Sheet registration for a printmaking device using trail edge sensors

1. A printmaking device for reducing process direction errors of a sheet in a registration device comprising:

a feed path adapted to move the sheet, the sheet including a first edge, a second edge, and a first side edge and a second side edge therebetween, wherein said first edge is approximately parallel to said second edge;

a printing module configured to print an image on the sheet; and

a sheet registration system along said feed path including a first pair of edge sensors, at least one point sensor, a registration controller, and at least one pair of registration nips;

said first pair of edge sensors being configured to measure and correct a first skew error of the sheet, wherein said first pair of edge sensors measure said first skew of one of the following edges of the sheet: said first edge, said second edge, said first side edge, and said second side edge;

said at least one point sensor being configured to measure a first arrival time of said first edge of the sheet at a first fixed reference to determine a first process direction position of the sheet;

said registration controller being configured to correct skew errors, lateral errors and process direction position; and

said at least one pair of registration nips along said feed path and operatively connected to said registration controller;

wherein said feed path moves a first side of the sheet in a process direction and said registration controller is configured to register said first side of the sheet by:

measuring a first skew error of the sheet at one of the following edges of the sheet: said first edge, said second edge, said first side edge, and said second side edge using said first pair of edge sensors;

determining a lateral position error of the sheet;

correcting said first skew error and said lateral position error by adjusting the sheet using said registration controller; then,

measuring a first arrival time of said first edge of the sheet at a first fixed reference to determine a first process direction position of the sheet using said at least one point sensor, wherein said first edge is the trail edge of the sheet;

correcting said first process direction position by adjusting the sheet using said registration controller; and

delivering said first side of the adjusted sheet to a first registration datum at a first predefined delivery time.

2. The printmaking device of claim 1 , wherein said printmaking device inverts and refeeds the sheet on a second side and said feed path moves the sheet along said feed path in said process direction and said registration controller registers said second side of the sheet by:

measuring a second arrival time of said first edge of the sheet at a second fixed reference to determine a second process direction position of the sheet using said at least one point sensor, wherein said second edge is the lead edge of the sheet;

correcting said second process direction position by adjusting the sheet using said registration controller; and

delivering said second side of the adjusted sheet to a second registration datum at a second predefined delivery time.

3. The printmaking device of claim 2 , wherein said sheet registration system further includes a second pair of edge sensors configured to measure a second skew error of the sheet.

4. The printmaking device of claim 3 , wherein said registration controller is configured to correct said second skew error.

5. The printmaking device of claim 4 , wherein said registration controller further registers said second side of the sheet by:

measuring said second skew error of the sheet at one of the following edges of the sheet: said first edge, said second edge, said first side edge, and said second side edge using said second pair of edge sensors; and

correcting said second skew error by adjusting the sheet using said registration controller.

6. The printmaking device of claim 1 , wherein said registration controller corrects said first process direction position of the sheet by changing a speed of one or more registration nips of said at least one pair of registration nips along the feed path.

7. A system for reducing process direction errors of a sheet in a registration device comprising:

a feed path configured to move the sheet in a process direction, the sheet having a first edge, a second edge, and a first side edge and a second side edge therebetween, wherein said first edge is approximately parallel to said second edge;

a first pair of edge sensors being configured to measure and correct a first skew of the sheet, wherein said first pair of edge sensors measure said first skew of one of the following edges of the sheet: said first edge, said second edge, said first side edge, and said second side edge;

at least one point sensor, said at least one point sensor being configured to measure a first arrival time of said first edge of the sheet at a first fixed reference to determine a first process direction position of the sheet;

a registration controller, said registration controller being configured to correct skew errors, lateral position errors, and a process direction position of the sheet; and

at least one pair of registration nips along the feed path and operatively connected to said registration controller;

wherein said feed path moves the sheet in a process direction and said registration controller is configured to register a first side of the sheet by:

measuring a first skew error of the sheet at one of the following edges of the sheet: said first edge, said second edge, said first side edge, and said second side edge using said first pair of edge sensors;

determining a lateral position error of the sheet;

correcting said first skew error and said lateral position error by adjusting the sheet using said registration controller; then,

measuring a first arrival time of said first edge of the sheet at a first fixed reference to determine a first process direction position of the sheet using said at least one point sensor, wherein said first edge is the trail edge of the sheet;

correcting said first process direction position by adjusting the sheet using said registration controller; and

delivering said first side of the adjusted sheet to a first registration datum at a first predefined delivery time.

8. The system of claim 7 , wherein said system inverts and refeeds the sheet on a second side and said feed path moves the sheet along said feed path in said process direction and said registration controller registers a second side of the sheet by:

measuring a second arrival time of said first edge of the sheet at a second fixed reference to determine a second process direction position of the sheet using said at least one point sensor;

correcting said second process direction position by adjusting the sheet using said registration controller; and

delivering said second side of the adjusted sheet to a second registration datum at a second predefined delivery time.

9. The system of claim 8 , wherein said system further includes a second pair of edge sensors configured to measure a second skew error of said second side of the sheet.

10. The system of claim 9 , wherein said registration controller is configured to correct said second skew error.

11. The system of claim 10 , wherein said registration controller further registers said second side of the sheet by:

measuring said second skew error of the sheet at one of the following edges of the sheet: said first edge, said second edge, said first side edge, and said second side edge using said second pair of edge sensors; and

correcting said second skew error by adjusting the sheet using said registration controller.

12. The system of claim 7 , wherein said registration controller corrects said first process direction position of the sheet by changing a speed of one or more registration nips of said at least one pair of registration nips along the feed path.