Encoder

What is Encoder

An encoder is an electromechanical device that is used to measure motion or position in form of digital signal and also used in many industries to provide feedback.  In the most basic terms, an encoder, regardless of the type, which will control or monitor position, direction, distance, speed or counts. they will use motion, under a variety of technologies and translate into electrical signal.

Different types of encoders 

There are various types of encoders which can be classified based on sensing technique, measuring technique etc. a broad classification is shown in the diagram-

Linear encoder-

Linear encoder is a sensor which is used to measure linear movement of object. This type of device can shift (move) in different direction but always travel along one axis. It can identify distance, displacement, speed and direction. Linear encoders are used in everything from metrology equipment, motion systems, inkjet printers, and digital calipers to high precision machining tools and coordinate measuring machines to steps, CNC mills, and manufacturing gantry tables, and semiconductor steppers. The linear encoder is installed above the magnetic scale, and when the scale is moved, the encoder reads out the distance travelled.

There are two types of linear encoders-

• absolute encoder ,and
• Incremental encoder

Absolute linear encoder-

Absolute encoders are used in applications that require a high speed unique digital output for each position and provide functional immunity from power interruptions. Absolute linear encoders create a unique position indication. In contrast, in absolute encoders each position is properly referenced with a unique code , corresponding to a unique pattern of bits in the various tracks. So, the position is always known and it is not necessary to define a context if the system is powered down or is turned off.

Incremental linear encoder-

Incremental information is obtained by just counting the pulses. Hence, it depends on the previous state and the value of the transition. Its largest drawback consists in the need for defining a starting position reference: this information is lost whenever the system is powered down or is turned off.

Rotary encoder | Shaft encoder-  

A rotary encoder, also known as a  shaft encoder, is an electro-mechanical device that converts the angular position or speed of a shaft or axle into an analog or digital output signal. it is an electromechanical transducer that converts a rotary position into an electronic signal that is suitable for providing input data to a wide range of electronic control devices. these are used for a wide variety of mechanical applications.

Similar to linear encoders,  rotary encoders are also categorized to absolute and incremental type.

 Absolute rotary encoder-

An absolute encoder’s output indicates current shaft position, making it an angle transducer. The output of an incremental encoder provides information about shaft speed, which is typically processed elsewhere into information such as position, speed and distance. Provides a unique electronic piece of information at each division of shaft position and it is used for positioning system. A rotary incremental encoder can use mechanical, optical, or magnetic sensors to detect rotational position changes. The mechanical type is commonly employed on electronic equipment as a manually operated “digital potentiometer” control.

Incremental rotary encoder-

Rotary incremental encoders report position changes without prompting to do so, and they convey this information at data rates that are orders of magnitude faster than most types of full shaft encoders. Because of this, incremental encoders are commonly used in applications that require accurate measurement of position and velocity.Provides homogeneous electronic pulses at each division of shaft rotation. It controls speed of motor.

Encoder technologies | physical Principle of encoder

Linear encoding technologies is used to optical, magnetic, inductive, capacitive and eddy current

Magnetic Encoder-

Magnetic linear encoders employ either active (magnetic) or passive (variable reluctance) scales and positioning can be realized using sense-coils, the Hall Effect or magneto resistive readaheads. Resolutions on the order of micrometers are ideal, with periods of scale thicker than those of optical encoders (typically a few hundred micrometers to several millimeters).

Optical encoder–

When specifying an optical encoder, it is important that the encoder has additional protection to prevent contamination from dust, vibration, and other conditions common to industrial environments. Typical incremental scale periods vary from hundreds of micrometers to sub-micrometers. Interpolation can provide resolutions as low as one nanometer. The light sources used include infrared LEDs, visible LEDs, miniature light-bulbs and laser diodes. This type of technology is the most widely used in encoder motion translating.

There are some example of an incremental optical type uses a beam of light that passes  through a disk  that has opaque lines in a specific pattern, somewhat like the spokes of a wheel.  On the other side of the disk is a photo sensing device that will interpret the light, based on the pattern on the disk, picture a shutter, blocking and unblocking the light. The pulse of light is then converted to an electrical signal to be sent back to the processor through the encoder’s output. Encoders have a wide range of uses which include “close loop” applications such as “servo or VFD control”,” measuring” and “counts”.

Capacitive Encoder-

they work by sensing capacitance between a reader and a scale. Typical application are digital calipers. One of the disadvantages is the susceptibility to uneven dirt, which can locally change the relative permeability.

The basic principle behind capacitive type is that they detect changes in capacitance using a high frequency reference signal. It is accomplished with three main parts—a stationary transmitter, a rotor, and a stationary receiver. (The capacitive encoder can also be provided in a “two-part” configuration with a rotor and a combined transmitter/receiver.) The rotor is etched with a sinusoidal pattern, and as it rotates, this pattern is followed by a high-frequency signal Controls the transmitter in a predictable manner.

Mechanical Encoder-

It is also known as conductive encoder. A series of peripheral copper tracks engraved on the PCB are used to encode information for sensing conductive fields via contact brushes. Mechanical encoders are economical but susceptible to mechanical wear. It is common in human interfaces such as digital multimeters.

Eddy current type-

The “eddy current type digital encoder and position reference”, gives an example of this type of encoder, which uses a scale coded with high and low permeability, nonmagnetic materials, which can be monitored by monitoring changes in the inductance of an AC circuit. Detected and decoded includes an inductive coil sensor. Maxon makes an example (rotary encoder) product (mile encoder).

Resolver and encoder-

Resolvers and encoders are both devices that translate mechanical motion into an electrical signal to determine the rotating location of a shaft. A resolver resembles a motor in that it contains a rotor with a primary (reference) winding and a stator with two secondary windings—sine (SIN) and cosine (COS)—that are mechanically phased 90 degrees apart. Voltages are induced in the stator windings when an AC voltage is applied to the rotor winding. These voltages are equal to the reference voltage multiplied by the sine or cosine of the angle of the input shaft from zero. The ratio of the voltages represents the absolute location of the input shaft, and the two voltages are compared by a resolver to digital converter (RDC).

Applications of encoder-

• Robotics, gate control ,drilling machines, conveyors, lathes, automation
• For VFD control, when running pump, on a VFD, to fill a tank full of  liquid then require a certain speed and want to verify that the pump VFD is at the required speed. An encoder on the VFD can be used for feedback of speed.
• An example for a measuring process. in this application , need to cut some aluminum products to a particular size and passing a long roll, meaning hundreds of feet, of the aluminum sheet through a cutting mechanism. Need to determine the amount of aluminum fed so that can cut the sheets to the standard size that will be used in a separate manufacturing process. an encoder attached to the conveyor and reading the material that is feeding through your cutting assembly will indicate the length of material that has been fed since the last cut.

To read more about following topics, click on individual links below-

• Encoding types
• Priority encoder
• Encoder and decoder
• Encoding meaning in hindi
• Different Types of display devices
• Digital Electronics