Multi-beam exposure apparatus having mirror tilt angle control, image forming apparatus that employs the exposure apparatus, and image forming method

• US 6,323,889 B1
• Filed: 11/12/1999
• Issued: 11/27/2001
• Est. Priority Date: 11/13/1998
• Status: Expired due to Fees

• Current Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation), Toshiba Tec Corporation (Toshiba Corporation)
• Original Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation), Toshiba Tec Corporation (Toshiba Corporation)
• Inventors: Miura, Tatsuyuki
• Primary Examiner(s): PENDEGRASS, JOAN H
• Application Number:
  US09/439,088
• Time in Patent Office: 746 Days
• Field of Search: 347/129, 347/134, 347/234, 347/235, 347/233, 347/242, 347/257, 359/204, 250/208.6, 250/578.1, 250/234, 250/235
• US Class Current: 347/234
• CPC Class Codes: G02B 26/123 Multibeam scanners, e.g. using multiple light sources or beam splitters
• CPC Class Codes: H04N 1/047 Detection, control or error compensation of scanning velocity or position H04N1/0402 and H04N1/17 take precedence
• 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 1/1911 Simultaneously or substantially simultaneously scanning picture elements on more than one main scanning line, e.g. scanning in swaths
• CPC Class Codes: H04N 2201/02425 Self-adjusting arrangements, e.g. compensating for temperature fluctuations
• CPC Class Codes: H04N 2201/02439 Positioning method
• CPC Class Codes: H04N 2201/0471 using dedicated detectors
• CPC Class Codes: H04N 2201/04712 using unbroken arrays of detectors, i.e. detectors mounted on the same substrate
• CPC Class Codes: H04N 2201/04729 in the main-scan direction
• CPC Class Codes: H04N 2201/04731 in the sub-scan direction
• CPC Class Codes: H04N 2201/04732 Detecting at infrequent intervals, e.g. once or twice per line for main-scan control
• 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 2201/04749 Detecting position relative to a gradient, e.g. using triangular-shaped masks, marks or gratings
• CPC Class Codes: H04N 2201/04762 using a reflecting element H04N2201/04765 takes precedence
• CPC Class Codes: H04N 2201/04789 in the main-scan direction
• CPC Class Codes: H04N 2201/04791 in the sub-scan direction
• CPC Class Codes: H04N 2201/04794 Varying the control or compensation during the scan, e.g. using continuous feedback or from line to line

Abstract

An exposure apparatus emits a number of laser beams to the predetermined positions on a single photosensitive drum. Galvano-mirrors are employed for controlling the distances between the laser beams in the main scanning direction and the sub-scanning direction. The angles of the mirrors of the galvano-mirrors are adjusted in such a manner as to eliminate the adverse effects caused by a drift, such as variations in the viscosity of the dampening agent of a mirror driving mechanism and variations in the magnetic force generated by a magnetic circuit. Without such adverse effects, the laser beams can be guided accurately to the predetermined positions on the photosensitive drum. The angles of the mirrors are monitored by checking whether the laser beams are incident on the predetermined positions on the detection areas of a beam position sensor.

Claims

1. An exposure apparatus comprising:

a plurality of light sources for emitting light beams, respectively;

light path alignment mirrors for synthesizing the light beams from the light sources together, such that the light beams are spaced apart from one another by predetermined distances in a first direction;

a deflection device for deflecting the light beams, emitted from the light sources and synthesized by the light path alignment mirrors, in a second direction perpendicular to the first direction;

a drift detection sensor for sensing at least one of the light beams emitted from the light sources and deflected by the deflection device, and for detecting how a given light path alignment mirror is drifted in the first direction; and

light path alignment mirror-driving units for correcting a drift of each of the light path alignment mirrors in accordance with a drift detected by the drift detection sensor.

2. An exposure apparatus according to claim 1, wherein

each of said light path alignment mirrors is movable in the first direction and includes a mirror for reflecting the light beams emitted from the light sources, and an angle at which the mirror reflects the light beams emitted from the light sources is determined by varying an angle of a reflection surface of the mirror by each of the light path alignment mirror-driving units.

3. An exposure apparatus according to claim 2, wherein each of said light path alignment mirror-driving units includes an electromagnetic driving circuit for driving the mirror in the first direction such that the mirror is tilted at an arbitrary angle, and each of said light path alignment mirror-driving units keeps the electromagnetic driving circuit in an active state.

4. An exposure apparatus according to claim 3, wherein each of said light path alignment mirror-driving units provide the corresponding optical path alignment mirror with an effective output which is low in a non-image formation mode and which is high in an image formation mode.

5. An exposure apparatus according to claim 3, wherein each of said light path alignment mirror-driving units keep the electromagnetic driving circuit in an active state within a predetermined period of time from a start of current supply, and each of the light path alignment mirrors is kept drifted in the first direction after the drift is detected by the drift detection sensor.

6. An exposure apparatus according to claim 3, wherein each of said light path alignment mirror-driving units stores data representing a drift amount and a drift direction which the drift detection sensor detects with respect to the drift detection sensor, predicts a length of time and a direction in which the light path alignment mirror should be driven, in accordance with the drift amount detected by the drift detection sensor, and actuates the electromagnetic driving circuit.

7. An exposure apparatus according to claim 3, wherein each of said light path alignment mirror-driving units checks a drift amount and a drift direction which the drift detection sensor detects with respect to the drift detection sensor, and drives the light path alignment mirror in a direction opposite to the drift direction for a predetermined length of time.

8. An exposure apparatus according to claim 3, wherein each of said light path alignment mirror-driving units drive the light path alignment mirror to correct a drift in the first direction in a period of time in which the deflection device warms up and becomes ready for predetermined operation.

9. An exposure apparatus according to claim 3, wherein each of said light path alignment mirror-driving units keeps the electromagnetic driving circuit in an actuated state until first and second light beams are detected as falling on a region that is within a predetermined range of the deflection device.

10. An exposure apparatus according to claim 1, wherein said drift detection sensor detects a timing for determining an image signal output time with respect to each of light beams deflected in the first direction by the deflection device.

11. An exposure apparatus according to claim 1, wherein said drift detection sensor includes a plurality of light detection elements arranged in parallel to one another and used for detecting the light beams deflected in the first direction by the deflection device, and said drift detection sensor senses an arbitrary light beam when the arbitrary light beam reaches a region between the light detection elements and supplies information on the arbitrary state to each of the light path alignment mirror-driving units.

12. An exposure apparatus according to claim 1, wherein said drift detection sensor includes a light detection element having a light detection area whose size varies in the first direction, and senses an arbitrary light beam when the arbitrary light beam passes a particular position predetermined on the light detection element in the first direction.

13. An exposure apparatus according to claim 12, wherein said light detection element includes at least two detection areas which are spaced from each other in the first direction, with a predetermined gap maintained, and a length of the detection areas, as viewed in the first direction, increases in directions away from the gap.

14. An exposure apparatus comprising:

a plurality of light sources for emitting light beams, respectively;

light path alignment mirrors for synthesizing the light beams from the light sources together, such that the light beams are spaced apart from one another by predetermined distances in a first direction;

a deflection device for deflecting the light beams, emitted from the light sources and synthesized by the light path alignment mirrors, in a second direction perpendicular to the first direction;

a drift detection sensor for sensing at least one of the light beams emitted from the light sources and deflected by the deflection device, and for detecting how each of the light path alignment mirrors is drifted in the first direction; and

light path alignment mirror-driving units for correcting a drift of each of the light path alignment mirrors in accordance with a drift detected by the drift detection sensor, each of said light path alignment mirror-driving units driving the light path alignment mirrors to correct a drift in the first direction in a period of time in which the deflection device warms up and becomes ready for a predetermined operation.

15. A mirror adjusting method for use in an exposure apparatus comprising:

a plurality of movable mirrors which are equal in number to light sources and which are electro-magnetically driven so that reflection surfaces thereof are tilted at such angles as to enable light beams from the light sources to be spaced by predetermined distances in a first direction;

a deflection device for deflecting the light beams, emitted from the light sources and synthesized by the movable mirrors, in a second direction;

a drift sensor, having at least two detection areas spaced by a predetermined distance in the first direction, for sensing the light beams emitted from the light sources and deflected by the deflection device, and for detecting how the movable mirrors are drifted in the first direction; and

a plurality of movable mirror drivers for correcting drifts of the movable mirrors in accordance with drifts detected by the drift detection sensor, such that the light beams emitted from the light sources can be regarded as one light beam,

said method being for adjusting the angles of the movable mirrors in the first direction in accordance with the light beams emitted from the light sources and being incident on the drift sensor, said method comprising the steps of;

supplying a predetermined driving current to each of the movable mirror drivers so as to set the angles of the movable mirror in a first state;

detecting a light position with the drift sensor;

checking whether or not a sensor output is produced, supplying a second driving current to each of the movable mirror drivers such that predetermined detection areas of the drift sensor are drifted, if the sensor output is not detected, and detecting the light position once again;

checking whether or not the sensor output is produced, supplying a third driving current to each of the movable mirror drivers such that the angles of the mirrors are adjusted and the sensor output is within a predetermined range, if the sensor output is detected, said third driving current having a smaller current value than the second driving current; and

supplying a fourth driving current to each of the movable mirror drivers if adjacent detection areas of the drift sensor sense a light beam reflected by the movable mirrors whose angles have been adjusted, said fourth driving current being equivalent in direction to the third driving current and corresponding in amount to one control step of the third driving circuit.

16. A method according to claim 15, wherein:

when the third driving current is supplied to each of the moveable mirror drivers, a beam moving direction is predicted on the basis of a beam position which the drift sensor senses at a last time and a beam position which the drift sensor senses at a time immediately before the last time, and a polarity of the third driving current is determined in accordance with the predicted beam moving direction.

17. A method according to claim 15, wherein:

when the third driving current is supplied to each of the moveable mirror driving circuits, a beam moving direction is predicted on the basis of a beam position which the drift sensor senses all at a last time and a beam position which the drift sensor senses at a time immediately before the last time, and

if the beam moving direction is a direction in which the light beams move away from the detection areas spaced in the first direction, the third driving current is switched in polarity to a driving current supplied last.

18. A method according to claim 15, wherein:

when the third driving current is supplied to each of the moveable mirror drivers, a beam moving direction is predicted on the basis of a beam position which the drift sensor senses at a last time and a beam position which the drift sensor senses at a time immediately before the last time, and

if the beam positions are close to a gap between the detection areas spaced in the first direction, the third driving current is switched in polarity to a driving current supplied last.