N Teeth With 1 Shifted to be Advanced Encoder Style

General Description

The N teeth with 1 shifted to be advanced encoder style describes those encoder patterns that consist of N equidistant teeth distributed about a wheel with one of those teeth shifted to be advanced relative to the direction of rotation. The shifted tooth is advanced half the equidistant displacement. Thus this would be 7.5° if 'N' was 24. This example is dipicted in the figure and is referred to as a 24 Shifted 1 (advanced) encoder.

Synchronization

The non-equidistant spacing is used to communicate synchronization information. Speaking generally, the shifted tooth is detected if the time from the last synchronous encoder edge to the last detected edge is less than half the previous observed tooth period.

A crank synchronization error will be flagged if, upon detecting the shifted tooth, the number of real teeth previously observed was incorrect. Thus the 24 Shifted 1 (advanced) pattern would issue a synchronization error if 23 normal teeth were not observed between observing the "shifted" tooth and observing the next "shifted" tooth.

A resynchronization can temporarily impact the behavior of crank-synchronous blocks. Impacts include a pulse not scheduling as expected, having it occur twice, or being malformed. The system will recover, but the initial impact is unavoidable because the correction to the crank angle position results in a step change in position that may disrupt the underlying pulse scheduling software.