What is the Difference between Absolute and Incremental Encoders?

Summary

This video explores various types of encoders, focusing on linear and rotary encoders with absolute and incremental measurement capabilities. It explains how encoders like optical, magnetic, inductive, capacitive, and laser work to provide feedback on position, speed, and direction. The script delves into practical applications, such as CNC machines and robotics, and clarifies the differences between absolute and incremental encoders, highlighting their respective advantages in safety-critical and setup-intensive environments. Aimed at helping viewers make informed choices for their specific needs, the video also encourages learning PLC programming for career advancement.

Takeaways

• 📊 Encoders are essential components in various applications, and this video script provides an in-depth look at different types and their uses.
• 🔄 There are two main sensing techniques for encoders: Linear and Rotary, with each category further divided into Absolute and Incremental measurement types.
• 🛠️ Linear Encoders use a transducer to measure distance between two points, and can be used in applications like CNC milling machines for precise movement.
• 🎯 Rotary Encoders, also known as Shaft Encoders, collect data based on the rotation of an object and can be used in applications ranging from computer input devices to robotics.
• 📐 Position Encoders are used to determine the mechanical position of an object, which can be either Absolute or Incremental, and are widely used in industrial applications for tooling and multi-axis positioning.
• 🌐 Optical Encoders interpret data in pulses of light, determining position, direction, and velocity, and can be used in applications like printers, CNC milling machines, and robotics, with Absolute or Incremental capabilities.
• 🔄 Absolute vs. Incremental: Absolute encoders, like Rotary Absolute, have a unique code pattern that allows for precise position detection, ideal for safety-critical applications. Incremental encoders, on the other hand, start at zero and count each revolution, useful for applications where the exact position is not crucial.
• 🛠️ For Rotary Absolute encoders, the slotted disc on a shaft, in conjunction with a stationary pickup device, produces a unique code pattern for each position, ensuring accurate positioning.
• 🚀 Incremental encoders begin their count at zero and record each revolution, making them suitable for applications where the exact position is not needed, but the relative change is.
• 📈 The script provides a practical example of using an incremental encoder to determine the travel count of an object on a conveyor, highlighting the difference between Absolute and Incremental measurements.

Q & A

What are the two main sensing techniques of encoders mentioned in the script?

The two main sensing techniques of encoders mentioned are Linear and Rotary.

What is the purpose of a Linear Encoder in an application?

A Linear Encoder uses a transducer to measure the distance between two points and can be used to determine the position of an object, such as in a CNC milling machine for precise movement measurements.

How does a Rotary Encoder differ from a Linear Encoder?

A Rotary Encoder collects data and provides feedback based on the rotation of an object, converting an object's angular position or motion, whereas a Linear Encoder measures the distance between two points.

What are the two types of encoder measurement types discussed in the script?

The two types of encoder measurement types discussed are Absolute and Incremental.

What is the difference between Absolute and Incremental Rotary Encoders?

Absolute Rotary Encoders can measure angular positions, while Incremental Rotary Encoders can measure distance, speed, and position based on the number of signals per revolution.

In which applications are Rotary Encoders commonly used?

Rotary Encoders are used in various applications such as computer input devices like mice and trackballs, as well as in robotics.

What is a Position Encoder and how is it used?

A Position Encoder is used to determine the mechanical position of an object, providing an absolute position or detecting a change in position relative to the encoder, and is widely used in industrial applications for tooling and multi-axis positioning.

How do Optical Encoders interpret data to determine position, direction, and velocity?

Optical Encoders interpret data in pulses of light, using a rotating disc with opaque segments that represent a particular pattern to determine the movement of an object for rotary or shaft applications, and exact position in linear functions.

What are the two types of Absolute Measurement Encoders mentioned in the script?

The two types of Absolute Measurement Encoders mentioned are Single-turn and Multi-turn, with Single-turn used for short distances and Multi-turn for longer distances and more complex positioning.

How does an Incremental Encoder determine the position of an object?

An Incremental Encoder creates an output signal each time the shaft rotates a measured amount, and the position is determined based on the count of signals from zero, without a definitive position unless a reference point is established.

What is the advantage of using an Absolute Encoder over an Incremental Encoder in safety-critical applications?

Absolute Encoders are preferred in safety-critical applications because they provide a high degree of certainty regarding the exact position at all times, based on the unique pattern produced, without the need for a reference point after power disruptions.

Outlines

00:00

🎥 Introduction to Encoder Types and Techniques

This video starts by revisiting the concept of encoders and their implementation. It outlines the various types of encoders, such as linear and rotary, and highlights their primary sensing techniques. The script emphasizes the importance of understanding different encoder technologies like magnetic, optical, inductive, capacitive, and laser. It briefly touches on the fundamental configurations, such as linear and rotary encoders, explaining their operational principles and applications, such as CNC milling machines for linear encoders and computer input devices for rotary encoders.

05:02

📏 Absolute vs Incremental Measurements Explained

The video delves into the differences between absolute and incremental measurements using rotary encoders as examples. Absolute encoders use a unique code pattern to determine the exact position, which is critical for safety and precision. In contrast, incremental encoders generate output signals based on the shaft's rotation, starting the count at zero upon power-up. The script provides an example with a conveyor system to illustrate how incremental encoders work and the necessity of a reference point for accurate positioning. The segment concludes by emphasizing the practical applications and the importance of choosing the right type of encoder based on specific requirements.

Keywords

💡Encoder

An encoder is a device that converts a physical quantity such as position, distance, speed, or direction into a digital signal. In the context of the video, encoders are essential for providing feedback on the movement and position of objects in various applications, such as CNC milling machines and robotics. The script discusses different types of encoders and their uses, making 'encoder' a central concept to the video's theme.

💡Linear Encoder

A linear encoder is a specific type of encoder that measures the distance between two points using a transducer. It can use a rod or cable to collect data on an object's movement, creating a linear output signal. The script mentions that linear encoders determine the position of an object, exemplified by their use in CNC milling machines where precise movement measurements are crucial.

💡Rotary Encoder

A rotary encoder, sometimes referred to as a shaft encoder, provides feedback based on the rotation of an object. It can convert an object's angular position or motion into a digital signal. The video script explains that rotary encoders are used in applications like computer mice and robotics, and they can measure angular positions or other variables like distance and speed.

💡Absolute Encoder

An absolute encoder is a type of encoder that provides a unique code for each position of the object it is measuring. The script describes that these encoders can measure angular positions and are capable of determining the exact position of an object, which is vital in applications where high accuracy and safety are paramount.

💡Incremental Encoder

Incremental encoders produce an output signal each time the object they are measuring rotates a measured amount. Unlike absolute encoders, they do not provide a unique code for each position but rather count the number of signals per revolution. The script uses an example of an incremental encoder in a conveyor system to illustrate how it counts the number of revolutions to determine the object's movement.

💡Position Encoder

A position encoder is used to determine the mechanical position of an object as an absolute position or to detect changes in position relative to itself. The video script discusses that position encoders are widely used in industrial settings for tooling and multi-axis positioning, emphasizing their importance in precise industrial applications.

💡Optical Encoder

An optical encoder interprets data in pulses of light to determine position, direction, and velocity. The script explains that these encoders use a rotating disc with opaque segments to create a pattern that can be read for both rotary and linear applications, highlighting their versatility in various machinery such as printers and CNC machines.

💡Magnetic Encoder

Although not explicitly detailed in the script, magnetic encoders are a type of electromechanical technology mentioned among various encoder technologies. They operate based on magnetic principles and can be used for position and speed detection in different applications.

💡Inductive Encoder

Inductive encoders, like magnetic encoders, are part of the electromechanical technologies listed in the script. They work based on electromagnetic induction and are used for position and speed sensing, offering a contactless solution for motion feedback in various environments.

💡Capacitive Encoder

Capacitive encoders are another form of electromechanical technology mentioned in the script. They operate using the principle of capacitance to measure position, offering high-resolution position sensing and are suitable for environments where other technologies might not be as effective.

💡Laser Encoder

Laser encoders are part of the electromechanical technologies category and are mentioned in the script. They use laser technology to provide precise measurements of position and distance, often used in high-precision applications where accuracy is critical.

Highlights

Introduction to various types of encoders and their applications.

Explanation of the two main sensing techniques: Linear and Rotary encoders.

Differentiating between absolute and incremental encoder measurement types.

Overview of electromechanical technologies used in encoders, such as magnetic, optical, inductive, capacitive, and laser.

Linear Encoders use a transducer to measure distance between two points.

Linear Encoders can be used in CNC milling machines for precise movement measurements.

Rotary Encoders provide feedback based on the rotation of an object.

Applications of Rotary Encoders in computer input devices and robotics.

Position Encoders determine the mechanical position of an object, either absolute or incremental.

Optical Encoders interpret data in pulses of light to determine position, direction, and velocity.

Optical Encoders' use in printers, CNC milling machines, and robotics.

All encoders produce an electrical signal that can be translated to various measurements.

Explanation of Rotary Absolute Encoders using a slotted disc and stationary pickup device.

Absolute Encoders' preference in applications requiring a high degree of certainty and safety.

Incremental Encoders create an output signal each time the shaft rotates a measured amount.

Incremental Encoders require a reference point for positioning due to the lack of position safeguards.

Example of using an Incremental Encoder for counting revolutions of a conveyor belt.

Summary of encoder variations and guidance on choosing the appropriate type for specific applications.

Invitation to learn PLC programming and advance one's career at realpars.com.

Transcripts

Previously, we discussed what an Encoder is

and how it can be implemented in your application.

In this video, we are going to discuss the various types of encoders

and which encoder may be used for which function.

before we get started on today's video

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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 are 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.

There is a plethora of information regarding Encoders

and it may seem hard to wrap your head arounded.

Descriptions like rotary or linear, optical and magnetic, absolute and incremental.

We touch on a few basics to help you understand what’s what and why.

Let’s first break these categories down a little

and explain a couple of the many configurations.

First, 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.

We will touch on Absolute and Incremental measurements a little later.

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.

Rotary or Shaft encoders, as previously stated,

may be “Absolute” or “Incremental”.

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 movement of an object

for “rotary” or “shaft” applications

while determining 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.

After explaining the main groups, you may be seeing a pattern.

All the encoders basically do the same thing,

produce an electrical signal which can then be translated to position,

speed, angle, etc.

Now that we have broken down the main groups,

let’s discuss the difference between Absolute and Incremental measurements.

To discuss the difference between absolute and incremental measurements,

we will use the Rotary Encoder type as an example.

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.

This type of measurement is preferred in applications

requiring a great degree of certainty

such as when safety is a primary concern.

Because the encoder knows, at all times,

its definitive position based on the unique pattern produced.

Absolute measurement encoders can be single-turn or multi-turn.

“Single-turn” encoders are used for measurements of short distance

while “multi-turn” would be more suitable for longer distances

and more complex positioning requirements.

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.

In the previous video,

when describing the use of an encoder for the purpose of counts,

that example is a good example of an incremental encoder.

Assume that the power has not been disrupted

and you have turned on the conveyor,

and placed the machine in setup mode.

As the encoder is turning the controller is receiving counts.

Let’s say the count range is 0 to 10000.

This is an incremental encoder so the absolute position is not known,

we just know that a full revolution of the shaft registers a count of 10000.

We’ll place the object on the conveyor and,

as soon as the entrance photo-eye sensor detects the object,

the current encoder count is captured.

Let’s say that number is 5232.

We will then capture the count with the object exiting

and being detected by the exit photo-eye.

We’ll say that the number is 6311.

So to determine the count of the full travel,

we will subtract 5232 from 6311

and determine that the object travel is 1079 counts.

By this example,

it is obvious that we do not know the absolute location of the object,

we just know that the travel count from the entrance to exit is 1079.

That doesn’t tell us that the object is three inches from the exit,

just entering, etc.

we just know that the object will enter,

a count will be captured,

and the object will exit and again, the count captured.

In the event that we did not see the object exiting within the allowable travel count,

plus or minus a deadband, the machine will fault and the process will stop.

There are many, many encoder variations out there

and we could go on for hours about the varying types.

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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