Position Detecting Apparatus Synchronism Error Threshold

The patent introduces a feedback mechanism where the detected position information is used to predict expected signal characteristics, and the actual detected signals are compared against these predictions. When deviations exceed a threshold, the system identifies potential errors caused by scratches or motes and corrects the position calculation, thereby maintaining reliability without sacrificing measurement precision.

The system performs preliminary calculations of expected signal phases and positions before final detection. By pre-computing what the signals should be under normal conditions, the system can quickly identify anomalies caused by scale contamination and prevent erroneous detection, thus improving reliability while preserving measurement accuracy.

The patent divides the scale into multiple pattern arrays with different spatial cycles (coarse and fine patterns). Each pattern array serves a specific function: the coarse pattern provides overall position range information while the fine pattern provides precise position measurement. This segmentation allows the system to achieve high measurement precision without requiring a single overly complex pattern, thereby managing device complexity effectively.

The patent extends the measurement capability by adding a dimensional aspect through multiple pattern cycles. Instead of relying on a single pattern density, the system uses patterns with different spatial frequencies (dimensions of measurement resolution), allowing simultaneous determination of both coarse and fine position information. This dimensional approach achieves high precision while keeping individual pattern structures relatively simple.