Method and apparatus for inner face scanning with multi beams

An apparatus for two light beams scanning simultaneously an inner face of a cylindrical drum, comprising:

• two deflecting elements for one-dimensionally deflecting the two light beams in mutually orthogonal directions, respectively;
• a spinner rotating coaxially with said cylindrical drum for deflecting said two light beams incident along a central axis of the cylindrical drum to scan the inner face of the cylindrical drum;
• angle detecting means for detecting a rotation angle of the spinner;
• a memory for storing deflection quantities of said deflecting elements necessary for one-dimensionally deflecting the light beams in mutually orthogonal directions in synchronism with the rotation of said spinner while keeping constant an interval between the two light beams;
• and
• deflecting element control means for driving said deflecting elements based on the deflection quantities stored in said memory;
• wherein in an X-Y rectangular coordinate system on an image focusing plane of the light beams, an X axis being a direction in which a first light beam of said two light beams reciprocates while being one-dimensionally deflected, a Y axis being a direction in which a second light beam of said two light beams reciprocates while being one-dimensionally deflected,
• the deflection quantity for said first light beam is
• x=r•cos(ωt+ψ) and y=0, and
• the deflection quantity for said second light beam is
• x=0and y=r•sin(ωt+ψ),
• where r is an interval between both light beams, ω is a rotation angular velocity of the spinner, t is a time and ψ is an offset angle in a maximum deflecting direction of said spinner.

A method for scanning an inner face of a cylindrical drum with plural light beams, said drum comprising a spinner rotating on a central axis of the drum to deflect each light beam to the inner face of the drum, said method comprising:

• passing one light beam along a central axis common with said spinner and the cylindrical drum and projecting said one light beam into the spinner;
• inclining other light beams in a plane including said central axis by a constant angle φY which is separately predetermined for each of said other light beams and further inclining said other light beams in a direction orthogonal to said plane by an angle φx which is determined in synchronism with a rotation angle θ of the spinner;
• wherein said angle φx is determined in accordance with the formula
• when θ≠θ0, φx=φy(1−cos(θ−θ0))/sin(θ−θ0), and
• when θ=θ0, φx=0, where θ0 is an offset angle in a maximum deflecting direction of the spinner;
• and
• wherein said inclination angle φy is determined in accordance with the formula
• d=f•φy
• where d is an interval between scanning lines drawn by said plural light beams on the inner face of the cylindrical drum, and f is a focal length of a common focusing lens on which the light beams are focused.

An apparatus for scanning an inner face of a cylindrical drum with plural light beams, said drum having a spinner rotating on a central axis of the drum to deflect said plural light beams to the inner surface of the drum, one of the plural light beams passing along a central axis common with said spinner and the drum to be projected to the spinner, comprising:

• angle detecting means for detecting a rotation angle θ of the spinner;
• and
• a light beam deflecting element for deflecting the other light beams in a plane including said central axis by a constant angle φy which is separately predetermined for each of the other light beams, and in a direction orthogonal to said plane including a rotation axis by an angle φx which is determined in synchronism with the rotation angle θ of the spinner;
• wherein said angle φx is determined in accordance with the formula
• when θ≠θ0, φx=φy(1−cos(θ−θ0))/sin(θ−θ0), and
• when θ=θ0, φx=0, where θ0 is an offset angle in a maximum deflecting direction of the spinner;
• and
• wherein said inclination angle φy is determined in accordance with the formula d=f•φy
• where d is an interval between scanning lines drawn by said plural light beams on the inner face of the cylindrical drum, and f is a focal length of a common focusing lens on which the light beams are focused.