Registration and transport unit for a sheet feeder

1. A sheet transport and registration apparatus comprising:

a first and second plurality of rollers mounted to define a first plurality of roller pairs, each roller pair having at least one drive roller for contacting a surface of a sheet to be transported through a series of nips formed by the roller pairs,

a registration plate for registering a side edge of the sheet,

a drive mechanism for rotating the drive rollers to drive the sheet through the series of nips with a first drive force component in the transport direction and a second drive force component in a direction transverse to the transport direction for driving the transported sheet against the registration plate, and

a contact pressure control mechanism to set a contact pressure at each roller pair that is sufficiently high that the sheet is engaged by the nip to be driven in the transport direction; and in the transverse direction when the side edge of the sheet is not registered at the registration plate, and that is sufficiently low that the sheet is driven in the transport direction but the sheet and the drive roller slide relative to one another in the transverse direction when an edge of the sheet is registered at the registration plate.

2. Apparatus as claimed in claim 1 , further comprising a guide mechanism for guiding the sheet.

3. Apparatus as claimed in claim 2 , the guide mechanism comprising a pair of parallel plates, a first plurality of apertures in each of the plates, the apertures in the first plate aligned with respective apertures in the second plate, the first plurality of rollers mounted on one side of the parallel plates at the apertures for contacting a first surface of a sheet located in a guidance slot between the plates, and the second plurality of rollers mounted on the other side of the parallel plates at the apertures for contacting a reverse surface of the sheet.

4. Apparatus as claimed in claim 3 , the plates being curved for turning a sheet on transportation thereof through a prescribed angle.

5. Apparatus as claimed in claim 4 , the drive rollers mounted on the outside of the curve and the other rollers of the roller pairs mounted on the inside of the curve.

6. Apparatus as claimed in claim 4 , the apparatus having a sheet input end and a sheet output end, the parallel plates, at at least one end, presenting a flared entry way to the guidance slot for entry of a sheet to the apparatus.

7. Apparatus as claimed in claim 6 , further comprising input and output extension units each extension unit having parallel members for transportation of the sheet along slots defined between respective parallel members, the slots in the input and output extension units aligned with the guidance slot at respective ends of the parallel plates.

8. Apparatus as claimed in claim 1 , each roller pair comprising the drive roller and an idler roller.

9. Apparatus as claimed in claim 1 , the drive rollers each having an axis of rotation angled to the transport direction.

10. Apparatus as claimed in claim 1 , the drive rollers generally equispaced along the length of the parallel plates in the transport direction.

11. Apparatus as claimed in claim 1 , the drive rollers generally aligned in the transport direction.

12. Apparatus as claimed in claim 1 , the drive rollers located close to the registration plate.

13. Apparatus as claimed in claim 1 , further comprising a second plurality of roller pairs mounted on the far side of the first plurality of roller pairs from the registration plate, the second plurality of roller pairs having drive rollers for driving a sheet in the transport direction.

14. Apparatus as claimed in claim 1 , the roller pairs confining a sheet transported thereby to a transport locus, the registration plate having a groove generally tracking the transport locus for sliding engagement of the side edge within the groove upon registration of the sheet at the registration plate.

15. Apparatus as claimed in claim 1 , further comprising a motor and power train for driving the drive rollers.

16. Apparatus as claimed in claim 1 , the drive rollers each having a relatively rigid hub portion and an elastic tire portion.

17. Apparatus as claimed in claim 1 , at least one of the roller pairs having an associated pressure control device to set the contact pressure of the drive roller against the other roller for a sheet gripped between the drive roller and the other roller.

18. Apparatus as claimed in claim 17 , the pressure control device having an adjustment means to adjust the contact pressure.

19. Apparatus as claimed in claim 18 , the adjustment means operable automatically in response to a detected change in a property of a sheet transported through the apparatus.

20. Apparatus as claimed in claim 1 , the drive rollers being frusto-conical in shape.

21. A method of transporting a sheet comprising using a series of nips formed by a plurality of roller pairs, each roller pair including a drive roller contacting one surface of the sheet and a reaction roller contacting the reverse surface of the sheet, the method comprising operating the drive rollers to apply to the sheet at said nips a first drive force component in a transport direction and a second drive force component in a direction transverse to the transport direction, and setting the contact pressures at the nips sufficiently high that the sheet is driven in the transport direction by the first drive force component, and is driven in the transverse direction by the second drive force component when the sheet is free to move in the transverse direction, and sufficiently low that the sheet and the drive roller slide relative to one another in the transverse direction if the sheet is prevented from moving in the transverse direction by a side edge of the sheet abutting a registration plate.