Linear Encoder : Structure, Working, Types, Wiring & Its Applications

Encoder is a type of electro-mechanical device used to change the motion into electrical feedback signal and this signal can be read by a controlling device to measure changes within speed, position, count, linear distance & direction. So these are fundamental components within high-volume and high-speed industrial applications. There are two types of encoders; a linear encoder & a rotary encoder. The main function of a linear encoder is to measure a linear path whereas a rotary encoder is used to measure a rotating motion. This article discusses an overview of a linear encoder, its working, types, and its applications.

What is Linear Encoder?

A linear encoder is a type of sensor or transducer used to monitor and measure the position, speed, direction, movement, or speed of an object. This device moves in various directions but travels along one axis always. It can detect speed, distance, direction, and displacement. These encoders are known as linear devices because they are used for measuring an object’s linear movements like its speed, distance, position, displacement, direction & acceleration. This device moves in different directions but travels always along a single axis. It can detect speed, distance, direction, and displacement.

The linear encoder accuracy is a combination of the accuracy of scale & the errors that occurred by the readhead. To indicate the encoder accuracy, the most common unit is µm/m or µm for each unit scale length. Linear encoder technologies are; optical, inductive, magnetic, eddy current & capacitive. These types of encoders can be used in different environments because of their protected housing like gaseous & liquid, solid, and bulk solids.

How Does Linear Encoder Work?

A linear encoder is paired with a scale that encodes position by reading the scale and changes into an analog (or) digital signal, after that it can be decoded into position through a motion controller or DRO (digital readout). This encoder can be either an absolute system or an incremental system. The motion in an absolute system can be determined through position above time whereas in an incremental system, the position can be determined through motion above time.

These encoders may be either open or enclosed. Open linear encoders are mainly used for maximum accuracy, low friction & low measurement hysteresis applications. Enclosed linear-type encoders are used in hostile, dirty environments like machine tools. These types of encoders usually include an aluminum extrusion surrounded by a metal or glass scale. These encoders may utilize glass or reflective scales where materials of scale contain chrome on metal, glass, plastics & ceramics.

Linear Encoder Structure

The linear encoder structure mainly includes signal units connected to a measuring scale which can be separated into three basic elements based on functional purposes Scale, Signal Source, and Transducer which are discussed below.

Scale is the significant part of this encoder which has marks on its plane and these marks help the sensing system in determining its present position.

The signal source transmits a signal that passes throughout the scale. Once it moves throughout the marks of scale, the signal can be distorted based on the mark type. Here, the type of signal mainly depends on the working principle.

Transducer is a receiver wherever the signal change goes. The transducer changes information regarding location into analog or digital signals. After that, the data received will move into connected PLC throughout wiring using several interfaces.

Different Types of Linear Encoders

Linear encoders are classified into different types based on measuring methods and technology. These encoders are available in two types based on measuring methods; absolute and incremental. Similarly, these encoders are available in two types based on technology like magnetic and optical.

Absolute Linear Encoder

This is a type of linear encoder used to accurately determine the present location of the reading head. The marks on the scale have an exclusive position code. Once the signal passes through them & appears at the receiver, then it has specific unique information regarding slider dislocation. These encoders are most frequently used in systems wherever a specific & precise displacement is necessary like CNC, elevators, press brakes, hydraulic cylinders, milling machines, linear actuators, milling machines, etc.

Incremental Linear Encoder

These encoders are used for detecting the position offset relative to particular points. In this encoder, the marks on the scale are the same as each other. Once the device is turned off, then information on the latest location status will disappear. So it requires some particular points to navigate on the surface of the scale. These encoders are used frequently to perform some simple operations wherever a particular angle is not so significant like elevators, conveyors, cranes, stepper motors, grinding machines, Jig borers, etc.

Magnetic Linear Encoder

Magnetic linear encoder utilizes a magnetic reader head to analyze changes within magnetic fluxes for analysis of displacement. This encoder’s scale includes a set of poles that are coded magnetically and also arranged in a precise method based on the strip type. Once a slider passes through every pole on the magnetic tape, the sensor will read current changes within the magnetic fields. Afterward, the transducer evaluates all obtained data through the coded position.

These types of encoders are more resistant as compared to optical-type encoders & are frequently used in surroundings exposed to debris, liquid contamination, dirt, vibration, pollution, steam & other kinds of ecological interference. These encoders’ performance can be simply affected by steel or iron magnetic chips because they can interfere with the magnetic field.

Linear Optical Encoder

The linear optical encoder uses a laser or light beam signal. To develop the light pulse quality & direction, extra elements are also mounted into the design. To perform this, opaque or transparent areas are located as marks on the scale. Generally, the optical scale is made from plastic, glass, or sometimes aluminum. Optical technology simply allows linear measurements the maximum accuracy & resolution. But the accuracy can be affected significantly by solid particles or pollution within a gap between the sensor, measuring surface, vibration & mechanical shocks.

Linear Encoder Wiring Diagram

The linear encoder wiring to perform data acquisition is shown below. This wiring uses the linear encoder, sensor, Arduino, and USB. The linear encoder measurement enters through the digital inputs to the Arduino board.

The measurements from the sensor’s sphere (IMU1) & sensor’s base (IMU2) also go through the Arduino board through an I2C serial bus. Additionally, the Arduino board calculates the encoder’s linear velocity, the relative angles between the platform & the sensor’s base in the inside of the spherical motion, as well as the relative acceleration between the sensor’s sphere & base. This data throughout the USB goes into the PC, wherever the algorithm is developed through the LabView software is applied. After that, the fluid velocity can be measured and compared to the velocity attained through the linear encoder.

How to Select a Linear Encoder?

The selection of a linear encoder can be done based on different factors which need to be considered like measuring length, resolution, accuracy, etc.

• Before choosing a linear encoder, the primary thing to consider is what kind of feedback is required for the application
• Selecting this type of encoder for your application mainly depends on different outputs, types of reading, etc.
• Measurement range is the distance measurement range or the highest distance measured.
• It depends on the resolution which is the minimum amount of measurement of distance that this encoder can make.
• It is based on electrical or digital output like analog voltage, analog current, fiber optic, parallel, SSI, or serial.
• It is based on a working principle.
• The resolution is the minimum detected movement by the encoder; high, low, and medium.
• It is based on accuracy which is the difference between the encoder’s real position & the readout position.
• Linearity is the highest difference from direct proportionality in between the measured distance & the o/p distance above the measuring range.
• The encoder speed is the maximum mechanical speed at which point the encoder can function.
• The operating temperature is the range of temperature on which the device should operate.

Advantages

The advantages of linear encoder include the following.

• Its installation is easy.
• It is simple to use and affordable.
• This encoder has a high resolution, high scale accuracy & repeatability
• Its traversing speed is high.
• It has large mounting tolerances.
• Resistant to dust, oil & harsh ecological conditions
• It needs no maintenance & cleaning.
• It is high tolerance to vibration & shock.
• This encoder has high reliability
• The disadvantages of encoders include the following.
• If the type of encoder is selected incorrectly & not mounted properly then errors can occur.
• If you enhance the amount of accuracy, then you have to enhance the number of channels.
• It is capable of measuring linearly moving objects only.

Applications

The applications of linear encoders include the following.

• These types of encoders are used in two major areas like measurements and positioning systems. The measurements mainly include laser scanners, CMMs or coordinate-measuring machines, calipers, traction testers, digital readouts, gear measurements & motion control. Positioning systems mainly include valves, servo motor systems, machine tools, robotics, semiconductor testing equipment, Wire-Bonder machines, digital presses & printers.
• These encoders are used in different machine tools like CMM machines, calipers, CNC machines, and stepper motors by above one contactor.
• These are used in rollers for measuring the longitudinal distance between the roller balls
• These are used in milling machines, elevators, press brakes, linear actuators, hydraulic cylinders, Stepper motors, Jig borers, Conveyors Cranes, Grinding machines, etc.
• These encoders can be used in different industries and maintenance diagnostic systems, Inc.
• These types of encoders help in detecting distance, speed, displacement, and direction & also controlling linear movements to the right & left through nanometer accuracy.
• This type of encoder is an outstanding choice to monitor the position, speed & control of systems like AC motors, servo motors & stepper-driven systems.
• This encoder can monitor the linear movements of the motor.
• These encoders are used in a linear system that uses stepper or servo motors to improve the machine’s performance & process quality.
• This encoder is used in servo applications to monitor the actual position of the load.
• A linear encoder is particularly designed wherever the travel is linear in place of the rotary.
• These encoders are required for welding, precision machining & laser applications.

What Does a Linear Encoder Measure?

A linear encoder is used to measure the linear movement of an object.

What Is Encoding Precision?

Encoding precision is the amount that consecutive measurements at a similar location change from each other.

Are Encoders Interchangeable?

Encoders are generally interchangeable easily with another

Thus, this is an overview of a linear encoder, its working, and its applications. The linear encoder must be calibrated in order to acquire high accuracy. This encoder’s calibration data can be stored at the computer and it will correct the encoder’s reading value. So, calibration of the encoder is very important to reduce any measurement uncertainty by simply ensuring the test equipment’s accuracy. Calibration measures & also control uncertainties or errors in measurement procedure to a suitable level. Calibration of an encoder is significant to remove misalignment, subdivisional errors & eccentricity; otherwise, it could decrease the encoder’s accuracy. Here is a question for you, what is a rotary encoder?