Magnetic and optical encoder technologies each have their advantages and disadvantages。
In terms of precision motion control, the encoder is an important component that converts mechanical motion into electrical signals. The encoder can be used in many applications such as automation equipment, industrial process control or robotics, and can provide data about position, speed, distance, and direction. There are currently three main encoder technologies on the market to choose from, including magnetic, optical and capacitive.
The magnetic encoder consists of a rotating disk with alternating magnetic poles and a Hall effect or magnetoresistive sensor, which works by detecting changes in the magnetic flux field. The magnetic encoder is stable and durable, can well deal with shock and vibration, and is not affected by oil, dust and moisture. However, they are susceptible to electromagnetic interference caused by electric motors and have a limited operating temperature range. Although magnetic encoders have also stopped many improvements, their resolution and accuracy are compared with optical and capacitive alternatives. Usually lower.
Compared with magnetic encoders, optical encoders can provide higher resolution and higher accuracy. The optical encoder consists of an LED light source (usually an infrared light source) and photodetectors located on both sides of the encoder disc made of glass or plastic. Although optical encoders have dominated the motion control market for decades, because optical encoders rely on the "field of view", they are particularly susceptible to dust, dirt and oil, as well as vibration and extreme temperatures. Damage. In addition, the optical encoder will consume up to 100 mA of current during operation, and its life will eventually be limited by the LED.
Capacitive encoders have better accuracy and durability。
The capacitive encoder is composed of three main components: a rotor, a fixed transmitter and a fixed receiver. The rotor contains a sine wave mode, and as the rotor rotates, the transmitter's high-frequency reference signal stops modulation in a predictable manner. The encoder detects the change of capacitive reactance on the receiving board, and uses a demodulation algorithm to convert it into an increment of rotational motion. Capacitive encoders are more stable and durable than optical encoders, can withstand various environmental pollutants, and are better able to withstand vibration and extreme temperatures. In addition, in the absence of LEDs, compared with optical encoders, it has a longer service life, smaller footprint and lower current consumption (6 to 18 mA). It will not be affected by electromagnetic interference and electrical noise, and is as stable as a magnetic encoder, but with higher accuracy and resolution.
In view of the digital characteristics of capacitive encoders, capacitive encoders also provide greater flexibility, allowing users to change the resolution of the encoder. When using other technologies, the resolution is determined by the encoder disc, which means that every time a different resolution is required, the optical or magnetic encoder must be changed. The programmable resolution available in capacitive encoders can not only be used for system optimization (especially when designing PID control loops), but also can reduce inventory, because one product model can be used for multiple applications. Capacitive technology also allows digital setting of index pulses and stop alignment for BLDC commutation encoders, and its built-in diagnostic function provides designers with a way to access system data in order to stop quick defect removal in the field.
Regardless of the system requirements, capacitive encoders can provide a versatile, cost-effective and reliable alternative to optical or magnetic sensing technology. Capacitive coding can not only provide excellent performance in terms of accuracy and reliability under any environmental conditions, but its inherent digital operation can also provide programmability and enhanced diagnostic functions, while still being compatible with traditional encoder functions.
Flexible termination of resolution programming can reduce inventory
Since CUI Devices launched the first generation of capacitive encoders in 2006, its AMT series has been proven to have a high degree of reliability and accuracy, and can handle many application problems encountered in optical and magnetic technologies. Using capacitive sensing technology, CUI Devices' incremental, absolute and commutation AMT modular encoders can provide highly durable solutions without sacrificing accuracy. The AMT series has up to 22 programmable resolutions, and the operating temperature range is -40 to 125°C. It can provide engineers with greater flexibility during the prototyping process, and purchase managers can greatly reduce the specifications required for consumption. The number of products.
Reprinted "Arrow Electronics"
