US 4,908,634 A · Laser power control for cut-paper printer

Abstract

Electric-photosensitive printing is accomplished with an LD providing a laser scanning beam that is modulated to affect printing, and the power output of the LED is maintained constant through negative feedback by a holding voltage provided by a capacitor having its charge determined only during a non-printing portion of the printing period wherein a plurality of sheets are printed. During the non-printing period, contact of the scanning laser beam with the electro-photosensitive material is disabled while the laser beam is maintained on so that its power may be measured and compared with a reference level to provide a feedback signal for controlling the output of the laser beam, particularly the feedback signal being provided to the holding capacitor only during the non-printing portion of the period, and the holding capacitor being isolated from the feedback signal during the printing portion of the period. As a specific embodiment, a rectangular sheet of electric-photosensitive material is replaceable wound around a drum so that its opposite ends are spaced apart to provide a seam to affect the disablement of the laser beam from contracting the electro-photosensitive material during the non-printing portion of the period, and a separate light source used to detect this seam portion to determine the non-printing portion of the period.

Claims28

Dependent claims

In a laser scanning printer system, wherein a laser beam is modulated to affect printing as it scans a rotatable member with a repeatable scan cycle of relative scan movement between the rotatable data recording medium and the laser beam, and feed relative movement at right angles to said scan movement between cycles, wherein the improvement comprises:

said rotatable member having a non-printing surface without any data handling capability, and extending for a length corresponding to at least one scan cycle, and being in the path of said laser beam only for a non-printing portion of the period representing the entire path of relative feed movement of laser beam and rotatable medium that traverses the entire data region of said recording medium in said feed direction;
and
means for correcting the power of the laser beam only during said non-printing portion so that the frequency of light reflection between said laser beam and said non-printing surface is equal to the frequency of scan lines divided by a relatively large whole number integer.

A laser scanning system as a part of an electro-photographic printing system, comprising:

a laser scanning light source producing a laser beam with a negative feedback;
a rotatable member having electro-photosensitive material thereon for producing a latent image according to the modulation of a lesser scanning beam produced by the laser scanning light source;
means for modulating the laser beam of the laser scanning light source for producing a latent image corresponding to a plurality of scan lines during the printing portion of a repeatable period or rotation of said rotatable member;
means for relatively moving said rotatable member and said laser beam for providing said scanning lines and line feed for the printable portion of the repeatable period, with said printable portion corresponding to a whole number multiple of a page length;
means for providing a stabilizing period determining control signal for a non-printable portion of said period;
means for disabling contact between said scanning laser beam and said electro-sensitive material on said rotatable member during said non-printable portion of said period even with said laser scanning light source being on;
means for detecting the power of said laser beam while it is maintained on during said non-printable portion of said period and thereby producing a correlated power signal;
and
means responsive to said power signal for controlling the negative feedback of said laser scanning light source to set the power of said laser scanning light source at a constant level during said non-printing portion of said period and including means for maintaining said level during the printing portion of said period independently of said means for detecting.

6 more elements

A method of electro-photosensitive printing, comprising the steps of:

producing a laser scanning beam with a negative feedback;
producing a latent image, on a rotatable member having electro-photosensitive material, according to modulation of the laser scanning beam;
modulating the laser scanning beam for producing a latent image corresponding to a plurality of scan lines during the printing portion of a repeatable period of rotation of said rotatable member;
relatively moving said rotatable member and said laser scanning beam for providing said scanning lines and line feed for the printable portion of the repeatable period, with said printable portion corresponding to a whole number multiple of a page length;
providing a stabilizing period determining control signal for a non-printable portion of said period;
disabling contact between said scanning laser beam and said electro-photosensitive material on said rotatable member during said non-printable portion of said period and maintaining said laser scanning beam on;
detecting the power of said laser beam while it is maintained on during said non-printable portion of said period and thereby producing a correlated power signal;
in response to said power signal, controlling the negative feedback of said laser scanning beam to set the power of said laser scanning beam at a constant level during said non-printing portion of said period, and maintaining said level during the printing portion of said period independently of said detecting.

5 more elements

Dependencies are inferred from the claim text.

Laser power control for cut-paper printer

Life of this patent

Laser power control for cut-paper printer

Life of this patent

Abstract

Claims28