Method and apparatus for accurate measurement of imaging surface speed in a printing apparatus

A method to determine the speed of a moving surface having a primary movement direction, the method comprising:

• receiving from a sensor a plurality of timestamps indicative of a plurality of reference patterns being moved on the moving surface;
• receiving encoder pulses from an encoder associated with the moving surface;
• receiving discrete clock pulses from an ROS master clock;
• and
• processing with a logic unit the received timestamps, encoder pulses, and discrete clock pulses to determine the speed of the moving surface by:
• counting the encoder pulses generated between a first timestamp and a second timestamp;
• determining a leading fractional encoder count relative to the first time stamp;
• determining a trailing fractional encoder count relative to the second time stamp;
• determining an elapsed interval of time between the first timestamp and the second timestamp.

A document processing system, comprising:

• a photoreceptor that continuously moves along a closed path;
• at least one raster output scanner (ROS) located along the closed path of the photoreceptor, the ROS operable to generate a latent image on a portion of the photoreceptor based on a clock input;
• a clock providing a clock output signal to the ROS;
• a sensor to detect a plurality of reference patterns being moved on the photoreceptor, wherein the sensor produces a timestamp when it detects a reference pattern;
• an encoder coupled to the photoreceptor, wherein movement of the photoreceptor causes the encoder to generate encoder pulses;
• a controller coupled with the ROS to selectively operate the document processing system according to a photoreceptor speed;
• and
• logic circuit to determine photoreceptor speed from the encoder pulses, the timestamp, and the clock output signal by:
• counting the number of encoder pulses generated by the encoder between a first timestamp and a second timestamp;
• determining a leading fractional encoder count relative to the first time stamp;
• determining a trailing fractional encoder count relative to the second time stamp;
• and
• determining an elapsed interval of time between the first timestamp and the second timestamp.