Absolute optical encoder with long range intensity modulation on scale

An absolute optical encoder comprising:

• a scale comprising at least a first dual-modulation scale track pattern extending along a measuring axis direction;
• a light source configured to illuminate the scale and the first dual-modulation scale track pattern;
• and
• a photo detector arrangement comprising a first detector track configured to receive light from the first dual-modulation scale track pattern;
• wherein the first dual-modulation scale track pattern is configured to provide a first intensity modulation component in light the first detector track receives from the first dual-modulation scale track pattern, and the first intensity modulation component of the first dual-modulation scale track pattern varies as a function of position along the measuring axis direction, and has a first spatial wavelength SW1 along the measuring axis direction;
• wherein the first dual-modulation scale track pattern is further configured to provide a second intensity modulation component in the light the first detector track receives from the first dual-modulation scale track pattern, and the second intensity modulation component varies as a function of position along the measuring axis direction;
• wherein in the first dual-modulation scale track pattern the first intensity modulation component repeats along the measuring axis direction a plurality of times over a measuring range of the absolute optical encoder, and the second intensity modulation component varies at a slower rate than the first intensity modulation component along the measuring axis direction;
• wherein the first detector track comprises a first array of detector elements arranged along the measuring axis direction;
• wherein each detector element in the first array is configured to receive both the first and second intensity modulation components;
• wherein the detector elements in the first array are configured to form a plurality of respective spatial phase groups, each respective spatial phase group configured to spatially filter the light received from the first dual-modulation scale track pattern and provide a respective signal having a respective spatial phase relative to the first spatial wavelength SW1 of the first intensity modulation component of the first dual-modulation scale track pattern;
• and
• wherein the respective signals of the respective spatial phase groups include the effects of the second intensity modulation component, such that a signal processing relationship combining respective signals of the respective spatial phase groups provides a value that is indicative of a first coarse resolution position of the first detector track relative to the second intensity modulation component of the first dual-modulation scale track pattern.