What is the Difference between Absolute and Incremental Encoders?
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There are many types of encoders but they basically fall into two main sensing techniques. Those being: Linear and Rotary.
Within those categories, there differing encoder measurement types such as absolute and incremental.
There are also various electromechanical technologies such as magnetic, optical, inductive, capacitive, and laser, to name a few.
The Linear Encoder uses a transducer to measure the distance between two points. These encoders can use a rod or a cable that is run between the encoder transducer and the object that will be measured for movement.
As the object moves, the transducer’s data collected from the rod or cable creates an output signal that is linear to the object's movement.
As the distance is measured, the Linear Encoder uses this information to determine the position of the object.
An example of where a Linear Encoder may be used is for a CNC milling machine where precise movement measurements are required for accuracy in manufacturing.
Linear Encoders can be “Absolute” or “Incremental” measurements.
A Rotary Encoder collects data and provides feedback based on the rotation of an object or in other words, a rotating device. Rotary Encoders are sometimes called Shaft Encoders.
This encoder type can convert an object’s angular position or motion based on the rotation of the shaft, depending on the measurement type used.
“Absolute Rotary Encoders” can measure “angular” positions while Incremental can measure things such as distance, speed, and position.
Rotary Encoders are employed in a wide variety of application areas such as computer input devices like mice and trackballs as well as robotics.
The next encoder, which is a “Position” Encoder, is used to determine the mechanical position of an object. This mechanical position is an “absolute” position.
They may also be used to determine a change in position between the encoder and object as well. The change in position in relation to the object and encoder would be an incremental change.
Position Encoders are widely used in the industrial arena for sensing the position of tooling and multi-axis positioning. The Position Encoder can also be Absolute or Incremental.
“Optical” Encoders interpret data in pulses of light which can then be used to determine such things as position, direction, and velocity.
The shaft rotates a disc with opaque segments that represent a particular pattern.
These encoders can determine the movement of an object for “rotary” or “shaft” applications while determining the exact position in “linear” functions.
Optical encoders are used in various applications such as printers, CNC milling machines, and robotics. Again, these encoders may be Absolute or Incremental.
In a Rotary “Absolute” measurement type encoder, a slotted disc on a shaft is used in conjunction with a stationary pickup device.
When the shaft rotates, a unique code pattern is produced.
This means that each position of the shaft has a pattern and this pattern is used to determine the exact position.
If the power to the encoder was lost and the shaft was rotated, when power is resumed, the encoder will record the absolute position as demonstrated by the unique pattern transmitted by the disc and received by the pickup.
For incremental measure encoders, the output signal is created each time that the shaft rotates a measured amount. That output signal is then interpreted based on the number of signals per revolution.
The incremental encoder begins its count at zero when powered on. Unlike the absolute encoder, there are no safeguards regarding the position.
Because the incremental encoder begins its count at zero in startup or power disruption, it is necessary to determine a reference point for all tasks requiring positioning.
Hopefully, we have given you a basic understanding of what’s out there and when you may want to choose one particular type over the other.
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#RealPars #AbsoluteEncoder #IncrementalEncoder
I actually learn something of great value with every video of yours that I view! Thanks, RealPars!
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I will surely pass this on to our creator team. We do go into more depth in our course library bit.ly/30AVJaR
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At work I wrote some software to use an incremental quadrature encoder to characterize the output of an absolute position magnetic encoder. Interesting to see how the particular placement of the magnet affects the absolute position encoder’s output
Thank you for clarification on transducers and encoders
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Thanks to team RealPars--- A Indian-- Engineering Student
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Great video explaining the difference between absolute and incremental! Thanks!
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Incremental are best in unpredictable motion/speed, long ways or/and high speed. Absolute in saw cutting machine, bending machine(the hidraulic piston), treading, drilling, or any repetitive work being mechanism or short(70cm) robotic arm with only one hemisphere of movement like human hand for safety reasons replacing workers at handpackaging cookies, wafers, bread, small packs in big one's, bags, lightbulbs, clocks, glasses, unpackaged items, cups, plates, saucepans, wine, handling freshly pressurized champagne wich sometimes explodes and injures the worker's hands.
For a three-bit absolute encoder, as shown in the example, the minimum measurement magnitude would be 1/8 of a full rotation (45 degrees). If they're so precise, how do they encode smaller increments? Or are their bit depth larger in real life?
A very resolute absolute encoder has 12 or more "tracks" which gives the device 12-bit resolution (1 bit per track). 2^12 = 4096 divisions/revolution. This level of resolution is provided optically by detecting light pulses produced by very small photodiodes, a precise mask disk and an LED light source. Up to 10,000 increment per revolution are now possible.
Wow...very clear explanation
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Love your videos. What software do you use to make your animations?
Hey!
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I am actually not sure about this as this is done by our graphic and animation department.
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The RealPars team wishes you a splendid new year as well!
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which software did you use for creating these videos. I really appreciate you have put a lot of effort into creating these videos, I wanted to create them in a similar fashion for my class seminars as well.
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I am actually not sure about this as this is done by our Graphic and Animation department.
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Could you please a simple video explaining difference between simotion and sinamics
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Do optical encoders require debounce filtering?
Hi Andrew,
Thank you for your question. The inclusion of the feature you mentioned in the encoder's electronics could vary based on the manufacturer and its intended use. To gain accurate information, I recommend consulting the operator's and data manual specific to your encoder.
Wishing you a fruitful learning experience with RealPars!
What application do you carry out the animations with?
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for absolute encoding, this article might be interesting:
en.m.wikipedia.org/wiki/Gray_code
by the way: when code is on a wheel, make sure it doesn't slip due to obstruction so a reset position might be s good idea ...
on the other hand: using a stepper motor might be as good as the incremental measuring as long as rotation of the axis is not obstructed.
Thanks for adding that!
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Nice video, please upload more part and technology of cnc machine
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Thank you for all video tutorial very helfull.
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I did not get it, can anyone can explain please. 5:39 how 111 code can precisely determine the degree. Since the video shows that 111 code is somewhere between 315 to 360 degrees. Or it is a mechanical counter like miles counter in an old car? In that case why do we need that laser system after all. Thanks.
The video shows a simplified version of an optical slotted disk absolute encoder with 3 bits of resolution. That is equivalent to 45 degrees. Actual encoders can have up to 28 independent light paths. 28-bit accuracy is equivalent to a resolution of 0.00000134 degrees. That would be a little tough to show in the video, so it was simplified to demonstrate the principle.
RealPars "crew", would you please define "absolute position" for me? Thank You.
@Mohammad Reza, I appreciate Mohammad.
But how does the absolute encoder know the exact position? In the example that starts at 5:20 when the code is 011 it could be 150° or 170° or anything in between
My best guess is they can increase the number of bits (slots on the disk)... The example here was a 3 bit encoder... You may use 4 or even more bits to make it more precise of the angles?
@@sagelioneldsouza8230 i see, so doing some calculations you need at least 9 bits to get a 360° precision
@@Lucianob98 yess :) Glad we figured it out🥂 Thanks
Kelmat is correct. The video shows a simplified example. With an absolute encoder, there is a distinct bit pattern for every position, so that the position can precisely be known. Many absolute encoders utilize multiple disks for position determination and many are able to determine absolute position over up to 4096 increments/turn.
I knew something didn't 'add up' with the binary code and the degrees so I thought it may have been a simplified example. Then I confirmed by looking it up (en.wikipedia.org/wiki/Rotary_encoder) and sure enough, an interruptor disc with many more slots is listed in the picture above. If you ask me, there is something hypnotic about the arrangement of these slots in a rotational pattern. But anyhow, I scroll down here to see if anyone had the same question and here I am!
What kind of PLC your are using in the course?
The PLC represented in the video is a Siemens S7-1500 series PLC. The lower-cost S7-1200 can be used to program all of the same examples shown in our videos as well.
Many thanks for your awesome videos. 👏👏Let's comment to support the channel. 👍
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thank you
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My friend I want a brief video about safety relays
Thanks for the topic suggestion, Kahlil. I will definitely go ahead and forward this to our creator team. Happy learning!
I think there is a mistake in this video. Please correct me if I am wrong. A CNC milling machine would typically use a rotary encoder located inside the stepper motors. A linear encoder is typically used in a digital readout (DRO) on a manual milling machine.
The use of linear or rotary encoders depends on the application, not on the "class" of the machine. in the video. a linear encoder is used with a CNC milling machine where the part is moved back and forth in a linear direction. If the machine were a CNC lathe, then a rotary type encoder would be used.
Nah bro,
So basically, the servo motor needs a rotary encoder to feedback to the drive by default.
A rotary encoder cannot see lost motion, such as backlash, but a linear encoder can, as it moves linearly along the axe.
A linear encoder on a cnc machine is only there in order to achieve greater accuracy.
With a stepper motor it is completely different to an ac servo, it doesn't require a rotary encoder, however you can add both a rotary and a linear encoder if you wish to achieve true closed loop control.
An incremental encoder can also have an index channel as well, so in that sense can it not also be an "absolute" encoder?
Not exactly. The index for an incremental encoder generates a pulse which allows the encoder to "home", such that an accurate "count" of position from the "home" position can be made. In an absolute encoder, each position has a unique pattern. The index pulse of an incremental encoder only provides a reference location given once for each revolution.
Is it possible to have a design that will allow the incremental encoder to act like an absolute encoder?
If the incremental and absolute encoders have the same reference (zero) position, they should both give the same result provided they both have the same resolution. In practice, that does not happen. The incremental encoder has a zero position wherever the position is when the encoder is powered on. It simply indicates how many turns the shaft has made since it was first enabled. So while it is possible to approximate the action of an absolute encoder with an incremental encoder, this is not often done because there would need to be another function required to position the shaft to a precise zero position.
@@realpars By integrating a microprocessor and an external battery
I designed a system that ensures that the incremental encoder position is kept in memory continuously. I converted it into a thesis and my thesis was accepted.
I really appreciate the video, content of video is quite enough to vive the idea of working of encoders. Can you please provide a video on "Heidenhain AK ERM 280" type encoders?
Hi Vikrant!
Thanks for your comment and your suggestion. I will pass this on to our course developers!
Thanks for sharing and happy learning!
Can you please tell me how encoder works in hydraulic intensifier?
Hi there,
Thanks for your comment!
That would make for a great future video course! I have gone ahead and passed this on to our course developers as a topic suggestion.
Thanks for sharing and happy learning!
Just subscribed!
Great! Welcome to the RealPars family, George!
how can i control the distance by using the encoder and how can we calculate the impulse
Hi Yahai,
Thanks for your comment!
I will pass this on to our course developers as a topic suggestion. This would make for a great future course video.
Happy learning!
So let's use the typical 1024 pulse per revolution shaft mounted encoder. That means each revolution of the motor send 1024 pulses to the motor controller, typically some kind of VFD or PLC which in turn controls the motor controller. Most applications are geared so that means we must take account the gear ratios between the motor and load. Let assume we are a 1:1 ratio and we are controlling rotational position scaled to units of degrees. It depends on the software used but in siemens motion control, you scale the units and define as rotational motion. This sets the units you use when setting acceleration or deceleration as degrees/sec/sec and position in degrees. You define the position of the movement in length units. Let's assume for simplicity we define 3600 length units per revolution of the motor, that means when I command the motor to move 3600 length units it will move the motor one revolution at whatever accelerating I defined. What the motor does depends on what type of movement you have chosen. There are several types of movements, ranging from absolute, relative, synchronization position and speed movements, gear in movements and other more complex movements. A simple position movement will be defined as either relative or absolute. A relative movement will move whatever length units you defined from its current position. An absolute move will move to that specific position. So let's say, our position is 3600 LU and we move relatively 10000 LU, the motor will move until the position is 13600 LU. An absolute move would have put the motor position at 10000 LU.
So to sum up, motion control is counting the encoder pulses from the motor and correlating that to some rotational or linear travel through defining this in meaningful units and issuing commands to the drive based on these units.
Awesome!!!
Thank you!
Correct
Thanks 👍
You're very welcome, Emilios!
Is there a way to preset a negative value?
No, the encoder position is always a positive number. If you want to establish a zero-reference and track position by + (clockwise) or - (c0unter-clockwise) from that reference, you could do that by keeping a separate integer variable that you can program with a value that increments up or down based on encoder position. That is a lot of work, and i find using the encoder's raw position value to be the best to use.
How does the incremental encoder know which direction it is moving/rotating?
It would only know by detection of the direction of rotation of the encoder drive shaft.
Can we make incremental to absolute or vice versa....
No. This would require changing out the device. The incremental and absolute encoder signals are very different in the way the position is determined. Absolute encoders use multiple light paths to determine an absolute position whereas an incremental encoder has one light signal that pulses each time a fractional movement of the rotating disk is detected.
Can you please help me to make a code for DMX512 stapper motor with encoder
Please help me
Is there actually encoders that output binary? I thought Gray Code was what they used.
With an absolute encoder, there is a distinct bit pattern for every position, so that the position can precisely be known. Many absolute encoders utilize multiple disks for position determination and many are able to determine absolute position over up to 4096 increments/turn.
Yes you are correct.
I don't quite understand the absolute rotary encoder. For example , the disk start from 0 degree and it's 000 binary , for it to rotate until 001, it needs 360/8(binary digits/different pattern) = 45 degree, how can it knows where is the disk ? is it 23 deg ? is it 40 deg ? because the binary is still 000 , the pattern doesn't change
For an absolute encoder, as the encoder disk turns, the "pattern" that is sensed is unique for every position that can be sensed. The encoder in the video is only a 3-bit encoder, capable of detecting changes of 360/8 or 45 -degrees. So you are correct: between 0 and 45 degrees, the pattern does not change. However, an actual encoder, say a 15-bit encoder, is able to discern 360/32768 or 0.011 degrees of rotation. Each increment has a unique pattern, so the encoder always knows where it is relative to the 0-degree, or home position.
@@realpars Ah I see. So a x bit encoder use x led arrays to detect and 2^x different patterns?
I have a absolute type encoder which is gray code output may i replace it with Binary coded absolute encoder? If you know please help me Thanks in advance.
Yes. HOWEVER, gray code and binary are not the same number system, so you would need to modify your PLC code to replace the gray code to absolute position conversion with a binary code to absolute position conversion.
@@realpars Thanks for your reply
Good
That's why Gray code is vital.
How are
Please I need bdf book for Plc from realpars
False! The absolute definition cannot account for the position angles between output changes. The only thing it could do is assume position angle based on current input to the motor and last known RPM. What that design us doing is giving an output every 1/6 rotation it seems.
However, if you were to add incremental pulses to the outter edge, you could know where the shaft is up to the resolution of the smallest gap between larger gaps. But if power is removed and restored it could only tell you which 1/6 its in and whether or not it is at an increment. But not which increment of that 1/6 it's at.
Am I right? Incremental Encoder used in cash sorting machine for counting.
In a sense, you are correct. The bills are mechanically pulled through a microprocessor scanner one at a time, and based on how many times a beam of light is interrupted, the machine knows how many bills it pulled through. While this is technically not an incremental encoder, it works pretty much the same. As the bills go through the cash sorter, combinations of Ultraviolet (UV), Magnetic (MG), and Infrared (IR) are used for counterfeit detection and pattern recognition is used for detecting the denomination and orientation.