# US 10,479,108 B2 · Image forming apparatus > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 10,479,108 B2 - Document ID: US10479108B2 - Status: Granted - Kind: B2 - Application number: 15/961,619 - Filed: 2018-04-24 - Published: 2018-11-01 - Granted: 2019-11-19 - Earliest claimed: 2017-05-01 - Assignees: Canon Kabushiki Kaisha - Applicants: Canon Kabushiki Kaisha - Inventors: Yusuke Morishita - Web page: https://patentgrep.com/patent/US10479108B2 ## CPC - B41J 2/471: {using dot sequential main scanning by means of a light deflector, e.g. a rotating polygonal mirror} - G02B 26/122: {Control of the scanning speed of the polygonal mirror} - G02B 26/124: {Details of the optical system between the light source and the polygonal mirror (G02B26/123, G02B26/127 take precedence)} - G02B 26/125: {Details of the optical system between the polygonal mirror and the image plane (G02B26/123, G02B26/127 take precedence; F-Theta lenses G02B13/0005)} - B41J: TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS - G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS ## Abstract An image forming apparatus including: a light source configured to emit a light beam; a rotary polygon mirror including a plurality of reflection surfaces each configured to deflect the light beam emitted by the light source so that the light beam scans a surface of a photosensitive member; a light receiving portion configured to output a light receiving signal by receiving the light beam reflected by each of the plurality of reflection surfaces; a conversion unit configured to convert the light receiving signal to a pulse signal; a measurement unit configured to measure pulse widths of a plurality of pulse signals corresponding to the plurality of reflection surfaces, respectively; and an identification unit configured to identify a rotation phase of the rotary polygon mirror based on a measurement result of the measurement unit and reference values to be compared with the measurement result. ## Claims ### Claim 1 An image forming apparatus comprising: a light source configured to emit a light beam; a rotary polygon mirror including a plurality of reflection surfaces each configured to deflect the light beam emitted by the light source so that the light beam scans a surface of a photosensitive member; plural count value holding units of a number that corresponds to a number of the plural reflection surfaces; a light receiving portion configured to output a light receiving signal by receiving the light beam reflected by each of the plurality of reflection surfaces; a conversion unit configured to convert the light receiving signal to a pulse signal; a measurement unit configured to measure pulse widths of a plurality of pulse signals corresponding to the plurality of reflection surfaces, respectively, wherein the measurement unit includes: a clock signal generation unit configured to generate a clock signal of a predetermined frequency; and a count unit configured to count the clock signal; and an identification unit configured to identify a rotation phase of the rotary polygon mirror based on a measurement result of the measurement unit and reference values to be compared with the measurement result, wherein the measurement unit measures pulse widths of the plurality of pulse signals by count values of the count unit, and wherein the count unit causes the count value holding units of the number of the reflection surfaces to sequentially hold the count values. ### Claim 2 (depends on 1) An image forming apparatus according to claim 1, further comprising a lens having no fθ characteristic and configured to guide the light beam deflected by the rotary polygon mirror onto the surface of the photosensitive member. ### Claim 3 (depends on 1) An image forming apparatus according to claim 1, further comprising a calculation unit configured to calculate average values of the count values held by the count value holding units of the number of the reflection surfaces, respectively, wherein the identification unit identifies a reflection surface corresponding to the rotation phase identified based on the average values and the reference values. ### Claim 4 (depends on 3) An image forming apparatus according to claim 3, wherein the identification unit identifies the reflection surface corresponding to the rotation phase by checking the average values against the reference values. ### Claim 5 (depends on 3) An image forming apparatus according to claim 3, wherein the identification unit identifies the reflection surface corresponding to the rotation phase based on a maximum value or a minimum value of the average values and the reference values. ### Claim 6 (depends on 1) An image forming apparatus according to claim 1, further comprising a storage configured to store the reference values in advance. ### Claim 7 An image forming apparatus comprising: a light source configured to emit a plurality of light beams; a rotary polygon mirror including a plurality of reflection surfaces each configured to deflect the plurality of light beams emitted by the light source so that the plurality of light beams scan a surface of a photosensitive member; plural count value holding units of a number that corresponds to a number of the plural reflection surfaces; a light receiving portion configured to output a plurality of light receiving signals by receiving the plurality of light beams reflected by each of the plurality of reflection surfaces; a conversion unit configured to convert the plurality of light receiving signals to a plurality of pulse signals; a changeover unit configured to change over between a measurement valid interval and a measurement invalid interval; and a measurement unit configured to measure a pulse width of a pulse signal in the measurement valid interval among the plurality of pulse signals corresponding to the plurality of reflection surfaces, respectively, wherein the measurement unit includes: a clock signal generation unit configured to generate a clock signal of a predetermined frequency; and a count unit configured to count the clock signal; and an identification unit configured to identify a rotation phase of the rotary polygon mirror based on a measurement result of the measurement unit and reference values to be compared with the measurement result, wherein the measurement unit measures pulse widths of the plurality of pulse signals by count values of the count unit, and wherein the count unit causes the count value holding units of the number of the reflection surfaces to sequentially hold the count values. ### Claim 8 (depends on 7) An image forming apparatus according to claim 7, further comprising a lens having no fθ characteristic and configured to guide the plurality of light beams deflected by the rotary polygon mirror onto the surface of the photosensitive member. ### Claim 9 (depends on 7) An image forming apparatus according to claim 7, further comprising a calculation unit configured to calculate average values of the count values held by the count value holding units of the number of the reflection surfaces, respectively, wherein the identification unit identifies a reflection surface corresponding to the rotation phase identified based on the average values and the reference values. ### Claim 10 (depends on 9) An image forming apparatus according to claim 9, wherein the identification unit identifies the reflection surface corresponding to the rotation phase by checking the average values against the reference values. ### Claim 11 (depends on 9) An image forming apparatus according to claim 9, wherein the identification unit identifies the reflection surface corresponding to the rotation phase based on a maximum value or a minimum value of the average values and the reference values. ### Claim 12 (depends on 7) An image forming apparatus according to claim 7, further comprising a storage configured to store the reference values in advance. ### Claim 13 An image forming apparatus comprising: a light source configured to emit two light beams; a rotary polygon mirror including a plurality of reflection surfaces each configured to deflect the two light beams emitted by the light source so that the two light beams scan a surface of a photosensitive member; plural count value holding units of a number that corresponds to a number of the plural reflection surfaces; a light receiving portion configured to output two light receiving signals by receiving the two light beams reflected by each of the plurality of reflection surfaces; a conversion unit configured to convert the two light receiving signals to two pulse signals; a measurement unit configured to measure pulse widths of continuous pulse signals output from the conversion unit in every other pulse signal, wherein the measurement unit includes: a clock signal generation unit configured to generate a clock signal of a predetermined frequency; and a count unit configured to count the clock signal; and an identification unit configured to identify a rotation phase of the rotary polygon mirror based on a measurement result of the measurement unit and reference values to be compared with the measurement result, wherein the measurement unit measures pulse widths of the two pulse signals by count values of the count unit, and wherein the count unit causes the count value holding units of the number of the reflection surfaces to sequentially hold the count values. ### Claim 14 (depends on 13) An image forming apparatus according to claim 13, further comprising a lens having no fθ characteristic and configured to guide the two light beams deflected by the rotary polygon mirror onto the surface of the photosensitive member.