Galvanometric optical scanning system having synchronization photodetectors

• US 4,800,271 A
• Filed: 06/23/1987
• Issued: 01/24/1989
• Est. Priority Date: 06/23/1987
• Status: Expired due to Term

• Current Assignee: National Research Council Canada
• Original Assignee: Canadian Patents and Development Limited
• Inventors: Blais, Francois
• Primary Examiner(s): Westin, Edward P.
• Assistant Examiner(s): Shami, Khaled
• Application Number:
  US07/065,386
• Time in Patent Office: 581 Days
• Field of Search: 250/234-236, 250/201 R, 350/6.5, 350/6.6, 350/6.7, 350/6.8, 350/6.91, 358/206, 358/208, 358/293
• US Class Current: 250/235
• CPC Class Codes: H04N 1/053 in main scanning direction, e.g. synchronisation of line start or picture elements in a line
• CPC Class Codes: H04N 1/1135 for the main-scan only
• CPC Class Codes: H04N 2201/02439 Positioning method
• CPC Class Codes: H04N 2201/0471 using dedicated detectors
• 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 2201/04744 by detecting the scanned beam or a reference beam
• CPC Class Codes: H04N 2201/04755 by controlling the position or movement of a scanning element or carriage, e.g. of a polygonal mirror, of a drive motor
• 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

A galvanometric optical scanning system is disclosed. In order to compensate errors in phase, zero drift etc., at least two synchronization photodetector means are provided in an optical path of scanning beam of light. The pulses produced by the photodetector means are processed to generate correction signals for various commpensations.

Claims

1. A galvanometric optical scanning system, comprising:

a scanning mirror rotatably supported on an axis;

mirror drive means for driving the said scanning mirror in an angularly reciprocating fashion about the said axis;

a light source for projecting a beam of light towards the scanning mirror to scan an object with the deflected beam of light deflected from the said scanning mirror;

galvanometer controller means for applying a drive signal to the said mirror drive means;

at least two synchronization photodetector means positioned in an optical path of the deflected beam to generate synchronization pulses upon impinging of the deflected beam thereon;

synchronization circuit means connected to said synchronization photodetector means for processing said synchronization pulses to generate correction signals indicative of phase variation φ

, offset E_off and gain drift E_gain of the drive signal, according to the following equations;

##EQU2## where t₁, t₂, t₃ and t₄ are timings of four synchronization pulses in each scan cycle and

T₁ =t₂ -t₁

T₂ =t₄ -t₃

and T_ref is a preset reference value; and

means for applying any or all of the said correction signals to the said galvanometer controller means so that the said drive signal is compensated.

2. The galvanometric optical scanning system, according to claim 1, wherein further comprising:

an optical window positioned between the said scanning mirror and the object to reflect a portion of the deflected beam of light; and

the said synchronization photodetector means positioned in an optical path of the said reflected portion of the deflected beam of light to generate synchronization pulses upon impinging of the said reflected portion thereon.

3. The galvanometric optical scanning system, according to claim 1, wherein:

the said synchronization photodetector means comprises at least a pair of photodiodes and are adjustable as to their locations.

4. The galvanometric optical scanning system, according to claim 3, wherein

the said synchronization photodetector means comprise a plurality of photodiodes, any pair of which can be activated to adjust the locations of the said synchronization photodetector means.

5. The galvanometric optical scanning system, according to claim 2, wherein

the said synchronization photodetector means comprises at least a pair of photodiodes and are adjustable as to their locations.

6. The galvanometric optical scanning system, according to claim 5, wherein:

the said synchronization photodetector means comprise a plurality of photodiodes, any pair of which can be activated to adjust the locations of the said synchronization photodetector means.