What is the critical difference between absolute and incremental encoders in robot positioning systems?

The critical difference between absolute and incremental encoders in robot positioning systems lies in their ability to retain positional information after a power cycle or system interruption. An absolute encoder provides a unique digital code for each position within its range of motion. This means that the robot controller can determine the exact position of the joint immediately upon startup, without needing to move the joint to a reference point or perform a homing sequence. An incremental encoder, on the other hand, only provides information about the change in position. It outputs a series of pulses as the joint rotates, and the robot controller must count these pulses to track the position. If power is lost, the controller loses track of the current position and must perform a homing sequence to re-establish the zero point. For example, if a robot uses absolute encoders on its joints and the power is interrupted, the robot knows the exact position of each joint as soon as power is restored. If it uses incremental encoders, it must move each joint to a predefined home position so the controller can reset the pulse counters. Absolute encoders are more robust in applications where maintaining positional awareness is critical, while incremental encoders are generally less expensive and suitable for applications where homing is acceptable. Absolute encoders provide immediate position data, while incremental encoders require continuous tracking.