Encoders Have Been Used in Space Exploration for Almost 70 Years

In our March 12th post, we identified different ways by which encoders can be categorized. In that post we focused on the first category - type of movement which encoders are able to monitor. Today we will discuss the second category: sensing technology used in most encoders.

Note: The descriptions and drawings in this post are intentionally simplified to provide an overview of the technologies used in these three kinds of encoders. Future posts will delve more deeply into actual construction and function of encoders and address more of the advantages of each

Optical encoders have been the most common encoder technology used for many years. To this day they provide the highest levels of precision, accuracy and resolution. Rotary encoders use an optical sensor to detect light that is transmitted through a disk (transmissive) or reflected from a disk (reflective). The disk is also sometimes called a code wheel. The transmissive optical encoder disk has alternating transparent and opaque lines. When the light is received by the sensor, the encoder puts out a high signal. Conversely, when the light is blocked by a line on the code wheel, the sensor puts out a low signal. On a reflective encoder disk the alternating lines are reflective and non-reflective. With a known pattern on the disk, the distance moved and speed of movement can be obtained using the signal information. Linear encoders use the same method with the only difference being a strip is used in place of rotary disk.

Magnetic encoders use code wheels with alternating magnetic poles or unique patterns distributed around the wheel according to the resolution required. A magnetic sensor in the encoder detects the change in the magnetic field as the wheel rotates and produces a digital pulse train. Magnetic encoders have an advantage over optical encoders in that they are can be used in areas which have higher humidity, dirt and dust. Magnetic encoders may also operate in various fluid environments. Magnetic encoders use less power than their optical counterparts, but typically do not provide the same resolution or positional accuracy as optical encoders due to inherent non-linearities in the magnetic field.

Use of a magnetic encoder may be preferable to an optical encoder when there is a chance for an optical disk to become fogged as moisture condenses on the code wheel. Consider an application where an optical encoder is held at a very low temperature and then the ambient temperature quickly increases. This quick temperature change can cause condensation on all surfaces of the encoder, including the optical code wheel. When the code wheel surface collects droplets of moisture, the light transfer of the code wheel image to the optical sensor can become distorted and a false or missing signal may occur on the output. With a magnetic encoder design, condensation of moisture is not an issue with the rotating magnet and magnetic sensor.

Capacitive encoders are a newer technology but inherently possess all of the same environmental advantages as the magnetic encoders. A capacitive encoder detects the changes in capacitance using a high frequency reference signal. The rotor has either a pattern etched into it or uses a specially shaped design as in the above drawings. When this rotor moves between the transmitter and receiver, that pattern modulates the high frequency signal of the transmitter. The receiver reads the modulations and those changes are translated into increments of rotary motion. Although capacitive encoders can be more susceptible to noise and electrical interference—the manufacturer of the encoder can mitigate that potential issue with appropriate engineering. Another benefit of using a capacitive encoder is the typically lower current draw - 10 milliamps is not uncommon.

There are advantages and disadvantages of each technology used. My suggestion is to determine your requirements and then compare specifications to ensure the encoder you are looking at will meet your needs. In a future post we will discuss how to choose an encoder. If you have any additional questions, please feel free to contact me via email or LinkedIn.

Have you ever seen the first encoder used in space? We will have that and more in our next 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

Mars Lander picture source - Space.com

"Calling All Innovators: The 2019 Create the Future Contest is Now Open!"
Submit your best new product ideas for a chance to win $20,000!

Sponsored by TechBriefs (This link leaves usdigital.com)

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/

Wire Measuring Machine from 1910-1920

In the previous blog, we offered many definitions of encoders and based on the definition chosen, the above wire measuring machine qualifies as an encoder. For now, ignore that picture and we will chat about it later in this blog.

My plan is to post the 2nd and 4th Tuesday of each month. The 2nd Tuesday will focus on encoder related concepts and the 4th Tuesday will focus on real world applications and solutions. Per that plan, today's post will discuss current uses of encoders which are happening all around us. Unless otherwise specified, the normal definition we will use when talking about encoders is the US Digital definition of encoder. "An encoder is a sensor which translates either rotary or linear mechanical motion into electrical signals, so a control system can determine the speed, acceleration and/or position of a mechanical system."

One very enjoyable part of my job is viewing the wide spectrum of industries which employ encoders. In fact, it is difficult now for me to think of an industry that cannot benefit from the use of encoders somewhere in their operation. Can you think of one?

One of the most popular usages of encoders is direct installation onto the rear of a motor. That application by itself can be used in a myriad of industries on both AC and DC motors. Robotics are one industry which uses a ton of motors and encoders to accomplish the automation required. The picture below shows a delta robot made by US Digital which was used at SPS 2018 to showcase some their encoders and motor driver. Note that each of the three motors have an encoder on it which is used to monitor the angle of the shaft and corresponding robot arm.

Speaking of robots, one of the fastest growing segments in robotics is that of the cobots (collaborative robots). In the past, cages were required when using robots in production, to isolate the robot from anyone in the area. Cobots on the other hand are robots which are designed to work right alongside workers with safety features built in to prevent injury to the workers. Some of those safety features include stopping when contacting an obstruction and moving at a much slower speed. Universal Robots is a major player in this industry. You may have seen one of their robots ring the closing bell at the New York Stock Exchange last year. But that function, although it was fun to watch, is almost an insult to the ability of these cobots as they are designed to do much more complicated tasks. The picture below shows the LMI Gocator which is used to scan 3D images of objects. Click on the picture below to see a video of it going through it's paces.

As innovative as these designs and use of available technologies are today, so was the wire measuring machine pictured at the top of this blog in its day. Last year I wanted to purchase a tool to measure cable for fabricating custom garage door cables. I found this "Improved Wire Measuring Machine" made by the John J. Waldman Company at a local auction and purchased it. I set it up and after testing the measuring tool found it to be quite accurate. I was oblivious to its significance at the time of the purchase, but if we define an encoder as a device which translates physical movement into useful information, this tool qualifies as an encoder. Below is a picture of the three parts making up the complete fabrication assembly including the spindle, the measuring machine and the coiler.

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 at steve.mathis@usdigital.com, and I will be glad to make any appropriate corrections in a future post. Previous Post →

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

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. Next Post →

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