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Encoders 007 - Encoders: Mechanical Configurations

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Encoders 007 - Encoders: Mechanical Configurations

We will continue in this post going through the various classification of encoders which were identified in my earlier post.

Mechanical Configurations

Mechanical configurations include differences based on whether the encoder comes with a shaft or will be installed onto an existing shaft. There are also different configurations based on the size of the motor, the required IP rating, and other environmental conditions.

Mechanical configurations

Motor feedback encoders may contain their own bearings, or they may use an existing bearing set such as that found on the tail shaft of a servo motor. The best configuration option to use is a function of the stability of the shaft/bearings to which the encoder is attached. Feedback encoders with bearings are typically used when the application shaft has a significant amount of axial or radial run out (eccentricity or vibration). The use of a shafted encoder with a motor will require some sort of flexible member, either a flexible shaft coupling or flexible body mount, to allow mechanical compliance with the application shaft operating irregularities.

Kit Encoder example

Modular encoders, also referred to as encoder kits, don’t contain their own internal shaft. They are assembled from components supplied by the encoder manufacturer and are designed to be attached to the tail shaft and end bell of the motor. These encoders rely on a mechanically stable motor shaft, as the shaft is responsible for holding the encoder’s internal rotating code wheel in a precise location relative to the encoder’s sensing module. For these applications, motor manufacturers put a considerable amount of effort in designing high-performance motors with very stable shaft/bearing assemblies. Because the modular design does not add the expense of the extra set of bearings that a motor feedback encoder does, modular encoders offer one of the most cost effective feedback solutions.

Modular encoders

When using a kit style encoder, another mechanical consideration is the size of the motor. Most encoder manufacturers supply a motor/encoder compatibility chart based on the motor size. It is recommended to use such a chart, like the one below, to help identify the appropriate encoder model.

Spec table sample
IP65 Rated encoder

Another mechanical configuration relates to environmental conditions. If the encoder will be installed in an environment that is subject to excessive dust and/or moisture, encoders are available with various IP ratings to meet those requirements. Magnetic and capacitive encoders would also be a potential candidate to meet some environmental concerns.

Modular encoders

Finally, there are many applications of encoders where they are inherently protected from physical contact. However, other encoders are located where they might be contacted by a person or object, therefore, requiring more physical protection. The above housing is machined from solid aluminum to provide the kind of protection needed in such an application.

Spider!!

If you are afraid of spiders, you might want to skip our next post which is scheduled for May 28th.

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

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Encoders 006 - Who Made the First Optical Encoder?

NASA robot

NASA doesn't just make spaceships!

Who Made the First Optical Encoder?

I have been researching the answer to that question for some time and although I have been able to gather some great information both from encoder manufacturers and my own research, at this point I do not have a definitive answer.

Optical encoder patent

When I initially tried searching for an answer, someone had answered the question online stating that the first optical encoder was made by David Cronin in 1964 - based on the date of his patent application (seen above).

First encoder used in space

First Encoder Used in Space

According to chapter 14 on encoders in Space Vehicle Mechanisms: Elements of Successful Design (A textbook that has been used by NASA), Tim Malcolm states that optical encoders were developed about 1951 to address a need for higher resolutions than what was available with other kinds of sensors. In 1958 Baldwin Electronics (now BEI Precision Systems and Space Company, Inc.) provided 18-bit optical encoders which were used in the Atlas missile guidance system. Those encoders were still functioning 36 years later when that article was written.

Back at the beginning, the life of the light source limited the encoder life. Many illumination sources were used based on the technology available at the time. Some light sources used include xenon flash tubes, incandescent lamps, and neon lamps. The first encoder used in space incorporated a redundant gas-filled incandescent light source but it only had a life requirement of 12,000 hours.

First LED encoder used in space

First LED Optical Encoder Used in Space

LED's were a big step forward by providing extended lifetimes with very little degradation. You may have heard a statement that optical encoders have reduced life due to dimming or burning out of the LED. Statements to that effect are contradicted by the chief scientist at BEI. In this same chapter, Tim Malcolm states as of the writing of the chapter (1996), "the concerns with the quality and life of these devices (LED's) which were common years ago have largely disappeared." He also noted that some encoder manufacturers had more than 10 years of continuous use with no encoder failures. Based on those statements, it would be safe to conclude that if your encoder supplier is using high-quality LED's, this should not be an issue.

I was fortunate enough to be able to get in touch with Timothy Malcolm and found out that the first optical encoders were actually made near the end of WWII. Although war is very costly, it has always been a great driver for the the development of new technologies. I will plan to share more about that in our post on May 28th.

Digital Optical Measuring Instrument

Heidenhain's Digital Optical Measuring Instrument

In a future post, we will provide information on how several of the oldest encoder companies came into being. The above photograph shows an optical counter made by Heidenhain, in the early 1960's, for accurate, reliable and easy positioning of slides and carriages on machine tools, gauges, and other instruments. It could actually measure measurements as small at 0.0001" - which is remarkable for that time period.

Encoders have been a key ingredient to space exploration in general from its inception. This is definitely true for NASA. I recommend checking out NASA’s website and articles like this one which mentions how they are used on the International Space Station on cameras to view earth. Here is also a video which gives some background on Valkyrie, the humanoid robot at the top of 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

Heidenhaim DOM Source - Heidenhain.de
Early space encoder pictures were provided by Timothy Malcolm.

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Encoders 005 - Common Technologies used by Encoders

Mars Lander

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

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

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

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

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Written by Steve Mathis
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Encoders 004 - Encoder Applications - Rotary, Linear & Inclinometers

Latte Printing, 3DPrint.com

Edible Printing Has Arrived!

In our last post we focused on encoders based on the type of movement which is being measured. In this post we will see those encoders being used in real world situations. Check out the video links throughout this post! Industries highlighted are Medical, Printing, Laser Engraving and Concentrated Solar Power.



Rotary encoders are indispensable in the medical arena.



Rotary encoders make their mark in many types of printers.



Linear encoders ensure the accuracy of laser etching and engraving machines.



Inclinometers assist CSP systems in achieving maximum efficiency.

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

Coffee picture source - 3dprint.com

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Written by Steve Mathis
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"My goal at US Digital is to work with the excellent teams here to contribute to the success of our customers by eliminating pain points and making it easy for them to do business with us."


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/

"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)

Written by Steve Mathis
Director of Customer Relations & Marketing

"My goal at US Digital is to work with the excellent teams here to contribute to the success of our customers by eliminating pain points and making it easy for them to do business with us."


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