Distortion correction apparatus for electro-optical reflectors which scan beams to produce images

• US 4,003,626 A
• Filed: 12/23/1974
• Issued: 01/18/1977
• Est. Priority Date: 06/14/1974
• Status: Expired due to Term

• Current Assignee: Eastman Kodak Company
• Original Assignee: Eastman Kodak Company
• Inventors: Newton, John E., Reinke, Robert V., Reifsteck, Robert L.
• Primary Examiner(s): Corbin, John K.
• Assistant Examiner(s): DELOS Reyes, B. Wm.
• Application Number:
  US05/535,245
• Time in Patent Office: 757 Days
• Field of Search: 350/6, 350/7, 350/21, 350/25, 350/254, 346/76 L, 346/108, 353/39, 355/52
• US Class Current: 359/202.1
• CPC Class Codes: G02B 26/101 with both horizontal and vertical deflecting means, e.g. raster or XY scanners colour television using laser beams scanning a display screen H04N9/3129
• CPC Class Codes: G06K 15/1228 involving the fast moving of a light beam in two directions G06K15/1233 - G06K15/129 take precedence
• CPC Class Codes: G06K 15/1295 using a particular photoreceptive medium
• CPC Class Codes: G09G 3/02 by tracing or scanning a light beam on a screen

Abstract

Apparatus is disclosed for use with image forming apparatus having a pair of galvanometers one of which, in response to a ramp signal rotates a mirror which scans lines in one direction across the image and the other of which in response to a staircase signal rotates another mirror in a direction perpendicular to the direction of the lines to scan successive ones of the lines. The apparatus includes circuits responsive to the galvanometer drive signal amplitudes for producing a compensating signal which is representative of the angular displacement of the mirrors and thus of the position to which the beam is scanned at any instant. This compensating signal and the signal which drives the galvanometer which scans the beam between successive lines are combined to adjust the angular displacement of the mirror which scans the beam in the direction between the successive lines, thus correcting the geometric distortion of the pin cushion type of the image.

Claims

1. In apparatus for correcting pin cushion distortion in a pattern formed in a plane which distortion occurs when light beams are scanned in two directions which are perpendicular to each other by first and second mirrors respectively rotatable about separate axes to thereby trace successive lines of said pattern in said plane, the improvement comprising:

a. means responsive to the angular displacement of said first mirror which scans said beam along said lines for providing a first signal proportional to the tangent of the angular displacement of said first mirror about its axis, such first signal representing the position of said beam in said pattern in a first of said two directions;

b. means responsive to the angular displacement of said second mirror which scans said beam along a path between said successive lines for providing a second signal proportional to the tangent of the angular displacement of said second mirror about its axis, such second signal representing the position of said beam in said pattern in a second of said two directions; and

c. means responsive to said first and second signals for modifying the angular displacement of said second mirror in accordance with the position of said beam in said pattern to correct said distortion.

2. The invention as set forth in claim 1 wherein said first and second signal responsive means includes means for squaring said first signal, and means for multiplying said second signal by said squared first signal to produce a third signal;

and wherein said invention further includes a first galvanometer responsive to said first signal for rotating said first mirror and a second galvanometer responsive to said third signal for rotating said second mirror.

3. In image generator apparatus which includes means for producing a beam of radiant energy having an information content, a rotatably mounted line scan reflector for angularly scanning the beam in the first of two directions across an image plane, a rotatably mounted page scan reflector for angularly displacing the beam in a second direction transverse to the first direction, and refracting means having a focal length f_o for receiving the beam of radiant energy after being reflected by the first and second reflectors for focusing the beam at the image plane to form images, image distortion correcting means, comprising;

a. means for producing a first signal proportional to the angular displacement of the line scan reflector as it scans the beam;

b. means for producing a second signal proportional to the angular displacement of the page scan reflector; and

c. means responsive to said first and second signals and the focal length f_o of the refracting means for producing a distortion compensation signal; and

d. means responsive to said distortion compensation signal for adjusting the angular displacement of the page scan reflector as the line scan deflector scans the beam in the first direction to correct for image distortion at the image plane.

4. The invention as set forth in claim 3 wherein said second signal is proportional to tan α

, and α

is proportional to the angular displacement of the page scan reflector, said first signal is proportional to tan β

, where β

is proportional to the angular displacement of the line scan reflector and said distortion compensation signal is proportional to the product of tan α

(√

tan² β

+ 1 -

     1) and f_o/2.