Wikipedia:VideoWiki/Incremental Encoder
| VideoWiki/Incremental Encoder (Tutorial) | |
|---|---|
| File:En.Video-Incremental Encoder.webm | |
| Link to Commons | |
| Steps for video creation | |
| Step 1 | Preview my changes (10 sec) |
| Step 2 | Upload to Commons (10 min) |
Introduction
An, incremental encoder, is an electromechanical sensor that has two output signals, A and B, which issue pulses when the device moves.[1] Together, the A and B signals indicate both the distance traveled and the direction of movement.
Types
Incremental encoders are generally classified as either rotary or linear.
Linear type
Linear encoders, such as these. move along a linear path. Each output pulse corresponds to a constant, linear distance.
Rotary type
Rotary encoders move by rotating a shaft about a central axis. Each output pulse corresponds to a constant angular change of the shaft.
Quadrature encoding
The pulses emitted on the A and B outputs are quadrature-encoded, meaning that when the encoder is moving at constant speed, the pulse on and off times will be equal
Phase difference
and there will be a 90 degree phase difference between A and B.[2]
Phase interpretation
The phase difference will be positive or negative, depending on the direction of movement. For example, in this diagram, B rises before A, so the phase difference is negative. However, when the encoder moves in the opposite direction, A will rise before B, resulting in a positive phase difference. The direction of movement is determined by measuring this phase difference.
Sensing method
Incremental encoders employ various techniques to generate output pulses. A commonly used method employs optical components, in which a light-emitting diode shines light on an optical detector. As the encoder moves, the light is periodically blocked by a mechanical interrupter. In the device shown here, the edge of a transparent disc passes between a light source and detector. The black bands on the disc block the light, whereas transparent areas between the bands allow light to pass.
Pulse generation
The optical detector will output alternating logic levels as the interrupter alternately blocks and passes light to the detector. The frequency of these optical interruptions is proportional to encoder speed.[1] Consequently, encoder speed can be determined by measuring the frequency of the encoder's output pulses.
Rotary encoder mechanism
One incremental encoder requires two of these mechanisms, to produce quadrature outputs. Rotary encoders typically use a single rotating disc which has two concentric optical interrupters, one for the A output and another for the B output. The patterns of the two interrupters are staggered to produce quadrature-encoded signals.
Linear encoder mechanism
Linear incremental encoders employ a similar technique, but use a linear scale to produce the output pulses.
Interface
Incremental encoders do not indicate absolute position; they only report incremental movements.[3] To determine absolute position, it is necessary to send the encoder signals to an incremental encoder interface such as this.
Counter
The interface keeps track of absolute position by counting encoder output pulses. It counts up when the quadrature phase difference is positive, and down when the difference is negative, or vice versa. To do this, interfaces typically employ a quadrature decoder to convert the A and B pulses into direction and count enable signals, which in turn control an up/down counter.
Applications
Incremental encoders report position changes in real-time, making them useful for precise measurement, and control, of position and velocity in a diverse range of applications.[4]
Trackballs
In human input devices such as trackballs,
Mice
and mechanical mice,
Mouse innards
two rotary incremental encoders are used to simultaneously monitor position on two different axes.
Conveyors
Material conveyors use incremental encoders as feedback devices for closed-loop speed control.
Radar speed
Radars use a single rotary incremental encoder in two different ways. The encoder's output pulse frequency is measured and used to control the rate of antenna rotation.
Radar bearing
The pulses are also counted as the antenna rotates, to keep track of the antenna angle. When the radar detects an object, the target bearing is indicated by the pulse count.
Pipeline inspection
Rotary incremental encoders are used to monitor the positions of of pipeline inspection tractors, such as this, as they travel through underground pipes. This is made possible by a tether cable which is towed behind the tractor. The incremental encoder monitors the length of cable that pays out as the tractor drives through the pipe. The exact location of the tractor can be determined by counting encoder output pulses.
Motion platforms
Incremental encoders are used to control motion platforms in aircraft simulators and amusement rides.
CNC
And to control tool speed in automated machining equipment such as CNC mills and lathes.
PCB mount
Some, rotary encoders are designed to be mounted on circuit boards. These typically have a knob attached to the shaft, and are used as hand-operated controls in electronic equipment.
CMM
Linear incremental encoders are best suited for cases in which movement occurs along a straight line. Common applications include position monitoring in coordinate measuring machines.
Steppers
and position control in steppers, used in semiconductor fabrication.
References
- ^ a b Sensoray. "Introduction to Incremental Encoders". Retrieved 18 July 2018.
- ^ Craig, K. "Optical Encoders" (PDF). Retrieved 25 July 2018.
- ^ "The Basics of How an Encoder Works" (PDF). Encoder Products Company. Retrieved 23 July 2018.
- ^ "Encoder Primer" (PDF). NASA Infrared Telescope Facility (IRTF). Institute for Astronomy, University of Hawaii. Retrieved 17 August 2018.