Magnetic technology has been used to make incremental encoders for quite some time. Auto makers use low resolution magnetic encoders in a variety of applications due to their robust nature. These encoders are used in ignition timing, crank position sensing, antilock braking and ignition timing. There are also myriad uses for this technology outside of the auto industry, with magnetic encoders used over competing technologies like optical encoders to eliminate issues involving vibration, moisture, dust, high temperature, high speeds and general wear.
Although cost effective, accurate, and robust in design, past magnetic encoder technology was limited to low resolution applications. In recent years the technology has come a long way. New signal processing and magnetic sensing technologies allow medium and high resolution magnetic encoders to meet a wider variety of application needs, with pulse counts that quite frankly, blow the past rates out of the water.
The fact that magnetic encoders require no moving parts such as seals or bearings provides magnetic encoder technology with a unique advantage, as these parts are the primary causes of encoder failures. The two basic components of magnetic encoders require no special adaptation components like straps and coupling.
The Magnet Target
The permanent magnet target wheel is the first component of the magnetic encoder, and is mounted on the rotating shaft of a pulley system or motor. The magnet target is magnetized with Multiple poles magnetize the magnet target. These poles are typically located around the periphery, but are sometimes located on the face. The pulse count needs for a particular application will determine the number of poles required. The dimensions of the rotor can be designed and built to fit any available shaft size.
There are a few ways magnetic target rotors can be mounted. A step on the shaft for the magnet to rest on is required for the most cost effective solution. The magnet rotor is compressed onto the step of the shaft using a screw on the end of the shaft. Adhesive can sometimes be used as an alternative. The magnet can also be press fitted onto the shaft using a second mounting method.
Rotating applications are not the only use for the magnet target. In linear moving applications the magnet target is formed into long strips. A steel backer adds dimensional stability for longer strips.
There are many magnetic material choices, with considerations including magnetic performance, structural requirements, fluid compatibility and temperature performance determining the optimal choice of material. Bonded manufacturing methods are used for the majority of magnet targets due to cost and performance considerations.
The Encoder Module
The encoder module, or magnetic sensor, is the second and only other component of the magnetic encoder, and is accompanied by dedicated signal conditioning components. The module is mounted directly on the end bell of the flange or motor of a pulley system. There is no mechanical wear to worry about, as there are no moving parts like bearings or seals in the encoder module. This, of course, is a benefit for applications that require a reduction in service and a long working life.