World's Largest Encoder? - see video link below
By Gts-tg - Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=64833365

Encoders 001—What is an Encoder?

Finally the time has arrived for this first post of my blog focused on encoders. The goal of this blog is to provide an easily accessible resource for anyone in the motion control industry from students to engineers. It is my desire to provide a platform for us to ask questions, make comments and solve problems together. There will be two posts each month. On the second Tuesday of each month, the focus will be more of an encoder concepts discussion. The fourth Tuesday of each month, the focus will be on real world applications and solving problems. For the present, to contact me for anything related to this blog you can message me through LinkedIn or email me at steve.mathis@usdigital.com

One of the most common question guys ask each other when they meet is—what do you do?—meaning your place of employment and your role there. Since working at US Digital, I have worked through several definitions to explain encoders when that question has been posed to me. In this post we will start from a very generic but practical definition and move towards more technical definitions.

The first recorded usage of the word encode comes from the 1930’s. It’s most basic meaning is to convert into code. Contrary to how encoding is done in the motion control industry, encoding has often been used to hide information from those who didn’t know the code. In the United States, one of the most famous such applications was the use of the Navajo language by “code talkers” in WWII. For even more security, the Navajo language was not used straight up but the Navajo recruits were asked to take their language and create a new code. For example, the Navajo word for a chicken hawk was used as code for a dive bomber. This encoding attempt was very successful—so much so that Major Howard Connor said the Marines would never have taken Iwo Jima without the assistance of the Navajo code talkers.

Translation—based on the previous paragraph, translation seems like an obvious choice for describing encoding. I have always enjoyed languages—studied Greek in college, speak Spanish and am in the process of learning Russian. In one sense, an encoder is a translator. It takes movement and changes that “information”, into a different kind of information—information that is useful.

Sensor with an Output—Encoders are included in the sensor category because the encoder “senses movement” when it happens. But sensing without reporting is of no value. When your brother hit you, there was no doubt you sensed that action. However, it was not until you reported the pain (MOM, he’s hitting me!), that you received the support you needed to prevent further pain. So it is with the encoder. It senses the movement and provides feedback to a control device. Fortunately, the encoders don’t yell at us but provide an electrical signal to a decoder to make sense of the message sent. When we use the broad term “movement”, that would require that inclinometers also be included as an encoder, but for the present, we will focus on rotational and linear movement.

The following definitions are the top results I found on a web search which is helpful to show how different vendors define an encoder—links are provided to each vendor’s website where the definition was found. In some cases, it will be obvious that the encoders being defined, are a specific type like an optical rotary encoder while other definitions provide a broader definition.

Anaheim Automation—a sensor of mechanical motion that generates digital signals in response to motion.

BEI Sensors—an electro-opto-mechanical device that attaches to a shaft and provides angular position information to a counter or controller.

Celera Motion—a device that converts position or motion to an electrical signal-usually a digital code.

Codechamp—an electromechanical device which has an electrical output in digital form proportional to the angular position of the input shaft.

CUI—a device used to measure the speed, direction of motion or position of a rotating shaft.

Dynapar—an electromechanical device that provides an electrical signal that is used for speed and/or position control.

EPC—a sensing device that provides feedback. Encoders convert motion to an electrical signal that can be read by some type of control device in a motion control system.

RLS—a device which can detect and convert mechanical motion to an analogue or digital coded output signal.

Timken—a communication device that controls the motion of an operating device.

TW Controls—a device that senses mechanical motion and translates the information (velocity, position, acceleration) into useful electrical data.

US Digital—a sensor that translates either rotary or linear mechanical motion into electrical signals, so that a control system can determine the speed, acceleration and/or position of a mechanical system.

Conclusion—I am sure that some of you noticed that some of these definitions seem to include facets of motion control which go beyond the actual function of the encoder. The elements of a definition of an encoder which must be included are 1) movement takes place, 2) an output of an encoded electrical signal is produced.

Having fun with Ancient “Encoders”

With the creative minds of our ancestors, although they didn’t have the electronics of our current encoders, nonetheless, they did have devices which translated physical movement into a different kind of information which was useful.

If you are like me—you may now be all defined out and are ready for a practical application. Although the word encoder was not used until the last century, that in no way means that some types of encoders were not made prior. One of my favorites is what is said by some to be the first odometer. The picture above is a reconstruction of the Hero odometer from the first century AD. However, even older than that is one believed to be designed by Archimedes over 200 years before Christ. Leonardo Da Vinci attempted unsuccessfully to reproduce that first odometer based on the faded drawings available to him. Fortunately for us, that problem has been solved in our time and we are now able to view a video of a reproduction of that first “encoder”.

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. In my next blog, in addition to showing a functioning “encoder” from about 1915, we will discuss some common current applications for encoders.

Please note that all hyperlinked text supply the source of the information provided.