A complete guide to buying encoders

In today’s globalized, digital, and continuously developing world, there is an encoder in nearly everything. From automation systems such as machinery, processes in factories, elevators, heat treating ovens, aircraft to robotics and a myriad of other applications. As such, encoders, also known as shaft encoders, play an important role in applications that require monitoring and/or controlling of a moving part. The history of encoders dates back to early 1960s when the very first encoder, by that time called a DOME- Digital Optical Measuring instrument- was developed by a German manufacturer.

Over its course of development, many names were assigned to what is today known as an encoder: an angular displacement sensor, a photo-pulse sensor, a rotation converter, etc. Yet, its functionality and usability has remained the same despite all the different adjustments and improvements carried out by means of automation and artificial intelligence technologies improvements. This draws attention to the reliance companies have on the components used in their machine tools, production lines, robotics, industry, or wherever motion or movement control is compulsory. On the market today there is a bewildering array of rotary encoders to choose from which calls for a clear explanation of their types, functionality, and benefits.

What is an encoder?

To precisely sense the motion of a rotary shaft and know its position, speed, and even its acceleration, an encoder is added to the shaft assembly. Used in machinery for motion feedback and motion control, encoders convert the motion to an electrical signal that can be read by some kind of control device in a motion control system. Nowadays, encoders are reliable products used in all sorts of industries. Their service life, given a proper operation, installation, and the connection is at least 50,000 hours which means approximately 6 years of operation, or perhaps more, depending on the particular operating conditions of the sensor including the encoder’s usage time.

The advantages of encoders include:

  • Low operating costs
  • Highly reliable and accurate – can operate in the harshest industrial environments
  • Eliminate mechanical failures
  • Immune to external interfaces
  • High resolution
  • Offer fully programable solutions
  • Provide complete adaptability, flexibility, and freedom for any breed of industrial application
  • Possibility to incorporate them in existing applications
  • Compact size
  • Fuses optical and digital technology (change maybe working)

An encoder usually consists of the following main elements:

  1. Encoder shaft
  2. Code disk
  3. Light sources
  4. Receiver (receiving infrared- IR)
  5. Optical - mechanical unit with gears
  6. Electronic board - containing signal processors and digital interface converters

 

 rotary encoder decomposed

 

There are many types of encoders, but they basically follow into two main sensing techniques:

1. Rotary encoders

rotary encoder

In the most basic terms, and as its name implies, a rotary encoder measures rotary motion. A rotary encoder is a device used in many industries to provide feedback -electrical signal- while it measures the number of rotations, the rotational angle, and the rotational position.

This type of encoder, depending on the measurement type used, can transform an object’s angular position/ motion based on the rotation of the shaft. Rotary encoders convert mechanical displacements into electrical signals that are being sent to a processor for interpretations. Rotary encoders can for instance be employed in computer input devices (mice, etc.) not to mention robotics.

2. Linear encoders

 

linear encoder

But encoders can also be linear, used to measure linear motions along a straight line. Linear encoders can use either a rod or a cable that is run between the encoder transducer and the object to be measured for movement. An output signal which is linear to the object’s movement is created as the object moves according to the transducer’s data collected from the rod/ cable.

The linear encoder uses the information collected to determine the position of the object in question as the distance is being measured. Linear encoders can have analog or digital outputs. A linear encoder can be used, for instance, in metrology instruments, mission systems, for a CNC milling machine where accurate movement measurements are a prerequisite for efficiency in manufacturing, etc.

Encoders are normally used for the following tasks:

  • Measuring angular positions
  • Positioning of objects, nodes, and structures
  • Identifying the position of objects, nodes, structures in space
  • Defining the exact position of objects, structures, units in conveyor systems
  • Defining the angles of inclination or rotation of objects, nodes, structures
  • Measurement of rotational movements

encoders application

Encoders measurement types:

  1. Incremental Encoders

Incremental encoders are one of the most used rotary encoders. They can be used in positioning and motor speed feedback applications, including servo/light, industrial or heavy-duty applications.

This type of encoder yields a pulse string in response to the amount of rotational displacement of the shaft that make up a binary code. That is to say, the main task of an incremental encoder is to calculate single pulses in one cycle. One cycle equals one revolution of the encoder disk. The number of output pulses are then being counted by a separate counter to determine the amount of rotation based on the count. To accurately count the number and degree of rotation from a certain input shaft position, the counter is reset at the reference position and the number of pulses passing through that position is added gradually by the counter. The resolution of incremental encoders is measured in pulses per revolution (ppr). Accordingly, the count for the number of rotations can be unlimited and the reference position can be selected as appropriate. One of the other important features of an incremental encoder is that a circuit can be added to generate twice or four times the number of pulses for one signal period when, for instance, high resolution is necessary.

When a disk with an optical pattern revolves along with the shaft, light passes through two slits which is then transmitted or blocked pursuant to those patterns. Following, the light that passes through those gaps is later converted into electrical currents in the detector elements, corresponding to each slit and is then received as two square waves. The two slits are established in such a way that the phase difference between the square wave outputs is one-fourth of the pitch.

When powered on, the incremental encoder begins its count at zero. Unlike the absolute encoders, there are no safeguards regarding the position. Given that an incremental encoder begins counting from zero regardless of where the shaft is or its previous position, in the event of power disruptions or in the startup of the control system, it is of paramount importance to determine a reference point for all tasks requiring positioning. Incremental encoders store the data in an external buffer/ counter. Among the advantages of an incremental encoders are their less complex nature, typically lower costs as well as their high noise immunity. Incremental encoders have a flexible scaling functionality as well as magnetic measuring principles including a resolution of up to 50,000 PPR.

  1. Absolute Encoders

Alike an incremental encoder, an absolute encoder also measures angle position based on the position of the shaft. Yet, in comparison with an incremental encoder, an absolute encoder retains the angle position measured regardless of whether the encoder is powered or not. Such an encoder knows its true new position even when a movement is made without power to the encoder or when power it is reapplied. Also, unlike incremental encoders that output a constant stream of ubiquitous pulses, absolute encoders have the capacity to output unique words/ bits for each given position. That is to say, absolute encoders read so-called states- a sequence of codes.

This type of measurement is preferred when safety is a primary concern or when a high degree of certainty is required, given that absolute encoders position themselves when the machine is powered on. The main task of an absolute encoder is to detect sequences of codes (states) in the course of the rotation of the encoder disk. The use of an absolute encoder grant solving a much wider range of tasks given that measurements are made by special digital codes not by means of pulse fixation.

With the entire surface of the disk divided into a certain number of sectors, this kind of encoder yield pulses is parallel to the rotation angle represented as an absolute value in 2n code. Simply put, each sector of the absolute encoder disk is assigned a specific numeric code. When the shaft begins to rotate, the absolute encoder reads out the absolute data, forming such a specific individual code (absolute code/value). As such, an absolute encoder has one output for each output code bit, and while the resolution increases, the value of outputs increases as well. Having reached the maximum value, the absolute encoder goes back to zero and the process of calculating the angular position is then repeated again. In case the shaft of the absolute encoder is rotated in the opposite direction, values (codes) in the reverse order will begin to form. In this way, the direction of the encoder shaft can be easily determined.

The advantages of using an absolute encoder include its higher overall resolution, better start up performance, better recovery from system or power failure, accurate motion detection ahead multiple axes as well as multiple output protocols to facilitate electronics integration. Moreover, when high-speed rotation makes it impossible to read the codes, the data can be read when the rotation speed slows.

absolute/incremental encoders 

 

When choosing an encoder, it is necessary to consider the following:

  • The type of encoder application (indoor or external installation)
  • Encoder sensing techniques – rotary or linear
  • Encoder measurement types – incremental or absolute
  • Output signal type (HTL, TTL, binary code, etc.)
  • Number of pulses for each revolution of the encoder disk
  • Encoder supply voltage
  • Encoder connector type
  • Encoder cost and delivery conditions
  • Additional requirements for encoder installation (mounting flange, mounting rode, etc.)
  • Necessary cable length
  • Type of flange needed on the shaft for a key
  • Bit width for absolute encoders
  • Axial shaft/ shaft hole diameter in mm

Encoders selection and buying process should only be made by experienced and qualified employees. Failing to comply with the terms of reference can usually lead to the breakdown of a lot of other expensive machinery or equipment included in the system design, increasing such the costs and time for damage control. As such, when choosing an encoder, appropriate attention should be paid to the experience and reliability of the supplier given the increasing number of companies operating in the market nowadays.

Buy encoders from the first B2B sector specific Marketplace - SourceMe

Since there is such a large number of alternatives for encoders and a vast range of suppliers to choose from it might be complicated for companies to search and actually find the right product that matches their requirements. Therefore, SourceMe was founded with the idea of giving machine builders the possibility to find quality encoders and trusted suppliers in less than 5 minutes. SourceMe is a platform that offers encoders in different sizes, models, and brands of best quality and prices.

Busines these, the supplier pages are up to date, containing a comprehensive company description which includes, for instance, founding date, company history, main markets, details about quality managements system compliance, companies’ case studies with relevant information and contact details. As such, having all this information nicely put together give machine builders a better, easier, and fun way to browse through trusted and reliable suppliers. Go have a look at our website www.sourceme.com and find your next supplier. To make it even easier for customers to find the best supplier, SourceMe places at buyers’ disposal a suppliers comparison feature as exhibited in the GIF below. In this way, buyers can select a number of products they are interested in, add them to the comparison feature, and later evaluate and choose the best supplier based on the information provided.

 

 

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