Optical Encoders VS Magnetic Encoders: Why FlexSense is the Ideal Solution for Encoder Applications

In today’s modern world, automation is all around us. From industrial robots to autonomous vehicles, automation is a part of our everyday lives. With the ever-evolving electronics world, mechanical components have merged with electronic devices creating what the industry refers to as ‘Mechatronic’.

Whether these automated devices are purely mechanical or electrical, they each revolve around one key component; the encoder.

The encoder is a fundamental component used to precisely control and move a variety of automated devices including; toys, doors, valves, vehicles, ships, robots, airplanes, trains and solar panels – just to name a few!

There are two main types of encoders:

  • Magnetic encoders
  • Optical encoders

Let's break them down. 


STRUCTURE OF MAGNETIC ENCODER

The magnetic encoder detects rotational position information as changes of the magnetic field converts them into electrical signals, and then outputs them. The simplest magnetic encoder consists of a permanent magnet and a magnetic sensor.

Hall Element

Hall elements used in magnetic encoders are made of semiconductor materials. The semiconductor materials used in Hall elements are mainly compound semiconductors.

Permanent Magnet

Magnetic encoders generally use cylindrical permanent magnets.

When the motor shaft rotates, the magnetic field created by the permanent magnet attached to the tip of the shaft also rotates. At this time, the magnetic field rotates with constant strength in the area near the centre of the rotation axis. The Hall element detects this change of magnetic field distribution and converts it into an electrical signal.

 

STRUCTURE OF OPTICAL ENCODER

The optical encoder is composed of a light emitting device (LED), photo sensors and a disc called a code wheel with slits (holes) in the radial direction. This encoder detects rotational position information as an optical pulse signal. When a code wheel attached to a rotating shaft, such as a motor, rotates, an optical pulse is generated depending on whether light emitted from a fixed light emitting element passes through a slit of the code wheel or not. The photo sensor detects the optical pulse, converts it into an electrical signal and then outputs it.

Components

LED: Light emitting devices used in optical encoders might be, for low-end applications, uncollimated infrared LEDs, or high-end collimated LEDs, and in some cases blue LEDs.

LENS (for uncollimated LED): The light emitted from the LED is diffused light with little directivity so that it is made parallel by using a convex lens.

CODE WHEEL: The code wheel is a disc with slits (holes) for passing/blocking the light emitted from the LED.

PHOTOSENSOR: The photo sensor is typically a photodiode or phototransistor made of a semiconductor.

Classification by Structure

Optical encoders are classified into one of two types according to their structure – Transmissive or Reflective. Transmissive encoders include a light emitting device (LED) and a photo sensor which sandwich the code wheel.

On a Reflective encoder, the LED and photo sensor are placed on the same side of the wheel and the light is reflected.

Flexsense illustrations

TT Electronics’ FlexSenseTM optical encoder sensor is available in both Transmissive and Reflective models and upon request, closed/loop controlling internal LED (for reflective layout) or external LED (for transmissive layout).

 

ENCODER CLASSIFICATION BY OUTPUT ELECTRICAL SIGNAL FORMAT: INCREMENTAL and ABSOLUTE

Optical encoders are also classified into two types depending on the format of the output electrical signal. There is an incremental method that outputs the angle change (movement amount) of the rotating disc, and an absolute method that outputs the absolute angle of the rotating disc.

FlexSenseTM is currently available for incremental encoders.

 

WHICH IS BETTER, MAGNETIC ENCODERS OR OPTICAL ENCODERS?

No matter the application, an encoder must support for the following market trends:

  • High accuracy
  • Small footprint
  • Flexibility
  • Short time to market

Optical encoders typically achieve much higher overall performance than magnetic encoders. Standard optical sensors offer some of the features mentioned above, but only TT Electronics’ FlexSenseTM encompasses all of those features in one single device, fully integrated with its software.

 


Flexsense highlight

 

FlexSenseTM offers unparalleled performance in a compact footprint (5 x 5 mm), with 4.096 fully programmable pixels, available in transmissive or reflective models, with the following features:

  • User-programmable photosensor pattern
  • 2 quadrature and 1 index tracks
  • 10-40mm code-wheel radii compatibility
  • 500-6k PPR resolution compatibility
  • -40C to 125C ambient operating temperature
  • Programmable auto-alignment
  • Closed-loop control

Find out more at www.ttelectronics.com/flexsense 

Author
Mario Garsi | Business Development Engineer

Mario Garsi | Business Development Engineer

Mario supports TT Electronics' optoelectronics business unit across EMEA by providing technical and sales support.

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