Meaning
Signal processing technique used to determine the position and direction of motion from two out-of-phase pulse streams. In motion control systems, quadrature decoding interprets the outputs of an incremental encoder to track the rotation of a motor or the travel of a linear slide. The two signals, usually labeled A and B, are offset by ninety degrees to provide spatial information.
The process stops providing accurate data if the pulse frequency exceeds the sampling rate of the processor.
Phase Relationship
Directional sensing is achieved by observing which signal leads the other. When signal A leads signal B, quadrature decoding identifies clockwise rotation, while signal B leading signal A indicates counter-clockwise movement. This logical determination happens at the hardware level in modern microcontrollers.
Resolution Enhancement
Counting every transition of both signals multiplies the effective precision of the encoder. Through quadrature decoding in 4x mode, a 1000-line encoder yields 4000 distinct positions per revolution. This captures the rising and falling edges of both channels.
Higher resolution allows for more precise positioning in robotics. This implementation requires high-speed digital inputs with hardware-based noise filtering to prevent false counts.
Velocity Calculation
Frequency analysis of the incoming pulse train provides the rate of movement. By timing the interval between edges during quadrature decoding, the system calculates the instantaneous RPM of the drive. Sudden changes in pulse width can indicate mechanical slips or vibrations.
Steady velocity feedback is necessary for maintaining synchronization in complex multi-axis machines.
