Scanning device

• US 5,654,817 A
• Filed: 02/06/1996
• Issued: 08/05/1997
• Est. Priority Date: 02/22/1995
• Status: Expired due to Fees

• Current Assignee: Barco Graphics nv
• Original Assignee: Barco Graphics nv
• Inventors: De Loor, Ronny
• Primary Examiner(s): Phan, James
• Application Number:
  US08/595,917
• Time in Patent Office: 546 Days
• Field of Search: 359/17, 359/201, 359/202, 359/212, 359/216-219, 250/234-236, 347/233, 347/235, 347/237, 347/241, 347/243, 347/244, 358/296, 358/302, 358/474, 358/481
• US Class Current: 359/201.1
• CPC Class Codes: B41J 2/473 using multiple light beams, wavelengths or colours
• CPC Class Codes: G02B 26/123 Multibeam scanners, e.g. using multiple light sources or beam splitters
• CPC Class Codes: H04N 1/0473 in subscanning direction, e.g. picture start or line-to-line synchronisation
• CPC Class Codes: H04N 1/1135 for the main-scan only
• CPC Class Codes: H04N 1/12 using the sheet-feed movement or the medium-advance or the drum-rotation movement as the slow scanning component, e.g. arrangements for the main-scanningsheet-feed movement by translatory movement of a flat picture-bearing surface H04N1/1008; main-scanning using oscillating or rotating mirrors H04N1/113; using multi-element arrays H04N1/19
• CPC Class Codes: H04N 1/192 Simultaneously or substantially simultaneously scanning picture elements on one main scanning line
• CPC Class Codes: H04N 2201/02441 using screws
• CPC Class Codes: H04N 2201/04712 using unbroken arrays of detectors, i.e. detectors mounted on the same substrate
• CPC Class Codes: H04N 2201/04734 Detecting at frequent intervals, e.g. once per line for sub-scan control
• CPC Class Codes: H04N 2201/04744 by detecting the scanned beam or a reference beam
• CPC Class Codes: H04N 2201/04765 using a solid-state deflector, e.g. an acousto-optic deflector
• CPC Class Codes: H04N 2201/04796 Varying the sub-scan control during the main-scan, e.g. for correcting skew, tilt or bow of a scanning beam

Abstract

A scanning device comprising a scanning member provided for pathwise scanning a medium along a scanning path by means of a scanning beam, said scanning member and said medium being mutually movable with respect to each other, characterized in that said scanning member comprises a plurality of N scanning modules, each i^th (1≦i≦N) scanning module being each time provided for scanning its assigned i^th segment of said scanning path and an end point of a j^th (1≦j≦N-1) segment corresponds with a starting point of a (j+1)^th segment, and wherein each i^th scanning module comprises deviation determining means provided for determining on at least one position situated along said i^th segment a cross-scan deviation between a predetermined scanning path and the path scanned by the scanning beam, said deviation determining means being connected with scanning beam steering means provided for determining upon receipt of said cross-scan deviation a first correction signal in such a manner -as to minimize said cross-scan deviation and for steering said scanning beam under control of said correction signal, and wherein said scanning beam steering means of a k^th (1≦k≦N) scanning module being provided for starting the scanning of its assigned k^th segment on an assigned time t_k within a scanning period ΔT for scanning the scanning path, the scanning beam steering means of each m^th scanning module (k≠m and 1≦m≦N) being provided for starting the scanning of their assigned m^th segment on time ##EQU1## if m>k and ##EQU2## if m<k, Δt_u being the time period for scanning the u^th segment.

Claims

1. A scanning device comprising a scanning member provided for pathwise scanning a medium along a scanning path by means of a scanning beam, said scanning member and said medium being mutually movable with respect to each other, characterised in that said scanning member comprises a plurality of N scanning modules, each i^th (1≦

i≦

N) scanning module being each time provided for scanning its assigned i^th segment of said scanning path and an end point of a j^th (1≦

j≦

N-1) segment corresponds with a starting point of a (j+1)^th segment, and wherein each i^th scanning module comprises deviation determining means provided for determining on at least one position situated along said i^th segment a cross-scan deviation between a predetermined scanning path and the path scanned by the scanning beam, said deviation determining means being connected with scanning beam steering means provided for determining upon receipt of said cross-scan deviation a first correction signal in such a manner as to minimize said cross-scan deviation and for steering said scanning beam under control of said correction signal, and wherein said scanning beam steering means of a k^th (1≦

k≦

N) scanning module being provided for starting the scanning of its assigned k^th segment on an assigned time t_k within a scanning period Δ

T for scanning the scanning path, the scanning beam steering means of each m^th scanning module (k≠

m and 1≦

m≦

N) being provided for starting the scanning of their assigned m^th segment on time ##EQU10## if m>

k and ##EQU11## if m<

k, Δ

t_u being the time period for scanning the u^th segment.

2. A scanning device as claimed in claim 1, characterized in that said deviation determining means are provided for determining said cross-scan deviation on a first respectively a second position situated at a starting respectively at an end of said i^th segment.

3. A scanning device as claimed in claim 1, characterized in that said deviation determining means are situated on a location situated outside a zone crossed by said scanning beam upon scanning the i^th segment, said i^th scanning module being provided to steer said scanning beam in order to reach said location.

4. A scanning device as claimed in claim 1, characterized in that each i^th scanning module further comprises a detector unit provided for detecting when said scanning beam has reached said starting point of the i^th segment and for generating a first control pulse indicating the latter, said detector unit being provided for verifying if said first control pulse coincides with said assigned time t_i assigned to segment i and for determining a second correction signal upon establishing that said first control pulse does not coincide with said assigned time t_i, said scanning beam steering means being connected with said detector unit and further provided for steering said scanning beam under control of said second correction signal in such a manner that said first control pulse and said assigned time t_i coincides.

5. A scanning device as claimed in claim 4, characterized in that said detector unit is situated on a further location situated outside a zone crossed by said scanning beam upon scanning the i^th segment, said i^th scanning module being provided to steer said scanning beam in order to reach said location.

6. A scanning device as claimed in claim 4, characterized in that said detector unit of each i^th scanning module is also provided for generating a second control pulse when said scanning beam of said i^th scanning module has reached the end point of its assigned i^th segment, said detector unit being further provided for determining Δ

t_u=i upon determining the time difference between said first and second control pulse.

7. A scanning device as claimed in claim 4, wherein said detector unit comprises a detector element provided for detecting when the scanning beams of said i^th and (i+1)^th scanning modules have reached the end point and the starting point, respectively, of said i^th and (i+1)^th segments.

8. A scanning device as claimed in claim 4, characterized in that said deviation determining means and/or said detector unit are coupled to said medium.

9. A scanning device as claimed in claim 1, characterized in that said deviation determining means are further provided for determining an image plane distance deviation between an actual scanning path and a nominal scanning path on said medium, said scanning beam steering means being further provided for determining upon receipt of said distance deviation a third correction signal and for steering said scanning beam under control of said third correction signal in such a manner as to compensate for said distance deviation.

10. A scanning device as claimed in claim 1, characterized in that said scanning beam steering means comprises an acousto-optical deflector provided for imposing a deflection on said scanning beam under control of said correction signal.