incremental Rotary Encoders
Now that we understand both types of rotary encoders, let’s compare their key differences.
| Feature | Absolute Rotary Encoder | Incremental Rotary Encoder |
|---|---|---|
| Position Feedback | Provides absolute position at all times | Provides relative position (counts changes) |
| Power Loss | Retains position after power loss | Loses position after power loss |
| Cost | More expensive | More affordable |
| Precision | Very precise, ideal for exact positioning | Good for general movement detection |
| Complexity | More complex, requires more maintenance | Simpler and easier to maintain |
| Speed | Slower compared to incremental encoders | High-speed operations are supported |
4. Which Rotary Encoder Is Right for Your System?
Choosing between absolute and incremental rotary encoders depends largely on your system’s specific needs. Here are a few scenarios to consider when deciding which one to use:
When to Choose an Absolute Rotary Encoder
- Critical Positioning: If your system requires highly precise position feedback, such as in robotics or CNC machines, an absolute rotary encoder is the better choice.
- Power Loss is a Concern: If your system needs to operate without losing position information during power outages, an absolute encoder is ideal, as it doesn’t require resetting after power loss.
- Complex Systems: For systems that need detailed feedback and can handle the higher cost, absolute encoders are usually the better option.
When to Choose an Incremental Rotary Encoder
- Cost-Effective Solutions: If your system doesn’t need exact positioning but only requires feedback on movement or rotation, an incremental encoder might be the best fit due to its lower cost.
- Simple Systems: For systems where you can afford a bit of complexity in the setup, but speed and affordability are more critical, incremental encoders are a solid option.
- High-Speed Applications: If the primary concern is speed and quick feedback, incremental encoders generally work better.
5. Practical Applications of Rotary Encoders
Absolute Rotary Encoders
- Robotics: In robotics, precise position feedback is essential for accurate movement, making absolute encoders a must-have.
- Elevator Systems: Elevators need absolute position feedback to ensure they stop at the correct floor, and absolute encoders fulfill this need.
- CNC Machines: Absolute encoders provide high-precision feedback for CNC machines, ensuring accurate cuts and movements.
Incremental Rotary Encoders
- Motor Control: Incremental encoders are commonly used in motor control systems where only relative position is needed.
- Industrial Automation: In automation applications, incremental encoders can provide feedback on machinery movement, helping to control the process.
- Printers and Scanners: Devices that rely on scanning or positioning often use incremental encoders for detecting movement.
Conclusion
In the world of position feedback, rotary encoders play a vital role in ensuring accurate and efficient performance in various applications. Whether you choose an absolute or incremental rotary encoder depends on your system’s needs—whether you prioritize cost, speed, precision, or reliability.
If you need absolute precision and can afford the extra complexity, an absolute rotary encoder will be the best choice. On the other hand, if your system works with general movement feedback and you need a simpler, more cost-effective solution, an incremental rotary encoder could be the perfect fit.
By understanding the key differences between these two types of encoders, you’ll be in a much better position to make an informed decision that benefits your system’s performance.