High-efficiency symmetrical scanning optics

• US 4,274,703 A
• Filed: 10/29/1979
• Issued: 06/23/1981
• Est. Priority Date: 08/01/1977
• Status: Expired due to Term

• Current Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Original Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Inventors: Fisli, Tibor
• Primary Examiner(s): Corbin, John K.
• Assistant Examiner(s): de los Reyes, B. W.
• Application Number:
  US06/088,804
• Time in Patent Office: 603 Days
• Field of Search: 350/6.8, 350/181, 350/285, 350/176, 350/175 SL, 350/190, 356/431, 356/444, 358/199
• US Class Current: 359/218.1
• CPC Class Codes: G02B 5/09 Multifaceted or polygonal mirrors , e.g. polygonal scanning mirrors; Fresnel mirrors

Abstract

To provide a relatively compact and linear underfilled multifaceted rotating polygon beam scanning system, there are imaging optics for bringing a input light beam to a tangentially extending line-like focus on successive facets of a rotating polygonal scanning element and for restoring the light beam reflected from the facets to a generally circular focus on an image plane. Each of the facets subtends a sufficient angle about the axis of rotation of the scanner to ensure that the input beam remains fully seated on a single facet while the reflected beam is being scanned through a desired scan angle. Furthermore, improved linearity is achieved because the scanning system is symmetrical in the tangential and sagittal planes at all points between the imaging optics and the polygonal scanning element.

Claims

1. A flying spot optical scanning system for sweeping an optical scanning spot across an imaging surface, said system comprising the combination of

a source for supplying a light beam

a beam scanning element having a plurality of reflective facets circumferentially distributed in a tangential plane about an axis of rotation;

means for rotating said scanning element on said axis of rotation, whereby said facets serially intercept and reflect said light beam;

lens means optically interposed between said source and said surface for serially focusing the light beam onto successive ones of said facets and for refocusing light reflected from said facets onto said surface, said lens means being substantially symmetrical about an optical axis which is essentially normal to said axis of rotation, said light beam underfilling and remaining fully seated on the facet upon which it is focused while the reflected light is scanned through a predetermined scan angle.

2. The flying spot scanning system of claim 1 wherein said lens means comprises a spherical lens which is substantially symmetrical about said optical axis, whereby said spherical lens operates in a symmetrical double pass mode to participate in focusing said light beam on said facet and in refocusing said reflected light onto said surface.

3. The flying spot scanning system of claim 2 wherein said lens means additionally comprises a cylinderical sagittal correction lens which is also substantially symmetrical about said optical axis, said spherical lens is positioned between said cylinderical lens and said scanning element, said light beam is applied to said cylinderical lens with a generally circular cross section, and said cylinderical lens has substantial power in a sagittal plane and negligible power in said tangential plane, whereby said cylinderical and spherical lenses operate in symmetrical double pass modes to serially bring said light beam to a tangentially extending line-like focus on said successive facets and to restore the light reflected from said facets to a generally circular focus on said surface.

4. The flying spot scanning system of claim 3 further including a prefocusing lens optically aligned between said source and said cylinderical lens for bringing said light beam to a focus at a point selected to cause said light beam to be substantially collimated in said tangential plane while being applied to said facets, thereby compensating for radial runout variations of said scanning element.

5. The flying spot scanning system of claim 2 wherein said lens means additionally comprises a pair of substantially identical cylinderical sagittal correction lens which are approximately equidistantly spaced from said spherical lens and substantially symmetrically positioned on opposite sides of said optical axis in a sagittal plane, said spherical lens is positioned between said cylinderical lenses and said scanning element, each of said cylinderical lenses has substantial power in said sagittal plane and negligible power in said tangential plane, and said light beam is applied to one of said cylinderical lenses with a substantially circular cross-sectional shape, whereby said one cylinderical lens and said spherical lens cooperate in bringing said light beam to a tangentially extending line-like focus on said successive facets, and the other cylinderical lens and said spherical lens cooperate in restoring said reflected light to a generally circular focus on said surface.

6. The flying spot scanning system of claim 5 further including a prefocusing lens optically aligned between said source and said one cylinderical lens for bringing said light beam to a focus at a point selected to cause said light beam to be substantially collimated in said tangential plane while being applied to said facets, thereby compensating for radial runout variations of said scanning element.