Multi-beam exposure unit

An optical exposure unit comprising:

• light sources which are arranged in correspondence with numbers indicated by N1 to NM (M is an integer not less than 1) and emit light beams;
• first lens means for converting the light beams emitted by each of said light sources into one of convergent light and collimated light, said lens means including one of a finite lens and collimate lens in number corresponding to a sum of N1 to NM;
• second lens means given lens power associated with a first direction to converge the light beams output from each of said lens means in only the first direction, the M sets of said second lens means being prepared;
• deflection means for deflecting the light beams output from said second lens means in a second direction perpendicular to the first direction, said deflection means including a reflection surface which is formed to be rotatable about a rotation axis extending in a direction parallel to the first direction as a center of rotation;
• and
• imaging means including at least one lens, and imaging each of the light beams deflected at an equal speed by said deflection means at a predetermined position, and
• wherein a distance L0 between a final lens surface and an image surface in a light scanning unit for irradiating M beam groups onto M image carriers falls within a range defined by:
• (ΔLMAX+LM+L1)/1.8>L0 L0>(ΔLMAX+LM+L1)/2
• where L1 is the distance between an optical axis of a system of second optical means and a scanning line on one end,
• LM is the distance between the optical axis of the system of the second optical means and a scanning line on the other end, and
• ΔLMAX is the distance, in a direction parallel to the optical axis of the system, between the scanning lines at the two ends.

An optical exposure unit comprising:

• light sources which are arranged in correspondence with numbers indicated by N1 to NM (M is an integer not less than 1) and emit light beams;
• first lens means for converting the light beams emitted by each of said light sources into one of convergent light and collimated light, said lens means including one of a finite lens and collimate lens in number corresponding to a sum of N1 to NM;
• second lens means given lens power associated with a first direction to converge the light beams output from each of said lens means in only the first direction, the M sets of said second lens means being prepared;
• deflection means for deflecting the light beams output from said second lens means in a second direction perpendicular to the first direction, said deflection means including a reflection surface which is formed to be rotatable about a rotation axis extending in a direction parallel to the first direction as a center of rotation;
• and
• imaging means including at least one lens, and imaging each of the light beams deflected at an equal speed by said deflection means at a predetermined position, and
• wherein an effective field angle φ of a beam deflected by said deflection means satisfies:
• φ>W/Lt
• where Lt is the distance between a reflection point on said deflection means and an image surface, and
• W is the effective image region width including a region where a horizontal synchronization signal is detected.

An optical exposure unit comprising:

• light sources which are arranged in correspondence with numbers indicated by N1 to NM (M is an integer not less than 1) and emit light beams;
• first lens means for converting the light beams emitted by each of said light sources into one of convergent light and collimated light, said lens means including one of a finite lens and collimate lens in number corresponding to a sum of N1 to NM;
• second lens means given lens power associated with a first direction to converge the light beams output from each of said lens means in only the first direction, the M sets of said second lens means being prepared;
• deflection means for deflecting the light beams output from said second lens means in a second direction perpendicular to the first direction, said deflection means including a reflection surface which is formed to be rotatable about a rotation axis extending in a direction parallel to the first direction as a center of rotation;
• and
• imaging means including at least one lens, and imaging each of the light beams deflected at an equal speed by said deflection means at a predetermined position, and
• wherein an incident angle of a beam to M sets of optical members given positive power in only a sub-scanning direction has a predetermined tilt, and a position of the beam is decentered from an optical axis of each of the optical members.

An optical exposure unit comprising:

• light sources which are arranged in correspondence with numbers indicated by N1 to NM (M is an integer not less than 1) and emit light beams;
• first lens means for converting the light beams emitted by each of said light sources into one of convergent light and collimated light, said lens means including one of a finite lens and collimate lens in number corresponding to a sum of N1 to NM;
• second lens means given lens power associated with a first direction to converge the light beams output from each of said lens means in only the first direction, the M sets of said second lens means being prepared;
• deflection means for deflecting the light beams output from said second lens means in a second direction perpendicular to the first direction, said deflection means including a reflection surface which is formed to be rotatable about a rotation axis extending in a direction parallel to the first direction as a center of rotation;
• and
• second optical means including a lens having a function of imaging Ni beams deflected by said deflection means to be scanned on a predetermined image surface at an equal speed, and correcting a surface inclination of said deflection means,
• wherein a scanning line is tilted from a direction perpendicular to a traveling direction of an image carrier by an angle:
• δ=tan−1 (Ni×p×k×/(4×π×W))
• where p is the scanning pitch in a sub-scanning direction, and
• k is the number of rotary polygonal mirror surfaces.

An optical exposure unit comprising:

• light sources which are arranged in correspondence with numbers indicated by N1 to NM (M is an integer not less than 1) and emit light beams;
• first lens means for converting the light beams emitted by each of said light sources into one of convergent light and collimated light, said lens means including one of a finite lens and collimate lens in number corresponding to a sum of N1 to NM;
• second lens means given lens power associated with a first direction to converge the light beams output from each of said lens means in only the first direction, the M sets of said second lens means being prepared;
• deflection means for deflecting the light beams output from said second lens means in a second direction perpendicular to the first direction, said deflection means including a reflection surface which is formed to be rotatable about a rotation axis extending in a direction parallel to the first direction as a center of rotation;
• and
• second optical means including a lens having a function of imaging Ni beams deflected by said deflection means to be scanned on a predetermined image surface at an equal speed, and correcting a surface inclination of said deflection means, wherein said unit satisfies:
• 10 η < ⅇ - 2 α 2 - 2 ⁢ π 8 ⁢ αζ
• where p is the beam pitch in a sub-scanning direction,
• β is the e−2 diameter, in a main scanning direction, of a beam/p,
• α is the e−2 diameter, in the sub-scanning direction, of the beam/p,
• ζ is the half exposure amount of a photosensitive body/average exposure energy, and
• η is the intensity of one beam relative to the peak intensity of the other beam at the middle point of a line connecting centers of two neighboring beams.

An optical exposure unit comprising:

• light sources which are arranged in correspondence with numbers indicated by N1 to NM (M is an integer not less than 1) and emit light beams;
• first lens means for converting the light beams emitted by each of said light sources into one of convergent light and collimated light, said lens means including one of a finite lens and collimate lens in number corresponding to a sum of N1 to NM;
• second lens means given lens power associated with a first direction to converge the light beams output from each of said lens means in only the first direction, the M sets of said second lens means being prepared;
• deflection means for deflecting the light beams output from said second lens means in a second direction perpendicular to the first direction, said deflection means including a reflection surface which is formed to be rotatable about a rotation axis extending in a direction parallel to the first direction as a center of rotation;
• and
• imaging means including at least one lens, and imaging each of the light beams deflected at an equal speed by said deflection means at a predetermined position, and
• wherein M sets of optical members given positive power in only a sub-scanning direction includes a one-sided cylinder lens consisting of glass, and a double-sided cylinder lens substantially equivalent to a material of a post-deflection optical system lens.