Elevator Encoder: Incremental Absolute Resolver Types, VVVF Speed Regulation, Floor Learning and Rollback Prevention

The encoder (also called incremental encoder, rotary encoder, or position transducer) is a critical feedback device in modern VVVF-controlled elevators. Types: (1) Incremental encoder — generates a fixed number of pulses per revolution (PPR), typically 1024, 2048, or 4096 PPR; outputs two channels (A and B) in quadrature (90° phase difference) to determine speed and direction; a Z (index) channel gives one pulse per revolution for absolute reference; (2) Absolute encoder — provides absolute position data directly without needing a reference pulse; more expensive but used in high-rise elevators and in PESSRAL safety applications; (3) Resolver — an analogue angular position sensor, more robust in harsh environments (high temperature, vibration) than optical encoders; used by some machine manufacturers. Mounting positions: (a) Motor shaft — directly measures motor rotation; combined with known roping ratio and rope diameter gives car position and speed; (b) Governor rope pulley — in some MRL designs, the encoder measures rope movement directly for position. Functions in VVVF elevator: (1) Speed regulation — the drive compares the encoder speed feedback with the speed profile reference (ramp generator) and adjusts output frequency/torque to follow the profile; achieves ±1–3 mm levelling; (2) Position calculation — car position is calculated by integrating pulses from a known reference floor; (3) Floor learning — during commissioning, the car runs a learning trip and records floor positions from encoder count; (4) Rollback prevention — encoder feedback detects any unexpected motion at start and the drive compensates before brake release.

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