Exploring linear encoders

A linear encoder is a sensor, transducer or readhead paired with a scale that encodes the position. A linear encoder helps in detecting linear movement as absolute position values without being in any kind of physical contact. The sensor takes helps from the scale in order to convert an encoded position into an analog or digital signal.

A linear encoder can either absolute or incremental. Some Linear Encoder technologies include optical, magnetic, inductive, capacitive and eddy current. Linear encoders are used in metrology instruments, motion systems and high precision machining tools ranging from digital calipers and coordinate measuring machines to stages, CNC mills, manufacturing gantry tables and semiconductor steppers.

Technologies of a linear encoder

  • Optical: optical encoders are having high resolution and therefore they are on top in the high resolution market. These encoders are commonly used in industrial automation applications. It is important for an optical encoder to use to have extra protection in order to prevent contamination of dust, vibration and other such conditions.
  • Magnetic: These encoders determine position with the help of sense-coils, Hall Effect or Magneto resistive read heads.
  • Capacitive: These encoders function on the base of capacitance between a reader and a scale.
  • Inductive: Inductive encoders are robust to contaminants. A very famous application of inductive technology is Inductosyn.
  • Eddy Current: This type of encoders use a scale coded with high and low permeability, and non-magnetic materials.

Principle of a linear encoder

A linear encoder works on two measuring principles – optical or magnetic. Optical encoders were once the first choice for high resolution applications. Now, there are many improvements made in magnetic encoder technology which permits to receive resolutions down to one micron. Magnetic encoders are used in many industrial applications because of their robust nature.

Optical encoders take help from a light source and a photo detector to determine the position while magnetic encoders use a reader head and a magnetic scale to determine position

Specifications and features of a linear encoder

  • Resolution is the smallest unit of distance measurement than an encoder can measure
  • Absolute encoder code it can be grey, binary, Binary Coded decimal, or other.
  • Incremental encoder signal it can be digital, square wave, analog/sine/cosine, single channel, pulse and direction, reference/index, or other
  • Measurement or range travel is actually the distance that is available for encoding
  • Electrical/digital output it can be analog, current, analog voltage, fiber optic, serial, parallel, SSI, or other
  • The encoders can be modular, linear to rotary, sealed, or probe style.
  • Signal quadrature is available It is just an arrangement in which two channels carry signals that are 90 degree out of phase.

Applications of a liner encoder

A linear encoder is used in a vast variety of applications such as wind power, solar panels, servo motors, packaging machines, machine tools, conveyors, automated storage or retrieval systems, elevators, sheet and web offset presses, medical equipment, robotics system, food handling equipment, valves or flow metering, overhead cranes, process monitoring equipment, steel making or foundry equipment, textile machinery, tire making equipment, test stands, construction equipment, and transportation.

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