US 4,230,902 A · Modular laser printing system

Abstract

A laser printing system having a plurality of modules is provided wherein one of the modules comprises a laser, modulator and part of the system optics, the light output from the module being directed to a rotating scanner. The components in the module are secured to a common base member to minimize relative movement between the components, the alignment between the output laser beam and a cylindrical lens, the cylindrical lens being one element of the module optics, thereby being substantially maintained so that the energy distribution of the laser beam focused onto a recording medium across a scan line is maintained at its optimum value. If the laser or other component in the module becomes defective, the module is removed and replaced with a similar module, the critical alignment between the laser beam and the cylindrical lens thereby being maintained. The module, when replaced, fits into a corresponding mating portion of the laser printing system so that the module output beam retains its relative alignment with system components external to the module.

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Drawings

Claims12

Dependent claims

In a laser printing system having means for generating a beam of high intensity light, a recording medium sensitive to said high intensity light, optical means comprising a plurality of optical elements interposed between said light generating means and said recording medium for imaging said beam to a spot at the surface of said medium, modulating means located between said light generating means and a scanner device for modulating the light beam in accordance with the information content of electrical signals, said scanner device comprising a multi-faceted polygon located in the path of said modulated beam between said beam generating means and said recording medium and having reflective facets for reflecting the beam incident thereon onto said medium, means for rotating said polygon such that the reflected light is scanned in successive traces across said medium, the improvement comprising:

a first module forming a part of said laser printing system, said first module comprising said light beam generating means and at least one of said optical elements, said light beam generating means and said at least one of said optical elements being mounted on a common base member, said first module being adapted to be removed from said laser printing system and replaced with a second module, similar to said first module, the beam of light provided by a beam generating means in said second module and exiting therefrom being maintained in optical alignment with other elements in said laser printing system external to said second module within predetermined tolerances, the light beam generated by said light beam generating means in said first module being in optical alignment with other elements in said laser printing system external to said first module and also being within said predetermined tolerances.

In a laser printing system having means for generating a beam of high intensity light, a recording medium sensitive to said high intensity light, optical means comprising a plurality of optical elements interposed between said light generating means and said recording medium for imaging said beam to a spot at the surface of said medium, modulating means located between said light generating means and a scanner device for modulating the light beam in accordance with the information content of electrical signals, said scanner device comprising a multi-faceted polygon located in the path of said modulated beam between said beam generating means and said recording medium and having reflective facets for reflecting the beam incident thereon onto said medium, means for rotating said polygon such that the reflected light is scanned in successive traces across said medium, the improvement comprising:

a first module forming a part of said laser printing system, said first module comprising said light beam generating means and at least one of said optical elements, said light beam generating means and said at least one of said optical elements being mounted on a common base member, said first module being adapted to be removed from said laser printing system and replaced with a second module, similar to said first module, the beam of light provided by a beam generating means in said second module and exiting therefrom being in substantial optical alignment with other elements in said laser printing apparatus external to said second module, said first and second modules including means through which said beam of high intensity light exits said first and second modules, said laser printing system including means associated therewith to locate and secure said first module or said second module whereby the beam of light exiting from said first module or said second module is in substantial optical alignment with other elements in said printing apparatus external to said first module or said second module.

A method for maintaining laser beam alignment in a laser printing system, said laser printing system comprising means for generating a beam of high intensity light, a recording medim sensitive to said high intensity light, optical means comprising a plurality of optical elements interposed between said light generating means and said recording medium for imaging said beam to a spot at the surface of said medium, modulating means located between said light generating means and a scanner device for modulating the light beam in accordance with the information content of electrical signals, the scanner device comprising a multi-faceted polygon located in the path of said modulated beam between said beam generating means and said recording medium and having reflective facets for reflecting the beam incident thereon onto said medium, and means for rotating said polygon such that the reflected light is scanned in successive traces across said medium, said method comprising the step of:

modularizing said laser printing system such that a first module is provided which comprises said light beam generating means at least one of said optical elements, said light beam generating means and said at least one of said optical elements being mounted on a common base member wherein the relative alignment of the beam of high intensity light with respect to the optical axis of said at least one of said optical elements is maintained within a first predetermined tolerance range,
removing said first module from the laser printing system when the performance of said light beam generating means is unacceptable, and
replacing said first module with a second module similar to said first module, the beam of light provided by a beam generating means in said second module and exiting therefrom being in optical alignment with other elements in said laser printing system external to said second module within a second predetermined tolerance range, the light beam generated by said light beam generating means in said first module being in optical alignment with other elements in said laser printing system external to said first module and also being within said second tolerance range.

A method for maintaining laser beam alignment in a laser printing system, said laser printing system comprising means for generating a beam of high intensity light, a recording medium sensitive to said high intensity light, optical means comprising a plurality of optical elements interposed between said light generating means and said recording medium for imaging said beam to a spot at the surface of said medium, modulating means located between said light generating means and a scanner device for modulating the light beam in accordance with the information content of electrical signals, the scanner device comprising a multi-faceted polygon located in the path of said modulated beam between said beam generating means and said recording medium and having reflective facets for reflecting the beam incident thereon onto said medium, and means for rotating said polygon such that the reflected light is scanned in successive traces across said medium, said method comprising the steps of:

modularizing said laser printing system such that a first module is provided which comprises said light beam generating means and at least one of said optical elements, said light beam generating means and said at least one of said optical elements being mounted on a common base member wherein the relative alignment of the beam of high intensity light with respect to the optical axis of said at least one of said optical elements is maintained within predetermined tolerances,
removing said first module from the laser printing system when the performance of said light beam generating means is unacceptable, and
replacing said first module with a second module similar to said first module, said laser printing system having locating and securing means associated therewith to locate and secure said first module or said second module, whereby the beam of light provided by a beam generating means in said first or second module and exiting therefrom is in substantial optical alignment with other elements in said printing system external to said first module or said second module.

Dependencies are inferred from the claim text.

Description3,974 words

Summary991 words

#Recently, printing systems utilizing lasers to reproduce information or laser sensitive mediums have been announced by various manufacturers. Typically, the system includes a laser for generating a laser beam, a modulator, such as an acousto-optic modulator, for modulating the laser beam in accordance with input information to be reproduced, a multi-faceted scanner for scanning the modulated laser beam across a medium on a line to line basis, various optical components to focus and align the laser beam onto the medium, the laser sensitive recording medium itself and, if necessary, a means for developing the information in human readable form. A typical representation of printing systems utilizing lasers is shown, for example, in U.S. Pat. No. 3,922,485, the patent disclosing the use of a xerographic drum as the recording medium and means for developing the latent electrostatic image formed on the drum.

#In some printing systems it is required that a cylindrical lens be interposed between the modulated laser beam and the scanner to provide a fan fold light output beam which fully illuminates at least one facet of the scanner. The cylindrical lens is preferably aligned with the laser beam to redistribute the energy of the modulated laser beam in a manner whereby the energy distribution of the laser beam incident on the recording medium is substantially symmetrical about the start of scan and end of scan positions of the medium, maximum energy ideally occuring at the center of the scanline. This is particularly important in those systems which utilize a xerographic recording medium.

#In general, the laser portion of the overall printing system is regarded as the "weak link" in that the laser would be the first component to fail or in some way become inoperative. The accepted approach, from a field service standpoint, to make the printing system operative, would be to remove the defective laser and replace it with another laser, either a new laser or a repaired laser. In regards to the configuration discussed above, it has been determined that the relative positioning of the laser beam with respect to the cylindrical lens is extremely critical, this critically affecting the energy distribution of the laser beam which scans the medium. If the laser beam is moved with respect to the cylindrical lens a small distance, say for example 0.001 of an inch in the scanning direction, the beam energy incident on the polygon facet will shift a substantial fraction of the facet aperture in the scanning or tangential direction, the displacement being determined by the magnification factor of the cylindrical lens which in turn will effect the beam energy distribution at the surface of the recording medium. The relatively tight tolerance required between the laser beam and the cylindrical lens has made it extremely time consuming and costly to replace the laser independently of the cylindrical lens and maintain the necessary tight tolerances therebetween.

Brief description of the drawings4 figures

#For a better understanding of the invention as well as other objects and features thereof, reference is made to the following description which is to be read in conjunction with the accompanying drawing wherein:

#FIG. 1 is a simplified representation of a laser printing system in accordance with the present invention;

#FIG. 2 is a graph illustrating the energy densities of a laser beam as it scans across a medium;

Detailed description2,863 words

#FIG. 1 illustrates a simplified representation of the optical and recording portions of the laser printing system in accordance with the present invention.

#A light source 1 provides the original light beam for utilization by the printing system. The light source 1 is preferably a laser, such as a helium-cadmium or helium-neon laser, which generates a collimated beam of monochromatic light 2. The monochromatic light beam is focused by spherical lens 3 onto modulator 4, the light beam 2 being modulated in conformance with the information contained in a video signal.

#Modulator 4 may be any suitable acousto-optic or electro-optical modulator for recording the video information in the form of a modulated light beam 6 at the output of the modulator 4. By means of the modulator 4 the information within the video signal is represented by the modulated light beam 6.

Modular laser printing system

Life of this patent

Modular laser printing system

Life of this patent

Life of this patent

Abstract

Drawings

Drawings

Claims12

Description3,974 words

Drawings

Classification4 codes

Life of this patent

Description3,974 words