Dishwasher with image-based position sensor

A dishwasher, comprising:

• a wash tub;
• a tubular spray element disposed in the wash tub and being rotatable about a longitudinal axis thereof, the tubular spray element including one or more apertures extending through an exterior surface thereof, and the tubular spray element in fluid communication with a fluid supply to direct fluid from the fluid supply into the wash tub through the one or more apertures;
• a tubular spray element drive coupled to the tubular spray element and configured to rotate the tubular spray element between a plurality of rotational positions about the longitudinal axis thereof;
• an imaging device configured to sense a rotational position of the tubular spray element about the longitudinal axis;
• and
• a controller coupled to the tubular spray element drive and the imaging device, wherein the controller is configured to calibrate the tubular spray element drive by:
• rotating the tubular spray element with the tubular spray element drive to a first rotational position sensed by the imaging device;
• rotating the tubular spray element with the tubular spray element drive to a second rotational position sensed by the imaging device;
• determining a time associated with rotating the tubular spray element from the first rotational position to the second rotational position;
• and
• determining a rotational rate of the tubular spray element based upon the determined time and a rotational offset between the first and second rotational positions.