Encoders 003 - Classification of Encoders

Interior of solar power system.

Interior of a Concentrated Solar Power System

Encoders are critical elements in a motion system because they provide position and/or velocity feedback to the motion controller, enabling the controller to close the positional control loop. The number of applications which require encoders is extensive and the types and sizes of encoders that serve these applications are just as numerous.

Encoders may be categorized in various ways as is shown in the list below. For this post, we will focus on the first category: Type of Movement being Measured.

Encoder Categories

  1. Type of Movement being Measured - Rotary encoders are the most common encoder type which provide information to be able to know the position/speed of a rotating shaft. Linear encoders provide the same information for anything moving in a straight line. Inclinometers give feedback as to the tilt of an object.
    Note: It is worth noting that the information received from rotary encoders can be used not only for shaft information but also to measure linear distances—like measuring wheels which are used in many applications.
  2. Sensing Technology used - the most common sensing types are optical, magnetic, and capacitive. Inclinometers use a variety of silicon solutions ranging from bubble devices to MEM's based technology.
  3. Mechanical Configuration - this refers to the footprint used as well as whether the encoder will mount to an existing shaft (encoder kit) or is provided with its own shaft (shafted encoder).
  4. Form of Output - some encoders only provide information to determine speed acting like a tachometer. Other encoders add additional information such as direction, index or exact position.
  5. Interface type - encoder outputs can be analog or digital. This can be broken down further into the type of communication protocol used for that output.


Type of Movement being Measured

Position/velocity encoders come in two mechanical configurations: linear and rotary.

As the name suggests, a linear encoder measures the position or velocity of an object moving in a straight line. Typical linear applications are the control of linear motors or X-Y tables such as those found on 3D and inkjet printers as well as laser etching and engraving machines. Linear encoders are also commonly found in devices such as metrology instruments including digital calipers.

Fluid handling pumps

A rotary encoder, on the other hand, is used to measure the angle or velocity of rotation of an object. Some typical uses include motor speed control (as in the pump examples pictured above), or the angular control of a movable PV array for solar tracking, or controlling the angular position of a robot arm.

Rotary encoders are available with different physical specifications to serve different working environments. For example, those used in harsh industrial applications must be designed to withstand rugged and extreme working conditions. Extreme temperatures, vibration, dirt and debris are some of the challenges that these encoders have to survive on a daily basis. As a result, industrial encoders tend to be big and solidly built to withstand the tough environment, and typically include some form of IP rating. For less harsh environments, such as those in electronics manufacturing, the emphasis may be on smaller size, lower cost or the ability to take advantage of more configuration options, while not compromising on longevity or high quality.

Inclinometers, also known as tilt sensors, are the third type of encoder mentioned based on the kind of movement being monitored. They are a device which provides feedback so that the angle of tilt of an object can be calculated with respect to gravity. Typical usages of inclinometers are for concentrated solar power (CSP), industrial equipment, aerial work platforms and dredges-as in the ship above.

Our post on March 25th will include videos from some of the applications identified in this post.

It is my goal to make this blog as informative, engaging and as accurate as possible. If you ever have some additional or contrary information, please contact me directly and I will be glad to make any appropriate corrections in a future post. Previous Post

GlassPoint solar system source - https://www.mercurynews.com/2016/10/18/solar-company-finds-an-unlikely-home-oil-fields/
Linear encoder drawing source - https://www.epiloglaser.com/laser-machines/legend-laser/legend-linear-encoders.htm
Dredging Ship source - https://www.seatools.com/subsea-solutions/dredging-monitoring-and-control/

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