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A method of error correction in a printing system includes engaging a sheet of print media with a perfector arm and detecting a relative position of the perfecter arm with respect to the sheet of print media when the perfecter arm has engaged the sheet of print media, the detecting being performed u

A method of error correction in a printing system includes engaging a sheet of print media with a perfector arm and detecting a relative position of the perfecter arm with respect to the sheet of print media when the perfecter arm has engaged the sheet of print media, the detecting being performed using a homing sensor that is configured to sense the perfecter arm while the perfecter arm is engaged with the sheet of print media. The relative position of the perfecter arm with respect to the sheet of print media is compared with an expected relative position and any difference between the relative position and expected relative position is compensated for when feeding the sheet of print media with the perfector arm to a print engine.

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1. A method of error correction in a printing system, said method comprising: engaging a sheet of print media with a rotating perfector arm, wherein said perfector arm is rotated by a belt which is driven by a motor;detecting a relative position of said perfector arm with respect to said sheet of pr

1. A method of error correction in a printing system, said method comprising: engaging a sheet of print media with a rotating perfector arm, wherein said perfector arm is rotated by a belt which is driven by a motor;detecting a relative position of said perfector arm with respect to said sheet of print media when said perfector arm has engaged said sheet of print media, said detecting being performed using a homing sensor that is configured to sense said perfector arm while said perfector arm is engaged with said sheet of print media;comparing said relative position of said perfector arm, as indicated by said homing sensor, with an expected relative position between said perfector arm and said sheet of print media, said expected relative position being determined by an encoder which is encoding a position of said motor, a difference between said relative position and said expected relative position of said perfector arm being attributable to said belt; andwhen feeding said sheet of print media with said perfector arm to a print engine, compensating for any difference between said relative position and said expected relative position by adjusting a position of said motor. 2. The method of claim 1, wherein a length of said belt equals a circumference of a sprocket on said motor that drives said belt times an integer number. 3. The method of claim 2, further comprising driving said perfector arm an integer number of rotations for each rotation of said belt. 4. The method of claim 3, further comprising performing an independent calibration, by repeating said detecting, comparing and compensating, for each of said integer number of rotations of said perfector arm. 5. The method of claim 1, in which said detecting of said relative position of said perfector arm with respect to said sheet further comprises: sensing said perfector arm with said homing sensor and recording a corresponding first encoder count of a drive motor coupled to said perfector arm;sensing a leading edge of said sheet of print media and recording a corresponding second encoder count of said drive motor; anddifferencing said first encoder count and said second encoder count to produce said relative position of said perfector arm with respect to said sheet of print media. 6. A method of error correction in a duplex printing system comprising: performing a calibration of a perfector arm with respect to a base structure, said calibration comprising: detecting motion of said perfector arm using a homing sensor, wherein an integer number of rotations of said perfecctor arm correspond to one rotation of a belt, said belt connecting said perfector arm to a drive motor having an encoder; anddifferencing an actual position of said perfector arm as indicated by said homing sensor with a position of said perfector arm as indicated by an encoder count from said encoder to produce a belt position dependent error; andcompensating for said belt position dependent error when feeding a sheet of print media with said perfector arm in said duplex printing system. 7. The method of claim 6, further comprising making a measurement of a position of said perfector arm with respect to said base structure using said homing sensor positioned to sense said perfector arm while said perfector arm is engaged with said sheet of print media;making a measurement of a location of said sheet of print media with respect to said base structure;differencing said measurement of said position of said perfector arm and said measurement of said location of said sheet of print media to produce a relative positioning relationship between said perfector arm and said sheet of print media;comparing said relationship to an expected relationship to find an error; andinputting said error into a control system, said control system altering an action of said drive motor to compensate for said error. 8. A duplex printing system comprising: an impression cylinder configured to hold a sheet of print media on a surface of said impression cylinder;a perfector arm, said perfector arm being configured to engage said sheet of print media, remove said sheet of print media from a surface of said impression cylinder, and reposition said sheet of print media on said impression cylinder such that an opposite side of said sheet of print media is presented for printing, said perfector arm being connected to a drive motor by a belt, said drive motor being configured to control motion of said perfector arm, wherein a sprocket of said drive motor has a circumference equal to a length of said belt divided by an integer number, such that a number of rotations of said sprocket equal to said integer number corresponds to one rotation of said belt;a homing sensor configured to detect passage of said perfector arm while said perfector arm is engaged with said sheet of print media; anda control system configured to accept output signals from said homing sensor and an encoder attached to said drive motor; said control system being further configured to use said output signals to calibrate said motion of said perfector arm through a motion corresponding to one rotation of said belt. 9. The system of claim 8, in which one rotation of said belt results in motion of said perfector arm through an integer number of rotations. 10. The system of claim 8, wherein said control system is configured to control said drive motor to adjust motion of said perfector arm based on both of said output signals from said homing sensor and said encoder attached to said drive motor. 11. The system of claim 8, further comprising a paper sensor, said paper sensor being configured to detect a leading edge of said sheet of print media during duplexing of said sheet of print media. 12. The system of claim 11, further comprising a control system configured to accept output from said homing sensor and said paper sensor and calculate an actual suction cup margin. 13. The system of claim 12, in which said control system is further configured to compare said actual suction cup margin to an expected suction cup margin to produce an error, said control system compensating for said error by controlling said drive motor. 14. The system of claim 11, in which said paper sensor and said homing sensor are optical sensors. 15. The system of claim 8, further comprising an additional perfector arm configured to operate in tandem with said perfector arm to increase throughput of said duplex printing system. 16. The method of claim 1, further comprising driving rotation of said perfector arm with a continuous belt on a sprocket, wherein said sprocket has a circumference equal to a length of said belt divided by an integer number, such that a number of rotations of said sprocket equal to said integer number corresponds to one rotation of said belt. 17. The method of claim 1, further comprising applying a first calibration factor to movement of said perfector arm during a first duplexing operation and applying a second different calibration factor to movement of said perfector arm during a second duplexing operation, wherein said first and second duplexing operations corresponding to one complete rotation of said belt that drives said perfector arm. 18. The method of claim 6, further comprising driving rotation of said perfector arm via said belt with a sprocket of said drive motor, wherein said sprocket has a circumference equal to a length of said belt times an integer number, such that a number of rotations of said sprocket equal to said integer number corresponds to one rotation of said belt. 19. The method of claim 6, further comprising applying a first compensating factor to movement of said perfector arm during a first duplexing operation and applying a second different compensating factor to movement of said perfector arm during a second duplexing operation, wherein said first and second duplexing operations corresponding to one complete rotation of said belt that drives said perfector arm. 20. The method of claim 8, further comprising a control system for applying a first compensating factor to movement of said perfector arm during a first duplexing operation and applying a second different compensating factor to movement of said perfector arm during a second duplexing operation, wherein said first and second duplexing operations corresponding to one complete rotation of said belt that drives said perfector arm.