Polygon signature correction
AssigneeXerox Corporation
InventorDouglas N. Curry
Life of this patent
Estimating the term…
Abstract
A circuit for correcting the data rate to compensate for polygon facet irregularities in a flying spot scanner is described. A crystal controlled oscillator is used to generate the system clock. As each facet becomes the current facet, a number of pulses appropriate for that facet are subtracted from the bit clock stream so that there will always be a constant ratio between data speed and scan speed regardless of the scan speed variations between individual facets.
Claims6
In a raster output scanning system of the type having a motor driving a rotating polygon, means for measuring the scan speed of each facet, and means responsive to each facet scan speed measurement for varying the bit clock during succeeding scans to compensate for each facet speed variation to produce lines of data of equal length independent of individual facet scan speed, or in a raster input scanning system of the type having a motor driving a rotation polygon, means for measuring the scan speed of each facet, and means responsive to each facet scan speed measurement for varying the bit clock during succeeding scans to compensate for the speed variation to acquire proper numbers of data bits independent of individual scan speed, the improvement comprising:
- a sample clock generator,
- means for calculating from the measurement for the current facet the number of sample clocks which must be removed from the stream of sample clocks, which determine the rate at which data is fed to the raster output or input scanner, to match the data rate to the current facet scan speed,
- means for deleting an evenly spaced number of sample clocks, equal to the calculated number, from the stream of sample clocks to create a corrected bit clock.
In a raster output scanning system of the type having a motor driving a rotating polygon, means for measuring the scan speed of each facet, and means responsive to each facet scan speed measurement for varying the bit clock during succeeding scans to compensate for each facet speed variation to produce lines of data of equal length independent of individual facet scan speed, or in a raster input scanning system of the type having a motor driving a rotation polygon, means for measuring the scan speed of each facet, and means responsive to each facet scan speed measurement for varying the bit clock during succeeding scans to compensate for the speed variation to acquire proper numbers of data bits independent of individual scan speed, the improvement comprising:
- a sample clock generator,
- means for calculating from the measurement for the current facet the number of sample clocks which must be removed from the stream of sample clocks, which determine the rate at which data is fed to the raster output or input scanner, to match the data rate to the current facet scan speed,
- means for deleting an evenly spaced number of sample clocks equal to the calculated number, from the stream of sample clocks to create a corrected bit clock,
- wherein said sample clocks are generated at a frequency N times greater than that required to deliver data to the raster scanner, and
- wherein the circuit further comprises a divide by N circuit for reducing the frequency of the sample clocks at the output of the means for deleting to reduce the effect of the deletions on the bit clock waveshape.
Dependencies are inferred from the claim text.