# US 4,397,521 A · Double pass optical system for raster scanners > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 4,397,521 A - Document ID: US4397521A - Status: Granted - Kind: A - Application number: 06/191,979 - Filed: 1980-09-29 - Granted: 1983-08-09 - Earliest claimed: 1980-09-29 - Assignees: Xerox Corporation - Inventors: Ronald L. Antos; Harry P. Brueggemann; David A. Grafton - Web page: https://patentgrep.com/patent/US4397521A ## CPC - G02B 26/127: {Adaptive control of the scanning light beam, e.g. using the feedback from one or more detectors (G02B27/0031 takes precedence)} - B41J 2/471: {using dot sequential main scanning by means of a light deflector, e.g. a rotating polygonal mirror} - G06K 15/1219: {Detection, control or error compensation of scanning velocity or position, e.g. synchronisation (G06K15/1223 takes precedence)} - H04N 1/036: for optical reproduction - H04N 1/053: in main scanning direction, e.g. synchronisation of line start or picture elements in a line - H04N 1/1135: {for the main-scan only} - 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-scanning}({sheet-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) - H04N 2201/02439: Positioning method - H04N 2201/0471: using dedicated detectors - H04N 2201/04732: Detecting at infrequent intervals, e.g. once or twice per line for main-scan control - H04N 2201/04744: by detecting the scanned beam or a reference beam - H04N 2201/04777: using a voltage controlled oscillator (H04N2201/04772 takes precedence) - H04N 2201/04794: Varying the control or compensation during the scan, e.g. using continuous feedback or from line to line - G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS - B41J: TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS - G06K: GRAPHICAL DATA READING (image or video recognition or understanding G06V); PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS - H04N: PICTORIAL COMMUNICATION, e.g. TELEVISION ## Abstract A raster scanner with laser for generating a scanning beam and compact folded optical system for transmitting the beam to the object to be scanned. The optical system includes a first mirror for guiding the laser beam forward along a downwardly inclined slope to the modulator, a second mirror below the modulator for intercepting the beam from the modulator and folding the intercepted beam to guide the beam backwards along a horizontal plane to a third mirror which folds the beam and guides the beam forward along an upwardly inclined slope against the mirrored facets of a rotating polygon, the polygon scanning the beam through a preset scan arc and returning the beam via a focusing lens to the third mirror, the third mirror folding the scan beam and guiding the scan beam forward, and a fourth mirror for intercepting the scan beam and guiding the beam to the object to be scanned. ## Claims ### Claim 1 In a raster scanner, the combination of: (a) a source of a high intensity beam of light; (b) a first mirror for intercepting said beam and reflecting said beam forward along a downwardly inclined slope; (c) a second mirror for intercepting the beam from said first mirror and folding said beam so that said beam is reflected backwards along a substantially horizontal plane; (d) a polygon for scanning said beam through a predetermined scan arc; and (e) a third mirror for intercepting the beam reflected from said second mirror and folding said beam so that said beam is reflected forward along an upwardly inclined slope toward said polygon; (f) said polygon intercepting the beam from said third mirror and reflecting said beam downwardly along said slope back to said third mirror; (g) said third mirror intercepting said scan beam from said polygon and reflecting said scan beam forward along said horizontal plane to the object to be scanned. ### Claim 2 (depends on 1) The raster scanner according to claim 1 including lens means for focusing said scan beam on the object to be scanned, said lens means being disposed astride the scan beam path between said polygon and said third mirror. ### Claim 3 (depends on 1, 2) The raster scanner according to claims 1 or 2 including a modulator for modulating said beam in response to image signals, said modulator being disposed astride the beam path between said first and second mirrors. ### Claim 4 (depends on 1) The raster scanner according to claim 1 in which the distance between said light source and said polygon is substantially equal to the distance between said polygon and the object to be scanned. ### Claim 5 In a raster scanner the combination of: (a) a beam of high intensity light; (b) plural mirrors cooperating to form an optical path for routing said light beam back and forth and up and down between at least two operating levels before discharge toward the object to be scanned whereby to provide a relatively compact folded optical path; said mirrors including: (1) a rotatable polygon for scanning said beam through a preset scan arc; (2) a first mirror for directing said beam at an angle from a first operating level to a second operating level; (3) a second mirror at said second operating level for intercepting said beam, said second mirror folding said beam and reflecting said beam along said second operating level; (4) a third mirror at said second operating level for intercepting said beam, said third mirror folding said beam and reflecting said beam at an angle from said second operating level toward said first operating level; said polygon intercepting said beam and reflecting said beam toward said third mirror, said third mirror folding the returned beam from said polygon and reflecting said beam along said second operating level; and (5) a fourth mirror at said second operating level for intercepting said beam, said fourth mirror reflecting said beam toward the object to be scanned; and (c) lens means for focusing said beam on the object to be scanned.