# US 6,294,778 B1 · Method and apparatus for recording a flat field image

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- Number: US 6,294,778 B1
- Document ID: US6294778B1
- Status: Granted
- Kind: B1
- Application number: 09/296,822
- Filed: 1999-04-22
- Granted: 2001-09-25
- Earliest claimed: 1999-04-22
- Assignees: ECRM Incorporated
- Inventors: Gregory G. Cappiello
- Web page: https://patentgrep.com/patent/US6294778B1

## CPC

- 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)}
- G02B 13/0005: {having F-Theta characteristic (scanning systems employing movable or deformable optical elements G02B26/10)}
- G02B 27/0031: {for scanning purposes}
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS

## Abstract

The invention features a flat field image printing apparatus. The printing apparatus includes: a light source responsive to an image modulated signal and producing a image modulated light beam; a beam deflector supported for rotary motion to deflect the image modulated light beam onto an image recording medium in response to the rotary motion; and a lens assembly configured to convert the deflected image modulated light beam into an achromatic focused beam spot which moves repeatedly in a first scan direction and over a range of scan angles to provide a highly resolved printed image across the recording medium. In other aspects, the invention features a high-speed printing apparatus employing multiple light sources, and an achromatic f-theta lens for use in such printing apparati.

## Claims

### Claim 1

A flat field image printing apparatus comprising:
a light source responsive to an image modulated signal and producing an image modulated light beam;
a beam deflector supported for rotary motion to deflect said image modulated light beam onto an image recording medium in response to said rotary motion; and
a lens assembly configured to convert said deflected image modulated light beam into an achromatic focused beam spot which moves repeatedly in a first scan direction and over a range of scan angles to provide a highly resolved printed image across said recording medium.

### Claim 2 (depends on 1)

The apparatus of claim 1 wherein said lens assembly is configured to produce an achromatic focused beam spot in the visible and near infrared spectral wavelength range.

### Claim 3 (depends on 1)

The apparatus of claim 1 wherein said lens assembly is configured to produce an achromatic focused beam spot in the spectral wavelength range of 670 nm to 780 nm.

### Claim 4 (depends on 1)

The apparatus of claim 1 wherein said range of scan angles spans −32° to +32°.

### Claim 5 (depends on 1)

The apparatus of claim 1 wherein said recording medium and said achromatic focused beam are configured to be translated relative to one another in a second direction perpendicular to said first scan direction in order to print a two-dimensional image.

### Claim 6 (depends on 5)

The apparatus of claim 5 wherein said recording medium comprises photosensitive film, plate, or paper.

### Claim 7 (depends on 5)

The apparatus of claim 5 wherein said recording medium comprises an electrostatic recording device.

### Claim 8

A flat field image printing apparatus comprising:
a light source responsive to an image modulated signal and producing an image modulated light beam;
a beam deflector supported for rotary motion to deflect said image modulated light beam onto an image recording medium in response to said rotary motion; and
a lens assembly configured to convert said deflected image modulated light beam into an achromatic focused beam spot which moves repeatedly in a first scan direction and over a range of scan angles to provide a highly resolved printed image across said recording medium,
wherein said lens assembly comprises
a first lens having a negative power,
a second lens having a positive power, and
a third lens having a positive power,
wherein said first, second and third lenses are arranged in the order from the object to tile image side and satisfy the following formulae (1) to (6)
−3.6<1<−3.0 (1)
1.6<2<2.0 (2)
1.5<3<1.8 (3)
ν1<34 (4)
44<v2<61 (5)
37<v3<51 (6)
where n is the power of the nth lens with respect to the total power of the lens assembly and vn represents the Abbe dispersion number of the nth lens.

### Claim 9

A flat field image printing apparatus comprising:
a light source responsive to an image modulated signal and producing an image modulated light beam;
a beam deflector supported for rotary motion to deflect said image modulated light beam onto an image recording medium in response to said rotary motion; and
a lens assembly configured to convert said deflected image modulated light beam into an achromatic focused beam spot which moves repeatedly in a first scan direction and over a range of scan angles to provide a highly resolved printed image across said recording medium,
wherein said lens assembly comprises
a first lens having a negative power and a refractive index in the range of 1.64 to 1.85,
a second lens having a positive power and a refractive index in the range of 1.60 to 1.75,
a third lens having a positive power and a refractive index in the range of 1.65 to 1.75, and
wherein said first, second and third lenses are arranged in the order from the object to the image side.

### Claim 10

An f-theta lens assembly configured to convert an image modulated light beam into an achromatic focused beam spot which moves repeatedly in a first scan direction and over a range of scan angles to provide a highly resolved image comprising
a first lens having a negative power,
a second lens having a positive power, and
a third lens having a positive power,
wherein said first, second and third lenses are arranged in the order from object to image side and satisfy the following formulae (1) to (6)
−3.6<ø1<−3.0 (1)
1.6<ø2<2.0 (2)
1.5<ø3<1.8 (3)
ν1<34 (4)
44<ν2<61 (5)
37<ν3<51 (6)
where øn is the power of the nth lens with respect to the total power of the lens assembly and νn represents the Abbe dispersion number of the nth lens.

### Claim 11 (depends on 10)

The lens assembly of claim 10 configured to produce an achromatic focused beam spot in the visible and near infrared spectral wavelength range.

### Claim 12 (depends on 10)

The lens assembly of claim 10 configured to produce an achromatic focused beam spot in the spectral wavelength range of 670 nm to 780 nm.

### Claim 13 (depends on 10)

The lens assembly of claim 10 wherein said range of scan angles spans −32° to +32°.

### Claim 14 (depends on 10)

The lens assembly of claim 10 wherein
said first lens has a refractive index in the range of 1.64 to 1.85,
said second lens has a refractive index in the range of 1.60 to 1.75, and
said third lens has a refractive index in the range of 1.65 to 1.75.

### Claim 15

A high-speed flat field image printing apparatus comprising:
a plurality of light sources responsive to an image modulated signal and producing a plurality of image modulated light beams having a plurality of wavelengths;
a beam deflector supported for rotary motion to deflect said plurality of image modulated light beams onto an image recording medium in response to said rotary motion; and
a lens assembly configured to convert said plurality of deflected image modulated light beams into a plurality of achromatic focused beam spots which move repeatedly in a first scan direction and over a range of scan angles to provide a highly resolved printed image across said recording medium.

### Claim 16 (depends on 15)

The apparatus of claim 15 wherein said lens assembly is configured to produce a plurality of achromatic focused beam spots having wavelengths in the visible and near infrared spectral wavelength range.

### Claim 17 (depends on 15)

The apparatus of claim 15 wherein said lens assembly is configured to produce a plurality of achromatic focused beam spots having wavelengths in the range of 670 nm to 780 nm.

### Claim 18 (depends on 15)

The apparatus of claim 15 wherein said range of scan angles spans −32° to +32°.

### Claim 19

A high-speed flat field image printing apparatus comprising:
a plurality of light sources responsive to an image modulated signal and producing a plurality of image modulated light beams having a plurality of wavelengths;
a beam deflector supported for rotary motion to deflect said plurality of image modulated light beams onto an image recording medium in response to said rotary motion; and
a lens assembly configured to convert said plurality of deflected image modulated light beams into a plurality of achromatic focused beam spots which move repeatedly in a first scan direction and over a range of scan angles to provide a highly resolved printed image across said recording medium,
wherein said lens assembly comprises
a first lens having a negative power,
a second lens having a positive power, and
a third lens having a positive power,
wherein said first, second and third lenses are arranged in the order from the object to the image side and satisfy the following formulae (1) to (6)
−3.6<1<−3.0 (1)
1.6<2<2.0 (2)
1.5<3<1.8 (3)
v1<34 (4)
44<v2<61 (5)
37<v3<51 (6)
where n is the power of the nth lens with respect to the total power of the lens assembly and vn represents the Abbe dispersion number of the nth lens.

### Claim 20

A high-speed flat field image printing apparatus comprising:
a plurality of light sources responsive to an image modulated signal and producing a plurality of image modulated light beams having a plurality of wavelengths;
a beam deflector supported for rotary motion to deflect said plurality of image modulated light beams onto an image recording medium in response to said rotary motion; and
a lens assembly configured to convert said plurality of deflected image modulated light beams into a plurality of achromatic focused beam spots which move repeatedly in a first scan direction and over a range of scan angles to provide a highly resolved printed image across said recording medium,
wherein said lens assembly comprises
a first lens having a negative power and a refractive index in the range of 1.64 to 1.85
a second lens having a positive power and a refractive index in the range of 1.60 to 1.75, and
a third lens having a positive power and a refractive index in the range of 1.65 to 1.75,
wherein said first, second and third lenses are arranged in the order from the object to the image side.

### Claim 21

A flat field image printing apparatus comprising:
a light source responsive to an image modulated signal and producing an image modulated light beam;
a beam deflector supported for rotary motion to deflect said image modulated light beam onto an image recording medium in response to said rotary motion; and
a f-theta lens assembly configured to convert said deflected image modulated light beam into an achromatic focused beam spot which moves repeatedly in a first scan direction and over a range of scan angles to provide a highly resolved printed image across said recording medium, wherein said f-theta lens assembly is configured to produce an achromatic focused beam spot over a range of wavelengths in the visible and near infrared spectral wavelength range.

### Claim 22 (depends on 21)

The apparatus of claim 21 wherein said f-theta lens assembly is configured to produce an achromatic focused beam spot in the spectral wavelength range of 670 nm to 780 nm.