Encoder feedback is crucial for closed-loop motion control, enhancing accuracy, reliability, and even energy efficiency in machinery and robotics. In this article, we explore the working principles of optical, magnetic, and capacitive encoders and provide guidance on choosing the right one for your application.
**What's Covered?**
- How Encoders Work
- Optical Encoders: Most Common
- Magnetic Encoders: Emerging
- Capacitive Encoders: Newest
- The Case for Magnetic Encoders
- 10 Things to Consider When Choosing Between Encoder Types
- FYI: Multi-Turn Mechanical Absolute Encoder
Encoders are typically mounted on a motor’s rear shaft and sense its rotation. While there are many types, this article focuses on rotary encoders. Each type uses a different method to track rotation, but all generate a pulse train as the motor turns. By analyzing these pulses, you can determine the motor’s position, speed, and direction.
For example, if an encoder has a resolution of 200 pulses per revolution, then 200 pulses indicate one full turn. Pulse frequency (in Hz) tells you the rotational speed, while the phase relationship between two channels (A and B) determines the direction.
Here’s a video showing how an encoder is used in a diverting conveyor system with a stepper motor:
[Embedded YouTube Video]
Now let’s dive deeper into the three main types of encoders.
### **Optical Encoders: Most Common**
Optical encoders are the most widely used due to their high precision, accuracy, and resolution. They operate using a light emitter (like an LED), a code wheel with slits, and a photo sensor. As the code wheel rotates, light passes through the slits or is blocked, creating a binary pulse signal that the output circuit interprets.
There are two main types: transmissive and reflective. Transmissive encoders use a disk with slits that allow light to pass through, while reflective encoders use a disk that reflects light back to the sensor. Reflective designs help save space.
Encoders can also be incremental or absolute. Incremental encoders track changes relative to a home position, whereas absolute encoders provide a unique position value at any time, even after power loss.
### **Magnetic Encoders: Emerging**
Magnetic encoders use a magnetized code wheel and a magnetic sensor instead of light. The code wheel has alternating north and south poles, and the sensor detects changes in magnetic polarity as it rotates. This generates a pulse signal similar to optical encoders but with lower power consumption.
Magnetic encoders are more robust in harsh environments like dusty or humid conditions. However, they can be affected by external magnetic interference. They are available in both incremental and absolute versions and can be used in rotary or linear applications.
### **Capacitive Encoders: Newest**
Capacitive encoders are a newer technology that offers environmental benefits similar to magnetic encoders. They detect changes in capacitance using a high-frequency reference signal. A transmitter sends a signal to a rotor with a patterned design, which modulates the signal. The receiver translates this into a pulse train.
Like optical encoders, capacitive encoders can be sensitive to electrical noise, so additional shielding may be needed. They are also available in various configurations, including rotary, linear, incremental, and absolute types.
### **Choosing the Right Encoder**
When selecting between optical, magnetic, and capacitive encoders, consider factors such as environmental conditions, required accuracy, power consumption, cost, and whether absolute or incremental feedback is needed. For critical applications where position accuracy is essential, absolute encoders are often the best choice. For cost-sensitive or less demanding applications, incremental encoders may suffice.
In summary, each encoder type has its advantages and limitations. Understanding their working principles and applications will help you make an informed decision when integrating them into your system.
5 Axis CNC Milling
5-axis CNC machine tools are the mainstay of DAYUE. These systems were once reserved for complex professional applications, and Dayue has realized the value of using 5-axis machine tools in every project. Many of them have been able to minimize delivery time, increase efficiency and therefore increase profitability. The following are some factors that guide their decision:
1. Save time - One of the most obvious advantages of a 5-axis CNC Milling machine is that it reduces the time required to complete the project. A standard 3-axis machine tool may require several different settings and more than 5 hours to complete, while its 5-axis machine tool can complete parts in a few operations, from start to completion in less than two hours.
There are two types of 5-axis machining: 5-sided (sometimes called 3 + 2 machining) and simultaneous 5-axis. Both methods are faster than traditional 3-axis machining, but 5-sided machining is faster and easier to program. Experts believe that simultaneous 5-axis machining will eventually produce a smoother surface finish, which is often required for competing aerospace applications.
2. Reduce the cost of parts-you can also use 5-axis machining to reduce the overall production cost of parts. Since traditional three-axis machine tools can only work on one side of one part at a time, parts that require multiple finishing surfaces need to be recalibrated, and in some cases, need to be reprogrammed. All of these increase the overall production time and labor, all of which are related to the cost of the final product.
3. Improved molding-molds made of liquid silicone rubber (LSR) or similar materials are becoming more and more complex. This is the result of design development in certain industries (such as medical device manufacturing), which require the increase of the versatility of their new products. In order to adapt to this situation, many manufacturers are transitioning to 5-axis machine tools. Now, almost every professional mold maker realizes the value of using advanced equipment to meet their needs.
Although three-axis machines are sufficient for milling simple molds, these devices may not even be able to handle some of the more complex designs that appear in today's products. They are simply not accurate or fast enough to meet evolving and strict industry standards. Such projects specifically require the use of modern 5-axis milling machines.
4. Compatible with CAD/CAM-In the past year or two, the technology behind computer-aided design and computer-aided manufacturing has developed by leaps and bounds. There used to be limited 5-axis machine tool software support, and almost all the most popular CAM software developers have upgraded their products to accommodate the other two axes. Autodesk`s Fusion 360 is a good example of how software programmers can support 5-axis milling machines. The final version of Fusion 360 represents the first time for developers to provide native support for 5-axis machining in their software, but it will certainly not be the last.
5. Suitable for general projects and special projects-Some manufacturers and machine shops have the impression that 5-axis machine tools are only used for special projects or highly complex parts. Although they can simplify complex tasks, this is not their only application. Like its more traditional CNC machine tools, five-axis milling machines are also good at simple parts and parts, requiring the least amount of work.
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